The Influence of the Collector Design on the fmaxvs. ft Characteristics for Different Types of Si-based RF Bipolar Transistors

In modern RF BJTs and HBTs the collector is usually designed as selectively implanted collector (SIC). Therefore in the present work we investigate the influence of various SIC profiles on f_t and f _max with respect to BV_CEO for four basic types of Si-based bipolar transistors: A SiGe HBT with a graded Ge content in the base, and second SiGe HBT having a much higher Ge content in the entire base, thus allowing a higher dopant concentration in the base than in the emitter. In addition, two conventional NPN BJTs with diffusion respectively drift as the dominant mechanisms for the electron transport through the base were investigated. This has been done by numerial device simulation using the 2-D simulator ATLAS presented in "Device Simulation Software" (2005), applying the hydrodynamic transport model and the Katayama-Toyabe impact ionisation model based in K. Katayama and T. Toyabe (1989). The accuracy of the simulated results has been recently confirmed by comparision with measured data of an experimental SiGe HBT as presented in C. Schippel et al. (2005)