A current trend to miniaturization and an increase in the operating frequency of the devices requires scaling down the dimensions of ceramic electronic components. In particular, piezoelectric layers of moderate thickness (-10-100 μm) are required for the development of piezoelectric sensors and actuators, vibration control devices, accelerometers, ultrasonic micromotors and many others. This is especially important for medical imaging transducers where the increase in the operating frequency can bring about unprecedented resolution required, for example, for the imaging of human eye. The development of such layers by using both bulk- and thin-film techniques encounters significant difficulties and increased manufacturing cost. This article is devoted to the novel technique for the development of thick piezoelectric films and composites based on the hybrid sol-gel route that provides unique features such as the tight control of the composition and volume ratio of the piezoelectric phase, small porosity and roughness, and an ability to tailor the properties for different applications. This technique has recently emerged as an alternative to the well-known methods such as screen printing and tape casting. The advantages and disadvantages of the conventional techniques as compared to the hybrid sol-gel route will be discussed. Recent results on the processing and characterization of Pb(Zr,Ti)O3 (PZT) and Pb(Mg,Nb)O3-PbTiO3 (PMN/PT) thick films done by our laboratory as well as the work of other groups will be presented. Finally, a range of applications will be described where such thick films and composites could give significant advantages over currently used piezoelectric materials.
Piezoelectric thick film composites: processing and applications