PULSED LASER DEPOSITION OF BZT-X(BST) COMPOSITE THIN FILMS

Abstract

Chapter I It gives the overview of ferroelectric phenomena, conditions required for a system to have ferroelectricity and the dependence of ferroelectric "hysteresis loop on temperature. An introduction to perovskite structure has also been given in this chapter. Finally i discussed BaTiO3, BaZrTiO3, BaSrTiO3 and BaZrTiO3-x(BaSrTiO3) structure. Chapter 2 Pulsed laser deposition technique has been used for the fabrication of BZT, BST, BZT-x(BST) thin films. Surface morphology of these thin films has been studied using X-ray diffractometer and FE-SEM. Radiant ferroelectric tester and 4294A Impedance analyzer gives the ferroelectric and dielectric properties respectively of these thin films. So, in chapter 2 these techniques has been discussed in detail. Chapter 3 Chapter 3 explored the influence of substrate temperature and oxygen partial pressure on the structural, dielectric and ferroelectric properties of BaZrTiO3 thin films deposited on LaNiO3 coated Si substrate by using pulsed laser deposition technique. The crystallinity, out-of-plane lattice parameter d, polarization P, dielectric constant Er(0) and tunability nr were found to increase with increasing substrate temperature and oxygen partial pressure. Improvement in crystallinity is believed to be the reason for the improved ferroelectric and dielectric properties. The increase in the out-of-plane lattice parameter (c) and increase in grain size causes the increases in tunability (nr) and polarization (P) . It has also been observed that the tetragonal distortion (ratio of out-of- plane and in -plane lattice parameter, c/a) of the films depends on the oxygen partial pressures. c/a ratio varies from 0.9067 at 1 Om torr to 1.0271 at 200m Torr, indicating the in-plain strain changes from tensile to compressive. The increase in c/a ratio could be the another reason for the significant improvement in the properties with increasing oxygen partial pressure. A high tenability of 62% measured at the frequency of 1MHz could be achieved for the film deposited at 750°C and 200 m Torr, showing that Ba(Zr,,Til_X)O3 thin films would be a suitable candidate for potential tunable devices° Chapter 4 The BSZT thin films were deposited via Pulsed laser deposition technique on LaNiO3-coated silicon substrates. The BSZT thin films found to have better larger particle size than BST and BZT thin films which leads to the increase in dielectric and ferroelectric properties. Dielectric properties were investigated as a function of temperature, frequency • and direct current electric field. The temperature dependent dielectric measurements revealed that the thin films have diffuse phase transition characteristics. The tunability of BSZT thin films is about 68%, at an applied field of 300 kV/cm and measurement frequency of 1 MHz. Chapter 5 future prospects has been discussed in this chapter