Hot-carrier effects in depletion-mode MOSFETs

Abstract

Under the same gate and drain bias, the substrate current in a depletion-mode MOSFET is smaller than in an enhancement-mode MOSFET. The difference, however, is gate bias dependent, being larger at low gate voltages and smaller at high gate bias. The phenomenon can be understood in terms of an effective gate-oxide thickness concept. Other hot-carrier effects in the depletion-mode MOSFET, such as gate current and hot-carrier-induced breakdown, can also be understood on the same basis. On the other hand, hole injection into the oxide at very low V G is larger in a depletion-mode device. Such large hole injection leads to a more negative V t after stressing. The maximum shift in V t (negative ΔV t) is comparable to that in an enhancement-mode device.