Research On Resistive Switehing Memory Based Binary Transition Metal Oxides

With the prevalence of customer electronic products such as smart phone, tablet computers and intelligent terminals based on internet technology, the increasing demands for nonvolatile memory (NVM) with large capacity, high density, low power and low cost have grown dramatically in recent years. To meet these requirements, semiconductor manufacturing technology has been moving forward under the guidance of Moore’s Law. During the advancement of semiconductor manufacturing process nodes, however, Flash memory, the mainstream of the traditional NVM technology, which is based on the floating-gate structure with charge storage mechanism, has encountered its technical bottleneck-charge leakage due to gate oxide thinning, charge coupling due to shortened distance between adjacent devices, etc. In addition, the high operation voltages and low operation speed hinder it to meet the requirements for high density and low power NVM applications. Thus, both industry and academia have exert great efforts to explore appropriate candidates for the next generation NVM. Some emerging nonvolatile memory technologies, for instance, FRAM (ferroelectric random access memory), MRAM (magnetic random access memory), PRAM (phase change random access memory) and RRAM (resistance random access memory), have attracted much attentions during the last decade. Due to its simple device structure, uncomplicated fabrication process which is compatible with modern CMOS process, low operation voltages, fast operation speed and excellent scaling potential, RRAM is considered to be one of the promised candidates for next generation NVM. This work focuses mainly on exploring doping effects on the resistive switching characteristics and the resistive switching mechanism of ZrO2and HfO2-based binary transition metal oxide (BTMO) RRAM devices which have controllable components, simple fabrication process and compatible with modern CMOS process.Low energy implantation process was adapted to fabricate HfO2-based RRAM devices. Experimental results demonstrate improved resistive switching characteristics in Pt/Ti/HfO2:Al/Pt and Pt/Ti/HfO2:Si/Pt devices after low energy ion implantation compared to the un-implanted Pt/Ti/HfO2/Pt device, such as lower set and reset voltages, higher endurance, etc. By doping nitrogen into HfO2film via NH3plasma treatment, Pt/Ti/HfO2:N/Pt device exhibits excellent uniformity in resistive switching characteristics, for instance, tight distributions in resistive switching voltages, high and low resistance state, and robust reliability in endurance and retention performance. Material analysis was carried out to elucidate the improvement in device performance for the nitrogen doping effect.By applying low constant current stress (CCS) on the Cu/ZrO2/Pt device, the device resistance was found to be two orders of magnitude lower than its original value (positive bias on Cu electrode). After low CCS treatment, lower forming voltage and constrained reset current were demonstrated in Cu/ZrO2/Pt device, and improved resistive switching characteristics were also demonstrated, such as lower set and reset voltage, higher endurance, etc. Simple theoretical model analysis shows that low CCS treatment could suppress the transient current which has significant impact on the device performance by lowering the transition voltage, thus better device performance can be achieved in the CCS-treated Cu/HfO2/Pt device.Resistive switching process in Ni/ZrO2/Pt device was carried out by in situ TEM (transmission electron microscopy) analysis. Nickel element was found to be the main component which comprised the conducting filaments (CF) in the Ni/ZrO2/Pt device. Detailed process of resistive switching in Ni/ZrO2/Pt device was elucidated according to the experimental results. It is proposed that Ni could be the third oxidizable metal material besides Cu and Ag which could be applied in CBRAM (conducting bridge random access memory) device as the oxidizable electrode material.