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

Abstract

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 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/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 Ta2O5. A larger plane spacing with Δd/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 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.

Deposition of highly oriented Ta<inf>2</inf>O<inf>5</inf> piezoelectric thin films on silicon for fabricating film bulk acoustic resonator structure by RF magnetron sputtering

“…5, the measured K 2 of the 1st mode of sample (b) was determined to be 0.10% and was smaller than that of sample (a). A similar phenomenon of the piezoelectricity decreasing when the (200) plane spacing slightly increases was observed for the deposition of a Ta 2 O 5 thin film on a SiO 2 substrate [8].…”

“…The preferential (200) orientation was clearly observed. For comparison, the XRD pattern of the Ta 2 O 5 thin film deposited on the SiO 2 substrate under the same conditions [8] is also shown in the lower part of Fig. 2.…”

“…The authors also reported that, in the deposition of Ta 2 O 5 thin films on SiO 2 substrates using an RF magnetron sputtering system with a long-throw sputter (LTS) cathode and an O 2 -radical source, a substrate temperature of 700˚C and an O 2 flow rate of 10 ccm were found to be optimum for obtaining a strong preferential (200) orientation, a strong piezoelectric property, and a smooth surface [8]. Under the optimum conditions, the electromechanical coupling factor (K 2 ) for the Rayleigh-type SAW of the oriented Ta 2 O 5 thin film with a normalized thickness of 0.21 was determined to be 0.88% and was 75% of the reported value for a film prepared by DC-diode sputtering.…”

“…1. The sputtering parameters under the optimum deposition conditions [8] are shown in Table I. A metal tantalum target of 50 mm diameter was used and the distance between the target and substrate was 100 mm.…”

Deposition of Highly Oriented Ta2O5 Piezoelectric Thin Films on Silicon for Fabricating Film Bulk Acoustic Resonator Structure by RF Magnetron Sputtering

“…6) The diffraction angle of the preferential peak was equal to that of the (200)-plane spacing in the unit cell of monoclinic Ta 2 O 5 , and a smooth surface with an rms roughness of approximately 8-10 nm was obtained. 6) In this study, Ta 2 O 5 thin films were deposited on Si substrates using the RF magnetron sputtering system under the optimum conditions 6) with the aim of obtaining an FBAR structure. First, to clarify the fabrication conditions necessary for obtaining a strongly piezoelectric property, the degree of orientation and the K 2 for the Rayleigh-type SAW were evaluated.…”