Name: Fabrication and Characterization of High-Q Silicon Nitride Membrane Resonators (Video) | JoVE Journal
Uploaded: 2025-08-08T13:20:00.000+00:00
Duration: 9 min 46 s
Description: Discover fabrication and characterization of high-Q silicon nitride membrane resonators for nanomechanics and quantum sensing applications. This method enables rapid design of devices for studying optical and mechanical properties.

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The authors would like to thank Roland Himmelhuber and the Optical Sciences Micro/Nano Fabrication Cleanroom for use of their facilities and helpful discussions.&#160; This work was supported by the National Science Foundation (NSF) through Awards No. 2239735 and No. 2330310. A.R.A. acknowledges support from a CNRS-UArizona iGlobes fellowship, and A.D.H. acknowledges support from a Friends of Tucson Optics Endowed Scholarship. Finally, the reactive ion etcher used for this study was funded by an NSF MRI grant, ECCS-1725571. The protocol was initially developed by A.R.A. and was later modified by A.D.H., C.A.C., and O.A.F. to optimize device fabrication. A.D.H. and D.J.W. co-wrote the manuscript with assistance from all co-authors.

The authors declare no competing interests.

One thing that is evident from the data in Figure 5 is that, while the Q of the torsional mode matches the simulated value, the flexural mode Q is lower than predicted. This does not fault the quality of the simulation but rather is a result of neglecting extrinsic loss mechanisms such as substrate mode coupling46 and clamping loss. The dissipation dilution model used in the protocol accounts for all intrinsic loss mechanisms and, therefore, sets an upper bound on the...

Silicon nitride membranes have played an important role in quantum optomechanics1 over the last two decades, beginning with the discovery that a commercial membrane (a TEM slide) can support drum modes with Q-frequency products exceeding 1013 Hz and be coupled to a high finesse optical cavity using the membrane-in-the-middle approach2,3,4. Gradually it was appreciated how tensile stress and mode shape affect the mechanical Q (through an effect called dissipation dilution5,6), spurring the invention of micropatterned membranes&#8212;trampoline7,8, 2D an1D phononic crystal9,10, fractal11, and perimeter mode resonators12&#8212;with Q factors as high as 109. In conjunction with cryogenics, these devices have enabled landmark experiments such as ground state cooling13,14, ponderomotive squeezing15, optomechanical entanglement16, and displacement measurement beyond the Standard Quantum Limit17,18. They also feature prominently in proposals for next generation optomechanical technologies and probes for new physics, including membrane-based force microscopes19, accelerometers20, spectroscopes21, quantum memories22, microwave-to-optical photon transducers23, and dark matter detectors24.
Despite their popularity, the design, fabrication, and characterization of silicon nitride membrane resonators remain a niche discipline within the optomechanics community, relying on bespoke techniques handed down by word of mouth and dissertations25,26,27,28,29,30,31,32. A recent review of interferometric characterization of nanomechanical resonators demystifies the latter task33, and modeling of dissipation dilution has become simple with commercial finite element simulation software28. Nanofabrication, however, remains an obstacle to entry, since the procedure, while straightforward, involves a sequence of delicate steps whose nuances are often left out of traditional verbal descriptions and process flow diagrams.
This article presents the design, fabrication, and characterization of a silicon nitride membrane resonator in video format, using a centimeter-scale nanoribbon34&#8212;a simple yet robust platform gaining popularity for torsional quantum optomechanics35,36 and precision measurement37,38&#8212;as an example (the procedure is readily adaptable to other resonator geometries). The design segment provides a basic overview of simulating membrane modes using commercial finite-element software. The fabrication sequence, which forms the core of the tutorial, covers substrate preparation, film deposition, patterning, etching, and release. The article concludes with a demonstration of characterization using the optical lever (OL) technique. This resource is intended as a practical starting point or refresher for researchers working with high-Q membrane resonators.

