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The status of and directions for high temperature electronics research and development were evaluated. Major objectives were to (1) identify common user needs; (2) put into perspective the directions for future work; and (3) address the problem of bringing to practical fruition the results of these efforts. More than half of the presentations dealt with materials and devices, rather than circuits and systems. Conference session titles and an example of a paper presented in each session are (1) User requirements: High temperature electronics applications in space explorations; (2) Devices: Passive components for high temperature operation; (3) Circuits and systems: Process characteristics and design methods for a 300 degree QUAD or AMP; and (4) Packaging: Presently available energy supply for high temperature environment.

In recent years, there was a growing need for electronics capable of sustained high-temperature operation for aerospace propulsion system instrumentation, control and condition monitoring, and integrated sensors. The desired operating temperature in some applications exceeds 600 C, which is well beyond the capability of currently available semiconductor devices. Silicon carbide displays a number of properties which make it very attractive as a semiconductor material, one of which is the ability to retain its electronic integrity at temperatures well above 600 C. An IR-100 award was presented to NASA Lewis in 1983 for developing a chemical vapor deposition process to grow single crystals of this material on standard silicon wafers. Silicon carbide devices were demonstrated above 400 C, but much work remains in the areas of crystal growth, characterization, and device fabrication before the full potential of silicon carbide can be realized. The presentation will conclude with current and future high-temperature electronics program plans. Although the development of silicon carbide falls into the category of high-risk research, the future looks promising, and the potential payoffs are tremendous.

The major challenges in making high temperature superconducting (HTSC) electronics viable are predominantly materials problems. Unlike their predecessors the metal oxide-based superconductors are integratable with other advanced technologies such as opto-electronics and micro-electronics. The materials problems to be addressed relate to the epitaxial growth of high quality films, highly oriented films on non-lattice matched substrates, heterostructures with atomically sharp interfaces of junctions and other novel devices, and the processing of these films with negligible deterioration of the superconducting properties. These issues are illustrated with results based on films prepared in-situ by a pulsed laser deposition process. Films with zero-transition temperatures of 90 K and critical current densities of 5 x 10(exp 6) A/sq cm at 77 K have been prepared by this technique. Ultra-thin films, less than 100 A show T(sub c) is greater than 80 K, supporting the idea of two-dimensional transport in these materials. By the use of appropriate buffer layers, films with T(sub c) of 87 K and J(sub c) of 6 x 10(exp 4) A/sq cm were fabricated on silicon substrates. Submicron structures with J(sub c) is greater than 2 x 10(exp 7) at 10 K were fabricated. Results on nonlinear switching elements, IR detectors, and microwave studies will be briefly summarized.

To meet the needs of the aerospace propulsion and space power communities, the high temperature electronics program at the Lewis Research Center is developing silicon carbide (SiC) as a high temperature semiconductor material. This program supports a major element of the Center's mission - to perform basic and developmental research aimed at improving aerospace propulsion systems. Research is focused on developing the crystal growth, characterization, and device fabrication technologies necessary to produce a family of SiC devices.

Work under Task 1 has begun on the evaluation of candidate high temperature transient liquid phase sintering (TLPS) systems as well as candidate high temperature polymer materials. In evaluating candidate metal and alloy systems, binary and available ternary phase diagrams are being reviewed to identify alloy systems that could be used in a high temperature application. The goal is to find a combination of metals and alloys that will go through TLPS at a temperature compatible with the polymer processing and that will form products that will be able to withstand the proposed high operating temperatures. DSC studies of some of these combinations have been done to confirm their potential. Metal powders studied so far include copper and various low melting point metals and alloys to ascertain the products formed by TLPS.

A novel metallization for aluminum nitride substrates to package silicon carbide integrated circuits for use at temperatures of 600 deg C and above was investigated. Chemical equilibrium calculations were used to determine the chemical compatibility of several refractory and transition metal disilicides with AlN and SiC. Tungsten disilicide, niobium disilicide, and titanium disilicide were selected for diffusion couple and thin film deposition studies. AlN-WSi2-SiC, AlN-NbSi2-SiC, and AlN-TiSi2-SiC diffusion couples were formed at 1000 deg C and 1200 deg C. WSi2, NbSi2, and TiSi2 thin films were deposited by RF sputtering on AIN substrates and heat treated at 900 deg C, 1000 deg C, and l200 deg C in an argon atmosphere, while WSi2 thin film was deposited on a single crystal SiC wafer and heat treated at 900 deg C. Sheet resistivities were measured, and interfaces were characterized by scanning and transmission electron microscopy imaging, electron diffraction, and energy dispersive x ray microanalysis spectroscopy. The results show that metal silicides appear to be promising as metallization for aluminum nitride for use at 600 deg C and above.

