JP2012117088A - Fine particle and method for production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide fine particles having a shape of single crystal-like cube or cuboid and excellent in sintering resistance, to provide electronic components using the fine particles as an internal electrode, and to provide a method for efficient production of the fine particles.SOLUTION: The fine particle is 1-200 nm on a side, has the shape of substantially cube or cuboid, and is composed of nickel and/or nickel oxide.

Description

  The present invention relates to fine particles, an electronic component having the fine particles in an internal electrode layer, and a method for producing the fine particles.

  For example, in a multilayer electronic component such as a ceramic capacitor, nickel particles (Ni particles) are used as an internal electrode layer, and miniaturization of Ni particles is required as electronic components are reduced in size and thickness.

  The production method of the nickel fine particle powder is roughly classified into a liquid phase synthesis method and a gas phase synthesis method. The liquid phase synthesis method mainly includes a liquid phase reduction method, which is a method of synthesizing Ni fine particles by reducing nickel hydroxide in an aqueous solution (see, for example, Patent Document 1).

  In addition, chemical vapor deposition methods and physical vapor deposition methods have been established as vapor phase synthesis methods. Chemical vapor deposition methods use gaseous raw materials and perform chemical reactions by heat, plasma, or light under reduced pressure and vacuum. This is a technique for promoting and synthesizing Ni fine particles (for example, see Patent Document 2). Further, the physical vapor deposition method is a method of obtaining Ni fine particles by evaporating a raw material solid target in vacuum by an ion beam or arc discharge heating.

  In the liquid phase synthesis method described above, spherical Ni ultrafine particles of about 20 to 100 nm can be obtained with a relatively good particle size distribution, but the crystallite size in the Ni particles is small, and the current MLCC field is progressing in thin-layer multilayering. Ni particles used in No. 1 are not mainstream from the viewpoint of oversintering.

  On the other hand, the current mainstream vapor phase synthesis method, both chemical vapor deposition method and physical vapor deposition method, can obtain spherical Ni particles with large crystallite size in Ni particles, but classification is poor due to poor particle size distribution. A process is required, and it is difficult to synthesize Ni ultrafine powder of 100 nm or less at present. Further, in the thermal plasma chemical vapor deposition method, spherical Ni fine particles having a large crystallite size in Ni particles and 100 nm or less can be obtained, but are not suitable for mass production.

  In addition, in the MLCC having an ultra-thin layer electrode structure, it is desirable that Ni particles are packed in the electrode dry coating film before firing at high density, but the spherical Ni powder produced by the above method has a close-packed structure. Even if it takes, the filling rate of Ni powder will be only about 74%. For this reason, even if Ni ultrafine particles with high crystallinity are obtained, Ni particles are oversintered during firing and do not exhibit a sufficient function as an internal electrode of MLCC.

JP 2001-203121 A JP-A-2005-248198

  The present invention has been made in view of such a situation, and the object thereof is excellent in sintering resistance, fine particles having a single crystal-like cubic or cuboid shape, and an electronic component using the fine particles as an internal electrode layer, It is to provide a production method for efficiently producing the fine particles.

  In order to achieve the above object, the fine particles according to the present invention are fine particles having a side of 1 to 200 nm, a substantially cubic or rectangular parallelepiped shape, and composed of nickel and / or nickel oxide.

  Since the fine particles according to the present invention are ultrafine particles having a substantially cubic or rectangular parallelepiped shape and composed of nickel and / or nickel oxide, these fine particles are included in the electrode dry coating film before firing. It becomes easy to pack densely. Therefore, it is possible to suppress the oversintering of the fine particles during firing, and it becomes easy to realize an electronic component having an ultrathin layer electrode structure with few electrode breaks.

The method for producing fine particles according to the present invention includes:
An electric current is applied to a wire made of nickel metal, and the fine particles obtained by scattering from the wire are collected near the wire.

  According to the method for producing fine particles according to the present invention, the above-described ultrafine particles can be produced easily and in large quantities at low cost.

