JPH04219359A - Electrically conductive zinc oxide sintered compact - Google Patents

Abstract

PURPOSE:To obtain the title sintered compact of improved electrical conductivity and transparency by calcining mixed powder comprised of ZnO and another oxide of an element with >=3 positive valency to effect coming to each specified resistivity and density. CONSTITUTION:First, a mixed powder with an average particle size of >=1mum is prepared by mixing (A) ZnO powder and (B) another oxide of an element with >=3 positive valency such as Al2O3 followed by heat treatment at 800-1300 deg.C. The mixed powder is then formed and sintered at >=1200 deg.C (pref. 1200-1450 deg.C), thus giving the objective sintered compact having the following characteristics:(1) containing 0.1-20atm%, based on the Zn, of the added element; (2) resistivity: <=10OMEGA.cm; (3) density: 3.4-4.5g/cm<3>. A transparent, electrically conductive ZnO thin film can be obtained using the present sintered compact as sputtering target.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive zinc oxide sintered body, a method for manufacturing the same, and uses thereof. From the conductive zinc oxide sintered body, a transparent conductive zinc oxide thin film having excellent transparency and conductivity can be formed by a sputtering method, particularly a DC magnetron sputtering method. In recent years, demand for these zinc oxide thin films has increased as transparent electrodes for solar cells and display devices, and conductive coatings for antistatic purposes.

0002

[Prior Art] A transparent conductive thin film of conductive metal oxide is
It is mainly formed by sputtering of metal oxides, and the metal oxides used here include indium oxide (ITO) doped with tin as a different element, and tin oxide (ITO) doped with antimony as a different element. ZAO) is used industrially.

[0003] However, although ITO has high transparency and can be formed into a thin film with low resistance, it is economically difficult because indium is expensive, and furthermore, it is chemically unstable, which limits its applicability. there were. Furthermore, although TAO is inexpensive and relatively chemically stable, it cannot be said to be a sufficient material because only a thin film with high resistance can be obtained.

Recently, IT has been developed by sputtering zinc oxide doped with a different element such as aluminum.
It has been reported that a transparent conductive thin film with a resistance as low as O and excellent transparency can be obtained (J. Appl. Phys.
, 55, p. 1029 (1988)).

Zinc oxide is a transparent conductive material that is inexpensive, chemically stable, and has excellent transparency and conductivity. However, the zinc oxide sintered bodies containing different elements that have been used for sputtering so far have a high resistivity of several kiloΩcm or more, so the applicable sputtering method is limited to high-frequency sputtering, and industrial DC sputtering could not be used.

[0006]

[Problems to be Solved by the Invention] High-frequency sputtering has a problem in that when the substrate temperature rises, the conductivity of the resulting zinc oxide transparent conductive film decreases. When forming a film on a target, the amount of power that can be input is extremely low, and the discharge is extremely unstable. If the power is applied forcibly, the target may crack or peel off from the backing plate. Therefore, a sufficient transparent conductive film could not be obtained by the conventional methods.

[0007]

[Means for Solving the Problems] As a result of intensive studies on conductive zinc oxide sintered bodies, the present inventors found that the average particle size was 1 μm.
By sintering a mixture of the above zinc oxide powder and an oxide of an element having a valence of trivalent or higher at a temperature of 1200°C or higher, the resistivity is 10 Ωcm or less and the sintered body density is 3.4 g/cm. It is possible to obtain a conductive zinc oxide sintered body with a thickness of cm3 to 4.5 g/cm3, and furthermore, by using this sintered body as a sputtering turbot, it is possible to obtain a conductive zinc oxide sintered body with excellent transparency and conductivity using the DC sputtering method. The present invention was completed by discovering that a transparent conductive zinc oxide thin film can be obtained.

[0008]

[Operation] The present invention will be explained in detail below.

[0009] Resistivity is 10 Ωcm or less, sintered body density is 3
．． The sintered body of the present invention having an average particle size of 4 g/cm3 to 4.5 g/cm3 is produced by mixing a mixture of zinc oxide powder with an average particle size of 1 μm or more and an oxide of an element having a valence of trivalent or higher at 1200 g/cm3 to 4.5 g/cm3.
Obtained by sintering at temperatures above ℃. Specifically, in order to make the resistivity of the sintered body 10 Ωcm or less, an element having a valence of positive trivalent or higher is dissolved in zinc oxide.
In order to sinter at a temperature of 00°C or higher and further control the sintered body density to 3.4 g/cm3 to 4.5 g/cm3 even at that sintering temperature, an average material that is relatively inert to sintering is used. A sintered body having the above-mentioned density is obtained by using a mixed powder of zinc oxide having a particle size of 1 μm or more and an oxide of an element having a valence of trivalent or higher.

[0010] A method for reducing the resistivity of the zinc oxide sintered body to 10 Ωcm or less will be explained.

