| Summary: | 碩士 === 逢甲大學 === 電機工程學系 === 107 === In this thesis, two kinds of interference filters were fabricated by dual electron-gun evaporation with ion assisted deposition. The interference filter was designed for the visible and mid-infrared bands. The mid-infrared filter is bandpass filters with a passband design band of 3 μm to 5 μm. The filters were designed by the Essential Macleod software.
The long-wavelength optical filter was fabricated by high and low index material. The high refractive index material is titanium dioxide with a refractive index of 2.357. The low refractive index material is silicon oxide with a refractive index of 1.467. In this study, two long-wavelength optical filters were prepared with 19 layers and 29 layers, of which 29 layers were designed with the addition of a widening layer. The transmittance results showed that the 29-layer long-wavelength optical filter was successful compared to the 19-layer. The cut-off band is widened and the cut-off band wavelength range is widened from 130 nm to 215 nm.
In this study, the center-wavelength of the mid-infrared bandpass filter was 4 μm, and the filters were deposited on double side-polished germanium and silicon substrate, which were designed by the combination of long wave pass and short wave pass in non-quarter wave film design. The passband transmittances met the specification, and the cutoff band transmittances were less than 1%, and the cutoff wavelengths were also consistent with the design.
In the mid-infrared bandpass film microstructure, the microstructure of the films were observed by FE-SEM. Dense microstructure in optical filters shows that the film is compressive. The interface stress proposed by Spaepen is used as the prototype basis. Experimentally, two kinds of materials were used to obtain the interfacial stress between two kinds of film materials by two different stacked films. Combined with the Ennos formula, the Ennos formula was used to add the interfacial force of the multilayer film to derive a new approximation for film stress prediction. The residual film stress mode of the multilayer film is verified by comparing the simulated residual stress of the multilayer film of the mid-infrared bandpass filters with the actual measurement results.
The actual thickness of the 20-layer mid-infrared bandpass filter is 8.03 μm. The predicted residual stress value of the interface force prediction formula is -0.247 GPa, and the measured value is -0.231 GPa. The actual thickness of the 23-layer mid-infrared bandpass filter is 10.1 μm. The predicted residual stress based on the interfacial force prediction formula is -0.167 GPa, and the measured value is -0.197 GPa. It has been proved by experiments that the measured results are very close to the predicted residual stress values of the modified Ennos formula considering the interfacial force, and can be applied to the prediction of the residual stress of the multilayer film.
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