High-frequency surface varactors

Experimental surface varactors constructed from germanium and silicon, with titanium dioxide films as a dielectric, are described. Measurements have been made to determine their behavior at frequencies up to 9 kMc. The capacitance ratio and specific capacitance change are in good agreement with the theory of surface varactors. The feasibility of high-frequency operation of this device is demonstrated on epitaxial-silicon surface varactors with zero-bias cutoff frequencies above 100kMc. From the analysis of the series resistance in practical structures, cutoff frequencies in the Teracycle range appear possible.