Simplified computer-aided analysis of double-diffused transistors including two-dimensional high-level effects

An approximate two-dimensional numerical analysis has been developed for studying double- (or triple-) diffused transistors. The program supplies dc and hf terminal characteristics (e.g., hfe, rbb, fT, IB, VBE) over a wide range of operating collector currents and voltages for a given set of physical device parameters (mask dimensions, impurity profile, etc.). The approach is based on obtaining a set of differential equations describing current flow in the longitudinal (emitter-collector) direction and a separate differential equation describing current flow in the lateral direction. The assumption is made of space-charge or space-charge-neutral regions with current- and voltage-dependent boundaries. The equations are valid for arbitrary injection levels and automatically include such high-level effects as conductivity modulation, base widening, and emitter current crowding. Both theoretical and experimental results are given for transistors with fTvalues between 100 MHz and 3 GHz. The validity of the approach is confirmed and some areas requiring further study are outlined. The technique described is felt to be particularly attractive for the design and optimization of high-power microwave devices, due to the small computer execution time and memory requirements.