Oxide superconductor

Abstract: An oxide superconductor comprising oxide superconductor layers (2) and metal material layers (1), which are alternately laminated by a plurality of times, characterized in that the oxide superconductor layers (2) and the metal material layers (1) are alternately laminated on each other in a spiral form by a plurality of times.

Description: The present invention relates to an oxide superconductor comprising oxide superconductor layers and metal material layers which are alternately laminated by a plurality of times. Such an oxide superconductor is known from DE-A-3 729 125. The oxide superconductor of the present invention is used in a transmission and distribution wire, a power cable, an equipment lead wire, a magnet wire, and, more particularly, to an oxide superconductor capable of supplying a large current with zero resistance or small alternating-current loss. An intermetallic compound such as NbTi, Nb 3 Sn, Nb 3 Aℓ, or V 3 G a and a metal such as Nb or Pb are used as superconductive magnets, magnetic shields, coaxial cables, and cavities by utilizing an ultra low-temperature refrigerant such as liquid helium. These metallic materials, however, are limited as resources. In addition, helium is used to increase cost, which limits the range of practical applications. To the contrary, some substances which can be rendered superconductive at low critical temperatures (Tc) by inexpensive refrigerants have been found, and extensive studies on practical use of such substances in a variety of applications have been actively made. As the high Tc materials described above, La 2-x Ba x CuO 4 and La 2-x Sr x CuO 4 oxide superconductors have critical temperatures of 30 to 45K; a Y(Dy,Er,Ho)Ba 2 Cu3O 7- δ oxide superconductor has a critical temperature of up to 95K; Bi-Sr-Ca-Cu-O based oxide superconductors such as Bi 2 Sr 2 CaCu 2 O 8 and Bi 2 Sr 2 Ca 2 Cu 3 O 10 oxide superconductors have critical temperatures of 80 to 110K; and Tℓ-Ba-Ca-Cu-O based oxide superconductors such as Tl 2 Ba 2 CaCu 2 O 8 , Tℓ 2 Ba 2 Ca 2 Cu 3 O 10 and TℓBa 2 Ca 2 Cu 7 O 8.5 oxide superconductors have critical temperatures of 90 to 125K. These oxide superconductors are manufactured as follows. A powder of each superconductor is kneaded with an organic binder to obtain a paste, and the paste is directly extrusion molded or screen-printed. Alternatively, the powder of each superconductor is filled in an Ag pipe or the like, and the pipe is elongated to obtain a conductor having a desired shape. In a superconductor, a metal stabilizing material is combined with a superconductor molded body to cope with a so-called quench phenomenon in which a superconductive state is lost. For the same purpose as in the oxide superconductor, it is proposed to combine a metal stabilizing material with an oxide superconductor. When the superconductive state is lost, the oxide superconductor becomes an insulator, and it is difficult to conduct heat or electric power to the metal stabilizing material. For this reason, a quench phenomenon more easily occurs. In particular, in alternating-current energization, heat may often be generated by a hysteresis loss. It is very important to appropriately provide a countermeasure against the quench phenomenon of the oxide superconductor. An oxide superconductor is generally brittle and its crystal has a laminar structure subjected to cleavage. The oxide superconductors tend to crack in installation works. In addition, when an oxide superconductor is used for a magnet, a Lorentz's force acts on the oxide superconductor to crack an oxide superconductor layer. As a result, a critical current density (Jc) is undesirably degraded. Furthermore, since the oxide superconductor has a laminar perovskite crystal structure, crystal anisotropy is strong, and a current flows in a direction parallel to the a-b plane. In order to obtain a high critical current density (Jc), the crystal must be oriented such that its C-axis is perpendicular to a current energization direction. However, since the crystal of the oxide superconductor thus manufactured tend to be oriented randomly, a sufficiently high critical current density Jc cannot be obtained. Patent Abstracts of Japan, Vol. 013, No. 201 (E-757), 12. May 1989 and JP-A-01-021828 disclose a method of manufacturing a superconductor cable. It is taught that a laminate structure consisting of Cu alloy (Y-Cu alloy, Ba-Cu alloy) plates and Cu plates having copper oxide dispersed therein is rolled and then subjected to a heat treatment for manufacturing a superconductor cable. It is an object to provide an oxide superconductor having excellent electromagnetic stability such as a high Jc and high mechanical strength and a method of manufacturing the same. According to the present invention, there is provided an oxide superconductor comprising oxide superconductor layers and metal material layers, which are alternately laminated by a plurality of