Study Of Resistive Switching Characteristics On Copper Doped Zinc Oxide Thin Film

Resistance random access memory is considered as one of the most potential competitors which could replace the traditional flash memory and become the next generation of nonvolatile high density memory, because of its low operating voltage, high read and write speed, long retention time, high storage density, and good prospects for miniaturization. Currently, resistive switching behavior has been observed in different materials, such as organics, solid electrolyte, perovskite compounds and transition metal oxides. As a direct wide-gap semiconductor material, ZnO shows excellent resistive switching behavior. In order to further improve the performance of resistive switching, researchers tried to dope Mn and Cu in ZnO and have made a certain achievements. However, there is still some controversy on the conduction mechanism of ZnO based resistive switching device.Copper doped ZnO(Cu:ZnO) ceramic targets with different doping concentration were prepared, then Cu:ZnO flims were grown by RF magnetron sputtering and resistive switching devices with sandwich structure were fabricated. In addition, the conduction mechanism was discussed on both body effect and interface effect on Cu:ZnO resistive switching device.For the research of Body effect, the influence of doping concentration on resistive switching behavior was studied firstly, the experimental results revealed that Cu:ZnO resistive switching with 2at% copper dop showed the best performance. In the optimization of process conditions, we found Cu:ZnO films grown at 450 ℃ substrate temperature exhibited excellent edurance characteristic due to its good crystallization. In addition, the influences of atmosphere and top electrode size on resistive switching phenomenon were investigated. The results indicated that oxygen vacancies played a key role in the resistive switching process, the larger oxygen vacancy concentration, the smaller switching ratio and threshold voltage. The electrical tests were done with different size of top electrode samples, and it shows that: the on-state currents of these devices could not be affected by electrode size, but the off-state currents increased with the electrode size.For the research of the interface effect, top metal electrodes with different work function such as Zn, Cu and Au were fabricated by thermal evaporation, and then the contact types between the metal and semiconductor were analyzed and discussed. The devices showed resistive switching behavior only when Schottky contact formed on the interface between the metal and semiconductor. Furthermore, annealing in argon would decrease the resistive switching ratio of these devices obviously. From these results, we confirmed that the interface barrier was a necessary condition for the formation of resistive switching phenomenon. Cu/CuO/ZnO/AZO double layer structure and the Cu/ZnO/AZO single layer structure resistive switching devices were fabricated, then their resistive switching characteristics were tested. The results show that double layer devices possess larger switch ratio and more stable cycle performance than single layer structure devices, meanwhile, the double layer devices work with higher threshold voltage and wider distribution voltage range, and both of them can keep retention very well.