| With the development of computer technology and information technology, non-volatile random access memory (NVRAM) has been favored widely. Conventional silicon-based memories have been reaching their physical and technological limit. A variety of new NVRAMs with high speed and high density have been developing rapidly in recent years such as MRAM, PRAM, FRAM and ReRAM. ReRAM has become a most promising candidate among these novel memories due to its high storage density, fast reading and writing speed, low power consumption, long time data retention, strong endurance, as well as compatiblility with CMOS process.ReRAM has a simple "sandwich" structure, which top electrode is metal, bottom electrode is metal or metal semiconductor and the middle layer is made of insulating medium. The middle layer plays an important role in the device performance. Organic materials have advantages of low cost, simple and thin film fabrication, as well as molecule structure designed purposely. Hence, here we focus on the study of preparation and characterization of ReRAM based on poly(o-methoxyaniline) (POMA).In this thesis, POMA was firstly dissolved in N, N-dimethyl formamide (DMF) to make the solution with concentration of 1 wt.%. POMA film was then deposited on ITO coated glass by spin-coating. A top Al electrode with a thickness of 200 nm was deposited on the POMA layer by E-beam evaporation through a shadow mask. Al/POMA/ITO ReRAM was finally fabricated and its relative measurements and analysis were carried out. After this, A1/POMA:GO/ITO and Al/POMA/GO/POMA/ITO devices were fabricated through similar procedures as above and their relative measurements were also carried out simply. By compared with Al/POMA/ITO device, we can get some conclusions. The research works and results are introduced as the following:(1) Preparation, characterization and mechanism analysis of Al/POMA/ITO ReRAMThe thickness of POMA film was about 50 nm based on AFM measurement. From the typical current density-voltage (J-V) curve of the Al/POMA/ITO device it can be seen that the POMA device exhibited very interesting bistable electrical behavior. The set voltage (Fset) was-1.15 V and the reset voltage (VRESET) was 2.9 V. The/ON/OFF of the device was about 103 at a read voltage of 0.5 V. From the endurance performance of the Al/POMA/ITO memory, we could see that the resistance values in low resistance state (LRS) and high resistance state (HRS) fluctuated in a certain range. The RON/OFF was about 103 and did not show markedly degradation within 100 cycles. The retention performance of the memory cell showed that both the LRS and HRS could be retained for more than 104 s. Little degradation of the memory device in both the LRS- and HRS-resistances indicated that the ReRAM was stable and non-volatile.To better understand the conduction and resistive switching mechanism of the memory device, the previous J-V curves were re-plotted in a log-log scale for the negative voltage sweep. An ohmic conduction behavior with linear relationship was observed in the LRS, which is evidence of a confined filamentary conduction. The switching characteristic in the HRS was in good agreement with the space charge limited current (SCLC) model. Then cell size dependence of both RHRS and RLRS were measured. The results showed that the RHRS decreased and the RLRS remained stable when the diameter of top electrode increased. The independence of RJRS on the cell area indicates that the conductive filaments are formed in the LRS. About the formation of conducting filaments, POMA+ chains are considered. Therefore, the observed bipolar switching behavior in the Al/POMA/ITO device could be ascribed to the formation and rupture of POMA+ filaments.(2) Preparation and simple characterization of two POMA ReRAM Devices enhanced by GOTo improve the stability of POMA ReRAM, we fabricated A1/POMA:GO/ITO and Al/POMA/GO/POMA/ITO devices.From the typical â… -â…¤ curve of the Al/POMA:GO/ITO device, we could see that the POMA device also exhibited bistable electrical behavior. The VSET was-1.5 V and VRESET was 3.3 V. The ION/OFF of the device was about 103 at a read voltage of 0.5 V. From the â… -â…¤ curves of 10 continuous cycles of this memory, we could see that this memory showed stable bistable electrical characterization. The ION/OFF was about 103 and did not show markedly degradation. Compared with that of Al/POMA/ITO device, the ranges of its VSET and VRESET narrowed obviously. This phenomenon showed that the addition of GO can improve the stability of POMA ReRAM.The typical â… -â…¤ curve of the Al/POMA/GO/POMA/TTO device also exhibited bistable electrical behavior. Its VSET was-1.2 V and VRESETt was 2.4 V. The ION/OFF of the device was about 102 at a read voltage of 0.5 V. From the â… -â…¤ curves of 10 continuous cycles of this memory, we could see that this memory also showed stable bistable electrical characterization. The ION/OFF was about 102 and did not show markedly degradation within 10 cycles. Compared with that of Al/POMA/ITO device, the ranges of its VSET and VRESET narrowed obviously, too. This phenomenon also showed that the addition of GO can improve the stability of POMA ReRAM. However, the ION/OFF of Al/POMA/GO/POMA/ITO device was just 102. Compared with Al/POMA/ITO device, they had the same current in LRS, while the current in HRS in Al/POMA/GO/POMA/ITO device was 10 times higher than that of Al/POMA/ITO device because of the good electrical conductivity of GO, which certainly contributed to the decrease of ION/OFF of Al/POMA/GO/POMA/ITO device.From the comparison of Al/POMA:GO/ITO device, A1/POMA/GO/POMA/ITO device and Al/POMA /ITO device, we can see that the addition of GO narrowed the ranges of VSET and VRESETt, which proved that the stability of POMA ReRAM was improved by GO. |
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