| Recently, nonvolatile resistive switching phenomena have attracted considerable attention due to the possible applications in the next generation of resistance random access memory (RRAM) with high speed, high density and low power consumption. Resistive switching (RS) has been widely observed in many oxides, but there are still many issueses to be solved. Firstly, the performance of RS device should be improved. Secondly, the understanding of physics and mechanism of RS are still an open question because of the complexity of RS due to the differences in materials, preparation methods and equipment involved. In this thesis, we have studied some key issues of RS materials and applications by improve the preparing methods and device structures; furthermore, the mechanism of RS has also been investigated. The main conclusions are as follows.1. A TiO2thin film was deposited on a NSTO substrate by pulsed laser deposition to form a Ag/TiO2/NSTO/In device. The bipolar resistive switching effect of this device was investigated. The current-voltage characteristics exhibited pronounced and stable bipolar resistive switching features. The device could be switched to low resistance state (LRS) at forward voltage and returned to high resistance state (HRS) at reverse voltage, and the resistive switching ratio RHRS/RLRS reached up to2×103at a read voltage of-0.5V. Moreover, the resistive switching ratio could be adjusted by changing the maximum value of the forward or reverse voltage, which shows promise for multilevel memories.2. YSZ thin film was deposited on NSTO substrate by pulsed laser deposition. This Pt/YSZ/NSTO heterostructure device exhibits high endurance, good time retention, and high resistive switching ratio of105at a read voltage-0.1V under+3V and-4V pulse voltages. Moreover, the resistance states could be reversible switched between multilevel resistance states by changing the magnitude of SET or RESET pulse voltages, which shows potential application in multilevel nonvolatile memory devices.3. The bipolar resistive switching effect in a SrTiO3/NiO stacked heterostructure which was epitaxially deposited on NSTO substrate by pulsed laser deposition. This heterostructure shows high resistive switching ratio of over104at the read voltage of-0.5V and an expected retention ability of ten years, which is better than that of NiO-based device. Moreover, the resistive switching ratio can be adjusted by changing the maximum applied voltage or compliance current, which shows promising for multilevel nonvolatile memories application.4. The resistive switching effects of ZnO, CeO2and CeO2/ZnO stacked heterostructure were deposited on NSTO substrates by pulsed laser deposition. The CeO2/ZnO stacked heterostructure shows high resistive switching ratio of over104at a read voltage of-0.5V and an expected retention ability of ten years, which is better than that of ZnO or CeO2based device. Furthermore, multilevel resistance states could be adjusted by changing the maximum value of the applied voltage, which shows promise for high-performance nonvolatile multilevel memory application. Studies indicated that the trap-mediated space charge limited conduction governs the low and high resistance states. The good resistive switching characteristics of CeO2/ZnO stacked heterostructure could be attributed to the carrier injection-trapped/detrapped process at the CeO2/ZnO interface and ZnO films in which oxygen vacancies act as "trapping center".5. Resistive random access memory using Zn0.6Mg0.4O (ZMO) as resistive switching layer was prepared on NSTO substrates by pulsed laser deposition. The Ag/ZMO/NSTO device exhibits reversible and stable bipolar resistive switching behavior with RS ratio of103under the-5V and+3V pulses. Furthermore, multilevel resistance states could be well-modulated by controlling the amplitude of SET and RESET voltages. The high RS ratio, low voltage read-out, reliable switching reproducibility and long data retention observed in this device suggest their great potential in non-destructive readout nonvolatile multilevel memories. Meanwhile, the electrical conduction was dominated by trap-controlled space-charge-limited conduction. Besides, the mechanism of the resistive switching was discussed by the process of carrier injection-trapped/detrapped, in which oxygen vacancies and Schottky-like barrier between ZMO/NSTO play important roles.6. The bipolar resistive switching effect in ZnO/BaTiO3/NSTO stacked heterostructure was fabricated by pulsed laser deposition. The ZnO/BaTiO3/NSTO device exhibits high performance with resistive switching ratio of104at read voltage0.1V, good endurance and an expected ten years time retention ability, which is better than that of ZnO or BaTiO3based device. Moreover, multilevel resistance states can be controlled by changing the amplitude of set or reset pulse voltages. It was concluded that the observed resistive switching behavior in the ZnO/BaTiO3/NSTO heterostructure was related to the modulation of ZnO/NSTO p-n junction’s depletion width, which was caused either by the BaTiO3ferroelectric polarization field effect and the carrier injection process under an electric field, or both simultaneously.7. The bipolar resistive switching effect of Nd0.05Bi0.9sFeO3(NBFO)/NSTO heterostructure was fabricated by pulsed laser deposition. This heterostructure shows high resistive switching ratio of over600at read voltage of-0.3V after applied5V/-8V pulse voltages. Moreover, the resistance states could be switched reversibly among multilevel resistance states by changing the magnitude of set or reset pulse voltages, which shows promise for multilevel nonvolatile memory application. The mechanism of resistive switching between high and low resistance states could be attributed to the carrier injection-trapped/detrapped process which changes the height and thickness of barrier at the NBFO/NSTO interface.8. The bipolar resistive switching effect of Pt/BaTiO3/NSTO heterostructure device which was fabricated by pulsed laser deposition has been investigated. This device exhibited reliable switching reproducibility, long data retention, and high resistive switching ratio of over103at read voltage-0.3V under applied5V and-10V sweeping or pulse voltages. Moreover, the resistance states could be switched reversibly among multilevel resistance states by changing the magnitude of set or reset pulse voltages, which shows promise for multilevel nonvolatile memory application. Meanwhile, the mechanism of resistive switching has been discussed through the first voltage sweeping process and conduction mechanism for both high and low resistance states, and it was concluded that the observed resistive switching behavior in the Pt/BaTiO3/NSTO heterostructure would be related to the modulation of BaTiO3/NSTO interface barrier, which was caused either by the BaTiO3ferroelectric polarization effect and the carrier injection-trapped/detrapped process under an electric field, or both simultaneously.9. Pt/La0.7Sr0.3MnO3(LSMO)/NBFO/NSTO ferroelectric tunnel junction was fabricated by pulsed laser deposition. This device exhibits a nonvolatile resistive switching with a resistance ratio of up to60under2V/-3V pulse voltages at room temperature. The low voltage readout, reliable resistance switching reproducibility and good time retention, indicate promise for non-destructive readout nonvolatile memories. In this metal/p-semiconductor/ferroelectric/n-semiconductor structure, the mechanism of resistive switching behavior could be attributed to the ferroelectric polarization enhanced field-induced charge redistribution at the semiconductor/ferroelectric interface, resulting in the modulation of the interface barrier height.10. Pt/NBFO/LSMO/NSTO ferroelectric junction was fabricated by pulsed laser deposition. We investigated the effect of a ferroelectric NBFO thin film on the resistive switching in the stacked LSMO/NSTO heterostructure forming a p-n junction. To promote the ferroelectric effect, the thin NBFO active layer was deposited on an epitaxially grown p-type LSMO film on a lattice-matched n-type NSTO single crystal. This heterostructure device exhibits high endurance, good time retention, and high resistive switching ratio of102at a read voltage-0.1V under+2V and-2V pulse voltages. It was concluded that the observed resistive switching behavior in the all-perovskite Pt/NBFO/LSMO/NSTO heterostructure was related to the modulation of LSMO/NSTO p-n junction’s depletion width, which was caused by the NBFO ferroelectric polarization field effect. |
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