The influence of collector designs on f_max versus f_t characteristics for different types of Si-based RF bipolar transistors

The cut-off frequency ft, the maximum frequency of oscillation fmax and the collector–emitter breakdown voltage BVCEO are computed for various types of Si-based bipolar transistors with different selectively implanted collector (SIC) profiles. In particular, the influence of SIC profiles on ft versus BVCEO and fmax versus BVCEO characteristics is investigated. Subsequently, the fmax versus ft behaviour is discussed. It is shown that for slow transistors (BJTs) there is a trade-off between ft and fmax. However, in the case of faster HBTs this trend can be reversed.