times, characterized in that the oxide superconductor layers and the metal material layers are alternately laminated on each other in a spiral form by a plurality of times and that the material of the metal material layer comprises Ag or Ag-alloy and wherein the oxide superconductor crystal particles are grown lanky in the longitudinal direction of the laminated body due to partial melting and recrystallization of the oxide superconductor. Therefore, both electromagnetic stability and mechanical strength which are indispensable factors of the superconductor can be obtained. According to an embodiment of the present invention, the metal material layers are discontinuously laminated in the circumferential direction of the superconductor because the stabilizing metal layers of the laminated body of the present invention serve as a barrier when the structure is used as a superconductor such as a power cable. Therefore, when the outer superconductor layer is not rendered superconductive, the current does not flow into the inner superconductor layer through the metal material interlayer. In order to uniformly flow a current in each superconductor layer of the multilayered structure, the metal material layers can be discontinuous in the circumferential direction of the conductor. For this purpose, the metal material layer may have a porous or net-like structure. Alternatively, a metal material sheet having a small width may be wound around the superconductor in a helical shape so as to partially expose the underlying superconductor layer. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view showing an example of oxide superconductors according to the present invention; Figs. 2 and 3are a sectional view of an oxide superconductor in which a metal powder (particles) is dispersed in an oxide superconductor layer, and a view for explaining a method of manufacturing it, respectively; and Fig. 4 is a view for explaining a crystal structure of an oxide superconductor layer of an oxide superconductor according to the present invention. Embodiments of oxide superconductors according to the present invention are shown in Figs. 1 and 2. Reference numerals 1 in Figs. 1 and 2 denote metal material layers; and 2, oxide superconductor layers. In the oxide superconductor shown in Fig. 1 the metal material layer 1 and the oxide superconductor layer 2 are formed in a spiral form, and the metal coating layer 3 is used as the outermost layer. According to the present invention, a plurality of superconductors shown in Fig. 1 can be bundled and wound around a metal material layer or an oxide superconductor layer. The spiral laminated structure shown in Fig. 1 can be obtained by alternately laminating the metal sheets and the oxide superconductor sheets and winding the resultant laminated body. Fig. 2 is a sectional view showing an embodiment of an oxide superconductor in which metal particles are dispersed in the oxide superconductor layer. Referring to Fig. 2 reference numerals 5 denote oxide superconductor layers in which metal particles are dispersed. A ring-like metal layer 3 is formed on the outer circumferential surface of the spiral body of the metal material and oxide superconductor layers 1 and 2. The oxide superconductor layers 5 containing the metal particles are arranged near the metal material layer 1. Each sectional shape of the superconductor of the present invention can be obtained by working such as rolling or drawing of the concentric superconductor. In each oxide superconductor layer described above, lanky crystal particles of which longitudinal direction are oriented in the longitudinal direction of the superconductor and includes at least one particle boundary in a direction perpendicular to the longitudinal direction. Since the lanky crystal is formed in the oxide superconductor layer in the current energization direction, the lanky crystal allow formation of a thinner wire. When the superconductor body is used as a conductor such as a magnet, higher stability can be obtained. Various types of oxide superconductors are used in the oxide superconductors of the present invention. Metal materials for the metal material layers are nonreactive with oxide superconductors and are excellent in electrical conductivity and thermal conduction. Examples of the metal material are Ag, Ag-Pd, Ag-Au, Ag-Cu, Ag-Mg, Ag-Pt, Ag-Ir, Au-Ag-Cu, Au-Pd-Ag. The lanky crystal particle shape in the oxide superconductor layer according to the present invention is given such that a ratio (aspect ratio) of the length in the longitudinal direction of the superconductor to the length (width) in a direction perpendicular to the longitudinal direction is 10 or more and generally falls within the range of 50 to 1,000 because the C-axis orientation can be improved and a high Jc value can be obtained. When the metal particles are dispersed at least in an oxide superconductor layer portion adjacent to the metal material layer, and