Preparation of AlN and LiNbO3 thin films on diamond substrates by sputtering method

Abstract

Diamond is attracting interest as a high velocity material because its elastic constant is the highest of all substances and the surface acoustic wave (SAW) velocity is more than 10000 m/s. Although diamond is not piezoelectric, its high acoustic propagation makes it a desirable substrate for SAW devices when coupled with piezoelectric thin films such as aluminum nitride (AlN) and lithium niobate (LiNbO3). Highly oriented AlN thin films and LiNbO3 thin films were prepared by a reactive sputtering method on polycrystalline diamond substrates. The average surface roughness (Ra) of the AlN thin films was below 2 nm by locating the diamond substrates at the position of 100 mm from the aluminum target. The full width at half maximum of the rocking curve for the AlN(002) peak of X-ray diffraction was approximately 0.2°. SAW characteristics with an interdigital transducer (IDT)/AlN/diamond structure were investigated. The average surface roughness of LiNbO3 thin films was 5 nm. If the highly oriented LiNbO3 films are deposited on a diamond substrate, the IDT/LiNbO3/diamond layered structure will be capable of wide-bandwidth application in SAW devices at high frequencies.