ZnO based SAW and FBAR devices for bio-sensing applications

•Smooth, low stress films of ZnO have been produced using a novel Sputtering system.•ZnO acoustic devices have been used to move, mix, pump, eject and atomise liquids.•Such surface acoustic wave devices have been shown to act as effective biosensors.•Film Bulk Acoustic Resonator (FBARs) biosensors can detect a mass below 1fg. ZnO thin film based surface and bulk acoustic wave devices are reviewed in this paper. The films were initially produced using a standard RF sputtering technique. However in order to produce lower stress, smoother films at low temperatures, a novel High Target Utilisation Sputtering (HiTUS) system has also been utilised. The ZnO acoustic devices have been used to move, mix, pump, eject and atomise liquids depending upon the amplitude of the signal and the condition of the surface. Such Surface Acoustic Wave (SAW) devices have also been shown to act as bio sensors but more sensitive detection is obtainable by the use of Film Bulk Acoustic Resonators (FBARs), the design and operation of which are described at the end of this review. Whilst the interaction of the acoustic wave with a fluid on its surface allows its rheological properties to be measured, such as viscosity, it is speculated that the combination of SAW and FBAR technologies may also provide new opportunities for rheometry on the microscale where fluids generally follow a non-Newtonian behaviour.