the thickness of each oxide superconductor layer is reduced to 1 mm or less and preferably 0.1 mm or less, the resultant oxide superconductor can be excellent in electrical conductivity and thermal conduction as a whole. Layers of an oxide superconductor or its precursor are alternately laminated with metal material layers by a desired number of times, and the laminated body is covered with the metal material. The laminated body with the coating is elongated as it is or into a desired shape. Predetermined heating and cooling are performed such that the laminated body is heated at a temperature to partially melt the oxide superconductor or its precursor or more and then cooled to recrystallize the oxide superconductor or its precursor. As the oxide superconductors, intermediate materials between source materials which can be converted into oxide superconductors and the oxide superconductors can be used as precursors in addition to the various oxide superconductors described above. The intermediate material is, e.g., a mixture, a coprecipitation mixture, or an oxygen deficient type composite oxides of oxide superconductor constituting elements, or an alloy of the above constituting elements. These precursors are heated in an atmosphere containing oxygen and are reacted into oxide superconductors. In order to alternately laminate an oxide superconductor or its precursor with the metal material by a desired number of times, it is easy to form sheets of the superconductor or its precursor, and the metal material sheets, and to alternately laminate these sheets to obtain a laminated structure. A method of forming the oxide superconductor or its precursor into a sheet can be a conventional method such as a doctor blade method, extrusion, or screen process printing. It is preferable to add a binder to the oxide superconductor or its precursor upon sheet formation because flexibility is imparted to the resultant sheet. The laminated body of sheets of the oxide superconductor or its precursor and the metal material sheets is heated to sinter the molded body, replenish oxygen to the sintered body, and adjust the crystal structure for the oxide superconductor, and to react the precursor into an oxide superconductor, to sinter the molded body, replenish oxygen to the sintered body, and adjust the crystal structures for the precursor. The oxide superconductor or its precursor is heated at a temperature to partially melt it or more because the lanky crystals are grown in the longitudinal direction during cooling and are oriented in the C-axis having a high conductivity. The laminated body is slowly moved in a furnace having a temperature gradient to facilitate lankiness of the crystals and C-axis orientation. The laminated body of the oxide superconductor sheets and the metal sheets is elongated by filling the laminated body into a metal vessel or covering the laminated body with a metal sheet because the oxide superconductor layers become more dense and are separated from the outer atmosphere to obtain a perfect moisture-proof structure, and are free from entrance of toxic substances. Any elongation method such as rolling, extrusion, groove rolling, swaging, or drawing can be applied. The oxide superconductor shown in Fig. 2 is manufactured as follows. As shown in Fig.3, a sheet A of the oxide superconductor 5 containing metal particles, a sheet B of the oxide superconductor 2 which does not contain the metal particles, and another sheet A are laminated on the metal sheet 1, and the resultant body is wound in a spiral shape such that the metal sheet 1 becomes the outermost layer. The spiral body is filled in a metal pipe. The resultant structure is elongated in a desired manner, and predetermined heating is performed. A crystal structure of an oxide superconductor layer of an oxide superconductor of the present invention will be described with reference to Fig. 4. Fig. 4 is a view showing part of a crystal structure of an oxide superconductor. An oxide superconductor layer 2 is formed on a metal material layer 1, and the oxide superconductor layer 2 is made of a plurality of lanky crystal particles 6 parallel to the axis of the superconductor. The particle boundary of the crystal particles has a pinning effect for restricting movement of a magnetic field. In a ferromagnetic magnet or AC energization, a high Jc can be stably obtained. A so-called Wind & React method can also be utilized wherein an elongated material of the laminated body is, for example, wound into a magnet coil and this coil is heated to obtain an oxide superconductor having good orientation. This method is very effective to form the oxide superconductor having poor workability into a magnet or the like. In a ceramic superconductor in which an Ag layer or an Ag alloy layer is combined with a ceramic superconductor layer, a high-strength, heat-resistant metal material can be embedded in the combined Ag or Ag alloy layer continuously