Epitaxial island with adjacent asymmetrical structure to reduce collection of injected current from the island into other islands

An integrated circuit of the type having a semiconductor substrate of one conductivity type, two large PN-junction isolated islands of the opposite conductivity type which large islands may alternately become forward biased with respect to said substrate, are each formed in and surrounded by one portion of said substrate, each of said two large islands having one side, another side and two lateral sides;

• said one substrate portion lying adjacent to and abutting one side of said each large island, a lateral of said sides of one of said large islands facing and being adjacent to a lateral of said sides of the other of said large islands, a plurality of small PN-junction isolated islands of the opposite conductivity type formed in said substrate and lying nearer to said one sides of said first and second large islands, wherein the improvement comprises:
• a) a first and second protective bipolar transistor formed respectively entirely at said other sides of said first and second large islands, each said protective transistor comprising:
• another portion of said substrate, abutting said said another side of said each large island, serving as the base region of the corresponding of said protective transistors;
• an opposite-conductivity type region formed in said base region, serving as the collector region of said corresponding protective transistor;
• and
• said corresponding large island serving as the emitter of said corresponding protective transistor;
• b) two circuit ground conductors connecting, respectively, said base regions of said two corresponding protective-transistors to a ground point in said integrated circuit;
• c) two electrical conductors, each connecting said collector region of one of said protective-transistors to a part of said one substrate portion that separates the corresponding of said large islands from said small islands.

An integrated circuit with PN-junction isolated islands with an asymmetric merged structure to reduce collection of injected current from a first island by a second island, said integrated circuit being of the type having a semiconductor substrate of one conductivity type, a first PN-junction isolated island of the opposite conductivity type formed in said substrate, which first island may momentarily become forward biased with respect to said substrate, at least a second PN-junction isolated island of said opposite conductivity type formed in and surrounded by one portion of said substrate lying adjacent to and abutting one side of said first island, which second island tends to collect injected carriers from said first momentarily forward-biased island, wherein the improvement comprises:

• a) a vertical protective bipolar transistor formed at another side of said first island, said protective transistor comprising:
• a region of one-type conductivity, serving as the base region of said protective transistor, and having been formed in an edge portion at said another side of said first island, said edge portion directly contacting and merging with an adjacent portion of said one-conductivity-type substrate;
• and
• a region of the opposite conductivity type serving as the collector region of said protective transistor, said collector region being formed in said base region;
• and
• said first island of opposite-conductivity type serving as the emitter of said protective transistor;
• b) a circuit ground conductor connecting a ground point in said integrated circuit to said base region;
• and
• c) an electrical conductor connecting said protective-transistor collector region to said semiconductor substrate region of one conductivity type that separates said one island from said second island.