JPH0729770B2 - Oxide powder and method for producing the same - Google Patents

Description

The present invention relates to indium oxide powder or indium oxide / tin oxide (hereinafter referred to as ITO) powder and a method for producing the same.

[Prior Art] In recent years, there has been a rapid increase in demand for ITO thin films as transparent conductive films used for transparent electrodes of solar cells and liquid crystal displays, touch panels and the like. The method for forming such an ITO thin film is a method of applying ITO fine particles to a base material, a method of applying an ITO precursor to a base material and then thermally decomposing it, or sputtering an ITO alloy target or an ITO sintered body target. Although a method of forming an ITO film on the material surface is known, at present, the sputtering method of an ITO sintered body is the most common.

The indium oxide and the ITO powder according to the present invention have extremely excellent performance as a raw material for a sputtering target (ITO sintered body) used when forming a transparent conductive film by such a sputtering method.

Conventionally, indium oxide, tin oxide powder or ITO powder is a method of thermally dehydrating or thermally decomposing each metal hydroxide, oxide hydrate, organic metal salt or inorganic metal salt powder, or each sol or gel. Alternatively, a precipitant is added to a mixed aqueous solution of an indium salt and a tin salt to generate a precipitate (JP-A-62-62).
No. 7627, JP-A-60-186416), or a method of thermally decomposing a product formed by hydrolysis (JP-A-58-36925) is known. The method of thermally decomposing a mixed organic acid salt obtained from an aqueous solution of a mixed organic acid of indium and tin, which the present inventors previously proposed (Japanese Patent Laid-Open No. 63-195101), is also a method of providing highly pure ITO powder. is there.

Usually, the ITO sintered body is manufactured by pressure-molding and sintering the mixed powder of indium oxide and tin oxide (ITO powder) obtained by the above method. It was very difficult to obtain a dense sintered body.

Most of the ITO sintered bodies using conventional powders are low density sintered bodies having a sintered density of about 65% of the theoretical density (up to 4.6 g / cm ³ ), and also have high electric resistance.

The sintered density of the ITO sintered body is about 7.1 g / cm ³ at a theoretical density of 100%.
Is.

Such a low-density ITO sintered body is easily cracked, and its electrical conductivity and thermal conductivity are low, so when using this as a target for sputtering film formation, the power that can be input is significantly reduced, so the film formation It has the drawbacks of low speed and unstable discharge state. Furthermore, in a low density ITO sintered body, a reducing substance (black substance) is generated on the surface of the sintered body during sputtering, and this substance is mixed with the transparent conductive film generated on the surface of the base material and causes deterioration of the film quality. Every time a reducing substance was generated on the body surface, the operation had to be stopped and removed. And this has been a serious obstacle to the continuous operation of sputtering.

Therefore, in order to solve such problems, high density ITO
Several methods for producing or treating raw material ITO powder that enables production of a sintered body have been proposed. For example, there is a method in which at least indium oxide powder out of indium oxide or tin oxide powder is calcined to form indium oxide or tin oxide having an average particle size of 3 to 6 μm, which is used (Japanese Patent Laid-Open No. 62-217).
51).

However, it is possible to obtain with such a relatively large particle size raw material.
The density of the ITO sintered body is at most 5 g / cm ³ , as can be seen from the examples described in the publication, which is not a sufficiently high density. Further, a method of using a coprecipitated ITO powder containing a precipitating agent as a raw material for a sintered body has been proposed (Japanese Patent Laid-Open No. 62-12009). However, the sintered density of the sintered body obtained by this method is
In 70% (5g / cm ³⁾ degree, not sufficiently dense.

[Problems to be Solved by the Invention] As described above, the indium oxide powder or the indium oxide powder capable of producing a high-density sintered body by an industrial method has been used.
Currently, no ITO powder has been obtained. The object of the present invention is 75% or more of the theoretical density, that is, the sintered density of 5.3 g / cm ³
The object is to provide an indium oxide powder or an ITO powder capable of producing a high density ITO sintered body having a sintered density of 85% or more of the theoretical density, that is, a sintered density of 6 g / cm ³ or more, and a production method thereof.

