Growth of highly c-axis oriented (B, Al)N film on diamond for high frequency surface acoustic wave devices

Abstract

Surface acoustic wave (SAW) devices based on an aluminum nitride (AlN)/diamond layered structure are attractive due to their high operating frequency. To enhance the operating frequency of a diamond SAW device, we demonstrated one piezoelectric layer on diamond by doping AlN with boron. In this study, highly c-axis-oriented wurtzite boron–aluminum nitride (B, Al)N films were deposited on diamond by a co-sputtering technique. The resulting films exhibit a higher piezoelectric coefficient d 33 and higher Young's modulus than AlN films. Moreover, the greater rigidity of (B, Al)N film further boosts the resonance frequency of a diamond SAW device. Considering the SAW wavelength (λ = 2 μm), the calculated surface acoustic velocities ( V S) of (B, Al)N on diamond is 8860 m/s that is higher than AlN on diamond (8720 m/s). We also find that the electromechanical coupling coefficient ( K 2) of a SAW device based on (B, Al)N on diamond was the same (~ 0.5%) as that of one based on AlN on diamond.