Masayoshi Koba

Ultra-thin fatigue-free Bi4Ti3O12 films for nonvolatile ferroelectric memories

We have developed a new low temperature growth technique for Bi 4 Ti 3 O 12 thin films using a MOCVD method in which an ultra-thin double buffer layer (5-nm thick Bi 4 Ti 3 O 12 /5-nm thick TiO 2 ) is used to control the crystallization and fine grain structure. The 100-nm thick Bi 4 Ti 3 012 thin films fabricated at 400°C showed an extremely smooth surface morphology and good electrical properties, namely, a large remanent polarization of P r = 11 μC/cm 2 , a coercive field of E c = 90 kV/cm and a low leakage current IL = 7 X 10 -9 A/cm 2 at 3 V. Moreover, we successfully fabricated 50-nm ultra thin Bi 4 Ti 3 O 12 films with P r = 9 μC/cm 2 and E c = 120 kV/cm at 3 V. For the first time, the fatigue free property, which is very important for nonvolatile ferroelectric memory (NVFRAM) applications, was confirmed up to 1 x 10 12 switching cycles.

MOCVD Growth of InP on 4-inch Si Substrate with GaAs Intermediate Layer

This letter describes the heteroepitaxy of InP on Si by MOCVD. A new epitaxial structure with a thin GaAs intermediate layer (InP/GaAs/Si) is proposed to alleviate the large lattice mismatch (8.4%) between InP and Si. Using this structure, a 4-inch InP single crystal with a mirror-like surface and good thickness uniformity (Δd/d=±10%) was obtained. Residual stress in the InP film was 5.7±108 dyn/ cm2 for the InP/GaAs/Si structure, as compared to 8.3×108 dyn/cm2 for the InP directly grown on Si. This shows that the GaAs intermediate layer is also effective in reducing the residual stress in the InP epilayer.

Fabrication of Ag-Doped Y1Ba2Cu3O7-x Superconducting Films on Cu Substrates by Electrophoretic Deposition

Ag-doped Y1Ba2Cu3O7-x superconducting films were fabricated on Cu substrates by electrophoretic deposition. The electrophoretic deposition was carried out using presintered Y1Ba2Cu3O7-x and Ag2O powder dispersed in distilled acetone. The deposited films were heat-treated in air at 900°C. The Ag-doped Y1Ba2Cu3O7-x films on Cu-coated YSZ exhibited a metallic temperature dependence of the resistance, and the zero-resistance state was obtained at 88 K. The critical current density and the grain growth were greatly improved by the Ag doping.

Epitaxial growth of InP on Si by OMVPE — defect reduction in epitaxial InP using InAsxP1−xInP superlattices

Abstract The heteroepitaxy of InP on Si substrates was investigated using OMVPE. A new epitaxial structure with a GaAs intermediate layer, 100 nm thick, was used to alleviate the 8.4% lattice mismatch between InP and Si. Four-inch size InP single crystal with a specular surface and good thickness uniformity ( Δd d =±8% ) was reproducibly obtained. It was found that the GaAs intermediate layer effectively reduced the residual stress in the InP epilayer and 8.4×10 8 dyn/cm 2 was obtained. The EPD of the as-grown epilayer, etched by HBr+H 3 PO 4 solution, was on the order of 10 8 cm −2 and it decreased to (2−4)×10 7 cm −2 by post growth annealing in PH 3 +PH 2 ambient. To further reduce crystalline defects, a buffer layer consisting of ten periods of InAs x P 1− x (2.5 nm)InP(2.5 nm) was formed between the InP epilayers grown on both as-grown and annealed InP/GaAs/Si substrates ( x =0.3). This superlattice buffer layer reduced the EPD of these epilayers to 30–50%. Using a stacked structure with superlattice buffer layer and annealed InP/GaAs/Si substrate, an InP epitaxial layer with EPD of 1×10 7 cm −2 was obtained.

