Fingerprint Sensor Dielectric Evaluation via Capacitive Coupling
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Solution Overview
Problem
Capacitive fingerprint sensors face performance degradation due to anomalies like material thickness variations, scratches, and dielectric or conductive structures on the sensor coating, which existing evaluation methods cannot effectively assess without physical contact or after the sensor is integrated into a product.
Innovation Solution
Evaluating the dielectric structure covering the sensing structures by sensing capacitive couplings across the sensor surface without physical contact, allowing for faster and more accurate production testing and post-delivery diagnostics, using a method that controls the potential of sensing structures to assess electrical properties and anomalies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a stamp test procedure is used to evaluate the dielectric structure, then defects can be detected, but the production process becomes slower and more complex
Solution Approach 1:
The patent replaces the mechanical stamp test procedure with an electrical evaluation method. Instead of physically touching the sensor surface with a stamp to detect defects, the system applies test voltages to sensing structures and measures capacitive coupling through the dielectric structure. This electrical substitution eliminates the need for mechanical contact, speeding up production while maintaining defect detection capability.
Solution Approach 2:
The fingerprint sensor itself is used to evaluate its own dielectric structure. The sensing structures and readout circuitry that are part of the sensor are utilized to apply test voltages and measure capacitive coupling, eliminating the need for separate external testing equipment. This self-evaluation approach simplifies the testing process and increases production efficiency.
2Adaptability or versatility
If the sensor is integrated into a product before evaluation, then post-delivery diagnostics become possible, but the evaluation process becomes more complex
Solution Approach 1:
The evaluation method uses the same sensing structures and readout circuitry for both fingerprint sensing and dielectric structure evaluation. The system can operate in different modes (fingerprint sensing mode and evaluation mode) using the same hardware components, eliminating the need for separate dedicated testing equipment and reducing overall system complexity.
Solution Approach 2:
The system evaluates the dielectric structure by changing the electrical parameters (applying different test voltages) rather than changing the physical state or configuration of the sensor. By manipulating voltage levels and measuring capacitive coupling under different electrical conditions, the system can assess dielectric properties without physical modification or complex mechanical testing apparatus.
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
Enables cost-efficient production and post-deployment diagnostics, detecting defects and conductive attacks on fingerprint sensors without physical contact, improving user experience and security.
Implementation Method 1
each sensing structure in the first set of sensing structures is controllable to provide a sensing signal indicative of a strength of a capacitive coupling between each sensing structure in the second set of sensing structures and the sensing structure in the first set of sensing structures
Data Source
Figure 1A~1C
Figure 2
Figure 3A~3B
AI summary
A method of evaluating a dielectric structure, comprising the steps of a) changing a potential difference between each sensing structure in a first set of sensing structures and each sensing structure in a second set of sensing structures, and to providing, for each sensing structure in the first set of sensing structures, a sensing signal indicative of a strength of a capacitive coupling between each sensing structure in the second set of sensing structures and the sensing structure in the first set of sensing structures; b) assign other sensing structures to the first set of sensing structures and the second set of sensing structures; c) performing step a) and step b) until a respective sensing signal has been provided for each sensing structure in the plurality of sensing structures; and d) providing an evaluation result based on the respective sensing signals.