Preparation Of NbO_x Films And Performance Optimization Of Resistive Random Access Memory

Due to high switching speed,low power consumption and easy integration,resistive random access memory（RRAM）is suitable for high-density information storage and high performance computing,as well as non-volatile logic operation and brain-like neuromorphic simulation.However,there are some problems in the practical application of RRAM,such as the difficulty of information recognition due to the low switching ratio of VCM-RRAM,the high dispersion of switching voltage of ECM-RRAM,and the issue about leakage current of RRAM in three-dimensional stacked structure.In this paper,pulse laser deposition and magnetron sputtering techniques were used to deposit NbO_x films.Firstly,the effect of Vo on the NbO_xfilms and resistive switching（RS）behavior of RRAM was studied.Then,from the aspects of the RS layer and electrode,the switching voltage dispersion of the device was optimized（N-doped NbO_x RS layer and Au-NPs modify the morphology of bottom electrode）.Finally,in order to solve the leakage current issue of RRAM in 3D integrated structure for practical applications,the prepared NbO_x films were self-assembled as 1S1R devices.The detailed information were as follows:（1）NbO_x films were deposited by pulsed laser deposition at different temperatures.As the deposition temperature increases,the particles in NbO_x film began to coalesce and boundries formed at different regions,and the boundaries was becoming denser.Besides,the Vo contentration of NbO_x films increased gradually and the distribution of Vo was denser,resulting in the formation of more conductive filament（CF）paths.The contentration and distribution of Vo in NbO_x films could be adjusted by increasing the deposition temperature.The SET process changed from abrupt process to stepwise process,RESET process changed from abrupt process to gradual process.Therefore,the formation and fracture of Vo CF and the RS behavior of RRAM could be regulated by Vo engineering.（2）N-doped NbO_x films were prepared by pulse laser deposition combine with in situ N-doping technique.The effect of N-doping on the properties of NbO_x films,the performances of Pt/NbO_x:N/Pt and Pt/NbO_x:N/Cu devices were studied.For the devices composed of different top electrodes,N-doping did not change the ohmic conduction mechanism of LRS,but changed from SCLC mechanism to hopping mechanism of HRS.After N doping,the V_set and V_reset of Pt/NbO_x:N/Pt device were significantly reduced,the stability（retention time and endurence）was significantly improved,and the switching ratio was also increased.It was mainly due to the formed of Vo-N groups by N doping,which greatly reduced the ionic conductivity and the total energy of the system.The distribution of V_set and V_reset was more centralized of Pt/NbO_x:N/Cu devices.The main reason was that the Vo-N group repelled adjacent Nb⁵⁺under Coulomb force,forming a relaxation Nb-Nbregion.The migration and diffusion of Cu²⁺was becoming easier and the Cu CF was localized in the Nb-Nbregion of NbO_x:N film.Therefore,the switching voltage and distribution dispersion were reduced of Pt/NbO_x:N/Cu devices by N doping.（3）NbO_x films were deposited on the substrate modified with different concentration of Au-NPs by magnetron sputtering technique.The RRAM performance was studied by changing the modified concentration of Au-NPs on bottom electrode.The diameters of Au-NPs were 10 nm.Among all the devices,the Au_min/NbO_x/W tip device modified by the lowest concentration of Au-NPs exhibited the best performances.V_set distribution of the device was the most centralized.V_reset decreased significantly and the distribution range was narrower.The resistance distribution in HRS and LRS of the device was more stable,the retention time increased to 2.5×10⁴ s without attenuation,and the stability of the device was significantly improved.The conductive mechanism of the device was not affected by the modification of Au-NPs on the bottom electrode.The conductive mechanism was SCLC mechanism of HRS and ohmic mechanism of LRS.When the bottom electrode of the devices was modified by the Au-NPs,CF preferred to grow around Au-NPs,reducing the randomness of CF and increasing the centralization of switching voltage dirtribution.However,when the modification concentration of Au-NPs was too high,the formation and rupture of CF were more random and the switching voltage distribution showed higher fluctuation of Pt-Au_max/NbO_x/W tip device.（4）NbO_x films with thickness of 100 nm were prepared by DC magnetron sputtering.The specific RS behavior was observed by adjusting I_ccof Pt/NbO_x/W tip device.The device exhibited a non-volatile RS behavior with I_cc of 5m A and volatile RS behavior with I_cc of 10 m A.Further increasing I_cc to 50 m A,the integrated 1S1R RS behavior was observed.Each of the RS behavior showed good stability and repeatability.The MS behavior of the device mainly came from the formation and fracture of Vo CF.The volatile RS behavior of the device was mainly due to the MIT of NbO₂ induced by joule heating.The 1S1R RS behavior was caused by the formation/rupture of Vo CF and the MIT of NbO₂.