PNPN Light sensitive semiconductor switch with phototransistor connected across inner base regions

Claim 1

In a PNPN semiconductor switch of the type comprising: an N type semiconductor substrate; a first P type diffused region formed in said substrate; a second P type diffused region formed in said substrate so as to be spaced apart from said first P type diffused region by a predetermined distance; a first N type diffused region formed in said second P type diffused region; a second N type diffused region formed in said second P type diffused region so as to be spaced apart from said first N type diffused region by a predetermined distance; a first gate insulating layer formed on a surface of said second P type diffused region between said first and second N type diffused regions; a P type gate electrode electrically connected to said second P type diffused region and said second N type diffused region; a first gate electrode of an N type polycrystalline silicon formed on a surface of said first gate insulating layer between said first and second N type diffused regions; a first resistance region of an N type polycrystalline silicon formed so as to extend from said first gate electrode to said P type gate electrode; a second gate insulating layer overlying said first gate electrode; a semiinsulating layer formed on a surface of said substrate except over said first and second P type diffused regions; an insulating layer overlying said semiinsulating layer; a second gate electrode formed on a surface of said second insulating layer over said first gate electrode; a cathode electrode electrically connected to said first N type diffused region; and an anode electrode electrically connected to said first P type diffused region and to said second gate electrode; the improvement which comprises a high resistance region having a low N type impurity concentration formed immediately beneath said first gate insulating layer and between said first and second N type diffused regions, said high resistance region acting a shunt resistor so as to thereby provide a high gate sensitivity for said PNPN semiconductor switch; and further comprising a phototransistor for amplifying a collector current caused by being exposed to light, wherein said phototransistor comprises: a third P type diffused region formed in said substrate so as to be spaced from said second P type diffused region by a predetermined distance; a third N type diffused region formed in said third P type diffused region; a fourth N type diffused region formed in said third P type diffused region so as to be spaced from said third N type diffused region by a predetermined distance; a third gate insulating layer formed on a surface of said third P type diffused region between said third and fourth N type diffused regions; a third gate electrode of an N type polycrystalline silicon formed on a surface of said third gate insulating layer between said third and fourth N type diffused regions; a base electrode electrically connected to said fourth N type diffused region and said third P type diffused region; a second resistance region of an N type polycrystalline silicon formed so as to extend from said third gate electrode to said base electrode; a semiinsulating layer formed on a surface of said substrate except over said second and third P type regions; an emitter electrode electrically connected to said third N type diffused region and to said P gate electrode; a fourth gate insulating layer formed on a surface of said third gate electrode; a fourth gate electrode disposed on a surface of said fourth gate insulating layer over said third gate electrode and electrically connected to said anode electrode; and another high resistance region having a low N type impurity concentration formed immediately beneath said third gate insulating layer and between said third and fourth N type diffused regions.