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Report
特色研究計畫-以刮刀塗佈技術製備垂
直式有機電晶體用於低成本有機發光
顯示器
交通大學物理研究所 孟心飛
交通大學光電系
冉曉雯
有機半導體實驗室研究生:
趙寅初、王凱瑞、徐永軒、羅芳財、
黃建豪、呂季遠、林洪正、蔡武衛
Limits of organic field-effect transistor
Long channel length ~ 5 micron
High operation voltage ~ 10 V
Low output current
Organic semiconductor
Vertical space-charge-limited transistor
Organic solid-state vacuum tube
Jc ~ 0.01 mA/cm2
App. Phys. Lett. 88, 223510(2006)
Space-charge-limited current (SCLC)
• No background carrier
• Current by injected carriers
• Organic semiconductor valence band in place of vacuum
Grid base fabrication
polystyrene nano-spheres as mask
O2 plasma
Advantages of SCLT




Short vertical channel ~ 300 nm
Low operation voltage ~ 2 V
No lithography for base grid
OLED driving


High current density ~ 100 mA/cm2
High aperture ratio by stacking
OLED driven by SCLT
Light emission




OLED efficiency 10 cd/A
Jc = 50 mA/cm2
Luminance = 5000
cd/m2
Active matrix by blade
coating
Ag
Al
TBPi
PO-01-TB
CBP
NPB
PEDOT
Al
OLED
SCLT
Cathode
Al
P3HT
Al
LiF
ETL
EML
HTL
MoO3
Collector
Al
Base
PVP
MoO3
Al
Glass
Emitter
Multi-layer blade coating of
organic semiconductors
50 -100 micron
moving gap
Rapid evaporation
Polymer film (wet)
Polymer film (dry)
ITO Substrate
Hot plate
Polymer solution
Gap
Emission
• layer
Multi-layer solution deposition for
energy
cathode
Electron
blocking
Emissive
Hole
blocking
anode
Appl. Phys. Lett. 93, 153308 (2008)
•
•
•
•
high efficiency
Arbitrary solvent
Large area uniformity
Low material waste
Compatible with roll-to-roll
process
Blade coating for OLED and vertical transistor
Organic layer
ITO
Hot plate
ITO
Hot plate
4×4 cm2
OLED
ITO
Hot plate
J. Appl. Phys. 110, 094501 (2011)
Hot wind
ITO
Hot plate
Other applications
RFID
Pressure sensor array



App. Phys. Lett. 95, 253306 (2009)
Short channel length
Short carrier transit
time
High frequency
Progress of SCLT performance
enough for OLED driving
2008-2012 國科會 卓越領航計劃
2011 交大 特色計劃
Enhancing the base control
Al (collector)
P3HT
base
350 nm
AlOx
AlOx
Al
Al
Al
• enlarge P3HT thickness
PVP
PVP
PVP
• enable large base potential (2.5 V)
to provide better control on channel
200 nm
• reach on/off ratio 300000 at 1.5 V
ITO (emitter)
Glass
Appl. Phys. Lett., 97, 223307, 2010
10
2.5% wt
3.5% wt
4.5% wt
1E-4
1
10
-1
10
-3
10
-5
10
-7
2
JC (mA/cm )
2
P3HT mobility (cm /V-s)
• enlarge PVP thickness
AlOx
1E-5
500
1000
1500
2000
2500
3000
3500
4000
VBE =
-1.10V
-0.50V
0.10V
0.70V
1.30V
1.90V
2.50V
0.0
0.5
1.0
-VCE (V)
1.5
Enhancing the base control
Al (collector)
P3HT
base
100 nm
AlOx
AlOx
AlOx
AlOx
Al
Al
Al
Al
PVP
PVP
PVP
ITO (emitter)
Glass
PVP
• reduce channel diameter (from
200 nm to 100 nm) by using PS
spheres with 100-nm diameter
• enlarge(b)
channel aspect ratio and
enhance base control
• obtain superior switching swing as
96 mV/dec (close to c-Si MOSFET
theoretical value, 60 mV/dec) with a
on/off ratio as 20000.
Appl. Phys. Lett. 98, 223303, 2011
(c)
(d)
2011 Breakthrough
toward a real technology

Jump in collector current



Organic semiconductor blade coating
Self-assembled monolayer
PS sphere by blade coating
2011 Breakthrough
toward a real technology

Jump in collector current



Organic semiconductor blade coating
Self-assembled monolayer
PS sphere by blade coating
Conduction in Organic Semiconductors



Van der Walls forces hold
molecules together
Charge transport is
dependent on -bonding
orbitals and quantum
mechanical wave-function
overlap (by hopping).
Effective mobility increases
with increasing temperature
and increasing carrier
concentration
Space-charge-limited current:
J 
9
8
 r 0 
V
L
2
3
Anisotropic Transport


