Name: fabrication and characterization of thickness mode piezoelectric devices for atomization and acoustofluidics
Uploaded: 2020-08-05T12:30:00
Description: Watch this Scientific Journal Video about Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics at JoVE.com

The authors are grateful to the University of California and the NANO3 facility at UC San Diego for provision of funds and facilities in support of this work. This work was performed in part at the San Diego Nanotechnology Infrastructure (SDNI) of UCSD, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (Grant ECCS&#8722;1542148). The work presented here was generously supported by a research grant from the W.M. Keck Foundation. The authors are also grateful for the support of this work by the Office of Naval Research (via Grant 12368098).

1. Thickness mode transducer fabrication via DC sputtering
<ol>
	<li>Wafer preparation
	<ol>
		<li>Place a 100 mm 128YX LN wafer in a clean glass dish of at least 125 mm diameter. Sonicate the wafer in at least 200 mL of acetone for 5 min.</li>
		<li>Repeat sonication with isopropyl alcohol and again with deionized water for 5 min each.</li>
		<li>Remove visible water from the surface using dry nitrogen.</li>
		<li>Completely remove water from the surface by placing the wafer on a hotplate at 100 &#176;C for 5 min. Ens...

<ol>
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P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+PZT-driven+atomizer+based+on+a+vibrating+flexible+membrane+and+a+micro-machined+trumpet-shaped+nozzle+array.">A PZT-driven atomizer based on a vibrating flexible membrane and a micro-machined trumpet-shaped nozzle array.</a> Microsystem Technologies. 15 (6), 865-873 (2009).</li><li>Lupascu, D., R&#246;del, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fatigue+in+bulk+lead+zirconate+titanate+actuator+materials.">Fatigue in bulk lead zirconate titanate actuator materials.</a> Advanced Engineering Materials. 7 (10), 882-898 (2005).</li><li>Kawamata, A., Hosaka, H., Morita, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-hysteresis+and+perfect+linear+piezoelectric+performance+of+a+multilayered+lithium+niobate+actuator.">Non-hysteresis and perfect linear piezoelectric performance of a multilayered lithium niobate actuator.</a> Sensors and Actuators A: Physical. 135 (2), 782-786 (2007).</li><li>Qi, A., Yeo, L., Friend, J., Ho, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Extraction+of+Liquid,+Protein+Molecules+and+Yeast+Cells+from+Paper+Through+Surface+Acoustic+Wave+Atomization.">The Extraction of Liquid, Protein Molecules and Yeast Cells from Paper Through Surface Acoustic Wave Atomization.</a> Lab on a Chip. 10 (4), 470-476 (2010).</li><li>Collignon, S., Manor, O., Friend, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Improving+and+Predicting+Fluid+Atomization+via+Hysteresis-Free+Thickness+Vibration+of+Lithium+Niobate.">Improving and Predicting Fluid Atomization via Hysteresis-Free Thickness Vibration of Lithium Niobate.</a> Advanced Functional Materials. 28 (8), 1704359 (2018).</li><li>Lawson, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+vibration+of+piezoelectric+plates.">The vibration of piezoelectric plates.</a> Physical Review. 62 (1-2), 71 (1942).</li><li>Fukushima, Y., Nishizawa, O., Sato, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+performance+study+of+a+laser+doppler+vibrometer+for+measuring+waveforms+from+piezoelectric+transducers.">A performance study of a laser doppler vibrometer for measuring waveforms from piezoelectric transducers.</a> IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control. 56 (7), 1442-1450 (2009).</li><li>Thoroddsen, S., Etoh, T., Takehara, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-speed+imaging+of+drops+and+bubbles.">High-speed imaging of drops and bubbles.</a> Annual Reviews in Fluid Mechanics. 40, 257-285 (2008).</li><li>Yule, A., Al-Suleimani, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=On+droplet+formation+from+capillary+waves+on+a+vibrating+surface.">On droplet formation from capillary waves on a vibrating surface.</a> Proceedings of the Royal Society of London Series A: Mathematical, Physical and Engineering Sciences. 456 (1997), 1069-1085 (2000).</li><li>Hirleman, E. 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The dimensions and aspect ratio of a transducer affects the vibration modes it produces. Because the lateral dimensions are &#64257;nite, there are always lateral modes in addition to the desired thickness modes. The above LDV methods can be used to determine dominant modes in the desired frequency range for a given transducer. A square with dimensions below 10 mm typically gives a close approximation to a thickness mode. Three by ten millimeter rectangles also work well. Movie 1 and Movie 2</str...

