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.