Charge transport in most organic semiconductor
including conjugated polymers is anisotropic.
Field-effect hole mobility in P3HT is higher than
0.1 cm2/Vs along the polymer backbone and the
- orbital stacking and is lower than 2×10-4
cm2/Vs along the insulating side chain
E.g. P3HT: poly(3-hexylthiophene)
Q: How to improve the output current
in organic transistor ?
A: Improving molecular packing in the
right direction!
For conventional FET:
Current flows in lateral direction.
Edge-on direction is required to obtain high mobility.
Reported methods:
Using high boiling point solvent to improve molecular packing
Using solvent annealing to improve molecular packing
Using SAM to control orientation !!
SAM treatment in OFETs


Nature 5, 222, 2006
SAMs (Self-Assemble Monolayers): HMDS and OTS
on SiO2 for P3HT FET
S
SAM
D
P3HT
Oxide
Gate
Our idea : SAM on vertical sidewalls
Conditions:
1.SAM: (a) HMDS and (b) OTS
1.Top injection :
a) using symmetric EC metal to reduce built-in potential barrier
b) Using MoO3/Al to adjust emitter work function as 5.3 eV
2.P3HT @ CB by both spin coating and blade coating (without spinning)
Results: improved pore filling

After OTS treatment, pore surface
becomes hydrophilic
STD (no SAM), spin coating
STD, blade coating
OTS treated, spin coating
Results: improved bulk mobility
OTS treated time : 2 (hours)
-2
2
Mobility(cm /Vs)
10
-3
10
-4
10
Spin-coating
STD OTS-18
450nm 450nm
Blade-coating
STD OTS-18 OTS-18
450nm 450nm 350nm
Results: material analysis
a
1800
OTS-18 treated
without SAM
1600
1200
P3HT
1000
800
600
Glass
400
P3HT
1200
1000
800
600
G lass
400
200
0
0
Out of plane
-200
0
5
10
1.0
15
20
0
25
d
0.8
0.6
Glass
0.4
0.2
OTS-18 treated
without SAM
500
550
600
650
Wavelength(nm)
700
5
10
15
20
Diffraction angle (2 Theta)
P3HT
0.0
Out of plane
-200
Diffraction angle (2 Theta)
Photoluminescence(a.u.)
OTS-18 treated
without SAM
1400
200
c
1800
1600
Intensity(a.u.)
Intensity(a.u.)
1400
b
750
25
Results: transistor performances
a
2
2.4 (V) , 54.7 (mA/cm )
2
10
0
10
-1
10
-2
10
10
-1
10
-2
10
-3
10
-4
JC
-5
JB
10
on/off ratio 10486 at 1.68V
0.0
0.5
1.0
1.5
-VCE(V)
2.0
2.5
0V
0.6V
1.2V
0V
0.6V
1.2V
0
-3
-4
VCE=
10
10
10
2
10
1
2
1
2
VBE(V)=
-0.90
-0.35
0.20
0.75
1.30
1.85
2.40
10
-JC(mA/cm )
c
3
10
-J(mA/cm )
b
VCE=-2 V
3.0
10
-1.0
-0.5
0.0
0.5 1.0
VB(V)
1.5
2.0
2.5
2011 Breakthrough
toward a real technology

