JP2009094149A - Multilayered inductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayered inductor that can obtain a sufficient gap dispersion number even when the number of turns is small, and reduce eddy current loss in a coil pattern nearby a gap and has a small DC resistance thereby has superior low loss characteristics. <P>SOLUTION: A plurality of coil layers (three layers 5, 6 and 7 in Fig. 1) each constituted by forming a nearly one-turn coil pattern 3 made of Ag and a magnetic gap layer 4 made of zirconia (ZrO<SB>2</SB>) on a magnetic body 2 made of NiZn ferrite are stacked through via holes 8 and connected in series. A three-turn multilayer inductor 10 is constituted having a configuration such that coil layers 9 and 11 having nearly the same constitution with upper and lower coil layers 5 and 7 of the stack are connected in parallel through via holes 12 respectively and stacked, and a plurality of plain magnetic body layers 13 with only magnetic bodies 2 made of, for example, NiZn ferrite are stacked while neither a coil pattern 3 nor a magnetic gap 4 is formed above and below the stack. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multilayer inductor in which a magnetic circuit is constituted by laminated magnetic materials, and more particularly to a multilayer inductor in which a magnetic gap layer made of a nonmagnetic material is provided in a part of a magnetic circuit.

  Various functional modules are incorporated in portable electronic devices such as recent cellular phones. However, since the power supply voltage required for each module differs, a voltage conversion circuit for converting the power supply voltage of the original battery (for example, a lithium ion battery) to the voltage required for the module, that is, a DC-DC converter is provided for each module. Necessary.

  An element that converts voltage in the DC-DC converter is an inductor. Conventionally, a winding type inductor in which a magnet wire coated with an insulating film is wound around a ferrite drum core and the drum core is surrounded by a cylindrical ferrite core has been widely used.

  However, due to structural problems, there are limits to miniaturization, low profile, and low cost, and monolithic, closed magnetic circuit multilayer inductors are attracting attention as an alternative.

  The multilayer inductor is formed by integrally firing a magnetic material (ferrite) and an internal coil pattern (Ag) by a sheet lamination method, a printing method, or the like, and simultaneously firing them. In addition, the monolithic (integral) structure has excellent characteristics such as high reliability, easy miniaturization and low profile, and easy cost reduction by mass production and cost reduction by miniaturization. .

  However, since conventional multilayer inductors have a multilayer structure based on ferrite, which is a magnetic material, magnetic paths exist between the layers of the coil pattern, and the flow of magnetic flux is not uniform as in the case of wire wound inductors. There is a problem that high inductance and direct current superimposition characteristics are difficult to obtain.

On the other hand, FIG. 2 of Patent Document 1 discloses a multilayer inductor in which a magnetic flux is not passed between coil patterns by filling a coil pattern forming region of each layer with a nonmagnetic material.
However, it is difficult to form by the sheet lamination method, and even the printing method is very complicated, and is not suitable for cost reduction.

  On the other hand, in FIG. 2 of Patent Document 2, the magnetic gap is distributed to all the coil layers or a coil layer close thereto, and the magnetic flux generated by the coils of each layer interlinks the magnetic gap of each layer so An inductor is also disclosed in which the eddy current loss on the coil pattern due to the high-frequency magnetic flux is improved.

FIG. 11 is a cross-sectional view of an example of the multilayer inductor 40 of Patent Document 2, in which a plurality of coil layers in which coil patterns 5, 6, and 7 are formed are laminated on a magnetic body 2 (ferrite), and external lead leads A magnetic gap 4 made of a nonmagnetic material is provided in the coil layer excluding the portion 15.
Japanese Patent Laid-Open No. 2-16507 WO2007 / 088914

  With the configuration of the multilayer inductor disclosed in Patent Document 1, it is difficult to manufacture by a sheet stacking method in which a magnetic layer having a coil pattern formed thereon is stacked. Further, there is a problem that the printing process becomes complicated even with the printing method.

  Further, in the configuration of Patent Document 2, when the number of turns of the coil is reduced in response to the reduction in inductance due to the higher frequency of the DC-DC converter in the future, the number of coil layers is reduced and the number of dispersed magnetic gaps is reduced. There is a problem that a sufficient dispersion effect cannot be obtained and the eddy current loss increases. In the example of FIG. 11, the inductor is a three-turn inductor, but in this case, the maximum number of gap dispersions is 3 (4 if the lead lead portion 15 is included). Therefore, the thickness of the magnetic gap cannot be made sufficiently thinner than the thickness of the coil pattern. As a result, the fringing (spreading) of the magnetic flux generated in the vicinity of the end face of the magnetic gap links the coil pattern and causes eddy current loss.

