P1H-3 Epitaxial Pb(Zr0.2Ti0.8)O3 Thin Layers for the Fabrication of Radio-Frequency Elastic Wave Transducers

In this paper, we investigate the capability of epitaxial Pb(Zr
_0.2
Ti
_0.8
)O
₃
thin films for RF applications. Films have been grown on insulating (001) SrTiO
₃
single crystal substrates by off-axis magnetron sputtering in 180 mTorr of an oxygen/argon mixture at a substrate temperature of 510degC. Contrary to PZT layers obtained by conventional sputtering or sol-gel techniques, still exhibiting granular structures, the films are extremely smooth and exhibit finite size effects around the (001) reflection peaks, allowing the measurement of the thickness (150 nm and 200 nm in this case). Curie temperature of the films is measured close to 680degC, which is much higher than standard PZT and allows for operating on an extended temperature range. Focused ion beam (FIB) etching techniques have been used to fabricate standard inter-digital transducers (IDTs). Electromechanical coupling in the vicinity of 3% with Q factors near 100 was found in the frequency range 3.5-5 GHz.