Semiconductor Surface Varactor

In reccnt years semiconductor p-n junctions have found wide use in parametric amplifiers, harmonic generators, and frequency modulators. These applications result from the fact that the space charge layer capacity of the junction is voltage dependent and thus easily variable. Another semiconductor varactor which in some instances shows a greater dependence of capacity upon voltage has been investigated recently.1'2 Unlike the junction varactor, the modus operandi of this new device is the change of the distribution of charge at a semiconductor surface with an applied normal field. Since the surface in a sense replaces the junction, the device has been termed a "surface varactor." The device has also been termed an "OX varactor" (for oxide-w-silicon) and an "MOS diode" (for metal-silicon oxide-silicon). 803 804 TIIE 13ELL SYSTEM TECHNICAL JOURNAL, MAY 19G2 The structure is shown in Fig. 1. It consists of an insulator (across which the normal field is applied) in intimate contact with a semiconducting material. The silicon-silicon dioxide system was used in all our experiments.