Optical Fingerprint Sensor Using Scattering Layer for Point Source Illumination
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Solution Overview
Problem
Conventional optical fingerprint sensors are too bulky for mobile devices and struggle to detect fine ridge and valley features through thick layers, such as smartphone cover glass, requiring cutouts and mechanical buttons that compromise device aesthetics and functionality.
Innovation Solution
An optical sensor design using a point light source or its approximation, with a scattering layer between the sensor substrate and cover layer, allowing light to pass through an aperture or being directed onto a small area of the scattering layer to mimic a point light source, enabling high-resolution imaging without secondary reflections and maintaining a featureless surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If conventional optical fingerprint sensors are used, then imaging capability is achieved, but device size becomes too bulky for mobile devices
Solution Approach 1:
The optical sensor is segmented into distinct functional layers: a cover layer with sensing surface, a scattering layer, and a sensor substrate with detector pixels. This segmentation allows each layer to be optimized independently, enabling compact overall size while maintaining high imaging resolution through the specialized scattering layer that creates point source illumination effects.
Solution Approach 2:
The patent transitions from conventional planar sensor design to a multi-layer vertical structure. By stacking the cover layer, scattering layer, and sensor substrate in three dimensions, the design achieves high-resolution imaging capability in a compact footprint suitable for mobile devices, effectively using the vertical dimension to overcome the size-resolution tradeoff.
2Reliability
If capacitive sensors are used to detect fingerprints through thick cover glass, then sensing capability is reduced, but device aesthetics are compromised due to required cutouts
Solution Approach 1:
The optical sensor design serves multiple functions within a single integrated structure: it provides high-resolution fingerprint imaging, maintains a featureless flush surface for device aesthetics, and works effectively through thick cover glass. The scattering layer enables the sensor to function as both an imaging device and a surface-covering element, eliminating the need for cutouts.
Solution Approach 2:
The scattering layer acts as an intermediary between the cover layer and sensor substrate, creating point source illumination that enables high-resolution imaging through thick cover glass. This intermediary layer allows the sensor to detect fingerprints through the cover glass without requiring direct contact or cutouts, maintaining both detection reliability and surface continuity.
3Measurement precision
If point source illumination is implemented, then optical efficiency and resolution are improved, but system complexity increases
Solution Approach 1:
The scattering layer automatically creates the point source illumination effect through its inherent light scattering properties when illuminated. The system uses the scattering layer's natural optical behavior to generate the required point source effect without additional optical elements, control mechanisms, or complex illumination systems, thereby maintaining high resolution while minimizing complexity.
Solution Approach 2:
The patent changes the optical parameters of the scattering layer (such as scattering coefficient, layer thickness, and material composition) to optimize the point source illumination effect. By adjusting these parameters, the system achieves high imaging resolution with a simple layered structure, avoiding the need for complex optical systems while maintaining measurement precision.
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 achieves high optical efficiency and resolution, eliminating secondary reflections, and allows for a compact form factor suitable for mobile devices without the need for cutouts or mechanical buttons, enhancing user experience and manufacturing simplicity.
Implementation Method 1
a scattering layer; wherein the scattering layer is disposed between the sensor substrate and the cover layer
Implementation Method 2
acquire image data, from one or more detector pixels, of an input object in contact with the sensing surface, wherein the image data corresponds to light from the light source that is reflected at the sensing surface of the cover layer
Data Source
AI summary
Disclosed are systems and methods for imaging an object. For example, an optical sensor for imaging an input object, comprises: a sensor substrate comprising detector pixels; a scattering layer; a cover layer including a sensing surface, wherein the scattering layer is disposed between the sensor substrate and the cover layer; and, a light source. The optical sensor is configured to: illuminate the light source causing light beams to emanate from the light source to produce an effect of a point light source at the scattering layer; and acquire image data, from one or more detector pixels, of an input object in contact with the sensing surface, wherein the image data corresponds to light from the light source that is reflected at the sensing surface of the cover layer.