JP2650293B2 - Manufacturing method of ceramic superconductor paste - Google Patents

Description

The present invention relates to a method for producing a ceramic high-temperature superconductor paste that is dense, has high adhesive strength to ceramics, and has excellent environmental stability.

To configure a fine superconductor wiring circuit that exhibits superconductivity at a high critical temperature on the surface of a ceramic substrate used for a substrate for a semiconductor integrated circuit, a substrate for an electronic circuit (including a hybrid IC substrate), and to attach various components. In addition, it is necessary to form a wiring circuit conductor having a high adhesive strength to a ceramic substrate, a dense and smooth surface, and excellent in plating and metal deposition properties and various environmental stability.

[Conventional technology and its problems]

As a method of forming such a superconductor wiring circuit conductor, conventionally, a mixed powder composed of barium carbonate, yttrium oxide, copper oxide or a mixed powder composed of barium oxalate, yttrium oxalate, copper oxalate as it is, or glass There is a thick film method using a thick film paste mixed with an organic binder together with powder. In general, in the conventional thick film method, noble metal powders such as silver, palladium, and gold, base metal powders such as copper and nickel, or mixed powders and alloy powders of these materials are formed on a ceramic substrate, a glass substrate, or a metal substrate coated with them. A thick film paste obtained by mixing the powder with an organic binder or a solvent is printed by a method such as screen printing or the like to form a wiring circuit and then fired.

[Problems to be solved by the invention]

However, recently, the performance and miniaturization of electronic devices have been remarkably improved, and in order to realize high-density mounting, it is necessary to extremely miniaturize a wiring circuit body. Another important problem is how to suppress the loss caused by the resistance of the circuit conductor. Therefore, expectations for lowering the resistance of circuit conductors are very high.

As a material suitable for such a demand, a superconductor wiring circuit board using a superconductor substance has been considered. The superconductor material is a material having a so-called superconductor critical temperature, in which the electrical resistance becomes zero when the temperature falls below a specific temperature. Examples of the ceramic superconductor material include lanthanum-barium-copper oxide and lanthanum-strontium-copper. Oxides (critical temperature 30-40K), yttrium-barium-copper oxide, yttrium-strontium-copper oxide, holmium-barium-copper oxide, holmium-strontium-copper oxide (critical temperature; 80-104K) Such alkaline earth elements-yttrium and / or lanthanide elements-copper oxide are well known. If these superconductor materials are used as wiring circuit conductors, it is possible to solve various problems caused by signal current loss due to electric resistance and heat generation, as well as miniaturization of the wiring circuit conductor, which is currently a problem. .

In order to form such a superconductor wiring circuit on a substrate, as described above, a superconductor raw powder or a superconductor substance powder and an organic binder are added together with a glass powder to a substrate surface of a ceramic or the like, or no glass powder is added. A method of printing by screen printing or the like using a thick film paste mixed with the above to form a wiring circuit pattern and baking it is conceivable.
Ceramic superconductor raw material powders include carbonates of alkaline earth metals such as barium and strontium, or oxides of yttrium oxalate or lanthanide elements, or mixed powders containing oxalate and copper oxide or copper oxalate as constituents. Is used. As the superconductor substance powder, a powder obtained by firing the above-mentioned raw material powder and then re-pulverized is used.
The superconductor wiring circuit is formed by printing and baking the above powder as a thick film paste. However, in such a method, various unpredictable problems occur in the superconductor wiring circuit due to the firing step. Firstly, since it fires at a high temperature of 900 ° C or higher, it reacts with the substrate in the firing step. For example, in a ceramic superconductor material showing a critical temperature of 93K, the resistance starts to decrease from around 80K, but the electrical resistance shows zero. The superconductivity deteriorates, for example, the critical temperature drops to 50K. Therefore, it is necessary to accurately control the temperature and time during firing. Second
As is well known, superconductors are not easily formed into a dense sintered body, so that the bonding strength with a substrate becomes about 5 MPa or less, and strong bonding may not be obtained. When glass powder is mixed as a countermeasure, for example, the critical temperature
Even with a substance of 93 K, the temperature is lowered to 30 to 50 K, and the superconductivity of the ceramic superconductor is significantly deteriorated. Third, the superconductivity is greatly degraded, for example, the superconductivity of the conventional ceramic superconductor is simply left as it is, and the critical temperature is lowered to 87K after 104 days of, for example, 104K. An even bigger problem is that when a superconductor thick film substrate is manufactured or exposed to an extremely low temperature state such as liquid nitrogen, it easily peels off, causing a problem in reliability. That is not.

