JPH04269878A - Formation method of electrode of superconducting magnetic sensor element - Google Patents

Abstract

PURPOSE:To improve the junction of an electrode to a lead wire at a filmlike superconducting magnetic sensor element which utilizes a magnetoresistance effect and to reduce the noise in an output voltage. CONSTITUTION:A part to be used as a four-pole electrode of an oxide superconducting film is coated with a noble metal such as Ag, Au, Pt or the like by a sputtering method or the like; a lead wire is joined to the noble metal by an ultrasonic soldering method; the electrode is formed. A contact resistance at the electrode part is reduced; the generation of Joule heat is suppressed even by an impressed current which is larger than a critical current density, the thermal fluctuation of a cooling medium at a superconductor is eliminated, the noise in an output voltage is reduced and the detection ability of a magnetic field is enhanced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming electrodes of a superconducting magnetic sensing element, and more particularly to a method for forming electrodes using a four-terminal method in which current electrodes and voltage electrodes are provided on a strip of superconducting thin film.

0002

[Prior Art] When measuring the properties of superconductors, mainly electrical resistance, Ag or Au is used in the bulk of oxides or superconducting films.
The lead wires were glued using paste.

0003

[Problems to be Solved by the Invention] Electrodes formed on a superconductor using the above method pose no particular problem when determining the critical temperature of a superconductor, but it is difficult to use a superconducting film as a magnetically sensitive element. When used as a superconductor, if a current ten times or more than the critical current is applied to the superconductor, the adhesion with the lead wire is weak and Joule heat is generated in the electrode portion due to the contact resistance. As a result, the area around the superconductor undergoes thermal fluctuations, making the properties of the superconductor unstable.

That is, the output voltage of the superconducting magnetic sensing element fluctuates due to the magnetoresistive effect, and the output voltage noise of the element increases.

[0005]

[Means for Solving the Problems] The present inventors fabricated electrodes on a superconducting magnetically sensitive element using various methods and measured the output voltage noise, and as a result, discovered a method that does not have the above problems. The present invention has now been completed.

That is, the gist of the present invention is to coat a portion of a film-like superconducting magnetic sensing element that utilizes a magnetoresistive effect, which is to be a four-terminal electrode, with a noble metal such as Ag, Au, or Pt by a physical method. A method for forming electrodes of a superconducting magnetic sensing element, characterized by bonding a lead wire to a noble metal using ultrasonic solder.

[0007]

DETAILED DESCRIPTION OF THE INVENTION Since oxide superconductors are ceramics, they have crystal grain boundaries that are insulating phases, and for this reason, when a magnetic field is applied, the critical current density decreases rapidly. In other words, when a magnetic field is applied from the outside while a critical current is applied, resistance occurs. By utilizing this property, it becomes possible to measure magnetic fields.

Oxide superconductors that can be used as superconducting magnetic sensing elements include Bi(Pb)-Sr-Ca-Cu.
-O system, Y-Ba-Cu-O system, Tl-Ba-Ca
Examples include high Tc superconductors such as -Cu-O and Tl-Sr-V-O.

[0009] Critical temperature is liquid nitrogen temperature (77.3K)
The following superconductors are impractical due to the lack of suitable cooling solvents, such as inexpensive liquid nitrogen.

[0010] Oxide superconductors whose critical temperature is higher than the temperature of liquid nitrogen have many types of elements constituting their crystals, so the film can be fabricated using a physical method that does not cause much non-uniformity of composition within the film. It is preferable to make it by

[0011] As physical methods, sputtering method,
Examples include vapor deposition method, MBE method and laser ablation method.

[0012] As the substrate supporting the film, MgO, S
rTiO3, LaGaO3, LaAlO3, etc. oxide single crystal, Ag, Au, Pt, Cu with an insulating buffer layer
metals such as, semiconductors such as Si, GaAs, etc. are used.

[0013] As raw materials for the oxide superconductor, oxide ceramics having the desired composition of the film, various oxides of the constituent components, metals, alloys, etc. are used.

[0014] When producing the film, the superconducting film may be produced directly by heating the substrate, or by producing an amorphous film without heating the substrate and heat-treating it to produce the superconducting film. that time,
The composition of the amorphous film may be one that becomes a superconductor after heat treatment.

[0015] The amorphous film is heat-treated for a predetermined period of time at the following temperature at which a superconducting compound is formed in each system to crystallize it.

