A new type of Josephson NDRO memory cell is presented, where a sense gate is coupled directly to the memory part, instead of the conventional magnetic coupling scheme. The memory cell operates without complexity of the sequence of signals, and the operation margin is shown to be 20%.

A high Tc superconducting quantum interference device (SQUID) magnetometer system is developed for the application to biological immunoassay. In this application, magnetic nanoparticles are used as magnetic markers to perform immunoassay, i.e., to detect binding reaction between an antigen and its antibody. The antibody is labeled with γ-Fe2O3 nanoparticles, and the binding reaction can be magnetically detected by measuring the magnetic field from the nanoparticles. Design and set up of the system is described, and the sensitivity of the system is studied in terms of detectable number of the magnetic markers. At present, we can detect 4106 markers when the diameter of the marker is 50 nm. Total weight of the magnetic nanoparticles becomes 520 pg in this case. An experiment is also conducted to measure antigen-antibody reaction with the present system. It is shown that the sensitivity of the present system is 10 times better than that of the conventional method using an optical marker. A one order of magnitude improvement of sensitivity will be realized by the sophistication of the present system.

The 4th harmonics of a Nd:YAG laser beam (266 nm) is applied to fabricate highly oriented Y1Ba2Cu3O7-δ -SrTiO3-Y1Ba2Cu3O7-δ multilayer structures. It has been shown that the emission temperature of a film surface will change during deposition, depending on deposition conditions, even though the heater temperature is constant. The change of substrate temperature is strongly correlated to film characteristics such as critical temperature, c-axis length, and resistivity. The insitu monitoring of the substrate temperature is useful for obtaining high-quality Y1Ba2Cu3O7-δ films reproducibly. It is also shown that a SrTiO3 layer prevents oxygen restoration in a Y1Ba2Cu3O7-δ underlayer. The relationship between oxygen deficiency and the annealing conditions is studied.

Rf properties of the coupling circuit between the dc SQUID and the multiturn input coil have been studied in order to investigate the origin of the degradation of the SQUID characteristics due to the input coil. It is pointed out that rf properties of the coupling circuit become important due to the existence of the rf currents generated from Jasephson junctions. The rf properties of the coupling circuit have been measured by using the expanded model of the circuit with Cu electrodes. We observe that resonant structures appear in rf properties of the coupling circuit. This means that the SQUID coil coupled to the input coil can not be expressed by a simple inductance, as is not the case of the isolated SQUID. It is shown that the resonant structures result from the standing wave occurring in the coupling circuit. It is also shown that the resonant structures can be suppressed with the damping resistors. Based on the experimental results, a circuit model of the coupling circuit is obtained, which explains well the experimental results. The obtained results are useful to study the effect of the input coil on SQUID characteristics.

Liquid-phase detection of biological targets utilizing magnetic marker and superconducting quantum interference device (SQUID) magnetometer is shown. In this method, magnetic markers are coupled to the biological targets, and the binding reaction between them is detected by measuring the magnetic signal from the bound markers. Detection can be done in the liquid phase, i.e., we can detect only the bound markers even in the presence of unbound (free) markers. Since the detection principle is based on the different magnetic properties between the free and bound markers, we clarified the Brownian relaxation of the free markers and the Neel relaxation of the bound markers. Usefulness of the present method is demonstrated from the detection of the biological targets, such as biotin-coated polymer beads, IgE and Candida albicans.

Magnetic immunoassays utilizing magnetic marker and high Tc superconducting quantum interference device (SQUID) have been performed. In this magnetic method, binding-reaction between an antigen and its antibody is detected by measuring the magnetic field from the magnetic marker. First, we discuss the magnetic property of the marker, and show that Fe3O4 particles with diameter of 25 nm can be used for remanence measurement. We also show a design of the SQUID for sensitive detection of the magnetic signal from the marker. Next, we developed a measurement system utilizing the SQUID and a reaction chamber with very low magnetic contamination. Finally, we conducted an experiment on the detection of the biological materials called IL8 and IgE. At present, a few atto-mol of IL8 and IgE has been detected, which shows the high sensitivity of the present method.

Recent progresses in high Tc superconducting quantum interference device (SQUID) magnetometers are discussed. First, intrinsic sensitivity of the SQUID at T=77 K is discussed. For this purpose, transport and noise properties of the bicrystal junction are clarified, and optimization of junction parameters is shown. We also discuss the quality of the SQUID from a comprehensive comparison between experiment and simulation of the SQUID characteristics. Next, we discuss issues to guarantee correct operation of the SQUID magnetometer in noisy environment, such as a method to avoid flux trapping due to earth magnetic field, high-bandwidth electronics and gradiometer. Finally, we briefly describe application fields of the high Tc magnetometer.

