JP2013014442A - Ferrite composition and electronic component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electronic component with which both reduction in power loss and a high magnetic flux density can be achieved under the environment of high frequency and low magnetic field, even if a used temperature or an environment temperature is lower than a room temperature; and to provide a ferrite composition suitable for the electronic part.SOLUTION: The ferrite composition is composed of major components, FeO, ZnO and MnO, and contains, with respect to 100 wt.% of major component, 50-300 ppm of SiOand 110-1,120 ppm of CaO as sub components. The minimum temperature Tsp of magnetic loss of a ferrite composition is in the range of 2-7°C. When the amount of FeOin the major component is set to be X mol%, the amount of ZnO to be Z mol% and the remainder to be manganese oxide, Tsp, X and Z satisfy the following formula (1): Tsp=21.6(X+0.52Z)-1,520, and (2): X≥58.0.

Description

  The present invention relates to a ferrite composition and an electronic component. More specifically, even when the operating temperature or the environmental temperature is kept below room temperature, an electronic component that can achieve both a low power loss and a high saturation magnetic flux density in a high frequency and low magnetic field environment. And a ferrite composition suitable for the electronic component.

  In recent years, various electronic devices have been rapidly reduced in size and weight, and in response to this, the demand for downsizing, higher efficiency, and higher frequency of electronic components used in electric circuits of various electronic devices has increased rapidly. Yes.

  For example, Ni-Zn ferrite has been conventionally used as a coil magnetic core for a DC-DC converter. However, since Ni—Zn ferrite has a relatively large power loss, it has been difficult to cope with downsizing, high efficiency, and high frequency of components such as a coil magnetic core.

  For such a problem, it is conceivable to use Mn—Zn ferrite instead of Ni—Zn ferrite. Conventionally, Mn—Zn ferrite has been used in power transformers and the like, and has been used in a low frequency and high magnetic field environment.

  In general, a ferrite used as a magnetic core of a transformer or the like has been required to have temperature characteristics that minimize magnetic loss in a temperature range higher than the actual operating temperature range. This is because there is a risk of causing a so-called thermal runaway in which the transformer heats up due to magnetic loss and the temperature of the transformer itself rises, and as a result, the magnetic loss further increases and the heat generation of the transformer increases. is there. In the case of a power transformer, the operating temperature range is usually a temperature near the operating temperature (for example, 80 ° C.).

  However, in recent years, for example, when the transformer is cooled using a fluorine-based inert liquid or the like, the environmental temperature or the use temperature can be set to an arbitrary temperature. In this case, the temperature at which the magnetic loss is minimized is not particularly limited, and it is only required that the absolute value of the magnetic loss is small.

  The DC-DC converter is advantageous for power saving, miniaturization, and weight reduction of electronic devices, and has a lower operating voltage and less risk of thermal runaway than a transformer. An electronic device in which such a DC-DC converter is mounted may be used in an environment maintained at a temperature lower than room temperature. Further, as described above, various electronic devices are required to have a high driving frequency (for example, 1 MHz or more) and to have a small loss in a high frequency region.

  Further, in the transformer and in the parts used for the DC-DC converter, a response to a large current is progressing. For this reason, a magnetic core used for such a component is required to have excellent direct current superposition characteristics that do not lower the inductance even with a large current. A high saturation magnetic flux density is indispensable for realizing an excellent DC superposition characteristic, and it is necessary to have a high saturation magnetic flux density particularly at the ambient temperature or the use temperature.

  Accordingly, there is a need for a ferrite composition that reduces magnetic loss in the high frequency region and has a high saturation magnetic flux density even when the environmental temperature or the use temperature is maintained at a temperature lower than room temperature.

As an example of a Mn—Zn ferrite having a low loss and a high saturation magnetic flux density, for example, in Patent Document 1, Fe ₂ O ₃ is 52.4 to 53.7 mol% and ZnO is 7.0 to 11 as main components. .5 mol%, and the remainder MnO, as an auxiliary component, and _CaO, and V 2 _{O 5,} and _{Nb 2 O 5, Al 2 O} 3 or _Bi 2 _{O 3} and a have been proposed Mn-Zn ferrite containing specified amounts Yes.

  However, as described in Patent Document 1, the Mn—Zn ferrite described above is a temperature (Pcv min) at which the magnetic loss in the low frequency region is minimized at 60 ° C. or more which is the actual driving temperature of the transformer. There is a problem that it cannot be used near a temperature lower than room temperature and in a high-frequency region.

