JPH01173765A - Superconductor film magnetic sensor - Google Patents

Abstract

PURPOSE:To obtain a magnetic sensor, which has a superior sensitivity characteristic to a weak magnetic field is well and whose consumption power is remarkedly little, by a method wherein a superconductor film of a thickness within a specified range is formed by a spray pyrolysis method. CONSTITUTION:A magnetic sensor is formed to form a superconductor film to generate a voltage, which corresponds to an applying magnetic field intensity and a measuring current intensity, by a spray pyrolysis method and the thickness of the film is formed within a range of 0.2-50mum. By this method, the thin superconductor film of a thickness within a prescribed range is used as a superconductor film magnetic sensor, which is uniformized the composition ratio of elements, is made small the particle diameters of its constituent particles, has a high density and an improved crystalline orientation property, is remarkably low in consumption power and has a superior sensitivity characteristic to a weak magnetic field as well.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a magnetic sensor made of a ceramic superconductor film that can perform measurements with a weak magnetic field 1.

<Prior Art> Conventionally, a magnetic sensor based on the magnetoresistive effect of a semiconductor or a magnetic material has generally been used to measure a magnetic field. Semiconductors include shape effects such as 1nSb and InAs, and magnetic materials trl.
Magnetic sensors using the distribution effect of Fe-Ni permalloy and CoNi have been put into practical use. Furthermore, when a particularly highly sensitive magnetic sensor is required, a 5QUID (i[1[4 quantum interference device)] has been used. Furthermore, recently, magnetic sensors that utilize ceramic superconductor film grain boundaries, which are different from conventional ones, have been proposed.

<Problems to be Solved by the Invention> A conventional magnetic sensor using a magnetoresistive effect has a characteristic in which the change in resistance with respect to a magnetic field follows a quadratic curve, as shown in FIG. Therefore, when the magnetic field to be measured is weak, the change in resistance is small, making it difficult to measure weak magnetic fields. On the other hand, 5QUID has extremely high sensitivity and can measure magnetic fields as weak as 10 crows, but it requires advanced technology to fabricate because it is fabricated by combining a Josephson element with an extremely thin insulating film formed between superconductors. It was not easy to use.

A magnetic sensor that utilizes the grain boundaries of a ceramic superconductor consists of an aggregate of particles that are bonded together, either through an extremely thin insulating film entirely interposed at the grain boundaries of the superconductor particles, or through point-like weak bonds between the particles. It is something. Even when a weak magnetic field is applied to the bonded portion of this ceramic superconductor, the superconducting state is broken and it becomes a normal conductive state and has electrical resistance.

A ceramic superconductor magnetic sensor was manufactured using a conventional powder sintering method, and all of its characteristics are shown in FIG. As shown in this figure, when the superconducting state of the grain boundaries begins to break down in a weak magnetic field, the resistance of the element increases rapidly as the strength of the magnetic field increases. This shows that this sensor has high sensitivity even in weak magnetic fields.

The sensitivity of this ceramic superconductor magnetic sensor is determined by the resistance generated at grain boundaries, so it can be increased by changing the number of grain boundaries. Therefore, by reducing the grain size and increasing the number of grain boundaries, a magnetic sensor can be made highly sensitive.

Conventional, common ceramic superconductors are made by weighing and mixing raw material powders to a predetermined ratio, heating them to 900 to 1000°C in an oxidizing atmosphere such as air to form an oxide compound, and then crushing them again. - Although the superconductor was made to have a uniform composition through the pressure forming and firing process, there is a limit to how small the particle size can be reduced using mechanical methods, and the filling rate [
Therefore, the grain size of the superconductor was not very small, and the number of grain boundaries was limited (up to about 1 μm), so the grain boundaries generated resistance. The sensitivity of ceramic superconductors was also limited by the above two reasons.

In addition, superconductors produced by the powder sintering method are bulk, and in order to make magnetoresistive elements, they are processed to make them thinner and thinner, but it is necessary to make them as thin as possible within a certain yield. teeth,
This was difficult, partly because the density of the material was not high. Therefore, the measurement current flowing through the sensor has also become considerably large.

