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
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