High temperature (HT) electronics applica-tions will require the development of a broad range ofdevices made using different materials. Among thesedevices, high-electron mobility transistors (HEMTs) madewith GaN and its alloys are attractive for high-power radiofrequency (RF) applications. In this manuscript, we testedAlGaN/GaN HEMT devices having similar to 140-nm gate length atdifferent temperatures up to 500 degrees C. Devices were fab-ricated using Air Force Research Laboratory's (AFRL's)140-nmT-gate process technology. The performancedegradation measured in different devices was analyzed byconsidering changes in different device parameters and byusing appropriate device physics. Cross-sectional materi-als characterization using scanning transmission electronmicroscopy (STEM) and electron energy loss spectroscopy(EELS) was performed to understand the origin of perfor-mance degradation. This understanding will allow us todesign a sub-mu m GaN-based process technology compat-ible with HT RF applications

High temperature (HT) electronics applications will require the development of a broad range of devices made using different materials. Among these devices, high-electron mobility transistors (HEMTs) made with GaN and its alloys are attractive for high-power radio frequency (RF) applications. In this manuscript, we tested AlGaN/GaN HEMT devices having <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim$</tex-math> </inline-formula> 140-nm gate length at different temperatures up to 500 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\circ}$</tex-math> </inline-formula> C. Devices were fabricated using Air Force Research Laboratory’s (AFRL’s) 140-nm <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</i> -gate process technology. The performance degradation measured in different devices was analyzed by considering changes in different device parameters and by using appropriate device physics. Cross-sectional materials characterization using scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) was performed to understand the origin of performance degradation. This understanding will allow us to design a sub- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu$</tex-math> </inline-formula> m GaN-based process technology compatible with HT RF applications.

Development of high-temperature compatible electronic devices is desired for several applications. Electronic devices made with wide bandgap and ultra-wide bandgap materials are suitable for these high temperature applications. In this article, we presented high temperature device data obtained from p-Ga203 field-effect transistors (FETs) and AIGaN/GaN high-electron mobility transistors (HEMTs) at temperatures up to 500 oC, We discussed device details, systematically analyzed the electrical data by considering insights obtained from materials characterization, and explained the variation in device parameters (such as transconductance, threshold voltage, contact resistance, gate leakage) with temperature and time.

Development of high-temperature compatible electronic devices is desired for several applications. Electronic devices made with wide bandgap and ultra-wide bandgap materials are suitable for these high temperature applications. In this article, we presented high temperature device data obtained from p-Ga203 field-effect transistors (FETs) and AIGaN/GaN high-electron mobility transistors (HEMTs) at temperatures up to 500 oC, We discussed device details, systematically analyzed the electrical data by considering insights obtained from materials characterization, and explained the variation in device parameters (such as transconductance, threshold voltage, contact resistance, gate leakage) with temperature and time.

The purpose of this work was to investigate the validity of Arrhenius accelerated-life testing when applied to gallium nitride (GaN) high electron mobility transistors (HEMT) lifetime assessments, where the standard assumption is that only critical stressor is temperature, which is derived from operating power, device channel-case, thermal resistance, and baseplate temperature. We found that power or temperature alone could not explain difference in observed degradation, and that accelerated life tests employed by industry can benefit by considering the impact of accelerating factors besides temperature. Specifically, we found that the voltage used to reach a desired power dissipation is important, and also that temperature acceleration alone or voltage alone (without much power dissipation) is insufficient to assess lifetime at operating conditions.

The intrinsic properties of gallium nitride (GaN) make it an ideal semiconductor material for microwave/millimeter wave power amplifiers. Numerous groups have demonstrated AlGaN/GaN high electron mobility transistors (HEMTs) with power densities exceeding 40 W/mm [1]. Operation at their maximum potential is impractical due to the lack of a viable cooling solution. The majority of high power GaN RF devices are fabricated on semi-insulating silicon carbide (SiC) substrates. This has been shown to be a viable solution albeit even SiC with its superior thermal conductivity (~350 W/m-°K), cannot overcome the heat loads being generated by the GaN HEMTs. It has become readily apparent as GaN device technology matures that thermal impediments are limiting it from realization of its true capability. One strategy under consideration is to substitute the SiC substrate with a much higher thermal conductivity diamond substrate (~2000 W/m-°K) to enhance localized thermal management. In 2006 AFRL demonstrated the first working AlGaN/GaN HEMT on a GaN/DIA wafer fabricated by Group4 and Emcore [2]. This early technology demonstration provided a pathway for future exploration of producing GaN based devices on polycrystalline CVD diamond substrates. For the past two years, the DARPA Near Junction Thermal Transport (NJTT) Program has explored the development of passive cooling approaches through integration of high thermal conductivity diamond in close proximity to the active transistor junction. In this work, AFRL provides an assessment of the electrical and thermal performance of diamond integrated GaN devices fabricated under the NJTT Program.

We performed an experiment on AlGaN/GaN HEMTs with high voltage and high power as stressors. We found that devices tested under high power generally degraded more than those tested under high voltage. In particular, the high-voltage-tested devices did not degrade significantly as suggested by some papers in the literature. The same papers in the literature also suggest that high voltages cause cracks and pits. However, the high-voltage-tested devices in this study do not exhibit cracks or pits in TEM images, while the high-power-tested devices exhibit pits.

In this paper, we discuss the progress in the application of silicon‐on‐diamond (SOD) and chemically vapour deposited (CVD) diamond wafers as an alternative solution to silicon and silicon carbide (SiC) substrates to enhance heat dissipation away from the active region of AlGaN/GaN high electron mobility transistors (HEMT) while decreasing thermal degradation due to thermal effects. The superior thermal conductivity and insulating properties of polycrystalline diamond (8–15 Wcm/K) free‐standing wafers have demonstrated certain advantages, mostly evident in the device performance and reliability. Two unique diamond growth applications engineered by sp3 Diamond Technologies Inc., and Group4 Labs Inc., are discussed and device performance data is presented from early attempts to our most current device research efforts. As single‐crystalline diamond wafers (∼20 Wcm/K) become more accessible and affordable, it is expected to see significant improvement over the current state of this technology.