JP3125816B2 - Flux quantum flow device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-temperature superconducting device operating at a temperature of liquid nitrogen or higher. More specifically, the present invention relates to a flux quantum flow element using a flux quantum formed by a magnetic flux penetrating into a superconductor and running in the superconductor by being driven by a bias current. , A logic element, a microwave amplifier, a microwave oscillator, and the like.

[0002]

2. Description of the Related Art A flux quantum flow device using a high-temperature superconductor is, for example, an IEEE Transaction O.
n Applied Superconductor
tyVol. 1 No. 2, p. 95 (1991), an element formed by forming a single layer of a high-temperature superconducting thin film on a substrate.

As shown in FIG. 1, the element has a region (hereinafter, referred to as a channel) 1 through which a flux quantum travels and a bias connected to the flux quantum for driving the flux quantum. It comprises a bias current line 2 for supplying current to the channel 1 and a control current line 3 for controlling the density of the traveling magnetic flux quantum. The channel 1 is formed with holes (dilute hole portions having superconductor characteristics) 4 at desired intervals so that magnetic flux quanta can easily penetrate, and is made thinner than other superconducting thin films.

In such a flux quantum flow element, the majority of the flux quanta 6 exist in a portion without a superconductor (a portion having a superconductor characteristic being lean), that is, in the hole 4. When the magnetic flux quantum is further supplied from the channel 1 before the hole 4, the number of the magnetic flux quantum 6 in the hole 4 increases,
The flux quanta 6 penetrate into the superconductor, in this case the channel 1 and are driven by the bias current and run through the channel 1.

At this time, a voltage (flow voltage) generated across the channel 1 is proportional to the number of magnetic flux quanta 6 passing through a cross section of the channel 1 per unit time. Therefore, by applying a magnetic field to the channel 1 with the control current line 3,
If the density of the magnetic flux quantum 6 penetrating the channel 1 is changed, the voltage generated in the channel 1 can be changed.
The above is the operation principle of the flux quantum flow element. In this conventional example, as shown in FIG. 2, the generated flow voltage is several tens of mV and the bias current is several mA. Only when was a stable flux quantum flow state realized. For this reason, this element has a fatal defect as a superconducting device that cannot be operated at high speed and is not suitable for high integration.

[0006]

According to the present invention, in order to lower the operating current level and the voltage level of the flux quantum flow element, the flux quantum flow is stably generated with a low bias current, and the condition for generating a low flow voltage is provided. It is an object to provide a device structure for realizing it.

[0007]

In the magnetic flux quantum flow device according to the present invention, the ground plane is formed of a superconductor, whereby the inductance of the hole portion is L, and the hole portion and the hole portion are connected to each other. When the critical current value of the superconductor is Ic and the magnetic flux amount of the magnetic flux quantum is φ ₀ ,

[0008]

(5) An element characterized by satisfying LIc <φ ₀ (1).

In another magnetic flux quantum flow element according to the present invention, the distance between the hole portions of the superconductor and the size of the hole portion are defined in a predetermined range. A magnetic flux quantum flow element characterized by being satisfied.

In the method of manufacturing a magnetic flux quantum flow element according to the present invention, a part of the superconductor constituting the running region is irradiated with an ion beam or an electron beam to change the hole-like portion into a normal conductor. And thereby satisfying the expression (1).

Further, in another method of manufacturing a magnetic flux quantum flow element according to the present invention, the hole-like portion is formed by reducing the amplitude of an order parameter of a superconductor. And a method for manufacturing a magnetic flux quantum flow element characterized by satisfying the following.

[0012]

In the flux quantum flow element, the holes and the normal region in the superconductor serve as pinning centers when the flux quantum moves in the superconductor. Also, when the flux quantum is in the hole, the bias current does not act,
Lorentz force from bias current does not work. Therefore, the force by which the flux quantum tries to penetrate the superconductor (channel) does not work. As a result, the flux quanta tends to stay in the pore. When more flux quanta are supplied from the front channel and stay in the hole, and when the flux quanta can no longer fit in the hole, the flux quanta begin to enter the channel, which is driven by bias current Being run all at once in the channel. This is the operation principle of the conventional flux quantum flow element, and is the reason why a high bias current is required and the generated voltage is large.

