Effect of polysilicon depletion on MOSFET I–V characteristics

MOSFET current (IDS) degradation as a function of polysilicon gate concentration (Np) and gate oxide thickness (tox) 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 Np decreases from 1.6 × 1019 cm−3 to 5 × 1018 cm−3 for a device with tox ≃ 7 nm, the drain current IDS decreases approximately 14% at | VGS − VTH | = 2 V and | VDS | = 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.