Hydrodynamic modeling of avalanche breakdown in a gate overvoltage protection structure

The breakdown of an overvoltage protection structure is analyzed in the temperature range from 298 to 523 K. The avalanche generation rates are modeled as a function of the carrier and lattice temperature. The generation rates are proportional to the carrier concentration. Careful attention is given to the pre-breakdown regime and to the breakdown process. The importance of various generation processes to the impact process is studied as well as the in ̄uence on variations of the ionization threshold energy and of the energy loss during the impact process. It is shown that the carrier generation inside the junction causes adiabatic carrier cooling, which leads to di€erent carrier heating e€ects at low and high lattice temperature. The behavior of carrier heating at room temperature is strongly a€ected by the asymmetric ®eld distribution inside the junction. The reason for this is the ®eld dependence of the used trap assisted band to band tunneling model and of the direct band to band tunneling model. It is shown that at room temperature, the onset of hole impact ionization plays an important role for the electron heating. This is di€erent at a temperature of 523 K, where the electrons dominate the onset of impact ionization. Ó 2000 Elsevier Science Ltd. All rights reserved.