Self-aligned, emitter-edge-passivated AlGaAs/GaAs heterojunction bipolar transistors with extrapolated maximum oscillation frequency of 350-GHz

The authors present self-aligned, emitter-edge-passivated AlGaAs/GaAs heterojunction bipolar transistors (HBTs) with extrapolated maximum oscillation frequency of 350 GHz. To the authors' knowledge, this is the highest f/sub max/ ever reported for an HBT. The self-aligned, emitter-edge-passivated dual-liftoff process reported here enhances the device RF performance and DC current gain. The current gain of a typical HBT with 2 emitter fingers each 2 mu m*10 mu m was measured to be more than 20 at current density of 5*10/sup 4/ cm/sup 2/. A record high maximum oscillation frequency of 350 GHz was extrapolated by assuming 6-dB/octave falloff rate from the unilateral gains obtained from the s-parameters measured up to 40 GHz.