The Mod Of The Graded Bst Thin Film Preparation And Characterization

Because of excellent ferroelectric and dielectric properties,(Ba,Sr)TiO₃ ferroelectric thin films have been widely investigated for electronic devices application, such as tunable microwave devices,dynamic random access memory,and pyroelectric detectors.Based on tremendous investigation of functional graded materials,a further research of graded BST thin film had been point out.In this thesis,the structure and electrical properties of graded BST thin films derived on Pt/Ti/SiO₂/Si substrate by MOD method was studied systematically.The main contents are as follow:Firstly,the preparation process of BST thin films(with single composition) was studied.By means of XRDθ/2θanalysis of BST thin films,the technique of the MOD processing was optimized,from which the precursor preparing parameter and heat treatment condition were defined.Then,using the optimized MOD process,BST thin films(with single composition) of various Ba/Sr ratio and graded BST thin films were derived.The microstructure and crystalline structure of graded BST films were examined by the X-ray diffraction, scanning electric microscopy,and atomic force microscopy.The XRD results exhibited that all the graded BST films were polycrystalline.The surface of all graded BST films was smooth detected by AFM.Sharp interface between different layers of the graded BST thin film could be demonstrated by SEM.It was shown that graded BST thin films had better dielectric property compared with BST thin films with single composition, the reason of which had been investigated in this thesis.In further research the BST thin films were annealed in different ambient,such as Ar/N₂,atmosphere,O₂,and hydroatmosphere.It indicated that the graded BST thin film annealed in hydroatmospheric ambient exhibited better dielectric properties,which had a dielectric tunability of 56%and a dielectric loss of 1.5%.