Dielectric charging phenomena in diamond films used in RF MEMS capacitive switches - The effect of film thickness
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2016-09-01 |
| Journal | Microelectronics Reliability |
| Authors | M. Koutsoureli, A. Zevgolatis, S. Saada, Christine Mer-Calfati, L. Michalas |
| Institutions | National and Kapodistrian University of Athens, Commissariat Ă lâĂnergie Atomique et aux Ănergies Alternatives |
| Citations | 2 |
| Analysis | Full AI Review Included |
Technical Analysis: RF MEMS Reliability Improvement via Nanocrystalline Diamond Thickness Control
Section titled âTechnical Analysis: RF MEMS Reliability Improvement via Nanocrystalline Diamond Thickness ControlâDocument Prepared For: Engineers and Scientists specializing in RF Microelectromechanical Systems (MEMS), Wide Bandgap Semiconductors, and High-Reliability Dielectrics.
Source Analysis: Dielectric charging phenomena in diamond films used in RF MEMS capacitive switches: The effect of film thickness
Executive Summary
Section titled âExecutive SummaryâThis paper investigates the critical role of film thickness in mitigating dielectric chargingâa primary failure mechanismâin Nanocrystalline Diamond (NCD) films utilized in RF MEMS capacitive switches.
- Core Finding: Thinner NCD films significantly enhance the reliability of RF MEMS switches by reducing overall dielectric charging and lowering defect density.
- Optimal Thickness: Films at 350 nm thickness exhibited the lowest conductivity and stored charge density (4.71 x 10-6 C/cm2).
- Conduction Mechanisms Identified: Current transport varies significantly based on field intensity: thermally activated hopping (low fields, < 130 kV/cm) transitions to Hill-modified Frenkel-Poole conduction (high fields, > 130 kV/cm).
- Defect Correlation: Increasing film thickness correlates directly with increased conductivity and higher defect density (N), suggesting a less desirable grain boundary structure in thicker films.
- Charging Mechanism: Thermally Stimulated Depolarization Current (TSDC) analysis confirmed that charges are trapped within the materialâs volume, emphasizing the importance of high-quality internal morphology.
- 6CCVD Relevance: The research confirms the necessity of high-precision MPCVD synthesis and rigorous thickness control in Polycrystalline Diamond (PCD) films for commercialization of high-performance RF MEMS devices.
Technical Specifications
Section titled âTechnical SpecificationsâExtracted quantitative data points relating NCD film thickness to key electrical properties.
| Parameter | 350 nm Film Value | 750 nm Film Value | Unit | Context |
|---|---|---|---|---|
| Growth Temperature | 1023 K (750 °C) | 1023 K (750 °C) | K | MPCVD Substrate Temperature |
| Low Field Intensity Threshold | 130 | kV/cm | Electric Field | Transition point for conduction mechanism |
| Low Field Activation Energy (EA) | 0.82 ± 0.02 | 0.66 ± 0.02 | eV | Thermally activated conduction (< 130 kV/cm) |
| High Field Activation Energy (Ei) | 0.84 ± 0.02 | 0.95 ± 0.01 | eV | Hill Conduction mechanism (> 130 kV/cm) |
| Mean Hopping Distance (s) | 52.3 ± 2.6 | 28.8 ± 0.5 | nm | Decreases with increasing thickness |
| Density of Centers (N) | (7.0 ± 1.0) x 1015 | (4.2 ± 0.2) x 1016 | cm-3 | Increases significantly with thickness (Defect Density) |
| Total Stored Charge (ÏTSDC) | (4.71 ± 0.07) x 10-6 | (7.94 ± 0.06) x 10-6 | C/cm2 | Dielectric Charging Metric (Lower is better) |
| Capacitor Area | 450 x 450 | ”m2 | Area | Utilized MIM capacitor test structure |
| TSDC Temperature Range | 200 - 450 | K | Temperature | Range for depolarization current measurement |
Key Methodologies
Section titled âKey MethodologiesâThe researchers fabricated Metal-Insulator-Metal (MIM) capacitors using NCD films deposited via Microwave Plasma Assisted Chemical Vapor Deposition (MPCVD).
