High power RF coaxial switch

NASA Technical Reports Server (NTRS)

Caro, E. R. (Inventor)

1980-01-01

A coaxial switch capable of operating in a vacuum with high RF power in the 1.2 GHz range without multipactor breakdown, and without relying on pressurization with an inert gas is described. The RF carrying conductors of the switch are surrounded with a high grade solid dielectric, thus eliminating any gaps in which electrons can accelerate.

RF MEMS Switches with SiC Microbridges for Improved Reliability

NASA Technical Reports Server (NTRS)

Scardelletti, Maximilian C.; Zorman, Christian A.; Oldham, Daniel R.

2008-01-01

Radio frequency (RF) microelectromechanical (MEMS) switches offer superior performance when compared to the traditional semiconductor devices such as PIN diodes or GaAs transistors. MEMS switches have a return loss (RL) better than -25 dB, negligible insertion loss (IL), isolation better than -30 dB, and near zero power consumption. However, RF MEMS switches have several drawbacks the most serious being long-term reliability. The ability for the switch to operate for millions or even billions of cycles is a major concern and must be addressed. MEMS switches are basically grouped in two categories, capacitive and metal-to-metal contact. The capacitive type switch consists of a movable metal bridge spanning a fixed electrode and separated by a narrow air gap and thin insulating material. The metal-to-metal contact type utilizes the same basic design but without the insulating material. After prolonged operation the metal bridges, in most of these switches, begin to sag and eventually fail to actuate. For the metal-to-metal type, the two metal layers may actually fuse together. Also if the switches are not packaged properly or protected from the environment moisture may build up and cause stiction between the top and bottom electrodes rendering them useless. Many MEMS switch designs have been developed and most illustrate fairly good RF characteristics. Nevertheless very few have demonstrated both great RF performance and ability to perform millions/billions of switching cycles. Of these, nearly all are of metal-to-metal type so as the frequency increases RF performance decreases.

Ultrananocrystalline diamond films with optimized dielectric properties for advanced RF MEMS capacitive switches

DOEpatents

Sumant, Anirudha V.; Auciello, Orlando H.; Mancini, Derrick C.

2013-01-15

An efficient deposition process is provided for fabricating reliable RF MEMS capacitive switches with multilayer ultrananocrystalline (UNCD) films for more rapid recovery, charging and discharging that is effective for more than a billion cycles of operation. Significantly, the deposition process is compatible for integration with CMOS electronics and thereby can provide monolithically integrated RF MEMS capacitive switches for use with CMOS electronic devices, such as for insertion into phase array antennas for radars and other RF communication systems.

Design and Optimization of AlN based RF MEMS Switches

NASA Astrophysics Data System (ADS)

Hasan Ziko, Mehadi; Koel, Ants

2018-05-01

Radio frequency microelectromechanical system (RF MEMS) switch technology might have potential to replace the semiconductor technology in future communication systems as well as communication satellites, wireless and mobile phones. This study is to explore the possibilities of RF MEMS switch design and optimization with aluminium nitride (AlN) thin film as the piezoelectric actuation material. Achieving low actuation voltage and high contact force with optimal geometry using the principle of piezoelectric effect is the main motivation for this research. Analytical and numerical modelling of single beam type RF MEMS switch used to analyse the design parameters and optimize them for the minimum actuation voltage and high contact force. An analytical model using isotropic AlN material properties used to obtain the optimal parameters. The optimized geometry of the device length, width and thickness are 2000 µm, 500 µm and 0.6 µm respectively obtained for the single beam RF MEMS switch. Low actuation voltage and high contact force with optimal geometry are less than 2 Vand 100 µN obtained by analytical analysis. Additionally, the single beam RF MEMS switch are optimized and validated by comparing the analytical and finite element modelling (FEM) analysis.

Flexible radio-frequency single-crystal germanium switch on plastic substrates

NASA Astrophysics Data System (ADS)

Qin, Guoxuan; Cai, Tianhao; Yuan, Hao-Chih; Seo, Jung-Hun; Ma, Jianguo; Ma, Zhenqiang

2014-04-01

This Letter presents the realization and characterizations of the flexible radio-frequency (RF)/microwave switches on plastic substrates employing single-crystal germanium (Ge) nanomembranes. The fabricated flexible Ge single-pole, single-throw (SPST) switches display high frequency responses (e.g., insertion loss of <1.3 dB at up to 30 GHz and isolation >10 dB at up to ˜13 GHz). RF performance tradeoff exists for the flexible Ge switches and the major affecting parameters are determined. The flexible Ge SPST switch shows better RF property to that of the flexible Si SPST switch. Underlying mechanism is investigated by theoretical analysis and modeling of switches with different structures.

A novel multi-actuation CMOS RF MEMS switch

NASA Astrophysics Data System (ADS)

Lee, Chiung-I.; Ko, Chih-Hsiang; Huang, Tsun-Che

2008-12-01

This paper demonstrates a capacitive shunt type RF MEMS switch, which is actuated by electro-thermal actuator and electrostatic actuator at the same time, and than latching the switching status by electrostatic force only. Since thermal actuators need relative low voltage compare to electrostatic actuators, and electrostatic force needs almost no power to maintain the switching status, the benefits of the mechanism are very low actuation voltage and low power consumption. Moreover, the RF MEMS switch has considered issues for integrated circuit compatible in design phase. So the switch is fabricated by a standard 0.35um 2P4M CMOS process and uses wet etching and dry etching technologies for postprocess. This compatible ability is important because the RF characteristics are not only related to the device itself. If a packaged RF switch and a packaged IC wired together, the parasitic capacitance will cause the problem for optimization. The structure of the switch consists of a set of CPW transmission lines and a suspended membrane. The CPW lines and the membrane are in metal layers of CMOS process. Besides, the electro-thermal actuators are designed by polysilicon layer of the CMOS process. So the RF switch is only CMOS process layers needed for both electro-thermal and electrostatic actuations in switch. The thermal actuator is composed of a three-dimensional membrane and two heaters. The membrane is a stacked step structure including two metal layers in CMOS process, and heat is generated by poly silicon resistors near the anchors of membrane. Measured results show that the actuation voltage of the switch is under 7V for electro-thermal added electrostatic actuation.

Laser method for forming low-resistance ohmic contacts on semiconducting oxides

DOEpatents

Narayan, Jagdish

1981-01-01

This invention is a new method for the formation of high-quality ohmic contacts on wide-band-gap semiconducting oxides. As exemplified by the formation of an ohmic contact on n-type BaTiO.sub.3 containing a p-n junction, the invention entails depositing a film of a metallic electroding material on the BaTiO.sub.3 surface and irradiating the film with a Q-switched laser pulse effecting complete melting of the film and localized melting of the surface layer of oxide immediately underlying the film. The resulting solidified metallic contact is ohmic, has unusually low contact resistance, and is thermally stable, even at elevated temperatures. The contact does not require cleaning before attachment of any suitable electrical lead. This method is safe, rapid, reproducible, and relatively inexpensive.

Method for forming low-resistance ohmic contacts on semiconducting oxides

DOEpatents

Narayan, J.

1979-10-01

The invention provides a new method for the formation of high-quality ohmic contacts on wide-band-gap semiconducting oxides. As exemplified by the formation of an ohmic contact on n-type BaTiO/sub 3/ containing a p-n junction, the invention entails depositing a film of a metallic electroding material on the BaTiO/sub 3/ surface and irradiating the film with a Q-switched laser pulse effecting complete melting of the film and localized melting of the surface layer of oxide immediately underlying the film. The resulting solidified metallic contact is ohmic, has unusually low contact resistance, and is thermally stable, even at elevated temmperatures. The contact does not require cleaning before attachment of any suitable electrical lead. This method is safe, rapid, reproducible, and relatively inexpensive.

High peak and high average radiofrequency power transmit/receive switch for thermal magnetic resonance.

PubMed

Ji, Yiyi; Hoffmann, Werner; Pham, Michal; Dunn, Alexander E; Han, Haopeng; Özerdem, Celal; Waiczies, Helmar; Rohloff, Michael; Endemann, Beate; Boyer, Cyrille; Lim, May; Niendorf, Thoralf; Winter, Lukas

2018-04-01

To study the role of temperature in biological systems, diagnostic contrasts and thermal therapies, RF pulses for MR spin excitation can be deliberately used to apply a thermal stimulus. This application requires dedicated transmit/receive (Tx/Rx) switches that support high peak powers for MRI and high average powers for RF heating. To meet this goal, we propose a high-performance Tx/Rx switch based on positive-intrinsic-negative diodes and quarter-wavelength (λ/4) stubs. The λ/4 stubs in the proposed Tx/Rx switch design route the transmitted RF signal directly to the RF coil/antenna without passing through any electronic components (e.g., positive-intrinsic-negative diodes). Bench measurements, MRI, MR thermometry, and RF heating experiments were performed at f = 297 MHz (B 0  = 7 T) to examine the characteristics and applicability of the switch. The proposed design provided an isolation of -35.7dB/-41.5dB during transmission/reception. The insertion loss was -0.41dB/-0.27dB during transmission/reception. The switch supports high peak (3.9 kW) and high average (120 W) RF powers for MRI and RF heating at f = 297 MHz. High-resolution MRI of the wrist yielded image quality competitive with that obtained with a conventional Tx/Rx switch. Radiofrequency heating in phantom monitored by MR thermometry demonstrated the switch applicability for thermal modulation. Upon these findings, thermally activated release of a model drug attached to thermoresponsive polymers was demonstrated. The high-power Tx/Rx switch enables thermal MR applications at 7 T, contributing to the study of the role of temperature in biological systems and diseases. All design files of the switch will be made available open source at www.opensourceimaging.org. © 2018 International Society for Magnetic Resonance in Medicine.

High output lamp with high brightness

DOEpatents

Kirkpatrick, Douglas A.; Bass, Gary K.; Copsey, Jesse F.; Garber, Jr., William E.; Kwong, Vincent H.; Levin, Izrail; MacLennan, Donald A.; Roy, Robert J.; Steiner, Paul E.; Tsai, Peter; Turner, Brian P.

2002-01-01

An ultra bright, low wattage inductively coupled electrodeless aperture lamp is powered by a solid state RF source in the range of several tens to several hundreds of watts at various frequencies in the range of 400 to 900 MHz. Numerous novel lamp circuits and components are disclosed including a wedding ring shaped coil having one axial and one radial lead, a high accuracy capacitor stack, a high thermal conductivity aperture cup and various other aperture bulb configurations, a coaxial capacitor arrangement, and an integrated coil and capacitor assembly. Numerous novel RF circuits are also disclosed including a high power oscillator circuit with reduced complexity resonant pole configuration, parallel RF power FET transistors with soft gate switching, a continuously variable frequency tuning circuit, a six port directional coupler, an impedance switching RF source, and an RF source with controlled frequency-load characteristics. Numerous novel RF control methods are disclosed including controlled adjustment of the operating frequency to find a resonant frequency and reduce reflected RF power, controlled switching of an impedance switched lamp system, active power control and active gate bias control.

Effects Of Environmental And Operational Stresses On RF MEMS Switch Technologies For Space Applications

NASA Technical Reports Server (NTRS)

Jah, Muzar; Simon, Eric; Sharma, Ashok

2003-01-01

Micro Electro Mechanical Systems (MEMS) have been heralded for their ability to provide tremendous advantages in electronic systems through increased electrical performance, reduced power consumption, and higher levels of device integration with a reduction of board real estate. RF MEMS switch technology offers advantages such as low insertion loss (0.1- 0.5 dB), wide bandwidth (1 GHz-100 GHz), and compatibility with many different process technologies (quartz, high resistivity Si, GaAs) which can replace the use of traditional electronic switches, such as GaAs FETS and PIN Diodes, in microwave systems for low signal power (x < 500 mW) applications. Although the electrical characteristics of RF MEMS switches far surpass any existing technologies, the unknown reliability, due to the lack of information concerning failure modes and mechanisms inherent to MEMS devices, create an obstacle to insertion of MEMS technology into high reliability applications. All MEMS devices are sensitive to moisture and contaminants, issues easily resolved by hermetic or near-hermetic packaging. Two well-known failure modes of RF MEMS switches are charging in the dielectric layer of capacitive membrane switches and contact interface stiction of metal-metal switches. Determining the integrity of MEMS devices when subjected to the shock, vibration, temperature extremes, and radiation of the space environment is necessary to facilitate integration into space systems. This paper will explore the effects of different environmental stresses, operational life cycling, temperature, mechanical shock, and vibration on the first commercially available RF MEMS switches to identify relevant failure modes and mechanisms inherent to these device and packaging schemes for space applications. This paper will also describe RF MEMS Switch technology under development at NASA GSFC.

Active high-power RF switch and pulse compression system

DOEpatents

Tantawi, Sami G.; Ruth, Ronald D.; Zolotorev, Max

1998-01-01

A high-power RF switching device employs a semiconductor wafer positioned in the third port of a three-port RF device. A controllable source of directed energy, such as a suitable laser or electron beam, is aimed at the semiconductor material. When the source is turned on, the energy incident on the wafer induces an electron-hole plasma layer on the wafer, changing the wafer's dielectric constant, turning the third port into a termination for incident RF signals, and. causing all incident RF signals to be reflected from the surface of the wafer. The propagation constant of RF signals through port 3, therefore, can be changed by controlling the beam. By making the RF coupling to the third port as small as necessary, one can reduce the peak electric field on the unexcited silicon surface for any level of input power from port 1, thereby reducing risk of damaging the wafer by RF with high peak power. The switch is useful to the construction of an improved pulse compression system to boost the peak power of microwave tubes driving linear accelerators. In this application, the high-power RF switch is placed at the coupling iris between the charging waveguide and the resonant storage line of a pulse compression system. This optically controlled high power RF pulse compression system can handle hundreds of Megawatts of power at X-band.

Investigation of electrical and optical properties of low temperature titanium nitride grown by rf-magnetron sputtering

NASA Astrophysics Data System (ADS)

Sosnin, D.; Kudryashov, D.; Mozharov, A.

2017-11-01

Titanium nitride is a promising material due to its low resistivity, high hardness and chemical inertness. Titanium nitride (TiN) can be applied as an ohmic contact for n-GaN and rectifying contact for p-GaN and also as a part of perovskite solar cell. A technology of TiN low temperature reactive rf-magnetron sputtering has been developed. Electrical and optical properties of titanium nitride were studied as a function of the rf-power and gas mixture composition. Reflectance and transmittance spectra were measured. Cross-section and surface SEM image were obtained. 250 nm thin films of TiN with a resistivity of 23.6 μOm cm were obtained by rf-magnetron sputtering at low temperature.

Nanoionics-Based Switches for Radio-Frequency Applications

NASA Technical Reports Server (NTRS)

Nessel, James; Lee, Richard

2010-01-01

Nanoionics-based devices have shown promise as alternatives to microelectromechanical systems (MEMS) and semiconductor diode devices for switching radio-frequency (RF) signals in diverse systems. Examples of systems that utilize RF switches include phase shifters for electronically steerable phased-array antennas, multiplexers, cellular telephones and other radio transceivers, and other portable electronic devices. Semiconductor diode switches can operate at low potentials (about 1 to 3 V) and high speeds (switching times of the order of nanoseconds) but are characterized by significant insertion loss, high DC power consumption, low isolation, and generation of third-order harmonics and intermodulation distortion (IMD). MEMS-based switches feature low insertion loss (of the order of 0.2 dB), low DC power consumption (picowatts), high isolation (>30 dB), and low IMD, but contain moving parts, are not highly reliable, and must be operated at high actuation potentials (20 to 60 V) generated and applied by use of complex circuitry. In addition, fabrication of MEMS is complex, involving many processing steps. Nanoionics-based switches offer the superior RF performance and low power consumption of MEMS switches, without need for the high potentials and complex circuitry necessary for operation of MEMS switches. At the same time, nanoionics-based switches offer the high switching speed of semiconductor devices. Also, like semiconductor devices, nanoionics-based switches can be fabricated relatively inexpensively by use of conventional integrated-circuit fabrication techniques. More over, nanoionics-based switches have simple planar structures that can easily be integrated into RF power-distribution circuits.

RF MEMS devices for multifunctional integrated circuits and antennas

NASA Astrophysics Data System (ADS)

Peroulis, Dimitrios

Micromachining and RF Micro-Electro-Mechanical Systems (RF MEMS) have been identified as two of the most significant enabling technologies in developing miniaturized low-cost communications systems and sensor networks. The key components in these MEMS-based architectures are the RF MEMS switches and varactors. The first part of this thesis focuses on three novel RF MEMS components with state-of-the-art performance. In particular, a broadband 6 V capacitive MEMS switch is presented with insertion loss of only 0.04 and 0.17 dB at 10 and 40 GHz respectively. Special consideration is given to particularly challenging issues, such as residual stress, planarity, power handling capability and switching speed. The need for switches operating below 1 GHz is also identified and a spring-loaded metal-to-metal contact switch is developed. The measured on-state contact resistance and off-state series capacitance are 0.5 O and 10 fF respectively for this switch. An analog millimeter-wave variable capacitor is the third MEMS component presented in this thesis. This variable capacitor shows an ultra high measured tuning range of nearly 4:1, which is the highest reported value for the millimeter-wave region. The second part of this thesis primarily concentrates on MEMS-based reconfigurable systems and their potential to revolutionize the design of future RF/microwave multifunctional systems. High-isolation switches and switch packets with isolation of more than 60 dB are designed and implemented. Furthermore, lowpass and bandpass tunable filters with 3:1 and 2:1 tuning ratios respectively are demonstrated. Similar methods have been also applied to the field of slot antennas and a novel design technique for compact reconfigurable antennas has been developed. The main advantage of these antennas is that they essentially preserve their impedance, radiation pattern, polarization, gain and efficiency for all operating frequencies. The thesis concludes by discussing the future challenges of RF MEMS, such as packaging and reliability.

A fully wafer-level packaged RF MEMS switch with low actuation voltage using a piezoelectric actuator

NASA Astrophysics Data System (ADS)

Park, Jae-Hyoung; Lee, Hee-Chul; Park, Yong-Hee; Kim, Yong-Dae; Ji, Chang-Hyeon; Bu, Jonguk; Nam, Hyo-Jin

2006-11-01

In this paper, a fully wafer-level packaged RF MEMS switch has been demonstrated, which has low operation voltage, using a piezoelectric actuator. The piezoelectric actuator was designed to operate at low actuation voltage for application to advanced mobile handsets. The dc contact type RF switch was packaged using the wafer-level bonding process. The CPW transmission lines and piezoelectric actuators have been fabricated on separate wafers and assembled together by the wafer-level eutectic bonding process. A gold and tin composite was used for eutectic bonding at a low temperature of 300 °C. Via holes interconnecting the electrical contact pads through the wafer were filled completely with electroplated copper. The fully wafer-level packaged RF MEMS switch showed an insertion loss of 0.63 dB and an isolation of 26.4 dB at 5 GHz. The actuation voltage of the switch was 5 V. The resonant frequency of the piezoelectric actuator was 38.4 kHz and the spring constant of the actuator was calculated to be 9.6 N m-1. The size of the packaged SPST (single-pole single-through) switch was 1.2 mm × 1.2 mm including the packaging sealing rim. The effect of the proposed package structure on the RF performance was characterized with a device having CPW through lines and vertical feed lines excluding the RF switches. The measured packaging loss was 0.2 dB and the return loss was 33.6 dB at 5 GHz.

Coaxial Switch

DTIC Science & Technology

2014-04-23

0005] RF coaxial switches are typically used in environments that are prone to mechanical shocks and vibrations . For example, in military...withstand mechanical shocks and vibrations and to maintain an RF connection throughout a shock or a vibration event. Attorney Docket No. 102139...3 of 16 [0006] It has been found that shocks and vibrations on prior art rotary-type coaxial switches may cause the shaft in the coaxial switch

Plasma Switch for High-Power Active Pulse Compressor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirshfield, Jay L.

2013-11-04

Results are presented from experiments carried out at the Naval Research Laboratory X-band magnicon facility on a two-channel X-band active RF pulse compressor that employed plasma switches. Experimental evidence is shown to validate the basic goals of the project, which include: simultaneous firing of plasma switches in both channels of the RF circuit, operation of quasi-optical 3-dB hybrid directional coupler coherent superposition of RF compressed pulses from both channels, and operation of the X-band magnicon directly in the RF pulse compressor. For incident 1.2 ?s pulses in the range 0.63 ? 1.35 MW, compressed pulses of peak powers 5.7 ?more » 11.3 MW were obtained, corresponding to peak power gain ratios of 8.3 ? 9.3. Insufficient bakeout and conditioning of the high-power RF circuit prevented experiments from being conducted at higher RF input power levels.« less

Improved ohmic contact of Ga-Doped ZnO to p-GaN by using copper sulfide intermediate layers

NASA Astrophysics Data System (ADS)

Gu, Wen; Xu, Tao; Zhang, Jianhua

2013-11-01

Copper sulfide (CuS) was used as the intermediate layer to build ohmic contact of Ga-Doped ZnO (GZO) transparent conduction layer (TCL) to p-GaN. The CuS and GZO layers were prepared by thermal evaporation and RF magnetron sputtering, respectively. Although the GZO-only contacts to p-GaN exhibit nonlinear behavior, ohmic contact with a specific contact resistance of 1.6 × 10-2 Ω cm2 has been realized by inserting 3 nm CuS layer between GZO and p-GaN. The optical transmittance of CuS/GZO film was measured to be higher than 80% in the range of 450-600 nm wavelength. The possible mechanism for the ohmic contact behavior can be attributed to the increased hole concentration of p-GaN surface induced by CuS films after annealing. The forward voltage of LEDs with CuS/GZO TCL has been reduced by 1.7 V at 20 mA and the output power has been increased by 29.6% at 100 mA compared with LEDs without CuS interlayer. These results indicated that using CuS intermediate layer could be a potential ohmic contact method to realize high-efficiency LEDs.

Low-voltage high-reliability MEMS switch for millimeter wave 5G applications

NASA Astrophysics Data System (ADS)

Shekhar, Sudhanshu; Vinoy, K. J.; Ananthasuresh, G. K.

2018-07-01

Lack of reliability of radio-frequency microelectromechanical systems (RF MEMS) switches has inhibited their commercial success. Dielectric stiction/breakdown and mechanical shock due to high actuation voltage are common impediments in capacitive MEMS switches. In this work, we report low-actuation voltage RF MEMS switch and its reliability test. Experimental characterization of fabricated devices demonstrate that proposed MEMS switch topology needs very low voltage (4.8 V) for actuation. The mechanical resonant frequency, f 0, quality factor, Q, and switching time are measured to be 8.35 kHz, 1.2, and 33 microsecond, respectively. These MEMS switches have high reliability in terms of switching cycles. Measurements are performed using pulse waveform of magnitude of 6 V under hot-switching condition. Temperature measurement results confirm that the reported switch topology has good thermal stability. The robustness in terms of the measured pull-in voltage shows a variation of 0.08 V °C‑1. Lifetime measurement results after 10 million switching cycles demonstrate insignificant change in the RF performance without any failure. Experimental results show that low voltage improves the lifetime. Low insertion loss (less than 0.6 dB) and improved isolation (above 40 dB) in the frequency range up to 60 GHz have been reported. Measured RF characteristics in the frequency range from 10 MHz to 60 GHz support that these MEMS switches are favorable choice for mm-wave 5G applications.

Design of DC-contact RF MEMS switch with temperature stability

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Junfeng; Nanjing Electronic Devices Institute, Nanjing, 210016; Li, Zhiqun, E-mail: zhiqunli@seu.edu.cn

In order to improve the temperature stability of DC-contact RF MEMS switch, a thermal buckle-beam structure is implemented. The stability of the switch pull-in voltage versus temperature is not only improved, but also the impact of stress and stress gradient on the drive voltage is suppressed. Test results show that the switch pull-in voltage is less sensitive to temperature between -20 °C and 100 °C. The variable rate of pull-in voltage to temperature is about -120 mV/°C. The RF performance of the switch is stable, and the isolation is almost independent of temperature. After being annealed at 280 °C formore » 12 hours, our switch samples, which are suitable for packaging, have less than 1.5% change in the rate of pull-in voltage.« less

Amorphous SiC as a structural layer in microbridge-based RF MEMS switches for use in software-defined radio

NASA Astrophysics Data System (ADS)

Parro, Rocco J.; Scardelletti, Maximilian C.; Varaljay, Nicholas C.; Zimmerman, Sloan; Zorman, Christian A.

2008-10-01

This paper reports an effort to develop amorphous silicon carbide (a-SiC) films for use in shunt capacitor RF MEMS microbridge-based switches. The films were deposited using methane and silane as the precursor gases. Switches were fabricated using 500 nm and 300 nm-thick a-SiC films to form the microbridges. Switches made from metallized 500 nm-thick SiC films exhibited favorable mechanical performance but poor RF performance. In contrast, switches made from metallized 300 nm-thick SiC films exhibited excellent RF performance but poor mechanical performance. Load-deflection testing of unmetallized and metallized bulk micromachined SiC membranes indicates that the metal layers have a small effect on the Young's modulus of the 500 nm and 300 nm-thick SiC MEMS. As for residual stress, the metal layers have a modest effect on the 500 nm-thick structures, but a significant affect on the residual stress in the 300 nm-thick structures.

Zero-static power radio-frequency switches based on MoS2 atomristors.

PubMed

Kim, Myungsoo; Ge, Ruijing; Wu, Xiaohan; Lan, Xing; Tice, Jesse; Lee, Jack C; Akinwande, Deji

2018-06-28

Recently, non-volatile resistance switching or memristor (equivalently, atomristor in atomic layers) effect was discovered in transitional metal dichalcogenides (TMD) vertical devices. Owing to the monolayer-thin transport and high crystalline quality, ON-state resistances below 10 Ω are achievable, making MoS 2 atomristors suitable as energy-efficient radio-frequency (RF) switches. MoS 2 RF switches afford zero-hold voltage, hence, zero-static power dissipation, overcoming the limitation of transistor and mechanical switches. Furthermore, MoS 2 switches are fully electronic and can be integrated on arbitrary substrates unlike phase-change RF switches. High-frequency results reveal that a key figure of merit, the cutoff frequency (f c ), is about 10 THz for sub-μm 2 switches with favorable scaling that can afford f c above 100 THz for nanoscale devices, exceeding the performance of contemporary switches that suffer from an area-invariant scaling. These results indicate a new electronic application of TMDs as non-volatile switches for communication platforms, including mobile systems, low-power internet-of-things, and THz beam steering.

Low power consumption resistance random access memory with Pt/InOx/TiN structure

NASA Astrophysics Data System (ADS)

Yang, Jyun-Bao; Chang, Ting-Chang; Huang, Jheng-Jie; Chen, Yu-Ting; Tseng, Hsueh-Chih; Chu, Ann-Kuo; Sze, Simon M.; Tsai, Ming-Jinn

2013-09-01

In this study, the resistance switching characteristics of a resistive random access memory device with Pt/InOx/TiN structure is investigated. Unstable bipolar switching behavior is observed during the initial switching cycle, which then stabilizes after several switching cycles. Analyses indicate that the current conduction mechanism in the resistance state is dominated by Ohmic conduction. The decrease in electrical conductance can be attributed to the reduction of the cross-sectional area of the conduction path. Furthermore, the device exhibits low operation voltage and power consumption.

Beam-Switch Transient Effects in the RF Path of the ICAPA Receive Phased Array Antenna

NASA Technical Reports Server (NTRS)

Sands, O. Scott

2003-01-01

When the beam of a Phased Array Antenna (PAA) is switched from one pointing direction to another, transient effects in the RF path of the antenna are observed. Testing described in the report has revealed implementation-specific transient effects in the RF channel that are associated with digital clocking pulses that occur with transfer of data from the Beam Steering Controller (BSC) to the digital electronics of the PAA under test. The testing described here provides an initial assessment of the beam-switch phenomena by digitally acquiring time series of the RF communications channel, under CW excitation, during the period of time that the beam switch transient occurs. Effects are analyzed using time-frequency distributions and instantaneous frequency estimation techniques. The results of tests conducted with CW excitation supports further Bit-Error-Rate (BER) testing of the PAA communication channel.

Design and Development of a Series Switch for High Voltage in RF Heating

NASA Astrophysics Data System (ADS)

Patel, Himanshu K.; Shah, Deep; Thacker, Mauli; Shah, Atman

2013-02-01

Plasma is the fourth state of matter. To sustain plasma in its ionic form very high temperature is essential. RF heating systems are used to provide the required temperature. Arching phenomenon in these systems can cause enormous damage to the RF tube. Heavy current flows across the anode-cathode junction, which need to be suppressed in minimal time for its protection. Fast-switching circuit breakers are used to cut-off the load from the supply in cases of arching. The crowbar interrupts the connection between the high voltage power supply (HVPS) and the RF tube for a temporary period between which the series switch has to open. The crowbar shunts the current across the load but in the process leads to short circuiting the HVPS. Thus, to protect the load as well as the HVPS a series switch is necessary. This paper presents the design and development of high voltage Series Switch for the high power switching applications. Fiber optic based Optimum triggering scheme is designed and tested to restrict the time delay well within the stipulated limits. The design is well supported with the experimental results for the whole set-up along with the series switch at various voltage level before its approval for operation at 5.2 kV.

Silicon Micromachining in RF and Photonic Applications

NASA Technical Reports Server (NTRS)

Lin, Tsen-Hwang; Congdon, Phil; Magel, Gregory; Pang, Lily; Goldsmith, Chuck; Randall, John; Ho, Nguyen

1995-01-01

Texas Instruments (TI) has developed membrane and micromirror devices since the late 1970s. An eggcrate space membrane was used as the spatial light modulator in the early years. Discrete micromirrors supported by cantilever beams created a new era for micromirror devices. Torsional micromirror and flexure-beam micromirror devices were promising for mass production because of their stable supports. TI's digital torsional micromirror device is an amplitude modulator (known as the digital micromirror device (DMD) and is in production development, discussed elsewhere. We also use a torsional device for a 4 x 4 fiber-optic crossbar switch in a 2 cm x 2 cm package. The flexure-beam micromirror device is an analog phase modulator and is considered more efficient than amplitude modulators for use in optical processing systems. TI also developed millimeter-sized membranes for integrated optical switches for telecommunication and network applications. Using a member in radio frequency (RF) switch applications is a rapidly growing area because of the micromechanical device performance in microsecond-switching characteristics. Our preliminary membrane RF switch test structure results indicate promising speed and RF switching performance. TI collaborated with MIT for modeling of metal-based micromachining.

Maximum powers of low-loss series-shunt FET RF switches

NASA Astrophysics Data System (ADS)

Yang, Z.; Hu, X.; Yang, J.; Simin, G.; Shur, M.; Gaska, R.

2009-02-01

Low-loss high-power single pole single throw (SPST) monolithic RF switch based on AlGaN/GaN heterojunction field effect transistors (HFETs) demonstrate the insertion loss and isolation of 0.15 dB and 45.9 dB at 0.5 GHz and 0.23 dB and 34.3 dB at 2 GHz. Maximum switching powers are estimated +47 dBm or higher. Factors determining the maximum switching powers are analyzed. Design principles to obtain equally high switching powers in the ON and OFF-states are developed.

Multi-functional properties of CaCu3Ti4O12 thin films

NASA Astrophysics Data System (ADS)

Felix, A. A.; Rupp, J. L. M.; Varela, J. A.; Orlandi, M. O.

2012-09-01

In this work, electric transport properties of CaCu3Ti4O12 (CCTO) thin films were investigated for resistive switching, rectifying and gas sensor applications. Single phase CCTO thin films were produced by polymeric precursor method (PPM) on different substrates and their electrical properties were studied. Films produced on LNO/Si substrates have symmetrical non-ohmic current-voltage characteristics, while films deposited on Pt/Si substrates have a highly asymmetrical non-ohmic behavior which is related to a metal-semiconductor junction formed at the CCTO/Pt interface. In addition, results confirm that CCTO has a resistive switching response which is enhanced by Schottky contacts. Sensor response tests revealed that CCTO films are sensitive to oxygen gas and exhibit n-type conductivity. These results demonstrate the versatility of CCTO thin film prepared by the PPM method for gas atmosphere or bias dependent resistance applications.

Carbon Nanotube Switches for Communication and Memory Applications

NASA Technical Reports Server (NTRS)

Kaul, Anupama B.; Epp, Larry; Wong, Eric W.; Kowalczyk, Robert

2008-01-01

Lateral CNT Switches: a) dc CNT switches were demonstrated to operate at low voltages, low powers and high speeds. b) RF simulations of switch in series configuration with metallized tube yielded good RF performance 1) Isolation simulated to be approx. 20 dB at 100 GHz. 2) Insertion loss simulated to be < 0.5 dB at 100 GHz. Vertical CNT Switches: a) Thermal CVD was used to mechanically constrain tubes in nanopockets; tubes not self-supporting. b) Demonstrated growth of vertically aligned arrays and single-few MWNTs using dc PECVD with Ni catalyst using optical lithography.

RF MEMS microswitches design and characterization

NASA Astrophysics Data System (ADS)

Lafontan, Xavier; Dufaza, Christian; Robert, Michel; Perez, Guy; Pressecq, Francis

2000-08-01

This paper presents the work performed in MUMPs on RF MEMS micro-switch. Concepts, design and characterization of switches are studied. The study particularly focuses on the electrical resistance characterization and modelization. The switches developed uses two different principle: overflowed gold and hinged beam. The realized contacts exhibited high on resistance (~20(Omega) ) due to nanoscopics asperities of contacts and insulating interfacial films. Results of a typical contact cleaning method are also presented.

High-Power X-Band Semiconductor RF Switch for Pulse Compression Systems of Future Colliders

NASA Astrophysics Data System (ADS)

Tantawi, Sami G.; Tamura, Fumihiko

2000-04-01

We describe the potential of semiconductor X-band RF switch arrays as a means of developing high power RF pulse compression systems for future linear colliders. The switch systems described here have two designs. Both designs consist of two 3dB hybrids and active modules. In the first design the module is composed of a cascaded active phase shifter. In the second design the module uses arrays of SPST (Single Pole Single Throw) switches. Each cascaded element of the phase shifter and the SPST switch has similar design. The active element consists of symmetrical three-port tee-junctions and an active waveguide window in the symmetrical arm of the tee-junction. The design methodology of the elements and the architecture of the whole switch system are presented. We describe the scaling law that governs the relation between power handling capability and number of elements. The design of the active waveguide window is presented. The waveguide window is a silicon wafer with an array of four hundred PIN/NIP diodes covering the surface of the window. This waveguide window is located in an over-moded TE01 circular waveguide. The results of high power RF measurements of the active waveguide window are presented. The experiment is performed at power levels of tens of megawatts at X-band.

Phase modulation in RF tag

DOEpatents

Carrender, Curtis Lee; Gilbert, Ronald W.

2007-02-20

A radio frequency (RF) communication system employs phase-modulated backscatter signals for RF communication from an RF tag to an interrogator. The interrogator transmits a continuous wave interrogation signal to the RF tag, which based on an information code stored in a memory, phase-modulates the interrogation signal to produce a backscatter response signal that is transmitted back to the interrogator. A phase modulator structure in the RF tag may include a switch coupled between an antenna and a quarter-wavelength stub; and a driver coupled between the memory and a control terminal of the switch. The driver is structured to produce a modulating signal corresponding to the information code, the modulating signal alternately opening and closing the switch to respectively decrease and increase the transmission path taken by the interrogation signal and thereby modulate the phase of the response signal. Alternatively, the phase modulator may include a diode coupled between the antenna and driver. The modulating signal from the driver modulates the capacitance of the diode, which modulates the phase of the response signal reflected by the diode and antenna.

Novel Sn-Based Contact Structure for GeTe Phase Change Materials.

PubMed

Simchi, Hamed; Cooley, Kayla A; Ding, Zelong; Molina, Alex; Mohney, Suzanne E

2018-05-16

Germanium telluride (GeTe) is a phase change material (PCM) that has gained recent attention because of its incorporation as an active material for radio frequency (RF) switches, as well as memory and novel optoelectronic devices. Considering PCM-based RF switches, parasitic resistances from Ohmic contacts can be a limiting factor in device performance. Reduction of the contact resistance ( R c ) is therefore critical for reducing the on-state resistance to meet the requirements of high-frequency RF applications. To engineer the Schottky barrier between the metal contact and GeTe, Sn was tested as an interesting candidate to alter the composition of the semiconductor near its surface, potentially forming a narrow band gap (0.2 eV) SnTe or a graded alloy with SnTe in GeTe. For this purpose, a novel contact stack of Sn/Fe/Au was employed and compared to a conventional Ti/Pt/Au stack. Two different premetallization surface treatments of HCl and deionized (DI) H 2 O were employed to make a Te-rich and Ge-rich interface, respectively. Contact resistance values were extracted using the refined transfer length method. The best results were obtained with DI H 2 O for the Sn-based contacts but HCl treatment for the Ti/Pt/Au contacts. The as-deposited contacts had the R c (ρ c ) of 0.006 Ω·mm (8 × 10 -9 Ω·cm 2 ) for Sn/Fe/Au and 0.010 Ω·mm (3 × 10 -8 Ω·cm 2 ) for Ti/Pt/Au. However, the Sn/Fe/Au contacts were thermally stable, and their resistance decreased further to 0.004 Ω·mm (4 × 10 -9 Ω·cm 2 ) after annealing at 200 °C. In contrast, the contact resistance of the Ti/Pt/Au stack increased to 0.012 Ω·mm (4 × 10 -8 Ω·cm 2 ). Transmission electron microscopy was used to characterize the interfacial reactions between the metals and GeTe. It was found that formation of SnTe at the interface, in addition to Fe diffusion (doping) into GeTe, is likely responsible for the superior performance of Sn/Fe/Au contacts, resulting in one of the lowest reported contact resistances on GeTe.

On the Application of Inverse-Mode SiGe HBTs in RF Receivers for the Mitigation of Single-Event Transients

NASA Astrophysics Data System (ADS)

Song, Ickhyun; Cho, Moon-Kyu; Oakley, Michael A.; Ildefonso, Adrian; Ju, Inchan; Buchner, Stephen P.; McMorrow, Dale; Paki, Pauline; Cressler, John. D.

2017-05-01

Best practice in mitigation strategies for single-event transients (SETs) in radio-frequency (RF) receiver modules is investigated using a variety of integrated receivers utilizing inverse-mode silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs). The receivers were designed and implemented in a 130-nm SiGe BiCMOS technology platform. In general, RF switches, low-noise amplifiers (LNAs), and downconversion mixers utilizing inverse-mode SiGe HBTs exhibit less susceptibility to SETs than conventional RF designs, in terms of transient peaks and duration, at the cost of RF performance. Under normal RF operation, the SET-hardened switch is mainly effective in peak reduction, while the LNA and the mixer exhibit reductions in transient peaks as well as transient duration.

MEMS switches having non-metallic crossbeams

NASA Technical Reports Server (NTRS)

Scardelletti, Maximillian C (Inventor)

2009-01-01

A RF MEMS switch comprising a crossbeam of SiC, supported by at least one leg above a substrate and above a plurality of transmission lines forming a CPW. Bias is provided by at least one layer of metal disposed on a top surface of the SiC crossbeam, such as a layer of chromium followed by a layer of gold, and extending beyond the switch to a biasing pad on the substrate. The switch utilizes stress and conductivity-controlled non-metallic thin cantilevers or bridges, thereby improving the RF characteristics and operational reliability of the switch. The switch can be fabricated with conventional silicon integrated circuit (IC) processing techniques. The design of the switch is very versatile and can be implemented in many transmission line mediums.

Effect of counterions on the formation of ohmic contact between p-Si and poly(pyrrole) film - An ac impedance analysis

NASA Technical Reports Server (NTRS)

Nagsubramanian, G.; Distefano, S.; Moacanin, J.

1986-01-01

Conditions under which poly(pyrrole) (PP) films form ohmic contact with single-crystal p-Si are described. Counterions affect both the conductivity and flatband potential, V(FB), values of poly(pyrrole). While paratoluene-sulfonate-doped PP acts like a switch, the impedance behavior of PP films doped with ClO4(-), BF4(-), or PF6(-) allows evaluation of the V(FB) of these films. The formation of 'quasi-ohmic' and 'nonohmic' contacts, respectively, of PP (ClO4) and PP films doped with other counterions, with p-Si, are explained in terms of conductivity of these films and V(FB) of PP films with respect to that of p-Si. PP film seems to passivate or block intrinsic surface states present on p-Si surface.

Ohmic ignition with high engineering beta based on the RFP

NASA Astrophysics Data System (ADS)

Sarff, J. S.; Anderson, J. K.; Chapman, B. E.; McCollam, K. J.

2017-10-01

The RFP configuration allows the possibility of ohmic ignition for fusion energy, eliminating the need for auxiliary heating by rf or neutral beam injection. Complex plasma-facing antennas and NBI sources are therefore not required, simplifying the difficult fusion materials challenge. While all toroidal configurations require a volume-average 〈 B 〉 >= 5 T, the field strength at the magnet in the RFP is only Bcoil 3T since plasma current generates almost all of the field. Engineering beta is therefore maximized. We summarize access to ohmic ignition by examining a Lawson-like power balance for an RFP fusion plasma comparable to the ARIES-AT advanced tokamak, which generates neutron wall loading Pn / A 5 MW/m2. The required energy confinement for ohmic ignition in an RFP is similar to that for a tokamak. Confinement in MST is comparable to a same-size, same-field tokamak plasma, but 〈 B 〉 in MST is only 1/20th that required for fusion. While transport could ultimately be dominated by micro turbulence, extrapolation of stochastic transport using Lundquist number scaling for MHD tearing indicates standard RFP confinement (not enhanced by current profile control) could be sufficient to access ohmic ignition. This bolsters the possibility for steady-state inductive sustainment using oscillating field current drive. The high beta and classical energetic ion confinement measured in MST also bolster the RFP's fusion potential. Work supported by U.S. DoE.

Examination of the temperature dependent electronic behavior of GeTe for switching applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Champlain, James G.; Ruppalt, Laura B.; Guyette, Andrew C.

2016-06-28

The DC and RF electronic behaviors of GeTe-based phase change material switches as a function of temperature, from 25 K to 375 K, have been examined. In its polycrystalline (ON) state, GeTe behaved as a degenerate p-type semiconductor, exhibiting metal-like temperature dependence in the DC regime. This was consistent with the polycrystalline (ON) state RF performance of the switch, which exhibited low resistance S-parameter characteristics. In its amorphous (OFF) state, the GeTe presented significantly greater DC resistance that varied considerably with bias and temperature. At low biases (<1 V) and temperatures (<200 K), the amorphous GeTe low-field resistance dramatically increased, resulting in exceptionally highmore » amorphous-polycrystalline (OFF-ON) resistance ratios, exceeding 10{sup 9} at cryogenic temperatures. At higher biases and temperatures, the amorphous GeTe exhibited nonlinear current-voltage characteristics that were best fit by a space-charge limited conduction model that incorporates the effect of a defect band. The observed conduction behavior suggests the presence of two regions of localized traps within the bandgap of the amorphous GeTe, located at approximately 0.26–0.27 eV and 0.56–0.57 eV from the valence band. Unlike the polycrystalline state, the high resistance DC behavior of amorphous GeTe does not translate to the RF switch performance; instead, a parasitic capacitance associated with the RF switch geometry dominates OFF state RF transmission.« less

Radio frequency switching network: a technique for infrared sensing

NASA Astrophysics Data System (ADS)

Mechtel, Deborah M.; Jenkins, R. Brian; Joyce, Peter J.; Nelson, Charles L.

2016-10-01

This paper describes a unique technique that implements photoconductive sensors in a radio frequency (RF) switching network designed to locate in real-time the position and intensity of IR radiation incident on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches in a two-layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous-doped silicon photoconductive sensors are inserted in GHz range RF transmission lines. By permitting signal propagation only when a sensor is illuminated, the RF signals are selectively routed from lower layer transmission lines to upper layer lines, thereby pinpointing the location and strength of incident radiation. Simulations based on a high frequency three-dimensional planar electromagnetics model are presented and compared to the experimental results. The experimental results are described for GHz range RF signal control for 300- and 180-mW incident energy from 975- to 1060-nm wavelength lasers, respectively, where upon illumination, RF transmission line signal output power doubled when compared to nonilluminated results. The experimental results are also reported for 100-W incident energy from a 1060-nm laser. Test results illustrate real-time signal processing would permit a structure to be controlled in response to incident radiation.

Investigation of regime switching from mode locking to Q-switching in a 2 µm InGaSb/AlGaAsSb quantum well laser.

PubMed

Li, Xiang; Wang, Hong; Qiao, Zhongliang; Guo, Xin; Wang, Wanjun; Ng, Geok Ing; Zhang, Yu; Xu, Yingqiang; Niu, Zhichuan; Tong, Cunzhu; Liu, Chongyang

2018-04-02

A two-section InGaSb/AlGaAsSb single quantum well (SQW) laser emitting at 2 μm is presented. By varying the absorber bias voltage with a fixed gain current at 130 mA, passive mode locking at ~18.40 GHz, Q-switched mode locking, and passive Q-switching are observed in this laser. In the Q-switched mode locking regimes, the Q-switched RF signal and mode locked RF signal coexist, and the Q-switched lasing and mode-locked lasing happen at different wavelengths. This is the first observation of these three pulsed working regimes in a GaSb-based diode laser. An analysis of the regime switching mechanism is given based on the interplay between the gain saturation and the saturable absorption.

Ultra-low switching energy and scaling in electric-field-controlled nanoscale magnetic tunnel junctions with high resistance-area product

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grezes, C.; Alzate, J. G.; Cai, X.

2016-01-04

We report electric-field-induced switching with write energies down to 6 fJ/bit for switching times of 0.5 ns, in nanoscale perpendicular magnetic tunnel junctions (MTJs) with high resistance-area product and diameters down to 50 nm. The ultra-low switching energy is made possible by a thick MgO barrier that ensures negligible spin-transfer torque contributions, along with a reduction of the Ohmic dissipation. We find that the switching voltage and time are insensitive to the junction diameter for high-resistance MTJs, a result accounted for by a macrospin model of purely voltage-induced switching. The measured performance enables integration with same-size CMOS transistors in compact memorymore » and logic integrated circuits.« less

Space Shuttle communications RF switch matrix

NASA Technical Reports Server (NTRS)

Winch, R.

1979-01-01

The Shuttle Orbiter communications equipment includes phase modulation (PM) and frequency modulation (FM) channels. The PM section has the capability of routing high levels of energy (175 W) from any one of four transmitters to any one of four antennas, mutually exclusive. The FM channel uses a maximum of 15-W power routed from either of two transmitters to one of two antennas, mutually exclusive. The paper describes the design and the theory of a logic-controlled RF switch matrix devised for the purposes cited. Both PM and FM channels are computer-controlled with manual overrides. The logic interface is realized with CMOS logic for low power consumption and high noise immunity. The interior of the switch matrix is maintained at a pressure of 15 psi (90% nitrogen, 10% helium) by an electron beam-welded encapsulation. The computational results confirm the viability of the RF switch matrix concept.

High-power microstrip RF switch

NASA Technical Reports Server (NTRS)

Choi, S. D.

1971-01-01

A microstrip-type single-pole double-throw (SPDT) switch whose RF and bias portions contain only a metallized alumina substrate and two PIN diodes has been developed. A technique developed to eliminate the dc blocking capacitors needed for biasing the diodes is described. These capacitors are extra components and could lower the reliability significantly. An SPDT switch fabricated on a 5.08 x 5.08 x 0.127-cm (2 x 2 x 0.050-in.) substrate has demonstrated an RF power-handling capability greater than 50 W at S-band. The insertion loss is less than 0.25 db and the input-to-off port isolation is greater than 36 db over a bandwidth larger than 30 MHz. The input voltage standing-wave ratio is lower than 1.07 over the same bandwidth. Theoretical development of the switch characteristics and experimental results, which are in good agreement with theory, are presented.

Silica-Based Optical Time-Shift Network.

DTIC Science & Technology

1996-03-01

consisted of semiconductor lasers and detectors, RF transfer -switches, low noise RF amplifiers (LNA), and T2L circuitries installed to enable switching...F/O TRANSFER BOX (1) RADIATING ELEMENTS 1:8 POWER DIVIDER (24 CARDS) 1.4 POWER DIVIDER (24) Tr/R MODULE (24) F/O DELAY WITH 2 TRANSFER SWITCHES AND 1...of the mode can travel is the velocity of light (= c/ni) in the outer clad, the part of it that lies beyond a critical radius Rc would not be able to

A Ku band 5 bit MEMS phase shifter for active electronically steerable phased array applications

NASA Astrophysics Data System (ADS)

Sharma, Anesh K.; Gautam, Ashu K.; Farinelli, Paola; Dutta, Asudeb; Singh, S. G.

2015-03-01

The design, fabrication and measurement of a 5 bit Ku band MEMS phase shifter in different configurations, i.e. a coplanar waveguide and microstrip, are presented in this work. The development architecture is based on the hybrid approach of switched and loaded line topologies. All the switches are monolithically manufactured on a 200 µm high resistivity silicon substrate using 4 inch diameter wafers. The first three bits (180°, 90° and 45°) are realized using switched microstrip lines and series ohmic MEMS switches whereas the fourth and fifth bits (22.5° and 11.25°) consist of microstrip line sections loaded by shunt ohmic MEMS devices. Individual bits are fabricated and evaluated for performance and the monolithic device is a 5 bit Ku band (16-18 GHz) phase shifter with very low average insertion loss of the order of 3.3 dB and a return loss better than 15 dB over the 32 states with a chip area of 44 mm2. A total phase shift of 348.75° with phase accuracy within 3° is achieved over all of the states. The performance of individual bits has been optimized in order to achieve an integrated performance so that they can be implemented into active electronically steerable antennas for phased array applications.

Development of a high-power solid-state switch using static induction thyristors for a klystron modulator

NASA Astrophysics Data System (ADS)

Tokuchi, Akira; Kamitsukasa, Fumiyoshi; Furukawa, Kazuya; Kawase, Keigo; Kato, Ryukou; Irizawa, Akinori; Fujimoto, Masaki; Osumi, Hiroki; Funakoshi, Sousuke; Tsutsumi, Ryouta; Suemine, Shoji; Honda, Yoshihide; Isoyama, Goro

2015-01-01

We developed a solid-state switch with static induction thyristors for the klystron modulator of the L-band electron linear accelerator (linac) at the Institute of Scientific and Industrial Research, Osaka University. This switch is designed to have maximum specifications of a holding voltage of 25 kV and a current of 6 kA at the repetition frequency of 10 Hz for forced air cooling. The turn-on time of the switch was measured with a matched resistor to be 270 ns, which is sufficiently fast for the klystron modulator. The switch is retrofitted in the modulator to generate 1.3 GHz RF pulses with durations of either 4 or 8 μs using a 30 MW klystron, and the linac is successfully operated under maximum conditions. This finding demonstrates that the switch can be used as a high-power switch for the modulator. Pulse-to-pulse variations of the klystron voltage are measured to be less than 0.015%, and those of RF power and phase are lower than 0.15% and 0.1°, respectively. These values are significantly smaller than those obtained with a thyratron; hence, the stability of the main RF system is improved. The solid-state switch has been used in normal operation of the linac for more than a year without any serious trouble. Thus, we confirmed the switch's robustness and long-term reliability.

Electronic interaction and bipolar resistive switching in copper oxide-multilayer graphene hybrid interface: Graphene as an oxygen ion storage and blocking layer

NASA Astrophysics Data System (ADS)

Singh, Bharti; Mehta, B. R.; Govind, Feng, X.; Müllen, Klaus

2011-11-01

This study reports a bipolar resistive switching device based on copper oxide (CuO)-multilayer graphene (MLG) hybrid interface in complete contrast to the ohmic and rectifying characteristics of junctions based on individual MLG and CuO layers. The observed shift and the occurrence of additional O1s, Cu2p, and C1s core level peaks indicate electronic interaction at the hybrid interfacial layer. Large changes in the resistive switching parameters on changing the ambient conditions from air to vacuum establish the important role of MLG as oxygen ion storage and blocking layer towards the observed resistive switching effect.

RF digital-to-analog converter

DOEpatents

Conway, Patrick H.; Yu, David U. L.

1995-01-01

A digital-to analogue converter for producing an RF output signal proportional to a digital input word of N bits from an RF reference input, N being an integer greater or equal to 2. The converter comprises a plurality of power splitters, power combiners and a plurality of mixers or RF switches connected in a predetermined configuration.

Finite element based contact analysis of radio frequency MEMs switch membrane surfaces

NASA Astrophysics Data System (ADS)

Liu, Jin-Ya; Chalivendra, Vijaya; Huang, Wenzhen

2017-10-01

Finite element simulations were performed to determine the contact behavior of radio frequency (RF) micro-electro-mechanical (MEM) switch contact surfaces under monotonic and cyclic loading conditions. Atomic force microscopy (AFM) was used to capture the topography of RF-MEM switch membranes and later they were analyzed for multi-scale regular as well as fractal structures. Frictionless, non-adhesive contact 3D finite element analysis was carried out at different length scales to investigate the contact behavior of the regular-fractal surface using an elasto-plastic material model. Dominant micro-scale regular patterns were found to significantly change the contact behavior. Contact areas mainly cluster around the regular pattern. The contribution from the fractal structure is not significant. Under cyclic loading conditions, plastic deformation in the 1st loading/unloading cycle smooth the surface. The subsequent repetitive loading/unloading cycles undergo elastic contact without changing the morphology of the contacting surfaces. The work is expected to shed light on the quality of the switch surface contact as well as the optimum design of RF MEM switch surfaces.

OVERMODED HIGH-POWER RF MAGNETIC SWITCHES AND CIRCULATORS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tantawi, Sami

2002-08-20

We present design methodology for active rf magnetic components which are suitable for pulse compression systems of future X-band linear colliders. These components comprise an array of active elements arranged together so that the total electromagnetic field is reduced and the power handling capabilities are increased. The active element of choice is a magnetic material (garnet), which can be switched by changing a biasing magnetic field. A novel design allows these components to operate in the low loss circular waveguide mode TE{sub 01}. We describe the design methodology, the switching elements and circuits.

A dual-stimuli-responsive fluorescent switch ultrathin film

NASA Astrophysics Data System (ADS)

Li, Zhixiong; Liang, Ruizheng; Liu, Wendi; Yan, Dongpeng; Wei, Min

2015-10-01

Stimuli-responsive fluorescent switches have shown broad applications in optical devices, biological materials and intelligent responses. Herein, we describe the design and fabrication of a dual-stimuli-responsive fluorescent switch ultrathin film (UTF) via a three-step layer-by-layer (LBL) technique: (i) encapsulation of spiropyran (SP) within an amphiphilic block copolymer (PTBEM) to give the (SP@PTBEM) micelle; (ii) the mixture of riboflavin (Rf) and poly(styrene 4-sulfonate) (PSS) to enhance the adhesion ability of small molecules; (iii) assembly of negatively charged SP@PTBEM and Rf-PSS with cationic layered double hydroxide (LDH) nanoplatelets to obtain the (Rf-PSS/LDH/SP@PTBEM)n UTFs (n: bilayer number). The assembly process of the UTFs and their luminescence properties, as monitored by fluorescence spectroscopy and scanning electron microscopy (SEM), present a uniform and ordered layered structure with stepwise growth. The resulting Rf-PSS/LDH/SP@PTBEM UTF serves as a three-state switchable multicolor (green, yellow, and red) luminescent system based on stimulation from UV/Vis light and pH, with an acceptable reversibility. Therefore, this work provides a facile way to fabricate stimuli-responsive solid-state film switches with tunable-color luminescence, which have potential applications in the areas of displays, sensors, and rewritable optical memory and fluorescent logic devices.Stimuli-responsive fluorescent switches have shown broad applications in optical devices, biological materials and intelligent responses. Herein, we describe the design and fabrication of a dual-stimuli-responsive fluorescent switch ultrathin film (UTF) via a three-step layer-by-layer (LBL) technique: (i) encapsulation of spiropyran (SP) within an amphiphilic block copolymer (PTBEM) to give the (SP@PTBEM) micelle; (ii) the mixture of riboflavin (Rf) and poly(styrene 4-sulfonate) (PSS) to enhance the adhesion ability of small molecules; (iii) assembly of negatively charged SP@PTBEM and Rf-PSS with cationic layered double hydroxide (LDH) nanoplatelets to obtain the (Rf-PSS/LDH/SP@PTBEM)n UTFs (n: bilayer number). The assembly process of the UTFs and their luminescence properties, as monitored by fluorescence spectroscopy and scanning electron microscopy (SEM), present a uniform and ordered layered structure with stepwise growth. The resulting Rf-PSS/LDH/SP@PTBEM UTF serves as a three-state switchable multicolor (green, yellow, and red) luminescent system based on stimulation from UV/Vis light and pH, with an acceptable reversibility. Therefore, this work provides a facile way to fabricate stimuli-responsive solid-state film switches with tunable-color luminescence, which have potential applications in the areas of displays, sensors, and rewritable optical memory and fluorescent logic devices. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05376e

Optical switching property of electromagnetically induced transparency in a Λ system

NASA Astrophysics Data System (ADS)

Zhang, Lianshui; Wang, Jian; Feng, Xiaomin; Yang, Lijun; Li, Xiaoli; Zhao, Min

2008-12-01

In this paper we study the coherent transient property of a Λ-three-level system (Ωd = 0) and a quasi- Λ -four-level system (Ωd>0). Optical switching of the probe field can be achieved by applying a pulsed coupling field or rf field. In Λ -shaped three-level system, when the coupling field was switched on, there is a almost total transparency of the probe field and the time required for the absorption changing from 90% to 10% of the maximum absorption is 2.9Γ0 (Γ0 is spontaneous emission lifetime). When the coupling field was switched off, there is an initial increase of the probe field absorption and then gradually evolves to the maximum of absorption of the two-level absorption, the time required for the absorption of the system changing from 10% to 90% is 4.2Γ0. In four-level system, where rf driving field is used as switching field, to achieve the same depth of the optical switching, the time of the optical switching is 2.5Γ0 and 6.1Γ0, respectively. The results show that with the same depth of the optical switching, the switch-on time of the four-level system is shorter than that of the three-level system, while the switch-off time of the four-level system is longer. The depth of the optical switching of the four-level system was much larger than that of the three-level system, where the depth of the optical switching of the latter is merely 14.8% of that of the former. The speed of optical switching of the two systems can be increased by the increase of Rabi frequency of coupling field or rf field.

Radio Frequency (RF) Micro-Electromechanical Systems (MEMS) Switches for Space Communications

NASA Technical Reports Server (NTRS)

Simons, Rainee N.; Ponchak, George E.; Scardelletti, Maximillian C.; Varaljay, Nicholas C.

2000-01-01

Micro-electromechanical systems (MEMS) is an emerging technology for radio frequency (RF) systems because it has the potential to dramatically decrease loss and improve efficiency. In this paper, we address the design and fabrication of novel MEMS switches being developed at NASA Glenn Research Center. Two types of switches are being developed: a microstrip series single pole single throw (SPST) switch and a coplanar waveguide (CPW) series SPST and single pole double throw (SPDT) switches. These are being fabricated as an integral part of 50 Ohm microstrip and CPW RF integrated circuits using microfabrication techniques. The construction of the switch relies on a cantilever beam that is partially supported by a dielectric post. The cantilever beam is electro-magnetically actuated. To decrease stiction, a Si3N4 thin film is deposited over the contact area. Thus, when the switch is closed, the ON-state insertion loss is governed by the parallel plate capacitance formed by the two contacts. The isolation in the OFF-state is governed by the parasitic capacitance when the cantilever is in the up position. RF MEMS switches have been demonstrated with 80% lower insertion loss than conventional solid state devices (GaAs Metal Semiconductor Field Effect Transistors (MESFETs) and Silicon PIN diodes) based switches. For example, a conventional GaAs five-bit phase shifter which is required for beam steering in a phased array antenna has approximately 7 dB of insertion loss at 26.5 GHz where as a comparable MEMS based phase shifter is expected to have only 2 dB of insertion loss. This translates into 56% lower power dissipation and therefore decreases the thermal load on the spacecraft and also reduces the power amplifier requirements. These benefits will enable NASA to build the next generation of deep space science crafts and micro/nano satellites.

Epitaxial VO2 thin-film-based radio-frequency switches with electrical activation

NASA Astrophysics Data System (ADS)

Lee, Jaeseong; Lee, Daesu; Cho, Sang June; Seo, Jung-Hun; Liu, Dong; Eom, Chang-Beom; Ma, Zhenqiang

2017-09-01

Vanadium dioxide (VO2) is a correlated material exhibiting a sharp insulator-to-metal phase transition (IMT) caused by temperature change and/or bias voltage. We report on the demonstration of electrically triggered radio-frequency (RF) switches based on epitaxial VO2 thin films. The highly epitaxial VO2 and SnO2 template layer was grown on a (001) TiO2 substrate by pulsed laser deposition (PLD). A resistance change of the VO2 thin films of four orders of magnitude was achieved with a relatively low threshold voltage, as low as 13 V, for an IMT phase transition. VO2 RF switches also showed high-frequency responses of insertion losses of -3 dB at the on-state and return losses of -4.3 dB at the off-state over 27 GHz. Furthermore, an intrinsic cutoff frequency of 17.4 THz was estimated for the RF switches. The study on electrical IMT dynamics revealed a phase transition time of 840 ns.

RF Reference Switch for Spaceflight Radiometer Calibration

NASA Technical Reports Server (NTRS)

Knuble, Joseph

2013-01-01

The goal of this technology is to provide improved calibration and measurement sensitivity to the Soil Moisture Active Passive Mission (SMAP) radiometer. While RF switches have been used in the past to calibrate microwave radiometers, the switch used on SMAP employs several techniques uniquely tailored to the instrument requirements and passive remote-sensing in general to improve radiometer performance. Measurement error and sensitivity are improved by employing techniques to reduce thermal gradients within the device, reduce insertion loss during antenna observations, increase insertion loss temporal stability, and increase rejection of radar and RFI (radio-frequency interference) signals during calibration. The two legs of the single-pole double-throw reference switch employ three PIN diodes per leg in a parallel-shunt configuration to minimize insertion loss and increase stability while exceeding rejection requirements at 1,413 MHz. The high-speed packaged diodes are selected to minimize junction capacitance and resistance while ensuring the parallel devices have very similar I-V curves. Switch rejection is improved by adding high-impedance quarter-wave tapers before and after the diodes, along with replacing the ground via of one diode per leg with an open circuit stub. Errors due to thermal gradients in the switch are reduced by embedding the 50-ohm reference load within the switch, along with using a 0.25-in. (approximately equal to 0.6-cm) aluminum prebacked substrate. Previous spaceflight microwave radiometers did not embed the reference load and thermocouple directly within the calibration switch. In doing so, the SMAP switch reduces error caused by thermal gradients between the load and switch. Thermal issues are further reduced by moving the custom, highspeed regulated driver circuit to a physically separate PWB (printed wiring board). Regarding RF performance, previous spaceflight reference switches have not employed high-impedance tapers to improve rejection. The use of open-circuit stubs instead of a via to provide an improved RF short is unique to this design. The stubs are easily tunable to provide high rejection at specific frequencies while maintaining very low insertion loss in-band.

RF digital-to-analog converter

DOEpatents

Conway, P.H.; Yu, D.U.L.

1995-02-28

A digital-to-analog converter is disclosed for producing an RF output signal proportional to a digital input word of N bits from an RF reference input, N being an integer greater or equal to 2. The converter comprises a plurality of power splitters, power combiners and a plurality of mixers or RF switches connected in a predetermined configuration. 18 figs.

Effects of sol aging on resistive switching behaviors of HfOx resistive memories

NASA Astrophysics Data System (ADS)

Hsu, Chih-Chieh; Sun, Jhen-Kai; Tsao, Che-Chang; Chen, Yu-Ting

2017-03-01

This work investigates effects of long-term sol-aging time on sol-gel HfOx resistive random access memories (RRAMs). A nontoxic solvent of ethanol is used to replace toxic 2-methoxyethanol, which is usually used in sol-gel processes. The top electrodes are fabricated by pressing indium balls onto the HfOx surface rather than by using conventional sputtering or evaporation processes. The maximum process temperature is limited to be 100 ℃. Therefore, influences of plasma and high temperature on HfOx film can be avoided. Under this circumstance, effects of sol aging time on the HfOx films can be more clearly studied. The current conduction mechanisms in low and high electric regions of the HfOx RRAM are found to be dominated by Ohmic conduction and trap-filled space charge limited conduction (TF-SCLC), respectively. When the sol aging time increases, the resistive switching characteristic of the HfOx layer becomes unstable and the transition voltage from Ohmic conduction to TF-SCLC is also increased. This suggests that an exceedingly long aging time will give a HfOx film with more defect states. The XPS results are consistent with FTIR analysis and they can further explain the unstable HfOx resistive switching characteristic induced by sol aging.

Influence of bending strains on radio frequency characteristics of flexible microwave switches using single-crystal silicon nanomembranes on plastic substrate

NASA Astrophysics Data System (ADS)

Qin, Guoxuan; Yuan, Hao-Chih; Celler, George K.; Ma, Jianguo; Ma, Zhenqiang

2011-10-01

This letter presents radio frequency (RF) characterization of flexible microwave switches using single-crystal silicon nanomembranes (SiNMs) on plastic substrate under various uniaxial mechanical tensile bending strains. The flexible switches shows significant/negligible performance enhancement on strains under on/off states from dc to 10 GHz. Furthermore, an RF/microwave strain equivalent circuit model is developed and reveals the most influential factors, and un-proportional device parameters change with bending strains. The study demonstrates that flexible microwave single-crystal SiNM switches, as a simple circuit example towards the goal of flexible monolithic microwave integrated circuits, can be properly operated and modeled under mechanical bending conditions.

Diplexer switch

NASA Technical Reports Server (NTRS)

Grauling, C. H., Jr.; Parker, T. W.

1977-01-01

Switch achieves high isolation and continuous input/output matching by using resonant coupling structure of diplexer. Additionally, dc bias network used to control switch is decoupled from RF input and output lines. Voltage transients in external circuits are thus minimized.

Uncertainty quantification in capacitive RF MEMS switches

NASA Astrophysics Data System (ADS)

Pax, Benjamin J.

Development of radio frequency micro electrical-mechanical systems (RF MEMS) has led to novel approaches to implement electrical circuitry. The introduction of capacitive MEMS switches, in particular, has shown promise in low-loss, low-power devices. However, the promise of MEMS switches has not yet been completely realized. RF-MEMS switches are known to fail after only a few months of operation, and nominally similar designs show wide variability in lifetime. Modeling switch operation using nominal or as-designed parameters cannot predict the statistical spread in the number of cycles to failure, and probabilistic methods are necessary. A Bayesian framework for calibration, validation and prediction offers an integrated approach to quantifying the uncertainty in predictions of MEMS switch performance. The objective of this thesis is to use the Bayesian framework to predict the creep-related deflection of the PRISM RF-MEMS switch over several thousand hours of operation. The PRISM switch used in this thesis is the focus of research at Purdue's PRISM center, and is a capacitive contacting RF-MEMS switch. It employs a fixed-fixed nickel membrane which is electrostatically actuated by applying voltage between the membrane and a pull-down electrode. Creep plays a central role in the reliability of this switch. The focus of this thesis is on the creep model, which is calibrated against experimental data measured for a frog-leg varactor fabricated and characterized at Purdue University. Creep plasticity is modeled using plate element theory with electrostatic forces being generated using either parallel plate approximations where appropriate, or solving for the full 3D potential field. For the latter, structure-electrostatics interaction is determined through immersed boundary method. A probabilistic framework using generalized polynomial chaos (gPC) is used to create surrogate models to mitigate the costly full physics simulations, and Bayesian calibration and forward propagation of uncertainty are performed using this surrogate model. The first step in the analysis is Bayesian calibration of the creep related parameters. A computational model of the frog-leg varactor is created, and the computed creep deflection of the device over 800 hours is used to generate a surrogate model using a polynomial chaos expansion in Hermite polynomials. Parameters related to the creep phenomenon are calibrated using Bayesian calibration with experimental deflection data from the frog-leg device. The calibrated input distributions are subsequently propagated through a surrogate gPC model for the PRISM MEMS switch to produce probability density functions of the maximum membrane deflection of the membrane over several thousand hours. The assumptions related to the Bayesian calibration and forward propagation are analyzed to determine the sensitivity to these assumptions of the calibrated input distributions and propagated output distributions of the PRISM device. The work is an early step in understanding the role of geometric variability, model uncertainty, numerical errors and experimental uncertainties in the long-term performance of RF-MEMS.

