Organic Thin Film Transistor

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Organic Thin Film Transistor
Edited by Song Ho, Kim
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Contents

• 1. What is the OTFT?
• 2. Structure of OTFT
• Application of OTFT
• Mechanism Operation
• 5. Pentacene TFT
• - Proposed Research
• - Fabrication of Pentacene TFT
• Characteristics Analysis
• 6. OTFT Materials

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What is the OTFT(organic thin-film transistor)?

• First Organic Transistor - 1986
• Using organic molecules (Polymers) rather than
  silicon for their active material.
• Semiconductor
• Advantages
• Less Complex Lower-cost Fabrication
• Solution Processing ?? Photolithographic
  patterning
• lower temperature manufacturing (60-120 C)
• Print-able Organic Transistors
• Mechanical flexibility
• compatibility with plastic substances foldable
  light weight
• Strong Optical Absorption and Efficient Emission

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Structure of OTFT (1)
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Structure of OTFT (2)
Various Structures of Organic Thin-Film Transistor
Drain
Source
Semiconductor
Dielectric
Gate/Substrate
Bottom-Contact
Top-Contact
Top-Gate
Bottom-Gate
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Structure of OTFT (3)

• Differences
• Carrier Transport
• Discrete Energy Levels
• Hopping
• Organic Active Layer
• Depletion Devices

• Very Similar to MOSFETs
• 3-Terminal Device
• Voltage Controled Switch

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Application of Organic TFT (1)
OLED Device
OLED Display
Liquid Crystal Device
Plastic TFT LCD
Organic Thin Film Transistor
E-paper, E-book
E-ink
Contactless Smart Card
Antenna
Materials Integration Technology
Wearable Computer
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Application of Organic TFT (2)
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Mechanism of Operation
bias on gate
negative
positive
hole accumulation in pentacene
depletion
hole flows to drain
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Pentacene TFT
substrate - corning 7059 glass gate
metal - Nickel gate dielectric
- SiO2 source/drain metal -
Palladium All deposition was performed by
Ion beam sputtering
Penn. state Univ.
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Proposed Research
1. Fabricate Pentacene TFT - gate
insulating layer with high dielectric constant
- reproducible patterning of pentacene film
- source/drain metal with large work
function - arrays of pentacene TFT 2.
Measurement Analysis - Vg- Id curve
- mobility, threshold voltage, subthreshold
slope 3. Evaluation
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Schematic Figure of Pentacene TFT
substrate - glass (Corning 7059)
gate metal - Al, Ni, Cr gate
dielectric - SiO2, V2O5, Al2O3
source/drain metal - Au active layer
- pentacene passivation layer
pentacene active layer
drain
drain
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Process Factors
Interfacial effect of metal/gate dielectric
- contact resistance, diffusion, dielectric
properties Adhesion of material - film
lifting, process unstableness Making smooth
film - the small surface roughness leads to
molecular ordering Photolithographic condition
for pentacene patterning - thickness of
resist, expose time, develop time -
resist/pentacene interface effect
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Fabrication Flow Chart
Gate sputter, evaporation wet etching
Gate dielectric sputter dry etching (RIE)
Source/drain sputter, evaporation wet etching,
lift-off
Pentacene ICBD, evaporation wet dry etching
Passivation CVD dry etching (RIE)
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Gate Dielectric Layer
Requirement fabricated at low temperature ( lt
300C) smooth surface roughness have a high
capacitance with low leakage current good
phase stability reproducibility
SiO2, V2O5, Al2O3
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Analysis of Gate Dielectric Layer
C-V
Electrical characteristics
I-V
Deposition by Reactive sputtering
AFM
Roughness
I-V
Au deposition on gate dielectric and annealing
Interfacial effect
RBS
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C-V Analysis of V2O5 Dielectric Material

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Deposition of Pentacene Film
 
Deposition technique
Evaporation ICBD (Ion Cluster Beam
Deposition) expected to evaluate
pentacene properties
Simple structure
estimate pentacene properties
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Patterning of Pentacene Film
Photolithographical method - using
photosensitized PVA as negative photoresist -
UV expose develop in water - etching
unwanted pentacene layer in oxygen plasma -
baking to remove water in pentacene layer
photosensitized PVA
pentacene
dielectric layer
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Operation Characteristics
Field effect mobility(?fe ) and the threshold
voltage(Vth) were obtained in the saturation
region using the relation Positive threshold
voltage arise from an initial accumulation layer
at the pentacene/dielectric interface -
positive gate voltage is required to turn the
device fully-off Large on/off current ratio can
be obtained with small gate voltage swing
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Different Structure of Pentacene TFT
pentacene active layer
3 mask steps no overlap gate-source,
gate-drain
gate dielectric
gate
source
drain
substrate
pentacene layer is normally conducting
no overlap gate-source, gate-drain large
drain current to flow at zero gate bias
devices are turned off by applying positive gate
bias transistor operating in depletion mode
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Structure of Pentacene
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Organic Semi-Conductors of Processing Type
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p-Type Materials of OTFT
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p-Type Materials
Structure and mobility of fused aromatic Compounds
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p-Type Materials
Oligo-thiophenes and Oligo-phenylenes
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p-Type Materials
Thiophenylenes and their mobilities
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p-Type Materials
Conjugated polymers for FET
Polythiophene materials for FET
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Hall Mobility Change of Polythiophenes
Hall mobility change of Poly(2-alkylthiophene)s
by arrangement and stereo chemistry
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n-Type Materials of OTFT
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Electron Mobilities of n-Type Materials
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n-Type Materials
Quinodimethane compounds
Tetracarboxylic anhydrides
Phthalocyanines
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n-Type Materials
Fluorinated n-type materials
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Physical Properties of Organic Dielectric
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Trends of OTFT Materials(Domestic)
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Trends of OTFT Materials(Abroad)
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Problem and Solution of OTFT
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Reference
1) ??? ??? ?? ? 17? 1? 2006? 2? ????? ?? ???,
??? 2)??? ??? ?? ? 14? 5? 2003? 10? ???????
?? ???? ?? ???,???,???,??? 3) ??? ??? ?? ? 15?
6? 2004? 12? ?????????? ???? ???,???,
???, ??? 4)???? 04/06 50 ??? OLED?? ? OTFT ???
???? ??? 3)??? ??? ?? ? 14? 1? 2003? 2? ??
???, ??? 5) University of the South Sewanee,
Tennessee September 2002, Eugene Donev
Designing and Implementing Organic Thin-Film
Transistors (OTFTs) 6) Adv. Mater. 2000, 12, No.
7 p.481 , Groenendaal, Friedrich Jonas, Dieter
Freitag, Harald Pielartzik, and John R.
Reynolds Poly(3,4-ethylenedioxythiophene) and
Its Derivatives Past, Present, and Future
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Reference
7) Ali Ali Afzali Afzali, Christos Christos D. D.
Dimitrakopoulos Dimitrakopoulos IBM Research
Division T. J. Watson Research Center T. J.
Watson Research Center Yorktown Heights, NY
Synthesis and Application of Pentacene Precursor
in OTFT 8) Chang Feng Yu ,Ching Fu Hsu, Yao Peng
Chen, and Yu Hua Ma Department of Information
and Communication Engineering Chaoyang University
of Technology Dependence of field-effect
mobility on the gate field for Pentancene
OTFTs 9) http//chem3.snu.ac.kr/
shlee/OTFT.htm 10) http//www.postech.ac.kr/
ce/lamp/research-4.html 11) http//www.organicid.c
om/structure.html