Challenges in Flexible Electronics Technology

Flexible Display Center at ASU

December 7, 2011

Doug Loy, Ph.D.Associate Director/Director of Technology

Flexible Display Centerdloy@asu.edu

Flex Electronic Challenges

• Intro to Flexible Display Center

• Why Flex

• Manufacturability Issues

• Approaches to flex

• FDC approach: Bond/Debond

• Summary

FDC Overview and Technology Focus

Flexible Display Center

• Founded in 2004

• Government/Industry/University Partnership

• Industrial Facility

• Commercial toolsets: 6” and Gen II Pilot Line

• Professional Staff

Mission

Enabling technology for commercial production of

flexible displays

EVG Advanced Coater

Honeywell Thin Film Material

DuPont Tejion Films (DTF) High Performance

Plastic

Technology

Commercialized

GD Mission Briefer

FFW, PEO Soldier, PM SWAR

FFW SF-PDA

Speed the development and commercialization of flexible display and electronics technology

Provide Technology

Demonstrators

SBIRs

Strategic Partnership with Industry

U.S. Army

SystemIntegrators

Electronic Materials

NC A&T

Applications

Commercial

Space

Security

Military

JTAC

UAV

Ph-AA

Tracking & LocatingHealth Monitors

Secure

Structures

Digital

Radiography

Inflatable craft

and habitatsFrontier

exploration

probes

Flexible

functionality

super-integration

Displays and

Health Monitors

Cyclical Development Program

TFT Autoprober

FDC Custom TestTFT Performance

& Array Yield

Pilot Line

Fabrication

Automated

E-Test

TFT Array

Simulation,

Design,

Layout,

Verification

Design Rulesfor highmanufacturingyield

Fabricated array

Integration,

Assembly,

Test

4” QVGA

Maskset

FDC Technology FocusTransition Glass-based High Information Content

Commercial Technology to Flexible Formats

Reflective

Electrophoretic

Ultra-low power

Sunlight readable

Near-video rates

Maps, position data, images, text

ElectrophoreticInk

Emissive

Organic Light Emitting Displays Low power

Vibrant full color

Full motion video

UAVs, vehicles, command posts

H

H

PhosphorescentOLED

Novel OLEDs

EPD Technology Demonstrators

Effective Management of

Plastic Substrate Challenges:

Distortion and Defectivity

210 ppi EPD on SS

High

Pixel Density

enables VGA resolution

at 3.8-in diagonal

3.8-in. QVGA EPD on PEN

World’s Highest

Temperature a-Si:H

directly fabricated on

polyester substrates

3.8-in. QVGA EPD on SS

Zero-defectivity

Effective Management of

SS Substrate Challenges:

Roughness and Stress

•Phosphorescent OLED

•Low T amorphous Si

•PEN substrate

Moving to OLED Displays

Monochrome Flex OLED Display

Confidential & Proprietary 12

White OLED on IGZO TFT backplane

QLED on a-Si TFT backplane

• 4.1” QVGA on PEN plastic– 2T1C pixel circuit– Bottom emission– 58% aperture– 98 dpi

• OLED and Quantum Dot QLED Frontplane

• IGZO and a-Si TFT Technology

• Encapsulation– 3M barrier laminate– UDC Unicoat™ conformal coat

GenII Sunic OLED Tool

Full Color OLED Displays

First FC OLED Display

ASU – FDC Confidential & Proprietary 15

Why Flex?

Why Flexible Displays & Electronics

• Rugged – lightweight –robust

• Design freedom

• Enable integration into more robust packages

Flexible Electronics as aCore Platform Technology

Integrate flexible TFT backplanes with frontplanes of different functionality to create new technology

Image-layer FrontplaneFlexible Displays

Sensing-layer FrontplaneFlexible Sensor Arrays

Sensors for Environmental Threat

Detection and Human Health/Performance

Monitoring

Images compliments of J. Wang ASU BDI

Flexible

DRG

Manufacturing challenges

Flex Manufacturing Challenges

• Handling of flexible substrates

• Increased defectivity

• Temperature constraints due to substrate

• Existing tool infrastructure meant for rigid substrates, i.e. silicon, glass

• Packaging and associated electronics

TFT Process Thermal/Pressure Profile

• TFT Processing

– Barrier Deposition

– Gate Metal

– Active Layer(s)