Transmit/receive 3-20 GHz 1.2 mW packaged double-pole-16-throw switching matrix for radar-based target detection

NASA Astrophysics Data System (ADS)

Azhari, Afreen; Kuwano, Yuki; Xiao, Xia; Kikkawa, Takamaro

2018-01-01

A 3-20 GHz transmit/receive (T/R) double-pole-16-throw (DP16T) switching matrix has been developed on a printed circuit board (PCB) to control sixteen antennas in a radar-based portable breast-cancer detection system. The DP16T switch consists of four 65 nm CMOS 0.01-20 GHz double-pole-four-throw (DP4T) switches. The proposed switch increase the number of T/R combinations to 224 from the 196 of a conventional switching matrix in order to construct high-resolution images. Using this switch and a 4 × 4 slot antenna array, a 10 × 10 mm2 aluminum target was detected with an 8-GHz-center-frequency Gaussian monocycle pulse. The power consumption of the switch is only 1.2 mW. To the best of the authors’ knowledge, this is the first T/R radio frequency (RF) DP16T switching matrix, which was realized with four CMOS DP4T switches on a PCB and was measured with RF PCB connectors.

A dual-stimuli-responsive fluorescent switch ultrathin film.

PubMed

Li, Zhixiong; Liang, Ruizheng; Liu, Wendi; Yan, Dongpeng; Wei, Min

2015-10-28

Stimuli-responsive fluorescent switches have shown broad applications in optical devices, biological materials and intelligent responses. Herein, we describe the design and fabrication of a dual-stimuli-responsive fluorescent switch ultrathin film (UTF) via a three-step layer-by-layer (LBL) technique: (i) encapsulation of spiropyran (SP) within an amphiphilic block copolymer (PTBEM) to give the (SP@PTBEM) micelle; (ii) the mixture of riboflavin (Rf) and poly(styrene 4-sulfonate) (PSS) to enhance the adhesion ability of small molecules; (iii) assembly of negatively charged SP@PTBEM and Rf-PSS with cationic layered double hydroxide (LDH) nanoplatelets to obtain the (Rf-PSS/LDH/SP@PTBEM)n UTFs (n: bilayer number). The assembly process of the UTFs and their luminescence properties, as monitored by fluorescence spectroscopy and scanning electron microscopy (SEM), present a uniform and ordered layered structure with stepwise growth. The resulting Rf-PSS/LDH/SP@PTBEM UTF serves as a three-state switchable multicolor (green, yellow, and red) luminescent system based on stimulation from UV/Vis light and pH, with an acceptable reversibility. Therefore, this work provides a facile way to fabricate stimuli-responsive solid-state film switches with tunable-color luminescence, which have potential applications in the areas of displays, sensors, and rewritable optical memory and fluorescent logic devices.

Electrical switching dynamics and broadband microwave characteristics of VO2 radio frequency devices

NASA Astrophysics Data System (ADS)

Ha, Sieu D.; Zhou, You; Fisher, Christopher J.; Ramanathan, Shriram; Treadway, Jacob P.

2013-05-01

Vanadium dioxide (VO2) is a correlated electron system that features a metal-insulator phase transition (MIT) above room temperature and is of interest in high speed switching devices. Here, we integrate VO2 into two-terminal coplanar waveguides and demonstrate a large resistance modulation of the same magnitude (>103) in both electrically (i.e., by bias voltage, referred to as E-MIT) and thermally (T-MIT) driven transitions. We examine transient switching characteristics of the E-MIT and observe two distinguishable time scales for switching. We find an abrupt jump in conductivity with a rise time of the order of 10 ns followed by an oscillatory damping to steady state on the order of several μs. We characterize the RF power response in the On state and find that high RF input power drives VO2 further into the metallic phase, indicating that electromagnetic radiation-switching of the phase transition may be possible. We measure S-parameter RF properties up to 13.5 GHz. Insertion loss is markedly flat at 2.95 dB across the frequency range in the On state, and sufficient isolation of over 25 dB is observed in the Off state. We are able to simulate the RF response accurately using both lumped element and 3D electromagnetic models. Extrapolation of our results suggests that optimizing device geometry can reduce insertion loss further and maintain broadband flatness up to 40 GHz.

Ohmic contact mechanism for RF superimposed DC sputtered-ITO transparent p-electrodes with a variety of Sn2O3 content for GaN-based light-emitting diodes

NASA Astrophysics Data System (ADS)

Kim, Tae Kyoung; Yoon, Yeo Jin; Oh, Seung Kyu; Lee, Yu Lim; Cha, Yu-Jung; Kwak, Joon Seop

2018-02-01

The dependence of the electrical and optical properties of radio frequency (RF) superimposed direct current (DC) sputtered-indium tin oxide (ITO) on the tin oxide (Sn2O3) content of the ITO is investigated, in order to elucidate an ohmic contact mechanism for the sputtered-ITO transparent electrodes on p-type gallium nitride (p-GaN). Contact resistivity of the RF superimposed DC sputtered-ITO on p-GaN in LEDs decreased when Sn2O3 content was increased from 3 wt% to 7 wt% because of the reduced sheet resistance of the sputtered-ITO with the increasing Sn2O3 content. Further increases in Sn2O3 content from 7 wt% to 15 wt% resulted in deterioration of the contact resistivity, which can be attributed to reduction of the work function of the ITO with increasing Sn2O3 content, followed by increasing Schottky barrier height at the sputtered ITO/p-GaN interface. Temperature-dependent contact resistivity of the sputtered-ITO on p-GaN also revealed that the ITO contacts with 7 wt% Sn2O3 yielded the lowest effective barrier height of 0.039 eV. Based on these results, we devised sputtered-ITO transparent p-electrodes having dual compositions of Sn2O3 content (7/10 wt%). The radiant intensity of LEDs having sputtered-ITO transparent p-electrodes with the dual compositions (7/10 wt%) was enhanced by 13% compared to LEDs having ITO with Sn2O3 content of 7 wt% only.

RF-photonic chirp encoder and compressor for seamless analysis of information flow.

PubMed

Zalevsky, Zeev; Shemer, Amir; Zach, Shlomo

2008-05-26

In this paper we realize an RF photonic chirp compression system that compresses a continuous stream of incoming RF data (modulated on top of an optical carrier) into a train of temporal short pulses. Each pulse in the train can be separated and treated individually while being sampled by low rate optical switch and without temporal loses of the incoming flow of information. Each such pulse can be filtered and analyzed differently. The main advantage of the proposed system is its capability of being able to handle, seamlessly, high rate information flow with all-optical means and with low rate optical switches.

RF switching network: a novel technique for IR sensing

NASA Astrophysics Data System (ADS)

Mechtel, Deborah M.; Jenkins, R. Brian; Joyce, Peter J.; Nelson, Charles L.

2016-05-01

Rapid sensing of near infrared (IR) energy on a composite structure would provide information that could mitigate damage to composite structures. This paper describes a novel technique that implements photoconductive sensors in a radio frequency (RF) switching network designed to locate in real time the position and intensity of IR radiation incident on a composite structure. In the implementation described here, photoconductive sensors act as rapid response switches in a two layer RF network embedded in an FR-4 laminate. To detect radiation, phosphorous doped silicon photoconductive sensors are inserted in GHz range RF transmission lines. Photoconductive sensors use semiconductor materials that are optically sensitive at material dependent wavelengths. Incident radiation at the appropriate wavelength produces hole-electron pairs, so that the semiconductor becomes a conductor. By permitting signal propagation only when a sensor is illuminated, the RF signals are selectively routed from the lower layer transmission lines to the upper layer lines, thereby pinpointing the location and strength of incident radiation on a structure. Simulations based on a high frequency 3D planar electromagnetics model are presented and compared to experimental results. Experimental results are described for GHz range RF signal control for 300 mW and 180 mW incident energy from 975 nm and 1060 nm wavelength lasers respectively, where upon illumination, RF transmission line signal output power doubled when compared to non-illuminated results. Experimental results are reported for 100 W incident energy from a 1060 nm laser. Test results illustrate that real-time signal processing would permit a structure or vehicle to be controlled in response to incident radiation

Enhanced bipolar resistive switching behavior in polar Cr-doped barium titanate thin films without electro-forming process

NASA Astrophysics Data System (ADS)

Thakre, Atul; Kumar, Ashok

2017-12-01

An enhanced, repeatable and robust resistive switching phenomenon was observed in Cr substituted BaTiO3 polar ferroelectric thin films; fabricated and deposited by the sol-gel approach and spin coating technique, respectively. An enhanced bistable bipolar resistive switching (BRS) phenomenon without electro-forming process, low switching voltage (˜ 2 V) and moderate retention characteristics of 104 s along with a high Roff/Ron resistance ratio ˜103 was achieved. The current conduction analysis showed that the space charge limited conduction (SCLC) and Schottky emission conduction dominate in the high voltage range, while thermally active charge carriers (ohmic) in the lower voltage range. The impedance spectroscopy study indicates the formation of current conducting path and rupturing of oxygen vacancies during SET and RESET process.

Silicon Carbide (SiC) MOSFET-based Full-Bridge for Fusion Science Applications

NASA Astrophysics Data System (ADS)

Ziemba, Timothy; Miller, Kenneth; Prager, James; Picard, Julian; Hashim, Akel

2014-10-01

Switching power amplifiers (SPAs) have a wide variety of applications within the fusion science community, including feedback and control systems for dynamic plasma stabilization in tokamaks, inductive and arc plasma sources, Radio Frequency (RF) helicity and flux injection, RF plasma heating and current drive schemes, ion beam generation, and RF pre-ionizer systems. SiC MOSFETs offer many advantages over IGBTs including lower drive energy requirements, lower conduction and switching losses, and higher switching frequency capabilities. When comparing SiC and traditional silicon-based MOSFETs, SiC MOSFETs provide higher current carrying capability allowing for smaller package weights and sizes and lower operating temperature. Eagle Harbor Technologies (EHT) is designing, constructing, and testing a SiC MOSFET-based full-bridge SPA. EHT will leverage the proprietary gate drive technology previously developed with the support of a DOE SBIR, which will enable fast, efficient switching in a small form factor. The primary goal is to develop a SiC MOSFET-based SPA for fusion science applications. Work supported in part by the DOE under Contract Number DE-SC0011907.

Effectiveness of BaTiO 3 dielectric patches on YBa 2Cu 3O 7 thin films for MEM switches

DOE PAGES

Vargas, J.; Hijazi, Y.; Noel, J.; ...

2014-05-12

A micro-electro-mechanical (MEM) switch built on a superconducting microstrip filter will be utilized to investigate BaTiO 3 dielectric patches for functional switching points of contact. Actuation voltage resulting from the MEM switch provokes static friction between the bridge membrane and BaTiO 3 insulation layer. Furthermore, the dielectric patch crystal structure and roughness affect the ability of repetitively switching cycles and lifetime. We performed a series of experiments using different deposition methods and RF magnetron sputtering was found to be the best deposition process for the BaTiO 3 layer. The effect examination of surface morphology will be presented using characterization techniquesmore » as x-ray diffraction, SEM and AFM for an optimum switching device. The thin film is made of YBa 2Cu 3O 7 deposited on LaAlO 3 substrate by pulsed laser deposition. In our work, the dielectric material sputtering pressure is set at 9.5x10 -6 Torr. The argon gas is released through a mass-flow controller to purge the system prior to deposition. RF power is 85 W at a distance of 9 cm. The behavior of Au membranes built on ultimate BaTiO 3 patches will be shown as part of the results. These novel surface patterns will in turn be used in modelling other RF MEM switch devices such as distributed-satellite communication system operating at cryogenic temperatures.« less

Design and simulation of RF MEMS SPST shunt and SPDT shunt-shunt switches for X-band and Ku-band applications

NASA Astrophysics Data System (ADS)

Lenka, Manas K.; Sharma, Amit; Sharma, Jaibir; DasGupta, Amitava

2012-10-01

This paper describes the design and simulation of RF MEMS SPST shunt and SPDT shunt-shunt switches with modified coplanar waveguide (CPW) configuration for X-band and Ku-band applications exhibiting high isolation and low insertion loss. By modifying the basic CPW structure for a six-strip membrane having length 720 μm, the resonant frequency can be reduced from 33.5 GHz to 13.5 GHz with isolation as high as -30 dB(-63 dB at resonant frequency) in Ku-band. Similar results are also found in case SPST and SPDT switches with other membrane types.

Moving Beyond 3D Hetero-Integration and Towards Monolithic Integration of Phase-Change RF Switches with SiGe BiCMOS

DTIC Science & Technology

2016-03-31

Corporation, Linthicum, Maryland *Corresponding author: Pavel.Borodulin@ngc.com Abstract: A chip -scale, highly-reconfigurable transmitter and...the technology has been used in a chip -scale, reconfigurable receiver demonstration and ongoing efforts to increase the level of performance and...circuit (RF-FPGA). It consists of a heterogeneous assembly of a SiGe BiCMOS chip with multiple 3D-integrated, low-loss, phase-change switch chiplets

Schottky Emission Distance and Barrier Height Properties of Bipolar Switching Gd:SiOx RRAM Devices under Different Oxygen Concentration Environments

PubMed Central

Chen, Kai-Huang; Tsai, Tsung-Ming; Cheng, Chien-Min; Huang, Shou-Jen; Chang, Kuan-Chang; Liang, Shu-Ping; Young, Tai-Fa

2017-01-01

In this study, the hopping conduction distance and bipolar switching properties of the Gd:SiOx thin film by (radio frequency, rf) rf sputtering technology for applications in RRAM devices were calculated and investigated. To discuss and verify the electrical switching mechanism in various different constant compliance currents, the typical current versus applied voltage (I-V) characteristics of gadolinium oxide RRAM devices was transferred and fitted. Finally, the transmission electrons’ switching behavior between the TiN bottom electrode and Pt top electrode in the initial metallic filament forming process of the gadolinium oxide thin film RRAM devices for low resistance state (LRS)/high resistance state (HRS) was described and explained in a simulated physical diagram model. PMID:29283368

High Peak Power Test and Evaluation of S-band Waveguide Switches

NASA Astrophysics Data System (ADS)

Nassiri, A.; Grelick, A.; Kustom, R. L.; White, M.

1997-05-01

The injector and source of particles for the Advanced Photon Source is a 2856-MHz S-band electron-positron linear accelerator (linac) which produces electrons with energies up to 650 MeV or positrons with energies up to 450 MeV. To improve the linac rf system availability, an additional modulator-klystron subsystem is being constructed to provide a switchable hot spare unit for each of the five exsisting S-band transmitters. The switching of the transmitters will require the use of SF6-pressurized S-band waveguide switches at a peak operating power of 35 MW. Such rf switches have been successfully operated at other accelerator facilities but at lower peak powers. A test stand has been set up at the Stanford Linear Accelerator Center (SLAC) Klystron Factory to conduct tests comparing the power handling characteristics of two WR-284 and one WR-340 switches. Test results are presented and their implications for the design of the switching system are discussed.

Application of RF-MEMS-Based Split Ring Resonators (SRRs) to the Implementation of Reconfigurable Stopband Filters: A Review

PubMed Central

Martín, Ferran; Bonache, Jordi

2014-01-01

In this review paper, several strategies for the implementation of reconfigurable split ring resonators (SRRs) based on RF-MEMS switches are presented. Essentially three types of RF-MEMS combined with split rings are considered: (i) bridge-type RF-MEMS on top of complementary split ring resonators CSRRs; (ii) cantilever-type RF-MEMS on top of SRRs; and (iii) cantilever-type RF-MEMS integrated with SRRs (or RF-MEMS SRRs). Advantages and limitations of these different configurations from the point of view of their potential applications for reconfigurable stopband filter design are discussed, and several prototype devices are presented. PMID:25474378

Radiometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strickland, J. I.

1985-07-02

A radiometer of the switched type has an R.F. switch connecting a detector selectively either to an antenna whose temperature (in terms of noise energy) is to be determined, or to a reference temperature, i.e. a resistive termination. The detector output is passed through an amplifier whose gain is switched between positive and negative values (for example +1 and -1) synchronously with the R.F. switch. The output of the switched gain amplifier is integrated to produce a rising voltage when the gain is positive and a falling one when it is negative. When it is positive the detector is connectedmore » to the antenna. By means of a zero crossing detector, a counter is started when this voltage crosses zero. After a fixed period, the R.F. switch and switched gain amplifier are reversed by the counter to cause the voltage to fall in accordance with the temperature of the resistive termination. The zero crossing detector and a counter measure the time interval until the voltage again crosses zero, such time interval being compared to the fixed period to provide a comparison of the unknown and reference temperatures independent of the gain of the detector, which is a valuable improvement over prior radiometers. Also, by measuring time rather than voltage, the arrangement facilitates providing a digital output more suitable for storage and transmission of the data than the analog output of prior radiometers. The instrument, which is relatively simple, rugged and compact, lends itself well to unattended use in monitoring the effect of rain storms on transmission in the 11.7 to 12.2 GHz band employed for satelite communication.« less

Paleoclassical transport explains electron transport barriers in RTP and TEXTOR

NASA Astrophysics Data System (ADS)

Hogeweij, G. M. D.; Callen, J. D.; RTP Team; TEXTOR Team

2008-06-01

The recently developed paleoclassical transport model sets the minimum level of electron thermal transport in a tokamak. This transport level has proven to be in good agreement with experimental observations in many cases when fluctuation-induced anomalous transport is small, i.e. in (near-)ohmic plasmas in small to medium size tokamaks, inside internal transport barriers (ITBs) or edge transport barriers (H-mode pedestal). In this paper predictions of the paleoclassical transport model are compared in detail with data from such kinds of discharges: ohmic discharges from the RTP tokamak, EC heated RTP discharges featuring both dynamic and shot-to-shot scans of the ECH power deposition radius and off-axis EC heated discharges from the TEXTOR tokamak. For ohmically heated RTP discharges the Te profiles predicted by the paleoclassical model are in reasonable agreement with the experimental observations, and various parametric dependences are captured satisfactorily. The electron thermal ITBs observed in steady state EC heated RTP discharges and transiently after switch-off of off-axis ECH in TEXTOR are predicted very well by the paleoclassical model.

High-Speed, high-power, switching transistor

NASA Technical Reports Server (NTRS)

Carnahan, D.; Ohu, C. K.; Hower, P. L.

1979-01-01

Silicon transistor rate for 200 angstroms at 400 to 600 volts combines switching speed of transistors with ruggedness, power capacity of thyristor. Transistor introduces unique combination of increased power-handling capability, unusally low saturation and switching losses, and submicrosecond switching speeds. Potential applications include high power switching regulators, linear amplifiers, chopper controls for high frequency electrical vehicle drives, VLF transmitters, RF induction heaters, kitchen cooking ranges, and electronic scalpels for medical surgery.

Multistate storage nonvolatile memory device based on ferroelectricity and resistive switching effects of SrBi2Ta2O9 films

NASA Astrophysics Data System (ADS)

Song, Zhiwei; Li, Gang; Xiong, Ying; Cheng, Chuanpin; Zhang, Wanli; Tang, Minghua; Li, Zheng; He, Jiangheng

2018-05-01

A memory device with a Pt/SrBi2Ta2O9(SBT)/Pt(111) structure was shown to have excellent combined ferroelectricity and resistive switching properties, leading to higher multistate storage memory capacity in contrast to ferroelectric memory devices. In this device, SBT polycrystalline thin films with significant (115) orientation were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates using CVD (chemical vapor deposition) method. Measurement results of the electric properties exhibit reproducible and reliable ferroelectricity switching behavior and bipolar resistive switching effects (BRS) without an electroforming process. The ON/OFF ratio of the resistive switching was found to be about 103. Switching mechanisms for the low resistance state (LRS) and high resistance state (HRS) currents are likely attributed to the Ohmic and space charge-limited current (SCLC) behavior, respectively. Moreover, the ferroelectricity and resistive switching effects were found to be mutually independent, and the four logic states were obtained by controlling the periodic sweeping voltage. This work holds great promise for nonvolatile multistate memory devices with high capacity and low cost.

Q-switched slab RF discharge CO laser

NASA Astrophysics Data System (ADS)

Ionin, A. A.; Kochetkov, Yu V.; Kozlov, A. Yu; Mokrousova, D. V.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.; Zemtsov, D. S.

2017-05-01

A compact repetitively pulsed cryogenically cooled slab RF discharge CO laser with double path V-type laser resonator equipped with external Q-switching system based on rotating mirror was developed and studied. The laser produced mid-IR (λ ~ 5-7 µm) radiation pulses of ~1 ÷ 2 µs duration (FWHM), peak power up to ~3 kW, and pulse repetition rate up to 130 Hz. Averaged output laser power reached 0.5 W, the laser spectrum consisted of ~80 laser lines with individual peak power up to 80 W.

Zinc Oxide-Based Schottky Diode Prepared Using Radio-Frequency Magnetron Cosputtering System

NASA Astrophysics Data System (ADS)

Lai, Bo-Ting; Lee, Ching-Ting; Hong, Jhen-Dong; Yao, Shiau-Lu; Liu, Day-Shan

2010-08-01

The rectifying property of a zinc oxide (ZnO)-based Schottky diode prepared using a radio-frequency (rf) magnetron cosputtering system was improved by enhancing the cosputtered ZnO crystal quality, thereby optimizing the ohmic contact resistance and compensating the Schottky contact surface states. An undoped ZnO layer with a high c-axis orientation and a low internal residual stress was achieved using a postannealing treatment. A homogeneous n-type ZnO-indium tin oxide (ITO) cosputtered film was deposited onto the undoped ZnO layer to optimize the ohmic contact behavior to the Al electrode. The Schottky contact surface of the undoped ZnO layer to the Ni/Au electrode was passivated using an oxygen plasma treatment. Owing to the compensation of the native oxygen vacancies (VO) on the undoped ZnO surface, the leakage current markedly decreased and subsequently led to a quality Schottky diode performance with an ideality factor of 1.23 and a Schottky barrier height of 0.82 eV.

Resistive switching properties and physical mechanism of cobalt ferrite thin films

NASA Astrophysics Data System (ADS)

Hu, Wei; Zou, Lilan; Chen, Ruqi; Xie, Wei; Chen, Xinman; Qin, Ni; Li, Shuwei; Yang, Guowei; Bao, Dinghua

2014-04-01

We report reproducible resistive switching performance and relevant physical mechanism of sandwiched Pt/CoFe2O4/Pt structures in which the CoFe2O4 thin films were fabricated by a chemical solution deposition method. Uniform switching voltages, good endurance, and long retention have been demonstrated in the Pt/CoFe2O4/Pt memory cells. On the basis of the analysis of current-voltage characteristic and its temperature dependence, we suggest that the carriers transport through the conducting filaments in low resistance state with Ohmic conduction behavior, and the Schottky emission and Poole-Frenkel emission dominate the conduction mechanism in high resistance state. From resistance-temperature dependence of resistance states, we believe that the physical origin of the resistive switching refers to the formation and rupture of the oxygen vacancies related filaments. The nanostructured CoFe2O4 thin films can find applications in resistive random access memory.

Bipolar resistive switching in graphene oxide based metal insulator metal structure for non-volatile memory applications

NASA Astrophysics Data System (ADS)

Singh, Rakesh; Kumar, Ravi; Kumar, Anil; Kashyap, Rajesh; Kumar, Mukesh; Kumar, Dinesh

2018-05-01

Graphene oxide based devices have attracted much attention recently because of their possible application in next generation electronic devices. In this study, bipolar resistive switching characteristics of graphene oxide based metal insulator metal structure were investigated for nonvolatile memories. The graphene oxide was prepared by the conventional Hummer's method and deposited on ITO coated glass by spin-coating technique. The dominant mechanism of resistive switching is the formation and rupture of the conductive filament inside the graphene oxide. The conduction mechanism for low and high resistance states are dominated by two mechanism the ohmic conduction and space charge limited current (SCLC) mechanism, respectively. Atomic Force Microscopy, X-ray diffraction, Cyclic-Voltammetry were conducted to observe the morphology, structure and behavior of the material. The fabricated device with Al/GO/ITO structure exhibited reliable bipolar resistive switching with set & reset voltage of -2.3 V and 3V respectively.

EFFECTS OF TiOx INTERLAYER ON RESISTANCE SWITCHING OF Pt/TiOx/ZnO/n+-Si STRUCTURES

NASA Astrophysics Data System (ADS)

Li, Hongxia; Lv, Xiaojun; Xi, Junhua; Wu, Xin; Mao, Qinan; Liu, Qingmin; Ji, Zhenguo

2014-08-01

In this paper, we fabricated Pt/TiOx/ZnO/n+-Si structures by inserting TiOx interlayer between Pt top electrode (TE) and ZnO thin film for non-volatile resistive random access memory (ReRAM) applications. Effects of TiOx interlayer with different thickness on the resistance switching of Pt/TiOx/ZnO/n+-Si structures were investigated. Conduction behaviors in high and low resistance state (HRS and LRS) fit well with the trap-controlled space-charge-limited conduction (SCLC) and Ohmic behavior, respectively. Variations of set and reset voltages and HRS and LRS resistances of Pt/TiOx/ZnO/n+-Si structures were investigated as a function of TiOx thickness. Switching cycling tests were attempted to evaluate the endurance reliability of Pt/TiOx/ZnO/n+-Si structures. Additionally, the switching mechanism was analyzed by the filament model.

Radio frequency-assisted fast superconducting switch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solovyov, Vyacheslav; Li, Qiang

A radio frequency-assisted fast superconducting switch is described. A superconductor is closely coupled to a radio frequency (RF) coil. To turn the switch "off," i.e., to induce a transition to the normal, resistive state in the superconductor, a voltage burst is applied to the RF coil. This voltage burst is sufficient to induce a current in the coupled superconductor. The combination of the induced current with any other direct current flowing through the superconductor is sufficient to exceed the critical current of the superconductor at the operating temperature, inducing a transition to the normal, resistive state. A by-pass MOSFET maymore » be configured in parallel with the superconductor to act as a current shunt, allowing the voltage across the superconductor to drop below a certain value, at which time the superconductor undergoes a transition to the superconducting state and the switch is reset.« less

The electric field in capacitively coupled RF discharges: a smooth step model that includes thermal and dynamic effects

NASA Astrophysics Data System (ADS)

Brinkmann, Ralf Peter

2015-12-01

The electric field in radio-frequency driven capacitively coupled plasmas (RF-CCP) is studied, taking thermal (finite electron temperature) and dynamic (finite electron mass) effects into account. Two dimensionless numbers are introduced, the ratios ε ={λ\\text{D}}/l of the electron Debye length {λ\\text{D}} to the minimum plasma gradient length l (typically the sheath thickness) and η ={ω\\text{RF}}/{ω\\text{pe}} of the RF frequency {ω\\text{RF}} to the electron plasma frequency {ω\\text{pe}} . Assuming both numbers small but finite, an asymptotic expansion of an electron fluid model is carried out up to quadratic order inclusively. An expression for the electric field is obtained which yields (i) the space charge field in the sheath, (ii) the generalized Ohmic and ambipolar field in the plasma, and (iii) a smooth interpolation for the transition in between. The new expression is a direct generalization of the Advanced Algebraic Approximation (AAA) proposed by the same author (2009 J. Phys. D: Appl. Phys. 42 194009), which can be recovered for η \\to 0 , and of the established Step Model (SM) by Godyak (1976 Sov. J. Plasma Phys. 2 78), which corresponds to the simultaneous limits η \\to 0 , ε \\to 0 . A comparison of the hereby proposed Smooth Step Model (SSM) with a numerical solution of the full dynamic problem proves very satisfactory.

RF assisted switching in magnetic Josephson junctions

NASA Astrophysics Data System (ADS)

Caruso, R.; Massarotti, D.; Bolginov, V. V.; Ben Hamida, A.; Karelina, L. N.; Miano, A.; Vernik, I. V.; Tafuri, F.; Ryazanov, V. V.; Mukhanov, O. A.; Pepe, G. P.

2018-04-01

We test the effect of an external RF field on the switching processes of magnetic Josephson junctions (MJJs) suitable for the realization of fast, scalable cryogenic memories compatible with Single Flux Quantum logic. We show that the combined application of microwaves and magnetic field pulses can improve the performances of the device, increasing the separation between the critical current levels corresponding to logical "0" and "1." The enhancement of the current level separation can be as high as 80% using an optimal set of parameters. We demonstrate that external RF fields can be used as an additional tool to manipulate the memory states, and we expect that this approach may lead to the development of new methods of selecting MJJs and manipulating their states in memory arrays for various applications.

RF MEMS and Their Applications in NASA's Space Communication Systems

NASA Technical Reports Server (NTRS)

Williams, W. Daniel; Ponchak, George E.; Simons, Rainee N.; Zaman, Afroz; Kory, Carol; Wintucky, Edwin; Wilson, Jeffrey D.; Scardelletti, Maximilian; Lee, Richard; Nguyen, Hung

2001-01-01

Radio frequency (RF) and microwave communication systems rely on frequency, amplitude, and phase control circuits to efficiently use the available spectrum. Phase control circuits are required for electronically scanning phase array antennas that enable radiation pattern shaping, scanning, and hopping. Two types of phase shifters, which are the phase control circuits, are most often used. The first is comprised of two circuits with different phase characteristics such as two transmission lines of different lengths or a high pass and low pass filter and a switch that directs the RF power through one of the two circuits. Alternatively, a variable capacitor, or varactor, is used to change the effective electrical path length of a transmission line, which changes the phase characteristics. Filter banks are required for the diplexer at the front end of wide band communication satellites. These filters greatly increase the size and mass of the RF/microwave systems, but smaller diplexers may be made with a low loss varactor or a group of capacitors, a switch and an inductor.

Bipolar resistive switching in Cu/AlN/Pt nonvolatile memory device

NASA Astrophysics Data System (ADS)

Chen, C.; Yang, Y. C.; Zeng, F.; Pan, F.

2010-08-01

Highly stable and reproducible bipolar resistive switching effects are reported on Cu/AlN/Pt devices. Memory characteristics including large memory window of 103, long retention time of >106 s and good endurance of >103 were demonstrated. It is concluded that the reset current decreases as compliance current decreases, which provides an approach to suppress power consumption. The dominant conduction mechanisms of low resistance state and high resistance state were verified by Ohmic behavior and trap-controlled space charge limited current, respectively. The memory effect is explained by the model concerning redox reaction mediated formation and rupture of the conducting filament in AlN films.

Trap-assisted tunneling in aluminum-doped ZnO/indium oxynitride nanodot interlayer Ohmic contacts on p-GaN

NASA Astrophysics Data System (ADS)

Ke, Wen-Cheng; Lee, Fang-Wei; Yang, Cheng-Yi; Chen, Wei-Kuo; Huang, Hao-Ping

2015-10-01

This study developed an Ohmic contact formation method for a ZnO:Al (AZO) transparent conductive layer on p-GaN films involving the introduction of an indium oxynitride (InON) nanodot interlayer. An antisurfactant pretreatment was used to grow InON nanodots on p-GaN films in a RF magnetron sputtering system. A low specific contact resistance of 1.12 × 10-4 Ω cm2 was achieved for a sample annealed at 500 °C for 30 s in nitrogen ambient and embedded with an InON nanodot interlayer with a nanodot density of 6.5 × 108 cm-2. By contrast, a sample annealed in oxygen ambient exhibited non-Ohmic behavior. X-ray photoemission spectroscopy results showed that the oxygen vacancy (Vo) in the InON nanodots played a crucial role in carrier transport. The fitting I-V characteristic curves indicated that the hopping mechanism with an activation energy of 31.6 meV and trap site spacing of 1.1 nm dominated the carrier transport in the AZO/InON nanodot/p-GaN sample. Because of the high density of donor-like oxygen vacancy defects at the InON nanodot/p-GaN interface, positive charges from the underlying p-GaN films were absorbed at the interface. This led to positive charge accumulation, creating a narrow depletion layer; therefore, carriers from the AZO layer passed through InON nanodots by hopping transport, and subsequently tunneling through the interface to enter the p-GaN films. Thus, AZO Ohmic contact can be formed on p-GaN films by embedding an InON nanodot interlayer to facilitate trap-assisted tunneling.

A Josephson Junction based SPDT switch

NASA Astrophysics Data System (ADS)

Zhang, Helin; Earnest, Nathan; Lu, Yao; Ma, Ruichao; Chakram, Srivatsan; Schuster, David

RF microwave switches are useful tools in cryogenic experiments, allowing for multiple experiments to be connected to a single cryogenic measurement chain. However, these switches dissipate a substantial amount of heat, preventing fast switching. Josephson junction (JJ) are a promising avenue for realizing millikelvin microwave switching. We present a JJ based single-pole-double throw (SPDT) switch that has fast switching time, no heat dissipation, large on/off contrast, and works over a wide bandwidth. The switch can be used for real-time switching between experiments, routing single photons, or even generating entanglement. We will describe the design of the switch and present experimental characterization of its performance.

Optically controlled switch-mode current-source amplifiers for on-coil implementation in high field parallel transmission

PubMed Central

Gudino, Natalia; Duan, Qi; de Zwart, Jacco A; Murphy-Boesch, Joe; Dodd, Stephen J; Merkle, Hellmut; van Gelderen, Peter; Duyn, Jeff H

2015-01-01

Purpose We tested the feasibility of implementing parallel transmission (pTX) for high field MRI using a radiofrequency (RF) amplifier design to be located on or in the immediate vicinity of a RF transmit coil. Method We designed a current-source switch-mode amplifier based on miniaturized, non-magnetic electronics. Optical RF carrier and envelope signals to control the amplifier were derived, through a custom-built interface, from the RF source accessible in the scanner control. Amplifier performance was tested by benchtop measurements as well as with imaging at 7 T (300 MHz) and 11.7 T (500 MHz). The ability to perform pTX was evaluated by measuring inter-channel coupling and phase adjustment in a 2-channel setup. Results The amplifier delivered in excess of 44 W RF power and caused minimal interference with MRI. The interface derived accurate optical control signals with carrier frequencies ranging from 64 to 750 MHz. Decoupling better than 14 dB was obtained between 2 coil loops separated by only 1 cm. Application to MRI was demonstrated by acquiring artifact-free images at 7 T and 11.7 T. Conclusion An optically controlled miniaturized RF amplifier for on-coil implementation at high field is demonstrated that should facilitate implementation of high-density pTX arrays. PMID:26256671

K-band high power latching switch. [communication satellite system

NASA Technical Reports Server (NTRS)

Mlinar, M. J.; Piotrowski, W. S.; Raue, J. E.

1980-01-01

A 19 GHz waveguide latching switch with a bandwidth of 1400 MHz and an exceptionally low insertion loss of 0.25 dB was demonstrated. The RF and driver ferrites are separate structures and can be optimized individually. This analysis for each structure is separately detailed. Basically, the RF section features a dual turnstile junction. The circulator consists of a dielectric tube which contains two ferrite rods, and a dielectric spacer separating the ferrite parts along the center of symmetry of the waveguide to form two turnstiles. This subassembly is indexed and locked in the center of symmetry of a uniform junction of three waveguides by the metallic transformers installed in the top and bottom walls of the housing. The switching junction and its actuating circuitry met all RF performance objectives and all shock and vibration requirements with no physical damage or performance degradation. It exceeds thermal requirements by operating over a 100 C temperature range (-44 C to +56 C) and has a high power handling capability allowing up to 100 W of CW input power.

Single-crystalline graphene radio-frequency nanoswitches

NASA Astrophysics Data System (ADS)

Li, Peng; Cui, Tianhong

2015-07-01

Growth of monolayer single-crystalline graphene (SCG) using the low-pressure chemical vapor deposition method is reported. Graphene’s superb quality and single-crystalline nature were characterized and verified by Raman microscopy, atomic force microscopy, and carrier mobility measurement. Radio-frequency (RF) nanoelectromechanical switches based on coplanar waveguide double-clamped SCG membrane were achieved, and the superb properties of SCG enable the switches to operate at a pull-in voltage as low as 1 V, with switch time in the nanosecond regime. Owing to their single-crystalline nature, the switches’ lifetime (>5000 times) is much longer than that of polycrystalline graphene ones reported. The RF devices exhibit good isolation (-30 dB at 40 GHz (Ka band)), which can be further improved by SCG’s conductivity variation due to actuation voltage.

Concepts, characterization, and modeling of MEMS microswitches with gold contacts in MUMPs

NASA Astrophysics Data System (ADS)

Lafontan, Xavier; Dufaza, Christian; Robert, Michel; Pressecq, Francis; Perez, Guy

2001-04-01

This paper demonstrates that RF MEMS micro-switches can be realized with a low cost MEMS technology such as MUMPs. Two different switches are proposed, namely the hinged beam switch and the gold overflowing switch. Their concepts, design and characterization are described in details. On-resistance as low as 5 - 6 (Omega) for the gold overflowing switch and 2 - 3 (Omega) for the hinged beam switch have been measured. Finally, experimental measurements showed that force and electrical current had strong influences on the overall electrical contact.

RF Behavior of Cylindrical Cavity Based 240 GHz, 1 MW Gyrotron for Future Tokamak System

NASA Astrophysics Data System (ADS)

Kumar, Nitin; Singh, Udaybir; Bera, Anirban; Sinha, A. K.

2017-11-01

In this paper, we present the RF behavior of conventional cylindrical interaction cavity for 240 GHz, 1 MW gyrotron for futuristic plasma fusion reactors. Very high-order TE mode is searched for this gyrotron to minimize the Ohmic wall loading at the interaction cavity. The mode selection process is carried out rigorously to analyze the mode competition and design feasibility. The cold cavity analysis and beam-wave interaction computation are carried out to finalize the cavity design. The detail parametric analyses for interaction cavity are performed in terms of mode stability, interaction efficiency and frequency. In addition, the design of triode type magnetron injection gun is also discussed. The electron beam parameters such as velocity ratio and velocity spread are optimized as per the requirement at interaction cavity. The design studies presented here confirm the realization of CW, 1 MW power at 240 GHz frequency at TE46,17 mode.

Wireless Chalcogenide Nanoionic-Based Radio-Frequency Switch

NASA Technical Reports Server (NTRS)

Nessel, James; Miranda, Felix

2013-01-01

A new nonvolatile nanoionic switch is powered and controlled through wireless radio-frequency (RF) transmission. A thin layer of chalcogenide glass doped with a metal ion, such as silver, comprises the operational portion of the switch. For the switch to function, an oxidizable electrode is made positive (anode) with respect to an opposing electrode (cathode) when sufficient bias, typically on the order of a few tenths of a volt or more, is applied. This action causes the metal ions to flow toward the cathode through a coordinated hopping mechanism. At the cathode, a reduction reaction occurs to form a metal deposit. This metal deposit creates a conductive path that bridges the gap between electrodes to turn the switch on. Once this conductive path is formed, no further power is required to maintain it. To reverse this process, the metal deposit is made positive with respect to the original oxidizable electrode, causing the dissolution of the metal bridge thereby turning the switch off. Once the metal deposit has been completely dissolved, the process self-terminates. This switching process features the following attributes. It requires very little to change states (i.e., on and off). Furthermore, no power is required to maintain the states; hence, the state of the switch is nonvolatile. Because of these attributes the integration of a rectenna to provide the necessary power and control is unique to this embodiment. A rectenna, or rectifying antenna, generates DC power from an incident RF signal. The low voltages and power required for the nanoionic switch control are easily generated from this system and provide the switch with a novel capability to be operated and powered from an external wireless device. In one realization, an RF signal of a specific frequency can be used to set the switch into an off state, while another frequency can be used to set the switch to an on state. The wireless, miniaturized, and nomoving- part features of this switch make it suitable for applications such as integration into garments, RFID (radio-frequency identification) tags, and conformal structures (e.g., aircraft wings, sounding rockets contours, etc). In the case of RFID tags the innovation will provide countermeasures to attempts for identity theft and other uninvited attempts for retrieval of information. It could also be applicable to the automotive industry as well as the aerospace industry for collision avoidance and phased array radar systems, respectively

The 30-GHz monolithic receive module

NASA Technical Reports Server (NTRS)

Sokolov, V.; Geddes, J.; Bauhahn, P.

1983-01-01

Key requirements for a 30 GHz GaAs monolithic receive module for spaceborne communication antenna feed array applications include an overall receive module noise figure of 5 dB, a 30 dB RF to IF gain with six levels of intermediate gain control, a five-bit phase shifter, and a maximum power consumption of 250 mW. The RF designs for each of the four submodules (low noise amplifier, some gain control, phase shifter, and RF to IF sub-module) are presented. Except for the phase shifter, high frequency, low noise FETs with sub-half micron gate lengths are employed in the submodules. For the gain control, a two stage dual gate FET amplifier is used. The phase shifter is of the passive switched line type and consists of 5-bits. It uses relatively large gate width FETs (with zero drain to source bias) as the switching elements. A 20 GHz local oscillator buffer amplifier, a FET compatible balanced mixer, and a 5-8 GHz IF amplifier constitute the RF/IF sub-module. Phase shifter fabrication using ion implantation and a self-aligned gate technique is described. Preliminary RF results obtained on such phase shifters are included.

A Study of Direct Digital Manufactured RF/Microwave Packaging

NASA Astrophysics Data System (ADS)

Stratton, John W. I.

Various facets of direct digital manufactured (DDM) microwave packages are studied. The rippled surface inherent in fused deposition modeling (FDM) fabricated geometries is modeled in Ansoft HFSS, and its effect on the performance of microstrip transmission lines is assessed via simulation and measurement. The thermal response of DDM microstrip transmission lines is analyzed over a range of RF input powers, and linearity is confirmed over that range. Two IC packages are embedded into DDM printed circuit boards, and their performance is analyzed. The first is a low power RF switch, and the second is an RF front end device that includes a low noise amplifier (LNA) and a power amplifier (PA). The RF switch is shown to perform well, as compared to a layout designed for a Rogers 4003C microwave laminate substrate. The LNA performs within datasheet specifications. The power amplifier generates substantial heat, so a thermal management attempt is described. Finally, a capacitively loaded 6dB Wilkinson power divider is designed and fabricated using DDM techniques and materials. Its performance is analyzed and compared to simulation. The device is shown to compare favorably to a similar device fabricated on a Rogers 4003C microwave laminate using traditional printed circuit board techniques.

Patent Abstract Digest. Volume II.

DTIC Science & Technology

1981-03-01

THE AIR FORCE SYSTEMS COMMAND United States Patent 191 [J 4,190,815 Albanese [45] Feb. 26, 1980 [541 HIGH POWER HYBRID SWITCH 3,659.227 4/1972...R.F. power are controlled and switched [22] Filed: Mar. 9, 1978 by means of a hybrid switching network that employs [511 nt. C. 2...broadband quadrature 3dB hybrid . Switching is accomplished by selectively inserting a [561 Referenees Cited 180 phase shift means into the lower power

Ka-Band, RF MEMS Switches on CMOS Grade Silicon with a Polyimide Interface Layer

NASA Technical Reports Server (NTRS)

Ponchak, George E.; Varaljay, Nicholas C.; Papapolymerou, John

2003-01-01

For the first time, RF MEMS switcbes on CMOS grade Si witb a polyimide interface layer are fabricated and characterized. At Ka-Band (36.6 GHz), an insertion loss of 0.52 dB and an isolation of 20 dB is obtained.

Mobile Atmospheric Pollutant Mapping System (MAPMS)

DTIC Science & Technology

1989-12-01

SHOULD DIRECT REQUESTS FOR COPIES OF THIS REPORT TO: DEFENSE TECHNICAL INFORMATION CENTER CAMERON STATION ALEXANDRIA, VIRGINIA 22314 UNCLASSIFIED...22 7. Flip-Flop Array ..... ............ .. 22 8. RF Switches and RF Power Splitter . 22 9. RFI Shielding ......... ............. 2? 10. Transient...Boxcar Averager ...... ............ .. 24 5. Spectrum Analyzer .... ........... .. 26 6. Laser Power Meters .... ........... ... 26 M. COMPUTER

RF waveguide phase-directed power combiners

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nantista, Christopher D.; Dolgashev, Valery A.; Tantawi, Sami G.

2017-05-02

High power RF phase-directed power combiners include magic H hybrid and/or superhybrid circuits oriented in orthogonal H-planes and connected using E-plane bends and/or twists to produce compact 3D waveguide circuits, including 8.times.8 and 16.times.16 combiners. Using phase control at the input ports, RF power can be directed to a single output port, enabling fast switching between output ports for applications such as multi-angle radiation therapy.

Characterization and reduction of gradient-induced eddy currents in the RF shield of a TEM resonator.

PubMed

Alecci, Marcello; Jezzard, Peter

2002-08-01

Radiofrequency (RF) shields that surround MRI transmit/receive coils should provide effective RF screening, without introducing unwanted eddy currents induced by gradient switching. Results are presented from a detailed examination of an effective RF shield design for a prototype transverse electromagnetic (TEM) resonator suitable for use at 3 Tesla. It was found that effective RF shielding and low eddy current sensitivity could be achieved by axial segmentation (gap width = 2.4 mm) of a relatively thick (35 microm) copper shield, etched on a kapton polyimide substrate. This design has two main advantages: first, it makes the TEM less sensitive to the external environment and RF interference; and second, it makes the RF shield mechanically robust and easy to handle and assemble. Copyright 2002 Wiley-Liss, Inc.

High-performance flexible resistive memory devices based on Al2O3:GeOx composite

NASA Astrophysics Data System (ADS)

Behera, Bhagaban; Maity, Sarmistha; Katiyar, Ajit K.; Das, Samaresh

2018-05-01

In this study a resistive switching random access memory device using Al2O3:GeOx composite thin films on flexible substrate is presented. A bipolar switching characteristic was observed for the co-sputter deposited Al2O3:GeOx composite thin films. Al/Al2O3:GeOx/ITO/PET memory device shows excellent ON/OFF ratio (∼104) and endurance (>500 cycles). GeOx nanocrystals embedded in the Al2O3 matrix have been found to play a significant role in enhancing the switching characteristics by facilitating oxygen vacancy formation. Mechanical endurance was retained even after several bending. The conduction mechanism of the device was qualitatively discussed by considering Ohmic and SCLC conduction. This flexible device is a potential candidate for next-generation electronics device.

Experimental investigation of mode transitions in asymmetric capacitively coupled radio-frequency Ne and CF4 plasmas

NASA Astrophysics Data System (ADS)

Liu, Gang-Hu; Liu, Yong-Xin; Bai, Li-Shui; Zhao, Kai; Wang, You-Nian

2018-02-01

The dependence of the electron density and the emission intensity on external parameters during the transitions of the electron power absorption mode is experimentally studied in asymmetric electropositive (neon) and electronegative (CF4) capacitively coupled radio-frequency plasmas. The spatio-temporal distribution of the emission intensity is measured with phase resolved optical emission spectroscopy and the electron density at the discharge center is measured by utilizing a floating hairpin probe. In neon discharge, the emission intensity increases almost linearly with the rf voltage at all driving frequencies covered here, while the variation of the electron density with the rf voltage behaves differently at different driving frequencies. In particular, the electron density increases linearly with the rf voltage at high driving frequencies, while at low driving frequencies the electron density increases slowly at the low-voltage side and, however, grows rapidly, when the rf voltage is higher than a certain value, indicating a transition from α to γ mode. The rf voltage, at which the mode transition occurs, increases with the decrease of the driving frequency/the working pressure. By contrast, in CF4 discharge, three different electron power absorption modes can be observed and the electron density and emission intensity do not exhibit a simple dependence on the rf voltage. In particular, the electron density exhibits a minimum at a certain rf voltage when the electron power absorption mode is switching from drift-ambipolar to the α/γ mode. A minimum can also be found in the emission intensity at a higher rf voltage when a discharge is switching into the γ mode.

Fabrication of a novel RF switch device with high performance using In0.4Ga0.6As MOSFET technology

NASA Astrophysics Data System (ADS)

Jiahui, Zhou; Hudong, Chang; Xufang, Zhang; Jingzhi, Yang; Guiming, Liu; Haiou, Li; Honggang, Liu

2016-02-01

A novel radio frequency (RF) switch device has been successfully fabricated using InGaAs metal-oxide-semiconductor field-effect transistor (MOSFET) technology. The device showed drain saturation currents of 250 mA/mm, a maximum transconductance of 370 mS/mm, a turn-on resistance of 0.72 mω·mm2 and a drain current on-off (Ion/Ioff) ratio of 1 × 106. The maximum handling power of on-state of 533 mW/mm and off-state of 3667 mW/mm is obtained. The proposed In0.4Ga0.6 As MOSFET RF switch showed an insertion loss of less than 1.8 dB and an isolation of better than 20 dB in the frequency range from 0.1 to 7.5 GHz. The lowest insertion loss and the highest isolation can reach 0.27 dB and more than 68 dB respectively. This study demonstrates that the InGaAs MOSFET technology has a great potential for RF switch application. Project supported by the National Natural Science Foundation of China (Nos. 61274077, 61474031), the Guangxi Natural Science Foundation (No. 2013GXNSFGA019003), the Guangxi Department of Education Project (No. 201202ZD041), the Guilin City Technology Bureau (Nos. 20120104-8, 20130107-4), the China Postdoctoral Science Foundation Funded Project (Nos. 2012M521127, 2013T60566), the National Basic Research Program of China (Nos. 2011CBA00605, 2010CB327501), the Innovation Project of GUET Graduate Education (Nos. GDYCSZ201448, GDYCSZ201449), the State key Laboratory of Electronic Thin Films and Integrated Devices, UESTC (No. KFJJ201205), and the Guilin City Science and Technology Development Project (Nos. 20130107-4, 20120104-8).

Structural insights into eRF3 and stop codon recognition by eRF1

PubMed Central

Cheng, Zhihong; Saito, Kazuki; Pisarev, Andrey V.; Wada, Miki; Pisareva, Vera P.; Pestova, Tatyana V.; Gajda, Michal; Round, Adam; Kong, Chunguang; Lim, Mengkiat; Nakamura, Yoshikazu; Svergun, Dmitri I.; Ito, Koichi; Song, Haiwei

2009-01-01

Eukaryotic translation termination is mediated by two interacting release factors, eRF1 and eRF3, which act cooperatively to ensure efficient stop codon recognition and fast polypeptide release. The crystal structures of human and Schizosaccharomyces pombe full-length eRF1 in complex with eRF3 lacking the GTPase domain revealed details of the interaction between these two factors and marked conformational changes in eRF1 that occur upon binding to eRF3, leading eRF1 to resemble a tRNA molecule. Small-angle X-ray scattering analysis of the eRF1/eRF3/GTP complex suggested that eRF1's M domain contacts eRF3's GTPase domain. Consistently, mutation of Arg192, which is predicted to come in close contact with the switch regions of eRF3, revealed its important role for eRF1's stimulatory effect on eRF3's GTPase activity. An ATP molecule used as a crystallization additive was bound in eRF1's putative decoding area. Mutational analysis of the ATP-binding site shed light on the mechanism of stop codon recognition by eRF1. PMID:19417105

Materiel Readiness Support Activity Automation Plan

DTIC Science & Technology

1986-09-01

Hardwire leased lines Sytek RF broadband cable modems Digital phone switched service Medium Speed - up to 56k baud RF modems Digital phone service High...dialing 121 I iI Medium Speed - up to 56k baud RF modems - up to 56k baud sync modem $2070 plus installation - $25 per month maintenance - $1200 per...security is to disconnect net- work, modem , and hardwire access (that is, all external access to the machine) after 5 p.m. (normal business hours

Detector power linearity requirements and verification techniques for TMI direct detection receivers

NASA Technical Reports Server (NTRS)

Reinhardt, Victor S. (Inventor); Shih, Yi-Chi (Inventor); Toth, Paul A. (Inventor); Reynolds, Samuel C. (Inventor)

1997-01-01

A system (36, 98) for determining the linearity of an RF detector (46, 106). A first technique involves combining two RF signals from two stable local oscillators (38, 40) to form a modulated RF signal having a beat frequency, and applying the modulated RF signal to a detector (46) being tested. The output of the detector (46) is applied to a low frequency spectrum analyzer (48) such that a relationship between the power levels of the first and second harmonics generated by the detector (46) of the beat frequency of the modulated RF signal are measured by the spectrum analyzer (48) to determine the linearity of the detector (46). In a second technique, an RF signal from a local oscillator (100) is applied to a detector (106) being tested through a first attenuator (102) and a second attenuator (104). The output voltage of the detector (106) is measured when the first attenuator (102) is set to a particular attenuation value and the second attenuator (104) is switched between first and second attenuation values. Further, the output voltage of the detector (106) is measured when the first attenuator (102) is set to another attenuation value, and the second attenuator (104) is again switched between the first and second attenuation values. A relationship between the voltage outputs determines the linearity of the detector (106).

Analog bus driver and multiplexer

NASA Technical Reports Server (NTRS)

Pain, Bedabrata (Inventor); Hancock, Bruce (Inventor); Cunningham, Thomas J. (Inventor)

2012-01-01

For a source-follower signal chain, the ohmic drop in the selection switch causes unacceptable voltage offset, non-linearity, and reduced small signal gain. For an op amp signal chain, the required bias current and the output noise rises rapidly with increasing the array format due to a rapid increase in the effective capacitance caused by the Miller effect boosting up the contribution of the bus capacitance. A new switched source-follower signal chain circuit overcomes limitations of existing op-amp based or source follower based circuits used in column multiplexers and data readout. This will improve performance of CMOS imagers, and focal plane read-out integrated circuits for detectors of infrared or ultraviolet light.

RF pulse shape control in the compact linear collider test facility

NASA Astrophysics Data System (ADS)

Kononenko, Oleksiy; Corsini, Roberto

2018-07-01

The Compact Linear Collider (CLIC) is a study for an electron-positron machine aiming at accelerating and colliding particles at the next energy frontier. The CLIC concept is based on the novel two-beam acceleration scheme, where a high-current low-energy drive beam generates RF in series of power extraction and transfer structures accelerating the low-current main beam. To compensate for the transient beam-loading and meet the energy spread specification requirements for the main linac, the RF pulse shape must be carefully optimized. This was recently modelled by varying the drive beam phase switch times in the sub-harmonic buncher so that, when combined, the drive beam modulation translates into the required voltage modulation of the accelerating pulse. In this paper, the control over the RF pulse shape with the phase switches, that is crucial for the success of the developed compensation model, is studied. The results on the experimental verification of this control method are presented and a good agreement with the numerical predictions is demonstrated. Implications for the CLIC beam-loading compensation model are also discussed.

System Control for the Transitional DCS.

DTIC Science & Technology

1978-12-01

hour. The equipment destroyed includes the TTC-39 switch, all RF and multiplex equipment, emergency power equipment, distribution frames, antennal and...switch executes loop test to Rhein Main ULS, activating a local alarm at Donnersberg. Since restoral activity has not already been completed, alarm is...ITEM COMMENTS (BYTES) Loop ID Switch number and physical loop number 6 (BCD). Loop circuit CCSD 8 Telephone number 3 Location Physical location of

Advanced optical fiber communication systems

NASA Astrophysics Data System (ADS)

Kazovsky, Leonid G.

1994-03-01

Our research is focused on three major aspects of advanced optical fiber communication systems: dynamic wavelength division multiplexing (WDM) networks, fiber nonlinearities, and high dynamic range coherent analog optical links. In the area of WDM networks, we have designed and implemented two high-speed interface boards and measured their throughput and latency. Furthermore, we designed and constructed an experimental PSK/ASK transceiver that simultaneously transmits packet-switched ASK data and circuit-switched PSK data on the same optical carrier. In the area of fiber nonlinearities, we investigated the theoretical impact of modulation frequency on cross-phase modulation (XPM) in dispersive fibers. In the area of high dynamic range coherent analog optical links, we developed theoretical expressions for the RF power transfer ratio (or RF power gain) and the noise figure (NF) of angle-modulated links. We then compared the RF power gains and noise figures of these links to that of an intensity modulated direct detection (DD) link.

Low-temperature DC-contact piezoelectric switch operable in high magnetic fields

NASA Astrophysics Data System (ADS)

Kaltenbacher, Thomas; Caspers, Fritz; Doser, Michael; Kellerbauer, Alban; Pribyl, Wolfgang

2013-11-01

A piezoelectric single-pole single-throw (SPST) switch has been developed, since there is no satisfying commercial low-resistance, high current DC-contact RF switch available which is operable at 4.2 K and in a high magnetic field of at least 0.5 T. This piezoelectric switch shows very low insertion loss of less than -0.1 dB within a bandwidth of 100 MHz when operated at 4.2 K. The switch could also be used to mechanically disconnect and connect electrodes or electrical circuits from one another.

Transparent resistive switching memory using aluminum oxide on a flexible substrate

NASA Astrophysics Data System (ADS)

Yeom, Seung-Won; Shin, Sang-Chul; Kim, Tan-Young; Ha, Hyeon Jun; Lee, Yun-Hi; Shim, Jae Won; Ju, Byeong-Kwon

2016-02-01

Resistive switching memory (ReRAM) has attracted much attention in recent times owing to its fast switching, simple structure, and non-volatility. Flexible and transparent electronic devices have also attracted considerable attention. We therefore fabricated an Al2O3-based ReRAM with transparent indium-zinc-oxide (IZO) electrodes on a flexible substrate. The device transmittance was found to be higher than 80% in the visible region (400-800 nm). Bended states (radius = 10 mm) of the device also did not affect the memory performance because of the flexibility of the two transparent IZO electrodes and the thin Al2O3 layer. The conduction mechanism of the resistive switching of our device was explained by ohmic conduction and a Poole-Frenkel emission model. The conduction mechanism was proved by oxygen vacancies in the Al2O3 layer, as analyzed by x-ray photoelectron spectroscopy analysis. These results encourage the application of ReRAM in flexible and transparent electronic devices.

Resistive switching phenomena of tungsten nitride thin films with excellent CMOS compatibility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Seok Man; Kim, Hee-Dong; An, Ho-Myoung

2013-12-15

Graphical abstract: - Highlights: • The resistive switching characteristics of WN{sub x} thin films. • Excellent CMOS compatibility WN{sub x} films as a resistive switching material. • Resistive switching mechanism revealed trap-controlled space charge limited conduction. • Good endurance and retention properties over 10{sup 5} cycles, and 10{sup 5} s, respectively - Abstract: We report the resistive switching (RS) characteristics of tungsten nitride (WN{sub x}) thin films with excellent complementary metal-oxide-semiconductor (CMOS) compatibility. A Ti/WN{sub x}/Pt memory cell clearly shows bipolar RS behaviors at a low voltage of approximately ±2.2 V. The dominant conduction mechanisms at low and high resistancemore » states were verified by Ohmic behavior and trap-controlled space-charge-limited conduction, respectively. A conducting filament model by a redox reaction explains the RS behavior in WN{sub x} films. We also demonstrate the memory characteristics during pulse operation, including a high endurance over >10{sup 5} cycles and a long retention time of >10{sup 5} s.« less

RF to millimeter wave integration and module technologies

NASA Astrophysics Data System (ADS)

Vähä-Heikkilä, T.

2015-04-01

Radio Frequency (RF) consumer applications have boosted silicon integrated circuits (IC) and corresponding technologies. More and more functions are integrated to ICs and their performance is also increasing. However, RF front-end modules with filters and switches as well as antennas still need other way of integration. This paper focuses to RF front-end module and antenna developments as well as to the integration of millimeter wave radios. VTT Technical Research Centre of Finland has developed both Low Temperature Co-fired Ceramics (LTCC) and Integrated Passive Devices (IPD) integration platforms for RF and millimeter wave integrated modules. In addition to in-house technologies, VTT is using module and component technologies from other commercial sources.

Improved multi-level capability in Si3N4-based resistive switching memory using continuous gradual reset switching

NASA Astrophysics Data System (ADS)

Kim, Sungjun; Park, Byung-Gook

2017-01-01

In this letter, we compare three different types of reset switching behavior in a bipolar resistive random-access memory (RRAM) system that is housed in a Ni/Si3N4/Si structure. The abrupt, step-like gradual and continuous gradual reset transitions are largely determined by the low-resistance state (LRS). For abrupt reset switching, the large conducting path shows ohmic behavior or has a weak nonlinear current-voltage (I-V) characteristics in the LRS. For gradual switching, including both the step-like and continuous reset types, trap-assisted direct tunneling is dominant in the low-voltage regime, while trap-assisted Fowler-Nordheim tunneling is dominant in the high-voltage regime, thus causing nonlinear I-V characteristics. More importantly, we evaluate the multi-level capabilities of the two different gradual switching types, including both step-like and continuous reset behavior, using identical and incremental voltage conditions. Finer control of the conductance level with good uniformity is achieved in continuous gradual reset switching when compared to that in step-like gradual reset switching. For continuous reset switching, a single conducting path, which initially has a tunneling gap, gradually responds to pulses with even and identical amplitudes, while for step-like reset switching, the multiple conducting paths only respond to incremental pulses to obtain effective multi-level states.

AlGaN Channel Transistors for Power Management and Distribution

NASA Technical Reports Server (NTRS)

VanHove, James M.

1996-01-01

Contained within is the Final report of a Phase 1 SBIR program to develop AlGaN channel junction field effect transistors (JFET). The report summarizes our work to design, deposit, and fabricate JFETS using molecular beam epitaxy growth AlGaN. Nitride growth is described using a RF atomic nitrogen plasma source. Processing steps needed to fabricate the device such as ohmic source-drain contacts, reactive ion etching, gate formation, and air bride fabrication are documented. SEM photographs of fabricated power FETS are shown. Recommendations are made to continue the effort in a Phase 2 Program.

Multiple-electrode radiofrequency ablation: simultaneous production of separate zones of coagulation in an in vivo porcine liver model.

PubMed

Laeseke, Paul F; Sampson, Lisa A; Haemmerich, Dieter; Brace, Chris L; Fine, Jason P; Frey, Tina M; Winter, Thomas C; Lee, Fred T

2005-12-01

A multiple-electrode radiofrequency (RF) system was developed based on switching between electrodes that allows for the simultaneous use of as many as three electrically independent electrodes. The purpose of this study was to determine if each multiple-electrode ablation zone is identical to an ablation zone created with conventional single-electrode mode. Nine female domestic pigs (mean weight, 90 kg) were used for this study. A prototype monopolar multiple-electrode RF ablation system was created with use of an RF generator and an electronic switching algorithm. A maximum of three electrodes can be used simultaneously by switching between electrodes at each impedance spike (30 omega greater than baseline levels). A total of 39 zones of ablation were created at open laparotomy in pig livers with use of a conventional single electrode (n = 9), two single electrodes simultaneously (n = 6 ablations; 12 ablation zones), or three single electrodes simultaneously (n = 6 ablations; 18 ablation zones). RF electrodes were spaced in separate lobes of the liver when multiple zones of coagulation were created simultaneously. Animals were euthanized after RF ablation, livers were removed, and ablation zones were sectioned and measured. Zones of coagulation created simultaneously with two or three electrodes were equivalent to ablation zones created with use of conventional single-electrode ablation. No significant differences were observed among control animals treated with a single electrode, those with two separate zones of ablation created simultaneously, and those with three simultaneously created ablation zones in terms of mean (+/-SD) minimum diameter (1.6 cm +/- 0.6, 1.6 cm +/- 0.5, and 1.7 cm +/- 0.4, respectively), maximum diameter (2.0 cm +/- 0.5, 2.3 cm +/- 0.5, 2.2 cm +/- 0.5, respectively), and volume (6.7 cm3 +/- 3.7, 7.4 cm3 +/- 3.8, and 7.8 cm3 +/- 3.9; P > .30, analysis of variance, pairwise t-test comparisons). A rapid-switching multiple-electrode RF system was able to simultaneously create as many as three separate ablation zones of equivalent size compared with single-electrode controls. This system would allow physicians to simultaneously treat multiple tumors, substantially reducing procedure time and anesthesia risk.

Radio Frequency Microelectromechanical Systems [Book Chapter Manuscript

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nordquist, Christopher; Olsson, Roy H.

2014-12-15

Radio frequency microelectromechanical system (RF MEMS) devices are microscale devices that achieve superior performance relative to other technologies by taking advantage of the accuracy, precision, materials, and miniaturization available through microfabrication. To do this, these devices use their mechanical and electrical properties to perform a specific RF electrical function such as switching, transmission, or filtering. RF MEMS has been a popular area of research since the early 1990s, and within the last several years, the technology has matured sufficiently for commercialization and use in commercial market systems.

Temperature-Dependent Electrical Conductivity of GeTe-Based RF Switches

DTIC Science & Technology

2015-03-31

Short, high temperature pulses result in a melt -quench cycle, amorphizing the GeTe and leaving the switch in the electrically insulating OFF state...Longer, lower temperature pulses result in the recrystallization of the GeTe, leaving the switch in the electrically conductive ON state. The...shown to vary only weakly with temperature. OFF-state S-parameters also exhibit slight temperature variation, with an inflection point of ~175

The Role of Work Function and Band Gap in Resistive Switching Behaviour of ZnTe Thin Films

NASA Astrophysics Data System (ADS)

Rowtu, Srinu; Sangani, L. D. Varma; Krishna, M. Ghanashyam

2018-02-01

Resistive switching behavior by engineering the electrode work function and band gap of ZnTe thin films is demonstrated. The device structures Au/ZnTe/Au, Au/ZnTe/Ag, Al/ZnTe/Ag and Pt/ZnTe/Ag were fabricated. ZnTe was deposited by thermal evaporation and the stoichiometry and band gap were controlled by varying the source-substrate distance. Band gap could be varied between 1.0 eV to approximately 4.0 eV with the larger band gap being attributed to the partial oxidation of ZnTe. The transport characteristics reveal that the low-resistance state is ohmic in nature which makes a transition to Poole-Frenkel defect-mediated conductivity in the high-resistance states. The highest R off-to- R on ratio achieved is 109. Interestingly, depending on stoichiometry, both unipolar and bipolar switching can be realized.

Interfacial Metal-Oxide Interactions in Resistive Switching Memories.

PubMed

Cho, Deok-Yong; Luebben, Michael; Wiefels, Stefan; Lee, Kug-Seung; Valov, Ilia

2017-06-07

Metal oxides are commonly used as electrolytes for redox-based resistive switching memories. In most cases, non-noble metals are directly deposited as ohmic electrodes. We demonstrate that irrespective of bulk thermodynamics predictions an intermediate oxide film a few nanometers in thickness is always formed at the metal/insulator interface, and this layer significantly contributes to the development of reliable switching characteristics. We have tested metal electrodes and metal oxides mostly used for memristive devices, that is, Ta, Hf, and Ti and Ta 2 O 5 , HfO 2 , and SiO 2 . Intermediate oxide layers are always formed at the interfaces, whereas only the rate of the electrode oxidation depends on the oxygen affinity of the metal and the chemical stability of the oxide matrix. Device failure is associated with complete transition of short-range order to a more disordered main matrix structure.

Thermal modeling for pulsed radiofrequency ablation: analytical study based on hyperbolic heat conduction.

PubMed

López Molina, Juan A; Rivera, María J; Trujillo, Macarena; Berjano, Enrique J

2009-04-01

The objectives of this study were to model the temperature progress of a pulsed radiofrequency (RF) power during RF heating of biological tissue, and to employ the hyperbolic heat transfer equation (HHTE), which takes the thermal wave behavior into account, and compare the results to those obtained using the heat transfer equation based on Fourier theory (FHTE). A theoretical model was built based on an active spherical electrode completely embedded in the biological tissue, after which HHTE and FHTE were analytically solved. We found three typical waveforms for the temperature progress depending on the relations between the dimensionless duration of the RF pulse delta(a) and the expression square root of lambda(rho-1), with lambda as the dimensionless thermal relaxation time of the tissue and rho as the dimensionless position. In the case of a unique RF pulse, the temperature at any location was the result of the overlapping of two different heat sources delayed for a duration delta(a) (each heat source being produced by a RF pulse of limitless duration). The most remarkable feature in the HHTE analytical solution was the presence of temperature peaks traveling through the medium at a finite speed. These peaks not only occurred during the RF power switch-on period but also during switch off. Finally, a physical explanation for these temperature peaks is proposed based on the interaction of forward and reverse thermal waves. All-purpose analytical solutions for FHTE and HHTE were obtained during pulsed RF heating of biological tissues, which could be used for any value of pulsing frequency and duty cycle.

