Optimized frequency characteristics of Si/SiGe heterojunction and conventional bipolar transistors

Abstract

The maximum oscillation frequency ( f max) and the unity current gain frequency ( f τ ) were calculated for both Si/Si 1− x Ge x heterojunction and conventional homojunction bipolar transistors. The frequency characteristics at different temperatures were compared by making calculations for 300 and 77 K. The frequency properties of both transistor types improved as the temperature decreased. However, the current gain of the Si/Si 1− x Ge x system increased with falling temperature while the current gain of the conventional transistor was constant. The Si/Si 1− x Ge x device would function at frequencies of up to 350 GHz at 77 K. The f max calculations were made with a model derived for submicrometer heterojunction bipolar transistors.