In this paper, we propose improved methods of liquid-phase detection of biological targets utilizing magnetic markers and a high-critical-temperature superconducting quantum interference device (SQUID). For liquid-phase detection, the bound and unbound (free) markers are magnetically distinguished by using Brownian relaxation of free markers. Although a signal from the free markers is zero in an ideal case, it exists in a real sample on account of the aggregation and precipitation of free markers. This signal is called a blank signal, and it degrades the sensitivity of target detection. To solve this problem, we propose improved detection methods. First, we introduce a reaction field, Bre, during the binding reaction between the markers and targets. We additionally introduce a dispersion process after magnetization of the bound markers. Using these methods, we can obtain a strong signal from the bound markers without increasing the aggregation of the free markers. Next, we introduce a field-reversal method in the measurement procedure to differentiate the signal from the markers in suspension from that of the precipitated markers. Using this procedure, we can eliminate the signal from the precipitated markers. Then, we detect biotin molecules by using these methods. In an experiment, the biotins were immobilized on the surfaces of large polymer beads with diameters of 3.3 µm. They were detected with streptavidin-conjugated magnetic markers. The minimum detectable molecular number concentration was 1.8×10-19 mol/ml, which indicates the high sensitivity of the proposed method.

Simple and quick tests at medical clinics have become increasingly important. Magnetic sensing techniques have been developed to detect biomarkers using magnetic nanoparticles in liquid-phase assays. We developed a biomarker assay that involves using an alternating current (AC) susceptibility measurement system that uses functional magnetic particles and magnetic sensing technology. We also developed compact biomarker measuring equipment to enable quick testing. Our assay is a one-step homogeneous assay that involves simply mixing a sample with a reagent, shortening testing time and simplifying processing. Using our compact measuring equipment, which includes anisotropic magneto resistance (AMR) sensors, we conducted high-sensitivity measurements of extremely small amounts of two biomarkers (C-reactive protein, CRP and α-Fetoprotein, AFP) used for diagnosing arteriosclerosis and malignant tumors. The results indicate that an extremely small amount of CRP and AFP could be detected within 15 min, which demonstrated the possibility of a simple and quick high-sensitivity immunoassay that involves using an AC-susceptibility measurement system.

Recent progress of highly sensitive magnetmeter utilizing high Tc dc superconducting quantum interference device (SQUID) is reviewed briefly. Performance parameters of the SQUID magnetometer, such as field resolution, dynamic response and usability in unshielded environment, are focused on. Relationship between these performance parameters and SQUID characteristics are discussed quantitatively, and key factors which dominate each performance are clarified. With this result, design principle to obtain high performance SQUID magnetometer operating at T77K is shown. Present status on the performance of the magnetometer is discussed by comparing experimental results with theoretical predictions. Issues to much improve the performance of the high Tc SQUID magnetometer are also discussed.

Properties of the flux-flow type Josephson oscillator coupled to a quasiparticle detector through a planar stripline cavity are investigated in the millimeter wave region. The present coupling scheme is essential for magnetic field isolation between the oscillator and the Josephson rf-devices, as well as filtering of spurious harmonics.

The minimum current of a two-junction SQUID gate has been studied theoretically. An analytical expression for the current-voltage characteristics of the SQUID gate has been obtained, which includes the minimum current of the SQUID gate. Studies have been made of the dependences of the minimum current on parameters of the SQUID gate such as an interlinked magnetic flux, a loop inductance and a resistance. It is shown that the minimum current of the SQUID gate depends strongly on the interlinked magnetic flux, while it becomes the same as that of a single junction in the absence of the magnetic flux. It is also shown that the obtained analytical results agree well with those of computer simulation.

Thermally activated magnetic-flux entry into a pickup coil through a flux dam in high Tc superconducting quantum interference device (SQUID) is studied. The behavior of this thermal activation is analyzed in terms of the circulating current flowing in the pickup coil. It is shown that the thermal activation can be prevented when the circulating current becomes much below a critical current of the flux dam. It is also shown that we need a long waiting time in order to realize this situation since the circulating current logarithmically decays with time in the case of the thermal activation. The relationship between the thermal activation and the circulating current is qualitatively confirmed with the experiment. We also show a method in order to forcibly reduce the circulating current instead of the thermal activation. In this case, we can prevent the thermal activation without the long waiting time.