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Review on advances in microcrystalline, nanocrystalline and ultrananocrystalline diamond films-based micro/nano-electromechanical systems technologies

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-01-25
JournalJournal of Materials Science
AuthorsOrlando Auciello, Dean M. Aslam
InstitutionsThe University of Texas at Dallas, Michigan State University
Citations89
AnalysisFull AI Review Included

Technical Documentation & Analysis: Diamond Films for MEMS/NEMS

Section titled “Technical Documentation & Analysis: Diamond Films for MEMS/NEMS”

Executive Summary

Section titled “Executive Summary”

This review validates MPCVD diamond films (SCD, PCD, NCD, UNCD) as the superior material platform for next-generation Micro/Nano-Electromechanical Systems (MEMS/NEMS), overcoming the fundamental mechanical and thermal limitations of silicon.

  • Superior Performance: Diamond exhibits the highest Young’s modulus (up to 1200 GPa), highest acoustic velocity (18,076 m/s), and lowest Coefficient of Friction (COF) (0.02-0.05 for UNCD), enabling high-frequency, low-wear, and high-reliability devices.
  • Transformational Materials: Ultrananocrystalline Diamond (UNCD), grown via Ar/CH4 MPCVD, is highlighted for its ultra-smooth surface (Ra 3-5 nm rms) and excellent dielectric properties, making it ideal for low-stiction NEMS and high-speed RF-MEMS switches.
  • High-Temperature Sensing: Boron-Doped Diamond (BDD PCD) is confirmed as the material of choice for piezo-resistive sensors, achieving high Gauge Factors (GF up to 100) and stability for operation at temperatures up to 600 °C, where conventional Si devices fail.
  • RF-MEMS Reliability Breakthrough: UNCD dielectric layers in capacitive RF-MEMS switches demonstrate recovery times 5-6 orders of magnitude quicker (< 50 ”sec) than traditional SiO2 or SiNx, solving the critical long-term reliability issue of charge trapping and stiction.
  • Biocompatibility & Integration: Diamond films are proven biocompatible and chemically inert, enabling integrated BioMEMS (neural probes, microfluidic channels) and complex heterostructures (e.g., PZT/UNCD) for energy harvesting and drug delivery.
  • Scalability: MPCVD is established as the preferred method for producing high-quality PCD films with uniform thickness and microstructure on large-area substrates (up to 100 mm wafers).

Technical Specifications

Section titled “Technical Specifications”

The following hard data points extracted from the review highlight the performance advantages of diamond materials relevant to MEMS/NEMS design:

ParameterValueUnitContext
Young’s Modulus (SCD)1050-1200GPaSuperior mechanical strength for high-frequency resonators.
Thermal Conductivity (SCD)~2100W/K·mHighest of any material, critical for heat dissipation.
Lowest COF (UNCD)0.02-0.05N/AIdeal for sliding/rolling interfaces (NEMS).
UNCD Surface Roughness3-5nm (rms)Achieved via Ar/CH4 MPCVD growth, minimizing stiction.
High-Temperature StabilityUp to 600°CStability in air, enabling high-T MEMS operation.
Band Gap (SCD)5.45eVExcellent electrical insulator and UV detector material.
BDD PCD Gauge Factor (GF)5 to 100N/AHigh sensitivity for piezo-resistive sensors.
Acoustic Phase Velocity18,076m/sEnables highest resonance frequencies for RF-MEMS.
RF-MEMS Dielectric Recovery< 50”secUNCD performance, 5-6 orders faster than SiO2/SiNx.
Ohmic Contact Resistivity~ 10-7Ω·cmAchieved using carbide-forming metals (Ti/Al) after annealing.

Key Methodologies

Section titled “Key Methodologies”

The research relies on advanced CVD techniques and precise post-processing to achieve the required film quality and device architecture.

