This document provides an introduction to organic electronics and flexible display technology, specifically focusing on organic thin-film transistors (OTFTs) and the company Plastic Logic. It discusses key milestones in organic electronics, principles of organic semiconductors and materials, properties and operation of OTFTs, and Plastic Logic's introduction and development of flexible displays using OTFT backplanes. It also covers challenges in establishing volume manufacturing of organic electronics, including process optimization, yield enhancement, and material and defect analysis.

1. Organic Electronics –
Introduction to OTFT & Plastic Logic’s
Flexible Display Technology
Dr. Octavio Trovarelli | 12th Dresden Microelectronics Academy | September 7, 2012

2. Introduction to Organic Electronics
Outline
● Organic Electronics – Key Milestones
● Principles of organic semiconductors and materials
● OTFT and properties
● Plastic Logic - Introduction
● Challenges in Establishing Volume Manufacturing
● Technical achievements and potential applications
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3. Organic Electronics – Some Key Milestones
● First organic TFT demonstrated (1986): low mobility <10-4 cm2/Vs
● First demonstration of clean field-effect mobilities within an order
of magnitude to that of a-Si: pentacene (1995), poly-3-
hexylthiophene (1997)
Current status:
● Mobilities of 0.1 – 1 cm2/Vs achievable now in a range of solution
PARC
processed OSCs (p-type & n-type)
● Reliability comparable to a-Si (p-type)
Demonstrators / Applications:
● First demonstration of integration of OTFT backplane with e-paper
(Lucent / E-Ink 1998) PolyIC
● Demonstration of 13.56 MHz (non-standard) RFID tag (Philips,
PolyIC 2007)
● QQVGA of flexible OLED display driven by OTFT backplane
(Sony 2007)
● 2007: Announcements by Polymer Vision and Plastic Logic to
commercialise OTFT technology in e-paper displays
Sony
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4. Why Organic Electronics?
Some advantages
● Organic transistors can be manufactured at relative low-T
compared to single-crystalline Si (>800°C) or a-Si:H
(>200°C), and
● On flexible plastic substrates (and even paper) on large
scales!
● Enabling novel products foldable, bendable, rollable, thin,
ultra-light, robust…
Comparison to conventional Si-based electronics
● Basic operation of OTFTs and MOSFET have similarities
and differences (see next pages)
● Materials, device structures and performance are very
different
● Plastic circuits not expected to replace silicon but…
… one should instead look for new and emerging applications
where inorganic transistors cannot be used due to their mechanical properties or cost.
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5. Organic Material Characteristics
● Organic Semiconductors: formed by conjugated organic materials – alternating single and
double bonds between covalently bound C- atoms
● Delocalised π-electrons provide both conduction and valence bands
Example: Benzene poly (p-phenylene)
t0
t1
+ -
- + Energy
+ -
+ - -
- + +
-
+ 4 t1
LUMO
π* “conduction” band
2 t0
π “valence” band
+
+ - 4 t1
-
HOMO
+
Density of States H. Sirringhaus
Unique attributes of organic semiconductors:
● Science: Low-dimensional, molecular semiconductors with strong electron – ion and electron
- electron interactions
● Technology: Compatible with solution-processing and direct-write printing; low-T processing
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6. Examples of “p-type” Organic Semiconductors
µ = 1-5 cm2/Vs
µ = 0.1 cm2/Vs
µ = 15-20 cm2/Vs
µ = 0.6 cm2/Vs
H. Sirringhaus
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7. Low-Temperature Solution Processing
Challenges:
● Control of molecular self-assembly from solution
● Understanding of defects
● Effect of dynamic disorder on electronic properties
S. Tretiak, LANL
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8. Organic Thin Film Transistors
● Organic Transistors are Field-Effect-Transistors (FET)
● Typical Structures:
H. Klauk
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9. Organic Thin Film Transistors
Typical material
● Typical contacting for p-type OTFT: thicknesses:
~0.1µm
~1µm
● Example of typical I-V characteristic curves of Pentacene-based p-type OTFT:
H. Klauk
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10. Transport in Organic Semiconductors