Bi-Pb-Sr-Ca-Cu-O system: 820-85
0°C Bi-Sr-Ca-Cu-O system: 850
~880℃V-Ba-Cu-O system:
900-1000℃ Tl-Ba-Ca-Cu-O system
: 900~1000℃ Tl-Sr-V-O system
: 800~1000℃

[0017] Furthermore, before heat treatment at these temperatures, the properties can be stabilized by pre-calcining at 700 to 800°C for 2 to 10 hours. After heat treatment, it is slowly cooled in a furnace.

Four-terminal electrodes, an electrode for applying current and an electrode for measuring voltage, are formed on the oxide superconducting film produced by the above method.

First, a noble metal such as Ag, Au, or Pt, which is difficult to oxidize, is applied to the portion of the oxide superconducting film that will become the four-terminal electrode using a physical method such as sputtering, vapor deposition, MBE, or laser ablation. Coating method. The thickness of the deposited noble metal is not particularly limited, but from the viewpoint of industrial production, it is preferably thinner than the thickness of the oxide superconducting film.

Ultrasonic solder is used to join the lead wire to the coated noble metal film. As a solder material, P
A b-Sn alloy to which Zn, Al, Ti, Si, Cu, etc. are added is used. When soldering, heat the soldering iron to 100-500℃,
Apply 0kHz ultrasound.

[0021]

[Operation] Since the terminal electrode is coated over the necessary area by a physical method, its contact resistance is extremely small. Furthermore, since the lead wires are soldered under ultrasonic treatment, the joints are tight and the generation of contact resistance is suppressed.

[0022]

EXAMPLE A thin film of the example was prepared by sputtering a MgO 2 single crystal onto a substrate without heating it. The following three types of sputtering targets were used.

■Bi0.5Pb0.5Ox (Bi2O3 and PbO
Mixed powder of) ■CaCu0.75Ox (CaCO
3 and CuO sintered powder at 950 °C)■SrCu0.7
5Ox (950℃ sintered powder of SrCO3 and CuO)

The thin film composition was adjusted by adjusting the deposition time of each target as follows.

■Bi0.5Pb0.5Ox: 6 seconds ■C
aCu0.75Ox: 58 seconds ■SrCu0.75Ox: 34 seconds

[0026] This single layer was stacked 400 times to obtain a 2 μm thin film. The composition of the obtained thin film was analyzed by EPMA, and the result was (Bi+Pb) 1.00.
Sr1.00Ca0.96Cu1.95Ox.

This film was calcined by heat treatment at 780° C. for 2 hours, and then heat treated at 844° C. for 65 hours to obtain a superconducting film.

After heat treatment, a 1 μm thick Ag film was coated on the portion of this film to be used as a four-terminal electrode by sputtering, and a lead wire was bonded to the film using ultrasonic waves to produce an electrode. For ultrasonic soldering, use USM-III manufactured by Asahi Glass Co., Ltd.
was used. The temperature during solder bonding was approximately 300° C., and the applied ultrasonic wave was 56 Hz.

As a result of measuring the sensitivity of the obtained magnetic sensing element in liquid nitrogen, the sensitivity was 15364.3μ with an applied current of 1mA.
A magnetic sensitivity of V/Gauss was obtained.

[0030] When the output voltage noise of this magnetic sensing element was measured using a spectrum analyzer when an applied current of 1 mA was applied, it was found to be 5 × 10-8 V/√H at 100 Hz.
It was z.

[0031] Comparative example lead wires were joined without using ultrasonic solder, but with Ag electrodes.
When the output noise was measured using Ag paste on the film, it was 2×10-6V/√Hz at 100Hz.
Met.

[0032]

[Effects of the Invention] By using the superconducting magnetic sensing element produced by the method of the present invention, the generation of Joule heat in the electrode portion is suppressed even when a high applied current is applied, and thermal fluctuations of the cooling medium are eliminated. Output voltage noise can be reduced and magnetic field detection ability improved.

Claims (1)

[Claims] Claim 1: A film-like superconducting magnetic sensing element that utilizes magnetoresistive effect has four-terminal electrodes containing Ag, Au, and P.
1. A method for forming electrodes of a superconducting magnetically sensitive element, which comprises coating a noble metal such as T by a physical method, and bonding a lead wire to the noble metal using ultrasonic solder.