EMITTER AND BASE TRANSIT-TIME OF POLYSCRYSTALLINE SILICON EMITTER CONTACT BIPOLAR-TRANSISTORS

We have formulated transit time in the neutral emitter region, tau-E, and in the neutral base region, tau-B, of polycrystalline silicon (polysilicon) emitter contact bipolar transistors. We studied the dependence of tau-E and tau-B on device parameters, and found that bandgap narrowing increases tau-E, but tau-B is insensitive to it. Tau-E is proportional to base width W(B) and tau-B to W(B)2. Then, tau-E is not negligible compared to tau-B when W(B) is less than 100 nm. Reducing emitter junction depth and polysilicon thickness are indispensible to developing shallow base bipolar transistors.