Influence of the lead-compound on PZT 30/70 thin film orientation
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Influence of the lead-compound on PZT 30/70 thin film orientation Mira Mandeljc, Barbara Malič, Marija Kosec, Goran Dražič Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia ABSTRACT Ferroelectric thin films based on Pb(Zr0.30Ti0.70)O3 (PZT 30/70) were prepared by Chemical Solution Deposition from lead oxide or lead acetate and transition metal alkoxides in 2methoxyethanol at 400 °C. The choice of the lead-compound determines the composition of the PZT-sols and as a consequence the course of the thermal decomposition. In the case of PbO the local atmosphere within the bulk of the film during heating is more reducing, i.e. the partial pressure of oxygen is lower, than in the case of Pb(OAc)2 based film. Thus, in the former case a continuous layer of Pt-Pb phase is formed at 400 °C, while in Pb(OAc)2 based film only a low amount of Pt-Pb inclusions could be determined by TEM. INTRODUCTION Ferroelectric lead zirconate titanate (PZT) thin films have been investigated for a wide range of applications, such as piezoelectric, pyroelectric, electro-optic and ferroelectric devices. Among various deposition techniques Chemical Solution Deposition (CSD) enables high purity, large deposition area, easy composition control and low processing temperatures [1]. CSD method involves the deposition of the PZT sol onto the substrate followed by a post deposition annealing process. For optimizing CSD processing conditions, such as decreasing the annealing temperature and control of the film orientation, the mechanisms involved in the nucleation and growth of the perovskite phase should be understood. Pb(Zr0.30Ti0.70)O3 (PZT 30/70) thin films on platinized silicon substrates were prepared by the 2-methoxyethanol route in which lead acetate and lead oxide were used as the lead-source. By careful control of solution chemistry and annealing conditions pure perovskite phase is obtained at as low as 400 oC, while at 375 oC the perovskite phase coexists with the amorphous phase [2, 3]. Generally, the crystallization of the amorphous PZT precursors both in bulk [2, 4] and thin film form [1, 5] occurs via the pyrochlore-type phase, however, the range of its stability reported to be above 450/550 oC. In PbO based films the perovskite phase is (111), and in Pb(OAc)2 based films it is (100) orientated [6]. The influence of the perovskite phase orientation on the electrical properties of the films is in agreement with literature [7-9]: (111) oriented PZT films exhibit higher values of Pr and Ec and lower ε than the (100) oriented films, namely 20 µC/cm2, 165 kV/cm and 380 and 17 µC/cm2, 90 kV/cm and 760, respectively [10]. The nucleation of (111) oriented perovskite phase on platinized silicon substrate is generally attributed to the presence of Pt3Ti [11], or TiOx phase [12], which form as a result of diffusion of Ti through the platinum, to sputter-deposited TiO2 nucleation layer [13] or to the PtPb phase, formed as a consequence of partial reduction of Pb2+ species [14-17]. Different authors report that the composition of
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