Large-signal HBT model with improved collector transit time formulation for GaAs and InP technologies

An analytical large-signal HBT model which accurately accounts for the intricate bias dependence of collector delay in devices fabricated in both GaAs and InP material systems is described. The strongly bias dependent collector delay function accounts for the variation of electron velocity with electric field of the collector, which has consequences for both the electron transit time and capacitance. It is shown that the new formulation significantly improves the prediction of the bias dependence of f/sub t/. As a result, simulations over a very wide range of operating conditions match measured data on a wide variety of devices. Distortion predictions are improved since the derivatives of the bias dependent delay are more accurately modeled. This new model is extracted on medium and high breakdown GaAs HBTs, and also on InP DHBTs. Simulation results are verified with comparisons to S-parameter and large-signal measurements.