Microwave power HBT design optimization

A key issue in the design of power microwave HBTs for high efficiency is the gain roll-off as device size is increased. Careful design is required to maintain adequate gain in order that the high power-added efficiency potential of these devices may be realized. This paper reviews the options for finger combination and the mechanisms controlling the gain scaling are quantified by modelling. This insight is then used to optimize the device layout of an improved common-emitter power device structure. Experimental devices have been fabricated and measured. Excellent gain scaling is demonstrated which verifies the design approach.