K.I. Arai

Microfabrication and characteristics of magnetic thin-film inductors in the ultrahigh frequency region

Thin-film inductors for 1 GHz-drive mobile communication handset application has been demonstrated. This is the possible practical application of soft magnetic films in 1 GHz range. Fe61Al13O26 with Ms=1.2u200aT, ρ=500 μΩu200acm, fr=2u200aGHz were used for the inductors. L=7.6u200anH, R=6.5u200aΩ, and Q=7.4 were obtained at 1 GHz in a 370 μm×370 μm square four turn spiral of line/space=11 μm/11 μm covered with 0.1-μm-thick slitted Fe61Al13O26 film with Cr underlayer. The L was increased over the flux saturated inductor by 8.6% without any degrade of quality factor.

A new permeance meter based on both lumped elements/transmission line theories

We have developed a new permeance meter in the 1 MHz-1.5 GHz range using either a microstrip pickup coil or a shielded loop pickup coil. Both pickup coils and the driving plates are free from LC resonance due to impedance matching. In the MHz range we must consider signal-to-noise ratio of the pickup coil. In the GHz range we must eliminate the voltage induced by the electric field, and an electromagnetic higher order mode in the driving plates.

Analysis of the inductance and the stray capacitance of the dry-etched micro inductors

Thin film inductors with meander coils or spiral coils were examined systematically. The minimum line spacing of the inductors was 1.5 mu m. In case of air core inductors, both inductance and stray capacitance were calculated from the dimension of the inductors, and they agreed well with measured values. With the application of a magnetic thin film, the inductance is increased and the degree of increase was proportional to the length of the coil. It is found that the capacitance between conductor and magnetic film is very significant and needs special consideration. >

Magnetomechanical coupling and variable delay characteristics by means of a giant ΔE effect in iron‐rich amorphous ribbon

The saturation magnetostriction constants λs of amorphous (Fe0.9Co0.1)xSiyBz and (Fe1−xCox)78Si8B14 ribbons were measured at room temperature by a three terminal capacitance method, and the largest constant λs was found to be 44×10−6 for the composition (Fe0.9Co0.1)0.83B0.14. The magnetomechanical coupling factor k and the giant ΔE effect of the amorphous Fe78Si10B12 ribbons were also observed. These values depended on the annealing of the ribbons in a magnetic field, and were larger than those previously reported. The largest coupling factor was found to be 0.75 for the ribbon annealed at 410u2009°C for 12 minutes and the largest ΔE effect to be 1.9 for a ribbon annealed at 410u2009°C for 10 minutes. The variable delay time, by using Fe78Si10B12 ribbons with 20, 15 and 5 μm thick was also measured from 150 kHz to 10 MHz as a function of the frequency.

Improved RF integrated magnetic thin-film inductors by means of micro slits and serface planalization techniques

Improvement of magnetic thin-film inductors for RF monolithic microwave integrated circuits (MMICs) is discussed. Surface planarization reduced the surface roughness down to R/sub a/=1.2 nm, which enhanced the quality factor by 14% over a nonplanarized inductor. The orthogonal bar slit pattern was the best among the fabricated slit patterns, L=7.55 nH (+12% of the air core), R=6.80 /spl Omega/ and Q=7.09 (+9%) were obtained for the orthogonal bar slit pattern (slit width=0.75 /spl mu/m) with surface planarization.

Fabrication and basic characteristics of dyr-etched micro inductions

Thin-film meander inductors having 10/sup -6/-m-range coil spacing were fabricated successfully by a dry-etching technique. The inductance measured with a microstrip line increased with coil spacing due to dielectric coupling between the meander lines. The maximum value of the applicable current density was examined, and it was clarified that magnetic thin films are required to provide high saturation magnetization in order to remain in the undersaturated region in case of high current density applications. It is concluded that these results provide a basis for developing thin-film micro inductors and transformers. >

A new 1 MHz-2 GHz permeance meter for metallic thin films

We have developed a permeance meter in the 1 MHz-2 GHz range using a shielded loop type pickup coil. The effect of grounding between drive coil and pickup coil was analyzed using time domain reflectometry (TDR). The grounding increased the output voltage and eliminated the multiple reflections in the drive coil. Using the grounding, magnetic thin film permeance can be measured accurately over a wide frequency range. The complex permeance is shown of a l /spl mu/m thick Co/sub 85/Nb/sub 12/Zr/sub 3/ film.

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. >

A new microstrip pickup coil for thin-film permeance meters

In this paper we propose an application of microstrip line for a single-turn pickup coil in the thin-film permeance meters. This coil has two electric ports with one terminated into 50 /spl Omega/. It is free from LC resonance up to a few GHz because the microstrip line does not resonates and because the stray capacitance between the pickup coil and the driving sheets is small as compared with the conventional figure-8 coil. We measured the thin film permeance up to 700 MHz which is the upper frequency limit of the driving sheets used. The proposed coil has a potential to measure thin-film permeances over the wide range from 1 MHz up to a few GHz. >

A new hybrid device using magnetostrictive amorphous films and piezoelectric substrates

A new hybrid device composed of a magnetostrictive amorphous FeSiB film on piezoelectric PZT substrate is described. DC and AC electric fields were applied to the PZT substrate and the magnetic properties of the magnetostrictive film were observed. Both the initial permeability and the coercive field of the film changed drastically (about 300%) due to the inverse magnetostrictive effect when electric fields were applied. A possible application of this hybrid element is a voltage controlled variable inductor. >