Studies On The Resistive Switching Properties Of SrTiO₃ Films

The ultimate nonvolatile data memory (NVM) should has characteristics such as high-density and low cost, fast write and read access, low energy operation,and high performance with respect to endurance (write cyclability) and retention. Today, Si -based Flash memory devices represent the most prominent NVM because of their high density and low fabrication costs. However, Flash suffers from low endurance, low write speed, and high voltages required for the write operations. Ferroelectric random access memory (FeRAM) and magneto-resistive random access memory (MRAM) cover niche markets for special applications. One reason among several others is that FeRAM as well as conventional MRAM exhibit technological and inherent problems in the scalability, i.e., in achieving the same density as Flash. To overcome the problems of current NVM, a variety of alternative memory is explored. Most notably, NVMs based on electrically switchable resistance have attracted considerable attention, often summarized under the umbrella term resistance (switching) random access memory, short RRAM. The A and B sites in Perovskite metal oxide could be easily replaced by other atoms, which may improve the properties of the film, causing great interests of scientists. The aims of this paper focus on resistive switching properties of pure SrTiO₃ film and La and V doped SrTiO₃, respectively.In the first chapter, the research progress of RRAM in recent years and the mechanism of resistance switching and the leakage current were introduced. At the end of this chapter the basis of this selected topics were explained. In the second chapter, the principle of sol-gel method was introduced as well as the experimental equipment and process. The configuration process of precursor solution of factors and considerations were also discussed in detail. Finally we draw the best experiment scheme.The details about the SrTiO₃ oxide thin films were deposited on Pt/Ti/SiO₂/Si by Sol-Gel method with high temperature annealing method is illustrated in chapters 3. We have studied the surface morphology, film thickness and chemistry value by atomic force microscope (AFM), scanning electron microscope (SEM), X-ray diffraction (XRD). The electrical measurement was performed by Keithley 4200-SCS semiconductor parameter analyzer. Setting a low compliance leads to the bipolar resistive switching, when Icc increases to 0.1 mA, soft breakdown occurs in the film and the Bipolar Resistive Switching (BRS) behavior disappears, while the unipolar resistive switching appears. The BRS behavior may be controlled by the interface and the URS behavior is likely bulk-controlled which can be explained by the filamentary model. The conduction mechanism of BRS behavior may be explained by the Schottky emission. The dominant conduction mechanisms of LRS and HRS currents of URS behavior are likely to be Ohmic and the trap-controlled space charge limited current behavior, respectively.In chapter 4, Sr0.99La0.01TiO₃ and SrTi0.99V0.01O₃ thin films were deposited on Pt/Ti/SiO₂/Si substrates by sol-gel method. Sr0.99La0.01TiO₃ shows BRS behavior in low voltage and low Icc and URS behavior appears in high voltage and high Icc, but BRS and URS can realize mutual conversion. The bipolar resistive switching in SrTi0.99V0.01O₃ needs lower voltage than that in pure SrTiO₃. The radio of high resistance and low resistance can reach four orders of magnitude.