An analytical model of threshold voltage for the full depletion cylindrical gate metal-oxide-semiconductor field-effect transistor(MOSFET)
is proposed to address the issue that polysilicon depletion effect is aggravated for deep submicron MOSFET. The potential Poisson's equation in the polysilicon depletion layer is solved to get the voltage drop in the polysilicon depletion layer
and the voltage drop is then used to modify the universal boundary conditions of the channel region. Then the 2D potential Poisson's equation in the channel is solved by using the superposition principle to construct the analytical models of surface potential and threshold voltage for the cylindrical gate MOSFET.These models are verified by device simulation software Sentaurus. The results show that the voltage drop in the polysilicon depletion layer would be larger and the corresponding threshold voltage shift would be more significant when the doping density of substrate is higher and the doping density of polysilicon is lower. Comparisons with existing models show that the precision of the derived analytical model is improved by more than 34%.
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references
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