Foldable OLED Device Neutral Plane Control
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Solution Overview
Problem
Flexible electronic displays face mechanical failure due to uneven strains when bent or folded, as the location of the neutral bending plane is challenging to control, leading to stress and strain on the display module, especially when slight variations in material properties or thickness occur.
Innovation Solution
The design of flexible OLED displays with varying Young's moduli and thicknesses for the upper and lower modules, including a cover window film, touch sensor, and circular polarizer, where specific stiffness ratios (e.g., LS/TW > 0.001, LS/(CP)W > 0.004, and LS/W^2 > 4×10^−6) are maintained to manage strain and stress, ensuring the OLED plane remains in compression and minimizing crack formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the display module is made flexible to enable bending or folding, then adaptability is improved, but mechanical reliability deteriorates due to uneven strains and stress concentration
Solution Approach 1:
The patent applies parameter changes by precisely controlling the thickness and Young's modulus of each layer in the display structure. By adjusting these parameters, the neutral bending plane is positioned within the display module, and the stiffness ratio is optimized to maintain the OLED plane in compression during bending, thereby preventing mechanical failure while preserving flexibility
Solution Approach 2:
The patent employs composite materials by constructing the display as a multi-layer structure with different materials (glass substrate, OLED layers, encapsulation layers, adhesive layers) having different mechanical properties. This composite structure allows the system to achieve both flexibility and mechanical reliability through the synergistic combination of materials with complementary properties
2Reliability
If the neutral bending plane is controlled to minimize strain in the display module, then mechanical reliability is improved, but device complexity increases due to precise control requirements
Solution Approach 1:
The patent simplifies the control complexity by establishing specific parameter ranges for layer thicknesses and stiffness ratios. By defining these parameters upfront (e.g., thickness ratios, Young's modulus relationships), the neutral plane positioning becomes a design specification rather than a complex control problem, reducing manufacturing complexity while ensuring reliability
3Duration of action of stationary object
If the OLED plane is maintained in compression to prevent crack formation, then durability is improved, but design flexibility is reduced due to stiffness ratio constraints
Solution Approach 1:
The patent resolves this contradiction by defining specific parameter ranges for the stiffness ratio (LS/TW) and layer thicknesses that simultaneously achieve OLED plane compression and acceptable design flexibility. These parameter specifications provide design guidelines that ensure durability while allowing variation within defined ranges
Solution Approach 2:
The patent applies local quality by differentiating the mechanical properties of specific layers (e.g., making the lower module stiffer than the upper module) to create the necessary compression state in the OLED plane, while allowing other parts of the structure to have varying properties for design flexibility
Data Source
AI summary
A flexible OLED display device that includes an upper module having a cover window film, a lower module, and a display module between the upper and lower modules. The display module includes an OLED and an OLED substrate. The stiffnesses of components in the display device are controlled to satisfy a particular relationship such that the bending stiffnesses of the upper and lower modules are tuned in order to position the neutral bending plane below the display module, which places the display into a state of compressive strain as opposed to zero strain. This design is suitable for a bifold flexible display in which the upper module can be folded to face itself.