Patent Grant
7907044
This application is a National Stage of International Application No. PCT/JP2007/051648 filed Jan. 31, 2007, claiming priority based on Japanese Patent Application Nos. 2006-023775, filed Jan. 31, 2006 and 2006-152542, filed May 31, 2006, the contents of all of which are incorporated herein by reference in their entirety.
The present invention relates to a laminate device having a magnetic circuit constituted by laminating coil patterns and magnetic material layers, particularly to a laminated inductor having non-magnetic or low-permeability magnetic gap layers in a magnetic circuit path, and a module (composite part) having semiconductor devices and other reactance elements mounted on a ferrite substrate having electrodes, etc.
Various portable electronic equipments (cell phones, portable information terminals PDA, note-type personal computers, portable audio/video players, digital cameras, digital video cameras, etc.) usually use batteries as power supplies, comprising DC-DC converters for converting power supply voltage to operation voltage. The DC-DC converter is generally constituted by integrated semiconductor circuits (active parts) including switching devices and control circuits, inductors (passive parts), etc. disposed as; discrete parts on a printed circuit board.
For the miniaturization of electronic equipments, the DC-DC converter has an increasingly higher switching frequency, using more than 1 MHz at present. Because semiconductor devices such as CPU are getting higher in speed, function and current and lower in operating voltage, low-voltage, high-current DC-DC converters are needed.
Passive parts used in power supply circuits for DC-DC converters, etc. are required to be smaller in size and height, and integrated with active parts. The inductor, one of passive parts, has conventionally been composed of a wire wound around a magnetic core, and its miniaturization is limited. Because lower inductance is needed in order that laminate devices are operable at higher frequencies, monolithic laminate devices having a closed magnetic path structure have become used.
The laminated inductor, an example of laminate devices, is produced by integrally laminating magnetic material (ferrite) sheets printed with coil patterns, and sintering them. The laminated inductor has excellent reliability with little magnetic flux leakage. However, because it has an integral structure, magnetic saturation partially occurs in a magnetic material in the laminated inductor by a DC magnetic field generated when a magnetization current is applied to the coil pattern, resulting in drastic decrease in inductance. Such laminated inductors have poor DC-superimposed characteristics.
To solve this problem, JP 56-155516 A and JP 2004-311944 A disclose a laminated inductor 50 having an open magnetic path structure comprising a magnetic gap layer between magnetic layers, as shown in
JP 2004-311944 A discloses a laminated inductor 50 comprising a magnetic gap layer 44 embedded at center between coil patterns, and a non-magnetic body 47 embedded around the coil patterns, as shown in
Accordingly, an object of the present invention is to provide an easily producible laminate device giving stable inductance in a range from small magnetization current to large magnetization current, with excellent DC-superimposed characteristics, and a module comprising such laminate device.
As a result of intense research in view of the above object, the inventors have found that in a laminate device containing coil patterns, the formation of pluralities of magnetic gap layers in regions each in contact with the coil pattern makes magnetic saturation less likely in a magnetic material portion even with large magnetization current, resulting in decrease in eddy current loss. The present invention has been completed based on such finding.
Namely, the laminate device of the present invention comprises magnetic layers and coil patterns alternately laminated, the coil patterns being connected in a lamination direction to form a coil, and pluralities of magnetic gap layers being disposed in regions in contact with the coil patterns.
The magnetic gap layers are preferably formed in contact with at least two coil patterns adjacent in a lamination direction. A magnetic flux generated from one coil pattern passes through a magnetic gap layer in contact therewith, but less through magnetic gap layers in contact with the other coil patterns, so that it flows around that one coil pattern. Because magnetic fluxes generated from two adjacent coil patterns are canceling each other in a magnetic material portion between the coil patterns, magnetic saturation is unlikely even with large magnetization current.