Fiber optic crossbar switch for automatically patching optical signals

NASA Technical Reports Server (NTRS)

Bell, C. H. (Inventor)

1983-01-01

A system for automatically optically switching fiber optic data signals between a plurality of input optical fibers and selective ones of a plurality of output fibers is described. The system includes optical detectors which are connected to each of the input fibers for converting the optic data signals appearing at the respective input fibers to an RF signal. A plurality of RF to optical signal converters are arranged in rows and columns. The output of each of the optical detectors are each applied to a respective row of optical signal converted for being converters back to an optical signal when the particular optical signal converter is selectively activated by a dc voltage.

Electrostatic Radio Frequency (RF) Microelectromechanical Systems (MEMS) Switches With Metal Alloy Electric Contacts

DTIC Science & Technology

2004-09-01

Serway , Raymond A. Physics for Scientists and Engineers . New York: Saunders College Publishing, 1986. 141. Sharvin, Y.V. Sov. Phys. JETP , 21 :655 (1965...III. Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1 Micro-Switch Physical Description . . . . . . . . . . . 17 3.2 MEMS...Insertion Loss . . . . . . . . . . . . . . . . . . . . . . . . 56 IMD Intermodulation Distortion . . . . . . . . . . . . . . . . 56 PVD Physical Vapor

RF performance of GaAs pHEMT switches with various upper/lower δ-doped ratio designs

NASA Astrophysics Data System (ADS)

Chiu, Hsien-Chin; Fu, Jeffrey S.; Chen, Chung-Wen

2009-02-01

AlGaAs/InGaAs pseudomorphic high-electron-mobility transistor (pHEMT) single-pole-single-throw (SPST) switches with various upper/lower δ-doped ratio designs were fabricated and investigated for the first time. Both off-state capacitance and the specific on-resistance ( Ron) of pHEMT are dominated factors and showed characteristics of sensitive to upper/lower δ-doped ratio for RF switch applications. By adopting the series-shunt architecture, upper/lower ratio of 3:1 switch achieved the lowest insertion loss compared to 4:1 design owing to the device shunt to ground (M2) of 4:1 design exhibited a worse fundamental signal isolation especially at high power level. As to the isolation under same architecture, however, due to the lowest Ron can be obtained, the 4:1 design provided better isolation performance. In addition, the M2 also dominated the second and third harmonics suppression and meanwhile, the lowest Ron of 4:1 design was found to be beneficial to the reduction of the harmonics power transmitted to the output terminal.

Multi-step resistive switching behavior of Li-doped ZnO resistance random access memory device controlled by compliance current

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Chun-Cheng; Department of Mathematic and Physical Sciences, R.O.C. Air Force Academy, Kaohsiung 820, Taiwan; Tang, Jian-Fu

2016-06-28

The multi-step resistive switching (RS) behavior of a unipolar Pt/Li{sub 0.06}Zn{sub 0.94}O/Pt resistive random access memory (RRAM) device is investigated. It is found that the RRAM device exhibits normal, 2-, 3-, and 4-step RESET behaviors under different compliance currents. The transport mechanism within the device is investigated by means of current-voltage curves, in-situ transmission electron microscopy, and electrochemical impedance spectroscopy. It is shown that the ion transport mechanism is dominated by Ohmic behavior under low electric fields and the Poole-Frenkel emission effect (normal RS behavior) or Li{sup +} ion diffusion (2-, 3-, and 4-step RESET behaviors) under high electric fields.

Trap-assisted tunneling in aluminum-doped ZnO/indium oxynitride nanodot interlayer Ohmic contacts on p-GaN

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ke, Wen-Cheng, E-mail: wcke@mail.ntust.edu.tw; Yang, Cheng-Yi; Lee, Fang-Wei

2015-10-21

This study developed an Ohmic contact formation method for a ZnO:Al (AZO) transparent conductive layer on p-GaN films involving the introduction of an indium oxynitride (InON) nanodot interlayer. An antisurfactant pretreatment was used to grow InON nanodots on p-GaN films in a RF magnetron sputtering system. A low specific contact resistance of 1.12 × 10{sup −4} Ω cm{sup 2} was achieved for a sample annealed at 500 °C for 30 s in nitrogen ambient and embedded with an InON nanodot interlayer with a nanodot density of 6.5 × 10{sup 8} cm{sup −2}. By contrast, a sample annealed in oxygen ambient exhibited non-Ohmic behavior. X-ray photoemission spectroscopy resultsmore » showed that the oxygen vacancy (V{sub o}) in the InON nanodots played a crucial role in carrier transport. The fitting I–V characteristic curves indicated that the hopping mechanism with an activation energy of 31.6 meV and trap site spacing of 1.1 nm dominated the carrier transport in the AZO/InON nanodot/p-GaN sample. Because of the high density of donor-like oxygen vacancy defects at the InON nanodot/p-GaN interface, positive charges from the underlying p-GaN films were absorbed at the interface. This led to positive charge accumulation, creating a narrow depletion layer; therefore, carriers from the AZO layer passed through InON nanodots by hopping transport, and subsequently tunneling through the interface to enter the p-GaN films. Thus, AZO Ohmic contact can be formed on p-GaN films by embedding an InON nanodot interlayer to facilitate trap-assisted tunneling.« less

Temporally resolved ozone distribution of a time modulated RF atmospheric pressure argon plasma jet: flow, chemical reaction, and transient vortex

NASA Astrophysics Data System (ADS)

Zhang, S.; Sobota, A.; van Veldhuizen, E. M.; Bruggeman, P. J.

2015-08-01

The ozone density distribution in the effluent of a time modulated RF atmospheric pressure plasma jet (APPJ) is investigated by time and spatially resolved by UV absorption spectroscopy. The plasma jet is operated with an averaged dissipated power of 6.5 W and gas flow rate 2 slm argon  +2% O2. The modulation frequency of the RF power is 50 Hz with a duty cycle of 50%. To investigate the production and destruction mechanism of ozone in the plasma effluent, the atomic oxygen and gas temperature is also obtained by TALIF and Rayleigh scattering, respectively. A temporal increase in ozone density is observed close to the quartz tube exit when the plasma is switched off due to the decrease in O density and gas temperature. Ozone absorption at different axial positions indicates that the ozone distribution is dominated by the convection induced by the gas flow and allows estimating the on-axis local gas velocity in the jet effluent. Transient vortex structures occurring during the switch on and off of the RF power also significantly affect the ozone density in the far effluent.

Monolithic control components for high power mm-waves

NASA Astrophysics Data System (ADS)

Armstrong, A.; Goodrich, J.; Moroney, W.; Wheeler, D.

1985-09-01

Monolithic PIN diode arrays are shown to provide significant advances in switching ratios, bandwidth, and high-power capability for millimeter control applications The PIN diodes are arranged in a series/parallel configuration and form an electronically controlled window for switching RF power by applying DC voltage. At Ka band, an SPST switch using the window array (WINAR) design typically has 0.6 dB insertion loss and 22 dB isolation over the 26.5 to 40.0 GHz band. The switch has over 500 W peak power and 25 W average power capability.

Nanotechnology-Enhanced Lubricants for RF MEMS Switches

DTIC Science & Technology

2011-03-01

and have greater capabilities. 2.1. Problem Background The Air Force employs numerous communication links between space -borne assets, airborne...beyond 10B of rated cold-switched life, such as high-value space -borne assets with 12+ year horizons to deployment. Warm-switched operation refers to...lids for 5 min. at 300W in oxygen 5. Stud bump substrates using a gold- silver alloy wire bonder – packages may be stored 6. Tack seal pre-form to lid

Optimization Of Shear Modes To Produce Enhanced Bandwidth In Ghz GaP Bragg Cells

NASA Astrophysics Data System (ADS)

Soos, J., I.; Rosemeier, R. G.; Rosenbaum, J.

1988-02-01

Applications of Gallium Phosphide (GaP) acousto-optic devices, at wavelengths from 570nm - 1.06um seem to be ideal for fiber optic modulators, scanners, deflectors, frequency shifters, Q-switches and mode lockers. One of the major applications are for RF spectrometers in early warning radar receivers and auto-correlators. Longitudinal GaP acousto-optic Bragg cells which have respectively operational frequencies in the range of 200 MHz - 3 GHz and diffraction efficiencies in the range of 120%/RF watt to 1%/RF watt have recently been fabricated. Comparatively, shear GaP devices which have operational frequencies in the range of 200 MHz to 2 GHz and diffraction efficiencies from 80%/RF watt to 7%/RF watt have also been constructed.

Electroforming free controlled bipolar resistive switching in Al/CoFe2O4/FTO device with self-compliance effect

NASA Astrophysics Data System (ADS)

Munjal, Sandeep; Khare, Neeraj

2018-02-01

Controlled bipolar resistive switching (BRS) has been observed in nanostructured CoFe2O4 (CFO) films using an Al (aluminum)/CoFe2O4/FTO (fluorine-doped tin oxide) device. The fabricated device shows electroforming-free uniform BRS with two clearly distinguished and stable resistance states without any application of compliance current, with a resistance ratio of the high resistance state (HRS) and the low resistance state (LRS) of >102. Small switching voltage (<1 volt) and lower current in both the resistance states confirm the fabrication of a low power consumption device. In the LRS, the conduction mechanism was found to be Ohmic in nature, while the high-resistance state (HRS/OFF state) was governed by the space charge-limited conduction mechanism, which indicates the presence of an interfacial layer with an imperfect microstructure near the top Al/CFO interface. The device shows nonvolatile behavior with good endurance properties, an acceptable resistance ratio, uniform resistive switching due to stable, less random filament formation/rupture, and a control over the resistive switching properties by choosing different stop voltages, which makes the device suitable for its application in future nonvolatile resistive random access memory.

Resistive switching characteristics of manganese oxide thin film and nanoparticle assembly hybrid devices

NASA Astrophysics Data System (ADS)

Abbas, Haider; Park, Mi Ra; Abbas, Yawar; Hu, Quanli; Kang, Tae Su; Yoon, Tae-Sik; Kang, Chi Jung

2018-06-01

Improved resistive switching characteristics are demonstrated in a hybrid device with Pt/Ti/MnO (thin film)/MnO (nanoparticle)/Pt structure. The hybrid devices of MnO thin film and nanoparticle assembly were fabricated. MnO nanoparticles with an average diameter of ∼30 nm were chemically synthesized and assembled as a monolayer on a Pt bottom electrode. A MnO thin film of ∼40 nm thickness was deposited on the nanoparticle assembly to form the hybrid structure. Resistive switching could be induced by the formation and rupture of conducting filaments in the hybrid oxide layers. The hybrid device exhibited very stable unipolar switching with good endurance and retention characteristics. It showed a larger and stable memory window with a uniform distribution of SET and RESET voltages. Moreover, the conduction mechanisms of ohmic conduction, space-charge-limited conduction, Schottky emission, and Poole–Frenkel emission have been investigated as possible conduction mechanisms for the switching of the devices. Using MnO nanoparticles in the thin film and nanoparticle heterostructures enabled the appropriate control of resistive random access memory (RRAM) devices and markedly improved their memory characteristics.

46. Building 102, view showing waveguide control switch used to ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

46. Building 102, view showing waveguide control switch used to achieve equal length adjustments and frequency control between separate Klystron tube radion frequency (RF) generators. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

Forming-free bipolar resistive switching in nonstoichiometric ceria films

NASA Astrophysics Data System (ADS)

Ismail, Muhammad; Huang, Chun-Yang; Panda, Debashis; Hung, Chung-Jung; Tsai, Tsung-Ling; Jieng, Jheng-Hong; Lin, Chun-An; Chand, Umesh; Rana, Anwar Manzoor; Ahmed, Ejaz; Talib, Ijaz; Nadeem, Muhammad Younus; Tseng, Tseung-Yuen

2014-01-01

The mechanism of forming-free bipolar resistive switching in a Zr/CeO x /Pt device was investigated. High-resolution transmission electron microscopy and energy-dispersive spectroscopy analysis indicated the formation of a ZrO y layer at the Zr/CeO x interface. X-ray diffraction studies of CeO x films revealed that they consist of nano-polycrystals embedded in a disordered lattice. The observed resistive switching was suggested to be linked with the formation and rupture of conductive filaments constituted by oxygen vacancies in the CeO x film and in the nonstoichiometric ZrO y interfacial layer. X-ray photoelectron spectroscopy study confirmed the presence of oxygen vacancies in both of the said regions. In the low-resistance ON state, the electrical conduction was found to be of ohmic nature, while the high-resistance OFF state was governed by trap-controlled space charge-limited mechanism. The stable resistive switching behavior and long retention times with an acceptable resistance ratio enable the device for its application in future nonvolatile resistive random access memory (RRAM).

Effect of AlN layer on the bipolar resistive switching behavior in TiN thin film based ReRAM device for non-volatile memory application

NASA Astrophysics Data System (ADS)

Prakash, Ravi; Kaur, Davinder

2018-05-01

The effect of an additional AlN layer in the Cu/TiN/AlN/Pt stack configuration deposited using sputtering has been investigated. The Cu/TiN/AlN/Pt device shows a tristate resistive switching. Multilevel switching is facilitated by ionic and metallic filament formation, and the nature of the filaments formed is confirmed by performing a resistance vs. temperature measurement. Ohmic behaviour and trap controlled space charge limited current (SCLC) conduction mechanisms are confirmed as dominant conduction mechanism at low resistance state (LRS) and high resistance state (HRS). High resistance ratio (102) corresponding to HRS and LRS, good write/erase endurance (105) and non-volatile long retention (105s) are also observed. Higher thermal conductivity of the AlN layer is the main reasons for the enhancement of resistive switching performance in Cu/TiN/AlN/Pt cell. The above result suggests the feasibility of Cu/TiN/AlN/Pt devices for multilevel nonvolatile ReRAM application.

(001) 3C SiC/Ni contact interface: In situ XPS observation of annealing induced Ni2Si formation and the resulting barrier height changes

NASA Astrophysics Data System (ADS)

Tengeler, Sven; Kaiser, Bernhard; Chaussende, Didier; Jaegermann, Wolfram

2017-04-01

The electronic states of the (001) 3C SiC/Ni interface prior and post annealing are investigated via an in situ XPS interface experiment, allowing direct observation of the induced band bending and the transformation from Schottky to ohmic behaviour for the first time. A single domain (001) 3C SiC sample was prepared via wet chemical etching. Nickel was deposited on the sample in multiple in situ deposition steps via RF sputtering, allowing observation of the 3C SiC/Ni interface formation. Over the course of the experiments, an upward band bending of 0.35 eV was observed, along with defect induced Fermi level pinning. This indicates a Schottky type contact behaviour with a barrier height of 0.41 eV. The subsequent annealing at 850 °C for 5 min resulted in the formation of a Ni2Si layer and a reversal of the band bending to 0.06 eV downward. Thus explaining the ohmic contact behaviour frequently reported for annealed n-type 3C SiC/Ni contacts.

Flexible microwave PIN diodes and switches employing transferrable single-crystal Si nanomembranes on plastic substrates

NASA Astrophysics Data System (ADS)

Qin, Guoxuan; Yuan, Hao-Chih; Celler, George K.; Zhou, Weidong; Ma, Zhenqiang

2009-12-01

This paper reports the realization of flexible RF/microwave PIN diodes and switches using transferrable single-crystal Si nanomembranes (SiNM) that are monolithically integrated on low-cost, flexible plastic substrates. High frequency response is obtained through the realization of low parasitic resistance achieved with heavy ion implantation before nanomembrane release and transfer. The flexible lateral SiNM PIN diodes exhibit typical rectifying characteristics with insertion loss and isolation better than 0.9 dB and 19.6 dB, respectively, from DC to 5 GHz, as well as power handling up to 22.5 dBm without gain compression. A single-pole single-throw (SPST) flexible RF switch employing shunt-series PIN diode configuration has achieved insertion loss and isolation better than 0.6 dB and 22.9 dB, respectively, from DC to 5 GHz. Furthermore, the SPST microwave switch shows performance improvement and robustness under mechanical deformation conditions. The study demonstrates the considerable potential of using properly processed transferrable SiNM for microwave passive components. Future investigations on transferrable SiNMs will lead to eventual realization of monolithic microwave integrated systems on low-cost flexible substrates.

Meta-metallic coils and resonators: Methods for high Q-value resonant geometries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mett, R. R.; Department of Physics and Chemistry, Milwaukee School of Engineering, Milwaukee, Wisconsin 53202; Sidabras, J. W.

A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approachesmore » the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz.« less

Meta-metallic coils and resonators: Methods for high Q-value resonant geometries

PubMed Central

Mett, R. R.; Hyde, J. S.

2016-01-01

A novel method of decreasing ohmic losses and increasing Q-value in metallic resonators at high frequencies is presented. The method overcomes the skin-depth limitation of rf current flow cross section. The method uses layers of conductive foil of thickness less than a skin depth and capacitive gaps between layers. The capacitive gaps can substantially equalize the rf current flowing in each layer, resulting in a total cross-sectional dimension for rf current flow many times larger than a skin depth. Analytic theory and finite-element simulations indicate that, for a variety of structures, the Q-value enhancement over a single thick conductor approaches the ratio of total conductor thickness to skin depth if the total number of layers is greater than one-third the square of the ratio of total conductor thickness to skin depth. The layer number requirement is due to counter-currents in each foil layer caused by the surrounding rf magnetic fields. We call structures that exhibit this type of Q-enhancement “meta-metallic.” In addition, end effects due to rf magnetic fields wrapping around the ends of the foils can substantially reduce the Q-value for some classes of structures. Foil structures with Q-values that are substantially influenced by such end effects are discussed as are five classes of structures that are not. We focus particularly on 400 MHz, which is the resonant frequency of protons at 9.4 T. Simulations at 400 MHz are shown with comparison to measurements on fabricated structures. The methods and geometries described here are general for magnetic resonance and can be used at frequencies much higher than 400 MHz. PMID:27587143

57. Building 105, another view of ion return RF balance ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

57. Building 105, another view of ion return RF balance tube system, and beginning of waveguide return connections to right of photograph; note bottoms of waveguide systems around circumference of scanner switch in upper part of photograph. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

38. View of DRS 1, 2, and 3 (structure nos. ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

38. View of DRS 1, 2, and 3 (structure nos. 735, 736, and 737) console fault locator for beam power status, radio frequency (RF) and intermediate frequency (IF) fault conditions, RF switches status and TR status. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

Opportunity of spinel ferrite materials in nonvolatile memory device applications based on their resistive switching performances.

PubMed

Hu, Wei; Qin, Ni; Wu, Guangheng; Lin, Yanting; Li, Shuwei; Bao, Dinghua

2012-09-12

The opportunity of spinel ferrites in nonvolatile memory device applications has been demonstrated by the resistive switching performance characteristics of a Pt/NiFe(2)O(4)/Pt structure, such as low operating voltage, high device yield, long retention time (up to 10(5) s), and good endurance (up to 2.2 × 10(4) cycles). The dominant conduction mechanisms are Ohmic conduction in the low-resistance state and in the lower-voltage region of the high-resistance state and Schottky emission in the higher-voltage region of the high-resistance state. On the basis of measurements of the temperature dependence of the resistances and magnetic properties in different resistance states, we explain the physical mechanism of resistive switching of Pt/NiFe(2)O(4)/Pt devices using the model of formation and rupture of conducting filaments by considering the thermal effect of oxygen vacancies and changes in the valences of cations due to the redox effect.

Electrical memory characteristics of a nondoped pi-conjugated polymer bearing carbazole moieties.

PubMed

Park, Samdae; Lee, Taek Joon; Kim, Dong Min; Kim, Jin Chul; Kim, Kyungtae; Kwon, Wonsang; Ko, Yong-Gi; Choi, Heungyeal; Chang, Taihyun; Ree, Moonhor

2010-08-19

Poly[bis(9H-carbazole-9-ethyl)dipropargylmalonate] (PCzDPM) is a novel pi-conjugated polymer bearing carbazole moieties that has been synthesized by polymerization of bis(9H-carbazole-9-ethyl)dipropargylmalonate with the aid of molybdenum chloride solution as the catalyst. This polymer is thermally stable up to 255 degrees C under a nitrogen atmosphere and 230 degrees C in air ambient; its glass-transition temperature is 147 or 128 degrees C, depending on the polymer chain conformation (helical or planar structure). The charge-transport characteristics of PCzDPM in nanometer-scaled thin films were studied as a function of temperature and film thickness. PCzDPM films with a thickness of 15-30 nm were found to exhibit very stable dynamic random access memory (DRAM) characteristics without polarity. Furthermore, the polymer films retain DRAM characteristics up to 180 degrees C. The ON-state current is dominated by Ohmic conduction, and the OFF-state current appears to undergo a transition from Ohmic to space-charge-limited conduction with a shallow-trap distribution. The ON/OFF switching of the devices is mainly governed by filament formation. The filament formation mechanism for the switching process is supported by the metallic properties of the PCzDPM film, which result in the temperature dependence of the ON-state current. In addition, the structure of this pi-conjugated polymer was found to vary with its thermal history; this change in structure can affect filament formation in the polymer film.

Low-loss plasmon-assisted electro-optic modulator.

PubMed

Haffner, Christian; Chelladurai, Daniel; Fedoryshyn, Yuriy; Josten, Arne; Baeuerle, Benedikt; Heni, Wolfgang; Watanabe, Tatsuhiko; Cui, Tong; Cheng, Bojun; Saha, Soham; Elder, Delwin L; Dalton, Larry R; Boltasseva, Alexandra; Shalaev, Vladimir M; Kinsey, Nathaniel; Leuthold, Juerg

2018-04-01

For nearly two decades, researchers in the field of plasmonics 1 -which studies the coupling of electromagnetic waves to the motion of free electrons near the surface of a metal 2 -have sought to realize subwavelength optical devices for information technology 3-6 , sensing 7,8 , nonlinear optics 9,10 , optical nanotweezers 11 and biomedical applications 12 . However, the electron motion generates heat through ohmic losses. Although this heat is desirable for some applications such as photo-thermal therapy, it is a disadvantage in plasmonic devices for sensing and information technology 13 and has led to a widespread view that plasmonics is too lossy to be practical. Here we demonstrate that the ohmic losses can be bypassed by using 'resonant switching'. In the proposed approach, light is coupled to the lossy surface plasmon polaritons only in the device's off state (in resonance) in which attenuation is desired, to ensure large extinction ratios between the on and off states and allow subpicosecond switching. In the on state (out of resonance), destructive interference prevents the light from coupling to the lossy plasmonic section of a device. To validate the approach, we fabricated a plasmonic electro-optic ring modulator. The experiments confirm that low on-chip optical losses, operation at over 100 gigahertz, good energy efficiency, low thermal drift and a compact footprint can be combined in a single device. Our result illustrates that plasmonics has the potential to enable fast, compact on-chip sensing and communications technologies.

Forced-rupture of cell-adhesion complexes reveals abrupt switch between two brittle states

NASA Astrophysics Data System (ADS)

Toan, Ngo Minh; Thirumalai, D.

2018-03-01

Cell adhesion complexes (CACs), which are activated by ligand binding, play key roles in many cellular functions ranging from cell cycle regulation to mediation of cell extracellular matrix adhesion. Inspired by single molecule pulling experiments using atomic force spectroscopy on leukocyte function-associated antigen-1 (LFA-1), expressed in T-cells, bound to intercellular adhesion molecules (ICAM), we performed constant loading rate (rf) and constant force (F) simulations using the self-organized polymer model to describe the mechanism of ligand rupture from CACs. The simulations reproduce the major experimental finding on the kinetics of the rupture process, namely, the dependence of the most probable rupture forces (f*s) on ln rf (rf is the loading rate) exhibits two distinct linear regimes. The first, at low rf, has a shallow slope, whereas the slope at high rf is much larger, especially for a LFA-1/ICAM-1 complex with the transition between the two occurring over a narrow rf range. Locations of the two transition states (TSs) extracted from the simulations show an abrupt change from a high value at low rf or constant force, F, to a low value at high rf or F. This unusual behavior in which the CACs switch from one brittle (TS position is a constant over a range of forces) state to another brittle state is not found in forced-rupture in other protein complexes. We explain this novel behavior by constructing the free energy profiles, F(Λ)s, as a function of a collective reaction coordinate (Λ), involving many key charged residues and a critical metal ion (Mg2+). The TS positions in F(Λ), which quantitatively agree with the parameters extracted using the Bell-Evans model, change abruptly at a critical force, demonstrating that it, rather than the molecular extension, is a good reaction coordinate. Our combined analyses using simulations performed in both the pulling modes (constant rf and F) reveal a new mechanism for the two loading regimes observed in the rupture kinetics in CACs.

Dual Switching Monopolar Radiofrequency Ablation Using a Separable Clustered Electrode: Comparison with Consecutive and Switching Monopolar Modes in Ex Vivo Bovine Livers

PubMed Central

Yoon, Jeong-Hee; Han, Joon Koo; Choi, Byung Ihn

2013-01-01

Objective To compare the in-vitro efficiency of dual-switching monopolar (DSM) radiofrequency ablation (RFA) using a separable clustered electrode (Octopus® electrodes) with consecutive monopolar (CM) and switching monopolar (SM) RFA techniques to create an ablative zone in the explanted bovine liver. Materials and Methods For DSM-RFA, we used a prototype, three-channel, dual generator RFA Unit and Octopus® electrodes with three, 17 gauge internally cooled electrodes. The RFA Unit allowed simultaneous radiofrequency (RF) energy delivery to two electrodes of the Octopus® electrodes as well as automatic switching among the three electrode pairs according to the impedance changes. RF energy was sequentially applied to one of the three electrodes for 24 minutes (group A; CM mode, n = 10) or alternatively applied for 12 minutes (group B; SM mode, n = 10) or concurrently applied to a pair of electrodes for 12 minutes (group C; DSM mode, n = 10) in explanted bovine livers. Changes in the impedance and current during RFA as well as the dimensions of the thermal ablative zones were compared among the three groups. Results The mean, delivered RF energy amounts in groups A, B, and C were 63.15 ± 8.6 kJ, 72.13 ± 5.4 kJ, and 106.08 ± 13.4 kJ, respectively (p < 0.001). The DSM mode created a significantly larger ablation volume than did the other modes, i.e., 68.1 ± 10.2 cm3 (group A), 92.0 ± 19.9 cm3 (group B), and 115.1 ± 14.0 cm3 (group C) (p < 0.001). The circularity in groups A, B, and C were 0.84 ± 0.06, 0.87 ± 0.04 and 0.90 ± 0.03, respectively (p = 0.03). Conclusion DSM-RFA using Octopus® electrodes can help create large ablative zones within a relatively short time. PMID:23690705

New vision in fractional radiofrequency technology with switching, vacuum and cooling.

PubMed

Elman, Monica; Gauthier, Nelly; Belenky, Inna

2015-04-01

Since the introduction of fractional technology, various systems were launched to the market. The first generation of fractional RF systems created epidermal ablation with coagulative/necrosis of the dermis with sufficient clinical outcomes, but with some limitations. The aim of this study was to evaluate the efficacy and safety of SVC technology, based on the principle of separate biological responses. Fifty-two patients were treated for 3-6 sessions using fractional RF handpiece and eight patients received combination treatments with non-invasive RF handpiece. All volunteers showed notable to significant improvement in the photoageing symptoms, without any significant complications or adverse events. Due to its wide spectrum of parameters, the SVC technology can promote different biological responses. Owing to the "Switching" technology, the control of energy depth penetration enables delivery of the necessary thermal dose to the targeted skin layer. In addition, this novel technology includes the "Vacuum" and "Cooling" mechanisms, each contributing to the safety of the treatment. The Smart Heat function reduces the necessary energy levels and thereby reduces the pain level and risks for side effects.

FERMILAB CRYOMODULE TEST STAND RF INTERLOCK SYSTEM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petersen, Troy; Diamond, J. S.; McDowell, D.

2016-10-12

An interlock system has been designed for the Fermilab Cryo-module Test Stand (CMTS), a test bed for the cryo- modules to be used in the upcoming Linac Coherent Light Source 2 (LCLS-II) project at SLAC. The interlock system features 8 independent subsystems, one per superconducting RF cavity and solid state amplifier (SSA) pair. Each system monitors several devices to detect fault conditions such as arcing in the waveguides or quenching of the SRF system. Additionally each system can detect fault conditions by monitoring the RF power seen at the cavity coupler through a directional coupler. In the event of amore » fault condition, each system is capable of removing RF signal to the amplifier (via a fast RF switch) as well as turning off the SSA. Additionally, each input signal is available for re- mote viewing and recording via a Fermilab designed digitizer board and MVME 5500 processor.« less

Fast shut-down protection system for radio frequency breakdown and multipactor testing.

PubMed

Graves, T P; Hanson, P; Michaelson, J M; Farkas, A D; Hubble, A A

2014-02-01

Radio frequency (RF) breakdown such as multipactor or ionization breakdown is a device-limiting phenomenon for on-orbit spacecraft used for communication, navigation, or other RF payloads. Ground testing is therefore part of the qualification process for all high power components used in these space systems. This paper illustrates a shut-down protection system to be incorporated into multipactor/ionization breakdown ground testing for susceptible RF devices. This 8 channel system allows simultaneous use of different diagnostic classes and different noise floors. With initiation of a breakdown event, diagnostic signals increase above a user-specified level, which then opens an RF switch to eliminate RF power from the high power amplifier. Examples of this system in use are shown for a typical setup, illustrating the reproducibility of breakdown threshold voltages and the lack of multipactor conditioning. This system can also be utilized to prevent excessive damage to RF components in tests with sensitive or flight hardware.

Composition-ratio influence on resistive switching behavior of solution-processed InGaZnO-based thin-film.

PubMed

Hwang, Yeong-Hyeon; Hwang, Inchan; Cho, Won-Ju

2014-11-01

The influence of composition ratio on the bipolar resistive switching behavior of resistive switching memory devices based on amorphous indium-gallium-zinc-oxide (a-IGZO) using the spin-coating process was investigated. To study the stoichiometric effects of the a-IGZO films on device characteristics, four devices with In/Ga/Zn stoichiometries of 1:1:1, 3:1:1, 1:3:1, and 1:1:3 were fabricated and characterized. The 3:1:1 film showed an ohmic behavior and the 1:1:3 film showed a rectifying switching behavior. The current-voltage characteristics of the a-IGZO films with stoichiometries of 1:1:1 and 1:3:1, however, showed a bipolar resistive memory switching behavior. We found that the three-fold increase in the gallium content ratio reduces the reset voltage from -0.9 to - 0.4 V and enhances the current ratio of high to low resistive states from 0.7 x 10(1) to 3 x 10(1). Our results show that the increase in the Ga composition ratio in the a-IGZO-based ReRAM cells effectively improves the device performance and reliability by increasing the initial defect density in the a-IGZO films.

Study of Ag/RGO/ITO sandwich structure for resistive switching behavior deposited on plastic substrate

NASA Astrophysics Data System (ADS)

Vartak, Rajdeep; Rag, Adarsh; De, Shounak; Bhat, Somashekhara

2018-05-01

We report here the use of facile and environmentally benign way synthesized reduced graphene oxide (RGO) for low-voltage non-volatile memory device as charge storing element. The RGO solutions have been synthesized using electrochemical exfoliation of battery electrode. The solution processed based RGO solution is suitable for large area and low-cost processing on plastic substrate. Room-temperature current-voltage characterisation has been carried out in Ag/RGO/ITO PET sandwich configuration to study the type of trap distribution. It is observed that in the low-voltage sweep, ohmic current is the main mechanism of current flow and trap filled/assisted conduction is observed at high-sweep voltage region. The Ag/RGO/ITO PET sandwich structure showed bipolar resistive switching behavior. These mechanisms can be analyzed based on oxygen availability and vacancies in the RGO giving rise to continuous least resistive path (conductive) and high resistance path along the structure. An Ag/RGO/ITO arrangement demonstrates long retention time with low operating voltage, low set/reset voltage, good ON/OFF ratio of 103 (switching transition between lower resistance state and higher resistance state and decent switching performance. The RGO memory showed decent results with an almost negligible degradation in switching properties which can be used for low-voltage and low-cost advanced flexible electronics.

Applications of Non-linearities in RF MEMS Switches and Resonators

NASA Astrophysics Data System (ADS)

Vummidi Murali, Krishna Prasad

The 21st century is emerging into an era of wireless ubiquity. To support this trend, the RF (Radio Frequency) front end must be capable of processing a range of wireless signals (cellular phone, data connectivity, broadcast TV, GPS positioning, etc.) spanning a total bandwidth of nearly 6 GHz. This warrants the need for multi-band/multi-mode radio architectures. For such architectures to satisfy the constraints on size, battery life, functionality and cost, the radio front-end must be made reconfigurable. RF-MEMS (RF Micro-Electro-Mechanical Systems) are seen as an enabling technology for such reconfigurable radios. RF-MEMS mainly include micromechanical switches (used in phase shifters, switched capacitor banks, impedance tuners etc.) and micromechanical resonators (used in tunable filters, oscillators, reference clocks etc.). MEMS technology also has the potential to be directly integrated into CMOS (Complementary metal-oxide semiconductor) ICs (Integrated Circuits) leading to further potential reductions of cost and size. However, RF-MEMS face challenges that must be addressed before they can gain widespread commercial acceptance. Relatively low switching speed, power handling, and high-voltage drive are some of the key issues in MEMS switches. Phase noise influenced by non-linearities, need for temperature compensation (especially Si based resonators), large start-up times, and aging are the key issues in Si MEMS Resonators. In this work potential solutions are proposed to address some of these key issues, specifically the reduction of high voltage drives in switches and the reduction of phase noise in MEMS resonators for timing applications. MEMS devices that are electrostatically actuated exhibit significant non-linearities. The origins of the non-linearities are both electrical (electrostatic actuation) and mechanical (dimensions and material properties). The influence of spring non-linearities (cubic and quadratic) on the performance of switches and resonators are studied. Gold electroplated fixed-fixed beams were fabricated to test the phenomenon of dynamic (or resonant) pull-in in shunt switches. The dynamic pull-in phenomenon was also tested on commercially fabricated lateral switches. It is shown that the resonant pull-in technique reduces the overall voltage required to actuate the switch. There is an additional reduction of total actuation voltage possible via applying an AC actuation signal at the correct non-linear resonant frequency. The demonstrated best case savings from operating at the non-linear resonance is 50% (for the lateral switch) and 60% (for the vertical switch) as compared to 25% and 40% respectively using a fixed frequency approach. However, the timing response for resonant pull-in has been experimentally shown to be slower than the static actuation. To reduce the switching time, a shifted-frequency method is proposed where the excitation frequency is shifted up or down by a discrete amount deltaO after a brief hold time. It was theoretically shown that the shifted-frequency method enables a minimum realizable switching time comparable to the static switching time for a given set of actuation frequencies. The influence of VDC on the effective non-linearities of a fixed-fixed beam is also studied. Based on the dimensions of the resonator and the type of resonance there is a certain VDC,Lin where the response is near linear (S ≈ 0). In the near-linear domain, the dynamic pull-in is the only upper bound to the amplitude of vibrations, and hence the amplitude of output current, thereby maximizing the power handling capacity of the resonator. Apart from maximizing the output current, it is essential to reduce the amplitude and phase variations of the displacement response which are due to noise mixing into frequency of interest, and are eventually manifested as output phase noise due to capacitive current nonlinearity. Two major aliasing schemes were analyzed and it was shown that the capacitive force non-linearity is the major source of mixing that causes the up-conversion of 1/f frequency into signal sidebands. The resonator's periodic response (displacement) is defined by a set of two first-order nonlinear ordinary differential equations that describe the modulation of amplitude and phase of the response. Frequency response curves of amplitude and frequency are determined from these modulation equations. The zero slope point on the amplitude resonance curve is the peak of the resonance curve where the phase (gammadc) of the response is +/-pi/2. For a strongly non-linear system, the resonance curves are skewed based on the amount of total non-linearity S. For systems that are strongly non-linear, the best region to operate the resonator is the fixed point that correspond to infinite slope (gammadc = +/-2pi/3) in the frequency response of the system. The best case phase noise response was analytically developed for such a fixed point. Theoretically at this fixed point, phase noise will have contributions only from 1/ fnoise and not from 1/f2 and 1/ f3. The resonators phase can be set by controlling the rest of the phase in the loop such that the total phase around the loop is zero or 2pi. In addition, this work has also developed an analytical model for a lateral MEMS switch fabricated in a commercial foundry that has the potential to be processed as MEMS on CMOS. This model accounts for trapezoidal cross sections of the electrodes and springs and also models electrostatic fringing as a function of the moving gap. The analytical model matches closely with the Finite Element (FEA) model.

MR-compatibility assessment of MADPET4: a study of interferences between an SiPM-based PET insert and a 7 T MRI system.

PubMed

Omidvari, Negar; Topping, Geoffrey; Cabello, Jorge; Paul, Stephan; Schwaiger, Markus; Ziegler, Sibylle I

2018-05-01

Compromises in the design of a positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system should minimize the deterioration of image quality in both modalities, particularly when simultaneous demanding acquisitions are performed. In this work, the advantages of using individually read-out crystals with high-gain silicon photomultipliers (SiPMs) were studied with a small animal PET insert for a 7 T MRI system, in which the SiPM charge was transferred to outside the MRI scanner using coaxial cables. The interferences between the two systems were studied with three radio-frequency (RF) coil configurations. The effects of PET on the static magnetic field, flip angle distribution, RF noise, and image quality of various MRI sequences (gradient echo, spin echo, and echo planar imaging (EPI) at 1 H frequency, and chemical shift imaging at 13 C frequency) were investigated. The effects of fast-switching gradient fields and RF pulses on PET count rate were studied, while the PET insert and the readout electronics were not shielded. Operating the insert inside a 1 H volume coil, used for RF transmission and reception, limited the MRI to T1-weighted imaging, due to coil detuning and RF attenuation, and resulted in significant PET count loss. Using a surface receive coil allowed all tested MR sequences to be used with the insert, with 45-59% signal-to-noise ratio (SNR) degradation, compared to without PET. With a 1 H/ 13 C volume coil inside the insert and shielded by a copper tube, the SNR degradation was limited to 23-30% with all tested sequences. The insert did not introduce any discernible distortions into images of two tested EPI sequences. Use of truncated sinc shaped RF excitation pulses and gradient field switching had negligible effects on PET count rate. However, PET count rate was substantially affected by high-power RF block pulses and temperature variations due to high gradient duty cycles.

Loaded delay lines for future RF pulse compression systems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, R.M.; Wilson, P.B.; Kroll, N.M.

1995-05-01

The peak power delivered by the klystrons in the NLCRA (Next Linear Collider Test Accelerator) now under construction at SLAC is enhanced by a factor of four in a SLED-II type of R.F. pulse compression system (pulse width compression ratio of six). To achieve the desired output pulse duration of 250 ns, a delay line constructed from a 36 m length of circular waveguide is used. Future colliders, however, will require even higher peak power and larger compression factors, which favors a more efficient binary pulse compression approach. Binary pulse compression, however, requires a line whose delay time is approximatelymore » proportional to the compression factor. To reduce the length of these lines to manageable proportions, periodically loaded delay lines are being analyzed using a generalized scattering matrix approach. One issue under study is the possibility of propagating two TE{sub o} modes, one with a high group velocity and one with a group velocity of the order 0.05c, for use in a single-line binary pulse compression system. Particular attention is paid to time domain pulse degradation and to Ohmic losses.« less

Thin TiOx layer as a voltage divider layer located at the quasi-Ohmic junction in the Pt/Ta2O5/Ta resistance switching memory.

PubMed

Li, Xiang Yuan; Shao, Xing Long; Wang, Yi Chuan; Jiang, Hao; Hwang, Cheol Seong; Zhao, Jin Shi

2017-02-09

Ta 2 O 5 has been an appealing contender for the resistance switching random access memory (ReRAM). The resistance switching (RS) in this material is induced by the repeated formation and rupture of the conducting filaments (CFs) in the oxide layer, which are accompanied by the almost inevitable randomness of the switching parameters. In this work, a 1 to 2 nm-thick Ti layer was deposited on the 10 nm-thick Ta 2 O 5 RS layer, which greatly improved the RS performances, including the much-improved switching uniformity. The Ti metal layer was naturally oxidized to TiO x (x < 2) and played the role of a series resistor, whose resistance value was comparable to the on-state resistance of the Ta 2 O 5 RS layer. The series resistor TiO x efficiently suppressed the adverse effects of the voltage (or current) overshooting at the moment of switching by the appropriate voltage partake effect, which increased the controllability of the CF formation and rupture. The switching cycle endurance was increased by two orders of magnitude even during the severe current-voltage sweep tests compared with the samples without the thin TiO x layer. The Ti deposition did not induce any significant overhead to the fabrication process, making the process highly promising for the mass production of a reliable ReRAM.

Ultra Low-Voltage Energy Harvesting

DTIC Science & Technology

2013-09-01

Power PV Photovoltaic R Resistance RF Radio Frequencies S Switch SPICE Simulation Program with Integrated Circuit Emphasis T Switching Cycle xiv...control experiment, a supercapacitor was connected to a photovoltaic (PV) source with a diode in between. The advantages of this circuit were a...Circuits to harvest thermal differences typically produce only 0.02 to 0.15 V, while low-power photovoltaic cells can generate 0.2 to 0.7 V and

Quasi-Optical Network Analyzers and High-Reliability RF MEMS Switched Capacitors

NASA Astrophysics Data System (ADS)

Grichener, Alexander

The thesis first presents a 2-port quasi-optical scalar network analyzer consisting of a transmitter and receiver both built in planar technology. The network analyzer is based on a Schottky-diode mixer integrated inside a planar antenna and fed differentially by a CPW transmission line. The antenna is placed on an extended hemispherical high-resistivity silicon substrate lens. The LO signal is swept from 3-5 GHz and high-order harmonic mixing in both up- and down- conversion mode is used to realize the 15-50 GHz RF bandwidth. The network analyzer resulted in a dynamic range of greater than 40 dB and was successfully used to measure a frequency selective surface with a second-order bandpass response. Furthermore, the system was built with circuits and components for easy scaling to millimeter-wave frequencies which is the primary motivation for this work. The application areas for a millimeter and submillimeter-wave network analyzer include material characterization and art diagnostics. The second project presents several RF MEMS switched capacitors designed for high-reliability operation and suitable for tunable filters and reconfigurable networks. The first switched-capacitor resulted in a digital capacitance ratio of 5 and an analog capacitance ratio of 5-9. The analog tuning of the down-state capacitance is enhanced by a positive vertical stress gradient in the the beam, making it ideal for applications that require precision tuning. A thick electroplated beam resulted in Q greater than 100 at C to X-band frequencies, and power handling of 0.6-1.1 W. The design also minimized charging in the dielectric, resulting in excellent reliability performance even under hot-switched and high power (1 W) conditions. The second switched-capacitor was designed without any dielectric to minimize charging. The device was hot-switched at 1 W of RF power for greater than 11 billion cycles with virtually no change in the C-V curve. The final project presents a 7-channel channelizer based on the mammalian cochlea. The cochlea is an amazing channelizing filter, covering three decades of bandwidth with over 3,000 channels in a very small physical space. Using a simplified mechanical cochlear model and its electrical analogue, a design method is demonstrated for RF and microwave channelizers that retains the desirable features of the cochlea including the ability to cascade a large number of channels (for multiple-octave frequency coverage), and a high-order stop-band rejection. A 6-pole response is synthesized in each channel using the top-C coupled topology. A constant absolute 3 dB bandwidth of around 4.3 MHz and an insertion loss of around 3.9 dB is measured in each channel. A high isolation (greater than 35 dB) is achieved between adjacent channels. A reflection loss of greater than 15 dB is measured at the input port over the entire channelizer bandwidth. Application areas for the demonstrated channelizer include wideband, contiguous-channel receivers for signal intelligence or spectral analysis.

Effects of Ohmic Resistance on Dynamic Characteristics and Impedance of Micro/Nano Cantilever Beam resonators

NASA Astrophysics Data System (ADS)

Rezazadeh, Ghader; Keyvani, Aliasghar; Sadeghi, Morteza H.; Bahrami, Manouchehr

2013-06-01

Effects of Ohmic resistance on MEMS/NEMS vibrating structures that have always been dismissed in some situations may cause important changes in resonance properties and impedance parameters of the MEMS/NEMS based circuits. In this paper it is aimed to present a theoretical model to precisely investigate the problem on a simple cantilever-substrate resonator. In this favor the Ohm's current law and charge conservation law have been merged to find a differential Equation for voltage propagation on the beam and because mostly nano structures are expected as the scope of the problem, modified couple stress theory is used to formulate the dynamic motion of the beam. The two governing equations were coupled and both nonlinear that have been solved simultaneously using a Galerkin based state space formulation. The obtained results that are in exact agreement with previous works show that dynamic pull-in voltage, switching time, and impedance of structure as a MEMS capacitor especially in frequencies higher than natural resonance frequency strongly relay on electrical resistance of the beam and substrate material.

Pegasus power system facility upgrades

NASA Astrophysics Data System (ADS)

Lewicki, B. T.; Kujak-Ford, B. A.; Winz, G. R.

2008-11-01

Two key Pegasus systems have been recently upgraded: the Ohmic-transformer IGCT bridge control system, and the plasma-gun injector power system. The Ohmic control system contains two new microprocessor controlled components to provide an interface between the PWM controller and the IGCT bridges. An interface board conditions the command signals from the PWM controller. A splitter/combiner board routes the conditioned PWM commands to an array of IGCT bridges and interprets IGCT bridge status. This system allows for any PWM controller to safely control IGCT bridges. Future developments will include a transition to a polyphasic bridge control. This will allow for 3 to 4 times the present pulse length and provide a much higher switching frequency. The plasma gun injector system now includes active current feedback control on gun bias current via PWM buck type power supplies. Near term goals include a doubling or tripling of the applied bias voltage. Future arc bias system power supplies may include a simpler boost type system which will allow access to even higher voltages using existing low voltage energy storage systems.

RF transmission line and drill/pipe string switching technology for down-hole telemetry

DOEpatents

Clark, David D [Santa Fe, NM; Coates, Don M [Santa Fe, NM

2007-08-14

A modulated reflectance well telemetry apparatus having an electrically conductive pipe extending from above a surface to a point below the surface inside a casing. An electrical conductor is located at a position a distance from the electrically conductive pipe and extending from above the surface to a point below the surface. Modulated reflectance apparatus is located below the surface for modulating well data into a RF carrier transmitted from the surface and reflecting the modulated carrier back to the surface. A RF transceiver is located at the surface and is connected between the electrically conductive pipe and the electrical conductor for transmitting a RF signal that is confined between the electrically conductive well pipe and the electrical conductor to the modulated reflectance apparatus, and for receiving reflected data on the well from the modulated reflectance apparatus.

Study of Pulsed vs. RF Plasma Properties for Surface Processing Applications

NASA Astrophysics Data System (ADS)

Tang, Ricky; Hopkins, Matthew; Barnat, Edward; Miller, Paul

2015-09-01

The ability to manipulate the plasma parameters (density, E/N) was previously demonstrated using a double-pulsed column discharge. Experiments extending this to large-surface plasmas of interest to the plasma processing community were conducted. Differences between an audio-frequency pulsed plasma and a radio-frequency (rf) discharge, both prevalent in plasma processing applications, were studied. Optical emission spectroscopy shows higher-intensity emission in the UV/visible range for the pulsed plasma comparing to the rf plasma at comparable powers. Data suggest that the electron energy is higher for the pulsed plasma leading to higher ionization, resulting in increased ion density and ion flux. Diode laser absorption measurements of the concentration of the 1S5 metastable and 1S4 resonance states of argon (correlated with the plasma E/N) provide comparisons between the excitation/ionization states of the two plasmas. Preliminary modeling efforts suggest that the low-frequency polarity switch causes a much more abrupt potential variation to support interesting transport phenomena, generating a ``wave'' of higher temperature electrons leading to more ionization, as well as ``sheath capture'' of a higher density bolus of ions that are then accelerated during polarity switch.

Advanced millimeter-wave security portal imaging techniques

NASA Astrophysics Data System (ADS)

Sheen, David M.; Bernacki, Bruce E.; McMakin, Douglas L.

2012-03-01

Millimeter-wave (mm-wave) imaging is rapidly gaining acceptance as a security tool to augment conventional metal detectors and baggage x-ray systems for passenger screening at airports and other secured facilities. This acceptance indicates that the technology has matured; however, many potential improvements can yet be realized. The authors have developed a number of techniques over the last several years including novel image reconstruction and display techniques, polarimetric imaging techniques, array switching schemes, and high-frequency high-bandwidth techniques. All of these may improve the performance of new systems; however, some of these techniques will increase the cost and complexity of the mm-wave security portal imaging systems. Reducing this cost may require the development of novel array designs. In particular, RF photonic methods may provide new solutions to the design and development of the sequentially switched linear mm-wave arrays that are the key element in the mm-wave portal imaging systems. Highfrequency, high-bandwidth designs are difficult to achieve with conventional mm-wave electronic devices, and RF photonic devices may be a practical alternative. In this paper, the mm-wave imaging techniques developed at PNNL are reviewed and the potential for implementing RF photonic mm-wave array designs is explored.

Single-Pole Double-Throw MMIC Switches for a Microwave Radiometer

NASA Technical Reports Server (NTRS)

Montes, Oliver; Dawson, Douglas E.; Kangaslahti, Pekka P.

2012-01-01

In order to reduce the effect of gain and noise instabilities in the RF chain of a microwave radiometer, a Dicke radiometer topology is often used, as in the case of the proposed surface water and ocean topography (SWOT) radiometer instrument. For this topology, a single-pole double-throw (SPDT) microwave switch is needed, which must have low insertion loss at the radiometer channel frequencies to minimize the overall receiver noise figure. Total power radiometers are limited in accuracy due to the continuous variation in gain of the receiver. High-frequency SPDT switches were developed in the form of monolithic microwave integrated circuits (MMICs) using 75 micron indium phosphide (InP) PIN-diode technology. These switches can be easily integrated into Dicke switched radiometers that utilize microstrip technology.

Electrochromic window with high reflectivity modulation

DOEpatents

Goldner, Ronald B.; Gerouki, Alexandra; Liu, Te-Yang; Goldner, Mark A.; Haas, Terry E.

2000-01-01

A multi-layered, active, thin film, solid-state electrochromic device having a high reflectivity in the near infrared in a colored state, a high reflectivity and transmissivity modulation when switching between colored and bleached states, a low absorptivity in the near infrared, and fast switching times, and methods for its manufacture and switching are provided. In one embodiment, a multi-layered device comprising a first indium tin oxide transparent electronic conductor, a transparent ion blocking layer, a tungsten oxide electrochromic anode, a lithium ion conducting-electrically resistive electrolyte, a complimentary lithium mixed metal oxide electrochromic cathode, a transparent ohmic contact layer, a second indium oxide transparent electronic conductor, and a silicon nitride encapsulant is provided. Through elimination of optional intermediate layers, simplified device designs are provided as alternative embodiments. Typical colored-state reflectivity of the multi-layered device is greater than 50% in the near infrared, bleached-state reflectivity is less than 40% in the visible, bleached-state transmissivity is greater than 60% in the near infrared and greater than 40% in the visible, and spectral absorbance is less than 50% in the range from 0.65-2.5 .mu.m.

A Pt/TiO(2)/Ti Schottky-type selection diode for alleviating the sneak current in resistance switching memory arrays.

PubMed

Park, Woo Young; Kim, Gun Hwan; Seok, Jun Yeong; Kim, Kyung Min; Song, Seul Ji; Lee, Min Hwan; Hwang, Cheol Seong

2010-05-14

This study examined the properties of Schottky-type diodes composed of Pt/TiO(2)/Ti, where the Pt/TiO(2) and TiO(2)/Ti junctions correspond to the blocking and ohmic contacts, respectively, as the selection device for a resistive switching cross-bar array. An extremely high forward-to-reverse current ratio of approximately 10(9) was achieved at 1 V when the TiO(2) film thickness was 19 nm. TiO(2) film was grown by atomic layer deposition at a substrate temperature of 250 degrees C. Conductive atomic force microscopy revealed that the forward current flew locally, which limits the maximum forward current density to < 10 A cm(-2) for a large electrode (an area of approximately 60 000 microm(2)). However, the local current measurement showed a local forward current density as high as approximately 10(5) A cm(-2). Therefore, it is expected that this type of Schottky diode effectively suppresses the sneak current without adverse interference effects in a nano-scale resistive switching cross-bar array with high block density.

New shielding configurations for a simultaneous PET/MRI scanner at 7T

PubMed Central

Peng, Bo J.; Wu, Yibao; Cherry, Simon R.; Walton, Jeffrey H.

2014-01-01

Understanding sources of electromagnetic interference are important in designing any electronic system. This is especially true when combining positron emission tomography (PET) and magnetic resonance imaging (MRI) in a multimodality system as coupling between the subsystems can degrade the performance of either modality. For this reason, eliminating radio frequency (RF) interference and gradient-induced eddy currents have been major challenges in building simultaneous hybrid PET/MRI systems. MRI requires negligible RF interference at the Larmor resonance frequency, while RF interference at almost any frequency may corrupt PET data. Moreover, any scheme that minimizes these interactions would, ideally, not compromise the performance of either subsystem. This paper lays out a plan to resolve these problems. A carbon fiber composite material is found to be a good RF shield at the Larmor frequency (300 MHz in this work) while introducing negligible gradient eddy currents. This carbon fiber composite also provides excellent structural support for the PET detector components. Low frequency electromagnetic radiation (81 kHz here) from the switching power supplies of the gradient amplifiers was also found to interfere with the PET detector. Placing the PET detector module between two carbon fiber tubes and grounding the inner carbon fiber tube to the PET detector module ground reduced this interference. Further reductions were achieved by adding thin copper (Cu) foil on the outer carbon fiber case and electrically grounding the PET detector module so that all 3 components had a common ground, i.e. with the PET detector in an electrostatic cage. Finally, gradient switching typical in MRI sequences can result in count losses in the particular PET detector design studied. Moreover, the magnitude of this effect depends on the location of the detector within the magnet bore and which MRI gradient is being switched. These findings have a bearing on future designs of PET/MRI systems. PMID:24380812

Silicon Carbide Mixers Demonstrated to Improve the Interference Immunity of Radio-Based Aircraft Avionics

NASA Technical Reports Server (NTRS)

Neudeck, Philip G.

1998-01-01

Concern over the interference of stray radiofrequency (RF) emissions with key aircraft avionics is evident during takeoff and landing of every commercial flight when the flight attendant requests that all portable electronics be switched off. The operation of key radio-based avionics (such as glide-slope and localizer approach instruments) depends on the ability of front-end RF receivers to detect and amplify desired information signals while rejecting interference from undesired RF sources both inside and outside the aircraft. Incidents where key navigation and approach avionics malfunction because of RF interference clearly represent an increasing threat to flight safety as the radio spectrum becomes more crowded. In an initial feasibility experiment, the U.S. Army Research Laboratory and the NASA Lewis Research Center recently demonstrated the strategic use of silicon carbide (SiC) semiconductor components to significantly reduce the susceptibility of an RF receiver circuit to undesired RF interference. A pair of silicon carbide mixer diodes successfully reduced RF interference (intermodulation distortion) in a prototype receiver circuit by a factor of 10 (20 dB) in comparison to a pair of commercial silicon-based mixer diodes.

On-board processing concepts for future satellite communications systems

NASA Technical Reports Server (NTRS)

Brandon, W. T. (Editor); White, B. E. (Editor)

1980-01-01

The initial definition of on-board processing for an advanced satellite communications system to service domestic markets in the 1990's is discussed. An exemplar system with both RF on-board switching and demodulation/remodulation baseband processing is used to identify important issues related to system implementation, cost, and technology development. Analyses of spectrum-efficient modulation, coding, and system control techniques are summarized. Implementations for an RF switch and baseband processor are described. Among the major conclusions listed is the need for high gain satellites capable of handling tens of simultaneous beams for the efficient reuse of the 2.5 GHz 30/20 frequency band. Several scanning beams are recommended in addition to the fixed beams. Low power solid state 20 GHz GaAs FET power amplifiers in the 5W range and a general purpose digital baseband processor with gigahertz logic speeds and megabits of memory are also recommended.

Modeling and simulation of enhancement mode p-GaN Gate AlGaN/GaN HEMT for RF circuit switch applications

NASA Astrophysics Data System (ADS)

Panda, D. K.; Lenka, T. R.

2017-06-01

An enhancement mode p-GaN gate AlGaN/GaN HEMT is proposed and a physics based virtual source charge model with Landauer approach for electron transport has been developed using Verilog-A and simulated using Cadence Spectre, in order to predict device characteristics such as threshold voltage, drain current and gate capacitance. The drain current model incorporates important physical effects such as velocity saturation, short channel effects like DIBL (drain induced barrier lowering), channel length modulation (CLM), and mobility degradation due to self-heating. The predicted I d-V ds, I d-V gs, and C-V characteristics show an excellent agreement with the experimental data for both drain current and capacitance which validate the model. The developed model was then utilized to design and simulate a single-pole single-throw (SPST) RF switch.

The Impact of Dielectric Material and Temperature on Dielectric Charging in RF MEMS Capacitive Switches

NASA Astrophysics Data System (ADS)

Papaioannou, George

The present work attempts to provide a better insight on the dielectric charging in RF-MEMS capacitive switches that constitutes a key issue limiting parameter of their commercialization. The dependence of the charging process on the nature of dielectric materials widely used in these devices, such as SiO2, Si3N4, AlN, Al2O3, Ta2O5, HfO2, which consist of covalent or ionic bonds and may exhibit piezoelectric properties is discussed taking into account the effect of deposition conditions and resulting material stoichiometry. Another key issue parameter that accelerates the charging and discharging processes by providing enough energy to trapped charges to be released and to dipoles to overcome potential barriers and randomize their orientation is the temperature will be investigated too. Finally, the effect of device structure will be also taken into account.

Signal Processing for Wireless Communication MIMO System with Nano- Scaled CSDG MOSFET based DP4T RF Switch.

PubMed

Srivastava, Viranjay M

2015-01-01

In the present technological expansion, the radio frequency integrated circuits in the wireless communication technologies became useful because of the replacement of increasing number of functions, traditional hardware components by modern digital signal processing. The carrier frequencies used for communication systems, now a day, shifted toward the microwave regime. The signal processing for the multiple inputs multiple output wireless communication system using the Metal- Oxide-Semiconductor Field-Effect-Transistor (MOSFET) has been done a lot. In this research the signal processing with help of nano-scaled Cylindrical Surrounding Double Gate (CSDG) MOSFET by means of Double- Pole Four-Throw Radio-Frequency (DP4T RF) switch, in terms of Insertion loss, Isolation, Reverse isolation and Inter modulation have been analyzed. In addition to this a channel model has been presented. Here, we also discussed some patents relevant to the topic.

Endurance and Cycle-to-cycle Uniformity Improvement in Tri-Layered CeO2/Ti/CeO2 Resistive Switching Devices by Changing Top Electrode Material

PubMed Central

Rana, Anwar Manzoor; Akbar, Tahira; Ismail, Muhammad; Ahmad, Ejaz; Hussain, Fayyaz; Talib, Ijaz; Imran, Muhammad; Mehmood, Khalid; Iqbal, Khalid; Nadeem, M. Younus

2017-01-01

Resistance switching characteristics of CeO2/Ti/CeO2 tri-layered films sandwiched between Pt bottom electrode and two different top electrodes (Ti and TaN) with different work functions have been investigated. RRAM memory cells composed of TaN/CeO2/Ti/CeO2/Pt reveal better resistive switching performance instead of Ti/CeO2/Ti/CeO2/Pt memory stacks. As compared to the Ti/CeO2 interface, much better ability of TaN/CeO2 interface to store and exchange plays a key role in the RS performance improvement, including lower forming/SET voltages, large memory window (~102) and no significant data degradation during endurance test of >104 switching cycles. The formation of TaON thinner interfacial layer between TaN TE and CeO2 film is found to be accountable for improved resistance switching behavior. Partial charge density of states is analyzed using density functional theory. It is found that the conductive filaments formed in CeO2 based devices is assisted by interstitial Ti dopant. Better stability and reproducibility in cycle-to-cycle (C2C) resistance distribution and Vset/Vreset uniformity were achieved due to the modulation of current conduction mechanism from Ohmic in low field region to Schottky emission in high field region. PMID:28079056

Nonpolar resistive memory switching with all four possible resistive switching modes in amorphous LaHoO{sub 3} thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Yogesh; Pavunny, Shojan P.; Katiyar, Ram S., E-mail: rkatiyar@hpcf.upr.edu

2015-09-07

We studied the resistive memory switching in pulsed laser deposited amorphous LaHoO{sub 3} (a-LHO) thin films for non-volatile resistive random access memory applications. Nonpolar resistive switching (RS) was achieved in Pt/a-LHO/Pt memory cells with all four possible RS modes (i.e., positive unipolar, positive bipolar, negative unipolar, and negative bipolar) having high R{sub ON}/R{sub OFF} ratios (in the range of ∼10{sup 4}–10{sup 5}) and non-overlapping switching voltages (set voltage, V{sub ON} ∼ ±3.6–4.2 V and reset voltage, V{sub OFF} ∼ ±1.3–1.6 V) with a small variation of about ±5–8%. Temperature dependent current-voltage (I–V) characteristics indicated the metallic conduction in low resistance states (LRS). We believe that themore » formation (set) and rupture (reset) of mixed conducting filaments formed out of oxygen vacancies and metallic Ho atoms could be responsible for the change in the resistance states of the memory cell. Detailed analysis of I–V characteristics further corroborated the formation of conductive nanofilaments based on metal-like (Ohmic) conduction in LRS. Simmons-Schottky emission was found to be the dominant charge transport mechanism in the high resistance state.« less

Crystal structure of release factor RF3 trapped in the GTP state on a rotated conformation of the ribosome

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Jie; Lancaster, Laura; Trakhanov, Sergei

2012-03-26

The class II release factor RF3 is a GTPase related to elongation factor EF-G, which catalyzes release of class I release factors RF1 and RF2 from the ribosome after termination of protein synthesis. The 3.3 {angstrom} crystal structure of the RF3 {center_dot} GDPNP {center_dot} ribosome complex provides a high-resolution description of interactions and structural rearrangements that occur when binding of this translational GTPase induces large-scale rotational movements in the ribosome. RF3 induces a 7{sup o} rotation of the body and 14{sup o} rotation of the head of the 30S ribosomal subunit, and itself undergoes inter- and intradomain conformational rearrangements. Wemore » suggest that ordering of critical elements of switch loop I and the P loop, which help to form the GTPase catalytic site, are caused by interactions between the G domain of RF3 and the sarcin-ricin loop of 23S rRNA. The rotational movements in the ribosome induced by RF3, and its distinctly different binding orientation to the sarcin-ricin loop of 23S rRNA, raise interesting implications for the mechanism of action of EF-G in translocation.« less

Switching bipolar hepatic radiofrequency ablation using internally cooled wet electrodes: comparison with consecutive monopolar and switching monopolar modes

PubMed Central

Yoon, J H; Woo, S; Hwang, E J; Hwang, I; Choi, W; Han, J K; Choi, B I

2015-01-01

Objective: To evaluate whether switching bipolar radiofrequency ablation (SB-RFA) using three internally cooled wet (ICW) electrodes can induce coagulations >5 cm in porcine livers with better efficiency than consecutive monopolar (CM) or switching monopolar (SM) modes. Methods: A total of 60 coagulations were made in 15 in vivo porcine livers using three 17-gauge ICW electrodes and a multichannel radiofrequency (RF) generator. RF energy (approximately 200 W) was applied in CM mode (Group A, n = 20) for 24 min, SM mode for 12 min (Group B, n = 20) or switching bipolar (SB) mode for 12 min (Group C, n = 20) in in vivo porcine livers. Thereafter, the delivered RFA energy, as well as the shape and dimension of coagulations were compared among the groups. Results: Spherical- or oval-shaped ablations were created in 30% (6/20), 85% (17/20) and 90% (18/20) of coagulations in the CM, SM and SB groups, respectively (p = 0.003). SB-RFA created ablations >5 cm in minimum diameter (Dmin) in 65% (13/20) of porcine livers, whereas SM- or CM-RFA created ablations >5 cm in only 25% (5/20) and 20% (4/20) of porcine livers, respectively (p = 0.03). The mean Dmin of coagulations was significantly larger in Group C than in Groups A and B (5.1 ± 0.9, 3.9 ± 1.2 and 4.4 ± 1.0 cm, respectively, p = 0.002) at a lower delivered RF energy level (76.8 ± 14.3, 120.9 ± 24.5 and 114.2 ± 18.3 kJ, respectively, p < 0.001). Conclusion: SB-RFA using three ICW electrodes can create coagulations >5 cm in diameter with better efficiency than do SM- or CM-RFA. Advances in knowledge: SB-RFA can create large, regular ablation zones with better time–energy efficiency than do CM- or SM-RFA. PMID:25873479

Bistable resistive memory behavior in gelatin-CdTe quantum dot composite film

NASA Astrophysics Data System (ADS)

Vallabhapurapu, Sreedevi; Rohom, Ashwini; Chaure, N. B.; Du, Shengzhi; Srinivasan, Ananthakrishnan

2018-05-01

Bistable memory behavior has been observed for the first time in gelatin type A thin film dispersed with functionalized CdTe quantum dots. The two terminal device with the polymer nanocomposite layer sandwiched between an indium tin oxide coated glass plate and an aluminium top electrode performs as a bistable resistive random access memory module. Butterfly shaped (O-shaped with a hysteresis in forward and reverse sweeps) current-voltage response is observed in this device. The conduction mechanism leading to the bistable electrical switching has been deduced to be a combination of ohmic and electron hopping.

A fast multipole method combined with a reaction field for long-range electrostatics in molecular dynamics simulations: The effects of truncation on the properties of water

NASA Astrophysics Data System (ADS)

Mathias, Gerald; Egwolf, Bernhard; Nonella, Marco; Tavan, Paul

2003-06-01

We present a combination of the structure adapted multipole method with a reaction field (RF) correction for the efficient evaluation of electrostatic interactions in molecular dynamics simulations under periodic boundary conditions. The algorithm switches from an explicit electrostatics evaluation to a continuum description at the maximal distance that is consistent with the minimum image convention, and, thus, avoids the use of a periodic electrostatic potential. A physically motivated switching function enables charge clusters interacting with a given charge to smoothly move into the solvent continuum by passing through the spherical dielectric boundary surrounding this charge. This transition is complete as soon as the cluster has reached the so-called truncation radius Rc. The algorithm is used to examine the dependence of thermodynamic properties and correlation functions on Rc in the three point transferable intermolecular potential water model. Our test simulations on pure liquid water used either the RF correction or a straight cutoff and values of Rc ranging from 14 Å to 40 Å. In the RF setting, the thermodynamic properties and the correlation functions show convergence for Rc increasing towards 40 Å. In the straight cutoff case no such convergence is found. Here, in particular, the dipole-dipole correlation functions become completely artificial. The RF description of the long-range electrostatics is verified by comparison with the results of a particle-mesh Ewald simulation at identical conditions.

Investigation into Contact Resistance And Damage of Metal Contacts Used in RF-MEMS Switches

DTIC Science & Technology

2009-09-01

mechanically cycled by a piezo- electric transducer ( PZT ). The resistance through the simulated switch was measured using a four-wire measurement technique...research, including a brief overview of contact theory. Then chapter 3 gives an overview of engi- 13 V I PZT Sample Mount Cantilever Lower Contact...as described in [3, 118]. The measurement of surface texture and 4These figures were published in Materials Selection in Mechanical Design, Michael F

SITE project. Phase 1: Continuous data bit-error-rate testing

NASA Technical Reports Server (NTRS)

Fujikawa, Gene; Kerczewski, Robert J.

