Abstract
This paper investigates several techniques for hardening CMOS curcuitry against transiently triggered latchup. Measurements of critical rise time are made on four variations of the p-n-p-n structure inherent to CMOS. For each structure the n-well and substrate shunt resistances are varied as is the substrate bias. These measurements are performed on both bulk and epi-samples using both topside and backside substrate contacts. Comparison of the parasitic bipolar transistors comprising the p-n-p-n structures reveals that differences in bipolar behavior do not completely explain the differences in p-n-p-n latchup behavior. Test results are used to rate the various hardening techniques.

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