Integrated ferroelectric monomorph transducers for acoustic imaging

Millimeter-sized ferroelectric monomorph sonar transducers have been built using sol-gel PZT on micromachined silicon wafers. The fabrication of monolithic transducer arrays on silicon wafers is described. Transducers have been tested in water in the frequency range of 0.5 to 4 MHz. Individual transducer diaphragms varied from 0.2 to 2 mm in size. Improvements to the sol-gel process have yielded high-quality, crack-free PZT films up to 12 μm in thickness, which leads directly to higher sensitivity and figure of merit for acoustic transducers. The longitudinal piezoelectric coefficient d33 is 140–180 pC/N, measured through a double beam laser interferometer. Remanent polarization of 34 μC/cm2, a coercive field of 42 kV/cm, and dielectric constant of 1400 were measured on 4-μm thick films. Results of air and in-water testing are presented, including frequency response, beam patterns, and output capacitance. High-resolution acoustic images of have been generated using these transducers and a four-element underwater acoustic lens. Potential applications for these transducers include high-frequency imaging sonars, medical ultrasound, ultrasonic communication links, and flaw detection (NDT).