1992-01-01

The Systems Integration, Test, and Evaluation (SITE) Project at NASA LeRC encompasses a number of research and technology areas of satellite communications systems. Phase 1 of this project established a complete satellite link simulator system. The evaluation of proof-of-concept microwave devices, radiofrequency (RF) and bit-error-rate (BER) testing of hardware, testing of remote airlinks, and other tests were performed as part of this first testing phase. This final report covers the test results produced in phase 1 of the SITE Project. The data presented include 20-GHz high-power-amplifier testing, 30-GHz low-noise-receiver testing, amplitude equalization, transponder baseline testing, switch matrix tests, and continuous-wave and modulated interference tests. The report also presents the methods used to measure the RF and BER performance of the complete system. Correlations of the RF and BER data are summarized to note the effects of the RF responses on the BER.

MR-compatibility assessment of MADPET4: a study of interferences between an SiPM-based PET insert and a 7 T MRI system

NASA Astrophysics Data System (ADS)

Omidvari, Negar; Topping, Geoffrey; Cabello, Jorge; Paul, Stephan; Schwaiger, Markus; Ziegler, Sibylle I.

2018-05-01

Compromises in the design of a positron emission tomography (PET) insert for a magnetic resonance imaging (MRI) system should minimize the deterioration of image quality in both modalities, particularly when simultaneous demanding acquisitions are performed. In this work, the advantages of using individually read-out crystals with high-gain silicon photomultipliers (SiPMs) were studied with a small animal PET insert for a 7 T MRI system, in which the SiPM charge was transferred to outside the MRI scanner using coaxial cables. The interferences between the two systems were studied with three radio-frequency (RF) coil configurations. The effects of PET on the static magnetic field, flip angle distribution, RF noise, and image quality of various MRI sequences (gradient echo, spin echo, and echo planar imaging (EPI) at 1H frequency, and chemical shift imaging at 13C frequency) were investigated. The effects of fast-switching gradient fields and RF pulses on PET count rate were studied, while the PET insert and the readout electronics were not shielded. Operating the insert inside a 1H volume coil, used for RF transmission and reception, limited the MRI to T1-weighted imaging, due to coil detuning and RF attenuation, and resulted in significant PET count loss. Using a surface receive coil allowed all tested MR sequences to be used with the insert, with 45–59% signal-to-noise ratio (SNR) degradation, compared to without PET. With a 1H/13C volume coil inside the insert and shielded by a copper tube, the SNR degradation was limited to 23–30% with all tested sequences. The insert did not introduce any discernible distortions into images of two tested EPI sequences. Use of truncated sinc shaped RF excitation pulses and gradient field switching had negligible effects on PET count rate. However, PET count rate was substantially affected by high-power RF block pulses and temperature variations due to high gradient duty cycles.

Comparisons of switching characteristics between Ti/Al2O3/Pt and TiN/Al2O3/Pt RRAM devices with various compliance currents

NASA Astrophysics Data System (ADS)

Qi, Yanfei; Zhao, Ce Zhou; Liu, Chenguang; Fang, Yuxiao; He, Jiahuan; Luo, Tian; Yang, Li; Zhao, Chun

2018-04-01

In this study, the influence of the Ti and TiN top electrodes on the switching behaviors of the Al2O3/Pt resistive random access memory devices with various compliance currents (CCs, 1-15 mA) has been compared. Based on the similar statistical results of the resistive switching (RS) parameters such as V set/V reset, R HRS/R LRS (measured at 0.10 V) and resistance ratio with various CCs for both devices, the Ti/Al2O3/Pt device differs from the TiN/Al2O3/Pt device mainly in the forming process rather than in the following switching cycles. Apart from the initial isolated state, the Ti/Al2O3/Pt device has the initial intermediate state as well. In addition, its forming voltage is relatively lower. The conduction mechanisms of the ON and OFF state for both devices are demonstrated as ohmic conduction and Frenkel-Poole emission, respectively. Therefore, with the combined modulations of the CCs and the stop voltages, the TiN/Al2O3/Pt device is more stable for nonvolatile memory applications to further improve the RS performance.

Nano- and micro-electromechanical switch dynamics

NASA Astrophysics Data System (ADS)

Pulskamp, Jeffrey S.; Proie, Robert M.; Polcawich, Ronald G.

2013-01-01

This paper reports theoretical analysis and experimental results on the dynamics of piezoelectric MEMS mechanical logic relays. The multiple degree of freedom analytical model, based on modal decomposition, utilizes modal parameters obtained from finite element analysis and an analytical model of piezoelectric actuation. The model accounts for exact device geometry, damping, drive waveform variables, and high electric field piezoelectric nonlinearity. The piezoelectrically excited modal force is calculated directly and provides insight into design optimization for switching speed. The model accurately predicts the propagation delay dependence on actuation voltage of mechanically distinct relay designs. The model explains the observed discrepancies in switching speed of these devices relative to single degree of freedom switching speed models and suggests the strong potential for improved switching speed performance in relays designed for mechanical logic and RF circuits through the exploitation of higher order vibrational modes.

Storage of RF photons in minimal conditions

NASA Astrophysics Data System (ADS)

Cromières, J.-P.; Chanelière, T.

2018-02-01

We investigate the minimal conditions to store coherently a RF pulse in a material medium. We choose a commercial quartz as a memory support because it is a widely available component with a high Q-factor. Pulse storage is obtained by varying dynamically the light-matter coupling with an analog switch. This parametric driving of the quartz dynamics can be alternatively interpreted as a stopped-light experiment. We obtain an efficiency of 26%, a storage time of 209 μs and a time-to-bandwidth product of 98 by optimizing the pulse temporal shape. The coherent character of the storage is demonstrated. Our goal is to connect different types of memories in the RF and optical domain for quantum information processing. Our motivation is essentially fundamental.

Optical plasma monitoring of Y-Ba-Cu-O rf sputter target transients

NASA Astrophysics Data System (ADS)

Klein, J. D.; Yen, A.

1989-12-01

The plasma emission spectra resulting from rf sputtering Y-Ba-Cu-O targets were observed as a function of sputter time. Although most lines of the observed spectra are not attributable to target species, peaks associated with each of the cation elements were resolved. The Ba and Cu peaks can be used as tracking indicators of process conditions. For example, switching from an O2/Ar sputter atmosphere to pure Ar enhanced the Ba peak much more than that associated with Cu. The emission spectra from a newly fabricated target exhibited a slow first-order transient response in seeking equilibrium with the rf plasma. The transient response of a previously sputtered target is also first order but has a much shorter time constant.

A flexible telecom satellite repeater based on microwave photonic technologies

NASA Astrophysics Data System (ADS)

Sotom, Michel; Benazet, Benoît; Maignan, Michel

2017-11-01

Future telecom satellite based on geo-stationary Earth orbit (GEO) will require advanced payloads in Kaband so as to receive, route and re-transmit hundreds of microwave channels over multiple antenna beams. We report on the proof-of-concept demonstration of a analogue repeater making use of microwave photonic technologies for supporting broadband, transparent, and flexible cross-connectivity. It has microwave input and output sections, and features a photonic core for LO distribution, frequency down-conversion, and cross-connection of RF channels. With benefits such as transparency to RF frequency, infinite RF isolation, mass and volume savings, such a microwave photonic cross-connect would compare favourably with microwave implementations, and based on optical MEMS switches could grow up to large port counts.

Design of 1 MHz Solid State High Frequency Power Supply

NASA Astrophysics Data System (ADS)

Parmar, Darshan; Singh, N. P.; Gajjar, Sandip; Thakar, Aruna; Patel, Amit; Raval, Bhavin; Dhola, Hitesh; Dave, Rasesh; Upadhay, Dishang; Gupta, Vikrant; Goswami, Niranjan; Mehta, Kush; Baruah, Ujjwal

2017-04-01

High Frequency Power supply (HFPS) is used for various applications like AM Transmitters, metallurgical applications, Wireless Power Transfer, RF Ion Sources etc. The Ion Source for a Neutral beam Injector at ITER-India uses inductively coupled power source at High Frequency (∼1 MHz). Switching converter based topology used to generate 1 MHz sinusoidal output is expected to have advantages on efficiency and reliability as compared to traditional RF Tetrode tubes based oscillators. In terms of Power Electronics, thermal and power coupling issues are major challenges at such a high frequency. A conceptual design for a 200 kW, 1 MHz power supply and a prototype design for a 600 W source been done. The prototype design is attempted with Class-E amplifier topology where a MOSFET is switched resonantly. The prototype uses two low power modules and a ferrite combiner to add the voltage and power at the output. Subsequently solution with Class-D H-Bridge configuration have been evaluated through simulation where module design is stable as switching device do not participate in resonance, further switching device voltage rating is substantially reduced. The rating of the modules is essentially driven by the maximum power handling capacity of the MOSFETs and ferrites in the combiner circuit. The output passive network including resonance tuned network and impedance matching network caters for soft switching and matches the load impedance to 50ohm respectively. This paper describes the conceptual design of a 200 kW high frequency power supply and experimental results of the prototype 600 W, 1 MHz source.

Strategies for dynamic soft-landing in capacitive microelectromechanical switches

NASA Astrophysics Data System (ADS)

Jain, Ankit; Nair, Pradeep R.; Alam, Muhammad A.

2011-06-01

Electromechanical dielectric degradation associated with the hard landing of movable electrode is a technology-inhibiting reliability concern for capacitive RF-MEMS switches. In this letter, we propose two schemes for dynamic soft-landing that obviate the need for external feedback circuitry. Instead, the proposed resistive and capacitive braking schemes can reduce impact velocity significantly without compromising other performance characteristics like pull-in voltage and pull-in time. Resistive braking is achieved by inserting a resistance in series with the voltage source whereas capacitive braking requires patterning of the electrode or the dielectric. Our results have important implications to the design and optimization of reliability aware electrostatically actuated MEMS switches.

Reconfigurable Patch-Slot Reflectarray Elements using RF MEMS Switches: A Subreflector Wavefront Controller

NASA Technical Reports Server (NTRS)

Rajagopalan, Harish; Rahmat-Samii, Yahya; Imbriale, William A.

2007-01-01

The purpose of this paper is to investigate potential reflectarray elements by taking into consideration the eventual implementation of MEMS technology for this particular application and detailed characterization of one of the potential element designs.

Optoelectronic Infrastructure for Radio Frequency and Optical Phased Arrays

NASA Technical Reports Server (NTRS)

Cai, Jianhong

2015-01-01

Optoelectronic integrated circuits offer radiation-hardened solutions for satellite systems in addition to improved size, weight, power, and bandwidth characteristics. ODIS, Inc., has developed optoelectronic integrated circuit technology for sensing and data transfer in phased arrays. The technology applies integrated components (lasers, amplifiers, modulators, detectors, and optical waveguide switches) to a radio frequency (RF) array with true time delay for beamsteering. Optical beamsteering is achieved by controlling the current in a two-dimensional (2D) array. In this project, ODIS integrated key components to produce common RF-optical aperture operation.

The microlasertron: An efficient switched-power source of mm wavelength radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palmer, R.B.

1986-12-01

An extension of W. Willis' ''Switched Power Linac'' is studied. Pulsed laser light falls on a photocathode wire, or wires, within a simple resonant structure. The resulting pulsed electron current between the wire and the structure wall drives the resonant field, and rf energy is extracted in the mm to cm wavelength range. Various geometries are presented, including one consisting of a simple array of parallel wires over a plane conductor. Results from a one-dimensional simulation are presented.

BPSK optical mm-wave signal generation by septupling frequency via a single optical phase modulator

NASA Astrophysics Data System (ADS)

Wu, Peng; Ma, Jianxin

2016-09-01

In this paper, we have proposed a novel and simple scheme to generate the BPSK optical millimeter wave (MMW) signal with frequency septupling by using an optical phase modulator (PM) and a wavelength selective switch (WSS). In this scheme, the PM is driven by a radio frequency (RF) BPSK signal at the optimized modulation index of 4.89 to assure the 4th and 3rd-order sidebands have equal amplitudes. An wavelength selective switch (WSS) is used to abstract the -4th and +3rd-order sidebands from the spectrum generated by RF BPSK signal modulating the lightwave to form the BPSK optical MMW signal with frequency septupling the driving RF signal. In these two tones, only the +3rd-order sideband bears the BPSK signal while the -4th-order sideband is unmodulated since the phase information is canceled by the even times multiplication of the phase of BPSK signal. The MMW signal can avoid the pulse walk-off effect and the amplitude fading effect caused by the fiber chromatic dispersion. By adjusting the modulation index to assure the two tones have equal amplitude, the generated optical MMW signal has the maximal opto-electrical conversion efficiency and good transmission performance.

High Efficiency Microwave Power Amplifier: From the Lab to Industry

NASA Technical Reports Server (NTRS)

Sims, William Herbert, III; Bell, Joseph L. (Technical Monitor)

2001-01-01

Since the beginnings of space travel, various microwave power amplifier designs have been employed. These included Class-A, -B, and -C bias arrangements. However, shared limitation of these topologies is the inherent high total consumption of input power associated with the generation of radio frequency (RF)/microwave power. The power amplifier has always been the largest drain for the limited available power on the spacecraft. Typically, the conversion efficiency of a microwave power amplifier is 10 to 20%. For a typical microwave power amplifier of 20 watts, input DC power of at least 100 watts is required. Such a large demand for input power suggests that a better method of RF/microwave power generation is required. The price paid for using a linear amplifier where high linearity is unnecessary includes higher initial and operating costs, lower DC-to-RF conversion efficiency, high power consumption, higher power dissipation and the accompanying need for higher capacity heat removal means, and an amplifier that is more prone to parasitic oscillation. The first use of a higher efficiency mode of power generation was described by Baxandall in 1959. This higher efficiency mode, Class-D, is achieved through distinct switching techniques to reduce the power losses associated with switching, conduction, and gate drive losses of a given transistor.

Charging and breakdown in amorphous dielectrics: Phenomenological modeling approach and applications

NASA Astrophysics Data System (ADS)

Palit, Sambit

Amorphous dielectrics of different thicknesses (nm to mm) are used in various applications. Low temperature processing/deposition of amorphous thin-film dielectrics often result in defect-states or electronic traps. These traps are responsible for increased leakage currents and bulk charge trapping in many associated applications. Additional defects may be generated during regular usage, leading to electrical breakdown. Increased leakage currents, charge trapping and defect generation/breakdown are important and pervasive reliability concerns in amorphous dielectrics. We first explore the issue of charge accumulation and leakage in amorphous dielectrics. Historically, charge transport in amorphous dielectrics has been presumed, depending on the dielectric thickness, to be either bulk dominated (Frenkel-Poole (FP) emission) or contact dominated (Fowler-Nordheim tunneling). We develop a comprehensive dielectric charging modeling framework which solves for the transient and steady state charge accumulation and leakage currents in an amorphous dielectric, and show that for intermediate thickness dielectrics, the conventional assumption of FP dominated current transport is incorrect, and may lead to false extraction of dielectric parameters. We propose an improved dielectric characterization methodology based on an analytical approximation of our model. Coupled with ab-initio computed defect levels, the dielectric charging model explains measured leakage currents more accurately with lesser empiricism. We study RF-MEMS capacitive switches as one of the target applications of intermediate thickness amorphous dielectrics. To achieve faster analysis and design of RF-MEMS switches in particular, and electro-mechanical actuators in general, we propose a set of fundamental scaling relationships which are independent of specific physical dimensions and material properties; the scaling relationships provide an intrinsic classification of all electro-mechanical actuators. However, RF-MEMS capacitive switches are plagued by the reliability issue of temporal shifts of actuation voltages due to dielectric charge accumulation, often resulting in failure due to membrane stiction. Using the dielectric charging model, we show that in spite of unpredictable roughness of deposited dielectrics, there are predictable shifts in actuation voltages due to dielectric charging in RF-MEMS switches. We also propose a novel non-obtrusive, non-contact, fully electronic resonance based technique to characterize charging driven actuation shifts in RF-MEMS switches which overcomes limitations in conventionally used methods. Finally, we look into the issue of defect generation and breakdown in thick polymer dielectrics. Polymer materials often face premature electrical breakdown due to high electric fields and frequencies, and exposure to ambient humidity conditions. Using a field-driven correlated defect generation model, coupled with a model for temperature rise due to dielectric heating at AC stresses, we explain measured trends in time-to-breakdown and breakdown electric fields in polymer materials. Using dielectric heating we are able to explain the observed lifetime and dielectric strength reduction with increasing dielectric thicknesses. Performing lifetime measurements after exposure to controlled humidity conditions, we find that moisture ingress into a polymer material reduces activation barriers for chain breakage and increases dielectric heating. Overall, this thesis develops a comprehensive framework of dielectric charging, leakage and degradation of insulators of different thicknesses that have broad applications in multiple technologies.

Development of Phase Change Materials for RF Switch Applications

NASA Astrophysics Data System (ADS)

King, Matthew Russell

For decades chalcogenide-based phase change materials (PCMs) have been reliably implemented in optical storage and digital memory platforms. Owing to the substantial differences in optical and electronic properties between crystalline and amorphous states, device architectures requiring a "1" and "0" or "ON" and "OFF" states are attainable with PCMs if a method for amorphizing and crystallizing the PCM is demonstrated. Taking advantage of more than just the binary nature of PCM electronic properties, recent reports have shown that the near-metallic resistivity of some PCMs allow one to manufacture high performance RF switches and related circuit technologies. One of the more promising RF switch technologies is the Inline Phase Change Switch (IPCS) which utilizes GeTe as the active material. Initial reports show that an electrically isolated, thermally coupled thin film heater can successfully convert GeTe between crystalline and amorphous states, and with proper design an RF figure of merit cutoff frequency (FCO) of 12.5 THz can be achieved. In order to realize such world class performance a significant development effort was undertaken to understand the relationship between fundamental GeTe properties, thin film deposition method and resultant device properties. Deposition pressure was found to be the most important deposition process parameter, as it was found to control Ge:Te ratio, oxygen content, Ar content, film density and surface roughness. Ultimately a first generation deposition process produced GeTe films with a crystalline resistivity of 3 ohm-mum. Upon implementing these films into IPCS devices, post-cycling morphological analysis was undertaken using STEM and related analyses. It was revealed that massive structural changes occur in the GeTe during switching, most notably the formation of an assembly of voids along the device centerline and large GeTe grains on either side of the so-called active region. Restructuring of this variety was tied to changes in ON-state resistance with increasing pulse number, where initially porous and granular GeTe was converted to large crystalline domains comprising the majority of the RF gap. A phenomenological model for this morphology was presented in which the OFF pulse melts a given width of GeTe and upon cooling the crystalline template outside the melt region acts as a template for an inward-propagating crystalline growth front. This model was further extended to explain observed morphology for ON pulses. The voids observed along the device centerline were connected to increasing OFF state resistance and a relatively stable ON state with increasing pulse number via a series resistance model. As a result of this analysis, OFF state resistance was suggested as an early indicator of device reliability. Finally, microstructural and electrical property observations were used as a basis for implementing improvements to the GeTe deposition process in the form of a heated substrate platform. It was shown that this provides a viable method for attaining stable as-deposited GeTe morphology and a substantially improved crystalline resistivity (2 ohm-mum). This body of work ultimately provides a blueprint which connects fundamental GeTe properties with deposition processes and device performance.

RF Communication Subsystem Integration Research

DTIC Science & Technology

2010-10-15

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On-board demux/demod

NASA Technical Reports Server (NTRS)

Sayegh, S.; Kappes, M.; Thomas, J.; Snyder, J.; Eng, M.; Poklemba, John J.; Steber, M.; House, G.

1991-01-01

To make satellite channels cost competitive with optical cables, the use of small, inexpensive earth stations with reduced antenna size and high powered amplifier (HPA) power will be needed. This will necessitate the use of high e.i.r.p. and gain-to-noise temperature ratio (G/T) multibeam satellites. For a multibeam satellite, onboard switching is required in order to maintain the needed connectivity between beams. This switching function can be realized by either an receive frequency (RF) or a baseband unit. The baseband switching approach has the additional advantage of decoupling the up-link and down-link, thus enabling rate and format conversion as well as improving the link performance. A baseband switching satellite requires the demultiplexing and demodulation of the up-link carriers before they can be switched to their assigned down-link beams. Principles of operation, design and implementation issues of such an onboard demultiplexer/demodulator (bulk demodulator) that was recently built at COMSAT Labs. are discussed.

Carbon nanotube switches for memory, RF communications and sensing applications, and methods of making the same

NASA Technical Reports Server (NTRS)

Kaul, Anupama B. (Inventor); Wong, Eric W. (Inventor); Baron, Richard L. (Inventor); Epp, Larry (Inventor)

2008-01-01

Switches having an in situ grown carbon nanotube as an element thereof, and methods of fabricating such switches. A carbon nanotube is grown in situ in mechanical connection with a conductive substrate, such as a heavily doped silicon wafer or an SOI wafer. The carbon nanotube is electrically connected at one location to a terminal. At another location of the carbon nanotube there is situated a pull electrode that can be used to elecrostatically displace the carbon nanotube so that it selectively makes contact with either the pull electrode or with a contact electrode. Connection to the pull electrode is sufficient to operate the device as a simple switch, while connection to a contact electrode is useful to operate the device in a manner analogous to a relay. In various embodiments, the devices disclosed are useful as at least switches for various signals, multi-state memory, computational devices, and multiplexers.

Considerations for an Earth Relay Satellite with RF and Optical Trunklines

NASA Technical Reports Server (NTRS)

Israel, David J.

2016-01-01

Support for user platforms through the use of optical links to geosynchronous relay spacecraft are expected to be part of the future space communications architecture. The European Data Relay Satellite System (EDRS) has its first node, EDRS-A, in orbit. The EDRS architecture includes space-to-space optical links with a Ka-Band feeder link or trunkline. NASA's Laser Communications Relay Demonstration (LCRD) mission, originally baselined to support a space-to-space optical link relayed with an optical trunkline, has added an Radio Frequency (RF) trunkline. The use of an RF trunkline avoids the outages suffered by an optical trunkline due to clouds, but an RF trunkline will be bandwidth limited. A space relay architecture with both RF and optical trunklines could relay critical realtime data, while also providing a high data volume capacity. This paper considers the relay user scenarios that could be supported, and the implications to the space relay system and operations. System trades such as the amount of onboard processing and storage required, the use of link layer switching vs. network layer routing, and the use of Delay/Disruption Tolerant Networking (DTN) are discussed.

Using the nonlinear control of anaesthesia-induced hypersensitivity of EEG at burst suppression level to test the effects of radiofrequency radiation on brain function

PubMed Central

Lipping, Tarmo; Rorarius, Michael; Jäntti, Ville; Annala, Kari; Mennander, Ari; Ferenets, Rain; Toivonen, Tommi; Toivo, Tim; Värri, Alpo; Korpinen, Leena

2009-01-01

Background In this study, investigating the effects of mobile phone radiation on test animals, eleven pigs were anaesthetised to the level where burst-suppression pattern appears in the electroencephalogram (EEG). At this level of anaesthesia both human subjects and animals show high sensitivity to external stimuli which produce EEG bursts during suppression. The burst-suppression phenomenon represents a nonlinear control system, where low-amplitude EEG abruptly switches to very high amplitude bursts. This switching can be triggered by very minor stimuli and the phenomenon has been described as hypersensitivity. To test if also radio frequency (RF) stimulation can trigger this nonlinear control, the animals were exposed to pulse modulated signal of a GSM mobile phone at 890 MHz. In the first phase of the experiment electromagnetic field (EMF) stimulation was randomly switched on and off and the relation between EEG bursts and EMF stimulation onsets and endpoints were studied. In the second phase a continuous RF stimulation at 31 W/kg was applied for 10 minutes. The ECG, the EEG, and the subcutaneous temperature were recorded. Results No correlation between the exposure and the EEG burst occurrences was observed in phase I measurements. No significant changes were observed in the EEG activity of the pigs during phase II measurements although several EEG signal analysis methods were applied. The temperature measured subcutaneously from the pigs' head increased by 1.6°C and the heart rate by 14.2 bpm on the average during the 10 min exposure periods. Conclusion The hypothesis that RF radiation would produce sensory stimulation of somatosensory, auditory or visual system or directly affect the brain so as to produce EEG bursts during suppression was not confirmed. PMID:19615084

Effect of ultrahigh-temperature continuous ohmic heating treatment on fresh orange juice.

PubMed

Leizerson, Shirly; Shimoni, Eyal

2005-05-04

The scope of this study is the effect of ohmic heating thermal treatment on liquid fruit juice made of oranges. Effects of ohmic heating on the quality of orange juice were examined and compared to those of heat pasteurization at 90 degrees C for 50 s. Orange juice was treated at temperatures of 90, 120, and 150 degrees C for 1.13, 0.85, and 0.68 s in an ohmic heating system. Microbial counts showed complete inactivation of bacteria, yeast, and mold during ohmic and conventional treatments. The ohmic heating treatment reduced pectin esterase activity by 98%. The reduction in vitamin C was 15%. Ohmic-heated orange juice maintained higher amounts of the five representative flavor compounds than did heat-pasteurized juice. Sensory evaluation tests showed no difference between fresh and ohmic-heated orange juice. Thus, high-temperature ohmic-heating treatment can be effectively used to pasteurize fresh orange juice with minimal sensory deterioration.

Automatic-Control System for Safer Brazing

NASA Technical Reports Server (NTRS)

Stein, J. A.; Vanasse, M. A.

1986-01-01

Automatic-control system for radio-frequency (RF) induction brazing of metal tubing reduces probability of operator errors, increases safety, and ensures high-quality brazed joints. Unit combines functions of gas control and electric-power control. Minimizes unnecessary flow of argon gas into work area and prevents electrical shocks from RF terminals. Controller will not allow power to flow from RF generator to brazing head unless work has been firmly attached to head and has actuated micro-switch. Potential shock hazard eliminated. Flow of argon for purging and cooling must be turned on and adjusted before brazing power applied. Provision ensures power not applied prematurely, causing damaged work or poor-quality joints. Controller automatically turns off argon flow at conclusion of brazing so potentially suffocating gas does not accumulate in confined areas.

Remote shock sensing and notification system

DOEpatents

Muralidharan, Govindarajan [Knoxville, TN; Britton, Charles L [Alcoa, TN; Pearce, James [Lenoir City, TN; Jagadish, Usha [Knoxville, TN; Sikka, Vinod K [Oak Ridge, TN

2010-11-02

A low-power shock sensing system includes at least one shock sensor physically coupled to a chemical storage tank to be monitored for impacts, and an RF transmitter which is in a low-power idle state in the absence of a triggering signal. The system includes interface circuitry including or activated by the shock sensor, wherein an output of the interface circuitry is coupled to an input of the RF transmitter. The interface circuitry triggers the RF transmitter with the triggering signal to transmit an alarm message to at least one remote location when the sensor senses a shock greater than a predetermined threshold. In one embodiment the shock sensor is a shock switch which provides an open and a closed state, the open state being a low power idle state.

Remote shock sensing and notification system

DOEpatents

Muralidharan, Govindarajan; Britton, Charles L.; Pearce, James; Jagadish, Usha; Sikka, Vinod K.

2008-11-11

A low-power shock sensing system includes at least one shock sensor physically coupled to a chemical storage tank to be monitored for impacts, and an RF transmitter which is in a low-power idle state in the absence of a triggering signal. The system includes interference circuitry including or activated by the shock sensor, wherein an output of the interface circuitry is coupled to an input of the RF transmitter. The interface circuitry triggers the RF transmitting with the triggering signal to transmit an alarm message to at least one remote location when the sensor senses a shock greater than a predetermined threshold. In one embodiment the shock sensor is a shock switch which provides an open and a closed state, the open state being a low power idle state.

Variations in the electrical short-circuit current decay for recombination lifetime and velocity measurements

NASA Technical Reports Server (NTRS)

Jung, Tae-Won; Lindholm, Fredrik A.; Neugroschel, Arnost

1987-01-01

An improved measurement system for electrical short-circuit current decay is presented that extends applicability of the method to silicon solar cells having an effective lifetime as low as 1 microsec. The system uses metal/oxide/semiconductor transistors as voltage-controlled switches. Advances in theory developed here increase precision and sensitivity in the determination of the minority-carrier recombination lifetime and recombination velocity. A variation of the method, which exploits measurements made on related back-surface field and back-ohmic contact devices, further improves precision and sensitivity. The improvements are illustrated by application to 15 different silicon solar cells.

Fabrication and analysis of radiofrequency MEMS series capacitive single-pole double-throw switch

NASA Astrophysics Data System (ADS)

Bansal, Deepak; Bajpai, Anuroop; Kumar, Prem; Kaur, Maninder; Rangra, Kamaljit

2016-10-01

A compact radiofrequency (RF) MEMS single-pole double-throw (SPDT) switch based on series capacitive configuration is proposed. The critical process parameters are analyzed to improve the fabrication process. A technique of cold-hot thermal shock for lift-off method is explored. The residual stress in the structure is quantified by lancet test structures that come out to be 51 MPa. Effect of residual stress on actuation voltage is explored, which changes its value from 24 to 22 V. Resonance frequency and switching speed of the switch are 11 kHz and 44 μs, respectively, measured using laser Doppler vibrometer. Measured bandwidth of the SPDT switch is 20 GHz (5 to 25 GHz), which is verified with finite element method simulations in high frequency structure simulator©; and an equivalent LCR circuit in advanced design system©;. Insertion loss of the switch lies in -0.1 to -0.5 dB with isolation better than -20 dB for the above-mentioned bandwidth.

Phase measurement for driven spin oscillations in a storage ring

NASA Astrophysics Data System (ADS)

Hempelmann, N.; Hejny, V.; Pretz, J.; Soltner, H.; Augustyniak, W.; Bagdasarian, Z.; Bai, M.; Barion, L.; Berz, M.; Chekmenev, S.; Ciullo, G.; Dymov, S.; Eversmann, D.; Gaisser, M.; Gebel, R.; Grigoryev, K.; Grzonka, D.; Guidoboni, G.; Heberling, D.; Hetzel, J.; Hinder, F.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Koop, I.; Kulikov, A.; Lehrach, A.; Lenisa, P.; Lomidze, N.; Lorentz, B.; Maanen, P.; Macharashvili, G.; Magiera, A.; Mchedlishvili, D.; Mey, S.; Müller, F.; Nass, A.; Nikolaev, N. N.; Nioradze, M.; Pesce, A.; Prasuhn, D.; Rathmann, F.; Rosenthal, M.; Saleev, A.; Schmidt, V.; Semertzidis, Y.; Senichev, Y.; Shmakova, V.; Silenko, A.; Slim, J.; Stahl, A.; Stassen, R.; Stephenson, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Tagliente, G.; Talman, R.; Thörngren Engblom, P.; Trinkel, F.; Uzikov, Yu.; Valdau, Yu.; Valetov, E.; Vassiliev, A.; Weidemann, C.; Wrońska, A.; Wüstner, P.; Zuprański, P.; Żurek, M.; JEDI Collaboration

2018-04-01

This paper reports the first simultaneous measurement of the horizontal and vertical components of the polarization vector in a storage ring under the influence of a radio frequency (rf) solenoid. The experiments were performed at the Cooler Synchrotron COSY in Jülich using a vector polarized, bunched 0.97 GeV /c deuteron beam. Using the new spin feedback system, we set the initial phase difference between the solenoid field and the precession of the polarization vector to a predefined value. The feedback system was then switched off, allowing the phase difference to change over time, and the solenoid was switched on to rotate the polarization vector. We observed an oscillation of the vertical polarization component and the phase difference. The oscillations can be described using an analytical model. The results of this experiment also apply to other rf devices with horizontal magnetic fields, such as Wien filters. The precise manipulation of particle spins in storage rings is a prerequisite for measuring the electric dipole moment (EDM) of charged particles.

Comparative study of RF reactive magnetron sputtering and sol-gel deposition of UV induced superhydrophilic TiOx thin films

NASA Astrophysics Data System (ADS)

Vrakatseli, V. E.; Amanatides, E.; Mataras, D.

2016-03-01

TiOx and TiOx-like thin films were deposited on PEEK (Polyether ether ketone) substrates by low-temperature RF reactive magnetron sputtering and the sol-gel method. The resulting films were compared in terms of their properties and photoinduced hydrophilicity. Both techniques resulted in uniform films with good adhesion that can be switched to superhydrophilic after exposure to UVA radiation for similar time periods. In addition, the sputtered films can also be activated and switched to superhydrophilic by natural sunlight due to the higher absorption in the visible spectrum compared to the sol-gel films. On the other hand, the as deposited sol-films remain relatively hydrophilic for a longer time in dark compared to the sputtered film due to the differences in the morphology and the porosity of the two materials. Thus, depending on the application, either method can be used in order to achieve the desirable TiOx properties.

Ku to V-band 4-bit MEMS phase shifter bank using high isolation SP4T switches and DMTL structures

NASA Astrophysics Data System (ADS)

Dey, Sukomal; Koul, Shiban K.; Poddar, Ajay K.; Rohde, Ulrich L.

2017-10-01

This work presents a micro-electro-mechanical system (MEMS) based on a wide-band 4-bit phase shifter using two back-to-back single-pole-four-throw (SP4T) switches and four different distributed MEMS transmission line (DMTL) structures that are implemented on 635 µm alumina substrate using surface micromachining process. An SP4T switch is designed with a series-shunt configuration and it demonstrates an average return loss of  >17 dB, an insertion loss of  <1.97 dB and maximum isolation of  >28 dB up to 60 GHz. A maximum area of the SP4T switch is ~0.76 mm2. Single-pole-single-throw and SP4T switches are capable of handling 1 W of radio frequency (RF) power up to  >100 million cycles at 25° C; they can even sustained up to  >70 million cycles with 1 W at 85 °C. The proposed wide-band phase shifter works at 17 GHz (Ku-band), 25 GHz (K-band), 35 GHz (Ka-band) and 60 GHz (V-band) frequencies. Finally,a 4-bit phase shifter demonstrates an average insertion loss of  <6 dB, return loss of  >10 dB and maximum phase error of ~3.8° at 60 GHz frequency over 500 MHz bandwidth. Total area of the fabricated device is ~11 mm2. In addition, the proposed device works well up to  >107 cycles with 1 W of RF power. To the best of the author’s knowledge, this is the best reported wide-band MEMS 4-bit phase shifter in the literature that works with a constant resolution.

Using optimal control methods with constraints to generate singlet states in NMR

NASA Astrophysics Data System (ADS)

Rodin, Bogdan A.; Kiryutin, Alexey S.; Yurkovskaya, Alexandra V.; Ivanov, Konstantin L.; Yamamoto, Satoru; Sato, Kazunobu; Takui, Takeji

2018-06-01

A method is proposed for optimizing the performance of the APSOC (Adiabatic-Passage Spin Order Conversion) technique, which can be exploited in NMR experiments with singlet spin states. In this technique magnetization-to-singlet conversion (and singlet-to-magnetization conversion) is performed by using adiabatically ramped RF-fields. Optimization utilizes the GRAPE (Gradient Ascent Pulse Engineering) approach, in which for a fixed search area we assume monotonicity to the envelope of the RF-field. Such an approach allows one to achieve much better performance for APSOC; consequently, the efficiency of magnetization-to-singlet conversion is greatly improved as compared to simple model RF-ramps, e.g., linear ramps. We also demonstrate that the optimization method is reasonably robust to possible inaccuracies in determining NMR parameters of the spin system under study and also in setting the RF-field parameters. The present approach can be exploited in other NMR and EPR applications using adiabatic switching of spin Hamiltonians.

Memristive behaviour of Si-Al oxynitride thin films: the role of oxygen and nitrogen vacancies in the electroforming process.

PubMed

Blázquez, O; Martín, G; Camps, I; Mariscal, A; López-Vidrier, J; Ramírez, J M; Hernández, S; Estradé, S; Peiró, F; Serna, R; Garrido, B

2018-06-08

The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole-Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching.

Memristive behaviour of Si-Al oxynitride thin films: the role of oxygen and nitrogen vacancies in the electroforming process

NASA Astrophysics Data System (ADS)

Blázquez, O.; Martín, G.; Camps, I.; Mariscal, A.; López-Vidrier, J.; Ramírez, J. M.; Hernández, S.; Estradé, S.; Peiró, F.; Serna, R.; Garrido, B.

2018-06-01

The resistive switching properties of silicon-aluminium oxynitride (SiAlON) based devices have been studied. Electrical transport mechanisms in both resistance states were determined, exhibiting an ohmic behaviour at low resistance and a defect-related Poole‑Frenkel mechanism at high resistance. Nevertheless, some features of the Al top-electrode are generated during the initial electroforming, suggesting some material modifications. An in-depth microscopic study at the nanoscale has been performed after the electroforming process, by acquiring scanning electron microscopy and transmission electron microscopy images. The direct observation of the devices confirmed features on the top electrode with bubble-like appearance, as well as some precipitates within the SiAlON. Chemical analysis by electron energy loss spectroscopy has demonstrated that there is an out-diffusion of oxygen and nitrogen ions from the SiAlON layer towards the electrode, thus forming silicon-rich paths within the dielectric layer and indicating vacancy change to be the main mechanism in the resistive switching.

Robust optical wireless links over turbulent media using diversity solutions

NASA Astrophysics Data System (ADS)

Moradi, Hassan

Free-space optic (FSO) technology, i.e., optical wireless communication (OWC), is widely recognized as superior to radio frequency (RF) in many aspects. Visible and invisible optical wireless links solve first/last mile connectivity problems and provide secure, jam-free communication. FSO is license-free and delivers high-speed data rates in the order of Gigabits. Its advantages have fostered significant research efforts aimed at utilizing optical wireless communication, e.g. visible light communication (VLC), for high-speed, secure, indoor communication under the IEEE 802.15.7 standard. However, conventional optical wireless links demand precise optical alignment and suffer from atmospheric turbulence. When compared with RF, they suffer a low degree of reliability and lack robustness. Pointing errors cause optical transceiver misalignment, adversely affecting system reliability. Furthermore, atmospheric turbulence causes irradiance fluctuations and beam broadening of transmitted light. Innovative solutions to overcome limitations on the exploitation of high-speed optical wireless links are greatly needed. Spatial diversity is known to improve RF wireless communication systems. Similar diversity approaches can be adapted for FSO systems to improve its reliability and robustness; however, careful diversity design is needed since FSO apertures typically remain unbalanced as a result of FSO system sensitivity to misalignment. Conventional diversity combining schemes require persistent aperture monitoring and repetitive switching, thus increasing FSO implementation complexities. Furthermore, current RF diversity combining schemes may not be optimized to address the issue of unbalanced FSO receiving apertures. This dissertation investigates two efficient diversity combining schemes for multi-receiving FSO systems: switched diversity combining and generalized selection combining. Both can be exploited to reduce complexity and improve combining efficiency. Unlike maximum ratio combing, equal gain combining, and selective combining, switched diversity simplifies receiver design by avoiding unnecessary switching among receiving apertures. The most significant advantage of generalized combining is its ability to exclude apertures with low quality that could potentially affect the resultant output signal performance. This dissertation also investigates mobile FSO by considering a multi-receiving system in which all receiving FSO apertures are circularly placed on a platform. System mobility and performance are analyzed. Performance results confirm improvements when using angular diversity and generalized selection combining. The precis of this dissertation establishes the foundation of reliable FSO communications using efficient diversity-based solutions. Performance parameters are analyzed mathematically, and then evaluated using computer simulations. A testbed prototype is developed to facilitate the evaluation of optical wireless links via lab experiments.

Effect of frequency on the uniformity of symmetrical RF CCP discharges

NASA Astrophysics Data System (ADS)

Liu, Yue; Booth, Jean-Paul; Chabert, Pascal

2018-05-01

A 2D Cartesian electrostatic particle-in-cell/Monte Carlo collision (PIC/MCC) model presented previously (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) is used to investigate the effect of the driving frequency (over the range of 15–45 MHz) on the plasma uniformity in radio frequency (RF) capacitively coupled plasma (CCP) discharges in a geometrically symmetric reactor with a dielectric side wall in argon gas. The reactor size (12 cm electrode length, 2.5 cm gap) and driving frequency are sufficiently small that electromagnetic effects can be ignored. Previously, we showed (Liu et al 2018 Plasma Sources Sci. Technol. 27 025006) that for 15 MHz excitation, Ohmic heating of electrons by the electric field perpendicular to the electrodes is enhanced in a region in front of the dielectric side wall, leading to a maximum in electron density there. In this work we show that increasing the excitation frequency (at constant applied voltage amplitude) not only increases the overall electron heating and density but also causes a stronger, narrower peak in electron heating closer to the dielectric wall, improving the plasma uniformity along the electrodes. This heating peak comes both from enhanced perpendicular electron heating and from the appearance at high frequency of significant parallel heating. The latter is caused by the presence of a significant parallel-direction RF oscillating electric field in the corners. Whereas at the reactor center the sheaths oscillate perpendicularly to the electrodes, near the dielectric edge they move in and out of the corners and must be treated in two dimensions.

Photocathode quantum efficiency of ultrathin Cs2Te layers on Nb substrates

NASA Astrophysics Data System (ADS)

Yusof, Zikri; Denchfield, Adam; Warren, Mark; Cardenas, Javier; Samuelson, Noah; Spentzouris, Linda; Power, John; Zasadzinski, John

2017-12-01

The quantum efficiencies (QE) of photocathodes consisting of bulk Nb substrates coated with thin films of Cs2Te are reported. Using the standard recipe for Cs2Te deposition developed for Mo substrates (220 Å Te thickness), a QE ˜11 % - 13 % at light wavelength of 248 nm is achieved for the Nb substrates, consistent with that found on Mo. Systematic reduction of the Te thickness for both Mo and Nb substrates reveals a surprisingly high residual QE ˜6 % for a Te layer as thin as 15 Å. A phenomenological model based on the Spicer three-step model along with a solution of the Fresnel equations for reflectance, R , leads to a reasonable fit of the thickness dependence of QE and suggests that layers thinner than 15 Å may still have a relatively high QE. Preliminary investigation suggests an increased operational lifetime as well. Such an ultrathin, semiconducting Cs2Te layer may be expected to produce minimal Ohmic losses for rf frequencies ˜1 GHz . The result thus opens the door to the potential development of a Nb (or Nb3Sn ) superconducting photocathode with relatively high QE and minimal rf impedance to be used in a superconducting radiofrequency (SRF) photoinjector.

Investigations on structural and electrical parameters of p-Si/ MgxZn1-xO thin film heterojunction diodes grown by RF magnetron sputtering technique

NASA Astrophysics Data System (ADS)

Singh, Satyendra Kumar; Hazra, Purnima

2018-05-01

This work reports fabrication and characterization of p-Si/ MgxZn1-xO thin film heterojunction diodes grown by RF magnetron sputtering technique. In this work, ZnO powder was mixed with MgO powder at per their weight percentage from 0 to 10% to prepare MgxZn1-xO target. The microstructural, surface morphological and optical properties of as-deposited p-Si/MgxZn1-xO heterostructure thin films have been studied using X-ray Diffraction, atomic force microscopy and variable angle ellipsometer. XRD spectra exhibit that undoped ZnO thin films has preferred crystal orientation in (002) plane. However, with increase in Mg-doping, ZnO (101) crystal plane is enhanced progressively due to phase segregation, even though preferred growth orientation of ZnO crystals is still towards (002) plane. The electrical characteristics of Si/ MgxZn1-xO heterojunction diodes with large area Al/Ti ohmic contacts are evaluated using semiconductor parameter analyzer. With rectification ratio of 27894, reverse saturation current of 20.5 nA and barrier height of 0.724 eV, Si/Mg0.5Zn0.95O thin film heterojunction diode is believed to have potential to be used in wider bandgap nanoelectronic device applications.

Microwave power transmission system studies. Volume 2: Introduction, organization, environmental and spaceborne systems analyses

NASA Technical Reports Server (NTRS)

Maynard, O. E.; Brown, W. C.; Edwards, A.; Haley, J. T.; Meltz, G.; Howell, J. M.; Nathan, A.

1975-01-01

Introduction, organization, analyses, conclusions, and recommendations for each of the spaceborne subsystems are presented. Environmental effects - propagation analyses are presented with appendices covering radio wave diffraction by random ionospheric irregularities, self-focusing plasma instabilities and ohmic heating of the D-region. Analyses of dc to rf conversion subsystems and system considerations for both the amplitron and the klystron are included with appendices for the klystron covering cavity circuit calculations, output power of the solenoid-focused klystron, thermal control system, and confined flow focusing of a relativistic beam. The photovoltaic power source characteristics are discussed as they apply to interfacing with the power distribution flow paths, magnetic field interaction, dc to rf converter protection, power distribution including estimates for the power budget, weights, and costs. Analyses for the transmitting antenna consider the aperture illumination and size, with associated efficiencies and ground power distributions. Analyses of subarray types and dimensions, attitude error, flatness, phase error, subarray layout, frequency tolerance, attenuation, waveguide dimensional tolerances, mechanical including thermal considerations are included. Implications associated with transportation, assembly and packaging, attitude control and alignment are discussed. The phase front control subsystem, including both ground based pilot signal driven adaptive and ground command approaches with their associated phase errors, are analyzed.

Atomic Layer Deposited Oxide-Based Nanocomposite Structures with Embedded CoPtx Nanocrystals for Resistive Random Access Memory Applications.

PubMed

Wang, Lai-Guo; Cao, Zheng-Yi; Qian, Xu; Zhu, Lin; Cui, Da-Peng; Li, Ai-Dong; Wu, Di

2017-02-22

Al 2 O 3 - or HfO 2 -based nanocomposite structures with embedded CoPt x nanocrystals (NCs) on TiN-coated Si substrates have been prepared by combination of thermal atomic layer deposition (ALD) and plasma-enhanced ALD for resistive random access memory (RRAM) applications. The impact of CoPt x NCs and their average size/density on the resistive switching properties has been explored. Compared to the control sample without CoPt x NCs, ALD-derived Pt/oxide/100 cycle-CoPt x NCs/TiN/SiO 2 /Si exhibits a typical bipolar, reliable, and reproducible resistive switching behavior, such as sharp distribution of RRAM parameters, smaller set/reset voltages, stable resistance ratio (≥10 2 ) of OFF/ON states, better switching endurance up to 10 4 cycles, and longer data retention over 10 5 s. The possible resistive switching mechanism based on nanocomposite structures of oxide/CoPt x NCs has been proposed. The dominant conduction mechanisms in low- and high-resistance states of oxide-based device units with embedded CoPt x NCs are Ohmic behavior and space-charge-limited current, respectively. The insertion of CoPt x NCs can effectively improve the formation of conducting filaments due to the CoPt x NC-enhanced electric field intensity. Besides excellent resistive switching performances, the nanocomposite structures also simultaneously present ferromagnetic property. This work provides a flexible pathway by combining PEALD and TALD compatible with state-of-the-art Si-based technology for multifunctional electronic devices applications containing RRAM.

Improved Ohmic-contact to AlGaN/GaN using Ohmic region recesses by self-terminating thermal oxidation assisted wet etching technique

NASA Astrophysics Data System (ADS)

Liu, J.; Wang, J.; Wang, H.; Zhu, L.; Wu, W.

2017-06-01

Lower Ti/Al/Ni/Au Ohmic contact resistance on AlGaN/GaN with wider rapid thermal annealing (RTA) temperature window was achieved using recessed Ohmic contact structure based on self-terminating thermal oxidation assisted wet etching technique (STOAWET), in comparison with conventional Ohmic contacts. Even at lower temperature such as 650°C, recessed structure by STOAWET could still obtain Ohmic contact with contact resistance of 1.97Ω·mm, while conventional Ohmic structure mainly featured as Schottky contact. Actually, both Ohmic contact recess and mesa isolation processes could be accomplished by STOAWET in one process step and the process window of STOAWET is wide, simplifying AlGaN/GaN HEMT device process. Our experiment shows that the isolation leakage current by STOAWET is about one order of magnitude lower than that by inductivity coupled plasma (ICP) performed on the same wafer.

Ferroelectric switch for a high-power Ka-band active pulse compressor

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirshfield, Jay L.

2013-12-18

Results are presented for design of a high-power microwave switch for operation at 34.3 GHz, intended for use in an active RF pulse compressor. The active element in the switch is a ring of ferroelectric material, whose dielectric constant can be rapidly changed by application of a high-voltage pulse. As envisioned, two of these switches would be built into a pair of delay lines, as in SLED-II at SLAC, so as to allow 30-MW μs-length Ka-band pulses to be compressed in time by a factor-of-9 and multiplied in amplitude to generate 200 MW peak power pulses. Such high-power pulses couldmore » be used for testing and evaluation of high-gradient mm-wave accelerator structures, for example. Evaluation of the switch design was carried out with an X-band (11.43 GHz) prototype, built to incorporate all the features required for the Ka-band version.« less

Predicting the performance of a power amplifier using large-signal circuit simulations of an AlGaN/GaN HFET model

NASA Astrophysics Data System (ADS)

Bilbro, Griff L.; Hou, Danqiong; Yin, Hong; Trew, Robert J.

2009-02-01

We have quantitatively modeled the conduction current and charge storage of an HFET in terms its physical dimensions and material properties. For DC or small-signal RF operation, no adjustable parameters are necessary to predict the terminal characteristics of the device. Linear performance measures such as small-signal gain and input admittance can be predicted directly from the geometric structure and material properties assumed for the device design. We have validated our model at low-frequency against experimental I-V measurements and against two-dimensional device simulations. We discuss our recent extension of our model to include a larger class of electron velocity-field curves. We also discuss the recent reformulation of our model to facilitate its implementation in commercial large-signal high-frequency circuit simulators. Large signal RF operation is more complex. First, the highest CW microwave power is fundamentally bounded by a brief, reversible channel breakdown in each RF cycle. Second, the highest experimental measurements of efficiency, power, or linearity always require harmonic load pull and possibly also harmonic source pull. Presently, our model accounts for these facts with an adjustable breakdown voltage and with adjustable load impedances and source impedances for the fundamental frequency and its harmonics. This has allowed us to validate our model for large signal RF conditions by simultaneously fitting experimental measurements of output power, gain, and power added efficiency of real devices. We show that the resulting model can be used to compare alternative device designs in terms of their large signal performance, such as their output power at 1dB gain compression or their third order intercept points. In addition, the model provides insight into new device physics features enabled by the unprecedented current and voltage levels of AlGaN/GaN HFETs, including non-ohmic resistance in the source access regions and partial depletion of the 2DEG in the drain access region.

Ferroelectric switching in epitaxial PbZr0.2Ti0.8O3/ZnO/GaN heterostructures

NASA Astrophysics Data System (ADS)

Wang, Juan; Salev, Pavel; Grigoriev, Alexei

As a wide-bandgap semiconductor, ZnO has gained substantial interest due to its favorable properties including high electron mobility, strong room-temperature luminescence, etc. The main obstacle of its application is the lack of reproducible and low-resistivity p-type ZnO. P-type doping of ZnO through the interface charge injection, which can be achieved by the polarization switching of ferroelectric films, is a tempting solution. We explored ferroelectric switching behavior of PbZr0.2Ti0.8O3/ZnO/GaN heterostructures epitaxially grown on Sapphire substrates by RF sputtering. The electrical measurements of Pt/PbZr0.2Ti0.8O3/ZnO/GaN ferroelectric-semiconductor capacitors revealed unusual behavior that is a combination of polarization switching and a diode I-V characteristics.

Compact field programmable gate array-based pulse-sequencer and radio-frequency generator for experiments with trapped atoms.

PubMed

Pruttivarasin, Thaned; Katori, Hidetoshi

2015-11-01

We present a compact field-programmable gate array (FPGA) based pulse sequencer and radio-frequency (RF) generator suitable for experiments with cold trapped ions and atoms. The unit is capable of outputting a pulse sequence with at least 32 transistor-transistor logic (TTL) channels with a timing resolution of 40 ns and contains a built-in 100 MHz frequency counter for counting electrical pulses from a photo-multiplier tube. There are 16 independent direct-digital-synthesizers RF sources with fast (rise-time of ∼60 ns) amplitude switching and sub-mHz frequency tuning from 0 to 800 MHz.

Improved modeling of GaN HEMTs for predicting thermal and trapping-induced-kink effects

NASA Astrophysics Data System (ADS)

Jarndal, Anwar; Ghannouchi, Fadhel M.

2016-09-01

In this paper, an improved modeling approach has been developed and validated for GaN high electron mobility transistors (HEMTs). The proposed analytical model accurately simulates the drain current and its inherent trapping and thermal effects. Genetic-algorithm-based procedure is developed to automatically find the fitting parameters of the model. The developed modeling technique is implemented on a packaged GaN-on-Si HEMT and validated by DC and small-/large-signal RF measurements. The model is also employed for designing and realizing a switch-mode inverse class-F power amplifier. The amplifier simulations showed a very good agreement with RF large-signal measurements.

Compact field programmable gate array-based pulse-sequencer and radio-frequency generator for experiments with trapped atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pruttivarasin, Thaned, E-mail: thaned.pruttivarasin@riken.jp; Katori, Hidetoshi; Innovative Space-Time Project, ERATO, JST, Bunkyo-ku, Tokyo 113-8656

We present a compact field-programmable gate array (FPGA) based pulse sequencer and radio-frequency (RF) generator suitable for experiments with cold trapped ions and atoms. The unit is capable of outputting a pulse sequence with at least 32 transistor-transistor logic (TTL) channels with a timing resolution of 40 ns and contains a built-in 100 MHz frequency counter for counting electrical pulses from a photo-multiplier tube. There are 16 independent direct-digital-synthesizers RF sources with fast (rise-time of ∼60 ns) amplitude switching and sub-mHz frequency tuning from 0 to 800 MHz.

Alternative Dielectric Films for rf MEMS Capacitive Switches Deposited using Atomic Layer Deposited Al2O3/ZnO Alloys

DTIC Science & Technology

2006-07-02

A s c c s r t h s l © K 1 b c A a e t s C t o 0 d Sensors and Actuators A 135 (2007) 262–272 Alternative dielectric films for rf MEMS capacitive...Zn concentrations in the alloy films , which was lower than expected. Atomic force microscopy images evealed an average surface roughness of 0.27 nm...that was independent of deposition temperature and film composition. The dielectric constants of he Al2O3/ZnO ALD alloys films were calculated to be

Analysis of emotionality and locomotion in radio-frequency electromagnetic radiation exposed rats.

PubMed

Narayanan, Sareesh Naduvil; Kumar, Raju Suresh; Paval, Jaijesh; Kedage, Vivekananda; Bhat, M Shankaranarayana; Nayak, Satheesha; Bhat, P Gopalakrishna

2013-07-01

In the current study the modulatory role of mobile phone radio-frequency electromagnetic radiation (RF-EMR) on emotionality and locomotion was evaluated in adolescent rats. Male albino Wistar rats (6-8 weeks old) were randomly assigned into the following groups having 12 animals in each group. Group I (Control): they remained in the home cage throughout the experimental period. Group II (Sham exposed): they were exposed to mobile phone in switch-off mode for 28 days, and Group III (RF-EMR exposed): they were exposed to RF-EMR (900 MHz) from an active GSM (Global system for mobile communications) mobile phone with a peak power density of 146.60 μW/cm(2) for 28 days. On 29th day, the animals were tested for emotionality and locomotion. Elevated plus maze (EPM) test revealed that, percentage of entries into the open arm, percentage of time spent on the open arm and distance travelled on the open arm were significantly reduced in the RF-EMR exposed rats. Rearing frequency and grooming frequency were also decreased in the RF-EMR exposed rats. Defecation boli count during the EPM test was more with the RF-EMR group. No statistically significant difference was found in total distance travelled, total arm entries, percentage of closed arm entries and parallelism index in the RF-EMR exposed rats compared to controls. Results indicate that mobile phone radiation could affect the emotionality of rats without affecting the general locomotion.

Design and dSpace interfacing of current fed high gain dc to dc boost converter for low voltage applications

NASA Astrophysics Data System (ADS)

Mukhopadhyay, Debraj; Das, Subhrajit; Arunkumar, G.; Elangovan, D.; Ragunath, G.

2017-11-01

In this paper a current fed interleaved DC - DC boost converter which has an isolated topology and used for high voltage step up is proposed. A basic DC to DC boost converter converts uncontrolled DC voltage into controlled DC voltage of higher magnitude. Whereas this topology has the advantages of lower input current ripple, lesser output voltage, lesser stress on switches, faster transient response, improved reliability and much lesser electromagnetic emission over the conventional DC to DC boost converter. Most important benefit of this interleaved DC to DC boost converter is much higher efficiency. The input current is divided into two paths, substantially ohmic loss (I2R) and inductor ac loss gets reduced and finally the system achieves much higher efficiency. With recent mandates on energy saving interleaved DC to DC boost converter may be used as a very powerful tool to maintain good power density keeping the input current manageable. Higher efficiency also allows higher switching frequency and as a result the topology becomes more compact and cost friendly. The proposed topology boosts 48v DC to 200 V DC. Switching frequency is 100 kHz and PSIM 9.1 Platform has been used for the simulation.

Resistive Switching in All-Printed, Flexible and Hybrid MoS2-PVA Nanocomposite based Memristive Device Fabricated by Reverse Offset

PubMed Central

Rehman, Muhammad Muqeet; Siddiqui, Ghayas Uddin; Gul, Jahan Zeb; Kim, Soo-Wan; Lim, Jong Hwan; Choi, Kyung Hyun

2016-01-01

Owing to the increasing interest in the nonvolatile memory devices, resistive switching based on hybrid nanocomposite of a 2D material, molybdenum disulphide (MoS2) and polyvinyl alcohol (PVA) is explored in this work. As a proof of concept, we have demonstrated the fabrication of a memory device with the configuration of PET/Ag/MoS2-PVA/Ag via an all printed, hybrid, and state of the art fabrication approach. Bottom Ag electrodes, active layer of hybrid MoS2-PVA nanocomposite and top Ag electrode are deposited by reverse offset, electrohydrodynamic (EHD) atomization and electrohydrodynamic (EHD) patterning respectively. The fabricated device displayed characteristic bistable, nonvolatile and rewritable resistive switching behavior at a low operating voltage. A decent off/on ratio, high retention time, and large endurance of 1.28 × 102, 105 sec and 1000 voltage sweeps were recorded respectively. Double logarithmic curve satisfy the trap controlled space charge limited current (TCSCLC) model in high resistance state (HRS) and ohmic model in low resistance state (LRS). Bendability test at various bending diameters (50-2 mm) for 1500 cycles was carried out to show the mechanical robustness of fabricated device. PMID:27811977

Effect of a PEDOT:PSS modified layer on the electrical characteristics of flexible memristive devices based on graphene oxide:polyvinylpyrrolidone nanocomposites

NASA Astrophysics Data System (ADS)

Kim, Woo Kyum; Wu, Chaoxing; Kim, Tae Whan

2018-06-01

The electrical characteristics of flexible memristive devices utilizing a graphene oxide (GO):polyvinylpyrrolidone (PVP) nanocomposite charge-trapping layer with a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)-modified layer fabricated on an indium-tin-oxide (ITO)-coated polyethylene glycol naphthalate (PEN) substrate were investigated. Current-voltage (I-V) curves for the Al/GO:PVP/PEDOT:PSS/ITO/PEN devices showed remarkable hysteresis behaviors before and after bending. The maximum memory margins of the devices before and after 100 bending cycles were approximately 7.69 × 103 and 5.16 × 102, respectively. The devices showed nonvolatile memory effect with a retention time of more than 1 × 104 s. The "Reset" voltages were distributed between 2.3 and 3.5 V, and the "Set" voltages were dispersed between -0.7 and -0.2 V, indicative of excellent, uniform electrical performance. The endurance number of ON/OFF-switching and bending cycles for the devices was 1 × 102, respectively. The bipolar resistive switching behavior was explained on the basis of I-V results. In particular, the bipolar resistive switching behaviors of the LRS and the HRS for the devices are dominated by the Ohmic and space charge current mechanisms, respectively.

Tri-state resistive switching characteristics of MnO/Ta2O5 resistive random access memory device by a controllable reset process

NASA Astrophysics Data System (ADS)

Lee, N. J.; Kang, T. S.; Hu, Q.; Lee, T. S.; Yoon, T.-S.; Lee, H. H.; Yoo, E. J.; Choi, Y. J.; Kang, C. J.

2018-06-01

Tri-state resistive switching characteristics of bilayer resistive random access memory devices based on manganese oxide (MnO)/tantalum oxide (Ta2O5) have been studied. The current–voltage (I–V) characteristics of the Ag/MnO/Ta2O5/Pt device show tri-state resistive switching (RS) behavior with a high resistance state (HRS), intermediate resistance state (IRS), and low resistance state (LRS), which are controlled by the reset process. The MnO/Ta2O5 film shows bipolar RS behavior through the formation and rupture of conducting filaments without the forming process. The device shows reproducible and stable RS both from the HRS to the LRS and from the IRS to the LRS. In order to elucidate the tri-state RS mechanism in the Ag/MnO/Ta2O5/Pt device, transmission electron microscope (TEM) images are measured in the LRS, IRS and HRS. White lines like dendrites are observed in the Ta2O5 film in both the LRS and the IRS. Poole–Frenkel conduction, space charge limited conduction, and Ohmic conduction are proposed as the dominant conduction mechanisms for the Ag/MnO/Ta2O5/Pt device based on the obtained I–V characteristics and TEM images.

75 FR 75464 - Notice of Public Information Collection(s) Being Reviewed by the Federal Communications...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-03

... type of switch software) to provide payphone specific coding digits for per-call compensation. The... Information; [cir] RF Exposure Information; [cir] Operational Description; [cir] Cover Letters; [cir] Software Defined Radio/Cognitive Radio Files In general, an applicant's submission is as follows: (a) FCC Form 731...

Photovoltaic properties of ferroelectric BaTiO3 thin films RF sputter deposited on silicon

NASA Technical Reports Server (NTRS)

Dharmadhikari, V. S.; Grannemann, W. W.

1982-01-01

Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 C by RF sputtering in an O2/Ar atmosphere. Analysis by X-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the RF sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

Advanced Millimeter-Wave Imaging Enhances Security Screening

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheen, David M.; Bernacki, Bruce E.; McMakin, Douglas L.

2012-01-12

Millimeter-wave imaging is rapidly gaining acceptance for passenger screening at airports and other secured facilities. This paper details a number of techniques developed over the last several years including novel image reconstruction and display techniques, polarimetric imaging techniques, array switching schemes, as well as high frequency high bandwidth techniques. Implementation of some of these methods will increase the cost and complexity of the mm-wave security portal imaging systems. RF photonic methods may provide new solutions to the design and development of the sequentially switched linear mm-wave arrays that are the key element in the mm-wave portal imaging systems.

Advanced Millimeter-Wave Security Portal Imaging Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sheen, David M.; Bernacki, Bruce E.; McMakin, Douglas L.

2012-04-01

Millimeter-wave imaging is rapidly gaining acceptance for passenger screening at airports and other secured facilities. This paper details a number of techniques developed over the last several years including novel image reconstruction and display techniques, polarimetric imaging techniques, array switching schemes, as well as high frequency high bandwidth techniques. Implementation of some of these methods will increase the cost and complexity of the mm-wave security portal imaging systems. RF photonic methods may provide new solutions to the design and development of the sequentially switched linear mm-wave arrays that are the key element in the mm-wave portal imaging systems.

Magnetics and Power System Upgrades for the Pegasus-U Experiment

NASA Astrophysics Data System (ADS)

Preston, R. C.; Bongard, M. W.; Fonck, R. J.; Lewicki, B. T.

2014-10-01

To support the missions of developing local helicity injection startup and exploiting advanced tokamak physics studies at near unity aspect ratio, the proposed Pegasus-U will include expanded magnetic systems and associated power supplies. A new centerstack increases the toroidal field seven times to 1 T and the volt-seconds by a factor of six while maintaining operation at an aspect ratio of 1.2. The poloidal field magnet system is expanded to support improved shape control and robust double or single null divertor operation at the full plasma current of 0.3 MA. An integrated digital control system based on Field Programmable Gate Arrays (FPGAs) provides active feedback control of all magnet currents. Implementation of the FPGAs is achieved with modular noise reducing electronics. The digital feedback controllers replace the existing analog systems and switch multiplexing technology. This will reduce noise sensitivity and allow the operational Ohmic power supply voltage to increase from 2100 V to its maximum capacity of 2400 V. The feedback controller replacement also allows frequency control for ``freewheeling''--stopping the switching for a short interval and allowing the current to coast. The FPGAs assist in optimizing pulse length by having programmable switching events to minimize energy losses. They also allow for more efficient switching topologies that provide improved stored energy utilization, and support increasing the pulse length from 25 ms to 50-100 ms. Work supported by US DOE Grant DE-FG02-96ER54375.

High Temperature Characteristics of Pt/TaSi2/Pt/W and Pt/Ti/W Diffusion Barrier Systems for Ohmic Contacts to 4H-SiC

NASA Technical Reports Server (NTRS)

Okojie, Robert S.; Lukco, Dorothy

2017-01-01

The degradation of ohmic contacts to 4H-SiC pressure sensors over time at high temperature is primarily due to two failure mechanisms: migrating bond pad Au and atmospheric O toward the ohmic contact SiC interface and the inter-metallic mixing between diffusion barrier systems (DBS) and the underlying ohmic contact metallization. We investigated the effectiveness of Pt/TaSi2/Pt/W (DBS-A) and Pt/Ti/W (DBS-B) in preventing Au and O diffusion through the underlying binary Ti/W or alloyed W50:Ni50 ohmic contacts to 4H-SiC and the DBS ohmic contact intermixing at temperature up to 700 C.

How coagulation zone size is underestimated in computer modeling of RF ablation by ignoring the cooling phase just after RF power is switched off.

PubMed

Irastorza, Ramiro M; Trujillo, Macarena; Berjano, Enrique

2017-11-01

All the numerical models developed for radiofrequency ablation so far have ignored the possible effect of the cooling phase (just after radiofrequency power is switched off) on the dimensions of the coagulation zone. Our objective was thus to quantify the differences in the minor radius of the coagulation zone computed by including and ignoring the cooling phase. We built models of RF tumor ablation with 2 needle-like electrodes: a dry electrode (5 mm long and 17G in diameter) with a constant temperature protocol (70°C) and a cooled electrode (30 mm long and 17G in diameter) with a protocol of impedance control. We observed that the computed coagulation zone dimensions were always underestimated when the cooling phase was ignored. The mean values of the differences computed along the electrode axis were always lower than 0.15 mm for the dry electrode and 1.5 mm for the cooled electrode, which implied a value lower than 5% of the minor radius of the coagulation zone (which was 3 mm for the dry electrode and 30 mm for the cooled electrode). The underestimation was found to be dependent on the tissue characteristics: being more marked for higher values of specific heat and blood perfusion and less marked for higher values of thermal conductivity. Copyright © 2017 John Wiley & Sons, Ltd.

Saccharomyces cerevisiae CTF18 and CTF4 Are Required for Sister Chromatid Cohesion

PubMed Central

Hanna, Joseph S.; Kroll, Evgueny S.; Lundblad, Victoria; Spencer, Forrest A.

2001-01-01

CTF4 and CTF18 are required for high-fidelity chromosome segregation. Both exhibit genetic and physical ties to replication fork constituents. We find that absence of either CTF4 or CTF18 causes sister chromatid cohesion failure and leads to a preanaphase accumulation of cells that depends on the spindle assembly checkpoint. The physical and genetic interactions between CTF4, CTF18, and core components of replication fork complexes observed in this study and others suggest that both gene products act in association with the replication fork to facilitate sister chromatid cohesion. We find that Ctf18p, an RFC1-like protein, directly interacts with Rfc2p, Rfc3p, Rfc4p, and Rfc5p. However, Ctf18p is not a component of biochemically purified proliferating cell nuclear antigen loading RF-C, suggesting the presence of a discrete complex containing Ctf18p, Rfc2p, Rfc3p, Rfc4p, and Rfc5p. Recent identification and characterization of the budding yeast polymerase κ, encoded by TRF4, strongly supports a hypothesis that the DNA replication machinery is required for proper sister chromatid cohesion. Analogous to the polymerase switching role of the bacterial and human RF-C complexes, we propose that budding yeast RF-CCTF18 may be involved in a polymerase switch event that facilities sister chromatid cohesion. The requirement for CTF4 and CTF18 in robust cohesion identifies novel roles for replication accessory proteins in this process. PMID:11287619

Modelling transport phenomena in a multi-physics context

NASA Astrophysics Data System (ADS)

Marra, Francesco

2015-01-01

Innovative heating research on cooking, pasteurization/sterilization, defrosting, thawing and drying, often focuses on areas which include the assessment of processing time, evaluation of heating uniformity, studying the impact on quality attributes of the final product as well as considering the energy efficiency of these heating processes. During the last twenty years, so-called electro-heating-processes (radio-frequency - RF, microwaves - MW and ohmic - OH) gained a wide interest in industrial food processing and many applications using the above mentioned technologies have been developed with the aim of reducing processing time, improving process efficiency and, in many cases, the heating uniformity. In the area of innovative heating, electro-heating accounts for a considerable portion of both the scientific literature and commercial applications, which can be subdivided into either direct electro-heating (as in the case of OH heating) where electrical current is applied directly to the food or indirect electro-heating (e.g. MW and RF heating) where the electrical energy is firstly converted to electromagnetic radiation which subsequently generates heat within a product. New software packages, which make easier solution of PDEs based mathematical models, and new computers, capable of larger RAM and more efficient CPU performances, allowed an increasing interest about modelling transport phenomena in systems and processes - as the ones encountered in food processing - that can be complex in terms of geometry, composition, boundary conditions but also - as in the case of electro-heating assisted applications - in terms of interaction with other physical phenomena such as displacement of electric or magnetic field. This paper deals with the description of approaches used in modelling transport phenomena in a multi-physics context such as RF, MW and OH assisted heating.

