Semiconductor variable capacitance element

Abstract

A variable capacitive element is comprised of a semiconductor substrate having a major surface and a capacitive region under the major surface of the semiconductor substrate, a floating electrode disposed on and electrically insulated from the semiconductor substrate through an insulating film for storing electric charge to build up an electric potential in the floating electrode according to the stored amount of electric charge to thereby determine an amount of capacitance of the capacitive region, and a control electrode for injecting electric charge into the floating electrode. A terminal electrode is electrically connected to the capacitive region for electrically connecting the capacitive region to an external circuit. The terminal electrode is capacitively coupled to the floating electrode. A given voltage is applied to the terminal electrode to adjust the electric potential of the floating electrode through the capacitive coupling between the terminal electrode and floating electrode. A capacitor is electrically connected between the terminal electrode and the external circuit for blocking an application of a DC voltage from the external circuit to the terminal electrode.