Research On Defect Control Of SrTiO₃ Material's Resistive Storage Performance

Although Leon O.Chua had put forward the concept of memory resistor in 1971,the foreign research boom of memory resistor began in 2008,which was based on TiO₂ material reported by Hewlett-Packard.In 2010 the academic circles in our country introduced memory resistor for the first time on a formal occasion.Although it was just an introductory report,it stimulated the domestic academic community's interest in memory resistor research.In 2009,there was only one master's dissertation devoted to introducing memory resistor,but by 2012,this number had increased to 11.Memristors have the advantages of long lifetime,low power consumption and high storage density.Memristor-based resistive switching has important application prospects in digital logic circuits,analog circuits and neural engineering.The resistance switching phenomenon of barium titanate has extremely high stability,fast response time,and can maintain the state before power off after power off and the potential for multi-level storage,and is a candidate material for memristors with great potential for application.However,there are various explanations for the reasons of electrical resistance,and even for the same materials,the interpretation of resistance changes cannot be unified.Therefore,the investigation of the resistance change mechanism is a very important issue.In this paper,strontium titanate?STO?is selected as the research object.Through the doping control of niobium?Nb?,neodymium?Nd?,lanthanum?La?and iron?Fe?,the influence of defects caused by doping on the resistance change properties of the material is investigated.The content of this paper is as follows:1 Through the doping regulation of Nb,the influence of defects caused by doping on the resistance change properties of the material is investigated.The 0.05wt%NbSTO and 0.7wt%NbSTO single crystals are selected as the research object.By XRD,Hall,XPS,Raman devices,EPR and other methods to explore the similarities and differences of different concentrations of niobium doped strontium titanate single crystal.It is found that the doping concentration has an effect on the surface defects of the single crystal.Hall test results show that the carrier concentration values of 0.05wt%NbSTO and 0.7wt%NbSTO single crystal are 1.36×10¹⁸cm^-33 and 1.06×10²⁰cm^-3,respectively.XPS and EPR characterization confirm the presence of oxygen vacancies in the single crystal.In addition,when the Pt electrode is plated on NbSTO,its EPR signal is significantly increased,indicating that the EPR active center at the Pt/NbSTO interface increased.The hole center is positively charged and can act as an electron capture center.After characterizing the single crystal,a Pt/NbSTO/In structure device is prepared.We find that the doping concentration has a great influence on the electrical properties of the device through the I-V test and the R-V test.In particular,the R-V curve of the Pt/0.05wt%NbSTO/In device is significantly different from the R-V curve of the Pt/0.7wt%NbSTO/In device.Base on the above test results,we investigate and analyze the internal resistance change mechanism,and believe that the resistance change is due to the capture and decapture process of electrons.The oxygen vacancy is the electron capture center.Combined with the test results,the basic physical change process is described.2 Through the doping control of La and Nd,the resistive properties of the material are explored.Selecting LaSTO and NdSTO single crystals as research objects.We performed electrical performance tests on the Pt/LaSTO devices and found that the devices exhibited electrical resistance.Comparing the EPR test results of LaSTO single crystals with NbSTO single crystals combined with I-V fitting analysis,we believe that the resistance change mechanism of Pt/LaSTO devices is the same as that of Pt/NbSTO,both of which originate from the change of the interface barrier.In addition,while testing the negative voltage region I-V of the Pt/NdSTO/In device,the pulse voltage magnitude and the pulse voltage time are changed.Through the test results,it is found that changing the size of the write voltage can realize a series of intermediate states,and adjusting the write pulse value and pulse time can achieve multi-level storage.3 Whether it is NbSTO,NdSTO or LaSTO devices,they are all N-type semiconductors.Therefore,we also consider changing the doping type of barium titanate and choosing P-type semiconductor for research.We use PLD technology to grow FeSTO thin film on NbSTO single crystal.Pt/FeSTO/0.7wt%NbSTO/In devices and Pt/FeSTO/0.05wt%NbSTO/In devices are prepared.AFM characterization results show that the film is of good quality.I-V test results show resistive storage performance.The C-V test results show that the device has a positively charged interface defect state,and the charge and discharge of the defect state causes the interface depletion layer to change.