A Comparative Analysis of Electrical and Optical Thermometry Techniques for AlGaN/GaN HEMTs

Gallium nitride (GaN)-based radio frequency (RF) power amplifiers are spearheading the deployment of next-generation wireless systems owing to the large power handling capability at high frequencies and high-power-added efficiency. Unfortunately, this high power density operation leads to severe overheating, which reduces its lifetime and efficiency. Thus, correctly characterizing the temperature rise is of crucial importance to properly design GaN devices and cooling solutions. Optical-based thermometry techniques such as Raman thermometry and infrared (IR) thermography are commonly used to estimate the peak temperature rise, but they are limited by optical access, topside metallization, and depth averaging. Gate resistance thermometry (GRT) offers an alternative method to measure the temperature without needing optical access to the channel. Therefore, in this work, Raman thermometry is used in conjunction with GRT and electrothermal modeling to determine the accuracy of each method for a field-plated GaN high electron mobility transistor (HEMT) under various bias conditions. While both Raman thermometry and GRT measured a similar temperature rise under fully open (FO) channel conditions, it was found that GRT was better at estimating the peak temperature under a partially pinched-off (PPO) bias condition due to the source-connected field plate (SCFP) restricting optical access to the drain side of the gate edge.