The Influence Of Doping On The Resistive Performance Of ZnO Film And Preparation Of Resistive Random Access Memory

In recent years,memorys have played an important role in information industry with the continuous development of information technology.As the size of memory continues to shrink,traditional Flash devices have encountered problems such as gate leakage and slow reading and writing speeds.So the non-volatile resistive random access memory(RRAM)has attracted great attention due to its advantages such as simple preparation process,high storage density,fast reading and writing speed,and compatibility with CMOS technology.Among many resistive materials,ZnO materials have the advantages of sufficient raw materials,simple preparation process,low price and non-toxicity,etc.Therefore,ZnO is one of the ideal candidate materials for the preparation of RRAM.In order to improve the operating voltage,uniformity and other resistive performance of ZnO RRAM,doping technology is selected.However,the selection of doping elements is not clear at present,and the mechanism of the influence of doping elements on the resistive performance is not conclusive.The first-principles calculation method based on density functional theory(DFT)is adopted to analyze the influence of doping elements to ZnO theoretically in this work.Then appropriate doping elements are selected to better improve the resistive performance.Finally,ZnO-based RRAM is prepared experimentally to verify the results of theoretical research.The main research contents and results of this article are as follows:Six metal atoms(Ga,Al,Cu,Ag,Mn,Ni)were doped respectively into the ZnO supercell containing oxygen vacancies.The results show that the energy band gap of ZnO reduced after doping.When Mn or Ni which are transition metal elements are doped,the energy band gap of ZnO disappears,the semi-metallic appears,and the mobility of electrons is greater.These indicating that the operating voltage of the device will be smaller after doping Mn or Ni.In addition,P-type dopants Cu and Ag can more effectively reduce the formation energy of oxygen vacancies,which indicating that the Forming voltage can be reduced.N-type dopants(Ga,Al,Mn,Ni)have weaker auxiliary effects,and the oxygen vacancy formation energy of Ni doping is the smallest in the four elements.According to the comprehensive consideration of the theoretical calculation results,the effect of improving resistance switching performance is best when Ni doping.Therefore,the changes of resistive performance and conduction mechanism of ZnO RRAM are observed experimentally after Ni doping.The ZnO film was prepared by magnetron sputtering in the experiment.First,the single factor method was used to optimize the experimental factors including substrate temperature,sputtering pressure and sputtering power.Finally,The optimized process parameters were determined as follows: sputtering power is 120 W,working pressure is 1 Pa and substrate temperature is 30 ?.The Ti/ZnO/ITO and Ti/ZnO:Ni/ITO devices were prepared under optimized process parameters,and the resistive performance of the devices was tested by semiconductor parameter analyzer.The results show that the Forming voltage and the Set voltage of the devices are decreased after Ni doping.Ni-doping also reduces the dispersion of the device's Forming voltage.After Ni doping,the devices can still achieve mstable conversion,has a good resistance switching window,and has a more uniform and stable high resistance distribution.Doping don't change the conduction mechanism of ZnO RRAM.The high resistance state follows the space-charge limited conductivity(SCLC)and the low resistance state follows Ohmic conduction.