KR950007088B1 - Bi-sr-ca-cu-o section target for superconductive thin film - Google Patents

Abstract

No content.

Description

Target material for Bi-Sr-Ca-Cu-O type superconducting film formation

The present invention is a target material used for forming a superconducting film on the surface of a substrate by, for example, a sputtering method. In particular, the present invention is a Bi-Sr having a high cooling effect, low resistivity, and excellent mechanical strength. A target material for forming a -Ca-Cu-O-based superconducting film.

In recent years, the test which forms a Bi-Sr-Ca-Cu-O type superconducting film in the surface of a board | substrate by the sputtering method is performed, for example.

A target material is used for formation of this Bi-Sr-Ca-Cu-O type superconducting film.

This target material is prepared by first preparing a powder of Bi oxide, Sr carbonate, Ca carbonate and Cu oxide having an average particle diameter of 10 μm or less as a raw material powder, and preparing Pb oxide as needed. After roasting and mixing at a predetermined ratio, the mixed powder was repeatedly subjected to baking and pulverizing two or three times to maintain the mixture at a temperature within the range of 700 to 800 ° C. for two hours. To form a ceramic powder, and then to this superconducting ceramic powder,

Atmosphere: Vacuum below 10 ^-2 torr

Heating temperature: 800 ~ 900 ℃

Pressure: 100 ~ 200kgf / ㎠

Heating holding time: It is manufactured by performing a vacuum hot press on the conditions of 1 to 4 hours.

Therefore, the prepared target material

(a) substantially Bi-Sr-Ca-Cu-O-based ceramics or Bi-Pb-Sr-Ca-Cu-O-based ceramics (hereinafter collectively referred to as Bi-Sr-Ca-Cu-O-based ceramics) It consists of (b) or 20 volume% or less of copper oxide (henceforth represented by CuO), and the remainder is a sintered compact of the composition which consists of Bi-Sr-Ca-Cu-O type ceramics substantially.

In addition, since the composition of the target material does not become a thin film composition as it is by the sputtering apparatus and sputtering conditions as mentioned above, the CuO content may be lacking, for example, when manufacturing superconducting ceramic powder. This is because it is manufactured to contain excess CuO in the range of 20 volume% or less.

However, in the above-described conventional target agent, the cooling efficiency is relatively low, and thus the temperature difference between the sputter surface and the cooling bottom of the target material during sputtering becomes large, so that the target material is easily broken due to thermal stress, and also the resistance is high. Because of the large size, relatively inexpensive DC 2-pole sputtering devices cannot be used, and therefore, expensive high-frequency sputtering devices are usually required. Moreover, mechanical strength is low and extremely fragile, and care must be taken in handling them. have.

Therefore, the present inventors conducted a study to solve the problem of the target material for forming a conventional Bi-Sr-Ca-Cu-O-based superconducting film from the viewpoint as described above, Bi-Sr-Ca-Cu-O 8 to 40 metal Cu powder in a state in which CuO coexists in powder of a ceramic-based ceramic (in this case, Cu may be supplied at the time of superconducting film formation, so a Bi-Sr-Ca-O-based ceramic may be used). After mixing and mixing in a proportion of volume%, for example, the target material produced by vacuum hot pressing under conditions of temperature: 400 to 900 ° C. and pressure: 100 to 200 kgf / cm 2 in a vacuum atmosphere is made of metal Cu. Either or both of the -Sr-Ca-O-based ceramics and the Bi-Sr-Ca-Cu-O-based ceramics have a uniformly dispersed structure with CuO contained as necessary. As a result, Bi-Sr- In the target material for forming a Ca-Cu-O-based superconducting film, the cooling efficiency can be improved by one step by the metal Cu constituting the base. In addition, the inventors have found that the resistance is significantly lowered and the mechanical strength is also improved to have high toughness.

The present invention has been made on the basis of the above-mentioned findings, and contains 8 to 40% by volume of metal Cu, 20% by volume or less of CuO as necessary, and the rest mainly contains complex oxides of Bi, Sr and Ca. A composition consisting of any one or both of Bi-Sr-Ca-O-based ceramics and Bi-Sr-Ca-Cu-O-based ceramics mainly composed of a composite oxide of Bi, Sr, Ca, and Cu, And a target material for forming a Bi-Sr-Ca-Cu-O-based superconducting film having a structure in which the ceramic or the ceramic and CuO are uniformly dispersed in the base of the metal Cu.