Modelling transport phenomena in a multi-physics context

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marra, Francesco

2015-01-22

Innovative heating research on cooking, pasteurization/sterilization, defrosting, thawing and drying, often focuses on areas which include the assessment of processing time, evaluation of heating uniformity, studying the impact on quality attributes of the final product as well as considering the energy efficiency of these heating processes. During the last twenty years, so-called electro-heating-processes (radio-frequency - RF, microwaves - MW and ohmic - OH) gained a wide interest in industrial food processing and many applications using the above mentioned technologies have been developed with the aim of reducing processing time, improving process efficiency and, in many cases, the heating uniformity. Inmore » the area of innovative heating, electro-heating accounts for a considerable portion of both the scientific literature and commercial applications, which can be subdivided into either direct electro-heating (as in the case of OH heating) where electrical current is applied directly to the food or indirect electro-heating (e.g. MW and RF heating) where the electrical energy is firstly converted to electromagnetic radiation which subsequently generates heat within a product. New software packages, which make easier solution of PDEs based mathematical models, and new computers, capable of larger RAM and more efficient CPU performances, allowed an increasing interest about modelling transport phenomena in systems and processes - as the ones encountered in food processing - that can be complex in terms of geometry, composition, boundary conditions but also - as in the case of electro-heating assisted applications - in terms of interaction with other physical phenomena such as displacement of electric or magnetic field. This paper deals with the description of approaches used in modelling transport phenomena in a multi-physics context such as RF, MW and OH assisted heating.« less

Heating of metallic implants and instruments induced by gradient switching in a 1.5-Tesla whole-body unit.

PubMed

Graf, Hansjörg; Steidle, Günter; Schick, Fritz

2007-11-01

To examine gradient switching-induced heating of metallic parts. Copper and titanium frames and sheets ( approximately 50 x 50 mm(2), 1.5 mm thick, frame width = 3 mm) surrounded by air were positioned in the scanner perpendicular to the static field horizontally 20 cm off-center. During the execution of a sequence (three-dimensional [3D] true fast imaging with steady precession [True-FISP], TR = 6.4 msec) exploiting the gradient capabilities (maximum gradient = 40 mT/m, maximum slew rate = 200 T/m/second), heating was measured with an infrared camera. Radio frequency (RF) amplitude was set to zero volts. Heating of a copper frame with a narrowing to 1 mm over 20 mm at one side was examined in air and in addition surrounded by several liters of gelled saline using fiber-optic thermography. Further heating studies were performed using an artificial hip made of titanium, and an aluminum replica of the hip prosthesis with the same geometry. For the copper specimens, considerable heating (>10 degrees C) in air and in gelled saline (>1.2 degrees C) could be observed. Heating of the titanium specimens was markedly less ( approximately 1 degrees C in air). For the titanium artificial hip no heating could be detected, while the rise in temperature for the aluminum replica was approximately 2.2 degrees C. Heating of more than 10 degrees C solely due to gradient switching without any RF irradiation was demonstrated in isolated copper wire frames. Under specific conditions (high gradient duty cycle, metallic loop of sufficient inductance and low resistance, power matching) gradient switching-induced heating of conductive specimens must be considered.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Ke-Wei; Division of Materials Science, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798; Fujihashi, Yuta

A master equation approach based on an optimized polaron transformation is adopted for dynamics simulation with simultaneous diagonal and off-diagonal spin-boson coupling. Two types of bath spectral density functions are considered, the Ohmic and the sub-Ohmic. The off-diagonal coupling leads asymptotically to a thermal equilibrium with a nonzero population difference P{sub z}(t → ∞) ≠ 0, which implies localization of the system, and it also plays a role in restraining coherent dynamics for the sub-Ohmic case. Since the new method can extend to the stronger coupling regime, we can investigate the coherent-incoherent transition in the sub-Ohmic environment. Relevant phase diagramsmore » are obtained for different temperatures. It is found that the sub-Ohmic environment allows coherent dynamics at a higher temperature than the Ohmic environment.« less

Microwave ablation versus radiofrequency ablation in the kidney: high-power triaxial antennas create larger ablation zones than similarly sized internally cooled electrodes.

PubMed

Laeseke, Paul F; Lee, Fred T; Sampson, Lisa A; van der Weide, Daniel W; Brace, Christopher L

2009-09-01

To determine whether microwave ablation with high-power triaxial antennas creates significantly larger ablation zones than radiofrequency (RF) ablation with similarly sized internally cooled electrodes. Twenty-eight 12-minute ablations were performed in an in vivo porcine kidney model. RF ablations were performed with a 200-W pulsed generator and either a single 17-gauge cooled electrode (n = 9) or three switched electrodes spaced 1.5 cm apart (n = 7). Microwave ablations were performed with one (n = 7), two (n = 3), or three (n = 2) 17-gauge triaxial antennas to deliver 90 W continuous power per antenna. Multiple antennas were powered simultaneously. Temperatures 1 cm from the applicator were measured during two RF and microwave ablations each. Animals were euthanized after ablation and ablation zone diameter, cross-sectional area, and circularity were measured. Comparisons between groups were performed with use of a mixed-effects model with P values less than .05 indicating statistical significance. No adverse events occurred during the procedures. Three-electrode RF (mean area, 14.7 cm(2)) and single-antenna microwave (mean area, 10.9 cm(2)) ablation zones were significantly larger than single-electrode RF zones (mean area, 5.6 cm(2); P = .001 and P = .0355, respectively). No significant differences were detected between single-antenna microwave and multiple-electrode RF. Ablation zone circularity was similar across groups (P > .05). Tissue temperatures were higher during microwave ablation (maximum temperature of 123 degrees C vs 100 degrees C for RF). Microwave ablation with high-power triaxial antennas created larger ablation zones in normal porcine kidneys than RF ablation with similarly sized applicators.

Voltage-induced Metal-Insulator Transitions in Perovskite Oxide Thin Films Doped with Strongly Correlelated Electrons

NASA Astrophysics Data System (ADS)

Wang, Yudi; Gil Kim, Soo; Chen, I.-Wei

2007-03-01

We have observed a reversible metal-insulator transition in perovskite oxide thin films that can be controlled by charge trapping pumped by a bipolar voltage bias. In the as-fabricated state, the thin film is metallic with a very low resistance comparable to that of the metallic bottom electrode, showing decreasing resistance with decreasing temperature. This metallic state switches to a high-resistance state after applying a voltage bias: such state is non-ohmic showing a negative temperature dependence of resistance. Switching at essentially the same voltage bias was observed down to 2K. The metal-insulator transition is attributed to charge trapping that disorders the energy of correlated electron states in the conduction band. By increasing the amount of charge trapped, which increases the disorder relative to the band width, increasingly more insulating states with a stronger temperature dependence of resistivity are accessed. This metal-insulator transition provides a platform to engineer new nonvolatile memory that does not require heat (as in phase transition) or dielectric breakdown (as in most other oxide resistance devices).

Light-induced new memory states in electronic resistive switching of NiO/NSTO junction

NASA Astrophysics Data System (ADS)

Wei, Ling; Li, G. Q.; Zhang, W. F.

2016-02-01

n-type and p-type NiO films were prepared on SrTiO3:Nb (NSTO) by controlling oxygen pressures during the process of pulsed laser deposition. The results of current-voltage (I-V) characteristics and photocurrent investigation indicate that the junction shows a typical electronic bipolar resistive switching (RS) behavior and the optical injection can add new resistance states. Photocurrents can obviously be modulated by different resistance states of NiO/NSTO junction. The linear fitting results of I-V curves reveal that the low resistance state follows Ohmic behavior and the high resistance state follows Schottky-emission mechanism. The depletion widths under forward and reverse bias in the dark and with the illumination were estimated respectively. Combined with the energy band structure, the mechanism of RS and photoresponse in the NiO/NSTO junction can be attributed to the variance of interfacial barrier during electrical and optical injection. These results pave the way for the application of the NiO/NSTO junction in the multilevel storage of optical-electrical devices.

Resistive switching characteristics of solution-processed Al-Zn-Sn-O films annealed by microwave irradiation

NASA Astrophysics Data System (ADS)

Kim, Tae-Wan; Baek, Il-Jin; Cho, Won-Ju

2018-02-01

In this study, we employed microwave irradiation (MWI) at low temperature in the fabrication of solution-processed AlZnSnO (AZTO) resistive random access memory (ReRAM) devices with a structure of Ti/AZTO/Pt and compared the memory characteristics with the conventional thermal annealing (CTA) process. Typical bipolar resistance switching (BRS) behavior was observed in AZTO ReRAM devices treated with as-deposited (as-dep), CTA and MWI. In the low resistance state, the Ohmic conduction mechanism describes the dominant conduction of these devices. On the other hand, the trap-controlled space charge limited conduction (SCLC) mechanism predominates in the high resistance state. The AZTO ReRAM devices processed with MWI showed larger memory windows, uniform distribution of resistance state and operating voltage, stable DC durability (>103 cycles) and stable retention characteristics (>104 s). In addition, the AZTO ReRAM devices treated with MWI exhibited multistage storage characteristics by modulating the amplitude of the reset bias, and eight distinct resistance levels were obtained with stable retention capability.

Effect of nitrogen-accommodation ability of electrodes in SiNx-based resistive switching devices

NASA Astrophysics Data System (ADS)

Yang, Mei; Wang, Hong; Ma, Xiaohua; Gao, Haixia; Wang, Bin

2017-12-01

Nitrides could create opportunities of tuning resistive-switching (RS) characteristics due to their different electrical properties and ionic chemistry with oxides. Here, we reported on the effect of nitrogen-accommodation ability of electrodes in SiNx-based RS devices. The Ti/SiNx/Pt devices show a self-compliance bipolar RS with excellent reliability. The W/SiNx/Pt devices provide an unstable RS and fall to an intermediate resistance state (IRS) after a set process. The low resistance states of the Ti/SiNx/Pt devices obey Ohmic conduction and Frenkel-Poole emission from a conductive channel. The IRS of the W/SiNx/Pt devices conforms to Schottky emission and Fowler-Nordheim tunneling from a conductive channel/insulator/electrode structure. A nitrogen-ion-based model is proposed to explain the experimental results. According to the model, the nitrogen-accommodation ability of the electrodes dominates the nitrogen-reservoir size and the nitrogen-ion migration at the metal/SiNx interface, modulating the RS characteristics of the SiNx memory devices.

Reconfigurable microwave photonic repeater for broadband telecom missions: concepts and technologies

NASA Astrophysics Data System (ADS)

Aveline, M.; Sotom, M.; Barbaste, R.; Benazet, B.; Le Kernec, A.; Magnaval, J.; Ginestet, P.; Navasquillo, O.; Piqueras, M. A.

2017-11-01

Thales Alenia Space has elaborated innovative telecom payload concepts taking benefit from the capabilities of photonics and so-called microwave photonics. The latter consists in transferring RF/microwave signals on optical carriers and performing processing in the optical domain so as to benefit from specific attributes such as wavelength-division multiplexing or switching capabilities.

Failover Switching Tests Between Two RF Communications Links

NASA Technical Reports Server (NTRS)

Brooks, David; Frantz, Brian; Hoder, Doug; Wilkins, Ryan

2003-01-01

This work presents a short report on the routing tests of the Ku band satcom and VHF line-of-sight communications systems on the Advanced Air Transportation Technologies (AATT) Aero/Mobile van. The first section is a description of the equipment used, followed by descriptions of the tests, the theoretical results, and finally, conclusions and the actual data.

Application of advanced on-board processing concepts to future satellite communications systems

NASA Technical Reports Server (NTRS)

Katz, J. L.; Hoffman, M.; Kota, S. L.; Ruddy, J. M.; White, B. F.

1979-01-01

An initial definition of on-board processing requirements for an advanced satellite communications system to service domestic markets in the 1990's is presented. An exemplar system architecture with both RF on-board switching and demodulation/remodulation baseband processing was used to identify important issues related to system implementation, cost, and technology development.

An explicit scheme for ohmic dissipation with smoothed particle magnetohydrodynamics

NASA Astrophysics Data System (ADS)

Tsukamoto, Yusuke; Iwasaki, Kazunari; Inutsuka, Shu-ichiro

2013-09-01

In this paper, we present an explicit scheme for Ohmic dissipation with smoothed particle magnetohydrodynamics (SPMHD). We propose an SPH discretization of Ohmic dissipation and solve Ohmic dissipation part of induction equation with the super-time-stepping method (STS) which allows us to take a longer time step than Courant-Friedrich-Levy stability condition. Our scheme is second-order accurate in space and first-order accurate in time. Our numerical experiments show that optimal choice of the parameters of STS for Ohmic dissipation of SPMHD is νsts ˜ 0.01 and Nsts ˜ 5.

Memristive switching induced by 100 MeV Ag7+ ion irradiation in Ag/La0.7Sr0.3MnO3/Ag planar structures

NASA Astrophysics Data System (ADS)

Bhavsar, K. H.; Joshi, U. S.; Mistry, B. V.; Khan, S. A.; Avasthi, D. K.

2011-09-01

Resistive random access memory is one of the candidate technologies for the promising next generation non-volatile memories with fast switching speed, low power consumption and non-destructive readout. The swift heavy ion (SHI)-induced resistive switching behavior of Ag/La0.7Sr0.3MnO3/Ag planar structures, grown on SiO2 substrates by the chemical solution deposition technique, has been investigated. Five identical samples were irradiated by 100 MeV Ag7+ ions with fluence values ranging from 1×1011 to 5×1013 ions/cm2 at the Materials Science beamline of the IUAC, New Delhi. Upon irradiation, systematic amorphization and grain elongation was observed in the grazing incidence X-ray diffraction and atomic force microscopy, respectively. Four-terminal I-V curves indicate typical non-ohmic behavior of pristine Ag/La0.7Sr0.3MnO3/Ag planar geometry at room temperature for several voltage-sweeping cycles. On the other hand, well-defined hysteresis loops with sharp on-off transition in the I-V curves were observed for the sample irradiated with 100 MeV Ag7+ ions at 1×1012 ions/cm2, indicating that the sample possesses low resistance state and high resistance state. A symmetrical resistance ratio (R high/R low) of ∼ 330% at-1.7 V has been achieved. The resistance switching is bipolar and may be attributed to SHI-induced defects in the device. Such defect-induced resistive switching has recently been proposed theoretically, and our results are direct evidence of the phenomenon.

Beam Measurement of 11.424 GHz X-Band Linac for Compton Scattering X-ray Source

NASA Astrophysics Data System (ADS)

Natsui, Takuya; Mori, Azusa; Masuda, Hirotoshi; Uesaka, Mitsuru; Sakamoto, Fumito

2010-11-01

An inverse Compton scattering X-ray source for medical applications, consisting of an X-band (11.424 GHz) linac and Q-switched Nd:YAG laser, is currently being developed at the University of Tokyo. This system uses an X-band 3.5-cell thermionic cathode RF gun for electron beam generation. We can obtain a multi-bunch electron beam with this gun. The beam is accelerated to 30 MeV by a traveling-wave accelerating tube. So far, we have verified stable beam generation (around 2.3 MeV) by using the newly designed RF gun and we have succeeded in beam transportation to a beam dump.

Investigation of microstructural and electrical properties of composition dependent co-sputtered Hf1-x Ta x O2 thin films

NASA Astrophysics Data System (ADS)

Das, K. C.; Tripathy, N.; Ghosh, S. P.; Mohanta, S. K.; Nakamura, A.; Kar, J. P.

2017-11-01

Tantalum doped HfO2 gate dielectric thin films were deposited on silicon substrates using RF reactive co-sputtering by varying RF power of Ta target from 15 W to 90 W. The morphological, compositional and electrical properties of Hf1-x Ta x O2 films were systematically investigated. The Ta content was found to be increased up to 21% for a Ta target power of 90 W. The evolution of monoclinic phase of Hf1-x Ta x O2 was seen from XRD study upto RF power of 60 W and afterwards, the amorphous like behaviour is appeared. The featureless smooth surface with the decrease in granular morphology has been observed from FESEM micrographs of the doped films at higher RF powers of Ta. The flatband voltage is found to be shifted towards negative voltage in the capacitance-voltage plot, which was attributed to the enhancement in positive oxide charge density with rise in RF power. The interface charge density has a minimum value of 7.85  ×  1011 eV-1 cm-2 for the film deposited at Ta RF power of 75 W. The Hf1-x Ta x O2 films deposited at Ta target RF power of 90 W has shown lower leakage current. The high on/off ratio of the current during the set process in Hf1-x Ta x O2 based memristors is found suitable for bipolar resistive switching memory device applications.

Micromachined sensor for stress measurement and micromechanical study of free-standing thin films for MEMS applications

NASA Astrophysics Data System (ADS)

Zhang, Ping

Microelectromechanical systems (MEMS) have a wide range of applications. In the field of wireless and microwave technology, considerable attention has been given to the development and integration of MEMS-based RF (radio frequency) components. An RF MEMS switch requires low insertion loss, high isolation, and low actuation voltage - electrical aspects that have been extensively studied. The mechanical requirements of the switch, such as low sensitivity to built-in stress and high reliability, greatly depend on the micromechanical properties of the switch materials, and have not been thoroughly explored. RF MEMS switches are typically in the form of a free-standing thin film structure. Large stress gradients and across-wafer stress variations developed during fabrication severely degrade their electrical performance. A micromachined stress measurement sensor has been developed that can potentially be employed for in-situ monitoring of stress evolution and stress variation. The sensors were micromachined using five masks on two wafer levels, each measuring 5x3x1 mm. They function by means of an electron tunneling mechanism, where a 2x2 mm silicon nitride membrane elastically deflects under an applied deflection voltage via an external feedback circuitry. For the current design, the sensors are capable of measuring tensile stresses up to the GPa range under deflection voltages of 50--100 V. Sensor functionality was studied by finite element modeling and a theoretical analysis of square membrane deflection. While the mechanical properties of thin films on substrates have been extensively studied, studies of free-standing thin films have been limited due to the practical difficulties in sample handling and testing. Free-standing Al and Al-Ti thin films specimens have been successfully fabricated and microtensile and stress relaxation tests have been performed using a custom-designed micromechanical testing apparatus. A dedicated TEM (transmission electron microscopy) sample preparation technique allows the investigation of the microstructures of these thin films both before and after mechanical testing to correlate the microstructural findings with the mechanical behavior. Major studies include grain boundary strengthening in pure Al, plastic deformation in pure Al by inhomogeneous deformation and localized grain thinning, solid solution and precipitate strengthening in Al-Ti alloys, and stress relaxation of Al and Al-Ti.

Novel flat datacenter network architecture based on scalable and flow-controlled optical switch system.

PubMed

Miao, Wang; Luo, Jun; Di Lucente, Stefano; Dorren, Harm; Calabretta, Nicola

2014-02-10

We propose and demonstrate an optical flat datacenter network based on scalable optical switch system with optical flow control. Modular structure with distributed control results in port-count independent optical switch reconfiguration time. RF tone in-band labeling technique allowing parallel processing of the label bits ensures the low latency operation regardless of the switch port-count. Hardware flow control is conducted at optical level by re-using the label wavelength without occupying extra bandwidth, space, and network resources which further improves the performance of latency within a simple structure. Dynamic switching including multicasting operation is validated for a 4 x 4 system. Error free operation of 40 Gb/s data packets has been achieved with only 1 dB penalty. The system could handle an input load up to 0.5 providing a packet loss lower that 10(-5) and an average latency less that 500 ns when a buffer size of 16 packets is employed. Investigation on scalability also indicates that the proposed system could potentially scale up to large port count with limited power penalty.

Research and development on advanced silicon carbide thin film growth techniques and fabrication of high power and microwave frequency silicon carbide-based device structures

NASA Astrophysics Data System (ADS)

Davis, Robert F.

1990-12-01

The RF operation of MESFETs and bipolar transistors fabricated from both alpha- and beta-SiC have been modeled. The results show that SiC has considerable promise for producing microwave power MESFETs with RF output power capability greater (approx. 4 times) than can be obtained with any of the commonly used semiconductors (e.g., GaAs), this due to the high breakdown field of SiC that allows high bias voltage to be applied. These device modeling efforts have been used as a guide to design a new MESFET mask set with a aS micron gate length and reduced gate pad area. For the first time, positive gain was observed for a SiC transistor at microwave frequencies. The highest values for Ft and Fmax were 2.9 GHz and 1.9 GHz, respectively. The highest current and power gains observed at 1.0 GHz were 8.5 dB and 7 db, respectively. Avalanche characteristics for a 6H-SiC IMPATT were observed for the first time. Heteroepitaxial growth of Ti on (0001) 6H-SiC has been achieved at room and elevated temperatures. Current voltage measurements display shifts toward ohmic behavior after annealing at 400 C. Molecular beam epitaxy equipment has been designed and commissioned.

A Model-Based Fast Protection System for High-Power RF Tube Amplifiers Used at the European XFEL Accelerator

NASA Astrophysics Data System (ADS)

Butkowski, Łukasz; Vogel, Vladimir; Schlarb, Holger; Szabatin, Jerzy

2017-06-01

The driving engine of the superconducting accelerator of the European X-ray free electron laser (XFEL) is a set of 27 radio frequency (RF) stations. Each of the underground RF stations consists of a multibeam horizontal klystron that can provide up to 10 MW of power at 1.3 GHz. Klystrons are sensitive devices with a limited lifetime and a high mean time between failures. In real operation, the lifetime of the tube can be significantly reduced because of failures. The special fast protection klystron lifetime management (KLM) system has been developed to minimize the influence of service conditions on the lifetime of klystrons. The main task of this system is to detect all events which can destroy the tube as quickly as possible, and switch off the driving RF signal or the high voltage. Detection of events is based on a comparison of the value of the real signal obtained at the system output with the value estimated on the basis of a high-power RF amplifier model and input signals. The KLM system has been realized in field-programmable gate array (FPGA) and implemented in XFEL. Implementation is based on the standard low-level RF micro telecommunications computing architecture (MTCA.4 or xTCA). The main part of the paper focuses on an estimation of the klystron model and the implementation of KLM in FPGA. The results of the performance of the KLM system will also be presented.

Probing domain switching dynamics in ferroelectric thick films by small field e31,f piezoelectric measurement

NASA Astrophysics Data System (ADS)

Cheng, Hongbo; Ouyang, Jun; Kanno, Isaku

2017-07-01

Epitaxial Pb(Zr0.53Ti0.47)O3 films were grown on (001) Pt/(001) MgO via rf-magnetron sputtering. Switching dynamics of 90° and 180° domains under bi-polar electric fields were probed by using small-field e31 ,f measurements in which the evolution of the transverse piezoelectric response with the bias voltage represents a set of fingerprints of the evolving domain structure. Furthermore, the asymmetric e31 ,f-V curves revealed a strong built-in electric field, which was verified by the standard polarization-electric field hysteresis measurement. Finally, X-ray 2θ-scan patterns under DC bias voltages were collected for the piezoelectric specimen. The domain switching sequence indicated by the XRD results is consistent with that revealed by the e31 ,f measurement.

High voltage systems (tube-type microwave)/low voltage system (solid-state microwave) power distribution

NASA Technical Reports Server (NTRS)

Nussberger, A. A.; Woodcock, G. R.

1980-01-01

SPS satellite power distribution systems are described. The reference Satellite Power System (SPS) concept utilizes high-voltage klystrons to convert the onboard satellite power from dc to RF for transmission to the ground receiving station. The solar array generates this required high voltage and the power is delivered to the klystrons through a power distribution subsystem. An array switching of solar cell submodules is used to maintain bus voltage regulation. Individual klystron dc voltage conversion is performed by centralized converters. The on-board data processing system performs the necessary switching of submodules to maintain voltage regulation. Electrical power output from the solar panels is fed via switch gears into feeder buses and then into main distribution buses to the antenna. Power also is distributed to batteries so that critical functions can be provided through solar eclipses.

Double Q-switch Ho:Sc2SiO5 laser by acousto-optic modulator combined with Cr2+:ZnSe saturable absorber

NASA Astrophysics Data System (ADS)

Yang, Xiao-tao; Zhang, Peng; Xie, Wen-qiang; Li, Lin-jun

2018-01-01

A double Q-switch (DQS) Ho:Sc2SiO5 laser modulated by a acousto-optic modulators (AOM) combined with a Cr2+:ZnSe saturable absorber (SA) was reported for the first time. The actively Q-switch (AQS) and passively Q-switch (PQS) were also studied. For the DQS mode, a maximum average output power of 2.49 W under the incident pump power of 12.5 W was obtained, corresponding to a slope efficiency of 24%. The characteristics of the DQS Ho:SSO laser versus different repetition frequencies (RF) of the AOM were researched. The maximum single-pulse energy of the DQS Ho:SSO laser was calculated to 1.98 mJ. The maximum peak power of the DQS Ho:SSO laser was 49.5 kW. The output beam quality factor M2 of DQS Ho:SSO laser was measured to be 1.15 with the highest peak power by knife-edge method at different positions.

Insulator Charging in RF MEMS Capacitive Switches

DTIC Science & Technology

2005-06-01

and Simulations,” Journal of Microelectromechanical Systems, 8: 208-217 (June 1999). 5. Neaman , Donald. Semiconductor Physics & Devices. Boston...227-230 (2001). 5. Sze, S.M. Semiconductor Devices: Physics and Technology. New York: Wiley, 1985. 6. Neaman , Donald A. Semiconductor Physics...Radiation Response of Hafnium-Silicate Capacitors,” IEEE Transactions on Nuclear Science, 49: 3191-3196 (December 2002). 3. Neaman , D.A

55. View from ground level in building no. 105 showing ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

55. View from ground level in building no. 105 showing lower radar scanner switch with eighty-eight 1-1/2" diameter copper ion return RF balance tube systems. - Clear Air Force Station, Ballistic Missile Early Warning System Site II, One mile west of mile marker 293.5 on Parks Highway, 5 miles southwest of Anderson, Anderson, Denali Borough, AK

Wavefront Correction for Large, Flexible Antenna Reflector

NASA Technical Reports Server (NTRS)

Imbriale, William A.; Jammejad, Vahraz; Rajagopalan, Harish; Xu, Shenheng

2010-01-01

A wavefront-correction system has been proposed as part of an outer-space radio communication system that would include a large, somewhat flexible main reflector antenna, a smaller subreflector antenna, and a small array feed at the focal plane of these two reflector antennas. Part of the wavefront-correction system would reside in the subreflector, which would be a planar patch-element reflectarray antenna in which the phase shifts of the patch antenna elements would be controlled via microelectromechanical systems (MEMS) radio -frequency (RF) switches. The system would include the following sensing-and-computing subsystems: a) An optical photogrammetric subsystem built around two cameras would estimate geometric distortions of the main reflector; b) A second subsystem would estimate wavefront distortions from amplitudes and phases of signals received by the array feed elements; and c) A third subsystem, built around small probes on the subreflector plane, would estimate wavefront distortions from differences among phases of signals received by the probes. The distortion estimates from the three subsystems would be processed to generate control signals to be fed to the MEMS RF switches to correct for the distortions, thereby enabling collimation and aiming of the received or transmitted radio beam to the required precision.

Multiplexed HTS rf SQUID magnetometer array for eddy current testing of aircraft rivet joints

NASA Astrophysics Data System (ADS)

Gärtner, S.; Krause, H.-J.; Wolters, N.; Lomparski, D.; Wolf, W.; Schubert, J.; Kreutzbruck, M. v.; Allweins, K.

2002-05-01

Using three rf SQUID magnetometers, a multiplexed SQUID array was implemented. The SQUIDs are positioned in line with 7 mm spacing and operated using one feedback electronics with sequential read out demodulation at different radio frequencies (rf). The cross-talk between SQUID channels was determined to be negligible. To show the performance of the SQUID array, eddy current (EC) measurements of aluminum aircraft samples in conjunction with a differential (double-D) EC excitation and lock-in readout were carried out. With computer-controlled continuous switching of the SQUIDs during the scan, three EC signal traces of the sample are obtained simultaneously. We performed measurements with an EC excitation frequency of 135 Hz to localize an artificial crack (sawcut flaw) of 20 mm length in an aluminum sheet with 0.6 mm thickness. The flaw was still detected when covered with aluminum of up to 10 mm thickness. In addition, measurements with varying angles between scanning direction and flaw orientation are presented.

Comprehensive analysis of sub-20 nm black phosphorus based junctionless-recessed channel MOSFET for analog/RF applications

NASA Astrophysics Data System (ADS)

Kumar, Ajay; Tripathi, M. M.; Chaujar, Rishu

2018-04-01

In this work, a comprehensive analog and RF performance of a novel Black Phosphorus-Junctionless-Recessed Channel (BP-JL-RC) MOSFET has been explored at 45 nm technology node (Gate length = 20 nm). The integration of black phosphorus with junctionless recessed channel MOSFET, leads to higher drain current of about 0.3 mA and excellent switching ratio (of the order of 1011) due to reduced off-current which leads to improvement in sub-threshold slope (SS) (67mV/dec). Further, RF performance metrics have also been studied with an aim to analyze high-frequency performance. The following FOMs have been evaluated: cut-off frequency (fT), maximum oscillator frequency (fMAX), stern stability factor, various power gains and parasitic capacitances at THz frequency range. Thus, in addition to the high packing density offered by RC MOSFET, the proposed design finds numerous application at THz frequency making it a promising candidate at wafer scale integration level.

Mixed-signal 0.18μm CMOS and SiGe BiCMOS foundry technologies for ROIC applications

NASA Astrophysics Data System (ADS)

Kar-Roy, Arjun; Howard, David; Racanelli, Marco; Scott, Mike; Hurwitz, Paul; Zwingman, Robert; Chaudhry, Samir; Jordan, Scott

2010-10-01

Today's readout integrated-circuits (ROICs) require a high level of integration of high performance analog and low power digital logic. TowerJazz offers a commercial 0.18μm CMOS technology platform for mixed-signal, RF, and high performance analog applications which can be used for ROIC applications. The commercial CA18HD dual gate oxide 1.8V/3.3V and CA18HA dual gate oxide 1.8V/5V RF/mixed signal processes, consisting of six layers of metallization, have high density stacked linear MIM capacitors, high-value resistors, triple-well isolation and thick top aluminum metal. The CA18HA process also has scalable drain extended LDMOS devices, up to 40V Vds, for high-voltage sensor applications, and high-performance bipolars for low noise requirements in ROICs. Also discussed are the available features of the commercial SBC18 SiGe BiCMOS platform with SiGe NPNs operating up to 200/200GHz (fT/fMAX frequencies in manufacturing and demonstrated to 270 GHz fT, for reduced noise and integrated RF capabilities which could be used in ROICs. Implementation of these technologies in a thick film SOI process for integrated RF switch and power management and the availability of high fT vertical PNPs to enable complementary BiCMOS (CBiCMOS), for RF enabled ROICs, are also described in this paper.

Biasable, Balanced, Fundamental Submillimeter Monolithic Membrane Mixer

NASA Technical Reports Server (NTRS)

Siegel, Peter; Schlecht, Erich; Mehdi, Imran; Gill, John; Velebir, James; Tsang, Raymond; Dengler, Robert; Lin, Robert

2010-01-01

This device is a biasable, submillimeter-wave, balanced mixer fabricated using JPL s monolithic membrane process a simplified version of planar membrane technology. The primary target application is instrumentation used for analysis of atmospheric constituents, pressure, temperature, winds, and other physical and chemical properties of the atmospheres of planets and comets. Other applications include high-sensitivity gas detection and analysis. This innovation uses a balanced configuration of two diodes allowing the radio frequency (RF) signal and local oscillator (LO) inputs to be separated. This removes the need for external diplexers that are inherently narrowband, bulky, and require mechanical tuning to change frequency. Additionally, this mixer uses DC bias-ability to improve its performance and versatility. In order to solve problems relating to circuit size, the GaAs membrane process was created. As much of the circuitry as possible is fabricated on-chip, making the circuit monolithic. The remainder of the circuitry is precision-machined into a waveguide block that holds the GaAs circuit. The most critical alignments are performed using micron-scale semiconductor technology, enabling wide bandwidth and high operating frequencies. The balanced mixer gets superior performance with less than 2 mW of LO power. This can be provided by a simple two-stage multiplier chain following an amplifier at around 90 GHz. Further, the diodes are arranged so that they can be biased. Biasing pushes the diodes closer to their switching voltage, so that less LO power is required to switch the diodes on and off. In the photo, the diodes are at the right end of the circuit. The LO comes from the waveguide at the right into a reduced-height section containing the diodes. Because the diodes are in series to the LO signal, they are both turned on and off simultaneously once per LO cycle. Conversely, the RF signal is picked up from the RF waveguide by the probe at the left, and flows rightward to the diodes. Because the RF is in a quasi- TEM (suspended, microstrip-like) mode, it impinges on the diodes in an anti-parallel mode that does not couple to the waveguide mode. This isolates the LO and RF signals. This operation is similar to a cross-bar mixer used at low frequencies, except the RF signal enters through the back-short end of the waveguide rather than through the side. The RF probe also conveys the down-converted intermediate frequency (IF) signal out to an off-chip circuit board through a simple LC low-pass filter to the left as indicated. The bias is brought to the diodes through a bypass capacitor at the top.

A liquid lens switching-based motionless variable fiber-optic delay line

NASA Astrophysics Data System (ADS)

Khwaja, Tariq Shamim; Reza, Syed Azer; Sheikh, Mumtaz

2018-05-01

We present a Variable Fiber-Optic Delay Line (VFODL) module capable of imparting long variable delays by switching an input optical/RF signal between Single Mode Fiber (SMF) patch cords of different lengths through a pair of Electronically Controlled Tunable Lenses (ECTLs) resulting in a polarization-independent operation. Depending on intended application, the lengths of the SMFs can be chosen accordingly to achieve the desired VFODL operation dynamic range. If so desired, the state of the input signal polarization can be preserved with the use of commercially available polarization-independent ECTLs along with polarization-maintaining SMFs (PM-SMFs), resulting in an output polarization that is identical to the input. An ECTL-based design also improves power consumption and repeatability. The delay switching mechanism is electronically-controlled, involves no bulk moving parts, and can be fully-automated. The VFODL module is compact due to the use of small optical components and SMFs that can be packaged compactly.

Ohmic Heating: An Emerging Concept in Organic Synthesis.

PubMed

Silva, Vera L M; Santos, Luis M N B F; Silva, Artur M S

2017-06-12

The ohmic heating also known as direct Joule heating, is an advanced thermal processing method, mainly used in the food industry to rapidly increase the temperature for either cooking or sterilization purposes. Its use in organic synthesis, in the heating of chemical reactors, is an emerging method that shows great potential, the development of which has started recently. This Concept article focuses on the use of ohmic heating as a new tool for organic synthesis. It presents the fundamentals of ohmic heating and makes a qualitative and quantitative comparison with other common heating methods. A brief description of the ohmic reactor prototype in operation is presented as well as recent examples of its use in organic synthesis at laboratory scale, thus showing the current state of the research. The advantages and limitations of this heating method, as well as its main current applications are also discussed. Finally, the prospects and potential implications of ohmic heating in future research in chemical synthesis are proposed. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Human auditory system response to pulsed radiofrequency energy in RF coils for magnetic resonance at 2.4 to 170 MHz.

PubMed

Röschmann, P

1991-10-01

The threshold conditions for an auditory perception of pulsed radiofrequency (RF) energy absorption in the human head have been studied on six volunteers with RF coils for magnetic resonance (MR) imaging. For homogeneous RF exposure with MR head coils in the 2.4- to 170-MHz range and pulse widths 3 microseconds less than or equal to Tp less than 100 microseconds, the auditory thresholds were observed at 16 +/- 4 mJ pulse energy. Localized RF exposure with optimized surface coils positioned flush with the ear lowers the auditory threshold to only 3 +/- 0.6 mJ. The hearing threshold of RF pulses with Tp greater than 200 microseconds occurs at more or less constant peak power levels of typically 150 +/- 50 W for head coils and as low as 20 W for surface coils. The results from this study confirm theoretical predictions from a thermoelastic expansion model and compare well with reported thresholds from near field antenna measurements at 425 to 3000 MHz. Details of the threshold dependence on RF pulse length reveal primary sites of RF to acoustic energy conversion at the mastoid and temporal bone region and the outer layer of the brain from where thermoelastically generated pressure transients excite audible pressure waves at the resonance modes of the skull around 1.7 kHz and of the brain around 11 kHz. If not masked by usually dominating noise from switched gradients, the conditions for hearing RF pulses, as applied to head coils in MR studies with flip angle alpha at main field B0, is given by Tp/ms less than or equal to 0.4 (alpha/pi)B0/[T]. At peak power levels up to 15 kW presently available in clinical MR systems, there is no evidence known for detrimental health effects arising from the RF auditory phenomenon which is a secondary cause associated with primary RF to thermal energy conversion in body tissues. To avoid the RF-evoked sound pressure levels in the head rising above the discomfort threshold at 110 dB SPL, an upper limit of 30 kW applied peak pulse power is suggested for head coils and 6 kW for surface coils.

Electrically Tuneable EBG Integrated Circuits

DTIC Science & Technology

2013-12-01

Surface Wave Propagation Along a Modulated Microstrip -Line-Based High Impedance Surface,‖ IEEE Trans. Antennas and Propagat., Vol. 56, No. 8, August...Heimlich, “Reconfigurable half- width microstrip leaky-wave antenna for fixed-frequency beam scanning”, Proceedings of 7th IEEE European Conference...patches, the structure would be an ideal microstrip configuration. Tuning is accomplished by using a pair of RF/microwave switches at opposite ends

High quality factor, fully switchable terahertz superconducting metasurface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scalari, G., E-mail: scalari@phys.ethz.ch; Maissen, C.; Faist, J.

2014-12-29

We present a complementary THz metasurface realised with Niobium thin film which displays a quality factor Q = 54 and a fully switchable behaviour as a function of the temperature. The switching behaviour and the high quality factor are due to a careful design of the metasurface aimed at maximising the ohmic losses when the Nb is above the critical temperature and minimising the radiative coupling. The superconductor allows the operation of the cavity with high Q and the use of inductive elements with a high aspect ratio. Comparison with three dimensional finite element simulations highlights the crucial role of the inductivemore » elements and of the kinetic inductance of the Cooper pairs in achieving the high quality factor and the high field enhancement.« less

The Selection of Q-Switch for a 350mJ Air-borne 2-micron Wind Lidar

NASA Technical Reports Server (NTRS)

Petros, Mulugeta; Yu, Jirong; Trieu, Bo; Bai, Yingxin; Petzar, Paul; Singh, Upendra N.

2008-01-01

In the process of designing a coherent, high energy 2micron, Doppler wind Lidar, various types of Q-Switch materials and configurations have been investigated for the oscillator. Designing an oscillator with a relatively low gain laser material, presents challenges related to the management high internal circulating fluence due to high reflective output coupler. This problem is compounded by the loss of hold-off. In addition, the selection has to take into account the round trip optical loss in the resonator and the loss of hold-off. For this application, a Brewster cut 5mm aperture, fused silica AO Q-switch is selected. Once the Q-switch is selected various rf frequencies were evaluated. Since the Lidar has to perform in single longitudinal and transverse mode with transform limited line width, in this paper, various seeding configurations are presented in the context of Q-Switch diffraction efficiency. The master oscillator power amplifier has demonstrated over 350mJ output when the amplifier is operated in double pass mode and higher than 250mJ when operated in single pass configuration. The repetition rate of the system is 10Hz and the pulse length 200ns.

Spin-Torque Diode Effect in Magnetic Tunnel Junctions

NASA Astrophysics Data System (ADS)

Suzuki, Yoshishige

2007-03-01

Spin-injection magnetization switching (SIMS) technique [1] made it possible to control magnetization by a direct current. A discovery of spontaneous rf oscillation from CPP-GMR nano-pillars and a real time observation of the switching process have revealed essential amplification function of a precession in the magnetic nano-pillars under a direct current [2]. Beside of those progresses, developments of giant tunneling magneto-resistive (GTMR) effect using an MgO barrier [3] made it possible to utilize a very large resistance change according to the magnetization switching. In this talk, several attempts to utilize interplay between spin-torque and giant-TMR effect will be presented referring to a ``spin-torque diode effect'' [4] and other properties such like rf noise control and possible signal amplification using magnetic tunnel junctions (MTJs). [1] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996) , L. Berger, Phys. Rev. B 54, 9353 (1996), and E. B. Myers, et al., Science 285, 867 (1999). [2] S. I. Kiselev et al., Nature 425, 380 (2003), I. N. Krivorotov et al., Science, 307, 228 (2005). [3] W. Wulfhekel, et al. Appl. Phys. Lett. 78, 509--511 (2001), M. Bowen, et al. Appl. Phys. Lett. 79, 1655--1657 (2001), J. Faure-Vincent, et al. Appl. Phys. Lett. 82, 4507--4509 (2003), S. Yuasa, et al., Jpn. J. Appl. Phys. Part 2, 43, L588 (2004), S. Yuasa, et al., Nature Mat. 3, 868 (2004), S. S. P. Parkin et al., Nature Mat. 3, 862 (2004), and D. D. Djayaprawira et al., Appl. Phys. Lett. 86, 092502 (2005). [4] A. A. Tulapurkar, et al., Nature, 438, 339 (2005).

Edge Ohmic Heating Experiment on HT-6M Tokamak

NASA Astrophysics Data System (ADS)

Gao, Xiang; Fan, Shuping; Li, Jian'gang; Meng, Yuedong; Luo, Jiarong; Yin, Fuxian; Zeng, Lei; Ding, Liancheng; Lin, Bili; Zhang, Wei; Han, Yuqing; Tong, Xingde; Luo, Lanchang; Gong, Xianzu; Jiang, Jiaguang; Wu, Mingjun; Yin, Fei

1994-03-01

An improved ohmic confinement has been achieved on HT-6M tokamak after application of edge ohmic heating pulse which makes plasma current rapidly ramp up (0.4 ms) in a ramp rate of 12 Ma/s. The improved ohmic confinement phase is characterized by (a) energy and particle confinement time increase, (b) non-symmetric increased density ne, (c) reduced Hα radiation, (d) increased Te and steeper Te, ne profile at the edge. The results from soft x-ray sawteeth inversion radius and βp + li/2 implied the anomalous current penetration.

Dual ohmic contact to N- and P-type silicon carbide

NASA Technical Reports Server (NTRS)

Okojie, Robert S. (Inventor)

2013-01-01

Simultaneous formation of electrical ohmic contacts to silicon carbide (SiC) semiconductor having donor and acceptor impurities (n- and p-type doping, respectively) is disclosed. The innovation provides for ohmic contacts formed on SiC layers having n- and p-doping at one process step during the fabrication of the semiconductor device. Further, the innovation provides a non-discriminatory, universal ohmic contact to both n- and p-type SiC, enhancing reliability of the specific contact resistivity when operated at temperatures in excess of 600.degree. C.

Effects of doping concentration ratio on electrical characterization in pseudomorphic HEMT-based MMIC switches for ICT system

NASA Astrophysics Data System (ADS)

Mun, Jae-Kyoung; Oh, Jung-Hun; Sung, Ho-Kun; Wang, Cong

2015-12-01

The effects of the doping concentration ratios between upper and lower silicon planar-doping layers on the DC and RF characteristics of the double planar doped pseudomorphic high electron mobility transistors (pHEMTs) are investigated. From the device simulation, an increase of maximum extrinsic transconductance and a decrease of total on- and off-state capacitances are observed, as well as an increase of the upper to lower planar-doping concentration ratios (UTLPDR), which give rise to an enhancement of the switching speed and isolation characteristics. On the basis of simulation results, two types of pHEMTs are fabricated with two different UTLPDRs of 4:1 and 1:2. After applying these two types' pHEMTs, single-pole-double-throw (SPDT) transmitter/receiver monolithic microwave integrated circuit (MMIC) switches are also designed and fabricated. The SPDT MMIC switch with a 4:1 UTLPDR shows an insertion loss of 0.58 dB, isolation of 40.2 dB, and switching speed of 100 ns, respectively, which correspondingly indicate a 0.23 dB lower insertion loss, 2.90 dB higher isolation and 2.5 times faster switching speed than those of 1:2 UTLPDR at frequency range of 2-6 GHz. From the simulation results and comparative studies, we propose that the UTLPDR must be greater than 4:1 for the best switching performance. With the abovementioned excellent performances, the proposed switch would be quite promising in the application of information and communications technology system.

In situ oxygen plasma cleaning of microswitch surfaces—comparison of Ti and graphite electrodes

NASA Astrophysics Data System (ADS)

Oh, Changho; Streller, Frank; Ashurst, W. Robert; Carpick, Robert W.; de Boer, Maarten P.

2016-11-01

Ohmic micro- and nanoswitches are of interest for a wide variety of applications including radio frequency communications and as low power complements to transistors. In these switches, it is of paramount importance to maintain surface cleanliness in order to prevent frequent failure by tribopolymer growth. To prepare surfaces, an oxygen plasma clean is expected to be beneficial compared to a high temperature vacuum bakeout because of shorter cleaning time (<5 min compared to ~24 h) and active removal of organic contaminants. We demonstrate that sputtering of the electrode material during oxygen plasma cleaning is a critical consideration for effective cleaning of switch surfaces. With Ti electrodes, a TiO x layer forms that increases electrical contact resistance. When plasma-cleaned using graphite electrodes, the resistance of Pt-coated microswitches exhibit a long lifetime with consistently low resistance (<0.5 Ω variation over 300 million cycles) if the test chamber is refilled with ultra-high purity nitrogen and if the devices are not exposed to laboratory air. Their current-voltage characteristic is also linear at the millivolt level. This is important for nanoswitches which will be operated in that range.

Effect of current compliance and voltage sweep rate on the resistive switching of HfO{sub 2}/ITO/Invar structure as measured by conductive atomic force microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, You-Lin, E-mail: ylwu@ncnu.edu.tw; Liao, Chun-Wei; Ling, Jing-Jenn

2014-06-16

The electrical characterization of HfO{sub 2}/ITO/Invar resistive switching memory structure was studied using conductive atomic force microscopy (AFM) with a semiconductor parameter analyzer, Agilent 4156C. The metal alloy Invar was used as the metal substrate to ensure good ohmic contact with the substrate holder of the AFM. A conductive Pt/Ir AFM tip was placed in direct contact with the HfO{sub 2} surface, such that it acted as the top electrode. Nanoscale current-voltage (I-V) characteristics of the HfO{sub 2}/ITO/Invar structure were measured by applying a ramp voltage through the conductive AFM tip at various current compliances and ramp voltage sweep rates.more » It was found that the resistance of the low resistance state (RLRS) decreased with increasing current compliance value, but resistance of high resistance state (RHRS) barely changed. However, both the RHRS and RLRS decreased as the voltage sweep rate increased. The reasons for this dependency on current compliance and voltage sweep rate are discussed.« less

On-board processing satellite network architecture and control study

NASA Technical Reports Server (NTRS)

Campanella, S. Joseph; Pontano, Benjamin A.; Chalmers, Harvey

1987-01-01

The market for telecommunications services needs to be segmented into user classes having similar transmission requirements and hence similar network architectures. Use of the following transmission architecture was considered: satellite switched TDMA; TDMA up, TDM down; scanning (hopping) beam TDMA; FDMA up, TDM down; satellite switched MF/TDMA; and switching Hub earth stations with double hop transmission. A candidate network architecture will be selected that: comprises multiple access subnetworks optimized for each user; interconnects the subnetworks by means of a baseband processor; and optimizes the marriage of interconnection and access techniques. An overall network control architecture will be provided that will serve the needs of the baseband and satellite switched RF interconnected subnetworks. The results of the studies shall be used to identify elements of network architecture and control that require the greatest degree of technology development to realize an operational system. This will be specified in terms of: requirements of the enabling technology; difference from the current available technology; and estimate of the development requirements needed to achieve an operational system. The results obtained for each of these tasks are presented.

Apple snack enriched with L-arginine using vacuum impregnation/ohmic heating technology.

PubMed

Moreno, Jorge; Echeverria, Julian; Silva, Andrea; Escudero, Andrea; Petzold, Guillermo; Mella, Karla; Escudero, Carlos

2017-07-01

Modern life has created a high demand for functional food, and in this context, emerging technologies such as vacuum impregnation and ohmic heating have been applied to generate functional foods. The aim of this research was to enrich the content of the semi-essential amino acid L-arginine in apple cubes using vacuum impregnation, conventional heating, and ohmic heating. Additionally, combined vacuum impregnation/conventional heating and vacuum impregnation/ohmic heating treatments were evaluated. The above treatments were applied at 30, 40 and 50  ℃ and combined with air-drying at 40 ℃ in order to obtain an apple snack rich in L-arginine. Both the impregnation kinetics of L-arginine and sample color were evaluated. The impregnated samples created using vacuum impregnation/ohmic heating at 50 ℃ presented a high content of L-arginine, an effect attributed primarily to electropermeabilization. Overall, vacuum impregnation/ohmic heating treatment at 50 ℃, followed by drying at 40 ℃, was the best process for obtaining an apple snack rich in L-arginine.

Harmonic Kicker RF Cavity for the Jefferson Lab Electron-Ion Collider EM Simulation, Modification, and Measurements

NASA Astrophysics Data System (ADS)

Overstreet, Sarah; Wang, Haipeng

2017-09-01

An important step in the conceptual design for the future Jefferson Lab Electron-Ion Collider (JLEIC) is the development of supporting technologies for the Energy Recovery Linac (ERL) Electron Cooling Facility. The Harmonic Radiofrequency (RF) kicker cavity is one such device that is responsible for switching electron bunches in and out of the Circulator Cooling Ring (CCR) from and to the ERL, which is a critical part of the ion cooling process. Last year, a half scale prototype of the JLEIC harmonic RF kicker model was designed with resonant frequencies to support the summation of 5 odd harmonics (95.26 MHz, 285.78 MHz, 476.30 MHz, 666.82 MHz, and 857.35 MHz); however, the asymmetry of the kicker cavity gives rise to multipole components of the electric field at the electron-beam axis of the cavity. Previous attempts to symmetrize the electric field of this asymmetrical RF cavity have been unsuccessful. The aim of this study is to modify the existing prototype for a uniform electric field across the beam pathway so that the electron bunches will experience nearly zero beam current loading. In addition to this, we have driven the unmodified cavity with the harmonic sum and used the wire stretching method for an analysis of the multipole electric field components.

Design of an RF System for Electron Bernstein Wave Studies in MST

NASA Astrophysics Data System (ADS)

Kauffold, J. X.; Seltzman, A. H.; Anderson, J. K.; Nonn, P. D.; Forest, C. B.

2010-11-01

Motivated by the possibility of current profile control a 5.5GHz RF system for EBW is being developed. The central component is a standard radar Klystron with 1.2MW peak power and 4μs typical pulse length. Meaningful experiments require RF pulse lengths similar to the characteristic electron confinement times in MST necessitating the creation of a power supply providing 80kV at 40A for 10ms. A low inductance IGBT network switches power at 20kHz from an electrolytic capacitor bank into the primary of a three-phase resonant transformer system that is then rectified and filtered. The system uses three magnetically separate transformers with microcrystalline iron cores to provide suitable volt-seconds and low hysteresis losses. Each phase has a secondary with a large leakage inductance and a parallel capacitor providing a boost ratio greater than 60:1 with a physical turns ratio of 13.5:1. A microprocessor feedback control system varies the drive frequency around resonance to regulate the boost ratio and provide a stable output as the storage bank discharges. The completed system will deliver RF to the plasma boundary where coupling to the Bernstein mode and subsequent heating and current drive can occur.

Agile Blocker and Clock Jitter Tolerant Low-Power Frequency Selective Receiver with Energy Harvesting Capability.

PubMed

Hasan, Abul; Helaoui, Mohamed; Ghannouchi, Fadhel M

2017-08-29

In this article, a novel tunable, blocker and clock jitter tolerant, low power, quadrature phase shift frequency selective (QPS-FS) receiver with energy harvesting capability is proposed. The receiver's design embraces and integrates (i) the baseband to radio frequency (RF) impedance translation concept to improve selectivity over that of conventional homodyne receiver topologies and (ii) broadband quadrature phase shift circuitry in the RF path to remove an active multi-phase clock generation circuit in passive mixer (PM) receivers. The use of a single local oscillator clock signal with a passive clock division network improves the receiver's robustness against clock jitter and reduces the source clock frequency by a factor of N, compared to PM receivers using N switches (N≥4). As a consequence, the frequency coverage of the QPS-FS receiver is improved by a factor of N, given a clock source of maximum frequency; and, the power consumption of the whole receiver system can eventually be reduced. The tunable QPS-FS receiver separates the wanted RF band signal from the unwanted blockers/interferers. The desired RF signal is frequency down-converted to baseband, while the undesired blocker/interferer signals are reflected by the receiver, collected and could be energy recycled using an auxiliary energy harvesting device.

Plasma Physics Challenges of MM-to-THz and High Power Microwave Generation

NASA Astrophysics Data System (ADS)

Booske, John

2007-11-01

Homeland security and military defense technology considerations have stimulated intense interest in mobile, high power sources of millimeter-wave to terahertz regime electromagnetic radiation, from 0.1 to 10 THz. While sources at the low frequency end, i.e., the gyrotron, have been deployed or are being tested for diverse applications such as WARLOC radar and active denial systems, the challenges for higher frequency sources have yet to be completely met for applications including noninvasive sensing of concealed weapons and dangerous agents, high-data-rate communications, and high resolution spectroscopy and atmospheric sensing. The compact size requirements for many of these high frequency sources requires miniscule, micro-fabricated slow wave circuits with high rf ohmic losses. This necessitates electron beams with not only very small transverse dimensions but also very high current density for adequate gain. Thus, the emerging family of mm-to-THz e-beam-driven vacuum electronics devices share many of the same plasma physics challenges that currently confront ``classic'' high power microwave (HPM) generators [1] including bright electron sources, intense beam transport, energetic electron interaction with surfaces and rf air breakdown at output windows. Multidimensional theoretical and computational models are especially important for understanding and addressing these challenges. The contemporary plasma physics issues, recent achievements, as well as the opportunities and outlook on THz and HPM will be addressed. [1] R.J. Barker, J.H. Booske, N.C. Luhmann, and G.S. Nusinovich, Modern Microwave and Millimeter-Wave Power Electronics (IEEE/Wiley, 2005).

Performance analysis of RF-sputtered ZnO/Si heterojunction UV photodetectors with high photo-responsivity

NASA Astrophysics Data System (ADS)

Singh, Satyendra Kumar; Hazra, Purnima; Tripathi, Shweta; Chakrabarti, P.

2016-03-01

In this paper, structural, electrical and ultraviolet photodetection parameters of RF sputtered-ZnO/Si heterojunction diodes are analyzed. In this work, ZnO thin film was deposited on bare Si substrate as well as Si substrate coated with ultrathin ZnO seed layer to exhibit the effect of seed layer on device performance. AFM image of as-grown ZnO films have exhibited the uniform growth ZnO film over the whole Si substrate with average roughness of 3.2 nm and 2.83 nm for ZnO with and without seed layer respectively. Stronger peak intensity along (002) direction, as shown in XRD spectra confirm that ZnO film grown on ZnO seed layer is having more stable wurtzite structure. Ti/Al point contacts were deposited on top of the ZnO film and a layer of Al was deposited on bottom of Si substrate for using as ohmic contacts for further device characterization at dark and under UV light of 365 nm wavelength. This process is repeated for both the films sequentially. The photo-responsivity of our proposed devices is calculated as 0.34 A/W for seed layer-mediated devices and 0.26 A/W for devices without seed layer. These values are very high as compare to the reported value of photo-responsivity for same kind of ZnO/Si heterojunction device prototypes prepared by other techniques.

Characterization of the geology, geochemistry, and microbiology of the radio frequency heating demonstration site at the Savannah River Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Eddy Dilek, C.A.; Jarosch, T.R.; Fliermans, C.B.

The overall objective of the Integrated Demonstration Project for the Remediation of Organics at Nonarid Sites at the Savannah River Site (SRS) is to evaluate innovative remediation, characterization, and monitoring systems to facilitate restoration of contaminated sites. The first phase of the demonstration focused on the application and development of in situ air stripping technologies to remediate sediments and groundwater contaminated with volatile organic compounds (VOCs). The second phase focused on the enhancement of the in situ air stripping process by adding selected nutrients to stimulate naturally occurring microorganisms that degrade VOCs. The purpose of the third phase was tomore » evaluate the use of heating technologies [radio frequency (rf) and ohmic heating] to enhance the removal of contamination from clay layers where mass transfer is limited. The objective of this report is to document pretest and post-test data collected in support of the rf heating demonstration. The following data are discussed in this report: (1) a general description of the site including piezometers and sensors installed to monitor the remedial process; (2) stratigraphy, lithology, and a detailed geologic cross section of the study site; (3) tabulations of pretest and post-test moisture and VOC content of the sediments; (4) sampling and analysis procedures for sediment samples; (5) microbial abundance and diversity; (6) three-dimensional images of pretest and post-test contaminant distribution; (7) volumetric calculations.« less

L-Band High Power Amplifiers for CEBAF Linac

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fugitt, Jock; Killion, Richard; Nelson, Richard

1990-09-01

The high power portion of the CEBAF RF system utilizes 340 5kW klystrons providing 339 separately controlled outputs. Modulating anodes have been included in the klystron design to provide for economically efficient operation. The design includes shunt regulator-type modulating anode power supplies running from the cathode power supply, and switching filament power supplies. Remotely programmable filament voltage allows maximum cathode life to be realized. Klystron operating setpoint and fast klystron protection logic are provided by individual external CEBAF RF control modules. A single cathode power supply powers a block of eight klystrons. The design includes circulators and custom extrusion andmore » hybrid waveguide components which have allowed reduced physical size and lower cost in the design of the WR-650 waveguide transmission system.« less

Fast ferroelectric phase shifters for energy recovery linacs

DOE PAGES

Kazakov, S. Yu; Shchelkunov, S. V.; Yakovlev, V. P.; ...

2010-11-24

Fast phase shifters are described that use a novel barium strontium titanate ceramic that can rapidly change its dielectric constant as an external bias voltage is changed. These phase shifters promise to reduce by ~10 times the power requirements for the rf source needed to drive an energy recovery linac (ERL). Such phase shifters will be coupled with superconducting radiofrequency cavities so as to tune them to compensate for phase instabilities, whether beam-driven or those caused by microphonics. The most promising design is presented, which was successfully cold tested and demonstrated a switching speed of ~30 ns for 77 deg, correspondingmore » to < 0.5 ns per deg of rf phase. As a result, other crucial issues (losses, phase shift values, etc.) are discussed.« less

Thermal and Lorentz Force Analysis of Beryllium Windows for the Rectilinear Muon Cooling Channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, Tianhuan; Li, D.; Virostek, S.

Reduction of the 6-dimensional phase-space of a muon beam by several orders of magnitude is a key requirement for a Muon Collider. Recently, a 12-stage rectilinear ionization cooling channel has been proposed to achieve that goal. The channel consists of a series of low frequency (325 MHz-650 MHz) normal conducting pillbox cavities, which are enclosed with thin beryllium windows (foils) to increase shunt impedance and give a higher field on-axis for a given amount of power. These windows are subject to ohmic heating from RF currents and Lorentz force from the EM field in the cavity, both of which willmore » produce out of the plane displacements that can detune the cavity frequency. In this study, using the TEM3P code, we report on a detailed thermal and mechanical analysis for the actual Be windows used on a 325 MHz cavity in a vacuum ionization cooling rectilinear channel for a Muon Collider.« less

Thermal and Lorentz force analysis of beryllium windows for a rectilinear muon cooling channel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Luo, T.; Stratakis, D.; Li, D.

Reduction of the 6-dimensional phase-space of a muon beam by several orders of magnitude is a key requirement for a Muon Collider. Recently, a 12-stage rectilinear ionization cooling channel has been proposed to achieve that goal. The channel consists of a series of low frequency (325 MHz-650 MHz) normal conducting pillbox cavities, which are enclosed with thin beryllium windows (foils) to increase shunt impedance and give a higher field on-axis for a given amount of power. These windows are subject to ohmic heating from RF currents and Lorentz force from the EM field in the cavity, both of which willmore » produce out of the plane displacements that can detune the cavity frequency. In this study, using the TEM3P code, we report on a detailed thermal and mechanical analysis for the actual Be windows used on a 325 MHz cavity in a vacuum ionization cooling rectilinear channel for a Muon Collider.« less

Planar doped barrier subharmonic mixers

NASA Technical Reports Server (NTRS)

Lee, T. H.; East, J. R.; Haddad, G. I.

1992-01-01

The Planar Doped Barrier (PDB) diode is a device consisting of a p(+) doping spike between two intrinsic layers and n(+) ohmic contacts. This device has the advantages of controllable barrier height, diode capacitance and forward to reverse current ratio. A symmetrically designed PDB has an anti-symmetric current vs. voltage characteristic and is ideal for use as millimeter wave subharmonic mixers. We have fabricated such devices with barrier heights of 0.3, 0.5 and 0.7 volts from GaAs and InGaAs using a multijunction honeycomb structure with junction diameters between one and ten microns. Initial RF measurements are encouraging. The 0.7 volt barrier height 4 micron GaAs devices were tested as subharmonic mixers at 202 GHz with an IF frequency of 1 GHz and had 18 dB of conversion loss. The estimated mismatch loss was 7 dB and was due to higher diode capacitance. The LO frequency was 100.5 GHz and the pump power was 8 mW.

Electronic transport mechanism in intrinsic and doped nanocrystalline silicon films deposited by RF-magnetron sputtering at low temperature

NASA Astrophysics Data System (ADS)

Benlakehal, D.; Belfedal, A.; Bouizem, Y.; Sib, J. D.; Chahed, L.; Zellama, K.

2016-12-01

The dependence on the temperature range, T, of the electronic transport mechanism in intrinsic and doped hydrogenated nanocrystalline silicon films, deposited by radiofrequency-magnetron sputtering at low substrate temperature, has been studied. Electrical conductivity measurements σ(T) have been conducted on these films, as a function of temperature, in the 93-450 K range. The analysis of these results clearly shows a thermally activated conduction process in the 273-450 K range which allows us to estimate the associated activation energy as well as the preexponential conductivity factor. While, in the lower temperature range (T < 273 K), a non-ohmic behavior is observed for the conductivity changes. The conductivity σ(T) presents a linear dependence on (T-1/4) , and a hopping mechanism is suggested to explain these results. By using the Percolation theory, further information can be gained about the density of states near the Fermi level as well as the range and the hopping energy.

Characteristics of n-GaN After Cl2/Ar and Cl2/N2 Inductively Coupled Plasma Etching

NASA Astrophysics Data System (ADS)

Han, Yan-Jun; Xue, Song; Guo, Wen-Ping; Sun, Chang-Zheng; Hao, Zhi-Biao; Luo, Yi

2003-10-01

A systematic study on the effect of inductively coupled plasma (ICP) etching on n-type GaN is presented. The optical and electrical properties and surface stoichiometry of n-type GaN are evaluated using room-temperature photoluminescence (PL) and current-voltage (I-V) characteristic measurements, and X-ray photoelectron spectroscopy (XPS), respectively. Investigation of the effect of additive gas (N2 and Ar) and RF power on these characteristics has also been carried out. It is shown that the decrease in the O/Ga ratio after ICP etching can suppress the deterioration of the near-band-edge emission intensity. Furthermore, N vacancy (VN) with a shallow donor nature and Ga vacancy (VGa) with a deep acceptor nature are generated after ICP etching upon the addition of Ar and N2 to Cl2 plasma, respectively. Lower ohmic contact resistance could be obtained when VN or ion-bombardment-induced defect is dominant at the surface. Improved etching conditions have been obtained based on these results.

Bottom-up on-crystal in-chip formation of a conducting salt and a view of its restructuring: from organic insulator to conducting "switch" through microfluidic manipulation.

PubMed

Puigmartí-Luis, Josep; Paradinas, Markos; Bailo, Elena; Rodriguez-Trujillo, Romen; Pfattner, Raphael; Ocal, Carmen; Amabilino, David B

2015-06-01

The chemical modification of an immobilized single crystal in a fluid cell is reported, whereby a material with switching functions is generated in situ by generating a chemical reagent in the flow. Crystals of the insulating organic crystal of TCNQ (tetracyanoquinodimethane) were grown in a microfluidic channel and were trapped using a pneumatic valve, a nascent technique for materials manipulation. They were subsequently reduced using solution-deposited silver to provide a conducting material in situ by a heterogeneous reaction. Removal of the new material from the chip proved it to be the silver salt of reduced TCNQ. Uniquely, conducting atomic force microscope (CAFM) studies show three regions in the solid. The localized original neutral organic material crystal is shown to be an insulator but to produce areas with Ohmic conducting characteristics after reduction. This inhomogeneous doping provides an opportunity for probing electrical materials properties side by side. Measurements with the CAFM witness this conducting material where the TCNQ is fully transformed to the silver salt. Additionally, an intermediate phase is observed that exhibits bipolar resistive switching typical of programmable resistive memories. Raman microscopy proves the conversion of the material in specific regions and clearly defines the intermediate phase region that could be responsible for the switching effect in related materials. This kind of "on crystal chemistry" exploiting immobilization and masking by a pneumatic clamp in a microfluidic channel shows how material can be selectively converted to give different functionalities in the same material piece, even though it is not a single crystal to single crystal conversion, and beckons exploitation for the preparation of systems relevant for molecular electronics as well as other areas where chemical manipulation of single crystals could be beneficial.

Impact of biofuels on contrail warming

NASA Astrophysics Data System (ADS)

Caiazzo, Fabio; Agarwal, Akshat; Speth, Raymond L.; Barrett, Steven R. H.

2017-11-01

Contrails and contrail-cirrus may be the largest source of radiative forcing (RF) attributable to aviation. Biomass-derived alternative jet fuels are a potentially major way to mitigate the climate impacts of aviation by reducing lifecycle CO2 emissions. Given the up to 90% reduction in soot emissions from paraffinic biofuels, the potential for a significant impact on contrail RF due to the reduction in contrail-forming ice nuclei (IN) remains an open question. We simulate contrail formation and evolution to quantify RF over the United States under different emissions scenarios. Replacing conventional jet fuels with paraffinic biofuels generates two competing effects. First, the higher water emissions index results in an increase in contrail occurrence (~ +8%). On the other hand, these contrails are composed of larger diameter crystals (~ +58%) at lower number concentrations (~ -75%), reducing both contrail optical depth (~ -29%) and albedo (~ -32%). The net changes in contrail RF induced by switching to biofuels range from -4% to +18% among a range of assumed ice crystal habits (shapes). In comparison, cleaner burning engines (with no increase in water emissions index) result in changes to net contrail RF ranging between -13% and +5% depending on habit. Thus, we find that even 67% to 75% reductions in aircraft soot emissions are insufficient to substantially reduce warming from contrails, and that the use of biofuels may either increase or decrease contrail warming—contrary to previous expectations of a significant decrease in warming.

