Analytical Performance of the Threshold Voltage and Subthreshold Swing of CSDG MOSFET

Abstract

In this research work, the threshold voltage and subthreshold swing of cylindrical surrounding double-gate (CSDG) MOSFET have been analyzed. These analyses are based on the analytical solution of 2D Poisson equation using evanescent-mode analysis (EMA). This EMA provides the better approach in solving the 2D Poisson equation by considering the oxide and Silicon regions as a two-dimensional problem, to produce physically consistent results with device simulation for better device performance. Unlike other models such as polynomial exponential and parabolic potential approximation (PPA) which consider the oxide and silicon as one-dimensional problem. Using the EMA, the 2D Poisson equation is decoupled into 1D Poisson equation which represent the long channel potential and 2D Laplace equation describing the impacts of short channel effects (SCEs) in the channel potential. Furthermore, the derived channel potential close-form expression is extended to determine the threshold voltage and subthreshold behavior of the proposed CSDG MOSFET device. This model has been evaluated with various device parameters such as radii Silicon film thickness, gate oxide thickness, and the channel length to analyze the behavior of the short channel effects in the proposed CSDG MOSFET. The accuracy of the derived expressions have been validated with the mathematical and numerical simulation.increases the packing density, and most importantly leads to better controllability of the gate over the channel [17,21]. The gate control results to enhancement of the subthreshold characteristics and greater immunity to SCEs. However, in terms of current drive the CSG MOSFETs have lesser current compared with the DG MOSFET, hence, its extensive use is limited for high performance application [22]. Thus, there is need to improve on the geometric structure of the CSG MOSFET to enhance the current drive, the gate control over the channel and further improve the SCEs immunity at the nanoscale regime.A novel structure, the cylindrical surrounding double gate (CSDG) MOSFET, was proposed by Srivastava et al. [12]. The geometry is similar to that of the CSG MOSFET with an internal core gate. The core gate enhances the channel control and improves the SCEs immunity. Additionally, the device allows for higher packing density and higher volume inversion than DG MOSFETs and CSG MOSFETs [23,24]. The explicit charge model based on the unified charge model was carried out by Srivastava et al. [25,26]. The authors analyzed the channel current for the novel structure to be higher than the single, DG MOSFET, and CSG MOSFET. However, the authors did not consider the subthreshold regime. Verma et al. [27] worked on the subthreshold regime of the CSDG MOSFET in which only the threshold voltage was analyzed.The proposed CSDG MOSFET is designed on a hollow concentric cylindrical structure in which a simple analytical channel potential model has been derived at subthreshold regime. The 2D Poisson equation is solved with the EMA as a boundary valued problem to obtain the mi...

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