The superconducting magnetic sensor of the present invention solves the above-mentioned problems, and the structure of the sensor with good characteristics can be obtained through a simple process.

Means for Solving Problems〉 The present invention uses a spray pyrolysis method for easily manufacturing ceramics, and manufactures a ceramic superconductor film.The elements constituting all the superconductors are water-soluble. Prepare a compound (such as a base), weigh a predetermined amount, and dissolve it in a sufficient amount of pure water. The spray pyrolysis method uses two sprays to form a film.
A ceramic superconductor film was created. Superconductors with small crystal grains, good controllability of grain boundaries, and high sensitivity as magnetic sensors by adjusting the spray speed, the growth rate of the film, and the firing temperature after film formation. It turns out that this can be done on membranes.

It was also found that when a ceramic superconductor film is produced using this spray pyrolysis method, its crystal axes are aligned and the density is #j higher than that obtained using the conventional powder firing method.

Effects> The present invention is capable of producing extremely small particle sizes, which are different from those determined by conventional mechanical processing precision, and by making a compound of the elements of a ceramic superconductor into an aqueous solution, it can be made uniform on an atomic basis. Can you do it? , a superconductor magnetoresistive sensor is fabricated using a spray pyrolysis method in which spraying is performed slowly or intermittently while stirring an aqueous solution. According to this method, when producing a ceramic superconductor, it is possible to control the particle size by controlling the growth rate and temperature conditions, and by controlling the atmosphere and temperature, the grain boundaries of the particles k? Furthermore, by selecting the substrate, the growth rate of the film, etc., the crystal orientation of the film to be produced can also be controlled. This spray pyrolysis method makes it possible to make the superconductor film extremely thin and have a small particle size by selecting the conditions for bursting the superconductor film, and also to control the state of the grain boundaries of the particles. By using the powder sintering method, it is possible to obtain a ceramic superconductor magnetoresistive element sensor that measures minute magnetic fields by modifying the measurement current that flows through the element for measurement, which is several orders of magnitude smaller. Embodiments of the invention will be described with reference to the drawings.

Example 1 Figure 1 shows a simple example of a superconducting magnetoresistive element having an extremely thin insulating film of minute ceramic particles or a point-like weak junction, which was fabricated using the spray pyrolysis method of the present invention. The element shown in the figure shows the composition of Y-Ba-CuO, and the raw materials used are Y(NO3)3x6H20 and Ba(NO3)2
and Cu(NO3)2.3H20 were weighed so as to have a predetermined composition ratio (Y Ba 2 Cu a ), dissolved in an amount of pure water that would sufficiently dissolve each component, and then
The magnetic sensor of the present invention was manufactured by the method shown in the figure.The solution 6 in which the nitrates of Y, Ba, and Cu dissolved in pure water was poured into the container 5 of the spray device and was thoroughly heated. While stirring, a spray gun 4 sprays compressed air 8 into a very small mist 7 of an aqueous solution 6.
The liquid was then sprayed onto a stabilized zirconia crystal substrate 1 that had been heated to about 600° C. with a heater 3.

In order to avoid increasing the speed of spraying and not lowering the temperature of the substrate 1, this spraying is repeated in small amounts approximately 100 times until the thickness is approximately 10 μm.
A film was prepared. This method uses nitrogen (N2) or oxygen (02) instead of compressed air from a spray gun.
The same process could be made using gas. In addition, we were able to fabricate a good film with a thickness of 0.5 μm to 50 μm, but the film with a thickness of about 1 μm to 10 μm had good characteristics as a magnetic sensor. The temperature of the substrate 1 is 300°C to 6°C.
It is possible to vary between 00°C and tc.

Membranes made using the spray pyrolysis method can be heated to 950°C in air.
After heating for about 30 minutes and slowly cooling, a ceramic superconductor film was obtained. This firing temperature ranges from 900℃ to 1000℃.
The firing time could be changed between 1 and 60 minutes depending on the film thickness, etc.

