JP2008230941A - LOW CORE LOSS Ni-Cu-Zn-BASED FERRITE FOR HIGH FREQUENCY POWER DEVICE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide low core loss Ni-Cu-Zn-based ferrite having a reduced rise in core loss due to a temperature change under an excitation condition of 1 to 5 MHz. <P>SOLUTION: The Ni-Cu-Zn-based ferrite comprises, as the main components, 45 to 50.5 mol% Fe<SB>2</SB>O<SB>3</SB>, 14 to 24 mol% ZnO, 19.4 to 39 mol% NiO and 2 to 18.6 mol% CuO, and comprises, as auxiliary components, 0.01 to 0.6 wt.% V<SB>2</SB>O<SB>5</SB>, wherein the ratio of NiO/CuO is 1.2 to 19. The temperature change of core loss when an alternating current magnetic field of 1 to 5 MHz is applied to a sintered compact is continuously ≤+0.1%/°C (including negative value) at 25 to 60°C. Alternatively, the above Ni-Cu-Zn-based ferrite has a C content of ≤450 ppm, sintered density of ≤5.30 g/cc, and an average crystal grain size of 0.3 to 5 μm. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a low-loss spinel ferrite for high-frequency power devices, and more particularly to a low-loss spinel ferrite for high-frequency power devices suitable for transformers and power choke coils driven at 1 to 5 MHz.

  Electronic devices such as mobile phones and PDAs tend to have higher frequencies and smaller sizes, and in recent years, choke coils that are driven at 1 MHz or higher are used as power supply circuit elements. Furthermore, high efficiency of the entire power supply circuit is important from the environmental viewpoint, and low loss of ferrite, which is a core material of the choke coil, is required.

  Conventional Ni-Cu-Zn ferrites for power have mainly been used under excitation conditions with a relatively low frequency of 500 kHz or less, and therefore, loss reduction at 500 kHz or less has been performed (for example, Patent Documents 1 to 5). ). When the above-described low-frequency low-loss Ni—Cu—Zn-based ferrite is used under high-frequency excitation conditions, not only does the loss become low, but the loss tends to increase as the temperature rises. Therefore, it is necessary to develop a new low-loss Ni—Cu—Zn ferrite for high-frequency power devices.

JP 2004-224634 A JP 2004-064057 A JP 2001-015322 A JP-A-10-007454 Japanese Patent Application Laid-Open No. 07-307212

  Ferrite sintered bodies have a large μ value compared to metal green compacts, and are therefore often used for transformers and inductors on power supply circuits. In particular, Ni-Cu-Zn-based ferrites have a larger specific resistance than Mn-Zn-based ferrites, so they are used as small inductors for power using a direct-winding structure or a laminated structure, and as high-frequency choke coils for signal systems. Yes. Accordingly, Ni-Cu-Zn-based ferrite materials have been developed with low loss in the low frequency region for power device applications and high μ in the high frequency region for signals.

  However, due to the recent increase in frequency and size of electronic equipment, Ni—Cu—Zn based ferrites developed for high frequency power device applications are becoming useful instead of conventional low frequency power device applications. In addition, when a conventional Ni-Cu-Zn ferrite low-loss material for low-frequency power device applications is used under high-frequency excitation conditions, the value of core loss is high, and the value increases with increasing temperature. There's a problem.

  An object of the present invention is to provide a low-loss Ni—Cu—Zn-based ferrite for a high-frequency power device with little increase in core loss due to temperature change under excitation conditions of 1 MHz to 5 MHz.

  In response to the above problem, in the spinel type Ni—Cu—Zn ferrite, the raw material powder composed of a specific main component blending ratio and additives is fired into a sintered body having a specific average crystal grain size and a magnetic domain structure. By suppressing the C content of the sintered body, the temperature change of core loss under high frequency excitation conditions of 1 MHz to 5 MHz is continuously + 0.1% / ° C. or less from 25 ° C. to 60 ° C. Thus, the present invention has been found.

More specifically, in a Ni—Cu—Zn-based ferrite expressed as x (NiO _(1-a) · CuO _a ) O · yZnO · zFe ₂ O ₃ , x + y + z = 100, Fe ₂ O ₃ When the content is 45 mol% or less, the saturation magnetic flux density is clearly reduced, which is not desirable for power device applications. On the other hand, when the Fe ₂ O ₃ content exceeds 50.5 mol%, the specific resistance tends to decrease clearly, which is not desirable. When the ZnO content is less than 14 mol%, the value of the core loss at 1 MHz to 5 MHz tends to increase obviously, which is not desirable. Further, when the ZnO content exceeds 24 mol%, the core loss temperature change under excitation conditions of 1 MHz to 5 MHz shows an increasing tendency exceeding + 0.1% / ° C. from 25 ° C. to 60 ° C., which is not desirable. Regarding the NiO / CuO ratio, when the NiO / CuO ratio exceeds 19, the sintering temperature rises, and the temperature change of the core loss under the excitation condition of 1 MHz to 5 MHz is + 0.1% / ° C. from 25 ° C. to 60 ° C. Is not desirable. Further, when the NiO / CuO ratio is less than 1.2, the core loss temperature change under excitation conditions of 1 MHz to 5 MHz exceeds + 0.1% / ° C. from 25 ° C. to 60 ° C., which is not desirable.

