Preparation And Ferroelectric Nanodomains Of Pb(Zr_0.30Ti_0.70)O₃ Thin Films

Ferroelectric thin films such as lead zirconate titanate(Pb(Zr_xTi_1-x)O₃) have been andergoing increasing study in recent years, as their suitability for use in non-volatile ferroelectric random access memory(NV-FRAM) and other applications has been recognized. As Ferroelectric thin films are being used in such devices with small dimensions, a technique with high lateral resolution that is capable of measuring Ferroelectric properties of thin films is needed. Recently, Atom force microscopy (AFM) techniques, developed in 1986, is very powerful to determine the Ferroelectric domain and the surface structures. In this thesis Pb(Zr_0.30Ti_0.70)O₃ (titanate (PbTiO₃, PT) /PZT/PT) thin films with good electrical properties have been prepared. The effects of the content of lead acetate used and the heat treatment temperature on such properties as the surface morphology and the electrical properties of PZT have been researched. Nanoscale domain structures and pilarization reverse behaviors in PT/PZT/PT thin films were investigated by piezoresponse force microscopy and surface potential detection.The PZT thin films with well-crystallized perovskite and good electric properties was deposited onto platinum coated silicon substrates with PbTiO₃(PT) seeding layers using a sol-gel process and rapid thermal annealing(RTA) techniques. The existence of the PT layer is helpful to reduce the heat treatment temperature and time. As well as to improve the electrical properties of the thin films. RTA technics will restrain Pb valatilization and the formation of pyrochlore. the PZT thin film with the highest oriented texture and best electric properties was obtainwhen excess 15% PbAc was used and heat treatment was made at 650℃ for 20 min. Its remanent polarization is 21μC/cm² and its coercive field is 37kV/cm. When the PZT thin film was heat treated in 650℃ for 20 min, the more excess Pb is added, the better surface morphology of the PT/PZT/PT thin film has.The ferroelectric film were polarized by at nanometer scale under positive or negative voltages applied by the AFM tip. Complex domain contrast is related to the arrangement of domains in grains and to the orientation of the grains in the film. The regions with reverse polarity are obviously light and dark in the piezoresponse phase image. The different domains of the PZT thin films reversing need different polarization voltages. Some domains can reverse at low polarization voltage, other domains reverse at high polarizationvoltage. The reason why nanoscale domains reverse after different voltage polarization was investigated by atom force microscopy piezoreponse mode. Complex domain contrast is related not only to the polarization field but also to the arrangement of domains in grains, the charge disfigurement and the orientation of the grains in the film. After the PT/PZT/PT thin films were polarized, the surface potential is changed along with the free charge of the surface voltage-applied points producing. the surface potential attenuation was observed after 3 hours.