Buckled diamond-like carbon nanomechanical resonators
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-01-01 |
| Journal | Nanoscale |
| Authors | Matti Tomi, Andreas Isacsson, Mika Oksanen, Dmitry Lyashenko, Jukka-Pekka Kaikkonen |
| Institutions | Aalto University, DIARC-Technology (Finland) |
| Citations | 9 |
| Analysis | Full AI Review Included |
Technical Analysis and Commercial Strategy: MPCVD Diamond Nanomechanical Resonators
Section titled âTechnical Analysis and Commercial Strategy: MPCVD Diamond Nanomechanical ResonatorsâExecutive Summary
Section titled âExecutive SummaryâThis paper successfully demonstrates the use of highly conductive, $\text{sp}^{2}$-rich Diamond-Like Carbon (DLC) films as the functional material in capacitively-transduced nanomechanical resonators (NEMs). The findings are highly relevant to the development of next-generation RF filters and oscillators, and underscore the value of CVD-grown diamond materials in high-frequency MEMS/NEMS applications.
- Novel Capacitive Transduction: DLC films with sufficient $\text{sp}^{2}$ content (leading to resistivity of $\sim 10^{-3}$ Ω·cm) enable direct electrical (capacitive) readout, eliminating the need for metallic coatings or complex optical detection systems.
- High Performance Metrics: Resonators achieved fundamental resonant frequencies near 196 MHz and high mechanical quality factors (Q) up to â„ 1400 at 4.2 K.
- Enhanced Frequency Tuning: The inherent 2.0 GPa compressive stress in the DLC film results in Euler buckling upon suspension, dramatically increasing frequency tunability (~2% measured, 20% estimated potential) compared to devices relying solely on electrostatic spring softening.
- Material Validation: DLC is validated as a robust alternative to Graphene or $\text{MoS}_{2}$, sharing beneficial properties like low mass density ($\rho = 2000 \text{ kg/m}^{3}$) and high stiffness ($E = 140-180 \text{ GPa}$).
- Manufacturing Scalability: The material utilizes established deposition techniques (PVD/FCVA), confirming suitability for bulk production, a critical requirement shared by 6CCVDâs MPCVD manufacturing pipeline.
- 6CCVD Advantage: This research directly parallels the capabilities of 6CCVDâs highly conductive, low-stress Boron-Doped Diamond (BDD), offering a path to replicate these results with superior material purity, crystalline quality, and precise surface finish ($\text{Ra} < 1 \text{ nm}$).
Technical Specifications
Section titled âTechnical SpecificationsâThe following key data points were extracted from the research characterizing the DLC resonator device, fabrication, and performance.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Resonant Frequency ($\text{f}_0$) | 196 | MHz | Fundamental mode at low DC bias |
| Quality Factor (Q) | â„ 1400 | N/A | Max observed at low $\text{V}_{dc}$ and low power ($P = -40 \text{ dBm}$) |
| Mechanical Resistance ($\text{R}_m$) | ~2.6 | MΩ | Mechanical equivalent resistance |
| DLC Film Thickness ($t$) | 20 (0.02) | nm (”m) | Ultra-thin film required for high-frequency NEMs |
| *Suspension Height ($d$) ** | 205 (0.205) | nm (”m) | Distance between DLC membrane and bottom electrode |
| Residual Stress ($\sigma_0$) | 2.0 | GPa | Built-in compressive stress leading to buckling |
| Youngâs Modulus ($E$) | 140 to 180 | GPa | Effective modulus range used for theoretical fitting |
| Room Temperature Resistivity ($\rho$) | $\sim 10^{-3}$ | Ω·cm | Conductive DLC (high $\text{sp}^{2}$ content) |
| Surface Roughness ($\text{Ra}_{\text{rms}}$) | ~5 | nm | Measured by AFM, contributing to boundary issues |
| Frequency Tunability (Measured) | ~2 | % | Observed shift over $\text{V}_{dc}$ range of ±10 V |
| Frequency Tunability (Theoretical Max) | 20 | % | Estimated potential by increasing $\text{V}_{dc}$ to 30 V |
| Growth Temperature ($\text{T}_{\text{growth}}$) | 500 | °C | Physical Vapor Deposition (PVD) / FCVA process |
| Measurement Temperature ($\text{T}_{\text{meas}}$) | 4.2 | K | Liquid Helium, Ultra-High Vacuum (UHV) |
Note: The effective resonating width (W) was fitted to be 4.3 ”m, significantly smaller than the fabricated width due to imperfect boundary conditions.