In the conventional element structure, the inductance of the hole portion of the superconductor is very large, and even if the size of the hole portion is 1 μm or less, a large number of magnetic flux quanta exist in the hole portion. It cannot exist and cannot realize a state in which a single flux quantum cannot exist stably.

In the present invention, in consideration of the above points, the inductance of the hole portion in the channel of the superconductor is reduced, and one magnetic flux quantum is localized and stably present in the hole portion. Make it impossible. By doing so, the flux quanta easily travels through the channel at low bias current levels because a portion of the flux quanta is always in the channel and is driven by the bias current. At this time, since the pinning force of the hole is weak, the magnetic flux quantum is less likely to be pinned to the hole. Therefore, the vehicle does not travel in a state where magnetic flux quanta are gathered at a high density. Therefore, the traveling of the magnetic flux quantum occurs stably from a low bias current level, and the generated flow voltage is small.

As described above, according to the present invention, it is possible to prevent the magnetic flux quantum from being trapped in the thin hole portion having the superconductor characteristic, thereby enabling low current and low voltage operation.

[0016]

EXAMPLES Examples of the present invention will be described below, but the present invention is not limited to these examples.

(Embodiment 1) FIG. 3 shows a plan structure of an element for explaining a first embodiment of the present invention. In the figure, 1 is a channel through which a flux quantum travels, 2 is a bias current line, 3 is a control current line, 4 is a hole of a superconductor (a thin hole portion of superconductor characteristics), and 5 is a high-temperature superconductor. 1 shows a single crystal substrate (5a) and an insulating layer (5b) epitaxially formed thereon.

As a method of manufacturing an element having this structure, for example,
YBa ₂ Cu ₃ O as substrate (ground plane) 5a
₇ is used as the insulating layer 5b.
NdGaO ₃ is grown thereon, and YBa ₂ Cu ₃ O ₇ is grown epitaxially thereon as a high-temperature superconductor. Then, the YBa ₂ Cu ₃ O ₇ film is patterned to form an element structure from the channel 1 to the hole 4 of the superconductor.

In this case, even if the size of the hole 4 formed in the channel 1 is about several microns, which is about the same as the conventional size, the YBa ₂ Cu ₃ O _{7 of the} substrate 5a works as a superconducting ground plane. , The inductance of the hole 4 is greatly reduced. Therefore, the amount of magnetic flux that can enter the hole 4 stably becomes very small, and even one flux quantum cannot completely enter. By using the single crystal of the high-temperature superconductor as the substrate 5a and using it as the superconducting ground plane, the condition that one magnetic flux quantum cannot be localized in one hole, that is,

[0020]

(6) It is possible to satisfy LIc <φ ₀ (1). Here, L is the inductance of the hole 4 of the superconductor. As shown in FIG. 4, Ic is a current value when a flux quantum starts to enter a constricted portion of the superconducting thin film when a current flows through the superconducting thin film confined by the hole 4. Φ ₀ is 2 × 10 ⁻¹⁵ Wb, which is the amount of magnetic flux of the magnetic flux quantum.

When this condition (Equation (1)) is satisfied, the magnetic flux quantum does not completely enter the hole 4 but partially enters the channel 1. At this time, the flux quantum effectively receives the driving force from the bias current, and a stable flow of the flux quantum is realized.

Further, in order to further stabilize the flow of the magnetic flux quantum, the shape of the bias current line 2 is changed so that the bias current flows uniformly in the entire channel as shown in FIG.

In this embodiment, a single crystal of a high-temperature superconductor is used as a ground plane, but MgO, SrT
iO _3, in order by epitaxial growth of NdGaO ₃ insulating substrate to a high temperature superconductor A / insulator / superconductor, such as B, and the high-temperature superconductor A ground plane, using a high-temperature superconductor B as an element It is also possible.

