Determination of mechanical material properties of piezoelectric ZnO films

This work describes the determination of mechanical properties of sputtered piezoelectric zinc oxide (ZnO) films. The residual stress of the thin ZnO films was measured using the wafer curvature and the sputter parameters for growth of films with low tensile stress determined. Tensile films are often preferred in membrane structures because, e.g., buckling is avoided. A membrane deflection method was applied to measure the plane-strain modulus of ZnO films on SiNx. A new model which includes the flexural rigidity of a multilayered membrane was used to calculate the residual stress and plane-strain modulus of the membrane layers. The measured plane-strain modulus for ZnO on SiNx is 115 GPa. Nano indenter experiments on a ZnO film deposited on a Al-SiO2-Si substrate revealed a similar value of 122 GPa for the plane-strain modulus. These results can be used for more accurate modeling of ZnO based microsensors and actuators, such as Lamb wave sensors.