Magnetoelectric Effect And Photovoltaic Effect And The Modulation Of Resistive Switching Effect In BiFeO₃-Based Films

All the time,multiferroic materials have broad application prospects in information storage devices,multi-functional microelectronic devices,sensors and other new electronic devices due to their two or more than two kinds of ferromagnetic order parameters,such as ferroelectric,ferromagnetic,ferroelastic and so on,and the coupling effects of various order parameters,such as magnetoelectric coupling effect.In recent years,with the development of science and technology,the potential physical properties of ferroelectric materials have been rediscovered,such as resistive switching effect,ferroelectric photovoltaic effect,etc.The interaction between these physical properties and multiferroic provides a new angle for multi-field modulation,high performance device design,and the multifunction and miniaturization of microelectronic devices.In this paper,the BiFeO₃-based material in single-phase multiferroic materials is chosen as the research object.Firstly,the magnetoelectric coupling properties of magnetoelectric composite films under the control of external magnetic field were studied;Then we studied the resistive switching of BiFeO₃ films by the modulation of ferroelectric photovoltaic effect,and realized the multi-resistance switching under the excitation of electric field and light field.The main research results of this paper are as follows:Polycrystalline Co/Bi_0.9La_0.1Fe_0.95Mn_0.05O₃ magnetoelectric composite films were successfully deposited on Pt/Ti/SiO₂/Si wafers by sol-gel method combined with magnetron sputtering technology;The macroscopic leakage current of the composite film has been greatly improved,and has good ferroelectricity and ferromagnetism at room temperature.The hysteresis loop of composite thin film with the applied magnetic field was measured,and we found that the ferroelectric polarization was modulated;That is,the saturation polarization decreases with the increase of magnetic field.By cutting out the influence of leakage current,it is found that the inhibition rate of external magnetic field to the residual polarization of composite film reaches 16%at H=1000 Oe.The I-V curves of Co/BLFMO composite films under different magnetic fields were measured by Keithley 2400 electrometer.We found that the resistance of composite films increased with the increase of external magnetic field.Last,the resistive switching properties of composite thin films under external magnetic field was measured.We found that with the increase of external magnetic field,the resistive switching field increases to some extent.For the above physical phenomena,we think that this inhibition originates from magnetostriction in the magnetic layer of Co,and the stress generated is transferred to the ferroelectric layer,which suppressed ferroelectric domain inversion and the ferroelectric polarization.Under a certain bias voltage,the conductance of thin films is dominated by grain boundaries and ferroelectric domains.Because the conductance at grain boundaries is rapidly saturated under small bias,the conduction process of thin films is dominated by ferroelectric domain with the increase of bias voltage.When the ferroelectric domain is completely reversed,the whole grains become completely conductive.However,due to the external magnetic field restraining the overturn of ferroelectric domains in the composite films,the conductance process is suppressed and the formation of conductive channels becomes difficult.Polycrystalline BiFeO₃ thin films were successfully prepared by sol-gel process on Pt/Ti/SiO₂/Si wafers,and showed good ferroelectric properties.The ferroelectric photovoltaic effect of thin film samples was measured by photovoltaic effect test system.We found that the open circuit voltage of BFO film under illumination is V_oc=0.28V,and the short circuit current density is J_sc=6.83 A/cm².At the same time,a typical unipolar resistive switching effect is observed.We suggested that the resistive switching in the film is derived from the formation and fuse of the conductive channels in the films ccording to the analysis of its conductance mechanism.We introduced light when we measure the resistive switching effect.It was found that at low resistance state,the resistance of thin films was not changed whether or not there is incident light.However,the resistance can be reduced by nearly two orders of magnitude at high resistance under illumination,and the three state effect of the film is achieved.This effect is mainly derived from the following physical mechanisms:Under light conditions,the photovoltaic effect of the film is produced.At low resistance,due to the metal conductivity mechanism,the photocurrent caused by the photovoltaic effect is very weak compared to the film itself,so the light has no effect on the resistance state.At high resistance,due to the semiconductor conductivity mechanism,the photocurrent caused by the photovoltaic effect is in the same order of magnitude as the current of the film itself,so a new photoresist state will be produced under the light.