Graded Index Matching Layer for Touch Display Reflection Suppression
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Solution Overview
Problem
Conventional touch screen displays face issues with increased reflection due to the significant index-of-refraction mismatch between silicon nitride and glass substrate layers, leading to glare and reduced visibility of displayed content.
Innovation Solution
The implementation of a graded index of refraction matching layer with embedded reverse matching sublayers between the display layers to minimize reflections, using a combination of silicon oxide and niobium oxide to adjust refractive indices, thereby reducing index mismatch and enhancing reflection suppression across multiple wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a silicon nitride layer is formed on a glass substrate layer, then the display structure is completed with necessary functional layers, but the significant index-of-refraction mismatch between the silicon nitride layer and the substrate causes increased reflection from the display
Solution Approach 1:
A matching layer with graded index of refraction is introduced between the silicon nitride layer and the glass substrate layer. This intermediary layer has an index of refraction that transitions from approximately 1.9 at the silicon nitride interface to approximately 1.5 at the glass substrate interface, thereby reducing the abrupt index mismatch and minimizing reflection at the interface.
Solution Approach 2:
The matching layer employs a graded index of refraction profile where the refractive index parameter changes continuously from one value (approximately 1.9) at the silicon nitride interface to another value (approximately 1.5) at the glass substrate interface. This gradual parameter change reduces reflection compared to an abrupt transition.
2Object-affected harmful factors
If a matching layer with graded index of refraction is introduced between the silicon nitride layer and the glass substrate layer, then reflection is reduced, but the device complexity increases
Solution Approach 1:
The matching layer is segmented into multiple sublayers, each with a different average index of refraction. The first sublayer has an average index of refraction of approximately 1.7, the second sublayer has an average index of refraction of approximately 1.6, and the third sublayer has an average index of refraction of approximately 1.55. This segmentation allows for controlled reflection reduction while maintaining manufacturability.
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
This configuration significantly reduces reflections, improving the visibility of displayed content by minimizing index-of-refraction discontinuities and providing enhanced reflection suppression at specific wavelengths, thereby enhancing the overall display performance.
Implementation Method 1
The index of refraction of silicon nitride is relatively high compared to that of the glass substrate material. For example, silicon nitride may have a refractive index of 1.9, whereas the glass substrate may have a refractive index of 1.5. As a result, there is a significant index-of-refraction mismatch between the silicon nitride layer and the substrate.
Implementation Method 2
If care is not taken, the index-of-refraction mismatch may give rise to increased reflection from the display.
Data Source
AI summary
An electronic device may include multiple display layers. The display layers may include a matching layer implemented using multiple graded index of refraction sublayers to help minimize reflections. The matching layer may include a first sublayer having a monotonically increasing index of refraction, a second (reverse matching) sublayer having a monotonically decreasing index of refraction, and a third sublayer having a monotonically increasing index of refraction. The second reverse matching sublayer may serve to induce an optical path difference that results in destructive inference at one or more specific wavelengths. The thickness of the reverse matching sublayer may be tuned to center the destructive interference at the desired wavelength(s). If desired, multiple matching layers each having their own reverse matching layers may be stacked on top of one another to provide reflectance suppression at multiple wavelengths.