Analysis of Self-heating of a SiGe HBT Designed for RF Applications According to the Percentage of Germanium

Abstract

The main purpose of this paper is to determine the impact of germanium percentage within the base of a SiGe heterojunction bipolar transistor (HBT) in order to analyze the effect of the device self-heating. We use the COMSOL Multiphysics commercial software. The model links the semiconductor module to the HTS (Heat Transfer in Solids) module. This allows to simulate the temperature distribution across the SiGe HBT device for germanium levels ranging from x  10 %, 20 % to x  30 %. We first determine the static gain () of the SiGe HBT by varying the percentages of germanium. In addition, we analyze the heat distribution on the component surface for the three considered levels of germanium in order to record the maximum temperature Tmax in the device. Indeed, for x  10 %, the maximum temperature is Tmax  377 K and is close to the base-collector junction. When the germanium fraction in the SiGe alloy is increased (x  20 %), the maximum temperature of self-heating decreases (Tmax  366 K), while for x  30 % the temperature of self-heating decreases more (Tmax  354 K) and it spreads over the entire component. This phenomenon degrades seriously the electrical performances of the HBT.