OLED SSL Stakeholder Meeting Hollis Beagi Josh Cummins October Introduction to OLED Design and Test Method Development

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1 OLED SSL Stakeholder Meeting Hollis Beagi Josh Cummins October 2017 Introduction to OLED Design and Test Method Development

2 3M FlexLab A cross functional technical team tasked with development of system level fundamental understanding of dynamic systems. Ab Abrasives Ad Adhesives Am Advanced Materials Ce Ceramics Co Advanced Composites Do Dental & Orthodontic Materials Em Electronic Materials Materials Fi Films Fl Fluoromaterials Nt Nanotechnology Nw Nonwoven Materials Po Porous Materials & Membranes Sm Specialty Materials Mo Molding Mr Microreplication Pd Particle & Dispersion Processing Successful New Product Growth Builds on Uncommon Connections Pe Predictive Engineering & Modeling Pm Polymer Processing Pp Precision Processing Processing Rp Radiation Processing Su Surface Modification Vp Vapor Processing An Analytical As Application Software Es Electronics & Software Fc Flexible Converting & Packaging In Inspection & Measurement Is Integrated Systems & Design Capabilities Pr Process Design & Control Se Sensors We Accelerated Weathering Ac Acoustic Control Bi Biotech Dd Drug Delivery Di Display Ec Energy Components Fe Flexible Electronics Fs Filtration, Separation, Purification Im Imaging Lm Light Management Applications Md Medical Data Management Mf Mechanical Fasteners Mi Microbial Detection and Control Op Optoelectronics Tt Track and Trace Wo Wound Management 2

3 Flexible OLED Overview

4 OLED Overview: Configuration 4

5 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 5

6 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 6

7 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 7

Modulus (E) & Poisson s ratio Thickness (t) Yield & Fracture stress/strain Fatigue behavior US20140367644A1

8 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 US A1 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 8

9 Test Method Development

10 Dynamic Bend Testing Capabilities Yuasa 3M Dual Hinge Bend Tester

11 Dynamic Bend Testing Capabilities Yuasa 3M Dual Hinge Bend Tester

2 0.1 0 Max Strain vs Fixed Distance (2mm gap) 0 5 10 15 Fixed Distance "f" [mm] Hinge design is important.

12 Strain (ΔL/L) Strained Bending Single-hinge and Mandrel Bend Designs (why we do not use these types) Mandrel Bend Motion Profile (f/ Yuasa website) pdf Moving the attachment adhesive out to the ends imparts less strain on the sample. Tom Corrigan, SEMS Max Strain vs Fixed Distance (2mm gap) Fixed Distance "f" [mm] 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

13 Dynamic Bend Testing Capabilities Yuasa 3M Dual Hinge Bend Tester

This may be due to differences in stress amplitude because: Sample stays flat against plates during bending 1)

14 Yuasa vs 3M Dual-Hinged Bend Tester We see different results (cycles to fail) for Multilayer samples on Yuasa vs 3M DH Bend Tester (see previous slides). This may be due to differences in stress amplitude because: Sample stays flat against plates during bending 1) Yuasa does not control shape of sample (force U-shape) during bending Sample bows above bend apex 2) Yuasa cannot open all the way to 180D flat or fully close to 90D folded during bending.

15 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) 15

16 Mechanical Failure Modes Local buckling due to adhesive shear and adhesion failure Inverted Bending due to severe global buckling Crazing (whitening) and Breakage due to film strain and fatigue dislocations 25 October 3M Confidential. 16

17 Effects of Plate, Fold Axis or Sample Misalignment Aligned plates 1 plate rotation around x-axis 1 plate rotation around x- axis, sample off centered 1 plate rotation around z- axis Stress contour plot: 8% increase 8% decrease 5% increase Strain contour plot: 9% increase 8% decrease 5% increase 17

Effects of Plate, Fold Axis or Sample Misalignment General Smile Pattern (root cause = curved plates confirmed by gap measurement using feeler

Plates B show smile pattern as compared to two replicates of data collected with plates A.

plates during folding) Improved capability with changes from Gen1 to Gen2 3M DH Bend Testers: Each stage of the control chart above represents a

18 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. 18

19 Flexible OLED Light Testing

20 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 B x Wire Leads B x Wire Leads Creased 20

21 Flex Testing *Thousand cycles 400k cycles total on same sample Room temp (70F, ~40% RH) 21

22 Flex Testing *Thousand cycles 400k cycles total on same sample Room temp (70F, ~40% RH) 22

23 Flex Testing 23

24 Intensity (count) Intensity (count) Flex Testing Intensity vs Wavelength for 6mm Bend Radius Flex Test Intensity vs Wavelength 3 mm Bend Radius Flex Test Wavelength (nm) Cycles 100 Cycles 1,000 Cycles 2,000 Cycles ,000 Cycles 4,000 Cycles 5,000 Cycles 10,000 Cycles ,000 Cycles 20,000 Cycles 25,000 Cycles 30,000 Cycles Wavelength (nm) 40,000 Cycles 50,000 Cycles 60,000 Cycles 80,000 Cycles 0 Cycles 100 Cycles 1000 Cycles 3000 Cycles 100,000 Cycles 130,000 Cycles 160,000 Cycles 200,000 Cycles 200k cycles total on same sample 10k additional cycles on same sample Room temp (70F, ~40% RH) 24

25 Flex Testing 25

26 OLED Overview Summary: Important Considerations 1. Adhesive properties 2. Tunability of Material Properties 3. Geometry 4. Process Parameters 5. Accurate Prediction 26

ME 243. Mechanics of Solids

ME 243. Mechanics of Solids ME 243 Mechanics of Solids Lecture 2: Stress and Strain Ahmad Shahedi Shakil Lecturer, Dept. of Mechanical Engg, BUET E-mail: sshakil@me.buet.ac.bd, shakil6791@gmail.com Website: teacher.buet.ac.bd/sshakil