Ferroelectric SrBi2Ta2O9 thin films made by one- and two-step metalorganic chemical vapor deposition

Ferroelectric SeB12Ta2O9 (SBT) thin films have been deposited on sapphire, S1 and Pt/T1/SiO2/S1 substrates by using one and two step MOCVD processes. It was found that nucleation of SBT started at a deposition temperature close to 500 degrees C and grain growth dominated at 700 degrees C or above. With increasing deposition temperature, the grain size of SBT thin films increased from 0.01 micrometers to 0.2 micrometers , but surface roughness and porosity of the films also increased. Therefore, in order to obtain dense and homogeneous SBT films that have low surface roughness, the films have to be deposited at a low temperature for nucleation, then be annealed at a higher temperature for grain growth, which is defined as a one-step deposition process. An alternate approach is to use a two-step deposition process. The first step is a nucleation step, to make a very thin nucleation layer of the desired materials or buffer layer at lower temperature. Even thought heterogeneous nucleation is preferred, homogeneous nucleation also takes place because the heterogeneous nucleation can not grow at the low temperature. The second step is a grain growth step: grains will grow from the nucleation layer or buffer layer at higher temperature. In this manner, high quality SBT thin films were obtained. The SBT thin films with grain size about 0.1 micrometers exhibit following properties: thickness: 0.16-0.19 micrometers , 2Pr:7.8-11 4 (mu) C/cm2 at 5V, Ec. 50-65 kV/cm, Ileakage: 8.0-9.5 X 10-9 A/cm2 at 150 kV/cm, dielectric constant 100-200, fatigue rate: 0.94-0.98 after 1010 cycles at 5V. The interface between SBT film and substrate, surface roughness, thickness uniformity, microstructures and ferroelectric properties of SBT thin films were also investigated.