Dual direction ESD clamp based on snapback NMOS cell with embedded SCR

摘要

In an ESD protection structure, dual direction ESD protection is provided by forming an n-well isolation ring around an NMOS device so that the p-well in which the NMOS drain is formed is isolated from the underlying p-substrate by the n-well isolation ring. By forming the n-well isolation ring the p-n-p-n structure of an embedded SCR for reverse ESD protection is provided. The width of the n-well isolation ring and its spacing from the NMOS drain are adjusted to provide the desired SCR parameters.