JP2005145781A - Ferrite sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the DC superposition characteristics of a magnetic material itself without damaging the original magnetic characteristics of the magnetic material and to dispense with formation of magnetic gap in a magnetic circuit. <P>SOLUTION: The ferrite sintered compact is formed by adding a small quantity (equal to or below several wt.%) of silicon (Si) powder or silica (SiO<SB>2</SB>) powder, alumina (Al<SB>2</SB>O<SB>3</SB>) powder or the like into ferrite powder composed essentially of Fe<SB>2</SB>O<SB>3</SB>, ZnO, CuO, and NiO and mixing and sintering the resultant powder. As the silicon, the pulverized particles of waste silicon wafer or the grinding chip of silicon wafer is used and as the silica, the pulverized particles of waste optical fiber is used. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a nickel-zinc ferrite sintered body. More specifically, by adding a small amount of powder such as silicon or silica, the inductance (L value) of the material itself when DC is applied (superposition) is improved. It relates to a ferrite sintered body. This technique is particularly suitable for a magnetic gap score of a small choke coil or inductance element.

  A choke coil incorporated in a secondary-side DC smoothing circuit of a switching power supply is required to have an inductance value exhibiting nonlinear characteristics with respect to a DC current value that flows while being superimposed on a winding. Therefore, in order to improve the inductance (L value) at the time of DC application (superimposition) in the choke coil and the inductance element, a configuration in which a magnetic gap is usually arranged in the magnetic circuit is adopted. For example, in a choke coil, the shape of a leg portion such as an EI core is devised to sandwich a nonmagnetic gap sheet, and in a multilayer inductor, a nonmagnetic layer is inserted to substantially form a gap portion.

  However, in the case of providing a magnetic gap by devising the core shape in a choke coil or the like, there is a problem in that precision processing is performed on the core or a mold having a complicated shape is required, which increases processes and equipment. In particular, when the core is downsized, the processing becomes even more cumbersome, the gap sheet mounting operation becomes difficult, and the assembling workability is significantly deteriorated. In the case of a multilayer inductor, it is necessary to combine two or more kinds of materials, the number of steps for arranging them increases, and problems such as a decrease in adhesion between different material layers occur.

In recent years, therefore, measures have been studied to improve the DC superposition characteristics even in a closed magnetic circuit structure without a magnetic gap by devising the magnetic material itself. For example, Patent Document 1 proposes a technique of adding ZrO ₂ to Ni—Zn ferrite. However, in this technique, it is necessary to contain a considerably large amount (10 to 20 wt%) of ZrO ₂ in order to improve the DC superposition characteristics, which not only increases the cost, but also the original magnetic characteristics of the magnetic material. There is a risk of damage.

By the way, in the semiconductor industry, grinding is performed when a silicon wafer is manufactured, and a large amount of grinding waste is generated. In addition, defective silicon wafers that are broken or scratched are also produced. Although these grinding scraps or waste silicon wafers are of high purity, they are difficult to recycle and are therefore disposed of as industrial waste. Furthermore, in order to advance communication technology or maintain reliability, replacement of old optical fibers with new optical fibers with a large transmission capacity is underway, and more and more optical fibers (high-purity ultrafine quartz glass fibers) will be used in the future. It is expected to be generated as waste. Such materials have high purity, and therefore, it is a big problem how to use them effectively instead of disposing them as waste.
JP 2003-112968 A

  The problem to be solved by the present invention is to improve the direct current superposition characteristics of the material itself and to eliminate the need to provide a magnetic gap without impairing the original magnetic characteristics of the magnetic material by adding a small amount of an inexpensive material. .

The inventors have studied the basic composition and characteristics of ferrite materials with the development goal of improving the DC superposition characteristics of the magnetic material itself, and have studied the magnetic permeability (ie, choke coil and inductance element) when the material is DC superposed. (Permeability corresponding to L value) was noted. As a result, by adding a small amount of silicon (Si), silica (SiO ₂ ), or alumina (Al ₂ O ₃ ) to the Ni—Cu—Zn-based ferrite material, the DC superposition characteristics are improved without providing a magnetic gap. That is, the present invention has been completed.

That is, the present invention relates to a ferrite powder obtained by adding 0.06 to 5 wt% of silicon (Si) powder to a ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, and sintering. It is a knot. Here, as silicon to be added to the ferrite powder, pulverized grains of waste silicon wafer or grinding waste of silicon wafer can be used.

The present invention also relates to a ferrite powder obtained by adding 0.6 to 5 wt% of silica (SiO ₂ ) powder to a ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, and sintering. It is a sintered body. Here, pulverized grains of waste optical fiber can be used as the silica powder added to the ferrite powder. As an additive, Si compound-containing glass powder having a softening point of 900 ° C. or less may be used. In addition, the same effect can be obtained by using an alumina (Al ₂ O ₃ ) powder or a powder of a material containing silica and / or alumina.

  The ferrite sintered body according to the present invention is useful, for example, for a choke coil or an inductance element. It can also be applied to a multilayer inductance element.

