Nano-structures on Micro-structures for Thin Anti-counterfeiting
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Solution Overview
Problem
Existing micro-optical anti-counterfeiting devices face challenges in controlling structural features smaller than the coherence length of visible light, leading to difficulties in achieving precise optical effects and high-volume production costs, particularly with micro-lens and micro-mirror arrays, which are not suitable for thin documents and offer limited space for engineering optical effects.
Innovation Solution
The development of optical devices featuring a combination of micro-structures and nano-structures on a planar substrate, where micro-structures have a thickness less than 50 μm and more than 1 μm, and nano-structures with feature sizes less than 500 nm, creating structural colors and optical effects through plasmonic or diffractive means, with the micro-structures directing light to interact with nano-structures above or below the device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If micro-lens arrays are used to display optical effects, then optical effects can be achieved, but the device thickness becomes too large (20 μm) for thin documents
Solution Approach 1:
The patent replaces traditional micro-lens arrays with a thin film structure containing micro-structures and nano-structures. This thin film approach maintains the optical effect display capability while reducing the device thickness to be suitable for thin documents like banknotes, eliminating the 20 μm thickness limitation of conventional micro-lens arrays.
Solution Approach 2:
The patent changes the structural parameters from conventional micro-lens dimensions to sub-wavelength nano-structures (features smaller than the coherence length of visible light). This parameter change enables the same optical effects to be achieved with dramatically reduced thickness, transforming the device from a bulky component to a thin-film security feature.
2Length of stationary object
If micro-mirror arrays are used to reduce thickness, then device thickness is reduced, but the space for engineering optical effects becomes limited
Solution Approach 1:
The patent employs a composite structure combining micro-structures (for light direction and overall optical path control) and nano-structures (for fine-tuned optical effects and color generation). This composite architecture provides both the thin profile of micro-mirrors and the extensive optical engineering capability needed for complex security effects, overcoming the limitations of single-scale structures.
Solution Approach 2:
The patent transitions from two-dimensional micro-mirror surfaces to three-dimensional hierarchical structures by adding nano-structures on top of micro-structures. This dimensional escalation creates vertical space for complex optical engineering while maintaining a thin overall profile, enabling sophisticated optical effects in a compact form factor.
3Ease of manufacture
If conventional micro-fabrication methods are used, then manufacturing is straightforward, but manufacturing precision for features smaller than coherence length is difficult to control
Solution Approach 1:
The patent uses preliminary patterning techniques where master molds with precise micro- and nano-structures are created first using advanced fabrication methods. These master molds then serve as templates for mass production through casting or embossing, concentrating the precision requirements in the initial mold creation step while enabling straightforward, high-precision replication in subsequent manufacturing steps.
Solution Approach 2:
The patent employs master mold and casting/embossing techniques to create precise copies of the micro- and nano-structure patterns. This copying approach allows complex sub-wavelength features to be manufactured with high precision in the master mold, then replicated accurately at low cost for high-volume production, separating the precision requirement from the mass production process.
4Manufacturing precision
If master mold design is performed with high precision, then optical effect accuracy is improved, but the cost per final product increases for high volume production
Solution Approach 1:
The patent performs the expensive, precision-intensive master mold design and fabrication as a one-time preliminary action. Once the master mold is created with the required nanometer-scale precision, it can be used repeatedly for mass production through low-cost casting or embossing processes, amortizing the high initial precision cost over millions of units and achieving both high accuracy and low per-unit cost.
Solution Approach 2:
The patent uses the precision master mold to create numerous low-cost copies through casting or embossing. The expensive precision work is done once in the master mold, then replicated cheaply in volume, allowing high optical effect accuracy to be maintained while achieving economy of scale for high-volume production of security features.
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 approach enables the creation of optical devices that display complex visual effects, such as color shifts and animations, while being suitable for thin documents, offering enhanced security features and cost-effective mass production by controlling the thickness and arrangement of nano-structures with nanometer precision.
Implementation Method 1
nano-structures with feature sizes less than 500 nm, creating structural colors and optical effects through plasmonic or diffractive means
Implementation Method 2
nano-structures with feature sizes less than 500 nm, creating structural colors and optical effects through plasmonic or diffractive means
Implementation Method 3
When the minimum feature sizes of an optical component are larger than both the wavelength and coherence length, the interaction of visible light with the optical component can be understood by considering light reflection and refraction
Data Source
AI summary
Described are optical elements or displays using micro-structures and nano-structures formed conformally thereon that operate to generate optical effects. Such elements and displays may be useful for applications such as displays, and anti-counterfeiting.