Note that if the film thickness of the superconductor to be produced is less than 0.2 μm, the filling rate and uniformity will deteriorate;
If it exceeds this level, the adhesion with the substrate 1 may deteriorate,
There was also a characteristic disadvantage in that the measurement current applied to the magnetic sensor during measurement had to be increased to reach the desired sensitivity. Second, the adhesion between the current electrode 10 and the voltage electrode 11t1 and the film 9 is made of titanium (Ti)! The electrodes were made by evaporating R, and a lead i%Mk was connected thereto using silver paste, and each electrode was connected to a constant current source 12 and an output voltage measuring device 13.

The superconducting magnetic sensor connected for measurement in the manner described above was immersed in liquid nitrogen (77K), and the results of measurements were shown in FIG. 3.

Figure 3 shows the result when a measurement current of 1 mA is passed through a magnetic sensor with a film thickness of 10 μm.As shown in this figure, when there is no magnetic field, the resistance of the magnetic sensor is zero, but even a small amount of magnetic field 14 When I4 was applied, resistance was generated, and the resistance increased rapidly with the strength of the applied magnetic field I4. This is the traditional
2 in Figure 4 of a magnetoresistive element using a semiconductor or magnetic material
It exhibits highly sensitive characteristics in weak magnetic fields, which are completely different from the characteristics of the following curve.

Figure 5 shows the characteristics of a 1 m thick magnetic sensor fabricated using a superconductor with the same composition as the present invention fabricated using the powder sintering method using the same method as the magnetic sensor of the present invention. The graph shown is 0. It has been confirmed that this magnetic sensor becomes more sensitive to the magnetic field when the flowing current Ik is increased.

As can be seen by comparing Figures 3 and 5, when the applied magnetic field is 100 oersted, the magnetic sensor of the present invention has a detection voltage of 1.4 mV at a measurement current I of 1 mA, and its resistance value is: It was 1400mA. On the other hand, in a magnetic sensor using the powder firing method (Fig. 5), the current I is 100 mA.
Then, the output voltage becomes 0.27mV, and the generated voltage is 2
．． It becomes 7mΩ.

As described above, the magnetic sensor according to the present invention has a magnetic field that rises near zero, and output sensitivity to increases in magnetic field strength that is much better than that of the magnetic sensor using the powder firing method.Moreover, it can achieve lower power consumption and higher sensitivity. It shows that

Example 2 In the same manner as in Example 1, a film was prepared using a spray pyrolysis method using an aqueous nitrate solution of Y, Ba and Cu, but each time a film of 1 to 3 μm was sprayed, the temperature was 750°C to 85°C.
Temporary firing in air at 0°C was repeated.

A magnetic sensor was manufactured using the same steps as in Example 1 except for performing this temporary firing. This magnetic sensor was constructed in the same manner as in Example 1, with a magnetic field of 100 oersted, a measurement current of ImA flowing through it, and a generated resistance of about 1500 mΩ being measured.

Example 3 The other conditions were the same as in Example 1. A film produced by the spray pyrolysis method was calcined at 750° C. to 850° C. for about 5 to 10 minutes at Fi5. All 5. I went there. It was also measured that a resistance of 1500 mΩ was generated under the same measurement conditions as in Example 1.

In the above embodiments, a stabilized zirconia crystal substrate was used as the substrate l, but even if strontium titanate (SrTiO3), which has fewer defects, is used as the substrate, the superconductor will still have a theoretical density. It was confirmed that the film density was 90% or more.

In addition to the above, the substrate may be made of an oxide such as sapphire, alumina magnesium oxide, or a semiconductor such as gallium arsenide or silicon, or the substrate may be provided with a buffer layer of silver, platinum, yttrium, barium, or copper oxide. A good film could be produced.

Did you know that this superconductor film produced by spray pyrolysis has crystal axes grown in the C-axis direction on the substrate? Co As an example, the X-ray diffraction graph of a sample formed on a srA substrate * is the 6th one.
In the figure, a diffraction signal appears only at the index diffraction angle of the C axis. The produced film had a high critical current of 7000 A/c-, and had excellent properties as a superconductor.

Furthermore, the fabricated superconductor film according to the present invention was coated with a photoresist, a precise resist pattern was created by a photolithography process, and an etching process using a phosphoric acid-based etchant was performed to form a complex pattern as shown in Fig. 7. superconductor film 2
1 can be made. The magnetic field detection part is thin in the area of this figure.
In addition, by forming the element in a zigzag shape, the resistance generated by the magnetic field can be increased, so that the sensitivity of the magnetic sensor can be increased.