<table><tbody><tr><td>100nm double sided Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt; on 4&#039;&#039; 200&amp;micro;m Si wafer</td><td>WaferPro</td><td></td><td>Standard Si3N4 wafers used to fabricate membrane resonators</td></tr><tr><td>13KHz Sonificator Quantrex 70</td><td>L&amp;amp;R Ultrasonics</td><td></td><td>Used in conjunction with acetone to strip contaminants and hardened resist from chip surfaces.</td></tr><tr><td>150 mm glass petri dish, 20 mm deep</td><td>Corning Incorporated</td><td>08-747F</td><td>For HMDS priming</td></tr><tr><td>150 mm plastic petri dish, 15 mm deep</td><td>Supertek</td><td>S01268</td><td>For wafer transport</td></tr><tr><td>2 &amp;mu;m syringe filter</td><td>Millipore Sigma</td><td>SLAP02550</td><td>For filtering resist particulate</td></tr><tr><td>50ml PYREX Griffin Borosilicate Glass Beaker</td><td>Corning Incorporated, Life Sciences</td><td></td><td>General liquid bath containers</td></tr><tr><td>Acetone 99.5% ACS grade&amp;nbsp;</td><td>Sigma Aldrich</td><td>179124</td><td>General purpose solvent used specifically to strip S1813 resist</td></tr><tr><td>CarboFib Tweezers&amp;nbsp;</td><td>TDI International</td><td>TDI 2ACFR-SA</td><td>General purpose, chemical-resistant tweezers for safe manipulation of chips in various baths</td></tr><tr><td>Compressed nitrogen gas cylinder</td><td>Locally provided</td><td></td><td>Drying and cleaning</td></tr><tr><td>DI Water</td><td>Locally provided</td><td></td><td>For cleaning chips/wafers by diluting corrosives</td></tr><tr><td>Disposable Capillary pipets 7.0-7.4mm</td><td>VWR Scientific</td><td></td><td>For HMDS priming</td></tr><tr><td>Emlimny USB Digital Microscope</td><td>Emlimney</td><td></td><td>For the long-distance monitoring of wet etch progress</td></tr><tr><td>Hexamethyldisilazane (HMDS)</td><td>Sigma Aldrich</td><td>440191</td><td>Wafer primer</td></tr><tr><td>HiCube HiPace 80 turbopump</td><td>Pfeiffer Vacuum</td><td></td><td>Turbomolecular pump used to pump down sample vacuum chambers</td></tr><tr><td>Hydrofluoric Acid 48%</td><td>Sigma Aldrich</td><td>695068</td><td>Acid washing and film thinner, diluted to 10% when used</td></tr><tr><td>ICP-RIE DSE, Versaline DSE III</td><td>Plasmatherm</td><td></td><td>For Si&lt;sub&gt;3&lt;/sub&gt;N&lt;sub&gt;4&lt;/sub&gt; etching</td></tr><tr><td>Isopropanol 99.5% ACS grade&amp;nbsp;</td><td>Sigma Aldrich</td><td>190764</td><td>Used to transition released membranes from liquid to air and for cleaning released films</td></tr><tr><td>Kapton Tape - 1 Mil, 1&amp;frasl;2&quot; x 36 yds</td><td>ULINE</td><td>S-7595</td><td>Used for securing wafers and chips to carrier wafers in the plasma etch step</td></tr><tr><td>LatticeAx 225</td><td>LatticeGear</td><td></td><td>Cleaving tool</td></tr><tr><td>Laurell WS 650 Spin Coater</td><td>Laurell Technologies Corporation</td><td></td><td>Spin coating machine for depositing uniform resist layers on wafers</td></tr><tr><td>Mask Less Aligner,&amp;nbsp; MLA150</td><td>Heidelberg Instruments</td><td></td><td>Photolithography machine &lt;img alt=&quot;Equation 1&quot; src=&quot;/files/ftp_upload/68706/68706eq02.jpg&quot; style=&quot;margin: auto;&quot;/&gt;=100nm</td></tr><tr><td>Methanol 99.8% ACS grade</td><td>Sigma Aldrich</td><td>179337</td><td>Used to transition released membranes from liquid to air and for cleaning released films</td></tr><tr><td>MF-319 developer</td><td>Kayaku</td><td></td><td>Developing exposed resist patterns</td></tr><tr><td>Microposit S1800 G2 Series Photoresists</td><td>Dow Chemical Company</td><td></td><td>For photolithography patterning. This work specifically uses S1813 resist.</td></tr><tr><td>MiniVac Controller</td><td>Varian</td><td>9290191</td><td>Vacuum chamber ion pump controller</td></tr><tr><td>MS-H280-Pro Hot plate</td><td>ONiLAB</td><td></td><td>General heating device</td></tr><tr><td>National Instruments NI PXI-1033</td><td>National Instruments</td><td></td><td>Data acquisition system chassis</td></tr><tr><td>Ni PXI-4461</td><td>National Instruments</td><td></td><td>Analog to digital converter for data acquisition</td></tr><tr><td>Potassium Hydroxide KOH Solution 45%</td><td>Sigma Aldrich</td><td>417661</td><td>Anisotropic silicon wet etchant</td></tr><tr><td>Sample Holder</td><td>Custom Made</td><td></td><td>Custom made for holding samples upright in different chemical baths</td></tr><tr><td>TLB-6700 Velocity External Cavity Diode Laser</td><td>New Focus</td><td>995</td><td>Optical lever laser source</td></tr><tr><td>Tunable Laser Controller</td><td>New Focus</td><td>TLB-6700</td><td>Laser controller</td></tr><tr><td>Vaclon Plus 55 starcell ion pump</td><td>Varian</td><td>9191340</td><td>Passice vacuum pump</td></tr><tr><td>Vacuum chamber</td><td></td><td></td><td>Vacuum chamber for isolating resonators</td></tr><tr><td>Visible quadrant cell photoreceiver</td><td>New Focus</td><td>23538-WX</td><td>Split photodiode for optical lever readout</td></tr></tbody></table>

