La-substituted Bi4Ti3O12, especially Bi3.25La0.75Ti3O12 (BLT0,75), thin films have attracted much attention because of their good fatigue resistance, lower deposition temperature than PZT or SBT and therefore great potential applications for ferroelectric non-volatile random access memories. Since such materials have highly anisotropic physical properties, improvement of their ferroelectric characteristics are expected for thin films with unique and preferred crystalline orientation. Thus, strong emphasis has been placed on an epitaxial growth technique like Pulsed Laser Deposition (PLD). However, until now, PLD suffers from weak uniformity control on large areas and intrinsic difficulties to extrapolate towards industrial applications.
Previous works demonstrated the possibility to deposit by magnetron technique BLT films as well crystallized as the films obtained by PLD. First, targets of Aurivillius phase Bi3.25La0.75Ti3O12 (BLT0,75) have been elaborated in our institute. Then, RF sputtering experiments were performed at room temperature with argon/oxygen mixture, in a pressure range of 20-50 mTorr. Optimisation of oxygen content in the gas phase allows to obtain BLT films, with a chemical composition close to Bi3.25La0.75Ti3O12. After 1h ex-situ annealing under oxygen at 650°C, BLT films deposited on Pt/TiO2/SiO2/Si (multilayer) substrates exhibit well defined rod-like grains morphology. A two steps deposition process appeared necessary to reach satisfying dielectric properties. The effect of annealing temperature, in the 550-750 °C range and duration of ex-situ annealing on the electrical properties will be presented.
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