Fabrication of Y-Ba-Cu-O superconducting films on Cu substrates by an electrophoretic deposition technique

Direct formation of Y1Ba2Cu3O7-x films on Cu substrates by electrophoretic deposition is studied, Electrophoretic deposition was carried out using presintered Y1Ba2Cu3O7-x powder dispersed in distilled acetone. The deposited films were annealed in air at 900°C. We succeeded in obtaining superconducting Y1Ba2Cu3O7-x films on Cu substrates. The films on Cu plates and Cu film/YSZ exhibited the zero-resistance state at 66 K and 76 K, respectively. Interfacial chemical reactions at the Y1Ba2Cu3O7-x/Cu interface are discussed. The achievement of the zero-resistance state is considered to be due to the reduction of the interfacial reactions.

Seeded Electron Beam Recrystallization of Large Area SOI Using Striped Tungsten Encapsulation Technique

Large area SOI (silicon on insulator) film with (001) orientation has been produced by applying a seeded electron beam recrystallization technique to the specimen with striped encapsulation. The encapsulation stripes consisted of tungsten and polysilicon. A pseudoline electron beam was scanned parallel to the stripes. A 400 µm×800 µm area had become a single crystal including subgrain boundaries in one sweep. These subgrain boundaries were confined to the region between the encapsulation stripes. The orientation of the crystal gradually rotates from (001)[110] to (103)[33] as recrystallization propagated away from the seed.

Magnetic field dependence of voltage noise in Y1Ba2Cu3O7-x ceramic superconductor film

Magnetic field dependence of voltage noise in a ceramic superconductor Y1Ba2Cu3O7-x film has been investigated. We have observed a maximum of the noise at about 10 Oe for the perpendicular field to the film surface. For the parallel field to the film surface, the noise increases slightly with the increase of the field. These noise characteristics are considered due to a motion of magnetic flux in the film.

EPITAXIAL GROWTH OF ZIRCONIA AND YTTRIA STABILIZED ZIRCONIA FILMS ON SAPPHIRE SUBSTRATES BY REACTIVE SPUTTERING

Epitaxial single crystal growth of zirconia (ZrO 2 ) and yttria stabilized zirconia (ZrO 2 ·Y 2 O 3 ) films on sapphire substrates was achieved for the first time by using reactive sputtering. And the relations of crystallographic orientations between the epitaxial films and sapphire substrates was determined. Yttria stabilized zirconia films seem to offer hiah quality SOI substrates, since the crystal structure of ZrO 2 ·Y 2 O 3 is cubic fluorite and its lattice constant is closely matched to those of semiconductors such as Si and GaAs.

Formation of Double Layered SOI With Controlled Crystal Orientation

For the crystal orientation control of multi-layered SOI (Silicon on Insulator) by the laser recrystallization technology, the shape and size of seeds were investigated. By utilizing dot seeds less than 3μm square instead of a line seed, the crystal orientation control of a SOI layer was successfully realized without causing evaporation of silicon. Moreover, the dot seed method enabled us to control the crystal orientation of multi-layered SOI by virtue of small heat flow through seed regions. In the mean time, it was proved that the SOI crystal orientation gradually rotated as the crystal propagated away from the seeds and that the degree of rotation in the second SOI layer was smaller than that in the first one.

Interconnection Technology for Three-Dimensional Integration

The technology of thermally stable and fully planarized multilevel interconnections with selective CVD-W vias and 31P+/11B+ implanted WSix/TiN/Si contacts has been developed for three-dimensional VLSIs. Via holes with high aspect ratios (about 3) and different depths (0.8–3.0 µm) were completely filled by selective W-CVD and subsequent etch-back, and the surface was planarized to below 0.2 µm using a previously reported interlevel insulation planarization technology. Metal-silicon reactions during high-temperature annealing were eliminated by the use of a TiN thin film (0.08 µm) containing oxygen as a diffusion barrier. By performing an additional 31P+ and 11B+ implantation into the interconnection, the ohmic contacts to n+ and p+ Si in this structure were also maintained even after annealing at 900°C for 6 hours.