The Resistive Switching Performance Of ZnO-TM(TM=Co, Cu) Films

Binary oxide-based resistive switching memory(RRAM)has recently attracted considerable attention as a candidate for next generation nonvolatile device because of its simple structure,low cost and so on.ZnO is found to be a promising material for RRAM,not only for the wide band gap and compatibility with CMOS process,but also wide applications in electronics and optics fields.Nevertheless,there has a lot of problems in the research of RRAM,such as the influence of the switching layer and the electrode materials on the resistive switching properties and the mechanisms of RS effects are unclear until now.In this work,ZnO,ZnO-Co and ZnO-Cu films are used as switching layers.The Pt are used as metal bottom electrodes and the metal Pt,Au,Cu and Co are used as top electrodes.The structure,the resistive switching properties and the mechanism of these films are investigated.The results are summarized as follows:(1)Pt/ZnO/TE(TE=Pt,Cu,Co)devices with different thickness of ZnO films and top electrode materials were deposited.It is found that the RS properties of pure ZnO switching matrix are strongly related with the electrode metals and the ZnO layer thickness.The set voltage increases with the thickness of ZnO film.The resistive switching behaviors are a result of the synergistic interplay beween the the work function,electronegativity,atomic size and ionic size of the metal electrodes.(2)The dissimilar resistive switching properties of Pt/ZnO-Co/TE(TE=Pt,Cu,Co)devices with the above Pt/ZnO/TE(TE=Pt,Cu,Co)devices were studied.Comparing with the pure ZnO films,the ZnO-Co films exhibit stable bipolar resistive switching performance such as forming-free progress,lower set voltage and good endurance.Additionally,the dependence of various active and insert electrodes on ZnO-Co films can be weakened.This phenomenon may demonstrate a positive effect from the distributed Co nanoparticles,which serve as conduction precursors and can significantly reduce the initial resistance values.Meanwhile,the Co particles dispersed in ZnO matrix may enhance the local electric field,and then correspondingly facilitate the formation of conductive paths,leading to a better switching performance.(3)Two kinds of metallic Cu and Co nanoparticles with different intrinsic characteristics were choosed to be dispersed in ZnO matrix.It is found that the resistive switching behaviors of ZnO-based films were strongly related with the metal nanoparticles which were dispersed in the matrix.The height of the entire potential wells of ZnO-Co and ZnO-Cu films are different,which due to the difference of work function between the ZnO and metal nanopartices.As a result,the set voltages of the two films are different.In conclusion,ZnO-TM(TM=Co,Cu)switching devices with different top electrodes were designed and the influence of electrodes and switching layers on the structure and resistive switching behaviors were investigated.Meanwhile,the mechanism of the RS effects were discussed and compared.It is found that the metal nanoparticles which were dispersed in the semiconductor(insulating layer)not only can reduce the initial resistance values and power resume,but also can enhance the local electric field and facilitate the formation of the conductive paths.This study can provide essential information for improving the resistive switching performance,better understanding the switching mechanism and realizing the multibit data storage.