P-N-P-N Transistor Switches

The design, fabrication, and electrical characteristics of silicon p-n-p-n transistors with α>1 for use as switches is discussed. The increase of alpha with injection level can be used to construct two terminal p-n-p-n switches. The high impedance characteristic has an impedance determined chiefly by the capacitance of the junctions. This capacity is of the order of tens of micromicrofarads. The low impedance portion of the switching characteristics has a slope resistance of a few ohms and a total voltage drop of approximately one volt. Methods of fabrication include suitable combinations of solid diffusion and alloying. Possible applications of p-n-p-n switches include function generators, photorelay, and talking path switches.