Liquid Metal Droplet and Micro Corrugated Diaphragm RF-MEMS for reconfigurable RF filters

NASA Astrophysics Data System (ADS)

Irshad, Wasim

Widely Tunable RF Filters that are small, cost-effective and offer ultra low power consumption are extremely desirable. Indeed, such filters would allow drastic simplification of RF front-ends in countless applications from cell phones to satellites in space by replacing switched-array of static acoustic filters and YIG filters respectively. Switched array of acoustic filters are de facto means of channel selection in mobile applications such as cell phones. SAW and BAW filters satisfy most criteria needed by mobile applications such as low cost, size and power consumption. However, the trade-off is a significant loss of 3-4 dB in modern cell phone RF front-end. This leads to need for power-hungry amplifiers and short battery life. It is a necessary trade-off since there are no better alternatives. These devices are in mm scale and consume mW. YIG filters dominate applications where size or power is not a constraint but demand excellent RF performance like low loss and high tuning ratio. These devices are measured in inches and require several watts to operate. Clearly, a tunable RF filter technology that would combine the cost, size and power consumption benefits of acoustic filters with excellent RF performance of YIG filters would be extremely desirable and imminently useful. The objective of this dissertation is to develop such a technology based upon RF-MEMS Evanescent-mode cavity filter. Two highly novel RF-MEMS devices have been developed over the course of this PhD to address the unique MEMS needs of this technology. The first part of the dissertation is dedicated to introducing the fundamental concepts of tunable cavity resonators and filters. This includes the physics behind it, key performance metrics and what they depend on and requirements of the MEMS tuners. Initial gap control and MEMS attachment method are identified as potential hurdles towards achieving very high RF performance. Simple and elegant solutions to both these issues are discussed in detail and have proved pivotal to this work. The second part of the dissertation focuses on the Liquid Metal Droplet RF-MEMS. A novel tunable RF MEMS resonator that is based upon electrostatic control over the morphology of a liquid metal droplet (LMD) is conceived. We demonstrate an LMD evanescent-mode cavity resonator that simultaneously achieves wide analog tuning from 12 to 18 GHz with a measured quality factor of 1400-1840. A droplet of 250-mum diameter is utilized and the applied bias is limited to 100 V. This device operates on a principle called Electro-Wetting On Dielectric (EWOD). The liquid metal employed is a non-toxic eutectic alloy of Gallium, Indium and Tin known as Galinstan. This device also exploits interfacial surface energy and viscous body forces that dominate at nanoliter scale. We then apply our Liquid Metal Droplet (LMD) RF-MEMS architecture to demonstrate a continuously tunable electrostatic Ku-Band Filter. A 2-pole bandpass filter with measured insertion loss of less than 0.4dB and 3dB FBW of 3.4% is achieved using a Galinstan droplet of 250mum diameter and bias limited to 100V. We demonstrate that the LMD is insensitive to gravity by performing inversion and tilt experiments. In addition, we study its thermal tolerance by subjecting the LMD up to 150° C. The third part of the dissertation is dedicated to the Micro-Corrugated Diaphragm (MCD) RF-MEMS. We present an evanescent-mode cavity bandpass filter with state-of-the-art RF performance metrics like 4:1 tuning ratio from 5 to 20 GHz with less than 2dB insertion loss and 2-6% 3dB bandwidth. Micro-Corrugated Diaphragm (MCD) is a novel electrostatic MEMS design specifically engineered to provide large-scale analog deflections necessary for such continuous and wide tunable filtering with very high quality factor. We demonstrate a 1.25mm radius and 2mum thick Gold MCD which provides 30mum total deflection with nearly 60% analog range. We also present a detailed and systematic MCD design methodology for relevant applications. To further demonstrate MCD versatility, we implement a bandstop MCD filter that cascades nine separate resonators to achieve a 6-24 GHz continuous tuning. The disseration concludes with a Galinstan Magnetohydrodynamic (MHD) micropump and summary of my doctoral work. Although presented at the very end of this dissertation, the MHD micropump was indeed the very starting point for all my doctoral research efforts. The invaluable lessons learned here paved the way for development of both LMD and MCD RF-MEMS.

Micromachined Radio Frequency (RF) Switches and Tunable Capacitors for Higher Performance Secure Communications Systems

DTIC Science & Technology

2003-04-01

range filters implemented with traditional semiconductor varactor diodes can require complex series-parallel circuit constructions to achieve sufficient...filter slice of the AIU and the varactor array modules are shown in Fig. 6.2. The complexity of the varactor array is clearly apparent. Further, it is...38 Fig. 6.2: Schematic of F-22 AIU UHF tracking filter, 2-pole filter, and varactor diode assembly

Influence of oxygen vacancies in ALD HfO2-x thin films on non-volatile resistive switching phenomena with a Ti/HfO2-x/Pt structure

NASA Astrophysics Data System (ADS)

Sokolov, Andrey Sergeevich; Jeon, Yu-Rim; Kim, Sohyeon; Ku, Boncheol; Lim, Donghwan; Han, Hoonhee; Chae, Myeong Gyoon; Lee, Jaeho; Ha, Beom Gil; Choi, Changhwan

2018-03-01

We report a modulation of oxygen vacancies profile in atomic layer deposition (ALD) HfO2-x thin films by reducing oxidant pulse time (0.7 s-0.1 s) and study its effect on resistive switching behavior with a Ti/HfO2-x/Pt structure. Hf 4f spectra of x-ray photoelectron microscopy (XPS) and depth profile confirm varied oxygen vacancies profiles by shifts of binding energies of Hf 4f5/2 and Hf 4f7/2 main peaks and its according HfO2-x sub-oxides for each device. The ultraviolet photoelectron spectroscopy (UPS) confirms different electron affinity (χ) of HfO2 and HfO2-x thin films, implying that barrier height at Ti/oxide interface is reduced. Current transport mechanism is dictated by Ohmic conduction in fully oxidized HfO2 thin films - Device A (0.7 s) and by Trap Filled Space Charge Limited Conduction (TF-SCLC) in less oxidized HfO2-x thin films - Device B (0.3 s) and Device C (0.1 s). A switching mechanism related to the oxygen vacancies modulation in Ti/HfO2-x/Pt based resistive random access memory (RRAM) devices is used to explain carefully notified current transport mechanism variations from device-to-device. A proper endurance and long-time retention characteristics of the devices are also obtained.

Ultra-thin ohmic contacts for p-type nitride light emitting devices

DOEpatents

Raffetto, Mark [Raleigh, NC; Bharathan, Jayesh [Cary, NC; Haberern, Kevin [Cary, NC; Bergmann, Michael [Chapel Hill, NC; Emerson, David [Chapel Hill, NC; Ibbetson, James [Santa Barbara, CA; Li, Ting [Ventura, CA

2012-01-03

A semiconductor based Light Emitting Device (LED) can include a p-type nitride layer and a metal ohmic contact, on the p-type nitride layer. The metal ohmic contact can have an average thickness of less than about 25 .ANG. and a specific contact resistivity less than about 10.sup.-3 ohm-cm.sup.2.

Two-photon Lee-Goldburg nuclear magnetic resonance: Simultaneous homonuclear decoupling and signal acquisition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Michal, Carl A.; Hastings, Simon P.; Lee, Lik Hang

2008-02-07

We present NMR signals from a strongly coupled homonuclear spin system, {sup 1}H nuclei in adamantane, acquired with simultaneous two-photon excitation under conditions of the Lee-Goldburg experiment. Small coils, having inside diameters of 0.36 mm, are used to achieve two-photon nutation frequencies of {approx}20 kHz. The very large rf field strengths required give rise to large Bloch-Siegert shifts that cannot be neglected. These experiments are found to be extremely sensitive to inhomogeneity of the applied rf field, and due to the Bloch-Siegert shift, exhibit a large asymmetry in response between the upper and lower Lee-Goldburg offsets. Two-photon excitation has themore » potential to enhance both the sensitivity and performance of homonuclear dipolar decoupling, but is made challenging by the high rf power required and the difficulties introduced by the inhomogeneous Bloch-Siegert shift. We briefly discuss a variation of the frequency-switched Lee-Goldburg technique, called four-quadrant Lee-Goldburg (4QLG) that produces net precession in the x-y plane, with a reduced chemical shift scaling factor of 1/3.« less

Gap cycling for SWIFT.

PubMed

Corum, Curtis A; Idiyatullin, Djaudat; Snyder, Carl J; Garwood, Michael

2015-02-01

SWIFT (SWeep Imaging with Fourier Transformation) is a non-Cartesian MRI method with unique features and capabilities. In SWIFT, radiofrequency (RF) excitation and reception are performed nearly simultaneously, by rapidly switching between transmit and receive during a frequency-swept RF pulse. Because both the transmitted pulse and data acquisition are simultaneously amplitude-modulated in SWIFT (in contrast to continuous RF excitation and uninterrupted data acquisition in more familiar MRI sequences), crosstalk between different frequency bands occurs in the data. This crosstalk leads to a "bulls-eye" artifact in SWIFT images. We present a method to cancel this interband crosstalk by cycling the pulse and receive gap positions relative to the un-gapped pulse shape. We call this strategy "gap cycling." We carry out theoretical analysis, simulation and experiments to characterize the signal chain, resulting artifacts, and their elimination for SWIFT. Theoretical analysis reveals the mechanism for gap-cycling's effectiveness in canceling interband crosstalk in the received data. We show phantom and in vivo results demonstrating bulls-eye artifact free images. Gap cycling is an effective method to remove bulls-eye artifact resulting from interband crosstalk in SWIFT data. © 2014 Wiley Periodicals, Inc.

Mapping B(1)-induced eddy current effects near metallic structures in MR images: a comparison of simulation and experiment.

PubMed

Vashaee, S; Goora, F; Britton, M M; Newling, B; Balcom, B J

2015-01-01

Magnetic resonance imaging (MRI) in the presence of metallic structures is very common in medical and non-medical fields. Metallic structures cause MRI image distortions by three mechanisms: (1) static field distortion through magnetic susceptibility mismatch, (2) eddy currents induced by switched magnetic field gradients and (3) radio frequency (RF) induced eddy currents. Single point ramped imaging with T1 enhancement (SPRITE) MRI measurements are largely immune to susceptibility and gradient induced eddy current artifacts. As a result, one can isolate the effects of metal objects on the RF field. The RF field affects both the excitation and detection of the magnetic resonance (MR) signal. This is challenging with conventional MRI methods, which cannot readily separate the three effects. RF induced MRI artifacts were investigated experimentally at 2.4 T by analyzing image distortions surrounding two geometrically identical metallic strips of aluminum and lead. The strips were immersed in agar gel doped with contrast agent and imaged employing the conical SPRITE sequence. B1 mapping with pure phase encode SPRITE was employed to measure the B1 field around the strips of metal. The strip geometry was chosen to mimic metal electrodes employed in electrochemistry studies. Simulations are employed to investigate the RF field induced eddy currents in the two metallic strips. The RF simulation results are in good agreement with experimental results. Experimental and simulation results show that the metal has a pronounced effect on the B1 distribution and B1 amplitude in the surrounding space. The electrical conductivity of the metal has a minimal effect. Copyright © 2014 Elsevier Inc. All rights reserved.

Rapid fabrication of pressure-driven open-channel microfluidic devices in omniphobic R(F) paper.

PubMed

Glavan, Ana C; Martinez, Ramses V; Maxwell, E Jane; Subramaniam, Anand Bala; Nunes, Rui M D; Soh, Siowling; Whitesides, George M

2013-08-07

This paper describes the fabrication of pressure-driven, open-channel microfluidic systems with lateral dimensions of 45-300 microns carved in omniphobic paper using a craft-cutting tool. Vapor phase silanization with a fluorinated alkyltrichlorosilane renders paper omniphobic, but preserves its high gas permeability and mechanical properties. When sealed with tape, the carved channels form conduits capable of guiding liquid transport in the low-Reynolds number regime (i.e. laminar flow). These devices are compatible with complex fluids such as droplets of water in oil. The combination of omniphobic paper and a craft cutter enables the development of new types of valves and switches, such as "fold valves" and "porous switches," which provide new methods to control fluid flow.

Estimation of intrinsic and extrinsic capacitances of graphene self-switching diode using conformal mapping technique

NASA Astrophysics Data System (ADS)

Singh, Arun K.; Auton, Gregory; Hill, Ernie; Song, Aimin

2018-07-01

Due to a very high carrier concentration and low band gap, graphene based self-switching diodes do not demonstrate a very high rectification ratio. Despite that, it takes the advantage of graphene’s high carrier mobility and has been shown to work at very high microwave frequencies. However, the AC component of these devices is hidden in the very linear current–voltage characteristics. Here, we extract and quantitatively study the device capacitance that determines the device nonlinearity by implementing a conformal mapping technique. The estimated value of the nonlinear component or curvature coefficient from DC results based on Shichman–Hodges model predicts the rectified output voltage, which is in good agreement with the experimental RF results.

Fabricating Ohmic contact on Nb-doped SrTiO{sub 3} surface in nanoscale

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Yuhang; National Key Laboratory of Shock Wave and Detonation Physics, Institute of Fluid Physics, Chinese Academy of Engineering Physics, Mianyang, Sichuan 621999; Shi, Xiaolan

2016-05-09

Fabricating reliable nano-Ohmic contact on wide gap semiconductors is an important yet difficult step in oxide nanoelectronics. We fabricated Ohmic contact on the n-type wide gap oxide Nb-doped SrTiO{sub 3} in nanoscale by mechanically scratching the surface using an atomic force microscopy tip. Although contacted to high work function metal, the scratched area exhibits nearly linear IV behavior with low contact resistance, which maintains for hours in vacuum. In contrast, the unscratched area shows Fowler–Nordheim tunneling dominated Schottky rectifying behavior with high contact resistance. It was found that the Ohmic conductivity in the scratched area was drastically suppressed by oxygenmore » gas indicating the oxygen vacancy origin of the Ohmic behavior. The surface oxygen vacancy induced barrier width reduction was proposed to explain the phenomena. The nanoscale approach is also applicable to macroscopic devices and has potential application in all-oxide devices.« less

Development of Numerical Methods to Estimate the Ohmic Breakdown Scenarios of a Tokamak

NASA Astrophysics Data System (ADS)

Yoo, Min-Gu; Kim, Jayhyun; An, Younghwa; Hwang, Yong-Seok; Shim, Seung Bo; Lee, Hae June; Na, Yong-Su

2011-10-01

The ohmic breakdown is a fundamental method to initiate the plasma in a tokamak. For the robust breakdown, ohmic breakdown scenarios have to be carefully designed by optimizing the magnetic field configurations to minimize the stray magnetic fields. This research focuses on development of numerical methods to estimate the ohmic breakdown scenarios by precise analysis of the magnetic field configurations. This is essential for the robust and optimal breakdown and start-up of fusion devices especially for ITER and its beyond equipped with low toroidal electric field (ET <= 0.3 V/m). A field-line-following analysis code based on the Townsend avalanche theory and a particle simulation code are developed to analyze the breakdown characteristics of actual complex magnetic field configurations including the stray magnetic fields in tokamaks. They are applied to the ohmic breakdown scenarios of tokamaks such as KSTAR and VEST and compared with experiments.

Electric field-triggered metal-insulator transition resistive switching of bilayered multiphasic VOx

NASA Astrophysics Data System (ADS)

Won, Seokjae; Lee, Sang Yeon; Hwang, Jungyeon; Park, Jucheol; Seo, Hyungtak

2018-01-01

Electric field-triggered Mott transition of VO2 for next-generation memory devices with sharp and fast resistance-switching response is considered to be ideal but the formation of single-phase VO2 by common deposition techniques is very challenging. Here, VOx films with a VO2-dominant phase for a Mott transition-based metal-insulator transition (MIT) switching device were successfully fabricated by the combined process of RF magnetron sputtering of V metal and subsequent O2 annealing to form. By performing various material characterizations, including scanning transmission electron microscopy-electron energy loss spectroscopy, the film is determined to have a bilayer structure consisting of a VO2-rich bottom layer acting as the Mott transition switching layer and a V2O5/V2O3 mixed top layer acting as a control layer that suppresses any stray leakage current and improves cyclic performance. This bilayer structure enables excellent electric field-triggered Mott transition-based resistive switching of Pt-VOx-Pt metal-insulator-metal devices with a set/reset current ratio reaching 200, set/reset voltage of less than 2.5 V, and very stable DC cyclic switching upto 120 cycles with a great set/reset current and voltage distribution less than 5% of standard deviation at room temperature, which are specifications applicable for neuromorphic or memory device applications. [Figure not available: see fulltext.

A Study on Ohmic Contact to Dry-Etched p-GaN

NASA Astrophysics Data System (ADS)

Hu, Cheng-Yu; Ao, Jin-Ping; Okada, Masaya; Ohno, Yasuo

Low-power dry-etching process has been adopted to study the influence of dry-etching on Ohmic contact to p-GaN. When the surface layer of as-grown p-GaN was removed by low-power SiCl4/Cl2-etching, no Ohmic contact can be formed on the low-power dry-etched p-GaN. The same dry-etching process was also applied on n-GaN to understand the influence of the low-power dry-etching process. By capacitance-voltage (C-V) measurement, the Schottky barrier heights (SBHs) of p-GaN and n-GaN were measured. By comparing the change of measured SBHs on p-GaN and n-GaN, it was suggested that etching damage is not the only reason responsible for the degraded Ohmic contacts to dry-etched p-GaN and for Ohmic contact formatin, the original surface layer of as-grown p-GaN have some special properties, which were removed by dry-etching process. To partially recover the original surface of as-grown p-GaN, high temperature annealing (1000°C 30s) was tried on the SiCl4/Cl2-etched p-GaN and Ohmic contact was obtained.

Bulk heterojunction polymer memory devices with reduced graphene oxide as electrodes.

PubMed

Liu, Juqing; Yin, Zongyou; Cao, Xiehong; Zhao, Fei; Lin, Anping; Xie, Linghai; Fan, Quli; Boey, Freddy; Zhang, Hua; Huang, Wei

2010-07-27

A unique device structure with a configuration of reduced graphene oxide (rGO) /P3HT:PCBM/Al has been designed for the polymer nonvolatile memory device. The current-voltage (I-V) characteristics of the fabricated device showed the electrical bistability with a write-once-read-many-times (WORM) memory effect. The memory device exhibits a high ON/OFF ratio (10(4)-10(5)) and low switching threshold voltage (0.5-1.2 V), which are dependent on the sheet resistance of rGO electrode. Our experimental results confirm that the carrier transport mechanisms in the OFF and ON states are dominated by the thermionic emission current and ohmic current, respectively. The polarization of PCBM domains and the localized internal electrical field formed among the adjacent domains are proposed to explain the electrical transition of the memory device.

Novel Co:MgF2 lidar for aerosol profiler

NASA Technical Reports Server (NTRS)

Acharekar, M. A.

1993-01-01

Lidars are of great interest because of their unique capabilities in remote sensing applications in sounding of the atmosphere, meteorology, and climatology. In this small business innovative research (SBIR) phase II program, laser sources including Co:MgF2, CTH:YAG, CTH:YSGG, CT:YAG, and Er:Glass were evaluated. Modulator of fused silica and TeO2 materials with Brewster's angle end faces were used with these lasers as acousto-optical (AO) Q-switches. A higher hold-off energy and hence a higher Q-switched energy was obtained by using a high power RF driver. The report provides performance characteristics of these lasers. The tunable (1.75-2.50 microns) Co:MgF2 laser damaged the TeO2 Q-switch cell. However, the CTH:YAG laser operating at 2.09 microns provided output energy of over 300 mJ/p in 50 ns pulse width using the fused silica Q-switch. This Q-switched CTH:YAG laser was used in a breadboard vertical aerosol profiler. A 40 cm diameter telescope, InSb and InGaAs detectors were used in the receiver. The data obtained using this lidar is provided in the report. The data shows that the eye safe lidar using CTH:YAG laser for the vertical aerosol density and range measurements is the viable approach.

Exploratory Phase Transition-Based Switches Using Functional Oxides

DTIC Science & Technology

2011-02-02

TECHNICAL REPORT Abstract Vanadium dioxide ( VO2 ) undergoes a sharp metal-insulator transition (MIT) in the vicinity of room temperature and there is...18 The mechanisms governing metal-insulator transition (MIT) in vanadium dioxide ( VO2 ) is an intensively explored subject in condensed matter...textured vanadium dioxide films were grown on single crystal Al2O3 (0001) substrates by RF-sputtering from a VO2 target (99.5%, AJA International Inc

Adjustable, High Voltage Pulse Generator with Isolated Output for Plasma Processing

NASA Astrophysics Data System (ADS)

Ziemba, Timothy; Miller, Kenneth E.; Prager, James; Slobodov, Ilia

2015-09-01

Eagle Harbor Technologies (EHT), Inc. has developed a high voltage pulse generator with isolated output for etch, sputtering, and ion implantation applications within the materials science and semiconductor processing communities. The output parameters are independently user adjustable: output voltage (0 - 2.5 kV), pulse repetition frequency (0 - 100 kHz), and duty cycle (0 - 100%). The pulser can drive loads down to 200 Ω. Higher voltage pulsers have also been tested. The isolated output allows the pulse generator to be connected to loads that need to be biased. These pulser generators take advantage modern silicon carbide (SiC) MOSFETs. These new solid-state switches decrease the switching and conduction losses while allowing for higher switching frequency capabilities. This pulse generator has applications for RF plasma heating; inductive and arc plasma sources; magnetron driving; and generation of arbitrary pulses at high voltage, high current, and high pulse repetition frequency. This work was supported in part by a DOE SBIR.

Advanced RF Front End Technology

NASA Technical Reports Server (NTRS)

Herman, M. I.; Valas, S.; Katehi, L. P. B.

2001-01-01

The ability to achieve low-mass low-cost micro/nanospacecraft for Deep Space exploration requires extensive miniaturization of all subsystems. The front end of the Telecommunication subsystem is an area in which major mass (factor of 10) and volume (factor of 100) reduction can be achieved via the development of new silicon based micromachined technology and devices. Major components that make up the front end include single-pole and double-throw switches, diplexer, and solid state power amplifier. JPL's Center For Space Microsystems - System On A Chip (SOAC) Program has addressed the challenges of front end miniaturization (switches and diplexers). Our objectives were to develop the main components that comprise a communication front end and enable integration in a single module that we refer to as a 'cube'. In this paper we will provide the latest status of our Microelectromechanical System (MEMS) switches and surface micromachined filter development. Based on the significant progress achieved we can begin to provide guidelines of the proper system insertion for these emerging technologies. Additional information is contained in the original extended abstract.

Non-Volatile Ferroelectric Switching of Ferromagnetic Resonance in NiFe/PLZT Multiferroic Thin Film Heterostructures.

PubMed

Hu, Zhongqiang; Wang, Xinjun; Nan, Tianxiang; Zhou, Ziyao; Ma, Beihai; Chen, Xiaoqin; Jones, John G; Howe, Brandon M; Brown, Gail J; Gao, Yuan; Lin, Hwaider; Wang, Zhiguang; Guo, Rongdi; Chen, Shuiyuan; Shi, Xiaoling; Shi, Wei; Sun, Hongzhi; Budil, David; Liu, Ming; Sun, Nian X

2016-09-01

Magnetoelectric effect, arising from the interfacial coupling between magnetic and electrical order parameters, has recently emerged as a robust means to electrically manipulate the magnetic properties in multiferroic heterostructures. Challenge remains as finding an energy efficient way to modify the distinct magnetic states in a reliable, reversible, and non-volatile manner. Here we report ferroelectric switching of ferromagnetic resonance in multiferroic bilayers consisting of ultrathin ferromagnetic NiFe and ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films, where the magnetic anisotropy of NiFe can be electrically modified by low voltages. Ferromagnetic resonance measurements confirm that the interfacial charge-mediated magnetoelectric effect is dominant in NiFe/PLZT heterostructures. Non-volatile modification of ferromagnetic resonance field is demonstrated by applying voltage pulses. The ferroelectric switching of magnetic anisotropy exhibits extensive applications in energy-efficient electronic devices such as magnetoelectric random access memories, magnetic field sensors, and tunable radio frequency (RF)/microwave devices.

Non-Volatile Ferroelectric Switching of Ferromagnetic Resonance in NiFe/PLZT Multiferroic Thin Film Heterostructures

PubMed Central

Hu, Zhongqiang; Wang, Xinjun; Nan, Tianxiang; Zhou, Ziyao; Ma, Beihai; Chen, Xiaoqin; Jones, John G.; Howe, Brandon M.; Brown, Gail J.; Gao, Yuan; Lin, Hwaider; Wang, Zhiguang; Guo, Rongdi; Chen, Shuiyuan; Shi, Xiaoling; Shi, Wei; Sun, Hongzhi; Budil, David; Liu, Ming; Sun, Nian X.

2016-01-01

Magnetoelectric effect, arising from the interfacial coupling between magnetic and electrical order parameters, has recently emerged as a robust means to electrically manipulate the magnetic properties in multiferroic heterostructures. Challenge remains as finding an energy efficient way to modify the distinct magnetic states in a reliable, reversible, and non-volatile manner. Here we report ferroelectric switching of ferromagnetic resonance in multiferroic bilayers consisting of ultrathin ferromagnetic NiFe and ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films, where the magnetic anisotropy of NiFe can be electrically modified by low voltages. Ferromagnetic resonance measurements confirm that the interfacial charge-mediated magnetoelectric effect is dominant in NiFe/PLZT heterostructures. Non-volatile modification of ferromagnetic resonance field is demonstrated by applying voltage pulses. The ferroelectric switching of magnetic anisotropy exhibits extensive applications in energy-efficient electronic devices such as magnetoelectric random access memories, magnetic field sensors, and tunable radio frequency (RF)/microwave devices. PMID:27581071

Non-Volatile Ferroelectric Switching of Ferromagnetic Resonance in NiFe/PLZT Multiferroic Thin Film Heterostructures

NASA Astrophysics Data System (ADS)

Hu, Zhongqiang; Wang, Xinjun; Nan, Tianxiang; Zhou, Ziyao; Ma, Beihai; Chen, Xiaoqin; Jones, John G.; Howe, Brandon M.; Brown, Gail J.; Gao, Yuan; Lin, Hwaider; Wang, Zhiguang; Guo, Rongdi; Chen, Shuiyuan; Shi, Xiaoling; Shi, Wei; Sun, Hongzhi; Budil, David; Liu, Ming; Sun, Nian X.

2016-09-01

Magnetoelectric effect, arising from the interfacial coupling between magnetic and electrical order parameters, has recently emerged as a robust means to electrically manipulate the magnetic properties in multiferroic heterostructures. Challenge remains as finding an energy efficient way to modify the distinct magnetic states in a reliable, reversible, and non-volatile manner. Here we report ferroelectric switching of ferromagnetic resonance in multiferroic bilayers consisting of ultrathin ferromagnetic NiFe and ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) films, where the magnetic anisotropy of NiFe can be electrically modified by low voltages. Ferromagnetic resonance measurements confirm that the interfacial charge-mediated magnetoelectric effect is dominant in NiFe/PLZT heterostructures. Non-volatile modification of ferromagnetic resonance field is demonstrated by applying voltage pulses. The ferroelectric switching of magnetic anisotropy exhibits extensive applications in energy-efficient electronic devices such as magnetoelectric random access memories, magnetic field sensors, and tunable radio frequency (RF)/microwave devices.

An All-Digital Fast Tracking Switching Converter with a Programmable Order Loop Controller for Envelope Tracking RF Power Amplifiers

PubMed Central

Anabtawi, Nijad; Ferzli, Rony; Harmanani, Haidar M.

2017-01-01

This paper presents a step down, switched mode power converter for use in multi-standard envelope tracking radio frequency power amplifiers (RFPA). The converter is based on a programmable order sigma delta modulator that can be configured to operate with either 1st, 2nd, 3rd or 4th order loop filters, eliminating the need for a bulky passive output filter. Output ripple, sideband noise and spectral emission requirements of different wireless standards can be met by configuring the modulator’s filter order and converter’s sampling frequency. The proposed converter is entirely digital and is implemented in 14nm bulk CMOS process for post layout verification. For an input voltage of 3.3V, the converter’s output can be regulated to any voltage level from 0.5V to 2.5V, at a nominal switching frequency of 150MHz. It achieves a maximum efficiency of 94% at 1.5 W output power. PMID:28919657

Fast switching wideband rectifying circuit for future RF energy harvesting

NASA Astrophysics Data System (ADS)

Asmeida, Akrem; Mustam, Saizalmursidi Md; Abidin, Z. Z.; Ashyap, A. Y. I.

2017-09-01

This paper presents the design and simulation of fast switching microwave rectifying circuit for ultra wideband patch antenna over a dual-frequency band (1.8 GHz for GSM and 2.4 GHz for ISM band). This band was chosen due to its high signal availability in the surrounding environment. New rectifying circuit topology with pair-matching trunks is designed using Advanced Design System (ADS) software. These trunks are interfaced with power divider to achieve good bandwidth, fast switching and high efficiency. The power divider acts as a good isolator between the trunks and its straightforward design structure makes it a good choice for a single feed UWB antenna. The simulated results demonstrate that the maximum output voltage is 2.13 V with an input power of -5 dBm. Moreover, the rectifier offers maximum efficiency of 86% for the input power of -5 dBm at given band, which could easily power up wireless sensor networks (WSN) and other small devices sufficiently.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grisi, Marco, E-mail: marco.grisi@epfl.ch; Gualco, Gabriele; Boero, Giovanni

In this article, we present an integrated broadband complementary metal-oxide semiconductor single-chip transceiver suitable for the realization of multi-nuclear pulsed nuclear magnetic resonance (NMR) probes. The realized single-chip transceiver can be interfaced with on-chip integrated microcoils or external LC resonators operating in the range from 1 MHz to 1 GHz. The dimension of the chip is about 1 mm{sup 2}. It consists of a radio-frequency (RF) power amplifier, a low-noise RF preamplifier, a frequency mixer, an audio-frequency amplifier, and fully integrated transmit-receive switches. As specific example, we show its use for multi-nuclear NMR spectroscopy. With an integrated coil of aboutmore » 150 μm external diameter, a {sup 1}H spin sensitivity of about 1.5 × 10{sup 13} spins/Hz{sup 1/2} is achieved at 7 T.« less

[Acceleration of osmotic dehydration process through ohmic heating of foods: raspberries (Rubus idaeus)].

PubMed

Simpson, Ricardo R; Jiménez, Maite P; Carevic, Erica G; Grancelli, Romina M

2007-06-01

Raspberries (Rubus idaeus) were osmotically dehydrated by applying a conventional method under the supposition of a homogeneous solution, all in a 62% glucose solution at 50 degrees C. Raspberries (Rubus idaeus) were also osmotically dehydrated by using ohmic heating in a 57% glucose solution at a variable voltage (to maintain temperature between 40 and 50 degrees C) and an electric field intensity <100 V/cm. When comparing the results from both experiments it was evident that processing time is reduced when ohmic heating technique was used. In some cases this reduction reached even 50%. This is explained by the additional effect to the thermal damage that is generated in an ohmic process, denominated electroporation.

Minimization of Ohmic Losses for Domain Wall Motion in a Ferromagnetic Nanowire

NASA Astrophysics Data System (ADS)

Tretiakov, O. A.; Liu, Y.; Abanov, Ar.

2010-11-01

We study current-induced domain-wall motion in a narrow ferromagnetic wire. We propose a way to move domain walls with a resonant time-dependent current which dramatically decreases the Ohmic losses in the wire and allows driving of the domain wall with higher speed without burning the wire. For any domain-wall velocity we find the time dependence of the current needed to minimize the Ohmic losses. Below a critical domain-wall velocity specified by the parameters of the wire the minimal Ohmic losses are achieved by dc current. Furthermore, we identify the wire parameters for which the losses reduction from its dc value is the most dramatic.

Comparison of nickel silicide and aluminium ohmic contact metallizations for low-temperature quantum transport measurements.

PubMed

Polley, Craig M; Clarke, Warrick R; Simmons, Michelle Y

2011-10-03

We examine nickel silicide as a viable ohmic contact metallization for low-temperature, low-magnetic-field transport measurements of atomic-scale devices in silicon. In particular, we compare a nickel silicide metallization with aluminium, a common ohmic contact for silicon devices. Nickel silicide can be formed at the low temperatures (<400°C) required for maintaining atomic precision placement in donor-based devices, and it avoids the complications found with aluminium contacts which become superconducting at cryogenic measurement temperatures. Importantly, we show that the use of nickel silicide as an ohmic contact at low temperatures does not affect the thermal equilibration of carriers nor contribute to hysteresis in a magnetic field.

Voltage Controlled Hot Carrier Injection Enables Ohmic Contacts Using Au Island Metal Films on Ge.

PubMed

Ganti, Srinivas; King, Peter J; Arac, Erhan; Dawson, Karl; Heikkilä, Mikko J; Quilter, John H; Murdoch, Billy; Cumpson, Peter; O'Neill, Anthony

2017-08-23

We introduce a new approach to creating low-resistance metal-semiconductor ohmic contacts, illustrated using high conductivity Au island metal films (IMFs) on Ge, with hot carrier injection initiated at low applied voltage. The same metallization process simultaneously allows ohmic contact to n-Ge and p-Ge, because hot carriers circumvent the Schottky barrier formed at metal/n-Ge interfaces. A 2.5× improvement in contact resistivity is reported over previous techniques to achieve ohmic contact to both n- and p- semiconductor. Ohmic contacts at 4.2 K confirm nonequilibrium current transport. Self-assembled Au IMFs are strongly orientated to Ge by annealing near the Au/Ge eutectic temperature. Au IMF nanostructures form, provided the Au layer is below a critical thickness. We anticipate that optimized IMF contacts may have applicability to many material systems. Optimizing this new paradigm for metal-semiconductor contacts offers the prospect of improved nanoelectronic systems and the study of voltage controlled hot holes and electrons.

Innovative food processing technology using ohmic heating and aseptic packaging for meat.

PubMed

Ito, Ruri; Fukuoka, Mika; Hamada-Sato, Naoko

2014-02-01

Since the Tohoku earthquake, there is much interest in processed foods, which can be stored for long periods at room temperature. Retort heating is one of the main technologies employed for producing it. We developed the innovative food processing technology, which supersede retort, using ohmic heating and aseptic packaging. Electrical heating involves the application of alternating voltage to food. Compared with retort heating, which uses a heat transfer medium, ohmic heating allows for high heating efficiency and rapid heating. In this paper we ohmically heated chicken breast samples and conducted various tests on the heated samples. The measurement results of water content, IMP, and glutamic acid suggest that the quality of the ohmically heated samples was similar or superior to that of the retort-heated samples. Furthermore, based on the monitoring of these samples, it was observed that sample quality did not deteriorate during storage. © 2013. Published by Elsevier Ltd on behalf of The American Meat Science Association. All rights reserved.

High magnetic field ohmically decoupled non-contact technology

DOEpatents

Wilgen, John [Oak Ridge, TN; Kisner, Roger [Knoxville, TN; Ludtka, Gerard [Oak Ridge, TN; Ludtka, Gail [Oak Ridge, TN; Jaramillo, Roger [Knoxville, TN

2009-05-19

Methods and apparatus are described for high magnetic field ohmically decoupled non-contact treatment of conductive materials in a high magnetic field. A method includes applying a high magnetic field to at least a portion of a conductive material; and applying an inductive magnetic field to at least a fraction of the conductive material to induce a surface current within the fraction of the conductive material, the surface current generating a substantially bi-directional force that defines a vibration. The high magnetic field and the inductive magnetic field are substantially confocal, the fraction of the conductive material is located within the portion of the conductive material and ohmic heating from the surface current is ohmically decoupled from the vibration. An apparatus includes a high magnetic field coil defining an applied high magnetic field; an inductive magnetic field coil coupled to the high magnetic field coil, the inductive magnetic field coil defining an applied inductive magnetic field; and a processing zone located within both the applied high magnetic field and the applied inductive magnetic field. The high magnetic field and the inductive magnetic field are substantially confocal, and ohmic heating of a conductive material located in the processing zone is ohmically decoupled from a vibration of the conductive material.

Hafnia-based resistive switching devices for non-volatile memory applications and effects of gamma irradiation on device performance

NASA Astrophysics Data System (ADS)

Arun, N.; Kumar, K. Vinod; Pathak, A. P.; Avasthi, D. K.; Nageswara Rao, S. V. S.

2018-04-01

Non-volatile memory (NVM) devices were fabricated as a Metal- Insulator-Metal (MIM) structures by sandwiching Hafnium dioxide (HfO2) thin film in between two metal electrodes. The top and bottom metal electrodes were deposited by using the thermal evaporation, and the oxide layer was deposited by using the RF magnetron sputtering technique. The Resistive Random Access Memory (RRAM) device structures such as Ag/HfO2/Au/Si were fabricated and I-V characteristics for the pristine and gamma-irradiated devices with a dose 24 kGy were measured. Further we have studied the thermal annealing effects, in the range of 100°-400°C in a tubular furnace for the HfO2/Au/Si samples. The X-ray diffraction (XRD), Rutherford Backscattering Spectrometry (RBS), field emission-scanning electron microscopy (FESEM) analysis measurements were performed to determine the thickness, crystallinity and stoichiometry of these films. The electrical characteristics such as resistive switching, endurance, retention time and switching speed were measured by a semiconductor device analyser. The effects of gamma irradiation on the switching properties of these RRAM devices have been studied.

Effect of Electropermeabilization by Ohmic Heating for Inactivation of Escherichia coli O157:H7, Salmonella enterica Serovar Typhimurium, and Listeria monocytogenes in Buffered Peptone Water and Apple Juice

PubMed Central

Park, Il-Kyu

2013-01-01

The effect of electric field-induced ohmic heating for inactivation of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in buffered peptone water (BPW) (pH 7.2) and apple juice (pH 3.5; 11.8 °Brix) was investigated in this study. BPW and apple juice were treated at different temperatures (55°C, 58°C, and 60°C) and for different times (0, 10, 20, 25, and 30 s) by ohmic heating compared with conventional heating. The electric field strength was fixed at 30 V/cm and 60 V/cm for BPW and apple juice, respectively. Bacterial reduction resulting from ohmic heating was significantly different (P < 0.05) from that resulting from conventional heating at 58°C and 60°C in BPW and at 55°C, 58°C, and 60°C in apple juice for intervals of 0, 10, 20, 25, and 30 s. These results show that electric field-induced ohmic heating led to additional bacterial inactivation at sublethal temperatures. Transmission electron microscopy (TEM) observations and the propidium iodide (PI) uptake test were conducted after treatment at 60°C for 0, 10, 20, 25 and 30 s in BPW to observe the effects on cell permeability due to electroporation-caused cell damage. PI values when ohmic and conventional heating were compared were significantly different (P < 0.05), and these differences increased with increasing levels of inactivation of three food-borne pathogens. These results demonstrate that ohmic heating can more effectively reduce bacterial populations at reduced temperatures and shorter time intervals, especially in acidic fruit juices such as apple juice. Therefore, loss of quality can be minimized in a pasteurization process incorporating ohmic heating. PMID:23995939

Effect of electropermeabilization by ohmic heating for inactivation of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in buffered peptone water and apple juice.

PubMed

Park, Il-Kyu; Kang, Dong-Hyun

2013-12-01

The effect of electric field-induced ohmic heating for inactivation of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in buffered peptone water (BPW) (pH 7.2) and apple juice (pH 3.5; 11.8 °Brix) was investigated in this study. BPW and apple juice were treated at different temperatures (55°C, 58°C, and 60°C) and for different times (0, 10, 20, 25, and 30 s) by ohmic heating compared with conventional heating. The electric field strength was fixed at 30 V/cm and 60 V/cm for BPW and apple juice, respectively. Bacterial reduction resulting from ohmic heating was significantly different (P<0.05) from that resulting from conventional heating at 58°C and 60°C in BPW and at 55°C, 58°C, and 60°C in apple juice for intervals of 0, 10, 20, 25, and 30 s. These results show that electric field-induced ohmic heating led to additional bacterial inactivation at sublethal temperatures. Transmission electron microscopy (TEM) observations and the propidium iodide (PI) uptake test were conducted after treatment at 60°C for 0, 10, 20, 25 and 30 s in BPW to observe the effects on cell permeability due to electroporation-caused cell damage. PI values when ohmic and conventional heating were compared were significantly different (P<0.05), and these differences increased with increasing levels of inactivation of three food-borne pathogens. These results demonstrate that ohmic heating can more effectively reduce bacterial populations at reduced temperatures and shorter time intervals, especially in acidic fruit juices such as apple juice. Therefore, loss of quality can be minimized in a pasteurization process incorporating ohmic heating.

Contact material optimization and contact physics in metal-contact microelectromechanical systems (MEMS) switches

NASA Astrophysics Data System (ADS)

Yang, Zhenyin

Metal-contact MEMS switches hold great promise for implementing agile radio frequency (RF) systems because of their small size, low fabrication cost, low power consumption, wide operational band, excellent isolation and exceptionally low signal insertion loss. Gold is often utilized as a contact material for metal-contact MEMS switches due to its excellent electrical conductivity and corrosion resistance. However contact wear and stiction are the two major failure modes for these switches due to its material softness and high surface adhesion energy. To strengthen the contact material, pure gold was alloyed with other metal elements. We designed and constructed a new micro-contacting test facility that closely mimic the typical MEMS operation and utilized this facility to efficiently evaluate optimized contact materials. Au-Ni binary alloy system as the candidate contact material for MEMS switches was systematically investigated. A correlation between contact material properties (etc. microstructure, micro-hardness, electrical resistivity, topology, surface structures and composition) and micro-contacting performance was established. It was demonstrated nano-scale graded two-phase Au-Ni film could possibly yield an improved device performance. Gold micro-contact degradation mechanisms were also systematically investigated by running the MEMS switching tests under a wide range of test conditions. According to our quantitative failure analysis, field evaporation could be the dominant failure mode for highfield (> critical threshold field) hot switching; transient thermal-assisted wear could be the dominant failure mode for low-field hot switching; on the other hand, pure mechanical wear and steady current heating (1 mA) caused much less contact degradation in cold switching tests. Results from low-force (50 muN/micro-contact), low current (0.1 mA) tests on real MEMS switches indicated that continuous adsorbed films from ambient air could degrade the switch contact resistance. Our work also contributes to the field of general nano-science and technology by resolving the transfer directionality of field evaporation of gold in atomic force microscope (AFM)/scanning tunneling microscope (STM).

Reconfigurable Antenna Aperture with Optically Controlled GeTe-Based RF Switches

DTIC Science & Technology

2015-03-31

duration (~100ns) but high amplitude raises the material’s temperature above the melting point . As a liquid, the atoms are randomly distributed...100ns, there is sufficient optical energy to heat and melt a 100nm thick GeTe PCM area of approximately 3µm 2 . Figure 3. Optimum PCM area...which tracks well with previously published thin film heater model [9]. Figure 4. Validation of Melt /Quench Thermal Model Optical Control: The

The 30 GHz solid state amplifier for low cost low data rate ground terminals

NASA Technical Reports Server (NTRS)

Ngan, Y. C.; Quijije, M. A.

1984-01-01

This report details the development of a 20-W solid state amplifier operating near 30 GHz. The IMPATT amplifier not only met or exceeded all the program objectives, but also possesses the ability to operate in the pulse mode, which was not called for in the original contract requirements. The ability to operate in the pulse mode is essential for TDMA (Time Domain Multiple Access) operation. An output power of 20 W was achieved with a 1-dB instantaneous bandwidth of 260 MHz. The amplifier has also been tested in pulse mode with 50% duty for pulse lengths ranging from 200 ns to 2 micro s with 10 ns rise and fall times and no degradation in output power. This pulse mode operation was made possible by the development of a stable 12-diode power combiner/amplifier and a single-diode pulsed driver whose RF output power was switched on and off by having its bias current modulated via a fast-switching current pulse modulator. Essential to the overall amplifier development was the successful development of state-of-the-art silicon double-drift IMPATT diodes capable of reproducible 2.5 W CW output power with 12% dc-to-RF conversion efficiency. Output powers of as high as 2.75 W has been observed. Both the device and circuit design are amenable to low cost production.

Ultra-thin ohmic contacts for p-type nitride light emitting devices

DOEpatents

Raffetto, Mark; Bharathan, Jayesh; Haberern, Kevin; Bergmann, Michael; Emerson, David; Ibbetson, James; Li, Ting

2014-06-24

A flip-chip semiconductor based Light Emitting Device (LED) can include an n-type semiconductor substrate and an n-type GaN epi-layer on the substrate. A p-type GaN epi-layer can be on the n-type GaN epi-layer and a metal ohmic contact p-electrode can be on the p-type GaN epi-layer, where the metal ohmic contact p-electrode can have an average thickness less than about 25 .ANG.. A reflector can be on the metal ohmic contact p-electrode and a metal stack can be on the reflector. An n-electrode can be on the substrate opposite the n-type GaN epi-layer and a bonding pad can be on the n-electrode.

Minimization of Ohmic losses for domain wall motion in ferromagnetic nanowires

NASA Astrophysics Data System (ADS)

Abanov, Artem; Tretiakov, Oleg; Liu, Yang

2011-03-01

We study current-induced domain-wall motion in a narrow ferromagnetic wire. We propose a way to move domain walls with a resonant time-dependent current which dramatically decreases the Ohmic losses in the wire and allows driving of the domain wall with higher speed without burning the wire. For any domain wall velocity we find the time-dependence of the current needed to minimize the Ohmic losses. Below a critical domain-wall velocity specified by the parameters of the wire the minimal Ohmic losses are achieved by dc current. Furthermore, we identify the wire parameters for which the losses reduction from its dc value is the most dramatic. This work was supported by the NSF Grant No. 0757992 and Welch Foundation (A-1678).

Comparison of nickel silicide and aluminium ohmic contact metallizations for low-temperature quantum transport measurements

PubMed Central

2011-01-01

We examine nickel silicide as a viable ohmic contact metallization for low-temperature, low-magnetic-field transport measurements of atomic-scale devices in silicon. In particular, we compare a nickel silicide metallization with aluminium, a common ohmic contact for silicon devices. Nickel silicide can be formed at the low temperatures (<400°C) required for maintaining atomic precision placement in donor-based devices, and it avoids the complications found with aluminium contacts which become superconducting at cryogenic measurement temperatures. Importantly, we show that the use of nickel silicide as an ohmic contact at low temperatures does not affect the thermal equilibration of carriers nor contribute to hysteresis in a magnetic field. PMID:21968083

Integrating a Microwave Radiometer into Radar Hardware for Simultaneous Data Collection Between the Instruments

NASA Technical Reports Server (NTRS)

McLinden, Matthew; Piepmeier, Jeffrey

2013-01-01

The conventional method for integrating a radiometer into radar hardware is to share the RF front end between the instruments, and to have separate IF receivers that take data at separate times. Alternatively, the radar and radiometer could share the antenna through the use of a diplexer, but have completely independent receivers. This novel method shares the radar's RF electronics and digital receiver with the radiometer, while allowing for simultaneous operation of the radar and radiometer. Radars and radiometers, while often having near-identical RF receivers, generally have substantially different IF and baseband receivers. Operation of the two instruments simultaneously is difficult, since airborne radars will pulse at a rate of hundreds of microseconds. Radiometer integration time is typically 10s or 100s of milliseconds. The bandwidth of radar may be 1 to 25 MHz, while a radiometer will have an RF bandwidth of up to a GHz. As such, the conventional method of integrating radar and radiometer hardware is to share the highfrequency RF receiver, but to have separate IF subsystems and digitizers. To avoid corruption of the radiometer data, the radar is turned off during the radiometer dwell time. This method utilizes a modern radar digital receiver to allow simultaneous operation of a radiometer and radar with a shared RF front end and digital receiver. The radiometer signal is coupled out after the first down-conversion stage. From there, the radar transmit frequencies are heavily filtered, and the bands outside the transmit filter are amplified and passed to a detector diode. This diode produces a DC output proportional to the input power. For a conventional radiometer, this level would be digitized. By taking this DC output and mixing it with a system oscillator at 10 MHz, the signal can instead be digitized by a second channel on the radar digital receiver (which typically do not accept DC inputs), and can be down-converted to a DC level again digitally. This unintuitive step allows the digital receiver to sample both the radiometer and radar data at a rapid, synchronized data rate (greater than 1 MHz bandwidth). Once both signals are sampled by the same digital receiver, high-speed quality control can be performed on the radiometer data to allow it to take data simultaneously with the radar. The radiometer data can be blanked during radar transmit, or when the radar return is of a power level high enough to corrupt the radiometer data. Additionally, the receiver protection switches in the RF front end can double as radiometer calibration sources, the short (four-microsecond level) switching periods integrated over many seconds to estimate the radiometer offset. The major benefit of this innovation is that there is minimal impact on the radar performance due to the integration of the radiometer, and the radiometer performance is similarly minimally affected by the radar. As the radar and radiometer are able to operate simultaneously, there is no extended period of integration time loss for the radiometer (maximizing sensitivity), and the radar is able to maintain its full number of pulses (increasing sensitivity and decreasing measurement uncertainty).

High Speed and High Functional Inverter Power Supplies for Plasma Generation and Control, and their Performance

NASA Astrophysics Data System (ADS)

Uesugi, Yoshihiko; Razzak, Mohammad A.; Kondo, Kenji; Kikuchi, Yusuke; Takamura, Shuichi; Imai, Takahiro; Toyoda, Mitsuhiro

The Rapid development of high power and high speed semiconductor switching devices has led to their various applications in related plasma fields. Especially, a high speed inverter power supply can be used as an RF power source instead of conventional linear amplifiers and a power supply to control the magnetic field in a fusion plasma device. In this paper, RF thermal plasma production and plasma heating experiments are described emphasis placed on using a static induction transistor inverter at a frequency range between 200 kHz and 2.5 MHz as an RF power supply. Efficient thermal plasma production is achieved experimentally by using a flexible and easily operated high power semiconductor inverter power supply. Insulated gate bipolar transistor (IGBT) inverter power supplies driven by a high speed digital signal processor are applied as tokamak joule coil and vertical coil power supplies to control plasma current waveform and plasma equilibrium. Output characteristics, such as the arbitrary bipolar waveform generation of a pulse width modulation (PWM) inverter using digital signal processor (DSP) can be successfully applied to tokamak power supplies for flexible plasma current operation and fast position control of a small tokamak.

Microsecond switchable thermal antenna

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ben-Abdallah, Philippe, E-mail: pba@institutoptique.fr; Benisty, Henri; Besbes, Mondher

2014-07-21

We propose a thermal antenna that can be actively switched on and off at the microsecond scale by means of a phase transition of a metal-insulator material, the vanadium dioxide (VO{sub 2}). This thermal source is made of a periodically patterned tunable VO{sub 2} nanolayer, which support a surface phonon-polariton in the infrared range in their crystalline phase. Using electrodes properly registered with respect to the pattern, the VO{sub 2} phase transition can be locally triggered by ohmic heating so that the surface phonon-polariton can be diffracted by the induced grating, producing a highly directional thermal emission. Conversely, when heatingmore » less, the VO{sub 2} layers cool down below the transition temperature, the surface phonon-polariton cannot be diffracted anymore so that thermal emission is inhibited. This switchable antenna could find broad applications in the domain of active thermal coatings or in those of infrared spectroscopy and sensing.« less

Development of a satellite microwave radiometer to sense the surface temperature of the world oceans

NASA Technical Reports Server (NTRS)

Hidy, G. M.; Hall, W. F.; Hardy, W. N.; Ho, W. W.; Jones, A. C.; Love, A. W.; Vannmell, M. J.; Wang, H. H.; Wheeler, A. E.

1972-01-01

A proposed S-band radiometer for determining the ocean surface temperature with an absolute accuracy of + or - 1 Kelvin and a resolution of + or - .1 Kelvin was placed under the Advanced Applications Flight Experiment for further development into Nimbus readiness state. The results of assessing the following are described: effects due to the state of the sea surface, effects caused by the intervening atmosphere, and effects associated with imperfections in the instrument itself. An extensive sea truth program is also described for correlation of aircraft test flight measurements or of satellite remote measurement to in-situ data. An improved radiometer design is a modified Dicke-switch type with temperature stabilized, microwave integrated circuit, front-end and with a pulsed injection-noise nulling system. The radiometer has a multimode rectangular horn antenna with very low ohmic losses and a beam efficiency of 98% or better.

FAST TRACK COMMUNICATION: Nanocrystalline silicon film growth morphology control through RF waveform tailoring

NASA Astrophysics Data System (ADS)

Johnson, Erik V.; Verbeke, Thomas; Vanel, Jean-Charles; Booth, Jean-Paul

2010-10-01

We demonstrate the application of RF waveform tailoring to generate an electrical asymmetry in a capacitively coupled plasma-enhanced chemical vapour deposition system, and its use to control the growth mode of hydrogenated amorphous and nanocrystalline silicon thin films deposited at low temperature (150 °C). A dramatic shift in the dc bias potential at the powered electrode is observed when simply inverting the voltage waveform from 'peaks' to 'troughs', indicating an asymmetric distribution of the sheath voltage. By enhancing or suppressing the ion bombardment energy at the substrate (situated on the grounded electrode), the growth of thin silicon films can be switched between amorphous and nanocrystalline modes, as observed using in situ spectroscopic ellipsometry. The effect is observed at pressures sufficiently low that the collisional reduction in average ion bombardment energy is not sufficient to allow nanocrystalline growth (<100 mTorr).

THz impulse radar for biomedical sensing: nonlinear system behavior

NASA Astrophysics Data System (ADS)

Brown, E. R.; Sung, Shijun; Grundfest, W. S.; Taylor, Z. D.

2014-03-01

The THz impulse radar is an "RF-inspired" sensor system that has performed remarkably well since its initial development nearly six years ago. It was developed for ex vivo skin-burn imaging, and has since shown great promise in the sensitive detection of hydration levels in soft tissues of several types, such as in vivo corneal and burn samples. An intriguing aspect of the impulse radar is its hybrid architecture which combines the high-peak-power of photoconductive switches with the high-responsivity and -bandwidth (RF and video) of Schottky-diode rectifiers. The result is a very sensitive sensor system in which the post-detection signal-to-noise ratio depends super-linearly on average signal power up to a point where the diode is "turned on" in the forward direction, and then behaves quasi-linearly beyond that point. This paper reports the first nonlinear systems analysis done on the impulse radar using MATLAB.

Effect of interfacial composition on Ag-based Ohmic contact of GaN-based vertical light emitting diodes

NASA Astrophysics Data System (ADS)

Wu, Ning; Xiong, Zhihua; Qin, Zhenzhen

2018-02-01

By investigating the effect of a defective interface structure on Ag-based Ohmic contact of GaN-based vertical light-emitting diodes, we found a direct relationship between the interfacial composition and the Schottky barrier height of the Ag(111)/GaN(0001) interface. It was demonstrated that the Schottky barrier height of a defect-free Ag(111)/GaN(0001) interface was 2.221 eV, and it would be dramatically decreased to 0.375 eV with the introduction of one Ni atom and one Ga vacancy at the interface structure. It was found that the tunability of the Schottky barrier height can be attributed to charge accumulations around the interfacial defective regions and an unpinning of the Fermi level, which explains the experimental phenomenon of Ni-assisted annealing improving the p-type Ohmic contact characteristic. Lastly, we propose a new method of using Cu as an assisted metal to realize a novel Ag-based Ohmic contact. These results provide a guideline for the fabrication of high-quality Ag-based Ohmic contact of GaN-based vertical light-emitting diodes.

A-O Q-switching of 2.1-μm laser

NASA Astrophysics Data System (ADS)

Zheng, Jia; Liu, Jingjiao; Tang, Yi; Hu, Yongzhao

2005-01-01

2.1μm solid state laser operating at room temperature is a very useful laser source for optical communication, medical care, air pollution monitoring and Lidar, etc. It is eye-safe. It is also a very ideal pump source for optic parametric oscillator to get 3μm -5μm radiation. In order to further explore its potential applications, higher peak power and shorter pulse width are very desirable. Q-switching the laser is a most practical way to realize those goals. Among the most common used Q-switching techniques, mechanical Q-switching is not preferred due to that it involves use of a rotating motor, which has lower life time and causes undesirable vibration. E-O Q-switch material in this wavelength range is very expensive and quite susceptible to optical damage. On the other hand, low OH concentration quartz material exhibits very low absorption at the 2.1μm. The Cr:Tm:Ho:YAG 2.1μm laser has undesirable lower gain from the laser efficiency point of view, but offers a feasibility of using the A-O device for the Q-switching even the laser is pulse pumped. The Cr:Tm:Ho:YAG 2.1μm laser is a so called quasi-three level laser, which is characterized as having a higher threshold and lower gain. This study is focused on the optimization of the laser resonator design and the A-O Q-switch design for a higher laser peak power and shorter pulse width. Factors considered in the study include AO Q-switch"s RF frequency, modulation depth, active aperture, resonator length, resonator loss and pumping design, etc. Experiment results are compared with the Q-switched quasi-three level laser model. Final result of the Q-switched 2.1μm laser after preliminary optimization will be presented.

Effect of reflective p-type ohmic contact on thermal reliability of vertical InGaN/GaN LEDs

NASA Astrophysics Data System (ADS)

Son, Jun Ho; Song, Yang Hee; Kim, Buem Joon; Lee, Jong-Lam

2014-11-01

We report on the enhanced thermal reliability of vertical-LEDs (VLEDs) using novel reflective p-type ohmic contacts with good thermal stability. The reflective p-type ohmic contacts with Ni/Ag-Cu alloy multi-layer structure shows low contact resistivity, as low as 9.3 × 10-6 Ωcm2, and high reflectance of 86% after annealing at 450°C. The V-LEDs with Ni/Ag-Cu alloy multi-layer structure show good thermal reliability with stress time at 300°C in air ambient. The improved thermal stability of the reflective ohmic contacts to p-type GaN is believed to play a critical role in the thermal reliability of V-LEDs. [Figure not available: see fulltext.

Degradation mechanisms of Ti/Al/Ni/Au-based Ohmic contacts on AlGaN/GaN HEMTs

DOE PAGES

Hwang, Ya-Hsi; Ahn, Shihyun; Dong, Chen; ...

2015-04-27

We investigated the degradation mechanism of Ti/Al/Ni/Au-based Ohmic metallization on AlGaN/GaN high electron mobility transistors upon exposure to buffer oxide etchant (BOE). The major effect of BOE on the Ohmic metal was an increase of sheet resistance from 2.89 to 3.69 Ω/ₜafter 3 min BOE treatment. The alloyed Ohmic metallization consisted 3–5 μm Ni-Al alloy islands surrounded by Au-Al alloy-rings. The morphology of both the islands and ring areas became flatter after BOE etching. Lastly, we used energy dispersive x-ray analysis and Auger electron microscopy to analyze the compositions and metal distributions in the metal alloys prior to and aftermore » BOE exposure.« less

Features of Stationary Photoconductivity of High-Ohmic Semiconductors Under Local Illumination

NASA Astrophysics Data System (ADS)

Lysenko, A. P.; Belov, A. G.; Kanevskii, V. E.; Odintsova, E. A.

2018-04-01

Photoconductivity has been thoroughly studied for a long time. However, most researchers have examined photoconductivity of semiconductors while illuminating the entire surface of samples. The present paper examines the effect of local exposure that ensures a high level of injection of free charge carriers upon the conductivity of high-ohmic cadmium telluride and semi-insulating gallium arsenide samples and upon the properties of ohmic contacts to samples. The authors found that regardless of the exposure area the value of transition resistance of ohmic contacts decreases and the concentration of the main charge carriers increases in the sample in proportion to radiation intensity. This research uncovered a number of previously unknown effects that are interesting from the physical point of view. This paper focuses on discussing these effects.

Stable CW Single Frequency Operation of Fabry-Perot Laser Diodes by Self-Injection Phase Locking

NASA Technical Reports Server (NTRS)

Duerksen, Gary L.; Krainak, Michael A.

1999-01-01

Previously, single-frequency semiconductor laser operation using fiber Bragg gratings has been achieved by tWo methods: 1) use of the FBG as the output coupler for an anti-reflection-coated semiconductor gain element'; 2) pulsed operation of a gain-switched Fabry-Perot laser diode with FBG-optical and RF-electrical feedback'. Here, we demonstrate CW single frequency operation from a non-AR coated Fabry-Perot laser diode using only FBG optical feedback.

Stable CW Single-Frequency Operation of Fabry-Perot Laser Diodes by Self-Injection Phase Locking

NASA Technical Reports Server (NTRS)

Duerksen, Gary L.; Krainak, Michael A.

1998-01-01

Previously, single-frequency semiconductor laser operation using fiber Bragg gratings (FBG) has been achieved by two methods: (1) use of the FBG as the output coupler for an anti-reflection-coated semiconductor gain element; (2) pulsed operation of a gain-switched Fabry-Perot laser diode with FBG-optical and RF-electrical feedback. Here, we demonstrate CW single frequency operation from a non-AR coated Fabry-Perot laser diode using only FBG optical feedback.

The Impact of GaN/Substrate Thermal Boundary Resistance on a HEMT Device

DTIC Science & Technology

2011-11-01

stack between the GaN and Substrate layers. The University of Bristol recently reported that this TBR in commercial devices on Silicon Carbide ( SiC ...Circuit RF Radio Frequency PA Power Amplifier SiC Silicon Carbide FEA Finite Element Analysis heff Effective Heat transfer Coefficient (W/m 2 K...substrate material switched from sapphire to silicon , and by another factor of two from silicon to SiC . TABLE 1: SAMPLE RESULTS FROM DOUGLAS ET AL. FOR

Signal Selector, Spectrum Receivers and Touch Panel Control for the SATCOM Signal Analyzer.

DTIC Science & Technology

1980-06-01

that the entire system may be exercised in a test mode with the push of a single button. Normally test functions are divided into separate areas so that...source. The major com- ponents of the SS include power dividers and RF switches. The second of the two modules is the Spectrum Receiver (SR). Four... dividers and adjustable attenuators may be mounted on the opposite side of the panel. Component size is res- tricted on the panel back side due to a two

Method for Fabricating and Packaging an M.Times.N Phased-Array Antenna

NASA Technical Reports Server (NTRS)

Xu, Xiaochuan (Inventor); Chen, Yihong (Inventor); Chen, Ray T. (Inventor); Subbaraman, Harish (Inventor)

2017-01-01

A method for fabricating an M.times.N, P-bit phased-array antenna on a flexible substrate is disclosed. The method comprising ink jet printing and hardening alignment marks, antenna elements, transmission lines, switches, an RF coupler, and multilayer interconnections onto the flexible substrate. The substrate of the M.times.N, P-bit phased-array antenna may comprise an integrated control circuit of printed electronic components such as, photovoltaic cells, batteries, resistors, capacitors, etc. Other embodiments are described and claimed.

Continuous-Wave Operation of a 460-GHz Second Harmonic Gyrotron Oscillator

PubMed Central

Hornstein, Melissa K.; Bajaj, Vikram S.; Griffin, Robert G.; Temkin, Richard J.

2007-01-01

We report the regulated continuous-wave (CW) operation of a second harmonic gyrotron oscillator at output power levels of over 8 W (12.4 kV and 135 mA beam voltage and current) in the TE0,6,1 mode near 460 GHz. The gyrotron also operates in the second harmonic TE2,6,1 mode at 456 GHz and in the TE2,3,1 fundamental mode at 233 GHz. CW operation was demonstrated for a one-hour period in the TE0,6,1 mode with better than 1% power stability, where the power was regulated using feedback control. Nonlinear simulations of the gyrotron operation agree with the experimentally measured output power and radio-frequency (RF) efficiency when cavity ohmic losses are included in the analysis. The output radiation pattern was measured using a pyroelectric camera and is highly Gaussian, with an ellipticity of 4%. The 460-GHz gyrotron will serve as a millimeter-wave source for sensitivity-enhanced nuclear magnetic resonance (dynamic nuclear polarization) experiments at a magnetic field of 16.4 T. PMID:17710187

Upgrade of the compact neutron spectrometer for high flux environments

NASA Astrophysics Data System (ADS)

Osipenko, M.; Bellucci, A.; Ceriale, V.; Corsini, D.; Gariano, G.; Gatti, F.; Girolami, M.; Minutoli, S.; Panza, F.; Pillon, M.; Ripani, M.; Trucchi, D. M.

2018-03-01

In this paper new version of the 6Li-based neutron spectrometer for high flux environments is described. The new spectrometer was built with commercial single crystal Chemical Vapour Deposition diamonds of electronic grade. These crystals feature better charge collection as well as higher radiation hardness. New metal contacts approaching ohmic conditions were deposited on the diamonds suppressing build-up of space charge observed in the previous prototypes. New passive preamplification of the signal at detector side was implemented to improve its resolution. This preamplification is based on the RF transformer not sensitive to high neutron flux. The compact mechanical design allowed to reduce detector size to a tube of 1 cm diameter and 13 cm long. The spectrometer was tested in the thermal column of TRIGA reactor and at the DD neutron generator. The test results indicate an energy resolution of 300 keV (FWHM), reduced to 72 keV (RMS) excluding energy loss, and coincidence timing resolution of 160 ps (FWHM). The measured data are in agreement with Geant4 simulations except for larger energy loss tail presumably related to imperfections of metal contacts and glue expansion.

Degradation Mechanisms for GaN and GaAs High Speed Transistors

PubMed Central

Cheney, David J.; Douglas, Erica A.; Liu, Lu; Lo, Chien-Fong; Gila, Brent P.; Ren, Fan; Pearton, Stephen J.

2012-01-01

We present a review of reliability issues in AlGaN/GaN and AlGaAs/GaAs high electron mobility transistors (HEMTs) as well as Heterojunction Bipolar Transistors (HBTs) in the AlGaAs/GaAs materials systems. Because of the complex nature and multi-faceted operation modes of these devices, reliability studies must go beyond the typical Arrhenius accelerated life tests. We review the electric field driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plate), and the effect of device fabrication processes for both DC and RF stress conditions. We summarize the degradation mechanisms that limit the lifetime of these devices. A variety of contact and surface degradation mechanisms have been reported, but differ in the two device technologies: For HEMTs, the layers are thin and relatively lightly doped compared to HBT structures and there is a metal Schottky gate that is directly on the semiconductor. By contrast, the HBT relies on pn junctions for current modulation and has only Ohmic contacts. This leads to different degradation mechanisms for the two types of devices.

Effect of silicide/silicon hetero-junction structure on thermal conductivity and Seebeck coefficient.

PubMed

Choi, Wonchul; Park, Young-Sam; Hyun, Younghoon; Zyung, Taehyoung; Kim, Jaehyeon; Kim, Soojung; Jeon, Hyojin; Shin, Mincheol; Jang, Moongyu

2013-12-01

We fabricated a thermoelectric device with a silicide/silicon laminated hetero-structure by using RF sputtering and rapid thermal annealing. The device was observed to have Ohmic characteristics by I-V measurement. The temperature differences and Seebeck coefficients of the proposed silicide/silicon laminated and bulk structure were measured. The laminated thermoelectric device shows suppression of heat flow from the hot to cold side. This is supported by the theory that the atomic mass difference between silicide and silicon creates a scattering center for phonons. The major impact of our work is that phonon transmission is suppressed at the interface between silicide and silicon without degrading electrical conductivity. The estimated thermal conductivity of the 3-layer laminated device is 126.2 +/- 3.7 W/m. K. Thus, by using the 3-layer laminated structure, thermal conductivity is reduced by around 16% compared to bulk silicon. However, the Seebeck coefficient of the thermoelectric device is degraded compared to that of bulk silicon. It is understood that electrical conductivity is improved by using silicide as a scattering center.

A Switched-Mode Breast Coil for 7 T MRI Using Forced-Current Excitation

PubMed Central

Bosshard, John C.; Rispoli, Joseph V.; Dimitrov, Ivan E.; Cheshkov, Sergey; McDougall, Mary Preston; Malloy, Craig; Wright, Steven M.

2015-01-01

In high-field magnetic resonance imaging, the radio frequency wavelength within the human body is comparable to anatomical dimensions, resulting in B1 inhomogeneity and nonuniform sensitivity patterns. Thus, this relatively short wavelength presents engineering challenges for RF coil design. In this study, a bilateral breast coil for 1H imaging at 7 T was designed and constructed using forced-current excitation. By forcing equal current through the coil elements, we reduce the effects of coupling between the elements to simplify tuning and to ensure a uniform field across both breasts. To combine the benefits of the higher power efficiency of a unilateral coil with the bilateral coverage of a bilateral coil, a switching circuit was implemented to allow the coil to be reconfigured for imaging the left, right, or both breasts. PMID:25706501

Switch over to the high frequency rf systems near transition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brennan, J.M.; Wei, J.

