JP6574574B2 - Multilayer inductor - Google Patents

Description

  The present invention relates to a multilayer inductor. Specifically, the present invention relates to a multilayer inductor provided with a layer made of hard ferrite and a layer made of soft ferrite.

  As is well known, a multilayer inductor is a laminate formed by sequentially laminating a paste-like metal printed as a conductor pattern on a paste-like magnetic material sheet called a green sheet, and firing the laminate. Are provided with external electrodes. In such a multilayer inductor, a conductive pattern of each layer is sequentially connected between the layers to form a coil that spirals around while being superimposed in the stacking direction, and the periphery of the coil is surrounded by an electrically insulating magnetic material. Will be. For this reason, the multilayer inductor has a feature that there is little magnetic leakage to the outside and a necessary inductance can be obtained with a relatively small number of turns, which is suitable for miniaturization and thinning.

  By the way, it can be said that the recent technical trend in integrated circuits such as CPUs and LSIs embedded in electronic devices is high frequency driving and low voltage driving. All of them mean that they are driven with a large current. Therefore, a large current flows through the inductor, which is a peripheral component of the integrated circuit. Accordingly, the inductor is required to have excellent DC superposition characteristics that do not cause magnetic saturation even with a large current. On the other hand, circuit components are required to be further downsized due to the demand for downsizing electronic devices.

  Therefore, the technical idea is that the magnetic flux is applied in the opposite direction to the magnetic flux generated by the coil to be biased (reverse bias), and the magnetic flux is increased until the base point of the BH characteristic is shifted to the negative side and magnetic saturation occurs. A multilayer inductor in which a layer made of a soft magnetic material (hereinafter referred to as a soft ferrite layer) and a layer made of a hard magnetic material that is a material of a permanent magnet (hereinafter referred to as a hard ferrite layer) are laminated inside the multilayer body. is there. In such a multilayer inductor, the hard ferrite layer functions as a permanent magnet, and the permanent magnet generates a magnetic flux opposite to the magnetic flux of the coil. Thereby, even if it is the same dimension, it is possible to flow a larger current. A laminated inductor incorporating such a permanent magnet is described in, for example, Patent Document 1 below.

JP 2006-196591 A

  In a multilayer inductor, the conductor pattern is usually formed using silver (Ag). As is well known, the melting point of Ag is as low as about 960 ° C. Therefore, the magnetic material constituting the multilayer inductor is required to have a characteristic that a sufficient sintered density can be obtained even when firing at a melting point of Ag or lower. Therefore, nickel copper zinc-based ferrite (Ni—Cu—Zn-based ferrite) containing Cu for enhancing the sinterability is used for the soft ferrite layer constituting the multilayer inductor regardless of the presence or absence of the hard ferrite layer. In the above-described multilayer inductor provided with a hard ferrite layer serving as a permanent magnet, barium ferrite (Ba ferrite) or strontium ferrite (Sr ferrite) is used as a hard magnetic material. As a sintering aid, low-melting glass is often used. However, as a result of repeated research by the present inventors for the purpose of improving the characteristics of a multilayer inductor having a hard ferrite layer serving as a permanent magnet, when a hard ferrite layer and a soft ferrite layer containing Cu are laminated and fired simultaneously, the interface between the layers Due to the reaction, it was found that Cu in the Ni—Cu—Zn ferrite segregates to the hard ferrite layer side, and there is a problem that the magnetic properties are deteriorated or the resistivity is lowered.

Accordingly, an object of the present invention is to provide a multilayer inductor that can be fired at a low temperature and has no characteristic deterioration due to segregation of Cu while providing a hard ferrite layer that becomes a permanent magnet.

The present invention for achieving the above object is a multilayer inductor including a sintered body in which a conductor pattern of Ag is formed in a magnetic body,
The sintered body comprises said magnetic material is integrally fired in a state where the hard ferrite layer acting as a permanent magnet containing a soft ferrite layer and the hard magnetic material containing soft magnetic material are stacked ,
The soft ferrite layer is formed by adding 1.5 to 3.0 wt% Bi ₂ O ₃ to Ni—Zn ferrite not containing Cu,
The hard ferrite layer is obtained by further adding 5.0 to 10 wt% Bi ₂ O ₃ to Ba ferrite containing SiO ₂ as an additive.
The multilayer inductor is characterized by this.

