Multi-lens Fingerprint Sensor for Compact Mobile Devices
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Solution Overview
Problem
Modern cell phone designs face challenges in accommodating fingerprint sensors due to limited space, increasing battery demands, and the cost and defect probability of large image sensor circuits, which necessitate a compact and efficient fingerprint imaging solution.
Innovation Solution
A fingerprint sensor system utilizing multiple microlenses with splayed fields of view and a processor to read and compare fingerprint patterns, featuring a microlens array with aligned openings in mask layers and pinholes to focus light on photodiode groups, allowing for high-resolution imaging within a smaller footprint.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single lens and single array of photosensors are used to image fingerprint surface, then a reasonable area of the finger can be imaged, but the lens and array require large space between them which is not available in cell phone
Solution Approach 1:
The single lens is divided into multiple microlenses arranged in an array, and the single photosensor array is divided into multiple photodiode groups. Each microlens focuses light from a specific region onto corresponding photodiode groups, enabling compact fingerprint imaging with reduced space requirements between the lens array and photosensor array.
2Use of energy by moving object
If battery size is increased to meet power demand, then power demand is satisfied, but the battery encroaches on space formerly occupied by single-lens fingerprint sensor optics
Solution Approach 1:
The microlens array and photodiode groups are configured with multiple small optical elements instead of single large elements, reducing the overall footprint of the fingerprint sensor optics and creating space for larger batteries while maintaining fingerprint imaging capability.
3Ease of manufacture
If large circuits are used in image sensor, then fabrication cost is relatively constant per wafer, but large circuits have higher probability of fabrication defects and are more expensive per circuit
Solution Approach 1:
The image sensor is divided into multiple smaller photodiode groups instead of using large photodiodes. This segmentation reduces the probability of fabrication defects in each individual photodiode while maintaining overall sensor functionality, and allows more circuits to be fabricated per wafer at lower cost.
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 a compact fingerprint sensor that fits between an OLED screen and a cell phone battery, providing high-resolution fingerprint imaging and effective user identification while minimizing space and cost, and incorporating anti-spoofing features for security.
Implementation Method 1
each group of photodiodes having a field of view determined by locations of a microlens, an opening of an upper mask layer, an opening of a lower mask layer, a pinhole in a metal layer, and the photodiode group in addition to optical characteristics of the microlens, each field of view being through the microlens
Implementation Method 2
A prior optical sensor for reading fingerprints used an electronic camera equipped with a single lens and an image sensor with a single array of photosensors to image a fingerprint surface
Data Source
AI summary
An image sensor for imaging fingerprints has multiple photodiode groups each with field of view through a microlens determined by optical characteristics of the microlens and locations of the microlens and openings of upper and lower mask layers. Many photodiode groups have fields of view outwardly splayed from a center-direct field of view. A diameter of openings of the upper mask layer distant from the group having a center-direct field of view is larger than openings of a 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 openings in the upper mask layer of photodiode groups with outwardly splayed fields of view larger than openings in the upper mask layer associated with photodiode groups having center-direct field of view.