Hideya Yamadera

Giant magneto-impedance effect in layered thin films

Giant Magneto-Impedance (GMI) of films with a layered structure has been studied. They are Co-Si-B/Cu/Co-Si-B, Co-Si-B/Ag/Co-Si-B, and Fe-Co-Si-B/Cu/Fe-Co-Si-B with a magnetic closed-loop structure. They also have a certain magnetic configuration, for which the uniaxial anisotropy is perpendicular to both the driving current and the external field. Consequently, both reactance X and resistance R of the films change remarkably due to the external field in the frequency range from 100 kHz to 10 MHz, at which the GMI effect hardly appears in the single layer films of the same thickness. The conductivity difference between the outer and inner layers is important in order to achieve a high impedance change ratio in this frequency range. As a result, the ratios /spl Delta/Z/|Z/sub 0/|=(Z/sub maximum/-Z/sub [Hext=0]/)/Z/sub [Hext=0]/ of Co-Si-B/Ag/Co-Si-B films are 440% for a field of 9 Oe at 10 MHz, and the average sensitivity is 49%/Oe. Furthermore, /spl Delta/Z/|Z/sub 0/| of Co-Si-B/Cu/Co-Si-B and Co-Si-B/Ag/Co-Si-B films at 1 MHz is as much as 140%, and the average sensitivity reaches 15%/Oe. The sensitivity at 1 MHz is higher than that of single-layer magneto-impedance films of the same thickness by three orders of magnitude.

Enhancement of giant magneto-impedance in layered film by insulator separation

Giant Magneto-Impedance (MI) effect of CoSiB/SiO/sub 2//Cu/SiO/sub 2//CoSiB films with line structures have been studied. Easy axes have been induced in perpendicular direction to the driving current, and the insulating SiO/sub 2/ layers have prevented the driving current from penetrating into the CoSiB layers. This structure has enabled the effective occurrence of resistance change at a frequency as low as several MHz. As a result, impedance change ratios /spl Delta/Z/Z/sub 0/=(Z/sub maximum/-Z(H/sub ext/=0))/Z(H/sub ext/=0) are much higher than that of any other layered film without insulating layers. The /spl Delta/Z/Z/sub 0/ at 20 MHz is as high as 700% at 11 Oe, and the maximum slope is 300%/Oe.

Thin film magnetic field sensor utilizing Magneto Impedance effect

Abstract Recently, the Magneto Impedance effect found in amorphous wires with soft magnetic properties is noticeable as a new principle for sensing magnetic filed. According to this effect, the impedance of the wire in the range of high frequencies over 10 MHz changes remarkably with the external magnetic field. This effect is expected to be promising for magnetic field sensor with high sensitivity. Therefore, we have attempted to introduce this effect into amorphous thin films to extend application fields, and a novel thin film sensor sensitive to small magnetic field based on the Magneto Impedance effect has been proposed. The sensor consists of half bridge of the individual detecting element with FeCoSiB/Cu/FeCoSiB multi-layer, which exhibits the large impedance change ratio more than 100% when an external magnetic field is applied. By the optimization of the operating point due to bias field and the signal processing with a synchronous rectifier circuit, no hysteresis, good linearity and good stability against temperature variation as well as high sensitivity in the sensor characteristics have been achieved. The variation of the sensor output with the temperature is largely reduced to one-third, compared to the conventional thin film sensor we developed formerly. The detection resolution of 10−3 Oe order higher than those of any other conventional thin film sensors is obtained.

Sensing of passing vehicles using a lane marker on a road with built-in thin-film MI sensor and power source

In a field test, we demonstrated the sensing of passing vehicles, using onroad lane markers with a built-in magneto impedance (MI) sensor and a self-contained power source. The vehicle-sensing rate was 100% in the field test and we found that the lane marker could detect vehicles with a high degree of accuracy. A thin-film MI sensor, which is very sensitive to small external magnetic fields, an analog circuit for driving/processing, and a digital circuit with EEPROM memory for storing the number of passing vehicles were incorporated into a thin aluminum plate marker. The lane marker also had a self-contained power source, consisting of a secondary battery and a solar battery, which eliminated the need for an external power supply.

