The Effect of Operating Frequency in the Radiation Induced Buildup of Trapped Holes and Interface States in MOS Devices

Both n-channel and p-channel MOS transistors, fabricated with a radiation hardened 3-4 um process, were irradiated at various operating frequencies and biases. The n-channel devices showed a larger rebound effect when alternately biased ´off´ and ´on´ during irradiation than for the cases of being biased either ´off´ or ´on´ during the irradiation. The p-channel devices showed a smaller threshold voltage shift when alternately biased ´off´ and ´on´ during irradiation compared to devices which were biased either ´off´ or ´on´ during the irradiation. The contributions of trapped holes and interface states on the observed threshold voltage shifts were determined through subthreshold current measurements. This research showed the source of this alternating bias effect on the radiation response of MOS devices to be reduced hole trapping and increased interface state buildup in n-channel MOS devices. In p-channel devices, reduced hole trapping is the primary source of this effect.