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Hybrid bulk acoustic wave and surface acoustic wave (BAW/SAW) devices attract extensive interests due to their high electromechanical coupling coefficient and quality factor. In this study, longitudinal BAW coupled SAW resonators with piezoelectric AlN inter-digital transducers (IDT) were simulated and fabricated on diamond substrates to increase the working frequency as well. The simulated figure of merit value is 104, 123 % improved comparing with the corresponding metal IDT of 46.5. The frequency response spectrum of single port reflection (S11) shows dominant harmonic resonance at 913 MHz with electromechanical coupling coefficient of 2.16 % and quality factor of 913. These results indicate mutual transductions between BAW and SAW occur with sufficient efficiency in hybrid structures, which is analyzed and interpreted by equivalent acoustic impedance theory. [Display omitted] • Diamond based longitudinal BAW coupled SAW resonators were designed and fabricated. • High figure of merit and working frequency can be achieved for the SAW devices. • The simulated figure of merit value is 104 on an Ag/AlN/Mo/Diamond/Si structure. • 913 MHz resonance with bandwidth of 2.16 % and quality factor of 913 was observed. • BAW-SAW mutual transduction is analyzed by equivalent acoustic impedance theory. [ABSTRACT FROM AUTHOR]

This paper describes an innovative electro-acoustic coupling structure with a Patterned Piezoelectric film as Inter-Digital Transducer (PP-IDT) on the diamond substrate for Surface Acoustic Wave (SAW) devices of better quality factor and frequency resolution. Theoretical analysis and Finite Element Method (FEM) are employed to investigate the dependence of microwave impedance characters on the thickness of piezoelectric and metal electrode layers. The systematic studies show that the PP-IDT structure can excite the mechanical vibration on the top surface of diamond substrate and derive the SAW. The quality factor increases remarkably in excess to 104 since the SAW is propagating below the diamond surface with little interface loss and transmission loss. Unlabelled Image • Diamond based piezoelectric layer is patterned as inter-digital transducer. • Quality factor of surface acoustic wave devices can be improved greatly. • Thickness of piezoelectric and electrode layer affects the performance. • Maximum quality factor is observed at optimal electrode thickness. [ABSTRACT FROM AUTHOR]