Structures and dielectrics of sputtered epitaxial TiO2/HfO2 superlattices
| Autor: | Jing-Wei Zhou, 周京蔚 |
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| Rok vydání: | 2015 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 103 RF magnetron sputtering has been used to deposit thin films of TiO2/HfO2 superlattices in alternating sequence on c-oriented sapphire substrates using titanium, or titanium dioxide, and Hafnium dioxide targets. The thin films thus obtained have higher dielectric constants and better insulation properties. The dielectric characteristics were studied on samples of different numbers of cycles and thickness ratios of the two oxides. Two series of samples, classified as series-A for [(TiO21nm/HfO21nm)10cycles and (TiO23nm/HfO21nm)10cycles], and as series-B for [(TiO21nm/HfO21nm)5cycles and (TiO23nm/HfO21nm)5cycles]. X-ray diffractometry (XRD) and transmission electron microscopy (TEM) have been conducted to examine the structural properties of the samples in relation to the dielectric properties, and lock-in amplifier used to measure the internal impedance of the samples from 0.1 Hz to 100kHz. Change of voltage as a function of frequency was used to calculate the values the frequency dependence of involved capacitance and inductance. TEM electron diffraction patterns showed that the HfO2 layers are of a few nanometer thick and grow epitaxially on the TiO2 thin film by assuming the same crystal structure of the underlying TiO2 layer. Traditional wisdom suggests that TiO2 thin films grown on c-sapphire should at best be twinned, if epitaxial at all. However, in this work, the structure of the obtained TiO2 was found to be epitaxial and twin-free. This is interpreted as associated with the overall chemical bonding forces among the Ti, O, and Al atoms of the TiO2 (011)-plane on sapphire (0001)-plane. This led to an ideal epitaxy with orientation relations of (TiO2)(011)//Al2O3(0001), TiO2[010]// Al2O3 [1120] and TiO2[001]// Al2O3 [1010]. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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