Dose-rate effects on the total-dose threshold-voltage shift of power MOSFETs

Radiation-hardened and -unhardened n-channel power MOSFETs were tested at dose rates approaching space-radiation levels. The hardened parts exhibited large superrecovery effects during and after very low total doses of ionizing radiation. The superrecovery was attributed to in situ interface-trap formation. These positive threshold shifts and the accompanying interface traps can reduce current-drive capability in power MOSFETs. The impact on space-system use is discussed. The threshold-voltage shift of the positively biased unhardened parts was dominated by generation of oxide trapped charge at all dose-rates; the threshold voltage of these parts decreased monotonically at all doses and dose rates examined.>