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6CCVD Research

Ultrasensitive and Reliable Diamond MEMS Magnetic Force Sensor with 3D Imaging at Room Temperature

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2025-05-12
JournalAdvanced Materials Technologies
AuthorsZilong Zhang, Keyun Gu, Zhijian Zhao, Zhibin Lei, Yi‐Hsiu Kao
InstitutionsNational Institute for Materials Science, Tohoku University
AnalysisFull AI Review Included

Executive Summary

Section titled “Executive Summary”

This research presents a highly sensitive and reliable magnetic force sensor utilizing a Single-Crystal Diamond (SCD) Micro-Electro-Mechanical System (MEMS) resonator, designed for robust room-temperature operation.

  • Ultra-High Sensitivity: The sensor achieves an ultra-low detectable force of 1.8 x 10-16 N/Hz1/2 at room temperature, significantly advancing performance compared to typical silicon resonators.
  • Exceptional Reliability: Resonant frequency fluctuation is remarkably low, measured at 7.89 x 10-4 Hz, ensuring stable and reliable operation without the need for complex cryogenic cooling.
  • High Magnetic Response: The device exhibits a high magnetic sensitivity of 0.303%/(mT/mm) and a fast response time of 98.8 ms in the fundamental (first) vibration mode.
  • 3D Imaging Capability: A 3D magnetic force imaging sensor based on the SCD platform was successfully demonstrated, capable of visualizing magnetic force distributions with a minimum detectable force of 5.5 pN.
  • Robust Material Platform: The use of SCD provides superior thermal conductivity, chemical stability, and high Q factor, enhancing durability and reliability in dynamic environments.
  • Fabrication Method: The SCD resonator was fabricated using the smart-cut method based on ion-implantation assisted lift-off (IAL) technology, followed by MPCVD growth, resulting in high crystal quality (FWHM 1.84 cm-1).

Technical Specifications

Section titled “Technical Specifications”
ParameterValueUnitContext
Detectable Force (Fmin)1.8 x 10-16N/Hz1/2Room Temperature, 1st Mode
Magnetic Sensitivity (1st Mode)0.303%/(mT/mm)Based on resonance shift
Resonant Frequency (1st Mode)23.170kHzWith NdFeB particle
Q Factor (1st Mode)6400-With NdFeB particle
Resonant Frequency Fluctuation (Δfmin)7.89 x 10-4HzRoom Temperature, 1st Mode
Response Time (1st Mode)98.8msDynamic switching of magnetic field gradient
Minimum Detectable Force (3D Imaging)5.5pNAchieved force level for imaging
Minimum Detectable Magnetic Field Gradient (1st Mode)1.12 x 10-5mT mm-1Calculated from Δfmin
SCD Cantilever Dimensions120 x 10 x 0.7”mLength x Width x Thickness
SCD Epilayer FWHM (Raman)1.84cm-1Post-MPCVD growth
NdFeB Coercive Field (Hc)1333.1OeVSM measurement
NdFeB Saturation Magnetization (Ms)111.9emu g-1VSM measurement
TCF (SCD Resonator)< 5ppm K-1Temperature Coefficient of Frequency

Key Methodologies

Section titled “Key Methodologies”

The SCD MEMS resonator was fabricated using the smart-cut method based on Ion-Implantation Assisted Lift-off (IAL), followed by heterogeneous integration with the magnetic particle.

  1. Substrate Preparation and Implantation:

    • Started with High Temperature High Pressure (HTHP) Type-Ib (100) SCD substrate (RMS roughness less than 1 nm).
    • Carbon ions (C+) were implanted at 180 keV energy with a dose of 1016 cm-2 to create a sacrificial layer.

  2. SCD Epilayer Growth (MPCVD):

    • A high-purity SCD epilayer was deposited using Microwave Plasma Chemical Vapor Deposition (MPCVD).
    • Process parameters included 0.5% methane concentration, 500 sccm hydrogen flow, 1 kW microwave power, and 840 °C working temperature.
    • Growth duration was 3 hours, converting the ion-damaged layer into a graphite-like sacrificial layer (~200 nm thick).

