Improvement of textured AlCu with Ta underlayer on LiNbO3 substrate

Abstract

Improving the lifetime of surface acoustic wave filters requires reduction of electromigration effects. We report on the growth mechanism of AlCu2% films deposited by the e-beam physical vapor deposition technique. The state of the art shows that the introduction of an underlayer that alters the surface free energy can change a film’s growth mode or improve the earliest stages of film formation. In this work, this will be achieved by using an ultra-thin (<5 nm) Ta underlayer between the LiNbO3 substrate and the AlCu2% film. The effects of the Ta underlayer on the microstructure of AlCu2%/LiNbO3 films are investigated. An increase in the surface energy of the LiNbO3 substrate is observed with the addition of a 1.3 nm thick Ta underlayer. The crystalline quality of the AlCu2% thin film with a Ta underlayer is measured using XRD techniques. A post-deposition heat processing technique is also used to recrystallize the films. The AlCu2%/1.3Ta/LiNbO3 film annealed at 250 °C improved the electrode quality with the increase of 16% of the grain size.