Fabrication And Dielectric Properties Of Lead Strontium Titanate Ferroelectric Thin Films

Ferroelectric thin films with perovskite structure have been widely drawn muchattention because of dielectric nonlinearity and low loss. Among these dielectricmaterials,(BaxSr1-x)TiO3(BST) and (PbxSr1-x)TiO3(PST) are confirmed to bepromising candidates for tunable device applications. Whereas in comparison to largedielectric loss and relatively high processing temperature of BST film, PST filmshows smaller grain size effect, lower crystallization temperature, high dielectricpermittivity and low dielectric loss, making it easier to be compatible with Simicro-electronics technology, thus promoting the development of the miniaturizationand integration for the modern devices.PST thin films with two different Pb/Sr ratio which are Pb0.9Sr0.1TiO3andPb0.4Sr0.6TiO3are investigated by a sol-gel deposition method in this paper. The rolesof element doping and buffer layers, which are the most common and effective waysto further improve the properties of thin films, on their microstructure and dielectricproperties are performed. Specific work and results are summarized as follows:1. La doped Pb0.82La0.08Sr0.1Ti0.98O3(PLST) thin films were synthesized atdifferent annealing temperatures of550-650°C. By comparing the effect of annealingtemperature on the microstructure and dielectric properties of PLST thin films, wefound that the PLST thin film which was annealed at600°C showed the bestdielectric properties, with the values of the dielectric constant and loss tangent were873and0.084at a frequency of1kHz, respectively. What’s more, the tunabilityreached to44%under the DC electric field of400kV/cm. After embeding LaNiO3buffer layer, the PLST film showed better-crystallized and had smaller grains. Itsdielectric constant increased from873to1140and the dielectric loss decreased from0.084to0.079at1kHz. In addition, the tunability and figure of merit of PLST thinfilm with the LNO layer are about68%and14.2respectively, which higher than60%and8.7of the one without the LNO layer.2. Pb0.4Sr0.6TiO3(PST) thin films were successfully synthesized using the sol-gelmethod. We introduced three different buffer layer films (La0.5Sr0.5CoO3、LaNiO3andTiO2), and the thickness of those films were all100nm. The results show that theLNO and TiO2buffer layers can promotes PST thin films a (110) preferred orientation,while the PST thin films without a buffer layer or with LSCO buffer layer exhibit a random orientation. The tunability of PST films with no、LSCO、LNO and TiO2bufferlayer are51.5%、44.6%、54.5%and11.5%, and the figure of merit are9.9、11.2、20.4and5.5, in proper order. Furthermore, on this basis, we also investigated theinfluence of TiO2buffer layer thickness on the microstructure and dielectric propertiesof PST thin films. The thickness of TiO2films are50nm,100nm and200nm. Theresults show that with the increase of the thickness of TiO2buffer layers, the (110)diffraction peak of the PST films gradually increases, all the dielectric constant,tunability and figure of merit gradually decreases, while the dielectric loss firstlydecreases then increases, which reaches a minimum at100nm thickness of TiO2film,only0.02, so that this work could have certain guiding significance for the study onreducing the loss of PST thin films.