Hidetaka Higashino

High Speed Optical TIR Switches Using PLZT Thin-Film Waveguides on Sapphire

We propose a new structure of the PLZT thin film optical TIR (Total Internal Reflection) switches with strip loaded type waveguides. Using these switches, we have achieved 2 GHz intensity modulation of LD light (0.83 µm) and 1 km optical fiber transmission. Both lumped constant electrode and traveling wave electrode were examined up to 26.5 GHz. From the calculation of velocity mismatch between the modulating wave and the light wave, it is estimated that the modulation bandwidth of these switches will be more than 100 GHz.

Pt‐coated substrate effect on oxide superconductive films in low‐temperature processing

Excellent films of a high Tc oxide superconductor were easily produced on Pt‐coated substrates at 650 °C. The film superconductivity was significantly improved by the Pt buffer layer. The c axis of the superconductive film was preferentially oriented perpendicularly to the plane with the crystalline oriented Pt coating layer.

Superconductivity in 2-μm-wide strip line of Gd-Ba-Cu-O thin film fabricated by low-temperature processes

The Gd-Ba-Cu-O film of 500 nm thickness was prepared on a (100) MgO single-crystal substrate at 650°C by an rf magnetron sputtering. This thin film having a smooth surface was patterned to a 2- µm wide and 100- µm long strip line by a conventional Ar ion beam etching (IBE) technique using the negative-type photoresist mask. Without any heat treatments, the patterned strip indicated a zero-resistivity temperature, Tc, of 69 K and critical current density, Tc, of 1.0×106 A/cm2 at 4.2 K.

Characteristics of interfaces for sputter deposited Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz structure

A depth profile of an Auger electron spectroscopy (AES) for a Bi2Sr2Ca1Cu2Ox/Bi2Sr2Cu1Oy/Bi2Sr2Ca1Cu2Oz structure was investigated. This multilayered structure was fabricated by an in situ sputtering process and used for sandwich‐type Josephson junctions. A little diffusion of Ca atoms from a top layer into the Bi2Sr2Cu1Oy layer was observed. It was confirmed that selective sputter etching during the AES measurement did not occur so seriously. The transition width at the two interfaces was estimated as about 10 nm, which was close to the depth resolution of our AES measurement. In addition, the interdiffusion between a Bi‐based oxide film and a MgO substrate was hardly observed.

Effects of Ar Ion-Beam Etching on Gd-Ba-Cu-O Superconducting Thin Films

The effects of Ar ion-beam etching were investigated for Gd-Ba-Cu-O superconducting thin films prepared on (100) MgO substrates at 650°C by rf magnetron sputtering. Etching at acceleration voltages below 2 kV did not change the zero-resistivity temperature and the critical current at 50 K in spite of a reduction of film thickness. A nonsuperconducting layer was formed near the surface. Surface analyses by X-ray photoelectron spectroscopy suggest that the crystal structure was deformed and the mean value of a Cu valence reduced to +1 by the Ar ion bombardment.

Molecular Arrangement Simulation of Pentacosadiynoic Acid Langmuir-Blodgett Films

A simulation of the molecular arrangement of 10,12-pentacosadiynoic acid (PDA) Langmuir-Blodgett (LB) films has been carried out. The PDA molecules were optimized to local minimum energy structures by the molecular mechanics technique using Allingers MM2 force field. The optimized molecules were arranged in the close-packed structures in a two-dimensional area where the closest atomic distances of the contacting molecules were restricted by the Van der Waals radii. The simulation results showed successful agreement with the reported experimental data.

High-Speed Optical TIR Switches with PLZT Thin Films

A new structure using strip-loaded waveguides is proposed for TIR switches with PLZT thin films. The TIR switches realized high-speed intensity modulation of LD light (0.83 μm) at 2 GHz. The modulation bandwidth of the lumped-constant electrodes and the traveling-wave electrodes was 7.1 GHz and more than 26.5 GHz, respectively. The modulation bandwidth is estimated to be more than 100 GHz.

Heterodyne mixing with a sandwich-type Josephson junction using a Bi-based high- oxide superconductor

A sandwich-type high- Josephson junction coupled with a coplanar-type transmission line was fabricated and heterodyne mixing characteristics were investigated. The junction was fabricated from a stacked film structure of (BSCCO/BSNCO/BSCCO) and the transmission line was made of sputter-deposited Pt film. The junction had a rectangular shape of . Current - voltage (I - V) curves of the junction showed weak-link-type characteristics. Two microwave sources of a frequency synthesizer and a sweep oscillator were used as a local oscillator (LO: 20 GHz) and a radio frequency signal source (RF: 19 GHz) for heterodyne mixing experiments. Intermediate signal (IF: 1 GHz) was transmitted through the transmission line and detected by a power meter. The conversion efficiency of -44 dB was estimated for an LO oscillator level of -23 dB m at 5.7 K when the junction was biased at the point below the first Shapiro step.

Planar SNS Josephson junctions using multilayer Bi system

Planar S/N/S Josephson junctions were successfully fabricated by multi-layered thin films of Bi-based high-Tc oxide superconductors. Two Bi2Sr2Ca1Cu2O(x) films and Bi2Sr2Cu1O(y) film were successively layered as superconducting electrodes and normal conducting buffer layer, respectively. These films were epitaxially deposited on (100) MgO substrate by in situ process of RF magnetron sputtering. Microjunction areas were defined by photolithography and Ar ion milling. These S/N/S type junctions clearly exhibited the AC Josephson effect under the irradiation of radio frequency waves of 12 GHz. More than 20th Shapiro steps were observed and those step heights were oscillated according to the irradiation power. These characteristics were stable and reproducible for different configuration of function area.

UV-light irradiation effects on oxide superconducting thin films

This paper reports on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x} thin films prepared on (100) MgO substrates by rf magnetron sputtering irradiated with ultra-violet (UV) light in He gas of about 500 Pa using a low pressure mercury lamp The zero-resistance temperature and the critical current density were gradually decreased with irradiation time. X-ray photoemission spectra showed that the mean Cu valence of the film was decreased approximately form +2 to +1 by the irradiation while the valence of Bl ions was not changed. These imply that the UV light tradition selectively reduces Cu ions and the superconductivity strongly depends on the Cu valence.