Kunio Nishioka

Angled etching of (001) rutile Nb–TiO2 substrate using SF6-based capacitively coupled plasma reactive ion etching

We demonstrated the plasma etching of a (001) rutile Nb–TiO2 substrate using SF6 plasma. A vertical etching profile and a smooth etched surface were obtained. In addition, the angled etching of a (001) rutile Nb–TiO2 substrate was achieved in a conventional SF6 reactive ion etching system for the first time. The etching angle was determined by the angle of the groove of the holder. We believe that our simple dry etching technique is suitable for the formation of a three-dimensional photonic crystal with complete photonic bandgap (CPBG) and optical waveguides.

SF6-Based Deep Reactive Ion Etching of (001) Rutile TiO2 Substrate for Photonic Crystal Structure with Wide Complete Photonic Band Gap

We demonstrated the fabrication of a photonic crystal structure of a (001) rutile TiO2 substrate by deep reactive ion etching (RIE) using SF6 plasma. A vertical etching profile and a smooth etched surface, which satisfy the requirements for optical device application, were obtained. We think that this proposed process is useful for the microfabrication of TiO2-crystal-based optical devices, such as photonic crystals with a complete photonic band gap (CPBG) and optical waveguides.

Calculation and fabrication of two-dimensional complete photonic bandgap structures composed of rutile TiO2 single crystals in air/liquid

Abstract Photoelectrochemical applications of photonic crystals are gathering great interests both from physicists and chemists. Here, we theoretically and experimentally present two-dimensional photonic bandgap (2D-PBG) structures based on rutile titanium dioxide (TiO2) single crystal that is a famous material because of the photoelectrochemical ability. The structures were the arrays of hollow hexagonal rutile TiO2 pillars in contact with air or a typical nonaqueous electrolyte solution, acetonitrile. Since the TiO2 refractive indices exhibit a strong dispersive behavior, the bandgap width was discussed from the viewpoint of the refractive index map that would be helpful for the real application of this structure. The 2D-PBG structures for both infrared light and visible light were fabricated by our established lithography technique for rutile TiO2 with and without Nb doping, i.e., photocatalytic TiO2 and high electron conductive TiO2, respectively. These structures show characteristic absorbance peaks or reflectance dips at wavelengths predicted by our theoretical calculations.

Energy dispersive X-ray spectroscopy analysis of Si sidewall surface etched by deep-reactive ion etching

We investigated the composition of a passivation film on a sidewall etched by deep-reactive ion etching (RIE) using SF6/O2 and C4F8 plasma, by energy-dispersive X-ray (EDX) spectroscopy. It was found that the compositions of carbon and fluorine in the passivation film on the etched sidewall depend on the width and depth of the etched trench. It is important to understand both the plasma behavior and the passivation film composition to carry out fabrication by deep-RIE. We consider that these results of the EDX analysis of an etched sidewall will be useful for understanding plasma behavior in order to optimize the process conditions of deep-RIE.