High Speed and Uniform Self-Aligned InGaAs/InP HBTs for 40 Gb/s Fiber Optic Communications Applications

Abstract

We have developed the InGaAs/InP heterojunction bipolar transistor (HBT) fabrication process technology, which is capable of producing multiplexer/demultiplexer-level ICs in high yield. A simple self-aligned process utilizing an overhung profile of an InGaAs emitter contact mesa enables narrow separation between the emitter contact mesa and base electrodes. With this fabrication process, we have obtained very high uniformity of HBT characteristics. The uniformity was evaluated by measuring HBT arrays consisting of two-dimensionally arranged 26×57 (1,482) HBTs. The average DC current gain at a collector current density of 1.0×105 A/cm2 is 37.8 and the standard deviation is only 4.7%. A current gain cut-off frequency, fT, of 190 GHz and a maximum oscillation frequency, fmax, of 280 GHz at a collector current, Ic, of 17 mA were achieved with a 0.8×5.8 µm2 emitter HBT. The uniformity of RF properties was also excellent. The average fT and fmax of the HBTs with a 0.8×5.8 µm2 emitter contact mesa at Ic of 15 mA were 190 GHz and 256 GHz, and the standard deviations were 1.6% and 2.3%, respectively.