| The fabrication processes and properties of access memory have important significance during the information technology era. Resistive random access memory (RRAM) has been extensively researched for the nonvolatile memory owing to its fast operation speed, low power consumption, simple structure and high integration density. RRAM has a metal-insulator (semiconductor)-metal structure. Up to now, resistive switching (RS) behaviors have been observed in binary oxides(ZnO、CuOx、 Al2O3、TiO2), perovskites(SrTiO3、SrZrO3), organics materials and so on. Among them, binary oxides have attracted particular attention and interests because of the easy deposition and compatibility with Complementary Metal-Oxide-Semiconductor Transistors (CMOS) technology.Al2O3 has been extensively studied since its excellent optical performance, high mechanical strength and hardness, good transparency and insulation. Al2O3 based RRAMs have been invented through traditional physical vapor deposition. However, atom layer deposition (ALD) prepared Al2O3 based RRAM has not been fully researched yet. Compared to other deposition methods, ALD can control the composition and thickness of the film precisely. At the same time, the ALD Al2O3 RRAM devices suffer from high forming voltage (VF) and poor stability due to nonuniform distribution of operation voltages and resistance states, mostly associated with high breakdown voltage.In this thesis, we fabricated Al2O3 based devices with resistive switching properties by ALD, and explored the influence of annealing process to the Al2O3 film. By using Zn doped method and the in-situ hydrogen plasma enhanced treatment (HPET) on ALD grown Al2O3 layers, we had successfully reduced the forming voltage of the ALD Al2O3 devices controllably and realized electroforming-free property with high uniformity. The main achievements are as follows:1. The fabrication technique of Al2O3 based RRAM was explored. Ti/Al2O3/Pt device with resistive switching properties had been fabricated successfully. Annealing process could depress the VF of Al2O3 based RRAM. We deposited the Al2O3 film on Pt electrode by ALD method and Ti electrode by electron beam evaporation and metal mask. The result of atomic force microscope (AFM) declared that the Al2O3 film had a smooth surface whose Rms was only 0.852nm. The Ti/Al2O3/Pt device had typical bipolar resistive switching (BRS) properties. The voltage of forming, SET and RESET were 7.5V,1.5V,-1.2V, respectively. The HRS/LRS ratio was 102-103 or so, and conductive filament theory could explain the resistive switching mechanism and the conductivity of the device obeyed the space charge limited current (SCLC) mechanism. After annealing process, the conductivity of the film was improved and the VF of Ti/Annealing Al2O3/Pt was depressed to 4.5V.2. We realized forming free property of Al2O3 based RRAM by doping Zn and in-situ hydrogen plasma enhanced treatment (HPET) method respectively. The uniformity of the device was also improved by HPET method. By controlling the cycles of Al2O3 and ZnO during ALD process, different content Zn was doped. When n(Al):n(Zn) was 29, VF was 3.95V; and n(Al):n(Zn) was 19,VF was 2.58V. As n(Al): n(Zn) was tuned to 9, the device realized forming free. At last, HPET could depress the VF, too. When the HPET time was 15s, the voltage of SET and RESET were 1.5V,-1V, respectively. The HRS/LRS ratio was more than 103 and the device could be swept over 100 times. The outstanding improvement of the electrical performance might attribute to the hydrogen plasma treatment to the Al2O3 film, and this method could be useful for other RRAM material systems as well. |
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