Multi-Layer Cover Window with Differential CTE for Foldable Displays
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Solution Overview
Problem
Display device cover windows face a trade-off between strength and flexibility, with existing solutions struggling to provide both high thermal resistance and foldability effectively.
Innovation Solution
A cover window design featuring a base film with multiple layers, each having a different coefficient of thermal expansion, where the upper layer has a higher CTE than the lower layer, and a coating layer with varying hardness regions, allowing for enhanced thermal resistance and flexibility while maintaining structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single-layer base film is used, then the structure is simple and manufacturing is easy, but the thermal resistance and flexibility cannot be simultaneously optimized
Solution Approach 1:
The base film is constructed as a composite structure with multiple layers (first base layer, second base layer, and third base layer) made of different materials with varying coefficients of thermal expansion. This composite structure enables simultaneous optimization of thermal resistance and flexibility, resolving the contradiction between strength and device complexity.
Solution Approach 2:
Different layers of the base film are assigned different material properties and thicknesses to perform specific functions. The first base layer provides foundational support, the second base layer (with higher CTE) enhances flexibility and thermal management, while the third base layer completes the composite structure. This local differentiation of material properties allows the overall structure to achieve both high thermal resistance and controlled flexibility.
2Strength
If the base film is made thicker to increase strength, then thermal resistance improves, but flexibility and foldability deteriorate
Solution Approach 1:
The multi-layer composite base film structure achieves high impact resistance without excessive thickness by utilizing the synergistic effects of different materials. Each layer contributes specific mechanical and thermal properties, allowing the overall structure to be both strong and flexible. The differentiated coefficients of thermal expansion among layers create internal stress distribution that enhances both strength and bendability.
Solution Approach 2:
The invention optimizes the thickness and material composition of each individual layer rather than simply increasing overall thickness. By carefully controlling the thickness parameters of the first, second, and third base layers, and selecting materials with appropriate mechanical properties, the structure achieves high strength-to-thickness ratio while maintaining flexibility for folding applications.
3Ease of manufacture
If a uniform thickness base film is used, then manufacturing is simple, but thermal expansion management and flexibility are compromised
Solution Approach 1:
The base film employs local quality differentiation where each layer has specific thickness and material properties optimized for its function. The first, second, and third base layers have different thicknesses and material compositions to manage thermal expansion locally while maintaining overall structural integrity. This approach balances manufacturing feasibility with thermal stability requirements.
Solution Approach 2:
The invention deliberately utilizes thermal expansion differences among the layers to achieve thermal stability. The second base layer is specifically designed with a higher coefficient of thermal expansion than the first and third layers, creating a composite structure that compensates for thermal deformation. This differential thermal expansion design allows the base film to maintain dimensional stability across temperature variations while remaining manufacturable.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a balance between thermal resistance and foldability, enabling the cover window to withstand external impacts and maintain image quality while being thermally stable and bendable.
Implementation Method 1
Each of the plurality of layers includes a folding part and a nonfolding part. Each of the plurality of layers has a different coefficient of thermal expansion.
Data Source
AI summary
A cover window for a display device includes a base film and a coating layer disposed on the base film. The base film includes a plurality of layers. Each of the plurality of layers includes a folding part and a nonfolding part. Each of the plurality of layers has a different coefficient of thermal expansion.