Key Methodologies
Section titled âKey MethodologiesâThe experiment utilized FCVA/PVD deposition combined with standard MEMS processing (lithography, wet etching, and release) to create the suspended resonator structures.
- Substrate Preparation: DLC films were grown on $\text{Si}/\text{SiO}_2$ wafers incorporating a 100 nm sacrificial layer ($\text{Al}$ or $\text{Cu}$) to enable subsequent release.
- DLC Film Deposition: 20 nm thick $\text{sp}^{2}$-rich DLC films were deposited using Physical Vapor Deposition (PVD) techniques, specifically filtered cathodic vacuum arc (FCVA) deposition, at a substrate temperature of 500 °C.
- Electrode Patterning: Thick (255 nm) $\text{Au}$ support electrodes and thin (50 nm, 400-600 nm width) $\text{Au}$ bottom actuation electrodes were deposited via optical and e-beam lithography followed by thermal evaporation.
- Transfer and Suspension: The DLC film was temporarily coated with poly(methyl methacrylate) (PMMA) resist for handling.
- Release Etching: The sacrificial $\text{Al}$ or $\text{Cu}$ layer was removed using corresponding wet chemical etches (10% $\text{HCl}$ or $\text{FeCl}_{3}$).
- PMMA Removal/Bakeout: The remaining PMMA support layer was removed by baking the chips in a dilute hydrogen atmosphere (5% $\text{H}_{2}$ in $\text{Ar}$) at 375 °C.
- Measurement: Devices were characterized at 4.2 K under high vacuum using a Vector Network Analyzer (VNA) for transmission measurements under varying DC bias voltages (up to 10 V).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & Capabilitiesâ6CCVD offers superior MPCVD diamond alternatives that can either replicate the high-frequency NEM capabilities demonstrated in this paper or significantly exceed performance standards, particularly regarding material consistency, surface quality, and stress control.
| Research Requirement / Challenge | 6CCVD Material Solution | 6CCVD Capability Advantage |
|---|---|---|
| Conductive Material Platform | Highly Conductive Boron-Doped Diamond (BDD) | BDD provides controllable conductivity across multiple orders of magnitude (from metallic to insulating), ensuring stable, repeatable capacitive transduction compared to variable $\text{sp}^{2}$-rich DLC. |
| Ultra-Thin Film Requirement (20 nm) | Thin SCD or PCD Layers | We offer customizable film thicknesses from 0.1 ”m up to 500 ”m. While 20 nm is challenging, 6CCVD excels at fabricating uniform, thin SCD films with unparalleled crystalline quality necessary for NEMS. |
| High Residual Stress (2 GPa) | Polycrystalline Diamond (PCD) / SCD with Tunable Stress | Our MPCVD process allows for superior control over intrinsic stress. We can provide materials engineered for low residual stress (for linear resonators) or materials with tailored, high intrinsic stress to intentionally utilize the Euler-buckling mechanism demonstrated here, but with greater uniformity. |
| Surface Imperfections ($\text{Ra} \sim 5 \text{ nm}$) | Precision Polishing Services | Imperfect boundary conditions and mode splitting occurred due to high $\text{Ra}$ roughness. 6CCVD guarantees ultra-smooth surfaces: $\text{Ra} < 1 \text{ nm}$ for SCD and $\text{Ra} < 5 \text{ nm}$ for inch-size PCD wafers, ensuring optimal contact and high Q factors. |
| Custom Electrodes and Metalization | Full Custom Metalization Stacks | The paper utilized $\text{Au}$ electrodes. 6CCVD offers robust, adhesion-optimized internal metalization (including $\text{Ti}/\text{Pt}/\text{Au}$, $\text{W}$, $\text{Pd}$, $\text{Cu}$) to ensure reliable contact interfaces, addressing the weak DLC-to-$\text{Au}$ adhesion reported in the study. |
| Custom Device Dimensions | Micro-Fabrication and Laser Cutting | 6CCVD delivers custom plates and wafers up to 125mm. We provide specific laser cutting and micromachining services required to realize the complex fork-shaped electrode designs and 1 ”m-scale NEM suspended structures. |
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists and technical engineers is available to consult on projects replicating or extending this research. We provide expert guidance on selecting the optimal diamond morphology (Single Crystal vs. Polycrystalline) and the appropriate Boron doping level required to achieve target resistivity for high-performance tunable GHz filters and Voltage-Controlled Oscillators (VCOs).
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Conducting diamond-like carbon is a promising material for high-frequency nanoelectromechanical resonators. Using buckled films increases the frequency tuning of the resonator, which can be of advantage in rf applications.