Measurement techniques for evaluating piezoelectric thin films

Piezoelectric thin films have been in use for over three decades as high frequency bulk acoustic wave (BAW) and surface acoustic wave (SAW) transducers and resonators, and as a SAW medium for acoustooptic, acoustoelectronic, and sensor interactions. Sputtered aluminum nitride (AlN) and zinc oxide (ZnO) films have been the dominant films used for acoustic wave device applications. Various measurement techniques have been used to evaluate the properties of these films and derive their acoustic properties. These measurement techniques are important in optimizing film deposition conditions, determining the required design parameters for device development, characterizing film structure, and in obtaining fundamental film constants. This paper focuses on the measurement techniques which have been used to quantify the acoustic properties of thin-film ZnO and AlN and have led to a better understanding of what properties are necessary for a good piezoelectric film. SAW measurement techniques are emphasized since they provide the most comprehensive information from which basic piezoelectric and acoustic device design parameters and constants can be derived.