  The present invention has been made in view of such circumstances, and even if the number of turns of the coil is reduced as the frequency is increased, a sufficient magnetic gap can be dispersed, and eddy current loss and loss due to DC resistance are reduced. Therefore, an object of the present invention is to provide a multilayer inductor that has a high Q and contributes to high efficiency of a DC-DC converter.

  In the multilayer inductor according to the present invention, magnetic layers and first coil patterns are alternately stacked, and the first coil patterns are connected in series in the stacking direction to form a coil, which is in contact with the first coil pattern. A laminated inductor having a plurality of magnetic gaps in the laminating direction, wherein a first magnetic gap pattern is formed in the region, and a second coil pattern connected in parallel to a part or all of the first coil patterns; The multilayer inductor is characterized in that a second magnetic gap pattern is formed in a region in contact with the second coil pattern.

  Therefore, the multilayer inductor of the present invention can sufficiently disperse the magnetic gap even when the number of turns of the coil is small, and the gap length per gap can be set sufficiently smaller than the thickness of the coil pattern. . As a result, the fringing of the magnetic flux in the gap portion is reduced, and eddy current loss due to the magnetic flux interlinking with the coil pattern can be reduced.

  In the multilayer inductor of the present invention, the magnetic gap is formed in the inner part surrounded by the coil and is not exposed at the end face of the inductor, so there is little leakage of the magnetic flux from the inductor, and this leakage magnetic flux is linked to the external electrode. Thus, the eddy current loss that occurs can be reduced.

The multilayer inductor according to the present invention is characterized in that the magnetic body is NiZn-based or NiCuZn ferrite, and the magnetic gap is formed of zirconia (ZrO ₂ ).

Therefore, in the multilayer inductor according to the present invention, the magnetic material is NiZn-based or NiCuZn-based ferrite, and the magnetic gap is formed of zirconia (ZrO ₂ ), so that the magnetic material and a different material forming the magnetic gap react. And stable inductor characteristics as designed.

  The multilayer inductor of the present invention is characterized in that the magnetic material is NiZn-based or NiCuZn-based ferrite, and the magnetic gap is formed of Zn ferrite.

  Therefore, in the multilayer inductor of the present invention, simultaneous firing between different materials of the NiZn-based ferrite that is the magnetic material and the Zn ferrite that is the magnetic gap is easy, and delamination and cracks are less likely to occur.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(First embodiment)
FIG. 1 is a cross-sectional view of the multilayer inductor 10 according to the first embodiment, and FIG. 2 is an exploded perspective view of the multilayer inductor 10 according to the first embodiment.

The coil layer is made of, for example, a magnetic body 2 made of NiCuZn ferrite, a coil pattern 5, 6, 7 of approximately one turn made of a conductive material such as Ag, and a magnetic gap pattern 4 made of a non-magnetic material such as zirconia (ZrO ₂ ). Is formed and configured. The coil layers on which the first coil patterns 5, 6 and 7 are formed are stacked and connected in series via the via hole 8. In addition, the coil layers on which the second coil patterns 9 and 11 having substantially the same configuration as the upper and lower coil layers 5 and 7 of the laminate are formed are stacked and connected in parallel through the via holes 12. The coil configured as described above is drawn out by the external lead lead portion 15 and the external lead portion 1. Further, a three-turn multilayer inductor 10 is configured in such a manner that a plurality of plain magnetic layers 13 made of, for example, NiCuZn ferrite, each of which is made of only NiCuZn ferrite, are stacked on top and bottom of the multilayer body. The multilayer inductor 10 is preferably formed by the LTCC (Low Temperature Co-fired Ceramics) method.

  In the multilayer inductor according to the first embodiment, the upper and lower coil patterns 5 and 7 are connected in parallel with the coils 9 and 11 having substantially the same shape through the through holes 12, and the upper, middle, and lower three coil patterns are the through coils. It is connected in series through the hole 8 and functions as a 3.5-turn coil as a whole. An electrical connection circuit diagram is shown in FIG.

  For example, the magnetic body 2 of each coil layer forms a green sheet (15 to 60 μm after drying) by using a soft ferrite paste by a doctor blade method, a calender roll method, or the like. A conductive paste made of an alloy containing Ag or the like is dried on the predetermined coil pattern 3 and then printed or applied to a thickness of 20 to 50 μm and a width of 100 to 400 μm. Further, a non-magnetic paste such as zirconia or Zn ferrite that becomes a magnetic gap is printed or applied to a predetermined magnetic gap pattern 4.

