Analyses of Short Channel Effects of Single-Gate and Double-Gate Graphene Nanoribbon Field Effect Transistors

Hojjatollah Sarvari,Zhi Chen,Amir Hossein Ghayour,Rahim Ghayour

doi:10.1155/2016/8242469

Abstract

Short channel effects of single-gate and double-gate graphene nanoribbon field effect transistors (GNRFETs) are studied based on the atomistic pz orbital model for the Hamiltonian of graphene nanoribbon using the nonequilibrium Green’s function formalism. A tight-binding Hamiltonian with an atomistic pz orbital basis set is used to describe the atomistic details in the channel of the GNRFETs. We have investigated the vital short channel effect parameters such as Ion and Ioff, the threshold voltage, the subthreshold swing, and the drain induced barrier lowering versus the channel length and oxide thickness of the GNRFETs in detail. The gate capacitance and the transconductance of both devices are also computed in order to calculate the intrinsic cut-off frequency and switching delay of GNRFETs. Furthermore, the effects of doping of the channel on the threshold voltage and the frequency response of the double-gate GNRFET are discussed. We have shown that the single-gate GNRFET suffers more from short channel effects if compared with those of the double-gate structure; however, both devices have nearly the same cut-off frequency in the range of terahertz. This work provides a collection of data comparing different features of short channel effects of the single gate with those of the double gate GNRFETs. The results give a very good insight into the devices and are very useful for their digital applications.

Highlights

In recent years, to resolve the severe limitations in scaling of conventional silicon transistors, many researchers have paid attention to one and two materials to be used as the channel of semiconductor devices especially nanoscale transistors, for examples, carbon nanotube (CNT) transistors [1], silicon nanowire transistors [2], FinFETs [3], and graphene nanoribbon transistors [4]
It is shown that the double gate (DG)-graphene nanoribbon field effect transistors (GNRFETs) has a higher ON current compared to the current of the SGGNRFET, because in the DG-GNRFET the gate controls the channel conductance more effectively
The single gate (SG) structure senses the effect of changing the channel length much more than the DG structure, where this can be due to less control of the gate bias on the device behavior in the SG than in the DG

Summary

Introduction

To resolve the severe limitations in scaling of conventional silicon transistors, many researchers have paid attention to one and two materials to be used as the channel of semiconductor devices especially nanoscale transistors, for examples, carbon nanotube (CNT) transistors [1], silicon nanowire transistors [2], FinFETs [3], and graphene nanoribbon transistors [4]. Ohmic contacts can be obtained by using heavily doped GNRs as source and drain regions. Dual- and triple-material gate structures which employ gate-material engineering with different work functions instead of doping engineering are another way to partially suppress the short channel effects in doped contact DG-GNRFETs [17]. According to the best of our knowledge, global investigations of short channel effects and high frequency parameters on single-gate and double-gate doped contact GNRFET devices are not reported so far. In order to investigate the short channel characteristics of the doped contact GNRFETs, we have applied a full quantum transport approach in mode space based on the NEGF formalism to solve the Schrodinger equation which is self-consistently coupled to a two-dimensional (2D) Poisson’s equation. The NEGF and simulation method details are the same as those given in our previous research articles, so we do not include them here [13, 19]

Device Structure

Theory and Simulation

Results and Discussion

Conclusion