Surface acoustic wave device properties of (B, Al)N films on 128° Y-X LiNbO_3 substrate

摘要

A c-axis orientated aluminium nitride (AlN) film on a 128° Y-X lithium niobate (LiNbO_3) surface acoustic wave (SAW) device which exhibit a large electromechanical coupling coefficient (k~2) and a high SAW velocity property, is needed for future communication applications. In this study, a c-axis orientated (B, Al)N film (with 2.6 at.% boron) was deposited on a 128° Y-X LiNbO_3 substrate by a co-sputtering system to further boost SAW device properties. The XRD and TEM results show that the (B, Al)N films show highly aligned columns with the c-axis perpendicular to the substrate. The hardness and Young's modulus of (B, Al)N film on 128° Y-X LiNbO_3 substrates are at least 17% and 7% larger than AlN films, respectively. From the SAW device measurement, the operation frequency characteristic of (B, Al)N film on 128° Y-X LiNbO_3 is higher than pure A1N on it. The SAW velocity also increases as (B, Al)N film thickness increases (at fixed IDT wavelength). Furthermore, the k~2 of (B, A1)N on the IDT/128° Y-X LiNbO_3 SAW device shows a higher value than AlN on it.