It is essential that the resistivity of the sintered body of the present invention is 10 Ωcm or less. It has a resistivity of 10Ωcm
This is because if the sintered body exceeds 100%, it becomes extremely difficult to stably form a zinc oxide thin film with excellent transparency and conductivity by industrial direct current sputtering, as described above. Originally, a sintered body of zinc oxide has high resistivity and is close to an insulator, but conductivity can be imparted by dissolving in zinc oxide an element having a valence of trivalent or higher. Therefore, in the present invention, a method has been discovered in which zinc oxide is sintered at a temperature of 1200° C. or higher, preferably 1200° C. to 1450° C., in which an element having a valence of trivalent or higher is dissolved in solid solution.

[0012] In the present invention, the elements having a valence of 3 or more that are added to impart conductivity include 3
Sc, Y of group A, B, Al, Ga, In, Tl of group 3B
, 4A group Ti, Zr, Hf, Th, 4B group C, Si
, Ge, Sn, Pb, V of group 5A, Nb, Ta, Pa,
5B group As, Sb, Bi, 6A group Cr, Mo, W,
U, 6B group Se, Te, Po, 7A group Mn, Tc,
Re, group 8 Fe, Co, Ni, Ru, Rh, Pd, O
S, Ir, Pt, and elements of the lanthanide and actinide series are applicable.

[0013] Further, the content of the additional element contained in the sintered body of the present invention is 0.1 atm% to 20 atm% with respect to zinc.
%, particularly preferably 0.5 atm% to 5 atm%.

Next, the density of the zinc oxide sintered body was set to 3.4 g/
A method for controlling the amount of g/cm3 to 4.5 g/cm3 will be explained.

The sintered body density of the sintered body of the present invention is 3.4 g/
cm3 to 4.5 g/cm3. Sintered body density is 4.5
If it exceeds g/cm3, a thin film with excellent transparency and conductivity can be obtained by sputtering in a low gas pressure region, but in a high gas pressure region, the obtained thin film is easily oxidized and a high resistance film is likely to be obtained. . In addition, the sintered body density is 3.4
If it is less than g/cm3, the reduction of the target surface during sputtering will be significant, the obtained thin film will have high resistance and be colored, and furthermore, the mechanical strength of the target will be low and it will become brittle, which is not preferable.

Zinc oxide is easy to sinter, and when zinc oxide alone is sintered at a sintering temperature of about 900°C, the theoretical density is 5.
．． It reaches close to 6g/cm3. Generally, the density of the sintered body can be controlled by lowering the sintering temperature. However, as mentioned earlier, lowering the sintering temperature suppresses the solid solution of different elements into zinc oxide, making it impossible to obtain a zinc oxide sintered body with a low resistance of 10 Ωcm or less. In this case, it is not possible to control the density of the sintered body by lowering the sintering temperature. Therefore, in the present invention, by using a powder that is relatively inert to sintering and has an average particle size of 1 μm or more, preferably 1 μm to 5 μm, the temperature at 1200° C. allows solid solution of different elements in zinc oxide. As mentioned above, it has been found that the density of the sintered body preferably falls within the range of 3.4 g/cm 3 to 4.5 g/cm 3 even at a temperature of 1200° C. to 1450° C.

Further, the raw material powder used in the present invention will be explained.

The raw material powder used in the present invention has an average particle size of 1
It is a mixture of zinc oxide powder of μm or more and a compound of an element having a valence of trivalent or higher.

Compounds of elements having a valence of trivalent or higher can be used without limitation as long as they become oxides by thermal decomposition, and include the oxides and hydroxides of the various elements listed above. , various salts, etc. can be used.

The method of mixing zinc oxide and the compound of an element having a valence of trivalent or higher is not particularly limited, and the mixing may be carried out in a dry or wet manner using a ball mill, a vibration mill, or the like. Alternatively, various salts of different elements may be dissolved in a suitable solvent such as water or alcohol, and mixed with zinc oxide powder in the form of a slurry. Furthermore, in order to uniformly disperse the different elements, a suitable precipitant is added to the mixed solution containing the zinc component and the different element components to form a coprecipitate, which is then heat treated to produce a mixed powder. Good too.

[0021] The average particle size of the raw material powder used in the present invention is 1μ.
m or more, preferably 1 μm to 5 μm. Powder with an average particle size of less than 1 μm is active in sintering, and sintering with it will only yield a sintered body with a density of 4.5 g/cm3 or more, which is undesirable. is 5
Powders exceeding .mu.m are not preferred because their moldability is significantly reduced.

A powder having an average particle size of 1 μm or more can be obtained by heat-treating a mixture of zinc oxide powder and an oxide powder of an element having a valence of trivalent or higher. For heat treatment, the temperature can be selected depending on the target particle size.
The temperature may be 800°C or higher and 1300°C or lower.

The sintered body of the present invention has the above average grain size of 1 μm.
It is obtained by molding raw material powder of m or more and sintering at a temperature of 1200° C. or more.

[0024] The molding method may be selected from a molding method suitable for the desired shape, and examples thereof include a mold press method and a cast molding method, but are not particularly limited.