  1. CVD Growth Techniques: Microwave Plasma CVD (MPCVD) is the most widely used technique, favored for its high quality, stability, and low contamination, particularly for electronic and optical applications. Hot Filament CVD (HFCVD) is also utilized for large-area scaling.
  2. Microstructure Control:
    • MCD: Grown using H2 (99%)/CH4 (1%) gas mixtures (grain size > 1 ”m).
    • NCD: Grown using H2 (96%)/CH4 (4%) gas mixtures (grain size 10-100s nm).
    • UNCD: Grown using Ar (99%)/CH4 (1%) gas mixtures, leveraging C2 dimers for ultra-small grain sizes (3-5 nm).
  3. Doping: Boron (B) is incorporated during growth (in-situ doping) using precursors like trimethyl boron (B(CH3)3) to achieve p-type semiconducting or semi-metallic properties for piezo-resistors and electrodes.
  4. Nucleation Enhancement: Bias Enhanced Nucleation/Growth (BEN-BEG) is employed to improve adhesion and uniformity on non-diamond substrates (e.g., Si) by accelerating C+ and CHx+ ions to form a strong Si-C interface.
  5. Patterning and Etching: Since diamond is chemically inert, selective dry etching techniques (Reactive Ion Etching, Inductively Coupled Plasma) using O2 plasma, often mixed with CF4 or SF6, are necessary for micromachining MEMS structures.
  6. Metalization: Carbide-forming metals (Ti, W, Mo) are used to form ohmic contacts, often requiring annealing (e.g., 450 °C) to induce a SiC layer at the interface, enhancing tunneling current.
  7. Planarization: Mechanical or thermo-chemical polishing techniques are required to reduce the high surface roughness of as-grown MCD films (Ra ≄ 1 ”m) to achieve the nanoscale smoothness required for reliable MEMS/NEMS sliding parts (Ra < 5 nm).

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

6CCVD is uniquely positioned to support and advance the research detailed in this review by providing highly customized, high-quality MPCVD diamond materials and integrated processing services.

Research Requirement (from Paper)6CCVD Solution & Capability
Material for High-Q RF-MEMS/NEMS (SCD/UNCD)Optical Grade SCD & Ultra-Smooth PCD (UNCD/NCD): We supply high-purity Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) films optimized for low-loss, high-frequency applications. Our UNCD/NCD films are ideal for replicating the high-Q resonators and low-COF sliding interfaces discussed.
Large Area PCD/UNCD Films (up to 100 mm wafers)Large Format Capability: 6CCVD routinely produces PCD plates and wafers up to 125 mm in diameter, exceeding the 100 mm scale demonstrated in the research, ensuring suitability for industrial-scale MEMS fabrication and scaling.
Piezo-resistive Sensors & Electrodes (Boron-Doped PCD, BDD)Custom Boron-Doped Diamond (BDD): We offer precise, controlled BDD doping levels for both SCD and PCD films, essential for achieving the high Gauge Factors required for high-sensitivity pressure sensors and for fabricating chemically stable neural electrodes.
Low Surface Roughness (Ra < 5 nm for MEMS interfaces)Advanced Polishing Services: We guarantee ultra-low surface roughness: Ra < 1 nm for SCD and Ra < 5 nm for inch-size PCD wafers, critical for minimizing stiction and improving device reliability in RF-MEMS switches and NEMS.
Integrated Heterostructures (e.g., Pt/PZT/Pt/TiAl/UNCD)Custom Metalization & Layer Stacks: 6CCVD provides in-house metal deposition (Au, Pt, Pd, Ti, W, Cu) and patterning services, enabling the fabrication of complex electrode/barrier layers (e.g., TiAl diffusion barriers, Pt electrodes) directly onto custom diamond substrates.
Precision Thickness Control (0.1 ”m to 500 ”m films)Custom Dimensions and Substrates: We offer SCD and PCD films with thickness control from 0.1 ”m up to 500 ”m, allowing engineers to design and fabricate precise, free-standing MEMS membranes and cantilevers, as well as thick substrates (up to 10 mm).
Global Logistics SupportWorldwide Shipping: We offer global shipping (DDU default, DDP available) to ensure rapid and reliable delivery of custom diamond materials to research facilities and manufacturing sites worldwide.

6CCVD specializes in providing the exact diamond material specifications required to replicate or advance the cutting-edge MEMS/NEMS research presented in this review. Our in-house PhD team can assist with material selection, doping optimization, and integration strategies for similar high-performance BioMEMS, RF-MEMS, and High-Temperature Sensor projects.

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

View Original Abstract

Abstract A comprehensive review is presented on the advances achieved in past years on fundamental and applied materials science of diamond films and engineering to integrate them into new generations of microelectromechanical system (MEMS) and nanoelectromechanical systems (NEMS). Specifically, the review focuses on describing the fundamental science performed to develop thin film synthesis processes and the characterization of chemical, mechanical, tribological and electronic properties of microcrystalline diamond, nanocrystalline diamond and ultrananocrystalline diamond films technologies, and the research and development focused on the integration of the diamond films with other film-based materials. The review includes both theoretical and experimental work focused on optimizing the films synthesis and the resulting properties to achieve the best possible MEMS/NEMS devices performance to produce new generation of MEMS/NEMS external environmental sensors and energy generation devices, human body implantable biosensors and energy generation devices, electron field emission devices and many more MEMS/NEMS devices, to produce transformational positive impact on the way and quality of life of people worldwide.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 1998 - Tribology issues and opportunities in MEMS
  2. 1998 - Tribology issues and opportunities [Crossref]

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