Carbon-based devices on flexible substrate

amountdollElectronics - Devices

Nov 2, 2013 (3 years and 11 months ago)

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2011.12.26

Chun
-
Chieh

Lu

Carbon
-
based devices on flexible substrate

1

Graphene

properties



Dimensions

-

Available in a wide range of platelet lengths (typically 1
-
20
μm
) and thicknesses


(approximately 0.34 nm to 100 nm)

-

Single layer
graphene

as thin as 0.34 nm



Strength

-

Fifty times stronger than steel

-

Ultra
-
high Young’s modulus (approximately 1,000
GPa
) and highest intrinsic strength (~ 130


GPa

estimated)



Conductivity

-

The highest thermal conductivity known today (up to ~ 5,300 W/(
mK
), five times that of


copper, at a density that is four times lower

-

Exceptional in
-
plane electrical conductivity (up to ~ 20,000 S/cm)



Transmittance

-

Absorptance

2.3% for single layer
graphene



Good performance of strength, conductivity and transmittance



Advantages for transparent and flexible electronics

2

3

Carbon
-
based transparent conducting film (TCF)

Carbon
-
based field effect transistor



Carbon
-
based transparent conducting films (TCFs)

Transfer to PET

Transfer to glass

Transmittance vs. Sheet resistance

4



Carbon
-
based transparent conducting films (TCFs)

Graphene

films bending and stretching test

5

Compared with ITO film:

6


Field
-
effect transistor in flexible regime:


logic gate, portable memory, display driving circuit, electronic tagging, RFID system…



Field
-
effect transistor needed in conventional process:


metal contact deposition in high vacuum and gate oxide grown in high temp. process



For flexible substrate:


(1) To develop
low temperature
,
printing processe
s for materials that form the channel


region, gate insulator and electrodes on soft substrates
with high thermal expansion


coefficients


(2) To overcome intrinsic limitations of
mechanical properties

associated with


conventional materials and circuits through development of new materials or device


architectures.



For example:


High
-
k inorganic dielectrics (HfO
2
, Al
2
O
3

and ZrO
2
) cannot be available for flexible


devices based on plastic substrates due to their high growth temperature.






Due to low temperature and printing process, ion gel can be used as good gate


dielectric of carbon
-
based field effect transistor on flexible substrate





Graphene

field
-
effect transistor on flexible substrate




Graphene

field
-
effect transistor on flexible substrate

poly(styrene
-

block
-
methyl
methacrylate
-
block
-
styrene) (PS
-
PMMA
-
PS)

triblock

copolymer

Process:

(1)
[EMIM][TFSI] : PS
-
PMMA
-
PS : solvent


= 0.7 : 9.3 : 90 (w/w)

(2) Drop
-
casted onto
graphene

(3) After the solvent was removed, an ion gel


film was formed through physical


association .

(4) Deposit gate electrodes (shadow mask)

7

Ion gel

=

+

+

solvent

+ :[EMIM]


-

:[TFSI]

凝膠




Graphene

field
-
effect transistor on flexible substrate

Electric double layer (EDL)



EDL capacitor with a dielectric of
sub


nanometer

thickness



Ion gels provided a specific


capacitance of
5.17
μF
/cm
2

at 10 Hz



FET devices can operate within a


low voltage region (~3 V) with a high on
-


current (~
mA
) on Si substrate.



Due to the ultrahigh capacitance of the ion


gel gate dielectric yielded this low
-
voltage,


high
-
current operation

8

C
-
V measurement




Graphene

field
-
effect transistor on flexible substrate

Transfer to PET substrate



Hole mobility: 203
±

57 50 cm
2
/Vs


Electron mobility: 91
±

50 cm
2
/Vs (at V
D
=
-
1 V)



Only 20% changes in
μ/μ
o

were

observed as the


bending radius was changed from 6 to 0.6 cm

9



Problem:


Low ON/OFF, gate electrode dimensions…




Carbon
-
based
logic gate
on flexible substrate

10

Graphene

: low ON/OFF but easily for large area fabrication

CNT: high ON/OFF but complicated fabrication



Using
graphene

as the electrode and CNT as device channel



All carbon

based field effect transistor on flexible substrate

5 layer
graphene


as electrode (270 Ω/

)

Network SWCNTs

as device channel

11




Carbon
-
based
logic gate
on flexible substrate



Using high source
-
drain current
to break metallic CNTs



Small hysteresis
that is caused by the interface trap states parasitized between


the gate electrode and dielectrics



Graphene
-
CNT device showed both a
high transmittance of 83.8%,
due to highly


transparent monolayer
graphene

for electrodes



12




Carbon
-
based
logic gate
on flexible substrate



Due to the
bundle problem of


CNTs
, the random network CNT


channels were optimized


as a function of CNT density and


channel width

The inverter gain was approximately 1.4,
and a supply voltage of 0
-
5 V was enough
to provide the switching functions



The PMOS inverter consisting of two p
-
type transistors

Reasonable device performance, such as
an on/off ratio of approximately 10
3

and a

mobility of approximately 81 cm
2
/Vs were
achieved at a density of 7.5 SWCNTs μm
-
1
.




Carbon
-
based
logic gate
on flexible substrate

13

Bending and stretching test


Carbon
-
based materials such as CNTs and
graphene

have large
potential in flexible electronics



Due to low temperature and printing process, ion gel can be
used as good gate dielectric of carbon
-
based field effect
transistor on flexible substrate



Using multilayer
graphene

as electrodes and network SWCNTs
as
device channel can
achieve the all carbon logic gate circuit
for transparent and flexible application

14

Summary