Physics based 2-D analytical model of triple material double gate tunnel field effect transistor

Abstract

Tunnel FETs are attractive new devices for low-power applications due to their low off-current and their potential for a small subthreshold swing. In this work, analytical models of potential, electric field, drain current and gate threshold voltage have been proposed for Triple Material Double Gate (TMDG) TFET structure. Surface potential and electric field are formulated by exploiting Gauss’s law in the lightly doped body region. A closed form expression of band-to-band tunneling current is developed by utilizing tunneling generation rate and the derived electric field model. An analytical model of gate threshold of TMDG TFET is derived from the surface potential equation based on its physical definition for TFETs. The developed models are then generalized for single and multiple material gate TFET structures. A numerical model of TMDG TFET structure is developed using ATLAS, Silvaco device simulator. The device parameters are chosen carefully based on the literature, so that the structure can provide high ON current, low leakage current and can suppress the ambipolar behavior of the device. The proposed models are then verified against the TCAD simulation results. The effects of varying device parameters and bias conditions on device performance are also analyzed. Based on the analysis, the validity range of the proposed models are defined and a solution to extend this validity range is suggested. The effect of Si film thickness on device’s electrical characteristics is also studied, the physics governing it is detailed and an optimum value of Si film thickness is suggested. Analytical models are crucial in understanding the characteristics of a device and the proposed models will be helpful for designing circuits containing single material gate and multiple material gate TFET devices.