Investigation On Performance And Mechanism Of Tantalum Oxide Based Low Power Resistive Memory

Recently,a series of novel nonvolatile memories(magnetic random access memory,ferroelectric random access memory,phase-change random access memory and resistive random access memory)have emerged in order to solve the limited-scale problem of mainstream nonvolatile memory-Flash memory.Resistive random access memory,RRAM for short,stands out from the others due to its advantages like simple structure,fast operation speed and high integration density.However,the low uniformity and high power consumption of RRAM still are the two fatal flaws for its application.In order to optimise the uniformity and power consumption of devices,the TaO_X with excellent endurance is chosen as the function layer in this thesis,and the main work is as follows:First,the films are deposited by magnetron sputtering and the RRAM device cells based on ITO/TaO_X/TiN are fabricated;the key factor,oxygen partial pressure of TaO_X deposition process,is optimized.And the effect of TaO_X thickness on the electrical characteristics of the devices is discussed.The optimal oxygen partial pressure is 5%(Ta₂O₅ ceramic target) and the optimal thickness is 10 nm,which can improve the endurance of the devices to 10⁵ cycles.Then,the performance of three structures(ITO/TaO_X/TiN,ITO/TaO_X/Pt and Ag/TaO_X/TiN) are compared in terms of electrodes engineering.The mechanism of ITO/TaO_X/TiN with low operating voltages[the mean set voltage(V_set)and reset voltage(V_reset)are 36 mV and -109 mV,respectively]and high uniformity is analyzed:The oxygen concentration gradient formed in the function layer because of the oxygen-rich property of ITO electrode,which facilitates the reduction of the operating voltage.Besides,the formed Ti ON interface layer in TaOx/TiN can prevent oxygen loss and confine the resistive switching near this layer,which results in high uniformity of ITO/TaO_X/TiN.In the end,the AlO_X layer is inserted in ITO/TaO_X/TiN structure.By selecting the appropriate location of Al O_X insert layer and adjusting the thickness of the Al O_X insert layer,the operating current of our devices can be reduced to 100 n A from the level of m A,and the power consumption for set/reset is reduced to 586 pW/40.2 nW.In addition,the w/Al O_X(10nm) sample can achieve an endurance of 10⁴ cycles in the operating current of 10?A.By calculation based on the Schottky emission formula,the barrier heights of devices are found to be almost doubled upon the incorporation of the AlO_X layer.And the gap between the broken conductive filaments is wider because of the extra oxygen ions provided by the AlO_X layer,which led to a decrease in the power consumption of devices and an enlargement of the devices'window.Base on the experimental results and analysis of this thesis,it is proved that the suitable electrode structure and insert layer can improve the uniformity of devices and reduce the power consumption of devices,respectively,which can lay a foundation for high uniformity and low power resistive random access memory.