Effect of polysilicon depletion on MOSFET I-V 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*10¹⁹ cm^-3 to 5*10¹⁸ cm^-3 for a device with t_ox approximately=7 nm, the drain current I_DS decreases approximately 14% at mod V_GS-V_TH mod =2 V and mod V_DS mod =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.