Preparation Of SBT Perovskite-Like Ceramics And Ferroelectric Thin Films Deposition On Cu Wafers

Recently, ferroelectric thin films as well as their applications in non-volatile ferroelectric random access memory (FRAM) are becoming research hot point. However, ferroelectric fatigue has been the main factor preventing the further development and widely applications of FRAM. In order to solve the problem, novel material and wafer, such as fatigue-free perovskite-like SrBi2Ta2O9 (SBT) ferroelectric film and copper single crystal wafer are introduced. The preparation of sputtering targets and deposition wafers, as well as the preparation of ferroelectric thin films are comprehensively explored in this paper.SBT ceramics and sputtering targets with different Bi₂O₃ additions are synthesized by solid state reaction. The effects of synthesis technique and Bi₂O₃ addition on the structure and properties of SBT perovskite-like ceramics are investigated. With as-prepared SBT targets, SBT films are deposited on copper single crystal wafers by radio frequency magnetron sputtering (RMP). Subsequently, the deposited SBT films are annealed at different temperatures at pure nitrogen. The structure and properties of SBT thin films are investigated.The experimental results indicate that the optimal quenched temperatures for BiTaO4 precursors and SBT powders are 900℃and 950℃, respectively in a two-stage process of SBT synthesis. After 1000℃sintering a typical perovskite-like structure SBT can be identified. The density of perovskite-like SBT ceramics, as well as the degree of c-axis preferred orientation and grain size will be increased obviously when raising the sintering temperature. Furthermore, the ferroelectricity increases while the dielectricity decreases as the sintering temperature higher. The Bi₂O₃ addition also influences the microstructure, and increases both the degree of c-axis preferred orientation and grain size of as-result SBT. The dielectricity and ferroelectricity also vary accompanying with the Bi₂O₃ addition. An optimal ferroelectricity can be obtained when the Bi₂O₃ addition is 5mol%. The perovskite-like SBT ceramic targets with different Bi₂O₃ additions are sintered at 1000℃for 2h. The shape and density of all targets are suitable for RMP. SBT films are deposited at an Ar/O2 mixture for 1.5～3h. Deposited SBT films are annealed at different temperatures at a pure nitrogen atmosphere to be crystallized. Grazing incidence X-ray diffraction (GIXRD) analysis results show that the perovskite-like SBT films start to be crystallized at 650℃and optimize at 780℃. However, GIXRD result also indicates the existence of Cu2O. The leakage current of SBT films is a little bit higher as a result of Cu atoms'diffusion at boundary and aggregation on the surfaces of SBT films. Oxygen vacancies attributed to the oxidation of Cu wafer and volatilization of Bi₂O₃ can be considered as the main reason of higher leakage current.