The Fabrication And Properties Of Binary Metal Oxides Thin Films Resistive Switching Memory Devices

With the development of integrated circuit technology,the mainstream Flash technology has become increasingly difficult to meet the needs of the market,its problems such as high operating voltage,low writing speed,and low storage density have become increasingly prominent.As one of the most potentia l candidates for the next-generation nonvolatile memory,the resistive random access memory?RRAM?has received increasing attention due to low power consumption,high storage density,high operating speed,good endurance.Binary metal oxides have been extensively studied because of their simple composition,ease of fabrication,and compatibility with CMOS technology.To improve the resistive switching behavior of device,impurity doping and multilayer are two effective methods.In this thesis,a series of resistive switching memories using HfO ₂/ZrO₂ and ZnO are fabricated,besides,the electrial performances and the resistive switching mechanism are investigated.Which provides new idea to improve resistive s witching behavior of RRAM.1.Ameliorating the composition of resistive memory devices based on HfO₂ is proposed to improve the resistive switching performance.The 5 different Hf_x Zr_?1-x?O₂?HZO,x=2,4,5,6,8?-based thin film RRAM devices were fabricated on Pt/Ti/SiO₂/Si substrates by pulsed laser deposition?PLD?.The resistive switching characteristics of HZO thin films were investigated,and the I-V behavior,endurance,retention,operating voltage were analyzed.It was found that Hf_0.5Zr_0.5O₂ thin film behaves best.Hf_0.5Zr_0.5O₂ thin film RRAM device shows a high ON/OFF ratio of over 10000 with no obvious degradation during 2500 endurance cycles,over 10⁵ s retention time,and the operating voltage is densely distributed with minimal values.The conductive mechanism of HZO films ware analyzed.The conduction behavior in the low resistance state is fitted by Ohmic machanism,in the low voltage region and high voltage region of high resistance state are well fitted by O hmic machanism and Schottky emission machanism.Although the devices demomstrate the different conduction mechanisms,the resistive switching behaviors can be explained by the formation and rupture of the conductive filaments.2.A multilayer structure is propositioned for resistive memory devices based on ZnO.The Al₂O₃/ZnO bilayer thin film RRAM decvide was fabriated on PET fiexible substrates by PLD at room temperature.The thicknesses of Al₂O₃ layers in different samples were 1 nm,5 nm and 8 nm,respectively.The resistive switching characteristics of Al₂O₃/ZnO bilayer thin films were investigated,and the I-V behavior,endurance,retention,operating voltage,feasibility were analyzed.It was found that the Al₂O₃/ZnO thin film with 5nm Al₂O₃ has the best resistive switching bahavior.Bilayer thin film RRAM device shows a high ON/OFF ratio of over 1000 with no obvious degradation during 200 endurance cycles,over 10³ s retention time,and excellent endurance against100 repeated bending.The conductive mechanism of ZnO films ware analyzed.Both single layer and bilayer thin films have same conductive mechanism,the conduction behavior in the low resistance state is fitted by Ohmic machanism,in the low voltage region and high voltage region of high resistance state are well fitted by Ohmic machanism and Space C harge Limited Conduction machanism.The resistive switching behaviors can be explained by the conductive filaments model.