| AVS 58th Annual International Symposium and Exhibition | |
| Thin Film Division | Thursday Sessions |
| Session TF1-ThM |
| Session: | Post-Deposition Processing and Characterization of Thin Films |
| Presenter: | Rony Snyders, UMons, Belgium |
| Authors: | R. Snyders, UMons, Belgium G. Geumez, UMons, Belgium S. Konstantinidis, UMons, Belgium |
| Correspondent: | Click to Email |
ZrO2 is a material used as thin films in numerous applications. One of the applications with the highest added value is its use as ionic conductor in, for example, fuel cell devices. Nevertheless, only the tetragonal and cubic polymorphs of ZrO2 exhibit these ionic conduction properties. Therefore, effort have to be made in order to synthesis phase pure tetragonal or, ideally, cubic ZrO2 thin films. It has been demonstrated that these polymorphs are generated when about 10% of oxygen vacancies are introduced in the material lattice. Recently, some works have demonstrated that it was possible to synthesize, by reactive high power impulse magnetron sputtering, cubic HfO2 (a compound very close to ZrO2) containing, as for cubic ZrO2, 5% of oxygen vacancies when working in the transition region of the poising curve. This implementation of this strategy was possible thanks to the smoothness of this transition using this peculiar sputtering technology.
In this work, we aim to apply such a strategy to grow tetragonal (or cubic) ZrO2 by reactive DC magnetron sputtering. Due to the very sharp metallic-to-poisoned mode transition, we used a plasma monitoring system (PEM) to work in stable conditions in that region.
A pure Zr metallic target is sputtered at constant current (0.2 A) at 10 mTorr in Ar/O2 mixtures using a DC magnetron sputtering source with an unbalanced magnetic field configuration. A PEM system is implemented in order to grow films in the transition region. The Zr line at 340 nm is monitored in real time. The deposited films were characterized by grazing angle X-Ray diffraction (GAXRD) and X-Ray photoelectron spectroscopy (XPS).
Discharge parameters (voltage, current) and XPS data reveal that the transition occurs for 4% < %O2 < 6%. For %O2 < 4%, the films are under-stoichiometric with a metallic character. In the transition, we measure a stoichiometry of about ZrO1.8. Finally, %O2 > 6%, the films are stoichiometric. In term of phase constitution, it has been demonstrated that working in the poisoned mode, the monoclinic phase is synthesized while in the transition, for which the compound is under-stoichiometric, the tetragonal (and maybe cubic) phase is grown. These data support, for the first time, the theoretical assumption about the oxygen vacancies-generated tetragonal (or cubic) phase of ZrO2. Finally, the thermal stability of the coatings has been studied: the as-grown samples have been annealed up to 1200°C. For annealing temperature up to 600°C, no modification of the phase constitution is observed while for an annealing temperature of 1200°C, the films experience a phase transition towards the monoclinic structure.