JPH05121788A - Temperature switch - Google Patents

Abstract

PURPOSE:To obtain a temperature switch which is able to execute a switching action at a low temperature or at a temperature of 100K or below by controlling current in a high-temperature oxide superconductor. CONSTITUTION:A high-temperature oxide superconductor is charge in S-N transition temperature depending on a flowing current. A high-temperature oxide superconductor decreases in S-N transition temperature with an increase in flowing current. Therefore, the S-N transition temperature of high-temperature oxide superconductor can be set to an optional point lower than a critical temperature by controlling current the oxide superconductor. By this setup, a switching element which takes advantage of the properties of superconductor that changes sharply in resistance at a low temperature (for instance, temperature range lower than critical temperature) can be obtained. It is preferable that a switching element changes sharply in resistance when it is turned from ON-state to OFF-state or vice versa. Depending on the design of a circuit, it is necessary that a normal switching element is larger than 1OMEGA in resistance as an absolute value in an ON state. It is desirable that a switching element is 1mOMEGA.cm or above in resistivity to attain a value of 1OMEGA in resistance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a temperature switch capable of ON / OFF controlling a current flowing in a circuit depending on ambient temperature.

[0002]

2. Description of the Related Art A switch using a superconducting-normal conducting transition (hereinafter referred to as "SN transition") of a superconductor is as follows.
Persistent current switches and flux pumps are known.

A permanent current switch is a switch that uses a high resistance matrix metal-based superconducting wire to cause a normal conduction transition by heating with a heater. When a constant magnetic field is generated in a permanent current mode such as a magnetic levitation type linear motor car and MRI. Is used for.

The magnetic flux pump is a switch that causes an SN transition by a magnetic field and is used to excite a magnet.

Both the persistent current switch and the flux pump described above are often used at 4.2K.

A semiconductor switch using BaTiO ₃ or the like is known as an element for detecting a temperature and performing a switching operation. This semiconductor switch is a switch whose specific resistance changes by three digits or more due to a phase transition from a ferroelectric substance to a paraelectric substance. The temperature at which such a semiconductor switch can be switched is limited to room temperature to about 200 ° C.

As a temperature switch for performing temperature switching at a low temperature, a combination of a sensor such as a thermocouple and a resistance thermometer, a relay and a power source is used.

[0008]

However, in such an element which is temperature-switched at a low temperature, it is necessary to combine a sensor and a relay, so that it cannot be made compact and it is made inexpensive. There was a problem that I could not do it.

An object of the present invention is to provide a temperature switch capable of performing switching by detecting the temperature of the element itself, such as a semiconductor switching element, at a low temperature of 100 K or less.

[0010]

A temperature switch according to the present invention is a temperature switch utilizing the SN transition of a superconductor, the superconductor being an oxide high temperature superconductor, and the SN transition of a superconducting current being caused by a passing current. It is characterized in that the transition temperature is controlled.

In the present invention, as the oxide high-temperature superconductor, for example, yttrium-based, bismuth-based and thallium-based oxide superconductors can be preferably used.

The high temperature oxide superconductor used is preferably a bulk material in which the ab plane is oriented parallel to the direction of current flow.

Further, in the present invention, the transition temperature of SN transition can be controlled by the amount of oxygen in the superconducting phase. Usually, the temperature of the SN transition can be lowered by reducing the amount of oxygen.

In the present invention, the oxide superconductor can be obtained by a method of mixing raw materials containing composition elements and then sintering the mixture. Further, the obtained sintered body is further prepared by a unidirectional solidification method. May be processed. For the unidirectional solidification method, for example, a laser pedestal method, a floating zone melting method, a Bridgman method, a zone melting method, or the like can be used.

The oxide high-temperature superconductor produced by the unidirectional solidification method is bulky and has a crystallographically oriented structure even when the growth diameter is changed, and thus exhibits a high critical current density.

