|M.Sc Student||Izhak Shturman|
|Subject||Preparation of Conductive Ceramic Films by a Sol-Gel Method|
|Department||Department of Chemical Engineering||Supervisors||Full Professor Grader Gideon|
|Dr. Shter Gennady|
|Full Thesis text|
One of the most promising methods for production of the high quality multicomponent oxide films is Chemical Solution Deposition (CSD). Deposition via the CSD method enables easy stoichiometric control, low capital cost and high quality films. One of the most widely used materials for micro electrical mechanical systems (MEMS) and non-volatile memories is PbZrxTi1xO3 (PZT) due its being piezoelectric and ferroelectric properties. When preparing PZT films, deposition is typically made on Platinum (Pt) electrodes. However, the Pt/PZT/Pt capacitors are prone to fast ferroelectric fatigue. It is known that the number of fatigue-free cycles can be increased by several orders of magnitude using conducting oxide electrodes such as LaNiO3 (LNO). The goal of this work was to investigate the influence of the CSD-derived LNO electrodes on the morphology and ferroelectric properties of the PZT/LNO structure.
Both LNO and PZT were prepared by the CSD method, and results are compared with those obtained with Pt bottom electrodes. More specifically, the microstructure and electrical properties of LNO electrodes and their influence on the PZT morphology and ferroelectric behavior were studied as a function of PbO excess. At 30% PbO excess, the undesired pyrochlore (Py) phase was not found in either PZT/LNO or PZT/Pt, but the PZT/LNO film was porous. Crystallization rate of PZT was faster over LNO than over Pt electrodes. Therefore, LNO bottom electrodes enable a smaller PbO excess to prevent the Py formation and decrease the film porosity. Additionally, the PZT crystallization temperature over LNO was found to be 500oC which is ~50oC lower than over Pt. The lower temperature also minimizes the elemental inter-diffusion across the PZT/LNO interface. Both remnant polarization (Pr) and coercive field (Ec) were improved in the PZT/LNO films in comparison with PZT/Pt films. Finally, the fatigue limit of PZT/LNO system was improved by about two orders of magnitude relative to that of the PZT/Pt system.