DFT based estimation of CNT parameters and simulation-study of GAA CNTFET for nano scale applications

Abstract

The device dimensions have been consistently scaling down since many developing technologies need smaller and faster integrated circuits for advancement and improvement in both performance and device density. Device dimensions have been decreased drastically from micron to sub nanometer regime. Traditionally, miniaturizing and performance improvement was obtained by tweaking the MOSFET-reducing the channel lengths and gate oxide thickness, increasing dielectric constants etc Unfortunately at 22 nm node it reached a dead end. However, at 22 nm node the tri-gate FinFET introduced by Intel Corporation have provided many possibilities for scaling the dimensions with satisfactory device performance. Further, the gate all around (GAA) carbon nano tube field effect transistor (CNTFET) provides high gain, high trans-conductance, reduced short channel effects and conditions for scaling the technology to sub nano scale. Due to surround gate structure this GAA CNTFET offers better control with integration of high_k stacked dielectric wrapped around the channel. In this paper, first properties of Carbon nanotube (CNT) have been comprehensively studied for various chirality and diameter and parameters viz. Density of States (DoS) and Band gap (Eg) are extracted by using MedeA tool's VASP 5.3 module. The various CNT chirality have been optimized and the extracted parameters used to model and simulate CNTFET using Silvaco's Devedit3D, Atlas and Atlas3D modeling and simulation modules. The device input (ID-VGS) and output (ID-VDS) characteristics have been intensively studied and parameters including ION/IOFF ratio, DIBL, sub threshold slope extracted and compared with the conventional devices. The GAA CNTFET device at 0.8 V supply voltage exhibits threshold voltage (VTH) 0.254 V, drain induced barrier lowering (DIBL) 72 mV/V, sub-threshold swing (SS) 63.29 mV/dec, and ION/ IOFF ratio 7.17e + 06. The results demonstrate improvement in device parameters for the GAA CNTFET device as compared to bulk silicon and FinFET devices.