JPH0940460A - Method for manufacturing titanic acid-based sintered body - Google Patents

Abstract

(57) An object of the present invention is to provide a method for producing a titanate-based sintered body having excellent material structure free from cracks and oxygen defects by eliminating residual stress and eliminating oxygen defects. SOLUTION: In a method of sintering BaTiO ₃ , SrTiO ₃ or a mixed powder thereof by hot pressing in a vacuum or an inert atmosphere, 1200 to 1300 ° C.
After sintering at the temperature of 30 ° C, press pressure is released
Performed pressureless heat treatment for holding for a predetermined time at a higher temperature,
Then, an annealing treatment is performed at a temperature of 1150 to 1350 ° C. in the air atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a titanic acid-based sintered body obtained by sintering BaTiO ₃ powder, SrTiO ₃ powder, or a mixed powder thereof, for example, a high dielectric constant on a substrate surface by a sputtering method. The present invention relates to a method for producing a titanic acid-based sintered body suitable as a target material used when forming a body thin film.

Titanic acid type sintered bodies are useful as functional ceramics in dielectric materials, thermistors, piezoelectric materials and the like. For example, (Ba _x Sr _1-x ) TiO ₃ (where 0 <x
The thin film of <1) has excellent properties as a dielectric thin film, and this thin film is manufactured by a sputtering method using a (Ba _x Sr _1-x ) TiO ₃ based sintered body as a target material.

[0003]

2. Description of the Related Art Conventionally, this target material is BaCO ₃ ,
It is manufactured by a method in which a mixed powder of SrCO ₃ and TiO ₂ is fired in the air, pulverized, and hot pressed. For example, in Japanese Unexamined Patent Publication No. 6-264230, Ba and Sr oxides or carbonates are mixed and fired, and the Ba and Sr composite oxides are pulverized to obtain Ba and Sr.
There is disclosed a method for producing a target material for producing a high dielectric thin film in which a composite oxide powder of r is produced, titanium powder or titanium oxide powder is mixed with this powder and hot pressed in a vacuum atmosphere.

However, when sintering is carried out at high temperature and high pressure by hot pressing, distortion is likely to occur inside the sintered body due to residual stress, and this distortion causes cracks in the sintered body during subsequent processing and heat treatment. There is.

Further, when hot-pressing in an inert atmosphere or vacuum, due to lack of oxygen component, oxygen defects are generated in the sintered body and the material structure of the sintered body becomes inhomogeneous, resulting in deterioration of material characteristics. Become. As a result, for example, when used as a target material for forming a dielectric thin film, the film composition becomes inhomogeneous,
There is a drawback that the film thickness tends to be non-uniform. When hot pressing in an air atmosphere to prevent the generation of oxygen defects, a mold that does not react with oxygen at high temperature and has high mechanical strength is required, and a die made of alumina is usually used. However, since alumina is difficult to process, it is difficult to produce a large-sized die.

[0006]

The present inventor has conducted research on preventing the generation of cracks and oxygen defects in the sintered body, and as a result, the residual stress is released when the heat treatment is performed after the hot pressing with the pressing pressure released. It has been found that the oxygen deficiency portion can be eliminated by further performing the annealing treatment in the air atmosphere.

The present invention has been completed on the basis of such findings, and its purpose is to solve the above problems, eliminate residual stress to suppress the occurrence of strain, and perform annealing treatment in the atmosphere. It is an object of the present invention to provide a method for producing a titanic acid-based sintered body having high density and high purity, which has a uniform material structure and does not generate cracks by eliminating the oxygen defect portion.

[0008]

A method for producing a titanic acid-based sintered body according to the present invention for achieving the above object is:
In a method of hot pressing TiO ₃ , SrTiO ₃ or a mixed powder thereof in a vacuum or an inert atmosphere and sintering, the press pressure is released after sintering at a temperature of 1200 to 1300 ° C. to 30 ° C. above the sintering temperature. The constitutional feature is that pressureless heat treatment is performed at a high temperature for a predetermined time, and then annealing is performed at a temperature of 1150 to 1350 ° C. in an air atmosphere.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A titanic acid-based sintered body is generally Ba
Using TiO ₃ powder, SrTiO ₃ powder or a mixed powder thereof (BaTiO ₃ / SrTiO ₃ powder) as a raw material, under vacuum or an inert atmosphere, the temperature is from 1200 to 130.
It is manufactured by hot pressing at 0 ° C., a pressure of 200 to 300 kg / cm ² , and a pressure condition.

