Method And Mechanism Of Metal Oxide Resistance Change Memory Performance Boost Research

With the development of semiconductor technology, the market demand for high-density, high-speed, low-power and low-cost nonvolatile memory is also increasing. But with the continuous scaling down in semiconductor process technology, the conventional Flash as the mainstream nonvolatile memory, is experiencing much more serious challenges, such as the limits in decrease of floating gate thickness. Therefore, searching for more superior next-generation nonvolatile memory becomes much more important and necessary in memory research field. Several novel nonvolatile memories, such as MRAM (Magneto-resistive RAM), FeRAM (Ferroelectric RAM), PRAM (Phase Change RRAM), are drawing intensive attention these days. But due to their own demerits, none of them performs good enough to replace Flash by now.Recently, a new type of RAM based on material's resistive-switching characteristics. RRAM (Resistive RAM), draws both scientific and commercial interests, because of its simple structure, superior scalability, long retention" ability, low-power operation, superior compatibility with CMOS process. And among various materials with resistive switching phenomenon, binary metal oxides are more popular for its simple component and countable stability. However, as an immature candidate memory, the research on RRAM's performance improvement and mechanism calls for further study.This work systematically studies the improvement of metal oxide (as NiO and ZnO) based RRAM and detailed analyzes the relative mechanism. Firstly, the paper studies the effect of the process of PVD (Physical Vapor Deposition) method to the electrical performance of NiOx based RRAM, then proposes a performance enhancement method by accuracy process-control of NiOx preparation, and successfully achieve a 5 times'larger resistive window and much better stability.Consequently, basing on RCB (Random Circuit Breaker) model and its analysis of the relationship of filament-breaking and electic field distribution, the paper further study the enhancement of NiOx based RRAM by introducing a Al2O3/NiOx/Al2O3 sandwich structure to improve the dispersion of VSET, VRESET and Resistive stability. Besides, a 10 times'larger resistive window is achieved by this means. After that, the paper manages to apply the Al2O3-assisted method to the improvement of ZnO based RRAM. By enlarging the resistance of off-state ZnO based RRAM, a 10 times larger resistive window is achieved. Then, the paper invetigates the influence of different compliance current to the on-state resistance, and also successfully demonstrates muti-level storage ability in Al2O3/ZnO/Al2O3 structure, then author provide this as a possible method in multi-level storage application.Finally, paper summarizes the conclusions for all works and makes an outlook for the RRAM reserach in future.