Jason P. Jones

Bio: Jason P. Jones is an academic researcher from Georgia Institute of Technology. The author has contributed to research in topics: Stress (mechanics) & Joule heating. The author has an hindex of 3, co-authored 3 publications receiving 42 citations.

Electro-Thermo-Mechanical Transient Modeling of Stress Development in AlGaN/GaN High Electron Mobility Transistors (HEMTs) (Postprint)

Abstract: : In this paper, we present a coupled small-scale electrothermal model for characterizing AlGaN/GaN HEMTs under direct current (DC) and alternating current (AC) power conditions for various duty cycles. The calculated electrostatic potential and internal heat generation data are then used in a large-scale mechanics model to determine the development of stress due to the inverse piezoelectric and thermal expansion effects. The electrical characteristics of the modeled device were compared to experimental measurements for validation as well as existing simulation data from literature. The results show that the operating conditions (bias applied and AC duty cycle) strongly impact the temperature within the device and the stress fluctuations during cyclic pulsing conditions. The peak stress from the inverse piezoelectric effect develops rapidly with applied bias and slowly relaxes as the joule heating increases the device temperature during the on state of the pulse leading to cyclic stresses in operation of AlGaN/GaN HEMTs.

Nanometer-Scale Strain Measurements in AlGaN/GaN High-Electron Mobility Transistors During Pulsed Operation

Abstract: Electric, thermal, and mechanical strain fields drive the degradation of AlGaN/GaN high-electron mobility transistors (HEMTs). The resulting mechanical strains within the devices are particularly important. However, a lack of high-resolution measurements of device deformation has limited progress in understanding the related phenomena. This paper presents the atomic force microscope measurements of thermomechanical deformation of AlGaN/GaN HEMT devices during pulsed operation. We investigate the devices with various operating conditions: drain–source voltage, $V_{\mathrm {\mathrm {DS}}}$ , of 0–50 V; drain–source power of 0–6 W/mm; and operating frequency of 55–400 kHz. As $V_{\mathrm {\mathrm {DS}}}$ increases, thermomechanical deformation decreases, especially in the region above the gate. An electrothermomechanical model closely matches with and helps to explain the measurements. According to the model, the maximum periodic tensile thermal stress, which occurs at the drain-side edge of the gate footprint, is 55% larger for $V_{\mathrm {\mathrm {DS}}} = 10$ V than for $V_{\mathrm {\mathrm {DS}}} = 48$ V for the same device power. The maximum tensile thermal stress in the device depends on the gate temperature and not the maximum device temperature. As $V_{\mathrm {\mathrm {DS}}}$ increases, the hotspot moves away from the gate, leading to lower gate temperature rise and lower tensile thermal stress.

Characterization of AlGaN/GaN HEMTs Using Gate Resistance Thermometry

Abstract: In this paper, gate resistance thermometry (GRT) was used to determine the channel temperature of AlGaN/GaN high electron-mobility transistors. Raman thermometry has been used to verify GRT by comparing the channel temperatures measured by both techniques under various bias conditions. To further validate this technique, a thermal finite-element model has been developed to model the heat dissipation throughout the devices. Comparisons show that the GRT method averages the temperature over the gate width, yielding a slightly lower peak temperature than Raman thermography. Overall, this method provides a fast and simple technique to determine the average temperature under both steady-state and pulsed bias conditions.

Self-Heating and Equivalent Channel Temperature in Short Gate Length GaN HEMTs

Abstract: In this paper, we study the self-heating mechanism and its impact on electrical performance of short gate length GaN high electron mobility transistors (HEMTs) based on electrothermal TCAD simulations. We propose an equivalent channel temperature to quantify the current degradation due to self-heating and also resolve the discrepancies between temperature measurements through electrical methods and thermal methods in the literature. We then explain the equivalent channel temperature’s behavior using the temperature- and field-dependent electron transport theory for short gate length HEMTs. The implications and guidelines to the various aspects of device design are also discussed.

Transient Thermal Characterization of AlGaN/GaN HEMTs Under Pulsed Biasing

Abstract: The development of steady-state thermal characterization techniques for AlGaN/GaN high-electron mobility transistors (HEMTs) has been used to measure the device’s peak temperature under DC conditions. Despite these methods enabling the accurate quantification of the device’s effective thermal resistance and power density dependence, transient thermometry techniques are necessary to understand the nanoscale thermal transport within the active GaN layer where the highly localized joule heating occurs. One technique that has shown the ability to achieve this is transient thermoreflectance imaging (TTI). The accuracy of TTI is based on using the correct thermoreflectance coefficient. In the past, alternative techniques have been used to adjust the thermoreflectance coefficient to match the correct temperature rise in the device. This paper provides a new method to accurately determine the thermoreflectance coefficient of a given surface and is validated via an electrical method: gate resistance thermometry (GRT). Close agreement is shown between the temperature rise of the passivated gate metal measured by TTI and the averaged gate temperature monitored by GRT. Overall, TTI can now be used to thermally map GaN HEMTs under pulsed conditions providing simultaneously a submicrosecond temporal resolution and a submicrometer spatial resolution.