Multiferroic Coupling Effects And Modification Study Of Bismuth Ferrite/Barium Strontium Titanate Bilayer Films

As a single-phase multiferroic oxide, BiFeO3(BFO) is suitable for applications such as magnetoelectric memories, sensors and actuators due to its coexistence of ferroelectric and magnetic properties at room temperature. However, BFO suffers from high leakage current density and small magnetization. And the BFO in film form is apt to react with Pt bottom electrode. In addition, its required high processing temperatures can not be compatible well with the interconnect technologies for semiconductor. In recent years, considerable developments can be seen in the research field of preparation and modification for BFO, but the above problems have not been solved simultaneously.The aim of this study was to prevent the reaction between the BFO film and Pt electrode, and obtain BFO-based multiferroic films with enhanced leakage and magnetic performances, then make integration of these films with third-generation semiconductors such as ZnO and SiC with high temperature resistance. To remove the stress effect between film and substrate, multiferroic one-dimensional nanomaterials were slso applied to prove the properties of the films.The Ba0.7Sr0.3TiO3(BSTO) was firstly used as a buffer layer to synthesize BFO/BSTO bilayer films. It was found that BSTO buffer layer could significantly prevent the reaction between the BFO film and Pt electrode. There was no second phase detected in the BFO/BSTO film, but the concentration of Fe2+ions was much higher than that of Fe3+ions in the BFO layer. In order to improve the leakage characteristics of the BFO/BSTO film, the effects of La and Mn doping on the BFO layer were further studied. It was found that the La and Mn co-doping could considerably reduce the Fe2+content in the film. In order to confirm this observation, the reduction of Fe2+concentration and leakage currents in the La and Mn doped BFO-based nanofibers were investigatedThe using of BSTO buffer layer could also increase the thickness of multiferroic films. Considering the device miniaturization, the BSTO buffer layer was been further optimized. The magnetic element Co doped BSTO (Ba0.7Sr0.3Ti0.95Co0.05O3, BSTCO) was then used as a buffer layer of the Bi0.9La0.1Fe0.95Mn0.05O3(BLFMO) film. It was found that both the magnetic and magnetodielectric properties of the BLFMO/BSTCO bilayer films were higher than those of the BLFMO/BSTO films. In addition, the BLFMO/BSTCO films were integrated with third-generation semiconductors such as ZnO and SiC, and the excellent ferroelectric properties of the multiferroic films could been maintained. To obtain BLFMO-based bilayer thin films with higher magnetic and magnetodielectric performances, the BSTO–Ni0.8Zn0.2Fe2O4(NZFO) composite film was then applied as the buffer layer. It was found that the BSTO–NZFO buffer layer could effectively improve the magnetic and magnetodielectric performances of the BLFMO film, but the electrical properties of the BLFMO/BSTO–NZFO film were weak. In addition, a rough surface was observed in the BLFMO/BSTO–NZFO film, and the special morphology of the BLFMO/BSTO–NZFO film was believed to be from the BSTO–NZFO buffer layer. Meanwhile, the formation mechanism of this special morphology had been proposed and further proved by the composite nanotubes.