The number of the coil patterns having the magnetic gap layers is preferably 60% or more of the number of turns of the coil. The coil is preferably formed by connecting the coil patterns of 0.75 turns or more to 2 turns or more. At least some of the coil pattern preferably has more than one turn. The coil pattern is preferably made of a low-melting-point metal such as Ag, Cu, etc., or its alloy. When each coil pattern has less than 0.75 turns, too many coil-pattern-caring layers are laminated. Particularly when each coil pattern has less than 0.5 turns, there is too large an interval between the coil patterns adjacent in a lamination direction. Some of the coil patterns acting as leads, etc. may have less than 0.75 turns.
With at least some of the coil patterns having more than one turn, the number of coil-pattern-carrying layers can be reduced. A coil pattern having more than one turn inevitably increases an area in which the coil pattern is formed, with a reduced cross section area of a magnetic path. However, the formation of a magnetic gap layer between adjacent coil patterns on a magnetic substrate layer provides inductance not smaller than that obtained when coil patterns having one turn or less are used. Such structure, however, makes magnetic saturation likely because of the reduction of a cross section area of a magnetic path, and increases floating capacitance between coil patterns opposing on the same magnetic substrate layer, thereby reducing a resonance frequency and lowering the quality coefficient Q of the coil. Accordingly, in the case of a 3216-size laminate device, for instance, a coil pattern on each layer preferably has 3 turns or less.
The magnetic gap layer is preferably made of a non-magnetic material or a low-permeability material having a specific permeability of 1-5. A ratio t2/t1 of the thickness t2 of the magnetic gap layer to the thickness t1 of the coil pattern is preferably 1 or less, more preferably 0.2-1.
With at least some of the coil patterns having such structure, the laminate device has improved DC-superimposed characteristics. Magnetic gap layers in contact with all coil patterns provide stable inductance in a range from small magnetization current to large magnetization current, and excellent DC-superimposed characteristics, which keeps the inductance from lowering.
The magnetic gap layer and the coil pattern may or may not be overlapping on the magnetic substrate layer. In any case, the magnetic gap layers are in contact with the coil patterns, and a magnetic flux generated from the coil pattern passes, through a magnetic gap layer formed on the same magnetic substrate layer, and flows along a loop through magnetic materials (magnetic substrate layers and magnetic-material-filled layers) around each coil pattern.
The magnetic gap layer preferably has at least one magnetic region. The magnetic region in the magnetic gap layer has such area and magnetic properties that it is more subjected to magnetic saturation with small magnetization current than in the magnetic layer between coil patterns adjacent in a lamination direction. With such structure, the inductance is high at small magnetization current, and lowers as the magnetization current becomes larger, but the magnetic region and the magnetic gap layer function as an integral magnetic gap, providing stable inductance.
The laminate device is subjected to stress due to the difference in sintering shrinkage and thermal expansion among the magnetic layers, the coil patterns and the magnetic gap layers, the warp of a laminate-device-mounting circuit board, etc. Because the magnetic properties of the magnetic layers are deteriorated by stress and strain, it is preferable to use Li ferrite suffering little change of permeability by stress (having excellent stress resistance). Thus obtained is a laminate device suffering little change of inductance by stress.
An example of the modules of the present invention is obtained by mounting the above laminate device on a dielectric substrate containing capacitors, together with a semiconductor part including a switching device. Another example of the modules of the present invention is obtained by mounting the above laminate device on a resin substrate, together with a semiconductor part including a switching device. A further example of the modules of the present invention is obtained by mounting a semiconductor part including a switching device on the above laminate device.
a) is a plan view showing a magnetic layer used in an example of the first laminate devices of the present invention.
b) is a cross-sectional view showing a magnetic layer used in an example of the first laminate devices of the present invention.
a) is a plan view showing another magnetic layer used in an example of the first laminate devices of the present invention.
b) is a cross-sectional view showing another magnetic layer used in an example of the first laminate devices of the present invention.
a) is a plan view showing another magnetic layer used in the second laminate device of the present invention.
b) is a cross-sectional view showing another magnetic layer used in the second laminate device of the present invention.
a) is a plan view showing another magnetic layer used in the third laminate device of the present invention.