- Substrate Preparation: Silicon wafers were utilized, topped with an electrode stack of TiW/Au.
- Nanoseeding: A proprietary nanoseeding technique (diamond nanocrystals dispersed in Polyvinyl Alcohol, PVA, via spin coating) was used to achieve high nucleation density and ensure a continuous diamond film.
- MPCVD Growth Conditions:
- Reactor Type: Home-made designed MPCVD system (2.45 GHz-2 kW SAIREM generator).
- Base Pressure: Approximately 10-6 mbar.
- Gas Mixture: 0.6% Methane (CH4) diluted in Hydrogen (H2).
- Total Pressure: 35 mbar.
- Microwave Power: 900 W.
- Substrate Temperature: Maintained at 1023 K (750 °C).
- Thickness Control: Film thickness was monitored in situ using a home-made laser interferometry system to stop growth precisely at the target thicknesses (350 nm, 600 nm, 750 nm).
- Characterization:
- I-V/Conductivity: Measured in a vacuum cryostat (Pressure ~ 10-3 Torr) between 300 K and 400 K using a Keithley 6487.
- Dielectric Charging: Investigated using Thermally Stimulated Depolarization Currents (TSDC) technique (200 K-450 K, 2.5 K/min heating rate).
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research validates the critical requirement for precise thickness control and high-quality MPCVD diamond material for achieving reliable RF MEMS dielectrics. 6CCVD is uniquely positioned to supply materials that meet or exceed these specifications, offering superior process control for next-generation diamond-based devices.
Applicable Materials
Section titled âApplicable MaterialsâThe research utilizes nanocrystalline diamond (NCD), which is a key variant of Polycrystalline Diamond (PCD).
| Application Requirement | 6CCVD Material Recommendation | Technical Advantage |
|---|---|---|
| RF MEMS Dielectric | Optical Grade PCD (Polycrystalline Diamond) | Extremely low loss tangent (tan ÎŽ) and high dielectric strength required for RF applications. |
| Precise Thin Films | PCD or NCD (Sub-micron thickness) | 6CCVD offers PCD down to 0.1 ”m (100 nm), allowing replication of the highly reliable 350 nm films or exploration of even thinner layers for improved performance (higher isolation, increased down-state capacitance). |
| Substrate Compatibility | Custom Substrate Bonding Services | Ability to grow NCD/PCD directly on Si, SiO2, or handle the required TiW/Au/Si stacks used in the paper. |
Customization Potential
Section titled âCustomization PotentialâThe MIM structure and precise electrode definition are central to this research. 6CCVD provides comprehensive manufacturing capabilities to support direct replication or advanced modification of this architecture.
- Precision Thickness Control: We routinely manage diamond film thickness across large wafers (up to 125mm) with the high uniformity necessary for reproducible electrical performance in the critical sub-micron range (0.1 ”m to 500 ”m).
- Custom Micro-Patterning: For the utilized 450 x 450 ”m2 capacitor area, 6CCVD offers high-resolution laser cutting and etching services to define structures far below the inch scale.
- Integrated Metallization: The paper required TiW/Au contacts. 6CCVD provides internal metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu, allowing researchers to test various electrode materials known to influence charge injection and trapping.
- Surface Finish: Maintaining the lowest possible surface roughness is critical for highly uniform thin films. 6CCVD guarantees surface polishing down to Ra < 5 nm for inch-size PCD wafers, ensuring optimal interface quality for reduced defect generation.
Engineering Support
Section titled âEngineering SupportâThe findings regarding the correlation between film thickness, defect density (N), and activation energy (Ei/EA) provide a clear roadmap for material optimization.
6CCVDâs in-house PhD team provides authoritative engineering consultation to assist clients in selecting optimal MPCVD parameters (e.g., CH4 concentration, pressure, and temperature) to achieve the lowest possible sp2/sp3 ratio and lowest defect density (N) necessary for high-reliability RF MEMS capacitive switches and similar high-frequency dielectric applications.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly. We deliver globally (DDU default, DDP available).