| In recent years, resistive random access memory based on the resistance switching (RS) effect has become the most powerful competitor and candidate for a new generation of non-volatile storage device and attracted considerable attention from both the scientific research and industry because of its significant advantages of non-volatile characteristics, high operation speed, low power consumption, high integration density and good compatibility with complementary metal oxide semiconductor, etc.. Although the RS has been obtained in a variety of materials, there are still many problems to be solved. On the one hand, the RS performance needs to be improved; on the other hand, the potential physical mechanism of RS is still controversial, which needs further understanding. Therefore, further development of new RS materials with better performance and study of the physical mechanism of RS effect are still very important. In this thesis, a variety of oxide thin films were prepared by pulsed laser deposition technique on Nb doped SrTiO3 substrates to form their heterostractures. The resistive switching effects and the associated magnetism of these films and heterostructures were studied. Close correlations between the resistive states and the magnetism were obtained and electric filed modulate resistive switching and magnetism were demonstrated. The corresponding mechanisms of the electric filed modulation on the resistive switching and magnetism were explored. The main results of this study are listed below:1. CuFe2O4 thin films were epitaxially grown on Nb doped (001) SrTiO3 (NSTO) single-crystal substrates by pulsed laser deposition (PLD) to form Pt/CuFe2O4/NSTO heterostructures. These heterostructures exhibit typical bipolar RS effect with maximum switching ratio of 105, good retention, excellent endurance, multi-level resistance states. The resistance state and saturation magnetization of the device can be regulated simultaneously by the external voltage, and the saturation magnetization of the CuFe2O4 thin films show corresponding changes associated with RS. The main origin for the changes in the resistance state and magnetism of the device can be attributed to the charge injection-trapping and detrapping process at the CuFe2O4/NSTO interface and the redistribution of the Cu2+ion on the tetrahedral sublattice induced by the migration of oxygen vacancies. The results of this study extend the application field of the CuFe2O4 heterojunction, and it shows the potential applications in the field of nonvolatile multi-level resistance random access memory (RRAM) and magnetoelectric multifunctional device.2. Fe2O3 thin films were epitaxially grown on NSTO substrates by PLD technique to form Pt/Fe2O3/NSTO devices. These devices exhibit typical bipolar RS effect with maximum switching ratio of 104, good retention and endurance, multi-level resistance states. When the resistance states of the devices are switched to LRS and HRS, both of the saturation magnetization and the coercive field of the Fe2O3 thin films show corresponding changes associated with the RS. The change of the resistance and magnetism of the devices can be ascribed to the charge injection-trapping and detrapping at the Fe2O3/NSTO interface and the conversion between the Fe2+and Fe3+due to the migration of oxygen vacancies. The results of the study show that the Fe2O3 possess important application potential in the non-volatiale multi-level RRAM and magnetoelectric multifunctional storage device.3. Pt/NiO/Nb:SrTiO3 heterostructures were prepared and the bipolar RS behavior with multilevel RS characteristics, a maximum RS ratio of 105, and stable endurance properties. The coexistence of nonvolatile resistive and magnetization switching in Pt/NiO/Nb:SrTiO3 heterostructures was demonstrated. Under simple application of voltage pulses, the saturation magnetization of the NiO layer increases by up to three times in the different resistance states. This electrical modulation of both the resistive and magnetization switching properties is attributed to the migration of oxygen vacancies and charge trapping and detrapping at the heterojunction interface. Our results provide a pathway towards the electrical switching of both resistance and magnetization, which is likely to be useful for RS and magnetic multifunctional device applications.4. The Pt/BiFeO3/NSTO devices prepared by pulsed laser deposition technique exhibit typical bipolar RS effect with maximum switching ratio of 105, multi-level resistance states, good retention. Moreover, the saturation magnetization of the BiFeO3 thin films show corresponding changes associated with the RS. The saturation magnetization at HRS is higher than that at LRS, which exhibit reversible and repeated switching. The change of the resistance and magnetism of the devices can be attributed to the modulation effect of the ferroelectric polarization reversal on the width of depletion region and the height of potential barrier of the p-n junction and the charge injection-trapping and detrapping process combined with the migration of oxygen vacancies at the BiFeO3/NSTO interface. The results of this study extend the application field of BiFeO3 in multiferroic RS multifunctional devices.5. The Pt/Mn3O4/NSTO devices prepared by PLD technique exhibit typical bipolar RS effect with maximum switching ratio of 104, excellent endurance, good retention, multi-level resistance states. Moreover, the films in the initial state exhibit ferromagnetism at room temperature. When the resistance states of the devices are switched to LRS and HRS, the saturation magnetization, the remanent magnetization and the coercive field of the Mn3O4 thin films simultaneously show corresponding changes associated with the RS. In these devices, the resistance state and magnetism show a close correlation. The results show that the change of the resistance and magnetism of the devices can be ascribed to the charge injection-trapping and detrapping process at the Mn3O4/NSTO interface and the conversion between the Mn3+(Oh) and Mn2+(Oh) due to the migration of oxygen vacancies. The results of this study show that the Mn3O4 possess application potential in the non-volatiale multi-level RRAM and magnetoelectric multifunctional storage device.6. Co3O4 thin films were epitaxially grown on NSTO substrates by PLD to form Pt/Co3O4/NSTO devices. These devices exhibit typical bipolar RS effect with maximum switching ratio of 10s, good retention and excellent endurance, multi-level resistance states and negative differential resistance. Moreover, the films in the initial state show ferromagnetism at room temperature. When the resistance states of the devices are switched to LRS and HRS, both the saturation magnetization and the remanent magnetization of the Co3O4 thin films show corresponding changes associated with the RS. The results of this study show that the change of the resistance and magnetism of the devices can be attributed to the charge injection-trapped/detrapped process at the Co3O4/NSTO interface and the conversion between the Co3+(Oh) and Co2+(Oh) due to the migration of oxygen vacancies. It shows that Co3O4 can be applied to the non-volatile multi-level RRAM, and also provides a new pathway for the realization of the magnetoelectric coupling effect in the magnetic oxide heterojunction.7. The Pt/Co:TiO2/NSTO devices prepared by PLD technique exhibit typical bipolar RS effect with maximum switching ratio of 103, good retention, excellent endurance, and multi-level resistance states. Moreover, the films in the initial state exhibit ferromagnetism at room temperature. When the resistance states of the devices are switched to LRS and HRS, the saturation magnetization of the thin films show corresponding changes associated with the RS. In these devices, the resistance state and magnetism show a close correlation. The results show that the change of the resistance and magnetism of the devices can be ascribed to the charge injection-trapping and detrapping process at the Co:TiO2/NSTO interface and the bound magnetic polaron model which shows significant associations with the oxygen vacancies concentration. The results of this study extend the application field of the Co:TiO2 as a dilute magnetic semiconductor material in magnetoelectric storage device. |
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