Insulated-gate field effect transistor having gate protection diode

Claim 1

An insulated gate field effect transistor with means for protecting against excessive gate voltage comprising a semiconductor substrate having a first conductivity type; an insulated gate field effect transistor formed in said substrate having source and drain regions of a second conductivity type opposite to said first conductivity type, source and drain electrodes respectively connected to said source and drain regions, and a gate electrode formed on an insulator film lying on said substrate in the region between said source and drain electrodes; a generally elongated first resistance region formed on said substrate separately from said transistor, having a high impurity concentration of said second conductivity type, an input terminal connected to one end of said resistance region, and an output terminal connected to the other end of said resistance region, a first P-N junction being formed at said one end between said resistance region and said substrate; a second region formed on said substrate in contact with said other end of said first region, a second P-N junction being formed between said second region and said resistance region at said other end, said second region having a relatively high impurity concentration of said first conductivity type as compared to said substrate, means for connecting said output terminal to said gate electrode, the breakdown voltage of said second P-N junction being lower than that of said first P-N junction, whereby the application of an excessive voltage to said input terminal causes a breakdown of said second P-N junction, such that a voltage reduced by the amount of the voltage drop across said first resistance region is developed at said output terminal, a third region of one of said first and second conductivity types formed in said substrate and having a high impurity concentration disposed adjacent to said other end of said first region, and a wiring layer formed on said substrate for grounding said third region.