Development of Superconducting Multilayer Wiring for Large Arrays of TES X-Ray Microcalorimeters

We are developing TES (Transition Edge Sensor) X-ray Microcalorimeters for future X-ray astronomy missions such as DIOS (Diffuse Intergalactic Oxygen Surveyor). Standard wiring for a large-format array requires narrow and closely-packed configuration. This can cause deleterious crosstalk especially in the Frequency Domain Multiplexing readout. Hence we have employed multilayer wiring technique. In this paper, we tested a deposition of a TES film on the multilayer wiring by sputtering. Our first trial showed that the TES pixels have large residual resistances >50?mΩ and small critical currents of <1?μA. To improve the coverage of the TES film on the wiring, we increased the thickness of TES film (Ti/Au thickness of 100/200?nm). Also to remove an oxidation layer on the Al wiring, we strengthened a reverse-sputtering (150 W, 3?min) before the sputtering of TES. After these treatments, the TES film showed a sharp transition with small residual resistance (～1?mΩ) and large critical current (>30?μA).     

Simulation of confined and enhanced optical near fields for a long narrow aperture in a pyramidal structure on a thick metallic screen

A new type of long narrow aperture in a pyramidal structure on a thick metallic screen is proposed, and optical wave scattering by this structure is simulated. This aperture structure provides high emission intensity and small spot size simultaneously through excitation of the surface plasmon polaritons on the sidewalls of the pyramidal structure. Scattering of optical waves by this structure in the thick metallic screen is solved numerically with a volume integral equation by generalized conjugate residual iteration and fast Fourier transformation. The basic characteristics of the near-field intensities of the aperture are investigated in detail.     

Analysis and numerical computation of diffraction of an optical field by a subwavelength-size aperture in a thick metallic screen by use of a volume integral equation

Diffraction of an optical field by an aperture in a thick metallic screen is analyzed numerically by use of a three-dimensional volume integral equation together with a generalized conjugate residual method and fast Fourier transformation. Numerical results were validated by reciprocity and the independence of the results of the truncated discretized volume size used in numerical calculations. Near and far fields of square, circular, and triangular apertures in a thick screen are obtained numerically. Some of the numerical results obtained in the present study agree with previously reported experimental results. The surface plasmon polaritons excited on the sidewalls of the aperture can explain the basic characteristics of near-field distribution of apertures. The Bethe-Bouwkamp theory was found to be insufficient to explain the basic characteristics of the near field around the subwavelength aperture in a practical metallic screen.     

Si Complies with GaN to Overcome Thermal Mismatches for the Heteroepitaxy of Thick GaN on Si

Heteroepitaxial growth of lattice mismatched materials has advanced through the epitaxy of thin coherently strained layers, the strain sharing in virtual and nanoscale substrates, and the growth of thick films with intermediate strain‐relaxed buffer layers. However, the thermal mismatch is not completely resolved in highly mismatched systems such as in GaN‐on‐Si. Here, geometrical effects and surface faceting to dilate thermal stresses at the surface of selectively grown epitaxial GaN layers on Si are exploited. The growth of thick (19 µm), crack‐free, and pure GaN layers on Si with the lowest threading dislocation density of 1.1 × 10⁷ cm^?2 achieved to date in GaN‐on‐Si is demonstrated. With these advances, the first vertical GaN metal–insulator–semiconductor field‐effect transistors on Si substrates with low leakage currents and high on/off ratios paving the way for a cost‐effective high power device paradigm on an Si CMOS platform are demonstrated     

Measurements of the surface tension for R290, R600a and R290/R600a mixture

The surface tensions of R290, R600a and R290/R600a mixture have been measured by the modified differential capillary-rise method. Twenty-two data points for R290 and 21 data points for R600a were obtained in the temperature range between 273 K and 354 K, and 43 data points for R290/R600a mixture on three isotherms of 278 K, 300 K and 320 K were obtained. The experimental uncertainties of temperature and surface tension are estimated to be within 20 mK and 0.2 mN m⁻¹, respectively. Surface tension correlations as a function of temperature for pure R290 and R600a were formulated in the temperature range between 253 K and critical temperature, and the correlation as a function of the composition for R290/R600a mixture was discussed at 278 K, 300 K and 320 K. It is found that the surface tension for R290/R600a mixture can be reproduced by the simple mixing rule by mole fraction with the correlations of both pure components.     

