Characterization of Anomalous Latch-up Effects by Means of Infrared Microscopy and Spice Simulation

Anomalous effects have been evidentiated during pulsed I/O overvoltage tests, such as ``window effects´´, i.e. disapparing of the latch-up concition for high I/O injected current. Infrared microscopy observation reveals that anomalous effects are due to the dy redistribution of supply current between different latch-up paths. This analysis is confirned by the SPICE similation of the lupped equivalent circuit of a CMOS output comprising two coupled pnpn parasitic structures.