3-D model of wrap around CNTEFT with multiple CNT channel and analytical modeling of its capacitances

Abstract

Wrap around CNTFET has gate around it except the bottom portion. Wrap around gate carbon nanotube field effect transistor (CNTFET) has the advantage of more accurately controlled channel than top gated CNTFET. 3-D simulation is performed using Finite Element Method (FEM) to model wrap around CNTFET with multi-CNT channel. For predicting the device speed, capacitance modeling is necessary. Along with gate to channel capacitance, there are fringing capacitance as well. Analytical expressions to model various capacitances of the same device are also derived from capacitances for 1-D FET with multiple cylindrical conducting channels incorporating screening effect due to multiple CNT. Various capacitances thus obtained exhibit remarkable improvement over planar top gate device with multiple conducting channels. This is attributed to the charge enhancement and better charge confinement in the channel of the wrap around CNTFET with multi-CNT channel. Capacitances are also extracted from the proposed FEM model. The extracted capacitances are in excellent agreement with the capacitances obtained from the analytical model presented in this study. Temperature distribution of wrap around CNTFET with multi-cnt is presented in this paper. For predicting the device characteristics, temperature modeling is necessary. Temperature distribution is changed due to multi-cnt as voltage of adjacent cnt affects temperature of mid cnt. Again it is also changed by temperature dependent thermal conductivity of single walled carbon nano tube (SWCNT). Current flow is changed both due to multi-cnt wrap around structure and due to the temperature change. So, temperature has a great impact on current modeling and thus on device characteristics. All these issues are considered in this paper using finite element method.