Study On The Electro-resistance Effect Of Ultra-thin BaTiO 3 Ferroelectric Thin Films

Ferroelectric tunnel junction can be utilized to realize the non-destructive readout of data due to the electroresistance switching effect caused by electron tunneling,which makes it a promising candidate for nonvolatile memories.How to enhance the electroresistance switching effect is significant for ferroelectric thin films in ferroelectric memory applications.Generally,researchers used asymmetric electrode materials,chose semiconductor crystals as the substrates or fabricated composite barriers to tune the height and width of ferroelectric tunnel junction and then to improve its performance.In order to further enhance the electroresistance switching effect of ferroelectric thin films,we propose Pb?Mg1/3Nb2/3?O₃-PbTiO₃ ferroelectric single crystal that has giant piezoelectric properties as the substrate,and take advantage of its converse piezoelectric effect to produce in-situ dynamic strain,and that can be used to manipulate the in-plane strain of deposited ferroelectric films,and then to manipulate domain structures,electrical properties and electroresistance switching effect.The main research contents and results are list as follows:?1?<100> oriented epitaxial SrRuO₃ films were grown on the <100> oriented PMN-PT substrates as a buffer layer as well as a conductive electrode by pulsed laser deposition.The effects of processing parameters on the crystalline quality,surface morphology and electrical conductivity of the films were investigated.The RMS is 0.54 nm and square resistance is 54.49 ? for the epitaxial SrRuO₃ thin film.?2?BaTiO₃ targets with pure perovskite structure and high density were prepared by the conventional solid-state reaction sintering method.Then,<001> oriented BaTiO₃ epitaxial single-crystal films were grown on SrRuO₃/PMN-PT heterogeneous structure by pulsed laser deposition.We studied systematically the evolution of domain structures with electric field and temperature for the BaTiO₃ thin films.The polarization switched and a single-domain structure was obtained with electric field increasing to 1272 kV/cm,while the polarization disappeared with temperature increasing to 130 oC,where a ferroelectric-paraelectric phase transition occurred.At room temperature,the remanent polarization?Pr?and coercive field?Ec?of the BaTiO₃ ferroelectric film were 10.92 ? C/cm2 and 63.07 kV/cm,respectively,and the dielectric constant??r?and dielectric loss?tan??of the films were about 389 and 0.094 at 1kHz,respectively.The values of Pr,Ec and ?r decreased with the in-plane strain of BaTiO₃ thin films increasing induced by PMN-PT substrate.?3?The effects of film thickness on electroresistance switching effect of the BaTiO₃ film was investigated using a conductive atomic force microscope.The electroresistance switching effect was improved with film thickness decreasing.The variation of the tunneling current of the film was up to 200% with the thickness decreased to 3 nm.The results may provide a theoretical foundation and technological support for developing high-density,high-speed and low-power ferroelectric memories.