Yukihisa Yoshida

A novel grounded coplanar waveguide with cavity structure

This paper presents a grounded coplanar waveguide (GCPW), which is useful in RF-MEMS devices in order to effectively reduce noise from neighboring transmission lines. The GCPW structures demonstrated here were fabricated by front-surface-only processes on a single silicon wafer. A silicon nitride membrane supports the coplanar waveguide, which is located above a ground plane formed on an etched silicon cavity We found that the insertion losses of the 50-/spl Omega/ GCPWs with a 26-/spl mu/m-wide signal line and a 6-/spl mu/m-deep cavity do not exceed 0.4 dB/mm up to 20 GHz, which agreed with the simulated loss. The demonstrated maximum depth of metallized cavity is 30 /spl mu/m, which enables the GCPWs loss to be as low as 0.08 dB/mm at 20 GHz.

Influence of Crystal Strain on Superconductivity of a-Axis Oriented YBa2Cu3Ox Films

Ion channeling measurements were executed to evaluate the crystal strain in a-axis oriented YBa2Cu3Ox (YBCO) films with different film thicknesses. The average Ba-Ba distance in the film plane as determined from the channeling angle of the Ba atomic row in the (and ) direction was found to be close to the lattice constant of the SrTiO3 substrate regardless of the film thickness. A similar result was also obtained for oxygen atoms. These results indicate that the films grow while matching their lattice constant to that of the substrate. The simultaneous strain relief induced by the increase in film thickness was suggested from the channeling yield in the obtained dip curve. Furthermore, the relaxed grain was confirmed near the surface of the 3500 A film from the Ba axial channeling. The influence of the crystal strain on the superconductivity of the a-axis oriented YBCO films is explained on the basis of variation in the site of apical oxygen.

SUPERCONDUCTIVITY OF EPITAXIALLY GROWN A-AXIS YBCO FILMS ON SRTIO3 SUBSTRATE

The a -axis oriented YBa 2 Cu 3 O x (YBCO) films were epitaxially grown on (100) SrTiO 3 substrate by dc-100 MHz hybrid plasma sputtering. The films prepared at different temperatures with and without in situ annealing had different superconductivity, which was improved with the degradation of the crystallinity of the films. The Raman spectra for the films were very similar to each other and to that expected for YBa 2 Cu 3 O 7 , in spite of the different superconductivity. This indicates the importance of the symmetry of the Cu–O chains rather than the oxygen content for the superconductivity. In Rutherford backscattering measurements using a 3.05 MeV He 2+ ion beam, an increase of dechanneling due to the barium atoms along the film depth was clearly observed only for the most improved superconducting film. This result suggests that the relief of the strain contained in the film is also important for improving the superconductivity in the case of a -axis oriented YBCO films.

Microstructures of a -axis oriented YBCO films made by hybrid plasma sputtering

Microstructures of a -axis oriented YBa 2 Cu 3 O 7− x films made by newly developed de 100 MHz hybrid plasma sputtering were investigated using transmission electron microscopy (TEM). The films deposited on (110) NdGaO 3 and (100) SrTiO 3 substrates were found to grow in a perfect epitaxial fashion and with clear interface. The plan view of the TEM image showed that both films were comprised of two kinds of grains having the c axis aligning along two perpendicular directions in the plane with equal probability. The structures of the grain boundary, however, were found to be very different for the two films from the plan views. The film on NdGaO 3 showed a lot of twist boundaries, while the film on SrTiO 3 consisted of many symmetrical tilt boundaries and basal-plane-faced tilt boundaries. The type of grain boundary is determined by the anisotropic growth rates of the film between c direction and a-b direction.

