Embedded scr protection device for output and input pad

Abstract

An embedded parasitic silicon controlled rectifier (SCR) in conjunction with a Gated-NMOS is created for protecting a chip input or output pad from electrostatic discharge ESD, by inserting a p+ diffusion and the n-well in the drain side and a part of the drain to forms a low-trigger, high efficiency SCR. The device layout is such that the drain connection is tightly tied together at the p+ diffusion and the n+ drain making that connection very short and, thereby, preventing latch-up. The parasitic SCR is contained entirely within the n+ diffusion (the source of the grounded gate NMOS transistor) at either side of the structure and, therefore, called an embedded SCR. For a 12 volt I/O device each of two n+ drains is placed in its own n-type doped drain (ndd) area straddling halfway the n-well. The structure is repeated as required and a p+ diffusion is implanted at both perimeters and connected to the nearest n+ source and a reference voltage.