Polycrystalline Pentacene
Factors influencing mobility in organic semiconductors:
● Overlapping degree of conjugated π-systems
● Chemical purity
● Neighbour molecules
● Degree of molecular order (crystallinity)
● Energy density and distribution of localized states
Typical values of mobilities of organic materials (RT):
10-5 – 10 cm2/Vs
Comparison: channel carrier mobilities in FET
Polycrystalline
a-Si:H Poly-Si Crystalline Si
Pentacene
~500 cm2/Vs (e-)
0.1 – 1 cm2/Vs ~0.5 cm2/Vs >50 cm2/Vs
~200 cm2/Vs (h+)
H. Klauk
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11. Mobility & Transistor Performance
limitations Logic
PolyIC
OLED displays
Sony
A. Salleo
Flexible E-paper displays
Vsd
I sd = W ⋅ µFET ⋅ Ci ⋅ (Vg − VT ) ⋅
L
Material challenges:
Plastic Logic
● High mobility
● Purity, stability in air, not toxic, solution processing
● Cost effective, high-volume availability, manufacturability
● Reliability: stable I_sat, V_th during product life-time
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12. OTFT – Basic Differences to MOSFET
● OTFT: “intrinsic” semiconductor in the channel and in the S / D contact region
● OTFTs operate in accumulation and not in inversion mode
● No selective doping no p-n junctions as in Si-MOSFETs
● “Shottky”-type barriers existing at the contacts:
Example of p-type OTFT:
barrier (ϕm >> EA) blocks e-
injection from D contact to LUMO
H. Klauk
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13. OTFT – Work Function Matching
● In general, HOMO-LUMO energy difference is large only one carrier type can
be efficiently injected / extracted
● Difficulty of CMOS technology with organic materials
H. Klauk
p-type n-type
Copper-Phthalocyanin F16CuPc
(CuPc)
Work function of Pentacene
some metals (eV)
Au 5.1 – 5.47
Pd 5.22 – 5.6
X = 3eV
IP = 4.9eV
Ca 2.87 X = 2.7eV X = 4.5eV
IP = 4.8eV IP = 6.3eV
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14. Origins of Plastic Logic
Cambridge became a scientific epicentre for the field of plastic electronics:
A research group of top scientists headed by Prof. Sir Richard Friend and Prof. Henning
Sirringhaus has a track record of world-leading innovations:
● Discovery of polymer electroluminescence in 1989
● Discovery of polymer electroluminescence in 1989
● First polymer FET (1988)
● First integration of polymer FET with polymer LED (1998)
● First polymer FET with mobility of 0.1 cm2/Vs (1999)
● Inkjet printing process for polymer FETs (2000)
● First n-type polymer FET (organic CMOS) (2005)
● First ambipolar light emitting transistor (2006)
● First ambipolar polymer FET with mobility > 2 cm2/Vs (2011)
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15. The Company Plastic Logic
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16. Plastic Electronics Technology
● Uses plastic instead of traditional silicon semiconductor and glass
● Fully industrialized flexible displays based on organic electronics
● Enables a revolutionary design and form-factor
Shatterproof, Thin, Large and Light Display
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17. Display Development History (Plastic Logic)
2002: 4x4 TFT 2003: 80x60 50 PPI 2004: 80x60 50PPI 2005: 80x60 100PPI
Array
2008: 1280x960 150PPI 2006: 800x600 100PPI 2005: 80x60 300PPI 2005: 80x60 10PPI
2011: 1920x1440 225PPI 2011: 75PPI Colour 2012: 75PPI Video (b/w & colour)
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18. Plastic Logic - Company History
Technology Development
10+ transistors 100+ transistors 1.2 M transistors Colour EPD 2.8 M transistors
Research, Process Development and Manufacturing
Cambridge Technology Dresden display factory
Cambridge University Center translating research First plastic electronics
Research in organic electronics into products factory in the world
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19. Backplane: OTFT, Pixel and Matrix Array
Pixel Design
Pixel Design (top-down view)
(cross-section)
Display Pixel Array
(top-down view)
Example: S2G2, S4G4, S4G3 pixels addressed
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20. Front plane: Electrophoretic Display Media
™
Principles of Operation
● Oppositely charged reflective submicron pigments are
encapsulated in a clear liquid
● Particles move in opposite directions in an electric field
● Partial capsule imaging is possible enabling high
resolution capability
● Bi-stable, turn the power off – the image stays!
