Introduction to OLED Design and Test Method Development · 2019-12-06 · OLED Flex Testing Objective 1: Develop test method for flexible OLED devices Objective 2: Test flexible OLED

Introduction to OLED Design and Test Method Development

OLED SSL Stakeholder MeetingHollis Beagi – Josh CumminsOctober 2017

2© 3M 2017. All Rights Reserved.

3M FlexLabA cross functional technical team tasked with development of system level fundamental

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Flexible OLED Overview


OLED Overview: Configuration


OLED Overview: Flexible Design Problem

Materials must meet following criteria without failure:

1. 50,000+ cycles of bending at ambient conditions

2. 5, 3, or 1 mm bending radius

3. Unfolding of display at hot and cold temperatures

4. Survive scratch and impact

5. Ball drop / device drop


OLED Overview: Important Terminology

Terms Important to Understanding OLED and Flexible Design:

1. Stress: force per unit area

2. Strain: amount of elongation or compression for a given load

3. Shear: force causing two surfaces to move parallel to each other

4. Elastic (Young’s) Modulus: determined by slope of initial linear region of stress-strain curve. Indicates relative springiness or rigidity of a material

5. Poisson’s Ratio: ratio of contraction of material in lateral direction to extension of material in stretch direction


OLED Overview: Important Terminology

Terms Important to Understanding OLED and Flexible Design:

6. Yield: point at which a specified amount of plastic deformation has occurred

7. Ultimate: maximum load or stress a material can withstand before breaking

8. Fatigue: repeated loading and unloading leading to failure

9. Neutral Axis: line or plane through a surface connecting points at which no extension or compression occurs during bending

10.Decoupling: separating or eliminating the interaction between surfaces/layers in a stack up of layers


OLED Overview: Theoretical Approaches

Design Strategy: Place the fragile layers at the neutral plane

What We Need To Know: For each layer….

• Modulus (E) & Poisson’s ratio

• Thickness (t)

• Yield & Fracture stress/strain

• Fatigue behavior

Assumptions: No delamination or slip between layers and plane sections remain plane

Success Metric: A good design keeps stresses/strain below failure levels in each layer subject to

adequate optical engineering

US20140367644A1

Test Method Development

Dynamic Bend Testing Capabilities3M Dual Hinge Bend TesterYuasa


Strained Bending – Single-hinge and Mandrel Bend Designs(why we do not use these types)

Moving the attachment adhesive out to the ends imparts less strain on the sample. Tom Corrigan, SEMS

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Fixed Distance "f" [mm]

Max Strain vs Fixed Distance(2mm gap)

Hinge design is important. Single hinge and mandrel bending will increase strain on the test stack, whereas dual

(or multiple) hinge designs can enable bending without added strain.

*Some images shown here taken from paper by Tom Corrigan

Mandrel Bend Motion Profile (f/ Yuasa website)https://www.yuasa-system.jp/pdf/tech/20151202_FS_en.pdf

https://www.yuasa-system.jp/pdf/tech/20151202_FS_en.pdf


Yuasa vs 3M Dual-Hinged Bend Tester

Sample bows above bend apex

Sample stays flat against plates during bending

We see different results (cycles to fail) for Multi-layer samples on Yuasa vs 3M DH Bend Tester (see previous slides).

This may be due to differences in stress amplitude because:

1) Yuasa does not control shape of sample (force U-shape) during

bending

2) Yuasa cannot open all the way to 180D flat

or fully close to 90D folded during bending.


Attachment Location

Natural bent conformation of thin film stacks is elliptical, not semicircular.

This must be considered when bonding / constraining the test stack during testing to

prevent undue strain.

Above: Large deflection shear deformable bending analysis (conducted by Fay Salmon, SEMS) shows that thin elastic films will conform to the shape of an ellipse.Left: Bent thin film stack image analysis and validation of bent shape conformation (Samad Javid, CRPL)

16. All Rights Reserved.25 October 2017© 3M 3M Confidential.

Crazing (whitening) and Breakage due to film strain and fatigue

dislocations

Local buckling due to adhesive shear and adhesion failure

Inverted Bendingdue to severe global buckling

Mechanical Failure Modes


Effects of Plate, Fold Axis or Sample Misalignment

8% increase 8% decrease 5% increaseStress contour plot:

9% increase 8% decrease 5% increase

Aligned plates

1° plate rotation around x-axis

1° plate rotation around x-axis, sample off centered

1° plate rotation around z-axis

Strain contour plot:


Effects of Plate, Fold Axis or Sample Misalignment

General Smile Pattern (root cause = curved plates – confirmed by gap measurement using feeler gauge)This graph shows cycles to break results for 4mil LmPEN (Low Melt PEN) tested at R2. Plates B show smile pattern as compared to two replicates of data collected with plates A.

Wave-form (root cause = bearings too loose, and torque occurring on one end of plate where drive belt is located, allowing “wave-like” motion of plates during folding)

Improved capability with changes from Gen1 to Gen2 3M DH Bend Testers:Each stage of the control chart above represents a change to tester design, which improved variability greatly. At this point, the primary source of variability between 3M DH Bend testers is due to slight differences in gap size as all issues with misalignment and plate curvature have been addressed.

Flexible OLED Light Testing


OLED Flex Testing

Objective 1: Develop test method for flexible OLED devices

Objective 2: Test flexible OLED devices to failure and characterize failure modes

• Started with optically in-active sample for TM development

• Look for mechanical failures first

• Test working OLED sample looking for change in light emission and/or failure

Sample ID Dimensions (cm) Thickness Contacts Notes

B3.1 14 x 1.5 10.7 Wire Leads

B3.2 14 x 1.5 10.2 Wire Leads Creased


Flex Testing

*Thousand cycles

400k cycles total on same sample

Room temp (70F, ~40% RH)


Flex Testing

*Thousand cycles




Flex Testing


Flex Testing



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Intensity vs Wavelength for 6mm Bend Radius Flex Test

0 Cycles 100 Cycles 1,000 Cycles 2,000 Cycles

3,000 Cycles 4,000 Cycles 5,000 Cycles 10,000 Cycles




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Intensity vs Wavelength 3 mm Bend Radius Flex Test

0 Cycles 100 Cycles 1000 Cycles 3000 Cycles

10k additional cycles on same sample


Flex Testing


1. Adhesive properties

2. Tunability of Material Properties

3. Geometry

4. Process Parameters

5. Accurate Prediction

OLED Overview Summary: Important Considerations

Documents

Introduction to OLED Design and Test Method Development · 2019-12-06 · OLED Flex Testing Objective 1: Develop test method for flexible OLED devices Objective 2: Test flexible OLED