Input protection circuit for use in semiconductor device having an

Abstract

In an input protection circuit, a bipolar protection device is constituted of a semiconductor substrate of a first conductivity type, a first diffused layer of a second conductivity type formed in the substrate and connected to an input signal pad, a second diffused layer of the second conductivity type formed in the substrate to extend in parallel to the first diffused layer but separately from the first diffused layer by a first space, and a third diffused layer of a high impurity concentration and of the first conductivity type formed in the first space in the substrate to extend in parallel to the first and second diffused layers, in junction with the second diffused layer but separately from the first diffused layer. When a backward biasing voltage is applied, the thickness of a depletion layer formed is made large, so that generation of hot carriers is minimized. Thus, increase of a leakage current caused because hot carriers generated by application of an overvoltage were injected into a field oxide film, can be prevented.