Epitaxial films of LGS, LGT, and LGN for SAW and BAW devices

Abstract

This paper presents the state of art in liquid phase epitaxial growth of high-quality LGS, LGT and LGN thin films. Langasites can be grown by Czochralski, but the defect structure and inhomogeneity of these crystals leads to several problems like non reproducibility in device parameters and fundamental properties measurements. Compared to any melt growth technique, oxide crystals grown from a solution, or single-crystalline films deposited on a substrate from a solution (e.g. by liquid phase epitaxy (LPE)) show a higher structural perfection, better homogeneity, and lower (native) defects density when substrate, solution, and growth parameters meet certain requirements. Also, the LPE film surface may develop into a facet e.g. in an extremely flat surface perfectly oriented in a given crystallographic plane that do not require further processing. X-, Y-, and Z-oriented LPE films of LGS, LGT and LGN could be homoepitaxially grown from a lead-oxide based high-temperature solution. Such films are of obvious interest for SAW devices, and further research may also lead to freestanding high-quality LPE films to be used as bulk resonators.