b) is a cross-sectional view showing another magnetic layer used in the third laminate device of the present invention.
a) is a plan view showing another magnetic layer used in the fourth laminate device of the present invention.
b) is a cross-sectional view showing another magnetic layer used in the fourth laminate device of the present invention.
a) is a plan view showing another magnetic layer used in the fifth laminate device of the present invention.
b) is a cross-sectional view showing another magnetic layer used in the fifth laminate device of the present invention.
a) is a plan view showing another magnetic layer used in the sixth laminate device of the present invention.
b) is a cross-sectional view showing another magnetic layer used in the sixth laminate device of the present invention.
The laminate devices of the present invention and their modules will be explained in detail below.
[1] First Laminate Device
(1) Structure of Laminate Device
The laminated inductor 10 comprises 11 layers (S1-S11), which has a coil part 1 formed by 7 coil-pattern-carrying layers 1a-1d each constituted by a magnetic substrate layer 2 provided with a coil pattern 3, and magnetic material parts 5 on both upper and lower sides of the coil part 1 each constituted by two magnetic substrate layers 2 free from a coil pattern. In the coil part 1, coil patterns 3 (3a-3d) each having 0.5 to 1 turn are connected via through-holes 6 to constitute a coil of 6.5 turns. Both ends of the coil extend to opposing side surfaces of the laminate device, and connected to external electrodes 200a, 200b obtained by baking a conductor paste of Ag, etc. As shown in
Each coil-pattern-carrying layer 1a-1d is formed for instance, by forming a soft ferrite paste into a green sheet for a magnetic substrate layer 2 by a doctor blade method, a calendering method, etc., printing or coating the green sheet with a conductive paste of Ag, Cu or their alloys in a predetermined coil pattern 3a-3d, printing or coating a predetermined region of the green sheet with a non-magnetic paste for forming a magnetic gap layer 4, and printing or coating a coil-pattern-free region of the green sheet with a magnetic paste for covering the magnetic gap layer 4 to substantially the same height as an upper surface of the coil pattern, thereby forming a magnetic-material-filled layer 2a-2d. The magnetic-material-filled layers 2a-2d may have different shapes depending on the shapes of the coil patterns 3a-3d on the magnetic substrate layer 2. Each magnetic substrate layer 2 constituting the magnetic material part 5 is constituted by the same green sheets as described above. After plural (7) coil-pattern-carrying layers 1a-1d are laminated with the coil patterns 3a-3d connected to via through-holes 6 to form a coil, one or more (2) magnetic substrate layers 2 are preferably laminated on both sides thereof as shown in
Because the shapes of the coil-pattern-carrying layers 1a-1d shown in
The magnetic gap layer 4 is formed by a magnetic gap layer paste such that it covers an entire region inside the coil pattern 3b in contact with the edge of the coil pattern 3b. Alternatively, a magnetic gap layer 4 having an opening may be first printed, and the coil pattern 3b may be printed in the opening. In this case, the coil pattern 3b covers an edge portion of the magnetic gap layer 4. In any case, an edge portion of each coil pattern 3 substantially overlaps an edge portion of the magnetic gap layer 4 after sintering. The overlapping of such magnetic gap layers 4 in a lamination direction reduces a magnetic flux of each coil pattern 3 crossing the other coil patterns.
The magnetic gap layer 4 is preferably thin and made of a non-magnetic material or a low-permeability material having a specific permeability of 1-5. Although the magnetic gap layer 4 made of a low-permeability material is inevitably thicker than that made of a non-magnetic material, it has suppressed variations of inductance by printing precision.
When the low-permeability material has a specific permeability more than 5, it has a low function as the magnetic gap layer 4. The low-permeability material having a specific permeability of 1-5 can be obtained by mixing non-magnetic oxide (zirconia, etc.) powder with magnetic powder. Also usable is Zn ferrite having a Curie temperature (for instance, −40° C. or lower) sufficiently lower than the use temperature of the laminate device. The Zn ferrite suffers sintering shrinkage close to that of the magnetic substrate layer 2.
