1. Field of the Invention
The present invention generally relates to Schottky-barrier diodes (SBD) and, more specifically, to a gated semiconductor device that can be forward biased to exhibit the low forward voltage of a Schottky-barrier diode or reverse biased to exhibit the high breakdown voltage of a P-N junction.
2. Description of the Prior Art
A Schottky barrier diode is a rectifying metal-semiconductor junction formed by plating, evaporating, or sputtering a variety of metals on N- or P-type semiconductor materials. Schottky diodes are fabricated from N-on-N.sup.+ or P-on-P.sup.+ epitaxial material where the P and N layers are optimized in thickness and carrier concentration. Generally, N-type silicon and N-type GaAs are used.
Schottky diodes are fabricated by a planar technique. A SiO.sub.2 layer is thermally grown or deposited on a semiconductor wafer, and windows are etched in the SiO.sub.2 by photolithography and etching techniques. Metals to form a Schottky diode are deposited by evaporation, sputtering, chemical vapor deposition (CVD), or plating techniques.
A conventional SBD usually exhibits a characteristic where in its reverse bias state, a high leakage current exists with a low breakdown voltage as compared to a P-N diode, which provides a high reverse breakdown voltage. If a P-N diode alone is used, its forward voltage is higher than that of an SBD. For a given diode area and forward current level, SBDs have a smaller forward voltage drop than does a P-N diode.
The general state of the art relative to Schottky diode fabrication and use is described in U.S. Pat. Nos. 4,801,983 to Ueno et al. and 4,811,065 to Cogan. Ueno et al. describes an SBD hard wired in series with source or drain of a FET. The gate electrode of the FET is used as a switching control electrode, and a current flowing through the switching circuit in a direction from the input terminal to the output terminal is controlled in accordance with a signal applied to the switching control electrode, but no provision is provided for electrically controlling the characteristics of the SBD as is so done in the instant invention.
The Cogan patent shows an SBD being hard wired in parallel to an N channel DMOS in order to prevent the body diode from turning on when forward voltages are applied. Of course, the SBD, being hard wired, is always electrically connected in the circuit, whereas in the present invention the gated SBD has two alternate current paths depending on the terminal bias voltages, allowing the SBD current to prevail when it is forward biased but suppressed when it is reversed biased.