Study Of Resistive Switching Characteristics And Mechanisms For Oxide RRAM With Different Electrode Materials

The current memory technology based on charge storage,such as floating gate Flash memory,is facing the challenge of high operating voltage,low switching speed,low power operation and the device scaling.Recently,several emerging nonvolatile memory devices such as the ferroelectric random access memory,magnetic random access memory,phase change memory,and resistive random access memory?RRAM?,have attracted extensive attentions.One of the promising candidates for the next generation of nonvolatile memory is the resistive random access memory?RRAM?due to its simple structure,fast switching speed,high density,low operating consumption,and compatibility with standard CMOS process.This study investigates the oxide RRAM with different electrode materials with TiN,Gd and N:ITO,which explores the ways to improve the resistive switching performance,and provides reliable experimental evidence for designing the RRAM memory cell or its integrated array with excellent performance.the results in this work also have some scientific value for understanding the resistive switching mechanism.The TiN electrode based RRAM devices was firstly investigated and the Ti N/Hf:SiO₂/Pt device demonstrated excellent bipolar resistive switching?RS?characteristics,the memory window was about 60.Moreover,the good endurance and outstanding uniformity was presented,The coefficient of variation of V_set,V_reset,R_on and R_off were found to be 5.05%,4.78%,4.18%,and 15.78%,respectively.The multilevel storage capability can be successfully obtained by varying either the stop voltage or the compliance current in the operation process.Combined with I-V fitting analysis,we found that the barrier between the conductive filament and the TiN electrode was increased when improve the stop voltage,thus the electron is hard to suppress and the HRS resistance increased.As a result,the TiN is an good electrode for RRAM application and the multilevel storage capability can help establish high-density RRAM device.Furthermore,we fabricated Gd/Gd:SiO₂/TiN RRAM device with Gd electrode,the memory window can be enlarged through decreasing forming compliance current?Forming C.C?,while the HRS and LRS resistance for Pt electrode device show no dependency on Forming C.C.The LRS current increased when reduce the Forming C.C.,the reason may be that Gd electrode was partly oxidized when applied forming C.C,which act as the extra series resistor.On the other hand,the HRS current decreased when reduce the Forming C.C.,a higher compliance may result in a robust filament,thus the higher HRS current was obtained.This work investigates the influence of Gd electrode on the RS performance,and provides guidelines for modify the memory window by selecting electrode materials.As for nitrogen doped ITO electrode based RRAM device of the N:ITO/HfO₂/TiN structure,we develop low temperature supercritical fluid nitridation?SCF-nitridation?technique to realize the nitridation for ITO electrode and further reduce the power to 120 nW.After the SCF-nitridation treatment,the memory window for the N:ITO electrode device was increased from 40 to 100.Moreover,the operation voltages and currents were remarkably decreased,in which the I_OFF was decreased to 65 nA,and the device exhibited high endurance?10⁷?.A oxygen-rich region was formed around the tip of filament with the effect of nitrogen doping,and the current mechanism was transferred from Ohmic conduction to Schottky emission,thus result in reducing the operation currents.This work provides reliable experimental evidence for obtaining low power,high uniformity,excellent endurance RRAM device.