Window Substrate with Stress Relief Layer for Foldable Displays
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Solution Overview
Problem
Flexible display devices, particularly foldable ones, face challenges in reducing folding stress while minimizing the thickness of the window glass to prevent damage from external impacts and maintain structural integrity during folding.
Innovation Solution
A window substrate is designed with a glass substrate, a bonding layer, and a stress relief layer, where the bonding layer and stress relief layer have thicknesses greater than the glass substrate, and are made of materials like acrylic, silicon, or urethane, providing increased modulus and yield strain to absorb external forces effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the thickness of window glass is increased to protect against external impacts, then impact resistance is improved, but folding stress increases
Solution Approach 1:
The window glass is divided into multiple layers (first window glass layer, second window glass layer) separated by bonding layers and stress relief layers. This segmentation allows each layer to be thinner individually, reducing overall folding stress, while the combined structure maintains impact resistance through distributed load bearing.
Solution Approach 2:
The patent uses composite material structures combining different glass layers with bonding layers and stress relief layers. The stress relief layers are made of materials with specific mechanical properties (modulus between 0.1-10 GPa) that differ from the glass layers, creating a composite structure that reduces folding stress while maintaining overall strength and impact resistance.
2Stress or pressure
If the thickness of window glass is decreased to reduce folding stress, then ease of folding is improved, but impact resistance deteriorates
Solution Approach 1:
The window glass is segmented into multiple thin layers (first window glass layer, second window glass layer) with intervening bonding and stress relief layers. This allows each individual glass layer to be thin (reducing folding stress) while the multi-layer composite structure provides cumulative impact resistance.
Solution Approach 2:
Different regions of the window substrate have different properties: the glass layers provide hardness and impact resistance, while the stress relief layers (with modulus 0.1-10 GPa) provide flexibility and stress reduction. This local differentiation allows thin glass layers to maintain impact resistance while the overall structure reduces folding stress.
3Strength
If bonding layer thickness is increased to improve adhesion, then bonding strength is improved, but device complexity increases
Solution Approach 1:
The bonding layers serve multiple functions simultaneously: they provide adhesion between glass layers, act as stress relief interfaces, and contribute to the overall flexibility of the window substrate. This multi-functionality reduces the need for separate dedicated components, simplifying the overall device structure despite the multi-layer configuration.
Solution Approach 2:
The bonding layers are integrated into a composite material system with specific modulus ranges (0.1-10 GPa for stress relief layers), creating a unified multi-functional component that simplifies design while maintaining bonding strength and stress relief capabilities.
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 reduces folding stress and enhances impact resistance, allowing the flexible display device to withstand external impacts like pen drops without breaking, while maintaining a thin profile for easier bending.
Implementation Method 1
a first stress relief layer disposed between the bonding layer and the glass substrate... a yield strain of the first stress relief layer may be equal to or greater than about 1.0 percent (%)
Implementation Method 2
the first stress relief layer may include a material of which modulus increases by application of an external force. the modulus of the first stress relief layer may be increased by an external force to a range equal to or greater than about 800 MPa and equal to or less than about 1 gigapascal (GPa)
Data Source
AI summary
A window substrate includes a glass substrate, a first bonding layer disposed on a first surface of the glass substrate, and a first stress relief layer disposed between the bonding layer and the glass substrate. The first bonding layer has a thickness greater than a thickness of the glass substrate.