There is an accelerating need for electronic devices and integrated circuits which operate at extremely high temperatures. Increasingly, electronics are finding applications in measurement and control systems in automotive and jet engine environments, for example, where temperatures can easily exceed 150 C. Wide band gap materials have shown promise for high temperature applications, however, cost and reliability issues presently limit their widespread use. GaAs MESFETs have shown some promise at temperatures as high as 400 C, however, high gate leakage currents and degraded breakdown characteristics lead to poor reliability and large variations in device characteristics. Recently, a greater than tenfold reduction in the threshold voltage temperature coefficient was demonstrated in the heterodimensional MESFET compared with GaAs MESFET. Heterodimensional devices have also demonstrated excellent operation to high breakdown voltage. The goal of this project is to explore the feasibility of developing heterodimensional technology for high power and/or high temperature applications.

The objective of this three-year program was to develop a technology of Josephson tunnel junctions capable of operating at temperatures above 10K. The superconducting electrode materials investigation were V3Si, Nb3Sn and Mo-Re. Tunnel barriers were formed mostly by oxidizing metallic overlayers of Al and Y. Superconductor/barrier interfaces were characterized by surface-analytical techniques. The results of characterization permitted fabricated of junctions with Nb3Sn and Mo-Re base electrodes and Pb, Pb-Bi and Mo-Re counterelectrodes having nearly ideal current-voltage characteristics. These counterelectrodes were deposited at temperatures not exceeding T = 100 C. The Mo-Re counterelectrode formed at low T had a critical temperature, Tc, of only 8K. A high-critical-temperature Nb3Sn counterelectrode requiring high deposition temperatures could not be fabricated successfully. The main cause of this negative result was the nonuniform coverage of the base with overlays which contained thin or defective spots. In contrast to Nb3Sn high-Tc NbN counterelectrodes were successfully fabricated and sumgap voltages exceeding 5 mV were measured at 4.2K. The report contains new information on artificial barriers and on Mo-Re and Nb3Sn superconducting films. (Author)

High-temperature environment operable sensors and electronics are required for long-term exploration of Venus and distributed control of next generation aeronautical engines. Various silicon carbide (SiC) high temperature sensors, actuators, and electronics have been demonstrated at and above 500 C. A compatible packaging system is essential for long-term testing and application of high temperature electronics and sensors in relevant environments. This talk will discuss a ceramic packaging system developed for high temperature electronics, and related testing results of SiC integrated circuits at 500 C facilitated by this high temperature packaging system, including the most recent progress.

A high temperature electronics program at NASA Lewis Research Center focuses on dielectric and insulating materials research, development and testing of high temperature power components, and integration of the developed components and devices into a demonstrable 200 C power system, such as inverter. An overview of the program and a description of the in-house high temperature facilities along with experimental data obtained on high temperature materials are presented.

HIGH TEMPERATURE ELECTRONICS PACKAGING

This article is from Sensors (Basel, Switzerland) , volume 13 . Abstract Pressure measurement under harsh environments, especially at high temperatures, is of great interest to many industries. The applicability of current pressure sensing technologies in extreme environments is limited by the embedded electronics which cannot survive beyond 300 °C ambient temperature as of today. In this paper, a pressure signal processing and wireless transmission module based on the cutting-edge Silicon Carbide (SiC) devices is designed and developed, for a commercial piezoresistive MEMS pressure sensor from Kulite Semiconductor Products, Inc. Equipped with this advanced high-temperature SiC electronics, not only the sensor head, but the entire pressure sensor suite is capable of operating at 450 °C. The addition of wireless functionality also makes the pressure sensor more flexible in harsh environments by eliminating the costly and fragile cable connections. The proposed approach was verified through prototype fabrication and high temperature bench testing from room temperature up to 450 °C. This novel high-temperature pressure sensing technology can be applied in real-time health monitoring of many systems involving harsh environments, such as military and commercial turbine engines.

As part of the AFOSR initiative, the High Temperature Electronics Assessment group has successfully completed the evaluation of high temperature electronics (HTE) technology in Japan. The group consists of Prof. Robert Davis of North Carolina State University, Prof. Hadis Morkoc of the University of Illinois, Mr. Kenichiro Nakano of Wright Laboratory, and Dr. S. Joe Yakura of AQARD. Between 25 May and 2 June 93, the assessment group visited Kyoto University in Kyoto, Nichia Chemical Industries in Tokushima, Sharp in Nara, Fujitsu Limited in Kawasaki, and the National Institute for Research in Inorganic Materials in Tsukuba. A report on the current status of U.S. and Japanese HTE technology is available by contacting Dr. C. Witt of AFOSR/NE.