Non-magnetic materials and low-permeability materials used for the magnetic gap layer 4 are ZrO2, glass such as B2O3—SiO2 glass and Al2O3—SiO2 glass, Zn ferrite, Li2O—Al2O3-4SiO2, Li2O—Al2O3-2SiO2, ZrSiO4, 3Al2O3-2SiO2, CaZrO3, SiO2, TiO2, WO3, Ta2O5, Nb2O5, etc. Pastes for the magnetic gap layer 4 are prepared, for instance, by blending zirconia (ZrO2) powder, an organic binder such as ethylcellulose, and a solvent by three rolls, a homogenizer, a sand mill, etc. Using zirconia that is not made dense at a sintering temperature of the laminate device, the difference in a thermal expansion coefficient alleviates a compression stress that the magnetic substrate layer 2 receives from the coil pattern 3, thereby preventing the magnetic substrate layer 2 from being cracked. When the magnetic gap layer 4 exposed outside should be made dense, it is preferable to add an oxide of Zn, Cu, Bi, etc. (for instance, Bi2O3) as a low-temperature-sintering-accelerating material.
a) and 6(b) show a coil-pattern-carrying layer 1b having a magnetic-material-filled layer 2a, which is obtained by printing or coating a magnetic paste in a region except for the coil pattern 3b such that it is substantially on the same level as an upper surface of the coil pattern 3b. The magnetic paste preferably contains ferrite powder having the same main component composition as that of the green sheet. However, the ferrite powder may be different in the diameters of crystal particles, the types and amounts of sub-components, etc. The magnetic paste is produced by blending the magnetic powder with a binder such as ethylcellulose, and a solvent. For instance, even when the coil pattern is as thick as 15 μm or more, the magnetic-material-filled layer 2a can make the pressure-bonded laminate free from steps, thereby preventing delamination after pressure-bonding.
A magnetic material for the magnetic substrate layer 2 and the magnetic-material-filled layer 2a is preferably Li ferrite having a main component composition represented by the formula of x(Li0.5Fe0.5)O-yZnO-zFe2O3, wherein x, y and z meet 0.05≦x≦0.55, 0.05≦y≦0.40, 0.40≦z≦0.55, and x+y+z=1, and further containing 2-30% by mass of Bi2O3. This Li ferrite is sinterable at 800-1000° C., and has low loss and high specific resistance. It also has a small squareness ratio and excellent stress characteristics. The partial substitution of ZnO with CuO enables low-temperature sintering, and the partial substitution of Fe2O3 with Mn2O3 improves specific resistance.
In addition to the above Li ferrite, soft ferrite such as Ni ferrite, Mg ferrite, etc. may be used. The magnetic substrate layer 2 and the magnetic-material-filled layer 2a are preferably made of Li ferrite or Mg ferrite whose magnetic properties change little by stress, more preferably Li ferrite, because they receive stress from the coil patterns, the magnetic gap layers, the external electrodes, etc. To reduce core loss, Ni ferrite is preferable.
(2) Operation Principle
In the laminate device of the present invention, the magnetic gap layers 4 each in contact with each coil pattern 3 are discontinuous. It has been considered that all magnetic fluxes should ideally flow through loops including pluralities of coils patterns, and that a magnetic flux through a small loop around each coil pattern is merely a leaked magnetic flux lowering inductance. In the present invention, however, among magnetic fluxes φa, φa′ generated from the coil patterns 3a, 3b (each flowing through the magnetic material 2 and each magnetic gap layer 4a, 4b around each coil pattern 3a, 3b), a magnetic flux φb (flowing around both coil patterns 3a, 3b), and a magnetic flux φc (flowing around the coil patterns 3a, 3b and other coil patterns), magnetic fluxes φb and φc are reduced by the magnetic gap layers 4a, 4b in contact with each coil pattern 3a, 3b, leaving substantially only the magnetic fluxes φa, φa′, as shown in
The magnetic flux φa around the coil pattern 3a and the magnetic flux φa′ around the coil pattern 3b share a magnetic material portion between the coil patterns 3a, 3b as a magnetic path. Because the magnetic fluxes φa, φa′ are directed oppositely in the magnetic material portion between the coil patterns 3a, 3b, a DC magnetic field is cancelled, failing to obtain large inductance, but local magnetic saturation is unlikely to occur by large magnetization current, Because only a slight magnetic flux crosses other coil patterns, the inductance obtained is the total inductance of the coil patterns 3, stable in a range from a small magnetization current to a large magnetization current.
