| Resistance random access memory(RRAM) is considered as one of the best potential candidates for development of the next generation of nonvolatile memory because of its advantages, such as low operating power consumption, high density due to simple device structure, and a fast switching speed of about several nanosecond. RRAM is based on the electric-field induced resistance change in a metal-insulator-metal(MIM) structure, is one of the most promising candidates for next-generation non-volatile memories. In our previous work, the crystal micstructure of the film plays an an importance role on their resistive switching(RS) properties in Ti/ Pr(Sr0.1Ca0.9)2Mn2O7(PSCMO)/Pt devices. Later, the Ag/ PSCMO/Pt device is introduced to research the changes of the magnetization in different resistive switching states and directions of magnetic field. The main research in the following two aspects:(1) Micstructure and forming voltage effect on Resistance Switching behaviours in Ti/PSCMO/Pt Devices.Two PSCMO films(PSCMO-1 and PSCMO-2) have been prepared by pulsed laser deposition, and the morphology of the films can be controlled through the different deposition condition. The two films are polycrystalline of single phase, and higher and sharper diffraction peaks in PSCMO-2 film measuring by X-ray diffractometer(XRD) and scanning electron microscopy(SEM). PSCMO-1 film grows with a near-random orientation, whereas columnar grains perpendicular to the substrate appeared in the PSCMO-2 film and the film thicknesses are 100 nm(PSCMO-1) and 140 nm(PSCMO-2), respectively. The crystal structure and microstructure of the films were characterized using a Philips X-Pert MRD X-ray diffractometer(XRD) and scanning electron microscopy(SEM). The normalized XRD patterns of the two PSCMO films reveals that no impurity is detected in the two films, and higher and sharper diffraction peaks in PSCMO-2 film. The SEM images of the two films show that PSCMO-1 film grows with a near-random orientation, whereas columnar grains perpendicular to the substrate appeared in the PSCMO-2 film and the film thicknesses are 100 nm(PSCMO-1) and 140 nm(PSCMO-2), respectively. In order to research the different RS behaviors in different crystallinity and orientation, Ti top electrodes with a diameter of 200 μm were deposited on the two PSCMO thin films through a metal shadow mask by magnetron sputtering(Ti/PSCMO/Pt). The two PSCMO devices show different bipolar resistance switching patterns without forming process. From the I-V curves, we can see the higher resistance ratio and larger hysteresis in Ti/PSCMO-2/Pt device than the Ti/PSCMO-1/Pt device. After a forming process in a higher voltage, the Ti/PSCMO-1/Pt device also displayed the higher resistance ratio and larger hysteresis forming a similar resistance switching patterns with Ti/PSCMO-2/Pt device. By fitting the I-V curves, we found that the conduction process in Ti/PSCMO-1/Pt device in lower forming voltage is dominated by Schottky barrier mechanism, which displays that the oxygen vacancies are moved along the interface between the top electrode Ti and PSCMO film. However, the oxygen vacancies are captureed into the vicinity of interface in Ti/PSCMO-2/Pt and Ti/PSCMO-2/Pt of higher forming voltage, which are dominated by trap-charged space-charge-limited current mechanism. Our results suggest that the crystal microstructure may play a critical role in oxygen vacancy movement, and result in the transformation of resistance switching along with a higher resistance ratio and larger hysteresis in the Ti/PSCMO-2/Pt device.(2) Magnetic change by resistive switching effect in Ag/PSCMO/Pt Devices.A PSCMO film about 200 nm was deposited on Pt/Ti/Si O2/Si(100) substrate by PLD and then prepared Ag top electrodes using thermal evaporation coating. The Ag/PSCMO/Pt device shows bipolar resistive switching characteristics, which are accompanied by magnetic modulations during the set and reset processes. In the magnetic field oriented parallel to the film substrate, the device triggered to low and high resistance state also shows the increasement of magnetization. In the low resistance state, the device shows a bigger ferromagnetic hysteresis loops with a remanent magnetization than that in high resistance state. In the magnetic field oriented perpendicular to the film substrate, although the magnetization of the device can be manipulated by the external voltage, the remanent magnetization and coercive field disappear, resulting in a weaker mag netism in high and low resistance state. Because oxygen ions migration and charge trapping/detrapping under external voltages is suggested to explain the RS effects, more oxygen ions captured into the Ag/PSCMO interface is likely responsible for the stronger magnetic change along the direction of magnetic field parallel to the film. |
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