Resistive Switching Properties Of Several Typical Metal-Oxide Semiconductor Thin Films

Current nonvolatile data memory has advantages of high-density,low-cost,fast read/write speed and low-power consumption.Facing the surge of big data,traditional data nonvolatile data memory technology may suffer great challenges in the furture.However,the scale of integrated circuit based on silicon semiconductor is close to its physical limit.Therefore,it is necessary to develop new storage technology to meet the growing demand of information storage.Among all kinds of memory technologies,resistance random access memory based on resistive switching(RS)effect is widely concerned.In this study,oxide films were prepared by magnetron sputtering and sol-gel method.The crystal structure,optical properties and electrical properties of the samples were studied by XRD,UV-Visible transmission spectrum and I-V measurement,respectively.The effects of substrate,annealing temperature and atmosphere on RS effect of samples were also studied.The main work includes the following four aspects:1.NiO thin film device was fabricated on FTO substrates by magnetron sputtering and its RS effect was studied.The device shows typical bipolar RS effect.Transition from low-resistive state(LRS)to high-resistive state(HRS)was observed under positive applied bias,which transition from HRS to LRS was observed under negative applied bias.However,the RS behavior is opposite to that reported in other literature.By comparing the differences of device structure and using the work function theory of metal electrode,above result are explained.NiO device does not show good fatigue characteristics.In the first 10 measurements,the resistance ratio of HRS/LRS reachs two orders of magnitude.In the subsequent tests,the resistance ratio decreases gradually and becomes one order of magnitude in the 25th measurement.When the number of measurements is more than 125,the resistance ratio decreases gradually to 1.Based on the analysis of the conduction mechanism,it is explained that the reason for the fatigue of the device is that the reversibility of the change of the trap energy level of NiO film under applied bias gradually disappears with the increase of the number of measurements.2.ZnO thin film devices were fabricated on different substrate by using magnetron sputtering method and sol-gel method.Good bipolar RS effect was obtained only in the device deposited on aluminum foil.The resistance variation law is the same as that of NiO film device.It is found that larger measurement range of voltage increases the resistance ratio of HRS/LRS.For ZnO thin film devices deposited on FTO/glass substrate,RS effect is studied by changing the annealing temperature and atmosphere.The experimental results show that the leakage current of ZnO film can be reduced by increasing the annealing temperature or the oxygen content in the annealing atmosphere.It is also found that UV illumination can enhance the resistive properties of ZnO thin film devices prepared by sol-gel method.Finally,it is found that the ZnO films prepared directly on mica substrate show preferred orientation along the c-axis.Although this sample does not show good RS effect,it can be used as electrode material.3.RS effect of Au/HfO₂/ZnO/mica flexible devices are studied.ZnO thin films was deposited on mica substrate by magnetron sputtering directly.The ZnO thin film shows outgoing linear I-V characteristics with current magnitude ofA.Compared with the current magnitude of m A of commercial FTO/glass substrate,it can reduce the power consumption effectively.HfO₂ thin film was deposited by sol-gel method.XRD analysis shows that the crystal structure of ZnO film is hexagonal phase,and it grows along the c-axis preferably.The crystal structure of HfO₂ film is cubic phase.Au/HfO₂/ZnO/mica devices exhibit analog-type RS.Based on the analysis of metal/semiconductor contact theory,it is found that analog-type RS is a result of the change of Schottky barrier at the interface under applied bias.A model of charge accumulation at interface was constructed to make quantitative relationship between RS effect and the charge density at the interface.The model can simulate I-V characteristics of analog-type RS effect well.Finally,the influence of bending strain on the RS effect is studied.The experimental results show that RS effect of our device are different in bending and flat condition.4.RS effect of Au/BFO/FTO/devices are studied.BFO thin films were prepared by sol-gel method.XRD analysis shows that the BFO film annealed at 500? is amorphous,and is polycrystalline when the annealing temperature is higher than 550?.The amorphous BFO thin film device shows digital-type RS effect with poor endurance.The polycrystalline BFO thin film devices show analog-type RS effect as similar as HfO₂ Thin film devices.This difference may be due to the Schottky barrier layer formed by the contact between polycrystalline BFO film and the electrode.The conduction characteristics are controlled by the interface barrier layer mainly.Therefore,the RS effect are originated from the change of the interface resistance.However,the resistance characteristics of amorphous BFO thin film devices are derived from the whole BFO layer.Finally,the photoelectric characteristics of BFO thin film devices annealed at 600? and 650? are studied.