Surface acoustic waves in strain-engineered K0.7Na0.3NbO3 thin films

• Published in: Applied physics letters Vol. 113; no. 5
• Main Authors: Liang, Sijia, Dai, Yang, von Helden, L., Schwarzkopf, J., Wördenweber, R.
• Format: Journal Article
• Language: English
• Published: Melville American Institute of Physics 30-07-2018
• Subjects: Acoustic properties; Applied physics; Compressive properties; Crystallography; Epitaxial growth; Ferroelectric materials; Ferroelectricity; Materials selection; Metalorganic chemical vapor deposition; Organic chemicals; Organic chemistry; Piezoelectricity; Plane strain; Substrates; Surface acoustic waves; Thick films; Thin films; Transition temperature; Wave propagation
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.5035464

Epitaxial K0.7Na0.3NbO3 thin films are grown via metal-organic chemical vapor deposition on (110)-oriented TbScO3. The films are strained due to the substrate–film lattice mismatch and therefore exhibit a strong and anisotropic modification of all its ferroelectric properties. The compressive in-plane strain leads to a reduction of the ferroelectric transition temperature from approximately 700 K for unstrained K0.7Na0.3NbO3 to 324 K and 330 K with maximum permittivities of 10 270 and 13 695 for the main crystallographic directions [001]TSO and [1
1
¯0]TSO, respectively. Moreover, the quite thin films (approx. 30 nm thick) exhibit very large piezoelectric properties. For instance, surface acoustic waves with intensities of up to 4.7 dB are recorded for wave propagation along the [1
1
¯0]TSO direction. The signal is smaller (up to 1.3 dB) along [001]TSO, whilst for the intermediate direction [1
1
¯2]TSO, the signal seems to vanish (<0.1 dB). The results indicate that the choice of material, (K,Na)NbO3, in combination with strain-engineering via epitaxial growth onto lattice-mismatched substrates represents a promising way to optimize ferroelectric materials for piezoelectric thin-film applications.