Noboru Miura

Highly transparent and flexible field emission devices based on single-walled carbon nanotube films

Single-walled carbon nanotubes (SWNTs) have been used successfully to fabricate highly transparent and flexible field emission displays (FEDs). Field emission measurements indicated that SWNTs films have great potential to work as building blocks for next generation transparent and flexible FEDs.

Atomic Composition and Structural Properties of Blue Emitting BaAl2S4:Eu Electroluminescent Thin Films

We have investigated the compositional and structural properties of blue emitting BaAl2S4:Eu electroluminescent thin films fabricated by switching electron-beam evaporation using two targets. The use of X-ray photoelectron spectroscopy (XPS) revealed that the ratio of barium to sulfur in thin films is 1.0:2.0, which is identical to the stoichiometry of BaAl2S4. The X-ray diffraction (XRD) peaks from the thin film were assigned to those of a BaAl2S4 crystal. The photoluminescence (PL) spectrum shows emission from the 4f65d→4f7 transition of the activated Eu2+ ions in BaAl2S4 crystals. These results indicate that the crystalline phase in thin films is only BaAl2S4. The thin films also contain a large amount of oxygen impurities, which result in the formation of an Al2O3 layer and amorphous barium aluminate.

Effects of Vacancies on the Dielectric and Piezoelectric Properties of (Na0.5K0.5)NbO3-SrTiO3 Solid Solution

Vacancies have been introduced to the perovskite A- and B-site to study their effects on the dielectric and the piezoelectric properties of the (Na 0.5 K 0.5 )NbO 3 -SrTiO 3 solid solution. It is found that, rather different from in the case of PZT ceramics, both A- and B-site vacancies do not soften piezoelectric properties of (Na 0.5 K 0.5 )NbO 3 -SrTiO 3 solid solution.

Electroluminescence spectra of rare-earth-doped ZnS1-xSex thin films

Abstract Electroluminescence has been measured for ZnS 1- X Se X thin films doped with rare-earth ions. As X increases the band-gap energy of the host decreases. The emission levels of trivalent rare-earth ions are not observed when the band-gap energy is narrower than the excitation levels. This is because of the energy transfer between the host and the emission center.

Vertical silicon waveguide coupler bent by ion implantation

We propose and demonstrate that vertically curved waveguides (VCWs) enable vertical coupling between silicon wire waveguides and optical fibers with low wavelength dependence and polarization dependence for wide telecommunication wavelength band light. To bend these VCWs, we implanted silicon ions into silicon wire cantilevers from the vertical direction. The internal stress distribution that was induced by ion implantation drove the bending force, and we achieved vertical bending of the waveguides, with curvature radii ranging from 3 to 25 μm. At a radius of curvature of 6 μm, we obtained a coupling loss of 3 dB using a lens fiber.

Optical Properties of Blue-Emitting BaAl2S4∶Eu Thin-Films for Inorganic EL Display

The optical properties of blue emitting BaAl2S4:Eu thin-films were studied. The emission peak is around 470 nm, whose FWHM (full width at half maximum) is 35 nm. The dielectric constant is 3.03 from transmission spectrum, and the optical band gap is approximately 4.6 eV. It is found that the cubic phase and orthorhombic phase exist in fabricated thin-films. Furthermore, the energy band structure of BaAl2S4:Eu thin-films from X-ray photo-electron spectra (XPS) and the absorption spectra were analyzed.

Vertically Curved Si Waveguide Coupler with Low Loss and Flat Wavelength Window

Silicon photonics enabling ultra-small photonic integrated circuits induces a necessity to develop efficient optical couplers that connect silicon waveguides with optical fibers or offchip other optical components. Vertical couplers are promising for both wafer-level testing and the integration of optical components on the chip surface, but so far grating couplers have been the only solution virtually. Very recently, we have developed a few-micron-scale vertically-curved silicon waveguide coupler “elephant coupler” formed by ion implantation method. This paper demonstrates that the coupler has high coupling efficiency, weak wavelength dependence, and weak incident angle dependence of wavelength window, which are not obtained by the grating couplers. The paper also demonstrates that the thermal annealing treatment can reduce optical propagation loss induced by the ion implantation.

In-plane switching mode-based liquid-crystal hybrid Si wired Mach–Zehnder optical switch

A Mach–Zehnder optical switch based on a Si wire waveguide embedded in a liquid crystal overcladding is developed. Switching operation at a wavelength of 1550 nm with a voltage-length product of 1.86 Vmm is obtained for a device with a 300-µm-long loop-back phase shifter. The switching speed is qualitatively evaluated under various alignment film conditions, and switch-off and switch-on times of 7.9 and 8.4 ms, respectively, are achieved when the alignment layer is appropriately positioned relative to the waveguides.

Fabrication and Characterization of Niobate Piezoelectric Ceramics with Sintering Aids

To fabricate high density (Na,K)NbO3-based piezoelectric ceramics, liquid sintering method using K5.4Cu1.3Ta10O29(KCT) and K4CuNb8O23(KCN) as sintering aids has been undergone. Experimental results show that KCT and KCN are both effective sintering aids for (Na,K)NbO3-based piezoelectric ceramics. The density of the samples increases with increasing the amount of KCT and KCN; the piezoelectric constant d33 decrease, and the mechanical quality factor Qm tends to increase.

Capacitance Temperature Sensor Using Ferroelectric (Sr0.95Ca0.05)TiO3 Perovskite

Thermometric properties of the capacitance temperature sensor with polycrystalline (Sr1−x Cax)TiO3 (x = 0.05) have been investigated at cryogenic temperatures. Ferroelectric state appeared at 31.8 K due to Ca doping. Temperature sensitivity S and dimensionless temperature sensitivity Sd at 2.5 K were 90 pF/K and 0.045, respectively. This capacitance temperature sensor could improve the accuracy of temperature sensing at cryogenic temperatures due to its large dimensionless temperature sensitivity.