In the ferrite sintered body according to the present invention, by adding a small amount of silicon (Si), silica (SiO ₂ ) or alumina (Al ₂ O ₃ ) to Ni—Cu—Zn ferrite, the magnetic properties of the material itself can be improved. The inductance (L value) at the time of DC application (superimposition) can be improved without loss. This eliminates the need to provide a magnetic gap in the magnetic path, so that particularly small choke coils and inductance elements can be manufactured inexpensively and easily. In addition, the multilayer inductance element can be configured with only one kind of material, and adverse effects caused by using different materials can be prevented.

Further, in the present invention, silicon wafer grinding waste and waste silicon wafer as silicon (Si), waste optical fiber as silica (SiO ₂ ), alumina substrate grinding waste and waste material as alumina (Al ₂ O ₃ ), or As materials containing alumina and silica, furnace materials, ceramics, and the like can be used, which contributes to a reduction in the amount of waste and can be used simply by pulverization, thereby reducing material costs.

In a preferred embodiment of the present invention, the silicon (Si) powder is 0.06 to 2 wt% (more preferably 0.06 to 0.02 wt%) with respect to the ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO. 1 wt% or less) A ferrite sintered body obtained by adding, mixing and sintering. Here, as silicon to be added to the ferrite powder, pulverized grains of waste silicon wafer or grinding waste of silicon wafer is used.

In another preferred embodiment of the present invention, 1 to ₃ wt% of silica (SiO ₂ ) powder is added to and mixed with ferrite powder containing Fe ₂ O ₃ , ZnO, CuO, and NiO as main components, and sintered. This is a ferrite sintered body. Here, as the silica added to the ferrite powder, pulverized grains of waste optical fiber are used.

  In addition, when Si compound containing glass powder whose softening point is 900 degrees C or less is used as an additive, low temperature sintering will be attained.

The ferrite material used in the present invention, Fe ₂ O _3: 40~48 mol%, ZnO: 18 to 25 mol% (however, Fe ₂ O ₃ and total 60-70 mole% of ZnO), CuO: 5~ A composition of 15 mol% and NiO: 16 to 28 mol% is preferable. This composition range has a remarkable effect at an applied magnetic field of 1000 A / m or more, and is effective for choke coils and inductance elements. Here, the range of Fe ₂ O ₃ and ZnO is selected so that the initial permeability μ is not too high and not too low. The amount of NiO is selected so that the saturation magnetic flux density Bs is as large as possible under these conditions, and the firing temperature is adjusted by the amount of CuO. Depending on the application, the effect of improving DC superposition characteristics can be obtained even within a wider composition range than the above.

(Example 1)
A high-purity silicon wafer having a particle size of 250 μm or less is compared with Ni—Zn-based ferrite powder having a composition of Fe ₂ O ₃ : 46 mol%, ZnO: 20 mol%, CuO: 11 mol%, and NiO: 23 mol%. 0 to 1 wt% of silicon (Si) powder obtained by pulverization was added (0 wt% is a comparative example), granulated and shaped according to a conventional method, and sintered at 1100 ° C. to prepare a ferrite sintered body. With respect to these ferrite sintered bodies, DC superposition characteristics (relationship of magnetic permeability μ with respect to DC applied magnetic field Hdc) were measured using the amount of silicon added as a parameter. The sample used for the measurement is a standard ring having an outer diameter of 25 mm, an inner diameter of 15 mm, and a thickness of 5 mm and 50 turns of winding.

  An example of the measurement result is shown in FIG. From the results shown in FIG. 1, when the silicon addition amount is 0.06 wt% or more, the DC applied magnetic field is 300 to 500 A / m or more (depending on the addition amount) compared to the case of no silicon addition (0 wt%: comparative example). It can be seen that the permeability is improved. Although not shown in the figure, a sample with a larger amount added was also prototyped, and it was found that if it was added too much, the L value decreased and the core loss tended to become very large. In that respect, the upper limit of the addition amount is about 5 wt%, but even if it is a small amount, the effect of adding Si can be sufficiently obtained, so that it is preferably 2 wt% or less. Actually, 1 wt% or less is sufficient.

(Example 2)
Silica (SiO ₂ ) powder is added in an amount of 0 to 3 wt% with respect to Ni—Zn ferrite powder having a composition of Fe ₂ O ₃ : 46 mol%, ZnO: 20 mol%, CuO: 7 mol%, and NiO: 27 mol%. % (0 wt% is a comparative example), granulated and shaped according to a conventional method, and fired at 1100 ° C. to prepare a ferrite sintered body. With respect to these ferrite sintered bodies, DC superposition characteristics (relationship of magnetic permeability μ with respect to DC applied magnetic field Hdc) were measured using the amount of silica added as a parameter. As in Example 1, the sample used for the measurement was obtained by winding 50 turns on a standard ring having an outer diameter of 25 mm, an inner diameter of 15 mm, and a thickness of 5 mm.

