Ferroelectric and piezoelectric properties of epitaxial PZT films and devices on silicon
Prof. Dr. Ing. D.H.A. Blank and Prof. Dr. ing. A.J.H.M. Rijnders
In this thesis, the integration of lead zirconate titanate Pb(Zr,Ti)O3 (PZT) thin films into piezoelectric microelectromechanical systems (MEMS) based on silicon is studied. In these structures, all epitaxial oxide layers (thin film/electrode/buffer-layer(s)) were deposited by pulsed laser deposition (PLD). First, the orientation control of PZT thin films on silicon has been studied. We found that by using a seedlayer (~4 Å) of Ru-deficient SrnRun-1O3n-2 between SRO bottom-electrode and CeO2/YSZ buffered (001)Si substrates, the orientation of PZT thin films can be switched from (110) to (001). When the conductive-oxide SRO electrodes were substituted for Pt, the accumulation of oxygen vacancies near the interface was prevented, and therefore the fatigue-free behavior was observed in the PZT/SRO capacitors up to 108 switching cycles. The effects film thickness on the microstructure and electrical properties of PZT(52/48) films have been also investigated in this chapter. In the film thickness range investigated, the microstructure and crystalline structure almost do not change with thickness. The thickness dependence of the remnant polarization and the dielectric constant is interpreted in terms of the interfacial layer at the film/electrode interface. The increased remnant polarization and dielectric constant is due to the reduction of interfacial effect in PZT films with an increase in film thickness. Moreover, the reduction of interfacial effect also leads to the decrease in coercive field. The integration of ferroelectric PZT thin films onto Si cantilever beams was investigated. The main focus of this chapter is on the development of piezo-cantilevers for optimization of the fabrication process as well as for understanding of the potential applications. As the results, using the PLD technique and MEMS micro-fabrication processes, piezoelectric PZT cantilever arrays with beam lengths ranging from 100 to 800 μm with widths ranging from 50 to 150 μm were designed and fabricated.