– Passivation

– Source/Drain

– Dielectric

– Planarization

– Conductor

– Passivation

• Must manage stress and CTE throughout entire process

Arizona State University Flexible Display Center

PEN Processing Temperature and Pressure Profile

0

50

100

150

200

250

0 200 400 600 800 1000 1200

Time Minutes

Tem

peratu

re C

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

Pressu

re T

orr

Temp. C

Press Torr

Handling Flexible Substrates

Stainless Steel

Limited flexibility

Stress management

Surface roughness: planarization layer

No manufacturing-ready “drop-in” replacements for glass

Plastic

Process T limit

Dimensional stability

Permeable to O2/H2O: barrier layer(s)

HS-PEN SS

Moisture Pickup of PET and PEN

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8 10 12 14

Time(hours)

Mo

istu

re(p

pm

)

PEN

PET

PEN

PET

• Moisture pickup will have a significant effect on dimensional

• The low moisture pickup of Teonex® Q65A is a significant advantage

compared to other substrates

Plastic SubstratesChallenges

HS-PEN Process T Limit: 200C Oligomer Crystallites & Scratches Permeable to H2O/O2

Dimensional Stability Thermal cycles material run-in Heat Stabilize

Elastic strain under deposited film stress material run-out

forgiving design rules

modified lower stress processes

modified substrate material system

Optical Micrographs Showing TFT Alignment at Corner Pixels

Oligomer Defectivity

Stress Manifestation: Bow/Warp

• Prevents automated handling

• Distorts photo resolution

• Makes testing and inspection difficult

PEN Defectivity

Approaches to Flex Processing

Approaches

• Framing

– Securing/gripping plastic at edges

– How to grip plastic to mitigate distortion, processing edge effects due to frame

• Laser Release - Transfer processes

– Spin on polymer, use of sacrificial layer for release

• Roll to roll

– Limited resolution, feature size leads to design constraints

FDC Bond/Debond Approach

• Utilizing existing industry standard tool infrastructure

• Minimize deviations from standard TFT processing cells

• Focus on developing manufacturableprocesses for ease of implementation

Critical EnablerSubstrate Temporary Bonding

Pilot Line Tools

Novel Adhesive Materials

Manufacturable Processes

Semiconductor-grade

Adhesive

Custom Solutions

Mechanical Release

No TFT degradation

No residue

No carrier damage

Perfect bond integrity

through entire fab

Bonded substrate Debonded substrateAfter TFT FabBonded substrate Debonded substrateAfter TFT Fab

Bond Integrity in Semi/FPD Processes

PECVD

200°C

Sputter

Al, Moly, ITO, Cr

Wet Etch

HF, HCl, NH4OH

Dry Etch

Fluorine, Chlorine, Oxygen

Photolithography

Solution Processed Films

Flexible Substrate System

• Substrate: PEN (Teonex Q65 from DTF)

• Adhesive key characteristics

– Maintain bond integrity throughout temp/vaccycles

– “Post-it note” release

• Carrier key characteristics

– Bow/warp: <60um for 150mm

– Bow/warp: <100um for Gen II

– Reusable carrier

TFT and De-Bond Process

• TFT Processing

– Barrier Deposition

– Gate Metal

– Active Layer(s)

– Passivation

– Source/Drain

– Dielectric

– Conductor

– Passivation

• Mitigation of CTE and stress is achieved with use of Flexible Substrate System

Arizona State University Flexible Display Center

PEN Processing Temperature and Pressure Profile

0

50

100

150

200

250

0 200 400 600 800 1000 1200

Time Minutes

Tem

peratu

re C

1.00E-04

1.00E-03

1.00E-02

1.00E-01

1.00E+00

1.00E+01

1.00E+02

1.00E+03

Pressu

re T

orr

Temp. C

Press Torr

Semi/FPD Process Compatability

• Known process compatibilities– Carriers are reusable– Multiple thermal cycles to

