Application of polysilicon emitters to high voltage bipolar transistors for realizing high quasi-saturation current limits under forced gain conditions

Using numerical simulation, it is demonstrated that for a given collector-emitter breakdown voltage (BV_ceo), the quasi-saturation current limit of the high voltage transistor under forced gain conditions can be tremendously increased by using a polysilicon emitter in place of the traditional deep diffused emitter. The numerical results are explained using the quasi-saturation analysis of high voltage bipolar transistors. It is further shown that emitter current crowding effects are less significant in polyemitter high voltage transistors compared to metal contacted deep diffused transistors