Fabrication and charicterization of high frequency SAW device with IDT/ZnO/AIN/Si configuration: role of AIN buffer

Abstract

Surface acoustic wave (SAW) devices with a ZnO/buffer/Si configuration have been fabricated, employing poly-AlN (deposited by RF magnetron sputtering) and epi-AlN (deposited by plasma-assisted MBE) as the buffer layer. In particular, the effects of the AlN buffers on the orientation of ZnO films as well as the performance of SAW devices are studied. Piezoelectric ZnO films are deposited using RF sputtering at a nominal condition of RF power of 300 W, O2/(Ar+O2) ratio of 10%, and substrate temperature of 300 °C. For all the deposited AlN and ZnO films, the X-ray diffraction (XRD) spectra and full width at half maximum (ω FWHM) of rocking curves are measured in terms of the deposition conditions, to characterize the c-axis preferred orientation and crystal quality. The frequency response characteristics (including S21) of the fabricated SAW devices are also measured. The experimental results indicate that the c-axis orientation and crystal quality of ZnO films are determined mainly by the properties of AlN buffer. Furthermore, the insertion loss of ZnO-SAW devices is found to be dependent on the crystal quality and surface morphology of AlN buffer. The correlations between the properties of AlN buffers and the characteristics of ZnO-SAW devices are also discussed in detail.