High-frequency characterization of heterojunction bipolar transistors using numerical simulation

Abstract

The high-frequency performance of semiconductor devices is estimated using a small-signal numerical calculation based on drift-diffusion equations. In particular, unity current gain frequency in the common-emitter configuration (f/sub T/) and maximum frequency of oscillation (f/sub max/) are calculated for a heterojunction bipolar transistor. f/sub max/ is calculated from numerically obtained y parameters using formulas for maximum available gain, Mason's invariant (U), and a passivity criterion. They all give the same value for f/sub max/. The influence of extrinsic and intrinsic base resistance on f/sub max/ is investigated for one device design. It is also found that a frequency used approximation formula for f/sub max/ is inaccurate, especially at higher current levels.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>