Therefore, for example, when a fiber-shaped high-temperature oxide superconductor is crystal-grown from the molten state in the unidirectional solidification method and used in the present invention, the superconductor has a small cross-sectional area and is long in the energizing direction. It is possible to provide a switch which has a high resistance in the normal conducting state, while allowing a current to flow with a high critical current and a high critical current density in the superconducting state.

Further, in such a fiber-shaped high-temperature oxide superconductor, it is preferable that the ab plane is oriented parallel to the current-carrying direction.

Further, in the temperature switch of the present invention, the sintered body obtained by crystallizing the sintered body by rolling or pressing can be used as an oxide high temperature superconductor. In this case, it is preferable that the a-b plane of the superconductor be oriented parallel to the energization direction.

On the other hand, in the temperature switch according to the present invention, a slit may be formed in the high temperature oxide superconductor so that the electric path is bent. As described above, when using the high temperature oxide superconductor in which the ab plane is oriented parallel to the energization direction, it is desirable that the slit be formed so as to be perpendicular to the ab plane.

In the temperature switch of the present invention, the specific resistance immediately after the transition from superconducting to normal conducting is preferably 1 mΩ · cm or more.

[0021]

The high-temperature oxide superconductor has a higher superconducting transition temperature and a higher specific heat than the conventional superconductors. As a result of detailed examination of the normal transition phenomenon of such an oxide high-temperature superconductor, the superconducting-normal conducting transition due to a magnetic field or current flow is substantially higher than that of other alloy-based superconductors at the same temperature. It turned out to be gradual.

The present inventors have paid attention to such a property,
We have realized a temperature switch using oxide high-temperature superconductors.

That is, in the present invention, in the oxide high temperature superconductor used as the superconductor, the temperature at which the SN transition is changed by the applied current. Such a change is, for example, as shown in FIG. 1, and the SN transition temperature becomes lower as the current increases.

Therefore, it is possible to control the temperature at which the SN transition occurs to an arbitrary temperature below the critical temperature (Tc) by adjusting the magnitude of the applied current. Where Tc
Means the temperature at which the resistance becomes 0 at a minute current and the temperature at which the Meissner effect appears at a minute magnetic field. That is, 7
When Jc = 10 ⁴ A / cm ² at 7K, 10 ⁴ A /
The temperature at which the SN transition occurs when a current of ² cm ² is applied is 7
It is 7K. In this case, when a current of 10 ⁴ A / cm ² or more is passed, the temperature of SN transition becomes 77 K or less.

In this way, the temperature switch of the present invention can be used as a switching element capable of utilizing a large resistance change at an arbitrary temperature of low temperature (for example, a region below the critical temperature).

In the present invention, the specific resistance immediately after the transition from superconducting to normal conducting as described above is preferably 1 mΩ · cm or more. The switch element preferably has a large change in resistance when turned on and off. Although it depends on the circuit design, a switch normally needs to have an absolute value of resistance of 1Ω or more in a normally conducting state.
In order to achieve the value of 1Ω or more, it is necessary to first improve the specific resistance of the superconductor. The specific resistance is, for example, 1 m
It is preferably Ω · cm or more.

The specific resistance can be changed by the amount of oxygen in the superconducting phase, the denseness of the structure, the orientation direction of the crystal, and the like.

FIG. 2 is a diagram showing the relationship between the amount of oxygen in the superconducting phase and the transition temperature. In the figure, x is Y ₁ Ba ₂ C
The composition ratio of oxygen in u ₃ O _x is shown. As shown in the figure, the temperature of the SN transition becomes lower as the amount of oxygen decreases. Thus, the specific resistance and the SN transition temperature can be controlled by the amount of oxygen in the superconducting phase.

When the switch is in the superconducting state,
A large current flows through the switching element. Therefore,
It is necessary that the critical current is large. On the other hand, in order to increase the absolute value of resistance in the normal conducting state, it is necessary that the cross-sectional area is small. In order to satisfy these requirements, the oxide superconductor is preferably a bulk body in which the ab plane is oriented in parallel with the current-carrying direction as described above. By using such a bulk material, a switch that can maintain a high critical current and a high critical current density can be realized.

