|M.Sc Student||Shuster Gregory|
|Subject||Growth and Characterization of Barium Strontium Titanate|
(BST) Thin Films
|Department||Department of Materials Science and Engineering||Supervisor||Professor Emeritus Emil Zolotoyabko|
|Full Thesis text|
Barium-strontium titanate, BaxSr1 − xTiO3 (BST), is a solid solution of two perovskites, barium titanate (BaTiO3) and strontium titanate (SrTiO3), which has high dielectric constant, low leakage current and good thermal stability. The Curie temperature of the paraelectric-ferroelectric phase transition in pure barium titanate is 130°C but with addition of a certain amount of strontium the Curie temperature can be considerably reduced which results in high dielectric permittivity (dielectric constant) at room temperature. Due to large and tunable dielectric constant, high electro-optic and other non-linear coefficients, BST is very promising material for photonic applications, for the usage in electro-optic modulators and optical waveguides, and in electrically tunable microwave devices.
Among several deposition techniques, metal-organic chemical vapor deposition (MOCVD) is the predominant approach for the fabrication of epitaxial BST thin films, because of excellent composition control and exceptional step coverage. Epitaxial BST thin films grown on large area substrates provide a platform for photonic devices scalable to mass production.
When designing new materials to be grown by MOCVD it is necessary to take into account the availability of chemical precursors with high vapor pressures. For the successful fabrication of BST films by MOCVD, the essential characteristics of each precursor (for Ba, Sr, and Ti ions) are high volatility, chemical stability in solution, and extended thermal stability at vaporization temperature. In addition, each precursor should be completely decomposed at deposition temperature and all the precursors should have a similar decomposition behavior.
In this work, we report the growth of high quality BST films by using a unique facility existing in the Technion - Rapid Thermal (RT) MOCVD. This research work includes the development of new stable chemical precursors, modification of the MOCVD apparatus to provide the oxide growth, finding optimal growth conditions and suitable characterization methods. The newly synthesized organo-metallic precursors exhibit better properties than the available precursors and in particular, they have significantly lower (by 30 °C) melting points.
We succeeded to grow BST films with thickness up to 1 μm, on the (001)-oriented single-crystal SrTiO3 substrates. HRXRD scans indicated that the films grown at 740 °C are in epitaxial relationship with the substrate. Optimum conditions for epitaxial growth of BST films by RT-MOCVD were established.