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21. Establishing Volume Manufacturing
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22. Dresden – Center for Organic Electronics
see also: http://www.oes-net.de/en/home.html
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23. Plastic Logic Dresden FAB – Timeline – Major Milestones
● Groundbreaking May 2007
● Fab and Office Buildings Completed
January 2008
● Clean Room
Validation / handover April 2008
● Equipment Move-in,
Installation and Start
April 2008 to August 2008
● Process Installation and Development
September 2008 to December 2009
● Production ramp in 2010
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24. R&D and Production Set-Up
Technology
Transfer
Cambridge R&D
Prototype Line (14”)
Cambridge R&D Prototype Line
● Proof of concepts
● Highly configurable process
● New designs in < 1 month
● 1” Chips to A4 displays
● R&D Engineers
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25. R&D and Production Set-Up
Technology
Transfer
Dresden Factory (Gen 3.5)
Dresden Gen. 3.5 Pilot and Production Facility
● Fully automated backplane manufacturing
● Qualified volume process
● Equipment development with suppliers
● Process and Test development
● Large scale reliability work
● Technology transfer
● Thousands of displays/week
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26. Competence in Organic and Printed Electronics
Manufacturing of OTFTs
● World’s largest flexible OE display (10.7”)
● High density (1.2 m OTFTs per display)
● Large area (Gen 3.5 | 780 x 650 mm | ~11 m OTFTs per glass plate)
● Full scale (24/7)
Development of OTFTs
● Process and stack development for the manufacture of flexible displays
● Material development with suppliers
● Strong IP position
● Unique tool development with suppliers
Broad network
● Wide portfolio of co-operations with suppliers, universities and institutes
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27. Organic Electronic Volume Production Set-Up: Challenges
Adaptation of equipment from the pilot-line set up in Cambridge
● From Lab to standard production equipment for flat panel Gen 3.5
● Industrialization of new specified and developed equipment prototypes
Verification of process specification for stable volume production
● Size of the backplane differs by factor 10! impact on processes
Test of new materials in volume production
● Specifications to be developed
● Selection and qualification of suppliers
Installation of production control and test concept
● Test structures to be developed
● Failure analysis to be developed
Identification of yield- and defects- key drivers
Training, know how for a new team
● with experience in silicon and volume production for new equipment, materials and process flows
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28. Process Differences have Consequences for Equipment
The key differentiators of our technology for organic and flexible
electronics are:
● Solution processing
● Direct-write fabrication techniques to avoid mask-alignment
● Combination of wet coating and dry patterning
● Low process temperatures to permit use of cheap flexible substrates
Our key focus areas for equipment and process know how are:
● Printing, spraying and other deposition of organic and inorganic materials
● Cleaning and conditioning of the layers
● Laser processing for printable electronics
We focus on the manufacturability
of these processes such as:
● Reproducibility
● Homogeneity
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29. Equipment / Process Differences
+ 400nm
Layer thickness [nm]
Equipment /
process 1
Equipment /
process 2
- 400nm
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30. Process Learning & Development
Printing process
Year 1
Thickness mean
Year 2
Thickness mean
Deposition process
Year 1
Thickness mean
Year 2
Thickness mean
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31. OTFT On-Resistance Improvement
Reduction of OTFT On-Resistance by factor of 5 over a year
● Always using the same materials and processes
● „Just“ optimising processing and handling conditions
OTFT Ron – Relative to current target
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32. Yield Enhancement Including Defect Density Improvement
● Defect density analysis throughout all process steps
● Factory and equipment design analysis
● Optical inspections
with defect analysis
Very small Embedded Embedded Surface
embedded particles residues particles
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33. Material Analysis and in-situ Measurements
New organic materials are normally
still analyzed separately in a laboratory
Production requires analysis of:
● Complex samples with layer stacks
● Thickness analysis of layers with
similar composition or behaviour
● In-situ measurements in the production flow
● Local material analysis in µm areas
Layer stacks
State of the art Failure Analysis techniques for Si had to be developed again
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34. Display Testing and Reliability
Test development for transistor and display parameters
● Definition of test specifications
● Electrical and Optical tests for production
● Test methods for OTFT and other characterisation structures
Testing includes handling and alignment of flexible displays
Reliability test development for quality and lifetime behavior
● Accelerated test under different environmental conditions for lifetime projections
● Based on existing models for Si-based integrated circuits
● Parameters adapted to organic materials in terms of
temperature sensitivities and reaction to cycling
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35. Reliability Testing
Name Test Purpose
Thermo cycling TST Mechanical robustness & CTE mismatch
High Temperature Storage HTS Storage of transport conditions
Advance Humidity Storage AHS Stability against moisture ingress
Low Temperature Storage LTS Storage of transport conditions
Real World Usage RWU Display use in non accelerated mode
Advance Humidity Operation AHO Accelerated operation at high humidity
Low Temperature Operation LTO Accelerated operation at low temperature
Ambient Operation AO Accelerated operation at ambient conditions
Solar storage SOR Solar robustness
Altitude test ALT Pressure sensitivity
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36. Reliability Problems During the Development Phase
Defects-driven fails
Line outs during operation
Equipment / Process-driven fails
Delamination during climatic tests Dead pixels during operational stress Inhomogeneity during operational stress
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37. Display Qualification Achieved in 2011
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38. Technical Achievements
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39. Flexible, robust, thin, lightweight and daylight readable OTFT-based displays
Transmissive display
Ultrathin display
Lightweight
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40. Plastic Logic’s Technology in Action
● Flexible Colour Plastic e-paper Display (LINK)
● Incredibly Robust Display: The Stomp Test! (LINK)
● Displays can be literally “cut” in half and they still work! (LINK)
● Demonstrator: Video-Rate Animation (LINK)
… and many more at: http://www.youtube.com/plasticlogic
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41. 41
World Class Leading Investors & Support
Additionally, we also acknowledge financial support from the German “Federal Ministry of
Education and Research“, grant number 13N10225.
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42. Thank You!
Contact: Octavio.Trovarelli@plasticlogic.com
www.plasticlogic.com
Further enquires: info@plasticlogic.com
Follow Plastic Logic!:
Especial thanks to Henning Sirringhaus and Hagen Klauk for some of the illustrations used in this presentation
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