Surface and geometry effects on the large signal base input voltage and input impedance of junction transistors

Experiments were performed to obtain design on information on the large signal base input voltage and input impedance of n-p-n switching transistors and p-n-p power transistors, with emphasis on the effects of surface and transistor geometry. The variation of surface recombination velocity was obtained by baking. The variation of transistor geometry included emitter diameter, base ring diameter, and dice thickness. For these experiments, the base resistivity was also varied. The experimental results are compared with calculation results based on theory, and show that the theory may be used to predict quantitatively the base input voltage and input impedance for a given design. The results, as can be expected, deviate in several interesting respects from what is predicted by the small signal or low-injection level base resistance. For example, the base input voltage and input impedance are not appreciably affected by base resistivity. The surface and geometry effects will be presented and discussed in detail.