In this FIG. 7, a rainbow current electrode 10 and a voltage electrode 11 are made in the same manner as in the embodiment of il, and a constant current circuit 12 and an output voltage measuring device 13 are connected to each other by means of a t-lead.
connected to. The output of this magnetic sensor was a high output voltage that was almost the same as the value calculated from its geometric shape.

The above describes a superconductor magnetic sensor made of Y-Ba-Cu-0 ceramics;
The present invention is applicable to any ceramic superconductor, not limited to the a-Cu-0 type.

The present invention has long been developed, which differs from the conventional powder sintering method, by making fine grains with a uniform composition, improving the grain boundaries by adjusting the film growth rate and firing conditions, and improving the structure of substrates and films. We have described an example of fabricating a magnetoresistive element using a highly sensitive ceramic superconductor film using the spray pyrolysis method, which requires orientation to a crystal axis with good characteristics under the growth conditions. In addition to spray pyrolysis, superconductors can be obtained by sputtering, CVD, and other methods.

The present invention has been described as an example of manufacturing a fine-grained ceramic superconductor magnetoresistive element with controlled grain boundaries using the spray pyrolysis method, but the firing conditions of this simple method, such as Kashima temperature and cooling rate, are By adjusting the atmosphere, a ceramic superconductor film with good characteristics can be produced and used for wiring, coils, magnetic shields, and other superconductor devices.

<Effects of the Invention> In order to create a magnetic sensor using a highly sensitive ceramic superconductor magnetoresistive element, the present invention makes the composition ratio of elements uniform, reduces the particle size of the constituent particles, and produces a superconductor magnetoresistive element. As a result, grain boundaries that generate resistance are controlled. Furthermore, if the spray pyrolysis method described in the preparation of the superconductor film of the present invention is used, the film will have a high density and an improved crystal orientation. Therefore, it is possible to fabricate a sensor using a magnetoresistive element with a precise pattern using photolithography and etching techniques.

From the above, the ceramic superconductor magnetoresistive element according to the present invention has excellent sensitivity characteristics even to weak magnetic fields.
Moreover, a magnetic sensor with extremely low power consumption can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a perspective view showing an embodiment of the superconducting magnetic sensor of the present invention, Fig. 2 is a schematic configuration diagram of a film forming apparatus using spray pyrolysis, and Fig. 3 is a magnetic field diagram of the superconducting magnetic sensor of the present invention. An example of the detection characteristics is a diagram showing gold, and Figure 4 is a semiconductor.
A schematic diagram showing the magnetic detection characteristics of a magnetic sensor made of a magnetic material, FIG. 5 is a diagram showing an example of the magnetic detection characteristics of a superconducting magnetic sensor using a powder firing method, and FIG.
FIG. 7 is an X-ray diffraction graph after heat-treating a superconductor film fabricated on a substrate by spray pyrolysis. 1 is a substrate, 2 is a substrate holder, 3 is a heater, 4 is a spray gun, 5 is a container, 6 is an aqueous solution of raw materials, 7 is a spray of an aqueous solution, 8 is a compressed air hose, 9 is a superconductor film, 10 is an electric current 11 is a voltage electrode, 12 is a constant current source, 13 is an output voltage measuring device, and 14 is a magnetic field to be measured. Agent Patent attorney Takeshi Sugiyama (and 1 other person) y, 2
Figure 10a 3rd m

Claims (1)

[Claims] 1. In a magnetic sensor that measures a magnetic field from the voltage of a ceramic superconductor film that generates a voltage corresponding to the strength of an applied magnetic field and the strength of a measurement current, A superconductor film magnetic sensor characterized in that the thickness is within the range of 0.2 μm to 50 μm. 2. Claim 1, characterized in that the ceramic superconductor film is produced by a spray pyrolysis method.
A superconductor film magnetic sensor as described in . 3. The superconductor film magnetic sensor according to claim 1 or 2, wherein the ceramic superconductor film is formed in a thin line shape or a zigzag shape.