Ultra-Precision Replication Technology for Fabricating Spiral-Structure Metamaterial

At a Glance

Metadata	Details
Publication Date	2020-08-28
Journal	Frontiers in Physics
Authors	Weiguo Zhang, Guodong Zhu, Xiaoqiang Zhu, Chunlei Du
Institutions	Chongqing Institute of Green and Intelligent Technology, Chongqing University
Citations	2
Analysis	Full AI Review Included

Ultra-Precision Diamond Solutions for Terahertz Metamaterial Fabrication

This technical documentation analyzes the research paper “Ultra-Precision Replication Technology for Fabricating Spiral-Structure Metamaterial” and outlines how 6CCVD’s advanced MPCVD diamond materials and fabrication services can support and extend this high-precision manufacturing methodology.

Executive Summary

The research successfully demonstrates a highly efficient, ultra-precision method for fabricating Spiral-Structure Metamaterials (SSM) for terahertz (THz) applications, relying critically on diamond-based tooling.

Core Achievement: Fabrication of SSM elements designed for the 30 µm wavelength range using a two-step process: Diamond Ultra-Precision Turning (D-UPT) of a metal mold, followed by compression molding replication.
Precision Tooling Requirement: The D-UPT process requires Single Crystal Diamond (SCD) tools capable of maintaining nanometer precision and minimizing wear during the machining of the 7075 Aluminum mold.
Superior Surface Quality: Achieved exceptional surface roughness (Ra) of 4.1 nm on the metal mold and 3.1 nm on the final Polyethylene (PE) product, confirming suitability for high-frequency optics.
High Dimensional Accuracy: The step height error between the PE product and the theoretical design was minimized to 0.19 µm, representing only 0.63% of the designed wavelength.
Efficiency and Scalability: The replication process allows for rapid, low-cost batch production, with individual SSM elements processed in less than 10 minutes.
6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade Single Crystal Diamond (SCD) for manufacturing the ultra-precision cutting tools, ensuring the highest possible mold accuracy and longevity required for industrial scale-up.

Technical Specifications

The following hard data points were extracted from the experimental results, highlighting the precision achieved in the mold fabrication and replication process.

Parameter	Value	Unit	Context
Designed Wavelength (λ)	30	µm	Target for Terahertz SSM application
SSM Component Diameter	50	mm	Size of the fabricated element
Total Step Depth Difference	55.56	µm	Corresponds to λ = 30 µm
Mold Surface Roughness (Ra)	4.1	nm	Achieved via Angular Feeding Method (Optimal)
Final PE Product Roughness (Ra)	3.1	nm	Achieved via Replication (Negligible optical influence)
Step Height Error (PE vs. Mold)	40	nm	0.1% replication error
Step Height Error (PE vs. Theoretical)	0.19	µm	0.63% of designed wavelength
Diamond Tool Curvature Radius	0.4	mm	Used for ultra-precision turning
Mold Processing Time (Angular Feed)	20	min	Total time for one-step roughing, semi-finishing, and finishing
Replication Processing Time	<10	min	High efficiency for batch production
Molding Pressure	0.22	MPa	Applied during heat preservation (130 °C)

Key Methodologies

The fabrication relies on the synergy between ultra-precision diamond turning for the mold and controlled compression molding for replication.

Mold Substrate Preparation: 7075 Aluminum was selected as the substrate material for the spiral phase plate mold.
Diamond Ultra-Precision Turning (D-UPT): Employed a diamond lathe (Moore Nanotech350FG) using a diamond cutter with a 0.4 mm radius of curvature.
Tool Path Optimization: The Angular Feeding Method was selected as the optimal strategy, yielding superior surface roughness (Ra 4.1 nm) and higher efficiency compared to the Radial Feeding Method.
Multi-Step Turning Scheme: The mold was processed using a scheme of one-step roughing (40 µm depth), one-step semi-finishing (10 µm depth), and one-step finishing (5 µm depth).
Anti-Adhesion Layer: A thin layer of fluorinated polymer was applied to the aluminum mold surface via steam plating coating to prevent adhesion during demolding.
Compression Molding: The PE substrate and the metal mold were assembled in a specialized fixture designed to prevent lateral sliding and ensure vertical pressure transmission.
Controlled Thermal Cycle: The assembly was heated to 130 °C, held under 0.22 MPa pressure for 5 minutes, and then cooled rapidly (20 °C/min) to <40 °C to solidify the PE structure.
Vertical Demolding: Mechanical devices ensured the mold and the PE SSM were separated vertically, minimizing mechanical damage caused by lateral sliding.

