Stereolithography of ceramic components - fabrication of photonic crystals with diamond structures for terahertz wave modulation

At a Glance

Metadata	Details
Publication Date	2015-01-01
Journal	Journal of the Ceramic Society of Japan
Authors	Soshu Kirihara
Institutions	The University of Osaka, Shanghai Shipbuilding Technology Research Institute
Citations	15
Analysis	Full AI Review Included

6CCVD Technical Documentation: Advanced Diamond Materials for Terahertz Photonic Crystals

Analysis of Research: Stereolithography of Ceramic Components for Terahertz Wave Modulation

Executive Summary

This documentation analyzes the fabrication of micro-sized alumina (Al₂O₃) diamond-structure photonic crystals via micro-stereolithography and subsequent high-temperature sintering for Terahertz (THz) wave modulation. The findings validate the feasibility of creating high-precision, low-loss resonators using engineered defects, demonstrating clear localized modes in the 0.4-0.5 THz range.

Feature	Achievement	6CCVD Value Proposition (Diamond)
Material Validation	Al₂O₃ lattices formed a complete photonic band gap (0.4 to 0.47 THz).	Diamond offers superior thermal conductivity and unmatched low-loss properties in the THz regime compared to ceramics.
Precision Manufacturing	Achieved final lattice constant of 375 µm with ±5 µm tolerance.	6CCVD provides SCD/PCD substrates with nanoscale surface roughness (Ra < 1 nm) for precise wafer-level fabrication methods (e.g., etching, bonding), surpassing limitations of additive ceramic sintering.
Functional Device	Resonators filled with water/ethanol showed sharp localized modes (0.410, 0.491 THz).	SCD serves as an ideal platform for integrating THz resonators and wave circuits due to its extreme material purity and dielectric stability.
Methodology	Stereolithographic additive manufacturing followed by 1500 °C sintering.	6CCVD supplies the foundational SCD/PCD materials, eliminating the high-shrinkage and defect risks associated with ceramic powder sintering.
Application Readiness	Potential for novel sensors (e.g., detecting defects, cancer cells, bacteria).	High-purity, large-area 6CCVD diamond enables scalable, high-performance THz sensor arrays.

Technical Specifications

Extracted and summarized data points detailing the design and processing parameters of the alumina photonic crystal devices.

Parameter	Value	Unit	Context
Designed Lattice Constant (a)	500	µm	Diamond-type structure
Final Sintered Lattice Constant (a’)	375	µm	Achieved after 23.8% horizontal shrinkage
Target Component Dimensions	5 × 5 × 5	mm	10 × 10 × 10 unit cells
Component Part Tolerance	±5	µm	Measured by Digital Optical Microscopy (DOM)
Design Slicing Layer Thickness	15	µm	CAD conversion to rapid prototyping format
Stereolithography Deposition Thickness	10	µm	Thickness of photo-polymerized layer
Alumina Particle Size	170	nm	Used 40% v/v in photosensitive acrylic resin
Dewaxing Temperature / Time	600 / 2	°C / h	For burning out the acrylic resin component
Sintering Temperature / Time	1500 / 2	°C / h	Processed in air; achieved 99% relative density
Alumina Dielectric Constant (ε_r)	9.8	N/A	Used for Plane Wave Expansion (PWE) calculation
Perfect Photonic Band Gap Range	0.4 to 0.47	THz	Verified for all crystal directions
Localized THz Mode Peaks (Water)	0.410 and 0.491	THz	Observed in defect-introduced resonators
Resonator Cell Spacing	150	µm	Spacing between two diamond lattice components in the sensor cell

Key Methodologies

The core fabrication sequence involved advanced additive manufacturing combined with high-temperature processing to achieve the required micro-lattice ceramic structure.

CAD Design: Diamond lattices were designed with a 500 µm lattice constant and an aspect ratio of 1.5. Models were sliced into 15 µm thick cross-sections.
Paste Preparation: Photosensitive acrylic resin (JL2019) was loaded with 40% v/v alumina nanoparticles (170 nm average diameter).
Micro-Stereolithography: Layers (10 µm thick) were spread and exposed using a high-resolution Digital Micro-Mirror Device (DMD) array (1024 x 768) driven by piezoelectric actuators.
Lamination: Two-dimensional solid patterns were laminated layer-by-layer to form the green composite precursor.
Dewaxing: Precursors were heated to 600 °C for 2 hours to completely burn out the acrylic resin binder.
Sintering: Components were subjected to 1500 °C for 2 hours in air, resulting in dense (99% relative density) alumina micro-lattices.
Defect Engineering: Point defects (cubic air cavities) and plane defects (twinned lattice interfaces) were intentionally introduced via CAD/CAM to localize THz wave energy and form sharp transmission peaks.

