Research On The Influence Of Components On The Microstructure And Physical Properties Of Ferroelectric Multilayer Films

Lead zirconate titanate(PbZr_xTi_1-xO₃,abbreviated as PZT)film has been widely applied in dynamic random access memories,infrared detectors and tunable microwave devices duo to its excellent piezoelectric,ferroelectric,pyroelectric and dielectric properties.It has been regarded as ideal media for building photonic devices with tunable characteristic parameters because of its high transparency from visible to infrared region,high refractive index,especially large electro-optical coefficient.Recent years,a simple and effective processing technique to fabricate quasiperiodic ferroelectric multilayers has been invented.And only one single chemical solution containing polymer is used in the new technology based on phase separation and electrostatic attraction.With this processing route many ferroelectric multilayers have been fabricated.It also has been investigated the relationship between the polymer content and kind,heat treatment temperature and the microstructure and optical property of the ferroelectric multilayers.To further optimize the electrical and optical performance of ferroelectric multulayers and promote their application in photonic band-gap engineering and integrated photoelectronics,it has been explored in detail in this thesis that the effect of the Zr or Ti content on the formation,microstructures of the PZT multilayers,and on their ferroelectric,dielectric and optical characteristics.The obtained main results are as following.?1?A series of PZT films had been fabricated by using spinning-coating/annealing process and precursor solutions with PVP additives.X-ray diffraction data show that each PZT film has been fully crystallized and has a polycrystalline structure with a110-preferred orientation.SEM images reveal that when Zr content x>0.9 PZT films have a relative dense across-section and no any delamination in the direction perpendicular to film surface,and when x<0.9 all the PZT films seem to exhibit layered structures.However,when 0.35?x?0.65 PZT films display evident and regular lamellar textures consisting of dense and porous PZT layers.All the observations could be well explained based on the formation condition of a ferroelectric multilayer with one single composition.?2?The reflectance spectra demonstrate that each PZT film with x<0.9 has an optical reflection-band.The PZT films with x in the range of 0.35⁰.65 exhibit the best Bragg optical reflection performance with peak reflectivities of over 70%and band widths of over 45 nm.These experimental data could be well clarified with thin films optical theory.?3?PZT films have apparently large low-frequency dielectric constants(>440Fm^-1)at room temperature,which are mainly contributed by the polarization of charges accumulating around nanopores.For these PZT films their P_r increase with x firstly,followed by a maximum,and then decrease at a given polarization electric filed,while the E_c decreases monotinaly with x.The PZT films with x>0.95 are in the antiferroelectric phase,and have double hysteresis loops.The PbZr_0.4Ti_0.6O₃?PbZr_0.5Ti_0.5O₃?PbZr_0.6Ti_0.4O₃ system exhibits good dielectric and ferroelectric performance,with a dielectric constant>550Fm^-11 and dielectric loss no more than0.06 at 10KHz,remanent polarization>24?C/cm² at 100V polarizing voltage.