JP3252999B2 - Flux quantum flow device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic flux quantum flow element, and more particularly to a high-temperature superconducting device operating at a temperature near or higher than the temperature of liquid nitrogen (77 K). More specifically, a device whose operation principle is a phenomenon (flux quantum flow) in which a flux quantum formed by a magnetic flux penetrating into a superconductor is driven by a bias current flowing through the superconductor and travels in the superconductor. The present invention relates to a certain flux quantum flow device, and specific applications are expected to be applied to logic devices, microwave amplifiers, microwave oscillators, and the like.

[0002]

2. Description of the Related Art A conventional flux quantum flow element is, for example, an IEEE Transaction Applied.
d Superconductivity Vol.
1, No. 2, p. 95 (1991), a device formed using a single layer of a high-temperature superconducting thin film deposited on a substrate. FIG. 3 is a schematic plan view of such a conventional flux quantum flow device. In the figure, 1
Is a channel through which a flux quantum flows, 2 is a bias current supply line, 3 is a control current supply line, 4 is a hole in a superconductor, 5 is a flux quantum entry end of the channel, and 6 is an interlayer insulating layer. FIG.
As shown in (1), a portion where the flux quantum Q travels (a flux quantum travel region, hereinafter this portion is referred to as a channel) 1 and a bias current supply line 2 which supplies a bias current for driving the flux quantum Q to the channel 1 And a control current supply line 3 for controlling the density of the traveling magnetic flux quantum Q. The bias current supply line 2 is connected to the channel 1, and the control current supply line 3 is provided near the flux quantum entry end 5 of the channel 1. Conventionally, holes 4 are formed at desired intervals in the channel 1 so that the magnetic flux quantum Q easily enters the channel 1, and the thickness of the channel 1 is made thinner than the superconducting film constituting the bias current supply line 2. is there.

In such a conventional flux quantum flow element, the majority of the flux quanta exist in the portion without the superconductor, that is, in the hole 4. Then, when the magnetic flux quantum Q is further supplied from the front portion of the hole of the channel 1, the number of magnetic flux quantum Q in the hole 4 increases, and the magnetic flux Q
Penetrates into the superconductor around the hole 4, in this case, into the channel, and runs through the channel 1 driven by the bias current. At this time, the traveling magnetic flux quantum Q
The voltage (flow voltage) induced across channel 1 is
It is proportional to the number of magnetic flux quanta Q passing through the cross section of the channel 1 per unit time. Therefore, the control current is supplied to the control current supply line 3
When a magnetic field is applied to the channel 1 by changing the density of the magnetic flux quantum penetrating the channel 1, the voltage induced in the channel 1 can be changed.

The operation principle of the flux quantum flow element has been described above. In the conventional example, the channel 1, the bias current supply line 2 and the control current supply line 3 are all formed of one (single-layer) superconducting thin film. Therefore, the control current supply line 3 is formed on the same plane at a position apart from the channel 1 and the bias current supply line 2 so as to be electrically insulated. Since the strength of the control magnetic field is inversely proportional to the distance, only a small part of the magnetic field generated by the control current is applied to the channel 1, the degree of magnetic field coupling between the control current supply line 3 and the channel 1 is small,
A large control current was required to cause the flux quantum Q to enter the channel 1. For this reason, the conventional example has a serious drawback that a large current gain cannot be obtained.

In the device structure of the prior art, since the channel 1, the bias current supply line 2 and the control current supply line 3 are all on the same plane, the area occupied by the device is separated from the area occupied by each device. It is the sum of the areas to perform. Therefore, this element has a drawback that the device occupies a very large area and is not suitable for high-speed operation and high integration.

Further, in the conventional example, since the flux quantum travels in the superconductor, the flux quantum travels at least about one order of magnitude compared to the case where the flux quantum travels in the tunnel barrier of a tunnel-type Josephson junction of a conventional metal-based low-temperature superconductor. Running speed was slow. For this reason, the flow voltage is also reduced by about one digit when the same number of flux quanta is run, and there is a problem that the gain cannot be increased.

