Koji Tsuru

Measurement of the resonance frequency of contactless IC cards using an electro-optic-sampling probe

We present a novel method of measuring the resonance frequency of contactless IC cards, which has been difficult to determine accurately, because of electromagnetic coupling between the antenna in the card and the measuring probe, even though it is a very important factor related to energy and data transmission. Using an electro-optic-sampling (EOS) probe, we made precise measurements of the resonance frequency without any influence from electromagnetic coupling.

Improvement of surface flatness on BiSrCaCuO film

This paper reports on the improvement of the surface flatness on BiSrCaCuO films. By keeping the film surface in contact with a MgO(100) plane during annealing, it is possible to greatly improve the surface flatness at each annealing temperature. The smooth surface is mainly made up of several-µm platelike crystals approximately 60 nm thick. The average surface roughness is determined by the annealing temperature, regardless of film thickness, in the range of 0.1–1.5 µm. As the critical temperature and surface morphology change due to the contacted MgO crystal plane, the improvement of surface flatness is considered to result from the crystal growth restriction on the film surface in contact with a MgO(100) plane.

In Situ Epitaxial Growth of Superconducting Bi2-Sr2-Can-1-Cun-Oy (n=1, 2) Thin Films by Two-Target Magnetron Sputtering under High Pressure

In situ superconducting thin films of Bi2-Sr2-Can-1-Cun -Oy (n=1,2) are grown epitaxially on Sr-Ti-O3 (100) and MgO (100) substrates by two-target rf magnetron sputtering under a high pressure of 0.5 Torr. During growth, film deposition materials are supplied alternately from Bi2-Sr2-Cu1.3-Oy and Ca-Cu-Oy targets to control the number of CuO2 layers. It is demonstrated that a sputtering gas pressure higher than 0.3 Torr effectively reduces the compositional deviation, which is normally caused by the resputtering effect. It is also demonstrated that alternate deposition from the two targets leads to controlled epitaxial growth with the c-axis perpendicular to the substrate. As grown epitaxial films thus prepared exhibit superconductivity at a T c as high as 79 K for Bi2-Sr2-Ca-Cu2-Oy films and 8 to 11 K for Bi2-Sr2-Cu-Oy films.

Design and evaluation of high security contact/contactless smart IC cards

This paper describes the specifications, features, and performance of a high security smart IC card developed by NTT. This card has a user memory capacity of 16 kbytes, a triple DES cryptogram, and both a contact and a contactless interface. Because the contactless interface specifications of the card are the same as those of phone cards currently used in payphones, this card can be used with a public payphone as a service terminal. This IC card enables secure storage of data and execution of cryptographic algorithms, making it possible to provide highly secure and more convenient services through different open networks.

Localized orientation control in BiSrCaCuO superconducting film

This letter reports on localized orientation control in BiSrCaCuO superconducting films. Uniformly oriented crystals, of which the c-axis exists in-plane, were grown on a MgO (110) plane by annealing them in contact with a MgO (100) plane. Thus, stripe patterns including oblique tapers in stripe edges were fabricated on MgO (100) crystals to produce locally appearing (110) planes. By annealing them in contact with a MgO (100) plane, the uniformly oriented crystals were confirmed to grow around oblique tapers in stripe edges fabricated on MgO (100) crystals.

Improvement of Critical Current in BiSrCaCuO Micropatterns by Oxygen Plasma Treatment

The influences of oxygen plasma on critical temperature and critical current density are studied using BiSrCaCuO micropatterns. Although a large critical temperature degradation as well as a slight decrease in a critical current is observed in 1.5–20 μm wide microbridges that have been put into an oxygen plasma, the critical temperatures are recovered by reducing excessive absorbed oxygen. Additionally, these recovered microbridges have higher critical current densities, whose improvement strongly depends on the microbridge width, 5–30 times than those without oxygen plasma treatment.