Because the laminate device of the present invention has a reduced large-loop magnetic flux with less magnetic flux leaking outside, thin magnetic material parts can be formed on both upper and lower sides of the coil part 1. In an inductor array comprising pluralities of coils in each laminate device, magnetic coupling between the coils can be reduced.
[2] Second Laminate Device
The coil-pattern-carrying layer 1b comprises a coil pattern 3 formed on a magnetic substrate layer 2, a magnetic gap layer 4 covering an entire region outside the coil pattern 3 in contact therewith, and a magnetic-material-filled layer 2a formed inside the coil pattern 3. For clarity,
[3] Third Laminate Device
[4] Fourth Laminate Device
Although all magnetic gap layers have openings 14 in the fourth laminate device, openings 14 may be formed only in some of the magnetic gap layers as shown in
[5] Fifth Laminate Device
This laminate device also has less magnetic flux crossing coil patterns on other layers, thereby exhibiting excellent DC-superimposed characteristics together with large inductance. Also, because of a reduced number of layers in the coil part 1, the laminate device can be made thinner.
[6] Sixth Laminate Device
[7] Seventh Laminate Device
This laminate device does not have magnetic gap layers 4 in uppermost and lowermost layers (S8, S3) in the coil part 1, but has them in all intermediate layers (S4-S7) (corresponding to ⅔ of the number of turns of the coil), thereby exhibiting excellent DC-superimposed characteristics.
[8] Eighth Laminate Device
[9] Ninth Laminate Device
This laminate device comprises external terminals 200a-200c, the external terminal 200a being the intermediate tap. An inductor L1 is formed between the external terminals 200a and 200b, and an inductor L2 is formed between the external terminals 200a and 200c. The laminate device shown in
An inductor array shown in
[10] DC-DC Converter Module
The laminate device 10 having magnetic gap layers 4 in contact with coil patterns 3 exhibits excellent DC-superimposed characteristics. Because only a slight magnetic flux leaks outside, the integrated semiconductor circuit IC may be disposed close to the inductor without generating noise in the integrated semiconductor circuit IC, thereby providing DC-DC converters with excellent conversion efficiency.
The DC-DC converter module may also be obtained by mounting the laminate device 10, an integrated semiconductor circuit IC, etc. on a printed circuit board or on a capacitor substrate containing capacitors Cin, Cout, etc.
Another example of DC-DC converter modules is a step-down, multi-phase DC-DC converter module having the equivalent circuit shown in
Although the laminate devices are produced by a sheet-laminating method above, they can be produced by a printing method shown in
The present invention will be explained in more detail referring to Examples below without intention of restricting the scope of the present invention.
100 parts by weight of calcined Ni—Cu—Zn ferrite powder (Curie temperature Tc: 240° C., and initial permeability at a frequency of 100 kHz: 300) comprising 49.0% by mol of Fe2O3, 13.0% by mol of CuO, and 21.0% by mol of ZnO, the balance being NiO, was blended with 10 parts by weight of an organic binder based on polyvinyl butyral, a plasticizer and a solvent by a ball mill, to form a magnetic material slurry, which was formed into green sheets.
Some of the green sheets were provided with through-holes 6, and the green sheets having through-holes 6 and those without through-holes were printed with a non-magnetic zirconia paste for forming magnetic gap layers 4 in a predetermined pattern, and then printed with a conductive Ag paste for forming coil patterns 3.
