Fingerprint Sensor Substrate Integration for Sensitivity
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Solution Overview
Problem
Capacitive fingerprint identification devices face challenges with reduced sensitivity due to the distance between sensing electrodes and the finger, leading to increased material costs, complex packaging, and decreased product reliability and yield, primarily because of the need for protective epoxy resin and additional components like sapphire films.
Innovation Solution
An interference-free fingerprint identification device is developed using a thin film transistor substrate with a sensing electrode layer connected to thin film transistors, a gate line layer, a data line layer, and shielding layers to reduce chip area, simplify packaging, and enhance sensing accuracy, allowing for increased sensing area and curved surface detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If epoxy resin is applied to protect the lead lines, then the lead lines are protected from damage, but the distance between the sensing electrodes and the finger increases, reducing sensitivity
Solution Approach 1:
The patent extracts the sensing circuit from the packaged IC chip form and integrates it directly into the fingerprint sensor substrate. This eliminates the epoxy resin package that caused the distance problem, while still protecting the lead lines through direct integration on the substrate level rather than through a thick protective package.
Solution Approach 2:
The patent transitions from a three-dimensional packaged structure (IC chip with epoxy resin package) to a planar integrated structure where the sensing circuit is directly formed on the substrate. This dimensional change eliminates the vertical distance introduced by the package while maintaining protection of the lead lines through the substrate structure itself.
2Measurement precision
If sapphire film with high dielectric coefficient is used to reduce distance, then sensitivity is increased, but material cost increases
Solution Approach 1:
The patent replaces expensive sapphire film with a cost-effective thin film transistor structure that achieves the same sensitivity improvement. The TFT-based sensing circuit provides the necessary electrical characteristics without requiring expensive exotic materials, thereby reducing material costs while maintaining performance.
Solution Approach 2:
The patent changes the fundamental operating parameters by using thin film transistors to actively control the sensing circuit operation. This allows for dynamic optimization of the sensing characteristics without relying on high dielectric coefficient materials, achieving sensitivity improvement through active electronics rather than passive material properties.
3Ease of manufacture
If opening is made in protection glass and button type chip is arranged, then the fingerprint identification chip can be integrated, but the package structure becomes complicated and product yield decreases
Solution Approach 1:
The patent merges the sensing circuit, lead lines, and protective structure into a single integrated thin film transistor substrate. This consolidation eliminates the need for separate button-type chip packaging and complex assembly through openings in protection glass, achieving integration while simplifying the overall package structure.
Solution Approach 2:
The thin film transistor substrate serves multiple functions simultaneously: it provides the sensing circuit, protects the lead lines, enables integration, and maintains a simple package structure. This multi-functionality eliminates the need for separate specialized components and complex packaging arrangements.
4Reliability
If sensing circuit is packaged in IC chip, then lead lines are protected, but the distance between sensing electrodes and finger increases, reducing signal-to-noise ratio
Solution Approach 1:
The patent replaces the mechanical packaging approach (IC chip in epoxy resin) with an electronic integration approach using thin film transistors. This substitution eliminates the mechanical distance introduced by packaging while maintaining protection of the lead lines through the integrated substrate structure, thereby improving the signal-to-noise ratio.
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 solution improves the signal-to-noise ratio, increases the effective sensing distance, reduces manufacturing costs, and enhances the accuracy and reliability of fingerprint identification while simplifying the package structure and increasing yield.
Implementation Method 1
capacitive identification technology
Implementation Method 2
thin film transistors are used to form a thin film transistor layer on a substrate
Implementation Method 3
A first shielding layer is disposed between the gate line layer and the data line layer
Data Source
AI summary
An interference-free fingerprint identification device includes a TFT substrate, a TFT layer having plural TFTs, a sensing electrode layer having plural fingerprint sensing electrodes, a gate line layer having plural gate lines, a data line layer having plural data lines, and a first shielding layer. Each fingerprint sensing electrode corresponds to a plurality of the TFTs, and is connected to sources or drains of at least two corresponding TFTs. At least two gate lines are electrically connected to gates of a plurality of the TFTs corresponding to a fingerprint sensing electrode. Each data line is electrically connected to a source or drain of a TFT in a plurality of the TFTs corresponding to a fingerprint sensing electrode. The first shielding layer is electrically connected to a source or drain of a TFT in a plurality of the TFTs corresponding to each fingerprint sensing electrode.