Electromechanical response of micromachined 1-3 piezoelectric composites: Effect of etched piezo-pillar slope

Micromachined single-crystal piezoelectric 1-3 composites are known for high electromechanical coupling coefficients, low acoustic impedance, high processing precision and uniformity, which are desired for high-frequency ultrasound transducers. In this article, based on Smith and Auld’s 1-3 composite thickness-mode oscillation model, the effect of etched side wall slope on the electromechanical characteristics of micromachined piezoelectric 1-3 composites was studied. In specific, strain constant, stiffness, dielectric constant, electromechanical coupling coefficient, acoustic impedance, longitudinal velocity, and frequency of micromachined 1-3 composites were deduced using the developed model. The analytical model was then verified by a COMSOL simulation and experimental measurements of a micromachined composite sample with pitch of 15.9 µm, thickness of 42.8 µm, and etched pillar slope angle of 83.8°. The measured center frequency was 49.05 MHz, electromechanical coupling coefficient was 0.66, dielectric constant was 1178, and strain constant was 26.90 C/m ² , which all agreed well with the analytical calculations. These results will be helpful in design and fabrication of high-frequency micromachined ultrasound transducers.