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 shifts are observed as for room-temperature stress: a systematic increase in the drain current, both in linear operation and in saturation, caused by a positive shift of the threshold voltage. The transconductance is hardly affected for the devices and stress conditions studied. The substrate current is reduced in forward operation and increases for the reverse mode after stress. This degradation is partly removed by post-stress storage at room temperature. The results obtained point towards electron trapping in the oxide as the main degradation mechanism at 4.2 K in pMOSTs, although some interference with the substrate-related transient behaviour is observed