Microwave Diamond-based HBAR as Ultrathin Film Sensor. Pt Deposition

Sensory properties of diamond-based HBAR were investigated by means of the Al, Sc, Mo and Pt thin and ultrathin film deposition. First the operational frequency ∼20 GHz of a sensor having a comparatively high $Q$ factor was applied with an aim decreasing the relative measurement error and increasing the sensitivity. Sensitivity on Pt film deposition was estimated as 0.5 nm. Dependences of the overtone's frequency shift vs. film thickness could be differed from the linearly proportional ones. Such peculiarities were explained in terms of an acoustic impedance difference between the films and diamond substrate. Experimental results were in close accordance with FEM model data. Prototypes of sensory elements developed have the important advantages over all other types of acoustoelectronic sensors owing to operating the SHF band up to 20 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. Investigated diamond-based 5th layered piezoelectric structure should be considered as a prospective platform creating a number of new generation sensors.