1. 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

2. Limits of organic field-effect transistor
Long channel length ~ 5 micron
High operation voltage ~ 10 V
Low output current
Organic semiconductor

3. Vertical space-charge-limited transistor
Organic solid-state vacuum tube
Jc ~ 0.01 mA/cm2
App. Phys. Lett. 88, (2006)

4. Space-charge-limited current (SCLC)
No background carrier
Current by injected carriers
Organic semiconductor valence band in place of vacuum

5. Grid base fabrication polystyrene nano-spheres as mask
O2 plasma

6. 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

7. OLED driven by SCLT OLED efficiency 10 cd/A Jc = 50 mA/cm2
Light emission
HTL
EML
Emitter
Base
ETL
Collector
LiF
PO-01-TB
CBP
P3HT
PVP Al
MoO3
Glass
NPB
TBPi Ag
OLED
SCLT
PEDOT
Cathode
OLED efficiency 10 cd/A
Jc = 50 mA/cm2
Luminance = 5000 cd/m2
Active matrix by blade coating

8. Multi-layer blade coating of organic semiconductors
micron
gap
moving
Rapid evaporation
Polymer solution
Polymer film (wet)
Gap
Polymer film (dry)
Appl. Phys. Lett. 93, (2008)
ITO Substrate
Hot plate
Emission
layer
Multi-layer solution deposition for high efficiency
Arbitrary solvent
Large area uniformity
Low material waste
Compatible with roll-to-roll process
Electron
blocking
Emissive
Hole
energy
cathode
anode

9. Blade coating for OLED and vertical transistor
ITO
Hot plate
ITO
Hot plate
Organic layer
4×4 cm2
OLED
Hot plate
ITO
Hot wind
Hot plate
ITO
J. Appl. Phys. 110, (2011)

10. Other applications RFID Pressure sensor array Short channel length
Short carrier transit time
High frequency
App. Phys. Lett. 95, (2009)

11. Progress of SCLT performance enough for OLED driving
國科會 卓越領航計劃
交大 特色計劃

12. Enhancing the base control
Appl. Phys. Lett., 97, , 2010

13. Enhancing the base control
Appl. Phys. Lett. 98, , 2011

14. 2011 Breakthrough toward a real technology
Jump in collector current
Organic semiconductor blade coating
Self-assembled monolayer
PS sphere by blade coating

15. 2011 Breakthrough toward a real technology
Jump in collector current
Organic semiconductor blade coating
Self-assembled monolayer
PS sphere by blade coating

16. 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:

17. 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)

18. 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 !!

19. SAM treatment in OFETs Nature 5, 222, 2006
SAMs (Self-Assemble Monolayers): HMDS and OTS on SiO2 for P3HT FET
Gate
Oxide
P3HT
SAM S D

20. Our idea : SAM on vertical sidewalls
Conditions:
SAM: (a) HMDS and (b) OTS
Top injection :
using symmetric EC metal to reduce built-in potential barrier
Using MoO3/Al to adjust emitter work function as 5.3 eV
CB by both spin coating and blade coating (without spinning)

21. Results: improved pore filling
After OTS treatment, pore surface becomes hydrophilic
OTS treated, spin coating
STD (no SAM), spin coating
STD, blade coating

22. Results: improved bulk mobility

23. Results: material analysisb c d

24. Results: transistor performances
VCE=-2 V b c

25. 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

26. Blade coating PS spheres
(a) PS sphere blade coating
(b) Conventional Dipping Method

27. PS Sphere Distribution in 1cm2
Active Region 1 2
1 cm 3
1 cm

28. 1 2 3

29. Transistor Performance (Blade Coating PS Spheres)
小面積(1mm2)元件輸出特性
On/off ratio ~ 40000
大面積(1cm2)元件輸出特性
On/off ratio ~ 5000

30. Connected OLED/SCLT Al/MoO3 pattern Top Emitter Off state On stateVE IE VB IB VC IC
0.00E+00
4.43E-04
-9.00E-01
1.16E-05
-4.50E+00
-4.60E-04
4.33E-04
1.09E-05
-4.45E-04
off VE IE VB IB VC IC
0.00E+00
1.44E-04
5.21E-05
-4.50E+00
-1.96E-04
1.43E-04
5.07E-05
-1.94E-04
On state
Off state
Total voltage : 6 V (across OLED and SCLT)
ON state: Base voltage = -0.9 V; OFF state: Base voltage = 0 V
42-b

31. Other solution-processed OTFT
Field-effect mobility
Operation voltage
On/off ratio
Channel material
Gate dielectric
2005 [JACS]
0.004
< 2 V
100
P3HT
Polymer dielectric CPVP-C6 (thickness nm)
2005 [ APL]
0.005
< 2V
200
SAM
2006 [Nature Material]
> 20 V
> 106
PBTTT
OTS-treated SiO2
2007 [OE]
0.017
3600
Plasma oxidation on Al gate
2007 [APL]
0.2 ~ 1.8
> 10 V
TIPS
HMDS-treated SiO2
2007 [JACS]
0.1
105
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
< 3 V
104~105
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
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
N/A
2011 [ Adv. Mat.]
7-11
C8-BTBT or C10-DNTT
CYTOP (Asahi Glass Co. for top-gate)
2011 [AIP Advances]
3.5
C8-BTBT
FTS-treated SiO2

32. 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.

33. Future Work
Develop process for integrated solution-processed OLED/SCLT.
Develop large-area array process for SCLT.
Integrate large-area SCLT array with large-area OLED to realize low-cost e-book (based on blade coating process).
Proposed process is introduced hereafter.

34. Integrated OLED / SCLT Two Approaches: Fabricating OLED on top of SCLT
Light emission
Two Approaches:
Fabricating OLED on top of SCLT
Connecting large-area OLED with SCLT array panel
HTL
EML
Emitter
Base
ETL
Collector
LiF
PO-01-TB
CBP
P3HT
PVP Al
MoO3
Glass
NPB
TBPi Ag
OLED
SCLT
PEDOT
Cathode
Light emission
Glass
OLED
Glass

35. 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

36. 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

37. 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

38. 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

39. 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)

40. Demonstration PS sphere blade coating process.
Solution processed OLED switched on and off by SCLT within 1-V base voltage.