Microwave surface and Lamb waves in a thin diamond plate: Experimental and theoretical investigation

Microwave surface and Lamb waves in a multilayered piezoelectric "Al-IDT/(Al_0.72Sc_0.28)N/(001)[110] diamond" structure designed as a SAW resonator were studied using both the experimental and modeling methods. In this structure, it is possible to generate Rayleigh, surface horizontal (SH_n) and Lamb waves simultaneously. The successful excitation of Lamb waves at operating frequencies up to 20 GHz has been obtained. We have developed a method for identifying mode types based on an analysis of the elastic displacement fields and the frequency dependences of the dispersive phase velocities of each wave, as the frequency increases. The experimental data on the frequency response is in close agreement with the calculated values. The influence of Pt film deposition on the shifts in the resonant frequency of Lamb wave modes has been studied in detail. Since the Pt film was deposited on the free surface of a diamond substrate, shifts in the resonant frequency of Rayleigh-type waves are absent, as expected. This serves as an additional indication to distinguish these types of waves from others. The effect of film deposition on the frequency response of Lamb waves could be taken into account when designing acoustoelectronic sensors that use this type of wave as an operational mode.