| With the rapid development of technologies such as 5G and big data technology,traditional memory devices are facing bottlenecks,like high-density integration and scaling.Therefore,the research on new non-volatile memories is of great significance.Among the new non-volatile memory devices,resistive random access memory has become a hopeful candidate for the next generation of memory due to the low power consumption,fast operation speed and high integration.On the other hand,flexible electronic devices have become a major research hotspot because of their lightness,portability and flexibility.Based on the development of technology,research on flexible resistive memory is attracting more and more attention.This thesis mainly studies the performances of Hf O_x-based flexible resistive memory with different top electrode materials.In this thesis the ultra-high vacuum magnetron sputtering process and the electron beam evaporation process are used to fabricate a sandwich structure memory cell on a flexible polyimide substrate.Atomic force microscope,X-ray photoelectron spectroscopy,four-probe test system and semiconductor parameter analyzer are used to analyze the electrical switching and film characteristics.After that,the performances of device are optimized and the effect of different electrodes to resistance mechanism is researched.First,the influence of the sputtering parameters to ITO on the electrical properties of the thin film is explored.The film preparation is optimized by adjusting the sputtering power and air pressure.An ITO film with a good electrical conductivity(18.6?/?in square resistance)and a high average transmittance(84.6%)is obtained,which can meet the requirements of electrode films.On the basis of optimizing the ITO film preparation process,the effects of Hf O_xfilm prepared by different sputtering candidates on the device performance are explored.The device performance is optimized by changing the thickness of the Hf O_x layer,oxygen partial pressure and sputtering power.According to the electrical characteristics,the device with a10nm Hf O_x prepared under the conditions of 15%oxygen partial pressure and 140 W sputtering power exhibit excellent resistive characteristics.The device can maintain an endurance of 200K switching cycles,and the distributions of switching voltage and resistance values of different status have also been improved.Secondly,in order to study the effect of different top electrodes on the performance,Al and Ni top electrodes were prepared by the e-beam evaporation.The devices based on Ni top electrodes exhibit lower operating voltages,while devices based on Al top electrodes exhibit lower operating currents and self-compliance characteristics.Finally,in order to optimize the flexibility of the flexible resistive memory,a bending test was performed on the device and the electrical characteristics of devices after the bending are also tested.It is found that the device based on the ITO top electrodes can maintain excellent performance even after a bending radius of 4 mm or after 10~3 times of bending,which proves that the devices have high flexibility.However,the performance of devices based on Al and Ni top electrodes show significant degradation after bending.To further explain this phenomenon,the switching mechanisms of the three devices are also analyzed.It is found that the device using the ITO top electrode is dominant by the space charge limiting current mechanism.However,the switching behavior of the electrode devices on Ni and Al top electrodes is mainly controlled by ion movement,so it is susceptible to mechanical bending and will cause performance degradation.In this thesis,the optimization of flexible resistive memory performance and the degradation caused by bending are studied.It is proved that the resistive characteristics of the device can be improved through electrode engineering,which provides a certain guide for the development of devices with better flexibility. |
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