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

Abstract

Ferroelectric SrBi2Ta 2 0 9 (SBT) thin films have been formed on silicon substrates at a crystallization temperature as low as 750 oc. The crystallization atmosphere (0 2 , N 2 , H20-vapor/N2) influenced the electrical characteristics of the Au/SBT/p-Si structures. The capacitance-voltage characteristics of the devices suggested that the defects in the interface region were smallest as the SBT film was crystallized in the H 2 0-vapor/N 2 atmosphere. The effect of the crystallization atmosphere on the SBT film and interface structures were quantitatively investigated by using X-ray reflectivity (XRR) method. It was confirmed that an interfacial layer was formed between the SBT film and the silicon substrate in any case. The interfacial layer was thickest in the case of H 2 0-vapor/N 2 atmosphere. However, the density of the interfacial layer was independent of the crystallization atmosphere. Furthermore, the crystallization duration dependence showed that the thickness of the interfacial layer increased with crystallization duration but the density remained a value ~2.5 g/cm 3 . The interfacial layer formation was mainly caused by oxidation of silicon.

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

“…Simulation fitting was carried out using a multilayer model with a rough interface on the basis of the theory and the formulas of XRR. [24][25][26][27] In this study, a two-layer model (SBT and interface oxide layer) with thicknesses, layer densities and interface rough-nesses as parameters 23) was employed and well fitted to the experimental data. From the results of the simulation fitting the annealing temperature dependences of the thickness and density of the SBT layer were evaluated as shown in Fig.…”

“…The SBT film crystallized only into the Aurivillius phase at annealing temperatures higher than 800 C. These changes agree well with the phase transformation from the fluorite phase to the Aurivillius phase reported elsewhere. 17,23) The normalized integrated intensities of XRD are replotted against 1=T, as shown in Fig. 6.…”

“…In this lower temperature region the crystal phase gradually transformed from fluorite to Aurivillius. 23,28) The crystallization and phase transformation kinetics have been investigated by Jung et al 28) and the activation energy for phase transformation reaction was evaluated to be $263 kJ/mol for unseeded film and $183 kJ/mol for seeded film. However, the films were much thicker than that in the present study and our film may be equivalent to the seeded layer in the previous paper.…”

“…XRR spectrum analysis was carried out by model calculation and fitting to the data. 22,23) All measurements were carried out at room temperature.…”

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.…”