Channel temperature measurement in hermetic packaged GaN HEMTs power switch using fast static and transient thermal methods

A GaN-based power device is a superior component for high-frequency and high-efficiency applications and especially for applications that involve megahertz power conversion. In this work, a fast process of static thermal resistance (R_th) and transient thermal impedance (Z_th) measurements are made and analyzed to determine the thermal characteristics of the channel temperature of a hermetically packaged GaN power device. Five temperature-sensitive parameters (TSPs) are measured at temperatures from 20 to 160 °C. Measurements and statistical analyses included variations with temperature of on-resistance (R_on), saturation drain current (I_Dsat), drain conductance (g_d), threshold voltage (V_th), and knee voltage (V_knee). The statistical analyses revealed the relationships between the heating curve parameter (R_on) and the cooling curve parameters (V_knee, I_Dsat, g_d, and V_th). The average thermal resistance values are extracted as follows: Maximum R_th is 2.99 °C W⁻¹, minimum R_th is 2.92 °C W⁻¹, and the variation among the five TSPs is <3%. Conventional optical-based techniques such as infrared (IR) and micro-Raman thermography are destructive to packaged devices. Therefore, this study developed the two reliable and fast non-destructive methods for estimating channel temperature with the following features: (1) They elucidate static and transient characteristics; (2) they involve heating and cooling; and (3) they evaluate transient thermal impedance (TTI) and safe operating area (SOA). The heating curve method has advantages over cooling curve method in terms of capturing time (40 vs. 400 s, respectively), and a lower power excitation is required to obtain the transient channel temperature response.