According to the present invention, after the raw material powder is sintered in this hot pressing step, the pressurizing system is released and the pressing pressure is removed, and the temperature is further raised by 30 ° C. or more for a predetermined time. The first is to apply a pressureless heat treatment to hold
Condition. Since the residual stress accumulated inside the sintered body is eliminated by the heat treatment in the non-pressurized state, the occurrence of residual strain inside the sintered body can be effectively prevented. In this case, the release of the press pressure is more effective in relaxing the residual stress as the press pressure is released to a non-pressurized state close to zero. Also,
The heat treatment temperature needs to be set higher than the sintering temperature, and is set to be at least 30 ° C. higher than the sintering temperature, but it is sufficient to set the high temperature to about 40 ° C. to relax the residual stress. The holding time is appropriately determined depending on the size and shape of the sintered body, but it is usually 10 to 30 minutes.

When hot pressing is performed in a vacuum or an inert atmosphere, the sintered body is apt to have a structural defect, that is, an oxygen defect due to lack of oxygen in the system. For example, BaTiO ₃ , Sr
When TiO ₃ is hot-press-sintered in a vacuum or an inert atmosphere, BaTiO _3−x and SrTiO _3−y are contained in the material structure.
Blackish gray oxygen defect portions such as (0 <x, y <1) are generated. When a raw material obtained by adding a binder containing carbon content to the raw material powder and granulating is used, the oxygen content is more consumed because the oxygen content is consumed by the binder component.

In the present invention, in order to eliminate the oxygen defect portion, the sintered body is annealed by holding the sintered body at a temperature of 1150 to 1350 ° C. for an appropriate time in the atmosphere.
Condition. By this annealing treatment, oxygen diffuses into the internal structure of the sintered body and oxygen is replenished in the oxygen defect portion, so that a sintered body having no oxygen defect can be manufactured. If the annealing temperature is lower than 1150 ° C., the diffusion rate of oxygen is slow, so that the supplement of oxygen into the sintered body becomes insufficient. On the other hand, if the temperature exceeds 1350 ° C, the sintered body is deformed or warped.

In this case, the density of the sintered body is 90% of the theoretical density.
It is preferable to sinter in a range of ˜95%.
When the density of the sintered body is less than 90% of the theoretical density, it is necessary to set a high heating temperature during the annealing treatment in order to increase the density of the sintered body. This is because it easily occurs. Further, if the density exceeds 95% of the theoretical density, the structure of the sintered body becomes dense, and it becomes difficult for oxygen to smoothly diffuse into the inside of the sintered body during the annealing treatment, and oxygen is sufficiently supplied to the oxygen defect portion. This is because

Raw material BaTiO ₃ powder, SrTiO 3
_{3 As} powder, purity is 2N or more, average particle size is 0.5 to 2μ
Fine powder of about m 2 is used. BaTiO ₃ and SrTi
A ball mill is used to mix the O ₃ powder, ethanol is added and mixed for 12 to 24 hours, dried, and then passed through a 60-mesh sieve to obtain a mixed powder raw material.

These raw material powders are uniformly filled in a die made of graphite, set in a hot press machine, and pressure-molded at room temperature. The pressurization is carried out by pressurizing to the pressure at the time of sintering and then depressurizing, and then the system is once evacuated and then replaced with an inert gas such as argon gas and kept at a pressure of about atmospheric pressure.

Next, heating is carried out at a heating rate of 5 to 20 ° C./min to raise the temperature to a predetermined temperature of 1200 to 1300 ° C. In this case, since BaTiO ₃ has a crystal transformation in the temperature range from room temperature to 150 ° C., it is desirable to set the pressure low up to this temperature range so that the volume change proceeds smoothly. In this way, when the temperature reaches the predetermined temperature, the pressure is increased to a predetermined pressure, for example, 300 kg / cm ² , and the temperature is maintained for an appropriate period of time to perform hot press sintering.

After hot press sintering in this way,
The press pressure is released to a non-pressurized state, and in this non-pressurized state, the temperature is higher by 30 to 40 ° C. than the sintering temperature by 5 to 15
The residual stress accumulated inside the sintered body is released by holding it for a minute. As a result, strain energy is removed, so that the generation of strain inside the sintered body is suppressed.