200C– Vacuum cycles to 1E-8Torr– Solvent Exposure: IPA,

Acetone– Plasma of various

chemistries, O2, O3, Fl, Cl, NH3, H2

– Base Exposure: NH4OH, – Acid: BOE, Nitric, Sulfuric,

Acetic, HCL– Films: Silicon Oxides, Silicon

Nitrides, Al, Mo, ITO

• Known process incompatibilities– Solvent: Hexanes, NMP,

PRS3000

– Temperature exceeding 240C

-200

-150

-100

-50

0

50

100

150

200

250

300

Sta

ck

Conta

ct

Gate

Conta

ct

a-S

i

SD

Via

Moly

/IT

O

Ove

rgla

ss

Dis

tort

ion

(p

pm

)

Distortion vs. Process Step

-200

-150

-100

-50

0

50

100

150

200

250

300

Sta

ck

Conta

ct

Gate

Conta

ct

a-S

i

SD

Via

Moly

/IT

O

Ove

rgla

ss

Dis

tort

ion

(p

pm

)

Distortion vs. Process Step

-200

-150

-100

-50

0

50

100

150

200

250

300

Sta

ck

Conta

ct

Gate

Conta

ct

a-S

i

SD

Via

Moly

/IT

O

Ove

rgla

ss

Dis

tort

ion

(p

pm

)

Distortion vs. Process Step

New Plastic TFT Process

Allows for glass TFT design rules on Plastic Substrates

1Q 2008 Baseline 180 °C Process

New180 °C Process

150 °C Process

3.83.8--in. QVGA (320x240) TFT Arrayin. QVGA (320x240) TFT Array

Upper

left

pixel

Lower

left

pixel

Upper

right

pixel

Lower

right

pixel

3.83.8--in. QVGA (320x240) TFT Arrayin. QVGA (320x240) TFT Array

Upper

left

pixel

Lower

left

pixel

Upper

right

pixel

Lower

right

pixel

Plastic Substrate System Solution

Bonding Process Elements

• Ceramic carrier– 150mm available– GenII available

• Adhesive– Henkel: currently available

commercially

• Adhesive Application– 150mm spin coat– GEN II

• Several suitable methods

• Flexible Substrate– Bond PEN to carrier

• Bond Cure

ASU – FDC Confidential & Proprietary 37

Carrier Clean

Carrier PEN

Carrier ID

Coat Adhesive

Cut to Size

Pre-Bond Bake

Size & Apply Protective Film

PEN to Carrier

Bond Cure

TFT Processing

37

Bonding Procedure

GEN II plate

6” wafer

Industry trends to larger mother-glass

Transition to Gen II Production

Supply Chain Scale-up

• Substrates

– PEN is commercially available from DTF in large volume quantities.

• Adhesives

– Transferred to Henkel commercial business unit

• Ceramic carrier

– Commercially available at GenII size

– Cost more than glass, but is reusable.

ASU – FDC Confidential & Proprietary

Gen II Ceramic Carrier

Gen II Carrier PEN bonded to Gen II Carrier

370mm x 470mm, 1.1mm thick

• Seven Patents/Patents pending on technology

• Research license executed: Fall 2009

• 2nd Research license executed 2011

• Commercial license in negotiation

• Evaluation license pending with Pacific Rim mfr

• Fielding additional inquiries

Process Technology Transfer

Summary

Summary

• Processes and protocols for producing electronic devices on plastic have been developed

• Existing tool infrastructure can be used with little or no modification providing for acceleration of manufacturing implementation

• Temporary bonding technology is a key enabler for flexible display & electronic manufacturing

Acknowledgements

• ASU and The Flexible Display Center gratefully acknowledge the substantial financial support of the U.S. Army through Cooperative Agreement W911NF-04-2-0005– Dr. David A. Morton, ARL, Cooperative Agreement Manager– Dr. Eric Forsythe, ARL, Associate PM

• The FDC acknowledges its members for their technical and financial contributions to the Center– Principal Members: EV Group, UDC, Flextech Alliance (formerly

USDC)– Associate Members: E Ink, Hewlett Packard, LG Display,

Honeywell, DuPont Teijin Films, AKT, Ito America, Litrex (Ulvac), EITI, Plextronics, Particle Measuring Systems, Mocon

– Technology User Members: General Dynamics, Raytheon, L-3 Communications, Boeing, BAE Systems

• The FDC Engineering Team