Resistive Switching Characteristics And Switching Mechanism Of Hafnium Oxide Based Resistive Memory

Conventional flash memories have remained in the lead in the nonvolatile memory?NVM?market segment.However,it is widely believed that flash memory will reach its physical limit in the short term.In the next generation of new non-volatile memory,Resistive Random Access Memory?RRAM?has the advantages of high storage density,fast transition speed,low power consumption,high storage density and other advantages.There are many materials that can be used in the middle layer of the resistive memory.Among them,the HfO_x based resistive devices have the advantages of high operating speed?ⁿs?,good endurance(¹0¹² cycles)and retention,and low voltage?<0.5V?which has gained wide attention.Despite such progresses,HfO_x based RRAM devices still have some shortcomings,such as high power consumption and low-density storage.The understanding of physical mechanisms governing RRAM device operations and their implications optimization requires further investigation.In this thesis,HfO_x-based RRAM was fabricated.The influence of HfO_x deposition process parameters such as different oxygen pressures and different thicknesses and MoS₂ intercalation on the performance of resistive devices was studied,and the resistive switching mechanism was analyzed.Secondly,the low power consumption and multilevel characteristics based on HfO_x resistive devices were studied and the corresponding resistive switching mechanism was proposed.Ni/HfO_x/TiN resistive devices were fabricated.The hafnium oxide thin films were prepared by magnetron sputtering using metal Hf target.The resistive switching characteristics of the devices were optimized by changing the thickness of hafnium oxide film and the oxygen partial pressure.The results show that when the thickness of HfO_x is 20 nm and the oxygen partial pressure is 6%,the device performance is the best,the endurance characteristic can reach10³ cycles,in addition,the uniformity of the switching voltage is improved.Through the linear fitting and temperature test,the conduction mechanism of Ni/HfO_x/TiN RRAM device in low resistance state is ohmic conduction mechanism,and the conduction mechanism in high resistance state is Schottky emission mechanism.The structure of Ag/HfO_x/TiN and Ag/HfO_x/MoS₂/HfO_x/TiN were fabricated and the effect of MoS₂ intercalation on the resistive switching characteristics was investigated.After inserting MoS₂,the endurance performance and the uniformity of the switching voltage are improved.Corresponding switching model is proposed according to the theory of Schottky emission theory.The HfO₂ ceramic target was used to fabricate a low-power resistive device with Ni/HfO_x/TiN structure.After the electrical test,the reset current of the resistive device can be as low as nA level.The Al/HfO_x/TiN multilevel characteristics resistive device was fabricated.The multilevel characteristics were achieved by adjusting the compliance current in the Set process and the stop voltage during the Reset process.In this paper,the resistive switching characteristics and switching mechanism of hafnium oxide based resistive memory were studied.First,by optimizing the growth process of hafnium oxide film and the intercalation of MoS₂,the endurance characteristics and the uniformity of the switching voltage were improved.Subsequently,a low power resistive device with Ni/HfO_x/TiN structure was fabricated and with a Reset current of nA level was obtained.Finally,based on the Al/HfO_x/TiN resistive switching device,the multilevel characteristics were achieved by changing the compliance current and the stop voltage during the Reset process.