Piezoelectric Thin Film Micro Structures: From Fabrication to Energy Harvesting

Paul Muralt
Ceramics Laboratory, Ecole Polytechnique Federale de Lausanne EPFL, Switzerland

Abstract

The field of piezoelectric thin film micro and nano systems combines an exciting richness of potential applications with many attractive scientific topics on materials processing and physical properties. This talk will address fabrication and performance issues of piezoelectric PZT (Pb(Zr,Ti)O3) an AlN thin films and their functional composite structures in MEMS devices. The crystalline quality of the material plays a crucial role, as a strong piezoelectricity is an effect of the crystalline lattice. For applications, one cannot compromise on materials performance. Whereas the sputter deposited AlN does not pose much problems to integration into silicon MEMS devices, a number of integration tasks must be well accomplished to obtain a dense, phase pure material with controlled texture, and a suitable film thickness in case of PZT. In the ferroelectric PZT, domain issues lead to complications, but as well to large opportunities for improving the response of the film. Results on various basic functional structures, with their applications will be shortly presented, the focus is however on energy harvesting. During recent years, energy harvesting from vibration and motion sources has attracted much interest. Electrical power generators based on piezoelectric materials were investigated, first as flexible piezoelectric bulk composite materials containing PZT ceramics, and later also as MEMS devices based on thin films, or even nanowires. In case of micro power devices, the main target applications are wireless communication, sensors, and wireless sensors. The progress in piezoelectric thin films and MEMS technology has lead to the development of demonstration devices that show sufficiently large power outputs and voltage levels, i.e. more than several 100 µW/cm2 at over one volt.

Biography

Paul Muralt is currently adjunct Professor at Swiss Federal Institute of Technology EPFL at Lausanne, Switzerland. He leads a group in thin film, MEMS, and nanotechnology activities at the Ceramics Laboratory of the Materials Science Institute. He received a diploma in experimental physics in 1978, and his PhD in solid-state physics from the Swiss Federal Institute of Technology ETH in Zurich in the years 1978 and 1984, respectively. From 1984 to 1986, he was post-doctoral fellow at the IBM Research Laboratory in Zurich, where he pioneered the application of scanning tunneling microscopy to the imaging of the electrical surface potential (STP). After a stay at the Free University of Berlin, he joined the Balzers group (today Oerlikon Corporation) in Liechtenstein in 1987. He specialized in sputter deposition techniques, and managed since 1991 a department for development and applications of Physical Vapor Deposition and Plasma Enhanced Chemical Vapor Deposition processes.

In 1993, he joined EPFL, where he started activities in ferroelectric and piezoelectric thin films and MEMS devices. He was in fact the first researcher starting silicon micromachining at EPFL, and published around 100 articles on the issue of ferroelectric and piezoelectric thin films, their integration and MEMS applications. More recent works deal with the fabrication and study of ferroelectric nano structures, and oxygen ion conductors for micro solid oxide fuel cell investigations. His work is 4000 times cited, including 32 papers that are cited more than 32 times. As teacher, he gives lectures in thin film deposition, micro and nanotechnology, surface analysis and basic ceramics. He authored or co-authored more than 200 scientific articles. He is MRS member and senior member of IEEE. He was a chair of the MRS spring meeting 2008, co-organized two MRS symposia, and is also active in program committees of the specialized ferroelectric meetings ISAF 2007 and ISIF 2008.