Research On Performance Of Flexible Resistive Memory Based On TiO₂

With the development of the technology,intelligent electronics are constantly being updated.In recent years,the demand for flexible electronic devices has been increasing,while the traditional memories are no longer suitable for this need.Resistive random access memory(RRAM),as a powerful competitor of the next-generation memory,has become a research hotspot for flexible memory.Flexible memory refers to a new type of memory which built on a flexible substrate.It can maintain the high performance and high reliability during mechanical deformation such as stretching and bending.Flexible RRAM devices are made up of a simple sandwich structure,namely electrodes,resistive layers and electrodes.This requires that the three layers of RRAM material must maintain structural integrity and performance stability during different stress conditions.In this paper,we mainly study the effect of the resistive layer on flexible RRAM devices.Among the many resistive memory,titanium oxide RRAM not only has the advantages of non-volatile RRAM,simple structure,low power consumption and high speed,but also the stability of the device is greatly improved by the two-layered medium structure.All these advantages make TiO2 available for the preparation of flexible memory.But whether different titanium oxide crystal orientations affect the performance of RRAM devices or not.And whether the performance of the device is stable in different temperatures or different deformation times.In order to figure out these questions,in this paper we used molecular dynamics and first principles methods,explore the influence of temperature on the mechanical properties of titanium oxide and clarified the temperature range in which the device can work stably.Then we calculated the mechanical properties and resistance of the material during different deformation times.In the next step,the effects of different deformation times on the mechanical and resistive properties of the materials were calculated to determine the feasibility of titanium oxide as a flexible resistive memory.The mechanical and electrical properties of the TiO2 were studied by molecular dynamics and first principles.Firstly,the potential energy,elastic constant,stress-strain curve,Poisson's ratio and Young's modulus of the<001>crystal orientation TiO2 structure at different temperatures were calculated by LAMMPS.It is found that the average potential energy of the system becomes larger as the temperature increases,which means that the atom becomes more active when the temperature rises.Then we analyzed the mechanical properties of<001>crystal orientation TiO2 at different temperatures.It is shown that the mechanical properties of TiO2 in the<001>crystal orientation can be kept stable around room temperature.Finally,we calculated the stress-strain curve of TiO2 under different tensile cycles.By comparing the elastic limit,Young's modulus and Poisson's ratio of each tensile,the trend of the mechanical properties of the material with the number of deformations was analyzed.These detailed calculations and analysis will help to improve some of the macroscopic characteristics of the device.For example,when preparing a flexible resistive memory based on TiO2 material,the range of normal operating temperature of the device can be determined,and the maximum deformation cycles can be known.In order to investigate the influence of strain on the electrical properties of flexible RRAM we used the first-principles method which based on density functional theory to calculate the resistive properties of TiO2 along the<001>direction,and discuss its changes at different elongation ratios.First,by controlling the time when the stress was applied to the model,we obtained 10 models with different strain rates.By calculating the I-V curve of each model's SET process,we obtained the maximum strain when the device can maintain a stable SET voltage.In the analysis of the I-V curve,the peak current of the SET process decreases monotonically with the increase of the strain rate.In order to investigate the cause of the peak current descend,we analyzed the state density of the system.The reason why the peak current decreased is that the curvature of the conduction band bottom increases,the effective mass of the electron increases,and the hole concentration decreases.These two reasons lead to the a continuous decrease in the peak current of TiO2.In summary,the effect of stretching on the flexibility and electrical properties of the device is studied in detail for the flexible RRAM based on TiO2,which plays a theoretical guiding role for related experimental research.