STUDYING MICROWAVE ACOUSTIC SENSORS BASED ON SYNTHETIC DIAMOND SUBSTRATES

Sensory properties of microwave diamond-based HBAR developed on the piezoelectric layered structure Al/AlN/Mo/(100) diamond were investigated by depositing the Al, Sc, and Mo thin and ultrathin films. Due to the increased quality factor in a microwave band inherent in this type of resonators, it is possible realizing a high sensitivity of the sensory element. The dependences of an overtone's frequency shift vs. a film thickness could be differed qualitatively from the linearly proportional ones. Such peculiarities were explained in terms of an acoustic impedance difference between the films and diamond substrate. The features in the dependences of a frequency shift vs a film thickness can be used to determine the phase velocity of a film material. Experimental results were in close accordance with Finite Element Modeling data. Real thickness sensitivity of about 5 nm is actually limited by the imperfection of modern thickness measurement tools. Prototypes of sensory elements have the important advantages over all other types of the acoustoelectronic sensors owing to the microwave operating frequencies up to 8 GHz, high chemical and biological inertness of the working diamond surface, resistance to the temperature load, abrasive wear resistance, and the possibility of a multiple-time application. Effective area of a sensory element can be equal to thousands of square microns or less, which makes it suitable for local measurements. Investigated diamond-based 5th layered piezoelectric structure should be considered as a prospective platform creating a number of new generation sensors.