  The dried thickness of the magnetic gap pattern is preferably 3 μm or more and thinner than the coil pattern. When the thickness of the Ag constituting the coil pattern is thick after drying and the step between the green sheet 2 and the coil pattern 3 is large, it may cause delamination between layers, insufficient adhesion, or voids. It is preferable to print or apply a magnetic paste in a region excluding the coil pattern so as to cover 4 and to be approximately the same height as the upper surface of the coil pattern. Further, the via hole 12 for the parallel connection may be additionally arranged not only near the vicinity of the start and end of winding of the second coil pattern but also at an arbitrary position of the second coil pattern.

  A plurality of coil layers formed by the above process are stacked and connected in series via the via hole 8 and in parallel via the via hole 12. Further, a plurality of plain magnetic layers 13 made only of the magnetic body 2 made of, for example, NiZn ferrite are stacked on the upper and lower sides of the multilayer body.

  The green laminate thus obtained was fired at 800 to 950 ° C. by simultaneously firing ferrite as a magnetic material, Ag as a conductor and zirconia or Zn ferrite as a non-magnetic material, and shrinking by about 20%. Become a unity.

  In this embodiment, although the number of turns of the coil is 3, the gap dispersion is 5, the gap length per gap can be reduced to 3/5, and can be set sufficiently smaller than the thickness of the coil pattern. Therefore, the fringing of the magnetic flux in the gap portion is reduced, and the eddy current loss due to the magnetic flux interlinking with the coil pattern can be reduced. Further, since two of the three turns are connected in parallel, the DC resistance of the inductor can be reduced to 2/3.

(Second Embodiment)
FIG. 4 is a cross-sectional view of the multilayer inductor according to the second embodiment. Although this example functions as a three-turn coil as in the first embodiment, the coil layer 6 in the upper, middle, and lower coil layers 5, 6, and 7 has a coil layer 14 and a via hole having substantially the same shape. 12 are connected in parallel.

  In this embodiment, although the coil pattern has 3 turns, the gap dispersion number is 4, and the gap length per gap can be reduced to 3/4, which can be set sufficiently smaller than the thickness of the coil pattern. Therefore, the fringing of the magnetic flux in the gap portion is reduced, and the eddy current loss due to the magnetic flux interlinking with the coil pattern can be reduced. Further, since one of the three turns is connected in parallel, the DC resistance of the inductor can be reduced to 5/6.

(Third embodiment)
FIG. 5 is a cross-sectional view of the multilayer inductor according to the third embodiment. This example functions as a three-turn coil as in the first embodiment, but all the coil layers 5, 6, 7 are arranged in parallel with the coil layers 9, 14, 11 having substantially the same shape and via holes 12. It is connected.

  In this embodiment, although the coil pattern has 3 turns, the gap distribution number is 6, the gap length per gap can be reduced to ½, and can be set sufficiently smaller than the thickness of the coil pattern. Therefore, the fringing of the magnetic flux in the gap portion is reduced, and the eddy current loss due to the magnetic flux interlinking with the coil pattern can be reduced. Further, since all the coil patterns are connected in parallel, the DC resistance of the inductor can be reduced to ½.

  As described above, the position and number of coils connected in parallel are arbitrary, and if the number of coils connected in parallel is large, the number of magnetic gap dispersion increases and the gap length per gap is shortened to reduce eddy current loss. And the direct current resistance can be reduced.

  Next, the manufacturing process of the multilayer inductor according to the first, second and third embodiments will be described.

As the NiCuZn ferrite, for example, a ferrite composition containing Fe ₂ O ₃ , ZnO, NiO and CuO as main components is used. 10% by weight of a binder is added to 100% by weight of the calcined powder, and kneaded with a plasticizer and a solvent by a ball mill to obtain a slurry for magnetic material combination. Using this slurry, a ferrite sheet having a thickness of 20 μm is molded using a sheet molding machine using a doctor blade method.

  Through holes are formed in a predetermined molded ferrite sheet, zirconia processed into a non-magnetic paste to be a magnetic gap is printed in a predetermined shape, and then the Ag processed into a paste to be a coil pattern is substantially omitted. A coil layer is obtained by printing a predetermined pattern so as to form a one-turn coil pattern. Note that the printing order of zirconia and Ag may be reversed. Moreover, in order to eliminate the level | step difference by the printing of a zirconia and Ag and to improve a laminating property, the paste of the same material as a ferrite sheet can also be printed.