Jump in collector current



Organic semiconductor blade coating
Self-assembled monolayer
PS sphere by blade coating  compatible
to roll-to-toll process
Blade coating PS spheres
(a) PS sphere blade coating
(b) Conventional Dipping Method
PS Sphere Distribution in 1cm2
1 cm
1 cm
Active Region
Transistor Performance
(Blade Coating PS Spheres)
小面積(1mm2)元件輸出特性
大面積(1cm2)元件輸出特性
On/off ratio ~ 40000
On/off ratio ~ 5000
0
2
-VCE (V)
V
BE
-1
-0.60V
-0.40V
-0.20V
0.00V
0.20V
0.40V
0.60V
10
2
10
-1.20V
0
-0.60V
10
0.00V
-1
0.60V
10
1.20V
-2
1.80V
10
2.40V
-3
10
-4
10
-5
10 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
Jc (mA/cm )
1
Jc (mA/cm )
10
VBE
-2
10
-3
10
-4
10
-5
10
0.0 0.2 0.4 0.6 0.8 1.0 1.2
-VCE (V)
Al/MoO3
pattern
Top Emitter
Connected OLED/SCLT
VE
IE
VB
on
IB
VC
IC
-4.60E-04
4.50E+00
0.00E+00 4.33E-04 -9.00E-01
1.09E-05
-4.45E-04
On state
4.50E+00
0.00E+00 4.43E-04 -9.00E-01 1.16E-05
VE
IE
VB
off
IB
VC
IC
-1.96E-04
4.50E+00
Off state
0.00E+00 1.43E-04 0.00E+00
5.07E-05
-1.94E-04
4.50E+00
0.00E+00 1.44E-04 0.00E+00 5.21E-05
Total voltage : 6 V (across OLED and SCLT)
ON state: Base voltage = -0.9 V;
OFF state: Base voltage = 0 V
42-b
Other solution-processed OTFT
Field-effect
mobility
Operation
voltage
On/off
ratio
Channel material
Gate dielectric
2005 [JACS]
0.004
<2V
100
P3HT
Polymer dielectric CPVP-C6 (thickness 10-20 nm)
2005 [ APL]
0.005
< 2V
200
P3HT
SAM
2006 [Nature
Material]
0.2-0.7
> 20 V
> 106
PBTTT
OTS-treated SiO2
2007 [OE]
0.017
<2V
3600
P3HT
Plasma oxidation on Al gate
2007 [APL]
0.2 ~ 1.8
> 10 V
> 106
TIPS
HMDS-treated SiO2
2007 [JACS]
0.1
<2V
105
P3HT
Ion-gel gate dielectric (for top gate); gel solution
mixed with stirring over 12 hrs
2008 [Nature
Materials, Adv.
Mat.]
1.8
1.6
0.8
<3V
104~10
5
P3HT
PQT-12
F8T2
Ion-gel gate dielectric (for top gate); slow
process: solvent evaporated for 24 hrs and the
ion-gel dried in vacuum over 2 days
2008 [Nature
Material, JACS,
APL]
1.5
> 20 V
> 106
diF-TESADT
PFBT-treated gold electrodes with HMDS-treated
SiO2
2009 [Adv. Mat.]
0.15
> 30 V
36700
PETV12T
PMMA, 500 nm
2009 [ Adv. Mat.]
0.34
0.1
0.1
> 20 V
N/A
PBTTT
P3HT
PQT-12
OTS-treated SiO2
2011 [ Adv. Mat.]
7-11
> 20 V
> 106
C8-BTBT or
C10-DNTT
CYTOP (Asahi Glass Co. for top-gate)
2011 [AIP
Advances]
3.5
> 20 V
> 106
C8-BTBT
FTS-treated SiO2
Summary



With high output current , low operation
voltage and high on/off current ratio, vertical
transistor SCLT is one of the best solution
processed transistor in the world.
Blade coating is successfully demonstrated on
OLED and SCLT. Particularly, blade coating PS
spheres facilitates the roll-to-roll large area
nanostructure colloidal lithography .
Solution processed OLED can be switched on
and off by SCLT within 1-V base voltage.
Future Work




Develop process for integrated solutionprocessed OLED/SCLT.
Develop large-area array process for
SCLT.
Integrate large-area SCLT array with
large-area OLED to realize low-cost ebook (based on blade coating process).
Proposed process is introduced hereafter.
Integrated OLED / SCLT
Light emission
Two Approaches:
 Fabricating OLED on top
of SCLT
 Connecting large-area
OLED with SCLT array
panel
Light emission
Glass
OLED
Glass
Ag
Al
TBPi
PO-01-TB
CBP
NPB
PEDOT
Al
OLED
Al
SCLT
Cathode
P3HT
Al
LiF
ETL
EML
HTL
MoO3
Collector
Al
Base
PVP
MoO3
Al
Glass
Emitter
Proposed Large Area Process
(示意圖,基板可放大)
100 um
10 um
Tentative process to define the bottom metal electrode:
Low-end lithography with lift-off process, blanket bar coating (similar to
blade coating) or interference lithography
Proposed Large Area Process
(示意圖,基板可放大)
100 um
10 um
 PVP coating and cross-linking
 10-um wide PR line formation (low-end photolithography, blanket bar
coating or interference lithography)
 PS spheres coating on PVP
Proposed Large Area Process
(示意圖,基板可放大)
100 um
10 um
 Base metal deposition with PR lift-off process
 Removing PS spheres by roller taping
Proposed Large Area Process
(示意圖,基板可放大)
100 um
10 um
 Plasma etch through nanometer holes
 SAM treatment on nanometer holes
 P3HT coating
Proposed Large Area Process
(示意圖,基板可放大)
100 um
10 um
 Passivation layer formation
 Pixel contact via formation and metal coating (patterned by liftoff process)
 Then: fabricating large-area OLED on top of array panel or connecting array
panel with OLED (on the other substrate)
Demonstration


PS sphere blade coating process.
Solution processed OLED switched on and off
by SCLT within 1-V base voltage.

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