Optical Metasurface Fingerprint Sensor Assembly for Compact Imaging

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Solution Overview

Problem

Conventional optical systems face limitations in achieving enhanced optical performance, particularly in visible and near-infrared imaging, due to challenges with aberrations, astigmatism, and the need for smaller form factors in consumer electronic devices such as fingerprint sensors.

Innovation Solution

Integration of optical metasurface arrays with pixelated sensor arrays and optical films, including refractive microlens arrays, infrared cutoff filters, and aperture arrays, to enhance signal-to-noise ratio, enable hyperspectral and polarization imaging, and facilitate liveness detection, while maintaining a compact design.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional optical elements (e.g., compound lenses) are used, then optical function is provided, but aberrations and astigmatism occur

Engineering Contradiction:

Improveoptical performanceVSAvoidaberrations and astigmatism

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent combines conventional optical elements with optical metasurfaces to create a hybrid optical system. The metasurface layer, composed of sub-wavelength meta-atoms, works in conjunction with traditional lenses and filters to correct optical aberrations and astigmatism while maintaining the desired optical functions, thereby improving overall system reliability without sacrificing performance

Inventive Principle:

Principle #40Composite materials

Solution Approach 2:

The metasurface introduces spatially varying optical properties through locally tuned meta-atoms. Each meta-atom can be designed with specific geometric parameters to provide localized phase, amplitude, or polarization modulation, enabling correction of position-dependent aberrations and astigmatism across the optical field

Inventive Principle:

Principle #3Local quality

2Reliability

If conventional optical systems are used, then imaging function is achieved, but device size is large

Engineering Contradiction:

Improveimaging capabilityVSAvoiddevice form factor

Core Design Contradiction:

ReliabilityVSVolume of moving object

Solution Approach 1:

The patent replaces bulky conventional optical components with planar metasurface structures. The metasurface achieves optical functions (focusing, filtering, polarization control) that traditionally required thick lens assemblies or multiple optical elements, thereby dramatically reducing the z-height and overall device volume while maintaining imaging capability

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention transitions from three-dimensional conventional optical elements (lenses with significant thickness) to two-dimensional metasurface structures. This dimensional reduction allows optical functions to be achieved in a planar format, enabling thinner and more compact device designs without compromising imaging performance

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

3Measurement precision

If signal-to-noise ratio is enhanced, then imaging quality improves, but device complexity increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidsystem structure

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent integrates multiple optical functions (focusing, spectral filtering, polarization control, noise rejection) into a single metasurface layer rather than requiring separate optical components for each function. This merging approach enhances signal-to-noise ratio through improved optical selectivity while actually reducing overall device complexity compared to traditional multi-component systems

Inventive Principle:

Principle #5Merging (Combining)

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

The integration of optical metasurface arrays with sensor assemblies improves imaging capabilities, including increased signal-to-noise ratio, hyperspectral imaging, and liveness detection, while reducing the physical size of the devices, making them suitable for consumer electronics like fingerprint sensors.

Implementation Method 1

Optical metasurfaces act locally on an amplitude, phase, or polarization of light, and impart a light phase shift that varies as a function of position on the surface

Methodology Applied

Scientific EffectOptical metasurface phase shift:

Implementation Method 2

an infrared (IR) cutoff filter

Methodology Applied

Scientific EffectInfrared cutoff filtering: Filter (optical)

Implementation Method 3

a refractive microlens array

Methodology Applied

Scientific EffectLight focusing: Lens

Data Source

PatentUS20240088185A1Sensor assemblies having optical metasurface films

Publication Date: 2024.03.14 3M INNOVATIVE PROPERTIES CO

AI summary

Fingerprint sensor assemblies using metasurface arrays. The sensor assemblies include an image sensor having a sensor pixel array and a metasurface array on the sensor pixel array. An optical filter such as an IR cutfilter or notch filter can be located on the metasurface array. The assemblies can also include a substrate, optical spacer, or optically clear adhesive between the sensor pixel array and the metasurface array. The fingerprint sensor assemblies can be incorporated into mobile devices.