Deposition of Ba_xSr_1-xTiO₃ in Atmospheric Pressure Flame: Combustion Monitoring and Optimisation of Thin Film Properties

Abstract

An atmospheric pressure spray flame was used to deposit barium-strontium-titanate (Ba_xSr_1-xTiO₃, BST) films by the combustion chemical vapour deposition (CCVD) process. CCVD flames with and without substrate were analysed as a function of spray droplet size and substrate deposition location. Emission spectroscopy and temperature pyrometry measurements were used to determine flame structure and temperature. Emissions from atomic and molecular species reach a maximum early in the flame zone and then decrease sharply, an observation indicative of very fast reaction rates. The spray droplet size has a marked effect on the surface morphology of deposited thin films: coarser sprays yield a rougher film surface while finer sprays produce a smooth, optically clear surface. Optimal conditions for the deposition of high performance ferroelectric BST films had a mean droplet size of 1-2 μm and deposition temperature between 1000 and 1100 °C. BST films deposited under optimised conditions on single crystal substrates were of the desired phase and showed a high degree of in plane orientation.