Takashi Ishiguro

MgO(200) Highly Oriented Films on Si(100) Synthesized by Ambient-Controlled Pulsed KrF Excimer Laser Deposition Method

MgO film growth on Si(100) using the ambient-controlled pulsed KrF excimer laser deposition method has been performed under a wide range of synthesis conditions: oxygen pressure (P O2 ) of 10-6–10-3 Torr, substrate temperature (T sub) of 100–300° C, and laser irradiation energy density on Mg metal target of 0.6–2.0 J/cm2. MgO(200) pole figures of MgO films are measured by the X-ray ( CuKα) diffraction method using Schulzs reflection attachment. Almost all MgO films have strong (200)-preferred orientation and rather weak (220)-preferred orientation. The crystallographic relation of the former case is MgO(200)//Si(100) and MgO[01*BAR*1*BAR*]//Si[01*BAR*1*BAR*]. MgO film with the highest degree of (200)-preferred orientation was fabricated under the optimized conditions of T sub=300° C, energy density= 1.5 J/cm2, and P O2 =1×10-4 Torr.

Oxygen Sensing Properties of SrTiO3 Thin Films

The oxygen sensing properties of SrTiO3-based thin films have been investigated at room temperature. First, nondoped SrTiO3 was investigated. Although such a material is highly sensitive, its electrical resistance was too high and not feasible for practical use. Donor (Nb5+) could lower the resistance of SrTiO3; however, the sensitivity was lost. UV-light irradiation or t2-type acceptor (Cr3+) doping could lower the resistance and yet maintain the sensitivity. In contrast to t2-type acceptor doping, e-type acceptor (Fe3+) doping could lower the resistance; however, the sensitivity was lost. In this paper, we discuss the phenomena from the viewpoint of polaron-controlled carrier conduction.

Solar Light Absorption Property of Sputtered Al–N Films with Enhanced Surface Roughness during Film Growth

Al–N films are formed on a glass substrate by rf sputtering using Ar and N2 gas mixture. The concentration of partial N2 gas pressure (cN2) is changed from 0.0%N2 to 16.0%N2. Optical properties are measured in the wavelength range of 0.24 to 2.60 µm. When cN2 is varied at the same film thickness, the specimen with 7.3%N2 shows the highest solar energy absorptance (α) for the air mass one. Then, as the film becomes thicker at this cN2, α increases to 0.95, which is a promising characteristic for application as a solar absorber coating. It is also observed by atomic force microscopy that the surface roughness is enhanced as the film becomes thicker. The essential reason for the high value of α is the antireflection effect due to the gradient-refractive index caused by the enhanced surface roughness during film growth.

CD-Compatible Write-Once Disc With High Refrectivity

A high reflectivity write-once disc with specifications satisfying the CD Standard has been developed. The new disc realizes a reflectivity greater than 70% and employs a simple configuration with a substrate, photo-absorption layer, reflection layer and protection layer. Since there is no space between layers, high durability is assured. Recording is performed when the substrate resin expands and intrudes into the photo-absorption layer, mixing with the decomposed dye materials. The specifications of the new disc are completely compatible with the current CD Standard, while the discs simple configuration realizes low cost processability.

Effect of N2 partial pressure on the structure of MgO thin films deposited by radio frequency-magnetron sputtering with single-crystal MgO target

We report the effect of N2 partial pressure on the structure of MgO thin films deposited on Si(100) substrates by radio frequency-magnetron sputtering in Ar+N2 mixture. The films were evaluated using x-ray diffractmeter. As increasing N2 partial pressure, the intensity of (200)MgO reflection increased and saturated above partial pressure of 4.4×10−1 Pa, which corresponds to N2 flow rate of 3 sccm. Effect of N2 gas on the structure of MgO thin films were investigated by plasma emission spectroscopy. The increase of the optical emission intensity of NH spectrum results in the increase of intensity of (200)MgO reflection. We found the strong relationship between the emission intensity of NH spectrum and intensity of (200)MgO reflection.

Oxygen-Concentration-Dependent Electrical Resistances of SrTiO3-Based Thin Films

In this paper, we show some results on oxygen-concentration-dependent electrical resistances of SrTiO3-based thin films and their possible new application. It is widely known that SrTiO3-based ceramics can be used as alternatives to ZrO2-based high-temperature oxygen sensors, which are categorized as ionic conductors operated at high temperatures, such as 1,273 K. In contrast, our thin-film-based devices, which are operated at room temperature, could be studied from the viewpoint of the polaron theory.

Solar Selective Absorber Coating Composed of Aluminum and Nitrogen with High Performance Induced by Surface Roughness

Pure Al film with surface roughness, incompletely nitrided Al film (Al–N film), and transparent AlN film are deposited in turn on a glass substrate by an rf sputtering method. The Al film as the infrared reflector with optimized surface roughness is prepared by a method of two-step deposition of an Al layer at two different substrate temperatures. By coating with an Al–N film, the Al film reduces its diffuse reflectance while maintaining its characteristic low emittance. It is also confirmed that the top layer of the AlN film can perform the role of antireflector coating even if the surface is rough. As a result, an optimized AlN/Al–N/Al film with surface roughness on the glass substrate realizes the high performance of a solar selective absorber, e.g., high solar absorptance of 0.92 and low normal emittance of 0.06 at 373 K.

SrTiO3-Based Microfabricated Oxygen Sensors

Semiconductive dielectric SrTiO3-based thin films are promising candidates for monitoring trace levels of oxygen during in situ monitoring of semiconductor manufacturing processes. In our preliminary studies, it was confirmed that SrTiO3-based thin films have a high oxygen sensitivity of ppb order at room temperature. In this paper, we will show that the prototype SrTiO3-based oxygen sensor detects trace levels of oxygen, even at ppb concentrations. It is expected that the SrTiO3-based sensor can be used for the real-time monitoring of residual oxygen in the future.

Determination of Pole Distribution for Thin Film on a Thick Substrate by X-Ray Diffraction

In the case of thin films grown on such a thick substrate that the X-rays cannot pass through, the available methods for measurement of X-rays to determine the pole distribution in the film are the reflection methods, although they have unobservable angle zones in common. In order to cover such a blind zone and to get a particular pole distribution in the film over the entire angle range, different pole distributions are obtained and are united into one normalized pole distribution by making reference to the pole distribution in an ideal sample with random orientation of crystallites. The simple combination method proposed here is applied to the determination of the normalized (002) pole distribution in sputtered hexagonal Co thin films.

In situ transmission infrared spectroscopy of hydroxylation of aluminum thin film and subsequent dehydration processes

A transmission Fourier-transform infrared spectroscopy apparatus for the in situ observation of chemical reaction in an aqueous solution has been developed. Reforming from an aluminum film to aluminum hydroxide (boehmite) during hydrothermal treatment and a subsequent dehydration process from boehmite to gamma alumina by heating in vacuum are quantitatively observed. According to the absorption peaks of the Al–O–H vibration of boehmite and the H–O–H vibration of liquid water, the hydrothermal reaction of the Al film occurs through two stages: the formation of boehmite and the penetration of excess water into the boehmite crystal.