Rear-Surface Optical Fingerprint Sensor in Flat Panel Display
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Solution Overview
Problem
Conventional optical fingerprint sensors face limitations in recognizing fingerprint patterns due to low directivity of diffused lights, requiring additional devices and increasing device thickness, while capacitive sensors are complex and sensitive to protective films, making them unsuitable for portable devices.
Innovation Solution
A flat panel display with an optical image sensor at the rear surface, featuring a display panel, a barrier plate with light transparent areas, and a light sensor, along with a lens film and flexible circuit board, allowing for image sensing without occupying the display area and maintaining device thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If conventional optical fingerprint sensors use diffused lights, then the sensing area can be covered, but the fingerprint pattern recognition accuracy deteriorates due to low directivity
Solution Approach 1:
The patent introduces a light guide plate as an intermediary component between the light source and the fingerprint sensor. The light guide plate receives light from the LED and guides it through its internal structure to provide both wide area coverage and improved directivity to the sensor, resolving the contradiction between covering the sensing area and maintaining recognition accuracy
Solution Approach 2:
The patent replaces the conventional direct illumination method with an optical guiding mechanism. Instead of using diffused lights that lack directivity or collimated lights that require complex scanning structures, the light guide plate creates an optimized optical path that achieves both wide coverage and high directivity without mechanical scanning components
2Measurement precision
If collimated lights are used to improve directivity, then fingerprint pattern recognition accuracy improves, but the sensing area is restricted to a small area
Solution Approach 1:
The light guide plate extends the optical path in the thickness dimension of the display device. By guiding light through the thickness direction rather than only in the plane, the system achieves collimated light effects over a wide area without restricting the sensing area, resolving the contradiction between directivity and area coverage
3Measurement precision
If additional devices are added to improve light directivity, then fingerprint recognition accuracy improves, but device thickness increases
Solution Approach 1:
The light guide plate serves multiple functions simultaneously: it acts as a structural component of the display device, a light distribution element, and an optical guiding mechanism. This multi-functionality allows the system to achieve improved fingerprint recognition accuracy without adding separate dedicated components that would increase device thickness
Solution Approach 2:
The patent merges the light guide function with the existing display structure. The light guide plate is integrated into the display device's layered structure, combining the illumination function with the mechanical support function, thereby achieving improved recognition accuracy without increasing overall device thickness
4Adaptability or versatility
If optical image sensor is placed at the rear surface, then design freedom and sensitivity improve, but the structure becomes more complex
Solution Approach 1:
The patent inverts the conventional sensor placement from the front surface to the rear surface of the display device. By placing the optical image sensor at the rear surface and using the display panel itself as the light source and transmission medium, the system achieves improved design freedom and sensitivity while the display panel structure itself serves the dual purpose of display and sensor housing
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 accurate fingerprint recognition without increasing device thickness or weight, providing design freedom and improved sensitivity by using ultra-thin optical image sensors and condensing lenses for enhanced light detection.
Implementation Method 1
uses a light source such as a light emitting diode (or LED) to irradiate lights and detects the lights reflected by ridges of the fingerprint using a CMOS (or, complementary metal oxide semiconductor) image sensor
Implementation Method 2
providing design freedom and improved sensitivity by using ultra-thin optical image sensors and condensing lenses for enhanced light detection
Data Source
AI summary
The present disclosure relates to a flat panel display embedding an optical imaging sensor such as a fingerprint image sensor. The present disclosure provides a flat panel display embedding an optical image sensor comprising: a display panel including a display area and a sensing area defined in the display area; a barrier plate having a light transparent area corresponding to the sensing area and disposed at a rear surface of the display panel; and a light sensor disposed under the barrier plate corresponding to the light transparent area.