SOI input protection circuit

摘要

In an input protection circuit having an SOI structure for protecting a MOSFET against breaking caused by a high voltage such as static electricity, a trench is provided in an SOI substrate to vertically pass through a silicon layer and a buried oxide film and reach the interior of a P-type silicon substrate. An n+ polysilicon layer is buried in the trench, to be connected with the silicon substrate by a P-N junction. A wire is connected to the n+ polysilicon layer. An end of the wire is connected to an input pad, and another end thereof is connected to an internal circuit. An input voltage is limited by an avalanche breakdown at the P-N junction in the interface between the n+ polysilicon layer and the P-type silicon substrate.