Preparation Of Lead-free Multiferroic Composite Thin Films And Research On Their Ferroelectric, Ferromagnetic Properties

Multiferroic composite films were widely used in microelectronics andintegrated circuits. The author have prepared （Ba0.9Ca0.1）（Ti0.9Zr0.1）O3（BCZT）ferroelectric thin film and CoFe2O4（CFO） ferromagnetic film by the sol-gelmethod. Subsequently, the author prepared2-2type layered BCZT/CFOmultiferroic composite films.Firstly, the author prepared the BCZT powders and BCZT thin films by thesol-gel method. The results show that BCZT materials prepared by using theorganic zirconium salt as raw materials have a lower annealing temperature thanthose prepared by using the inorganic zirconium salt. The films deposited onPt/Ti/SiO₂/Si substrate are denser and more flat than those deposited on Si substrate.The author also studied the impacts of different annealing process on themicrostructures and properties of thin films. The results show that the filmsprepared under complex annealing process （CAP） have a （100） preferredorientation. Compared with those prepared under simple annealing process （SAP）and ordinary annealing process （OAP）, the films prepared under CAP have higherdielectric constant （ε） and smaller leakage current （tanδ） at the same frequency,larger remanent polarization （P_r） and smaller coercive field （E_c）.Then, the powders and films of CFO were prepared by the sol-gel method. Thepre-annealing temperatures of CFO films were set at390℃and the final annealingtemperatures were650℃, which were determined by the results of DSC and XRDanalysis of the prepared CFO powders. The films deposited on Pt/Ti/SiO₂/Sisubstrate have a denser and more flat surface than those deposited on Si substrate.The root-mean-square roughness of film is about4.69nm. The author depositedCFO thin films with different thicknesses. The results show that, when thethicknesses of the films are smaller, saturation magnetization （M_s） and residualmagnetization （M_r） of the films increase and coercive forces （H_c） decrease withincreasing the thicknesses of films. However M_rdecreases and H_cincreases withincreasing the thicknesses of the films when thicknesses of the films are greaterthan a certain value. H_cof the CFO films is greater that of the CFO powders.Finally, on the basis of the above experiments, the author prepared BCZT/CFOcomposite films with different thickness of CFO films by the sol-gel method. The XRD results show that the composite thin films have CFO phase, BCZT phase, andno impurity phases. With increasing the thicknesses of CFO films in the compositefilms, P_rof the compose thin films decreases, E_c of the compose thin filmsincreases, Ms and M_r of the compose thin films increase, H_c of the compose thinfilms decrease.