[Means for solving the problem]

The present inventors have conducted extensive research on firing of a superconductor thick film wiring circuit board, and as a result, it is difficult for ceramic superconductors to produce a dense sintered body, This is because the adhesive layer is not formed, and it has been found that the above-mentioned problem occurs in the thick film paste in which the superconductor material powder and the organic binder are mixed. Then, the present inventors, in order to solve such a problem, as a result of intensive research, desorbed oxygen at a high temperature to the ceramic superconductor raw material powder or ceramic superconductor material powder, and formed a liquid phase to form an adhesive layer. When certain metal oxides are mixed into a thick film paste, 750
The present inventors have found that a ceramic superconductor wiring circuit conductor having excellent adhesion even in a wide firing temperature range of up to 950 ° C. and having high density and high reliability can be formed, and the present invention has been accomplished.

Accordingly, the present invention is to provide a method for producing a ceramic superconductor thick film paste which improves the conventional disadvantages of the ceramic superconductor thick film wiring circuit board, has excellent superconducting properties, and provides a high adhesive strength to the substrate. is there. That is, the present invention provides a metal oxide which has low reactivity with ceramic superconductor material powder, releases oxygen in the firing step, and forms a liquid phase to promote the densification of the ceramic superconductor. A ceramic superconductor thick film paste by mixing materials.

Ceramic superconductor material powder, after dispersing an alkaline earth element and yttrium and / or a lanthanide element oxide or carbonate in a dispersion medium composed of an organic solvent, copper oxalate is generated in the dispersion medium, Next, the solid content or coprecipitate was separated from the dispersion medium to obtain a superconductor raw material powder, which was then fired at a temperature of 950 ° C. or lower.
Incidentally, the superconductor raw material powder containing copper oxalate as a coprecipitate,
It can be produced by dispersing a powder of an oxide or carbonate of an alkaline earth element and yttrium and / or a lanthanide element in a dispersion medium composed of an organic solvent and generating copper oxalate in situ. That is, the above oxide or carbonate powder is dispersed in a dispersion medium in a predetermined molar ratio in advance into a slurry, and an equivalent amount or more of oxalic acid is added to copper used in the slurry, and a predetermined amount of copper is further added thereto. It can be easily produced by adding a salt and reacting nitric acid with a copper salt in a dispersion medium. As another method, a carbonate of an alkaline earth element, an oxide of an yttrium and / or a lanthanide element, and copper oxide are mixed at a predetermined molar ratio, and the mixture is fired in the air at 950 ° C. In addition, in the method of the present invention, as long as the superconductor raw material powder does not adversely affect the superconductivity, there is no problem even if it is manufactured by a method other than the above.

[Action]

In the present invention, a certain metal oxide is added to and mixed with the ceramic superconductor thick film paste. This metal oxide releases oxygen in the firing step and generates a liquid phase at a high temperature. Usually, silver oxide is preferably used. That is, when silver oxide is uniformly mixed with the superconductor material powder and baked as a thick film paste, oxygen is easily released to form metallic silver.

At this time, it was found that the generated metallic silver did not react with the ceramic superconductor, but segregated at the grain boundary multiple bonding point of the ceramic superconductor at the end of firing only by accelerating the densification of the ceramic superconductor. In the method of the present invention, the metal oxide that releases oxygen at a high temperature in the superconductor paste releases oxygen inside the ceramic superconductor during the firing process, and thus is considered to improve the superconductivity of the ceramic superconductor. . In particular, it is considered that silver oxide not only forms a liquid phase after releasing oxygen and densifies the sintered body, but also improves the adhesiveness by well wetting the substrate. This is considered to have the same effect as long as oxygen is released during sintering and a liquid phase is formed and the substrate is well wetted. It may be a metal oxide or a mixture of a plurality of metal oxides containing or not containing silver oxide.

