Crystallization and Structural Phase Transformation in Sub-100-nm-Thick SrBi₂Ta₂O₉ Thin Film

Abstract

Crystal phase and structural properties in sub-100-nm-thick SrBi2Ta2O9 (SBT) thin films deposited on silicon substrates have been quantitatively investigated by X-ray diffraction (XRD) and X-ray reflection (XRR) analyses. The simulation fitting of XRR showed that the density and the surface roughness of the SBT film increased and saturated as the annealing temperature increased, indicating the phase transformation from fluorite to Aurivillius and the grain growth were enhanced by the high-temperature annealing. The SBT film was composed of small crystals of fluorite-type and Bi-layered Aurivillius phase after crystallization at temperatures of 730–785°C for 1 h. When annealing temperature was higher than 800°C, the film crystallized into a single phase of Bi-layered Aurivillius. It was also shown that the average crystal size in the SBT film increased with annealing temperature and saturated to be ∼75 nm at annealing temperatures higher than 800°C. The annealing temperature dependence of the integrated intensity of the diffraction suggested that the activation energy of the crystallization into the Aurivillius phase was significantly changed at ∼800°C. The change in the activation energy had a close relationship with the structural phase transformation of fluorite to Aurivillius and the grain growth.

Interfacial Layer Formation during Crystallization of Sol-Gel Derived SrBi2Ta2O9 Thin Films on Silicon

“…The intensity of the peaks labeled "S" for the orthorhombic phase (ferroelectric) with the space group A2 1 am (Bi-layered Aurivillius phase) increased and that labeled "F" for the fluorite-type (space group: Fm3m) decreased with the duration [5,23]. This phase transformation from the fluorite to the orthorhombic phase was the same as that reported elsewhere [24] and almost independent of the crystallization atmosphere.…”

“…5. The density of the SBT layer was lower than that of the single crystal reported by Rae et al [23], indicating that the film contains many defects and low-density grain-boundary regions [24]. The interfacial layer was thickest in the H 2 0-vapor/N 2 case, while the density was almost independent of the crystallization atmosphere.…”

Bismuth titanate ferroelectric nanofilms formed directly on Si(100) substrates for memory application

“…Bismuth titanate (BiT, BLT) is well known as a ferroelectric material, but the properties and size effect of the nanofilms on Si substrates are still under discussion. Compared to other materials such as SBT, BLT can be crystallized at lower temperatures 39,40) which is an advantage in the process. In addition, HfO 2 -based materials give rise to several crystal phases, and the control of which is important for the use of ferroelectricity.…”

Enhanced Crystallization of Strontium Bismuth Tantalate Thin Films by Irradiation of Elongated Pulses of KrF Excimer Laser

“…Thin SBT films have excellent endurance properties and small coercive fields after crystallization at high temperatures. In the case of conventional furnace annealing, [1][2][3] the substrate temperatures necessary for crystallization are as high as 700 to 800 C. However, such high substrate temperatures cause atomic diffusion from the SBT film to the substrate and chemical reaction at their interface, which damages the device performance, when the SBT film is used in Si-based ultralarge-scale integration processes. 4) Therefore, it is necessary to lower the substrate temperature for SBT crystallization.…”