Multi-Layered Flexible Window for Foldable Displays
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Solution Overview
Problem
Flexible display devices with foldable or bendable windows are prone to damage from external impacts due to their susceptibility to mechanical stress, which affects their durability and reliability.
Innovation Solution
A multi-layered window structure comprising a base layer, a first layer with magnesium fluoride or magnesium oxide, a second layer with silicon dioxide and other fluorides, a third layer with metal materials for chemical resistance, and a fourth layer with a fluorine-containing polymer for scratch resistance and low reflectance, enhancing mechanical strength and durability while maintaining low reflectance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a flexible window is used in a foldable display device, then the device can be folded or bent for convenient carrying, but the window becomes more easily damaged by external impact
Solution Approach 1:
The window is constructed as a multi-layer composite structure where each layer serves a specific function: the base layer provides flexibility, the second layer (silicon dioxide, fused silica, fluorine-doped fused silica) provides mechanical strength and chemical resistance, the third layer (metal materials like iron, copper, nickel, zirconium, hafnium, aluminum, silver, gold, chromium, tin, zinc, indium, or titanium) provides solvent resistance and enhanced durability, and the fourth layer (fluorine-containing polymer) provides scratch resistance and low reflectance. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both foldability and impact resistance.
Solution Approach 2:
Different regions of the window structure are assigned different material properties to address specific requirements: the base layer is designed for flexibility to enable folding, while the subsequent layers are designed with progressively higher hardness and chemical resistance to protect against external impacts and environmental degradation. This local differentiation of material qualities allows the window to simultaneously achieve adaptability and reliability.
2Reliability
If the third layer is made thicker to improve chemical and solvent resistance, then durability increases, but the reflectance increases which affects display quality
Solution Approach 1:
The thickness of the third layer is precisely controlled within the range of 2 nm to 10 nm to optimize the balance between chemical resistance and reflectance. This parameter optimization ensures that the metal layer provides sufficient solvent resistance while maintaining low reflectance for high display quality. Additionally, the fourth layer (fluorine-containing polymer) is applied to further reduce reflectance to about 6.0% or less at a wavelength of 550 nm, compensating for any reflectance from the third layer.
3Reliability
If multiple layers are added to the window structure to improve durability and resistance, then mechanical strength and chemical resistance increase, but the device complexity increases
Solution Approach 1:
The window is divided into four distinct functional layers, with each layer addressing a specific requirement: base layer for flexibility, second layer for mechanical strength and chemical resistance, third layer for solvent resistance, and fourth layer for scratch resistance and reflectance control. This segmentation allows each layer to be optimized independently for its specific function, achieving comprehensive durability without unnecessary complexity.
Solution Approach 2:
Each layer in the multi-layer structure serves multiple functions simultaneously. For example, the second layer provides both mechanical strength and chemical resistance, while the third layer provides both solvent resistance and contributes to the overall structural integrity. The fourth layer simultaneously provides scratch resistance and reflectance control. This multi-functionality reduces the need for additional specialized layers, thereby limiting the increase in device complexity.
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 multi-layered window structure significantly increases the chemical and grinding resistance, wear resistance, and mechanical strength of the display device, reducing surface reflectance and enhancing durability and reliability, especially when the third layer is optimized to be thin and composed of solvent-resistant metals like iron, copper, or nickel.
Implementation Method 1
At a wavelength of about 550 nm, the refractive index of the second layer may be about 1.3 to about 1.6. At a wavelength of about 550 nm, reflectance on an upper surface of the fourth layer may be about 6.0% or less. At a wavelength of about 550 nm, a refractive index of the first layer may be about 1.3 to about 1.5, and at a wavelength of about 550 nm, a refractive index of the fourth layer may be about 1.3 to about 1.5.
Implementation Method 2
At a wavelength of about 550 nm, the refractive index of the second layer may be about 1.3 to about 1.6. At a wavelength of about 550 nm, a refractive index of the first layer may be about 1.3 to about 1.5, and at a wavelength of about 550 nm, a refractive index of the fourth layer may be about 1.3 to about 1.5.
Data Source
AI summary
A window includes a base layer, a first layer disposed on the base layer, a second layer disposed on the first layer, a third layer disposed on the second layer, and a fourth layer disposed on the third layer. The second layer includes silicon dioxide (SiO2), fused silica, fluorine-doped fused silica, magnesium fluoride (MgF2), calcium fluoride (CaF2), aluminum fluoride (AlF3), yttrium fluoride (YF3), ytterbium fluoride (YbF3), aluminum oxide (Al2O3), and/or magnesium oxide (MgO). The third layer includes iron (Fe), copper (Cu), nickel (Ni), zirconium (Zr), hafnium (Hf), aluminum (Al), silver (Ag), gold (Au), chromium (Cr), tin (Sn), zinc (Zn), indium (In), and/or titanium (Ti).