Switching properties of polysilicon emitter transistor operating in saturation

Saturation behaviour of a polysilicon emitter transistor is studied using the analysis of the most fundamental parameter, the saturation time constant, and correlated with the physical structure. The analysis takes into account the effect of the polysilicon/monosilicon interface in the emitter and n/n+ type transition interface due to buried layer diffusion in the collector. It is shown that the effect of the polysilicon/monosilicon interface is crucial to transistor behaviour which is operating in saturation for shallower emitter junction depths and apart from the charge storage in the collector region bounded by the n/n+ interface.