A low-voltage triggering SCR for on-chip ESD protection at output and input pads

A novel silicon-controlled rectifier (SCR) structure for on-chip protection against electrostatic discharge (ESD) stress at output or input pads is presented. The SCR switches to an ON state at a trigger voltage determined by the gate length of an incorporated nMOS-like structure. Thus the SCR can be designed to consistently trigger at a voltage low enough to protect nMOS transistors from ESD. The capability of protection circuits using the new SCR design is experimentally demonstrated. The tunability of the SCR trigger voltage with reference to the nMOS breakdown voltage is successfully exploited to improve the human-body-model ESD failure threshold of an output buffer from 1500 V to 5000 V