[Means for Solving Problems] The inventors of the present invention have made a raw material I for producing a high density ITO sintered body.
As a result of extensive studies on TO powder, the primary particle size is 1 μm
In the following fine ITO powder having a BET surface area of 15 m ² / g or more and a specific surface area determined from the particle size distribution of 2 m ² / g or more and high dispersibility, the sintered density of 75% or more of the theoretical density, that is, 5.3 Sintered density of g / cm ³ or more, more than 85% of theoretical density, that is, high density sintered body of 6 g / cm ³ or more can be obtained, and such powder has a primary particle size of 1 μm. The inventors have found that the following ITO powder can be obtained by pulverizing by using a vibrating pulverizer satisfying the condition that the diameter of the pulverizing container is less than 10 times the vibration amplitude, and have completed the present invention.

In the case of ITO powder in the powder of the present invention, the ratio of indium oxide to tin oxide in the powder is indium oxide / weight ratio.
Tin oxide = 98/2 to 80/20, particularly preferably 92/8 to 85/15. When the content of tin oxide is smaller than 2% or larger than 20%, a sintered body made of this cannot have a high conductivity. The primary particle diameter of the indium oxide powder or ITO powder of the present invention must be 1 μm or less, preferably 1 μm to 0.01 μm, and particularly preferably 0.5 μm to 0.03 μm. If the primary particle size is greater than 1, the sinterability does not increase even if the dispersibility is high, while the primary particle size is 0.01μ.
If it is smaller than m, it becomes extremely difficult to suppress aggregation,
It does not easily become a powder with good sinterability.

Although powders according to the conventional technique which satisfy the above-mentioned primary particle size can be obtained, they are aggregated and are not powders having good sinterability. The indium oxide powder and the ITO powder of the present invention are characterized by having such a primary particle size and yet being highly dispersed, that is, not agglomerated. The common means of assessing the dispersibility of the powder, BET surface area, there is a particle size distribution, powder of the present invention the specific surface area determined from the BET surface area of 15 m ² / g or more, i.e. 15m ² / g~50m ² / g, and a specific surface area as determined from the particle size distribution is 2m ² / g or more words 2m ² / g~5m ²
/ g, more preferably 3 m ² / g or more. BET surface area is 1
The powder of less than 5 m ² / g is an agglomerated powder and has poor sinterability.
On the other hand, a powder having a BET surface area larger than necessary is porous or has a rough surface, and on the contrary, the sinterability is deteriorated. Therefore, the BET surface area is preferably 50 m ² / g or less.

Up to now, no ITO powder has been proposed that satisfies all the above-mentioned conditions, and if any of these conditions is not satisfied, the sinterability of the powder is insufficient, which is not preferable.

The method for producing an ITO powder satisfying all of the above conditions is a method for producing an ITO powder having a primary particle size of 1 μm or less and then mechanically crushing (pulverizing) it under certain conditions.
As a method of improving the sinterability of the ceramic powder, it is generally known to mechanically pulverize the powder, but particularly in the case of indium oxide and ITO powder, sinterability is obtained by any pulverization method. It does not improve.

As a mechanical pulverizing method of the oxide powder, there are generally a ball mill, a dyno mill, a sand mill, a homogenizer, a vibrating mill, and the like, but as a pulverizing method of the powder capable of obtaining the effects of the present invention, a pulverizer having a high pulverizing efficiency, For example, it is necessary to grind using a vibration type grinder such as a vibration mill.
It is not possible to obtain, with a low pulverization efficiency, for example, a rotary ball mill that satisfies the conditions of the present invention.

The most important point in the pulverization using the vibration pulverizer in the present invention is that the diameter of the pulverization container depends on the vibration amplitude of the vibration pulverizer.
Use less than 10 times. When the diameter of the crushing container becomes larger than 10 times the amplitude of the vibration crusher, not only the movement of the crushing medium inside the crushing container becomes irregular, but also
Most of the grinding media only make small vibrations or slides in the lower part of the grinding container during grinding, which significantly reduces the grinding efficiency. Such a phenomenon is particularly remarkable when the grinding medium is small, for example, when a grinding medium having a diameter of about 2 mm used for fine grinding is used. Further, if the powder is pulverized in such a state, the powder becomes amorphous rather than dispersed, that is, the crystal breaks selectively. Therefore, the pulverization treatment under such conditions rather reduces the sinterability of the powder.