(Embodiment 2) When the critical current Ic of the superconductor is large, as described in Embodiment 1, simply providing a ground plane on the element causes one magnetic flux in the hole of the superconductor. In some cases, the condition that no quantum enters cannot be satisfied. In such a case, it is necessary to further reduce the size of the hole. Here, as a second embodiment, a device structure capable of reducing the size of the hole portion of the superconductor is provided.

FIG. 5 is a plan view of an element structure for explaining a second embodiment of the present invention. In the figure, 1 is a channel through which a flux quantum travels, 2 is a bias current line, 3 is a control current line, 4
Reference numeral 5 denotes a hole portion having a dilute superconductor characteristic, and reference numeral 5 denotes a single crystal substrate (5a) of a high-temperature superconductor and an insulating layer (5b) epitaxially grown thereon.

The difference between this structure and the first embodiment is that
In order to form the hole-shaped portion 4 small, instead of processing the superconductor by etching, a part of the superconductor is damaged by, for example, ion irradiation or the like, and is changed to a normal conductor. It is. That is, in this case, the inside of the hole of the superconductor is a normal conductor.

In such a manufacturing method, since the exposed portion of the superconductor is damaged and changed to a normal conductor, the fine pattern is formed by forming a resist pattern in consideration of the lateral spread of the damage in advance. Holes can be easily formed.

An example of a manufacturing process for realizing this element structure will be described with reference to FIG. The superconductor of the channel 1 is protected by the resist 7, and the superconductor corresponding to the hole portion 4 is exposed using lithography. Then, the portion is irradiated with an electron beam or an ion beam (for example, argon ion) to damage the superconductor and reduce the superconducting critical temperature to below the operating temperature of the element or to change this portion to a normal conductor. Change to According to this method, as shown in FIG. 7, the size of the hole-shaped portion 4 can be reduced to such an extent that one magnetic flux quantum 6 cannot be fully inserted.

(Embodiment 3) Another method for reducing the value of LIc described in Embodiment 1 is realized. The method of the present embodiment
This is not a method of providing a superconductor hole in the channel of the device.
In this method, the amplitude of the order parameter of the superconductor at the location corresponding to the hole is reduced by, for example, ion beam irradiation, and the superconductivity at the location is reduced, thereby maintaining a state where magnetic flux quanta easily enter the channel. On the other hand, this is a method for realizing a state in which one flux quantum cannot stably enter a portion (a hole in a broad sense) having a weak superconductivity.

FIG. 8 is a sectional view of an element structure for explaining a third embodiment of the present invention. In the figure, reference numeral 1 denotes a channel through which a flux quantum travels, 3 denotes a control current line, 5 denotes a single-crystal substrate 5a of a high-temperature superconductor and an insulating layer 5b epitaxially grown thereon, and 4 denotes a superconductor. This is a portion where the amplitude of the order parameter of the body becomes small (that is, a hole portion where the superconductor characteristic is weakened), and is a hole in a broad sense.

The difference of this structure from the second embodiment is that instead of changing a part of the superconductor to a normal conductor, a portion having reduced superconductivity is formed as a hole of the superconductor. It is.

In this embodiment, ion irradiation is used as a means for reducing the order parameter of the superconductor. However, various known methods such as the use of grain boundaries can be applied. Not even.

Further, in the above description of the embodiment, although not particularly mentioned in order to avoid the complexity of the description, the channel constituted by the superconductor has a larger film thickness than that of the bias current line superconductor. It is composed of a thin superconductor. This is to prevent the flux quantum from escaping to the bias current line. However, since this device is based on the principle that the flux quanta travels in the superconductor, the channel portion of this device is not a superconducting weak coupling that shows the Josephson effect. Therefore, the traveling flux quantum is not an Josephson flux quantum but an abrikosov flux quantum present in the second-class superconductor.

[0034]

According to the present invention, since a magnetic flux quantum flow is stably generated at a low bias current and a magnetic flux is generated at a low magnetic flux quantum density, the flow voltage generated during operation can be reduced. Therefore, this element can operate at high speed and can avoid the drawback that it is not suitable for high integration because it generates less heat during operation.