in the longitudinal direction of the superconductor directly or through a noble metal layer. The Ag or Ag alloy is used as the metal material layer of the ceramic superconductor constituted by the ceramic superconductor layer and the metal material layer according to the present invention, and the high-strength, heat-resistant metal material can be continuously embedded in the Ag or Ag alloy layer in the longitudinal direction of the superconductor. Therefore, elongation deformation of the superconductor by a tension or the like can be prevented. The high-strength, heat-resistant metal material may be directly embedded in the Ag or Ag alloy layer. However, a noble metal layer is preferably coated on the high-strength, heat-resistant metal material, and the metal material with the noble metal layer is embedded into the Ag or Ag alloy layer to prevent oxidation of the metal material. As described above, the Ag or Ag alloy layer is used as the metal material layer combined with the ceramic superconductor due to the following reasons. Since Ag or an Ag alloy is excellent in oxygen permeability, a sufficient amount of oxygen is supplied to the ceramic superconductor during heating, thereby obtaining a high Jc. In addition, since Ag or an Ag alloy has a high heat conductivity, a quenching phenomenon, i.e., a thermal transition from superconductivity to normal conductivity, can be suppressed, and the energization amount can be increased. Any metal material combined with the ceramic superconductor can be used according to the present invention if it is excellent in oxygen permeability and thermal conduction. For example, an Ag alloy such as Ag-Ir, Ag-Pd, or Ag-Au can be used. As the ceramic superconductor materials intermediate materials between source materials which can be converted into ceramic superconductors and the ceramic superconductors can be used as precursors in addition to the various ceramic superconductors described above. The intermediate material is, e.g., a mixture, a coprecipitation mixture, or an oxygen deficient type composite oxides of ceramic superconductor constituting elements, or an alloy of the above constituting elements. These precursors are heated in an atmosphere containing oxygen and are reacted into ceramic superconductors. Since the metal material is distributed in the form of a layer in the oxide superconductor layer in the oxide superconductor of the present invention, it is excellent in electrical conductivity and thermal conduction. Therefore, quenching and the hysteresis loss by AC energization can be suppressed. The crystal structure of the oxide superconductor layers partitioned by the metal material layers is constituted by crystal particles grown lanky in the longitudinal direction of the superconductor. Accordingly the number of particle boundaries accounting for energization resistance is small in the energization direction, and at least one particle boundary is contained in a direction perpendicular to the lanky crystal particles. Therefore, a uniform, high Jc can be obtained. The laminated body of the oxide superconductor and the metal are heated at a temperature to partially melt the oxide superconductor or more, and is then cooled to recrystallize the oxide superconductor such that crystallization of the molten oxide superconductor progresses to portions between the metal layers. Therefore, the crystal particles are grown lanky in the longitudinal direction and are oriented in the C-axis. The present invention will be described in detail by way of its examples. Example 1 Bi 2 O 3 , SrO, CaO, and CuO were mixed such that Bi : Sr : Ca : Cu was given as an atomic ratio of 2 : 2 : 1 : 2, the resultant powder was pre-burnt in air at 850°C for three hours, and the pre-burnt body was pulverized and classified to obtain a pre-burnt powder of Bi 2 Sr 2 CaCu 2 O x having an average particle size of 8/µm. Ten vol% of methyl cellulose and 10 vol% of methyl cellosolve as binders were mixed with the pre-burnt powder, and the resultant mixture was kneaded by a roll. From the kneaded mass, a tape-like green sheet having a thickness of 0.7 mm was formed by a doctor blade method. This green sheet was placed on an Ag sheet having a thickness of 0.7 mm, and the laminated body was wound in a spiral form such that the Ag sheet faces outward, thereby obtaining a rod having a diameter of 15 mm. The rod was heated to 150°C to eliminate volatile components such as binders, and then heated in air at 800°C for an hour. The heated body was then cooled, and the cooled body was filled in an Ag pipe having an inner diameter of 15 mm and a wall thickness of 2 mm. This Ag pipe was sealed in a vacuum, and subjected to hot isostatic pressing (HIP) at 500°C and 1,000 atm. The Ag pipe filled with the spiral body and subjected to HIP was formed into a 5.0-mm diameter wire material by swaging. This wire material was rolled into plate materials having thicknesses of 2.5 mm, 1.0 mm, and 0.5 