Reduction of VT Shift Due to Avalanche-Hot-Carrier Injection using Graded Drain Structures in Submicron N-Channel MOSFET

In order to evaluate the VT shift due to hot-carriers in submicron n-channel FETs with several kinds of graded junction structures as compared with a conventional structures, long term stress tests were conducted. As a result, it was found that the VT shifts observed in these devices were caused not by channel-hot-electron but by an avalanche-hot-carrier, which is probably a hot hole, and that the VT shift can be suppressed pronouncedly by the graded drain structures. This paper describes VT shift characteristics due to avalanche-hot-carriers compared with those due to channel-hot-carriers as well as the analysis of VT shift reduction mechanism in the graded drain structured devices.