JP 2003-128458 A

  The present invention has been made in view of such a situation, and even when the use temperature or the environmental temperature is maintained at a temperature lower than room temperature, the power loss is reduced and high in a high frequency and low magnetic field environment. It is an object of the present invention to provide an electronic component capable of achieving both a saturation magnetic flux density and a ferrite composition suitable for the electronic component.

  As a result of diligent studies to achieve the above object, the present inventors have found that when the content of iron oxide in the ferrite composition is relatively large, It was found that a conventionally known formula does not hold. Then, instead of the conventional equation, a relational expression for obtaining the temperature at which the magnetic loss is minimized is found, and by using this equation, the magnetic loss is reduced and the high saturation magnetic flux is obtained in a specific temperature range where the magnetic loss is minimized. The inventors have found that both the density and the density can be achieved, and have completed the present invention.

That is, the ferrite composition according to the present invention is
The main component is composed of iron oxide, zinc oxide, and manganese oxide,
A ferrite composition containing silicon oxide in an amount of 50 to 300 ppm in terms of SiO _{2 and} calcium oxide in an amount of 110 to 1120 ppm in terms of CaO with respect to 100% by weight of the main component,
The minimum temperature Tsp of the magnetic loss of the ferrite composition is in the range of 2 to 7 ° C .;
When the content of the iron oxide in the main component is X mol% in terms of Fe ₂ O ₃ , the content of the zinc oxide is Z mol% in terms of ZnO, and the balance is the manganese oxide, the Tsp and the X And Z satisfies the following formulas (1) and (2).
Tsp = 21.6 (X + 0.52Z) -1520 Formula (1)
X ≧ 58.0 Formula (2)

  In the present invention, in consideration of use in the vicinity of a temperature lower than room temperature, when the temperature (Tsp) at which the magnetic loss is minimized is in the range of 2 to 7 ° C., the above formulas (1) and (2) are It is used to determine the composition of the main component, and the content of the subcomponent is within the specific range. By doing in this way, the ferrite composition which can reduce a power loss (Pcv) also in a high frequency area | region (for example, 1 MHz or more) can be obtained, keeping saturation magnetic flux density Bs high.

  The electronic component according to the present invention has a ferrite core composed of the ferrite composition described above, and is used in a frequency region of 1 MHz or more.

  Since the Tsp of the ferrite composition is in the temperature range of 2 to 7 ° C., the electronic component according to the present invention is suitable as a component whose operating temperature or environmental temperature is near a temperature lower than room temperature. In addition, power saving can be realized because both reduction of power loss and high saturation magnetic flux density are compatible.

  Such electronic components are not particularly limited, but include coil components of DC-DC converters used in various electronic devices. Examples of the coil component include an inductor and a choke coil. Moreover, the electronic component according to the present invention can be suitably used for the transformer by cooling the transformer to a temperature near Tsp. Examples of transformer parts include power transformers for switching and inverters.

FIG. 1 shows a ferrite core for a DC-DC converter according to an embodiment of the present invention.

  Hereinafter, the present invention will be described based on embodiments shown in the drawings.

  As the ferrite core for the DC-DC converter according to this embodiment, in addition to the toroidal type shown in FIG. 1, FT type, ET type, EI type, UU type, EE type, EER type, UI type, drum type, pot Examples include molds and cup types. A desired coil magnetic core is obtained by winding a predetermined number of turns around the ferrite core for the DC-DC converter.

  The ferrite core for a DC-DC converter according to this embodiment is composed of the ferrite composition according to this embodiment.

  The ferrite composition according to this embodiment is a Mn—Zn ferrite and contains iron oxide, manganese oxide, and zinc oxide as main components. The temperature (Tsp) at which the magnetic loss of the ferrite composition according to this embodiment is minimized is in the range of 2 to 7 ° C.

  Conventionally, in Mn—Zn ferrite, the temperature showing Tsp has been explained by the magnetocrystalline anisotropy. That is, it is said that the magnetic loss has a minimum value at a temperature of K1 = 0 where the sign of the magnetocrystalline anisotropy constant K1 changes from a negative value to a positive value as the temperature rises.

