pMOSFETs biased with Vgs<Vgd during Co60 g irradiation have shown substantial differences between the forward and reverse sub threshold characteristics, induced by a non-uniform charge distribution in the gate oxide. Correspondingly, modest differences have been observed in the over-threshold I-V characteristics. After irradiation, the forward subthreshold curves can shift a higher or lower gate voltages than the reverse ones. The former behaviour has been observed in long-channel devices, in agreement with the classical MOS theory and numerical simulations. The latter result has been obtained in short-channel devices, and it has been correlated to a parasitic punch-through conduction mechanism
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