Fingerprint Sensor Cover Layer Plasmonic Nanostructures
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Solution Overview
Problem
Conventional fingerprint sensing devices face challenges with thick color layers that affect sensor performance, limited color resolution, and color instability due to the use of pigments, which are difficult to fine-tune and prone to changes over time.
Innovation Solution
A fingerprint sensing device with a cover layer featuring a three-dimensional plasmonic array of electrically isolated nanostructures that reduces reflected light within specific visible ranges, allowing for tailored visual appearance and high-resolution color representation without the need for pigments, achieved through nanoimprint lithography or photolithography.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional color layers with pigments are used to achieve desired color and glossiness, then the visual appearance is improved, but the layer thickness increases (more than 40μm) which increases the distance between finger and sensing chip, deteriorating sensor performance
Solution Approach 1:
The patent changes the physical parameters of the cover layer by introducing a three-dimensional pattern with specific geometric features (height, width, spacing) that control light interaction. This replaces the conventional approach of changing color through pigment concentration with changing color through structural parameters, achieving color effect with minimal thickness increase
Solution Approach 2:
The patent transitions from a two-dimensional flat color layer to a three-dimensional patterned structure. The vertical dimension (height of protrusions) is introduced to create optical effects, allowing color control without increasing lateral thickness, thus resolving the contradiction between visual appearance and sensing distance
2Illumination intensity
If conventional pigment-based color layers are used, then color can be achieved, but the resolution of resulting patterns is limited to about 100μm due to application technology constraints
Solution Approach 1:
The patent replaces mechanical/screen printing processes with lithographic techniques (photolithography or nanoimprint lithography) that use light or molds to define patterns. This substitution enables much finer pattern resolution beyond the 100μm limit of conventional application technologies
Solution Approach 2:
The patent changes the manufacturing approach parameters from screen printing to lithography, which operates at different scale parameters and enables sub-100μm feature sizes. This parameter change in the manufacturing process directly enables higher pattern resolution
3Illumination intensity
If color pigments are used to achieve desired color, then color can be obtained, but fine tuning of colors is difficult and color may change as pigment ages, deteriorating color stability
Solution Approach 1:
The patent changes the mechanism of color generation from chemical (pigment absorption) to physical (structural light interference). By adjusting geometric parameters (height, width, spacing of protrusions) rather than chemical composition, color fine-tuning becomes precise and reproducible, and color stability is improved since the structure does not degrade like organic pigments
Solution Approach 2:
The patent substitutes chemical pigments with physical structural coloration. The color arises from the physical geometry of the three-dimensional pattern interacting with light, replacing the chemical mechanism of pigment absorption. This substitution eliminates color fading and shifting associated with pigment degradation
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 solution enables a fingerprint sensor with a desired visual appearance, higher color resolution, and improved hydrophobic properties, reducing water adherence and enhancing authenticity through angle-dependent color effects, while eliminating the need for additional materials and processing steps associated with pigments.
Implementation Method 1
the three-dimensional pattern being a plasmonic array comprising a plurality of electrically conductive nanostructures
Implementation Method 2
configured to reduce the amount of reflected light within a predetermined sub-range of the visible range
Data Source
Figure 1~2b
Figure 2c~3c
Figure 3d~3f
AI summary
There is provided a fingerprint sensing device comprising: a sensing chip comprising an array of sensing elements, the sensing elements being configured to be connected to readout circuitry for detecting a capacitive coupling between each of the sensing elements and a finger placed on a sensing surface of the sensing device; a cover layer arranged vertically above the sensing elements to cover at least a portions of the sensing elements, wherein an outer surface of the cover layer form the sensing surface of the sensing device; wherein the cover layer comprises a three-dimensional pattern configured to reduce the amount of reflected light within a predetermined sub-range of the visible range, wherein the three-dimensional pattern comprises an array of nanostructures or a reflective diffraction grating. There is also provided a method for manufacturing a fingerprint sensing device.