Resistive Switching Of BaTiO₃ Films Modified With Light Irradiation And Buffer Layers

It has been reported for a long time that the characteristics of Ba TiO₃ film resistance switching have been studied.In the research of Ba TiO₃ thin film resistance switching memory device,there is a large set/reset voltage（>1V）.The performance parameters of the resistance switching based on the MIM structure of Ba TiO₃ thin film,such as in set/reset voltage,storage window and homogeneity,are not satisfactory.Therefore,researchers began to improve the resistance switching performance of Ba TiO₃ thin films by doping and interface modification.It is remarkable that the working current and set/reset voltage of Ba TiO₃ film are improved significantly by doping or inserting buffer layer material.The resistance ratio of high/low resistance state and the retention time of the device are generally improved.In this paper,ZnO film,HfO₂ film,Al₂O₃ film and BiFeO₃ film are chosen as buffer layer.In the same position of Ba TiO₃ film,different buffer layers are inserted to form multilayer structure device.The characteristics of resistance switching before and after adding buffer layer,and the performance parameters of resistance switching under different bias voltage when different light irradiation intensity is added in the measurement process are studied.Finally,the photoelectric properties of BiFeO₃/Ba TiO₃ composite films were studied in the form of composite films.The main research contents and conclusions are as follows:（1）Firstly,Ag/BaTiO₃/Ag memory cells were prepared by magnetron sputtering.Then the resistance switching characteristics of the memory cell under different bias voltage in dark conditions are compared.The results show that with the increase of bias voltage,the bipolar resistance switching effect is more obvious.The more rapidly the process of setting/resetting under positive and negative bias changes,the more symmetrical the storage window is.When the bias voltage is 0.8V and the negative bias voltage is scanned to 0.36V,the device jumps from low resistance state to high resistance state twice.（2）Ag/BaTiO₃/ZnO/Ag memory cell was prepared by inserting ZnO buffer layer into Ba TiO₃thin film by magnetron sputtering.The characteristics of the resistance switching with different bias voltage and different light irradiation intensity are compared.The results show that the device has excellent bipolar resistance switching characteristics under different bias voltage when measured in dark.When the reading voltage is 0.22V,the resistance switching ratio of the device is greater than10³.With the increase of bias voltage,the set/reset voltage of the device increases and its distribution range is wider.V_set changes from 0.18V～0.36V to 0.3V～0.63V,V_reset changes from-0.1V～-0.2V to-0.18V～-0.35V.And the range of set/reset voltage is more obvious.Then,the I-V curves measured under different light irradiation intensities（20uw/cm²,100uw/cm² and 250uw/cm²）show very obvious bipolar resistance switching effect.With the increase of light intensity,the high/low resistance ratio of the device decreases from>10⁴ to>10,and the storage window becomes more and more asymmetric.The set/reset voltage increases and the distribution range becomes more and more dispersed.V_set changes from 0.2V～0.3V to 0.2V～0.4V,and V_reseteset changes from-0.1V～-0.2V to-0.1V～-0.16V.（3）Ag/BaTiO₃/HfO₂/Ag memory cell was prepared by inserting buffer layer HfO₂ into Ba TiO₃ thin film by magnetron sputtering.The effects of different light irradiation intensity on the resistance switching characteristics of the BaTiO₃/HfO₂ memory cell under different bias voltage are compared.The results show that the current-voltage curves of the memory cell with different bias voltages in the dark show a more obvious bipolar resistance switching effect.With the increase of bias voltage,the resistance of high resistance state becomes more and more stable.But the high/low resistance ratio is getting smaller（from 10³ to 10）.In the process of measurement,the I-V curve shows a very obvious bipolar resistance switching effect when different light irradiation intensity is added.With the increase of light irradiation intensity,the gate current of the memory cell generally increases（the change is more obvious under the positive bias voltage）.The resistance switching effect is generally smaller,but the storage window becomes more symmetrical.（4）The Ag/Ba TiO₃/Al₂O₃/Ag memory cell was prepared by radio frequency（RF）magnetron sputtering.The I-V curves of the BaTiO₃/Al₂O₃ memory cell with different bias voltage in the dark are compared.With the increase of bias voltage,the I-V curve of the device shows more obvious bipolar resistance switching effect.The set/reset voltage of the device is small,and the resistance switching ratio is 10⁴ at the reading voltage of 0.3V.（5）The Ag/Ba TiO₃/BiFeO₃/Ag memory cell was prepared by inserting buffer layer BiFeO₃film into Ba TiO₃ film by RF magnetron sputtering.And the BiFeO₃-BaTiO₃ composite film device was prepared by using BiFeO₃-Ba TiO₃ composite target.The resistance switching characteristics of Ag/BaTiO₃/BiFeO₃/Ag memory cells with different bias voltages under dark conditions are studied.The device has very obvious bipolar resistance switching effect under different bias voltage.At the reading voltage of 0.2V,the resistance switching ratio of the device is greater than 100.However,with the increase of bias voltage,the set/reset voltage distribution is more dispersed,V_set changes from 0.46V to 0.7V～1.3V,and the storage window under negative bias voltage is smaller.At last,I studied the photoelectric properties of Bi FeO₃-Ba TiO₃ composite films at different annealing temperatures.The results show that with the increase of annealing temperature,the current and the photoelectric response ratio of the device increase,so it has a very obvious photoconductivity effect.