In the additive, when V ₂ O ₅ is added in an amount of 0.01 wt% or more, the temperature change of the core loss under the excitation condition of 1 to 5 MHz becomes + 0.1% / ° C. or less from 25 ° C. to 60 ° C. In addition, when the V ₂ O ₅ addition amount exceeds 0.6 wt%, the temperature change of the core loss under the excitation condition of 1 to 5 MHz shows a rising tendency exceeding + 0.1% / ° C. from 25 ° C. to 60 ° C. Not desirable.

  The above composition is selected, the sintered density is 5.30 g / cc or less, the average crystal grain size is 0.3 to 5 μm or less, and the number of domain walls existing in one crystal grain is 3 or less, By forming a sintered body having a C content of 450 ppm or less, the temperature change of core loss under excitation conditions of 1 to 5 MHz is + 0.1% / ° C. or less from 25 ° C. to 60 ° C. A Zn-based ferrite sintered body can be obtained.

  According to the present invention, a Ni—Cu—Zn-based ferrite having a small core loss temperature change can be obtained by selecting the composition, adjusting the C content, the sintered density, and the average crystal grain size. In addition, by using such Ni—Cu—Zn based ferrite, it is possible to provide an electronic component for high frequency power device applications.

The Ni—Cu—Zn-based ferrite sintered body according to the present invention can be manufactured, for example, by the following powder metallurgical method. As the main _{component, Fe 2 O 3 45~50.5mol%,} ZnO14~24mol%, NiO19.4~39mol%, consists _{CuO 2 ~18.6mol%, V 2 O} 5 0.01~0 as a sub-component. Ni—Cu—Zn based ferrite raw material powder is wet-mixed so that the NiO / CuO ratio is 1.2 to 19 including 6 wt%, and calcining is performed at 800 ° C. to 1000 ° C. for 2 to 8 hours. Then, it grind | pulverizes and granulates, shape | molds in a required shape, and sinters in 900 degreeC-1040 degreeC air | atmosphere.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Main components _{Fe 2 O 3 48.9mol%, ZnO20mol} %, the balance being NiO and CuO, the component ratio is represented in table 1, further V ₂ O ₅ with respect to the main component of the total weight 0.20 wt% After blending and wet mixing, the mixture was calcined in air at 800 to 1000 ° C. for 2 to 8 hours and then pulverized. Thereafter, a binder was added and molded at 2 ton / cm to obtain a toroidal green compact having an outer diameter of 19 mm, an inner diameter of 13 mm, and a height of 5 mm. The obtained green compact was fired at 900 ° C. to 1040 ° C. in an air atmosphere after the binder removal treatment.

  The obtained sintered body was wound with three turns on the primary side and the secondary side, respectively, excited at 3 MHz and 20 mT, and the core loss at 25 ° C. to 140 ° C. was measured. Table 1 shows the core loss temperature change with respect to the NiO / CuO ratio.

  From the results of Table 1, the temperature change of the core loss shows a negative tendency from 25 ° C. to 60 ° C. in the range of NiO / CuO ratio of 2-16. Further, when the NiO / CuO ratio is 1.2 to 19, the temperature change of the core loss is + 0.1% / ° C. or less from 25 ° C. to 60 ° C. Accordingly, a NiO / CuO ratio in the range of 1.2 to 19 is useful.

The main component is 48.9 mol% Fe ₂ O _3, 20 mol% ZnO, the balance is NiO and CuO, and the component ratio is NiO / CuO ratio = 2.34. V ₂ O ₅ was mixed at 0.20 wt%, and a sintered body was obtained by the same process as in Example 1.

  The obtained sintered body was mirror-polished, and the surface of the sintered body etched in 130 ° C. phosphoric acid was observed with an optical microscope, and an arbitrary straight line was drawn on the optical microscope photograph to obtain 30 crystal grains. The average crystal grain size was obtained by averaging the slice lengths. The relationship between the obtained average crystal grain size and the core loss temperature change is shown in FIG.

  From FIG. 1, the core loss temperature change is more negative as the average crystal grain size is smaller. Further, a sintered body having an average crystal grain size of 0.3 μm or less is industrially difficult, and if the average crystal grain size is 5 μm or less, it is within + 0.1% / ° C. A range of crystal grain size of 0.3-5 μm is useful.