Other aspects of the invention include Ni-Zn ferrite and 1.5-3.0 wt% Bi. ₂ O ₃ And a first layer that is a soft ferrite layer that does not contain Cu, Ba ferrite, and SiO ₂ And 5.0-10 wt% Bi ₂ O ₃ And a step of obtaining a magnetic body and a step of forming an Ag conductor pattern on the above-mentioned laminated body. A method for manufacturing a multilayer inductor characterized by the following.

  According to the multilayer inductor of the present invention, while providing a hard ferrite layer serving as a permanent magnet, it can be fired at a low temperature, has no segregation of Cu, and has excellent magnetic properties and a high sintered density.

It is a figure which shows element mapping of the laminated sintered compact which consists of a hard ferrite layer and a soft ferrite layer.

=== Multilayer Inductor ===
As described above, a multilayer inductor having a permanent magnet layer has a problem that Cu is segregated when conventional Ni—Cu—Zn ferrite is used for the soft magnetic layer. Therefore, in the multilayer inductor according to the embodiment of the present invention, the soft ferrite layer is formed using a soft magnetic material mainly composed of nickel-zinc based ferrite (Ni-Zn ferrite) not containing Cu. Specifically, bismuth oxide (Bi ₂ O ₃ ) is contained as a subcomponent in both the soft ferrite layer and the hard ferrite layer.

=== Soft ferrite layer ===
In the multilayer inductor according to the example of the present invention, first, in order to evaluate the characteristics of the soft ferrite layer, Ni—Zn ferrite not containing Cu is a main component and the additive amount of Bi ₂ O _{3 as} a subcomponent is different. Eight kinds of sintered bodies of soft magnetic materials were produced as samples.

<Sample preparation procedure>
As a sample preparation procedure, first, Fe ₂ O ₃ , ZnO, and NiO, which are raw materials of Ni—Zn ferrite, which is the main component, are mixed at a ratio of 49.0 mol%, 23.0 mol%, and 28.0 mol%, respectively. The mixture was calcined at 950 ° C. Bi2O3 was added to the powder obtained by further pulverizing the powder obtained by this pre-baking in an amount corresponding to each of the different types of samples. Next, a binder (for example, PVA aqueous solution) is added to the mixture and mixed, and granulated to form a powder having an appropriate particle size (for example, 1 μm). Thereafter, the granulated powder was formed into a desired shape and fired at about 900 ° C. lower than the melting point of Ag for 3 hours to obtain Ni—Zn ferrite containing Bi ₂ O ₃ as an accessory component.

<Characteristic evaluation>
The maximum magnetic flux density Bm and sintering density d at 3000 A / m were measured for various samples prepared by the above-described procedure.

Table 1 below shows characteristics of various samples corresponding to the soft ferrite layer in the multilayer inductor.

As shown in Table 1, the eight added amount is different for the samples A-G _Bi 2 _{O 3,} the lowest sample A addition amount of _Bi 2 _{O 3} with 1.0 wt%, the maximum magnetic flux density Bm = 311 (mT) and the sintered density d = 0.06 (g / cm ³ ). Further, when looking at the maximum magnetic flux density Bm of samples A to G, the amount of Bi ₂ O ₃ added increases sharply in sample B with an added amount of 1.5 wt% compared to sample A with 1.0 wt%. In the sample C of 0 wt%, the maximum magnetic flux density Bm becomes a maximum value (396 mT), and thereafter, the maximum magnetic flux density Bm gradually decreases as the amount of Bi ₂ O ₃ added increases. However, even in the sample G with the added amount of 7.0 wt%, the maximum magnetic flux density Bm = 352 mT, and a sufficiently large value is maintained. Note Sample Looking sintering density d of A-G, Bi ₂ O as the additive amount of ₃ is large sintered density d is can be seen high. From the above, it was confirmed that the necessary sintered density d was obtained by adding Bi ₂ O ₃ even if Cu was not contained in the soft ferrite layer. When Bi ₂ O ₃ was added in an amount of 1.5 wt% or more, the maximum magnetic flux density Bm increased rapidly, and a large value could be maintained up to 7.0 wt%. Therefore, a more preferable lower limit of the Bi ₂ O ₃ addition amount may be 1.5 wt% or more. Regarding the upper limit, in consideration of the increasing / decreasing tendency of the maximum magnetic flux density Bm with respect to the addition amount of Bi ₂ O ₃ shown in Table 1 of 5.0 wt% and 7.0 wt%, Bi is a rare metal, and the like. It may be 0 wt% or less.

