Y. Hayashi

Dependence of magnetostriction of sputtered Tb-Fe films on preparation conditions

Amorphous Tb-Fe thin films prepared by the sputtering method in the compositional range Tb/sub x/Fe/sub 1-x/ (x=0-0.5) are investigated in view of their potential for use in electromagnetic thin film actuators. The magnetostriction and the coercive force for the Tb-Fe films are examined for different sputtering conditions to obtain both soft magnetic properties and large magnetostriction in this system. As a result, Tb-Fe thin films having large magnetostrictions (180*10/sup -6/ at 1 kOe) and low coercive force (60-70 Oe) are obtained. These films are prepared under the conditions of the composition of 45-50 at.% Tb, Ar gas pressure of 4 mTorr, RF input power of 200 W and using water cooled substrates. A trial actuator using magnetostrictive thin films is also reported. >

Characteristics and analysis of a thin film inductor with closed magnetic circuit structure

A spiral inductor with closed magnetic circuit was fabricated by an RF sputtering machine and photolithography techniques. The inductance was twice as large as that of a reference sandwiched inductor. The authors analyzed the frequency characteristics of the proposed inductor from three points of view: inner current distribution, flux distribution, and eddy current in the magnetic film. The calculated results agree with the measured ones. It is demonstrated that the current distribution inside the inductors is mostly limited to within the area of the conductor up to several hundred megahertz. The frequency characteristics are influenced by the eddy current loss in the Permalloy film and the stray capacitance between the inductor and the ground plane. The permeability of the Permalloy film is less than that of its as-deposited state, but the closed magnetic circuit structure helps to reduce the influence of the demagnetizing field. >

Fabrication of Thin-Film Actuators Using Magnetostriction

We fabricated two kinds of cantilever actuator and a traveling machine by using magnetostrictive Tb-Fe and Sm-Fe thin films on a polyimide substrate. No power supply cable is required for their actuation, because they are driven by an external magnetic field. The magnetostrictive cantilevers exhibited a large deflection in low magnetic fields. Their unique characteristics suggest that magnetostriction can be used as the driving mechanism of microactuators.

Tb-Fe Sputtered Films with Large Magnetostriction for Use in Magnetomechanical Thin-Film Devices

We examined the magnetostriction and coercive force of amorphous Tb-Fe films sputter-deposited under different conditions (rf input power, Ar gas pressure, Tb content, etc.). Here we discuss the possibility of obtaining both soft magnetic properties and a large magnetostriction in this system. Soft magnetic properties and large magnetostriction were obtained simultaneously in sputtered Tb-Fe thin films prepared with a Tb content of 45 to 50 at%, under an Ar gas pressure of 4 mTorr and with an rf input power of 200 W. This material has strong potential for use in magnetomechanical thin-film devices.

Magnetic properties of Fe-Si thin films sputtered in mixed gas atmospheres

An examination is reported of the magnetic properties and crystal structure of films prepared by sputtering with air or oxygen added to the Ar atmosphere. The coercive force of the film deposited in air plus Ar decreased to 1/5 of that of the film deposited in pure Ar, the crystal orientation changed, and the grain size became smaller. The coercive force of the films deposited in oxygen plus Ar decreased by a like amount. The initial permeability increased accordingly. It is suggested that these changes of the magnetic properties were caused by oxidation of Si in the films. >

Electrochemical fabrication of nanocomposite films containing magnetic metal nanoparticles

Controlling the structure composed of soft and hard magnetic phases at the nanoscale is the key to fabricating nanocomposite magnets with efficient exchange coupling. In our previous study, nanocomposite films containing ferrite nanoparticles were fabricated by a combination of electrophoretic deposition and electroplating to show one possibility of controlling the structure of nanocomposite magnets three-dimensionally by applying self-assembly of magnetic nanoparticles. To expand this combination method to the fabrication of nanocomposite magnets, the use of magnetic metal nanoparticles is desired. In this paper, we attempted to fabricate nanocomposite films composed of Fe?Co nanoparticles in a Fe?Pt matrix by this combination method. Through cross-sectional observation and XRD analysis, a nanostructure composed of Fe?Co nanoparticles embedded in a L10 Fe?Pt matrix was confirmed. These results indicate that this method is capable of producing composite materials containing metal magnetic nanoparticles.

