Gate Bias Effect on the 60-MeV Proton Irradiation Response of 65-nm CMOS nMOSFETs

The response to a 60-MeV proton irradiation of nMOSFETs fabricated in a 65-nm CMOS technology using a 1.4-nm gate oxide is reported. A strong dependence on the gate bias during the exposure is found. Whereas no degradation is observed for 0-V bias, soft or hard breakdown occurs under normal operational conditions, i.e., 1.2 V on the gate. Furthermore, it is noted that the breakdown happens preferentially at the source-gate junctions. Possible mechanisms are discussed, whereby at the moment, it is believed that a synergy between the radiation damage in the thin gate oxide and the gate current flow under constant voltage may explain the observations. Furthermore, it is shown that the tendency for a breakdown at the source-gate junction is correlated with a higher source-gate current prior to irradiation. This could point to some processing-induced prerad local degradation of the gate oxide, which develops into a breakdown leakage site under biased 60-MeV proton irradiation