The Resistive Switching Performance Of ZnO-and BN- Based Thin Films

Resistive random access memory has recently attracted considerable attention as a candidate for next-generation nonvolatile memory devices because of its advantanges such as simple structure,small cell,high-density integration,and good endurance.The present studies mainly focus on exploring the new resistive switching(RS)materials,optimizing the RS performance,and studying the underlying mechanisms.In this paper,ZnO and BN are chosen as the switching matrixes,a series of ZnO-and BN-based films were fabricated by a magnetron sputtering technique.And the effect of doping and electrode materials on RS properties and the related mechanisms are investigated.(1)Different metal(Mn,Cu,Co)nanoparticles dispersed ZnO films were designed and fabricated.And their RS properties are compared.It is found that the RS behaviors of ZnO-based films were strongly related with the doping metal nanoparticles.The phenomena can be explained by the different barrier heights of the potential well,formed by difference of the work functions between doping metal and ZnO.The metallic behavior of ZnO-Cu film at low resistance state(LRS)means that its RS may result from the formation of metallic Cu conductive filaments;Whereas the semiconductive behaviors of ZnO-Co and ZnO-Mn films at LRS imply that their RS properties may be not related with metallic conductive filaments.In order to further explore the related mechanism,a Co/ZnO/Co sample with Co as top and bottom electrodes is designed.The conductivity,magnetic properties and magnetoresistance(MR)of the sample during switching from high resistance state(HRS)to LRS are measured.The results shows that the semiconductivity of the sample,the larger saturation magnetization(M_s)of the sample at HRS than one at LRS.And no MR can be observed.The phenomena further illuminate no clear migration of the Co atoms during RS process.The accumulation of oxygen vancancies due to the migration of oxygen ions may be responsible for the RS prtoperties.(2)Both Pt/BN/Co samples with differet BN layer thicknesses and Pt/BN/M(M=Cu,Co,Au)samples with different top electrodes are designed and deposited.They exhibit bipolar RS behaviours.The setting voltages are increased with increasing BN layer thickness.Besides of the BN layer thicknesses,the RS properties are strongly related with the instrinstic characteristics of the electrode materials such work function and electronegativity etc.We also designed a Pt/BN-Co/Au samples with Co nanoparticles dispersed ZnO film as the matrix.The small setting voltage of the Pt/BN-Co/Au sample compared with the Pt/BN/Au one may be due to the reduction of the initial resistance of BN-Co thin film by Co doping.Moreover,the existence of Co nanoparticles in the ZnO switching matrix can enhance the local electrical feld to some extent,decrease the operating voltages,and correspondingly reduce the power consumption.By analyzing XPS result of the Pt/BN/Co sample,comparing the M_ss of Pt/BN/Co sample with Pt/BN-Co/Au one,it is found that the accumulation of nitrogen vancancies due to the migration of nitrogen ions may be responsible for the RS of the BN-based samples.In conclusion,a series of RS samples with pure ZnO,BN films and metallic nanoparticles dispersed ZnO and BN films as matrixes,several kinds of metals as electrodes are designed and deposited.Their microstructures,RS and magnetic properties are explored.It is found that metallic Cu conductive filaments can be responsible for RS of the ZnO-and BN-based sample with Cu as the dispersed nanoparticles or electrode.Whereas,for the ZnO-and BN-based sample with Co,Mn,Au etc.as the dispersed nanoparticles or electrodes,their RS may be related with the accumulation of oxygen vacancies or nitrogen ones due to the migration of oxygen ions or nitrogen ones.Additionally,for the ZnO-and BN-based samples with ferromagnetic Co as the dispersed nanoparticles or electrodes,their M_ss can be modulated during RS process.Therefore,the study can supply a clue for searching novel RS materials,designing mulfi-functional devices,and exploring the related mechanisms in future.