A Base-Emitter Self-Aligned Multi-Finger Si_1-xGe_x/Si Power Heterojunction Bipolar Transistor

With a crystal orientation dependent on the etch rate of Si in KOH-based solution, a base-emitter self-aligned large-area multi-finger configuration power SiGe heterojunction bipolar transistor (HBT) device (with an emitter area of about 880μm²) is fabricated with 2μm double-mesa technology. The maximum dc current gain is 226.1. The collector--emitter junction breakdown voltage BV_CEO is 10V and the collector-base junction breakdown voltage BV_CBO is 16V with collector doping concentration of 1×10¹⁷cm^-3
and thickness of 400nm. The device exhibited a maximum oscillation frequency f_max of 35.5 GHz and a cut-off frequency f_T of 24.9GHz at a dc bias point of I_C=70mA and the voltage between collector and emitter is V_CE=3 V. Load
pull measurements in class-A operation of the SiGe HBT are performed at
1.9GHz with input power ranging from 0dBm to 21dBm. A maximum output
power of 29.9dBm (about 977mW) is obtained at an input power of 18.5dBm
with a gain of 11.47dB. Compared to a non-self-aligned SiGe HBT with the same heterostructure and process, f_max and f_T are improved by about 83.9% and 38.3%, respectively.