EFFECT OF POLYSILICON DEPLETION ON MOSFET IV CHARACTERISTICS

MOSFET current (I(DS)) degradation as a function of polysilicon gate concentration (N(P)) and gate oxide thickness (t(ox)) is demonstrated using measured and simulated results. It is found that as the oxide thickness and/or polysilicon gate concentration decrease, the I-V degradation becomes more pronounced. Experimental data show that as N(P) decreases from 1.6 x 10(19) cm-3 to 5 x 10(18) cm-3 for a device with t(ox) congruent-to 7 nm, the drain current I(DS) decreases approximately 14% at \V(GS) - V(TH)\ = 2 V and \V(DS)\ = 2.5 V. The measured data are in general agreement with the theoretical results based on a modified Pao-Sah model that takes into account the polysilicon depletion effect.