  An example of the measurement result is shown in FIG. From the results shown in FIG. 2, when the silica addition amount is 0.6 wt% or more, the magnetic permeability is 300 to 800 A / m or more (depending on the addition amount) in comparison with the case of no silica addition (0 wt%). It can be seen that it has improved. Although not shown in the drawing, a sample with a larger amount of silica added was also prototyped, and it was also found that in this case too much L value decreases and the core loss tends to become very large. In that respect, the upper limit of the addition amount is about 5 wt%, and even if it is a small amount, a sufficient silica addition effect can be obtained, and therefore it is preferably 3 wt% or less.

(Example 3)
The Si compound (low melting point glass) powder is 0 with respect to the Ni—Zn ferrite powder having the composition of Fe ₂ O ₃ : 46 mol%, ZnO: 20 mol%, CuO: 7 mol%, and NiO: 27 mol%. The ferrite sintered body was produced by adding .about.1.5 to 1.5 wt%, granulating, forming and firing according to a conventional method. Si compounds used herein, the composition is SiO _2: 80 mol%, B ₂ O _3: 15.9 mol%, Al ₂ O _3: 0.4 mol%, K ₂ O: 3.2 mol% of low Melting point borosilicate glass. Further, the ferrite powder as a base material is pulverized so as to be fine particles so as to be suitable for low-temperature sintering. Firing was performed at 900 ° C. With respect to these ferrite sintered bodies, DC superposition characteristics (relationship of permeability μ with respect to DC applied magnetic field Hdc) were measured using the amount of Si compound added as a parameter. The result is shown in FIG. It can be seen that the direct current superimposition characteristics are improved as in the silica-added example 2.

In the present invention, when pulverization is effected to make fine particles, even normal SiO ₂ addition can be fired at about 900 ° C. If the glass has a low melting point, it can be fired even at a lower temperature (about 850 ° C.).

Example 4
Alumina (Al ₂ O ₃ ) powder is added in an amount of 0 to 1 wt% to the same Ni—Zn-based ferrite powder as in Example 2 (0 wt% is a comparative example), and granulated, shaped and fired according to a conventional method. By doing so, a ferrite sintered body was produced. With respect to these ferrite sintered bodies, the DC superposition characteristics (relationship of the magnetic permeability μ with respect to the DC applied magnetic field Hdc) were measured using the alumina addition amount as a parameter. The result is shown in FIG. It can be seen that the DC superimposition characteristics are improved as in the second embodiment.

As shown in Example 2 and Example 4, since both silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) are effective, DC superposition characteristics are improved even if both are mixed. It is thought that.

As can be seen from the examples, in the present invention, by adding a small amount of silicon (Si), silica (SiO ₂ ), and alumina (Al ₂ O ₃ ), the inductance of the material itself when DC is superimposed is improved. Needless to say, the same effect can be obtained by using pulverized grains of waste optical fiber, which is high-purity quartz glass, as silica, and the waste optical fiber can be effectively used. Moreover, low temperature glass can be used for low temperature sintering. As alumina, grinding scraps of an alumina substrate, pulverized particles of waste materials, or the like can be used.

As a result of conducting the same experiment in the case of adding various other compounds, as shown in FIG. 5, for example, when TiO ₂ : 0.5 wt%, MgO: 1 wt%, NaCl: 1 wt% is not added. Almost the same curve was obtained, and no effect of addition was observed. The same was true for ZrO ₂ . From these facts, it can be seen that other additives are ineffective in a small amount, and the remarkableness of Si and SiO ₂ is particularly remarkable. Compared to the addition of SiO _2, the addition of Si improves the DC superposition characteristics even in a small amount, and has the effect of reducing the coercive force Hc and the core loss.

DC superimposition characteristic diagram with Si addition amount as parameter. DC superposition characteristic diagram with SiO ₂ addition amount as parameter. DC superimposition characteristic diagram with Si compound addition amount as parameter. DC superimposition characteristic diagram with the addition amount of Al ₂ O ₃ as a parameter. DC superimposition characteristic diagram with various compounds as parameters.

Claims (7)

A ferrite sintered body obtained by adding 0.06 to 5 wt% of silicon (Si) powder to a ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, and sintering.   2. The ferrite sintered body according to claim 1, wherein the silicon added to the ferrite powder is pulverized grains of waste silicon wafer or grinding scraps of silicon wafer. A ferrite sintered body obtained by adding 0.6 to 5 wt% of silica (SiO ₂ ) powder to a ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, and sintering.   The ferrite sintered body according to claim 3, wherein the silica powder added to the ferrite powder is a pulverized grain of waste optical fiber. _{Fe 2 O 3, ZnO, CuO} , and NiO ferrite powder based on the Si compound containing glass powder having a softening point of 900 ° C. or less, and mixed 0.5 to 5 wt% additive in terms of SiO _2, sintered Ferrite sintered body formed. A ferrite sintered body obtained by adding 0.5 to 5 wt% of alumina (Al ₂ O ₃ ) powder to a ferrite powder mainly composed of Fe ₂ O ₃ , ZnO, CuO, and NiO, and then sintering. The ferrite sintered body according to any one of claims 1 to 6, which is a material for a choke coil or an inductance element.

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