Direct determination of base transit time for heterojunction bipolar transistors without cutoff frequency measurement

An accurate extraction method, based on a simple Z parameter equation at low frequencies, is developed to determine the base transit time of heterojunction bipolar transistors without cutoff frequency measurement that may suffer an inaccuracy. This new technique has much smaller uncertainty than the previous cutoff frequency method, because the determination of collector charging time is not needed to extract the base transit time using this method.