The sintered body obtained in the above process shows a blackish gray color due to oxygen defects and has a black appearance.
The cross section is gray. The present invention eliminates oxygen defects by subjecting this sintered body to an annealing treatment to replenish the oxygen defect portions with oxygen. The annealing treatment is carried out by a method of heating to a temperature of 1150 to 1350 ° C. in an electric furnace and performing a heat treatment in an air atmosphere. Oxygen deficiency portions disappear due to diffusion and supplementation of oxygen to the oxygen deficiency portions by the treatment. be able to.

The titanic acid-based sintered body thus obtained has excellent material characteristics such that cracks are not generated due to residual stress and oxygen defects are not present in the internal structure. Therefore, it is extremely useful as a functional titanate-based ceramic including a target material used when a high dielectric thin film is formed on the surface of a substrate by, for example, a sputtering method.

[0020]

EXAMPLES Examples of the present invention will be specifically described below in comparison with comparative examples. However, the scope of the invention is not limited to these examples.

Examples 1 to 8 Production of Sintered Body: BaTiO ₃ powder [manufactured by Kyoritsu Kiln Co., Ltd., average particle size 1.0 μm, purity 2N], SrTi as raw materials
O ₃ powder [Kyoritsu Kiln Co., Ltd., average particle size 1.7 μm, purity
2N], mixed powders were prepared by putting these powders in a ball mill, adding methanol for 12 to 24 hours to perform wet mixing, drying at 150 ° C., and then passing through a 60 mesh sieve. These raw material powders were uniformly filled in a graphite die, set in a hot press machine, pressurized at room temperature to the pressure for sintering and then depressurized, and the system was evacuated and then argon gas was fed. And maintained in an argon atmosphere at 700 Torr. Then, after raising the temperature to a predetermined temperature at a temperature rising rate of 10 ° C./min, the press pressure was raised to a predetermined pressure to perform hot press sintering.

Pressureless heat treatment and annealing treatment:
This sintered body was heat-treated at a temperature 40 ° C. higher than the sintering temperature for 10 minutes in a state where the pressurizing system of the hot press device was released and the press pressure was zero, and the residual stress accumulated inside the sintered body Was released. Then, the sintered body was transferred to an electric furnace in an air atmosphere, heated at a predetermined temperature for a predetermined time and annealed to produce a titanate-based sintered body.

The hot press sintering conditions of the thus obtained sintered body and the conditions of the heat treatment and the annealing treatment in the non-pressurized state are summarized in Table 1. Table 2 shows the state of cracks generated when the sintered body was processed and adhered to a graphite plate with a resin, the state of oxygen defects by visual observation, and the density of the sintered body.

Comparative Examples 1 to 8 For comparison, sintered bodies were produced without heat treatment and pressureless annealing. Table 1 shows the sintering conditions at this time, and Table 2 also shows the state of crack generation and oxygen defects.

[0025]

[Table 1]

[0026]

[Table 2]

From the results shown in Tables 1 and 2, it is possible to produce a high-density titanic acid-based sintered body in which crack generation is reduced and oxygen defects are reduced by performing the pressureless heat treatment and the annealing treatment of the present invention. I understand.

[0028]

As described above, according to the method for producing a titanate-based sintered body of the present invention, the residual stress inside the sintered body is obtained by subjecting the sintered body obtained by hot pressing to heat treatment without pressure. Are effectively released, so that the occurrence of cracks during product processing can be significantly reduced. Further, since oxygen is diffused and supplemented to the oxygen defect portion generated in the sintered body structure by the annealing treatment of heating in the air atmosphere, defects in the material structure are removed, and a high density sintered body having a uniform structure can be manufactured. . Therefore, it is extremely useful as a method for producing a functional ceramic including a target material for forming a high dielectric thin film on the surface of a base material by a sputtering method.

Claims (1)

[Claims] 1. A method of hot pressing BaTiO ₃ , SrTiO ₃ or a mixed powder thereof in a vacuum or an inert atmosphere to sinter at 1200 to 1300 ° C.
After sintering at the temperature of
A method for producing a titanic acid-based sintered body, which comprises performing a pressureless heat treatment of holding at a temperature higher than ℃ for a predetermined time and then performing an annealing treatment at a temperature of 1150 to 1350 ℃ in an air atmosphere.