Thin, multi-lens, optical fingerprint sensor having pinholes in a mask layer sized to compensate for expected illumination of different fields of view
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Solution Overview
Problem
Modern cellphones face challenges in accommodating large fingerprint sensors due to limited space, which affects battery size and increases production costs and defects, necessitating a smaller and more efficient sensor design.
Innovation Solution
A multi-lens optical fingerprint sensor with pinholes in a mask layer is designed to compensate for varying illumination, allowing for a smaller sensor area by using microlenses and pinholes to splay outwardly angled fields of view, with larger pinholes for outwardly angled photodiodes to balance light admission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If a single-lens fingerprint sensor with a large image sensor array is used to image a reasonable area of the finger, then the field of view is sufficient, but the sensor requires considerable space between lens and array of photosensors, increasing device size
Solution Approach 1:
The patent divides the single lens into multiple microlenses arranged in an array, with each microlens focusing light onto a corresponding photodiode group. This segmentation allows the sensor to achieve a comprehensive field of view across the fingerprint area while maintaining a compact form factor, as each microlens-photodiode unit can be positioned closely together without requiring the large spacing needed for a single-lens system.
2Area of moving object
If the image sensor array is made larger to capture a reasonable area of the finger, then the field of view is adequate, but the fabrication cost increases exponentially and defect probability rises
Solution Approach 1:
By segmenting the sensor into multiple small photodiode groups, each served by a dedicated microlens, the patent reduces the area of individual photodiode units. This segmentation strategy lowers fabrication costs and defect rates associated with large integrated circuits, while the collective array of small units still provides sufficient field of view for fingerprint imaging.
Solution Approach 2:
The patent employs different pinhole diameters in the mask layer for different regions of the sensor array. Specifically, photodiode groups with outwardly angled fields of view have larger pinhole diameters than those with center-direct fields of view. This parameter change compensates for illumination variations across the sensor array, ensuring uniform light distribution while maintaining a compact, cost-effective sensor design.
3Ease of manufacture
If photodiode groups with outwardly splayed fields of view use the same pinhole size as center-direct groups, then manufacturing is simpler, but illumination uniformity is compromised
Solution Approach 1:
The patent applies different pinhole diameters to different regions of the mask layer based on the specific illumination requirements of each photodiode group. Photodiode groups with outwardly splayed fields of view receive larger pinholes to compensate for reduced light admission, while center-direct groups use smaller pinholes. This local differentiation ensures uniform illumination across all photodiode groups while maintaining manufacturing feasibility through standardized fabrication processes.
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 design enables a smaller, less expensive fingerprint sensor that fits within the limited space of a cellphone, improving battery capacity and reducing production costs while maintaining image quality.
Implementation Method 1
each field of view being through the microlens
Implementation Method 2
locations and sizes of pinholes of upper and lower mask layers
Implementation Method 3
multiple photodiode groups each having a field of view
Data Source
AI summary
An image sensor for imaging fingerprints has multiple photodiode groups each having a field of view determined by pinholes of upper and lower mask layers and a metal layer, each field of view being through a microlens. Many photodiode groups have fields of view outwardly splayed from a group having a center-direct field of view. A diameter of pinholes of the metal layer distant from the group having a center-direct field of view have larger diameter than a pinhole of the photodiode group having a center-direct field of view. A method of matching illumination of a group of photodiodes with center-direct field of view to illumination of photodiode groups having outwardly splayed fields of view includes sizing a pinhole in the metal layer of photodiode groups with outwardly splayed fields of view larger than a pinhole associated with of photodiode groups having a center-direct field of view.