6CCVD Solutions & Capabilities

This research validates the critical need for materials capable of supporting high-frequency THz wave localization and modulation. While the paper successfully uses sintered alumina, diamond offers significant, next-generation performance benefits, including superior thermal management and significantly lower intrinsic dielectric loss tangent, making it the ideal choice for scaling high-Q resonators and advanced THz circuitry.

Applicable Materials

To replicate and extend this research with optimized performance for THz applications, 6CCVD recommends the following CVD diamond materials:

High Purity Single Crystal Diamond (SCD):
- Recommendation: Electronic/Optical Grade SCD.
- Benefit: Provides the highest purity and lowest intrinsic loss tangent in the THz and sub-THz regime, essential for maximizing the quality factor (Q) of localized resonant modes. Its excellent thermal properties are crucial for high-power THz source applications.
Polycrystalline Diamond (PCD):
- Recommendation: Optical/Thermal Grade PCD.
- Benefit: Suitable for applications requiring large area coverage (up to 125 mm) or cost-effective manufacturing of integrated THz components, maintaining a high dielectric constant (approx. 5.7) and excellent thermal stability superior to alumina.
Boron-Doped Diamond (BDD):
- Recommendation: Heavy Boron-Doped PCD (p-type semiconductor).
- Benefit: If the application requires integrating active THz components or requires conductive microstructures (e.g., tunable antennas or active defect regions), 6CCVD can supply BDD films tailored for controlled resistivity.

Customization Potential

The ceramic stereolithography method is inherently limited by material shrinkage and minimum feature size resolution. 6CCVD’s advanced processing techniques offer deterministic and scalable manufacturing solutions for photonic structures:

Research Requirement	6CCVD Capability	Advantage
Custom Dimensions	Plates/Wafers up to 125 mm (PCD).	Enables large-area fabrication of THz sensor arrays or integrated wave circuits, far exceeding the 5x5x5 mm components used in the paper.
Thickness Control	SCD and PCD films available from 0.1 µm to 500 µm. Substrates up to 10 mm thick.	Precise control over the optical path length and lattice height, critical for optimized Bragg diffraction and band gap tuning.
Micro-Structure Definition	Ultra-high precision laser cutting and deep reactive ion etching (DRIE) services.	Achieve deterministic micro-structuring and defect placement (e.g., air cavities, twinned interfaces) on diamond surfaces with superior resolution and edge quality compared to the sintered ceramic method’s ±5 µm tolerance.
Surface Finish	SCD Polishing: Ra < 1 nm. PCD Polishing: Ra < 5 nm.	Ensures minimal scattering losses at THz frequencies and enables smooth interface bonding for multi-layer devices (such as the twin-crystal setup demonstrated in the paper).
Metalization	Custom application of Au, Pt, Pd, Ti, W, Cu.	If the THz resonator is integrated into a micro-electronic circuit or requires electrode contacts for tuning, 6CCVD provides in-house metalization services.

Engineering Support

6CCVD’s in-house PhD material science team specializes in customizing diamond properties for demanding photonic and electronic applications. We are prepared to assist engineers and scientists with material selection, defect engineering strategy, and integration methods for similar Terahertz Wave Resonator and Photonic Crystal Filter projects.

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

View Original Abstract

Photonic crystals with periodic variations in dielectric constants can theoretically exhibit forbidden gaps as a result of Bragg diffraction, thus prohibiting electromagnetic wave transmissions. The diffraction wavelengths are comparable to the lattice constants. In this study, diamond-type dielectric lattices with isotropic periodicities were identified as the perfect structure to open photonic band gaps for all crystal directions, and were then successfully processed. Stereolithographic additive manufacturing was customized to create photonic crystals with micro-sized diamond-like lattices. Photosensitive acrylic resin containing alumina nanoparticles was spread on a glass substrate with a mechanical knife edge. Cross-sectional layers, photo-polymerized by micro-pattern exposures, were laminated to create composite precursors. Next, dense components were obtained by dewaxing the precursors and subjecting them to sintering heat treatments. Structural defects consisting of point- and plane-cavities were introduced into the diamond photonic crystals by using computer-aided design, manufacture, and evaluation in order to study the characteristic resonance modes. These lattice misfits localize the electromagnetic waves strongly through multiple reflections, and wave amplifications enable transmission peak formations in the photonic band gaps according to the defect size. These photonic crystal resonators with micro-lattice patterns can be applied as wavelength filters in the terahertz frequency range. Terahertz waves in the far infrared range can be used in various types of novel sensors to detect dust on electric circuits, defects on material surfaces, cancer cells in human skin, and bacteria in vegetables.

Tech Support

Original Source

DOI: https://doi.org/10.2109/jcersj2.123.816