1988-01-01

The purpose of this note is to point out that since bunch narrowing naturally occurs in the acceleration process in the vicinity of transition, it should be possible to switch over to the high frequency system close to transition when the bunch has narrowed enough to fit directly into the high frequency bucket. The advantage of this approach is the simplicity, no extra components or gymnastics are required of the low frequency system. The disadvantage, of course, is for protons which do not go through transition. But on the other hand, there is no shortage of intensity for protons andmore » so it should be possible to keep the phase space area low for protons, and then matching to the high frequency bucket should be easily accomplished by adiabatic compression. 3 refs., 7 figs.« less

Remarks on the thermal stability of an Ohmic-heated nanowire

NASA Astrophysics Data System (ADS)

Timsit, Roland S.

2018-05-01

The rise in temperature of a wire made from specific materials, due to ohmic heating by a DC electrical current, may lead to uncontrollable thermal runaway with ensuing melting. Thermal runaway stems from a steep decrease with increasing temperature of the thermal conductivity of the conducting material and subsequent trapping of the ohmic heat in the wire, i.e., from the inability of the wire to dissipate the heat sufficiently quickly by conduction to the cooler ends of the wire. In this paper, we show that the theory used to evaluate the temperature of contacting surfaces in a bulk electrical contact may be applied to calculate the conditions for thermal runaway in a nanowire. Implications of this effect for electrical contacts are addressed. A possible implication for memory devices using ohmic-heated nanofilms or nanowires is also discussed.

Spin caloritronic nano-oscillator

DOE PAGES

Safranski, C.; Barsukov, I.; Lee, H. K.; ...

2017-07-18

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y 3Fe 5O 12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y 3Fe 5O 12 layer. This leads to excitation of auto-oscillations of the Ymore » 3Fe 5O 12 magnetization and generation of coherent microwave radiation. Thus, our work paves the way towards spin caloritronic devices for microwave and magnonic applications.« less

Spin caloritronic nano-oscillator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Safranski, C.; Barsukov, I.; Lee, H. K.

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y 3Fe 5O 12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y 3Fe 5O 12 layer. This leads to excitation of auto-oscillations of the Ymore » 3Fe 5O 12 magnetization and generation of coherent microwave radiation. Thus, our work paves the way towards spin caloritronic devices for microwave and magnonic applications.« less

Modulators for the S-band test linac at DESY

NASA Astrophysics Data System (ADS)

Bieler, M.; Choroba, S.; Hameister, J.; Lewin, H.-Ch.

1995-07-01

The development of adequate modulators for high peak power klystrons is one of the focus points for linear collider R&D programs. For the DESY/THD S-band linear collider study 150 MW rf-pulse power at 50 Hz repetition rate and 3 μs pulse duration is required [1]. Two different modulator schemes are under investigation. One is the conventional line type pulser, using a pulse forming network and a step up transformer, the other one is a hard tube pulser, using a dc power source at the full klystron voltage and a switch tube. This paper is focused on the modulator development for the S-band Test Linac at DESY. After a short overview over the test linac and a brief description of the 150 MW S-band klystron the circuitry of the line type pulse (LTP) is given. A hard tube pulser (HTP), which switches the high voltage directly from a storage capacitor to the klystron, has been built up at DESY. Circuitry and the results of the commissioning of the switch tube are reported.

A high power microwave triggered RF opening switch.

PubMed

Beeson, S; Dickens, J; Neuber, A

2015-03-01

A 4-port S-band waveguide structure was designed and fabricated such that a signal of any amplitude (less than 1 MW) can be switched from a normally closed state, <0.5 dB insertion loss (IL), to an open state >30 dB IL by initiating plasma in a gas cell situated at the junction of this waveguide and one propagating a megawatt level magnetron pulse. The 90/10 switching time is as low as 20 ns with a delay of ∼30 ns between the onset of the high power microwave pulse and the initial drop of the signal. Two ports of this device are for the high power triggering pulse while the other two ports are for the triggered signal in a Moreno-like coupler configuration. In order to maintain high isolation, these two sets of waveguides are rotated 90° from each other with a TE111 resonator/plasma cell located at the intersection. This manuscript describes the design and optimization of this structure using COMSOL 4.4 at the design frequency of 2.85 GHz, comparison of simulated scattering parameters with measured "cold tests" (testing without plasma), and finally the temporal waveforms of this device being used to successfully switch a low power CW signal from 2 W to <5 mW on a sub-microsecond timescale.

Impact of oxygen stoichiometry on electroforming and multiple switching modes in TiN/TaOx/Pt based ReRAM

NASA Astrophysics Data System (ADS)

Sharath, S. U.; Joseph, M. J.; Vogel, S.; Hildebrandt, E.; Komissinskiy, P.; Kurian, J.; Schroeder, T.; Alff, L.

2016-10-01

We have investigated the material and electrical properties of tantalum oxide thin films (TaOx) with engineered oxygen contents grown by RF-plasma assisted molecular beam epitaxy. The optical bandgap and the density of the TaOx films change consistently with oxygen contents in the range of 3.63 to 4.66 eV and 12.4 to 9.0 g/cm3, respectively. When exposed to atmosphere, an oxidized Ta2O5-y surface layer forms with a maximal thickness of 1.2 nm depending on the initial oxygen deficiency of the film. X-ray photoelectron spectroscopy studies show that multiple sub-stoichiometric compositions occur in oxygen deficient TaOx thin films, where all valence states of Ta including metallic Ta are possible. Devices of the form Pt/Ta2O5-y/TaOx/TiN exhibit highly tunable forming voltages of 10.5 V to 1.5 V with decreasing oxygen contents in TaOx. While a stable bipolar resistive switching (BRS) occurs in all devices irrespective of oxygen content, unipolar switching was found to coexist with BRS only at higher oxygen contents, which transforms to a threshold switching behaviour in the devices grown under highest oxidation.

Plasma-assisted ohmic contact for AlGaN/GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Zhang, Jiaqi; Wang, Lei; Wang, Qingpeng; Jiang, Ying; Li, Liuan; Zhu, Huichao; Ao, Jin-Ping

2016-03-01

An Al-based ohmic process assisted by an inductively coupled plasma (ICP) recess treatment is proposed for AlGaN/GaN heterostructure field-effect transistors (HFETs) to realize ohmic contact, which is only needed to anneal at 500 °C. The recess treatment was done with SiCl4 plasma with 100 W ICP power for 20 s and annealing at 575 °C for 1 min. Under these conditions, contact resistance of 0.52 Ωmm was confirmed. To suppress the ball-up phenomenon and improve the surface morphology, an Al/TiN structure was also fabricated with the same conditions. The contact resistance was further improved to 0.30 Ωmm. By using this plasma-assisted ohmic process, a gate-first HFET was fabricated. The device showed high drain current density and high transconductance. The leakage current of the TiN-gate device decreased to 10-9 A, which was 5 orders of magnitude lower than that of the device annealed at 800 °C. The results showed that the low-temperature ohmic contact process assisted by ICP treatment is promising for the fabrication of gate-first and self-aligned gate HFETs.

Influence of infrared final cooking on color, texture and cooking characteristics of ohmically pre-cooked meatball.

PubMed

Yildiz Turp, Gulen; Icier, Filiz; Kor, Gamze

2016-04-01

The objective of the current study was to improve the quality characteristics of ohmically pre-cooked beef meatballs via infrared cooking as a final stage. Samples were pre-cooked in a specially designed-continuous type ohmic cooker at a voltage gradient of 15.26 V/cm for 92 s. Infrared cooking was then applied to the pre-cooked samples at different combinations of heat fluxes (3.706, 5.678, and 8.475 kW/m(2)), application distances (10.5, 13.5, and 16.5 cm) and application durations (4, 8, and 12min). Effects of these parameters on color, texture and cooking characteristics of ohmically pre-cooked beef meatballs were investigated. The appearance of ohmically pre-cooked meatball samples was improved via infrared heating. A dark brown layer desired in cooked meatballs formed on the surface of the meatballs with lowest application distance (10.5 cm) and longest application duration (12 min). The texture of the samples was also improved with these parameters. However the cooking yield of the samples decreased at the longest application duration of infrared heating. Copyright © 2015 Elsevier Ltd. All rights reserved.

Ohmic cooking of whole beef muscle--evaluation of the impact of a novel rapid ohmic cooking method on product quality.

PubMed

Zell, Markus; Lyng, James G; Cronin, Denis A; Morgan, Desmond J

2010-10-01

Cylindrical cores of beef semitendinosus (500g) were cooked in a combined ohmic/convection heating system to low (72 degrees C, LTLT) and high (95 degrees C, HTST) target end-point temperatures. A control was also cooked to an end-point temperature of 72 degrees C at the coldest point. Microbial challenge studies on a model meat matrix confirmed product safety. Hunter L-values showed that ohmically heated meat had significantly (p<0.05) lighter surface-colours (63.05 (LTLT) and 62.26 (HTST)) relative to the control (56.85). No significant texture differences (p>/=0.05) were suggested by Warner-Bratzler peak load values (34.09, 36.37 vs. 35.19N). Cook loss was significantly (p<0.05) lower for LTLT samples (29.3%) compared to the other meats (36.3 and 33.8%). Sensory studies largely confirmed these observations. Cook values were lower for LTLT (3.05) while HTST and the control were more comparable (6.09 and 7.71, respectively). These results demonstrate considerable potential for this application of ohmic heating for whole meats. Copyright (c) 2010 The American Meat Science Association. Published by Elsevier Ltd. All rights reserved.

An “ohmic-first” self-terminating gate-recess technique for normally-off Al2O3/GaN MOSFET

NASA Astrophysics Data System (ADS)

Wang, Hongyue; Wang, Jinyan; Li, Mengjun; He, Yandong; Wang, Maojun; Yu, Min; Wu, Wengang; Zhou, Yang; Dai, Gang

2018-04-01

In this article, an ohmic-first AlGaN/GaN self-terminating gate-recess etching technique was demonstrated where ohmic contact formation is ahead of gate-recess-etching/gate-dielectric-deposition (GRE/GDD) process. The ohmic contact exhibits few degradations after the self-terminating gate-recess process. Besides, when comparing with that using the conventional fabrication process, the fabricated device using the ohmic-first fabrication process shows a better gate dielectric quality in terms of more than 3 orders lower forward gate leakage current, more than twice higher reverse breakdown voltage as well as better stability. Based on this proposed technique, the normally-off Al2O3/GaN MOSFET exhibits a threshold voltage (V th) of ˜1.8 V, a maximum drain current of ˜328 mA/mm, a forward gate leakage current of ˜10-6 A/mm and an off-state breakdown voltage of 218 V at room temperature. Meanwhile, high temperature characteristics of the device was also evaluated and small variations (˜7.6%) of the threshold voltage was confirmed up to 300 °C.

Study of degradation processes kinetics in ohmic contacts of resonant tunneling diodes based on nanoscale AlAs/GaAs heterostructures under influence of temperature

NASA Astrophysics Data System (ADS)

Makeev, M. O.; Meshkov, S. A.

2017-07-01

The artificial aging of resonant tunneling diodes based on nanoscale AlAs/GaAs heterostructures was conducted. As a result of the thermal influence resonant tunneling diodes IV curves degrade firstly due to ohmic contacts' degradation. To assess AlAs/GaAs resonant tunneling diodes degradation level and to predict their reliability, a functional dependence of the contact resistance of resonant tunneling diode AuGeNi ohmic contacts on time and temperature was offered.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arutyunyan, S. S., E-mail: spartakmain@gmail.com; Pavlov, A. Yu.; Pavlov, B. Yu.

The fabrication of a two-layer Si{sub 3}N{sub 4}/SiO{sub 2} dielectric mask and features of its application in the technology of non-fired epitaxially grown ohmic contacts for high-power HEMTs on AlGaN/GaN heterostructures are described. The proposed Si{sub 3}N{sub 4}/SiO{sub 2} mask allows the selective epitaxial growth of heavily doped ohmic contacts by nitride molecular-beam epitaxy and the fabrication of non-fired ohmic contacts with a resistance of 0.15–0.2 Ω mm and a smooth surface and edge morphology.

Improved Turn-On and Operating Voltages in AlGaN-Based Deep-Ultraviolet Light-Emitting Diodes

NASA Astrophysics Data System (ADS)

Hao, Guo-Dong; Taniguchi, Manabu; Tamari, Naoki; Inoue, Shin-ichiro

2017-10-01

While good ohmic contact formation has been achieved on both p-GaN and n-AlGaN surfaces, the turn-on and operating voltages of AlGaN-based deep-ultraviolet light-emitting diodes (DUV-LEDs) remain very high. We find that this critical problem is mainly caused by the large difference between the annealing temperatures required for ohmic contact formation on the p-GaN and high Al-fraction n-AlGaN surfaces. We studied the effects of the high-temperature annealing treatments required for n-ohmic contact formation on the subsequent p-ohmic contact formation process in DUV-LEDs. The results show that post-annealing treatment at high temperature is necessary to form an ohmic contact on n-Al0.7Ga0.3N, but a treatment temperature of 900°C or more could cause severe degradation of the specific contact resistivity and the bulk resistivity of p-GaN. We conclude that 900°C is the optimum temperature to form an ohmic contact on n-Al0.7Ga0.3N in DUV-LEDs, where p-GaN and n-Al0.7Ga0.3N act as the p- and n-ohmic contact layers, respectively. We also found that the specific contact resistivity of p-GaN can be reduced by an additional low-temperature annealing treatment after the high-temperature annealing step; this effect can be attributed to the enhancement of the hole concentration in the p-GaN surface contact region. Finally, DUV-LEDs that emit at 280 nm were fabricated using four different annealing treatments during processing. A considerable reduction in the series resistance and thereby in the operating voltage was confirmed using the annealing process proposed above, consisting of a high-temperature anneal at 900°C followed by a low-temperature anneal at 500°C for 3 min.

Improved passive optical network architectures to support local area network emulation and protection

NASA Astrophysics Data System (ADS)

Wong, Elaine; Nadarajah, Nishaanthan; Chae, Chang-Joon; Nirmalathas, Ampalavanapillai; Attygalle, Sanjeewa M.

2006-01-01

We describe two optical layer schemes which simultaneously facilitate local area network emulation and automatic protection switching against distribution fiber breaks in passive optical networks. One scheme employs a narrowband fiber Bragg grating placed close to the star coupler in the feeder fiber of the passive optical network, while the other uses an additional short length distribution fiber from the star coupler to each customer for the redirection of the customer traffic. Both schemes use RF subcarrier multiplexed transmission for intercommunication between customers in conjunction with upstream access to the central office at baseband. Failure detection and automatic protection switching are performed independently by each optical network unit that is located at the customer premises in a distributed manner. The restoration of traffic transported between the central office and an optical network unit in the event of the distribution fiber break is performed by interconnecting adjacent optical network units and carrying out signal transmissions via an independent but interconnected optical network unit. Such a protection mechanism enables multiple adjacent optical network units to be simultaneously protected by a single optical network unit utilizing its maximum available bandwidth. We experimentally verify the feasibility of both schemes with 1.25 Gb/s upstream baseband transmission to the central office and 155 Mb/s local area network data transmission on a RF subcarrier frequency. The experimental results obtained from both schemes are compared, and the power budgets are calculated to analyze the scalability of each scheme.

Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies

NASA Astrophysics Data System (ADS)

Kotadiya, Naresh B.; Lu, Hao; Mondal, Anirban; Ie, Yutaka; Andrienko, Denis; Blom, Paul W. M.; Wetzelaer, Gert-Jan A. H.

2018-02-01

Barrier-free (Ohmic) contacts are a key requirement for efficient organic optoelectronic devices, such as organic light-emitting diodes, solar cells, and field-effect transistors. Here, we propose a simple and robust way of forming an Ohmic hole contact on organic semiconductors with a high ionization energy (IE). The injected hole current from high-work-function metal-oxide electrodes is improved by more than an order of magnitude by using an interlayer for which the sole requirement is that it has a higher IE than the organic semiconductor. Insertion of the interlayer results in electrostatic decoupling of the electrode from the semiconductor and realignment of the Fermi level with the IE of the organic semiconductor. The Ohmic-contact formation is illustrated for a number of material combinations and solves the problem of hole injection into organic semiconductors with a high IE of up to 6 eV.

Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies.

PubMed

Kotadiya, Naresh B; Lu, Hao; Mondal, Anirban; Ie, Yutaka; Andrienko, Denis; Blom, Paul W M; Wetzelaer, Gert-Jan A H

2018-04-01

Barrier-free (Ohmic) contacts are a key requirement for efficient organic optoelectronic devices, such as organic light-emitting diodes, solar cells, and field-effect transistors. Here, we propose a simple and robust way of forming an Ohmic hole contact on organic semiconductors with a high ionization energy (IE). The injected hole current from high-work-function metal-oxide electrodes is improved by more than an order of magnitude by using an interlayer for which the sole requirement is that it has a higher IE than the organic semiconductor. Insertion of the interlayer results in electrostatic decoupling of the electrode from the semiconductor and realignment of the Fermi level with the IE of the organic semiconductor. The Ohmic-contact formation is illustrated for a number of material combinations and solves the problem of hole injection into organic semiconductors with a high IE of up to 6 eV.

Ohmic Inflation of Hot Jupiters: an Analytical Approach

NASA Astrophysics Data System (ADS)

Ginzburg, Sivan; Sari, Re'em

2015-12-01

Many giant exoplanets in close orbits have observed radii which exceed theoretical predictions.One suggested explanation for this discrepancy is heat deposited deep inside the atmospheres of these hot Jupiters.We present an analytical model for the evolution of such irradiated, and internally heated gas giants, and derive scaling laws for their cooling rates and radii.We estimate the Ohmic dissipation resulting from the interaction between the atmospheric winds and the planet's magnetic field, and apply our model to Ohmically heated planets.Our model can account for the observed radii of many inflated planets, but not the most extreme ones.We show that Ohmically heated planets have already reached their equilibrium phase and they no longer contract.We show that it is possible to re-inflate planets, but we confirm that re-heating timescales are longer by about a factor of 30 than cooling times.

Ohmic contact formation between metal and AlGaN/GaN heterostructure via graphene insertion

NASA Astrophysics Data System (ADS)

Sung Park, Pil; Reddy, Kongara M.; Nath, Digbijoy N.; Yang, Zhichao; Padture, Nitin P.; Rajan, Siddharth

2013-04-01

A simple method for the creation of Ohmic contact to 2D electron gas in AlGaN/GaN high electron-mobility transistors using Cr/graphene layer is demonstrated. A weak temperature dependence of this Ohmic contact observed in the range 77 to 300 K precludes thermionic emission or trap-assisted hopping as possible carrier-transport mechanisms. It is suggested that the Cr/graphene combination acts akin to a doped n-type semiconductor in contact with AlGaN/GaN heterostructure, and promotes carrier transport along percolating Al-lean paths through the AlGaN layer. This use of graphene offers a simple method for making Ohmic contacts to AlGaN/GaN heterostructures, circumventing complex additional processing steps involving high temperatures. These results could have important implications for the fabrication and manufacturing of AlGaN/GaN-based microelectronic and optoelectronic devices/sensors of the future.

AlGaN channel field effect transistors with graded heterostructure ohmic contacts

NASA Astrophysics Data System (ADS)

Bajaj, Sanyam; Akyol, Fatih; Krishnamoorthy, Sriram; Zhang, Yuewei; Rajan, Siddharth

2016-09-01

We report on ultra-wide bandgap (UWBG) Al0.75Ga0.25N channel metal-insulator-semiconductor field-effect transistors (MISFETs) with heterostructure engineered low-resistance ohmic contacts. The low intrinsic electron affinity of AlN (0.6 eV) leads to large Schottky barriers at the metal-AlGaN interface, resulting in highly resistive ohmic contacts. In this work, we use a reverse compositional graded n++ AlGaN contact layer to achieve upward electron affinity grading, leading to a low specific contact resistance (ρsp) of 1.9 × 10-6 Ω cm2 to n-Al0.75Ga0.25N channels (bandgap ˜5.3 eV) with non-alloyed contacts. We also demonstrate UWBG Al0.75Ga0.25N channel MISFET device operation employing the compositional graded n++ ohmic contact layer and 20 nm atomic layer deposited Al2O3 as the gate-dielectric.

Simulation of the Plasma Density Evolution during Electron Cyclotron Resonance Heating at the T-10 Tokamak

NASA Astrophysics Data System (ADS)

Dnestrovskij, Yu. N.; Vershkov, V. A.; Danilov, A. V.; Dnestrovskij, A. Yu.; Zenin, V. N.; Lysenko, S. E.; Melnikov, A. V.; Shelukhin, D. A.; Subbotin, G. F.; Cherkasov, S. V.

2018-01-01

In ohmically heated (OH) plasma with low recycling, an improved particle confinement (IPC) mode is established during gas puffing. However, after gas puffing is switched off, this mode is retained only for about 100 ms, after which an abrupt phase transition into the low particle confinement (LPC) mode occurs in the entire plasma cross section. During such a transition, energy transport due to heat conduction does not change. The phase transition in OH plasma is similar to the effect of density pump-out from the plasma core, which occurs after electron cyclotron heating (ECH) is switched on. Analysis of the measured plasma pressure profiles in the T-10 tokamak shows that, after gas puffing in the OH mode is switched off, the plasma pressure profile in the IPC stage becomes more peaked and, after the peakedness exceeds a certain critical value, the IPC-LPC transition occurs. Similar processes are also observed during ECH. If the pressure profile is insufficiently peaked during ECH, then the density pump-out effect comes into play only after the critical peakedness of the pressure profile is reached. In the plasma core, the density and pressure profiles are close to the corresponding canonical profiles. This allows one to derive an expression for the particle flux within the canonical profile model and formulate a criterion for the IPC-LPC transition. The time evolution of the plasma density profile during phase transitions was simulated for a number of T-10 shots with ECH and high recycling. The particle transport coefficients in the IPC and LPC phases, as well as the dependences of these coefficients on the ECH power, are determined.

Completely transparent ohmic electrode on p-type AlGaN for UV LEDs with core-shell Cu@alloy nanosilk network (Conference Presentation)

NASA Astrophysics Data System (ADS)

Cai, Duanjun; Wang, Huachun; Huang, Youyang; Wu, Chenping; Chen, Xiaohong; Gao, Na; Wei, Tongbo T.; Wang, Junxi; Li, Shuping; Kang, Junyong

2016-09-01

Metal nanowire networks hold a great promise, which have been supposed the only alternative to ITO as transparent electrodes for their excellent performance in touch screen, LED and solar cell. It is well known that the difficulty in making transparent ohmic electrode to p-type high-Al-content AlGaN conducting layer has highly constrained the further development of UV LEDs. On the IWN-2014, we reported the ohmic contact to n, p-GaN with direct graphene 3D-coated Cu nanosilk network and the fabrication of complete blue LED. On the ICNS-2015, we reported the ohmic contact to n-type AlGaN conducting layer with Cu@alloy nanosilk network. Here, we further demonstrate the latest results that a novel technique is proposed for fabricating transparent ohmic electrode to high-Al-content AlGaN p-type conducting layer in UV LEDs using Cu@alloy core-shell nanosilk network. The superfine copper nanowires (16 nm) was synthesized for coating various metals such as Ni, Zn, V or Ti with different work functions. The transmittance showed a high transparency (> 90%) over a broad wavelength range from 200 to 3000 nm. By thermal annealing, ohmic contact was achieved on p-type Al0.5Ga0.5N layer with Cu@Ni nanosilk network, showing clearly linear I-V curve. By skipping the p-type GaN cladding layer, complete UV LED chip was fabricated and successfully lit with bright emission at 276 nm.

Flexible carbon-based ohmic contacts for organic transistors

NASA Technical Reports Server (NTRS)

Brandon, Erik (Inventor)

2007-01-01

The present invention relates to a system and method of organic thin-film transistors (OTFTs). More specifically, the present invention relates to employing a flexible, conductive particle-polymer composite material for ohmic contacts (i.e. drain and source).

33S nuclear magnetic resonance spectroscopy of biological samples obtained with a laboratory model 33S cryogenic probe

NASA Astrophysics Data System (ADS)

Hobo, Fumio; Takahashi, Masato; Saito, Yuta; Sato, Naoki; Takao, Tomoaki; Koshiba, Seizo; Maeda, Hideaki

2010-05-01

S33 nuclear magnetic resonance (NMR) spectroscopy is limited by inherently low NMR sensitivity because of the quadrupolar moment and low gyromagnetic ratio of the S33 nucleus. We have developed a 10 mm S33 cryogenic NMR probe, which is operated at 9-26 K with a cold preamplifier and a cold rf switch operated at 60 K. The S33 NMR sensitivity of the cryogenic probe is as large as 9.8 times that of a conventional 5 mm broadband NMR probe. The S33 cryogenic probe was applied to biological samples such as human urine, bile, chondroitin sulfate, and scallop tissue. We demonstrated that the system can detect and determine sulfur compounds having SO42- anions and -SO3- groups using the S33 cryogenic probe, as the S33 nuclei in these groups are in highly symmetric environments. The NMR signals for other common sulfur compounds such as cysteine are still undetectable by the S33 cryogenic probe, as the S33 nuclei in these compounds are in asymmetric environments. If we shorten the rf pulse width or decrease the rf coil diameter, we should be able to detect the NMR signals for these compounds.

New Generation of Superconducting Solenoids for Heavy-Ion Linac Application

NASA Astrophysics Data System (ADS)

Ostroumov, P. N.; Kim, S. H.; Lessner, E. S.; Shepard, K. W.; Laxdal, R. E.

2002-01-01

The beam dynamics of superconducting (SC) heavy-ion linacs operating in the velocity range below 0.4c require a compact accelerating-focusing lattice. The use of SC solenoids together with SC RF resonators within a common cryostat can solve the real-estate problem. The solenoids must have low fringe fields to avoid magnetic-flux capture in the SC RF resonators. Also, incorporating dipole steering coils together with the SC solenoids in one magnet assembly can increase the compactness of the linac lattice. R&D work has been carried out to determine the feasibility of combining the three elements of high solenoid field, low fringe field, and integral dipole field, into one compact package. A 9-Tesla magnet has been initially designed and will be prototyped, with the goal of eventually developing 14-Tesla solenoids of similar design. The most important design issues are: (1) to minimize stray field in the RF cavity region using SC bucking coils and (2) to achieve adequate mechanical stability of the transverse dipole windings in the presence of forces produced by the solenoid/bucking coil assembly. The assembly, including terminals, switches, and protection circuit, are designed to fit inside a 25-cm diameter helium reservoir. The results of the preliminary design of the solenoid, including numerical simulations of the beam dynamics, are reported.

Methane mitigation timelines to inform energy technology evaluation

NASA Astrophysics Data System (ADS)

Roy, Mandira; Edwards, Morgan R.; Trancik, Jessika E.

2015-11-01

Energy technologies emitting differing proportions of methane (CH4) and carbon dioxide (CO2) vary significantly in their relative climate impacts over time, due to the distinct atmospheric lifetimes and radiative efficiencies of the two gases. Standard technology comparisons using the global warming potential (GWP) with a fixed time horizon do not account for the timing of emissions in relation to climate policy goals. Here we develop a portfolio optimization model that incorporates changes in technology impacts based on the temporal proximity of emissions to a radiative forcing (RF) stabilization target. An optimal portfolio, maximizing allowed energy consumption while meeting the RF target, is obtained by year-wise minimization of the marginal RF impact in an intended stabilization year. The optimal portfolio calls for using certain higher-CH4-emitting technologies prior to an optimal switching year, followed by CH4-light technologies as the stabilization year approaches. We apply the model to evaluate transportation technology pairs and find that accounting for dynamic emissions impacts, in place of using the static GWP, can result in CH4 mitigation timelines and technology transitions that allow for significantly greater energy consumption while meeting a climate policy target. The results can inform the forward-looking evaluation of energy technologies by engineers, private investors, and policy makers.

Hot electrons injection in carbon nanotubes under the influence of quasi-static ac-field

NASA Astrophysics Data System (ADS)

Amekpewu, M.; Mensah, S. Y.; Musah, R.; Mensah, N. G.; Abukari, S. S.; Dompreh, K. A.

2016-07-01

The theory of hot electrons injection in carbon nanotubes (CNTs) where both dc electric field (Ez), and a quasi-static ac field exist simultaneously (i.e. when the frequency ω of ac field is much less than the scattering frequency v (ω ⪡ v or ωτ ⪡ 1, v =τ-1) where τ is relaxation time) is studied. The investigation is done theoretically by solving semi-classical Boltzmann transport equation with and without the presence of the hot electrons source to derive the current densities. Plots of the normalized current density versus dc field (Ez) applied along the axis of the CNTs in the presence and absence of hot electrons reveal ohmic conductivity initially and finally negative differential conductivity (NDC) provided ωτ ⪡ 1 (i.e. quasi- static case). With strong enough axial injection of the hot electrons, there is a switch from NDC to positive differential conductivity (PDC) about Ez ≥ 75 kV / cm and Ez ≥ 140 kV / cm for a zigzag CNT and an armchair CNT respectively. Thus, the most important tough problem for NDC region which is the space charge instabilities can be suppressed due to the switch from the NDC behaviour to the PDC behaviour predicting a potential generation of terahertz radiations whose applications are relevance in current-day technology, industry, and research.

Application of an Al-doped zinc oxide subcontact layer on vanadium-compensated 6H-SiC photoconductive switches

NASA Astrophysics Data System (ADS)

Zhou, Tian-Yu; Liu, Xue-Chao; Huang, Wei; Dai, Chong-Chong; Zheng, Yan-Qing; Shi, Er-Wei

2015-04-01

Al-doped ZnO thin film (AZO) is used as a subcontact layer in 6H-SiC photoconductive semiconductor switches (PCSSs) to reduce the on-state resistance and optimize the device structure. Our photoconductive test shows that the on-state resistance of lateral PCSS with an n+-AZO subcontact layer is 14.7% lower than that of PCSS without an n+-AZO subcontact layer. This occurs because a heavy-doped AZO thin film can improve Ohmic contact properties, reduce contact resistance, and alleviate Joule heating. Combined with the high transparance characteristic at 532 nm of AZO film, vertical structural PCSS devices are designed and their structural superiority is discussed. This paper provides a feasible route for fabricating high performance SiC PCSS by using conductive and transparent ZnO-based materials. Project supported by the Innovation Program of the Shanghai Institute of Ceramics (Grant No. Y39ZC1110G), the Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-EW-W10), the Industry-Academic Joint Technological Innovations Fund Project of Jiangsu Province, China (Grant No. BY2011119), the Natural Science Foundation of Shanghai (Grant No. 14ZR1419000), the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 61404146), and the National High-tech R & D Program of China (Grant Nos. 2013AA031603 and 2014AA032602).

Quad-channel beam switching WR3-band transmitter MMIC

NASA Astrophysics Data System (ADS)

Müller, Daniel; Eren, Gülesin; Wagner, Sandrine; Tessmann, Axel; Leuther, Arnulf; Zwick, Thomas; Kallfass, Ingmar

2017-05-01

Millimeter wave radar systems offer several advantages such as the combination of high resolution and the penetration of adverse atmosphere like smoke, dust or rain. This paper presents a monolithic millimeter wave integrated circuit (MMIC) transmitter which offers four channel beam steering capabilities and can be used as a radar or communication system transmitter. At the local oscillator input, in order to simplify packaging, a frequency tripler is used to multiply the 76.6 - 83.3 GHz input signal to the intended 230 - 250 GHz output frequency range. A resistive mixer is used for the conversion of the intermediate frequency signal into the RF domain. The actual beam steering network is realized using an active single pole quadruple throw (SP4T) switch, which is connected to a integrated Butler matrix. The MMIC was fabricated in a 35 nm InGaAs mHEMT process and has a size of 4.0 mm × 1.5 mm

Materials challenges for repeatable RF wireless device reconfiguration with microfluidic channels

NASA Astrophysics Data System (ADS)

Griffin, Anthony S.; Sottos, Nancy R.; White, Scott R.

2018-03-01

Recently, adaptive wireless devices have utilized displacement of EGaIn within microchannels as an electrical switching mechanism to enable reconfigurable electronics. Device reconfiguration using EGaIn in microchannels overcomes many challenges encountered by more traditional reconfiguration mechanisms such as diodes and microelectromechanical systems (MEMS). Reconfiguration using EGaIn is severely limited by undesired permanent shorting due to retention of the liquid in microchannels caused by wetting and rapid oxide skin formation. Here, we investigate the conditions which prevent repeatable electrical switching using EGaIn in microchannels. Initial contact angle tests of EGaIn on epoxy surfaces demonstrate the wettability of EGaIn on flat surfaces. SEM cross-sections of microchannels reveal adhesion of EGaIn residue to channel walls. Micro-computed tomography (microCT) scans of provide volumetric measurements of EGaIn remaining inside channels after flow cycling. Non-wetting coatings are proposed as materials based strategy to overcome these issues in future work.

Observation of Q-switching and mode-locking in two-section InAs/InP (100) quantum dot lasers around 1.55 mum.

PubMed

Heck, Martijn J R; Bente, Erwin A J M; Smalbrugge, Barry; Oei, Yok-Siang; Smit, Meint K; Anantathanasarn, Sanguan; Nötzel, Richard

2007-12-10

First observation of passive mode-locking in two-section quantum-dot lasers operating at wavelengths around 1.55 mum is reported. Pulse generation at 4.6 GHz from a 9 mm long device is verified by background-free autocorrelation, RF-spectra and real-time oscilloscope traces. The output pulses are stretched in time and heavily up-chirped with a value of 20 ps/nm, contrary to what is normally observed in passively mode-locked semiconductor lasers. The complete output spectrum is shown to be coherent over 10 nm. From a 7 mm long device Q-switching is observed over a large operating regime. The lasers have been realized using a fabrication technology that is compatible with further photonic integration. This makes the laser a promising candidate for e.g. a mode-comb generator in a complex photonic chip.

Simulation of concomitant magnetic fields on fast switched gradient coils used in advanced application of MRI

NASA Astrophysics Data System (ADS)

Salinas-Muciño, G.; Torres-García, E.; Hidalgo-Tobon, S.

2012-10-01

The process to produce an MR image includes nuclear alignment, RF excitation, spatial encoding, and image formation. To form an image, it is necessary to perform spatial localization of the MR signals, which is achieved using gradient coils. MRI requires the use of gradient coils that generate magnetic fields, which vary linearly with position over the imaging volume. Safety issues have been a motivation to study deeply the relation between the interaction of gradient magnetic field and the peripheral nerve stimulation. In this work is presented a numerical modeling between the concomitant magnetic fields produced by the gradient coils and the electric field induced in a cube with σ conductivity by the gradient field switching in pulse sequences as Eco planar Imaging (EPI), due to this kind of sequence is the most used in advance applications of magnetic resonance imaging as functional MRI, cardiac imaging or diffusion.

Nanoelectronics: Opportunities for future space applications

NASA Technical Reports Server (NTRS)

Frazier, Gary

1995-01-01

Further improvements in the performance of integrated electronics will eventually halt due to practical fundamental limits on our ability to downsize transistors and interconnect wiring. Avoiding these limits requires a revolutionary approach to switching device technology and computing architecture. Nanoelectronics, the technology of exploiting physics on the nanometer scale for computation and communication, attempts to avoid conventional limits by developing new approaches to switching, circuitry, and system integration. This presentation overviews the basic principles that operate on the nanometer scale that can be assembled into practical devices and circuits. Quantum resonant tunneling (RT) is used as the center-piece of the overview since RT devices already operate at high temperature (120 degrees C) and can be scaled, in principle, to a few nanometers in semiconductors. Near- and long-term applications of GaAs and silicon quantum devices are suggested for signal and information processing, memory, optoelectronics, and radio frequency (RF) communication.

Manipulating Conduction in Metal Oxide Semiconductors: Mechanism Investigation and Conductance Tuning in Doped Fe2O3 Hematite and Metal/Ga2O3/Metal Heterostructure

NASA Astrophysics Data System (ADS)

Zhao, Bo

This study aims at understanding the fundamental mechanisms of conduction in several metal oxide semiconductors, namely alpha-Fe2O 3 and beta-Ga2O3, and how it could be tuned to desired values/states to enable a wide range of application. In the first effort, by adding Ti dopant, we successfully turned Fe2O3 from insulating to conductive by fabricated compositionally and structurally well-defined epitaxial alpha-(TixFe1-x)2 O3(0001) films for x ≤ 0.09. All films were grown by oxygen plasma assisted molecular beam epitaxy on Al2O3(0001) sapphire substrate with a buffer layer of Cr2O3 to relax the strain from lattice mismatch. Van der Pauw resistivity and Hall effect measurements reveal carrier concentrations between 1019 and 1020 cm-3 at room temperature and mobilities in the range of 0.1 to 0.6 cm2/V˙s. Such low mobility, unlike conventional band-conduction semiconductor, was attributed to hopping mechanism due to strong electron-phonon interaction in the lattice. More interestingly, conduction mechanism transitions from small-polaron hopping at higher temperatures to variable range hopping at lower temperatures with a transition temperature between 180 to 140 K. Consequently, by adding Ti dopant, conductive Fe 2O3 hematite thin films were achieved with a well-understood conducting mechanism that could guide further device application such as spin transistor and water splitting. In the case of Ga2O3, while having a band gap as high as 5 eV, they are usually conductive for commercially available samples due to unintentional Si doping. However, we discovered the conductance could be repeatedly switched between high resistance state and low resistance state when made into metal/Ga2O3 /metal heterostructure. However, to obtain well controlled switching process with consistent switching voltages and resistances, understanding switching mechanism is the key. In this study, we fabricated resistive switching devices utilizing a Ni/Ga2O3/Ir heterostructure. Bipolar switching, non-volatility, and repeatable switching are tested for the devices fabricated. Following previous discoveries on Ni/Ga2O3 single crystal which shows interface barrier type change (Schottky ↔ Ohmic) upon annealing accompanied by defects migration, characterization of the interface behavior on resistive switching cell Ni/Ga2O 3(thin film)/Ir under two different resistive states was performed using X-ray photoemission spectroscopy (XPS). Most interestingly, feathers in XPS spectrum of Ga allow for a unique nondestructive approach to investigate interface by XPS through electron transparent top contact. Theoretical modeling shows that Ga migrate towards the interface upon switching to low resistive state, indicating a possible mechanism that involves interfacial switch through barrier height modifying. Such device holds potential to become the next generation of non-volatile memory device, resistive RAM.

Ohmic heating pretreatment of algal slurry for production of biodiesel.

PubMed

Yodsuwan, Natthawut; Kamonpatana, Pitiya; Chisti, Yusuf; Sirisansaneeyakul, Sarote

2018-02-10

Suspensions of the model microalga Chlorella sp. TISTR 8990 were pretreated by ohmic heating to facilitate release of lipids from the cells in subsequent extraction and lipase-mediated transesterification to biodiesel. After ohmic pretreatment, the moist biomass was suspended in a system of water, hexane, methanol and immobilized lipase for extraction of lipids and simultaneous conversion to biodiesel. The ohmic pretreatment was optimized using an experimental design based on Taguchi method to provide treated biomass that maximized the biodiesel yield in subsequent extraction-transesterification operation. The experimental factors were the frequency of electric current (5-10 5  Hz), the processing temperature (50-70 °C), the algal biomass concentration in the slurry (algal fresh weight to water mass ratio of 1-3) and the incubation time (1-3 min). Extraction-transesterification of the pretreated biomass was carried out at 40 °C for 24 h using a reaction systems of a fixed composition (i.e. biomass, hexane, methanol, water and immobilized enzyme). Compared to control (i.e. untreated biomass), the ohmic pretreatment under optimal conditions (5 Hz current frequency, 70 °C, 1:2 mass ratio of biomass to water, incubation time of 2-min) increased the rate of subsequent transesterification by nearly 2-fold. Copyright © 2017 Elsevier B.V. All rights reserved.

Magnetostatic Waves-Based Integrated Optic Bragg Cell Modules With Applications To RF Signal Processing

DTIC Science & Technology

1992-06-30

18-722, 1985. (b)N. Koshizuka, K. Ando, and T. Okuda, "Growth-Induced Birefringence in LPE - grown Iron Garnet Films ," in Proc. Int. Sy ,p...J. Martin, R. Wolf, R. C. LeCraw, and S. L. Black,"Switching and modulation of light in magneto-optic waveguides of garnet films ," Appl. Phys. Lett...in an Yttrium Iron Garnet Film ," Soy. Tech. Phys. Lett., Vol..1, pp.386-387, 1985. (c) A. A. Solomko. Yu. A. Gaidai, A. V. Dovzhenko, M. V

Wireless Video System for Extra Vehicular Activity in the International Space Station and Space Shuttle Orbiter Environment

NASA Technical Reports Server (NTRS)

Loh, Yin C.; Boster, John; Hwu, Shian; Watson, John C.; deSilva, Kanishka; Piatek, Irene (Technical Monitor)

1999-01-01

The Wireless Video System (WVS) provides real-time video coverage of astronaut extra vehicular activities during International Space Station (ISS) assembly. The ISS wireless environment is unique due to the nature of the ISS structure and multiple RF interference sources. This paper describes how the system was developed to combat multipath, blockage, and interference using an automatic antenna switching system. Critical to system performance is the selection of receiver antenna installation locations determined using Uniform Geometrical Theory of Diffraction (GTD) techniques.

Multi-level resistive switching behaviors and retention characteristics in ZnO/Nb:SrTiO3 heterojunction

NASA Astrophysics Data System (ADS)

Ren, Yong; Li, Jiachen; Zhang, Weifeng; Jia, Caihong

2017-10-01

Epitaxial ZnO thin films were grown on SrTiO3:Nb (NSTO) substrates by rf magnetron sputtering method. The multi-level resistance states were observed by applying different amplitudes and/or polarities of voltage pulses, which is supposed to be related to the drift of oxygen vacancies. Furthermore, the decay of retention is also corresponding to the migration of oxygen vacancies. The retention and cycle stability implies that the ZnO/Nb:SrTiO3 heterojunctions are promising for high density memory application.

Bistability in a complementary metal oxide semiconductor inverter circuit.

PubMed

Carroll, Thomas L

2005-09-01

Radiofrequency signals can disrupt the operation of low frequency circuits. A digital inverter circuit would seem to be immune to such disruption, because its output state usually jumps abruptly between 0 and 5 V. Nevertheless, when driven with a high frequency signal, the inverter can have two coexisting stable states (which are not at 0 and 5 V). Slow switching between these states (by changing the rf signal) will produce a low frequency signal. I demonstrate the bistability in a circuit experiment and in a simple model of the circuit.

Titanium dioxide thin films deposited by pulsed laser deposition and integration in radio frequency devices: Study of structure, optical and dielectric properties

NASA Astrophysics Data System (ADS)

Orlianges, Jean-Christophe; Crunteanu, Aurelian; Pothier, Arnaud; Merle-Mejean, Therese; Blondy, Pierre; Champeaux, Corinne

2012-12-01

Titanium dioxide presents a wide range of technological application possibilities due to its dielectric, electrochemical, photocatalytic and optical properties. The three TiO2 allotropic forms: anatase, rutile and brookite are also interesting, since they exhibit different properties, stabilities and growth modes. For instance, rutile has a high dielectric permittivity, of particular interest for the integration as dielectric in components such as microelectromechanical systems (MEMS) for radio frequency (RF) devices. In this study, titanium dioxide thin films are deposited by pulsed laser deposition. Characterizations by Raman spectroscopy and X-ray diffraction show the evolution of the structural properties. Thin films optical properties are investigated using spectroscopic ellipsometry and transmission measurements from UV to IR range. Co-planar waveguide (CPW) devices are fabricated based on these films. Their performances are measured in the RF domain and compared to simulation, leading to relative permittivity values in the range 30-120, showing the potentialities of the deposited material for capacitive switches applications.

Fundamental Scaling of Microplasmas and Tunable UV Light Generation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manginell, Ronald P.; Sillerud, Colin Halliday; Hopkins, Matthew M.

2016-11-01

The temporal evolution of spectral lines from microplasma devices (MD) was studied, including impurity transitions. Long-wavelength emission diminishes more rapidly than deep UV with decreasing pulse width and RF operation. Thus, switching from DC to short pulsed or RF operation, UV emissions can be suppressed, allowing for real-time tuning of the ionization energy of a microplasma photo-ionization source, which is useful for chemical and atomic physics. Scaling allows MD to operate near atmospheric pressure where excimer states are efficiently created and emit down to 65 nm; laser emissions fall off below 200 nm, making MD light sources attractive for deepmore » UV use. A first fully-kinetic three-dimensional model was developed that explicitly calculates electron-energy distribution function. This, and non-continuum effects, were studied with the model and how they are impacted by geometry and transient or DC operation. Finally, a global non-dimensional model was developed to help explain general trends MD physics.« less

Fully kinetic particle simulations of high pressure streamer propagation

NASA Astrophysics Data System (ADS)

Rose, David; Welch, Dale; Thoma, Carsten; Clark, Robert

2012-10-01

Streamer and leader formation in high pressure devices is a dynamic process involving a hierarchy of physical phenomena. These include elastic and inelastic particle collisions in the gas, radiation generation, transport and absorption, and electrode interactions. We have performed 2D and 3D fully EM implicit particle-in-cell simulation model of gas breakdown leading to streamer formation under DC and RF fields. The model uses a Monte Carlo treatment for all particle interactions and includes discrete photon generation, transport, and absorption for ultra-violet and soft x-ray radiation. Central to the realization of this fully kinetic particle treatment is an algorithm [D. R. Welch, et al., J. Comp. Phys. 227, 143 (2007)] that manages the total particle count by species while preserving the local momentum distribution functions and conserving charge. These models are being applied to the analysis of high-pressure gas switches [D. V. Rose, et al., Phys. Plasmas 18, 093501 (2011)] and gas-filled RF accelerator cavities [D. V. Rose, et al. Proc. IPAC12, to appear].

Design of a Low-Energy FARAD Thruster

NASA Technical Reports Server (NTRS)

Polzin, K. A.; Rose, M. F.; Miller, R.; Best, S.; Owens, T.; Dankanich, J.

2007-01-01

The design of an electrodeless thruster that relies on a pulsed, rf-assisted discharge and electromagnetic acceleration using an inductive coil is presented. The thruster design is optimized using known performance,scaling parameters, and experimentally-determined design rules, with design targets for discharge energy, plasma exhaust velocity; and thrust efficiency of 100 J/pulse, 25 km/s, and 50%, respectively. Propellant is injected using a high-speed gas valve and preionized by a pulsed-RF signal supplied by a vector inversion generator, allowing for current sheet formation at lower discharge voltages and energies relative to pulsed inductive accelerators that do not employ preionization. The acceleration coil is designed to possess an inductance of at least 700 nH while the target stray (non-coil) inductance in the circuit is 70 nH. A Bernardes and Merryman pulsed power train or a pulse compression power train provide current to the acceleration coil and solid-state components are used to switch both powertrains.

Towards Self-Clocked Gated OCDMA Receiver

NASA Astrophysics Data System (ADS)

Idris, S.; Osadola, T.; Glesk, I.

2013-02-01

A novel incoherent OCDMA receiver with incorporated all-optical clock recovery for self-synchronization of a time gate for the multi access interferences (MAI) suppression and minimizing the effect of data time jitter in incoherent OCDMA system was successfully developed and demonstrated. The solution was implemented and tested in a multiuser environment in an out of the laboratory OCDMA testbed with two-dimensional wavelength-hopping time-spreading coding scheme and OC-48 (2.5 Gbp/s) data rate. The self-clocked all-optical time gate uses SOA-based fibre ring laser optical clock, recovered all-optically from the received OCDMA traffic to control its switching window for cleaning the autocorrelation peak from the surrounding MAI. A wider eye opening was achieved when the all-optically recovered clock from received data was used for synchronization if compared to a static approach with the RF clock being generated by a RF synthesizer. Clean eye diagram was also achieved when recovered clock is used to drive time gating.

Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sung, C., E-mail: csung@physics.ucla.edu; White, A. E.; Greenwald, M.

2016-04-15

Long wavelength turbulent electron temperature fluctuations (k{sub y}ρ{sub s} < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local,more » electrostatic ion-scale simulations (k{sub y}ρ{sub s} ≲ 1.7) performed at r/a ∼ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. In contrast, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. In addition, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].« less

Extended Heat Deposition in Hot Jupiters: Application to Ohmic Heating

NASA Astrophysics Data System (ADS)

Ginzburg, Sivan; Sari, Re'em

2016-03-01

The observed radii of many giant exoplanets in close orbits exceed theoretical predictions. One suggested origin for this discrepancy is heat deposited deep inside the atmospheres of these “hot Jupiters”. Here, we study extended power sources that distribute heat from the photosphere to the deep interior of the planet. Our analytical treatment is a generalization of a previous analysis of localized “point sources”. We model the deposition profile as a power law in the optical depth and find that planetary cooling and contraction halt when the internal luminosity (I.e., cooling rate) of the planet drops below the heat deposited in the planet’s convective region. A slowdown in the evolutionary cooling prior to equilibrium is possible only for sources that do not extend to the planet’s center. We estimate the ohmic dissipation resulting from the interaction between the atmospheric winds and the planet’s magnetic field, and apply our analytical model to ohmically heated planets. Our model can account for the observed radii of most inflated planets, which have equilibrium temperatures of ≈1500-2500 K and are inflated to a radius of ≈ 1.6{R}J. However, some extremely inflated planets remain unexplained by our model. We also argue that ohmically inflated planets have already reached their equilibrium phase, and no longer contract. Following Wu & Lithwick, who argued that ohmic heating could only suspend and not reverse contraction, we calculate the time it takes ohmic heating to re-inflate a cold planet to its equilibrium configuration. We find that while it is possible to re-inflate a cold planet, the re-inflation timescales are longer by a factor of ≈ 30 than the cooling time.

Ohmic contacts to semiconducting diamond

NASA Astrophysics Data System (ADS)

Zeidler, James R.; Taylor, M. J.; Zeisse, Carl R.; Hewett, C. A.; Delahoussaye, Paul R.

1990-10-01

Work was carried out to improve the electron beam evaporation system in order to achieve better deposited films. The basic system is an ion pumped vacuum chamber, with a three-hearth, single-gun e-beam evaporator. Four improvements were made to the system. The system was thoroughly cleaned and new ion pump elements, an e-gun beam adjust unit, and a more accurate crystal monitor were installed. The system now has a base pressure of 3 X 10(exp -9) Torr, and can easily deposit high-melting-temperature metals such as Ta with an accurately controlled thickness. Improved shadow masks were also fabricated for better alignment and control of corner contacts for electrical transport measurements. Appendices include: A Thermally Activated Solid State Reaction Process for Fabricating Ohmic Contacts to Semiconducting Diamond; Tantalum Ohmic Contacts to Diamond by a Solid State Reaction Process; Metallization of Semiconducting Diamond: Mo, Mo/Au, and Mo/Ni/Au; Specific Contact Resistance Measurements of Ohmic Contracts to Diamond; and Electrical Activation of Boron Implanted into Diamond.

Dramatically enhanced non-Ohmic properties and maximum stored energy density in ceramic-metal nanocomposites: CaCu3Ti4O12/Au nanoparticles

PubMed Central

2013-01-01

Non-Ohmic and dielectric properties of a novel CaCu3Ti4O12/Au nanocomposite were investigated. Introduction of 2.5 vol.% Au nanoparticles in CaCu3Ti4O12 ceramics significantly reduced the loss tangent while its dielectric permittivity remained unchanged. The non-Ohmic properties of CaCu3Ti4O12/Au (2.5 vol.%) were dramatically improved. A nonlinear coefficient of ≈ 17.7 and breakdown electric field strength of 1.25 × 104 V/m were observed. The maximum stored energy density was found to be 25.8 kJ/m3, which is higher than that of pure CaCu3Ti4O12 by a factor of 8. Au addition at higher concentrations resulted in degradation of dielectric and non-Ohmic properties, which is described well by percolation theory. PMID:24257060

Surface hole gas enabled transparent deep ultraviolet light-emitting diode

NASA Astrophysics Data System (ADS)

Zhang, Jianping; Gao, Ying; Zhou, Ling; Gil, Young-Un; Kim, Kyoung-Min

2018-07-01

The inherent deep-level nature of acceptors in wide-band-gap semiconductors makes p-ohmic contact formation and hole supply difficult, impeding progress for short-wavelength optoelectronics and high-power high-temperature bipolar electronics. We provide a general solution by demonstrating an ultrathin rather than a bulk wide-band-gap semiconductor to be a successful hole supplier and ohmic contact layer. Free holes in this ultrathin semiconductor are assisted to activate from deep acceptors and swept to surface to form hole gases by a large electric field, which can be provided by engineered spontaneous and piezoelectric polarizations. Experimentally, a 6 nm thick AlN layer with surface hole gas had formed p-ohmic contact to metals and provided sufficient hole injection to a 280 nm light-emitting diode, demonstrating a record electrical-optical conversion efficiency exceeding 8.5% at 20 mA (55 A cm‑2). Our approach of forming p-type wide-band-gap semiconductor ohmic contact is critical to realizing high-efficiency ultraviolet optoelectronic devices.

Nanoscale electro-structural characterisation of ohmic contacts formed on p-type implanted 4H-SiC

NASA Astrophysics Data System (ADS)

Frazzetto, Alessia; Giannazzo, Filippo; Lo Nigro, Raffaella; di Franco, Salvatore; Bongiorno, Corrado; Saggio, Mario; Zanetti, Edoardo; Raineri, Vito; Roccaforte, Fabrizio

2011-12-01

This work reports a nanoscale electro-structural characterisation of Ti/Al ohmic contacts formed on p-type Al-implanted silicon carbide (4H-SiC). The morphological and the electrical properties of the Al-implanted layer, annealed at 1700°C with or without a protective capping layer, and of the ohmic contacts were studied using atomic force microscopy [AFM], transmission line model measurements and local current measurements performed with conductive AFM. The characteristics of the contacts were significantly affected by the roughness of the underlying SiC. In particular, the surface roughness of the Al-implanted SiC regions annealed at 1700°C could be strongly reduced using a protective carbon capping layer during annealing. This latter resulted in an improved surface morphology and specific contact resistance of the Ti/Al ohmic contacts formed on these regions. The microstructure of the contacts was monitored by X-ray diffraction analysis and a cross-sectional transmission electron microscopy, and correlated with the electrical results.

Formation of ohmic contacts to MOCVD grown p-GaN by controlled activation of Mg

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaminska, E.; Piotrowska, A.; Barcz, A.

2000-11-27

We report on the formation of low resistivity ohmic contacts to p-GaN, r{sub c} < 10{sup {minus}4}{Omega}cm{sup 2}, by increasing the concentration of the active Mg in the subcontact zone, via Zr-mediated release of hydrogen. We have investigated the process of evolution of hydrogen from MOCVD grown p-GaN via Zr-based metallization, and determined the optimum processing conditions (temperature and gas ambient) for fabrication of low resistance ohmic contacts. When the process is conducted in N{sub 2} flow, the metallization remains stable at temperatures required to achieve the ohmic behavior, and the morphology of the metal/semiconductor interface is unaltered by suchmore » a heat treatment. The processing in O{sub 2}, on the contrary, causes the interdiffusion of metallization constituents and the incorporation of oxygen into the semiconductor subcontact region, which could be responsible for increased resistivity of these contacts.« less

Ohmic contacts to Al-rich AlGaN heterostructures

DOE PAGES

Douglas, E. A.; Reza, S.; Sanchez, C.; ...

2017-06-06

Due to the ultra-wide bandgap of Al-rich AlGaN, up to 5.8 eV for the structures in this study, obtaining low resistance ohmic contacts is inherently difficult to achieve. A comparative study of three different fabrication schemes is presented for obtaining ohmic contacts to an Al-rich AlGaN channel. Schottky-like behavior was observed for several different planar metallization stacks (and anneal temperatures), in addition to a dry-etch recess metallization contact scheme on Al 0.85Ga 0.15N/Al 0.66Ga 0.34N. However, a dry etch recess followed by n +-GaN regrowth fabrication process is reported as a means to obtain lower contact resistivity ohmic contacts onmore » a Al 0.85Ga 0.15N/Al 0.66Ga 0.34N heterostructure. In conclusion, specific contact resistivity of 5×10 -3 Ω cm 2 was achieved after annealing Ti/Al/Ni/Au metallization.« less

Evaluation of non-thermal effects of electricity on ascorbic acid and carotenoid degradation in acerola pulp during ohmic heating.

PubMed

Jaeschke, Débora Pez; Marczak, Ligia Damasceno Ferreira; Mercali, Giovana Domeneghini

2016-05-15

The effect of electric field on ascorbic acid and carotenoid degradation in acerola pulp during ohmic heating was evaluated. Ascorbic acid kinetic degradation was evaluated at 80, 85, 90 and 95°C during 60 min of thermal treatment by ohmic and conventional heating. Carotenoid degradation was evaluated at 90 and 95°C after 50 min of treatment. The different temperatures evaluated showed the same effect on degradation rates. To investigate the influence of oxygen concentration on the degradation process, ohmic heating was also carried out under rich and poor oxygen modified atmospheres at 90°C. Ascorbic acid and carotenoid degradation was higher under a rich oxygen atmosphere, indicating that oxygen is the limiting reagent of the degradation reaction. Ascorbic acid and carotenoid degradation was similar for both heating technologies, demonstrating that the presence of the oscillating electric field did not influence the mechanisms and rates of reactions associated with the degradation process. Copyright © 2015 Elsevier Ltd. All rights reserved.

Lack of dependence on resonant error field of locked mode island size in ohmic plasmas in DIII-D

DOE PAGES

Haye, R. J. La; Paz-Soldan, C.; Strait, E. J.

2015-01-23

DIII-D experiments show that fully penetrated resonant n=1 error field locked modes in Ohmic plasmas with safety factor q 95≳3 grow to similar large disruptive size, independent of resonant error field correction. Relatively small resonant (m/n=2/1) static error fields are shielded in Ohmic plasmas by the natural rotation at the electron diamagnetic drift frequency. However, the drag from error fields can lower rotation such that a bifurcation results, from nearly complete shielding to full penetration, i.e., to a driven locked mode island that can induce disruption.

Fabrication of optically reflecting ohmic contacts for semiconductor devices

DOEpatents

Sopori, Bhushan L.

1995-01-01

A method is provided to produce a low-resistivity ohmic contact having high optical reflectivity on one side of a semiconductor device. The contact is formed by coating the semiconductor substrate with a thin metal film on the back reflecting side and then optically processing the wafer by illuminating it with electromagnetic radiation of a predetermined wavelength and energy level through the front side of the wafer for a predetermined period of time. This method produces a thin epitaxial alloy layer between the semiconductor substrate and the metal layer when a crystalline substrate is used. The alloy layer provides both a low-resistivity ohmic contact and high optical reflectance.

Deterministic quantum controlled-PHASE gates based on non-Markovian environments

NASA Astrophysics Data System (ADS)

Zhang, Rui; Chen, Tian; Wang, Xiang-Bin

2017-12-01

We study the realization of the quantum controlled-PHASE gate in an atom-cavity system beyond the Markovian approximation. The general description of the dynamics for the atom-cavity system without any approximation is presented. When the spectral density of the reservoir has the Lorentz form, by making use of the memory backflow from the reservoir, we can always construct the deterministic quantum controlled-PHASE gate between a photon and an atom, no matter the atom-cavity coupling strength is weak or strong. While, the phase shift in the output pulse hinders the implementation of quantum controlled-PHASE gates in the sub-Ohmic, Ohmic or super-Ohmic reservoirs.

Field-effect P-N junction

DOEpatents

Regan, William; Zettl, Alexander

2015-05-05

This disclosure provides systems, methods, and apparatus related to field-effect p-n junctions. In one aspect, a device includes an ohmic contact, a semiconductor layer disposed on the ohmic contact, at least one rectifying contact disposed on the semiconductor layer, a gate including a layer disposed on the at least one rectifying contact and the semiconductor layer and a gate contact disposed on the layer. A lateral width of the rectifying contact is less than a semiconductor depletion width of the semiconductor layer. The gate contact is electrically connected to the ohmic contact to create a self-gating feedback loop that is configured to maintain a gate electric field of the gate.

Switched-beam radiometer front-end network analysis

NASA Technical Reports Server (NTRS)

Trew, R. J.; Bilbro, G. L.

1994-01-01

The noise figure performance of various delay-line networks fabricated from microstrip lines with varying number of elements was investigated using a computer simulation. The effects of resistive losses in both the transmission lines and power combiners were considered. In general, it is found that an optimum number of elements exists, depending upon the resistive losses present in the network. Small resistive losses are found to have a significant degrading effect upon the noise figure performance of the array. Extreme stability in switching characteristics is necessary to minimize the nondeterministic noise of the array. For example, it is found that a 6 percent tolerance on the delay-line lengths will produce a 0.2 db uncertainty in the noise figure which translates into a 13.67 K temperature uncertainty generated by the network. If the tolerance can be held to 2 percent, the uncertainty in noise figure and noise temperature will be 0.025 db and 1.67 K, respectively. Three phase shift networks fabricated using a commercially available PIN diode switch were investigated. Loaded-line phase shifters are found to have desirable RF and noise characteristics and are attractive components for use in phased-array networks.

Tailoring the graphene/silicon carbide interface for monolithic wafer-scale electronics.

PubMed

Hertel, S; Waldmann, D; Jobst, J; Albert, A; Albrecht, M; Reshanov, S; Schöner, A; Krieger, M; Weber, H B

2012-07-17

Graphene is an outstanding electronic material, predicted to have a role in post-silicon electronics. However, owing to the absence of an electronic bandgap, graphene switching devices with high on/off ratio are still lacking. Here in the search for a comprehensive concept for wafer-scale graphene electronics, we present a monolithic transistor that uses the entire material system epitaxial graphene on silicon carbide (0001). This system consists of the graphene layer with its vanishing energy gap, the underlying semiconductor and their common interface. The graphene/semiconductor interfaces are tailor-made for ohmic as well as for Schottky contacts side-by-side on the same chip. We demonstrate normally on and normally off operation of a single transistor with on/off ratios exceeding 10(4) and no damping at megahertz frequencies. In its simplest realization, the fabrication process requires only one lithography step to build transistors, diodes, resistors and eventually integrated circuits without the need of metallic interconnects.

Development of a 5.5 m diameter vertical axis wind turbine, phase 3

NASA Astrophysics Data System (ADS)

Dekitsch, A.; Etzler, C. C.; Fritzsche, A.; Lorch, G.; Mueller, W.; Rogalla, K.; Schmelzle, J.; Schuhwerk, W.; Vollan, A.; Welte, D.

1982-06-01

In continuation of development of a 5.5 m diameter vertical axis windmill that consists in conception, building, and wind tunnel testing, a Darrieus rotor windpowered generator feeding an isolated network under different wind velocity conditions and with optimal energy conversion efficiency was designed built, and field tested. The three-bladed Darrieus rotor tested in the wind tunnel was equiped with two variable pitch Savonius rotors 2 m in diameter. By means of separate measures of the aerodynamic factors and the energy consumption, effect of revisions and optimizations on different elements was assessed. Pitch adjustement of the Savonius blades, lubrication of speed reducer, rotor speed at cut-in of generator field excitation, time constant of field excitation, stability conditions, switch points of ohmic resistors which combined with a small electric battery simulated a larger isolated network connected with a large storage battery, were investigated. Fundamentals for the economic series production of windpowered generators with Darrieus rotors for the control and the electric conversion system are presented.

All-dielectric band stop filter at terahertz frequencies

NASA Astrophysics Data System (ADS)

Yin, Shan; Chen, Lin

2018-01-01

We design all-dielectric band stop filters with silicon subwavelength rod and block arrays at terahertz frequencies. Supporting magnetic dipole resonances originated from the Mia resonance, the all-dielectric filters can modulate the working band by simply varying the structural geometry, while eliminating the ohmic loss induced by the traditional metallic metamaterials and uninvolved with the complicated mechanism. The nature of the resonance in the silicon arrays is clarified, which is attributed to the destructive interference between the directly transmitted waves and the waves emitted from the magnetic dipole resonances, and the resonance frequency is determined by the dielectric structure. By particularly designing the geometrical parameters, the profile of the transmission spectrum can be tailored, and the step-like band edge can be obtained. The all-dielectric filters can realize 93% modulation of the transmission within 0.04 THz, and maintain the bandwidth of 0.05 THz. This work provides a method to develop THz functional devices, such as filters, switches and sensors.

Effect of ohmic heating of soymilk on urease inactivation and kinetic analysis in holding time.

PubMed

Li, Fa-De; Chen, Chen; Ren, Jie; Wang, Ranran; Wu, Peng

2015-02-01

To verify the effect of the ohmic heating on the urease activity in the soymilk, the ohmic heating methods with the different electrical field conditions (the frequency and the voltage ranging from 50 to 10 kHz and from 160 to 220 V, respectively) were employed. The results showed that if the value of the urease activity measured with the quantitative spectrophotometry method was lower than 16.8 IU, the urease activity measured with the qualitative method was negative. The urease activity of the sample ohmically heated was significantly lower than that of the sample conventionally heated (P < 0.01) at the same target temperature. It was concluded that the electrical field enhanced the urease inactivation. In addition, the inactivation kinetics of the urease in the soymilk could be described with a biphasic model during holding time at a target temperature. Thus, it was concluded that the urease in the soymilk would contain 2 isoenzymes, one is the thermolabile fraction, the other the thermostable fraction, and that the thermostable isoenzyme could not be completely inactivated when the holding time increased, whether the soymilk was cooked with the conventional method or with the ohmic heating method. Therefore, the electric field had no effect on the inactivation of the thermostable isoenzyme of the urease. © 2015 Institute of Food Technologists®

Wave induced density modification in RF sheaths and close to wave launchers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Van Eester, D., E-mail: d.van.eester@fz-juelich.de; Crombé, K.; Department of Applied Physics, Ghent University, Ghent

2015-12-10

With the return to full metal walls - a necessary step towards viable fusion machines - and due to the high power densities of current-day ICRH (Ion Cyclotron Resonance Heating) or RF (radio frequency) antennas, there is ample renewed interest in exploring the reasons for wave-induced sputtering and formation of hot spots. Moreover, there is experimental evidence on various machines that RF waves influence the density profile close to the wave launchers so that waves indirectly influence their own coupling efficiency. The present study presents a return to first principles and describes the wave-particle interaction using a 2-time scale modelmore » involving the equation of motion, the continuity equation and the wave equation on each of the time scales. Through the changing density pattern, the fast time scale dynamics is affected by the slow time scale events. In turn, the slow time scale density and flows are modified by the presence of the RF waves through quasilinear terms. Although finite zero order flows are identified, the usual cold plasma dielectric tensor - ignoring such flows - is adopted as a first approximation to describe the wave response to the RF driver. The resulting set of equations is composed of linear and nonlinear equations and is tackled in 1D in the present paper. Whereas the former can be solved using standard numerical techniques, the latter require special handling. At the price of multiple iterations, a simple ’derivative switch-on’ procedure allows to reformulate the nonlinear problem as a sequence of linear problems. Analytical expressions allow a first crude assessment - revealing that the ponderomotive potential plays a role similar to that of the electrostatic potential arising from charge separation - but numerical implementation is required to get a feeling of the full dynamics. A few tentative examples are provided to illustrate the phenomena involved.« less

SCIDAC Center for simulation of wave particle interactions CompX participation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey, R.W.