Ultrasound atomization has been studied for almost a century and although there are many applications, there are limitations in understanding the underlying physics. The &#64257;rst description of the phenomenon was made by Wood and Loomis in 19271, and since then there have been developments in the &#64257;eld for applications ranging from delivering aerosolized pharmaceutical &#64258;uids2 to fuel injection3. Although the phenomenon works well in these applications, the underlying physics is not well understood4,5,6.
A key limitation in the &#64257;eld of ultrasonic atomization is the choice of material used, lead zirconate titanate (PZT), a hysteretic material prone to heating7 and lead contamination with elemental lead available from the inter-grain boundaries8,9. Grain size and mechanical and electronic properties of grain boundaries also limit the frequency at which PZT can operate10. By contrast, lithium niobate is both lead-free and exhibits no hysteresis11, and can be used to atomize &#64258;uids an order of magnitude more efficiently than commercial atomizers12. The traditional cut of lithium niobate used for operation in the thickness mode is the 36-degree Y-rotated cut, but the 127.86-degree Y-rotated, X-propagating cut (128YX), typically used for surface acoustic wave generation, has been shown to have a higher surface displacement amplitude in comparison with the 36-degree cut13 when operated in resonance and low loss. It has also been shown that thickness mode operation offers an order of magnitude improvement in atomizer efficiency over other modes of vibration13, even when using LN.
The resonance frequency of a piezoelectric device operating in the thickness mode is governed by its thickness t: the wavelength &#955; = 2t/n where n = 1, 2,... is the number of anti-nodes. For a 500 &#181;m thick substrate, this corresponds to a wavelength of 1 mm for the fundamental mode, which can then be used to calculate the fundamental resonance frequency, f = v/&#955; if the wave speed, v, is known. The speed of sound through the thickness of 128YX LN is approximately 7,000 m/s, and so f = 7 MHz. Unlike other forms of vibration, particularly surface-bound modes, it is straightforward to excite higher-order thickness mode harmonics to much higher frequencies, here to 250 MHz or more, though only the odd-numbered modes may be excited by uniform electric &#64257;elds14. Consequently, the second harmonic (n = 2) near 14 MHz cannot be excited, but the third harmonic at 21 MHz (n = 3) can. Fabrication of efficient thickness mode devices requires depositing electrodes onto opposing faces of the transducer. We use direct current (DC) sputtering to accomplish this, but electron-beam deposition and other methods could be used. Impedance analysis is useful to characterize the devices, particularly in &#64257;nding the resonance frequencies and electromechanical coupling at these frequencies. Laser Doppler vibrometry (LDV) is useful to determine the output vibration amplitude and velocity without contact or calibration15, and, via scanning, the LDV provides the spatial distribution of surface deformation, revealing the mode of vibration associated with a given frequency. Finally, for the purposes of studying atomization and &#64258;uid dynamics, high-speed imaging can be employed as a technique to study the development of capillary waves on the surface of a sessile drop16,17. In atomization, like many other acoustofluidic phenomena, small droplets are produced at a rapid rate, over 1 kHz in a given location, too quickly for high-speed cameras to observe with sufficient &#64257;delity and &#64257;eld of view to provide useful information over a sufficiently large droplet sample size. Laser scattering may be used for this purpose, passing the droplets through an expanded laser beam to (Mie) scatter some of the light in re&#64258;ection and refraction to produce a characteristic signal that may be used to statistically estimate the droplet size distribution.
It is straightforward to fabricate piezoelectric thickness mode transducers, but the techniques required in device and atomization characterization have not been clearly stated in the literature to date, hampering progress in the discipline. In order for a thickness mode transducer to be effective in an atomization device, it must be mechanically isolated so that its vibration is not damped and it must have a continuous &#64258;uid supply with a &#64258;ow rate equal to the atomization rate so that neither desiccation nor &#64258;ooding occur. These two practical considerations have not been thoroughly covered in the literature because their solutions are the result of engineering techniques rather than pure scienti&#64257;c novelty, but they are nonetheless critical to studying the phenomenon. We present a transducer holder assembly and a liquid wicking system as solutions. This protocol offers a systematic approach to atomizer fabrication and characterization for facilitating further research in fundamental physics and myriad applications.

