“…Improvements in dcvicc f,,,,, performance due to base-undercut techniques have also rcccntly been reported for AIGaAs/GaAs HBTs [9]. The direct impact on device maximum available gain performance can be observed from the simple equation for f,,, given below: 3 illustratcs the fT and f,,,, performance improvement of a 1x4 pm HBT with base-undercut compared to a non-undercut device. A peak fT and f,,,, (from MAG) of 55 GHz and 100 GHz is achieved with the base undercut dcviccs and occurs at an lCc 2 3.5 mA, corresponding to a current density of J,= SS kA/cni'.…”