| Summary: | 碩士 === 國立臺灣師範大學 === 機電科技學系 === 102 === This study is to investigate MFIS (Metal/Ferroelectric/Insulator/Semiconductor) structure capacitors. Ferroelectric materials have a Perovskite structure. It generated ferroelectric polarization and remnant polarization. Those properties are suitable for nonvolatile memory materials. BiFeO3 is one of the Ferroelectric materials that have been attracted to attention recently. Although BiFeO3 possesses many merits such as high Curie temperature (about 850-860 ℃), high Neel temperature (about 370-397 ℃) and large remnant polarization, it possesses demerit of large leakage current. In order to improve this problem, we resolved it in a way of Nb-doped BiFeO3 thin film.
The purpose of this study is to find the optimum combination of factors in the manufacture of MFIS capacitors (Al/BiFeO3+Nb/HfO2/p-Si substrate) using Taguchi Method, and then discuss the effects of process conditions on leakage current and memory window. Based on the electrical property measurements (I-V and C-V), SNR (S/N ratio) was calculated. As a Result, the leakage current and the memory window indicated same trends. We obtained the optimal recipe which was 700℃ for RTA temperature, 5 W for DC power of Nb sputtering and 15 for Argon-to-Oxygen ratio. According to physical characterization (XRD) analysis results, Nb ions replaced iron ions at annealing temperature at 700 ℃, which this means that oxygen vacancies were reduced by Nb-doping. Although the more Nb-doping, the more Nb ions replace Fe ions, but excessive Nb-doping induces the increase of the leakage current and reduces the memory widow.
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