To remove a step between the printed zirconia paste layer and the printed Ag paste layer, an imprinted region was printed with a paste of the same Ni—Cu—Zn ferrite as that of the green sheet to form magnetic-material-filled layers 2a-2d.
As shown in
Sample B was produced in the same manner as in Sample A, except that magnetic gap layers 4 as thick as 5 μm were not formed on upper and lower layers (S3, S9) but only on intermediate layers (S4-S8).
A single magnetic gap layer having the same thickness as the total gap length (15 μm) of the laminate device 10 (Sample A) was formed on a layer S5 to produce a laminate device (sample C).
With DC current of 0-1000 mA supplied to Samples A to C, their inductance (f=300 kHz, Im=200 μA) was measured by an LCR meter (4285A available from HP) to evaluate their DC-superimposed characteristics. The results are shown in
A laminate device (laminated inductor, Sample 4) of 3.2 mm×1.6 mm and 1.0 mm in thickness having 7-μm-thick magnetic gap layers formed on all of 16 coil-pattern-carrying layers was produced in the same manner as in Example 1, except for using calcined Li—Mn—Zn ferrite powder (Curie temperature Tc: 250° C., and initial permeability at a frequency of 100 kHz: 300) comprising 3.8% by mass of Li2CO3, 7.8% by mass of Mn3O4, 17.6% by mass of ZnO, 69.8% by mass of Fe2O3, and 1.0% by mass of Bi2O3, in place of the calcined Ni—Cu—Zn ferrite powder. To be free from a step, each coil-pattern-carrying layer was printed with a Ni—Zn ferrite paste in a region in which the zirconia paste and the Ag paste were not printed. After sintering, the magnetic substrate layer had a thickness of 40 μm, the coil pattern had a thickness of 20 μm and a width of 300 μm, and a region inside the coil pattern was 2.2 mm×0.6 mm.
Obtained as Comparative Examples were a laminate device (Sample 1) produced in the same manner as in Sample 4 except for forming no magnetic gap layer, a laminate device (Sample 2) produced in the same manner as in Sample 4 except for forming only one magnetic gap layer on an intermediate layer, and a laminate device (Sample 3) produced in the same manner as in Sample 4 except for discontinuously forming three magnetic gap layers via magnetic layers free from magnetic gap layers.
The laminate devices (laminated inductors) of Samples 1-4 were measured with respect to DC-superimposed characteristics and DC-DC conversion efficiency. The DC-DC conversion efficiency was measured on each laminate device assembled in a measuring circuit shown in
(1)Current when the inductance was reduced to 80% of that with no current load.
Decrease in inductance when DC current was superimposed was smaller in the laminate device of the present invention (Sample 4) having magnetic gap layers in all coil-pattern-carrying layers than in the conventional laminate device (Sample 1) free from magnetic gap layers, and the conventional laminate devices (Samples 2 and 3) having magnetic gap layers only in limited coil-pattern-carrying layers. Specifically, current when the inductance was reduced to 80% of that with no current load (3.9 μH) was 900 mA in the laminate device of the present invention (Sample 4), drastically improved as compared with Comparative Examples (Samples 1-3).
The laminated inductor of this Example (Sample 4) exhibited about 3% higher DC-DC conversion efficiency than those of Comparative Examples (Samples 1-3). It is considered that because the laminated inductor of this Example suffered less magnetic saturation in magnetic material portions between adjacent coil patterns (smaller magnetic loss), it exhibited improved DC-DC conversion efficiency.
A laminated inductor (Sample 5) was produced in the same manner as in Sample 4, except that a Li—Mn—Zn ferrite layer was formed in a rectangular opening 14 of 0.3 mm×0.3 mm provided in a region including the center axis of a coil in the magnetic gap layer. The laminated inductor of Sample 5 was measured with respect to DC-superimposed characteristics and DC-DC conversion efficiency. The results are shown in Table 2 and
The laminated inductor of this Example (Sample 5) exhibited larger inductance than the second laminate device (Sample 4) at low DC current. Their inductance was substantially on the same level at high DC current. The DC-DC conversion efficiency of this Example was about 1% improved.
