METHOD FOR PRODUCING SUPERCONDUCTING CIRCUIT

Abstract: A method of producing a superconducting circuit by forming a film having a superconducting phase on a substrate and applying a laser beam to a part of the superconducting phase to cause transition of the part of the superconducting phase into a non-superconducting phase.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a method of producing a superconducting circuit on a substrate. Description of the Related Art In order to produce a superconducting circuit on a substrate by a well-known method, the upper surface of the substrate is masked to form a superconducting thin film only in a prescribed portion or ion etching is performed on a superconducting thin film formed on the substrate to partially scrape off the thin film. However, such a method has disadvantages of difficulty in fine working, inferiority in working accuracy and complicatedness in process. EP-A-0 286 106, a document under Art. 54(3)EPC, discloses a method of producing a superconducting circuit by irradiating with a laser beam regions of a superconducting thin film, the irradiated regions being converted into non-superconducting material SUMMARY OF THE INVENTION An object of the present invention is to provide a method of producing a superconducting circuit, which can achieve fine working with high accuracy through simple steps. Provided according to the present invention is a method of producing a superconducting circuit which is formed by a superconducting phase showing superconductivity at a prescribed working temperature and a non-superconducting phase showing no superconductivity at the prescribed working temperature. The method comprises a step of forming a film having the superconducting phase on a substrate and a step of applying an YA6 or excimer laser beam to a part of the superconducting phase of the film to cause transition of the part of the superconducting phase into the non-superconducting phase. In the present invention, the film formed on the substrate must be transformable into a non-superconducting state by heat treatment at a high temperature. Such a film is prepared from ceramic superconductive material, for example. Well-known ceramic superconductive materials are those having perovskite structure such as Y-Ba-Cu oxides, Y-Sr-Cu oxides, La-Ba-Cu oxides and La-Sr-Cu oxides. Elements of such materials may be partially replaced by other elements. Further, the film formed on the substrate in the present invention must be already in a superconducting state before exposure to the laser beam. In general, a film which is composed of a superconductive material and formed on a substrate by sputtering or the like is in a non-superconducting state immediately after formation. In such case, the film is brought into the superconducting state by a prescribed heat treatment, before being exposed to the laser beam. According to the present invention, the superconducting film is subjected to heat treatment by partial exposure to the laser beam, to change its composition, crystal structure and the like, so that the part exposed to the laser beam is converted into a non-superconducting phase showing no superconductivity. The film remains in the superconducting phase showing superconductivity except for the part exposed to the laser beam. Thus, a superconducting circuit can be produced by this superconducting phase and the non-superconducting phase of the part exposed to the laser beam. In the present invention, the superconducting circuit is produced by a laser beam, the diameter of which can be considerably finely worked. According to the present invention, therefore, the superconducting circuit can be finely worked with high accuracy through simple steps. These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing a state of an embodiment of the present invention during scanning with a laser beam; Fig. 2 is a perspective view showing the embodiment after scanning with the laser beam; Fig. 3 is a perspective view for illustrating a method of measuring the temperature-resistance characteristic of a part not exposed to the laser beam; Fig. 4 is a perspective view for illustrating a method of measuring the temperature-resistance characteristic by mounting one of the terminals on a part exposed to the laser beam; Fig. 5 is a perspective view for illustrating another embodiment of the present invention; and Fig. 6 illustrates the current-voltage characteristic of the embodiment shown in Fig. 5. DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 The (100) surface of a strontium titanate substrate 1 of 15 x 15 mm in size was employed as a substrate surface to form a thin film 2 of Y₁Ba 1.9 Cu 2.8 O x on the substrate of 0.7 µm in thickness by RF magnetron sputtering. Atmosphere gas was prepared by a mixture of argon and oxygen containing 50 % of oxygen under pressure of 10,66 Pa (8 x 10⁻² Torr.), and the substrate temperature was 650°C. The thin film 2 thus obtained was subjected with the substrate 1 to heat treatment in oxygen ventilation at 920°C for two hours, to be converted into a superconducting state. An Nd:YAG laser of 1.06 µm in wavelength was employed to scan the film 2 with a laser beam 3 as shown in Fig. 1, thereby to define a part 4 exposed to the laser beam 3 under conditions of laser power of 100 W/cm², a scanning speed of 1 mm/sec., and a laser beam spot diameter of 100 µm. The exposed part 4 is illustrated in a hatched manner in Fig. 1. A platinum-rhodium thermocouple was placed in proximity to the exposed part 4, to measure its temperature. The result was 2000°C. Referring to Fig. 1, numeral 1 indicates the substrate. Then, as shown in Fig. 2, a film 2 was scanned with a laser beam 50 times at intervals of 100 µm, to define an exposed part 4 of 5 mm in width. As shown in Fig. 3, terminals were mounted on portions not exposed to the laser beam, to measure the temperature-resistance characteristic by a four-terminal method. The temperature at which all resistance was lost, i.e., the critical temperature, was 86 K. The measurement limit of the apparatus was 10⁻⁷ Ω. Then, as shown in Fig. 4, one of four terminals was mounted on the exposed part 4 to measure the temperature-resistance characteristic. No superconducting state was attained at the temperature of liquid helium (4 K). As obvious from comparison of the aforementioned results of temperature-resistance characteristics, it has been confirmed that the exposed part 4 was converted into a non-superconducting phase showing no superconductivity by exposure to the laser beam. Referring to Figs. 2 to 4, numeral 1 indicates the substrate, numeral 2 indicates the film and numeral 4 indicates the part exposed to the laser beam. Example 2 Similarly to Example 1, a film was formed on a substrate, and exposed to a laser beam from an Nd:YAG laser (1.06 µm in wavelength). The laser beam was adjusted to be 100 µm in spot diameter, with a scanning speed of 1 cm/sec. and laser power of 100 W/cm². Fig. 5 shows a film 12 formed on a substrate 11, which was exposed to the laser beam to define exposed parts 14. Superconducting phases 15 and 16 held between the exposed parts 14 were employed as terminals to measure the current-voltage characteristic at a temperature of 77 K. Fig. 6 shows the result. As obvious from Fig. 6, it has been confirmed that a boundary portion between the superconducting phases 15 and 16 formed bridge-type Josephson junction.