[Brief description of the drawings]

FIG. 1 is a plan view of a conventional flux quantum flow element.

FIG. 2 is a graph showing a relationship between a bias current and a flow voltage of a conventional device.

FIG. 3, showing a first embodiment of the present invention, is a plan view of a magnetic flux quantum flow element according to the present invention.

FIG. 4 is an explanatory diagram for defining a bias current.

FIG. 5 shows a second embodiment of the present invention, and is a plan view of a magnetic flux quantum flow element according to the present invention.

FIG. 6 shows a second embodiment of the present invention, and is a cross-sectional view of a magnetic flux quantum flow element according to the present invention.

FIG. 7 is an enlarged plan view of the vicinity of a hole portion of a magnetic flux quantum flow element according to a second embodiment of the present invention.

FIG. 8 shows a third embodiment of the present invention and is a cross-sectional view of a magnetic flux quantum flow element according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 Superconductor channel through which flux quantum flows 2 Bias current line 3 Control current line 4 Rare hole-shaped portion of superconductor characteristics 5 Superconductor and insulator constituting ground plane 5a Superconductor constituting ground plane Body 5b Insulating layer constituting ground plane 6 Magnetic flux quantum 7 Resist

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-47-36790 (JP, A) JP-A-62-117194 (JP, A) JP-A-64-119794 (JP, A) (58) Investigation Field (Int.Cl. ⁷ , DB name) H01L 39/22-39/24 H01L 39/00

Claims (4)

(57) [Claims] 1. A magnetic flux quantum traveling region comprising a high-temperature superconductor, a bias current supply line connected thereto, and a magnetic flux quantum write control current line. An element in which a plurality of rare-hole portions having superconductor characteristics are provided in the flux quantum traveling region, and the ground plane is formed of a superconductor, whereby the inductance of the hole portion is L, When the critical current value of the superconductor between the hole-like portions is Ic and the amount of magnetic flux of the magnetic flux quantum is φ ₀ , the following expression is satisfied: LIc <φ ₀ (1) A flux quantum flow element characterized by the above-mentioned. 2. A magnetic flux quantum traveling region comprising a high-temperature superconductor, a bias current supply line connected thereto, and a magnetic flux quantum write control current line. An element in which a plurality of rare-hole portions having superconductor characteristics are provided in a magnetic flux quantum traveling region, wherein the distance between the hole portions and the hole portions of the superconductor is defined in a predetermined range. Accordingly, when the inductance of the hole portion is L, the critical current value of the superconductor between the hole portions is Ic, and the amount of magnetic flux of the magnetic flux is φ ₀ , A magnetic flux quantum flow element characterized by satisfying LIc <φ ₀ (1). 3. A magnetic flux quantum traveling region composed of a high-temperature superconductor, a bias current supply line connected thereto, and a magnetic flux quantum writing control current line. A method for manufacturing an element in which a plurality of rare-hole portions having superconductor characteristics are provided in a flux quantum traveling region, wherein the pore portion is formed by ionizing a part of a superconductor constituting the traveling region. It is formed by irradiating a beam or an electron beam to change into a normal conductor, whereby the inductance of the hole portion is L, and the critical current value of the superconductor between the hole portions is Ic, a method of manufacturing a flux quantum flow element, characterized by satisfying the following formula: LIc <φ ₀ (1), where φ ₀ is the magnetic flux amount of the magnetic flux quantum. 4. A magnetic flux quantum traveling region comprising a high-temperature superconductor, a bias current supply line connected thereto, and a magnetic flux quantum write control current line. What is claimed is: 1. A method for manufacturing a device in which a plurality of rare-hole portions having superconductor characteristics are provided in a magnetic flux quantum traveling region, wherein the hole portions are formed by reducing the amplitude of an order parameter of a superconductor. Thus, the inductance of the hole portion is L, the critical current value of the superconductor between the hole portions is Ic, and the amount of magnetic flux quantum is φ.
_A method of manufacturing a magnetic flux quantum flow device, characterized by satisfying: LIc <φ ₀ (1) when _{0 is set} .