Graphene Devices: from Transistor to Barristor

Hyun-Jong Chung

Konkuk University (formerly Samsung Advanced Institute of Technology)

• Thinnest material

• Mechanical strength: 5 times steel

• Thermal conductor: 2 times diamond

• Resistivity: Half of Copper

• Mobility : 100 times Silicon’s

• Current density : 100 times Copper

Property Value

Conductivity 1.0 μΩcm

Mobility ~ 200,000 cm2/Vs

Thermal conductivity 5300 W/mK

Mechanical property Young’s modulus: 1 Tpa Tensile strength: 20 Gpa

Flexibility Failure strain > 20%

Transparency 97 % @ 1 layer

High surface 2,630 m2/g

Graphene

from “Rise of Graphene”

Transistor Application

Memory

Capacitor

Interconnect

ITO

OPV Structural Material

THz Image Sensor

Thermal Management

Data Storage

Communication

Others

Application

Market Size (BCC Research Report 2011 and IT SOC magazine 2009)

Transistor Application 73%

Memory 21%

Capacitor 3%

Interconnect 1%

ITO 1%

OPV 1%

Structural Material 0%

THz Image Sensor 0%

Graphene Transistor

mobility ~ 1,400 cm2/Vs

bandgap 1.05 eV

e vs. h asymmetric mobility

mobility ~ 200,000 cm2/Vs

bandgap 0 eV

e vs. h massless

Structure

Turning off the device, …

e

e

NO!

How Badly Turned off?

kx

ky

kx

ky 100~

10

10~

11

13

OFF

ON

I

I

Ion/Ioff~102 , D=2.2V/nm

X. Li et al. Science (2008)

F. Xia et al. Nano Lett.. (2010)

w=5nm, Ion/Ioff~106, μ=100-200cm2/Vs

L. Ci, Nature Materials(2012)

1st Approach: Bandgap of Graphene

F. Schwierz, Nature Nanotechnology(2012)

2nd Application: RF Transistor

• Is it satisfactory? No!

• However, maybe, possibly, it could take one part of Si circuit…

Graphene Tr. in the Industry’s Viewpoint

Processes for Nothing-on- Graphene Structure

1. Taking one part in Si circuits 1. Nothing-on-Graphene Structure

2. Greater fMAX for amplification

1. ‘pinch-off’ like condition. 2. Maybe bandgap required.

3. Higher on-/off-current ratio. 1. Bandgap > 0.36eV for logic

Summary of Graphene Transistors

RF Transistor without Bandgap

Logic Transistor with Bandgap

Switching without Mobility Mobility without Switching Dilemma

Question!!!

Graphene, Again!

• Key Idea: Density Control Barrier Control

New approach to turn off!!!

kx

ky

Graphene

kx

ky

Graphene

Schottky Barrier

Semiconductor Semiconductor

Schottky Barrier

Fermi-level Pinning

FM1

FM2

FM2

FM2

• Considering Band alignment - Si

Fabrication

+

0.0 0.5 1.0

10-12

10-9

10-6

10-3

Cu

rren

t(A

)

Gate Voltage(V)

60mV/dec

28nm CMOS

GB

theoretical SS

1expexp2*

kT

eV

kT

ΦTAAI B

From Nature

• Current Flow.

Remind

Graphene Silicon

Schottky Barrier Height

Graphene Silicon

Schottky Barrier Height

ON

OFF

-2 -1 0 1 2

0

3

6

9

Vbias

(V)

Cu

rre

nt(A

)

0.06 0.09 0.12 0.15 0.18 0.210.26

0.28

0.30

0.32

0.34

0.36

0.38

0.40

0.42

F(e

V)

EF(eV)

S

-1 0 1 2 3 4 50.25

0.30

0.35

0.40

0.45

Vgate(V)

FB

(eV

)

0.08

0.12

0.16

0.20

0.24

E

F(e

V)

•Turn-on Voltage Shift • Reverse Current Increase

1expexp2*

kT

eV

kT

ΦTAAI B

-0.5 0.0 0.5 1.00

1

2

3

4

5

Curr

ent

Density (A

/cm

2)

Vbias (V)

Graphene/p-Si

Graphene/n-Si

I-V Characteristic

Vbias(V)

Curr

ent(㎂

)

Application: Barristor Logic

VDD

VOUT VIN

p-GSD

n-GSD

-4 -2 0 2 4

0.01

0.1

1

Vout (V

)

Vin (V)

VDD = 2.0V Gain ~ 1.2

0.45

0.48

0.51

0.54

0.57

Output state, (SUM,CARRY)

VS

UM

/ V

DD

(V

)(0,0) (0,1) (1,0) (1,1)

Input state, (A,B)

(0,0) (1,0) (1,0) (0,1)

0.4

0.5

0.6

0.7

0.8 VC

AR

RY

/ VD

D (V

)

-2 -1 0 1 2

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

101

Curr

ent (

A)

Vbias (V)

Reverse bias Forward bias

Vgate=-5V 5V

10-5

10-4

10-3

10-2

10-1

100

Cu

rre

nt (

A)

Forward

Ion/Ioff ~ 105

Vbias = 0.3 V

V=0.3V

Vgate I

-5 -4 -3 -2 -1 0 1 2 310

-3

10-2

10-1

100

Curr

ent (

A)

Vgate(V)

Reverse

Ion/Ioff ~ 103

Vbias = -1.5 V

V=-1.5V

Vgate I

Current(㎂

)

Vgate(V) -5 0 5

Barristor or Tunneling Transistor

Samsung

Graphene-Si

Science 2012

Manchester University

Graphene-hBN

Science 2012

UCLA

Graphene-MoS2

Nature Mat. 2013

Manchester University

Graphene-WS2

Nature Nano. 2012

• Thermionic Emission Current

• Tunneling Current

Current Mechanisms

• Current through Graphene-Semiconductor Junction: Graphene-Si (Graphene-MoS2)

• On/Off ratio limited by Workfunction Modulation

Thermionic Emission Current

Yang et. al Science (2012)

• Current through Graphene-Insulator Junction

• Depends mostly on density of states: therefore has the same problem with transistor

• Low Voltage Operation

Tunneling Current

Britnell et. al Science (2012)

Britnell et. al Nano Lett. (2013)

Britnell et. al Science (2012)

• Current through Graphene-Insulator Junction

• Determined by more complex way.

• High Voltage Operation. However, …

Tunneling + Thermionic Current

Georgiou et. al Nat. Nano. (2012)

Where are we?

Britnell et. al Science (2012) Yu et. al Nat. Mat. (2012) Yang et. al Science (2012) Georgiou et. al Nat. Nano. (2012)

Ojeda-Aristizaval et. al Arxiv

Acknowledgement

Prof. Sang Wook Lee

Konkuk University

SAIT

Hyeon-Chul Kim Junho Lee Hanbyeol Lee Doowha Choi

Hak Seong Kim Ho Ang Yoon

Seongjun Park Jinsung Heo Kyeongeun Byeon David Seo

Heejun Yang

CNRS

Phillip Kim

Columbia

What is Graphene? W

ork

-Funct

ion (

eV)

5

4.5

4

Thank you for any discussions and comments

hjchung@konkuk.ac.kr