Harnessing the energy that is released in fusion reactions would provide a safe and abundant source of power to meet the growing energy needs of the world population. The next step toward the development of fusion as a practical energy source is the construction of ITER, a device capable of producing and controlling the high performance plasma required for self-sustaining fusion reactions, or “burning” plasma. The input power required to drive the ITER plasma into the burning regime will be supplied primarily with a combination of external power from radio frequency waves in the ion cyclotron range of frequencies andmore » energetic ions from neutral beam injection sources, in addition to internally generated Ohmic heating from the induced plasma current that also serves to create the magnetic equilibrium for the discharge. The ITER project is a large multi-billion dollar international project in which the US participates. The success of the ITER project depends critically on the ability to create and maintain burning plasma conditions, it is absolutely necessary to have physics-based models that can accurately simulate the RF processes that affect the dynamical evolution of the ITER discharge. The Center for Simulation of WavePlasma Interactions (CSWPI), also known as RF-SciDAC, is a multi-institutional collaboration that has conducted ongoing research aimed at developing: (1) Coupled core-to-edge simulations that will lead to an increased understanding of parasitic losses of the applied RF power in the boundary plasma between the RF antenna and the core plasma; (2) Development of models for core interactions of RF waves with energetic electrons and ions (including fusion alpha particles and fast neutral beam ions) that include a more accurate representation of the particle dynamics in the combined equilibrium and wave fields; and (3) Development of improved algorithms that will take advantage of massively parallel computing platforms at the petascale level and beyond to achieve the needed physics, resolution, and/or statistics to address these issues. CompX provides computer codes and analysis for the calculation of the electron and ion distributions in velocity-space and plasma radius which are necessary for reliable calculations of power deposition and toroidal current drive due to combined radiofrequency and neutral beam at high injected powers. It has also contributed to ray tracing modeling of injected radiofrequency powers, and to coupling between full-wave radiofrequency wave models and the distribution function calculations. In the course of this research, the Fokker-Planck distribution function calculation was made substantially more realistic by inclusion of finite-width drift-orbit effects (FOW). FOW effects were also implemented in a calculation of the phase-space diffusion resulting from radiofrequency full-wave models. Average level of funding for CompX was approximately three man-months per year.« less

A low insertion loss GaAs pHEMT switch utilizing dual n +-doping AlAs etching stop layers design

NASA Astrophysics Data System (ADS)

Chien, Feng-Tso; Lin, Da-Wei; Yang, Chih-Wei; Fu, Jeffrey S.; Chiu, Hsien-Chin

2010-03-01

A low insertion loss single-pole-single-throw (SPST) pseudomorphic high electron mobility transistor (pHEMT) switch utilizing the n +-type doping in AlAs etching stop layer was fabricated and investigated. This novel design reduces device sheet resistance resulting in an improvement of dc and rf power performance. In addition, the gate recess selectivity for GaAs/AlAs interface was not sacrificed after highly n +-type doping in AlAs etching stop layer. The pHEMT with n +-AlAs etching stop layer, also named Modified pHEMT (M-pHEMT), demonstrated a lower sheet resistance ( Rsh) of 65.9 Ω/γ, a higher maximum drain-to-source current ( Idmax) of 317.8 mA/mm and a higher peak transconductance ( gm) of 259.3 mS/mm which are superior to standard pHEMT performance with values of 71.9 Ω/γ, 290.3 mA/mm and 252.1 mS/mm, respectively. Due to a significant sheet resistance improvement from this novel epitaxial design, an SPST pHEMT switch was realized to manifest its industrial application potential. The results achieved an on-state insertion loss of 1.42 dB, an off-state isolation of 13.02 dB at 0.9 GHz, which were superior to traditional pHEMT switch under same condition of operation with values of 1.68 dB and 11.42 dB, respectively. It is proved that dual n +-doping AlAs etching stop layers scheme is beneficial for low loss microwave switches applications.

Al 0.85Ga 0.15N/Al 0.70Ga 0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

DOE PAGES

Baca, Albert G.; Klein, Brianna A.; Allerman, Andrew A.; ...

2017-12-09

AlGaN-channel high electron mobility transistors (HEMTs) are among a class of ultra wide-bandgap transistors that are promising candidates for RF and power applications. Long-channel Al xGa 1-xN HEMTs with x = 0.7 in the channel have been built and evaluated across the -50°C to +200°C temperature range. These devices achieved room temperature drain current as high as 46 mA/mm and were absent of gate leakage until the gate diode forward bias turn-on at ~2.8 V, with a modest -2.2 V threshold voltage. A very large I on/I off current ratio, of 8 × 10 9 was demonstrated. A near idealmore » subthreshold slope that is just 35% higher than the theoretical limit across the temperature range was characterized. The ohmic contact characteristics were rectifying from -50°C to +50°C and became nearly linear at temperatures above 100°C. An activation energy of 0.55 eV dictates the temperature dependence of off-state leakage.« less

Al 0.85Ga 0.15N/Al 0.70Ga 0.30N High Electron Mobility Transistors with Schottky Gates and Large On/Off Current Ratio over Temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baca, Albert G.; Klein, Brianna A.; Allerman, Andrew A.

AlGaN-channel high electron mobility transistors (HEMTs) are among a class of ultra wide-bandgap transistors that are promising candidates for RF and power applications. Long-channel Al xGa 1-xN HEMTs with x = 0.7 in the channel have been built and evaluated across the -50°C to +200°C temperature range. These devices achieved room temperature drain current as high as 46 mA/mm and were absent of gate leakage until the gate diode forward bias turn-on at ~2.8 V, with a modest -2.2 V threshold voltage. A very large I on/I off current ratio, of 8 × 10 9 was demonstrated. A near idealmore » subthreshold slope that is just 35% higher than the theoretical limit across the temperature range was characterized. The ohmic contact characteristics were rectifying from -50°C to +50°C and became nearly linear at temperatures above 100°C. An activation energy of 0.55 eV dictates the temperature dependence of off-state leakage.« less

Influence of Nb Doping Concentration on Bolometric Properties of RF Magnetron Sputtered Nb:TiO2- x Films

NASA Astrophysics Data System (ADS)

Reddy, Y. Ashok Kumar; Shin, Young Bong; Kang, In-Ku; Lee, Hee Chul

2018-03-01

The present study directly addresses the improved bolometric properties by means of different Nb doping concentrations into TiO2- x films. The x-ray diffraction patterns do not display any obvious diffraction peaks, suggesting that all the films deposited at room temperature had an amorphous structure. A small binding energy shift was observed in x-ray photo electron spectroscopy due to the change of chemical composition with Nb doping concentration. All the device samples exhibit linear I- V characteristics, which attests to the formation of good ohmic contact with low contact resistance between the Nb:TiO2- x (TNO) film and the electrode (Ti) material. The performance of the bolometric material can be evaluated through the temperature coefficient of resistance (TCR), and the absolute value of TCR was found to be increased from 2.54% to 2.78% with increasing the Nb doping concentration. The voltage spectral density of 1/ f noise was measured in the frequency range of 1-60 Hz and found to be decreased with increase of Nb doping concentration. As a result, for 1 at.% Nb-doped TNO sample exhibits improved bolometric properties towards the good infrared image sensor device.

Structural investigation of MF, RF and DC sputtered Mo thin films for backside photovoltaic electrode

NASA Astrophysics Data System (ADS)

Małek, Anna K.; Marszałek, Konstanty W.; Rydosz, Artur M.

2016-12-01

Recently photovoltaics attracts much attention of research and industry. The multidirectional studies are carried out in order to improve solar cells performance, the innovative materials are still searched and existing materials and technology are optimized. In the multilayer structure of CIGS solar cells molybdenum (Mo) layer is used as a back contact. Mo layers meet all requirements for back side electrode: low resistivity, good adhesion to the substrate, high optical reflection in the visible range, columnar structure for Na ions diffusion, formation of an ohmic contact with the ptype CIGS absorber layer, and high stability during the corrosive selenization process. The high adhesion to the substrate and low resistivity in single Mo layer is difficult to be achieved because both properties depend on the deposition parameters, particularly on working gas pressure. Therefore Mo bilayers are applied as a back contact for CIGS solar cells. In this work the Mo layers were deposited by medium frequency sputtering at different process parameters. The effect of substrate temperature within the range of 50°C-200°C and working gas pressure from 0.7 mTorr to 7 mTorr on crystalline structure of Mo layers was studied.

Formation of gallium vacancies and their effects on the nanostructure of Pd/Ir/Au ohmic contact to p-type GaN.

PubMed

Kim, Kyong Nam; Kim, Tae Hyung; Seo, Jin Seok; Kim, Ki Seok; Bae, Jeong Woon; Yeom, Geun Young

2013-12-01

The properties of Pd/Ir/Au ohmic metallization on p-type GaN have been investigated. Contacts annealed at 400 degrees C in O2 atmosphere demonstrated excellent ohmic characteristics with a specific contact resistivity of 1.5 x 10(-5) Omega-cm2. This is attributed to the formation of Ga vacancies at the contact metal-semiconductor interfacial region due to the out-diffusion of Ga atoms. The out-diffusion of Ga atoms was confirmed by X-ray photoelectron spectroscopy depth profiles, high-resolution transmission electron microscopy, and electron energy loss spectroscopy using a scanning transmission electron microscope.

Two-step deposition of Al-doped ZnO on p-GaN to form ohmic contacts.

PubMed

Su, Xi; Zhang, Guozhen; Wang, Xiao; Chen, Chao; Wu, Hao; Liu, Chang

2017-12-01

Al-doped ZnO (AZO) thin films were deposited directly on p-GaN substrates by using a two-step deposition consisting of polymer assisted deposition (PAD) and atomic layer deposition (ALD) methods. Ohmic contacts of the AZO on p-GaN have been formed. The lowest sheet resistance of the two-step prepared AZO films reached to 145 Ω/sq, and the specific contact resistance reduced to 1.47 × 10 -2 Ω·cm 2 . Transmittance of the AZO films remained above 80% in the visible region. The combination of PAD and ALD technique can be used to prepare p-type ohmic contacts for optoelectronics.

Skyrmions Driven by Intrinsic Magnons

NASA Astrophysics Data System (ADS)

Psaroudaki, Christina; Loss, Daniel

2018-06-01

We study the dynamics of a Skyrmion in a magnetic insulating nanowire in the presence of time-dependent oscillating magnetic field gradients. These ac fields act as a net driving force on the Skyrmion via its own intrinsic magnetic excitations. In a microscopic quantum field theory approach, we include the unavoidable coupling of the external field to the magnons, which gives rise to time-dependent dissipation for the Skyrmion. We demonstrate that the magnetic ac field induces a super-Ohmic to Ohmic crossover behavior for the Skyrmion dissipation kernels with time-dependent Ohmic terms. The ac driving of the magnon bath at resonance results in a unidirectional helical propagation of the Skyrmion in addition to the otherwise periodic bounded motion.

Two-step deposition of Al-doped ZnO on p-GaN to form ohmic contacts

NASA Astrophysics Data System (ADS)

Su, Xi; Zhang, Guozhen; Wang, Xiao; Chen, Chao; Wu, Hao; Liu, Chang

2017-07-01

Al-doped ZnO (AZO) thin films were deposited directly on p-GaN substrates by using a two-step deposition consisting of polymer assisted deposition (PAD) and atomic layer deposition (ALD) methods. Ohmic contacts of the AZO on p-GaN have been formed. The lowest sheet resistance of the two-step prepared AZO films reached to 145 Ω/sq, and the specific contact resistance reduced to 1.47 × 10-2 Ω·cm2. Transmittance of the AZO films remained above 80% in the visible region. The combination of PAD and ALD technique can be used to prepare p-type ohmic contacts for optoelectronics.

Suppression of surface segregation of the phosphorous δ-doping layer by insertion of an ultra-thin silicon layer for ultra-shallow Ohmic contacts on n-type germanium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamada, Michihiro; Uematsu, Masashi; Itoh, Kohei M., E-mail: kitoh@appi.keio.ac.jp

2015-09-28

We demonstrate the formation of abrupt phosphorus (P) δ-doping profiles in germanium (Ge) by the insertion of ultra-thin silicon (Si) layers. The Si layers at the δ-doping region significantly suppress the surface segregation of P during the molecular beam epitaxial growth of Ge and high-concentration active P donors are confined within a few nm of the initial doping position. The current-voltage characteristics of the P δ-doped layers with Si insertion show excellent Ohmic behaviors with low enough resistivity for ultra-shallow Ohmic contacts on n-type Ge.

Fabrication of optically reflecting ohmic contacts for semiconductor devices

DOEpatents

Sopori, B.L.

1995-07-04

A method is provided to produce a low-resistivity ohmic contact having high optical reflectivity on one side of a semiconductor device. The contact is formed by coating the semiconductor substrate with a thin metal film on the back reflecting side and then optically processing the wafer by illuminating it with electromagnetic radiation of a predetermined wavelength and energy level through the front side of the wafer for a predetermined period of time. This method produces a thin epitaxial alloy layer between the semiconductor substrate and the metal layer when a crystalline substrate is used. The alloy layer provides both a low-resistivity ohmic contact and high optical reflectance. 5 figs.

Formation and characterization of Ni/Al Ohmic contact on n+-type GeSn

NASA Astrophysics Data System (ADS)

Zhang, Xu; Zhang, Dongliang; Zheng, Jun; Liu, Zhi; He, Chao; Xue, Chunlai; Zhang, Guangze; Li, Chuanbo; Cheng, Buwen; Wang, Qiming

2015-12-01

In this study, a Ni/Al Ohmic contact on a highly doped n-type GeSn has been investigated. A specific contact resistivity as low as (2.26 ± 0.11) × 10-4 Ω cm2 was obtained with the GeSn sample annealed at a temperature of 450 °C for 30 s. The linear Ohmic behavior was attributed to the low resistance of the Ni(GeSn) phase; this behavior was determined using glancing-angle X-ray diffraction, and the quantum tunneling current through the Schottky barrier narrowed because of high doping; this phenomenon was confirmed from the contact resistance characteristics at different temperatures from 45 to 205 K.

Formation of Ohmic contact to semipolar (11-22) p-GaN by electrical breakdown method

NASA Astrophysics Data System (ADS)

Jeong, Seonghoon; Lee, Sung-Nam; Kim, Hyunsoo

2018-01-01

The electrical breakdown (EBD) method was used to obtain Ohmic contact to semipolar (11-20) p-GaN surfaces using the Ti/SiO2/ p-GaN structure. The EBD method by which the electrical stress voltage was increased up to 70 V with a compliance current of 30 mA resulted in an Ohmic contact with a specific contact resistance of 3.1×10-3 Ωcm2. The transmission electron microscope (TEM) analysis revealed that the oxygen was slightly out-diffused from SiO2 layer toward Ti surface and the oxidation occurred at the Ti surface, while the GaN remained unchanged.

Improved supervised classification of accelerometry data to distinguish behaviors of soaring birds.

PubMed

Sur, Maitreyi; Suffredini, Tony; Wessells, Stephen M; Bloom, Peter H; Lanzone, Michael; Blackshire, Sheldon; Sridhar, Srisarguru; Katzner, Todd

2017-01-01

Soaring birds can balance the energetic costs of movement by switching between flapping, soaring and gliding flight. Accelerometers can allow quantification of flight behavior and thus a context to interpret these energetic costs. However, models to interpret accelerometry data are still being developed, rarely trained with supervised datasets, and difficult to apply. We collected accelerometry data at 140Hz from a trained golden eagle (Aquila chrysaetos) whose flight we recorded with video that we used to characterize behavior. We applied two forms of supervised classifications, random forest (RF) models and K-nearest neighbor (KNN) models. The KNN model was substantially easier to implement than the RF approach but both were highly accurate in classifying basic behaviors such as flapping (85.5% and 83.6% accurate, respectively), soaring (92.8% and 87.6%) and sitting (84.1% and 88.9%) with overall accuracies of 86.6% and 92.3% respectively. More detailed classification schemes, with specific behaviors such as banking and straight flights were well classified only by the KNN model (91.24% accurate; RF = 61.64% accurate). The RF model maintained its accuracy of classifying basic behavior classification accuracy of basic behaviors at sampling frequencies as low as 10Hz, the KNN at sampling frequencies as low as 20Hz. Classification of accelerometer data collected from free ranging birds demonstrated a strong dependence of predicted behavior on the type of classification model used. Our analyses demonstrate the consequence of different approaches to classification of accelerometry data, the potential to optimize classification algorithms with validated flight behaviors to improve classification accuracy, ideal sampling frequencies for different classification algorithms, and a number of ways to improve commonly used analytical techniques and best practices for classification of accelerometry data.

Improved supervised classification of accelerometry data to distinguish behaviors of soaring birds

PubMed Central

Suffredini, Tony; Wessells, Stephen M.; Bloom, Peter H.; Lanzone, Michael; Blackshire, Sheldon; Sridhar, Srisarguru; Katzner, Todd

2017-01-01

Soaring birds can balance the energetic costs of movement by switching between flapping, soaring and gliding flight. Accelerometers can allow quantification of flight behavior and thus a context to interpret these energetic costs. However, models to interpret accelerometry data are still being developed, rarely trained with supervised datasets, and difficult to apply. We collected accelerometry data at 140Hz from a trained golden eagle (Aquila chrysaetos) whose flight we recorded with video that we used to characterize behavior. We applied two forms of supervised classifications, random forest (RF) models and K-nearest neighbor (KNN) models. The KNN model was substantially easier to implement than the RF approach but both were highly accurate in classifying basic behaviors such as flapping (85.5% and 83.6% accurate, respectively), soaring (92.8% and 87.6%) and sitting (84.1% and 88.9%) with overall accuracies of 86.6% and 92.3% respectively. More detailed classification schemes, with specific behaviors such as banking and straight flights were well classified only by the KNN model (91.24% accurate; RF = 61.64% accurate). The RF model maintained its accuracy of classifying basic behavior classification accuracy of basic behaviors at sampling frequencies as low as 10Hz, the KNN at sampling frequencies as low as 20Hz. Classification of accelerometer data collected from free ranging birds demonstrated a strong dependence of predicted behavior on the type of classification model used. Our analyses demonstrate the consequence of different approaches to classification of accelerometry data, the potential to optimize classification algorithms with validated flight behaviors to improve classification accuracy, ideal sampling frequencies for different classification algorithms, and a number of ways to improve commonly used analytical techniques and best practices for classification of accelerometry data. PMID:28403159

Improved supervised classification of accelerometry data to distinguish behaviors of soaring birds

USGS Publications Warehouse

Sur, Maitreyi; Suffredini, Tony; Wessells, Stephen M.; Bloom, Peter H.; Lanzone, Michael J.; Blackshire, Sheldon; Sridhar, Srisarguru; Katzner, Todd

2017-01-01

Soaring birds can balance the energetic costs of movement by switching between flapping, soaring and gliding flight. Accelerometers can allow quantification of flight behavior and thus a context to interpret these energetic costs. However, models to interpret accelerometry data are still being developed, rarely trained with supervised datasets, and difficult to apply. We collected accelerometry data at 140Hz from a trained golden eagle (Aquila chrysaetos) whose flight we recorded with video that we used to characterize behavior. We applied two forms of supervised classifications, random forest (RF) models and K-nearest neighbor (KNN) models. The KNN model was substantially easier to implement than the RF approach but both were highly accurate in classifying basic behaviors such as flapping (85.5% and 83.6% accurate, respectively), soaring (92.8% and 87.6%) and sitting (84.1% and 88.9%) with overall accuracies of 86.6% and 92.3% respectively. More detailed classification schemes, with specific behaviors such as banking and straight flights were well classified only by the KNN model (91.24% accurate; RF = 61.64% accurate). The RF model maintained its accuracy of classifying basic behavior classification accuracy of basic behaviors at sampling frequencies as low as 10Hz, the KNN at sampling frequencies as low as 20Hz. Classification of accelerometer data collected from free ranging birds demonstrated a strong dependence of predicted behavior on the type of classification model used. Our analyses demonstrate the consequence of different approaches to classification of accelerometry data, the potential to optimize classification algorithms with validated flight behaviors to improve classification accuracy, ideal sampling frequencies for different classification algorithms, and a number of ways to improve commonly used analytical techniques and best practices for classification of accelerometry data.

Flexible, Carbon-Based Ohmic Contacts for Organic Transistors

NASA Technical Reports Server (NTRS)

Brandon, Erik

2005-01-01

A low-temperature process for fabricating flexible, ohmic contacts for use in organic thin-film transistors (OTFTs) has been developed. Typical drainsource contact materials used previously for OTFTs include (1) vacuum-deposited noble-metal contacts and (2) solution-deposited intrinsically conducting molecular or polymeric contacts. Both of these approaches, however, have serious drawbacks.

Control quantum evolution speed of a single dephasing qubit for arbitrary initial states via periodic dynamical decoupling pulses.

PubMed

Song, Ya-Ju; Tan, Qing-Shou; Kuang, Le-Man

2017-03-08

We investigate the possibility to control quantum evolution speed of a single dephasing qubit for arbitrary initial states by the use of periodic dynamical decoupling (PDD) pulses. It is indicated that the quantum speed limit time (QSLT) is determined by initial and final quantum coherence of the qubit, as well as the non-Markovianity of the system under consideration during the evolution when the qubit is subjected to a zero-temperature Ohmic-like dephasing reservoir. It is shown that final quantum coherence of the qubit and the non-Markovianity of the system can be modulated by PDD pulses. Our results show that for arbitrary initial states of the dephasing qubit with non-vanishing quantum coherence, PDD pulses can be used to induce potential acceleration of the quantum evolution in the short-time regime, while PDD pulses can lead to potential speedup and slow down in the long-time regime. We demonstrate that the effect of PDD on the QSLT for the Ohmic or sub-Ohmic spectrum (Markovian reservoir) is much different from that for the super-Ohmic spectrum (non-Markovian reservoir).

Formation of low resistance ohmic contacts in GaN-based high electron mobility transistors with BCl3 surface plasma treatment

NASA Astrophysics Data System (ADS)

Fujishima, Tatsuya; Joglekar, Sameer; Piedra, Daniel; Lee, Hyung-Seok; Zhang, Yuhao; Uedono, Akira; Palacios, Tomás

2013-08-01

A BCl3 surface plasma treatment technique to reduce the resistance and to increase the uniformity of ohmic contacts in AlGaN/GaN high electron mobility transistors with a GaN cap layer has been established. This BCl3 plasma treatment was performed by an inductively coupled plasma reactive ion etching system under conditions that prevented any recess etching. The average contact resistances without plasma treatment, with SiCl4, and with BCl3 plasma treatment were 0.34, 0.41, and 0.17 Ω mm, respectively. Also, the standard deviation of the ohmic contact resistance with BCl3 plasma treatment was decreased. This decrease in the standard deviation of contact resistance can be explained by analyzing the surface condition of GaN with x-ray photoelectron spectroscopy and positron annihilation spectroscopy. We found that the proposed BCl3 plasma treatment technique can not only remove surface oxide but also introduce surface donor states that contribute to lower the ohmic contact resistance.

Investigation of impurity transport using laser blow-off technique in the HL-2A Ohmic and ECRH plasmas

NASA Astrophysics Data System (ADS)

Kai, Zhang; Zheng-Ying, Cui; Ping, Sun; Chun-Feng, Dong; Wei, Deng; Yun-Bo, Dong; Shao-Dong, Song; Min, Jiang; Yong-Gao, Li; Ping, Lu; Qing-Wei, Yang

2016-06-01

Impurity transports in two neighboring discharges with and without electron cyclotron resonance heating (ECRH) are studied in the HL-2A tokamak by laser blow-off (LBO) technique. The progression of aluminium ions as the trace impurity is monitored by soft x-ray (SXR) and bolometer detector arrays with good temporal and spatial resolutions. Obvious difference in the time trace of the signal between the Ohmic and ECRH L-mode discharges is observed. Based on the numerical simulation with one-dimensional (1D) impurity transport code STRAHL, the radial profiles of impurity diffusion coefficient D and convective velocity V are obtained for each shot. The result shows that the diffusion coefficient D significantly increases throughout the plasma minor radius for the ECRH case with respect to the Ohmic case, and that the convection velocity V changes from negative (inward) for the Ohmic case to partially positive (outward) for the ECRH case. The result on HL-2A confirms the pump out effect of ECRH on impurity profile as reported on various other devices.

Ohmic ITBs in Alcator C-Mod

NASA Astrophysics Data System (ADS)

Fiore, C. L.; Rowan, W. L.; Dominguez, A.; Hubbard, A. E.; Ince-Cushman, A.; Greenwald, M. J.; Lin, L.; Marmar, E. S.; Reinke, M.; Rice, J. E.; Zhurovich, K.

2007-11-01

Internal transport barrier plasmas can arise spontaneously in ohmic Alcator C-Mod plasmas where an EDA H-mode has been developed by magnetic field ramping. These ohmic ITBs share the hallmarks of ITBs created with off-axis ICRF injection in that they have highly peaked density and pressure profiles and the peaking can be suppressed by on-axis ICRF. There is a reduction of particle and thermal flux in the barrier region which then allows the neoclassical pinch to peak the central density. Recent work on ITB onset conditions [1] which was motivated by turbulence studies [2] points to the broadening of the Ti profile with off-axis ICRF acting to reduce the ion temperature gradient. This suppresses ITG instability driven particle fluxes, which is thought to be the primary mechanism for ITB formation. The object of this study is to examine the characteristics of ohmic ITBs to find whether the stability of plasmas and the plasma parameters support the onset model. [1]K. Zhurovich, et al., To be published in Nuclear Fusion [2] D. R. Ernst, et al., Phys. Plasmas 11, 2637 (2004)

Improvement of electrical and optical properties of p-GaN Ohmic metals under ultraviolet light irradiation annealing processes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chae, S.W.; Yoon, S.K.; Kwak, J.S.

2006-05-15

We report the improvement of electrical and optical properties of p-GaN Ohmic metals, ZnNi(10 nm)/Au(10 nm), by ultraviolet (UV) light irradiation. After UV light irradiation, the specific contact resistance of p-GaN decreased slightly from 2.99x10{sup -4} to 2.54x10{sup -4} {omega} cm{sup 2}, while the transmittance of the contact layer increased form 75% to 85% at a wavelength of 460 nm. In addition, the forward voltage of InGaN/GaN light-emitting diode chip at 20 mA decreased from 3.55 to 3.45 V, and the output power increased form 18 to 25 mW by UV light irradiation. The low resistance and high transmittance ofmore » the p-GaN Ohmic metals are attributed to the reduced Shottky barrier by the formation of gallium oxide and the increased oxidation of p-Ohmic metals, respectively, due to ozone generated form oxygen during UV light irradiation.« less

Sintered Cr/Pt and Ni/Au ohmic contacts to B 12P 2

DOE PAGES

Frye, Clint D.; Kucheyev, Sergei O.; Edgar, James H.; ...

2015-04-09

With this study, icosahedral boron phosphide (B 12P 2) is a wide-bandgap semiconductor possessing interesting properties such as high hardness, chemical inertness, and the reported ability to self-heal from irradiation by high energy electrons. Here, the authors developed Cr/Pt and Ni/Au ohmic contacts to epitaxially grown B 12P 2 for materials characterization and electronic device development. Cr/Pt contacts became ohmic after annealing at 700 °C for 30 s with a specific contact resistance of 2×10 –4 Ω cm 2, as measured by the linear transfer length method. Ni/Au contacts were ohmic prior to any annealing, and their minimum specific contactmore » resistance was ~l–4 × 10 –4 Ω cm 2 after annealing over the temperature range of 500–800 °C. Rutherford backscattering spectrometry revealed a strong reaction and intermixing between Cr/Pt and B 12P 2 at 700 °C and a reaction layer between Ni and B 12P 2 thinner than ~25 nm at 500 °C.« less

Orbiter CCTV video signal noise analysis

NASA Technical Reports Server (NTRS)

Lawton, R. M.; Blanke, L. R.; Pannett, R. F.

1977-01-01

The amount of steady state and transient noise which will couple to orbiter CCTV video signal wiring is predicted. The primary emphasis is on the interim system, however, some predictions are made concerning the operational system wiring in the cabin area. Noise sources considered are RF fields from on board transmitters, precipitation static, induced lightning currents, and induced noise from adjacent wiring. The most significant source is noise coupled to video circuits from associated circuits in common connectors. Video signal crosstalk is the primary cause of steady state interference, and mechanically switched control functions cause the largest induced transients.

A Low-Cost Miniaturized Laser Heterodyne Radiometer (Mini-LHR) for Near-ir Measurements of CO2 and CH4 in the Atmospheric Column

NASA Technical Reports Server (NTRS)

Steel, Emily Wilson

2016-01-01

The miniaturized laser heterodyne radiometer (mini-LHR) is a ground-based passive variation of a laser heterodyne radiometer that uses sunlight to measure absorption of CO2 andCH4 in the infrared. Sunlight is collected using collimation optics mounted to an AERONET sun tracker, modulated with a fiber switch and mixed with infrared laser light in a fast photoreciever.The amplitude of the resultant RF (radio frequency) beat signal correlates with the concentration of the gas in the atmospheric column.

MST's Programmable Power Supplies: Bt Update, Bp Prototype

NASA Astrophysics Data System (ADS)

Holly, D. J.; Chapman, B. E.; McCollam, K. J.; Morin, J. C.; Thomas, M. A.

2013-10-01

MST's toroidal field programmable power supply (Bt PPS) has now been in operation for several years and has provided important new capabilities. One of the primary goals for the Bt PPS is the partial optimization of inductive current profile control, involving control of the poloidal electric field. The Bt PPS has achieved fluctuation reduction over MST's entire range of Ip. At the largest Ip, the Bt PPS achieves fluctuation reduction with a smaller poloidal electric field than the previous passive system, implying that substantially longer periods of current profile control may be possible. The Bt PPS has also been used to produce Ohmic tokamak plasmas in MST. With an applied toroidal field of 0.135 T, and q(a) > 2, the estimated energy confinement time is roughly consistent with neo-Alcator scaling. Driving q(a) < 2 with larger Ip, the confinement time degrades, but the discharge duration does not terminate prematurely. To fully optimize current profile control and to test MST operational limits, a PPS is also needed for the Bp circuit. Currently in prototype stage, the Bp PPS will feature a number of innovations to increase its flexibility and performance. Isolated charging, control, and monitor systems will eliminate charging relays, reduce coupling between modules, and minimize capacitor heating. Seven-level pulse width modulation will reduce output ripple and switching losses. Solid state shorting bars will eliminate shorting relays and minimize wiring. A balanced switching algorithm will minimize capacitive noise generation. Work supported by U. S. D. o. E.

Technology achievements and projections for communication satellites of the future

NASA Technical Reports Server (NTRS)

Bagwell, J. W.

1986-01-01

Multibeam systems of the future using monolithic microwave integrated circuits to provide phase control and power gain are contrasted with discrete microwave power amplifiers from 10 to 75 W and their associated waveguide feeds, phase shifters and power splitters. Challenging new enabling technology areas include advanced electrooptical control and signal feeds. Large scale MMIC's will be used incorporating on chip control interfaces, latching, and phase and amplitude control with power levels of a few watts each. Beam forming algorithms for 80 to 90 deg. wide angle scanning and precise beam forming under wide ranging environments will be required. Satelllite systems using these dynamically reconfigured multibeam antenna systems will demand greater degrees of beam interconnectivity. Multiband and multiservice users will be interconnected through the same space platform. Monolithic switching arrays operating over a wide range of RF and IF frequencies are contrasted with current IF switch technology implemented discretely. Size, weight, and performance improvements by an order of magnitude are projected.

Preliminary measurements of neutrons from the D-D reaction in the COMPASS tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dankowski, J., E-mail: jan.dankowski@ifj.edu.pl; Kurowski, A.; Twarog, D.

Recent results of measured fast neutrons created in the D-D reaction on the COMPASS tokamak during ohmic discharges are presented in this paper. Two different type detectors were used during experiment. He-3 detectors and bubble detectors as a support. The measurements are an introduction for neutron diagnostic on tokamak COMPASS and monitoring neutrons during discharges with Neutral Beam Injection (NBI). The He-3 counters and bubble detectors were located in two positions near tokamak vacuum chamber at a distance less than 40 cm to the centre of plasma. The neutrons flux was observed in ohmic discharges. However, analysis of our resultsmore » does not indicate any clear source of neutrons production during ohmic discharges.« less

New flange correction formula applied to interfacial resistance measurements of ohmic contacts to GaAs

NASA Technical Reports Server (NTRS)

Lieneweg, Udo; Hannaman, David J.

1987-01-01

A quasi-two-dimensional analytical model is developed to account for vertical and horizontal current flow in and adjacent to a square ohmic contact between a metal and a thin semiconducting strip which is wider than the contact. The model includes side taps to the contact area for voltage probing and relates the 'apparent' interfacial resistivity to the (true) interfacial resistivity, the sheet resistance of the semiconducting layer, the contact size, and the width of the 'flange' around the contact. This relation is checked against numerical simulations. With the help of the model, interfacial resistivities of ohmic contacts to GaAs were extracted and found independent of contact size in the range of 1.5-10 microns.

Electronically tunable metamaterials using subwavelength magnetoresponsive particles

NASA Astrophysics Data System (ADS)

Allen, Monica; Allen, Jeffery; Parrow, Jacob; Asif, Sajid; Iftikar, Adnan; Wenner, Brett; Braaten, Benjamin

We demonstrate tunability of material properties of an engineered electromagnetic material in the RF regime using microparticles that respond to static magnetic biasing fields. The magnetic particles align with field lines creating a short/inductive state of the switch in the addressed voxel. When the biasing magnetic field is removed, the switch returns to an open/capacitive state. Each voxel measures 1.5 mm x 1.5 mm x 0.508 mm in the x, y, and z direction respectively, with a 0.9 mm diameter cylindrical cavity. The cavity is along the z-axis and is partially filled with microparticles composed of a magnetite core with Ag coating. Cu foil placed on the top and bottom encloses the particles in the cavity and acts as the biasing electrodes. Switching between inductive and capacitive states in spatially addressed voxels controls the cumulative ɛ and μ of the host material (i.e., layer) and controls the phase of an incident wave. We present finite element based models of prototype voxels with experimental measurements that validate the models on a host. This research can be applied to real-time tuning of material parameters with subwavelength voxel precision enabling wave control/manipulation as well as devices for switching and software-dictated tunable impedance capabilities. Authors JWA, MSA and BRW are grateful for support from AFOSR Lab Task 17RWCOR397 (Dr. H. Weinstock). NDSU was supported by (FA-8651-15-2-002) from the US Air Force Research Laboratory Munitions Directorate.

Novel techniques and devices for in-situ film coatings of long, small diameter tubes or elliptical and other surface contours

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hershcovitch, Ady; Blaskiewicz, Michael; Brennan, Joseph Michael

In this study, devices and techniques that can, via physical vapor deposition,coat various surface contours or very long small aperture pipes, are described. Recently, a magnetron mole was developed in order to in-situ coat accelerator tube sections of the Brookhaven National Lab relativistic heavy ion collider that have 7.1 cm diameter with access points that are 500 m apart, for copper coat the accelerator vacuum tube in order to alleviate the problems of unacceptable ohmic heating and of electron clouds. A magnetron with a 50 cm long cathode was designed fabricated and successfully operated to copper coat a whole assemblymore » containing a full-size, stainless steel, cold bore, of the accelerator magnet tubing connected to two types bellows, to which two additional pipes made of accelerator tubing were connected. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system, which is enclosed in a flexible braided metal sleeve, is driven by a motorized spool. To increase cathode lifetime, movable magnet package was developed, and thickest possible cathode was made, with a rather challenging target to substrate distance of less than 1.5 cm. Optimized process to ensure excellent adhesion was developed. Coating thickness of 10 μm Cu passed all industrial tests and even exceeded maximum capability of a 12 kg pull test fixture. Room temperature radio frequency (RF) resistivity measurement indicated that 10 μm Cu coated stainless steel accelerator tube has conductivity close to copper tubing. Work is in progress to repeat the RF resistivity measurement at cryogenic temperatures. Over 20 years ago, a device using multi axis robotic manipulators controlling separate robotic assemblies resulted in nine-axes of motion combined with conformal shape of the cathodes that can adapt to various curved surface contours was developed and successfully used for depositing optical coating on aircraft canopies. The techniques can be utilized for in situ coating of elliptical and other surface contour RF cavities and long beam pipes with thick superconducting films. Plans are to incorporate ion assisted deposition in those techniques for attaining dense, adherent and defect free coatings.« less

Novel techniques and devices for in-situ film coatings of long, small diameter tubes or elliptical and other surface contours

DOE PAGES

Hershcovitch, Ady; Blaskiewicz, Michael; Brennan, Joseph Michael; ...

2015-07-30

In this study, devices and techniques that can, via physical vapor deposition,coat various surface contours or very long small aperture pipes, are described. Recently, a magnetron mole was developed in order to in-situ coat accelerator tube sections of the Brookhaven National Lab relativistic heavy ion collider that have 7.1 cm diameter with access points that are 500 m apart, for copper coat the accelerator vacuum tube in order to alleviate the problems of unacceptable ohmic heating and of electron clouds. A magnetron with a 50 cm long cathode was designed fabricated and successfully operated to copper coat a whole assemblymore » containing a full-size, stainless steel, cold bore, of the accelerator magnet tubing connected to two types bellows, to which two additional pipes made of accelerator tubing were connected. The magnetron is mounted on a carriage with spring loaded wheels that successfully crossed bellows and adjusted for variations in vacuum tube diameter, while keeping the magnetron centered. Electrical power and cooling water were fed through a cable bundle. The umbilical cabling system, which is enclosed in a flexible braided metal sleeve, is driven by a motorized spool. To increase cathode lifetime, movable magnet package was developed, and thickest possible cathode was made, with a rather challenging target to substrate distance of less than 1.5 cm. Optimized process to ensure excellent adhesion was developed. Coating thickness of 10 μm Cu passed all industrial tests and even exceeded maximum capability of a 12 kg pull test fixture. Room temperature radio frequency (RF) resistivity measurement indicated that 10 μm Cu coated stainless steel accelerator tube has conductivity close to copper tubing. Work is in progress to repeat the RF resistivity measurement at cryogenic temperatures. Over 20 years ago, a device using multi axis robotic manipulators controlling separate robotic assemblies resulted in nine-axes of motion combined with conformal shape of the cathodes that can adapt to various curved surface contours was developed and successfully used for depositing optical coating on aircraft canopies. The techniques can be utilized for in situ coating of elliptical and other surface contour RF cavities and long beam pipes with thick superconducting films. Plans are to incorporate ion assisted deposition in those techniques for attaining dense, adherent and defect free coatings.« less

Plasma Confinement in the UCLA Electric Tokamak.

NASA Astrophysics Data System (ADS)

Taylor, Robert J.

2001-10-01

The main goal of the newly constructed large Electric Tokamak (R = 5 m, a = 1 m, BT < 0.25 T) is to access an omnigeneous, unity beta(S.C. Cowley, P.K. Kaw, R.S. Kelly, R.M. Kulsrud, Phys. fluids B 3 (1991) 2066.) plasma regime. The design goal was to achieve good confinement at low magnetic fields, consistent with the high beta goal. To keep the program cost down, we adopted the use of ICRF as the primary heating source. Consequently, antenna surfaces covering 1/2 of the surface of the tokamak has been prepared for heating and current drive. Very clean hydrogenic plasmas have been achieved with loop voltage below 0.7 volt and densities 3 times above the Murakami limit, n(0) > 8 x 10^12 cm-3 when there is no MHD activity. The electron temperature, derived from the plasma conductivity is > 250 eV with a central electron energy confinement time > 350 msec in ohmic conditions. The sawteeth period is 50 msec. Edge plasma rotation is induced by plasma biasing via electron injection in an analogous manner to that seen in CCT(R.J. Taylor, M.L. Brown, B.D. Fried, H. Grote, J.R. Liberati, G.J. Morales, P. Pribyl, D. Darrow, and M. Ono. Phys. Rev Lett. 63 2365 1989.) and the neoclassical bifurcation is close to that described by Shaing et al(K.C. Shaing and E.C. Crume, Phys. Rev. Lett. 63 2369 (1989).). In the ohmic phase the confinement tends to be MHD limited. The ICRF heating eliminates the MHD disturbances. Under second harmonic heating conditions, we observe an internal confinement peaking characterized by doubling of the core density and a corresponding increase in the central electron temperature. Charge exchange data, Doppler data in visible H-alpha light, and EC radiation all indicate that ICRF heating works much better than expected. The major effort is focused on increasing the power input and controlling the resulting equilibrium. This task appears to be easy since our current pulses are approaching the 3 second mark without RF heating or current drive. Our initial experience with current profile control, needed for high beta plasma equilibrium, will be also discussed.

Acousto-optic RF signal acquisition system

NASA Astrophysics Data System (ADS)

Bloxham, Laurence H.

1990-09-01

This paper describes the architecture and performance of a prototype Acousto-Optic RF Signal Acquisition System designed to intercept, automatically identify, and track communication signals in the VHF band. The system covers 28.0 to 92.0 MHz with five manually selectable, dual conversion; 12.8 MHZ bandwidth front ends. An acousto-optic spectrum analyzer (AOSA) implemented using a tellurium dioxide (Te02) Bragg cell is used to channelize the 12.8 MHz pass band into 512 25 KHz channels. Polarization switching is used to suppress optical noise. Excellent isolation and dynamic range are achieved by using a linear array of 512 custom 40/50 micron fiber optic cables to collect the light at the focal plane of the AOSA and route the light to individual photodetectors. The photodetectors are operated in the photovoltaic mode to compress the greater than 60 dB input optical dynamic range into an easily processed electrical signal. The 512 signals are multiplexed and processed as a line in a video image by a customized digital image processing system. The image processor simultaneously analyzes the channelized signal data and produces a classical waterfall display.

WDM-PON access network with lightwave source centralized full-duplex link based on SSB-OOFDM for wired and 60 GHz band wireless alternative accesses

NASA Astrophysics Data System (ADS)

Ma, Jianxin; Wang, Zhao; Zheng, Guoli

2014-04-01

A novel lightwave centralized full-duplex WDM-PON access network based on single sideband optical orthogonal frequency-division multiplexing (SSB-OOFDM) is proposed for providing wired and 60-GHz band wireless accesses alternately. At the OLT, the multi-channels with 10-Gb/s 4-QAM-RF-OFDM signals are SSB modulated on the optical local oscillators (OLOs). At the RN, one OOFDM signal along with two OLOs is abstracted and switched to the corresponding HONU, where the signal can be downconverted to the 10-GHz or 60-GHz band RF-OFDM signal by one OLO for wired or wireless access, while the other one is used to bear the uplink signal. Since the HONU is free from the light sources, the system complexity and cost are reduced. Full duplex transmission over 25 km fiber have been demonstrated that the error vector magnitude (EVM) of the down- and up-link signals are much below the FEC limit for both the wired and 60-GHz band wireless access services.

Development of a micro nuclear magnetic resonance system

NASA Astrophysics Data System (ADS)

Goloshevsky, Artem

Application of Nuclear Magnetic Resonance (NMR) to on-line/in-line control of industrial processes is currently limited by equipment costs and requirements for installation. A superconducting magnet generating strong fields is the most expensive part of a typical NMR instrument. In industrial environments, fringe magnetic fields make accommodation of NMR instruments difficult. However, a portable, low-cost and low-field magnetic resonance system can be used in virtually any environment. Development of a number of hardware components for a portable, low-cost NMR instrument is reported in this dissertation. Chapter one provides a discussion on a miniaturized Helmholtz spiral radio-frequency (RF) coil (average diameter equal to 3.5 mm) and an NMR probe built around a capillary (outer diameter = 1.59 mm and inner diameter = 1.02 mm) for flow imaging. Experiments of NMR spectroscopy, static and dynamic (flow) imaging, conducted with the use of the miniaturized coil, are described. Chapter two presents a microfabricated package of two biaxial gradient coils and a Helmholtz RF coil. Planar configuration of discrete wires was used to create magnetic field gradients. Performance of the microfabricated gradient coils while imaging water flow compared well with a commercial gradient set of much larger size. Chapter three reports on flow imaging experiments with power law fluids (aqueous solutions of sodium salt of carboxymethyl cellulose (CMC)) of different viscosities, carried out in the NMR probe with the miniaturized RF coil and capillary. Viscosities of the CMC solutions were determined based on the curve fits of the velocity profiles and simultaneous measurements of the flow rates. The curve fits were carried out according to the power law model equations. The NMR viscosity measurements compared well with measurements of the same CMC samples, performed on a conventional rotational rheometer. A portable, home-built transceiver, designed for NMR applications utilizing a miniaturized RF coil, is described in chapter four. The maximum RF power, occurring in the transceiver, was 21.5 dBm. Two transistor-transistor logic (TTL) switches functioned as an active duplexer. A quadrature detection scheme was used. The transceiver, combined with a filter/amplifier module, data acquisition (DAQ and RF generating PC boards, was successfully tested in NMR spectroscopy experiments at low magnetic field. It was demonstrated that, starting with the RF probe, a typical, large size NMR instrument can be miniaturized without impairment to the quality of the data. Such an instrument will be readily used in many industrial process control applications (e.g. for analysis of material properties and identification of chemicals).

Device and Container for Reheating and Sterilization

NASA Technical Reports Server (NTRS)

Sastry, Sudhir K.; Heskitt, Brian F.; Jun, Soojin; Marcy, Joseph E.; Mahna, Ritesh

2012-01-01

Long-duration space missions require the development of improved foods and novel packages that do not represent a significant disposal issue. In addition, it would also be desirable if rapid heating technologies could be used on Earth as well, to improve food quality during a sterilization process. For this purpose, a package equipped with electrodes was developed that will enable rapid reheating of contents via ohmic heating to serving temperature during space vehicle transit. Further, the package is designed with a resealing feature, which enables the package, once used, to contain and sterilize waste, including human waste for storage prior to jettison during a long-duration mission. Ohmic heating is a technology that has been investigated on and off for over a century. Literature indicates that foods processed by ohmic heating are of superior quality to their conventionally processed counterparts. This is due to the speed and uniformity of ohmic heating, which minimizes exposure of sensitive materials to high temperatures. In principle, the material may be heated rapidly to sterilization conditions, cooled rapidly, and stored. The ohmic heating device herein is incorporated within a package. While this by itself is not novel, a reusable feature also was developed with the intent that waste may be stored and re-sterilized within the packages. These would then serve a useful function after their use in food processing and storage. The enclosure should be designed to minimize mass (and for NASA's purposes, Equivalent System Mass, or ESM), while enabling the sterilization function. It should also be electrically insulating. For this reason, Ultem high-strength, machinable electrical insulator was used.

Analytical models of Ohmic heating and conventional heating in food processing

NASA Astrophysics Data System (ADS)

Serventi, A.; Bozzoli, F.; Rainieri, S.

2017-11-01

Ohmic heating is a food processing operation in which an electric current is passed through a food and the electrical resistance of the food causes the electric power to be transformed directly into heat. The heat is not delivered through a surface as in conventional heat exchangers but it is internally generated by Joule effect. Therefore, no temperature gradient is required and it origins quicker and more uniform heating within the food. On the other hand, it is associated with high energy costs and its use is limited to a particular range of food products with an appropriate electrical conductivity. Sterilization of foods by Ohmic heating has gained growing interest in the last few years. The aim of this study is to evaluate the benefits of Ohmic heating with respect to conventional heat exchangers under uniform wall temperature, a condition that is often present in industrial plants. This comparison is carried out by means of analytical models. The two different heating conditions are simulated under typical circumstances for the food industry. Particular attention is paid to the uniformity of the heat treatment and to the heating section length required in the two different conditions.

Analysis of plasma termination in the JET hybrid scenario

NASA Astrophysics Data System (ADS)

Hobirk, J.; Bernert, M.; Buratti, P.; Challis, C. D.; Coffey, I.; Drewelow, P.; Joffrin, E.; Mailloux, J.; Nunes, I.; Pucella, G.; Pütterich, T.; de Vries, P. C.; Contributors, JET

2018-07-01

This paper analyses the final phase of hybrid scenario discharges at JET, the reduction of auxiliary heating towards finally the Ohmic phase. The here considered Ohmic phase is mostly still in the current flattop but may also be in the current ramp down. For this purpose a database is created of 54 parameters in 7 phases distributed in time of the discharge. It is found that the occurrence of a locked mode is in most cases preceded by a radiation peaking after the main heating phase either in a low power phase and/or in the Ohmic phase. To gain insight on the importance of different parameters in this process a correlation analysis to the radiation peaking in the Ohmic phase is done. The first finding is that the further away in time the analysed phases are the less the correlation is. This means in the end that a good termination scenario might also be able to terminate unhealthy plasmas safely. The second finding is that remaining impurities in the plasma after reducing the heating power in the termination phase are the most important reason for generating a locked mode which can lead to a disruption.

Immersed finger-type indium tin oxide ohmic contacts on p-GaN photoelectrodes for photoelectrochemical hydrogen generation.

PubMed

Liu, Shu-Yen; Sheu, J K; Lee, M L; Lin, Yu-Chuan; Tu, S J; Huang, F W; Lai, W C

2012-03-12

In this study, we demonstrated photoelectrochemical (PEC) hydrogen generation using p-GaN photoelectrodes associated with immersed finger-type indium tin oxide (IF-ITO) ohmic contacts. The IF-ITO/p-GaN photoelectrode scheme exhibits higher photocurrent and gas generation rate compared with p-GaN photoelectrodes without IF-ITO ohmic contacts. In addition, the critical external bias for detectable hydrogen generation can be effectively reduced by the use of IF-ITO ohmic contacts. This finding can be attributed to the greatly uniform distribution of the IF-ITO/p-GaN photoelectrode applied fields over the whole working area. As a result, the collection efficiency of photo-generated holes by electrode contacts is higher than that of p-GaN photoelectrodes without IF-ITO contacts. Microscopy revealed a tiny change on the p-GaN surfaces before and after hydrogen generation. In contrast, photoelectrodes composed of n-GaN have a short lifetime due to n-GaN corrosion during hydrogen generation. Findings of this study indicate that the ITO finger contacts on p-GaN layer is a potential candidate as photoelectrodes for PEC hydrogen generation.

Influence of infrared final cooking on polycyclic aromatic hydrocarbon formation in ohmically pre-cooked beef meatballs.

PubMed

Kendirci, Perihan; Icier, Filiz; Kor, Gamze; Onogur, Tomris Altug

2014-06-01

Effects of infrared cooking on polycyclic aromatic hydrocarbon (PAH) formation in ohmically pre-cooked beef meatballs were investigated. Samples were pre-cooked in a specially designed-continuous type ohmic cooking at a voltage gradient of 15.26V/cm for 92s. Infrared cooking was applied as a final cooking method at different combinations of heat fluxes (3.706, 5.678, 8.475kW/m(2)), application distances (10.5, 13.5, 16.5cm) and application durations (4, 8, 12min). PAHs were analyzed by using high performance liquid chromatography (HPLC) equipped with a fluorescence detector. The total PAH levels were detected to be between 4.47 and 64μg/kg. Benzo[a] pyrene (B[a]P) and PAH4 (sum of B[a]P, chrysene (Chr), benzo[a]anthracene (B[a]A) and benzo[b]fluoranthene (B[b]F)) levels detected in meatballs were below the EC limits. Ohmic pre-cooking followed by infrared cooking may be regarded as a safe cooking procedure of meatballs from a PAH contamination point of view. Copyright © 2014 Elsevier Ltd. All rights reserved.

Ohmic Heating of an Electrically Conductive Food Package.

PubMed

Kanogchaipramot, Kanyawee; Tongkhao, Kullanart; Sajjaanantakul, Tanaboon; Kamonpatana, Pitiya

2016-12-01

Ohmic heating through an electrically conductive food package is a new approach to heat the food and its package as a whole after packing to avoid post-process contamination and to serve consumer needs for convenience. This process has been successfully completed using polymer film integrated with an electrically conductive film to form a conductive package. Orange juice packed in the conductive package surrounded with a conductive medium was pasteurized in an ohmic heater. A mathematical model was developed to simulate the temperature distribution within the package and its surroundings. A 3-D thermal-electric model showed heating uniformity inside the food package while the hot zone appeared in the orange juice adjacent to the conductive film. The accuracy of the model was determined by comparing the experimental results with the simulated temperature and current drawn; the model showed good agreement between the actual and simulated results. An inoculated pack study using Escherichia coli O157:H7 indicated negative growth of viable microorganisms at the target and over target lethal process temperatures, whereas the microorganism was present in the under target temperature treatment. Consequently, our developed ohmic heating system with conductive packaging offers potential for producing safe food. © 2016 Institute of Food Technologists®.

Application of low frequency pulsed ohmic heating for inactivation of foodborne pathogens and MS-2 phage in buffered peptone water and tomato juice.

PubMed

Kim, Sang-Soon; Choi, Won; Kang, Dong-Hyun

2017-05-01

The purpose of this study was to inactivate foodborne pathogens effectively by ohmic heating in buffered peptone water and tomato juice without causing electrode corrosion and quality degradation. Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes were used as representative foodborne pathogens and MS-2 phage was used as a norovirus surrogate. Buffered peptone water and tomato juice inoculated with pathogens were treated with pulsed ohmic heating at different frequencies (0.06-1 kHz). Propidium iodide uptake values of bacterial pathogens were significantly (p < 0.05) larger at 0.06-0.5 kHz than at 1 kHz, and sub-lethal injury of pathogenic bacteria was reduced by decreasing frequency. MS-2 phage was inactivated more effectively at low frequency, and was more sensitive to acidic conditions than pathogenic bacteria. Electrode corrosion and quality degradation of tomato juice were not observed regardless of frequency. This study suggests that low frequency pulsed ohmic heating is applicable to inactivate foodborne pathogens effectively without causing electrode corrosion and quality degradation in tomato juice. Copyright © 2016. Published by Elsevier Ltd.

State transition of a non-Ohmic damping system in a corrugated plane.

PubMed

Lü, Kun; Bao, Jing-Dong

2007-12-01

Anomalous transport of a particle subjected to non-Ohmic damping of the power delta in a tilted periodic potential is investigated via Monte Carlo simulation of the generalized Langevin equation. It is found that the system exhibits two relative motion modes: the locked state and the running state. In an environment of sub-Ohmic damping (0=2D_(eff)(delta){t(delta_eff} . Our result shows that the effective power index delta_(eff) can be enhanced and is a nonmonotonic function of the temperature and the driving force. The mixture of the two motion modes also leads to a breakdown of the hysteresis loop of the mobility.

Novel analytical model for optimizing the pull-in voltage in a flexured MEMS switch incorporating beam perforation effect

NASA Astrophysics Data System (ADS)

Guha, K.; Laskar, N. M.; Gogoi, H. J.; Borah, A. K.; Baishnab, K. L.; Baishya, S.

2017-11-01

This paper presents a new method for the design, modelling and optimization of a uniform serpentine meander based MEMS shunt capacitive switch with perforation on upper beam. The new approach is proposed to improve the Pull-in Voltage performance in a MEMS switch. First a new analytical model of the Pull-in Voltage is proposed using the modified Mejis-Fokkema capacitance model taking care of the nonlinear electrostatic force, the fringing field effect due to beam thickness and etched holes on the beam simultaneously followed by the validation of same with the simulated results of benchmark full 3D FEM solver CoventorWare in a wide range of structural parameter variations. It shows a good agreement with the simulated results. Secondly, an optimization method is presented to determine the optimum configuration of switch for achieving minimum Pull-in voltage considering the proposed analytical mode as objective function. Some high performance Evolutionary Optimization Algorithms have been utilized to obtain the optimum dimensions with less computational cost and complexity. Upon comparing the applied algorithms between each other, the Dragonfly Algorithm is found to be most suitable in terms of minimum Pull-in voltage and higher convergence speed. Optimized values are validated against the simulated results of CoventorWare which shows a very satisfactory results with a small deviation of 0.223 V. In addition to these, the paper proposes, for the first time, a novel algorithmic approach for uniform arrangement of square holes in a given beam area of RF MEMS switch for perforation. The algorithm dynamically accommodates all the square holes within a given beam area such that the maximum space is utilized. This automated arrangement of perforation holes will further improve the computational complexity and design accuracy of the complex design of perforated MEMS switch.

Junction-side illuminated silicon detector arrays

DOEpatents

Iwanczyk, Jan S.; Patt, Bradley E.; Tull, Carolyn

2004-03-30

A junction-side illuminated detector array of pixelated detectors is constructed on a silicon wafer. A junction contact on the front-side may cover the whole detector array, and may be used as an entrance window for light, x-ray, gamma ray and/or other particles. The back-side has an array of individual ohmic contact pixels. Each of the ohmic contact pixels on the back-side may be surrounded by a grid or a ring of junction separation implants. Effective pixel size may be changed by separately biasing different sections of the grid. A scintillator may be coupled directly to the entrance window while readout electronics may be coupled directly to the ohmic contact pixels. The detector array may be used as a radiation hardened detector for high-energy physics research or as avalanche imaging arrays.

Enhancement of ohmic and stochastic heating by resonance effects in capacitive radio frequency discharges: a theoretical approach.

PubMed

Mussenbrock, T; Brinkmann, R P; Lieberman, M A; Lichtenberg, A J; Kawamura, E

2008-08-22

In low-pressure capacitive radio frequency discharges, two mechanisms of electron heating are dominant: (i) Ohmic heating due to collisions of electrons with neutrals of the background gas and (ii) stochastic heating due to momentum transfer from the oscillating boundary sheath. In this work we show by means of a nonlinear global model that the self-excitation of the plasma series resonance which arises in asymmetric capacitive discharges due to nonlinear interaction of plasma bulk and sheath significantly affects both Ohmic heating and stochastic heating. We observe that the series resonance effect increases the dissipation by factors of 2-5. We conclude that the nonlinear plasma dynamics should be taken into account in order to describe quantitatively correct electron heating in asymmetric capacitive radio frequency discharges.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Zhoufei; Ouyang, Xiaolong; Gong, Zhihao

An extended hierarchy equation of motion (HEOM) is proposed and applied to study the dynamics of the spin-boson model. In this approach, a complete set of orthonormal functions are used to expand an arbitrary bath correlation function. As a result, a complete dynamic basis set is constructed by including the system reduced density matrix and auxiliary fields composed of these expansion functions, where the extended HEOM is derived for the time derivative of each element. The reliability of the extended HEOM is demonstrated by comparison with the stochastic Hamiltonian approach under room-temperature classical ohmic and sub-ohmic noises and the multilayermore » multiconfiguration time-dependent Hartree theory under zero-temperature quantum ohmic noise. Upon increasing the order in the hierarchical expansion, the result obtained from the extended HOEM systematically converges to the numerically exact answer.« less

Zeroth-order design report for the next linear collider. Volume 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Raubenheimer, T.O.

This Zeroth-Order Design Report (ZDR) for the Next Linear Collider (NLC) has been completed as a feasibility study for a TeV-scale linear collider that incorporates a room-temperature accelerator powered by rf microwaves at 11.424 GHz--similar to that presently used in the SLC, but at four times the rf frequency. The purpose of this study is to examine the complete systems of such a collider, to understand how the parts fit together, and to make certain that every required piece has been included. The ``design`` presented here is not fully engineered in any sense, but to be assured that the NLCmore » can be built, attention has been given to a number of critical components and issues that present special challenges. More engineering and development of a number of mechanical and electrical systems remain to be done, but the conclusion of this study is that indeed the NLC is technically feasible and can be expected to reach the performance levels required to perform research at the TeV energy scale. Volume II covers the following: collimation systems; IP switch and big bend; final focus; the interaction region; multiple bunch issues; control systems; instrumentation; machine protection systems; NLC reliability considerations; NLC conventional facilities. Also included are four appendices on the following topics: An RF power source upgrade to the NLC; a second interaction region for gamma-gamma, gamma-electron; ground motion: theory and measurement; and beam-based feedback: theory and implementation.« less

Global climate impacts of country-level primary carbonaceous aerosol from solid-fuel cookstove emissions

NASA Astrophysics Data System (ADS)

Lacey, Forrest; Henze, Daven

2015-11-01

Cookstove use is globally one of the largest unregulated anthropogenic sources of primary carbonaceous aerosol. While reducing cookstove emissions through national-scale mitigation efforts has clear benefits for improving indoor and ambient air quality, and significant climate benefits from reduced green-house gas emissions, climate impacts associated with reductions to co-emitted black (BC) and organic carbonaceous aerosol are not well characterized. Here we attribute direct, indirect, semi-direct, and snow/ice albedo radiative forcing (RF) and associated global surface temperature changes to national-scale carbonaceous aerosol cookstove emissions. These results are made possible through the use of adjoint sensitivity modeling to relate direct RF and BC deposition to emissions. Semi- and indirect effects are included via global scaling factors, and bounds on these estimates are drawn from current literature ranges for aerosol RF along with a range of solid fuel emissions characterizations. Absolute regional temperature potentials are used to estimate global surface temperature changes. Bounds are placed on these estimates, drawing from current literature ranges for aerosol RF along with a range of solid fuel emissions characterizations. We estimate a range of 0.16 K warming to 0.28 K cooling with a central estimate of 0.06 K cooling from the removal of cookstove aerosol emissions. At the national emissions scale, countries’ impacts on global climate range from net warming (e.g., Mexico and Brazil) to net cooling, although the range of estimated impacts for all countries span zero given uncertainties in RF estimates and fuel characterization. We identify similarities and differences in the sets of countries with the highest emissions and largest cookstove temperature impacts (China, India, Nigeria, Pakistan, Bangladesh and Nepal), those with the largest temperature impact per carbon emitted (Kazakhstan, Estonia, and Mongolia), and those that would provide the most efficient cooling from a switch to fuel with a lower BC emission factor (Kazakhstan, Estonia, and Latvia). The results presented here thus provide valuable information for climate impact assessments across a wide range of cookstove initiatives.

Wireless Medical Devices for MRI-Guided Interventions

NASA Astrophysics Data System (ADS)

Venkateswaran, Madhav

Wireless techniques can play an important role in next-generation, image-guided surgical techniques with integration strategies being the key. We present our investigations on three wireless applications. First, we validate a position and orientation independent method to noninvasively monitor wireless power delivery using current perturbation measurements of switched load modulation of the RF carrier. This is important for safe and efficient powering without using bulky batteries or invasive cables. Use of MRI transmit RF pulses for simultaneous powering is investigated in the second part. We develop system models for the MRI transmit chain, wireless powering circuits and a typical load. Detailed analysis and validation of nonlinear and cascaded modeling strategies are performed, useful for decoupled optimization of the harvester coil and RF-DC converter. MRI pulse sequences are investigated for suitability for simultaneous powering. Simulations indicate that a 1.8V, 2 mA load can be powered with a 100% duty cycle using a 30° fGRE sequence, despite the RF duty cycle being 44 mW for a 30° flip angle, consistent with model predictions. Investigations on imaging artifacts indicates that distortion is mostly restricted to within the physical span of the harvester coil in the imaging volume, with the homogeneous B1+ transmit field providing positioning flexibility to minimize this for simultaneous powering. The models are potentially valuable in designing wireless powering solutions for implantable devices with simultaneous real-time imaging in MRI-guided surgical suites. Finally in the last section, we model endovascular MRI coil coupling during RF transmit. FEM models for a series-resonant multimode coil and quadrature birdcage coil fields are developed and computationally efficient, circuit and full-wave simulations are used to model inductive coupling. The Bloch Siegert B1 mapping sequence is used for validating at 24, 28 and 34 microT background excitation. Quantitative performance metrics are successfully predicted and the role of simulation in geometric optimization is demonstrated. In a pig study, we demonstrate navigation of a catheter, with tip-tracking and high-resolution intravascular imaging, through the vasculature into the heart, followed by contextual visualization. A potentially significant application is in MRI-guided cardiac ablation procedures.

Paradoxical arthritis occurring during anti-TNF in patients with inflammatory bowel disease: histological and immunological features of a complex synovitis.

PubMed

Alivernini, Stefano; Pugliese, Daniela; Tolusso, Barbara; Bui, Laura; Petricca, Luca; Guidi, Luisa; Mirone, Luisa; Rapaccini, Gian Ludovico; Federico, Francesco; Ferraccioli, Gianfranco; Armuzzi, Alessandro; Gremese, Elisa

2018-01-01

Paradoxical arthritis under tumour necrosis factor inhibitor (TNF-i) for inflammatory bowel disease (IBD) has been described. This study aims to evaluate the histological features of paired synovial tissue (ST) and colonic mucosa (CM) tissue in patients with IBD developing paradoxical arthritis under TNF-i. Patients with IBD without history of coexisting joint involvement who developed arthritis under TNF-i were enrolled. Each patient underwent ST biopsy and ileocolonoscopy with CM biopsies. ST and CM paired samples were stained through immunohistochemistry (IHC) for CD68, CD21, CD20, CD3 and CD117. Clinical and immunological parameters (anticitrullinated peptides antibodies (ACPA)-immunoglobulin (Ig)M/IgA rheumatoid factor (RF)) were collected. Psoriatic arthritis (PsA) and ACPA/IgM-RF/IgA-RF negative rheumatoid arthritis (RA) were enrolled as comparison. 10 patients with IBD (age 46.0±9.7 years, 13.2±9.9 years of disease duration, 2.5±1.6 years of TNF-i exposure, six with Crohn's disease and four with ulcerative colitis, respectively) were studied. At ST level, IHC revealed that patients with IBD with paradoxical arthritis showed more similar histological findings in terms of synovial CD68 + , CD21 + , CD20 + , CD3 + and CD117 + cells compared with PsA than ACPA/IgM-RF/IgA-RF negative RA. Analysing the CM specimens, patients with IBD showed the presence of CD68 + , CD3 + , CD117 + and CD20 + cells in 100%, 70%, 60% and 50% of cases, respectively, despite endoscopic remission. Finally, addition of conventional disease-modifying antirheumatic drugs and switch to ustekinumab were more effective than swapping into different TNF-i in patients with IBD with paradoxical arthritis. Patients with IBD may develop histologically proven synovitis during TNF-i, comparable to PsA. The inhibition of inflammatory pathways alternative to TNF (IL12/1L23) may be an effective therapeutic option for severe paradoxical articular manifestations.

Paradoxical arthritis occurring during anti-TNF in patients with inflammatory bowel disease: histological and immunological features of a complex synovitis

PubMed Central

Alivernini, Stefano; Pugliese, Daniela; Tolusso, Barbara; Bui, Laura; Petricca, Luca; Guidi, Luisa; Mirone, Luisa; Rapaccini, Gian Ludovico; Federico, Francesco; Ferraccioli, Gianfranco; Armuzzi, Alessandro; Gremese, Elisa

2018-01-01

Objective Paradoxical arthritis under tumour necrosis factor inhibitor (TNF-i) for inflammatory bowel disease (IBD) has been described. This study aims to evaluate the histological features of paired synovial tissue (ST) and colonic mucosa (CM) tissue in patients with IBD developing paradoxical arthritis under TNF-i. Methods Patients with IBD without history of coexisting joint involvement who developed arthritis under TNF-i were enrolled. Each patient underwent ST biopsy and ileocolonoscopy with CM biopsies. ST and CM paired samples were stained through immunohistochemistry (IHC) for CD68, CD21, CD20, CD3 and CD117. Clinical and immunological parameters (anticitrullinated peptides antibodies (ACPA)-immunoglobulin (Ig)M/IgA rheumatoid factor (RF)) were collected. Psoriatic arthritis (PsA) and ACPA/IgM-RF/IgA-RF negative rheumatoid arthritis (RA) were enrolled as comparison. Results 10 patients with IBD (age 46.0±9.7 years, 13.2±9.9 years of disease duration, 2.5±1.6 years of TNF-i exposure, six with Crohn’s disease and four with ulcerative colitis, respectively) were studied. At ST level, IHC revealed that patients with IBD with paradoxical arthritis showed more similar histological findings in terms of synovial CD68+, CD21+, CD20+, CD3+ and CD117+ cells compared with PsA than ACPA/IgM-RF/IgA-RF negative RA. Analysing the CM specimens, patients with IBD showed the presence of CD68+, CD3+, CD117+ and CD20+ cells in 100%, 70%, 60% and 50% of cases, respectively, despite endoscopic remission. Finally, addition of conventional disease-modifying antirheumatic drugs and switch to ustekinumab were more effective than swapping into different TNF-i in patients with IBD with paradoxical arthritis. Conclusion Patients with IBD may develop histologically proven synovitis during TNF-i, comparable to PsA. The inhibition of inflammatory pathways alternative to TNF (IL12/1L23) may be an effective therapeutic option for severe paradoxical articular manifestations. PMID:29657833

REACTOR

DOEpatents

Spitzer, L. Jr.

1962-01-01

The system conteraplates ohmically heating a gas to high temperatures such as are useful in thermonuclear reactors of the stellarator class. To this end the gas is ionized and an electric current is applied to the ionized gas ohmically to heat the gas while the ionized gas is confined to a central portion of a reaction chamber. Additionally, means are provided for pumping impurities from the gas and for further heating the gas. (AEC)