Optimisation of extrinsic base doping of a SiGe heterojunction bipolar transistor integrated in a BiCMOS 55 nm technology for high frequency performances

This work presents an optimisation of the frequency performance of a new technology of a SiGe heterojunction bipolar transistor (HBT), realised in an industrial BiCMOS55 process technology with a double poly-silicon, self-aligned, selective epitaxial growth (DPSA-SEG) architecture, produced by ST microelectronics. This technology features high attractive performances (f(T)/f(max) = 320/370 GHz). The simulation results are produced by using 2D COMSOL Multiphysics software, based on the drift diffusion model (DDM) and interface semiconductor. Our findings concentrated on the optimisation of the intrinsic and extrinsic base doping on the dynamic properties of HBT. The doping of the extrinsic base significantly affects the frequencies fT and f(max) of the HBT compared to the doping of the intrinsic base. The maximum oscillation frequency reached was f(max) = 630 GHz for a doping of 2.10(19) cm(-3 )of the poly silicon base (extrinsic base) whereas the transition frequency climbed to fT = 351. 6 GHz for the same extrinsic base doping.