organic thin film transistor

ICML Hanyang University

Polymeric Materials for Information & Communication

Organic Thin Film Transistor

Edited by Song Ho, Kim



1. What is the OTFT?

2. Structure of OTFT

3. Application of OTFT

4. Mechanism Operation

5. Pentacene TFT

- Proposed Research

- Fabrication of Pentacene TFT

Characteristics & Analysis

6. OTFT Materials

Contents



• 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

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



Structure of OTFT (1)




Various Structures of Organic Thin-Film Transistor

Bottom-Contact Top-ContactTop-Gate

Bottom-Gate

Source Drain

DielectricSemiconductor

Gate/Substrate



• Very Similar to MOSFETs

• 3-Terminal Device– Voltage Controled Switch


•Differences –Carrier Transport

•Discrete Energy Levels•Hopping

–Organic Active Layer–Depletion Devices



Organic Thin Film Transistor

OLED Device

Liquid Crystal Device

E-ink

Antenna

MaterialsIntegration Technology

OLED Display

Plastic TFT LCD

E-paper, E-book

Contactless Smart Card

Wearable Computer

Application of Organic TFT (1)



FlexibleOLED

FlexibleLCD

OrganicMemory

ImageSensor

BioSensor

OrganicLaser

Smart CardRFID Tag

E-paper

OTFT

ICTechnology

OpticalTechnology

BioTechnologyApparel

Technology

SensorTechnology

Memory device

Technology

LCDTechnology

OLEDTechnology

E-PaperTechnology

ElectricalFabric

Application of Organic TFT (2)



_

_

gate

gate dielectric

pentacenesource drain

glass substrate

bias on gate

hole accumulation in pentacene

negative

hole flows to drain

positive

depletion

Mechanism of Operation



• substrate - corning 7059 glass • gate metal - Nickel • gate dielectric - SiO2

• source/drain metal - Palladium All deposition was performed by

Ion beam sputteringPenn. state Univ.

Pentacene TFT



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

Proposed Research



drain

pentacene active layer

• substrate - glass (Corning 7059)

• gate metal - Al, Ni, Cr

• gate dielectric - SiO2, V2O5, Al2O3

• source/drain metal - Au

• active layer - pentacene

• passivation layer

substrate

gatesource

gate dielectric

passivation layer

drain

Schematic Figure of Pentacene TFT



• 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

Process Factors



Gate sputter, evaporation

wet etching

Gate sputter, evaporation

wet etching

Gate dielectric sputter

dry etching (RIE)

Gate dielectric sputter

dry etching (RIE)

Source/drain sputter, evaporation

wet etching, lift-off

Source/drain sputter, evaporation

wet etching, lift-off

Pentacene ICBD, evaporation

wet & dry etching

Pentacene ICBD, evaporation

wet & dry etching

Passivation CVD

dry etching (RIE)

Passivation CVD

dry etching (RIE)

Fabrication Flow Chart



Requirement • fabricated at low temperature ( < 300°C) • smooth surface roughness • have a high capacitance with low leakage current • good phase stability

• reproducibility

SiO2, V2O5, Al2O3

Gate Dielectric Layer



C-VC-V

I-VI-V

AFMAFM

Electrical

characteristicsElectrical

characteristics

RoughnessRoughness

Interfacial

effectInterfacial

effectRBSRBS

I-VI-VAu deposition on gate dielectric

and annealing

Au deposition on gate dielectric

and annealing

Deposition by

Reactive sputtering

Analysis of Gate Dielectric Layer



-5 0 5 10 15

0.0

2.0x10-7

4.0x10-7

6.0x10-7

8.0x10-7

1.0x10-6

R.T

200µµ 2hr

200µµ 3hr

300µµ

400µµ

SiO2

Cap

acit

ance

(

F/c

m2)

Voltage (V)

C-V Analysis of V2O5 Dielectric Material



• Evaporation • ICBD (Ion Cluster Beam Deposition)

expected to evaluate pentacene properties

Deposition technique

Simple structure

estimate pentacene properties

Deposition 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

dielectric layerpentacenephotosensitized PVA

Patterning of Pentacene Film



• 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

Operation Characteristics



substrate

gate

pentacene active layer

source

gate dielectric

drain

• 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

• 3 mask steps

• no overlap gate-source, gate-drain

Different Structure of Pentacene TFT



Number Name133 Pentacene

Benzo[b]naphthacene 2,3:6,7-Dibenzanthracene beta,beta'-Dibenzanthracene 2,3,6,7-Dibenzoanthracene lin-Dinaphthanthracene lin-Naphthanthrene

CAS: 135-48-8 M W: 278 L / B: 2.226Width: 7.447 Length: 16.577 Thickness: 3.885

Structure of Pentacene



Organic Semi-Conductors of Processing Type



p-Type Materials of OTFT



Structure and mobility of fused aromatic Compounds

p-Type Materials



Oligo-thiophenes and Oligo-phenylenes

p-Type Materials



Thiophenylenes and their mobilities

p-Type Materials



Polythiophene materials for FET

Conjugated polymers for FET

p-Type Materials



Hall mobility change of Poly(2-alkylthiophene)s by arrangement and stereo chemistry

Hall Mobility Change of Polythiophenes



n-Type Materials of OTFT



Electron Mobilities of n-Type Materials



Tetracarboxylic anhydrides

Quinodimethane compounds

Phthalocyanines

n-Type Materials



Fluorinated n-type materials

n-Type Materials



Physical Properties of Organic Dielectric



Trends of OTFT Materials(Domestic)



Trends of OTFT Materials(Abroad)



Low conductivity and low carrier mobility of Organic semi-conductor

Structure of General FETLow Current and low operating speed

Improvement of physical propertiesSearching of New materials

Improvement ofDevice Structure

New mechanism

High puritycrystallinity

Phase Transition FET

SIT

Problem and Solution of OTFT



Reference

1) 고분자 과학과 기술 제 17 권 1 호 2006 년 2 월 ‘유기반도체 재료’ 하승규 , 권오식2) 고분자 과학과 기술 제 14 권 5 호 2003 년 10 월 ‘ 유기트랜지스터 재료 연구개발 동향’ 권순기 , 김윤희 , 김형선 , 안준환3) 고분자 과학과 기술 제 15 권 6 호 2004 년 12 월 ‘ 고분자박막트랜지스터 개발동향’ 김보성 , 이용욱 , 홍문표 , 정규하 4) 화학세계 04/06 50 ‘ 단분자 OLED 재료 및 OTFT 재료의 개발동향’ 권순기3) 고분자 과학과 기술 제 14 권 1 호 2003 년 2 월 ‘유기’ 하승규 , 권오식5) 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’



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.com/structure.html

organic thin film transistor

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