Weak point and improvement of CMOS Schmitt Trigger Circuit used in Microcontroller about ND-mode ESD

In this study, We investigated weak point and improvement about ND-mode ESD of CMOS Schmitt trigger circuit embeded in Microcontroller. Junction spiking conditions on NMOS of the CMOS Schmitt trigger circuit were Vcc Common mode, ND-mode 1.4kV, and 0.81.2 sec zap interval (pin to pin). Failure mechanism by LNPN action formed in CMOS Schmitt trigger circuit was reproduced. We have identified Root Cause and improved circuits to achieve ESD damage free.