INTEGRATED FERROELECTRIC MONOMORPH TRANSDUCERS FOR ACOUSTIC IMAGING

Millimeter-sized ferroelectric monomorph sonar transducers have been b uilt using sol-gel PZT on micromachined silicon wafers. The fabricatio n of monolithic transducer arrays on silicon wafers is described. Tran sducers have been tested in water in the frequency range of 0.5 to 4 M Hz. Individual transducer diaphragms varied from 0.2 to 2 mm in size. Improvements to the sol-gel process have yielded high-quality, crack-f ree PZT films up to 12 mu m in thickness, which leads directly to high er sensitivity and figure of merit for acoustic transducers. The longi tudinal piezoelectric coefficient d(33) is 140 - 180 pC/N, measured th rough a double beam laser interferometer. Remanent polarization of 34 mu C/cm(2), a coercive field of 42 kV/cm, and dielectric constant of 1 400 were measured on 4-mu m thick films. Results of air and in-water t esting are presented, including frequency response, beam patterns, and output capacitance. High-resolution acoustic images or have been gene rated using these transducers and a four-element underwater acoustic l ens. Potential applications for these transducers include high-frequen cy imaging sonars, medical ultrasound, ultrasonic communication links, and flaw detection (NDT).