研究目的
To enhance the torsional fracture strength of single crystal silicon resonators for micro mirrors application by introducing a diamond-like carbon coating and to understand the effects of deposition bias voltage on strength and deviation.
研究成果
DLC coating significantly improved the torsional fracture strength of SCS resonators by 11.1–30.0%, with higher bias voltages yielding greater strength and reduced deviation due to increased compressive residual stress. The torsional strength correlated well with tensile strength, supporting the use of DLC coatings for enhancing MEMS mirror reliability. Future work could optimize deposition parameters and explore other environmental conditions.
研究不足
The study was conducted at atmospheric pressure and room temperature, which may not represent all operational environments. The low number of vibration cycles (up to 1.2×10^5) might not fully account for fatigue effects, though it was deemed negligible. Uncontrolled factors in deposition, such as substrate current, could affect results, as seen with the -600 V bias sample. The nonlinearity of resonators introduced instability in measurements.
1：Experimental Design and Method Selection:
The study used a plasma enhanced chemical vapor deposition (PECVD) technique to coat silicon torsional mirror resonators with diamond-like carbon (DLC) films at different bias voltages (-200 V, -400 V, -600 V) to investigate effects on fracture strength. Torsional tests were conducted using a custom-made system with piezoelectric actuation and laser-based amplitude measurement.
2：Sample Selection and Data Sources:
Samples were fabricated from a silicon-on-insulator (SOI) wafer with (100) surface orientation. Ten resonators were tested for each deposition condition (bare and three bias voltages).
3：List of Experimental Equipment and Materials:
Equipment included PECVD tool (Shinkoseiki ACV-1060), piezoelectric actuator (NTK Ceratec PAC166J), position sensitive detector (Hamamatsu Photonics S3270-01), CCD camera (Hozan L-835), laser (Global Laser 1260-03), FESEM (Hitachi SU-8020), Raman spectrometer (Horiba LabRAM-HR800), profilometer (Veeco DektakXT-S), nanoindenter (Elionix ENT-2100), and various fabrication tools (e.g., stepper Nikon NSR2205i11D, ICP-RIE Samco RIE-iPB800). Materials included silicon wafers, DLC films, chromium films, and chemicals like piranha solution and BHF acid.
4：0). Materials included silicon wafers, DLC films, chromium films, and chemicals like piranha solution and BHF acid. Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: Fabrication involved patterning and etching the SOI wafer, depositing DLC films with PECVD at specified biases, and removing supporting beams with laser trimming. Torsional tests involved oscillating resonators at resonance, increasing amplitude until fracture, and measuring with laser and PSD. Characterization included Raman spectroscopy, thickness measurement, residual stress calculation, nanoindentation, and SEM observation of fracture surfaces.
5：Data Analysis Methods:
Data were analyzed using Weibull statistics for strength distribution, Stoney's formula for residual stress, Oliver-Pharr method for hardness and modulus, and theoretical models for resonant frequency and fracture strength correlation.
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Position sensitive detector
S3270-01
Hamamatsu Photonics
Used to detect the reflected laser spot and measure the angular amplitude of the resonators.
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FESEM
SU-8020
Hitachi
Used for observing the fracture surfaces of the torsional beams.
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Profilometer
DektakXT-S
Veeco
Used to measure film thickness and wafer curvature for residual stress calculation.
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PECVD tool
ACV-1060
Shinkoseiki
Used for depositing diamond-like carbon films on silicon resonators via plasma enhanced chemical vapor deposition.
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Piezoelectric actuator
PAC166J
NTK Ceratec
Used to oscillate the torsional mirror resonators at their resonant frequency during torsional tests.
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CCD camera
L-835
Hozan
Equipped on an optical microscope for aligning the laser beam to the mirror plate.
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Laser
1260-03
Global Laser
Used to project a laser spot on the mirror for amplitude measurement.
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Raman spectrometer
LabRAM-HR800
Horiba
Used for qualitative analysis of chemical composition of DLC films.
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Nanoindenter
ENT-2100
Elionix
Used to measure hardness and elastic modulus of DLC films via nanoindentation.
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Stepper
NSR2205i11D
Nikon
Used for patterning the device layer during fabrication.
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ICP-RIE system
RIE-iPB800
Samco
Used for etching silicon layers via Bosch process.
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Double-sided mask aligner
PEM-800
Union Optics
Used for patterning the backside chromium film.
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Oxygen plasma asher
FA-1
Samco
Used for removing fluorocarbon passivation film.
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Laser trimming tool
HL-10
Hoya Candeo Optoronics
Used to remove supporting beams prior to torsional tests.
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Electron beam deposition system
EB1200
Canon Anelva
Used for depositing chromium film on the backside handle layer.
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