Limitations of current compact transit-time models for III¿V-based HBTs

This paper investigates the accuracy limitations of common compact bipolar transistor models towards higher frequencies. The device under test is a InGaP/GaAs HBT, simulated by the FBH HBT model. The results, however, analogously hold for similar bipolar devices and models. The investigation is based on an analytical approach that explains how the model approximations impact simulation accuracy. A model extension is proposed that improves the model at higher frequencies. Measurements are compared with large-signal model simulations that prove the analytical reasoning and highlight the relevance of the effect under realistic operation conditions.