  The coil layer thus formed is electrically connected in series via the via hole 8 and in parallel via the via hole 12, and the first coil pattern and the second coil pattern are connected to each other in a predetermined manner. In order to obtain the number of turns and the number of dispersed gaps, a plurality of plain ferrite sheets 13 are laminated, and a plurality of plain ferrite sheets 13 are laminated on the laminated coil layers. The obtained laminate is pressure-bonded at a constant pressure, then processed into a desired shape, and fired in the atmosphere at 900 ° C. for 4 hours to obtain a rectangular parallelepiped (for example, 2.5 × 2.0 × 1.0 mm) sintered body. Further, a conductive paste for external electrodes (for example, Ag) is applied to the opposing end surfaces (for example, 2.0 × 1.0 mm surfaces) of the sintered body, and then a baking process is further performed at 630 ° C. for 15 minutes to form a multilayer inductor. obtain.

  As described above, in the present invention, even for an inductor having a small number of turns, a layer printed with a coil pattern connected in parallel to a part or all of the coil patterns is provided and connected in parallel. As many magnetic gaps as the number of coil patterns can be dispersed. Therefore, even if the number of turns is small, sufficient magnetic gap dispersion can be obtained and eddy current loss can be suppressed. Further, the DC resistance of the inductor can be reduced by the coils connected in parallel.

  For the conventional multilayer inductor of FIG. 11 and the multilayer inductor of the present invention of FIG. 1, the magnetic flux density interlinking the coil patterns was calculated. In the conventional multilayer inductor, the number of turns is 3 turns, and a total gap of 30 μm is dispersed in the three coil layers other than the uppermost coil layer. On the other hand, the configuration of the multilayer inductor of the present invention has the same number of turns of 3 turns, but a coil layer connected in parallel to 2 turns is added, and a total of 30 μm is added to 5 coil layers including the added 2 coil layers. The gap is dispersed. The simulation was performed using the electromagnetic field analysis software J-MAG Ver8.4 of Japan Research Institute Solutions under the conditions of a frequency of 2 MHz and an excitation current of 0.1 App.

  The magnetic flux density interlinking the coil pattern is 5.0 mT at the maximum in the case of the conventional multilayer inductor, but it is found that it is about 3.5 mT in the case of the multilayer inductor of the present invention, which is reduced by about 30%. Further, when the eddy current loss is calculated, it is 2.98 mW in the conventional structure, whereas the structure of the present invention is 1.83 mW, and it is found that the eddy current loss can be reduced by about 40%.

  Furthermore, actual device prototypes of the conventional multilayer inductor and the multilayer inductor of the present invention were manufactured, and the device characteristics (Q frequency characteristics, DC resistance) and efficiency characteristics when applied to a DC-DC converter operating at 3 MHz were measured. did.

  The inductor is a 30 μm-thick NiCuZn-based low-temperature-fired ferrite magnetic sheet, and the coil pattern is dried with Ag paste, then printed to a width of 360 μm with a thickness of 40 μm, and dried inside the coil pattern with zirconia paste. After printing with a thickness of 6 μm. A plurality of coil layers thus produced were laminated so as to have a predetermined number of turns and gap dispersion numbers, and then fired to form external electrodes, thereby producing a laminated inductor. The outer shape of the obtained inductor is 2.5 × 2.0 × 1.0 mm, the number of turns of the coil is 4.5 turns, and the magnetic gap is distributed in three coil layers other than the coil layer at the start and end of winding. Further, in the element of the present invention, a coil layer connected in parallel to one coil layer among the three coil layers is additionally inserted, and the gap is dispersed in a total of four coil layers. FIG. 6 shows a cross-sectional view thereof. From the figure, the conventional multilayer inductor has a gap dispersion number of 3, and the multilayer inductor of the present invention has a gap dispersion number of 4.

The measurement results will be described in detail below. First, the frequency characteristics of Q were measured with an excitation amplitude of 1 V within a frequency range of 70 kHz to 30 MHz using Agilent Technologies 4285A. The results are shown in Fig. 7. The multilayer inductor of the present invention improved by 29% compared to the conventional multilayer inductor at the maximum value.
Next, the DC resistance was measured by a four-terminal method using Agilent Technology 3458A. The conventional multilayer inductor was 75 mΩ, but the multilayer inductor of the present invention was 67 mΩ, a 12% reduction.

