Influence of a piezoelectric ZnO intermediate layer on Rayleigh waves propagating in Sc43%AlN57%/ZnO/diamond hetero-structures subjected to uniaxial stress

Abstract

Surface acoustic waves (SAWs) are of practical importance across several fields. Particularly, a wide range of SAW devices is available, which are based on the stacking piezoelectric layered hetero-structures. As such, efficient and stable algorithm of analyzing electromechanical coupling factor (K2) should be of specific interest, inspiring a variety of piezoelectric layered structures. Motivated by the above considerations, this paper exploits the performance of Sc43% AlN57%/ZnO/diamond piezoelectric hetero-structures using matrix and polynomial methods. Consequently, dispersion curves, the electromechanical coupling factor and profiles of Rayleigh waves are calculated, in which the properties of hexagonal intermediate ZnO layer are varied. Here, $$ (0001) - [10\bar{1}0]{\text{ZnO}} $$ or $$ (11\bar{2}0) - [0001]{\text{ZnO}} $$ directions of the middle layer were integrated with Sc43% AlN57%/diamond to be a composite hetero-structure with a larger K2 of SAW. Accordingly, a commercial ZnO specimen was characterized by scanning electron microscopy (SEM) as well as Raman and XRD spectroscopy to determine its available crystallographic directions and the C-axis hexagonal character. Comparing with conventional AlN/diamond hetero-structures, the inclusion of ZnO as the intermediate layer provides with an excellent electromechanical coupling factor which significantly improves the $$ (11\bar{2}0) - [0001] $$ structure. However, comparing with the ZnO/diamond hetero-structure, a high phase velocity (Vph) was observed. Therefore, the development of a well-balanced structure that maximizes the values of Vph and K2 is systematically challenging. Moreover, it was found that initial stresses have a significant effect on the Rayleigh wave velocities. Fundamental A0 Lamb mode can be generated in piezoelectric hetero-structures when the properties of substrate remain very low relative to the film. Numerical results obtained in this paper can provide a deeper insight into the nature of the Rayleigh wave behaviors in piezoelectric hetero-structures, involving a ZnO intermediate layer.