Furthermore, if a fiber-shaped oxide superconductor whose ab plane is oriented parallel to the current-carrying direction is used, the cross-sectional area can be made smaller and the absolute value of the resistance can be increased, and a high critical current can be obtained. And a high critical current density can be maintained.

In a non-oriented sintered bulk body, it is difficult to obtain a high critical current density even if the critical current is high, and it is generally difficult to increase the absolute value of resistance. In the case of an oriented thin film, it is difficult to obtain a high critical current even if the critical current density is high. Moreover, since the specific resistance is small, it is difficult to increase the absolute value of the resistance.

However, depending on conditions such as switching current, this non-oriented sintered bulk body or oriented thin film can also be used.

Further, in order to set the resistance in the normal conducting state to 1 Ω or more, it is necessary to devise the cross-sectional area and length of the oxide high temperature superconductor.

For example, if the superconductor is fiber-shaped as described above, its cross-sectional area can be reduced and the superconductor can be lengthened to increase the resistance value. In this case, in order to keep the critical current density high in the superconducting state, it is sufficient to orient the ab plane in the superconductor in parallel with the conduction direction as described above.

Further, as shown in FIG. 3, by forming the slit 2 in the high temperature oxide superconductor 1, the electric path is bent and extended. The more the slits are alternately formed, the longer the electric path from the one end 1a to the other end 1b of the electric path formed by the superconductor 1. By extending the electric path in this manner, the resistance of the oxide superconductor can be increased without changing the size of the oxide superconductor. Further, the length of the electric path can be controlled by the number of slits formed, and thus the resistance value can be controlled.

[0036]

EXAMPLES Example 1 Bi ₂ Sr ₂ Ca ₁ Cu produced by a laser pedestal method
Linear bulk material with a composition of ₂ Ox (diameter 1 mm, length 10 c
m) was used as a switch to produce a circuit as shown in FIG.

This bulk material had a Tc of 87K as measured by a DC four-terminal method by applying a current of 1 mA.
The resistivity just above the normal conduction transition is 2 mΩ · cm, and the critical current density (Jc) at 77K is 5000 A / c.
m was ² (Ic = 39.2A).

In the circuit shown in FIG. 4, when the switch was cooled to be in the superconducting state, 50 A was flowing in the circuit.
The SN transition temperature of the switch was 65K.

Above 65K, the switch became a normal conductor of 3Ω and the current flowing through the circuit was 1.6A. That is, in this case, the current flowing through the load at 65K is 5
It was possible to switch to 0A: 1.6A≈30: 1.

As described above, Ic = 39.2A
, The S-N transition temperature is 77K, while Ic = 50A
The S-N transition temperature is 65K, and S
The transition temperature of the -N transition is controlled.

Example 2 Y ₁ B prepared by a unidirectional solidification method from a semi-molten state
From a bulk body having a composition of a ₂ Cu ₃ Ox, a sample having a size of 0.5 mm square and a size of 1.7 cm was cut out and heat-treated to set the oxygen amount x to 6.6. The Tc (current 1. mA) of this sample is 60.
K, and the specific resistance was 3 mΩ · cm.

This sample was incorporated as a switch in the circuit shown in FIG. 5, and the switch was cooled to be in a superconducting state. When the circuit was in the superconducting state, 10 A was flowing in the circuit, and the SN transition temperature of the switch was 45K.

Above 45K, the switch became a normal conductor of 2Ω and the current flowing through the circuit was 0.9A. That is, in this case, the current flowing through the load at 45K could be switched to 10A: 0.9A≈10: 1.

Example 3 A diameter of 3.5 mm and a length of 10 cm were obtained by an ordinary solid-phase sintering method.
The sample of was produced. This sample has Tc = 87K,
The specific resistance was 2 mΩ · cm. Also, Jc at 77K
Was 400 A / cm ² (Ic = 39.2 A).

