Annealing Temperature Effects On The Ferroelectric Properties And Residual Stress Of Bi_3.15(Eu_0.7Nd_0.15)Ti₃O₁₂ Thin Films

As bismuth layered structure ferroelectrics (BLSFs) thin film has excellent piezoelectric, ferroelectric, pyroelectric and electro-optical and other properties, the electrical devices based on BLSFs thin film have a very large field of prospects in the field of functional materials. BLSFs have been recognized as the promising film materials for non-volatile ferroelectric random access memories (NvFeRAMs) due to the lead-free chemical composition, and other good electrical properties. BLSFs ferroelectric thin film has a high breakdown strength and a relatively high dielectric constant, so it can be widely used in dynamic random access memory (DRAM), ferroelectric random access memory (FeRAM), ferroelectric field effect transistors (FeFET), optical storage, optical displays and other optoelectronic devices. Bi4Ti3O12 (BIT) is a typical layered calcium titanium structure of ferroelectric material, but the remnant polarization of BIT is not high enough for commercial application. In order to improve the electrical characteristics of BIT thin films, scientists use cosubstitution ions mothod to make many new types of materials, hoping to find better quality materials. To improve the remnant polarization of BLSFs ferroelectric thin films, A- and A-sites cosubstituted Bi3.15(Eu0.7Nd0.15)Ti3O12 (BENT) thin films were prepared by metal organic decomposition (MOD) at different annealing temperatures 600, 650, 700 and 750°C.(1)The A- and A-sites cosubstituted BENT thin films annealed at 600, 650, 700 and 750°C are of crack-free surface and Bi-layered perovskite polycrystalline phase without any pyrochlore phase and the other phases related to Eu and Nd BENT thin film annealed at 650°C is of the largest remnant polarization 2Pr (103μC/cm² under 260 KV/cm), the largest dielectric constantεr (1046 at 200 KHz), and the lowest leakage current (1.15×10^-8 A/cm² under 225 KV/cm) among all of BENT thin films, and the value of 2Pr is largest among those of the previous BIT-based thin films. The moderate annealing temperature can be used to control Bi amount in the cosubstituted BENT thin films. Not only the free mobile holes, ionic and electronic defects induced by Bi excess, but also the structural defects produced by Bi evaporation can inhibit the polarization switching. The enhanced remnant polarization is reasonably explained via the displacement effect. The improved ferroelectric properties could make the cosubstituted BENT thin film to be a promising candidate for NvFeRAMs.(2) In ferroelectric thin film residual stress is an important factor for the thin film mechanical properties, because once at the certain level they will lead to film/substrate component failure. Therefore, stress residual estimation is an important issue in the micro view of the measurement of material properties. We focus on the traditional sin2ψmethod, which based on X-ray diffraction, to measure the residual stress estimation in the BENT ferroelectric films, then discuss the relationships between the residual stress and annealing temperature, the residual stress and remnant polarization.