Rayleigh and shear-horizontal surface acoustic waves simultaneously generated in inclined ZnO films for acoustofluidic lab-on-a-chip

Hua-Feng Pang, Ran Tao, Jingting Luo, Xiaosong Zhou, Jian Zhou, Glen McHale, Julien Reboud, Hamdi Torun, Desmond Gibson, Kai Tao, Honglong Chang, Yong-Qing Fu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
5 Downloads (Pure)


There are significant challenges in controlling uniformity of crystal inclination angles, growth orientations and film thicknesses to generate dual-mode surface acoustic waves (e.g., Rayleigh ones and shear-horizontal ones) for lab-on-a-chip applications. In this study, we demonstrate large area (up to three inches) and uniformly inclined piezoelectric ZnO films, sputtering-deposited on silicon using a glancing angle deposition method. Characterization using X-ray diffraction showed that the inclined ZnO films have an average crystal inclination angle of 29.0°, apart from the vertical (0002) orientation, at a substrate tilting angle of 30o. Reflection signals of ZnO/Si surface acoustic wave devices clearly show the generations of both shear horizontal surface acoustic waves and Rayleigh waves. The Rayleigh waves enable efficient acoustofluidic functions including streaming and transportation of sessile droplets. Excitation direction of Rayleigh waves on the acoustofluidics versus the inclined angle direction has apparent influences on the acoustofluidic performance due to the anisotropic microstructures of the inclined films. The same device has been used to demonstrate biosensing of biotin/streptavidin interactions in a liquid environment using the shear-horizontal surface acoustic waves, to demonstrate its potential for integration into a complete lab-on-a-chip device.

Original languageEnglish
Article number128336
Number of pages8
JournalSurface and Coatings Technology
Early online date4 Mar 2022
Publication statusPublished - 25 Jul 2022


  • acoustofluidics
  • c-axis inclined orientation
  • shear horizontal-SAW
  • ZnO film


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