Further, it is known that this temperature coincides with a so-called secondary peak of magnetic permeability where the magnetic permeability is maximized. The above K1 increases monotonously with increasing temperature, but Fe ²⁺ has a positive K1, so when the amount of Fe ²⁺ increases (ie, the amount of Fe ₂ O ₃ increases), the temperature of the secondary peak Moves to the low temperature side.

Based on the above findings and experimental results, page 79 of “Electronic Material Series Ferrite” (published by Maruzen Co., Ltd., 1988) has an Fe ₂ O ₃ content of X mol% and a ZnO content of Z mol%. The following formula is described as a formula for obtaining Tsp.
Tsp = -45.5 (X + 0.2Z) +2620

Further, it is known that a high saturation magnetic flux density can be easily obtained by increasing the amount of Fe ₂ O ₃ . However, when the amount of Fe ₂ O ₃ increases, the saturation magnetic flux density is considered to be influenced not only by the amount of Fe ₂ O ₃ but also by the ratio of the amount of Fe ₂ O _{3 and the} amount of ZnO.

Tsp of the ferrite composition according to this embodiment is in the range of 2 to 7 ° C. In such a ferrite composition, it is conceivable to increase the saturation magnetic flux density by increasing Tsp within the above range by increasing the amount of Fe ₂ O ₃ . Therefore, if it is attempted to determine the Fe ₂ O ₃ content and the ZnO content using the above formula, for example, Tsp becomes −200 ° C. or less, which is not realistic.

Therefore, it is considered that the above formula for obtaining Tsp does not hold when the amount of Fe ₂ O ₃ is large (eg, 58 mol% or more). However, since there is nothing which is an index for determining the Tsp if the amount of _Fe 2 _{O 3} is large, if the amount of _Fe 2 _{O 3} is large, in the high frequency range above 1 MHz, the ferrite composition having a high saturation magnetic flux density There was no knowledge about.

Therefore, the present inventors have conducted intensive experiments and found that when the content of iron oxide in the ferrite composition is relatively large, Tsp and iron oxide and zinc oxide have a relationship different from the above formula. I found it. That is, when the content of iron oxide in the ferrite composition is X mol% in terms of Fe ₂ O ₃ and the content of zinc oxide is Z mol% in terms of ZnO, Tsp, X and Z are as follows: The following expressions (1) and (2) are satisfied.
Tsp = 21.6 (X + 0.52Z) -1520 Formula (1)
X ≧ 58.0 Formula (2)

Therefore, in this embodiment, in 100 mol% of the main component, the content (X) of iron oxide and the content (Z) of zinc oxide satisfy the above formula (1) in terms of Fe ₂ O ₃ and ZnO. To be decided. X is preferably 58.0 to 66.0 mol%, more preferably 61.0 to 66.0 mol%.

  When the content of iron oxide is large, the temperature (Tsp) at which magnetic loss is minimized and the content of iron oxide and zinc oxide satisfy the above relational expression. The optimum iron oxide and zinc oxide content that falls within the range is determined. The remainder of the main component is composed of manganese oxide.

  The ferrite composition according to the present embodiment contains silicon oxide and calcium oxide as subcomponents in addition to the main component calculated by the above formula. By including such a subcomponent, the absolute value of power loss can be reduced and a high saturation magnetic flux density can be obtained.

The content of silicon oxide is 50 to 300 ppm, more preferably 50 to 200 ppm in terms of SiO _{2 with} respect to 100% by weight of the main component. Even if the content of silicon oxide is large or too small, power loss in the high frequency region tends to deteriorate.

  The content of calcium oxide is 110 to 1120 ppm, more preferably 730 to 1120 ppm in terms of CaO with respect to 100% by weight of the main component. Even if the content of calcium oxide is large or too small, power loss in the high frequency region tends to deteriorate.

  Note that the ferrite composition according to the present embodiment may include oxides of inevitable impurity elements.

  Specifically, B, C, P, S, Cl, As, Se, Br, Te, I, Li, Na, Mg, Al, K, Ga, Ge, Sr, Cd, In, Sn, Sb, Typical metal elements such as Ba, Pb, and Bi, and transition metal elements such as Sc, Ti, V, Cr, Co, Ni, Cu, Y, Zr, Nb, Mo, Pd, Ag, Hf, and Ta can be given.

  Next, an example of a method for producing a ferrite composition according to this embodiment will be described.

