Study On Switching Effect And Conductive Mechanism Of Ni-Zn Ferrite Thin Film Memristor

At present,the size of CMOS memory is close to the molar limit,and the problem of’memory wall’has become increasingly prominent,which has become a bottleneck restricting the future sustainable development.Therefore,it is imperative to develop new memory technologies and computing devices with larger capacity and higher processing speed,and the invention of memristors provides new ideas for researchers.At present,the development direction of memristive devices includes many fields and has wide application value.In order to improve the performance of memristors,researchers have explored many memristor materials,among which ferrite materials are the focus of current research.In this paper,the memristor is prepared by nickel zinc ferrite material,and three different experimental schemes are used to study the NZFO composite film memristor under different conditions.Then the composition,structure,morphology and resistance switching performance of the prepared samples were tested based on various characterization techniques.The main research results are as follows:（1）The relationship between deposition process parameters and NZFO film switching effect.Firstly,NZFO thin films with different thicknesses were deposited on alumina substrates by pulsed laser deposition to obtain a thin film memristor with Pt/NZFO/Pt sandwich structure.The relationship between resistance switching characteristics and NZFO film thickness was studied in detail,and the mechanism of resistance switching was discussed.The structural characterization shows that the thickness of the prepared NZFO film varies continuously from 210 nm to 600 nm,and the I-V measurement confirms that the NZFO film with a thickness of 400 nm has a stable set/reset voltage,a large memory window and good retention.Studies have shown that the resistance switching mechanism is mainly determined by the formation and rupture of the conductive path,and the resistance switching behavior of Pt/NZFO/Pt can be adjusted by the thickness of the NZFO film,indicating that the thickness also affects the resistance switching effect.Secondly,the relationship between the prepared oxygen pressure and the resistance switching characteristics of the thin film memristor is studied in detail,and the resistance switching mechanism is further explored.The test results show that the NZFO particles increase with the increase of oxygen pressure.At the same time,the I-V measurement shows that the NZFO film prepared at 0.1 Pa has a stable set/reset voltage,a large memory window and good retention.Studies have shown that the conductive path is composed of oxygen vacancies,and the resistance switching behavior of Pt/NZFO/Pt can be adjusted by preparing oxygen pressure,indicating that oxygen pressure will also affect the resistance switching effect.In summary,oxygen vacancies play a crucial role in the process of switching behavior,and oxygen vacancies can be regulated by changing the preparation oxygen pressure and film thickness.Finally,the process parameters of NZFO thin film memristor with high retention,high memristive window and high stability are clarified,and the process technology of high memristive performance is formed.（2）The effect of Ni and Ti buffer layers on the resistance switching characteristics of NZFO thin film memristors.NZFO thin film memristors with different buffer layers（Ni,Ti）were prepared by pulsed laser deposition.The structural characterization shows that Ti and Ni buffer layers can improve the surface morphology of the composite film,reduce the porosity of the film interface,and improve the quality of the film.I-V measurements confirm that the composite film with Ti buffer layer has good resistance switching behavior,including stable set/reset voltage,large memory window,good retention and excellent repeatability.This is attributed to the buffer layer enhances the adhesion between the electrode and the NZFO layer,making the formation and rupture of the filament very stable on the buffer layer.In contrast,the composite film with Ni buffer layer only has a smaller memory window.It may be that the Ni element in the Ni buffer layer enters the NZFO layer and acts as a reducing agent for other elements in the NZFO layer,resulting in an increase in the content of Fe²⁺,which is closely related to oxygen vacancies.This change will accelerate the switching process.In summary,adding a buffer layer can improve the stability of the resistance switch,but will reduce the memory window.This study shows that it is feasible to improve the performance of memristors by adding metal buffer layers,and also provides a theoretical basis for the future research of complex structure memristors.（3）The effect of Mn ion doping on the resistance switching characteristics of NZFO thin film memristors.Firstly,NZFO films with different Mn ion doping concentrations were prepared by pulsed laser deposition.The structural characterization shows that Mn ion doping does not have a significant effect on the crystal structure of the NZFO film,but will directly affect the content of oxygen vacancies in the sample.At the same time,I-V measurements show that the NZFO thin film memristor with Mn substitution of x=0.15 has good endurance time（100 cycles）,high data retention and stable set/reset voltage.Studies have shown that Mn doping plays an important role in the generation and distribution of oxygen vacancies,and appropriate Mn doping can optimize the resistance switching behavior.In summary,doping an appropriate amount of Mn element in ferrite can improve the stability and retention of resistance switching.This study shows that it is feasible to improve the performance of memristors by metal ion doping,and high-performance thin film memristors can be prepared.