Millimeter-sized ferroelectric monomorph sonar transducers have been built using sol-gel PZT on micromachined silicon wafers. First generation transducer arrays with diaphragms varying in size from 0.2 to 2 mm were tested. Second generation 8 X 8 arrays have also been built and tested in water in the frequency range of 0.3 to 2 MHz.Improvements to the sol-gel process have yielded highquality, crack-free PZT films up to 12 pm in thickness, which leads directly to higher sensitivity and figure of merit for acoustic transducers. The longitudinal piezoelectric coefficient d33 is 140 to 240 pC/N, measured through a double beam laser interferometer. Remanent polarization of 28 pC/cm2, a coercive field of 30 kV/cm, and dielectric constant of 1400 were measured on 4-pm thick films. Test results are presented, including frequency response, beam patterns, and sensitivity.High-resolution acoustic images 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).

This article reports the fabrication of thick films of lead zirconate titanate (PZT) on platinum-buffered silicon substrates by screen printing. Crack-free films, up to 12 μm on a single pass, show a dielectric permittivity of 200, tangent losses of 0.05, remanent polarization of 2.5 μC/cm2, and coercive field of 40 kV/cm. The field-induced longitudinal piezoelectric coefficient d33 at 40 kV/cm dc bias and 4 kV/cm alternating field corresponded to 50 pC/N. The magnitude of the piezoelectric voltage coefficient g33, computed from the strain coefficient and dielectric permittivity, under the same conditions, was found to be 36×10−3 V m/N, higher than that of a poled PZT bulk ceramic in comparison. These results are promising for a broad variety of sensor applications.

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