Under-display fingerprint sensor with improved contrast ratio
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Solution Overview
Problem
Conventional optical fingerprint sensors are difficult to miniaturize due to their bulky components, and capacitive fingerprint sensors face challenges in being integrated under a display panel without obstructing the protective cover, such as glass, on electronic devices like smartphones.
Innovation Solution
An under-display fingerprint sensor system that converts circularly-polarized light reflected from a fingerprint into linearly-polarized light using a light selection layer, with lenses refracting and focusing this light onto image sensors, allowing for fingerprint imaging without obstructing the display panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional optical systems (prisms, mirrors, lenses) are used in fingerprint sensors, then light reflection and imaging functions are achieved, but device volume increases making miniaturization difficult
Solution Approach 1:
The patent extracts and eliminates bulky optical components (prisms, mirrors, lenses) from the fingerprint sensor system. Instead of using these separate components for light reflection and imaging, the invention integrates the optical functions directly into the display panel structure, keeping only the essential imaging sensor and removing unnecessary intermediate optical elements.
Solution Approach 2:
The patent merges the optical reflection function with the display panel structure. The display panel itself serves as the light source and optical system, combining multiple functions (display, lighting, fingerprint sensing) into a single integrated structure, thereby reducing overall device volume while maintaining reliability.
2Ease of operation
If capacitive fingerprint sensor is mounted on front surface, then fingerprint detection is enabled, but protective cover (glass) cannot fully cover the display panel
Solution Approach 1:
The patent moves the fingerprint sensor from the front surface (2D plane) to the back side of the display panel (another dimension). By positioning the imaging sensor on the rear surface and using the display panel thickness as the optical path, the sensor can detect fingerprints through the glass cover without compromising the protective cover's integrity or aesthetic appearance.
Solution Approach 2:
The display panel acts as an intermediary medium between the fingerprint sensor and the glass cover. Light reflected from the fingerprint passes through the glass cover and display panel to reach the sensor, allowing the sensor to be positioned behind the display while still detecting fingerprints through the protective cover.
3Volume of moving object
If fingerprint sensor is positioned under display panel, then device miniaturization is achieved, but contrast ratio of fingerprint image decreases
Solution Approach 1:
The patent changes the polarization state of light as a key parameter to improve contrast ratio. By using circularly polarized light from the display panel and analyzing the polarization changes after reflection from fingerprints, the system achieves high contrast images even with the sensor positioned behind the display panel, maintaining measurement precision while enabling miniaturization.
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 the integration of fingerprint sensors under display panels without obstructing protective covers, enhancing device miniaturization and usability by effectively capturing fingerprint images through polarized light manipulation.
Implementation Method 1
a light selection layer, being disposed under a display panel, configured for converting a downward circularly-polarized light that is reflected in a region below a valley of a fingerprint into a downward linearly-polarized light
Implementation Method 2
a sensor polarizer, being disposed under the sensor retarder, configured for passing the downward linearly-polarized light, and configured for converting the unpolarized light into the sensor linearly-polarized light, wherein a light amount of the unpolarized light is reduced by the sensor polarizer
Implementation Method 3
a plurality of lenses, being disposed apart from the light selection layer, configured for refracting the downward linearly-polarized light and the sensor linearly-polarized light that propagate in a perpendicular direction toward each focal point
Implementation Method 4
configured for deviating the downward linearly-polarized light and the sensor linearly-polarized light that propagate at an angle other than perpendicular from the focal point
Implementation Method 5
an image sensor having a plurality of light receiving units disposed at each focal point of the plurality of lenses to receive the downward linearly-polarized light and the sensor linearly-polarized light that are refracted toward each focal point
Data Source
AI summary
Under-display fingerprint sensor of generating a fingerprint image disclosed. Under-display fingerprint sensor includes a light selection layer, being disposed under a display panel, configured for converting a downward circularly-polarized light into a downward linearly-polarized light, and configured for converting an unpolarized light into a sensor linearly-polarized light, a plurality of lenses, being disposed apart from the light selection layer and configured for refracting the downward linearly-polarized light and the sensor linearly-polarized light that propagate in a perpendicular direction toward each focal point, and an image sensor having a plurality of light receiving units disposed at each focal point of the plurality of lenses to receive the downward linearly-polarized light and the sensor linearly-polarized light that are refracted toward each focal point.