fabrication and characterization of high-q silicon nitride membrane resonators

Fabrication and Characterization of High-Q Silicon Nitride Membrane Resonators

Silicon nitride membranes are a widely used optomechanical resonator platform, offering high mechanical Q, low optical loss, and enhanced optomechanical coupling using a panoply of strain, phononic-crystal, and photonic-crystal engineering techniques. Despite their ubiquity, fabrication and characterization of silicon nitride membranes often rely on tacit knowledge shared between research groups. This article presents a detailed video walk-through of the design, fabrication, and characterization of a contemporary silicon nitride membrane resonator (specifically, a centimeter-scale Si3N4 nanoribbon supporting torsional modes with Q-factors exceeding 108 at room temperature). The protocol covers finite element simulation, wafer- and chip-scale processing, and optical lever-based readout. Special attention is given to photolithographic patterning, dry- and wet-etching, device handling, and ringdown measurement. The tutorial is intended as both a practical entry point for newcomers and a reference for experienced groups replicating or adapting similar devices. All procedures are demonstrated in standard university cleanroom and benchtop environments.

We demonstrate the protocol by fabricating a wafer consisting of several 100 nm thick diagonal ribbon resonators34 and characterizing their first few vibrational modes. In this work, the ribbon is 7 mm long and 400 µm wide with 662 µm diameter fillets. We note that while the OL used in this work is naturally suited to torsional modes, it can also detect transverse flexural modes by positioning the beam at a location of non-zero angular deflection. As an illustration, we use the OL to measure both ...

This article traces the life cycle of a silicon nitride membrane resonator, from design through fabrication to characterization.

Silicon nitride membranes are a widely used optomechanical resonator platform, offering high mechanical Q, low optical loss, and enhanced optomechanical ...

