| Summary: | 碩士 === 國立中興大學 === 材料工程學研究所 === 92 === Low temperature coating technology for depositing thin films on flexible substrates is one of the most important issues in flat panel displays (FPD) research. Tantalum pentoxide (Ta2O5-X) thin films belong to high-valence oxides, having low optical loss, high refractive index, and good chemical stability, and find applications in optoelectronic devices.
Tantalum pentoxide thin films were prepared by RF magnetron sputtering under different O2/Ar flow ratio, deposition time, and RF power. Three different types of substrate including polyethylene terephthalate (PET), glass, and Si were used in this study. Effects of processing parameters on the microstructure and optical properties of the coatings were investigated. It is found from ellipsometry (at a wavelength of 632.8 nm) and atomic force microscopy that the deposition rate of the films decreases with increasing O2/Ar ratios, and vice versa for the refractive index and surface roughness. The average surface roughness of the Ta2O5-x coatings is 1.5 nm. From x-ray energy dispersive spectroscopy (EDS), it is obtained that the Ta:O atomic ration of the films produced with O2/Ar ratios ranging from 0.6 to 1.25 is 1:1.40 to 1:2.41, respectively. The films prepared at low O2/Ar flow ratio are amorphous, whereas the one that was prepared at high flow ratio consists of a mixture of nanocrystalline and amorphous phases. In respect to the RF power, it is found that the crystallinity and packing density of the films improve with the RF power.
Measurement of the optical transmittance of Ta2O5-x films indicates that when the film thickness is less than 25 nm, the transmission is about 95%. As the film thickness approaches about 100 nm, the optical transmission of the Ta2O5-x films on glass and PET substrate was decreases to 83% and 65%, respectively. In addition, the energy band gap of the films on the glass and PET substrates were estimated to be 4.2 ± 0.02 eV and 3.75 ± 0.02 eV, respectively.
In summary, this study demonstrates obtained that Ta2O5-x thin films with good optical properties can be made by properly control of the O/Ar flow ratio and RF power of the coating system.
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