SAW Streaming in ZnO Surface Acoustic Wave Micromixer and Micropump

Surface acoustic wave (SAW) devices were fabricated based on ZnO thin films using magnetron sputtering. When the acoustic wave travels along the surface of the ZnO SAW device with liquid droplet on its path, the momentum of the acoustic wave will be coupled into the liquid. When the applied voltage is below 3V, and the ZnO surface is not treated, the acoustic wave could only induce internal streaming in liquid. The streaming speed is strongly dependent on the applied voltage, which can be used as a micromixer. After the ZnO surface was silanization treated thus realizing a hydrophobic surface, the coupled energy into the liquid from the acoustic wave is efficient to move the droplet from hundred nanoliters to tens of microliters along the wave path. When the voltage is sufficiently high, a mist consisting of small droplets was generated and shot out, which can be explained from SAW heating effect.