Hot carrier degradation in n-MOSFETs used as pass transistors

The hot carrier properties of n-MOS devices in the pass transistor mode are examined. In this mode, damage occurs at both source and drain junctions of the transistor. It is shown that the damage at each junction proceeds independently, and that the damage at each junction is additive. It is found, consequently, that the pass transistor is more sensitive to hot carrier damage than a transistor in the inverter mode, with lifetimes based on the linear region g_m change being 3-4 times lower. Using a saturated current (I_dsat ) definition, the lifetimes for pass transistors can be about an order of magnitude lower than for transistors operated in only one source/drain orientation, assuming similar voltage conditions. About half of this reduction in lifetime is because degradation occurs at both junctions, and the other half is due to the fact that degradation at the source junction causes a much more dramatic effect upon I_dsat than damage at the drain junction