Strain-impedance properties of a CoSiB/Cu/CoSiB layered film

A type of strain sensor element utilizing the magnetostrictive effect and the magneto-impedance effect was presented and the strain-impedance properties of the element were evaluated. The strain-impedance (SI) element constructed from a CoSiB/Cu/CoSiB layered film was prepared on a Corning No. 0313 glass substrate by magnetron sputtering under a magnetic field. The element was composed of an inner copper conductive layer and outer magnetostrictive layers which covered the conductive layer. The Co73Si12B15 negative magnetostriction films (λ=−6×10−6) were adopted as magnetostrictive layers and magnetic anisotropy was induced perpendicular to the applied strain direction. Impedance Z drastically changed with applied compressive strain e up to −2×10−3 and exhibited a good reversibility and reproducibility. The impedance change ratios ΔZ/Z0=(Zmax−Z[e=0])/Z[e=0] of the element were 40% at 15 MHz and 24% at 1 MHz. The maximum gauge factor Gmax defined as the maximum fractional change in impedance to strain (ΔZ/Z...

Magneto-impedance effect of a layered CoNbZr amorphous film formed on a polyimide substrate

To produce magnetic field sensors for use on irregular surfaces, thin-film-type elements that can detect a magnetic field by the magneto-impedance (MI) effect were formed on 20-/spl mu/m-thick polyimide substrates by sputtering. The thin-film MI element has a layered configuration with the conductive Cu film surrounded by ferromagnetic CoNbZr magnetic films. Excellent soft magnetic properties could be obtained for the CoNbZr amorphous magnetic films by optimizing preparatory conditions and inserting an SiO/sub 2/ buffer layer between the element and the polyimide sheet. To detect the magnetic field acting on the MI element by means of an impedance change, the element was shaped into a meander pattern. The MI element exhibits an impedance change of more than 100% and shows good temperature stability compared to that of conventional thin-film MI elements fabricated on glass substrates.

Micromachined Thin Film MI Element for Integrated Magnetic Sensor

A micromachined thin film magnetoimpedance (MI) element was developed and its MI properties were investigated. Consisting of a SiN/Al/NiFe/SiO2 film, it was formed on a Si (100) wafer and fabricated by photolithography and etching. Ni80Fe20 film with nearly zero magnetostriction prepared by bias magnetron sputtering under a magnetic field was adopted as a magnetic layer in the MI element and magnetic anisotropy was induced parallel to the driving current direction. Sensitivity defined as the maximum fractional change in impedance increased with thickness and length, and was greatest for a width of 20 mum. The values for which the MI element had the best properties were 38% for the sensitivity, 1446 ppm/degC for the temperature coefficient of impedance TCZ and 712 ppm/degC for the temperature coefficient of sensitivity TCS at the driving frequency of 100 MHz. These values were much better than those of conventional magnetoresistance (MR) sensors. Therefore, these micromachined thin film MI elements have great potential for use in high sensitive integrated magnetic sensors.

Micromachined layered thin film magnetoimpedance element

This paper presents a micromachined layered magnetoimpedance (MI) element consisting of a CoNbZr/Al/CoNbZr film and its MI properties were investigated. Sensitivity defined as maximum fractional change in impedance changed with thickness and dimension. The values for which MI element had the best properties were 45% for the sensitivity, 5% for the fractional change in impedance dependent on temperature. These values were much better than those of integrated magnetoresistance (MR) sensors. Therefore, these micromachined elements have great potential use in integrated magnetic sensors.

Application for electric resistance element of granular films

Thin film electric resistance elements were presented, utilizing granular films of CoAlO. Electrical properties of the films show dependence with metal content and granular nanostructure. The values of /spl alpha/ and /spl beta/ in the optimum metal content were as low as those of conventional metal film resistances. Sheet resistance values were observed to be much higher than those of conventional metal film resistances. Therefore, granular films are useful for application to thin film resistance for purpose of minimizing the resistance element.