Fabrication, Characterization, and Simulation of Glass Devices with AlN Thin-Film Transducers for Excitation of Ultrasound Resonances

We present the fabrication of 570-$\mu \mathrm{m}$-thick millimeter-sized soda-lime-silicate float-glass blocks with a 1-$\mu \mathrm{m}$-thick $\mathrm{Al}\mathrm{N}$ thin-film piezoelectric transducer sandwiched between thin metallic electrodes and deposited on the top surface. The electromechanical properties are characterized by electrical-impedance measurements in the frequency range from 0.1 to 10 MHz with a peak-to-peak voltage of 0.5 V applied to the electrodes. We measure the electrical-impedance spectra of 35 devices, all of width 2 mm, but with nine different lengths ranging from 2 to 6 mm and with two to seven copies of each individual geometry. Each impedance spectrum exhibits many resonance peaks, and we carefully measure the five most prominent ones in each spectrum. We compare the resulting 173 experimental resonance frequencies with simulation results from a finite-element-method model that we develop. When we use the material parameters from the manufacturer, we obtain an average relative deviation of the 173 simulated resonance frequencies from the experimental values of $(-4.6\pm 0.1)\mathrm{\%}$. When we optimize the values of the Young’s modulus and Poisson’s ratio of the float glass in the simulation, this relative deviation decreases to $(-0.5\pm 0.1)\mathrm{\%}$. Our results suggest a method for an accurate in situ determination of the acoustic parameters at ultrasound frequencies of any elastic solid onto which a thin-film transducer can be attached.