Name: fabrication of nanoheight channels incorporating surface acoustic wave actuation via lithium niobate for acoustic nanofluidics
Uploaded: 2020-02-05T13:30:00
Description: Watch this Scientific Journal Video about Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics 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&#8211;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. Nano-height channel mask preparation
<ol>
	<li>Photolithography: With a pattern describing the desired shape of the nanoheight channels (Figure 1B), use normal photolithography and lift-off procedures to produce nanoheight depressions in an LN wafer. These depressions will become nanoheight channels upon wafer bonding in a later step. 
	NOTE: The lateral dimensions of the nanoscale depressions are microscale in this protocol. Electron beam or He/Ne ion beam lithogr...

<ol>
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M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+parametric+study+of+ICP-RIE+etching+on+a+lithium+niobate+substrate.">A parametric study of ICP-RIE etching on a lithium niobate substrate.</a> 10th IEEE International Conference on Nano/Micro Engineered and Molecular Systems. , 485-486 (2015).</li><li>Queste, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Deep+reactive+ion+etching+of+quartz,+lithium+niobate+and+lead+titanate.">Deep reactive ion etching of quartz, lithium niobate and lead titanate.</a> JNTE (Journ&#233;es Nationales sur les Technologies) Proceedings. , (2008).</li><li>Xu, J., Wang, C., Tian, Y., Wu, B., Wang, S., Zhang, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Glass-on-LiNbO3+heterostructure+formed+via+a+two-step+plasma+activated+low-temperature+direct+bonding+method.">Glass-on-LiNbO3 heterostructure formed via a two-step plasma activated low-temperature direct bonding method.</a> Applied Surface Science. 459, 621-629 (2018).</li><li>Tulli, D., Janner, D., Pruneri, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Room+temperature+direct+bonding+of+LiNbO3+crystal+layers+and+its+application+to+high-voltage+optical+sensing.">Room temperature direct bonding of LiNbO3 crystal layers and its application to high-voltage optical sensing.</a> Journal of Micromechanics and Microengineering. 21 (8), 085025 (2011).</li><li>Sridhar, M., Maurya, D. 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Room-temperature bonding is key to fabricating SAW-integrated nanoslit devices. Five aspects need to be considered to ensure successful bonding and sufficient bonding strength.
Time and power for plasma surface activation 
Increasing the plasma power will help increase the surface energy and accordingly increase the bonding strength. But the downside of increasing the power during plasma surface activation is the increase in surface roughness, which may adversely affect t...

