The Mechanism Of Resistance Switching In Ga₂O₃-Based Resistance Random Access Memory:a Theoretical Study

In the new generation of non-volatile memory,RRAM has attracted the attention of researchers due to its simple MIM structure,low power consumption,and good scalability.So far,there have been many materials that can exhibit resistive switching characteristics under the electric field or electrical excitation.Among them,binary metal oxides are widely used in the researches related to resistive random access memory due to their simple structure,low cost,and easy control of composition,and?-Ga₂O₃ has the characteristics of high thermal stability,chemical stability,low carrier mobility,wide band gap and sensitivity to oxygen,making it a promising resistive material.For more than 50 years,researchers have never stopped exploring the micro-mechanism of resistive switching behavior,but the resistive switching mechanism is still controversial,and there is no unified view.Nevertheless,in binary metal oxide RRAM,the theory of conductive filaments is accepted by most researchers.However,in the?-Ga₂O₃ RRAM,the resistance switching behavior and resistance switching mechanism dominated by oxygen vacancies((1)are still not clear enough.Therefore,the work in this paper thoroughly studied the role of oxygen vacancies((1)in the?-Ga₂O₃ RS system through the first principles.First,this paper has systematically studied the formation process of oxygen vacancy conductive filaments((1-)in the?-Ga₂O₃ RRAM.The results show that there are at least three oxygen vacancy conductive filaments with different low resistance states(LRS)in?-Ga₂O₃ RRAM,indicating its great potential in multilevel storage applications.In addition,since the charge density of single oxygen vacancies is ellipsoidal distribution,and the formation energy of single-component oxygen vacancy clusters is lower than that of mixed-component oxygen vacancy clusters,the conductive filaments tend to be formed along the[010]direction by single-component oxygen vacancy clusters,rather than by mixed-component oxygen vacancy clusters.Moreover,the lowest migration barrier E_migs and the lowest long-range diffusion activation energy E_acts of the three oxygen vacancies in?-Ga₂O₃are also inconsistent,and the migration barrier and activation energy of these oxygen vacancies in the+2 charge state((1)are also lower than those in the neutral state.It means that the formation voltage and operating voltage of conductive filaments with different compositions are also inconsistent.In other words,when there are three kinds of oxygen vacancies(1,(1 and(1 in the?-Ga₂O₃ crystal at the same time,the multilevel oxygen vacancy conductive filaments can be formed in turn by adjusting the magnitude of the applied voltage on the?-Ga₂O₃ RRAM.Meanwhile,the forward migration energy of(1was distinguished from the reversed migration path,so that the conductive filament formation and rupture were not an inverse process in experiment.The detailed mechanisms were revealed by the charge density and migration process of these(1.These results not only understood the(1 conductive filament in?-Ga₂O₃ RRAM,but also predicted the potential multilevel storage application for?-Ga₂O₃ memory.Secondly,the influence of different metal dopants on the oxygen vacancies in?-Ga₂O₃ was studied.In this paper,according to the number of valence electrons of the doped metal,the doping is divided into three doping types:p-type,Ga-type and n-type.Then,the effects of Mg,Zn,Al,In,Ti,Sn on the formation energy of oxygen vacancies,migration barriers and electronic structure of filaments in the?-Ga₂O₃ system were discussed.It can be found that regardless of the distance between the oxygen vacancy or its cluster and the doping site,p-type doping can significantly reduce the formation energy and migration barrier of oxygen vacancy in the crystal,and effectively promote the formation of oxygen vacancy conductive filament and reduce the operating voltage of the device;In Ga-type and n-type doping,due to the influence of distance,the change curve of oxygen vacancy formation energy far away from the doping site is relatively smooth,and formation energy are larger than the formation energy in the undoped system.For oxygen vacancies close to the doping site,In and Sn show a tendency to promote the formation of oxygen vacancy conductive filaments near the dopant,while Al and Ti increase the difficulty of the formation of oxygen vacancy conductive filaments,and it is not easy to form oxygen vacancy conductive filaments near the dopant.Moreover,Ga-type doping has an adverse effect on the migration of oxygen vacancies.And n-type doping can also reduce the migration barrier of oxygen vacancies to a certain extent.It is worth noting that if the migration of oxygen vacancies is considered from a dynamic perspective,it can be found that Zn,Mg,In and Sn have a tendency to attract oxygen vacancies to diffuse toward them,while Al and Ti have a tendency to drive out oxygen vacancies.Especially for the In-doped system,the migration barrier for oxygen vacancies to diffuse toward it is smaller than the corresponding migration barrier in the undoped system,and the migration barrier for oxygen vacancies to diffuse away from In atom is larger than the corresponding migration barrier in the undoped system,indicating that In doping greatly limits the spatial distribution of oxygen vacancies and can improve the stability of device data storage.Accordingly,this work provides theoretical guidance for the specific selection of metal dopants in?-Ga₂O₃ RRAM devices.