Graphene Based Transistors For Digital And Analog Application :A Simulation Study

Vishal Anand Agam Gupta Abhishek Anand 1204059 1204056

1204055

Project Supervisor: Dr. M. W. Akram

Contents:-

• Motivation

• Introduction

• Basics of Graphene

• Simulation on Software

• Project Roadmap

Motivation:-

Moore’s Law observed in 1965 by Gordon Moore suggested that, over the history of computing hardware, the number of transistors in a dense integrated circuit has doubled approximately every two years.

The trend that was followed so far in the electronics industry but with devices becoming increasingly small and reaching the limit we now had to explore other frontiers for this.

The shortcomings of some devices with respect to some parameters forced us to consider the introduction of new channel material. By using this new channel material, new FET devices can be optimized.

Ref:[1].www.intelcorporations.com

Beyond C-MOS

Ref:-[2] Roadmap for 22 nm and beyond H. Iwai * Frontierl Research Center, Tokyo Institute of Technology, 4259-J2-68, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan

So What’s The Way Out ???TWO

OPTIONS

NEW DEVICE

STRUCTURE

FinFET

NEW CHANNEL MATERIAL

CARBON NANOTUBE GRAPHENE SHEET FinFET

Ref:-[3] www.google.com

What Is Graphene ?

Thermodynamically stable graphene sheet was first discovered in 2004 by Giem and Novoselov.

Graphene is a two –dimensional sheet of sp2 bonded carbon atoms arranged ina honeycomb crystal structure with two carbon atoms in each unit cell.

Sp2 hybrids of each carbon atom contribute to form sigma bond with three other carbon atoms in triangular planar structure of Graphene,P orbitals are normal to planar structure and can bind to form half filled pi-band.

Ref:- [4]Fabrication and Characterization of Graphene Field Effect Transistors by Sam Vaziri

Graphite

Single-layer GrapheneSingle-wall Carbon Nanotub

Ref:- [5] K. S. Novoselov et al., “Electric Field Effect in Atomically Thin Carbon Films,” Science, 306 (2004) 666.

Graphene Electronic Properties :• Semi-metal or zero-gap semiconductor •  Linear dispersion relation Optoelectronics •  Massless dirac fermions, v ~ c/300 Intrinsic carrier mobility (suspended graphene in vacuum 2,00,000 cm2 V-1s-1

•  Carrier mobility of graphene on SiO2 at room-temperature 10,000- 20,000 cm2 V-1s-1 •  Maximum current density J > 108 A/cm2

• Velocity saturation vsat = 5 x 107 cm/s (10 x Si, 2 x GaAs)Fig:-Dispersion relation of graphene in fist Brillouin zone

Ref:-[6] Fabrication and Characterization of Graphene Field Effect Transistors by Sam Vaziri

1. Mechanical properties

•  Young’s modulus: ~1.10 TPa (Si ~ 130 GPa)•  Elastically stretchable by 20%•  Strongest material known•  Flexible

2. Thermal conductivity

•  ∼5.000 W/m•K at room temperature Diamond: ∼2000 W/m•K, 10 x higher than Cu, Al

3. Transparent (only 1 atom thin)  Transparent flexible conductive electrodes 4. High surface to volume ratio

5. Most important advantage of Graphene technology is that it is compatible with standard sllicon technology making it easy and cost effective to integrate with the existing CMOS fabrication plants.

Comparison Between Graphene And Sillicon Mosfet

• GFET has higher switching speed due to high mobility of carriers

• GFET’s Thermodynamically more stable

• Shorter and thin channel length resulting in high packing density

Ref:-[7] A. Betti, G. Fiori, and G. Iannaccone, “Atomistic investigation of lowfield mobility in graphene nanoribbons,” IEEE Trans. Electron Devices,vol. 58, no. 9, pp. 2824–2830, Sep. 2011.

Unconventional Use Of Unconventional Properties :

• 1 Transistor Rectifier•  1 Transistor Frequency Doubler

[8] I. Imperiale, S. Bonsignore, A. Gnudi, E. Gnani, S. Reggiani, and G. Baccarani, “Computational study of graphene nanoribbon FETs for RF applications,” in Proc. IEEE IEDM, Dec. 2010, pp. 732–735.

Simulation Side

• We will be using NanoTCAD ViDES as our simulation software.

• The current version of NanoTCAD ViDES is a python module, which integrates the C and Fortran subroutines already developed in the past version of the NanoTCAD ViDES simulator, which is able to simulate nanoscale devices, through the self-consistent solution of the Poisson and the Schroedinger equations, by means of the Non-Equilibrium Green’s Function (NEGF) formalism.

Why device simulation???

They allow to:

• predict the device behaviour

• understand the physical mechanisms underlying the device operation

• test the impact of device design parameters on the device performance (device optimization)

The module developed so far has a set of predefined functions, which allow to compute transport in:-

• Two-dimensional materials (2D materials like MoS2, WSe2 and metal dichalcogenides in generals)

• Silicene• Graphene Nanoribbons• Carbon Nanotubes• Two-dimensional graphene FET• Two-dimensional bilayer graphene FET

The user can anyway define his own device and material through the exploitation of the Hamiltonian command

HamiltonianSynopsys: Hamiltonian(n,Nc)

Hamiltonian is the NanoTCAD ViDES class, which allow the definition of a general Hamiltonian within the semi-empirical tight-binding model. As inputs, it requires the number of atoms n in the slice, and the number of slices Nc of the material to be considered. Nc must be at least larger than 4.

Some of the attributes of Hamiltonian class are as follows:- • Nc : (int) the number of slices• n : (int) the number of atoms within each slice• x: (numpy array of length n*Nc) x coordinates of the atoms• y: (numpy array of length n*Nc) y coordinates of the atoms• z: (numpy array of length n*Nc) z coordinates of the atoms• Phi: (numpy array of length n*Nc) potential of the atoms• Eupper : (double) the upper energy limit for which the NEGF is

computed in the nanoribbon• Elower : (double) the lower energy limit for which the NEGF is

computed in the nanoribbon• charge_T : (function) function which computes the free charge and

the transmission coefficient in the energy interval specified by Eupper and Elower with an energy step equal to dE in correspondence of each C atoms of the nanoribbon

Template of 2D Metal Di Chalcogenides Field Effect Transistor.

Ref:-[9] ViDES manual

Ref:-[10] ViDES manual

Structure of top gated graphene field-effect transistor is used in our simulations

Ref:-[11] ViDES manual

The Id-Vds characteristics of the top gate graphene field-effect transistor at VG = 0.1V, 0.2V, 0.4V, 0.6V, 0.8V (bottom to up).

Ref[12]:- ViDES manual

Ref:-[13] ViDES manual

Script

Source:-[14] ViDES manual

Project Roadmap

Study & Analysis of the Topic Working on Basics

of Software

Implementation on Software

Effects of device parameter

variations on the performance

parameters of Analog & Digital

Devices

Introduction of new parameters by

modifying & writing the script

file