Optical Fingerprint Sensor Layout for Flexible Display Integration
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Solution Overview
Problem
The integration of optical fingerprint sensors with display panels is challenging due to difficulties in accurate lamination in existing manufacturing processes, and there is a need for an improved optical biometric imaging device that can capture fingerprints and other biometric features with sufficient resolution while allowing the display panel to flex without contacting the image sensor.
Innovation Solution
An optical biometric imaging device is designed with the image sensor separated from the display panel, forming a parallel plate capacitor with an air gap, allowing for accurate determination of the distance between the finger and the image sensor, and incorporating capacitive readout circuitry to distinguish intentional contact from accidental touches, with a frame and spacer to manage the distance and prevent damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the image sensor is integrated directly with the display panel, then manufacturing complexity is reduced, but the display panel cannot flex without contacting the image sensor and causing damage
Solution Approach 1:
The system is divided into separate components: the display panel and the image sensor are positioned at different distances from the finger contact surface. The first electrically conductive structure is on the image sensor, while the second electrically conductive structure is on the display panel, creating distinct functional zones that allow independent optimization of each component's position and flexibility characteristics.
Solution Approach 2:
A capacitor formed by two electrically conductive structures acts as an intermediary mechanism between the display panel and the image sensor. This capacitor measures the distance between the finger and the image sensor, enabling the system to compensate for variations in distance caused by display panel flexing without requiring direct physical contact between the flexible display and the rigid image sensor.
2Ease of manufacture
If the image sensor is placed at a fixed distance from the display panel, then manufacturing is simplified, but accurate fingerprint capture requires precise distance control between finger and sensor
Solution Approach 1:
The capacitor serves as a feedback mechanism that continuously measures the distance between the finger and the image sensor. Based on this measured distance, the system can adjust imaging parameters such as exposure time, gain, or focus to compensate for distance variations, ensuring accurate fingerprint capture even when the exact finger-to-sensor distance varies due to display panel flexing or user pressing force.
3Ease of operation
If the display panel is allowed to flex freely, then user comfort is improved, but the distance between finger and image sensor becomes unpredictable
Solution Approach 1:
The capacitor acts as an intermediary measurement device that indirectly determines the finger-to-sensor distance by measuring the distance between the finger and the display panel, combined with knowledge of the fixed offset between the display panel and image sensor. This approach maintains display flexibility while providing the information needed to compensate for distance variations in the imaging system.
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 enables accurate fingerprint capture and differentiation between intentional and accidental contact, simplifies manufacturing, and allows the display panel to flex without contacting the image sensor, enhancing the integration of optical fingerprint sensors with display panels.
Implementation Method 1
capacitive readout circuitry arranged and configured to detect a capacitance between the first electrically conductive structure and the second electrically conductive structure
Data Source
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AI summary
There is an optical biometric imaging device (102) configured to capture an image of an object (104) in contact with an outer surface (106) of the biometric imaging device (102), the biometric imaging device (102) comprising: an image sensor (200) comprising a photodetector pixel array (202) and image sensor circuitry configured to capture an image of the object (104) in contact with the outer surface of the imaging device (102); the image sensor (200) comprising a first electrically conductive structure (206) arranged adjacent to an active sensing area (208) of the photodetector pixel array (202); a display panel (210) arranged on top of and at a distance from the image sensor (200), the display panel (210) comprising a second electrically conductive structure (212) on a bottom side (214) of the display panel (210) and arranged to face the first electrically conductive structure (206) of the image sensor (200); and capacitive readout circuitry arranged and configured to detect a capacitance between the first electrically conductive structure (206) and the second electrically conductive structure (212).