Magnetic Properties of Nanostructured Film Composed of Co-Ferrite Nanoparticles and Metal Co Prepared by Combination of Electrophoretic Deposition and Electroplating

The nanostructured film composed of the Co-ferrite embedded in the metal Co matrix was fabricated by the electrophoretic deposition (EPD) of Co-ferrite particles and electroplating of metal Co in combination. Metal Co as the soft magnetic material and Co-ferrite nanoparticle (10-40 nm) as the hard magnetic material were utilized. In this film, the small clusters of the Co-ferrite nanoparticles deposited by the EPD on the Cu sputtered substrate are embedded in electroplating the metal Co. The structure, like the granular, composed of Co-ferrite nanoparticles and metal Co was observed in the cross-section image of the nanostructured film. The nanostructured film barely exhibited the magnetic properties given the saturation magnetization from metal Co and the coercivity from Co-ferrite nanoparticles.

Magnetostriction of Sm-Fe Thin Films Fabricated by a Sputtering Method

The magnetostriction and magnetic properties of sputtered SmxFe100-x (3¿x¿54) thin films at room temperature were investigated. Films had an amorphous structure for x¿12. The magnetostriction ¿ of the films increased rapidly under weak fields (≪1 kOe) and reached maximum values in the range 130 to 160×10¿6 at 16 kOe for x=30 to 40, suggesting that Sm-Fe films can be used in microactuators and sensors. The magnetic properties did not show a clear dependence on the sputtering conditions, such as the input power, Ar gas pressure, or substrate temperature (¿250°C).

Basic Study of Fabricating High Sensitive Strain Sensor Using Magnetostrictive Thin Film on Si Wafer

We tried to fabricate a strain sensor element using magnetostrictive film on a Si wafer for realizing microelectromechanical systems (MEMS) applications. The principle of the sensor is based on the inverse-magnetostriction effect. In our previous study, the same sensor element on thin conventional glass substrate exhibited ultrahigh sensitivity as a strain sensor due to well-induced uniaxial magnetic anisotropy to the width direction of rectangular FeSiB layers. The uniaxial anisotropy was realized by residual stress among FeSiB, molybdenum as conductive layer, and the substrate after field annealing. However, contrary to the previous results, in this paper, by utilizing Si wafer for the substrate, it was found that uniaxial anisotropy of the rectangular FeSiB layer was induced to the longitudinal direction. The reason of the result was due to the large difference of the coefficient of thermal expansion between the thin glass substrate and Si wafer. Therefore, rotation of magnetic moment of the FeSiB layer from the longitudinal direction to the width direction by applying compressive stress was observed by magnetic Kerr effect microscopy. The results indicate that the sensor element on the Si wafer will have suitable properties as MEMS-type strain sensor.

Noise suppression and crosstalk analysis of on-chip magnetic film-type noise suppressor

This paper discusses near field, conduction and crosstalk noise suppression of magnetic films with uniaxial anisotropy on transmission lines for a film-type noise suppressor in the GHz frequency range. The electromagnetic noise suppressions of magnetic films with different permeability and resistivity were measured and simulated with simple microstrip lines. The experimental and simulated results of Co-Zr-Nb and CoPd-CaF2 films agreed with each other. The results indicate that the higher permeability leads to a better near field shielding, and in the frequency range of 2–7 GHz, a higher conduction noise suppression. It also suggests that the higher resistivity results in a better crosstalk suppression in the frequency range below 2 GHz. These results can support the design guidelines of the magnetic film-type noise suppressor used in the next generation IC chip.