Impact of the emitter length scaling on electrical characteristics of horizontal current bipolar transistor with single polysilicon region

Emitter length scaling of HCBT with single polysilicon region is investigated by 3D device simulations with the emphasis on the high frequency characteristics. It is shown that collector current and junction capacitances have linear dependence on the emitter length. Collector resistance can be represented by two components which appear in parallel, one that scales proportionally with the emitter length and a constant part which describes lateral portion of the extrinsic transistor. Cut-off frequency is improved for small emitter area devices due to current spreading in the collector region which reduces the current density and causes the base push-out at higher collector currents. The effect cannot be captured by scalable transistor model and separate set of model parameters is needed for transistors with very small emitter size.