During this project, GaN has been grown on lithium gallate with much improved structural quality, excellent optical properties and much improved electrical properties superior nitride properties resulted from a detailed investigation and understanding of the surface chemistry of LGO. As a polar material, LGO has a cation terminated (lithium and gallium face and an anion (oxygen) face. It was determined that nitride films grown on the anion face cracked and peeled where as films grown on the cation face are smooth and adherent. Having identified the proper face for growth and determined the upper limit of substrate temperatures, high quality growth of GaN on LGO was then possible.

A high temperature communications circuit includes a power conductor for concurrently conducting electrical energy for powering circuit components and transmitting a modulated data signal, and a demodulator for demodulating the data signal and generating a serial bit stream based on the data signal. The demodulator includes an absolute value amplifier for conditionally inverting or conditionally passing a signal applied to the absolute value amplifier. The absolute value amplifier utilizes no diodes to control the conditional inversion or passing of the signal applied to the absolute value amplifier.

This report presents the results of a series of life tests of silicon Integrated Injection Logic (I2L) microcircuits designed to operate for long periods at temperatures as high as 300 C. The technology needed to design and fabricate these microcircuits was previously developed under Contract N00173-79-C-0010. Two life tests were conducted: an operating-life test at 300 C and a nonoperating-life test at 360 C. Ten chip packages, each containing four identical ring oscillator/counter test circuits, were tested at each temperature. A total of 80 microcircuits were fabricated using two different metallization processes. None of the 300 C test specimens failed; 24 circuits of the 40 completed 3206 hours, and 16 completed 2342 hours.

The objective of the first year's work was to investigate A15 superconductor/barrier oxide interfaces, identify oxide depth profiles, and determine resulting tunneling characteristics using soft tunnel junction counterelectrodes. Bilayers consisting of Nb and vanadium-silicon (A15) base electrodes and thin Y, Al, and Si barriers have been deposited in-situ and oxidized in humid air for up to three days. XPS analysis was used to compare the barrier coverage, uniformity, oxidation, and ability to protect the base electrode from oxidation for three deposition techniques: dc magnetron sputtering, dc diode sputtering, and reactive diode sputtering followed by pyrolysis. Y and Al have been found to be fully oxidized due to long oxidation times. In the above conditions the overlayers did not protect the superconductors from oxidation/hydration, and the surface of oxidized vanadium-silicon was also degraded by atomic segregation. The tunneling I-V characteristics exhibited very high leakage currents also suggestive of incomplete superconductor coverage by the metallic overlayer. Mo-Re was investigated for its potential as a high-critical-temperature counterelectrode. A very low oxidation rate was found indicating potential compatibility with yttrium hydroxide-sealed barriers. Low temperature growth (60 C) of MoRe (86 at. % Mo) with only a 5% decline in critical temperature has been demonstrated. Work will continue in a closed system to eliminate the base superconductor degradation, reduce leakage and study high-critical-temperature counterelectrodes.

There is a growing desire to install electronic power and control systems in high temperature harsh environments to improve the accuracy of critical measurements, reduce the amount of cabling and to eliminate cooling systems. Typical target applications include electronics for energy exploration, power generation and control systems. Technical topics presented in this book include:• High temperature electronics market• High temperature devices, materials and assembly processes• Design, manufacture and testing of multi-sensor data acquisition system for aero-engine control• Future applications for high temperature electronicsHigh Temperature Electronics Design for Aero Engine Controls and Health Monitoring contains details of state of the art design and manufacture of electronics targeted towards a high temperature aero-engine application. High Temperature Electronics Design for Aero Engine Controls and Health Monitoring is ideal for design, manufacturing and test personnel in the aerospace and other harsh environment industries as well as academic staff and master/research students in electronics engineering, materials science and aerospace engineering.

