Ultra-high speed AlGaAs/GaAs heterojunction bipolar transistors

The characteristic device performance of AlGaAs/GaAs ballistic collection transistors (BCTs) and applications of this device to integrated circuits are considered. The BCT structure reduces the collector transit times, which leads to an increase in cutoff frequency. Although near-ballistic collection only occurs in a relatively narrow collector voltage range, the cutoff frequency can be maximized at a desired collector voltage. This feature is useful when applying BCTs to logic gates. A propagation delay time of 1.9 ps/gate has been obtained in an ECL (emitter coupled logic) ring oscillator configured of BCTs. The maximum toggle frequency of a one-by-two frequency divider consisting of eight NOR-gates is as high as 20.2 GHz. These results demonstrate the high-speed potential of BCTs.<>