Fabrication and Evaluation of Highly Oriented Ta 2 O 5 Piezoelectric Thin Films Prepared by Radio Frequency Magnetron Sputtering

Highly X -axis-oriented tantalum pentoxide (Ta 2 O 5 ) piezoelectric thin films were deposited on a SiO 2 substrate using an RF-magnetron sputtering system with a metal tantalum target and an O 2 -radical source. The degree of orientation, Rayleigh-type surface acoustic wave properties, and surface morphology were evaluated. The deposition condition with the substrate temperature T S of 700 °C and O 2 flow rate of 10 ccm was found to be optimum for obtaining a strongly piezoelectric property. Under the optimum condition, the coupling factor of the oriented Ta 2 O 5 thin film with a normalized thickness h /λ of 0.21 was determined to be 0.88% and was 75% of the reported value. The diffraction angle of the preferential peak under the optimum condition was equal to that of the (200)-plane spacing d (200) in the unit cell of monoclinic Ta 2 O 5 . A larger plane spacing with Δ d / d (200) =2.9% exists preferentially at T S =600 °C, and the piezoelectricity is considered to be zero or very weak. When T S was higher than 700 °C and the O 2 flow rate was more than 8 ccm, a smooth surface with the rms roughness of approximately 8–10 nm was obtained. A correlation was found in which a strongly piezoelectric property was obtained when the thin film had a smooth surface.