Study Of Resistive Switching Mechanism And Device Based On Memristor

With the development of the semiconductive technology,the scalability is recognized as a bottleneck in the Flash memory that considers as the mainstream technology of the non-volatile random access memory.A large variety of new type memory devices have been regarded that have great potential in fulfilling the ultra-high density storage demands.Among those numerous novel techniques,memristor is considered as the most potential in replacing traditional Flash memory devices as it offers various advantages including simple structure,low operation voltage,high endurance and multi-bit data storage ability.The resistive switching(RS)effect of such technique has been observed in large amount of materials,including multiple oxides,solid electrolytes,organic materials and metal-oxides.Considering the simple architecture and excellent CMOS compatibility,NiO shows its great potential to be used in the memristor.However,various technical problems have yet awaited being solved.Instances are the un-known resistive switching mechanism,repeatability of device parameters and difficulty in storage window.Therefore,the study of the mechanism of the RS had been demonstrated in this article,where the influence derived from the composition of oxides,crystallization and filament properties had been researched.Secondly,by studying the influence of fabricating process and insterted layer,high performance NiO memristor were fabricated with significant enhanced storage window,paving the way for multi-storage.Additionally,flexible NiO memristor was implemented by using the near-field electrospinning technique,offering an alternative in fabricating high performance devices.The main results were as following:(1)It had been acknowledged that the microstructures inside oxides were extremely sensitive to fabricating process,thus influencing functionality of the device.Therefore,the influence of fabricating process was kept studying in this field.Specifically,the sputtering gas components had great influence on the device properties such as the storage window and the variation of the resistance,which had been studied in details.In this article,it was found the best RS performance was achieved when the oxygen content was 10%.Fast annealing process also helped to enhance this performance dramatically,since it enabled a secondary oxidization process which took place inside the device.The performance of storage windows,stable parameters crystallization,and stress status could be optimized by simply tuning the experimental parameters,such as the heat annealing temperatures and duration,providing the fundamental understanding in optimization the devices and implementing the RS effects in multi-modes.(2)The main mechanism for RS device included the bulk effect and the local effect which based on the filament.The generation and rupture in filament influenced the electronic properties in macro-scales,which was interested by numerous research groups.In this article,we found that the mechanisms were distinct in the process of generation and rupture with different electrodes,such as the devices where Au and Co were used as the top electrodes.Specifically,Au/NiO/Pt showed a classical fuse-break mechanism,where unipolar switchings were observed in both positive and negative bias voltage range.In contrast,the Co/NiO/Pt could be considered as a typical electrochemical metallization,where the generation and rupture of the filament took place as the Co ions moved,implementing the biopolar RS.Secondly,in order to improve the electronic properties,the structure of memristor had developed from the simply sandwiched structure to multi-layered structures.In this project,Ta was used as the inserted layer and the effects on the status of the filament were studied in detail.By analyzing the I-V curve,differences had been observed on the changing of current jumping phenomenon and the varying of switching voltage when the locations,thickness and the numbers of inserted layers varied,which provided better guidance in understanding multilayered memristor.Additionally,the study in heating effects inside the device was essential in improving the devices‘ stability as there was large amount of Joule Heat when the current stimulated the memristor to implement the RS property.Thus,numeric simulations using two different algorithms-finite difference and finite element protocols were carried out,showing the heating effects varied with the different components,the diameter of the conductive path and compliance current.This project was beneficial in providing an improved device.(3)As the development of memristor,it was tend to enhance the function of device from basic RS effect to other applications.Therefore,providing a practical manner that could improve the diversity of the memristor was essential in broadening the RS effect in applications.By studying the inserted layer deposition parameters and the oxidized layer properties,the storage window was enhanced 4 order of magnitude higher than the traditional values and thus implemented the multi-storage and high storage density.Additionally,the inverse proportional trend of the switching voltage and the standard free energy(SFE)had been demonstrated by studying the NiO device with distinct electrodes,thus providing new protocol in tuning the switching voltages.(4)Novel protocols in fabricating flexible electronic devices had been interested by an increasing number of researchers since 21 st century.In this article,the near-field electrospinning was utilized to fabricate low-cost,flexible memristor.The NiO fibres were synthesized through electrospinning.Additionally,incorporated with designed microfluidic techniques,pure silver electrodes were also synthesized with high conductivity.The assembled device which incorporated both silver and NiO fibres showed the classic RS property,which opened up new avenue in fabricating flexible devices.