Yutaka Nonomura

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.

New resonant accelerometer based on rigidity change

We propose a new resonant accelerometer based on the principle of a resonator rigidity change caused by the applied acceleration. The rigidity change of the resonator consisting of parallel beams is induced by a change in its cross-sectional shape. The feasibility of this sensing principle was confirmed by FEM analysis. A frequency change rate of 10%/g was calculated, and the sensor was fabricated by surface micromachining technology using an SOI wafer. Furthermore, we confirmed that the double resonator structure which was designed based on the same principle had a lower cross-axis sensitivity.

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.

Adhesive wafer bonding using a molded thick benzocyclobutene layer for wafer-level integration of MEMS and LSI

This paper describes a wafer bonding process using a 50 µm thick benzocyclobutene (BCB) layer which has vias and metal electrodes. The vias were fabricated by molding BCB using a glass mold. During the molding, worm-like voids grew between BCB and the mold due to the shrinkage of polymerizing BCB. They were completely removed by subsequent reflowing in N2. After patterning Al on the reflowed BCB for the electrodes and via connections, bonding with a glass substrate was performed. Voidless bonding without damage in the vias and electrodes was achieved. Through the process, the control of the polymerization degree of BCB is important, and thus the polymerization degree was evaluated by Fourier transform infrared spectroscopy. The developed process is useful for the wafer-bonding-based integration of different devices, e.g. micro electro mechanical systems and large-scale integrated circuits.

An SOI 3-axis accelerometer with a zigzag-shaped Z-electrode for differential detection

We have developed a fully-differential 3-axis accelerometer with a novel zigzag-shaped Z-electrode, which is used for motion controls of automobiles and robots.

Determination of engine misfiring using magnetoelastic torque sensor

A method for the determination of engine misfiring has been achieved with a magnetic-head-type torque sensor based on the magnetoelastic effect. Sensor signal treatment using fast Fourier transformation (FFT) is introduced into this method to detect the misfiring cylinders. It has been confirmed that the determination of the misfiring cylinders is successful experimentally in a multicylinder engine such as the four-cycle engine having eight cylinders. In addition, this method is superior in accuracy to the conventional method with rotation speed detection, as well as ease of sensor installation.

An SOI tactile sensor with a quad seesaw electrode for 3-axis complete differential detection

This paper presents a novel SOI capacitive tactile sensor with a quad-seesaw electrode for 3-axis complete differential detection, which enables integration with a CMOS. For differentially detecting 3-axis forces, the tactile sensor is composed of four rotating plates individually suspended by torsion beams. In this study, to demonstrate the working principle, we fabricated a test device that integrates an SOI substrate with the quad-seesaw electrode and an anodically bondable LTCC substrate with fixed electrodes as an alternative to the CMOS. The experimental results of the test device successfully demonstrated the working principle as well as 3-axis differential detection with a matrix operation.

Real time measurement of instantaneous torque by magnetostrictive sensor

A novel torque measurement system has been developed using a magnetostrictive sensor and a digital sensor processing technique. This system contains a miniature magnetostrictive sensor, a digital signal processor (DSP), and a rotary encoder. The miniature sensor does not require a special space for installation. Generally, inexpensive commercial steels with high strength are used for the torque drive shaft of an automobile, although their magnetic properties are quite poor. With this system, instantaneous torque can be accurately measured in real time, even of a shaft made of a commercial steel. Therefore, the application of this system to automobiles would be effective. The torque was measured within an error of 2% FS in spite of using a commercial shaft (carbon steel S43C).<<ETX>>