Growth and characterization of epitaxial oxide thin films

• Main Author: Garg, Ashish
• Published: University of Cambridge 2001
• Subjects: 669; Thin Films
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540838

Epitaxial oxide thin films are used in many technologically important device applications. This work deals with the deposition and characterization of epitaxial WO3 and SrBi2Ta2O9 (SBT) thin films on single crystal oxide substrates. WO3 thin films were chosen as a subject of study because of recent findings of superconductivity at surfaces and twin boundaries in the bulk form of this oxide. Highly epitaxial thin films would be desirable in order to be able to create a device within a film without patterning it, by locally creating superconducting regions (e.g. twins) within an otherwise defect free film by reducing or doping the film with Na. Films were deposited by reactive magnetron sputtering at various temperatures on single crystal SrTiO3 (100) and R-sapphire substrates. X-ray diffraction studies showed that the optimised films were highly (001) oriented, quality of epitaxy improving with decreasing deposition temperature. AFM studies revealed columnar growth of these films. Films were heat treated with Na vapour in order to reduce or dope them with Na. Low temperature measurements of the reduced films did not show existence of any superconductivity. SBT is a ferroelectric oxide and its thin films are attractive candidates for non-volatile ferroelectric random access memory (FRAM) applications. High structural anisotropy leads to a high degree of anisotropy in its ferroelectric properties which makes it essential to study epitaxial SBT films of different orientations. In this study, SBT films of different orientations were deposited on different single crystal substrates by pulsed laser ablation. Highly epitaxial c-axis oriented and smooth SBT films were deposited on SrTiO3 (100) substrates. AFM studies revealed the growth of these films by 3-D Stranski-Krastanov mode. However, these films did not exhibit any ferroelectric activity. Highly epitaxial (116)-oriented films were deposited on SrTiO3 (110) substrates. These films were also very smooth with root mean square (RMS) roughness of 15-20 Å. Films deposited on TiO2 (110) were partially a-/b-axis oriented and showed the formation of c-axis oriented SBT and many impurities. Completely a-/b-axis oriented SBT films were deposited on LaSrAlO4 (110) substrates. Films deposited at non-optimal growth temperatures showed the formation of many impurities. Attempts were also made towards depositing Sr2RuO4 films on LaSrAlO4 (110) substrates, which can act as a bottom electrode for ferroelectric SBT films.