<table border="0" cellpadding="0" cellspacing="0" style="width:1452px;" width="1452">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Amplifier</td>
			<td style="width:345px;">Amplifier Research, Souderton, PA, USA</td>
			<td style="width:412px;">5U1000</td>
			<td style="width:483px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Articulating arm</td>
			<td style="width:345px;">Fisso, Zurich, Switzerland</td>
			<td style="width:412px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">CF4 Objective</td>
			<td style="width:345px;">Edmund Optics, Barrington, NJ, USA</td>
			<td></td>
			<td>Objective used for high speed imaging</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Dicing saw</td>
			<td style="width:345px;">Disco, Tokyo, Japan</td>
			<td>Disco Automatic Dicing Saw 3220</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Fiber Fragrance Diffuser Wick</td>
			<td style="width:345px;">Weihai Industry Co., Ltd., Weihai, Shandong, China</td>
			<td colspan="2">https://www.weihaisz.com/Fiber-Fragrance-Diffuser-Wick_p216.html</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">High Speed Camera</td>
			<td style="width:345px;">Photron, San Diego, USA</td>
			<td style="width:412px;">Fastcam Mini</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Laser Doppler Vibrometer</td>
			<td style="width:345px;">Polytec, Waldbronn, Germany</td>
			<td style="width:412px;">UHF120</td>
			<td>Non-contact laser doppler vibrometer</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:212px;">Laser Scattering Droplet size measurement system</td>
			<td style="width:345px;">Malvern Panalytical, Malvern, UK</td>
			<td style="width:412px;">STP5315</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Lithium niobate substrate</td>
			<td style="width:345px;">PMOptics,Burlington, MA, USA</td>
			<td style="width:412px;">PWLN-431232</td>
			<td style="width:483px;">4&#8221; double-side polished 0.5 mm thick 128&#176;Y-rotated cut lithium niobate</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Luer-lock syringes</td>
			<td style="width:345px;">Becton Dickingson, New Jersey, USA</td>
			<td style="width:412px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Nano3 cleanroom facility</td>
			<td style="width:345px;">UCSD, La Jolla, CA, USA</td>
			<td style="width:412px;"></td>
			<td>Fabrication process is performed in it.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Network Analyzer</td>
			<td style="width:345px;">Keysight Technologies, Santa Rosa, CA, USA</td>
			<td style="width:412px;">5061B</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Oscilloscope</td>
			<td style="width:345px;">Keysight Technologies, Santa Rosa, CA, USA</td>
			<td style="width:412px;">InfiniiVision 2000 X-Series</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">PSV Acquistion Software</td>
			<td style="width:345px;">Polytec, Waldbronn, Germany</td>
			<td style="width:412px;">Version 9.4</td>
			<td>LDV Software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">PSV Presentation Software</td>
			<td style="width:345px;">Polytec, Waldbronn, Germany</td>
			<td style="width:412px;">Version 9.4</td>
			<td>LDV Software</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Signal generator</td>
			<td style="width:345px;">NF Corporation, Yokohama, Japan</td>
			<td style="width:412px;">WF1967 multifunction generator</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Single Post Connector</td>
			<td style="width:345px;">DigiKey, Thief River Falls, MN</td>
			<td>ED1179-ND</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Sputter deposition</td>
			<td style="width:345px;">Denton Vacuum, NJ, USA</td>
			<td style="width:412px;">Denton 18</td>
			<td>Denton Discovery 18 Sputter System</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Surface Mount Spring Contacts</td>
			<td style="width:345px;">DigiKey, Thief River Falls, MN</td>
			<td style="width:412px;">70AAJ-2-M0GCT-ND</td>
			<td style="width:483px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">Teflon wafer dipper</td>
			<td style="width:345px;">ShapeMaster, Ogden, IL, USA</td>
			<td style="width:412px;">SM4WD1</td>
			<td>Wafer Dipper 4&#34;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:212px;">XYZ Stage</td>
			<td style="width:345px;">Thor Labs, Newton, New Jersey, USA</td>
			<td style="width:412px;">MT3</td>
			<td>Optical table stages</td>
		</tr>
	</tbody>
</table>

fabrication and characterization of thickness mode piezoelectric devices for atomization and acoustofluidics

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid more efficiently, in terms of &#64258;ow rate per power input, than those that rely on Rayleigh waves and other modes of vibration in LN or lead zirconate titanate (PZT). The complete device is composed of a transducer, a transducer holder, and a &#64258;uid supply system. The fundamentals of acoustic liquid atomization are not well known, so techniques to characterize the devices and to study the phenomena are also described. Laser Doppler vibrometry (LDV) provides vibration information essential in comparing acoustic transducers and, in this case, indicates whether a device will perform well in thickness vibration. It can also be used to &#64257;nd the resonance frequency of the device, though this information is obtained more quickly via impedance analysis. Continuous &#64258;uid atomization, as an example application, requires careful &#64258;uid flow control, and we present such a method with high-speed imaging and droplet size distribution measurements via laser scattering.

Thickness mode piezoelectric devices were fabricated from 128YX lithium niobate. Figure 1 shows a complete assembly to hold the transducer in place with a custom transducer holder used with the passive &#64258;uid delivery system developed for continuous atomization. The characterization steps for these devices include determination of the resonant frequency and harmonics using an impedance analyzer (Figure 2). The fundamental frequency of the devices was found ...

Watch this Scientific Journal Video about Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics at JoVE.com

Fabrication and Characterization of Thickness Mode Piezoelectric Devices for Atomization and Acoustofluidics

Fabrication of piezoelectric thickness mode transducers via direct current sputtering of plate electrodes on lithium niobate is described. Additionally, reliable operation is achieved with a transducer holder and &#64258;uid supply system and characterization is demonstrated via impedance analysis, laser doppler vibrometry, high-speed imaging, and droplet size distribution using laser scattering.

We present a technique to fabricate simple thickness mode piezoelectric devices using lithium niobate (LN). Such devices have been shown to atomize liquid ...

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