=== Hard ferrite layer ===
Next, in order to evaluate the characteristics of the hard ferrite layer in the multilayer inductor according to the example of the present invention, samples of sintered bodies of various hard magnetic materials having different amounts of Bi ₂ O ₃ added to typical hard magnetic materials are sampled. As produced. Schematically, various hard magnetic materials in which the addition amount of Bi ₂ O ₃ is adjusted are sintered to a general hard magnetic material containing SiO ₂ which is a general additive in Ba ferrite. It was.

<Sample preparation procedure>
The preparation procedure of the sample corresponding to the hard ferrite layer is almost the same as the sample corresponding to the soft ferrite layer described above except that the raw materials are different. Here, among the raw materials of Ba ferrite which is the main component of the hard ferrite layer, Fe ₂ O ₃ and BaCO ₃ which are raw materials of the ferrite itself are mixed at a ratio of 85.0 mol% and 15.0 mol%, respectively, and the mixture is mixed. Pre-baking was performed at 900 ° C. SiO ₂ and Bi ₂ O ₃ were added to the powder obtained by further pulverizing the powder obtained by this preliminary firing. SiO ₂ is a well-known additive in general Ba ferrite and is 0.4 wt% here. That is, if the mixture up to here is granulated and fired, a general Ba ferrite is obtained. However, the hard ferrite layer constituting the multilayer inductor according to the present embodiment contains Bi ₂ O ₃ which is the same additive as the soft ferrite layer. Therefore, Bi ₂ O ₃ in an amount corresponding to the sample was added together with 0.4 wt% of SiO ₂ to the powder composed of the ferrite material after temporary firing. Next, a material obtained by adding a binder to a mixture of the raw material of ferrite that has undergone preliminary firing and SiO ₂ and Bi ₂ O ₃ as additives and granulating is formed and granulated. And that the molded product was fired for 3 hours at about 900 ° C., to obtain a Ba ferrite containing _Bi 2 _{O 3} as an auxiliary component.

<Characteristic evaluation>
About the sample produced by the procedure mentioned above, residual magnetic flux density Br, coercive force Hc, and sintered density d were measured.

Table 2 below shows the characteristics of the sample corresponding to the hard ferrite layer.

As shown in Table 2, in 8 types of samples H to N having different amounts of Bi ₂ O ₃ added, the holding power Hc does not have a clear tendency with respect to the amount of Bi ₂ O ₃ added. Although there is an increase / decrease, it can be said that it is substantially constant in the range of 1.0 wt% to 7.0 wt%. Regarding the sintered density d, the amount of Bi ₂ O ₃ added was 1.0 wt%, and the smallest sample H was 3.62 g / cm ³ , and the tendency was that the sintered density d increased as the amount added increased. . The residual magnetic flux density Br tends to increase as the addition amount increases up to the addition amount of 5.0 wt%. If it exceeds 5.0 wt%, the tendency to saturate. When the added amount is 1.5 wt% or more, the sintered density d exceeds 4 g / cm ^3, and the increasing tendency of the residual magnetic flux density Br is remarkable. Therefore, the added amount of Bi ₂ O ₃ is 1.5 wt%. desirable. The upper limit may be adjusted so that the shrinkage rate during firing does not greatly deviate from the shrinkage rate of the soft magnetic material constituting the soft ferrite layer, and it seems that there is no need to set an optimum upper limit value. However, considering the upper limit addition amount of a general additive, it seems appropriate to set it to about 10 wt%. In any case, there was no problem at all with the addition amount of 7.0 wt%.

=== Characteristics at the laminated interface ===
In an actual multilayer inductor, the above-described soft ferrite layer and hard ferrite layer are fired simultaneously as an integral sintered body (hereinafter, “laminated sintered body”). Therefore, two types of laminated sintered bodies having different soft ferrite compositions were produced. One type is a laminated sintered body obtained by firing the soft magnetic material used when preparing Sample C and the hard magnetic material used when preparing Sample J, which are fired at 900 ° C. for 3 hours. is there. The other type is a soft magnetic material made of Ni—Cu—Zn ferrite to which 2.0 wt% of CuO is added instead of Bi ₂ O ₃ in sample C, and the hard magnetic material used in producing sample J. It is a laminated sintered body obtained by firing a laminated product at 900 ° C. for 3 hours. And the dispersion state of the element near the lamination | stacking interface of each kind of laminated sintered compact was investigated using the fluorescent X-ray-spectroscopy etc. The dispersion state was visualized by elemental mapping.

