The microwave performance of SiGe/Si HBTs and amplifiers

In this paper, we analyze the SiGe/Si HBT´s microwave performance, including the following factors: (1) when the base width reduces to the lower hundreds angstrom, the emitter delay time and the collector delay time became more important factors for the cutoff frequency f_T of SiGe HBTs; (2) the influence of the low doping emitter layer on the emitter delay time; (3) besides the capacitance resulting from the change of the fixed charges in the heterojunction, the free carrier injection in the emitter base space charge region results in additional capacitance for a heterojunction operating at forward bias; (4) hence, we give the equivalent circuits of SiGe HBTs, analyze and optimize the cutoff frequency of SiGe HBTs, and simulate the microwave performance of SiGe HBTs and its amplifier. The novel f_T=10 GHz SiGe HBTs and amplifier have been fabricated, the results of testing are in agreement with those of simulation