A two-dimensional model for fully depleted cylindrical/surrounding gate MOSFET is proposed to address the issues that the short channel effects(SCEs)of deep submicron MOSFET are more obvious with the decrease of channel length

and that mobile charge has a significant impact on surface potential when the device is working in strong-inversion regions. Taking account of the effects of both depletion charge and free charge

an one-dimensional potential model is obtained by solving one-dimensional Poisson's equation with the boundary conditions at the interface of the channel and the oxide layer. Then the Laplace equation is solved by using the boundary conditions at the source and drain regions to construct the accurate two-dimensional surface potential model. Then analytical models for both the threshold voltage and the subthreshold slope are derived. These models are verified by device simulation software Sentaurus. The results show that the proposed model is applicable from the sub-threshold region to the strong-inversion region in different channel doping conditions

and overcomes the shortcomings that the intrinsic model is not valid under the heavy doping conditions and the model based on only depletion charge fails in the strong-inversion region.Comparisons with existing models show that the error of threshold voltage reduces by 45.5%.