Further, a patent (Japanese Patent Application No. 5-277047) for using a layered structure of an oxide high-temperature superconductor for a channel of a flux quantum flow element has already been filed, but in this patent, a layered superconductor is used. The superconducting crystal film is oriented so that the c-axis (axis perpendicular to the layer) is parallel to the substrate surface. Therefore, the axis of the flux quantum traveling through the channel is substantially perpendicular to the substrate, which is different from the device structure in which the axis of the flux quantum is parallel to the substrate as in the present invention.

Further, when a magnetic field is applied to a bulk of BaSrCaCuO single crystal in parallel to the ab plane and a current is caused to flow in the c-axis direction, a phenomenon in which a flux quantum flow voltage is observed at both ends of the crystal in the c-axis direction has been described in 199 Applied. Super
conductivityConference (AS
C94) (Abstracts p.32 EIC)
-10), but no example of applying this phenomenon to a device has been published yet.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to improve the degree of magnetic coupling between the magnetic field generated by the control current supply line and the channel of the flux quantum flow element in the conventional device structure, An object of the present invention is to provide a flux quantum flow element that realizes an amplifying action.

Another object of the present invention is to provide a layered superconductor in which the layered structure is easily formed when the layered superconductor is used for a channel and the c-axis of which is oriented in a direction perpendicular to the substrate surface. An object of the present invention is to facilitate the production of a superconducting thin film of a channel by using it for a channel of an element and to improve the flow characteristics by improving the crystallinity of the thin film.

Still another object of the present invention is to use a superconducting thin film having a layered structure parallel to the substrate surface for a channel so that the flow voltage can be arbitrarily designed depending on the number of channels, that is, the thickness of the intrinsic Josephson junction. To be able to control it.

[0012]

According to the first aspect of the present invention, there is provided a magnetic flux quantum flow element comprising: a magnetic flux quantum traveling region formed of a high-temperature superconducting thin film; A bias current supply line, and a control current supply line for controlling the density of magnetic flux quanta provided in the vicinity of the region, and the axis of the magnetic flux quantum traveling in the magnetic flux quantum travel region corresponds to the magnetic flux quantum travel region. It is characterized by being substantially parallel to the substrate surface of the substrate serving as the base of the high-temperature superconducting thin film to constitute.

According to a second aspect of the present invention, in the magnetic flux quantum flow element according to the first aspect, the magnetic flux quantum traveling region has a layered structure as the magnetic flux quantum traveling region and has a weak superconductivity. A high-temperature superconducting thin film having a structure in which a crystal layer and a superconducting crystal layer are alternately repeated is used, and the flux quantum travels through the weakly superconducting crystal layer. According to the third aspect of the present invention, the magnetic flux quantum flow element according to the first aspect has a layered structure as the magnetic flux quantum running region, and a crystal layer having weak superconductivity. A high-temperature superconducting thin film with a structure in which strong superconducting crystal layers are alternately repeated, and a strong superconducting layer forms an intrinsic Josephson junction through a weak superconducting layer. Using the thin film The feature is that the flux quantum travels through the barrier layer of the Sefson junction.

According to a fourth aspect of the present invention, in the magnetic flux quantum flow element according to the first aspect, the control current supply line is provided above the magnetic flux quantum traveling region. It is characterized by being.

According to a fifth aspect of the present invention, in the magnetic flux quantum flow device according to the first aspect, the bias current from the bias current supply line is formed by the high temperature superconducting thin film. And flows through the magnetic flux quantum traveling region in a direction substantially perpendicular to the substrate.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the prior art, since the device structure is a planar structure, the device occupation area is large and it is difficult to achieve high integration. Since there are control lines, the device size can be significantly reduced, high-speed operation can be realized, and a compact device suitable for high integration can be provided.

Further, in the conventional example, since the flux quantum travels in the superconductor, the flux quantum travels in the tunnel barrier of the tunnel type Josephson junction of the conventional metal-based low-temperature superconductor compared to the case where the flux quantum travels in the tunnel barrier. Although the traveling speed was slow by at least about one digit, in the present invention, the speed is increased to about the same order as that of a conventional metallic Josephson junction. As a result, the flow voltage increases, and the current gain also increases by about one digit.

