Measurement of Microwave Dielectric Properties of Diamond Films Using Split-cylinder Resonator Method
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-01-01 |
| Journal | Journal of Inorganic Materials |
| Authors | SU Jing-Jie, Yang Zi, Yifeng Li, Tang Weizhong, Xiao-Ming An |
| Institutions | University of Science and Technology Beijing, Beijing Institute of Nanoenergy and Nanosystems |
| Citations | 1 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: MPCVD Diamond for Ka-Band Dielectric Applications
Section titled âTechnical Documentation & Analysis: MPCVD Diamond for Ka-Band Dielectric ApplicationsâExecutive Summary
Section titled âExecutive SummaryâThis analysis focuses on research validating the superior microwave dielectric properties of diamond films synthesized via Microwave Plasma Chemical Vapor Deposition (MPCVD) compared to DC Arc Plasma Jet (DC Arc Jet) methods, specifically in the critical Ka frequency band (27-40 GHz).
- Core Achievement: Successful characterization of ultra-low loss diamond films in the Ka band using a novel split-cylinder resonator apparatus.
- Material Superiority: MPCVD-grown diamond exhibited significantly higher quality, achieving a dielectric loss tangent (tan$\delta$) of $1.38 \times 10^{-4}$ at 29.280 GHz, approximately 5.4 times lower than the DC Arc Jet alternative.
- Purity Validation: MPCVD films demonstrated exceptionally high purity, confirmed by a narrow Raman FWHM (2.0 cm-1) and ultra-low estimated nitrogen impurity ($0.7 \times 10^{-6}$).
- Application Focus: The study establishes MPCVD diamond as the preferred material for high-power, high-frequency microwave applications, such as fusion reactor windows (gyrotrons) and advanced radar systems operating above 27 GHz.
- Technical Relevance for 6CCVD: This paper underscores the necessity of high-power MPCVDâ6CCVDâs core manufacturing methodâto achieve the material quality required for state-of-the-art dielectric components.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data was extracted from the measurement comparison of high-quality diamond films synthesized by MPCVD and DC Arc Plasma Jet methods.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Measurement Frequency (MPCVD) | 29.280 | GHz | Ka Band |
| Relative Permittivity ($\epsilon_{r}$) | 5.60 ± 0.07 | N/A | MPCVD Diamond Film |
| Dielectric Loss Tangent (tan$\delta$) | 1.38 Ă 10-4 | N/A | Ultra-Low Loss, Best Performance |
| Measurement Frequency (DC Arc Jet) | 30.004 | GHz | Ka Band |
| Relative Permittivity ($\epsilon_{r}$) | 5.77 ± 0.09 | N/A | DC Arc Plasma Jet Diamond Film |
| Dielectric Loss Tangent (tan$\delta$) | 7.49 Ă 10-4 | N/A | Inferior performance (5.4x higher loss) |
| Raman FWHM (MPCVD) | 2.0 | cm-1 | Quality marker (closer to natural Type IIa diamond) |
| Nitrogen Impurity (MPCVD) | 0.7 Ă 10-6 | N/A | Estimated from UV absorption at 270 nm |
| MPCVD Film Thickness | 277 | ”m | Double-sided polished sample |
| DC Arc Jet Film Thickness | 213 | ”m | Double-sided polished sample |
| Resonator Design Frequency ($f_{011}$) | 35 | GHz | TE$_{011}$ mode (Target for Ka Band testing) |
Key Methodologies
Section titled âKey MethodologiesâThe study relied on two key areas: diamond synthesis and characterization using a specialized resonant structure.
1. Diamond Film Synthesis
Section titled â1. Diamond Film SynthesisâThe research compared two distinct Chemical Vapor Deposition (CVD) methods for producing high-quality freestanding diamond films:
-
Microwave Plasma Chemical Vapor Deposition (MPCVD):
- Purity Advantage: Provides an exceptionally clean deposition environment, minimizing impurities (especially Nitrogen), which are known to increase dielectric loss.
- Recipe Parameters:
- Power: 9.2 kW
- Pressure: 15.8 kPa
- Temperature: 1030 °C
- Gas Flow (CH${4}$/H${2}$): 7/200 sccm
-
DC Arc Plasma Jet:
- Process Disadvantage: Utilizes a gas recycling mode to conserve precursor gases (CH${4}$, H${2}$, Ar), which is noted to increase the concentration of impurities, thereby degrading the microwave performance.
