Skip to content
6CCVD Research

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

As an expert material scientist, here is an analysis of the research paper on diamond films for Micro/Nano-Electromechanical Systems (MEMS/NEMS), tailored for an engineering audience.

Executive Summary

Section titled “Executive Summary”
  • Core Value Proposition: Diamond films (MCD, NCD, UNCD) provide mechanical, tribological, and electronic properties orders of magnitude superior to Silicon, enabling MEMS/NEMS operation in harsh, high-temperature, and high-frequency environments.
  • Tribological Breakthrough (UNCD): Ultrananocrystalline diamond (UNCD) exhibits the lowest coefficient of friction (0.02-0.05) and nanoscale smoothness (3-5 nm RMS), effectively eliminating surface stiction and wear in moving components.
  • RF-MEMS Reliability Solved: Integrating UNCD as a dielectric layer in capacitive RF-MEMS switches achieved charge/discharge recovery times of approximately 100 ”s, representing a 5-6 order of magnitude improvement over conventional SiO2/SiNx dielectrics.
  • High-Temperature Sensing: Boron-doped polycrystalline diamond (PCD) piezo-resistors demonstrated high Gauge Factors (up to 100) and stability, making them ideal for pressure and acceleration sensors operating above 300 °C.
  • Biomedical Integration: Successful fabrication of integrated piezoelectric oxide (PZT or AlN) and UNCD heterostructures enables new generations of biocompatible devices, including neural probes, drug delivery valves, and biopower generators.
  • Cold Cathode Emitters: Nitrogen-incorporated UNCD (N-UNCD) films function as robust cold cathodes, achieving stable electron field emission at low electric fields (~3 V/”m) for extended lifetimes (over 1000 hours).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Young’s Modulus (Diamond)1050-1200GPaHigh mechanical stiffness
Thermal Conductivity (SCD)~2100W/KmHighest of any material
Thermal Conductivity (UNCD)Low-Ideal thermal insulation layer
Band Gap (Diamond)5.45eVWide bandgap semiconductor
UNCD Grain Size3-5nmSmallest polycrystalline grain size
UNCD Surface Roughness (RMS)3-5nmIndependent of film thickness
UNCD Coefficient of Friction (COF)0.02-0.05-Ultra-low friction, anti-stiction
PCD Piezo-resistive Gauge Factor (GF)5 to 100-For pressure/acceleration sensors
RF-MEMS Switch Recovery Time (UNCD)~100”s5-6 orders < SiO2/SiNx
Diamond Acoustic Phase Velocity18,076m/sHighest available thin-film material
N-UNCD Field Emission Field~3V/”mLow operating voltage for cold cathodes
PZT/UNCD Polarization25”C/cm2Ferroelectric performance in integrated structure
AlN Piezoelectric Coefficient5.3pm/VHighest reported for (002) oriented AlN films
High-Temperature Operation Limit (Diamond)600°CChemically stable in air

Key Methodologies

Section titled “Key Methodologies”

  1. Chemical Vapor Deposition (CVD) Techniques:

    • MCD/NCD Growth: Typically uses Microwave Plasma CVD (MPCVD) or Hot Filament CVD (HFCVD) with hydrogen-rich gas mixtures (e.g., H2 (99%)/CH4 (1%)). H atoms are critical for etching graphitic sp2 impurities.
    • UNCD Growth: Patented MPCVD process using an Argon-rich gas mixture (Ar (99%)/CH4 (1%)). This chemistry promotes C2 dimers as the primary growth species, resulting in the ultra-small 3-5 nm grains.

  2. Nucleation and Adhesion Enhancement:

    • Conventional Seeding: Substrate surface abrasion or sonication in a methanol/diamond nanoparticle solution.
    • Bias Enhanced Nucleation/Growth (BEN-BEG): Applying a negative voltage (e.g., -200 V to -350 V) to the substrate during CVD to accelerate plasma ions (C+, CHx+). This induces Si-C carbide formation, significantly improving diamond film adhesion to Si substrates.

  3. Doping for Conductivity:

    • P-Type Doping: Boron (B) is the most successful dopant, incorporated during CVD using precursors like trimethyl boron (B(CH3)3, TMB) to achieve semiconducting or semi-metallic properties required for piezo-resistors and electrodes.

  4. Patterning and Etching:

    • Dry Etching: Required due to diamond’s chemical inertness. Uses plasma techniques (RIE, ICP) with O2 gas to generate volatile CO and CO2 molecules.
    • Column Suppression: Small additions of CF4 or SF6 to the O2 plasma are used to suppress the formation of undesirable diamond columns, ensuring complete removal of PCD layers for MEMS release.

  5. Heterostructure Fabrication (PZT/UNCD):

    • Barrier Layer: A TiAl (Titanium Aluminum) barrier layer (30-40 nm thick) is deposited on the UNCD film prior to PZT growth. This layer prevents oxygen atoms (from the PZT growth environment at 450-550 °C) from diffusing into and chemically etching the underlying UNCD carbon film.
    • Piezoelectric Layer Growth: PZT (Lead-Zirconate-Titanate) or AlN (Aluminum Nitride) films are grown via Pulsed Laser Deposition (PLD) or reactive sputter deposition, respectively, to achieve the active actuation layer.

Commercial Applications

Section titled “Commercial Applications”

  • RF and Microwave Systems:

    • Product: High-reliability, low-power RF-MEMS capacitive switches (UNCD dielectric).
    • Industry: 5G/6G wireless communications, Radar, and high-linearity electronics.

  • Biomedical and Implantable Devices:

    • Product: All-diamond neural probes, cochlear implant position sensors, and biosensors (PCD/UNCD).
    • Industry: Neuroprosthetics, medical diagnostics, and long-term human body implants (leveraging diamond’s biocompatibility).

  • Energy Harvesting and Power Sources:

    • Product: MEMS biopower generators (PZT/UNCD cantilevers) that convert mechanical vibration into electricity.
    • Industry: Implantable medical devices (pacemakers, defibrillators) to replace conventional Li-ion batteries, reducing the need for invasive replacement surgery.

  • Harsh Environment and High-Temperature Sensing:

    • Product: Piezo-resistive pressure, acceleration, and force sensors (B-doped PCD).
    • Industry: Automotive safety (airbag deployment sensors), aerospace, industrial process monitoring, and geothermal applications.

  • Vacuum and Field Emission Technology:

    • Product: Robust cold cathode electron field emitters (N-UNCD).
    • Industry: Miniaturized mass spectrometers for space exploration, long-life electron sources, and advanced display technologies (Field Emission Displays, FEDs).

  • Microfluidics and Lab-on-a-Chip:

    • Product: All-diamond microfluidic channels and active drug delivery valves (UNCD/AlN heterostructures).
    • Industry: Chemical/biochemical analysis, thermal management (micro-coolers for CPUs), and portable diagnostic systems.
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]

Reads Similar to This

Study of nitrocarburizing plasmas using advanced spectroscopic diagnostics Peculiarities of admittance spectroscopy study of wide bandgap semiconductors on the example of diamond Temperature Measurement of Trapped, Thermally Sensitive Single Particles in an Optical Trap Using Raman Spectroscopy