When this sample was used as a switch in the circuit shown in FIG.
It was 0A, and 16.7A flowed at 65K and above. 65
With K, the current flowing through the load could be switched to 50A: 16.7A≈3: 1.

Example 4 Y ₁ prepared by sputtering on a MgO single crystal
A thin film with a composition of Ba ₂ Cu ₃ Ox is 1 μm thick and 5 m wide.
m and a length of 5 mm were patterned and heat-treated to set the oxygen amount x in the superconducting phase to 6.9. At this time, Tc is 85K
And the specific resistance was 0.2 mΩ · cm. This sample was assembled as a switch in the circuit of FIG. This switch is 10 A: 0.9 A at 45 K as in the case of the second embodiment.
Was able to switch to.

Example 5 Bi ₂ Sr crystal grown from the molten state by the floating zone melting method
₂ Ca ₁ Cu ₂ Ox composition fiber superconductor (2 m
mφ, length 12.5 cm) is used as a switch, and FIG.
A circuit as shown in was prepared.

The fiber-shaped superconductor had a Tc of 82 K as measured by a DC four-terminal method with a current of 1 mA applied. Also, the specific resistance just above the normal conduction transition is 2.5 mΩ ・
cm, and Jc at 77K is 1200 A / cm ² (I
c = 37.7A).

In the circuit shown in FIG. 4, when the switch was cooled and brought into a superconducting state, 50 A was passed through the circuit. The SN transition temperature of the switch was 66K. Thus, the SN transition temperature is 77K at Ic = 37.7A, while the SN transition temperature is 66K at Ic = 50A, and the SN transition temperature is controlled by the applied current.

Above 66K, the switch became a 1.0 Ω normal conductor and the current flowing through the circuit was 4.5A. That is, in this case, the current flowing through the load at 66K could be switched to 50A: 4.5A≈11: 1.

Example 6 Bi grown from a molten state by laser pedestal method
A fiber-shaped superconductor (0.5 mmφ, length 3.3 cm) having a composition of ₂ Sr ₂ Ca ₁ Cu ₂ Ox was used as a switch to prepare a circuit as shown in FIG.

The fiber-shaped superconductor had a Tc of 87K as measured by a DC four-terminal method with a current of 1 mA applied. Also, the specific resistance just above the normal conduction transition is 1.5 mΩ ・
cm, and Jc at 77K is 8000 A / cm ² (I
It was c = 15.7A).

In the circuit shown in FIG. 6, when the switch was cooled to be in the superconducting state, 25 A was passed through the circuit.
The SN transition temperature of the switch was 68K.

Above 68 K, the switch became a 2.4 Ω normal conductor and the current flowing in the circuit was 1 A. That is, in this case, the current flowing through the load at 68K is 2
It was possible to switch to 5A: 1A = 25: 1.

Example 7 Bi ₂ Sr ₂ Ca ₁ Cu ₂ Ox was formed by the usual solid phase sintering method.
A sample having the composition of was prepared.

Next, this sample was rolled into a width of 5 mm, a length of 16.3 mm and a thickness of 0.5 mm. In addition, at the center of this rolled sample, use a diamond saw
A slit having a length of mm and a length of 14.3 mm was formed.

FIG. 7 shows a sample having slits formed therein.
In the high temperature oxide superconductor 11, the width 1 is
A slit 12 having a length of mm and a length of 14.3 mm is formed. When this superconductor is used for switching, a current is passed from one end 11a to the other end 11b of the electric path formed by the slit to be bent.

1 m for the sample with this slit
When a current was applied to A and measured by a DC four-terminal method, Tc was 86K, and the specific resistance immediately above the normal conduction transition was 2.6 mΩ · cm. In addition, 77K of this superconductor
Jc was 700 A / cm ² (Ic = 7 A).

When the sample in which the slit was formed was used for the switch of the circuit shown in FIG. 8 and the switch was cooled to be in the superconducting state, 10 A flowed in the circuit. The SN transition temperature of the switch was 68K.

