STUDY OF ELECTRICAL AND SWITCHING PROPERTIES IN FERROELECTRIC COMPOSITE FILMS

Abstract

The relationship between properties and crystallographic microstructure is one of fundamental importance in materials science. Hysteretic and nonlinear dielectric behavior in ferroelectric materials has been studied since 1950s. These materials are used in various electronic devices such as nonvolatile electronic memories (e.g. FERAM) and tunable microwave component. Ferroelectric materials need processing in film form due to the requirement of low operating voltages in above devices. Many ferroelectric materials such as barium titanate (BaTiO3), barium strontium titanate (BST), lead zirconium titanate (PZT), potassium nitrate (KNO3), sodium nitrite (NaNO,) and cesium nitrate (CsNO3) have been studied. The ferroelectric films of these materials are made by various fabrication methods. Recently, composites of ferroelectric and polymer are emerging as a new class of dielectric and electronic materials due to their interesting properties. This dissertation work is aimed to study the ferroelectric and switching properties of ferroelectric - polymer composite films. The composite films of KNO3 and poly ethylene oxide (KNO3: PEO) and KNO3. NaNO2 and poly vinyl alcohol {(KNO3: NaNO2): PVA} are prepared by the solvent cast technique. The x - ray diffraction (XRD) experiment was employed to investigate the structural information of the pure and the composite films. The structural distortion c/a ratio were also calculated and found to be maximum for the composite film containing equal wt.% of KNO3 and PEO. Crystalline size is also determined in KNO3: PEO as well as {(KNO3:NaNO2): PVA} composite films. The information about surface morphology such as grain size, shape and porosity of the pure and composite films have been studied using field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM). The FESEM images of KNO3 and PEO composite films show the homogeneous distribution of KNO3 particles in composite film containing 50 wt.% of each .The AFM images of KNO3, NaNO2 and poly - vinyl alcohol (PVA) composite films shows the distribution of KNO3 and NaNO2 particles in PVA. The thermal behavior and phase transition temperatures in both types of composite films were studied by differential scanning calorimetry (DSC). The optimum value of remanent polarization (Pr = 3.7tC/cm2) was obtained in the 50 wt.% KNO3: PEO composite films prepared by the solvent cast method. The improved properties have been attributed to well grown grains, less porosity. In the case of KNO3. NaNO2 and PVA composite films the optimum value of remanent polarization Pr = 69.24 1.C/cm2 was obtained in the composite film which contain 30wt.% of KNO3, 20 wt. % of NaNO2 and 50 wt.% of PVA. The polarization switching properties are very important because the net switched charge limits the resolving power and switching time limits the running speed of read- • write memory devices. The switching response in 50 wt.% KNO3: PEO composite film and the composite film containing 30wt.% of KNO3, 20 wt.% of NaNO2 and 50 wt.% of PVA have been studied using bipolar square pulses. The switching parameters such as switching current and switching time have been calculated.