  First, starting materials (raw materials of main components and raw materials of subcomponents) are weighed and mixed so as to have a predetermined composition ratio to obtain a raw material mixture. Examples of the mixing method include wet mixing using a ball mill and dry mixing using a dry mixer. It is preferable to use a starting material having an average particle size of 0.1 to 3 μm.

As a raw material for the main component, iron oxide (α-Fe ₂ O ₃ ), zinc oxide (ZnO), manganese oxide (Mn ₃ O ₄ ), or a composite oxide can be used. In addition, various compounds that become oxides or composite oxides by firing can be used. Examples of the oxide that becomes the above-mentioned oxide upon firing include simple metals, carbonates, oxalates, nitrates, hydroxides, halides, organometallic compounds, and the like. In addition, although the content of manganese oxide in the main component is calculated in terms of MnO, Mn ₃ O ₄ is preferably used as the main component material.

As a raw material of the subcomponent, as in the case of the raw material of the main component, not only an oxide but also a composite oxide or a compound that becomes an oxide after firing may be used. In the case of silicon oxide (SiO ₂ ), it is preferable to use SiO ₂ . In the case of calcium oxide (CaO), it is preferable to use calcium carbonate (CaCO ₃ ).

  Next, the raw material mixture is calcined to obtain a calcined material. Calcining causes thermal decomposition of raw materials, homogenization of ingredients, formation of ferrite, disappearance of ultrafine powder due to sintering and grain growth to an appropriate particle size, and converts the raw material mixture into a form suitable for the subsequent process. Done for. Such calcination is preferably performed at a temperature of 800 to 1100 ° C. for about 1 to 3 hours. The calcination may be performed in the air (air), or may be performed in an atmosphere having a higher oxygen partial pressure or in a pure oxygen atmosphere than in the air. The mixing of the main component raw material and the subcomponent raw material may be performed before calcining or after calcining.

  Next, the calcined material is pulverized to obtain a pulverized material. The pulverization is performed in order to break down the coagulation of the calcined material to obtain a powder having appropriate sinterability. When the calcined material forms a large lump, wet pulverization is performed using a ball mill or an attritor after coarse pulverization. The wet pulverization is performed until the average particle diameter of the calcined material is preferably about 1 to 2 μm.

  Next, the pulverized material is granulated (granular) to obtain a granulated product. The granulation is performed in order to convert the pulverized material into aggregated particles having an appropriate size and convert it into a form suitable for molding. Examples of such a granulation method include a pressure granulation method and a spray drying method. The spray drying method is a method in which a commonly used binder such as polyvinyl alcohol is added to the pulverized material, and then atomized in a spray dryer and dried at a low temperature.

  Next, the granulated product is molded into a predetermined shape to obtain a molded body. Examples of the molding of the granulated product include dry molding, wet molding, and extrusion molding. The dry molding method is a molding method in which a granulated product is filled in a mold and compressed and pressed (pressed). The shape of the molded body is not particularly limited, and may be appropriately determined according to the application. In the present embodiment, the shape is a toroidal shape.

  Next, the compact is fired to obtain a sintered body (the ferrite composition of the present embodiment). This firing is performed in order to obtain a dense sintered body by causing sintering in which the powder adheres at a temperature below the melting point between the powder particles of the molded body containing many voids. Such firing is preferably performed at a temperature of 900 to 1300 ° C. for usually 2 to 5 hours. The main calcination may be performed in the atmosphere (air) or in an atmosphere having a higher oxygen partial pressure than in the atmosphere.

  Through such steps, the ferrite composition according to the present embodiment is manufactured.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to such embodiment at all, Of course, in the range which does not deviate from the summary of this invention, it can implement in various aspects. .

  For example, in the above-described embodiment, in order to obtain a toroidal shape, the shape is formed before the main baking, but may be formed (processed) after the main baking.

  Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.

First, Fe ₂ O ₃ , ZnO, and Mn ₃ O ₄ were prepared as main components. SiO ₂ and CaCO ₃ were prepared as auxiliary component materials.

  Next, the prepared raw material powder is weighed so as to have the content calculated by the above formula (1), and the subcomponent raw material powder has the amounts shown in Tables 1 and 2. After weighing in such a manner, the mixture was wet mixed with a ball mill for 5 hours to obtain a raw material mixture.

  Next, the obtained raw material mixture was calcined in air at 950 ° C. for 2 hours to obtain a calcined material, and then wet pulverized with a ball mill for 20 hours to obtain a pulverized material having an average particle diameter of 1.5 μm. Obtained.