A laminate device (Sample 9) was produced in the same manner as in Sample 4, except that the number of coil-pattern-carrying layers was 8, that a coil pattern on each layer had 2 turns, and that 5-μm-thick magnetic gap layers were formed on all layers. After sintering, each ferrite layer had a thickness of 40 μm, each coil pattern had a thickness of 20 μm, a width of 150 μm, and an interval of 50 μm, and a region inside the coil pattern was 1.9 mm×0.3 mm.
A laminated inductor (Sample 6) was produced in the same manner as in Sample 9 except for forming no magnetic gap layer. A laminated inductor (Sample 7) was produced in the same manner as in Sample 9 except for forming only one magnetic gap layer on an intermediate layer. A laminated inductor (Sample 8) was produced in the same manner as in Sample 9 except for discontinuously forming three magnetic gap layers via magnetic layers free from magnetic gap layers.
The laminated inductors of Samples 6-9 were measured with respect to DC-superimposed characteristics and DC-DC conversion efficiency. The results are shown in Table 3 and
(1)Current when the inductance was reduced to 80% of that with no current load.
The laminate device of this Example (Sample 9) exhibited increased inductance as compared with the laminate device of Example 2 (Sample 4) having one turn of a coil pattern on each layer. The laminate device of the present invention (Sample 9) having magnetic gap layers in all magnetic layers provided with coil patterns suffered less decrease in inductance when DC current was superimposed, as compared with the conventional laminated inductor (Sample 6) having no magnetic gap layer, and the conventional laminated inductors (Samples 7 and 8) having magnetic gap layers only in limited magnetic layers. Specifically, the laminate device of the present invention (Sample 9) had L of 8.8 μH with no current load, and current drastically improved to 280 mA when the inductance was reduced to 80% of that with no current load. The laminate device of this Example (Sample 9) also exhibited about 9% higher DC-DC conversion efficiency than Comparative Examples (Samples 6-8).
A laminate device (Sample 10) was produced in the same manner as in Sample 9, except that a Li—Mn—Zn ferrite layer was formed in a rectangular opening 14 of 0.3 mm×0.3 mm formed in a region including the center axis of a coil in the magnetic gap layer 4. After sintering, each ferrite layer had a thickness of 40 μm, and each coil pattern had a thickness of 20 μm and 2 turns. The laminate device of Sample 10 was measured with respect to DC-superimposed characteristics and DC-DC conversion efficiency. The results are shown in Table 4 and
The laminate device of this Example (Sample 10) exhibited larger inductance at low DC current as compared with the laminate device of Example 4 (Sample 9), though substantially on the same level at high DC current. It also exhibited about 2% higher DC-DC conversion efficiency.
A laminate device (Sample 11) of 3.2 mm×1.6 mm and 1.0 mm in thickness was produced in the same manner as in Sample 4, except that the number of coil-pattern-carrying layers was 10, and that 5-μm-thick magnetic gap layers were formed on all layers. A laminate device (Sample 12) was produced in the same manner as in Sample 11, except that the number of coil-pattern-carrying layers was 12. In both Samples 11 and 12 after sintering, the magnetic substrate layer had a thickness of 40 μm, and the coil pattern had a thickness of 20 μm and 2 turns. The laminate devices were measured with respect to DC-superimposed characteristics and DC-DC conversion efficiency. The results are shown in Table 5 and
(1)Current when the inductance was reduced to 80% of that with no current load.
As the number of coil-pattern-carrying layers increased, the inductance with no current load and the DC-DC conversion efficiency increased. Also, both laminate devices exhibited large current when the inductance was reduced to 80% of that with no current load.
