| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 102 === In this study, we investigate the properties of TiO2 thin films grown by atomic layer deposition method (ALD) and apply them to the resistive random access memory devices (ReRAM). For the application in the ReRAM devices, various characterization methods, such as transmission electron microscopy (TEM), X-ray photoelectron microscopy (XPS), are used to analyze the properties of TiO&;#172;2 thin films. Based on the experimental results, it shows that TiO2 films with different properties, such as the crystal structure, the chemical composition and the concentration of oxygen vacancies, can be grown by tuning the growth parameters.
Besides, because some fractures in the polycrystalline TiO2 films are observed in the cross-sectional TEM images, it proves the existence of the residual stress. In this study, TEM techniques are used to measure the residual stress in thin films. According to the experimental results, we infer the residual stress is thermal stress. During the growth, amorphous TiO2 films are deposited on the substrates, and crystallize to release the thermal strain energy at the critical thickness in the cooling process. In the ReRAM devices, amorphous TiO2 thin films are used to reduce the concentration of the defects; at the same time, the thickness of thin films is reduced to avoid the high accumulated strain energy and the fracture problems.
Based on these experimental results, we successfully apply ALD-grown TiO2 films to the ReRAM devices and investigate the I-V characteristics of the two different device structures, Pt/TiO2/Pt and FTO/TiO2/ITO. It shows that the stability of the devices with the Pt/TiO2/Pt structure is not good enough because its resistive switching mechanism. On the other hand, the stability and the operating characteristics are improved significantly using the conducting metal oxides, such as the FTO and ITO thin films, as electrodes.
Key words: Titanium oxide, Atomic layer deposition, Transmission electron microscopy, Strain analysis, Resistive random access memory.
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