Tetsuhiko Mizoguchi

A magnetic thin film inductor and its application to a MHz switching dc-dc converter

The authors propose a novel structured magnetic thin film inductor using rotation magnetization only. The thin film inductor has a sandwich structure, which consists of a double-rectangular spiral coil between top and bottom CoZrNb amorphous thin films. The sputtered CoZrNb amorphous magnetic thin films have uniaxial magnetic anisotropy induced by direct current field annealing. The easy magnetization axis is directed to the main axis of the rectangular spiral coil. Hence, only the rotation magnetization process dominates in this device. The typical specifications are as follows; 3.5/spl times/5.5 mm in size, inductance of 1 /spl mu/H constant up to 10 MHz, and a quality factor of 10 at 10 MHz. A MHz switching chopper dc-dc converter has been developed by using this thin film inductor, bare-chip semiconductor devices (a power MOSFET and a Schottky barrier diode), and a multilayer ceramic capacitor. This converter with a 0.1 cc volume has an output power over 1 W at 5 MHz switching, and the power density exceeds 10 W/cc (160 W/in/sup 3/). >

Planar inductor with ferrite layers for DC-DC converter

We fabricated planar inductors with ferrite layers by a screen printing, photolithography, and electroplating process. The screen printing method made it possible to obtain a coil spacing filled with ferrite. In this structure, the perpendicular leakage magnetic flux preferentially passes through the coil spacing and bypasses the copper conductor line, a path that is expected to reduce eddy current loss. Trial samples of a planar inductor with ferrite layers achieved a high-quality Q factor of 40-70 at 5 MHz. Magnetic field analysis revealed that the eddy current loss of the conductor line was only 2.4% of total loss.

Study of high power planar inductor

A method for planar inductor design has been established on the basis of a discussion of the magnetic flux density distribution. Planar inductors for miniature DC-DC converters have been developed using this design method. This converter is much smaller and thinner than conventional ones, and has an output power/volume ratio of 1.7 W/cc. A spiral coil with a very small distance between the conductors and a low loss magnetic sheet are required for the development of high Q planar inductors. >

Nd-Fe-B-Co-Al based permanent magnets with improved magnetic properties and temperature characteristics

Magnetic properties of Nd-Fe-B-Co-Al alloy magnets have been studied with respect to both boron and aluminum concentration. Both cobalt and aluminum substitution for iron is remarkably effective for increasing magnetic hardness in the low boron concentration region. The following magnetic properties were attained for Nd 15 Fe 62.5 B 5.5 Co 16 Al 1 : Br=13.2KG, iHc=11.0kOe, (BH) max =41.0MGOe and T c =500°C. The reversible temperature coefficient of remanence in the above magnet was -0.071%/°., approximately one-half that for the Nd 15 Fe 77 B 8 magnet. It was observed that Laves phase Nd(Fe, Co) 2 precipitates in cobalt containing magnets. The authors think that the addition of aluminum makes this Nd(Fe, Co) 2 magnetic phase non-magnetic; which is considered to be the cause of coercivity increase.

Magnetic field generator useful for a magnetic resonance imaging instrument

A magnetic field generator comprises a permanent magnet, and pole pieces magnetically connected to the permanent magnet. The pole pieces are disposed to face each other to generate a magnetic field between them, and have a specific resistance of 20 μΩ-cm or more. The permanent magnet comprises a sintered alloy including iron as a main component, a rare earth element including yttrium, cobalt, and boron. The permanent magnet includes, as its main part, a strong magnetic Fe-rich phase of a tetragonal system, as well as a non-magnetic Laves phase, and preferably has a maximum energy product of 38 MGOe or more.

