Evaluation of Piezoelectric Ta 2 O 5 Thin Films Deposited on Sapphire Substrates

X -axis-oriented tantalum pentoxide (Ta 2 O 5 ) piezoelectric thin films were deposited on sapphire (Al 2 O 3 ) substrates, from which single crystallization due to epitaxial growth can be expected, using an RF magnetron sputtering system. The crystallinity and Rayleigh-type surface acoustic wave (R-SAW) propagation properties of the thin films were evaluated. From the measured diffraction (X-ray diffraction) patterns and the spotted pattern in the measured pole figures, in which poles were arranged to form the vertices of a hexagon, the possibility of the crystallization of hexagonal Ta 2 O 5 with a (203)-plane oriented in the c -Al 2 O 3 substrate plane due to epitaxial growth was shown. For the first mode of the R-SAW on the Ta 2 O 5 / R -plane Al 2 O 3 sample, a coupling factor of 1.65% and a phase velocity of 5,120 m/s were obtained for a normalized thickness of 0.175. Unfortunately, no increase in coupling factor and no major improvement in propagation loss were observed upon the crystallization of hexagonal Ta 2 O 5 .