Theory of Thermal Time Constants in GaN High-Electron-Mobility Transistors

TLDR: In this article, the authors present a fundamental study of the transient thermal behavior of GaN HEMTs to aid in understanding the complex contributions of multidimensional thermal spreading, multiple epitaxial layers, multiple gate fingers, and thermal boundary resistance to the temperature rise.

Abstract: Due to the high dissipated power densities present in GaN high-electron-mobility transistors (HEMTs) in high-power radio frequency applications, thermal analysis and thermal management of these devices are important in achieving their full potential. In this paper, we present a fundamental study of the transient thermal behavior of GaN HEMTs to aid in understanding the complex contributions of multidimensional thermal spreading, multiple epitaxial layers, multiple gate fingers, and thermal boundary resistance to the temperature rise. This complex behavior cannot be accurately described by one or two thermal time constants. Rather, a broad spectrum of time constants from ~1 ns up to several milliseconds are present in the device due to aggressive multidimensional thermal spreading from the narrow region of power dissipation next to each HEMT gate through the substrate, die attach, and package. In order to accurately model the temperature response, at least one time constant per decade over the timescale of interest is required. These findings are crucial in developing an intuitive understanding of the transient thermal behavior of GaN HEMTs and properly accounting for transient temperature rise in electrothermal modeling of high-power GaN-based amplifiers.