Effect Of Strain On The Electrical Properties Of Polycrystalline LaNiO₃ And Au-LaNiO₃ Composite Films

Ferroelectric thin films PbZrxTi1-xO3(PZT)are widely used in ferroelectric memory(FRAM)due to excellent properties such as ferroelectricity and piezoelectricity.PZT films grown on conventional noble metal Pt electrodes have serious phenomenon of electrode polarization fatigue,which affects the stability of the electronic device.The use of conductive metal oxide electrode instead of the traditional metal electrode can effectively improve the electrical polarization fatigue of ferroelectric thin film.Among them,LaNiO3(LNO)is expected to be the preferred metal oxide electrode material due to good metal conductivity,crystal structure similar to that of PZT.However,the resistivity of the LNO electrode is much greater than that of the metal Pt electrode,which is not conducive to reducing the power consumption of the electronic device.The purpose of this study is to further improve the conductivity of the LNO thin film,which is of great significance to its application in ferroelectric devices.LNO and Au-LNO thin films prepared by sol-gel method were studied as the research objects.The structure and properties of the films were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),four probe,PPMS electrical transport measurements.The mechanism of the strain on the crystal structure and electrical conductivity of polycrystalline LNO and Au-LNO composite films were systematically analyzed.The main works are as follows:The LNO thin films were grown on the substrate Si by sol-gel method.The influence of heating temperature and stabilizer on the growth of LNO thin film was studied.The results show that the LNO films under MEA have the best crystallinity and the lowest resistivity when the heating temperature is 923K.Adding Au can significantly reduce the room temperature resistivity and metal-to-insulator transition temperature of the LNO films.The improvement of the conductivity of LNO by adding Au is due to the improvement of the crystalline quality of LNO and the reduction of oxygen vacancy concentration.LNO and Au-LNO films were successfully prepared on substrate LAO,substrate LSAT and substrate STO by sol-gel method.The effects of epitaxial strain on the structure and electrical conductivity of polycrystalline LNO and Au-LNO films were investigated.The surface morphology,microstructure and electrical properties of the thin films were analysed,The influence mechanism of the strain on the electrical conductivity of LNO and Au-LNO composite films was revealed.The LNO and Au-LNO films were successfully prepared on substrate Si,substrate Al2O3 and substrate MgO by sol-gel method.The effects of thermal strain on the structure and electrical conductivity of polycrystalline LNO and Au-LNO films were investigated.The intrinsic mechanism of the resistivity changes of LNO and Au-LNO composite films was analyzed under different strain states.The effect of external strain on the micro structure of polycrystalline thin films was analyzed from two aspects,the change of lattice constant was caused by macroscopic strain and defect concentration was caused by microscopic strain.The change trend of film resistivity with strain state was determined by the effect both of them.