| Sustained advances in information technologies over the past decades have given us computers with powerful processing capabilities due to high-speed/high-density nonvolatile memories(NVMs). Nevertheless, conventional nonvolatile memory(such as flash memory)scaling is expected to come up against technical and physical limits in the near future. In order to overcome this problem, some concepts of emerging nonvolatile memory, have been proposed by researchers. Candidates for next-generation nonvolatile memories based on new materials, including phase-change random access memory(RAM), ferroelectric RAM,magnetic RAM, and resistive switching RAM(RRAM). However, among these memories,RRAM, which based on resistive switching phenomenon found in some materials, have attracted a great deal of attention, because of its advantages including simple structure, low power consumption, high on/off ratio, fast read-write speed, long retention time and compatibility with semiconductor process. Various polycrystalline and amorphous transition metal oxides(TMOs), including TiO2, ZrO2, ZnO, and Hf O2, have found their applications in RRAMs. However, the resistance switching mechanism of TiO2-based RRAM is clear: the formation and disruption of Tin O2n-1(or so-called Magnéli phase) conducting filaments. Hence,our research focus is on the TiO2-based RRAM, research works are summarized as follows:(1) The conductive model based on itanium oxide resistive device was prepared. The oxygen vacancy formation energy and the conductive filaments bands diagram of the fabricated devices with or without doping were calculated by the first principles, and the electrical properties of the device was also analyzed in detail.(2) The TiO2 thin film was prepared on Pt/Ti/SiO2/Si substrate using the sol-gel method,and its microstructure has been characterized by corresponding methods. Then, electrical measurements of Pt/TiO2/Pt device were performed using a Keithley 4200-SCS analyzer the coexistence phenomenon of unipolar and bipolar resistive switching behaviors was observed in the Pt/TiO2/Pt device, and there was no forming process in it. The distribution of switching voltages and resistance values of high-resistance state was discrete, the stability of Pt/TiO2/Pt device needs a further improvement.(3) We synthesized various TiO2 films doped with trivalent(La3+) or bivalent(Fe3+)elements via the sol-gel method and compared their resistive switching characteristics. In contrast to the pure TiO2 device, La3+- and Fe3+-doped devices exhibited some better resistive switching properties, including a lower set voltage and a higher stability of switching voltageand high-resistance state. Especially the La3+-doped sample, acquires a better switching performance in contrast to Fe3+ doped samples. It was attributed to the bivalent dopant-induced enhancement in oxygen vacancy generation. Furthermore, the dopant-induced decrease in oxygen vacancy formation energy calculated by theoretical method was experimentally supported by results of our work.(4) In addition, we also explored the La3+ doped titanium oxide resistance variable memory Pt top electrode for Ag as the top electrode caused by impact, in which Ag+ play those conducting filaments which is one of the most important role. With Pt as the top electrode structures are compared. Ag/TiO2:La/Pt system resistive parameters of uniformity has been significantly improved, such as converting voltage and high and low resistance state resistance. After 100 times of repeated cycles, the resistance of the device disappears due to the loss of the device. |
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