Fingerprint Sensor Critical Angle Light Filtering
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Solution Overview
Problem
Fingerprint recognition sensors face challenges in achieving high contrast ratios and reducing noise and thickness, while also allowing for flexible light source positioning, due to issues with ambient light interference and internal reflection affecting image quality.
Innovation Solution
The design incorporates a photo sensor with a first and second matrix, each with openings, and a cover layer that filters light based on critical angles, ensuring only light above a certain angle is incident on the sensor, and includes a light source positioned below the finger to minimize ambient light impact, along with a light absorbing and metal layers to enhance contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a black matrix is installed on the upper portion of the fingerprint sensor to prevent ambient light interference, then the degree of definition of the fingerprint image is improved, but the contrast ratio of the fingerprint image deteriorates due to internal reflection from the valley regions
Solution Approach 1:
The sensor is divided into two distinct regions: a first sensor region with a first black matrix for ambient light blocking, and a second sensor region with a second black matrix for controlling internal reflection. This segmentation allows each region to perform its specific function independently, resolving the contradiction between improving definition and maintaining contrast ratio.
Solution Approach 2:
Different black matrix configurations are applied to different regions of the sensor. The first black matrix in the first sensor region has specific optical properties for ambient light rejection, while the second black matrix in the second sensor region has different optical properties for controlling internal reflection from valley regions. This local differentiation allows simultaneous optimization of both definition and contrast ratio.
2Measurement precision
If multiple matrices and openings are added to control light paths and improve image quality, then the contrast ratio and clarity are improved, but the device complexity increases
Solution Approach 1:
The first black matrix and second black matrix are integrated into a unified sensor structure with coordinated light paths. The matrices work together as a combined system rather than separate components, and the openings are positioned to enable both matrices to function simultaneously. This merging reduces overall complexity compared to having completely separate systems.
Solution Approach 2:
The black matrices serve multiple functions: they block ambient light, control internal reflection, and define optical paths for both ridge and valley regions. The openings in both matrices work together to guide light from different finger regions to appropriate sensor areas. This multi-functionality reduces the need for additional separate components.
3Loss of information
If light absorbing layers and metal layers are added to enhance contrast, then the fingerprint image contrast ratio is improved, but the thickness of the sensor increases
Solution Approach 1:
The optical properties of the black matrices are optimized to achieve high contrast ratio enhancement with minimal thickness. By adjusting the optical parameters (absorption coefficients, refractive indices) and geometric parameters (thickness, opening sizes) of the matrices and openings, high contrast is achieved without requiring thick additional layers.
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 configuration improves the contrast ratio and clarity of fingerprint images, reduces noise, and allows for thinner sensor designs, enhancing applicability and precision in device integration.
Implementation Method 1
light having an angle, formed by a normal line on the one surface of the cover layer and a path of the light incident on the cover layer, that is greater than a critical angle, sequentially passes through the second opening and the first opening and is incident on the photo sensor
Implementation Method 2
a photo sensor for sensing light that is diffuse-reflected from a finger of a user and incident on the photo sensor, or that is transmitted through the finger and incident on the photo sensor
Implementation Method 3
a first light absorbing layer including a light absorbing material, and a first metal layer positioned on the first light absorbing layer
Data Source
AI summary
A fingerprint recognition sensor according to an exemplary embodiment of the present invention includes: a photo sensor for sensing light that is diffuse-reflected from a finger of a user and incident on the photo sensor, or that is transmitted through the finger and incident on the photo sensor; a first matrix positioned on the photo sensor and including a first opening; a second matrix positioned on the first matrix and including a second opening; and a cover layer including one surface contacting the finger and positioned on the second matrix, wherein, from among light that is diffuse-reflected from the finger and incident on the cover layer or that is transmitted through the finger and incident on the cover layer, light having an angle, formed by a normal line on the one surface of the cover layer and a path of the light incident on the cover layer, that is greater than a critical angle, sequentially passes through the second opening and the first opening and is incident on the photo sensor.