In the target material of the present invention, the content of the metal Cu is limited to 8 to 40% by volume. When the content is less than 8% by volume, desired cooling efficiency, resistivity and mechanical strength cannot be ensured, and the content is 40%. If the capacity% is exceeded, the relative amount of Cu becomes too large in relation to CuO contained in the range of 20% by volume or less, if necessary, so that a superconducting film having a predetermined composition cannot be formed. Decided.

Next, the target material of this invention is demonstrated concretely by an Example.

As raw material powders, both Bi-Sr-Ca-Cu-O-based ceramic powders and Bi-Sr-Ca-Cu-O-based ceramic powders each having an average particle diameter of 5 µm or less, and each having a composition shown in Table 1 In this case, when synthesizing these ceramic powders, CuO in the amount shown in the first table is also coexisted if necessary, metal Cu powder is prepared, and these raw material powders are blended in the compounding composition shown in the first table. After mixing, vacuum hot place is carried out in a vacuum atmosphere of 10 ^-3 torr at a temperature of 750 ° C., a pressure of 150 kgf / cm 2, and a holding time of 3 hours. In addition, the target materials 1-11 and the comparative target materials 1-4 of the present invention which had the above-mentioned ceramics or a structure uniformly dispersed with the above-mentioned ceramics and CuO and had a diameter of 50 mm x thickness: 4 mm were prepared, respectively.

TABLE 1

(*; Outside the scope of the present invention)

In addition, the content of the metal Cu which forms the base material of the comparative target materials 1-4 is out of the range of this invention.

In addition, the conventional target materials 1 and 2 were manufactured on the same conditions except the metal Cu powder is not mix | blended for the purpose of a comparison, and the temperature in vacuum hot press was raised to 850 degreeC.

Subsequently, the thermal conductivity and the resistivity were also measured for the purpose of evaluating the cooling efficiency of the various target materials obtained as a result, and the drag force was measured for the purpose of evaluating the mechanical strength.

Subsequently, these various target materials were charged to a direct current magnet tone sputtering apparatus (you may use a high frequency magnetron sputtering apparatus),

The whole atmosphere of pressure: 10 ^-4 ~10 ^-1 torr

Atmosphere: Ar or Ar containing 5 to 50% oxygen

Power supply: 100 ~ 600W, Substrate material: MgO single crystal with 100mm ² planar dimension

Substrate heating: 7000 ℃ or not heating

Board-Target Distance: 50 ~ 130mm

The thickness of the thin film is sputtered under the condition of 2 占 퐉, and the thin film after the sputtering is held in the air at a temperature of 850 ° C for 30 hours, followed by annealing treatment under the condition of no-cooling. The critical temperature (Tc) was measured by the 4-terminal method. These measurement results are shown in the first table.

From the results shown in Table 1, all of the target materials 1 to 11 of the present invention exhibit a higher thermal conductivity (cooling efficiency) and cut-off force (mechanical strength) than the conventional target materials 1 and 2, and also have a low resistivity. Although it is possible to form a superconducting film having properties equivalent to that of the target material, as shown in Comparative target materials 1 to 4, when the Cu content is lower than the range of the present invention, the desired improvement effect cannot be obtained with the above characteristics. On the other hand, it is clear that if the content is higher, the desired superconducting film cannot be formed.

As described above, since the target material of the present invention has no compositional problem in forming the superconducting film and has excellent cooling efficiency thereon, even if high speed spurting is performed, no breakage due to thermal stress and the resistivity are significantly low. As well as sputtering, it is possible to form a thin film by direct current two-pole sputtering, and also has industrially useful characteristics such as easy handling because of high mechanical strength.

Claims (2)

Metal Cu: 8-40% by volume, the remainder being a ceramic mainly composed of one or both of Bi, Sr, Ca composite oxide and Bi, Sr, Ca, Cu composite oxide, and unavoidable impurities A target material for forming a Bi-Sr-Ca-Cu-O-based superconducting film, characterized in that it comprises a composition made of a metal material and a structure in which the ceramic is uniformly dispersed in a base of metal Cu. Metal Cu: 8 to 40% by volume, and 20% by volume or less of copper oxide, the rest of which is either or both of the complex oxides of Br, Sr, and Ca, and the complex oxides of Bi, Sr, Ca, and Cu. Bi-Sr-Ca- characterized by having a composition mainly composed of a ceramic, an inevitable impurity, and a structure in which the ceramic and copper oxide are uniformly dispersed in the base of the metal Cu. Target material for Cu-O type superconducting film formation.