Preparation And Characterization Of Barium Strontium Titanate Ferroelectric Thin Films By Sol-gel Method

Abstract:Ferroelectric materials exhibit ferroelectric, dielectric, pyroelectric effect and piezoelectric effect and other properties, which are widely used in solid state integrated devices. The trends of miniaturization and high integration electronic device promote the development of thin films and integrated devices. Among the ferroelectric thin film materials, barium strontium titanate BaxSr1-xTiO3(BST) with perovskite structure, possessing a high dielectric constant, dielectric nonlinearity, low leakage current and high temperature stability, attracts lots of attention, but its dielectric loss is large. Sol-gel method is an important method for the preparation of BST thin films with high performances, which is of great problems during the preparation process. By systemly studying the process of film preparation can optimize its performance. This paper mainly studied the mechanisms of BST sols prepared by Pechini method and Acetate method, the heat treatment regime of BST thin films, the effect of Ba/Sr ratio, the effect of thickness and Co-doped on microstructure and properties of BST thin films. The main results are as follows:(1) Stable BST sols were prepared by Pechini method and Acetate method, repectively. The mechanisms of BST sols were studied. The results show that wettability between BST sol prepared by acetate and substrate is well, and the corresponding thin films are uniform, dense and crack-free.(2) The heat treatment regime BST films, effect of Ba/Sr ratio and the thickness on its performance were studied. The results show that BST thin films with good crystallinity and high density are obtained after pyralyzing at400℃for30min and annealing at800℃for15min under oxygen atmosphere. Curie temperature of BaxSr1-xTiO3(x=0.6,0.7,0.8,0.9) thin films increase with the increase of Ba content. The grain size increases linely with the increasing thickness of the Ba0.8Sr0.2TiO3thin films ranging from160to378nm. The Curie temperature shifts due to the dead layer. The dielectric constant and dielectric loss increase with the increase of the thickness under a constant frequency. The dielectric constant of the Ba0.8Sr0.2TiO3thin film whose Curie temperature is below the room temperature with the grain size of30～40nm and thickness of 300nm decreases with the increase of temperature because of size effect.(3) Ba0.8Sr0.2TiO3thin films doped with Co were characterized. The results show that the doping of Co not only contributes to dielectric constant and dielectric loss of BSCT thin films decreasing, but also the tunability decreasing. The samples doped with3mol%Co are suitable for tunable devices.