Effects of ionizing radiation on the noise properties of DMOS power transistors

The 1/f noise properties of DMOS (double-diffused MOS) power transistors were examined as a function of total ionizing dose. The results indicate that radiation causes significant changes in the frequency dependence of the noise of the power MOSFETs studied. Before exposure to radiation, the noise power spectral density indicated a 1/f/sup lambda / relationship where lambda ranged from approximately 0.5 to 1.0. As the total dose level increased. lambda approached unity, while the magnitude of the noise increased proportionally with the radiation-induced charge density. In addition, noise measurements were performed after irradiation, while the devices were annealing under a +or-12 V bias. It was found that, under the +12 V bias, lambda increased and under the -12 V bias, lambda decreased. Finally, no correlation was found between the pre-irradiation 1/f noise magnitude and the radiation hardness of these DMOS power transistors. >