(A) study on the infrared electrochromic window for shutter-less infrared camera

Abstract

In this dissertation, an infrared electrochromic window for a shutter-less infrared camera was proposed to overcome the problems such as size, stability, and image freezing of an infrared camera using a convention-al shutter. The proposed infrared window is used to package the infrared sensor module and consists of two chapters. The first chapter is about anti-reflection (AR) coating. Silicon (Si) and germanium (Ge), which are mainly used as windows in the middle-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) regions, can transmit only about 50% of the incident infrared radiation due to reflection at the window surface. Therefore, many researches on antireflection coatings for increasing the transmittance of windows have been conducted. In this study, nickel oxide (NiO) material was firstly proposed and applied to the antireflec-tion coating. The nickel oxide thin films were deposited on both sides of the silicon window by RF sputter-ing method, and the silicon windows deposited with nickel oxide showed a significant increase in transmit-tance in both the MWIR and LWIR regions. In addition, it was confirmed that the defect inside the NiO film was decreased by annealing after the deposition of the nickel oxide thin film and from this, the infrared window having improved transmittance could be fabricated. The second theme is about infrared electrochromic windows, which actually change the infrared transmit-tance and enable shutter-less operation. As an electrochromic material, tungsten oxide ($WO_3$) and nickel oxide were used, and a tantalum oxide film ($Ta_2O_5$) was deposited between the two films as an ion conduct-ing layer. $WO_3$ thin films and NiO thin films were changed in transmittance by hydrogen injection. To in-crease transmittance modulation, $WO_3$ thin films and NiO thin films were deposited at various oxygen par-tial pressure and sputtering pressure and measured the structural and electrochromic properties. The infrared electrochromic window was fabricated by using the electrochromic films which showed the best electro-chromic properties. The transmittance ratio of the fabricated window before and after the coloration was 0.66 in the MWIR and 0.77 in the LWIR regions, respectively.