Improvement Technology of SOI-based Lateral SiGe HBT for High-frequency and High-power Performance

To improve the current gain β and breakdown voltages V_CBO and V_CEO under high frequency, as well as enhance the high-frequency and high power performance effectively, a model of npn silicon-on-insulator (SOI)-based lateral SiGe heterojunction bipolar transistor (HBT) was established by SILVACO TCAD. The research shows that an electron acceleration field is introduced in the trapezoidal profile design of Ge mole fraction in base and decreases the effective width of the base region, which shortens the base transit time and hence increases the cutoff frequency f_T. At the same time, it is also conducive to decreasing the electrons recombination in the base region, which increases the transport cofficient of the base and β. However, for a given amount of substance of Ge in base, the Ge mole fraction at the collector-base edge is increased as the kink point of the trapezoidal profile of Ge mole fraction shifts from emitter-base junction to collector-base juntion. The collector current handling capability of the device was degraded. Therefore, the value of Ge mole fraction needs to be optimized. Meanwhile, a positive substrate bias design forms an electron accumulation layer above the buried oxygen layer, which modulates the effective doping concentration and improves the injection efficiency of the emitter junction. As a result, the β is increased. However, the breakdown characteristics is degraded. Furthermore, a novel SOI-based lateral SiGe HBT with a composite substrate-voltage structure and a trapezoidal Ge profile in base was proposed. Compared with the conventional device, the peak of the current gain β_m of the novel device was increased 84.8, the breakdown voltages including V_CBO and V_CEO of the device were improved by 41.3% and 21.2%, respectively, with a peak of the cutoff frequency f_Tm of 306.88 GHz, which effectively expand the high-frequency and high power performance of SOI-based lateral bipolar transistor.