| SrBi2Ta2O9(SBT)is known as a kind of ferroelectric material with perovskite-like structure structure,which has excellent anti-fatigue property,and does not contain heavy metals such as lead,so it has no pollution to the environment.Meanwhile,as a ternary oxide,SBT has the potential to become a resistive medium.After many experiments,it is found that the device based on Pt/SBT/Pt structure has excellent bipolar resistance switching property.So that the device based on Pt/SBT/Pt structure has the characteristics of ferroelectricity polarization reversal and resistance switching,which can be used to realize multistate storage.In this paper,SBT thin films are prepared by sol-gel method and the morphology and structure of the films are characterized by SEM,AFM and XRD.The ferroelectric properties of the thin films are tested by ferroelectric analyzer,and the semiconductor properties and the resistance properties of the films are analyzed by the semiconductor analyzer.The specific work and results are summarized as follows:(1)In this work,SBT thin films were prepared on Pt(111)/Ti/SiO2/Si substrates by sol-gel method.The results of comparative experiments show that the SBT films prepared at 750 ? annealing temperature have good ferroelectric properties.SEM and AFM results show that the surface of SBT films is smooth and flat,and there are no obvious cracks and defects.The roughness is about 10 nm,the thickness is 280 nm,and the grain size is about 250 nm.XRD results show that SBT thin films are polycrystalline films with highly(115)textured orientation and the lattice matching between thin film and Pt(111)substrate electrode is good.(2)Pt/SBT/Pt structure of SBT thin films was prepared by direct current sputtering.The ferroelectric properties show that the residual polarization(2Pr)of the SBT thin film tend to 35?C/cm2 and the coercive field(2EC)is approximately 248.5 kV/cm with sweep voltages of ±20 V at room temperature.Meanwhile the SBT films have no obvious fatigue phenomenon after 109 polarization reversal,and it shows good retention performance after 104s test.(3)The Pt/SBT/Pt device has excellent bipolar resistive switching performance.When the compliance currents(Icc)is 0.05 mA,its operating voltage Vset is 11.3 V,VReret is-8.5 V.The Pt/SBT/Pt devices have good cyclic tolerance.After 103 transitions between high and low resistance states,the storage window between high and low resistance states is always greater than 103.In the low resistance state,the conduction law of the device corresponds to the ohmic conduction law.The conduction law in the high resistance state is in accordance with the space charge-limited current mechanism(SCLC).The resistance transition of Pt/SBT/Pt device is based on the formation and breakage of oxygen vacancy conductive filament,but its essence is the redox reaction of oxygen vacancy.(4)The Pt/SBT/Pt device goes through four storage states in turn under the periodic voltage sweeping in a sequence of 0 V ? +14 V ?-14 V ? 0 V,and the four storage states are ferroelectric polarization upward and high resistive state(FPU+HRS),ferroelectric polarization upward and low resistive state(FPU+LRS),ferroelectric polarization downward and low resistive state(FPD+LRS),ferroelectric polarization downward and high resistive state(FPD+HRS)respectly.Forward coercive voltage(Vc),forward operating voltage(Vset),reversed coercive voltage(-Vc)and reversed operating voltage(Vreset)are the dividing points of the four storage states,that is,the switching transition voltage of the four-valued storage state.At the Vc,-Vc,Pt/SBT/Pt device occurs ferroelectricity polarization reversal.At the Vset,Vreset,Pt/SBT/Pt device occurs resistance state switching.Therefore the scanning voltage can be controlled to switch the storage state of the device to realize the writing of the stored data.(5)SBT thin film can be used as gate dielectric in field effect transistor.The ferroelectricity polarization reversal of SBT film can regulate field effect transistors to realize the on and off of transistors,The transfer characteristic curves of the devices show the shape of the butterfly curve.There are storage windows about 7 V in the gate voltage scanning range of 10 V,and the storage window shrinks with the reduction of the gate voltage scanning range. |
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