TRANSISTORS, TRIODE, SILICON, PNP SWITCHING

The design of the PNP silicon switching transistor is discussed in detail. Assuming the desired switching times of 10 and 15 nano seconds for turn-on and turn-off respectively, the switching time constants are determined and shown to be obtainable by present techniques. Junction capacitances will be met by shallow diffusions and small unit geometry. Collectorbase junction areas of 12 sq mils and 2 sq mils are discussed. The collector-base breakdown voltage of 50 volts is based upon the resistivity and thickness of the epitaxial layer 1.4 ohm-cm and 0.12 mils respectively. For an emmiter-base breakdown voltage greater than 6 volts, a base surface concentration of 10 to the 18th power atoms/cc is needed. The diffusion techniques for obtaining a base depth of 0.035 mils are presented with special attention given to the N+ base contact region. Because of the low base surface concentration, contact to the base region necessitates specific diffusion in the contact area to reduce the contact resistance. Breakdown voltage data are presented in conjunction with diffusion procedures. Use of bi-metallic contacts resulted in low contact resistance. (Author)