A ceramic- and thick-film-materials-based prototype electronic package designed for silicon carbide (SiC) high-temperature sensors and electronics has been successfully tested at 500 C in an oxygen-containing air environment for 500 hours. This package was designed, fabricated, assembled, and electronically evaluated at the NASA Glenn Research Center at Lewis Field with an in-house-fabricated SiC semiconductor test chip. High-temperature electronics and sensors are necessary for harsh-environment space and aeronautical applications, such as space missions to the inner solar system or the emission control electronics and sensors in aeronautical engines. Single-crystal SiC has such excellent physical and chemical material properties that SiC-based semiconductor electronics can operate at temperatures over 600 C, which is significantly higher than the limit for Si-based semiconductor devices. SiC semiconductor chips were recently demonstrated to be operable at temperatures as high as 600 C, but only in the probe station environment because suitable packaging technology for sensors and electronics at temperatures of 500 C and beyond did not exist. Thus, packaging technology for SiC-based sensors and electronics is immediately needed for both application and commercialization of high-temperature SiC sensors and electronics. In response to this need, researchers at Glenn designed, fabricated, and assembled a prototype electronic package for high-temperature electronics, sensors, and microelectromechanical systems (MEMS) using aluminum nitride (AlN) substrate and gold (Au) thick-film materials. This prototype package successfully survived a soak test at 500 C in air for 500 hours. Packaging components tested included thick-film high-temperature metallization, internal wire bonds, external lead bonds, and a SiC diode chip die-attachment. Each test loop, which was composed of thick-film printed wire, wire bond, and lead bond was subjected to a 50-mA direct current for 250 hours at 500 C.

The development of intelligent instrumentation systems is of high interest in both public and private sectors. In order to obtain this ideal in extreme environments (i.e., high temperature, extreme vibration, harsh chemical media, and high radiation), both sensors and electronics must be developed concurrently in order that the entire system will survive for extended periods of time. The semiconductor silicon carbide (SiC) has been studied for electronic and sensing applications in extreme environment that is beyond the capability of conventional semiconductors such as silicon. The advantages of SiC over conventional materials include its near inert chemistry, superior thermomechanical properties in harsh environments, and electronic properties that include high breakdown voltage and wide bandgap. An overview of SiC sensors and electronics work ongoing at NASA Glenn Research Center (NASA GRC) will be presented. The main focus will be two technologies currently being investigated: 1) harsh environment SiC pressure transducers and 2) high temperature SiC electronics. Work highlighted will include the design, fabrication, and application of SiC sensors and electronics, with recent advancements in state-of-the-art discussed as well. These combined technologies are studied for the goal of developing advanced capabilities for measurement and control of aeropropulsion systems, as well as enhancing tools for exploration systems.

Packaging made primarily of aluminum nitride has been developed to enclose silicon carbide-based integrated circuits (ICs), including circuits containing SiC-based power diodes, that are capable of operation under conditions more severe than can be withstood by silicon-based integrated circuits. A major objective of this development was to enable packaged SiC electronic circuits to operate continuously at temperatures up to 500 C. AlN-packaged SiC electronic circuits have commercial potential for incorporation into high-power electronic equipment and into sensors that must withstand high temperatures and/or high pressures in diverse applications that include exploration in outer space, well logging, and monitoring of nuclear power systems. This packaging embodies concepts drawn from flip-chip packaging of silicon-based integrated circuits. One or more SiC-based circuit chips are mounted on an aluminum nitride package substrate or sandwiched between two such substrates. Intimate electrical connections between metal conductors on the chip(s) and the metal conductors on external circuits are made by direct bonding to interconnections on the package substrate(s) and/or by use of holes through the package substrate(s). This approach eliminates the need for wire bonds, which have been the most vulnerable links in conventional electronic circuitry in hostile environments. Moreover, the elimination of wire bonds makes it possible to pack chips more densely than was previously possible.

HIGH TEMPERATURE ELECTRONICS PACKAGING

The major challenges in making high temperature superconducting (HTSC) electronics viable are predominantly materials problems. Unlike their predecessors, the metal oxide-based superconductors are integratable with other advanced technologies such as opto-electronics and micro-electronics. The materials problems to be addressed relate to the epitaxial growth of high quality films, highly oriented films on non-lattice matched substrates, heterostructures with atomically sharp interfaces of junctions and other novel devices, and the processing of these films with negligible deterioration of the superconducting properties. These issues are illustrated with results based on films prepared in-situ by a pulsed laser deposition process. Films with zero-transition temperatures of 90 K and critical current densities of 5 x 10(exp 6) A/sq cm at 77 K have been prepared by this technique. Ultra-thin films, less than 100 A show T(sub c) is greater than 80 K, supporting the idea of two-dimensional transport in these materials. By the use of appropriate buffer layers, films with T(sub c) of 87 K and J(sub c) of 6 x 10(exp 4) A/sq cm were fabricated on silicon substrates. Submicron structures with J(sub c) is greater than 2 x 10(exp 7) at 10 K were fabricated. Results on nonlinear switching elements, IR detectors, and microwave studies will be briefly summarized.

