Research On Resistive Characteristics Of HfO2-based RRAM

As the traditional memory represented by flash has encountered technical bottlenecks,many new memories have been proposed in which the resistive memory?RRAM?,by virtue of its simple structure,low voltage,low power consumption,fast operation and scalability,COMS technology compatibility,etc,so as to become the focus of people's research.However,the current micro-mechanism for the RRAM memory resistance phenomenon is different.There are many of the theory of the phenomenon of resistance.The conductive filament model is gradually recognized by most people.The conductive filament model is divided into two cases:one is the metal conductive channel formed by the migration of the doped metal element;the other is the oxygen vacancy conductive filament formed by the generation and migration of the intrinsic defect oxygen vacancy.Many experiments have proved these two kinds of resistance mechanism,and these two kinds of defects to improve the macro characteristics of RRAM devices have a great effect.Therefore,we deeply study the role of the two kinds of defects in the resistive system,which is very important for understanding the mechanism of RRAM device and improving the macroscopic performance of RRAM devices.In order to study the microcosmic aspect of oxygen vacancies in RRAM,we first study the clusters of oxygen vacancies and clusters formation energies to obtain the most easily formed orientations and cluster shapes of local oxygen vacancies;then,the optimal orientation and the optimal shape of the oxygen vacancies are obtained.The microcosmic principle of the oxygen vacancy conductive filament is illustrated by the analysis of the composition of the conductive filament.The migration barrier of oxygen vacancy is calculated,and the migration path of single oxygen vacancy in HfO₂ super-cell is analyzed.These detailed analyzes and calculations will help to improve some of the device's macro characteristics.For example,in the preparation of RRAM based on HfO₂ materials,by controlling the direction and shape of the conductive filament can reduce the formation of RRAM device voltage,improve the storage stability of the device.In order to study the effect of oxygen vacancy conductive filament and metal conductive filament on the performance of RRAM,we first discuss the existence of metal Ni in the HfO₂,which can be calculated from the formation energy of systems.And then the optimum concentration of Ni conductive filaments in HfO₂ was obtained by comparing the formation energies of the five Ni doped concentration models,the density of partial charge states,and the highest isosurface values.The influence of the presence of oxygen vacancies on the Ni conductive filaments and the effect of Ni doped on the oxygen vacancies were discussed.First,we analyze the effect of oxygen vacancies on the uniformity of the metal conductive filament by calculating the isosurface plots of partial charge density of the system.By analyzing the density and the highest isosurface value of the system,the oxygen vacancy conductive filament has the effect of aggregation.And the doped Ni can control formation and disconnection of oxygen vacancy conductive filament.This is advantageous to improve the ratio of the switching devices and the stability of RRAM.Finally,the influence of the relative positions of the two filaments is considered.It is found that the interaction is the largest when the two kind of conductive filaments are closest to each other.At this time,a stable conductive filament is formed in the system,and the stability is the strongest.When the relative position of oxygen vacancy is far away,the influence between oxygen vacancy and Ni is weak.And two conductive filaments can be obtained when the position of the metal Ni is adjacent to the oxygen vacancy,but the electrical conductivity of the device is the worst.In summary,the influence of two kinds of conductive filaments in RRAM devices based on HfO₂ resistive materials are discussed in detail.The results of this paper provide a method and enlightenment for improving the macroscopic properties of the memory based on oxide,which has a certain theoretical guidance for the experimental research.