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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Representative Results
  • Discussion
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

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.

Abstract

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.

Introduction

Controllable nanoscale fluid transport in nanochannels—nanofluidics1—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 thermophoresis<....

Protocol

1. Nano-height channel mask preparation

  1. 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.......

Representative Results

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' 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.......

Discussion

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.......

Acknowledgements

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–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).

....

Materials

NameCompanyCatalog NumberComments
AbsorberDragon Skin, Smooth-On, Inc., Macungie, PA, USADragon Skin 10 MEDIUM
AmplifierMini-Circuits, Brooklyn, NY, USAZHL–1–2W–S+
CameraNikon, Minato, Tokyo, JapanD5300
DeveloperFuturrex, NJ, USARD6
Diamond tip engraving penMalco, Memphis, TN, USAMalco A50 USA Made Carbide Tipped Scribe
Dicing sawDisco, Tokyo, JapanDisco Automatic Dicing Saw 3220
Heating ovenCarbolite, Hope Valley, UKHTCR 6/28High Temperature Clean Room Oven - HTCR
Hole drillerDremel, Mount Prospect, IllinoisModel #40004000 High Performance Variable Speed Rotary
Inverted microscopeAmscope, Irvine, CA, USAIN480TC-FL-MF603
Lithium niobate substratePMOptics, Burlington, MA, USAPWLN-4312324" double-side polished 0.5 mm thick 128° Y-rotated cut lithium niobate
Mask alignerHeidelberg Instruments, Heidelberg, GermanyMLA150
Nano3 cleanroom facilityUCSD, La Jolla, CA, USAFabrication process is performed in it.
Negative photoresistFuturrex, NJ, USANR9-1500PY
OscilloscopeKeysight Technologies, Santa Rosa, CA, USAInfiniiVision 2000 X-Series
Plasma surface activationPVA TePla, Corona, CA, USAPS100Tepla Asher
Polarizer sheetEdmund Optics, Barrington, NJ, USA#86-182
RIE etcherOxford Instruments, Abingdon, UKPlasmalab 100
Signal generatorNF Corporation, Yokohama, JapanWF1967 multifunction generator
Sputter depositionDenton Vacuum, NJ, USADenton 18Denton Discovery 18 Sputter System
Teflon wafer dipperShapeMaster, Ogden, IL, USASM4WD1Wafer Dipper 4"

References

  1. Eijkel, J. C., Van Den Berg, A. Nanofluidics: what is it and what can we expect from it?. Microfluidics and Nanofluidics. 1 (3), 249-267 (2005).
  2. Longhurst, M. J., Quirke, N. Temperature-driven pumping of fluid through sin....

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Nanoheight ChannelsSurface Acoustic WaveLithium NiobateAcoustic NanofluidicsNanofabricationPlasma BondingPhotolithographyReactive Ion EtchingChromium EtchingSolvent Cleaning

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