Study On The Fabrication And Characteristics Of The Ferroelectric Thin Films For Ferroelectric Memories

In the dissertations, based on the Sol-Gel fabrication technologies, a series of Bi4Ti3O12(BTO) and Pb(ZrxTi1-x)O3(PZT) ferroelectric films are deposited on Silicon wafers, the optimum fabrication conditions are investigated. The samples are characterized by some microscopic probes such as XRD and SEM, and combined with the measurements of ferroelectric properties, the correspondence of structural characteristics and ferroelectric properties are discussed. In addition, the theoretical analysis and mathematical simulations of the model of ferroelectric capacitors based on the hysteresis loop are carried out. The main results are included below:The BTO ferroelectric thin films were prepared on the P-type silicon wafers with varies annealing temperatures range from 550 to 850 centidegree. The technology parameters and process controlling flow of the fabrication for the BTO films are explored through experiments and the optimal technology scheme is obtained. The annealing temperature dependence of feeroelectric properties is displayed through the corresponding polarization vs. gate-voltage(P-V) hysteresis . The result show that the proper anneal temperature is in the range of 650～700 centidegree with Pr=8.1μC/cm2 and Ec=50.4kV/cm.In the process of Sol-Gel fabrication technologies, a PT seed layer is grown between PZT film layer and Si substrates, then the PZT films is prepared and treated by Rapid Thermal Anneal(RTA) technique in oxygenic atmosphere. The experimental result indicates that PT seed layer can ameliorate the structure characteristic and lowers the annealing temperature, while shortens the time. RTA technology is helpful to form the pervoskite structure which is exhibited by XRD pattern.Basing on the experimental results, a model of ferroelectric capacitors based on hysteresis loop is proposed combined with polarization theory of electric and S.L.Miller's ferroelectric capacitor switching theory. By analysising the microstructure of ferroelectric, a crystal cell of ferroelectric compound is equilent as a dipole, Analysis the switching property of dipole in the electric filed. A formula was derived according the statistic principle, different distribution functions are used to fit the probability of dipole switching. Our model show good agreement with the experimental data for both saturated and minor loops, and the model could easily be linked to cir analog cuit simulative software.