Research On The Resistive Switching Properties And Its Mechanisms Based On Hafnium Oxide Thim Film

With the critical demanding of high speed information processing technology on the density and speed of memory devices,charge based Flash memory is suffering from reaching the physical limits.The resistive random access memory?RRAM?is considered as the most promising candidate for the next generation nonvolatile memory due to its simple structure,superior scalability,fast switching speed,long endurance and so on.O_xides based resistive switching memories have attracted much attention in recent years,and especially for hafnium oxide.Up to date many companies and research institutions are working to improve the performance of the devices.Although progress has been made,some performances still need to be improved such as high operation current,large variability of switching parameters and so on.This dissertation is focused on hafnium oxide thin film RRAM devices.The specific studying content includes the effects of different top electrodes and structures on device performance,test and analysis of the resistive switching properties,and the research of the resistive switching mechanism.In this dissertation,TiN is employed as bottom electrode,and hafnium oxide layer is deposited by magnetron sputtering.The RRAM devices with difference top electrodes?Ni and Ta?are fabricated and compared.In the process of device fabrication,micro structure and morphology are characterized by XRD,SEM,EDX,AFM and so on.The electrical properties are characterized by Semiconductor Parameter Analyzer of B1500 A under the circumstance of high and low temperature probe station.The research progress is as follows:1.The comparative experiment with different top electrodes?Ni,Ta?shows that: Ni/HfO₂/TiN RRAM devices exhibits ultra-low Reset current?sub-100nA?and bipolar resistive switching behavior.The bipolar resistive switching Ta/HfO₂/TiN RRAM devices have better electrical uniformity.Finally,the resistive switching mechanisms of Ni/HfO₂/TiN and Ta/HfO₂/TiN RRAM devices are analyzed by using I-V fitting and temperature dependence.2.HfO_x/HfO₂ and HfO_x/BN bilayer resistive switching devices are fabricated.The resistive switching performance and its mechanism are analyzed.Thin insertion HfO_x layer with oxygen deficient is deposited by reactive magnetron sputtering.The Ta/HfO_x/HfO₂/TiN bilayer structure resistive switching devices were fabricated.HfO_x film acts as reservoir of oxygen vacancy and results to high uniformity characteristics of bipolar resistive switching RRAM devices?Cycle to Cycle and Device to Device?.In addition,four stable and controllable multi-level states were achieved by applying different stop voltages during the Reset process.The oxygen-vacancies based conductive filament formation/rupture was responsible for the resistive switching mechanism.The current conduction mechanisms of low and high resistance state were ohmic conduction and space charge limited current?SCLC?,respectively.By inserting low permittivity and high resistivity BN thin film,Ta/HfO₂/BN/TiN bilayer resistive switching devices were fabricated.The insertion of BN layer reduces the power of device?Reset current of was reduced from 1mA to 100?A?.In addition,the uniformity was improved to a certain degree?Cycle to Cycle?.The low permittivity BN film acts as the barrier layer for the electrons injection and results in the less oxygen vacancies filament.The restriction of oxygen filament leads to the low power consumption and improves the uniformity.The current conduction mechanism of low resistance change is transformed from ohmic conduction into SCLC because of the insertion of BN layer.