Effect and Applications of High Temperature Heat Treatment on Optical Thin Films

• Main Authors: Wen-Hao Cho, 卓文浩
• Other Authors: Cheng-Chung Lee
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/82166512503431028300

博士 === 國立中央大學 === 光電科學與工程學系 === 104 === In this study, the influence of solid state diffusion on refractive index of thin films had been studied using thermal annealing method at high temperature. Base on solid state diffusion mechanism, we prepared three different material pairs, including Ta2O5/TiO2, Al2O3/MgO, Al2O3/ZnO. Each of these material pairs represented a different diffusion situation. Only interdiffusion phenomenon appeared at the interface of Ta2O5 and TiO2 at annealing temperature of 800oC and made the graded refractive index layer. According to the concept, we could design the rugate filter employed the suitable material pair. In Al2O3/MgO case, MgAl2O4 spinel layer growth between MgO and Al2O3 during annealing process of 800oC. Besides, some voids developed in the MgO layer and the apparent refractive index of MgO layer was decreased. The voids were caused by the faster diffusion rate of MgO than Al2O3 and increased the refractive index difference of 28.5% between high and low refractive index materials in the multilayer. Base on the reaction mechanism of Al2O3 and MgO, (Al2O3 MgO)8 Al2O3 multilayer would become (MgAl2O4 MgO+voids)8 MgAl2O4 after annealing process of 800oC for 4 hours. After annealing process, the positions of high and low refractive index materials exchanged, and the effective refractive indices of MgO layers were decreased due to the presence of voids. Beside, the refractive index difference of the multilayer was increased by 28%. Therefore, the reflective filter with 61% reflection at 300nm was obtained. The same as Al2O3/MgO pair, ZnAl2O4 spinel layer growth between ZnO and Al2O3 during annealing process of 800oC. A lot of voids developed in ZnO layer and caused much decrease in refractive index. The porosity of ZnO layer after annealing process achieves 58.6 % and the refractive index decreased to 1.357 at 550 nm wavelength.