Next, this pulverized material was dried, and then granulated by adding 1.0% by weight of polyvinyl alcohol as a binder to 100% by weight of the pulverized material, and granulated with a 20 mesh sieve to obtain granules. This granule was pressure-molded at a pressure of 196 MPa ( ² ton / cm ² ) to obtain a molded body having a toroidal shape (size = outer diameter 22 mm × inner diameter 12 mm × height 6 mm).

  Next, each of these molded bodies was fired at 1270 ° C. for 2.5 hours while appropriately controlling the oxygen partial pressure to obtain a toroidal core sample as a sintered body. The obtained sample was subjected to fluorescent X-ray analysis to measure the composition of the ferrite core. The results are shown in Tables 1 and 2.

<Power loss (Pcv)>
A primary winding and a secondary winding are wound three times on the obtained toroidal core sample, and the power loss at −10 to 50 ° C. is measured under the condition of 1 MHz-50 mT. Tsp) was determined, and Tsp and power loss Pcv at 4 ° C. were calculated (unit: kW / m ³ ). The measurement was performed using a BH analyzer (SY-8217 manufactured by Iwasaki Tsushinki Co., Ltd.). The results are shown in Tables 1 and 2.

<Saturation magnetic flux density (Bs)>
After winding the winding 60 times on the obtained toroidal core sample, the saturation magnetic flux density Bs when a magnetic field of 2 kA / m was applied using a BH curve tracer (Model BHS40 manufactured by Riken Denshi Co., Ltd.) Measurements were made at 4 ° C., room temperature and 100 ° C. (unit: mT). The results are shown in Tables 1 and 2.

<Sintered body density>
About the obtained toroidal core sample, the sintered compact density was computed from the dimension and weight of the sintered compact after baking. The sintered body density was good at 4.81 g / cm ³ or more. The results are shown in Tables 1 and 2.

  Tables 1 and 2 show Pcv / Bs indicating the ferrite core quality factor based on Pcv and Bs at 4 ° C. The smaller Pcv or the larger Bs, the smaller this Pcv / Bs. Therefore, it is preferable that the value of Pcv / Bs is smaller because a reduction in power loss and a higher saturation magnetic flux density can be achieved at the same time. In this example, Pcv / Bs at 4 ° C. was 1.40 or less.

  From Table 1, it was confirmed that the Tsp obtained by the calculation and the Tsp obtained by the measurement of Pcv almost coincided. Moreover, in the sample which concerns on Examples 1-7, it has confirmed that Tsp was in the range of 2-7 degreeC. Furthermore, in the samples according to Examples 1 to 7, the power loss (Pcv) in the high frequency region (1 MHz) is low and the high saturation magnetic flux density (Bs) is obtained, and the quality expressed by Pcv / Bs at 4 ° C. It was confirmed that the coefficient was good.

Further, from Table 2, even when subcomponents (SiO ₂ and CaO) are included, Tsp does not change, and the content is within the scope of the present invention (Examples 8 to 12). It was confirmed that both a reduction in loss and a high saturation magnetic flux density can be achieved, and the quality factor is improved.

  In the electronic component according to the present invention, power loss is reduced in a use temperature and an environmental temperature range lower than room temperature, and a high saturation magnetic flux density is obtained. For this reason, even when the electronic component according to the present invention is used in various electronic devices and the like, consumption of the battery and the like can be suppressed, and power saving can be realized.

Claims (2)

The main component is composed of iron oxide, zinc oxide, and manganese oxide,
A ferrite composition containing silicon oxide in an amount of 50 to 300 ppm in terms of SiO _{2 and} calcium oxide in an amount of 110 to 1120 ppm in terms of CaO with respect to 100% by weight of the main component,
The minimum temperature Tsp of the magnetic loss of the ferrite composition is in the range of 2 to 7 ° C .;
When the content of the iron oxide in the main component is X mol% in terms of Fe ₂ O ₃ , the content of the zinc oxide is Z mol% in terms of ZnO, and the balance is the manganese oxide, the Tsp and the X And Z satisfies the following formulas (1) and (2).
Tsp = 21.6 (X + 0.52Z) -1520 Formula (1)
X ≧ 58.0 Formula (2)   The electronic component which has a ferrite core comprised from the ferrite composition of Claim 1, and is used in a frequency range of 1 MHz or more.

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