Our research aims to explore the unique optical and mechanical properties of freestanding silicon nitride thin films. Our fabrication procedure allows us to rapidly design and characterize these devices, which allows us to make quicker advancements in the field of nano mechanics. Looking ahead, our group plans on using these devices to study the quantum properties of angular sensing to develop on ship accelerometers and to design experiments for probing physics on this tabletop scale.To begin, obtain a glass Petri dish containing a clean double-sided silicon nitride wafer. Place a few drops of HMDS along the edge of a glass Petri dish using a disposable capillary pipette. Under a fume hood cover the Petri dish.Heat it on a hot plate at 90 degrees Celsius for one minute. to evaporate the HMDS and allow it to adhere to the silicon nitride. After priming, place the wafer inside a spin coder.Now use a needle and syringe to extract no more than four milliliters of S1813 Photo resist. Gently flick the syringe and dispense a small amount of fluid to remove any air bubbles. Safely remove the syringe needle and attach a two micrometer filter.Flick the syringe again and dispense three to five drops to remove air bubbles in the filter Deposit the resist drop by drop onto the center of the wafer to form a large pool. As the pool expands, continue depositing resist near its edge to keep it centered. Use the needle tip to pop any surface bubbles that appear before proceeding.Now lock the spin coder lid and set it to spin to create a uniform 1.5 micrometer thick layer across the wafer. Remove the wafer and place it on a hot plate to soft bake. After one minute, remove the wafer from the hot plate.To define the device patterns, load the coated wafer into a massless alignment photolithography machine. Center it to minimize global rotation and offset errors. Load the populated wafer file onto the computer and convert it to a compatible format for the MLA software.Begin patterning the top side layer with resonator designs. After alignment, select the option to include global rotation error load beam exposure parameters by setting the beam intensity to 140 millijoules per square centimeter at a wavelength of 375 nanometers. Now fill a large dish with approximately 75 milliliters of MF319 developer and another with deionized water.Once the photolithography exposure is complete, unload the wafer from the photolithography machine. Then transfer it into the MF 3 1 9 developer for 20 seconds. Gently swirl the dish in a circular motion to agitate and remove the exposed resist for an additional 40 seconds.Then transfer the wafer to the deionized water dish to dilute off residual developer. Rinse both sides of the wafer using a spray gun, use a compressed nitrogen gas gun to remove remaining water from the wafer surface, applying low pressure and proper orientation to prevent damage. Load the developed wafer into a reactive ion etcher to transfer the resist patterns onto the silicon nitride film.Run the etching process for five seconds per cycle with the given settings. Repeat the process until all wafer regions not protected by the resist layer turn silver indicating the substrate is exposed. Finally, remove the wafer from the reactive ion etcher for backside patterning.To release the patterned resonators from their silicon substrate. The wafer is diced or cleaved and processed at the chip scale. Carefully peel the diced chips from their tape.Dip the chips into a sonicated acetone bath for at least 30 seconds to remove resist and surface contaminants. Optionally, to thin the silicon nitride film or remove stuck on contaminants, dip the chip into a 10%hydrofluoric acid buffer solution to remove 1.55 nanometers of silicon nitride per minute. Immediately place the clean chip into a custom PTFE holder under a fume hood.The chip holder is then gently lowered into a 45%solution potassium hydroxide bath maintained at 86 degrees Celsius. Cover the solution to maintain a uniform thermal gradient. After the silicon around the resonator is fully etched and the film is released, stop the reaction by removing the vessel from the hot plate.Without exposing the chip gradually pipette out the potassium hydroxide solution and replace it with deionized water, always maintaining the liquid level above the chip to prevent shattering the device. To avoid cross-contamination, transfer the chip holder and a clean beaker into a fresh bath of deionized water. Then transfer the chip holder into the clean beaker containing deionized water.After the transfer, remove both beakers. Gradually replace the deionized water with isopropyl alcohol in the same way, ensuring the liquid level always remains above the chip. Repeat with methanol.After the last bath, remove the chip and dry it carefully along the device plane using a gentle nitrogen stream. The device is characterized in a vacuum chamber operating below 10 to the power of negative seven millibars with optical lever readout. To set up an optical lever, place a focusing lens after a fiber collimator and a beam splitter between the focusing lens and the sample.Focus a collimated laser beam onto the sample with a spot size similar to the largest feature being measured. Align the laser beam close to normal incidents onto the sample by retro reflecting into an optical fiber, which simplifies later alignment. Place a balanced photo detector along the reflected beam path, positioned beyond the rail length of the beam to maximize sensitivity.with the laser incident on the split or quadrant photo detector, the detector output is sent to a digitizer. Compute the real-time power spectral density of the signal using the Fast Fourier transform method. To identify specific mode peaks, compare the location of thermal noise peaks in the broadband signal to predicted Eigenfrequencies from simulations.Take a root means square average of several power spectral density estimates to confirm the peaks. Begin energy ring down by tracking the integral under the power spectral density peak at the resonant frequency to measure stored energy. To drive the mode, apply energy either by placing a Piezo Actuator on the side or by sending a second laser beam to the sample, modulate the Piezo voltage or the beam intensity at the resonant frequency.Once the drive is stopped, track the exponential decay of the oscillation energy to determine the damping rate. Then calculate the modal Q by dividing the resonant frequency by the damping rate COMSOL simulations of the ribbon geometry revealed a 53 kilohertz flexural mode and a 70 kilohertz torsional mode. The flexural mode has the largest angular displacement, halfway between the center of the ribbon and its fillets.A GDS2 design was created with 37 chips of 12 square millimeters each, showing a variety of geometries for fabrication. Power spectral density analysis demonstrates the effectiveness of the optical lever in reading out the angular displacement of both modes.

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Discover fabrication and characterization of high-Q silicon nitride membrane resonators for nanomechanics and quantum sensing applications. This method enables rapid design of devices for studying optical and mechanical properties.

Fabrication and Characterization of High-Q Silicon Nitride Membrane Resonators

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