Controllable nanoscale fluid transport in nanochannels&#8212;nanofluidics1&#8212;occurs on the same length scales as most biological macromolecules, and is promising for biological analysis and sensing, medical diagnosis, and material processing. Various designs and simulations have been developed in nanofluidics to manipulate fluids and particle suspensions based on temperature gradients2, Coulomb dragging3, surface waves4, static electric fields5,6,7, and thermophoresis8 over the last fifteen years. Recently, SAW has been shown9 to produce nanoscale fluid pumping and draining with sufficient acoustic pressure to overcome the dominance of surface and viscous forces that otherwise prevent effective fluid transport in nanochannels. The key benefit of acoustic streaming is its ability to drive useful flow in nanostructures without concern over the details of the chemistry of the fluid or particle suspension, making devices that utilize this technique immediately useful in biological analysis, sensing, and other physicochemical applications.
Fabrication of SAW-integrated nanofluidic devices requires fabrication of the electrodes&#8212;the interdigital transducer (IDT)&#8212;on a piezoelectric substrate, lithium niobate10, to facilitate generating the SAW. Reactive ion etching (RIE) is used to form a nanoscale depression in a separate LN piece, and LN-LN bonding of the two pieces produces a useful nanochannel. The fabrication process for SAW devices has been presented in many publications, whether using normal or lift-off ultraviolet photolithography alongside metal sputter or evaporation deposition11. For the LN RIE process to etch a channel in a specific shape, the effects on the etch rate and the channel&#39;s final surface roughness from choosing different LN orientations, mask materials, gas flow, and plasma power have been investigated12,13,14,15,16. Plasma surface activation has been used to significantly increase surface energy and hence improve the strength of bonding in oxides such as LN17,18,19,20. It is likewise possible to heterogeneously bond LN with other oxides, such as SiO2 (glass) via a two-step plasma activated bonding method21. Room-temperature LN-LN bonding, in particular, has been investigated using different cleaning and surface activation treatments22.
Here, we describe in detail the process to fabricate 40 MHz SAW-integrated 100-nm height nanochannels, often called nanoslit channels (Figure 1A). Effective fluid capillary filling and fluid draining by SAW actuation demonstrates the validity of both nanoslit fabrication and SAW performance in such a nanoscale channel. Our approach offers a nano-acoustofluidic system enabling investigation of a variety of physical problems and biological applications.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Absorber</td>
			<td>Dragon Skin, Smooth-On, Inc., Macungie, PA, USA</td>
			<td>Dragon Skin 10 MEDIUM</td>
			<td></td>
		</tr>
		<tr>
			<td>Amplifier</td>
			<td>Mini-Circuits, Brooklyn, NY, USA</td>
			<td>ZHL&#8211;1&#8211;2W&#8211;S+</td>
			<td></td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>Nikon, Minato, Tokyo, Japan</td>
			<td>D5300</td>
			<td></td>
		</tr>
		<tr>
			<td>Developer</td>
			<td>Futurrex, NJ, USA</td>
			<td>RD6</td>
			<td></td>
		</tr>
		<tr>
			<td>Diamond tip engraving pen</td>
			<td>Malco, Memphis, TN, USA</td>
			<td>Malco A50 USA Made Carbide Tipped Scribe</td>
			<td></td>
		</tr>
		<tr>
			<td>Dicing saw</td>
			<td>Disco, Tokyo, Japan</td>
			<td>Disco Automatic Dicing Saw 3220</td>
			<td></td>
		</tr>
		<tr>
			<td>Heating oven</td>
			<td>Carbolite, Hope Valley, UK</td>
			<td>HTCR 6/28</td>
			<td>High Temperature Clean Room Oven - HTCR</td>
		</tr>
		<tr>
			<td>Hole driller</td>
			<td>Dremel, Mount Prospect, Illinois</td>
			<td>Model #4000</td>
			<td>4000 High Performance Variable Speed Rotary</td>
		</tr>
		<tr>
			<td>Inverted microscope</td>
			<td>Amscope, Irvine, CA, USA</td>
			<td>IN480TC-FL-MF603</td>
			<td></td>
		</tr>
		<tr>
			<td>Lithium niobate substrate</td>
			<td>PMOptics, Burlington, MA, USA</td>
			<td>PWLN-431232</td>
			<td>4&#34; double-side polished 0.5 mm thick 128&#176; Y-rotated cut lithium niobate</td>
		</tr>
		<tr>
			<td>Mask aligner</td>
			<td>Heidelberg Instruments, Heidelberg, Germany</td>
			<td>MLA150</td>
			<td></td>
		</tr>
		<tr>
			<td>Nano3 cleanroom facility</td>
			<td>UCSD, La Jolla, CA, USA</td>
			<td></td>
			<td>Fabrication process is performed in it.</td>
		</tr>
		<tr>
			<td>Negative photoresist</td>
			<td>Futurrex, NJ, USA</td>
			<td>NR9-1500PY</td>
			<td></td>
		</tr>
		<tr>
			<td>Oscilloscope</td>
			<td>Keysight Technologies, Santa Rosa, CA, USA</td>
			<td>InfiniiVision 2000 X-Series</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasma surface activation</td>
			<td>PVA TePla, Corona, CA, USA</td>
			<td>PS100</td>
			<td>Tepla Asher</td>
		</tr>
		<tr>
			<td>Polarizer sheet</td>
			<td>Edmund Optics, Barrington, NJ, USA</td>
			<td>#86-182</td>
			<td></td>
		</tr>
		<tr>
			<td>RIE etcher</td>
			<td>Oxford Instruments, Abingdon, UK</td>
			<td>Plasmalab 100</td>
			<td></td>
		</tr>
		<tr>
			<td>Signal generator</td>
			<td>NF Corporation, Yokohama, Japan</td>
			<td>WF1967 multifunction generator</td>
			<td></td>
		</tr>
		<tr>
			<td>Sputter deposition</td>
			<td>Denton Vacuum, NJ, USA</td>
			<td>Denton 18</td>
			<td>Denton Discovery 18 Sputter System</td>
		</tr>
		<tr>
			<td>Teflon wafer dipper</td>
			<td>ShapeMaster, Ogden, IL, USA</td>
			<td>SM4WD1</td>
			<td>Wafer Dipper 4&#34;</td>
		</tr>
	</tbody>
</table>

fabrication of nanoheight channels incorporating surface acoustic wave actuation via lithium niobate for acoustic nanofluidics

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order surface acoustic wave (SAW) devices generate tremendous acceleration on their surface, up to 108 m/s2, in turn responsible for many of the observed effects that have come to define acoustofluidics: acoustic streaming and acoustic radiation forces. These effects have been used for particle, cell, and fluid manipulation at the microscale, although more recently SAW has been used to produce similar phenomena at the nanoscale through an entirely different set of mechanisms. Controllable nanoscale fluid manipulation offers a broad range of opportunities in ultrafast fluid pumping and biomacromolecule dynamics useful for physical and biological applications. Here, we demonstrate nanoscale-height channel fabrication via room-temperature lithium niobate (LN) bonding integrated with a SAW device. We describe the entire experimental process including nano-height channel fabrication via dry etching, plasma-activated bonding on lithium niobate, the appropriate optical setup for subsequent imaging, and SAW actuation. We show representative results for fluid capillary filling and fluid draining in a nanoscale channel induced by SAW. This procedure offers a practical protocol for nanoscale channel fabrication and integration with SAW devices useful to build upon for future nanofluidics applications.

We perform fluid capillary filing and SAW-induced fluid draining in nano-height LN slits after successful fabrication and bonding of SAW integrated nanofluidic devices. Surface acoustic waves are generated by IDTs actuated by an amplified sinusoidal signal at the IDTs&#39; resonance frequency of 40 MHz, and the SAW propagates into the nanoslit via a piezoelectric LN substrate. The behavior of the fluid in the nanoslit interacting with SAW may be observed using an inverted microscope.
We demons...

Watch this Scientific Journal Video about Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics at JoVE.com

Fabrication of Nanoheight Channels Incorporating Surface Acoustic Wave Actuation via Lithium Niobate for Acoustic Nanofluidics

We demonstrate fabrication of nanoheight channels with the integration of surface acoustic wave actuation devices upon lithium niobate for acoustic nanofluidics via liftoff photolithography, nano-depth reactive ion etching, and room-temperature plasma surface-activated multilayer bonding of single-crystal lithium niobate, a process similarly useful for bonding lithium niobate to oxides.

Controlled nanoscale manipulation of fluids is known to be exceptionally difficult due to the dominance of surface and viscous forces. Megahertz-order ...

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