The Effect of Ionizing Radiation on the Breakdown Voltage of Power MOSFETS

The drain-source breakdown voltage of power MOSFETs is shown to be a strong function of the total dose of ionizing radiation to which the device has been exposed. For the n-channel MOSFETS studied, the breakdown voltage after exposure is reduced from the unirradiated value. The cause for the effect is postulated to be the trapping of radiation-generated charge in the field oxide and the generation of interface traps at the field oxide-silicon interface. The devices studied varied in breakdown voltage between 60 and 500 V and used field plates and/or field rings to terminate the high voltage junction. The magnitude of the drain-source voltage applied to the device during irradiation is shown to have a strong influence on the total shift in breakdown voltage. It is also found that the method of junction termination has some influence on the total shift. These influences occur because the electric field in the oxide during irradiation depends both upon the applied drain-source voltage and the method of junction termination. Implications of the results of this work on device applications are briefly discussed.