〔Example〕

Ba / Y is composed of barium carbonate with an average particle size of 1.0 μm and a purity of 99.5% and yttrium oxide with an average particle size of 1.2 μm and a purity of 99.9%.
Weigh and mix so that the molar ratio is 2/1, and mix in a ball mill.
The mixture was wet-mixed for 0 hour and dried to obtain a mixed powder. Then
Oxalic acid was added to the mixed powder so that the molar ratio of Ba / Y / oxalic acid was 2/1/3, and the mixture was stirred and mixed with a three-one motor to prepare a slurry. Separately, 1 mol of 99.3% copper nitrate is added to ethanol 10
A solution was added to 00 ml.

The above-mentioned ethanol solution of copper nitrate was dropped at a rate of 150 ml / min to the slurry so that the molar ratio of Ba / Y / oxalic acid / Cu was 2/1/3/3, thereby producing a precipitate.

After standing for about 12 hours to age the precipitate, the solid content was washed with excess ethanol, and then ground and mixed for 3 hours using zirconia balls to remove barium, yttrium and copper oxalate having an average particle size of 1.0 μm. Containing mixed powder was obtained.
3% by weight of an acrylic resin as a binder was added to the mixed powder, mixed, and then dried to obtain granules.

Then, the granules were heated and heated at a rate of 100 ° C./hour,
It was fired in the air at a temperature of 950950 ° C. for 2 to 10 hours to obtain a ceramic superconductor. The obtained ceramic superconductor was observed for its crystal state to determine whether the crystal structure was an orthorhombic structure of Ba ₂ Y ₁ Cu ₃ O _7-α , and the electrical resistance from room temperature to liquid nitrogen temperature. It was measured and evaluated. Next, the thus obtained ceramic superconductor was wet-pulverized in ethanol for 1 to 10 hours using zirconia balls to obtain a ceramic superconductor material powder having an average particle diameter of 1 μm. The ceramic superconductor material powder was mixed with 0.1 to 50 parts by weight of silver oxide powder (particle size: 0.5 μm) to obtain a mixed powder. Next, 5 parts by weight of ethyl cellulose (manufactured by Hercules, Inc., product number N-7) was added to 100 parts by weight of the mixed powder, and a mixed solvent of an equal amount of terbineol-ethylene glycol monobutyl ether was added. After mixing for 10 hours, a ceramic superconductor thick film paste was obtained. Next, this thick film paste was screen-printed on a zirconia ceramic substrate (thickness: 1 mm) and fired in the air at a temperature of 750 to 950 ° C. for 0.1 to 6 hours to produce a ceramic superconducting thick film wiring circuit board.

Figures 1 to 5 show that the granules are fired at 900 ° C for 3 hours,
A ceramic superconductor thick film wiring circuit board obtained by using a superconductor material powder prepared by ball milling for 5 hours to form a thick film paste by the method described above, screen printing on a zirconia substrate, and then firing the printed substrate at 900 ° C. for 1 hour. 4 shows the temperature characteristics of the electric resistance of the sample.

FIG. 6 shows the temperature characteristics of the electrical resistance of a ceramic superconductor prepared by forming a paste having no silver oxide into a sheet having a thickness of 1 mm and firing at 900 ° C. for 1 hour, and FIG. 7 shows 30 parts by weight of silver oxide. This is the result of mixing. FIG. 8 shows a superconductor paste without silver oxide added in the same manner as described above.
The measurement example of the temperature characteristic of the electric resistance when printing and firing on a zirconia substrate was shown. The critical temperature at which the electrical resistance becomes zero is 100 to 105 K for the superconductor wiring circuit board to which silver oxide is added.
105K at 4.5 and 10 parts by weight of silver oxide
The weight of 18,27,36 was 100K. Although not shown, it was confirmed that when the addition amount was 50 parts by weight or more, the temperature became 97K. The ceramic superconductor without added silver oxide was 80 to 104K, and the one baked on a zirconia substrate was 93
It was K. In addition, all of the samples to which silver oxide was added and fired at 750 to 970 ° C. were dense ceramic bodies having an orthorhombic crystal structure of Ba ₂ Y ₁ Cu ₃ O _7-α .

From these examples, baking after printing the paste,
It has been found that a similar superconductor can be obtained not only by an essential method for obtaining a superconductor but also by a method in which a paste is processed into a sheet or the like and then fired.