A laminated inductor (Sample 13) of 3.2 mm×1.6 mm and 1.0 mm in thickness was produced in the same manner as in Sample 4, except that the number of coil-pattern-carrying layers was 12, and that 10-μm-thick magnetic gap layers were formed on all layers. A laminated inductor (Sample 14) was produced in the same manner as in Sample 13, except that 15-μm-thick magnetic gap layers were formed on all layers. A laminated inductor (Sample 15) was produced in the same manner as in Sample 13, except that 20-μm-thick magnetic gap layers were formed on all layers. In any of the laminated inductors of Samples 13-15 after sintering, the magnetic substrate layer had a thickness of 40 μm, and the coil pattern had a thickness of 20 μm and 2 turns. The laminate devices of Samples 13-15 were measured with respect to DC-superimposed characteristics and DC-DC conversion efficiency. The results are shown in Table 6 and
(1)Current when the inductance was reduced to 80% of that with no current load.
As the magnetic gap layers became thicker, the inductance with no current load decreased, but the inductance when the current was reduced to 80% of that with no current load was drastically improved. The laminate device (Sample 15), in which the magnetic gap layer was as thick as 20 μm, the same as the coil pattern, exhibited lower conversion efficiency than those of the other laminate devices. This appears to be due to the fact that the magnetic gap layer had large magnetic resistance, thereby increasing the amount of a magnetic flux leaking to the coil pattern, which in turn increased eddy current loss and thus lowered conversion efficiency.
Although the laminate device of the present invention has been explained above, the number of coil-pattern-carrying layers, the number of turns of a coil pattern on each layer, the thickness and material of the coil pattern and the magnetic gap layer, etc. are not restricted to those described in Examples. The proper adjustment of these parameters can provide laminate devices having magnetic properties desired for electronic equipments used.
The laminate devices of the present invention having the above monolithic structure have excellent DC-superimposed characteristics, and DC-DC converters comprising them exhibit high conversion efficiency and are usable at large current. Accordingly, DC-DC converters comprising the laminate devices of the present invention are useful for various portable electronic equipments using batteries, such as cell phones, portable information terminals PDA, note-type personal computers, portable audio/video players, digital cameras, digital video cameras, etc.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-023775 | Jan 2006 | JP | national |
| 2006-152542 | May 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/051648 | 1/31/2007 | WO | 00 | 7/30/2008 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2007/088914 | 8/9/2007 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5206620 | Watanabe et al. | Apr 1993 | A |
| 5469399 | Sato et al. | Nov 1995 | A |
| 5572478 | Sato et al. | Nov 1996 | A |
| 6459351 | Maki et al. | Oct 2002 | B1 |
| 6504466 | Katsurada | Jan 2003 | B1 |
| 6515568 | Maki et al. | Feb 2003 | B1 |
| 7380328 | Ahn et al. | Jun 2008 | B2 |
| 20020140539 | Takashima et al. | Oct 2002 | A1 |
| 20030068998 | Yamakawa et al. | Apr 2003 | A1 |
| 20040032706 | Kemmochi et al. | Feb 2004 | A1 |
| 20040207488 | Kono et al. | Oct 2004 | A1 |
| 20060152325 | Nakao et al. | Jul 2006 | A1 |
| 20070182519 | Tsuzuki et al. | Aug 2007 | A1 |
| 20070230221 | Lim et al. | Oct 2007 | A1 |
| Number | Date | Country |
|---|---|---|
| 1282969 | Feb 2001 | CN |
| 02-165607 | Jun 1990 | JP |
| 06-224043 | Aug 1994 | JP |
| 07-021791 | Jan 1995 | JP |
| 2001-044037 | Feb 2001 | JP |
| 2003-158467 | May 2003 | JP |
| 2003-347124 | Dec 2003 | JP |
| 2004-343084 | Dec 2004 | JP |
| 2005-045108 | Feb 2005 | JP |
| 2005045108 | Feb 2005 | JP |
| 2005-053759 | Mar 2005 | JP |
| 2005-150168 | Jun 2005 | JP |
| 2005-268455 | Sep 2005 | JP |
| 2006-216916 | Aug 2006 | JP |
| 2005032226 | Apr 2005 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20090051476 A1 | Feb 2009 | US |
