Touch Panel Symmetric Refractive Index Design
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Solution Overview
Problem
Conventional capacitive touch panels suffer from optical issues such as rainbow mura phenomenon due to refractive index mismatches between layers, leading to poor optical performance and visible wiring outlines.
Innovation Solution
A touch panel with a multi-layer structure where layers are symmetrically distributed in terms of refractive index, including a substrate, first conductive layer, insulating layer, shading layer, and protective layer, with refractive indices between 1.5 and 2.2, to achieve high transmittance and low reflection, and improved mechanical performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bridge insulation members with refractive index of about 1.5 are used between conductive wires, then the conductive wires are insulated from each other, but the refractive index mismatch causes visible wiring outlines and poor optical performance
Solution Approach 1:
The patent changes the refractive index parameter of the insulating layer from the conventional 1.5 to a range of 1.7-2.2, matching the refractive index of the conductive wires. This parameter change eliminates the refractive index mismatch that causes visible wiring outlines while maintaining the insulation function.
Solution Approach 2:
The patent applies different refractive indices to different layers locally - the insulating layer has a refractive index of 1.7-2.2 while the protective layer has a refractive index of 1.5-1.6. This local differentiation optimizes optical performance at each interface while maintaining overall functionality.
2Shape
If the black matrix layer has larger thickness at periphery region, then the shading area is formed, but a height difference is created causing rainbow mura phenomenon at edges
Solution Approach 1:
The patent changes the refractive index parameter of the protective layer to 1.5-1.6, matching the substrate's refractive index. This creates optical symmetry that compensates for the thickness difference in the black matrix layer, eliminating the rainbow mura phenomenon while preserving the shading area.
Solution Approach 2:
The patent accepts the asymmetric thickness distribution of the black matrix layer (thicker at periphery) but compensates with symmetric refractive index design. The protective layer's refractive index is specifically chosen to create optical symmetry that counteracts the geometric asymmetry, preventing rainbow mura.
3Adaptability or versatility
If transparent conductive layer is patterned to form electrodes, then the touch-sensing area is created, but the patterned edges create height difference with the black matrix layer
Solution Approach 1:
The patent changes the refractive index parameter of the protective layer to match the substrate (1.5-1.6), creating optical symmetry that compensates for thickness variations introduced during the patterning process. This allows the transparent conductive layer to be patterned for touch-sensing functionality without creating visible optical defects.
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 symmetric refractive index distribution enhances optical characteristics by preventing rainbow mura and reducing the visibility of wiring outlines, while the insulating layer provides better mechanical stability.
Implementation Method 1
the refractive index of the bridge insulation members 92 is lower than the refractive index of the first electrodes 90 and the second electrodes 91, and thereby the conditions of refraction of light through the bridge insulation member 92 and through the electrodes are different
Implementation Method 2
a user may easily see the outline of the wirings of the first electrodes 90 and the second electrode 91
Data Source
AI summary
A touch panel has a substrate on which a first conductive layer, an insulating layer, a second conductive layer and a protective layer are formed in order. The second conductive layer and the first conductive layer form a touch-sensing area. The protective layer and the substrate have the same refractive index; and the first conductive layer, the insulating layer and the second conductive layer have the same refractive index so that the whole layered structure substantially has a symmetrical distribution of refractive indices, and leading to having optical characteristics of high transmittance and low reflectance.