mm. The plate materials were heated at 920°C for an hour, and the oxide superconductor layers were partially melted. Thereafter, the plate materials were gradually cooled to 860°C over three hours, heated at 860°C for eight hours, maintained at 820°C for six hours and then cooled. By this series of heating and cooling operations, plate-like oxide superconductors were manufactured. Example 2 Plate-like oxide superconductors were manufactured following the same procedures as in Example 1 except that Ag pipes filled with spiral bodies and subjected to HIP were rolled without swaging to obtain plate members having thicknesses of 10 mm, 7.5 mm, and 5 mm. Example 3 Fifteen % of an Ag powder (particles) having a diameter of 1 µm were mixed with a pre-burnt Bi 2 Sr 2 CaCu 2 O x powder, binders as in Example 1 were mixed with the resultant powder mixture, and a green sheet having a thickness of 0.15 mm was formed by a doctor blade method. The green sheets containing the Ag powder were placed on the upper and lower surfaces of a 0.7-mm thick green sheet as in Example 1, and the resultant body was placed on a 0.7-mm thick Ag sheet. The resultant body was wound in a spiral form such that the Ag sheet faced outward, thereby obtaining a rod having a diameter of 15 mm. Thereafter, from the rod, a plate-like oxide superconductor having a thickness of 1.0 mm was manufactured following the same procedures as in Example 1. Example 4 A plate-like oxide superconductor having a thickness of 1.0 mm was manufactured following the same procedures as in Example 3 except that 0.15-mm thick green sheets placed on the upper and the lower surfaces of the 0.7-mm thick green sheet comprised green sheets without containing an Ag powder. Comparative Example 1 Plate-like oxide superconductors were manufactured following the same procedures as in Examples 1 and 2 except that heating at 920°C for an hour for partial melting in heating of the plate materials and subsequent gradually cooling were omitted in Examples 1 and 2. Crystal particle shapes, Jc values, and crystal orientations of the oxide superconductor layers of the oxide superconductors thus obtained were measured. The critical current densities Jc were measured by a four-terminal method at 77K using 1 µV/cm as a standard. Crystal orientation F was calculated by the following equation such that an internal oxide superconductor layer was exposed and irradiated with X-rays, and diffraction intensities of the exposed portions were substituted: F = (Po - Poo)/(1 - Poo) where Po is the diffraction intensity ratio of the oxide superconductor layer Poo is the diffraction intensity ratio of the uniformly mixed oxide superconductor powder Po or Poo = ΣI(ooℓ)/ I(hkℓ) where (hkℓ) is the intensity of the (hkℓ) diffraction beam. The crystal particle shapes were represented by measuring lengths and widths of crystal particles. Results are summarized in Table 1 below together with the manufacturing conditions. As is apparent from Table 1, the examples (sample Nos. 1 to 8) of the present invention had higher critical current densities Jc than comparative examples (sample Nos. 9 to 14). In the samples of the examples of the present invention, since the oxide superconductor layers were heated at a temperature to partially melt the oxide superconductors during heating or more, the lanky crystal particles were oriented in the C-axis during cooling and were grown in the longitudinal direction of the superconductor. The particle boundaries which accounted for energization resistance in the direction perpendicular to the longitudinal direction were reduced. In addition, the particle boundaries in the longitudinal direction exhibited the pinning effect. In the samples of the examples of the present invention, when the thickness of the oxide superconductor layer is decreased, the critical current density Jc is increased. This is considered to be attributable to the fact that a ratio of the length of the crystal particle to its width is increased when the thickness of the oxide superconductor layer is decreased, thereby increasing C-axis orientation of the crystal particles. In addition, in the sample (No. 7) in which the Ag powder (particles) is distributed in the oxide superconductor layer portion near the metal material layer, a higher Jc is obtained than the sample (No. 8) in which the Ag powder is not distributed. This is because the thermal conduction and electrical conductivity from the oxide superconductor layer to the metal material layer are improved due to the presence of the Ag powder. To the contrary, in the comparative examples, the oxide superconductor layer heated by a low heating temperature was not partially melted, and the crystal structure of the oxide superconductor was constituted by isometric crystals. As a result, the particle boundaries in a direction perpendicular to the longitudinal direction were increased, and the crystal particle were oriented randomly. Therefore, the