Semiconductor device having a lateral transistor

Claim 1

A semiconductor device comprising a semiconductor substrate of one type conductivity, an epitaxial layer of the opposite type conductivity on a surface of the substrate, vertical zones of the one type conductivity extending through the epitaxial layer to form islands of the opposite type conductivity, a buried layer being located approximately at the epitaxial layer-substrate interface of one of the islands, said buried layer having a higher conductivity than that of the island, a lateral bipolar transistor within said one island, said lateral transistor comprising a surface emitter zone of one type conductivity, an adjacent surface collector zone of one type conductivity and spaced from the buried layer, the intervening island material constituting the transistor base zone of opposite type conductivity, said emitter zone comprising a first portion of one type conductivity extending vertically from the buried layer toward the epitaxial layer surface, said emitter zone further comprising a second portion of one type conductivity extending vertically from the epitaxial layer surface to a depth equal to that of the collector zone, said second emitter portion being coextensive with part of the first emitter portion and being spaced closer to the collector zone than the emitter first portion, means for biasing the emitter zone in the forward direction to inject carriers into the base zone and means for biasing the collector zone in the reverse direction to collect the injected carriers, whereby the major carrier injection from the emitter zone occurs from the second portion located closer to the collector and in one type conductivity material of lower conductivity.