TEM Studies on Microstructure of a-Axis Oriented YBCO Films

The microstructure of a-axis oriented YBCO films made by newly developed dc-100MHz hybrid plasma sputtering was investigated using the transmission electron microscopy. The films employed in this study were grown on (110) NdGaO3 and (100) SrTiO3 substrates and were confirmed to have an excellent crystallinity by X-ray diffraction and Rutherford backscattering measurements. The interface between the film and the substrate was found to be very sharp for both films. From the plan view of the TEM image, both films were found to consist of two kinds of grains having the c-axis aligning along two perpendicular directions in the plane with equal probability. For the film on NdGaO3 substrate, many twist boundaries which has a (100) boundary plane parallel to the surface could be observed, while the film on SrTiO3 had only symmetrical tilt boundaries and basal-plane-faced tilt boundaries, which have (013)(0 \(\bar 1\)3) and (001)(010) planes as boundary plane respectively. The difference can be explained from the anisotropic growth rates of the film between c direction and a-b direction.

Development of open air silicon deposition technology by silane-free atmospheric pressure plasma enhanced chemical transport under local ambient gas control

Open air silicon deposition was performed by combining silane-free atmospheric pressure plasma-enhanced chemical transport and a newly developed local ambient gas control technology. The effect of air contamination on silicon deposition was investigated using a vacuum chamber, and the allowable air contamination level was confirmed to be 3 ppm. The capability of the local ambient gas control head was investigated numerically and experimentally. A safe and clean process environment with air contamination less than 1 ppm was achieved. Combining these technologies, a microcrystalline silicon film was deposited in open air, the properties of which were comparable to those of silicon films deposited in a vacuum chamber.

Raman Spectroscopic Study of YBa2Cu4O8 Thin Film Grown from Amorphous Precursor.

Raman spectroscopic study was performed on YBa2Cu4O8 (Y124) thin films prepared by in situ annealing of sputtered precursor. The amorphous precursors were deposited at 450° C in 50 mTorr. The films are a-axis oriented. The ratio of the vibrational intensity of oxygen in double Cu–O chain to that of apical oxygen (I O d /I O a ) corresponded well to the volume fraction of the Y124 phase in the films. With decrease in the composition Cu/Y, depending on oxygen pressure during deposition, the double Cu–O chain is suffered by the oxygen defects, which was confirmed by observing decreases in I O d /I O a and the appearance of the 537 cm-1 mode. The Y124 growth around the boundary of the stability region (1≤P O2 ≤200 Torr, 625≤T≤820° C) between Y124 and Y123 indicates that higher temperature and higher oxygen pressure during in situ annealing is preferable for the growth of Y124 films. The Y124 films annealed at 820° C under 200 Torr O2 showed I O d /I O a of 1.00, which is the same as the result for Y124 bulk prepared by a high-pressure technique.

Single Phase a-axis YBCO Films Epitaxially Grown on NdGaO3

YBa2Cu3O7−x (YBCO) thin films on NdGaO3 (110) have been prepared using a newly developed DC-94.92MHz hybrid plasma magnetron sputtering. The hybrid plasma was generated by applying a negative bias voltage to the RF cathode. The YBCO films showed an excellent crystallinity with the a-axis being perpendicular to the plane of the substrate. A full width at half maximum (FWHM) value of 0.027° in the rocking curve through the (200) peak and χmin of 3.8% in the Rutherford backscattering channeling measurement were achieved. The interface between the film and the substrate was found to be very sharp by cross-sectional transmission electron microscopy (TEM). The surface of the films were also very smooth.

New Substrate La1−xNdxGaO3 for High-Tc YBa2Cu3Ox Epitaxial Films

La0.66Nd0.34GaO3(LNGO) single-crystalline boules were successfully grown by the Czochralski method. The boules have no crack and few twins. The structure of LNGO is orthorhombic with the lattice constants; aO=5.49lA, bO=5.492A, cO=7.766A. The length of cell-edges along both and are 3.883A, which are close to the length of b-axis or a third of c-axis length for YBa2Cu3Ox(YBCO). YBCO films grown on a (110) plane of these substrate were epitaxial. The crystallinity of the films was very good; the value of FWHM for YBCO (200) peak was 72sec (0.020deg.), which is comparable with that of the substrate.