Gallium Nitride high-electron mobility transistors (HEMT) devices show great promise in their ability to tolerate the high temperature environments of advanced radar systems. This paper examines how GaN HEMT junction temperature determination can vary, owing to factors such as packaging variability, measurement error, and uncertainty in material property data. To demonstrate the impact of these variables, this paper uses practical examples of infrared thermography, micro-Raman thermography, device transient electro-thermal response analysis on GaN HEMT devices, and finite element analysis (FEA). These variations in temperature are combined into a probability model to estimate how life prediction will change as a function of these various factors. Keywords IntroductionAs a nascent technology compared to GaAs, Si, or nonsolid state technology, GaN-on-SiC transistors have not established a history of reliability from which end-users of the technology can establish its long term replacement and refurbishment costs.[1] Nonetheless, GaN provides a number of distinct advantages over older technologies, including improved heat transfer properties, wider bandgap energy, higher operational temperatures, and higher frequency performance. [2] In lieu of historical reliability information, the consumers of this technology must depend on accelerated lifetime testing (ALT) of parts where a predicted operational lifetime, on the order of millions of hours, is extrapolated from faster failures (hundreds of hours) achieved at highly elevated temperatures. The validity of this extrapolation is dependent on three assumptions: 1) that the physics of failure for the GaN device is analogous to previous technologies, allowing for a loglinear extrapolation (the Arrhenius model) through timetemperature space, 2) that the ALT is exciting the same predominant failure as occurs in fielded devices under standard operating conditions, and 3) that the operational temperature of the device is known. [3] This paper focuses on this third assumption, using empirical (micro-Raman thermography, transient thermal testing using the T3ster from Mentor Graphics, and midwave infrared thermography) and finite-difference modeling (ANSYS-Fluent) techniques to assess the measure, spatialuniformity, and statistical variability in temperature measurements on GaN transistor devices.

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In this paper, the authors will discuss the development and implementation of a test stand to assess the impact of temperature on the performance of commercial X-band gallium nitride (GaN) on silicon carbide (SiC) high electron mobility transistors (HEMTs) designed for radio frequency (RF) communications platforms. The devices are tested under a range of operating temperatures and under a range of electrical operating conditions of variable gate and source-drain voltages to assess the impact of temperature on core operational parameters of the device such as channel resistance and transconductance. This test capability includes infrared thermography and transient thermal impedance measurements of the device. In addition to the experimental effort, the initial construction of a finite-volume numerical analysis model of the device will be discussed. The focus of these models will be the accurate assessment of device thermal impedance based on assumed thermal loads and eventually the assessment of accumulated thermal stresses at the material interfaces within the device and package structure.