Advances in piezoelectric thin films for acoustic biosensors, acoustofluidics and lab-on-chip applications

Recently piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating and sorting, patterning, pumping, mixing, nebulization and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin-film acoustic wave devices have a great potential for various sensing and actuating applications, allowing for the implementation of integrated, disposable, or bendable/flexible lab-on-a-chip devices. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parameters, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends identified.