Design and performance of C-band transistors

Recent advances in microwave transistor technology have resulted in significant improvements in the high-frequency performance of small-signal npn bipolar transistors. By suitable choice of collector thickness either fTor fmaxmay be optimized: fT= 15 GHz and fmax= 26 GHz have been obtained. Typical devices exhibit a noise figure of 4 dB at 4 GHz. The improved technology comprises: one-micron anti-reflection chromium masks prepared by direct ultraviolet exposure of photoresist in the step-and-repeat camera; arsenic diffused emitters which provide a very steep impurity concentration gradient at the emitter-base junction, do not exhibit the emitter dip effect and result in improved high-frequency performance compared with phosphorus emitter devices (1, 2); and low-resistance aluminum-silicon contacts compatible with shallow emitter-base junctions.