LIQUID-HELIUM TEMPERATURE HOT-CARRIER DEGRADATION OF SI P-CHANNEL MOSTS

Results of a systematic study of the hot-carrier degradation of pMOSTs stressed at 4.2 K are reported. To a first approximation, the same sh ifts are observed as for room-temperature stress: a systematic increas e in the drain current, both in linear operation and in saturation, ca used by a positive shift of the threshold voltage. The transconductanc e is hardly affected for the devices and stress conditions studied. Th e substrate current is reduced in forward operation and increases for the reverse mode after stress. This degradation is partly removed by p ost-stress storage at room temperature. The results obtained point tow ards electron trapping in the oxide as the main degradation mechanism at 4.2 K in pMOSTs, although some interference with the substrate-rela ted transient behaviour is observed.