Includes bibliographical references and index

This report summarizes the barrier metallization developments accomplished in a program intended to develop 300 C electronic controls capability for potential on-engine aircraft engine application. In addition, this report documents preliminary life test results at 300 C and above and discusses improved design practices required for high temperature integrated injection logic semiconductors. Previous Phase I activities focused on determining the viability of operating silicon semiconductor devices over the - 55 C to +300 C temperature range. This feasibility was substantiated but the need for additional design work and process development was indicated. Phase II emphasized the development of a high temperature metallization system as the primary development need for high temperature silicon semiconductor applications.

The performance of high temperature superconductor (HTS) passive microwave circuits up to X-band was encouraging when compared to their metallic counterparts. The extremely low surface resistance of HTS films up to about 10 GHz enables a reduction in loss by as much as 100 times compared to copper when both materials are kept at about 77 K. However, a superconductor's surface resistance varies in proportion to the frequency squared. Consequently, the potential benefit of HTS materials to millimeter-wave communications requires careful analysis. A simple ring resonator was used to evaluate microstrip losses at Ka-band. Additional promising components were investigated such as antennas and phase shifters. Prospects for HTS to favorable impact millimeter-wave communications systems are discussed.

No abstract available

Auger electron spectroscopy was employed to characterize the diffusion barrier properties of molybdenum in the CrSi2/Mo/Au metallization system. The barrier action of Mo was demonstrated to persist even after 2000 hours annealing time at 300 C in a nitrogen ambient. At 340 C annealing temperature, however, rapid interdiffusion was observed to have occurred between the various metal layers after only 261 hours. The presence of controlled amounts of oxygen in the Mo layer is believed to be responsible for suppressing the short circuit interdiffusion between the thin film layers. Above 340 C, its is believed that the increase in the oxygen mobility led to deterioration of its stuffing action, resulting in the rapid interdiffusion of the thin film layers along grain boundaries.

The four tasks of this three-year program address properties fundamental to (1) enhancing the superconducting properties of HTS films, (2) the application of HTS films in passive microwave circuits, (3) the realization of HTS digital electronics, and (4) the development of new superconducting devices. Progress during the first year included significant enhancements in the properties of superconducting YBCO films. One of these, the elimination of surface roughness due to Cu. particles, was essential for the subsequent growth of high quality multilayer structures. For the first time, uniform large-area YBCO films were sputtered on both sides of a substrate with properties equal or superior to those of single-sided smaller-area films. Two new device configurations were developed: the integration of a ferroelectric film on a YBCO electrode compatible with ferroelectric memory cells and a step-edge S-N-S josephson junction using in-situ deposited gold as the normal metal. SQUIDs fabricated with such junctions had the highest yield of any HTS junction configuration. Epitaxial superconducting Ba-K-Bi-O films were deposited and the gap energy was measured as a function of temperature in low-leakage S-I-N tunnel junctions. Epitaxial YBCO/insulator/YBCO trilayers using Sr-Ti-O and La-Al.

The development of electronic devices for use in high temperature environments is addressed. The instrumentational needs of planetary exploration, fossil and nuclear power reactors, turbine engine monitoring, and well logging are defined. Emphasis is place on the fabrication and performance of materials and semiconductor devices, circuits and systems and packaging.

We use numerical simulation to investigate the high-temperature (up to 500K) operation of SOI MOSFETs with Aluminum-Nitride (AIN) buried insulators, rather than the conventional silicon-dioxide (SiO2). Because the thermal conductivity of AIN is about 100 times that of SiO2, AIN SOI should greatly reduce the often severe self-heating problem of conventional SOI, making SOI potentially suitable for high-temperature applications. A detailed electrothermal transport model is used in the simulations, and solved with a PDE solver called PROPHET In this work, we compare the performance of AIN-based SOI with that of SiO2-based SOI and conventional MOSFETs. We find that AIN SOI does indeed remove the self-heating penalty of SOL However, several device design trade-offs remain, which our simulations highlight.

We use numerical simulation to investigate the high-temperature (up to 500K) operation of SOI MOSFETs with Aluminum-Nitride (AIN) buried insulators, rather than the conventional silicon-dioxide (SiO2). Because the thermal conductivity of AIN is about 100 times that of SiO2, AIN SOI should greatly reduce the often severe self-heating problem of conventional SOI, making SOI potentially suitable for high-temperature applications. A detailed electrothermal transport model is used in the simulations, and solved with a PDE solver called PROPHET In this work, we compare the performance of AIN-based SOI with that of SiO2-based SOI and conventional MOSFETs. We find that AIN SOI does indeed remove the self-heating penalty of SOL However, several device design trade-offs remain, which our simulations highlight.

