The Resistance Switching Behaviors Of CoFe₂O₄ And SnFe₂O₄ Thin Films

As a powerful competitor to the next-generation non-volatile memory,resistive random access memory?RRAM?has the advantage of being compatible with current Si-based CMOS process,simple structure,fast erase speed and high storage density.Therefore,it has attracted tremendous attention from the researchers and electronic manufacturers.CoFe₂O₄?CFO?is a kind of traditional spinel-based ferrites,and it has been widely used in the fields of resonators,sensors,microwave devices,and electronic devices.But there is still relatively less research on its resistance switching?RS?behavior.In fact,the investigation of CFO-based RS material will provide meaningful insights.On the one hand,the unique magneto-electrical properties of CFO provide the possibility of multilevel storage.On the other hand,more oxygen vacancies?V_O?could be generated due to the existence of tunable valence states of the transition metals(Fe^2+/3+and Co^2+/3+),and thus provide more constituent elements for the formation of conductive filaments?CFs?.However,due to the high random nature in the formation and rupture of CFs,CFO devices still suffer from several technical issues such as a large distribution of set voltage and high power consumption in the reset process,which has limited the development of CFO-based RS material.In this paper,bilayer structure was developed to improve the RS characteristics of CFO thin films.First,the base layer with different crystalline,morphologies,and conductive properties was prepared through controlling the oxygen partial pressure by molecular beam epitaxy?MBE?method.Furthermore,the effect of MBE inserted layer on the RS properties and optimization mechanism of CFO thin films was investigated.On the other hand,we explored the thickness effect on the RS behavior of SnFe₂O₄?SFO?thin films.On the basis of the CFs model,we explained the variation of the RS behavior in SFO thin films.The results show that bilayer structure plays an important role in the optimization of RS behavior of CFO thin films.On the one hand,the MBE layer acts as V_O reservoirs,and creates preferred V_O transport channels.On the other hand,the local-electric-field-enhancement effect around the MBE nano-bumps greatly reduces the randomness nature in the formation and rupture of CFs.Thus,the bilayer CFO device shows more stable RS parameters.In addition,the investigation of Pt/SFO/Pt devices indicates that the thickness of SFO thin films performs a significant role in the RS properties.As the spin-coating cycles increase,the thicker SFO film needs a relative larger forming voltage,which will induce more V_O in the film to start the RS process.The device with the easy availability of the V_O will contribute to the stable switching behavior.