Fingerprint Sensor with Variable Permittivity Protection Layer
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Solution Overview
Problem
Active self-capacitive fingerprint sensors require a thicker sensing distance, which can limit their integration with display devices and affect sensing sensitivity.
Innovation Solution
A fingerprint sensor design with a sensor substrate, sensor pixels, and a sensor protection layer having regions of different permittivity, including a high permittivity region on the sensor electrode and a low permittivity region on the peripheral area, to optimize sensing distance and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a thicker sensing distance is used in active self-capacitive fingerprint sensors, then sensing sensitivity is improved, but integration with display devices is limited
Solution Approach 1:
The sensor protection layer is divided into two regions with different permittivities: a first region with high permittivity (≥7) positioned over the sensor electrode to enhance capacitance change and sensing sensitivity, and a second region with low permittivity (1-7) positioned in peripheral areas to maintain appropriate sensing distance and prevent interference. This local differentiation resolves the contradiction by optimizing each region for its specific function.
Solution Approach 2:
The sensor protection layer uses composite material structure combining regions of different permittivity values. The first region contains materials with high permittivity (such as inorganic fillers by first ratio) while the second region contains materials with low permittivity (inorganic fillers by second ratio lower than first ratio). This composite approach allows simultaneous achievement of enhanced sensitivity and proper integration dimensions.
2Measurement precision
If the sensing distance is increased to improve sensitivity, then capacitance change detection is enhanced, but device integration becomes more difficult
Solution Approach 1:
By creating local quality differences in the sensor protection layer through permittivity variation, the invention enhances capacitance change detection in the sensing region while maintaining compact overall device structure for easy integration. The high permittivity first region amplifies capacitance signals locally without requiring increased overall sensing distance.
Solution Approach 2:
The invention changes the permittivity parameter of the sensor protection layer material to resolve the contradiction. By selecting materials with specific permittivity values (first ratio of inorganic fillers for high permittivity, second ratio for low permittivity), the system achieves enhanced capacitance detection while maintaining appropriate physical dimensions for device integration.
3Measurement precision
If a uniform permittivity structure is used in the sensor protection layer, then manufacturing is simplified, but sensing sensitivity is reduced
Solution Approach 1:
The sensor protection layer implements local quality differentiation with two distinct permittivity regions. The first region with high permittivity (inorganic fillers by first ratio) enhances sensing sensitivity over the electrode area, while the second region with low permittivity (inorganic fillers by second ratio) maintains appropriate electrical characteristics in peripheral areas. This localized optimization achieves superior sensing performance.
Solution Approach 2:
The sensor protection layer employs composite material structure combining high permittivity and low permittivity regions. By using different ratios of inorganic fillers (first ratio vs. second ratio) in different regions, the invention achieves enhanced sensing sensitivity while maintaining manufacturability through systematic material distribution.
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 design improves sensing sensitivity while meeting the required sensing distance, enhancing the recognition of fingerprints and palm prints by adjusting capacitance changes effectively.
Implementation Method 1
each of the sensor pixels includes a sensor electrode... configured to sense a capacitance change corresponding to a touch of a user... the sensor electrode may be configured to form a second capacitor together with a finger of the user when a touch occurs
Implementation Method 2
the sensor protection layer may include a first region having a first permittivity and a second region having a second permittivity less than the first permittivity... the first permittivity may be a relative dielectric constant in a range of 7 or more, and the second permittivity may be a relative dielectric constant in a range of 1 to less than 7
Data Source
AI summary
A fingerprint sensor according to an exemplary embodiment of the present inventive concept includes a sensor substrate; a plurality of sensor pixels sensing a capacitance change corresponding to a touch of a user, wherein each of the sensor pixels includes a sensor electrode; and a sensor protection layer disposed on the sensor substrate and the plurality of sensor pixels, wherein the sensor protection layer may include a first region having a first permittivity and a second region having a second permittivity less than the first permittivity.