Conventionally, ceramic superconductors containing barium, yttrium, and copper have been described as having a large deterioration in superconductivity with time, whereas the ceramic superconductor according to the present invention has been left in air at room temperature of 60% humidity for 90 days. It was found that the rate of change of the critical temperature indicating superconductivity was 5% or less, and the adhesive strength was not changed at all.

Thus, the reason that it is extremely stable and has little deterioration over time is as follows.
This is probably because the ceramic superconductor has a dense and uniform structure. Therefore, in order to confirm this, using ceramic superconductor material powder manufactured in the same manner as in the example, a ceramic superconductor paste with and without silver oxide was prepared, and this was screen-printed on a zirconia substrate. Then, it was baked in the air at 750 to 950 ° C. for 3 hours to obtain a ceramic superconductor thick film wiring circuit board, and the adhesive strength was measured.

Table 1 shows an example of the results. All of the samples to which silver oxide was added exhibited an adhesive strength of 15 Mpa or more, while those to which no silver oxide was added had a bond strength of 5 Mpa or less, and easily peeled off when exposed to liquid nitrogen temperature. The sintering state of the separated and dropped ceramic superconductor was not shown, but was porous, and no adhesive layer was observed on the separated surface. From this time, at the end of sintering, ceramic superconductors have thermal properties that are inconsistent with the thermal properties of the substrate, so that densification is suppressed even if sintering is in progress. It was considered that almost no adhesive strength could be obtained because the liquid phase that promotes adhesion was not segregated. On the other hand, those containing silver oxide are indispensable for the formation of ceramic superconductors during the firing process. Oxygen is generated inside the sintered body, and the nascent metallic silver promotes the liquid phase sintering of the ceramic superconductor to improve the densification. It is considered that segregation occurs at the grain boundary triple bond point and at the interface between the surface layer and the substrate, resulting in improvement in densification, resistance to environmental degradation, and improvement in adhesive strength.

[Brief description of the drawings]

1 to 5 are graphs showing an example of a temperature change of electric resistance of a ceramic superconductor thick film wiring circuit board according to the present invention, and FIG. 6 shows an electric power of a ceramic superconductor obtained by sintering a paste without adding silver oxide. Measurement example of temperature change of resistance,
FIG. 7 is a measurement example of the temperature change of the electric resistance of the sintered body of the paste added with 30 parts by weight, and FIG. 8 shows the temperature characteristic of the electric resistance when the paste used in FIG. 6 is printed and fired on a zirconia substrate. It is a graph shown.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication location H01L 39/24 ZAA H01L 39/24 ZAAZ (72) Inventor Masami Koshimura Yokoze, Yokoze-cho, Chichibu-gun, Saitama 2270 Mitsubishi Mining Cement Co., Ltd. Ceramics Research Laboratory (72) Inventor Seiji Ito 2453-21 Iiyama Odaika, Atsugi City, Kanagawa Prefecture Tanaka Massey Co., Ltd. Atsugi Plant (56) References JP-A 64-65060 (JP, A) JP-A-1-133924 (JP, A) Jan. J. Appl. Phys. , Vol. 26, No. 5 (1987), p. L832-L833

Claims (4)

(57) [Claims] 1. A method for producing a ceramic superconductor paste in which a ceramic superconductor material powder is mixed with an organic binder and a solvent, wherein a metal oxide material powder capable of releasing oxygen during the firing step is added to the superconductor material powder in an amount of 0.1%. A method for producing a ceramic superconductor paste, wherein the paste is mixed in an amount of from 50 to 50 parts by weight. 2. The method for producing a ceramic superconductor paste according to claim 1, wherein the metal oxide material powder to be mixed is silver oxide, palladium oxide, and / or a mixture or alloy oxide containing these. 3. The method for producing a superconductor paste according to claim 1, wherein the superconductor material powder is composed of an oxide containing alkaline earth element, yttrium and / or lanthanide element and copper as constituents. Method. 4. A superconductor material powder containing an oxide or a carbonate of an alkaline earth element and yttrium and / or a lanthanide element is dispersed in a dispersion medium composed of an organic solvent, and then copper oxalate is dispersed in the dispersion medium. 2. The method for producing a superconductor paste according to claim 1, wherein the solid content or the coprecipitate is separated and heat-treated from a dispersion medium.