Hydrodynamic modeling of avalanche breakdown in a gate overvoltage protection structure

The breakdown of an overvoltage protection structure is analyzed in the tem perature range from 298 to 523 K. The avalanche generation rates are modele d as a function of the carrier and lattice temperature. The generation rate s are proportional to the carrier concentration. Careful attention is given to the pre-breakdown regime and to the breakdown process. The importance o f various generation processes to the impact process is studied as well as the influence on variations of the ionization threshold energy and of the e nergy loss during the impact process. It is shown that the carrier generati on inside the junction causes adiabatic carrier cooling, which leads to dif ferent carrier heating effects at low and high lattice temperature. The beh avior of carrier heating at room temperature is strongly affected by the as ymmetric field distribution inside the junction. The reason for this is the field dependence of the used trap assisted band to band tunneling model an d of the direct band to band tunneling model. It is shown that at room temp erature, the onset of hole impact ionization plays an important role for th e electron heating. This is different at a temperature of 523 K. where the electrons dominate the onset of impact ionization. (C) 2000 Elsevier Scienc e Ltd. All rights reserved.