Oxygen Vacancy Engineered Performance Of Rutile TiO₂-based Resistive Switching Memory

With the advent of the era of big data analysis and artificial intelligence,there is a growing need for research in the field of new solid-state storage devices and computing architectures.At present,resistive memory mainly includes ferroelectric memory,magnetoresistive memory,phase change memory and resistive memory.Among these memories,TiO₂ resistive memory has become one of the representatives of new-memory because of its simple device structure,low power consumption and well data retention performance.However,some noticeable problems lie in the current TiO₂ resistive memory,such as low switching voltage ratio,poor cycle tolerance,and unclear resistance switching mechanism,which makes the integration and large-scale application of TiO₂ resistive memory still facing challenges.Some studies suggest that the rutile TiO₂ is helpful to improve the performance of resistive memory,but it is necessary to further optimize the preparation technology,and explore its structure and performance regulation mechanism.Based on this,this paper takes the rutile TiO₂ thin film as the research object..First,in order to make the electrons in the device more easily transported in the vertical direction,we explore the preparation process of nanorod array rutile TiO₂ thin film,and study the key factors affecting its growth.Secondly,the oxygen vacancies of the TiO₂ film were regulated by ultraviolet(UV)light treatment for different times.Subsequently,the resistive memory devices with a structure of Ag/TiO₂/FTO were fabricated with nanorod array rutile TiO₂ film as the dielectric layer and fluorine-doped tin oxide(FTO)conductive glass as the bottom electrode.Finally,the performances of different resistive memory devices are characterized and analyzed,and the mechanism of the effect of oxygen vacancies on the device performances is revealed.The main research contents of this paper are as follows:(1)We explore the preparation techniques of nanorod array rutile TiO₂ thin films by sol-gel method,slurry method and hydrothermal method,respectively.The results show that the sol-gel method cannot form rutile TiO₂ under the annealing condition of 600?in terms of crystal phase control,which is not conducive to its large-scale application in devices,while the rutile TiO₂ films with higher crystallinity can be prepared under mild conditions by the slurry method and the hydrothermal method.In terms of film morphology and structure control,the films prepared by the slurry method are stacked with disordered nanorod-like rutile TiO₂,and their continuity and uniformity are poor.The nanorod array rutile TiO₂ film with uniform specifications are successfully prepared only by the hydrothermal method.In addition,we study the effects of different placement methods of FTO,hydrothermal time and annealing temperature on the formation of TiO₂ thin films.The results show that vertical placement of FTO,hydrothermal treatment for more than two hours,and the annealing temperature of 450?are the most favorable for the growth of nanorod array rutile TiO₂ thin films.Moreover,X-ray diffraction and X-ray energy spectrometer analysis show that the prepared nanorod array TiO₂are uniformly arranged pure rutile crystal structure.(2)In addition,the resistive memory devices with Ag/TiO₂/FTO structure are designed and fabricated,and their performances are characterized and analyzed.The results show that these devices display a typical bipolar resistive switching characteristic.Then,we study the influence rule and action mechanism of UV light on TiO₂ thin films treated with different time on the performance of resistive memory.The results show that the optimal devices are obtained after UV treatment for 25 min.Compared with the reference devices,the optimal devices treated with UV light exhibits the advantages of forming-free state and high uniformity,and their On/Off ratio are increased by 5.6 times.Finally,the XPS is used to analyze the mechanism of UV irradiation to improve device performance.The results show that UV light irradiation reduced the concentration of oxygen vacancy of the TiO₂film,which is the main reason for enhancing the stability of the resistive switching process and reducing the power consumption of the resistive memory.Moreover,the conduction mechanism of the devices is explored by redrawing and fitting the I-V curve of the device.The results show that the Space Charge Limited Current and Ohmic Contact are mainly responsible for the resistance-switching.Comprehensive analysis,the electrochemical and thermochemical modes can be employed to explain the resistive switching behavior.