  Preferably, the fine particles are collected and further reduced. By performing the reduction treatment, the ultrafine particles made of nickel oxide among the collected fine particles can be reduced to conductive ultrafine particles made of nickel.

  Preferably, the collection of the fine particles is performed by a glass collecting plate.

The electronic component according to the present invention is
An internal electrode layer containing the fine particles described above;
And an insulating layer sandwiched between the internal electrode layers.

Alternatively, the electronic component according to the present invention is
An internal electrode layer containing the fine particles described above;
And a semiconductor layer sandwiched between the internal electrode layers.

FIG. 1 is a schematic view showing an example of a production apparatus for producing Ni fine particles according to an embodiment of the present invention. FIG. 2 is a transmission electron micrograph of Ni fine particles according to an example of the present invention. FIG. 3 is a graph showing the particle size distribution of Ni fine particles according to an example of the present invention. FIG. 4 is a graph showing the particle size distribution of Ni fine particles according to another embodiment of the present invention.

Hereinafter, the present invention will be described based on embodiments shown in the drawings.
First, based on FIG. 1, the microparticle manufacturing apparatus 2 for manufacturing microparticles according to an embodiment of the present invention will be described.

  As shown in FIG. 1, the fine particle manufacturing apparatus 2 has a chamber 4. A wire 6 is arranged inside the chamber 4. A power source 8 is connected to both ends of the wire 6 so that a voltage is applied. The power source 8 is generally disposed outside the chamber 4, but may be disposed inside the chamber 4.

Inside the chamber 4, a collecting plate 10 is disposed near the wire 6 and above the wire 6. Although the distance of the wire 6 and the collection board 10 is not specifically limited, Preferably, it is 1-500 mm, More preferably, it is 5-10 mm. When in these distance ranges, it becomes easy to obtain nickel fine particles to be described later. If these distances are too close, the repair plate tends to deform due to heat, and if they are too far, the repair efficiency tends to decrease.
The collection plate 10 may be made of, for example, ceramics (glass, polycrystal, single crystal), metal (stainless steel, copper, etc.), heat resistant resin (fluorine resin (eg, Teflon (registered trademark)), polyimide, etc.). preferable. Further, the collecting plate 10 may include a cooling means for cooling the collecting plate 10 to a predetermined temperature, or a heater for heating the collecting plate 10 to a predetermined temperature.

Although the wire diameter of the wire 6 is not specifically limited, Preferably it is 0.02-2.00 mm, More preferably, it is 0.45-0.70 mm. When the wire diameter is in this range, nickel fine particles described later can be easily obtained. If the wire diameter is too small, the production amount per unit current tends to decrease. If the wire diameter is too large, the oxidation reaction tends not to proceed sufficiently.
The cross-sectional shape of the wire 6 is not particularly limited, and examples thereof include a circle, a triangle, a square, a polygon, an ellipse, and the like, and preferably a circle. The length of the wire 6 is preferably 35 mm. The wire 6 is made of Ni, nichrome, an alloy containing nickel, or a ceramic containing nickel, and is preferably made of Ni.

The voltage applied to both ends of the wire 6 by the power source 8 is preferably a pulse voltage, or a direct current or an alternating voltage, and the energization time per time is preferably 1 to 600 seconds, more preferably 10 to 300 seconds. is there. The value of the voltage at this time is preferably 2.2 to 4.0 V, and more preferably 2.2 to 3.0. If the voltage is too small, disconnection is difficult and nickel fine particles cannot be obtained. If the voltage is too high, the particle size distribution tends to spread. The particle diameter can be controlled by controlling the voltage applied to both ends of the wire 6. The current density per unit area in the cross section of the wire 6 is, for example, 10 to 1000 A / mm ² .

