A two-dimensional avalanche breakdown model of submicron MOSFET's

Negative resistance characteristics observed at breakdown result in a severe decrease in the highest voltage applicable to short-channel N-MOSFET's. The excess substrate current generated by impact ionization causes a significant voltage drop across the substrate resistance. This current forward-biases the source-substrate junction strongly enough to turn on the junction at relatively low drain voltages because of its positive feed-back effect. This results in the decrease in breakdown voltage and negative resistance characteristics. Based on the above, an accurate breakdown model for MOSFET's is presented. This model is composed of a two-dimensional analysis of the electric field, calculation of the multiplication factor, and feed-back of the resulting potential modification due to the substrate current in the two-dimensional analysis. Calculated current-voltage curves with negative resistance agree excellently with experiments for short-channel N-MOSFET's. The model predicts that P-MOSFET's will be preferable to N-MOSFET's from the breakdown point of view especially for submicron channel lengths.