That is, in the present invention, a high-temperature superconducting thin film having a layered structure, for example, an intrinsic Josephson junction expressed by BaSrCaCuO or the like is used as a flux quantum flow channel to constitute a flux quantum flow element. A high temperature superconducting thin film having a layered structure in which the c-axis is oriented perpendicular to the substrate surface and the ab surface is parallel to the substrate surface. Is also excellent.)
The barrier layer of the Josephson junction, that is, a layer having low superconductivity, is used as a channel through which flux quantum flows. By doing so, the axis of the flowing magnetic flux quantum becomes parallel to the substrate surface. Further, in this device structure, the control current supply line is provided above the intrinsic Josephson junction forming the channel. In this way, most of the magnetic field generated by the control current is efficiently applied to the barrier layer or channel of the intrinsic Josephson junction, and the direction of the magnetic field is parallel to the film surface (substrate). In such a structure, the degree of magnetic field coupling between the control current supply line and the channel is almost 1
It is improved to nearly 00%. Also, in this structure, the control current supply line is provided above the channel, so that the occupation area of the control current supply line is zero, and furthermore, the space for separating the control current supply line from the channel is not required, so the device size is further increased. This is very advantageous for high-speed operation and high integration of the device.

[0019]

FIG. 1 shows the structure of a magnetic flux quantum flow element for explaining an embodiment of the present invention. (A) is a perspective view, (B)
Is a sectional view of a part thereof. In FIG. 1, reference numeral 1 denotes a weak layer made of superconductivity (a channel in which a flux quantum Q runs and a flow voltage is induced at both ends), 1 'denotes a layer having strong superconductivity, 2 denotes a bias current supply line, and 3 denotes a bias current supply line. This is a control current supply line. Reference numeral 6 denotes an interlayer insulating layer that electrically insulates the channel from the control current supply line. Reference numeral 7 denotes a portion of the superconducting thin film that has been mesa-etched from the surface to a certain depth (hereinafter abbreviated as "mesa etch"). The device pattern 10 is a substrate. FIG. 2 is a sectional view taken along line AA 'of FIG. The flux quantum Q flows in a channel 1 parallel to the plane of the substrate 10.

In order to form such a device structure, first, a high-temperature superconducting BaSrCaCuO thin film 8 having a layer structure, for example, is epitaxially grown on a substrate (eg, MgO) by vapor deposition or sputtering. At this time, the thin film is grown so that the c-axis of the crystal structure of the thin film 8 is oriented perpendicular to the substrate surface and the ab plane is parallel to the substrate surface. In a high-temperature superconducting thin film having a strong layered structure, a thin film having such a crystal orientation is most likely to grow, and the obtained film has excellent crystallinity. In this manner, a thin film 8 in which the layers 1 'having strong superconductivity and the layers 1 having weak superconductivity are alternately laminated as shown in FIG. 1B is formed on the substrate. Next, using the photoresist patterned by photolithography as a mask, the thin film is etched (ion milling or chemical etching) to the substrate surface to form a device pattern 9 (bias current supply line 2, voltage terminal, etc.). Then, similarly, the thin film is etched to a certain depth using a photoresist patterned by photolithography as a mask to form a groove 7 (mesa-etched portion). In this way, a part of the layered superconducting thin film is cut out from the other thin film part to a certain depth from the surface by the mesa etch. This portion becomes a so-called intrinsic Josephson junction. In other words, this part has a structure in which layers with strong superconductivity and layers with weak superconductivity are alternately laminated (FIG. 1).
(B)), where the weakly superconductive portion plays the role of the barrier layer of the Josephson junction. Therefore, when a current (bias current) flows from this thin film surface toward the substrate surface and a voltage is measured between the thin film surface and the substrate surface, a superconducting current (Josephson current) flows at zero voltage. A current-voltage characteristic in the form of a large number of junctions connected in series is obtained. This is an intrinsic Josephson junction. The number of junctions connected in series can be obtained by dividing the depth of the mesa etch by the thickness of one unit of the laminated structure. In the present invention, the barrier portion of the intrinsic Josephson junction is used as the flow channel 1. In particular, in the case of a BaSrCaCuO thin film, this barrier layer is insulative, and the flux quantum travels through this barrier at a speed as high as that of a conventional metal-based superconductor tunnel-type Josephson junction barrier. Intrinsic Josephson junction is Mesa etch 7
Is connected to the bias current supply line 2 below. The control current supply line 3 is provided on the channel 1, that is, on the intrinsic Josephson junction via the interlayer insulating layer 6. To manufacture this, an insulating layer 6 is deposited on the intrinsic Josephson junction, patterned, and a superconducting thin film serving as the control current supply line 3 is deposited and patterned thereon. The control current supply line 3 does not necessarily need to be a superconductor, but may be a normal conductor metal.