A gas inlet 12 and a gas outlet 14 are formed in the chamber 4, and the inside of the chamber 4 is under a predetermined atmosphere. As the gas filling the inside of the chamber 4, oxygen or a mixed gas of oxygen and nitrogen or an inert gas is preferable. The internal pressure of the chamber 4 is preferably 1 to 10 ⁶ Pa, more preferably 10 ⁴ to 10 ⁵ Pa. The concentration of oxygen gas in the atmospheric gas is preferably 25% or more, more preferably 99.5% or more.

  According to the apparatus 2 according to the present embodiment, fine particles as shown in FIG. 2 adhere to the surface of the collection plate 10 toward the wire 6. The fine particles are substantially fine particles having a cubic or rectangular parallelepiped shape (hereinafter also collectively referred to as a cubic shape) and made of nickel and / or nickel oxide. One side of the fine particles is preferably 1 to 200 nm, more preferably 4 to 100 nm. The side of the fine particles means the side of the largest size among the sides of the cubic or rectangular parallelepiped fine particles. If one side of the fine particles is too large, the internal electrode thickness of the capacitor is increased, and the capacitor cannot be reduced in size. . Fine particles of 1 nm or less whose side size is too small are difficult to disperse and difficult to manufacture.

  The reason why such ultrafine particles are deposited on the collecting plate 10 by energizing the wire 6 can be explained as follows, for example.

  By heating the wire in an oxidizing atmosphere, an oxide film is formed on the surface of the wire. Even when the temperature of the wire becomes high and the melting point of nickel is reached, the melting point of the oxide film is still higher, so that the electric current is maintained without disconnection. When the wire breakage occurs at a higher temperature, the melt inside the wire is exposed, and a vapor phase of nickel or nickel oxide is ejected therefrom. It is thought that nanocrystals having a shape close to a cube grew predominantly by rapidly cooling the gas phase until reaching the collecting plate.

  In addition, you may perform the reduction process of the microparticles | fine-particles comprised with the nickel and / or nickel oxide adhering to the surface of the collection board 10. FIG.

  The nickel particles thus obtained are used as a conductive paste for forming an internal electrode layer of a multilayer ceramic capacitor, for example. After the conductive paste containing nickel particles of the present embodiment is printed directly on the support film or on the surface of the dielectric green sheet to form the electrode pattern printed film, before the electrode pattern printed film is dried or during drying In addition, it is preferable to apply a magnetic field to the printed film.

  By applying a magnetic field to the printed film, the cubic nickel fine particles contained in the printed film are arranged in the printed film by the magnetic field, and a pre-fired electrode dry coating film composed of higher density nickel fine particles is obtained.

Since the fine particles according to the present embodiment are ultra-fine particles having a substantially cubic or rectangular parallelepiped shape, it is easy to densely fill these fine particles in the dry electrode film before firing. To reduce the size and increase the capacity of MLCC, the thinner the internal electrode layer, the better. However, this thickness strongly depends on the particle size and shape of the nickel particles used as a raw material.
For example, even if the spherical particles are packed most closely, the filling rate is about 74%. Therefore, when an electrode layer having a thickness similar to the particle size is produced, an electrode formed by oversintering in the sintering process is used. Cutting occurs, and the MLCC internal electrode does not function sufficiently. On the other hand, if cubic or cuboidal nickel fine particles, which are fine particles according to the present experimental form, are used, the filling rate can be made close to 100%, so that oversintering hardly occurs, and a uniform thickness comparable to the particle size. It is possible to produce an internal electrode layer having Therefore, it is possible to suppress oversintering of fine particles during firing, and it becomes easy to realize a multilayer ceramic capacitor having an ultrathin layer electrode structure with few electrode interruptions.

  The present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

  For example, the insulating layer sandwiched between the internal electrode layers formed using the conductive paste containing fine particles according to the present invention is not limited to the dielectric layer, and may be other insulating layers, or a semiconductor layer such as a varistor layer. There may be.

Hereinafter, although this invention is demonstrated based on a more detailed Example, this invention is not limited to these Examples.
Example 1

  As the wire 6 accommodated inside the chamber 4 shown in FIG. 1, a pure nickel wire having a cross-sectional outer diameter of 0.5 mm and a length of 35 mm was used. A power source 8 was connected to both ends of the wire 6.

