Two-step metalorganic chemical vapor deposition growth of piezoelectric ZnO thin film on SiO2/Si substrate

Piezoelectric ZnO thin films deposited on semiconductor substrates are used for surface and bulk acoustic wave and devices, which offer advantages such as low power consumption, circuit miniaturization, and cost reduction by integration with microwave monolithic integrated circuit technology. Furthermore, temperature compensated surface acoustic wave (SAW) devices, which are attractive for both communication and sensor technologies, may be achieved in the ZnO/SiO2/Si system as ZnO and Si have positive temperature coefficients of delay, while SiO2 has a negative one. In the present work, ZnO thin films were grown on SiO2/Si substrates by metalorganic chemical vapor deposition. The structural properties of the films were investigated using x-ray diffraction, scanning electron microscopy, and scanning probe microscopy. A two-step growth process was developed to obtain ZnO films with both good crystalline quality and surface morphology. The SAW properties of the ZnO/SiO2/Si system were investigated through modeling and computer simulation based on the transfer matrix method. Acoustic velocity dispersion data obtained from measurement on testing structures agree well with the dispersion curves predicted by computer simulation. The results show that the ZnO/SiO2/Si system is promising for fabricating low-loss SAW devices.