Yoshihiro Someno

Helicon plasma deposition of a TiO2/SiO2 multilayer optical filter with graded refractive index profiles

Thirty one layer TiO2/SiO2 optical filters with graded refractive index profiles were fabricated by helicon plasma sputtering at room temperature. Multilayer films were deposited on glass (BK7) and Si (100) substrates simultaneously and sequentially. The measured transmittance spectrum exhibited a reflectance of 99.8% at a central wavelength of 730 nm and high transmittance over the wavelength region outside of the reflected band as a result of the suppression of the sidelobes. The experimental transmittance spectrum corresponded almost completely with that calculated based on the optical multilayer film theory and using the measured refractive indices of TiO2, SiO2 and TiO2–SiO2 composite films. Transmission electron microscopic observations confirmed the expected microstructure of the filter.

Microstructure and optical properties of amorphous TiO2-SiO2 composite films synthesized by helicon plasma sputtering

Abstract Composite films of TiO 2 –SiO 2 have been deposited on Si(100) wafers and glass (BK7) substrates by helicon plasma sputtering at room temperature. The results of X-ray diffraction and high resolution transmission electron microscopic observation showed that all of the composite films have an amorphous structure. The observation of scanning electron microscopy exhibited that the surfaces of all of the composite films have dense smooth morphology. The refractive index and the transmittance of the composite films varied gradually in the whole composition range of the TiO 2 –SiO 2 binary system. TiO 2 –SiO 2 composite films exhibited a transmittance of more than 90% compared with that of the glass (BK7) substrate. The relationship between refractive index and TiO 2 content for the composite films can be described using the Lorentz–Lorenz model

Preparation of epitaxial AlN films by electron cyclotron resonance plasma‐assisted chemical vapor deposition on Ir‐ and Pt‐coated sapphire substrates

AlN epitaxial films have been fabricated on Ir‐ and Pt‐coated α‐Al2O3 substrates via electron cyclotron resonance plasma‐assisted chemical vapor deposition (ECRPACVD) using an AlBr3‐N2‐H2‐Ar gas system at substrate temperatures ranging from 500 to 700 °C. The epitaxial relationships between AlN films and substrates were determined by x‐ray diffraction, x‐ray pole figure, and reflection high‐energy electron diffraction. The results are useful in practical applications, such as AlN/metal/α‐Al2O3 structure in surface acoustic wave (SAW) devices.

LOW-TEMPERATURE EPITAXIAL GROWTH OF ALN FILMS ON SAPPHIRE BY ELECTRON CYCLOTRON RESONANCE PLASMA-ASSISTED CHEMICAL VAPOR DEPOSITION

Abstract AlN films have been epitaxially grown onto (0001) sapphire substrates, for the first time, by electron cyclotron resonance plasma-assisted chemical vapor deposition using an AlBr 3 H 2 N 2 gas mixture at substrate temperature as low as 650°C. This method of film growth was shown to lead to good epitaxial AlN with a very smooth surface morphology. X-ray diffraction analysis showed that the c -plane of AlN films was parallel to that of the sapphire. X-ray pole-figure analysis showed that the [1210] direction of AlN is parallel to the [1010] direction of sapphire. The epitaxial growth of AlN was further verified by reflection high energy electron diffraction.

Design and experimental approach of optical reflection filters with graded refractive index profiles

A novel optical multilayer filter with graded refractive index profiles using a quarterwave stack was designed. This filter exhibits a high reflectance band, a sharp cutoff and a wide transmittance region as the result of sidelobe suppression. A 31 layer TiO2/SiO2 high reflectance filter with a graded refractive index profile was fabricated by helicon plasma sputtering on BK7 and Si (100) substrates. The deposition system was operated under ambient gas pressure of 1.8×10−1 Pa at room temperature. The measured transmittance of the spectrum was in good accord with calculated results. Transmission electron microscopic observations confirmed the expected microstructure of the filter.

Low-Temperature Growth of Polycrystalline AlN Films by Microwave Plasma CVD

The growth of polycrystalline AlN film at a rate of 60 nmmin-1 was accomplished at a substrate temperature of 550°C by a coaxial-line-type microwave plasma chemical vapor deposition (CVD) method using the AlBr3-H2-N2 gas system. Excellent c-axis orientation was observed on the film having a half-width rocking curve of (001)AlN (Δθ50) of 2.1 degrees. No carbon or bromine was detected by the AES measurements.

Optical properties of titania/silica multilayer filters prepared by helicon plasma sputtering

Seven-layer optical multilayer filters with alternating layers of titania and silica were fabricated by helicon plasma sputtering at room temperature. The reflectance of the filters around the design wavelengths of 800 and 1300 nm are up to 95.80% and 95.32%, respectively. Their reflected bands have the full widths at half maximum of about 360 and 600 nm, respectively. The measured transmittance spectra correspond well with the calculated results based on the optical multilayer film theory with measured refractive indices of 2.44 and 1.48 for TiO2 and SiO2, respectively. Microstructures of the TiO2 and SiO2 films and TiO2/SiO2 multilayer films were investigated.

Preparation of AlN-Al2O3 Composite Films by Microwave Plasma Chemical Vapor Deposition

AlN-Al2O3 composite films were prepared by microwave plasma chemical vapor deposition using an AlBr3-H2-N2-N2O-Ar gas mixture on a Si substrate. They were examined with respect to their deposition rate, microstructure, compositions, and refractive indices. Four crystallinity phase regions were observed by X- ray diffractometer as a function of N2O gas flow rate and substrate temperature: A, c-axis oriented AlN; B, lower-oriented AlN; C, amorphous; and D, amorphous +β-NH4Br. Composite films composed of AlN and Al2O3 microcrystals having an average grain size of 50 nm were detected by transmission electron microscopy observation. Refractive indices, optical band gaps, and surface roughness were also determined.

Low-Temperature Synthesis of C-Axis-Oriented Polycrystalline Aluminum Nitride Films by Electron Cyclotron Resonance Plasma Chemical Vapor Deposition Using AlBr3-N2-H2-Ar Gas System

Aluminum nitride (AlN) thin films have been synthesized on silicon substrates via microwave-excited electron cyclotron resonance (ECR) assisted chemical vapor deposition (CVD) at substrate temperatures ranging from 300 to 400°C from the AlBr3-N2-H2-Ar gas system. The resultant films were characterized using X-ray diffraction, scanning and transmission electron spectroscopies, transmission electron diffraction, infrared transmission spectroscopy, and Auger electron spectroscopy. The study of these analyses shows that highly c-axis-oriented polycrystalline AlN films, free of bromine and hydrogen impurities, can be deposited by the ECR plasma CVD method.

Design and preparation of a 33-layer optical reflection filter of TiO2–SiO2 system

Multilayer optical reflection filters with several kinds of graded refractive index profiles were designed. The effects of the number of layers of multilayer films and grading functions of refractive index profiles on the optical filter characteristics were examined by using simulation. A 33-layer optical reflection filter with a linear refractive index profile was found to be optimal in terms of both optical performance and manufacture. The designed 33-layer TiO2–SiO2 reflection filter was fabricated by helicon plasma sputtering. The optical performance of the prepared multilayer film agreed well with that of the designed filter. The measured transmittance spectrum exhibited a sharp cutoff stop band around a central wavelength of 1340 nm and a wide pass region with high transmittance of about 90%. The reflectance of the stop band was greater than 99.0% in the wavelength region from 1208 to 1518 nm.