Fingerprint Sensing Unit Reducing Light Reflection
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Solution Overview
Problem
Fingerprint sensing units in display devices suffer from external light reflection, which degrades display quality due to their multilayer structure with different refractive indices, leading to light reflection or total reflection at interlayer interfaces.
Innovation Solution
A fingerprint sensing unit design featuring a substrate with a buffer layer and insulating layers, where the sensing electrode directly contacts the buffer layer, reducing the area covered by insulating layers and minimizing light reflection by eliminating interfaces with different refractive indices between the substrate and the sensing electrode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a multilayer structure with different refractive indices is used in the fingerprint sensing unit, then the sensing functionality is achieved, but light reflection occurs at interlayer interfaces degrading display quality
Solution Approach 1:
The patent extracts and removes the insulating layer from specific regions to create openings that expose the buffer layer. This selective removal eliminates the harmful refractive index interface between the insulating layer and other layers, thereby reducing light reflection while preserving the sensing functionality in the exposed regions.
Solution Approach 2:
The patent applies different structural configurations to different regions of the fingerprint sensing unit. In sensing regions, openings expose the buffer layer to minimize reflection, while in non-sensing regions, the insulating layer remains to provide electrical insulation. This local differentiation resolves the contradiction between sensing performance and reflection reduction.
2Reliability
If insulating layers are added to the fingerprint sensing unit, then electrical insulation is provided, but the number of interfaces with different refractive indices increases causing more light reflection
Solution Approach 1:
The patent selectively removes the insulating layer in specific openings to eliminate harmful refractive index interfaces. By extracting the insulating layer only where necessary for optical performance while maintaining it in other regions for electrical insulation, the patent resolves the contradiction between providing electrical insulation and reducing light reflection.
3Reliability
If the sensing electrode is covered by insulating layers, then electrical insulation is maintained, but light reflection increases and display quality degrades
Solution Approach 1:
The patent creates a local quality distinction by exposing the buffer layer in specific openings above the sensing electrode while maintaining insulating layers in other areas. This allows the sensing electrode to be electrically insulated where needed while having direct optical access to the buffer layer in sensing regions, thereby improving display quality without compromising electrical insulation.
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 design significantly reduces external light reflection, thereby enhancing the display quality of display devices by minimizing interlayer reflections and improving the sensing unit's performance.
Implementation Method 1
a capacitive type uses sensing electrodes to recognize a fingerprint by sensing a capacitance difference based on a distance between a ridge and a valley of the fingerprint
Implementation Method 2
When each layer has a different refractive index, light reflection or total reflection may occur at interlayer interfaces
Implementation Method 3
When each layer has a different refractive index, light reflection or total reflection may occur at interlayer interfaces
Data Source
AI summary
A fingerprint sensing unit includes a substrate; a buffer layer disposed on the substrate; a thin film transistor disposed on the buffer layer; an insulating layer disposed on the buffer layer and that has an opening that exposes at least a portion of the buffer layer; and a sensing electrode disposed on the portion of the buffer layer that is exposed by the opening, where the sensing electrode is connected to the thin film transistor. A display device that includes the fingerprint sensing unit can reduce internal reflection of external light.