Failure of On-Chip Power-Rail ESD Clamp Circuits During System-Level ESD Test

Four different on-chip power-rail electrostatic discharge (ESD) protection circuits, (1) with typical RC-triggered; (2) with NMOS+PMOS feedback; (3) with PMOS feedback; and (4) with cascaded PMOS feedback, have been designed and fabricated in a 0.18-mum CMOS technology to investigate their susceptibility to system-level ESD test. During the system-level ESD test, where the ICs in a system have been powered up, the feedback loop used in the power-rail ESD clamp circuit provides the lock function to keep the main ESD device in a "latch-on" state. The latch-on ESD device, which is often designed with a larger device dimension to sustain high ESD level, conducts a huge current between the power lines to perform a latchup-like failure after the system-level ESD test. From the experimental results, two kinds of on-chip power-rail ESD clamp circuits with feedback structures are highly sensitive to transient-induced latchup-like failure than others