Next, the molded powder is sintered, and the sintering temperature in the present invention is preferably 1200°C or higher, particularly preferably 1200°C to 1450°C. Sintering temperature is 1200℃
If it is less than 1, the solid solution of the element having a valence of trivalent or higher into zinc oxide will be insufficient, and a sintered body with a resistance of 10 Ωcm or less will not be obtained, which is not preferable.

The sintering time is 1 to several tens of hours, preferably 2 to 10 hours. If this time is shorter than 1 hour, sintering or solid solution of different elements in zinc oxide will be insufficient, and if it is longer than necessary, the density, conductivity, etc. will not change, which is economically unfavorable.

[0027] Also, the temperature increase rate during sintering is 1 to 300°C/
time, preferably 50 to 200°C/hour. If this temperature increase rate is faster than necessary, sintering will be insufficient and cracks will occur during sintering, which is not preferable. On the other hand, if the temperature increase rate is longer than necessary, it is economically unfavorable.

The sintering atmosphere of the present invention is not particularly limited, and the sintering may be carried out in the air or the like.

A conductive zinc oxide sintered body can be obtained by the method described above. The sintered body thus obtained can be used as a sputtering target.

[0030]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto.

Example 1 Zinc oxide powder and aluminum oxide powder were mixed together in a ball mill.
After mixing for 5 hours, the mixed powder was heat treated at 1000°C,
A powder with an average particle size of 3 μm was obtained. This powder has a diameter of 3
The material was placed in an inch mold, molded at a pressure of 1 t/cm2, and then sintered in air at 1400°C. The obtained sintered body is
It exhibited a density of 4.0 g/cm3 and a resistivity of 1.2 mΩcm. The density of the sintered body was determined by dividing the mass of the sintered body by the volume calculated from the diameter and thickness of the sintered body, and the resistivity was determined by the usual DC four-probe method.

Using this sintered body as a sputtering target, direct current sputtering was performed in a pure argon atmosphere, a sputtering pressure of 1.0 Pa, an input power of 4 W/cm2,
Film formation was performed at a substrate temperature of 150°C.

The obtained thin film had a thickness of 20,000 nm.
The resistivity is 0.8mΩcm and the light transmittance is 92%.
Met.

Example 2 Zinc oxide powder and aluminum oxide powder were mixed together in a ball mill.
After mixing for 5 hours, the mixed powder was heat treated at 1200°C,
A powder with an average particle size of 4.5 μm was obtained. This powder was molded in the same manner as in Example 1 and sintered at 1400° C. in air. The density of the obtained sintered body was 3.8 g/cm3, and the resistivity was 1.5 mΩcm.

This sintered body was sputtered in the same manner as in Example 1.

The obtained thin film had a thickness of 20,000 nm.
The resistivity is 1.2 mΩcm and the light transmittance is 90%.
Met.

Example 3 Zinc oxide powder and indium oxide powder were mixed in a ball mill for 15 minutes.
After mixing for a period of time, the mixed powder was heat treated at 1000° C. to obtain powder with an average particle size of 2.5 μm. This powder was used in Example 1.
It was molded in the same manner as above and sintered at 1400°C in air. The density of the obtained sintered body was 4.2 g/cm3, and the resistivity was 1.0 mΩcm.

This sintered body was sputtered in the same manner as in Example 1.

The obtained thin film had a thickness of 20,000 nm.
The resistivity is 0.8mΩcm and the light transmittance is 81%.
Met.

Comparative Example 1 Zinc oxide powder and aluminum oxide powder were mixed in a ball mill.
The mixture was mixed for 5 hours to obtain a mixed powder with an average particle size of 0.8 μm. The obtained mixed powder was molded in the same manner as in Example 1, and then sintered at 1000°C. The sintered body thus obtained had a density of 4.1 g/cm 3 and a resistivity of 2 kΩcm.

Using the sintered body as a sputtering target, DC sputtering was carried out under the same conditions as in Example 1, but stable glow discharge could not be obtained. The thin film obtained by intermittent sputtering was colored black, had a thickness of 20,000 nm, and had a resistivity that varied from 2 to 25 mΩcm depending on the location. or,
The light transmittance was also as low as 75%.

[0042]

Effects of the Invention The conductive zinc oxide sintered body of the present invention can be used as a target for DC sputtering, and the zinc oxide thin film obtained by sputtering has excellent conductivity and transparency.

Claims (3)

[Claims] Claim 1: Contains an element with a valence of trivalent or higher, has a resistivity of 10 Ωcm or less, and has a sintered body density of 3.4 g
/cm3 to 4.5g/cm3. 2. A mixed powder consisting of zinc oxide and an oxide of an element having a valence of trivalent or higher and having an average particle size of 1 μm or more is sintered at a temperature of 1200° C. or higher. The method for producing a conductive zinc oxide sintered body according to claim 1. 3. A sputtering target comprising the conductive zinc oxide sintered body according to claim 1.