Infrared microscopy study of anomalous latchup characteristics due to current redistribution in different parasitic paths

Anomalous effects such as abrupt variations of the latchup current in steady-state conditions and window effects, i.e. the existence of a well-defined interval of I/O injected currents for latchup to occur, can occur during pulsed latchup tests. Infrared microscopy allows the correlation of electrical characteristics with latchup current distribution and reveals that anomalous effects are due to the dynamic competition between different latchup paths. This is confirmed by a SPICE simulation of the lumped equivalent circuit of a CMOS output comprising two coupled p-n-p-n parasitic structures.<
>