Silicon surface alloy transistors for high-frequency switching and chopper-amplifier applications

These pnp silicon transistors are made by an electrochemical process involving optical monitoring of base width and evaporation of aluminium on to controlled areas through a stainless steel mask. Subsequent alloying produces an extremely thin base region which allows the transistor to retain its high-frequency performance down to extremely low operating levels. The combination of low saturation resistance and high turn-on voltage can be used to produce very simple high-speed switching circuits operating over a wide temperature range, and the same characteristics contribute to low drift rates in chopper-amplifier circuits.