| At present,the basic and applied research on the memristor is gradually becoming one of the most active hotspots in such related fields as condensed matter physics,materials science,semiconductor physics and micro-nanoelectronic devices,information technology and artificial intelligence.Although the configuration of the memristor is so simple,the corresponding resistive switching mechanisms of its constituent materials are very complex and intertwined.And there are still lack of the deep understanding and the reliable experimental evidences.This is also one of the key problems restricting the improvement of the overall performances of the memristor,which urgently needs to be solved step by step through in-depth basic research.In this thesis,the author firstly introduces the memristor's concept,structure,principle and basic performance parameters,and briefly reviews the research status of oxide memristors and some problems faced by researchers,then systematically summarizes the research work entitled“Study on memristive performance of TiO2nanotube array film and its influencing factors”during the master's degree.Herein the main research contents and results are as follows:(1)The Cu/TiO2/Ti nanotube array film memristors are designed and prepared,and the influence of TiO2film thickness on their nonvolatile resistive performances are investigated.From the test results,we find that the resistive switching performance of the memristors are closely related to the thickness of the TiO2nanotube array film regulated by anodizing time.When the oxidation time is within 20 min,the resistive switching behavior of the device is dominated by the ionic resistive switching(i RS)mechanism,and when the oxidation time is increased to 30 min,the resistive switching behavior of the device is gradually dominated by the electronic resistive switching(eRS)mechanism.But when the anodizing time exceeds 45 min,the I-V curve of the device gradually deviates from the characteristic hysteresis loop of the memristor,showing a complex shape.In addition,the charge transport in the samples follows the SCLC model.The research results show that the memristive performance of the TiO2nanotube array film anodized for 30 min is more stable,which means there is an optimal thickness value for the TiO2nanotube array film under this situation.(2)A series of the MTop/TiO2/Ti nanotube array film memristors(including Au/TiO2/Ti,Cu/TiO2/Ti,Al/TiO2/Ti,Ti/TiO2/Ti)are designed and prepared,and the influence of different metal top electrodes on their nonvolatile resistive performances are investigated.From the test results,we find that as the electronegativity of the top electrode metal increases,the ON/OFF ratio of the device also increases.Although the ON/OFF ratio of Au/TiO2/Ti is relatively higher than that of Cu/TiO2/Ti,the former requires a larger operating voltage and has a great HRS fluctuation,so the Cu/TiO2/Ti structure has certain advantages.While the other two types of Ti/TiO2/Ti and Al/TiO2/Ti,due to smaller electronegative for their top electrodes,are easy to form a sub-oxide layer between the interface of the metal and dielectric layer,which would make the stability of the resistive switching performance deterioration.More interestingly,the different electronegativity of the top electrodes will lead to the contact barriers changing,which in turn affects the memristive performance of the device.The fitting analysis of the test data proves that Cu/TiO2/Ti conforms to the SCLC mechanism,Al/TiO2/Ti conforms to the P-F emission mechanism,Au/TiO2/Ti conforms to the Schottky emission mechanism,and Ti/TiO2/Ti conforms to the hopping mechanism.The above research results show that the resistive switching performance of the memristor with the same dielectric layer will be significantly affected by the electronegativity of the top electrode metal.(3)The Cu/TiO2/Ti nanotube array film memristors are designed and prepared by liquid-phase reduction treatment in a NaBH4solution at room temperature for different time,and the effects of oxygen vacancy concentration on the memristive performance of the device are investigated.From the test results,we find that with the increase of the reduction time,the morphology of the device does not change significantly,but it has a significant impact on the memristive performance of the device,showing the law of first rising and then suppressing,until the memristive performance is lost.Preliminary research results show that only if the concentration of oxygen vacancies in the TiO2/Ti nanotube array film is kept within a reasonable range,can the overall performance of the device be optimized. |
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