Kazuo Chinone

Micro-imaging system using scanning DC-SQUID microscope

A micro-imaging system in a low temperature environment has been developed for the study of superconducting films and magnetic films and for the inspection of superconducting integrated circuits. The system consists of a micro DC-SQUID, a cryostat, a precise scanning stage, and a computer. Two different types of micro DC-SQUIDs were designed. One was a magnetometer (Bz) with a one-turn pick-up coil with a diameter of 10 /spl mu/m, and the other was a gradiometer (dBz/dx) with a planar first-order derivative pick-up coil. Each micro DC-SQUID was integrated on a 3 mm /spl times/3 mm Si chip using thin Nb film fabrication technology. Preliminary experiments were made using the system and several magnetic images were obtained. We present observations of a thin superconducting Nb film pattern by applying the Meissner screening and the magnetic domains of a thin garnet ((YBi)/sub 3/(FeAl)/sub 5/O/sub 12/) film.

Development of biomagnetic measurement system for mice with high spatial resolution

We have been developing a mice biomagnetic measurement system using a dc superconducting quantum interference device magnetometer for a comparative magnetoencephalogram study of transgenic and wild mice. In this study, we adopted a magnetometer with a pickup coil of 1.0mm diameter and 0.7mm lift-off distance to improve spatial resolution and magnetic field sensitivity. The magnetocardiogram of a wild mouse was measured as the initial application of the system. The bipolar peak positions in a magnetic field map separated by 5.6mm were clearly detected with the maximum amplitude of 88pT.

Strong, easy-to-manufacture, transition edge x-ray sensor

We developed a membrane structure with a silicon-on-insulator (SOI) wafer by using a micromachining technique to create a transition edge x-ray sensor. In this membrane structure, the part of the SOI layer between the silicon nitride (SiNx) film and the buried oxide layer was etched from the front side to form the SiNx membrane. Advantages of this membrane are that (a) it is stronger than conventional membranes and is therefore suitable for large format arrays, (b) the Si etching time is reduced from 12 h (for conventional etching) to 4 h, and (c) all the fabrication processes are done from the front of the wafer, thus simplifying the manufacturing process.

Observation of Superconducting Device Using Magnetic Imaging System with a Micro-DC Superconducting Quantum Interference Device Magnetometer

A magnetic imaging system with a micro-DC superconducting quantum interference device magnetometer has been developed to evaluate superconducting films and to inspect a superconducting device with a high spatial resolution. A superconducting device, i.e., a DC-SQUID made of a superconducting Nb thin film, was observed using the system. The shape of the device was identified by applying the Meissner effect. The trapped fluxes in the device were clearly visible. In addition, the input current and the shielding current flowing on the device were detected by feeding a current to the device. It was confirmed experimentally that the magnetic imaging system was effective in studying superconducting devices.

An integrated DC SQUID gradiometer for biomagnetic application

A first-order off-diagonal gradiometer was fabricated and tested. The gradiometer consisted of two field pickup coils and a planar DC SQUID (superconducting quantum interference device) with two superconducting loops connected in parallel, two multiturn input coils, and a modulation-feedback coil. The size of the pickup coils was 6*6 mm/sup 2/ with a base line of 8 mm. The overall size of the gradiometer was 15*7.5 mm/sup 2/. The resolution of the magnetic field gradient of the gradiometer increased from 11 to 1.8 pT/m square root Hz (the noise limits), corresponding to the frequencies from 1 Hz to 600 Hz. The resolution became nearly white in a frequency range above 600 Hz. The intrinsic balance of the gradiometer was better than 1000 p.p.m. for the field perpendicular to its plane. >

Nondestructive detection of dislocations in steel using a SQUID gradiometer

We have developed a magnetic flux imaging system. The magnetic flux image (MFI) shows the distribution of magnetic flux density over a plate like specimen. The change of the pattern in the MFI by tensile deformation has been investigated in a carbon steel without applying magnetic field using the system. A clear striped pattern appeared after deformation by fine plastic strain between 0.2 and 1.0% before strain-hardening. Luders bands, which are groups of slip bands, appeared on the plate surface and were observed at the corresponding locations of the stripes in the MFIs. This shows that the fine deformation is nondestructively detected using the MFI.

Development of Integrated Direct Current Superconducting Quantum Interference Device Gradiometer for Nondestructive Evaluation

A Direct Current Superconducting Quantum Interference Device (DC-SQUID) gradiometer for nondestructive evaluation was developed. A pick-up coil and a DC-SQUID were integrated on a 3×3 mm2 Si chip. In order to raise the spatial resolution of the gradiometer, a coplanar concentric second-order derivative coil was adopted as a pick-up coil. The pick-up coil consisted of a one-turn outer coil and a four-turn inner coil connected in series and counterclockwise to each other. The diameters of the outer coil and the inner coil were 2 mm and 1 mm, respectively. The size of the pick-up coil was determined by calculating the spatial resolution in relation to the bottom thickness of the cryostat. The high spatial resolution of the DC-SQUID gradiometer was experimentally confirmed.

Development of scanning SQUID microscope for studying superconducting films and devices

A micro-imaging system using a low-temperature superconductor (LTS) scanning SQUID microscope (SSM) has been developed for the study of superconducting films and devices. The system consists of a micro DC-SQUID, a cryostat, a precise scanning stage, and a control unit. The spatial resolution was improved by reducing the size of the pick-up coil of the micro DC-SQUID. A cryostat without liquid nitrogen makes the operation of the system easy and speedy. Preliminary experiments were made using the system and several magnetic images were obtained. We present observations of trapped fluxes in two types of superconducting thin film: a single-crystal-like Nb film grown epitaxially and a polycrystalline Nb film. We also present observations of a SQUID array, which consists of 50 DC-SQUIDs connected in series.

Scanning DC-SQUID system with high spatial resolution for NDE

We have developed a scanning DC-SQUID system with a high spatial resolution for NDE. The SQUID system is composed of a concentric multiloop DC-SQUID gradiometer using Nb/AlOx/Nb Josephson junction, a non-magnetic scanning stage, a cryostat and a computer for gathering data and controlling the system. We have developed the concentric multi-loop gradiometer (d/sup 2/Bz/dr/sup 2/, r/sup 2/=x/sup 2/+y/sup 2/) to have a higher spatial resolution and reduce background noise. The gradiometer was integrated on a single 3/spl times/3 mm/sup 2/ Si chip. To reduce the standoff distance between the specimen and the pick-up coil, a cryostat with a thin bottom space was developed. A scanning stage was made of nonmagnetic materials and was driven by air pressure using a rod-less cylinder to avoid making magnetic noise.

Applications of high-resolution MFM system with low-moment probe in a vacuum

Magnetic force microscopy (MFM) is very useful for observing magnetic domain structures. However, due to stray fields from an MFM probe, observations of small magnetic domain structures are limited. The authors have developed a high-resolution MFM system that utilizes a low-moment probe and a quality (Q)-controlled prove driver, which allows high-quality measurement in a vacuum without disturbing domain structures. Using this system, a resolution finer than 20 nm was achieved. In this paper, the advantages of this MFM are demonstrated using a Permalloy honeycomb nanonetwork and a Permalloy semicircular loop.