| Thin films of ferroelectric relaxor solid solutions, Pb(Zr xTi1-x)O3-Pb(Zn1/3,Nb2/3)O 3 or PZT-PZN, have been fabricated using the sol-gel process on non-conducting ZrO2 surfaces for energy harvesting applications. The sol-gel process used to fabricate these films is a modification of the inverted mixing order (IMO) process that has been previously developed for PZT.1 The relaxor thin films, also prepared using the sol-gel process, are susceptible to formation of the undesired non-ferroelectric pyrochlore phase.2 We adopted a strategy based on three key parameters to obtain single-phase perovskite thin films. The first is the use of a PbTiO3 (PT) seed layer, which has been shown to be effective for perovskite phase nucleation. 3 The second, is the use of excess lead in the starting solution, and the third is the use of a high ramp rate anneal for film crystallization. It is shown that by using these three process parameters one can eliminate the undesired pyrochlore phase. The ability to obtain single phase PZT-PZN perovskite films depends on balancing two competing processes. The first is lead loss during film annealing, which tends to favor nucleation of the pyrochlore phase.4 The second is the nucleation rate of the perovskite phase, which requires the presence of excess lead. The fast-ramp rate anneal increases the perovskite phase nucleation before significant lead is lost from the film. With this scheme we were able to eliminate the pyrocholore phase. The film morphology, as seen in SEM micrographs, shows the benefit of the PT seed layer. Electrical characterization of these films was performed using inter-digitated electrode structures. The results indicate a very strong dependence of the electrical properties on film thickness. The quality of the capacitance "butterfly" loops improved significantly with increasing film thickness. The dielectric constant was extracted from interdigitated electrode structures for three thickness values (270, 540 and 810 nm including a PT layer for nucleation purposes) and was found to be 205, 470 and 803, and the capacitance density per effective area were 167, 470 and 655 pF/mm 2. The reason for the increase in the capacitance is likely due to increasing grain size with film thickness. The coercive voltage for the three thicknesses was found to be +/-10V. We used the interdigitated electrode structure in order to operate the cantilever in d33 mode (d33 generates 2 times higher device performance than that of the d31).5... |
