Abstract of the Disclosure

A varactor diode (voltage dependent capacitance) is made utilizing a MOS (Metal-Oxide-Semiconductor) structure. In order to obtain a very high dC/dV characteristic, a self-registered, opposite-conductivity source region is surface-diffused into the base region of the MOS structure surrounding the metal capacitor plate. This region is electrically connected to the base. In operation, the application of a sufficient voltage across the capacitor causes charge carriers of conductivity-type opposite to that of the base region to be drawn from the opposite-conductivity diffused source region into the base region beneath the metallic film, increasing the charge thereat at a rapid rate. The region becomes conductivity-inverted, and dC/dV in the inversion region of the C-V curve is high. Operation of the capacitance in this region permits high sensitivity and high frequency operation.

• Figure 1 is a vertical cross-sectional schematic view of a MOS varactor diode constructed in accord with one embodiment of the present invention.
• Figure 2 is a plan view, in schematic, of an alternative embodiment of the device of Figure 1.
• Figure 3 is a vertical cross-sectional view of the device of Figure 2 taken along the section line 3'-3".
• Figure 4 is a plan view of yet another alternative embodiment of the invention.

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