  Further, the sintered body is processed to a thickness of 50 μm, the crystal grains are observed using Lorentz microscopy, a diagonal line is drawn so as to be the longest in the crystal grains, and the length is defined as the crystal grain size. did. In addition, the under focus image and the over focus image of the crystal grains were observed, and the number of domain walls existing in the grains was measured. Using this result, the relationship between the number of domain walls present in one grain and the core loss temperature change is shown in FIG.

  From FIG. 2, if the number of domain walls per crystal grain is 2 or less, the temperature change of the core loss tends to be negative from 25 ° C. to 60 ° C. If the number of domain walls per crystal grain is 3 or less, the temperature change of the core loss is + 0.1% / ° C. or less from 25 ° C. to 60 ° C. Therefore, a range in which the number of domain walls present in one crystal grain of the sintered body is 3 or less is useful.

  Further, the C content was investigated by performing gas analysis of the sintered body, and the relationship between the obtained C content and core loss temperature change is shown in FIG.

  FIG. 3 shows that the temperature change of the core loss from 25 ° C. to 60 ° C. is improved by lowering the C content. Further, it can be seen that when the C content is 450 ppm or less, the tendency is + 0.1% / ° C. or less. Therefore, the range of C content of 450 ppm or less is useful.

The main component is 48.9 mol% Fe ₂ O _3, 14 to 24 mol% ZnO, the balance is NiO and CuO, and the component ratio is NiO / CuO ratio = 2.34. On the other hand, 0.20 wt% of V ₂ O ₅ was blended, and a sintered body was obtained by the same process as in Example 2. The obtained toroidal sintered body is wound with 3 turns on the primary side and the secondary side, respectively, and when an alternating magnetic field of 3 MHz and 80 A / m is applied, the applied magnetic field is applied to the horizontal axis and the sintered body. It was obtained by measuring the slope of a straight line connecting a point represented by a magnetic flux density (T) corresponding to the maximum applied magnetic field (A / m) and the origin in an orthogonal coordinate system with the generated magnetic flux density as the vertical axis. The relationship between the value and the temperature change of the core loss from 25 ° C. to 60 ° C. is shown in FIG.

  As shown in FIG. 4, when the slope value decreases, the core loss temperature change is improved toward a negative tendency. Further, when the inclination is 0.0005 or less, it is + 0.1% / ° C. or less. Therefore, when an AC magnetic field of 3 MHz and 80 A / m is applied to the sintered body, the maximum applied magnetic field (A / m) in an orthogonal coordinate system with the applied magnetic field as the horizontal axis and the magnetic flux density generated in the sintered body as the vertical axis. A range in which the slope of the straight line connecting the point represented by the magnetic flux density (T) corresponding to and the origin is 0.0001 or more and 0.0005 or less is useful.

The figure which shows the average crystal grain diameter in Example 2, and a core loss temperature change relationship. The figure which shows the relationship between the number of domain walls which exist in one grain in Example 2, and a core loss temperature change. The figure which shows the relationship between the C content in Example 2, and the temperature change of a core loss. The figure which shows the relationship between the inclination of the straight line which connected the point represented by the magnetic flux density (T) corresponding to the largest applied magnetic field (A / m) in Example 3, and the origin, and the temperature change of a core loss.

Claims (5)

As the main _{component, Fe 2 O 3 45~50.5mol%,} ZnO14~24mol%, NiO19.4~39mol%, consists CuO2~18.6mol%, V ₂ O ₅ 0.01~0.6 as a sub-component Ni-Cu-Zn-based ferrite having a NiO / CuO ratio of 1.2 to 19 and containing 25% by weight, the temperature change of the core loss when an AC magnetic field of 1 to 5 MHz is applied to the sintered body is 25. A low-loss Ni—Cu—Zn-based ferrite for high-frequency power devices, characterized by being continuously + 0.1% / ° C. or lower (including negative) from ℃ to 60 ° C.   The low-loss Ni for high-frequency power devices according to claim 1, wherein the density of the sintered body is 5.30 g / cc or less and the average crystal grain size of the sintered body is 0.3 to 5 µm. -Cu-Zn based ferrite.   The low-loss Ni-Cu for high-frequency power devices according to claim 1, wherein when a magnetic field is applied to the sintered body, the number of domain walls present in one crystal grain of the sintered body is 3 or less. -Zn-based ferrite.   The low-loss Ni—Cu—Zn-based ferrite for high-frequency power devices according to claim 1, wherein the content of C as an impurity component is 450 ppm or less.   When an AC magnetic field of 3 MHz and 80 A / m is applied to a toroidal sintered body without voids, the maximum applied magnetic field (in the orthogonal coordinate system with the applied magnetic field as the horizontal axis and the magnetic flux density generated in the sintered body as the vertical axis, The slope of a straight line connecting a point represented by a magnetic flux density (T) corresponding to (A / m) and the origin is 0.0001 or more and 0.0005 or less. The low-loss Ni—Cu—Zn-based ferrite for high-frequency power devices according to any one of the above.

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