Inside the chamber 4, a collecting plate 10 was disposed at a distance of 7.5 mm at the shortest distance from the wire 6. The collection plate 10 was a glass plate having a thickness of 0.7 mm. Inside the chamber 4, oxygen gas having a purity of 99.5% or more was flowed. The internal pressure of the chamber 4 was 10 ⁵ Pa.

The voltage applied to both ends of the wire 6 from the power source 8 was a DC voltage of 2.2 V, and the energization time per time was 140 seconds. During this time, the current density per unit area in the cross section of the wire 6 was 354.8 A / mm ² immediately after the start of energization, and thereafter decreased, and 66.3 A / mm ² immediately before the disconnection.

When the wire 6 was energized, it was observed that the entire wire 6 was red hot and the surface was deformed. When the wire was disconnected, the ends were rounded and smoke was observed. When the collection plate 10 was visually observed, white deposits were observed on the collection plate 10. This deposit
When taken with a transmission electron microscope, an image as shown in FIG. 2 was obtained. It was confirmed that fine particles having a side of 1 to 15 nm and a substantially cubic or cuboid shape were obtained. When the fine particles were analyzed by X-ray diffraction, peaks of nickel and nickel oxide were observed. When the particle size distribution of the obtained fine particle powder was determined by observation with a transmission electron microscope, it was confirmed that the particle size was sharp as shown in FIG.

Further, when the fine particles obtained as described above were heat-treated in a hydrogen atmosphere at 250 ° C. for 30 minutes, it was confirmed that nickel was bonded on the surface while maintaining the cubic shape. From this, it was found that a highly conductive film with suppressed oversintering can be obtained.
Example 2

In the same manner as in Example 1 except that the voltage applied to both ends of the wire 6 from the power source 8 was changed to 2.6 to 3.0 V and the energization time per one time was 2 to 60 seconds. 6 was energized. When the particle size distribution of the fine particle powder was determined by observation with a transmission electron microscope, the particle size was 2 to 20 nm as shown in FIG. It was confirmed that as the applied voltage increased, the particle size distribution expanded, and the particle size at which the frequency peaked increased. From this, it was found that the particle size of the fine particles can be controlled by changing the applied voltage.
Comparative Example 1

The wire 6 was energized in the same manner as in Example 1 except that argon gas was used as the gas flowing into the chamber 4. During energization, no smoke was observed even when red hot or disconnected. The collection plate 10 was photographed with a transmission electron microscope, but fine particles were not confirmed.
Comparative Example 2

  The wire 6 was energized in the same manner as in Example 1 except that the gas flowing inside the chamber 4 was air. Upon energization, it was observed that the entire wire 6 was red-hot, the surface of the wire was deformed, and sparks were also observed. When the collection plate 10 was photographed with an optical microscope, spherical fine particles having a diameter of 100 to 500 μm were confirmed.

2 ... Fine particle production apparatus 4 ... Chamber 6 ... Wire 8 ... Power supply 10 ... Collection plate

Claims (6)

  Fine particles having a side of 1 to 200 nm, a substantially cubic or rectangular parallelepiped shape, and composed of nickel and / or nickel oxide. An internal electrode layer comprising the fine particles according to claim 1;
And an insulating layer sandwiched between the internal electrode layers. An internal electrode layer comprising the fine particles according to claim 1;
And an electronic component having a semiconductor layer sandwiched between the internal electrode layers. A method for producing the fine particles according to claim 1,
A method for producing fine particles, wherein an electric current is passed through a wire made of nickel, and the fine particles obtained by scattering from the wire are collected near the wire.   The method for producing fine particles according to claim 4, wherein the fine particles are collected and further subjected to a reduction treatment.   The method for producing fine particles according to claim 4, wherein the collection of the fine particles is performed by a glass collecting plate.

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