Two-Substrate Fingerprint Sensor Segmentation for Cost and Sensitivity
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Solution Overview
Problem
Capacitive semiconductor fingerprint sensors face challenges in production cost, sensitivity, and accuracy due to the need for a large pressing area and inadequate protection from perspiration and electrostatic discharge, with sapphire substrates being expensive and inefficient.
Innovation Solution
A two-substrate fingerprint recognition device with a first substrate having electrodes and conductive connection pads, and a second substrate with selecting switch circuits and connection pads, allowing for improved sensing sensitivity and signal-to-noise ratio without the need for a sapphire substrate, integrated into a touch display panel manufacturing process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sapphire substrate is used to protect the fingerprint sensor, then the sensing sensitivity and signal-to-noise ratio are improved, but the production cost is greatly increased
Solution Approach 1:
The device is divided into two separate substrates: a first substrate for fingerprint sensing and a second substrate for protection. This segmentation allows each substrate to be optimized independently - the first substrate can be thin for high sensitivity while the second substrate provides protection, avoiding the need for expensive sapphire while maintaining sensing performance.
Solution Approach 2:
A spacer layer is introduced as an intermediary between the first substrate and second substrate. This spacer maintains the optimal distance for sensing sensitivity while allowing the use of cheaper materials instead of sapphire, thus reducing cost while preserving measurement precision.
2Reliability
If a common protection glass with thickness of 200-300 μm is used, then the chip is protected from perspiration and electrostatic discharge, but the capacitive sensor cannot distinguish small variations in charge amount
Solution Approach 1:
The protection function is separated from the sensing function by using two distinct substrates. The first substrate remains thin to enable sensitive charge detection, while the second substrate provides the necessary protection, thus resolving the contradiction between protection and sensitivity.
Solution Approach 2:
The spacer acts as an intermediary that maintains the critical thin distance between the sensing surface and the protective layer, enabling both protection and high sensitivity to charge variations to coexist.
3Measurement precision
If the sensing area is increased to improve fingerprint recognition, then the sensing performance is enhanced, but the chip area occupied by sensing electrodes increases, resulting in higher production cost
Solution Approach 1:
The sensing area is extended in the vertical dimension by introducing a spacer that creates a three-dimensional sensing volume, rather than only expanding the two-dimensional chip area. This allows enhanced fingerprint recognition without proportionally increasing chip real estate and production cost.
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
Enhances fingerprint recognition accuracy and reduces production costs by minimizing the use of expensive components and integrating the device into existing touch display panel manufacturing processes, improving sensitivity and stability without the need for a sapphire substrate.
Implementation Method 1
capacitive fingerprint sensors... the capacitance sensors are densely integrated in a chip. When a finger presses the surface of the chip, the capacitance sensors in the chip will produce a fingerprint image according to the amount of charge of the fingerprint
Implementation Method 2
The anisotropic conductive film is provided between the first substrate and the second substrate, wherein the anisotropic conductive film electrically connects the plurality of electrodes to the plurality of connection pads
Data Source
AI summary
A two-substrate fingerprint recognition device includes a first substrate and a second substrate. A plurality of electrodes, a plurality of connection pads and a plurality of connection traces are deployed on one surface of the first substrate. A plurality of conductive connection pads, a plurality of connection pads, a plurality of connection traces and a plurality of switch circuits are deployed on one surface of the second substrate that faces the first substrate. At least one electrode connection pad of the second substrate is electrically connected to a corresponding electrode of the first substrate.