Piezoelectric thick-film materials and sensors

The preparation, poling methods, and characteristics of PZT-based thick films obtained with standard hybrid microelectronics methods are summarized. The microstructure of the films is characterized by substantial porosity which, in turn, is responsible for the particular piezoelectric properties of the films, including low permittivity, high piezoelectric coefficients, and nonlinear behavior over wide pressure ranges. The flexibility in designing piezoelectric sensors for mechanical quantities (pressure, acceleration, torque) and chemical quantities (humidity) is emphasized, with examples given of the prototypes developed. Furthermore, these films offer the possibility of launching elastic waves in nonpiezoelectric substrates; the structures achieved can be used for the implementation of new classes of sensors and biosensors. The advantages of thick films in comparison with ceramic materials, in terms of low-voltage operation and easy change of shape, size, and operating mode, are demonstrated