## 1 Introduction  
With the wide application of SAW devices in the field of fifth-generation (5G) mobile communications [1; 2], the requirements for their performance are increasing. They are gradually developing towards high frequence, large electromechanical coupling coefficients, and high-temperature stability [3; 4; 5]. There are three main approaches to the realization of high-frequency devices: (1) By improving the photolithography precision. The SAW device operating frequency is related to the electrode width of the IDT [6]. However, high-precision lithography is expensive and the electrode is too fine for the device power tolerance to be tested [7]. (2) By selecting waves with higher sound speeds, such as Rayleigh wave < SH wave < Sezawa wave [8]. (3) With the development of piezoelectric thin-film technology, by selecting the advantages of multilayer dielectrics composed of different materials. It is possible to improve the phase velocity and electromechanical coupling coefficients of SAW devices, as well as the temperature stability, which reduces the photolithographic accuracy required for device production [9; 10]. Devices of common piezoelectric materials, such as LiNbO\({}_{3}\) and LiTaO\({}_{3}\), are difficult to integrate on chip with other circuits or microelectromechanical systems (MEMS) devicesdue to the limitation of the cut angle, and the range of applications is greatly restricted [11]. The SAW devices based on piezoelectric thin films using ZnO and AlN can be fabricated on a variety of substrates, which makes them very suitable for integration with other parts of the system, and they have high research value in the fabrication of high-frequency SAW devices [12; 13]. ZnO piezoelectric films have the advantages of favorable piezoelectricity, easy preparation, low insertion loss, etc. Relevant studies have shown that ZnO piezoelectric films have a high degree of orientation in any substrate deposition, which is because ZnO crystals will always grow in the direction of the lowest free energy at the surface, and thus, ZnO piezoelectric films have better consistency [14; 15; 16]. Among various substrates, diamond substrates have extremely high sound velocity, which is conducive to the production of high-frequency SAW devices [17]. In addition, the thermal conductivity of a diamond is very high; thus, it can effectively transfer and disperse heat, thereby improving the power tolerance of SAW devices. Reference [18] investigated the properties of acoustic surface waves propagating in structures of ZnO/Si and ZnO/AlN/Si. The numerical analysis involved examining the \(v_{\text{p}}\), \(k^{2}\), and _TCF_ of the first two mode frequencies of the SAWs in the ZnO/Si structure. Then, the results of the analysis were compared to the experimental data. Reference [19] achieved a \(k^{2}\) of 6.6% for the Rayleigh mode by employing embedded electrodes based on the ZnO/SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) structure, which is feasible for the fabrication of a broadband acoustic surface wave device, but the selected Rayleigh wave is only available for a low \(v_{\text{p}}\) of 2960 m/s. The propagation characteristics of acoustic surface waves in ZnO film/R-sapphire structures were investigated in reference [20]. The Rayleigh wave was found to have a large \(k^{2}\) of 4.95% and a phase velocity of 5300 m/s in ZnO film/R-sapphire substrates, but the _TCF_ of their devices was not satisfactory. In order to improve the operating frequency, bandwidth, and temperature stability of piezoelectric single-crystal ZnO SAW devices, in this work, we introduced a novel ZnO/SiO\({}_{2}\)/diamond-layered structure in the design of SAW devices. A 3D model was established using the finite element method (FEM). The eigenfrequency solving and frequency domain simulation were carried out to obtain the effects of ZnO piezoelectric thin film, SiO\({}_{2}\) temperature complementary layer, and electrode thickness on the performance of Rayleigh and Sezawa waves. Then, a performance comparison between Rayleigh and Sezawa waves was made.