On the other hand, if the diameter of the crushing container is less than 10 times the amplitude of the vibration crusher and the crushing process is performed, the movement of the crushing medium inside the crushing container becomes extremely uniform, and the crushing of the powder agglomerates efficiently Will be resolved. In addition, such a crushing treatment also suppresses the crystal destruction of the powder due to the crushing. In addition, since abrasion of the grinding medium is remarkably suppressed by such efficient grinding, it is possible to maintain the processed powder in high purity.

Further, the grinding medium used for grinding is important, and it is preferable to use one having a high specific gravity from the viewpoint of grinding efficiency. In addition, since the mixing of impurities into the powder during such a pulverizing treatment brings about a decrease in the conductivity of the ITO sintered body using the same, the pulverizing medium used in the present invention has a high specific gravity and is resistant to abrasion. It is preferable to use excellent ones. As a dispersion medium having a high specific gravity and excellent abrasion resistance, for example, zirconia beads, hard carbon coated beads, diamond coated beads and the like are excellent. In particular, even if the hard carbon-coated beads and the diamond-coated beads are worn, no problem occurs because the impurity carbon is removed as carbon dioxide at the sintering temperature of the ITO powder. On the other hand, alumina beads and glass beads pose a problem of impurities due to abrasion, and resin beads are too light to obtain a crushing effect. The size of the grinding medium used in the present invention is preferably 5 mm or less, and particularly preferably 2 mm or less, which enables fine grinding. Further, in order to improve the pulverization efficiency and the dispersibility of the powder, it is preferable to add a liquid to the powder to be pulverized to form a slurry state. As the liquid to be added here, it is possible to use water and various organic solvents, but it is particularly preferable to use water in terms of abrasion resistance of the dispersion medium. It is also effective to add various dispersants to the slurry. The amount of water added to form the above slurry has a viscosity of 50 cps to 500 cps from the viewpoint of grinding efficiency.
It is preferable to add it in the range of 0 cps. If the viscosity of this slurry is higher or lower, the pulverization efficiency will decrease. The amount of water added to prepare such a slurry depends on the properties such as the particle size of the powder to be treated and the grinding medium used for grinding, but generally powder / water = 80/20
The range is up to 10/90. The crushing time is about 1 hour to 100 hours, and particularly preferably 5 hours to 30 hours.

Furthermore, the ITO powder of the present invention is obtained by pulverizing the product obtained by co-precipitating the solution containing indium and tin used as raw materials and calcining it to obtain an oxide by the above-mentioned method. It has a uniform composition and thus forms a uniform film when sintered and used as a target. The above method may be the general method described above, and the calcination is performed at 300 to 800 ° C. By performing the above-mentioned pulverization treatment, the ITO powder becomes highly dispersed, and the ITO powder satisfying the conditions defined in the present invention can be obtained. That is, the primary particle diameter is 1 μm or less, the BET surface area is 15 m ² / g or more, and the specific surface area obtained from the particle size distribution is 2 m ² / g or more.

[Advantages of the Invention] When the ITO powder of the present invention is used as a raw material for a sintered body, the pores inside the sintered body are reduced during sintering, and the sintered body has a large sintering shrinkage, that is, a sintered density of 5.3 g / cm ³ Above, most are sintered density 6g / cm ³
The above sintered body can be formed. Sintered particles obtained from conventional ITO powder have an irregular shape because the sintering progresses unevenly in the parts that are not agglomerated in the secondary particles of the ITO powder and in the parts that are not agglomerated. Although it has many pores between the particles, the sintered body of the ITO powder of the present invention is considered to be dense because densely packed sintered particles are formed because the sintering proceeds uniformly. .

When such a high density ITO sintered body is used as a target, the obtained transparent conductive film also has extremely high quality, and therefore, extremely excellent performance can be expected as a sintered body raw material powder for a sputtering target.

In particular, since co-precipitated ITO has a uniform distribution of tin in the sintered body, a uniform transparent conductive film can be obtained in a wide range.

[Examples] Hereinafter, the present invention will be described based on Examples, but the present invention is not limited thereto.

