Effects of rapid thermal annealing treatment on 0·95(Na_0·5Bi_0·5)TiO₃-0·05BaTiO₃thin films

Abstract

A 0?95(Na 0?5 Bi 0?5 )TiO 3 -0?05BaTiO 3 z1 wt-%Bi 2 O 3 (NBT-BT3) ceramic was used as target to deposit the NBT-BT3 thin films. The excess 1 wt-%Bi 2 O 3 was used to compensate the vapourisation of Bi 2 O 3 during the depositing processes. The optimal deposition parameters were substrate temperature of 500uC, radio frequency power of 100 W, chamber pressure of 10 mtorr and oxygen concentration of 40%. Rapid thermal annealing treated processes were carried out on NBT-BT3 thin films from 600 to 800uC in ambient or in oxygen atmosphere for 1 min. The surface morphologies and thicknesses of NBT-BT3 thin films were characterised by field emission scanning electron microscopy, and the thickness was ,216 nm. It would be shown that the NBT-BT3 thin films annealed in oxygen atmosphere had the smaller grain size, larger memory window, smaller leakage current density, larger remanent and saturation polarisation and smaller coercive field than the NBT-BT3 thin films annealed in ambient atmosphere.

Effect of thermal treatment on structure and leakage current of Na0.5Bi0.5TiO3 thin films

“…2 can be caused by the increase of structure defects after a thermal treatment. In accordance with [2,4,5] the conduction in NBT is determined by oxygen vacancies and associated with V O defects. Therefore, it may be assumed that evaporation of bismuth during the annealing process of NBT thin films leads to the formation of V Bi 3+''' vacancies, which stimulate appearance of V O 2-•• vacancies.…”

“…Fig. 3 shows the fitting of experimental results and the ln J -E 1/2 curve exhibits the linear relation in the electrical field region 30 − 70 kV/cm, which indicates that Schottky emitted charge carriers [4] mainly contribute to leakage current of the films annealed at Т = 700°С.…”

“…3, the leakage current density linearly relates to the square root of the applied electric field. The linear variations of leakage current densities correspond to the Schottky emission mechanism or to the Poole-Frenkel emission mechanism [3,4]. In most cases, the Schottky type emission of electrons from the electrodes dominates in the region of small fields.…”

“…In most cases, the Schottky type emission of electrons from the electrodes dominates in the region of small fields. In the region of strong electric fields, the most probable conduction mechanism is the Poole-Frenkel mechanism of charge carrier in oxides [3,4]. Fig.…”

“…High values of leakage currents which are comparable with (or bigger then) the switching currents mask the ferroelectric properties of the films. The values of leakage currents and ferroelectric properties of NBT films depend on several factors such as the methods of film formation, the structure of the lower electrode, the crystallization temperature, the concentration of defects [2,4]. Therefore, the purpose of this work is to study the effect of NBT films heat treatment on the formation of the structure and the leakage current values.…”