Gradient Layer Cover Glass for Scratch and Delamination Resistance
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Solution Overview
Problem
Conventional cover glasses for electronic devices are prone to scratches and delamination due to their soft material interfaces, which compromise their fracture strength and durability.
Innovation Solution
A cover glass design featuring a gradient layer that transitions from silicon oxynitride to silicon dioxide, providing increased hardness and resistance to delamination, combined with a hard coat layer and optional intermediate layers to enhance scratch resistance and reduce reflectance through destructive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a hard coat layer is applied on glass sheet, then scratch resistance is improved, but delamination occurs at the material interface
Solution Approach 1:
The patent applies a gradient layer with gradually changing compositional parameters between the hard coat layer and glass sheet. The gradient layer transitions from silicon oxynitride near the hard coat layer to silicon dioxide near the glass sheet, creating a continuous parameter transition that eliminates abrupt material interfaces and prevents delamination while maintaining scratch resistance.
Solution Approach 2:
The patent creates a composite structure consisting of four layers: glass sheet, gradient layer, hard coat layer, and exterior layer. This composite material system combines materials with different properties (SiO2, SiON, SiN) in a graded arrangement, where the gradient layer acts as an intermediate composite that bridges the mechanical and chemical properties between the hard coat and glass substrate.
2Strength
If chemically-strengthened glass is used for cover glass, then fracture resistance is improved, but the glass becomes softer and more prone to scratches
Solution Approach 1:
The patent applies local quality by adding functional layers with different properties at specific locations. The hard coat layer (SiN) provides high hardness and scratch resistance at the surface, while the glass sheet maintains its chemically-strengthened properties for fracture resistance in the bulk. Each layer performs its specialized function locally without compromising the other.
Solution Approach 2:
The patent creates a composite material system where chemically-strengthened glass provides bulk fracture resistance while surface layers (hard coat and exterior layers) provide scratch resistance. The composite structure combines the advantages of different materials: the strength of strengthened glass and the hardness of nitride coatings.
3Ease of manufacture
If discrete layers are used in coating structure, then manufacturing is simplified, but delamination occurs at material interfaces
Solution Approach 1:
The patent uses parameter changes to create a gradient layer where composition transitions continuously from silicon oxynitride to silicon dioxide. This gradual parameter transition eliminates abrupt material interfaces that cause delamination, while the gradient layer can still be manufactured using modified PVD or CVD processes with controlled composition variation.
Solution Approach 2:
The gradient layer acts as an intermediary between the hard coat layer and glass sheet, providing a transitional zone that mediates the mechanical and chemical properties between the two materials. This intermediary layer with graded composition prevents direct contact between dissimilar materials, eliminating interface delamination problems.
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 gradient layer design significantly enhances the cover glass's resistance to scratches and delamination, maintaining its mechanical integrity and reducing reflectance, thereby improving the durability and usability of electronic devices.
Implementation Method 1
reducing reflectance through destructive interference
Implementation Method 2
A gradient layer is deposited on the hard coat layer
Data Source
AI summary
An electronic device can include a housing, a display positioned within the housing; and a cover glass disposed over the display and attached to the housing. The cover glass can include a glass sheet; a hard coat layer disposed on the glass sheet, having a hardness greater than a hardness of the glass sheet; and a gradient layer deposited on the hard coat layer and having a composition that transitions from a first composition at the hard coat layer to a second composition at a top surface of the gradient layer. The first composition can be predominantly a composition of the hard coat layer and the second composition is different than the first composition. The second composition can be predominantly SiO2. The hard coat layer can include SiON. The cover glass can include an intermediate gradient layer disposed between the glass sheet and the hard coat layer.