Example 1 An indium / tin mixed acetic acid solution containing indium / tin at a ratio of 90/10 was concentrated to obtain an indium / tin mixed acetic acid salt, and the acetic acid salt was thermally decomposed to prepare an ITO powder. Water was added to this powder to make a 50% slurry, which was then ground for 20 hours in a vibration mill (vibration amplitude 10 mm, grinding container diameter 50 mm) using hard carbon-coated metal beads having a diameter of 2 mm as a grinding medium.
The powder after treatment has a primary particle size of about 0.3 μm, a BET surface area of 17 m ² / g, and a specific surface area determined from a particle size distribution of 3.5 m ² / g by electron microscopic observation. All the conditions in paragraph 1 were satisfied.

The powder was pressure-molded with a mold to obtain a 3.7 g / cm ³ molded body, which was then sintered at 1400 ° C. in atmospheric air. The temperature rising rate in sintering was 100 ° C./hour, the temperature holding rate was 1400 ° C. for 10 hours, and the temperature lowering rate was 100 ° C./hour. Under these sintering conditions, a sintered body having a sintered density of 5.7 g / cm ³ and a specific resistance of 3 × 10 ⁻⁴ Ω · cm was obtained.

FIG. 1 shows a scanning electron micrograph (× 2000) showing the grain structure on the surface of the sintered body.

Example 2 The sintered body obtained in Example 1 was used to form a film by DC magnetron sputtering (condition is input power: 4 w /
cm ² , pressure: 0.6 Pa (5 × 10 ^-3 torr), substrate temperature: 350 ° C)
As a result, as shown in Table 1, a transparent conductive film having an extremely low resistance was obtained.

Example 3 Indium acetate and tin acetate were pyrolyzed to prepare indium oxide and tin oxide, respectively, and then mixed so that the indium oxide / tin oxide ratio was 90/10. Thereafter, a sintered body was prepared under the same conditions as in Example 1 and had a sintered density of 5.4 g / c.
A sintered body having m ³ and a specific resistance of 9 × 10 ⁻⁴ Ω · cm was obtained.

The primary particle size of the mixed powder observed by an electron microscope is 0.3μ.
m, BET surface area was 17 m ² / g, and the specific surface area determined from the particle size distribution was 3.5 m ² / g.

Example 4 The sintered body obtained in Example 3 was used to form a film by DC magnetron sputtering (conditions are the same as in Example 2). As a result, as shown in Table 1, it was extremely similar to Example 2. A transparent conductive film having low resistance was obtained.

Comparative Example 1 Commercially available indium oxide powder and tin oxide powder (reagent) 9
After mixing so as to be 0:10, the mixture was molded and sintered under the same conditions as in Example 1. When sintered, the sintered density was 4.7 g / cm ³ , and the specific resistance was 2 × 10 ^−3.
A Ω · cm sintered body was obtained.

The primary particle diameter of the mixed powder observed by an electron microscope is 0.05μ.
Although m satisfies the condition of the present invention, the specific surface area determined from the particle size distribution was 2 m ² / g and the BET surface area was 8 m ² / g.

Comparative Example 2 Using the sintered body obtained in Comparative Example 1, a film was formed by DC magnetron sputtering under the same conditions as in Example 2. Table 1 shows the specific resistance of the formed film. As shown in Table 1, a transparent conductive film having a low resistance as in Examples was not obtained.

Table 1 Comparative resistance (× 10 ⁻⁴ Ω · cm) Example 2 2.1 Example 4 2.2 Comparative example 3 3.5

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph (2000 times) as a substitute for a drawing, which shows the particle structure of the surface of the sintered body obtained in Example 1.

Claims (3)

[Claims] 1. A primary particle size of 1 μm or less and a BET surface area of 15 m ² /
An indium oxide powder and / or an indium oxide / tin oxide powder satisfying all the conditions that the specific surface area determined from the particle size distribution is 2 m ² / g or more. 2. The powder according to claim 1, wherein the indium oxide / tin oxide powder is prepared by a coprecipitation method. 3. Indium oxide having a primary particle size of 1 μm or less
A method for producing indium oxide or indium oxide / tin oxide powder, which comprises mechanically crushing tin oxide powder or indium oxide powder using a vibration type crusher having a crushing container diameter of less than 10 times the vibration amplitude.