Effect of fiber array irregularities on microscopic interfacial normal stress states of transversely loaded UD-CFRP from viewpoint of failure initiation

A detailed investigation has been carried out to determine the effect of local fiber array irregularities and controlling fiber distribution parameters on microscopic interfacial normal stress states for transversely-loaded unidirectional carbon fiber (CF)/epoxy composites. Linear elastic finite element analyses were carried out for two-dimensional image-based models composed of about 70 fibers. The relationship between the geometrical distribution of two adjacent fibers and the interfacial normal stresses (INSs) is investigated for all fibers in different image-based models. Three boundary conditions for loading were selected: Case A involved cooling from the curing temperature (the difference in temperature was ?155 K); Case B involved transverse loading of 75 MPa chosen as an example of macroscopic transverse fracture strength; and Case C involved both cooling from the curing temperature and transverse loading of 75 MPa. High compressive INSs due to the difference in the coefficients of thermal expansion are observed at the location of the shortest interfiber distance for Case A (cooling). High tensile INSs are observed at the location of the shortest interfiber distance and where the fiber alignment angle to the loading direction is small for Case B (loading). For Case C (cooling and loading), the high thermal residual compressive INSs and the high mechanical tensile INSs compensate each other, and the INSs at a short interfiber distance are much lower than those for Case B. These results clearly indicate the importance of the contribution of the thermal residual stresses to the transverse tensile failure initiation of CF/epoxy laminates.     

Synthesis of calcium carbonate vaterite crystals and their effect on stabilization of suspension polymerization of MMA

Spherical calcium carbonate vaterite crystals were synthesized and the effect of them on stabilization of suspension polymerization of methyl methacrylate was investigated. Suspension polymerization of methyl methacrylate could be stabilized with calcium carbonate vaterite crystals and sodium dodecylbenzene sulfonate of the concentrations from 25 to 100 ppm. Poly(methyl methacrylate) beads coated with spherical calcium carbonate vaterite crystals were prepared. With an increase in the concentration of sodium dodecylbenzene sulfonate from 25 to 100 ppm, the amount of calcium carbonate vaterite crystals adhered on the surface of poly methyl methacrylate bead increased and the mean diameters of the polymer beads decreased.     

Intermetallic compound formation between lead-free solders (Sn) and Cu or Ni electrodes

A kinetic model based on the principle of maximum degradation rate of the total system free energy, MDR law using thermodynamic data, is proposed and successfully applied to the selection of the first intermetallic compound (IMC) phase in Cu/Sn and Ni/Sn diffusion couples. The first phases predicted with this model for Cu/Sn and Ni/Sn are Cu₆Sn₅ and Ni₃Sn₄, respectively, resulting in good agreement with experimental observations.     

Novel organosiloxane vapor annealing process for improving properties of porous low-k films

A novel 1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS)-vapor annealing method was developed for improving the mechanical strength of porous silica films with a low dielectric constant. TMCTS molecules react with Si-OH groups on the pore wall surfaces to form the polymer network which results in the high hydrophobicity and reinforcement of the silica wall. This method can be used to recover plasma damages induced by etching and ashing in fabricating Cu/low-k interconnects.     

High-temperature fracture of composite materials

The high-temperature fracture of composite materials containing strong particles is discussed on the basis of micromechanical models in which the recovery effect by diffusion of atoms is taken into account. The results of the calculations are compared with experimental results on 21Cr-4Ni-9Mn steels which consist of equiaxed grains containing rod-like M₂₃ C₆ carbide particles. The internal stresses acting in the particles and the grains are calculated on the basis of the model. The fracture mode of the material changes from transgranular to grain boundary fracture with increasing temperature, and the elongation of the material increases as a result. These experimental observations can be interpreted in terms of the calculation results of the constant stress model in which non-uniform distribution of plastic strain is assumed, but the calculated results of the constant strain model cannot explain the experimental results.