US Patent 7494854 Turn-on-efficient bipolar structures for on-chip ESD protection

A semiconductor device suitable for applications in an electrostatic discharge (ESD) protection circuit, including a semiconductor substrate, a first well formed in the substrate, a second well formed in the substrate, and a first doped region formed in the second well, wherein the first well, the second well, and the first doped region collectively form a parasitic bipolar junction transistor (BJT), and wherein the first well is the collector of the BJT, the second well is the base of the BJT, and the first doped region is the emitter of the BJT.