Multi-Lens Optical Fingerprint Sensor for Thin Under-Display Imaging
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Solution Overview
Problem
The challenge is to create a fingerprint sensor that is compact enough to fit between an OLED screen and a battery in a cellphone, while minimizing space and cost, given the constraints of increasing battery size and power demand, and the higher expense and defect rate of large integrated circuits.
Innovation Solution
The solution involves an image sensor with multiple photodiode groups having fields of view determined by microlenses and pinholes, with outwardly splayed angles to reduce sensor size and cost, and larger pinholes in the metal layer to compensate for non-uniform illumination, allowing for a smaller and less expensive fingerprint sensor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single lens and single array of photosensors are used to image fingerprints, then the sensor can capture the fingerprint area, but the sensor size becomes large requiring considerable space between lens and photosensors
Solution Approach 1:
The patent divides the single lens into multiple microlenses arranged in an array, and divides the single array of photosensors into multiple groups. Each microlens focuses light from a specific angular direction onto its corresponding photodiode group. This segmentation allows the sensor to capture light from different angles simultaneously, enabling a smaller overall sensor size while maintaining the ability to image the entire fingerprint area.
Solution Approach 2:
The patent introduces angular dimensionality by orienting microlenses at different angles relative to the fingerprint surface. Photodiode groups are positioned to receive light at specific angles, creating a multi-dimensional light collection system. This angular distribution allows compact packaging of the optical system within the limited cellphone space while maintaining comprehensive fingerprint coverage.
2Area of stationary object
If larger integrated circuits are used for the image sensor, then the sensor area increases to capture fingerprints, but fabrication costs increase exponentially and defect rates increase
Solution Approach 1:
The image sensor is segmented into multiple smaller photodiode groups, each associated with specific microlenses. This segmentation allows the total sensor area to be divided into smaller functional units that can be fabricated more efficiently. Smaller circuits per unit reduce fabrication costs and defect rates while the collective array maintains the required imaging area for fingerprint capture.
3Area of stationary object
If photodiode groups have outwardly splayed fields of view to reduce sensor size, then sensor area decreases, but peripheral photodiodes receive less illumination requiring larger pinholes
Solution Approach 1:
The patent applies local quality by varying the pinhole sizes in the upper black mask layer based on position. Central photodiode groups receive light through smaller pinholes, while peripheral photodiode groups with outwardly splayed fields of view receive light through larger pinholes. This local adaptation compensates for the reduced light admission at peripheral positions, ensuring uniform illumination across all photodiode groups while maintaining the compact sensor design.
4Quantity of substance
If battery size is increased to meet power demand, then battery capacity increases, but available space for fingerprint sensor optics is reduced
Solution Approach 1:
The optical system is segmented into multiple microlenses and photodiode groups arranged in a compact configuration. This segmentation enables the fingerprint sensor to occupy significantly less area than a conventional single-lens system, freeing up space in the cellphone for larger battery capacity while maintaining full fingerprint imaging capability.
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 fingerprint sensor that can image a wider fingerprint area, reducing costs and maintaining image quality, while fitting within the limited space of a cellphone, thus addressing the need for compactness and affordability.
Implementation Method 1
each having a field of view determined by location and characteristics of a microlens of an array of microlenses as well as and locations and sizes of pinholes
Implementation Method 2
multiple photodiode groups each having a field of view determined by location and characteristics of a microlens
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.