  3. Patterning and Etching:

    • A 150 nm thick Aluminum (Al) film was deposited and patterned as a metal mask.
    • The patterned SCD was dry-etched using Reactive Ion Etching (RIE) with Inductively Coupled Plasma (ICP) in a pure oxygen environment.

  4. Post-Fabrication Annealing and Cleaning:

    • Annealing 1: Samples were annealed at 1100 °C for 3 hours under ultrahigh vacuum (less than 10-7 Pa) to reduce defects and enhance Q-factors.
    • Oxygen Etching: Employed to remove defective surface layers (non-diamond) resulting from ion implantation.
    • Annealing 2: Samples were annealed again at 650 °C for 10 hours in an oxygen environment to further improve Q-factors.

  5. Device Assembly (Heterogeneous Integration):

    • The free SCD cantilever was cut from the substrate using a glass needle.
    • The cantilever was transferred onto a Si substrate using a micromanipulator and secured with conductive glue, followed by curing at 180 °C.
    • A 14 ”m diameter NdFeB magnetic particle was attached to the cantilever tip using conductive adhesive.
    • The NdFeB particle was magnetized using a 694 mT magnetic field prior to testing.

Commercial Applications

Section titled “Commercial Applications”

The combination of high sensitivity, exceptional reliability, and room-temperature operation makes this SCD MEMS magnetic force sensor highly valuable across several advanced technological sectors:

  • Biomedical and Medical Diagnostics:

    • Non-invasive biomedical magnetic detection, including highly sensitive detection of biomagnetic signals from human organs.
    • Magnetic Resonance Imaging (MRI)-inspired sensing, offering portable, room-temperature alternatives to complex cryogenic SQUID systems.
    • Detection of biological molecules (e.g., DNA) due to the fN-level force sensitivity potential.

  • Microelectronic and Spintronic Systems:

    • Localized field mapping and characterization of magnetic field distributions in microelectronic devices.
    • Probing nanoscale structural phenomena and material properties using advanced Magnetic Resonance Force Microscopy (MRFM) techniques.

  • Industrial and Aerospace Automation:

    • Precise measurement of magnetic fields and forces in sensitive industrial environments.
    • Applications requiring robust, durable sensors capable of operating reliably in extreme or dynamic conditions (high temperature, chemical stability).

  • Advanced Material Characterization:

    • Mapping 3D magnetic force distributions with high spatial resolution for material science research and quality control.
    • Characterization of magnetic materials (like NdFeB) and magnetic domain structures.
View Original Abstract

Abstract Developing magnetic force sensors with a simple structure, high sensitivity, and exceptional reliability at room temperature remains challenging due to frequency fluctuations and noise suppression issues. In this work, an ultra‐sensitive and highly reliable magnetic force sensor is presented by integrating a single‐crystal diamond (SCD) MEMS resonator with a permanent magnetic particle. The magnetic particle serves as the sensing element, enabling precise detection of magnetic field gradients under a field bath. The SCD‐based MEMS sensor exhibits outstanding performance, achieving an ultra‐low detectable force of 1.8 × 10 −16 N/Hz 1/2 , a high magnetic sensitivity of 0.303%/(mT/mm), and a response time of 98.8 ms in the first mode at room temperature. Notably, the resonant frequency fluctuation is remarkably low, reaching 7.89 × 10 −4 Hz at room temperature, ensuring stable and reliable operation. Furthermore, a 3D magnetic force imaging sensor based on the SCD platform, capable of visualizing the 3D distribution of magnetic forces is demonstrated. This work lays a solid foundation for the advancement of SCD MEMS‐based magnetic imaging sensors, offering unparalleled sensitivity, reliability, and tunable spatial resolution for next‐generation magnetic imaging applications.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2012 - in SQUID Sensors: Fundamentals, Fabrication and Applications

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