  FIG. 1 shows the results of element mapping in the two types of laminated sintered bodies (1a, 1b) produced. FIGS. 1A and 1C are element mappings for Bi and Cu in a laminated sintered body (hereinafter also referred to as sintered body 1a) that does not contain Cu in the soft ferrite layer. FIGS. D) is an element mapping of Bi and Cu in a laminated sintered body (hereinafter also referred to as “sintered body 1b”) having Ni—Cu—Zn ferrite as a soft ferrite layer. In the figure, the degree of distribution of elements is expressed by shading, and the concentration is lower (lighter) as there are more specific elements. 1A to 1D, the white dotted line in the figure is the laminated interface 2, and the upper side of the drawing with respect to the laminated interface 2 is the hard ferrite layer 3 and the lower side is the soft ferrite layer 4.

First, from FIG. 1 (A), Bi ₂ O ₃ is added to both the hard ferrite layer 3 and the soft ferrite layer 4 in the sintered body 1a corresponding to the embodiment of the present invention. Bi is distributed in both of the soft ferrite layers 4 and there is no great difference in the degree of distribution. On the other hand, in the sintered body 1b as a comparative example, Bi is contained only in the hard ferrite layer 3, and when looking at FIG. 1B, some Bi is also present in the soft ferrite side 4 not containing Bi in the vicinity of the lamination boundary 2. It can be seen that is distributed.

  Looking at the distribution of Cu, first, in the sintered body 1a shown in FIG. 1 (C), not only the hard ferrite layer 3 but also the soft ferrite layer 4 does not contain Cu. Thus, no Cu distribution is observed. On the other hand, in the sintered body 1b in which the soft ferrite layer 4 is made of conventional Ni—Cu—Zn ferrite, as shown in FIG. 1D, a large amount of Cu is segregated at the lamination boundary 2, and Ni—Cu— It can be confirmed that the Cu concentration in the Zn ferrite layer is not uniform. That is, it is expected that the magnetic properties and electrical properties of a single Ni—Cu—Zn ferrite are not obtained. As described above, in the multilayer inductor according to the example of the present invention, since the soft ferrite layer 3 has the same configuration as the sintered body 1a not containing Cu, there is substantially no interface reaction and the magnetic characteristics are deteriorated. And the problem that the resistivity is reduced does not occur.

1a, 1b laminated sintered body, 2 laminated interface, 3 hard ferrite layer,
4 Soft ferrite layer

Claims (3)

A multilayer inductor including a sintered body in which a Ag conductor pattern is formed in a magnetic body,
The sintered body comprises said magnetic material is integrally fired in a state where the hard ferrite layer acting as a permanent magnet containing a soft ferrite layer and the hard magnetic material containing soft magnetic material are stacked ,
The soft ferrite layer is formed by adding 1.5 to 3.0 wt% Bi ₂ O ₃ to Ni—Zn ferrite not containing Cu,
The hard ferrite layer is obtained by further adding 5.0 to 10 wt% Bi ₂ O ₃ to Ba ferrite containing SiO ₂ as an additive.
A multilayer inductor characterized by that. Ni-Zn ferrite and 1.5-3.0wt% Bi ₂ O ₃ And a first layer that is a soft ferrite layer that does not contain Cu, Ba ferrite, and SiO ₂ And 5.0-10 wt% Bi ₂ O ₃ A step of integrally firing a laminated body in which a second layer to be a hard ferrite layer containing is laminated to obtain a magnetic body;
Forming an Ag conductor pattern on the laminate;
A method of manufacturing a multilayer inductor, comprising: A method of manufacturing a multilayer inductor according to claim 2,
The first layer is Fe ₂ O ₃ , ZnO, and NiO were mixed at a ratio of 49.0 mol%, 23.0 mol%, and 28.0 mol%, respectively, and the Ni—Zn ferrite raw material that was pre-fired was mixed with 1.5 to 3.0 wt% Bi. ₂ O ₃ Is added,
The second layer is Fe ₂ O ₃ And BaCO ₃ Are mixed in a ratio of 85.0 mol% and 15.0 mol%, respectively, and pre-baked Ba ferrite raw material, ₂ And 5.0-10 wt% Bi ₂ O ₃ And added,
A method for manufacturing a multilayer inductor, comprising: