Research On Flexible Reactive Memory Based On Low Temperature Atomic Layer Deposition Technology

With the development of semiconductor technique, people are now able to get more and more sophisticated and advanced electronic products. At the same time, as the proposal of the concept of flexible mobile phone by Apple and Nokia, people are then paying more attention to the future flexible electronic products. At present, though there are some semiconductor manufactures fabricating and selling flexible display devices such as Light Emitted Device in attempt to create such industry, it is still under exploratory stage and there is still a big gap in performances between the flexible electronics and the CMOS based silicon products. To achieve the goal of manufacturing flexible electronics in large scale, it is necessary to fabricate the elementary devices at first such as the memory devices on the flexible substrate, as the memory device always does not have a lower requirement than the other functional devices such as logic, RF and sensor devices.In addition, as to the continuous expansion of the information society, people are now having increasing need for memory, the requirement of high storage density, fast programming and reading speed, low cost and low energy is also greater and greater day after day. Nowadays, the conventional flash memory is facing austere challenge as its limitation of structure and scalability. Thus, the several new non-volatile memory (NVM) candidates are now become the focus of research. While these new NVMs still have some shortages and could not become the replacer of the flash memory. Recently, resistive random access memory (RRAM), one of the new NVMs, was receiving increasing attention by the industry and academia due to its simple structure, high scalability, long retention, low operational voltage, and compatible process with CMOS processing.This work firstly compares RRAM with other NVM candidates and introduces the promising thin film deposition technique-atomic layer deposition (ALD). Then through comparison with other low temperature thin film deposition methods with low temperature atomic layer deposition (LTALD), illustrating the reason and advantages to use LTALD to fabricate thin films.Then, this paper introduces the method of fabricating binary metal oxide on the flexible substrate by LTALD and the materials characterizations of the films, showing that the thin film by LTALD is equable in quality with the thin film by conventional ALD. This result makes it possible for depositing thin films on the flexible substrate by low temperature and for thin film device fabrication at low temperature. Next, this work introduces the fabrication method of binary metal oxide based flexible resistive random access memory (FRRAM) by LTALD along with the testing and analysis of TiN/Al2O3/ITO and TiN/HfO2/ITO structure based memory on resistive characteristics, endurance and retention. The work also sorts out and summarizes the conduction mechanisms of the FRRAM on the basis of metal-insulator-metal (MIM) structure with high-k metal thin film oxide.Lastly, through the usage of stack structure, the performances of the FRRAMs have been optimized. By optimization of the structure, thickness of the Al2O3layer, the FRRAM has showed excellent resistive and retentive characteristics with a highly uniform and less distributed operation voltage during endurance test. Simultaneously, through the study of the conduction mechanism and impedance analysis of the stack based FRRAM, the paper obtains the micro scale resistive mechanisms and the equivalent circuits, which provides the investigation method for future FRRAM research.At the end of the paper, it concludes the work in this paper and makes the prospect of the development of FRRAM and flexible electronics.