Design And Mechanism On The TaO_x-based RRAM Device

With the development of integrated circuit processing technique,the FLASH memory based on the floating gate structure has encountered technological difficulties with the decreasing feature size leading to charge leakage.Resistive random access memory?RRAM?is currently one of the promising candidates to replace FLASH memory,which is demonstrated to have simple structure,high speed,high scalability,CMOS compatibility and high-density integration potential.Tantalum oxide has been the research hotspot of RRAM due to its many advantages,such as good thermal stability,high dielectric constant and two stable phases of TaO₂ and Ta₂O₅.In this dissertation,the main research contents are as follows: optimizing growth process parameters of TaO_x thin film and discussing the performance of different top electrodes RRAM devices;Fabrication of bilayer RRAM devices and optimizing the performance of bilayer RRAM devices to reduce the power consumption.Based on the study of electrical characteristics of TaO_x-based RRAM device,the switching mechanism of RRAM devices is further explored.The single-layer TaO_x-based RRAM devices are prepared and optimized.Influence of conditions of different ratio of oxygen and argon on TaO_x thin film growth is investigated and the influence of ratio of O₂ and Ar on the microstructure and element composition of TaO_x thin film is showed by the test results of SEM and EDS.And based on W top electrode,the influence of ratio of O₂ and Ar on 15-nm-thick single-layer TaO_x-based RRAM devices is discussed and the best ratio of O₂ and Ar is 2:38.With optimization ratio of O₂ and Ar,the influence of different electrodes on the electrical characteristics of RRAM devices is discussed,and the RRAM devices with electrode of W,Cu and Ni are fabricated.The electrical characteristics of RRAM devices with W,Cu and Ni are compared and investigated,and the switching models of RRAM devices with different top electrodes are proposed.Based on the analysis of characteristic of single-layer TaO_x-based RRAM devices,the switching model of RRAM based on Cu conductive filaments is investigated using Monte Carlo method.The microcosmic growth process of conductive filament is analyzed with simulation,which further explains the phenomenon of resistive switching.Based on the research of single-layer TaO_x-based RRAM,the bilayer RRAM devices are fabricated.The influence of the thickness of film on device performance,especially to Reset current is investigated.On the one hand,the W/TaO_x/Ta₂O₅/TiN structure is fabricated,and the thickness of Ta₂O₅ layer is 6 nm and thicknesses of TaO_x layer is 5,10,15,20 nm respectively.The influence of different thicknesses of TaO_x is analyzed,and the switching model based on oxygen vacancy conductive filaments is proposed.On the other hand,the structure of Cu/TaO_x/Al Ox/TiN is fabricated,with the thickness of AlOx of 1,2,3,4 nm respectively.The electrical characteristic of the structure is investigated and its mechanism is analyzed.Acting as a barrier layer,AlOx layer blocks electron injection,and the Reset current can be reduced to 500 nA,and the power-consumption is reduced effectively.