Thermal characterization of high voltage GaN-on-Si Schottky Barrier Diodes (SBD) for designing an on-chip thermal shutdown circuit for a power HEMT

Thermal characterization of large multi-finger AlGaN/GaN Schottky Barrier Diodes (SBDs) fabricated on GaN-on-Si high voltage power substrates is reported. An accurate thermal model was developed for the device structure to estimate the device temperature near the 2-DEG in HEMT switches for various power densities. Raman thermography and infrared imaging were used under DC bias conditions for temperature measurement and mapping of heat distribution in the devices. Temperature rise vs. power density, and temperature rise vs. device area are presented. The assumption of uniform temperature distribution throughout the channel holds well for smaller power devices typically used in microwave and RF circuits. However, for the substantially larger high voltage power diodes and HEMTs used in automotive, power conversion and motor drive applications, the temperature distribution is not homogeneous from the center of the die to the outer edge. Detailed knowledge of the temperature distribution across the die is essential for system level thermal management. Thermal simulation, characterization results and the temperature coefficient of the sense SBD are used to design a novel self-protecting thermal shutdown circuit integrated with a discrete 600V power HEMT.