5 MHz switching micro DC-DC converter using planar inductor

The authors describe a high frequency switching DC-DC converter using a novel developed planar inductor. The planar inductor has a sandwich structure, which consists of a 50 /spl mu/m thick copper rectangular spiral coil between upper and lower 6 /spl mu/m thick FeCoBC amorphous magnetic films. The typical specifications of the inductor are as follows: 5.50/spl times/6.55 mm/sup 2/ in size, inductance of 0.30 /spl mu/H constant up to 10 MHz, DC resistance of 0.16 Ohms, a maximum quality factor of 8 at 2 MHz, and a maximum DC current of 1.6 A at -6 dB inductance point. A 5 MHz switching step up converter has been developed, which has the planar inductor, Nch lateral MOSFETs for main switch, a low Vf Schottky barrier diode, multilayered ceramic capacitors and a MHz operation PWM control IC. These components have been surface-mounted on circuit board, and then molded by epoxy resin. The novel developed DC-DC converter has 1.3/spl times/1.4/spl times/0.2 cm/sup 3/ in size, 2 W of rating output power and 80% of typical efficiency, when an input voltage is 3.6 V and an output voltage is 4.7 V.

Oblique-field annealing effect for in-plane magnetic anisotropy of soft magnetic Co-Nb-Zr thin films

The effect of annealing in a magnetic field applied obliquely to the surface of soft magnetic thin films has been investigated. This annealing method was found to be extremely effective to control in-plane magnetic anisotropy without a change of annealing temperature and to suppress local anisotropy dispersion. For sputtered amorphous Co/sub 85.5/Nb/sub 8.9/Zr/sub 5.6/ thin films, it has been found that the in-plane uniaxial anisotropy energy was varied from 250 J/m/sup 3/ to near zero with the coercive force H/sub c/ less than 6.5 A/m by changing the oblique-field annealing angle /spl alpha/. Experimental values of in-plane anisotropy energy agreed well with calculated ones predicted from /spl alpha/ and intrinsic anisotropy induced by quasi-directional ordering. These films showed good high frequency characteristics for applying to miniaturized inductive devices. >

Effect of Ga addition to NdFeCoB on their magnetic properties

It was found that the Ga addition to NdFeCoB magnets was very effective for improving their magnetic properties. Magnets with high boron concentration had a high coercive force and magnets with low boron concentration had a high‐energy product. The following magnetic properties were obtained: (1) Nd14.5FebalCo16Ga1B9.5:Br=12.0 kG, IHc=15.3 kOe, (BH)max=34 MGOe, Tc=500 °C (2) Nd14.5FebalCo16Ga1B5.5:Br=13.1 kG, IHc=12.2 kOe, (BH)max=40 MGOe, Tc=500 °C. It was also found that NdFeCoGaB magnets with very low boron concentration still had a relatively high coercive force.

Nd‐Fe‐B‐Co‐Al based permanent magnets with improved magnetic properties and temperature characteristics

Magnetic properties have been studied with respect to the boron concentration on Nd‐Fe‐B based magnets. The combined addition of cobalt and aluminum in a Nd‐Fe‐B magnet is remarkably effective for increasing magnetic hardness in the region of low boron concentration. The following magnetic properties were attained for Nd15Fe62.5B5.5Co16Al1 :Br=13.2 kG, iHc=11.0 kOe, (BH)max=41.0 MGOe, and Tc=500 °C. The reversible temperature coefficient of the remanence of the magnet is −0.071%/deg, approximately one‐half of the Nd15Fe77B8 magnet.

Magnetic properties of Nd-Fe-B magnets with both Co and Al addition

Magnetic properties of Nd-Fe-B based magnets with both cobalt and aluminum addition have been investigated with respect to cobalt and aluminum concentration. Structural analyses were carried out for the sintered bodies. In cobalt containing alloys, Nd(Fe,Co) 2 phase was clearly observed by X-ray diffractometer, SEM and TEM, especially for the magnet with more than 30 at % cobalt. The coercive force behavior versus aluminum content for cobalt containing magnets can be divided into two stages. The first stage in which coercive force increases abruptly with the small amount addition of aluminum may result from Nd(Fe,Co) 2 phase being nonmagnetic by the addition of aluminum. The quantity of this Nd(Fe,Co) 2 phase increases with increasing cobalt content. It was shown that the greater the quantity of cobalt in the sintered body, the greater the addition of aluminum becomes necessary for obtaining high coercive force.