This paper reviews ceramic substrates and thick-film metallization based packaging technologies in development for 500degC silicon carbide (SiC) electronics and sensors. Prototype high temperature ceramic chip-level packages and printed circuit boards (PCBs) based on ceramic substrates of aluminum oxide (Al2O3) and aluminum nitride (AlN) have been designed and fabricated. These ceramic substrate-based chiplevel packages with gold (Au) thick-film metallization have been electrically characterized at temperatures up to 550degC. A 96% alumina based edge connector for a PCB level subsystem interconnection has also been demonstrated recently. The 96% alumina packaging system composed of chip-level packages and PCBs has been tested with high temperature SiC devices at 500degC for over 10,000 hours. In addition to tests in a laboratory environment, a SiC JFET with a packaging system composed of a 96% alumina chip-level package and an alumina printed circuit board mounted on a data acquisition circuit board was launched as a part of the MISSE-7 suite to the International Space Station via a Shuttle mission. This packaged SiC transistor was successfully tested in orbit for eighteen months. A spark-plug type sensor package designed for high temperature SiC capacitive pressure sensors was developed. This sensor package combines the high temperature interconnection system with a commercial high temperature high pressure stainless steel seal gland (electrical feed-through). Test results of a packaged high temperature capacitive pressure sensor at 500degC are also discussed. In addition to the pressure sensor package, efforts for packaging high temperature SiC diode-based gas chemical sensors are in process.

A new metal demonstrated to form ideal rectifying Schottky diode junctions to n-type SiC, and further, not to limit the thermal and power density capability of SiC devices and circuits in any way The following properties were demonstrated between kT and 1050 C: (1) metal does not spall, peel or scratch, (2) metal/n-SiC junction remains abrupt, (3) I-V unchanged by thermal exposure, (4) barrier height = 1.78 +/- 0.1 eV.

A novel metallization for aluminum nitride substrates and related interconnection materials were investigated for packaging silicon carbide devices for use at temperatures up to 600 deg C. Aluminum nitride substrates were metallized with refractory metals using both thin and thick film metallization techniques. Excellent metallization adhesions (>- 10 ksi) were achieved at low sheet resistivities for both films. Phase diagrams were used to select potential bond pad, die attach and wire bond materials. Diffusion couples were constructed to screen the selected candidates. Gold and platinum were found to be stable bond pad materials on the refractory metallizations at 700 deg C. Gold-gold and platinum-platinum pad-wire combinations were suitable for use at temperatures of 600 deg C and beyond. Platinum-gold, copper-gold, and nickel-gold pad-wire combinations could be used with refractory metallized aluminum nitride substrate up to 400 deg C.

The overall objective of this program was to develop a materials and fundamental device base for high-transition-temperature superconducting (HTS) electronics capable of operating at 50K. Progress is reported on four tasks which address problems fundamental to the understanding of the superconducting state in HTS films, the application of HTS films in passive microwave circuits, the realization of HTS digital electronics, and the development of new superconducting devices. Large-area epitaxial YBCO films with low rf losses developed under this program and techniques for depositing them on both sides of single-crystal substrates were used in other Westinghouse and government-funded programs to develop HTS channelized filterbanks, delay lines, UHF antenna matching networks, and low-phase-noise resonators. An understanding was achieved of the role of oxygenation during film growth and the effect of film microstructure on rf losses. For HTS digital circuit fabrication, both active devices step-edge and edge-type YBCO Josephson junctions and trilayer BKBO junctions and passive structures were developed, such as crossovers,

This final report of ITRI's panel of experts consists of an executive summary, an introductory chapter, and six chapters by panelists on various aspects of wide bandgap electronics. The report also contains site reports for the various companies, labs, universities, and government offices that the panel visited in Europe. Comparisons are made between developments in Europe and the United States.

During the second year of performance under this program, the atomic segregation on A15 surfaces was evaluated and resulted in Nb3Sn replacing V3Si as the tunnel junction high-Tc base electrode. A process of all-refractory test junction patterning by wet and/or reactive ion etching was implemented. Epitaxial, textured tunnel barrier structures of the form Al/Al2O3, Y/Y2O3, and Al/Al2O3/Al, have been fabricated. Tunnel junctions with Nbm Nb3Sn, and Mo-Re base and Pb-Bi counterelectrodes have been formed with the barrier structures and had excellent I-V characteristics. Junctions with Nb counterelectrodes exhibited high subgap leakage currents. The Mo(65)Re(35) alloy was found to be an ideal material for counterelectrodes having Tc=12K. Originator-supplied keywords include: superconductors, films, Josephson, junctions, niobium, molybdenum, A15, and XPS. (Author).

