US Patent 7612410 Trigger device for ESD protection circuit

The present invention is a trigger device useful, for example, in triggering an SCR in an ESD protection circuit. Illustratively, an NMOS trigger device comprises a gate and heavily doped P and N regions in a P-well on opposite sides of the gate. A first N type source/drain extension and a first P-type pocket region extend from the P region toward the N region with the pocket region located under the source/drain extension and extending under the gate. A second N-type source/drain extension and a second P-type pocket region extend from the N region toward the P region with the pocket region located under the source/drain extension and extending under the gate. Preferably, the gate itself is heavily doped so that one half of the gate on the side adjacent the heavily doped P region is also heavily doped with dopants of P-type conductivity and the other half of the gate on the side adjacent the heavily doped N region is also heavily doped with dopants of N-type conductivity. Doping the gate increases the threshold voltage by about one Volt due to an increase in the work function on the source side of the gate.