Above 68 K, the switch became a 1.0 Ω normal conductor and the current flowing through the circuit was 0.91 A. That is, in this case, the current flowing through the load at 68K could be switched to 10A: 0.91A≈11: 1.

Example 8 A sample having a composition of Y ₁ Ba ₂ Cu ₃ Ox was prepared by a usual solid phase sintering method.

Next, this superconductor is pressed to have a width of 7 m.
The sample was m, the length was 34 mm, and the thickness was 0.5 mm. After that, it was processed by a CO ₂ laser to form two slits each having a width of 1 mm and a length of 32 mm at intervals of 2 mm.

A superconductor having slits is shown in FIG. As shown in the figure, in the oxide high temperature superconductor 21, two slits 22 are alternately formed at intervals of 2 mm. When this superconductor is used for a switch, a current flows from one end 21a of the electric path bent by the slit to the other end 21b.

Next, the superconductor having slits was heat-treated to set the oxygen amount x to 6.6.

When the sample after the heat treatment was applied with 1 mA and measured by the DC four-terminal method, Tc was 62 K, and the specific resistance just above the normal conduction transition was 3.2 mΩ · cm. Furthermore, the Jc at 62K of this superconductor is 400
It was A / cm ² (Ic = 4A).

In the circuit shown in FIG. 10, the superconductor was used as a switch, and when the switch was cooled to be in a superconducting state, 8 A was flowing in the circuit. The SN transition temperature of the switch was 45K.

On the other hand, at 45 K and above, the switch became a 3.2 Ω normal conductor, and the current flowing through the circuit was 0.58 A. That is, in this case, the current flowing through the load at 45K could be switched to 8A: 0.58A≈13.8: 1.

[0068]

As described above, since the temperature switch according to the present invention can perform temperature switching at low temperature, it is used as a temperature control temperature switch for a cryopump and a cold head of a cryogenic refrigerator. You can Further, by using a heater in the load shown in the above figures and attaching the switch according to the present invention to the cold head, it is possible to obtain a temperature switch capable of constant ON / OFF control of the temperature of the cold head.

Since the switch according to the present invention serves as both the sensor and the temperature controller, it can be made more compact than the conventional temperature switch in which the temperature sensor, the temperature controller, the power supply and the heater are combined. It can be manufactured at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a current flowing through an oxide superconductor and a transition temperature.

FIG. 2 is a diagram showing the relationship between the amount of oxygen in the superconducting phase of an oxide superconductor and the transition temperature.

FIG. 3 is a perspective view showing an example of a temperature switch having a slit formed according to the present invention.

FIG. 4 is a circuit diagram of an embodiment according to the present invention.

FIG. 5 is a circuit diagram of another embodiment according to the present invention.

FIG. 6 is a circuit diagram of another embodiment according to the present invention.

FIG. 7 is a perspective view showing a temperature switch manufactured in Example 7.

FIG. 8 is a circuit diagram of another embodiment according to the present invention.

FIG. 9 is a perspective view showing a temperature switch manufactured in Example 8 according to the present invention.

FIG. 10 is a circuit diagram of another embodiment according to the present invention.

[Explanation of symbols]

 1, 11, 21 Oxide high temperature superconductor 2, 12, 22 Slit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenichi Sato 1-3-3 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. Osaka Works

Claims (4)

[Claims] 1. A temperature switch utilizing the superconducting-normal conducting transition of a superconductor, wherein the superconductor is an oxide high temperature superconductor, and the transition temperature of the superconducting-normal conducting transition is controlled by a current flowing in the superconducting phase. The temperature switch, which is characterized in that 2. The temperature switch according to claim 1, wherein the transition temperature is further controlled by the amount of oxygen in the superconducting phase. 3. The temperature switch according to claim 1, wherein the oxide high temperature superconductor is manufactured by a unidirectional solidification method. 4. The temperature switch according to claim 1, wherein a slit is formed in the oxide high-temperature superconductor so that the electric path formed by the oxide high-temperature superconductor is bent.