Evaluation of piezoelectric Ta₂O₅thin films deposited on SrTiO₃substrates

Abstract

Tantalum pentoxide (Ta2O5) piezoelectric thin films were deposited on (100) and (110) planes of strontium titanate (SrTiO3) substrates using an RF magnetron sputtering system. The crystallinity and Rayleigh-type surface acoustic wave propagation properties of the thin films were evaluated. The possibility that the Ta2O5 thin films were crystallized to orthorhombic Ta2O5 on SrTiO3 substrates by providing a buffer layer deposited without applying O2 radical power was demonstrated. From measured pole figures, it is considered that the crystalline Ta2O5/SrTiO3(100) sample has two lattice arrangements orthogonal to each other, and the crystalline Ta2O5/SrTiO3(110) sample has a single lattice arrangement. For a normalized film thickness h/λ of 0.45, the propagation loss for the deposition on SrTiO3(110) was 0.02 dB/λ, whereas that for the X-axis-oriented Ta2O5 thin film on SiO2 substrate was 0.21 dB/λ. Unfortunately, the coupling factor of the crystalline thin film was less than 0.3% for h/λ ranging from 0.29 to 0.45.

Deposition and evaluation of Ta2O5 piezoelectric thin film on Pt crystal film

“…16) In addition, Ta 2 O 5 thin films also have a high dielectric constant. 17) The crystal systems of Ta 2 O 5 , such as orthorhombic β-Ta 2 O 5 , 18,19) hexagonal δ-Ta 2 O 5 , 18,20) and orthorhombic λ-Ta 2 O 5 , [21][22][23] have been investigated.…”

“…The methods of depositing a single-crystal Ta 2 O 5 film, which is expected to have a higher electromechanical coupling factor (K 2 ) and a smaller PL than an oriented thin film, have been investigated. 19,20) However, no effective method has been found thus far.…”

“…We examined the epitaxial growth of single-crystal Ta 2 O 5 films on platinum (Pt) crystal films deposited on Si substrates because the lattice constant of Pt is close to that of orthorhombic β-Ta 2 O 5 19) with piezoelectricity. 26) In addition, by utilizing high-density Pt, we can expect the concentration of particle displacement of SAWs, which leads to an enhancement of K 2 .…”

Propagation properties of leaky surface acoustic wave on water-loaded piezoelectric substrate

“…With the spread of mobile communication apparatus, further improvement of the characteristics of surface acoustic wave (SAW) devices is required. In particular, to obtain a high frequency, driving stationarity with temperature, and a high electromechanical coupling factor, substrate structures such as thin-film loading structures [1][2][3][4][5][6][7][8][9][10][11][12] and bonding structures between material substrates 13,14) have been studied. Along with these studies, the accurate evaluation of the acoustical losses of substrate materials and loaded thin films is required to design SAW devices.…”

High coupling and highly stable leaky surface acoustic waves on LiTaO3 thin plate bonded to quartz substrate

“…In particular, to obtain a high frequency, a large electromechanical coupling factor (K 2 ), a large quality (Q) factor, and a small temperature coefficient of frequency (TCF), SAW propagation modes have been studied by focusing on the material of the substrate used. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] Leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) have a higher phase velocity than Rayleigh-type SAWs (R-SAW), 18) which is advantageous for application to high-frequency SAW devices. [19][20][21] However, they have inherent attenuation because they lose energy by continuously radiating bulk waves into the substrate.…”