Optical Fingerprint Sensor Module With Capacitive Contact Detection
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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, which complicates the integration of these sensors into consumer devices like smartphones for in-display fingerprint sensing.
Innovation Solution
An optical biometric imaging device is designed with an image sensor and capacitive readout circuitry, where the image sensor is separated from the display panel by a distance, forming a parallel plate capacitor to detect capacitance changes, allowing for accurate adjustment of image acquisition and distinguishing between accidental and intentional contacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If optical fingerprint sensor is integrated with display panel through direct lamination, then in-display fingerprint sensing is achieved, but manufacturing complexity and difficulty of accurate lamination increase
Solution Approach 1:
The device is divided into separate functional modules: the image sensor assembly and the display panel are kept as distinct components rather than being directly laminated. This segmentation allows each module to be manufactured and tested independently, reducing overall manufacturing complexity while maintaining the in-display fingerprint sensing capability.
Solution Approach 2:
A capacitive sensing structure is introduced as an intermediary between the image sensor and the display panel. This intermediary layer enables the transmission of capacitive signals from the fingerprint through the display panel to the image sensor below, allowing in-display sensing without direct contact or complex lamination between the sensor and panel.
2Length of stationary object
If display panel is placed close to image sensor for thin design, then device thickness is reduced, but accurate lamination and alignment become more difficult
Solution Approach 1:
The capacitive sensing structure serves as an intermediary that allows the display panel to be positioned at an optimized distance from the image sensor. This mediator enables accurate capacitive signal detection even when the panels are not in direct contact, reducing the need for extremely precise lamination while maintaining thin device profile.
Solution Approach 2:
The system utilizes changes in capacitive parameters (capacitance values) to detect fingerprint patterns. By monitoring capacitance variations rather than relying on direct optical contact, the system can maintain accurate fingerprint sensing with greater tolerance in the distance and alignment between the display panel and image sensor.
3Measurement precision
If capacitive readout circuitry is added to detect capacitance changes, then ability to distinguish intentional contact is improved, but device complexity increases
Solution Approach 1:
The capacitive readout circuitry is integrated into the existing image sensor structure, allowing the same hardware to serve multiple functions: capturing optical images of the fingerprint and simultaneously detecting capacitive changes to distinguish intentional contact. This multi-functionality reduces overall device complexity despite the added capability.
Solution Approach 2:
The capacitive sensing function is merged with the optical imaging function in the image sensor assembly. By combining these two sensing modalities into a single integrated structure, the system achieves both high measurement precision for contact detection and reduced device complexity through component consolidation.
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 simplifies the manufacturing process by allowing for flexible integration of the image sensor with the display panel, enabling accurate fingerprint capture and distinguishing between different contact forces, enhancing the reliability of in-display fingerprint sensing.
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
Implementation Method 2
image sensor comprising a photodetector pixel array and image sensor circuitry configured to capture an image of an object in contact with an outer surface of the imaging device
Data Source
AI summary
There is an optical biometric imaging device configured to capture an image of an object in contact with an outer surface of the biometric imaging device, the biometric imaging device comprising: an image sensor comprising a photodetector pixel array and image sensor circuitry configured to capture an image of the object in contact with the outer surface of the imaging device; the image sensor comprising a first electrically conductive structure arranged adjacent to an active sensing area of the photodetector pixel array; a display panel arranged on top of and at a distance from the image sensor, the display panel comprising a second electrically conductive structure on a bottom side of the display panel and arranged to face the first electrically conductive structure of the image sensor; and capacitive readout circuitry arranged and configured to detect a capacitance between the first electrically conductive structure and the second electrically conductive structure.