Calculation Of The Collector Signal Delay Time Of Hbts Based On A Piecewise-Linear Velocity Profile

We present a systematic method for calculating the frequency-dependent collector signal delay time tau(CT)\u27 and the cutoff frequency f(T) of the heterojunction bipolar transistor (HBT). The method is developed based on the assumption that f(T) is limited by tau(CT)\u27. Furthermore, a piecewise-liner drift velocity profile is employed to account for velocity overshoot in the base-collector junction. Previous works employing the low-frequency approximation or the step-wise drift velocity profile, which assumes a constant velocity in the overshoot region, are also briefly reviewed and discussed