Plenary
PUSHING THE PERFORMANCE OF ELECTRO-MECHANICAL THIN FILMS

Today we are witnessing the advent of the 4^th industrial revolution, and are heading towards a largely robotized world. This requires a lot of analogue electro-mechanical devices. Piezoelectricity plays an important role in any electro-mechanical conversion and is used today in about 100 applications. The increasing importance of miniaturized devices results in a demand for piezoelectric thin films, which serve as integrated materials in micro and nano devices. This talk will deal with the present status of the performance of such films for varies applications.

Whereas the strongest piezoelectric effects are realized in ferroelectric phases of perovskite oxides such as Pb(Zr,Ti)O₃ (PZT), wurtzite thin films like aluminum nitride (AlN) are superior at GHz frequency applications because of their higher mechanical quality factors, and their extremely well reproducible and stable properties. The most recent innovation in this thin film material is a solid solution with scandium nitride to obtain much larger piezoelectric coefficients. An interesting competition for property determination is observed between density functional theory and experiment. AlScN will fill a gap between AlN and PZT, and looks interesting for energy harvesting. For actuators, however, PZT or related materials in thin films form will remain the champions in force per voltage figures. An astonishingly high piezoelectric stress of 600 MPa can be produced in PZT thin films with only 30V/mm electric field. This limit was found to be governed by the mechanical resistance of PZT. In the context of energy harvesting and sensors, imprinting phenomena in PZT thin films in general, and particularly with interdigitated electrodes are of interest. Results are presented as a function of dopants and film textures.