Influence of spinel substrate and over-layer for enhanced SAW and AO properties with KNbO3 thin film

摘要

Surface acoustic wave (SAW) propagation characteristics have been studied using modeling calculations for a potassium niobate (KNbO3) thin film-layered structure with [001] and [110] orientation on a single crystal spinel (MgAl2O4) substrate, and a spinel buffer layer on silicon. Variation in the electromechanical coupling and acoustic attenuation has been compared. A significantly high value of coupling factor (kmax2=23%) is obtained for the [001]KNbO3/spinel structure by introducing an optimum thickness of spinel over-layer for potential wide bandwidth SAW device applications. The dispersion characteristics with the [110] KNbO3 orientation indicate an initial peak in the coupling coefficient value (kmax2=8.8%) at a relatively low KNbO3 film thickness that appears attractive for fabricating devices with thinner films. The KNbO3 film with [001] orientation is found attractive for efficient acousto-optic (AO) device application with the formation of a symmetric waveguide structure (spinel(0.5 Μm)/KNbO3(1.0 Μm)/spinel). A high value of k2=23.5% with 50% diffraction efficiency has been obtained for the spinel(0.5 Μm)/KNbO3(1.0 Μm)/spinel structure at 1 GHz SAW frequency and 633 nm optical wavelength at a very low input drive power of 15.4 mW.