critical current densities Jc became low. In the sample in which the metal particles such as Ag particles were dispersed, the mechanical strength, especially, toughness, could be increased. It was found that cracks caused during installation works or by Lorentz's forces could be prevented. Example 5 Influences of the thicknesses of the oxide superconductor layers, and heating conditions on crystal orientation of oxide superconductor layers were taken into consideration. Green sheets as in Example 1 were placed on 0.7-mm thick Ag sheets, respectively, and the laminated body were wound in spiral form such that the Ag sheet faces outward. The spiral bodies were subjected to HIP as in Example 1. The HIP-treated bodies were heated at 920°C for an hour under the same conditions as in Example 1 or in air to partially melt the oxide superconductor layers. The bodies were then moved at a rate of 1 cm/five hours in a furnace having a temperature gradient and cooled from 920°C to 820°C at a rate of 40°C/cm. Crystal orientation F of the oxide superconductors thus obtained were measured following the same procedures as in Example 1. Results are summarized in Table 2 together with the manufacturing conditions. No. No. of laminating Green Sheets Thickness of Superconductor Layer (mm) Temperature Gradient in Furance during Cooling F % 1 1 0.6 No 40 2 2 0.8 " 15 3 4 1.7 " 5> 4 4 1.7 Yes 35 As is apparent from Table 2, the crystal orientation is increased when the thickness of the oxide superconductor layer is decreased. When the thickness exceeds 1 mm, crystal orientation is rarely exhibited. Crystal orientation of the sample moved in the furnace having a temperature gradient was greatly increased even if the thickness of the oxide superconductor layer was large. As has been described above, in the oxide superconductor of the present invention, the metal is finely distributed in the oxide superconductor in the form of a layer. The oxide superconductor is excellent in thermal and electrical conductivities. The oxide superconductor layer present between the metal layers is constituted by lanky crystal oriented in the C-axis. The oxide superconductor layer has particle boundaries which exhibit the pinning effect, so that the oxide superconductor has excellent superconductive characteristics such as a higher critical current density (Jc) and excellent mechanical characteristics (bending characteristics). In addition, a laminated body of an oxide superconductor or its precursor and a metal is heated at a temperature to partially melt the oxide superconductor or its precursor or more, thereby easily manufacturing the superconductor described above and providing remarkable industrial effect.

Claims: An oxide superconductor comprising oxide superconductor layers (2,5) and metal material layers (1), which are alternately laminated by a plurality of times, characterized in that the oxide superconductor layers (2) and the metal material layers (1) are alternately laminated on each other in a spiral form by a plurality of times and that the material of the metal material layer (1) comprises Ag or Ag-alloy and wherein the oxide superconductor crystal particles are grown lanky in the longitudinal direction of the laminated body due to partial melting and recrystallization of the oxide superconductor. An oxide superconductor according to claim 1, characterized in that the oxide superconductor is a material selected from the group consisting of La 2-x Ba x CuO 4 , La 2-x Sr x CuO 4 , YBa 2 Cu 3 O 7-δ , DyBa 2 Cu 3 O 7-δ , ErBa 2 Cu 3 O 7-δ , HoBa 2 Cu 3 O 7-δ , Bi 2 Sr 2 CaCu 2 O 8 , Bi 2 Sr 2 Ca 2 Cu 3 O 10 , Tl 2 Ba 2 CaCu 2 O 8 , Tl 2 Ba 2 Ca 2 Cu 3 O 10 , and TlBa 2 Ca 2 Cu 7 O 8.5 . An oxide superconductor according to claim 1, characterized in that the Ag alloy is selected from the group consisting of Ag-Pd, Ag-Au, Ag-Cu, Ag-Mg, Ag-Pt, Ag-Ir, Au-Ag-Cu and Au-Pd-Ag. An oxide superconductor according to claim 1, characterized in that the oxide superconductor layer (2) contains lanky crystal particles of which longitudinal direction are oriented in a longitudinal direction of the superconductor and includes at least one particle boundary in a direction perpendicular to the longitudinal direction. An oxide superconductor according to claim 1, characterized in that the superconductor has a rectangular, tape-like convex, concave, or polygonal cross section obtained by working. An oxide superconductor comprising a plurality of oxide superconductors of claim 1, which are bundled and covered with a metal material layer (1) or an oxide superconductor layer (2).

Inventors: ENOMOTO N, KIKUCHI HIROYUKI, SHIGA SHOJI, UNO NAOKI, ENOMOTO, N., KIKUCHI, HIROYUKI, SHIGA, SHOJI, UNO, NAOKI, Enomoto, N., c/o The Furukawa electric co., ltd., Uno, Naoki, c/o The Furukawa electric co., ltd.
Applicants: FURUKAWA ELECTRIC CO LTD, THE FURUKAWA ELECTRIC CO., LTD.
Application year: 1990
Main classification: H01L39
IPC codes: H01L39