6CCVD Solutions & Capabilities

The success of this ultra-precision replication technology hinges entirely on the quality and longevity of the diamond tooling used to create the master mold. 6CCVD is uniquely positioned to supply the foundational diamond materials and advanced processing required to industrialize this process.

Applicable Materials

Application Requirement	6CCVD Material Recommendation	Technical Justification
Ultra-Precision Tooling	Optical Grade Single Crystal Diamond (SCD)	Provides the necessary hardness, thermal stability, and low defect density for manufacturing SPDT tools capable of achieving Ra < 1 nm on metal molds, ensuring maximum tool life and precision repeatability.
Advanced Molds/Substrates	Optical Grade Polycrystalline Diamond (PCD)	For applications requiring higher thermal conductivity or larger area molds (beyond 50 mm), 6CCVD offers PCD wafers up to 125 mm, providing superior wear resistance compared to aluminum.
High-Power THz Optics	Boron-Doped Diamond (BDD)	If the application were extended to high-power THz or electro-optical modulation, BDD offers tunable conductivity and high thermal management capabilities not found in PE.

Customization Potential

The research highlights the need for precise dimensions, specialized surface finishes, and interface engineering (anti-adhesion coatings). 6CCVD’s in-house capabilities directly address these needs:

Custom Dimensions: 6CCVD supplies plates and wafers in custom dimensions, supporting the scaling of this technology. We offer PCD wafers up to 125 mm in diameter, significantly larger than the 50 mm component demonstrated.
Thickness Control: We provide precise thickness control for both SCD and PCD materials, ranging from 0.1 µm to 500 µm, and substrates up to 10 mm thick, suitable for robust mold backing plates.
Ultra-Low Roughness Polishing: To ensure the highest quality mold surface, 6CCVD guarantees Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD substrates, critical for replicating nanometer-scale features without error.
Custom Metalization & Interface Layers: The paper required an anti-adhesion coating. 6CCVD offers in-house metalization (Au, Pt, Pd, Ti, W, Cu) for creating custom adhesion layers, electrical contacts, or specialized interface coatings directly onto diamond substrates or molds.

Engineering Support

6CCVD’s in-house PhD team specializes in optimizing material selection and processing parameters for complex micro- and nano-fabrication projects. We can assist engineers and scientists in:

Tooling Optimization: Consulting on the optimal SCD crystal orientation and geometry for specific D-UPT applications, minimizing tool wear (as observed when cutting PE) and maximizing mold precision.
Material Integration: Providing expertise on integrating diamond substrates into complex optical systems, including thermal management and mechanical mounting strategies for similar terahertz optics elements projects (e.g., terahertz lenses or beam splitters).

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Spiral-structure metamaterial (SSM) is of great importance, however, there are fewer methods to fabricate SSM due to limitations of material particularity and working accuracy. In this paper, a systematic scheme for fabricating SSM is proposed by employing the metal mold making with diamond-based ultra-precision turning technique and then molding replication method. By studying the path planning algorithm of the turning, molding error law, and a technique of how to compensate for the error, a solution for SSM is consequently formed. Our experimental results show a satisfying SSM with a surface roughness under 5 nm and a surface shape error under 0.63% of the designed wavelength (30 um). Moreover, this SMM element is processed within 10 min, with low cost materials and processes. Based on these advantages, our SSM processing scheme shows a remarkable potential in precise fabricating phase plates and industrialized application of terahertz metamaterial in the future.

Tech Support

Original Source

DOI: https://doi.org/10.3389/fphy.2020.00267

References

2015 - Freely tunable broadband polarization rotator for terahertz waves [Crossref]
2016 - Discrimination of orbital angular momentum modes of the terahertz vortex beam using a diffractive mode transformer [Crossref]
2012 - Design of a terahertz polarization rotator based on a periodic sequence of chiral-metamaterial and dielectric slabs [Crossref]
2016 - A high extinction ratio THz polarizer fabricated by double-bilayer wire grid structure [Crossref]
2008 - Improving diffraction efficiency of DOE in wide waveband application by multilayer micro-structure [Crossref]
2016 - Analysis of Ag nanoparticle resist in fabrication of transmission-enhanced subwavelength structures [Crossref]
2016 - Fabrication of large area diffractive optical elements by laser direct writing [Crossref]
2004 - Microfabrication Technology
2002 - Micro-Optical Elements, System and Application
2013 - Enhancement of the machinability of silicon by hydrogen ion implantation for ultra-precision micro-cutting [Crossref]