| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 88 === In this work, two kinds of thin films, ferroelectric, and oxide electrode were prepared by pulsed-laser deposition method. Ferroelectric thin films of calcium-modified lead titanate (Pb1-XCaXTiO3, PCT) were deposited on Pt, La0.5Sr0.5MnO3/Pt, and La0.5Sr0.5MnO3/IrO2 bottom electrodes, respectively. The property of crystalline, thin film quality, electrical, and electric fatigue is investigated.
Experimental results show that polarization decreases when calcium contents (X) increase. When X equals 0.24 and 0.3, PCT exhibit a typical ferroelectric property. Moreover, lower tendency remanent polarization generates when X equals 0.4 and 0.5, and dielectric constant ( ) becomes the maximum value when X equals 0.3. Leakage current density of the above four kinds of PCT thin film is huge. As mentioned above, ferroelectric property of PCT thin films deposit on Pt bottom electrode do not exhibit well. Thus, we used the buffer layer material to improve the thin film ferroelectric property.
We use LSMO for the buffer layer bottom electrode material to enhance the crystalline growth and the thin film structure density. Hence, leakage current density decreases than that deposits in Pt. In addition, after 1 switching cycles fatigue testing, the coercive electric field is decreased.
The property of PCT thin films deposit on LSMO/IrO hybrid oxide electrode is improved in fatigue testing than those deposit on Pt metal electrode. Thus, ferroelectric thin films property is improved for using buffer layer and oxide electrode. On the other hand, IrO is earlier aging with time increased.
Alternatively, we prepared PCT thin films by Sol-Gel method. From experimental results, comparing the thin films deposit with the PLD and Sol-Gel method. The properties of remanent polarization and coercive electric field are very similar. Smaller leakage current density generate in Sol-Gel method, on the other hand, larger dielectric constant, and storage charge density generate in PLD method.
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