7. Conclusions and feature trends
Porous piezoceramics find nowadays many applications as ultrasonic transducers. The
introduction of a controlled porosity into a piezoelectric ceramic could in fact strongly
improve the acoustic performances for this kind of applications.
In this chapter the more recent literature on the processing of porous ceramics has been
reviewed. The decisive influence of the processing method on the material’s microstructure
and properties was pointed out as well as the role of the application needed for the choice of
the more suitable processing route for the production of porous ceramics. The sacrificial
templating methods provide a straightforward way for the fabrication of macroporous
ceramics with porosities and average pore sizes ranging from 20% to 90% and 1–700 µm
respectively. The possibility to easily tailor the morphology and amount of porosity makes
this method effective for the production of porous piezoceramics. The combination of this
technique with the tape-casting process allows the production of sub-millimetre porous and
porous-graded piezoelectric structure.
Reducing the piezoceramic thickness is a key point to reach higher resonance frequency and,
as a consequence, high resolutions medical transducers application. In this respect, the drive
toward device miniaturization has created a strong interest in PZT thick-film technology
and as a consequence into the screen printing process. With thicknesses in the range 5–80µm, screen-printed PZT thick films fill an important technological gap between thin-film
and bulk ceramics offering the advantage of miniature scale and direct integration into
hybrid electronic packages. This technique therefore could be very promising for the
production of porosity-graded structure for high-frequency (from 20 to 50 MHz) ultrasonic
transducers.