Micromachines (Apr 2024)

Surface Acoustic Wave Resonator Chip Setup for the Elimination of Interfering Conductivity Responses

  • Bastian E. Rapp,
  • Achim Voigt,
  • Marian Dirschka,
  • Michael Rapp,
  • Kerstin Länge

DOI
https://doi.org/10.3390/mi15040501
Journal volume & issue
Vol. 15, no. 4
p. 501

Abstract

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A surface acoustic wave (SAW) resonator chip setup is presented that eliminates interfering signal responses caused by changes in the electrical environment of the surrounding media. When using a two-port resonator, applying electrically shielding layers between the interdigital transducers (IDTs) can be challenging due to the limited dimensions. Therefore, a layered setup consisting of an insulating polymer layer and a conductive gold layer was preferred. The SAW resonators were provided with polycarbonate housings, resulting in SAW resonator chips. This setup enables easy application of a wide range of coatings to the active part of the resonator surface, while ensuring subsequent electrical and fluidic integration of the resonator chips into a microfluidic array for measurements. The signal responses of uncoated SAW resonators and those with polymer coatings with and without a gold layer were tested with aqueous potassium chloride (KCl) solutions up to 3 mol/L, corresponding to conductivities up to 308 mS/cm. The use of a polymer coating at the thickness of the first Love mode resonance and a conductive gold layer completely reduced the electrical impact on the SAW resonator signal response, making small signals resulting from changes in viscosity and density of the KCl solutions visible.

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