Fabrication and Evaluation of Highly Oriented Ta2O5 Piezoelectric Thin Films Prepared by Radio Frequency Magnetron Sputtering

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Highly $X$-axis-oriented tantalum pentoxide (Ta2O5) piezoelectric thin films were deposited on a SiO2 substrate using an RF-magnetron sputtering system with a metal tantalum target and an O2-radical source. The degree of orientation, Rayleigh-type surface acoustic wave properties, and surface morphology were evaluated. The deposition condition with the substrate temperature $T_{\text{S}}$ of 700 °C and O2 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 Ta2O5 thin film with a normalized thickness $h/\lambda$ 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 Ta2O5. A larger plane spacing with $\Delta d/d_{(200)}=2.9$% exists preferentially at $T_{\text{S}}=600$ °C, and the piezoelectricity is considered to be zero or very weak. When $T_{\text{S}}$ was higher than 700 °C and the O2 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.
2010-07-25