1 research outputs found
BaTiO<sub>3</sub> Thin Films from Atomic Layer Deposition: A Superlattice Approach
A superlattice
approach for the atomic layer deposition of polycrystalline
BaTiO<sub>3</sub> thin films is presented as an example for an effective
route to produce high-quality complex oxide films with excellent thickness
and compositional control. This method effectively mitigates any undesirable
reactions between the different precursors and allows an individual
optimization of the reaction conditions for the Ba–O and the
Ti–O subcycles. By growth of nanometer thick alternating BaÂ(OH)<sub>2</sub> and TiO<sub>2</sub> layers, the advantages of binary oxide
atomic layer deposition are transferred into the synthesis of ternary
compounds, permitting extremely high control of the cation ratio and
superior uniformity. Whereas the BaÂ(OH)<sub>2</sub> layers are partially
crystalline after the deposition, the TiO<sub>2</sub> layers remain
mostly amorphous. The layers react to polycrystalline, polymorph BaTiO<sub>3</sub> above 500 °C, releasing H<sub>2</sub>O. This solid-state
reaction is accompanied by an abrupt decrease in film thickness. Transmission
electron microscopy and Raman spectroscopy reveal the presence of
hexagonal BaTiO<sub>3</sub> in addition to the perovskite phase in
the annealed films. The microstructure with relatively small grains
of ∼70 Å and different phases is a direct consequence
of the abrupt formation reaction. The electrical properties transition
from the initially highly insulating dielectric semiamorphous superlattice
into a polycrystalline BaTiO<sub>3</sub> thin film with a dielectric
constant of 117 and a dielectric loss of 0.001 at 1 MHz after annealing
at 600 °C in air, which, together with the suppression of ferroelectricity
at room temperature, are very appealing properties for voltage tunable
devices