In order for future aerospace propulsion systems to meet the increasing requirements for decreased maintenance, improved capability, and increased safety, the inclusion of intelligence into the propulsion system design and operation becomes necessary. These propulsion systems will have to incorporate technology that will monitor propulsion component conditions, analyze the incoming data, and modify operating parameters to optimize propulsion system operations. This implies the development of sensors, actuators, and electronics, with associated packaging, that will be able to operate under the harsh environments present in an engine. However, given the harsh environments inherent in propulsion systems, the development of engine-compatible electronics and sensors is not straightforward. The ability of a sensor system to operate in a given environment often depends as much on the technologies supporting the sensor element as the element itself. If the supporting technology cannot handle the application, then no matter how good the sensor is itself, the sensor system will fail. An example is high temperature environments where supporting technologies are often not capable of operation in engine conditions. Further, for every sensor going into an engine environment, i.e., for every new piece of hardware that improves the in-situ intelligence of the components, communication wires almost always must follow. The communication wires may be within or between parts, or from the engine to the controller. As more hardware is added, more wires, weight, complexity, and potential for unreliability is also introduced. Thus, wireless communication combined with in-situ processing of data would significantly improve the ability to include sensors into high temperature systems and thus lead toward more intelligent engine systems. NASA Glenn Research Center (GRC) is presently leading the development of electronics, communication systems, and sensors capable of prolonged stable operation in harsh 500C environments. This has included world record operation of SiC-based transistor technology (including packaging) that has demonstrated continuous electrical operation at 500C for over 2000 hours. Based on SiC electronics, development of high temperature wireless communication has been on-going. This work has concentrated on maturing the SiC electronic devices for communication purposes as well as the passive components such as resistors and capacitors needed to enable a high temperature wireless system. The objective is to eliminate wires associated with high temperature sensors which add weight to a vehicle and can be a cause of sensor unreliability. This paper discusses the development of SiC based electronics and wireless communications technology for harsh environment applications such as propulsion health management systems and in Venus missions. A brief overview of the future directions in sensor technology is given including maturing of near-room temperature "Lick and Stick" leak sensor technology for possible implementation in the Crew Launch Vehicle program. Then an overview of high temperature electronics and the development of high temperature communication systems is presented. The maturity of related technologies such as sensor and packaging will also be discussed. It is concluded that a significant component of efforts to improve the intelligence of harsh environment operating systems is the development and implementation of high temperature wireless technology

Progress is reported on four tasks which address problems fundamental to the understanding of the superconducting state in HTS films, the application of HTS films in passive microwave circuits, the realization of HTS digital electronics, and the development of new superconducting devices. An anti- correlation between critical temperature an normal state resistivity was observed at certain compositions in the YBCO, LSCO, and BKBO systems. The criticality of optimizing both oxidation steps involved in YBCO growth to obtain low rf surface resistances was demonstrated. A new insulating material, Sr-Al- Ta-0 (SAT), was developed as an epitaxial insulator in multilayer YBCO circuits to replace Sr-Ti-O. The dc resistivity and surface morphology were as good as those of Sr-Ti-O while the real and imaginary parts of the dielectric constant were greatly superior. Systematic studies were made of the processing parameters for step-edge S-N-S YBCO Josephson junctions. The critical parameters for junction reproducibility were found to be a step angle of approximately 15 deg and a high-conductivity normal-metal barrier. All-BKBO tunnel junctions were demonstrated with Sr-Ti-O tunnel barriers which exhibited a superconducting gap structure to within 2K of the transition temperature of the BKBO electrodes. Epitaxial Sr-Ti-O films were also used as buffer layers to permit single- orientation BKBO films to be grown on practical La-Al-0 or Nd-Ga-0 substrates. Superconductors, Yttrium, Barium, Cooper, Oxides, High, Critical, Temperature, Thin films, Tunneling, Barriers, Sputtering.

Air Force currently has a strong need for the development of compact capacitors which are mechanically robust and thermally stable for operation in a variety of aerospace power conditioning applications. These applications demand better reliability and flexibility in the power system design as well as decreased thermal load for electronic system cooling. While power conditioning capacitors typically use polycarbonate (PC) dielectric films in wound capacitors for operation from -55 deg C to 125 deg C, future power electronic systems would require the use of polymer dielectrics that can reliably operate at elevated temperatures up to or even exceeding 350 deg C. The focus of this research is the generation and dielectric evaluation, up to 350 deg C, of metallized free-standing thin films derived from high temperature polymer systems such as fluorinated polybenzoxazoles (6F-PBO) and fluorenyl polyesters incorporating diamond-like hydrocarbon units (FDAPE). The discussion will be centered mainly on variable temperature dielectric measurements of film capacitance, dissipation factor and insulation resistance, and the effects of thermal cycling on film dielectric performance. Initial studies clearly point to the dielectric stability of these films for high temperature power conditioning applications, as indicated by relatively minor variations ( 2 %) in measured film capacitance over the entire range of temperatures studied. Comparison will also be made with the reported variable temperature dielectric properties of the state-of-the-art high temperature FPE films.