- Recipe Parameters:
- Power: 13.5 kW
- Pressure: 3.5 kPa
- Temperature: 1000 °C
- Gas Flow (CH${4}$/H${2}$/Ar): 0.015/6/2 sccm
2. Dielectric Measurement
Section titled â2. Dielectric Measurementâ- Method: Split-Cylinder Resonator Method.
- Operating Band: Ka Band (27-40 GHz).
- Mode: TE$_{011}$ mode, with a cavity resonance set around 35 GHz.
- Validation: The systemâs accuracy was confirmed using four sapphire single crystal samples (Type <0001>) of varying diameters (18.2 mm to 30.0 mm), confirming low variability in measured $\epsilon_{r}$ (9.40-9.45) and tan$\delta$ ($0.26 \times 10^{-4}$ to $0.27 \times 10^{-4}$).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD is an expert supplier of MPCVD diamond, specializing in the high-purity materials required to replicate and advance the microwave dielectric research presented in this paper.
The paper clearly demonstrates that the performance achieved is directly correlated with the cleanliness and control offered by high-power MPCVDâour core competency.
Applicable Materials
Section titled âApplicable MaterialsâTo achieve the ultra-low loss and high purity required for Ka-band dielectric windows and substrates, 6CCVD recommends:
| 6CCVD Material | Description & Application | Required Specs Matched |
|---|---|---|
| Optical Grade SCD | Premium Single Crystal Diamond (SCD) offering the lowest possible impurity concentration (e.g., N < 1 ppb). Essential for maximizing performance in high-power, low-loss windows. | Ultra-low loss (tan$\delta$ < 10-4), high thermal conductivity. |
| High-Purity Polycrystalline (PCD) | Suitable for large-area substrates where high purity ($N \ll 1$ ppm) and excellent thermal management are critical. Ideal balance of performance and cost efficiency for inch-scale requirements. | Large diameter capability (up to 125 mm), high purity (low $\epsilon_{r}$). |
Customization Potential
Section titled âCustomization PotentialâThe research samples required specific, double-sided polished films with precise thicknesses (213 ”m and 277 ”m) and diameters (18.2 mm). 6CCVD is uniquely positioned to supply these exact specifications globally.
- Dimensional Accuracy: We offer PCD plates/wafers up to 125 mm in diameter and custom films cut to specific diameters (e.g., 18.2 mm) for resonator testing.
- Thickness Control: SCD and PCD films can be grown and polished precisely within the required range (0.1 ”m - 500 ”m), meeting the critical tolerances demonstrated in the paper.
- Surface Finish: High-quality microwave components require exceptional surface smoothness to minimize scattering and loss. We guarantee polishing down to Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD.
- Post-Processing: Although not used in this specific paper, 6CCVD provides in-house metalization services (Au, Pt, Pd, Ti, W, Cu) for customers requiring high-frequency signal electrodes or integration layers on their diamond films.
Engineering Support
Section titled âEngineering SupportâThis research highlights the direct correlation between film synthesis conditions (e.g., purity control, gas handling) and dielectric performance. 6CCVDâs in-house PhD team provides specialized consultation to engineers and scientists working on:
- Gyrotron and High-Power Microwave Windows: Assisting with material selection (thickness, purity, $\epsilon_{r}$ control) for Ka-band and higher frequency systems.
- Dielectric Substrates: Advising on optimal material grade (SCD vs. PCD) and surface preparation for low-loss, high-thermal-load passive devices.
Call to Action: For custom specifications, material consultation for high-frequency applications, or to explore our high-purity MPCVD diamond catalog, visit 6ccvd.com or contact our engineering team directly. We offer global shipping (DDU default, DDP available) to accelerate your research timeline.
View Original Abstract
Regarding to the difficulties in measuring microwave dielectric properties of diamond films due to their characteristics of low dielectric loss and small thickness, a split-cylinder resonator apparatus was established.By measuring dielectric performances of sapphire samples with different diameters, the capability of the split-cylinder resonator for measuring low dielectric loss materials was demonstrated, and the influence of sampleâs diameter on measurement results was studied.Then by using the split-cylinder resonator apparatus, dielectric properties of high quality diamond films prepared by two different methods, microwave plasma chemical vapor deposition (MPCVD) and DC arc plasma jet, were measured in the Ka band.Results show that the diamond film deposited by MPCVD method has a higher quality than that of the diamond film deposited by the DC arc plasma jet method, which is consistent with the results of their Raman and UV-visible absorption spectra.The results indicate that both the relative dielectric constant and the loss tangent of the sample deposited by MPCVD method are lower than those of the sample prepared by DC arc plasma jet method.