Foldable Display Layer Dimensions for Delamination Resistance
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Solution Overview
Problem
Foldable display devices face issues with delamination due to high stress and shear deformation in adhesive layers, particularly at the edges during folding and unfolding, leading to significant changes in optical and physical properties that render the device unusable.
Innovation Solution
A foldable display device structure with layers having varying dimensions along the folding axis, where the light emitting diode substrate layer is larger than other layers, and offset configurations to reduce peeling pressure at interfaces prone to delamination, using finite element analysis to optimize layer widths and adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the cover window and shock absorber are made thin to enable folding, then the display device becomes foldable, but the adhesive layers experience high stress and shear deformation leading to delamination
Solution Approach 1:
The patent divides the adhesive layer into multiple sub-layers (first adhesive layer, second adhesive layer, third adhesive layer) with different thicknesses and positions. The first adhesive layer has thickness t1, the second has t2, and the third has t3, creating a segmented structure that distributes stress more effectively during folding compared to a single uniform adhesive layer.
Solution Approach 2:
The patent applies different adhesive layer thicknesses at different locations within the display device. The first adhesive layer has a first average thickness, the second adhesive layer has a second average thickness, and the third adhesive layer has a third average thickness. This local variation in quality allows optimization of adhesion strength where needed while maintaining flexibility where required, reducing delamination risk during folding operations.
2Reliability
If the adhesive enhancement layer is added to prevent delamination, then adhesion is improved, but shear deformation of OCA or OCR is prevented which is required for folding
Solution Approach 1:
The patent segments the adhesive enhancement function across multiple adhesive layers rather than using a single thick enhancement layer. The first, second, and third adhesive layers are distributed at different positions and thicknesses, allowing the structure to achieve adhesion strength while maintaining the ability to deform shear during folding.
Solution Approach 2:
The patent changes the thickness parameter of the adhesive layers to optimize both adhesion and deformability. By controlling the thicknesses t1, t2, and t3 of the different adhesive layers, the structure achieves sufficient adhesion strength while maintaining the shear deformation capability needed for folding, avoiding the brittleness that would result from a single thick enhancement layer.
3Reliability
If the light emitting diode substrate layer dimension is made larger than other layers, then peeling pressure is redistributed to more adhesive layers, but the device complexity increases
Solution Approach 1:
The patent introduces asymmetric layer dimensions where the light emitting diode substrate layer has a dimension along the folding axis that is larger than the corresponding dimension of other layers. This asymmetric configuration creates a stepped structure that redistributes peeling pressure to multiple adhesive layers, improving delamination resistance while accepting the resulting structural complexity.
Data Source
AI summary
A foldable display device includes a plurality of layers bonded to each other. The plurality of layers includes a light emitting diode substrate layer, a cover window layer including a window film through which light from a first surface of the light emitting diode substrate layer is emitted, a shock-absorber layer located on a second surface of the light emitting diode substrate layer. The second surface is a surface opposite to the first surface. A dimension of the light emitting diode substrate layer measured along a folding axis is larger than a dimension of at least one layer in the plurality of layers.