This paper reviews ceramic substrates and thick-film metallization based packaging technologies in development for 500 C silicon carbide (SiC) electronics and sensors. Prototype high temperature ceramic chip-level packages and printed circuit boards (PCBs) based on ceramic substrates of aluminum oxide (Al2O3) and aluminum nitride (AlN) have been designed and fabricated. These ceramic substrate-based chip-level packages with gold (Au) thick-film metallization have been electrically characterized at temperatures up to 550 C. A 96% alumina based edge connector for a PCB level subsystem interconnection has also been demonstrated recently. The 96% alumina packaging system composed of chip-level packages and PCBs has been tested with high temperature SiC devices at 500 C for over 10,000 hours. In addition to tests in a laboratory environment, a SiC JFET with a packaging system composed of a 96% alumina chip-level package and an alumina printed circuit board mounted on a data acquisition circuit board was launched as a part of the MISSE-7 suite to the International Space Station via a Shuttle mission. This packaged SiC transistor was successfully tested in orbit for eighteen months. A spark-plug type sensor package designed for high temperature SiC capacitive pressure sensors was developed. This sensor package combines the high temperature interconnection system with a commercial high temperature high pressure stainless steel seal gland (electrical feed-through). Test results of a packaged high temperature capacitive pressure sensor at 500 C are also discussed. In addition to the pressure sensor package, efforts for packaging high temperature SiC diode-based gas chemical sensors are in process.

The NASA aerospace program, in particular, requires breakthrough instrumentation inside the combustion chambers of engines for the purpose of, among other things, improving computational fluid dynamics code validation and active engine behavioral control (combustion, flow, stall, and noise). This environment can be as high as 600 degrees Celsius, which is beyond the capability of silicon and gallium arsenide devices. Silicon-carbide- (SiC-) based devices appear to be the most technologically mature among wide-bandgap semiconductors with the proven capability to function at temperatures above 500 degrees Celsius. However, the contact metalization of SiC degrades severely beyond this temperature because of factors such as the interdiffusion between layers, oxidation of the contact, and compositional and microstructural changes at the metal/semiconductor interface. These mechanisms have been proven to be device killers. Very costly and weight-adding packaging schemes that include vacuum sealing are sometimes adopted as a solution.

The extension of the range of operating temperatures of electronic components and systems for planetary exploration is examined. In particular, missions which utilize balloon-borne instruments to study the Venusian and Jovian atmospheres are discussed. Semiconductor development and devices including power sources, ultrastable oscillators, transmitters, antennas, electromechanical devices, and deployment systems are addressed.

We use numerical simulation to investigate the high-temperature (up to 500K) operation of SOI MOSFETs with Aluminum-Nitride (AIN) buried insulators, rather than the conventional silicon-dioxide (SiO2). Because the thermal conductivity of AIN is about 100 times that of SiO2, AIN SOI should greatly reduce the often severe self-heating problem of conventional SOI, making SOI potentially suitable for high-temperature applications. A detailed electrothermal transport model is used in the simulations, and solved with a PDE solver called PROPHET In this work, we compare the performance of AIN-based SOI with that of SiO2-based SOI and conventional MOSFETs. We find that AIN SOI does indeed remove the self-heating penalty of SOL However, several device design trade-offs remain, which our simulations highlight.

This report summarizes the progress made on the BN-Al(x)Ga(1-x)N based Heterostructure Field Effect Transistor (HFET) development program under contract number F49620-93-C-0059. The goal of this program is to develop high temperature heterostructure insulating gate (HIG) FET devices for integrated circuits operating in harsh environments. In particular, the insulator materials proposed for the device structure included CVD BN/AIN. While the HIGFET processed with the MIS structures employing BN/AIN and Si3N4 as the insulators yielded low transconductances, tremendous progresses have been made on the optimization of AlGaN/GaN based FET structure growth and the following device processing. These are highlighted by the operation of AlGaN/GaN based heterostructure FETs (HFETs) at 300 deg C. The same device also exhibited a cutoff frequency(f sub T) and maximum frequency of oscillation (fmax) of 22 GHz and 70 GHz at room temperature with a reasonable DC transconductance (23 mS/mm). jg p5