Optimization of base-to-emitter spacer thickness to maximize the frequency response of bipolar transistors

The impacts of base-to-emitter spacer thickness on the unity gain frequency (fT), base resistance (rB), base collector capacitance (CBC) and maximum oscillation frequency (fmax) of a bipolar junction transistor (BJT) are studied. Using the extracted Y-parameters from a simulated device with structural parameters calibrated to an actual process, the resulting fT and fmax with different spacer thickness is reported. A tradeoff between peak fT and fmax is observed and the process window to obtain high fT and fmax is proposed.