JP2003300774A - LOW LOSS Ni-Zn BASED FERRITE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a low loss Ni-Zn based ferrite with which a thinner and more compact low loss transformer can be obtained. <P>SOLUTION: The ferrite has a composition containing, as the main components, by mol, 48.5 to 50.5% Fe<SB>2</SB>O<SB>3</SB>, >3 to 12% CuO and 24 to 36% ZnO, and the balance NiO, and containing, as an assistant component, ≤0.15% (exclusive of zero) V<SB>2</SB>O<SB>5</SB>, and has the minimum value of core loss in the range of 20 to 140°C. Further, the minimum value of the above core loss measured in 50 kHz, 150 mT is ≤250 kW/m<SP>3</SP>, and saturation magnetic flux density is ≥300 mT. <P>COPYRIGHT: (C)2004,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low-loss Ni--Zn ferrite used for a transformer such as a liquid crystal backlight or a switching power supply. 2. Description of the Related Art In recent years, there has been a remarkable progress in miniaturization and weight reduction of electronic devices such as portable devices. For this reason, inverters for liquid crystal backlights, switching power supplies, and the like used in such electronic devices have been developed. There is a demand for further reduction in thickness, size, and weight. In the above unit, the transformer occupies a large part in both volume and power loss, and there is a strong demand for downsizing and high efficiency. In general, characteristics required for a transformer core include a small core loss at a driving frequency, a high saturation magnetic flux density, a high Curie temperature, and a high specific resistance. The reason why the core loss is required to be small at the drive frequency is that if the core loss is large, not only efficiency as a transformer is deteriorated, but also there is a risk that electronic equipment is destroyed due to thermal runaway due to self-heating. [0003] Further, a larger saturation magnetic flux density and a higher magnetic permeability are advantageous for miniaturization, and a ferrite material having a large magnetic permeability and a high saturation magnetic flux density is desired. As this ferrite material, there are a Mn-Zn-based ferrite and a Ni-Zn-based ferrite. For such a purpose, the Mn-Zn-based ferrite has been mainly used. The reason is generally that Mn
This is because -Zn based ferrite has higher saturation magnetic flux density, higher magnetic permeability, and lower loss than Ni-Zn based ferrite. [0004] However, in the case of using a Mn-Zn ferrite core to make a transformer for an inverter for a liquid crystal backlight, which is particularly required to be thin and small, the following problems arise. there were. On the other hand, the output voltage of a transformer for a liquid crystal backlight inverter, which is becoming thinner and smaller, is increasing, and when the volume resistivity is as low as about 10 Ω · m like a Mn—Zn ferrite core, In consideration of the insulation space distance between the core and the coil, the insulation space distance between the core and the terminal, and the insulation between the core and the lead wire, it is necessary to secure a required withstand voltage. These problems will be described with reference to FIG. FIG. 5A is a development view of each component of the transformer. The core 1 is incorporated into a bobbin 4 on which a winding 3 is wound with an insulating sheet 2 interposed therebetween. A terminal 5 is provided on the bobbin 4. FIG. 5B shows a state after the transformer is assembled. FIG. 5 (b) shows that the location (a) in FIG. 5 (b) requires an insulating space distance between the core and the coil, and as a result, the transformer itself becomes large, which hinders thinning and miniaturization.
(B) also requires the insulation space distance between the core and the terminal, which also hinders thinning and miniaturization.
5 (b) and (c) show that the insulation between the core and the lead wire is also required, which hinders the reduction in thickness and size. The insulation distance relates to corona discharge and dielectric breakdown due to high voltage, and also relates to the electric field gradient due to the core shape. On the other hand, when a Ni—Zn-based ferrite having a volume resistivity as high as 10 ⁶ Ω · m or more is used, the problem of the dielectric strength with respect to the core can be easily solved, and it is necessary to secure the space as described above. Therefore, the transformer can be made thinner and smaller. Therefore, an object of the present invention is to reduce the loss by optimizing the composition of the Ni—Zn-based ferrite, and to further reduce the thickness and size of the low-loss thin transformer. SUMMARY OF THE INVENTION The present invention is directed to a method for producing a semiconductor device, comprising, as main components, 48.5 mol% or more and 50.5 mol% or less of Fe ₂ O _3, more than 3 mol% of CuO and 12 mol% or less of ZnO.