Claims: A method of producing a superconducting circuit formed by a superconducting phase showing superconductivity at a prescribed working temperature and a non-superconducting phase showing no superconductivity at said prescribed working temperature, said method comprising: a step of forming a film of a ceramic superconducting material (2; 12) having said superconducting phase on a substrate (1; 11) and a step of applying an YAG or excimer laser beam (3) to a part of said superconducting phase on said film (2; 12) to cause transition of said part of said superconducting phase into said non-superconducting phase (4; 14). A method in accordance with claim 1, wherein said film forming step comprises a step of forming said film (2; 12) by sputtering. A method in accordance with claim 2, wherein said film (2; 12) forming step comprises a step of performing heat treatment in an oxygen atmosphere of said film (2; 12) formed by said sputtering. A method in accordance with claim 1, wherein said film forming step comprises a step of forming a film (2; 12) of a ceramics superconductive material. A method in accordance with claim 4, wherein said film forming step comprises a step of forming a film (2; 12) of at least one ceramics superconducting material selected from a group of Y-Ba-Cu oxides, Y-Sr-Cu oxides, La-Ba-Cu oxides and La-Sr-Cu oxides.

Inventors: HAYASHI, NORIKI C/O OSAKA WORKS, MIYAZAKI, KENJI C/O OSAKA WORKS, TAKANO, SATOSHI C/O OSAKA WORKS, YOSHIDA, NORIYUKI C/O OSAKA WORKS
Applicants: SUMITOMO ELECTRIC INDUSTRIES LIMITED
Application year: 1988
Main classification: H01L39
IPC codes: C01G1, C04B41, H01L39, H01B12, H01B13