Hot carrier effects in MOS transistors

Degradation of MOS transistors subjected to hot carrier injection is discussed. We find that the lifetime of both standard-and graded drain transistors is proportional to
\exp[A/(DV_{ds})-B/ L_{eff}
; where A,B and D are constants. A and B are the same for both transistor types while D=1 for standard and D=0.8 for graded drain transistors. D represents the reduction of the electric field obtained by adding the graded drain. From a comparison of I-V curves before and after the hot carrier stress we conclude that the degradation is almost entirely caused by the generation of interface states. From a thorough analysis with the charge pumping technique we find that the interface state generation predominantly takes place inside the drain junction, over a very small part of L
eff
.