24 mol% or more and 36 mol% or less, with the balance being NiO,
As subcomponent _V 2 _O 5 0.15wt% or less made (not including 0), has a minimum value of core loss between 20 ° C. to 140 ° C., 50 kHz, the minimum value of the core loss measured at 150mT Is 250 kW / m ³ or less, and a low-loss Ni—Zn ferrite having a saturation magnetic flux density of 300 mT or more. The Ni—Zn ferrite according to the present invention has a main component composition of 48.5 mol% or more and 50.50 mol% or more.
5 mol% or less, CuO more than 3 mol%, 12 mol% or less, ZnO 24 mol% to 36 mol%, balance
NiO was used. The main component was limited to such a range for the following reason. When Fe ₂ O ₃ is less than 48.5 mol%, the core loss becomes large, and 50.5 mol%
If it exceeds, the specific resistance is sharply reduced, and the insulating property, which is a characteristic of Ni-Zn series, is lowered, which is inappropriate. CuO is 3
If it is less than mol%, only a sintered material having a low sintering density and a small magnetic permeability can be obtained, and if it exceeds 12 mol%, the core loss increases. If ZnO is less than 24 mol%, the core loss increases, and if it exceeds 36 mol%, the temperature at which the minimum value of the core loss is obtained is set in a temperature range (20 ° C.
To 140 ° C.). 250k core loss
When it exceeds W / m ³ , for example, when it is used for a transformer for a liquid crystal inverter, heat generation due to core loss becomes a serious problem. NiO is the balance of the above-mentioned Fe ₂ O ₃ , CuO and ZnO. However, if the amount of NiO is small, the temperature at which the minimum value of the core loss is obtained does not become low in the temperature range in which the core is actually used (20 ° C. to 140 ° C.) On the contrary, if the number is large, the core loss increases. [0007] As an auxiliary component, 0.15 wt% or less of V ₂ O _{5 is} added as a composite. In general, ferrite loss can be broadly classified into three types: hysteresis loss, eddy current loss, and residual loss. Comparing the loss of the ferrite according to the present invention and the loss of the Ni—Zn-based ferrite containing no V ₂ O ₅ , the ferrite according to the present invention mainly shows that the hysteresis loss is reduced among the above three losses. Conventional Ni-Z
It was found that the loss was greatly reduced as compared with the n-type ferrite. The hysteresis loss is a loss generated by irreversible movement of the domain wall. In order to reduce the hysteresis loss, it is necessary to reduce inclusions that hinder domain wall movement. However, if the number of inclusions is excessively reduced, the domain wall moves over a long distance, and conversely increases the hysteresis loss. By adding and including a predetermined amount of V ₂ O ₅ , the inclusions can be controlled, and as a result,
It is believed that the hysteresis loss is reduced. Furthermore, when the added amount of V ₂ O ₅ is large, the saturation magnetic flux density (Bs) decreases, and a saturation magnetic flux density of 300 mT or more cannot be obtained. Therefore, the added amount of V ₂ O ₅ is specified to be 0.15 wt% or less so as to obtain low loss and high saturation magnetic flux density. Since the number of magnetic domain walls depends on the average crystal grain size, the crystal grain size is preferably large, and the average crystal grain size is preferably 5 μm or more. To obtain a high saturation magnetic flux density, the porosity is 3
% Is also preferable. (Example 1) Fe ₂ O ₃ , NiO, Zn
Raw material powder of O and CuO is 49.7 mol of Fe ₂ O ₃
%, ZnO 32.0 mol%, CuO 5.8 mol
%, NiO 12.5 mol%, and a predetermined amount of ion-exchanged water was added thereto and mixed with a ball mill for 4 hours.
