Optimization of submicron microwave transistors by lateral scaling

Interdigitated microwave bipolar transistors with submicron dimensions have been manufactured to study the effects that occur when the emitter width is reduced to values well below one micron. The DC current gain normalized to the total emitter area shows an optimum as a function of emitter width for 0.5 μm wide emitters. The sidewalk of the emitters contribute significantly to the measured reverse biased emitter-base depletion layer capacitances. The maximum value of the transit-frequency f_T at a given value of V_CE does not significantly depend on the emitter width. The device with the smallest emitters had the lowest measured base resistance and, consequently, the highest maximum frequency of oscillation, f_max.