Multilayer Bi-Layer Stack for Scratch-Resistant Optical Substrates
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Solution Overview
Problem
Existing cover substrates for consumer electronic products face challenges in maintaining scratch resistance and optical performance, as they often suffer from microductile scratches and abrasion damage, which degrade the appearance and functionality of displays, and current solutions compromise either scratch resistance or optical properties.
Innovation Solution
A stack of N bi-layers with different compositions and microstructures, having a thickness of at least 5 nm, is applied to the substrate, achieving a refractive index between 1.2 and 2.2 and a hardness of 15 GPa or greater, providing enhanced scratch resistance and retained optical clarity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single-layer scratch-resistant coating is applied to the substrate, then scratch resistance is improved, but optical properties (transmission, reflectivity, color consistency) deteriorate
Solution Approach 1:
The patent divides the scratch-resistant coating into multiple layers with different compositions and functions. The first layer (higher hardness material) provides scratch resistance, while the second layer (lower refractive index material) optimizes optical properties by reducing interference effects and improving light transmission. This segmentation allows each layer to specialize in one function, resolving the contradiction between scratch resistance and optical performance.
Solution Approach 2:
The patent uses composite materials by combining two different materials in a layered structure. The first layer uses a higher hardness material (such as silicon oxide, silicon nitride, or silicon oxynitride) for scratch resistance, while the second layer uses a material with lower refractive index (such as magnesium fluoride, silicon oxide, or silicon oxynitride) for optical optimization. This composite approach enables simultaneous achievement of both scratch resistance and good optical properties.
2Reliability
If hard coating materials are used to prevent scratches, then durability is improved, but optical clarity and color consistency deteriorate
Solution Approach 1:
The patent segments the coating into two layers where the first layer (hard material) handles durability and the second layer (optically optimized material) handles clarity. This functional segmentation allows the hard material to provide durability without compromising optical properties, as the second layer compensates for any optical interference caused by the first layer.
Solution Approach 2:
The patent applies local quality by giving each layer different properties tailored to its specific function. The first layer has high hardness for durability, while the second layer has optimized refractive index for optical clarity. This local optimization of properties in different regions (layers) of the coating resolves the contradiction between durability and optical clarity.
3Strength
If abrasion-resistant solutions are applied to the substrate, then resistance to multiple contact events is improved, but scratch resistance from single contact events deteriorates
Solution Approach 1:
The patent segments the protective coating into two specialized layers: the first layer (harder material) is optimized for resisting single-contact scratches through its high hardness, while the second layer (softer, more ductile material) provides abrasion resistance through better adherence and flexibility. This segmentation allows each layer to address different damage mechanisms without interfering with the other's function.
Solution Approach 2:
The patent applies local quality by tailoring the properties of each layer to specific protective functions. The first layer has high hardness locally optimized for scratch resistance, while the second layer has different properties (lower hardness, better adherence) locally optimized for abrasion resistance. This local differentiation resolves the contradiction between single-event scratch resistance and multi-event abrasion resistance.
Data Source
AI summary
Optically transparent articles and structures that include or are otherwise disposed on a substantially transparent substrate. These articles and structures also include a stack of N (N>2) bi-layers on the substrate, the stack having a thickness of at least 5 nm. Each bi-layer is defined by (a) a first layer; and (b) a second layer disposed on the first layer, the layers having at least one of different compositions and different microstructures. The stack has a stack refractive index between about 1.2 and about 2.2 or between about 100% and about 150% of a refractive index of the substrate, and a stack hardness of 15 GPa or greater when measured with a Berkovich Indenter Hardness Test along an indentation depth in the range from about 10% to about 50% of the thickness of the stack disposed on a glass test substrate having a hardness between 6.5 and 8 GPa.