After calcining at 0 ° C. for 1.5 hours, this is cooled in a furnace and crushed with a 40-mesh sieve. After a while, V ₂ O ₅
The raw material powder of 0 to 1% by weight was added, and again a predetermined amount of ion-exchanged water was added and pulverized by a ball mill for 6 hours.
The pulverized slurry material is dried and crushed. 1 wt% of a binder (polyvinyl alcohol) was added to the mixture, and the mixture was granulated. The granules sized with a 40-mesh sieve were dried using a dry compression molding machine and a metal mold to an outer diameter of 29.5 mm.
A ring-shaped core having an inner diameter of 17.7 mm and a height of 5.9 mm was molded at a molding pressure of 196 MPa, and baked at 1100 ° C. for 1.5 hours in the air. After measuring the fired density of each of the obtained samples by the Archimedes method, an LCR meter 428 made by HP was used.
The inductance (L) was measured at a frequency of 100 kHz and an applied current of 1 mA using 4 A, and the magnetic permeability (μ
i) was calculated. Thereafter, using a BH analyzer SY-8232 manufactured by Iwasaki Communication Equipment, frequency 50 kHz, magnetic flux density 1
The loss (core loss) was measured in a temperature range of 20 to 140 ° C. under a measurement condition of 50 mT. Finally, the applied magnetic field 1 was measured using a DC hysteresis loop tracer 3257 manufactured by Yokogawa Electric Corporation.
The magnetic flux density (Bs) was measured at 000 A / m. In addition,
The approximate values of the core constant are as follows: magnetic path length 60 mm, cross-sectional area 24 mm
² , volume 1450 mm ³ . Table 1 and FIG. 1 show the measurement results. Note that the core loss described in the column of core loss Pcv in Table 1 is a minimum value, and the minimum value is indicated by the temperature described in parentheses. In addition, V ₂ O ₅ is out of the range of the present invention, and No. ₅ of the comparative example. 1, No. 5, no. For 6 and 7,
The numbers are in parentheses. [Table 1] FIG. 1 is a diagram showing the relationship between the added amount of V ₂ O ₅ , the core loss, and the saturation magnetic flux density Bs in the first embodiment.
In order to set the core loss Pcv to 250 kW / m ³ or less and the saturation magnetic flux density to 300 mT or more, the addition amount of V ₂ O ₅ is set to 0.
It is understood that the content is preferably set to 15 wt% or less. A more preferable addition amount is 0.005 to 0.1 wt%, and further preferably 0.025 to 0.075 wt%. Also, when the crystal structure of the obtained sintered body was observed,
It was found that when the added amount of V ₂ O ₅ exceeds 0.15 wt%, the crystal enlarges, the pores in the grains increase, and the sintering density decreases. No. of this embodiment. In samples 2 to 4, the average crystal grain size was 5 μm or more and the porosity was 3 μm.
% Or less. (Example 2) Fe ₂ O ₃ , NiO, Zn
49.8 mol of Fe ₂ O ₃ as raw material powder of O and CuO
%, ZnO 28.5 mol%, CuO 5.8 mol
% And NiO 15.9 mol% are weighed and mixed with a predetermined amount of ion-exchanged water in a ball mill for 4 hours.
After calcining at 0 ° C. for 1.5 hours, this is cooled in a furnace and crushed with a 40-mesh sieve. After a while, V ₂ O ₅
The raw material powder of 0 to 1% by weight was added, and again a predetermined amount of ion-exchanged water was added and pulverized by a ball mill for 6 hours.
The pulverized slurry material is dried and crushed. 1 wt% of a binder (polyvinyl alcohol) was added to the mixture, and the mixture was granulated. The granules sized with a 40-mesh sieve were dried using a dry compression molding machine and a metal mold to an outer diameter of 29.5 mm.