  Next, FIG. 8 shows a circuit configuration of a DC-DC converter operating at 3 MHz. The output voltage Vo is compared and amplified by the reference voltage Ref and the error amplifier EA, modulated to a pulse width by the pulse width modulation circuit PWM, applied to the gates of the two MOSFETs, and the two MOSFETs are complementarily turned on and off at a frequency of 3 MHz. . By the switching operation of the two MOSFETs, the input voltage Vi is stepped down through the inductor L to obtain a necessary output voltage Vo. The conversion efficiency η of the DC-DC converter was measured by changing the output current when the conventional multilayer inductor was used as the inductor element L of this circuit and when the multilayer inductor of the present invention was used. If the input current is Ii and the output current is Io, η = VoxIo / (VixIi) × 100 (%). FIG. 9 shows the results when operating as a step-down DC-DC converter with Vi = 3.6V and Vo = 1.8V. In both cases, the efficiency changes abruptly when the output current is in the vicinity of 100 mA. This is because the control mode of the output voltage of the control IC changes with this output current as a boundary.

  It was found that the multilayer inductor of the present invention can improve the efficiency by 0.8% at the maximum efficiency and 0.17% at the maximum output current as compared with the conventional multilayer inductor. Here, the improvement in efficiency at the maximum efficiency mainly contributes to the improvement of the Q characteristic described above, and the improvement in efficiency at the maximum output current mainly contributes to the reduction of the DC resistance described above.

  As described above, it was confirmed that the present invention is effective in the frequency characteristics of Q, the direct current resistance, and the efficiency of the DC-DC converter. However, the direct current superposition characteristics were not deteriorated by the present invention as shown in FIG. .

Similar results were obtained when Zn ferrite containing Fe ₂ O ₃ , ZnO, and CuO as main components was used as the magnetic gap instead of zirconia.

  According to the present invention, in a multilayer inductor having dispersed magnetic gaps, even if the number of turns is small, a sufficient number of gap dispersions can be obtained, so that eddy current loss in a coil pattern near the gap can be reduced. . In addition, since some or all of the coil layers are connected in parallel, the DC resistance of the inductor can also be reduced.

It is sectional drawing of the multilayer inductor which concerns on 1st Embodiment. 1 is an exploded perspective view of a multilayer inductor according to a first embodiment. It is an electrical equivalent circuit diagram of the multilayer inductor according to the first embodiment. It is sectional drawing of the multilayer inductor which concerns on 2nd Embodiment. It is sectional drawing of the multilayer inductor which concerns on 3rd Embodiment. It is a schematic diagram which shows the cross section of a prototype element. It is a graph which shows the frequency characteristic of Q of a prototype element. This is a circuit configuration of a DC-DC converter. It is a graph which shows the efficiency of a DC-DC converter. It is a graph which shows the direct current | flow superimposition characteristic of a prototype element. It is a schematic diagram which shows the cross section of the conventional multilayer inductor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 External drawer | drawing-out part 2 Magnetic body 4 Magnetic gap 5 Upper coil layer 6 Middle coil layer 7 Lower coil layer 8 Via hole which electrically connects a coil pattern of upper, middle, and lower in series 9 Coil layer 10 connected in parallel with an upper coil layer 11 is a cross-sectional view of the multilayer inductor according to the first embodiment. 11 Coil layer 12 connected in parallel with the lower coil layer. Via hole 13 electrically connected in parallel with the upper, middle and lower coil patterns. Solid magnetic layer 14 Parallel with the middle coil. Coil layer 15 to be connected External lead portion 20 Cross section of multilayer inductor according to second embodiment 30 Cross section of multilayer inductor according to third embodiment 40 Cross section of conventional multilayer inductor

Claims (4)

A magnetic layer and a first coil pattern are alternately stacked, the first coil pattern is connected in series in the stacking direction to form a coil, and a first magnetic gap pattern is formed in a region in contact with the first coil pattern. In a multilayer inductor having a plurality of magnetic gaps in the stacking direction,
A second coil pattern connected in parallel to some or all of the first coil patterns is provided, and a second magnetic gap pattern is formed in a region in contact with the second coil pattern. Multilayer inductor.   The multilayer inductor according to claim 1, wherein the first and second magnetic gap patterns are provided so as to be surrounded by the first coil pattern and the second coil pattern, respectively. Laminated inductor. 3. The multilayer inductor according to claim 1, wherein the magnetic body is formed of NiZn-based or NiCuZn-based ferrite, and the first gap pattern and the second gap pattern are formed of zirconia (ZrO ₂ ). Laminated inductor.   4. The multilayer inductor according to claim 1, wherein the magnetic body is formed of NiZn-based or NiCuZn-based ferrite, and the first gap pattern and the second gap pattern are formed of Zn ferrite. Laminated inductor.

Images