A ring-shaped core having an inner diameter of 17.7 mm and a height of 5.9 mm was molded at a molding pressure of 196 MPa, and baked at 1100 ° C. for 1.5 hours in the air. After measuring the fired density of each of the obtained samples by the Archimedes method, an LCR meter 428 made by HP was used.
The inductance (L) was measured at a frequency of 100 kHz and an applied current of 1 mA using 4 A, and the magnetic permeability (μ
i) was calculated. Thereafter, using a BH analyzer SY-8232 manufactured by Iwasaki Communication Equipment, frequency 50 kHz, magnetic flux density 1
The loss (core loss) was measured in a temperature range of 20 to 140 ° C. under a measurement condition of 50 mT. Finally, the applied magnetic field 1 was measured using a DC hysteresis loop tracer 3257 manufactured by Yokogawa Electric Corporation.
The magnetic flux density (Bs) was measured at 000 A / m. In addition,
The approximate values of the core constant are as follows: magnetic path length 60 mm, cross-sectional area 24 mm
² , volume 1450 mm ³ . Table 2 and FIG. 2 show the measurement results. In Table 2, the core loss described in the column of core loss Pcv is a minimum value, and the minimum value is indicated by the temperature described in parentheses. In addition, V ₂ O ₅ is out of the range of the present invention, and No. ₅ of the comparative example. 8, No. 12, No. For 13 and 14, the numbers are in parentheses. [Table 2] FIG. 2 is a diagram showing the relationship between the added amount of V ₂ O ₅ , the core loss, and the saturation magnetic flux density Bs in the _second embodiment.
In order to set the core loss Pcv to 250 kW / m ³ or less and the saturation magnetic flux density to 300 mT or more, the addition amount of V ₂ O ₅ is set to 0.
It is understood that the content is preferably set to 15 wt% or less. A more preferable addition amount is 0.005 to 0.1 wt%, and further preferably 0.025 to 0.075 wt%. Also, when the crystal structure of the obtained sintered body was observed,
It was found that when the added amount of V ₂ O ₅ exceeds 0.15 wt%, the crystal enlarges, the pores in the grains increase, and the sintering density decreases. No. of this embodiment. Samples 9 to 10 have an average crystal grain size of 5 μm or more and a porosity of 3
% Or less. FIG. 3 shows an example of the structure of a horizontal transformer constituted by using the Ni—Zn ferrite of the present invention. FIG. 4 shows an improved structure of a vertical transformer. In either case, the size could be reduced as compared with the case of using Mn-Zn based ferrite. The Ni-Zn ferrite of the present invention has a low loss and a high saturation magnetic flux density.
Transformers such as inverters for liquid crystal backlights, switching power supplies, and the like in which n-based ferrite has been used can be reduced in loss and made thinner and smaller. [0016]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a characteristic diagram showing a relationship between an added amount of V ₂ O ₅ , a core loss, and a saturation magnetic flux density in one example according to the present invention. FIG. 2 is a characteristic diagram showing a relationship between an added amount of V ₂ O ₅ , a core loss, and a saturation magnetic flux density in one example according to the present invention. FIG. 3 is a diagram showing one embodiment of a transformer using a Ni—Zn-based ferrite according to the present invention. FIG. 4 is a view showing another embodiment of the transformer using the Ni—Zn ferrite according to the present invention. FIG. 5 is a diagram illustrating a structural example of a transformer using a conventional Mn—Zn-based ferrite. [Description of Signs] 1 core 2 insulating sheet 3 winding 4 bobbin 5 bobbin terminal

Claims (1)

Claims: 1. A _Fe 2 _O 3 as a main component 48.5mo
1% to 50.5mol%, CuO more than 3mol% to 12mol%, ZnO 24mol% to 36mo
1% or less, balance NiO and V ₂ O ₅
0.15 wt% or less (excluding 0)
With a minimum of core loss between 140 ° C., 50 kHz,
The minimum value of the core loss measured at 150 mT is 250 k
A low-loss Ni-Zn based ferrite having a saturation magnetic flux density of 300 mT or more at W / m ³ or less.