In this bias structure, as shown in the sectional view of FIG. 2, since the control current supply line 3 is above the channel 1, the magnetic field generated around the control line 3 by the control current is parallel to the substrate surface. Thus, the barrier layer of the intrinsic Josephson junction, that is, the channel 1 is applied from the lateral direction. Part of this magnetic field becomes flux quanta and penetrates into the channel 1. In this case, most of the magnetic field generated by the control current is efficiently applied to the barrier layer or channel 1 of the intrinsic Josephson junction. In such a structure, the control current supply line 3
The degree of magnetic field coupling between the channel and channel 1 is improved to almost 100%. Further, in this structure, since the control current supply line 3 is provided above the channel 1, the occupation area as an additional space required for providing the control current supply line 3 becomes zero, and the control current supply line 3 and the channel Since a space on a plane for separating 1 is not required, the device size is reduced. This enables high-speed operation and high integration of the device.

In the device structure of this embodiment, the flux quantum Q
Flows through the barrier portion or flow channel 1 of the intrinsic Josephson junction. There are many barrier layers for intrinsic Josephson junctions, the number being determined by the depth of the mesa etch 7. Therefore, with this element structure, a flux quantum flow element (multi-channel flow element) having a large number of flux quantum flow channels can be manufactured easily and with good reproducibility. In the multi-channel flow element, since the flow of the magnetic flux quantum occurs in each channel, the flow voltage increases in proportion to the number N of the channels. Therefore, the gain can be greatly improved.

As described above, in this embodiment, the flow voltage of the flux quantum flow element can be designed to a desired value by determining the number of channels of the multi-channel flow element using the parameter of the depth of the mesa etch 7.

In FIGS. 1 and 2, the scale and shape are arbitrarily set for convenience of explanation, and the present invention is not limited to the illustrated example.

In this embodiment, the case where the high-temperature superconducting thin film has a layered structure and an intrinsic Joffson junction is formed has been described. However, the essential point of the present invention is that the intrinsic junction is formed. In addition, even if an intrinsic junction is not formed, it is sufficient that a layer having a weak superconductivity and a magnetic flux quantum can travel to a certain extent or less in a plane parallel to the substrate in the layered structure. Such a case also falls within the scope of the present invention.

[0026]

According to the first aspect of the present invention, in the magnetic flux quantum flow element, a magnetic flux quantum traveling region formed of a high temperature superconducting thin film, a bias current supply line connected to the region, and a vicinity of the region. A flux quantum density control line provided in the magnetic flux quantum travel region, the axis of the flux quantum traveling in the flux quantum travel region is substantially parallel to the substrate surface of the substrate which is the base of the high-temperature superconducting thin film constituting the flux quantum travel region. With this configuration, the flux quantum flow speed in the channel of the flux quantum flow element can be increased, and a large current gain can be obtained.

According to the second aspect of the present invention, in the magnetic flux quantum flow element, the magnetic flux quantum traveling region has a layered structure, and includes a crystal layer having weak superconductivity and a crystal layer having strong superconductivity. By using a high-temperature superconducting thin film having a structure that is alternately repeated, and having a configuration in which the flux quantum travels through a crystal layer having weak superconductivity, the above-described effect can be achieved more efficiently, The degree of freedom in design increases.

According to the third aspect of the present invention, in the magnetic flux quantum flow element, the magnetic flux quantum traveling region has a layered structure, and includes a crystal layer having a weak superconductivity and a crystal layer having a strong superconductivity. A high-temperature superconducting thin film having a structure repeated alternately, wherein a strong superconducting layer forms an intrinsic Josephson junction through a weak superconducting layer, With the configuration in which the flux quantum travels through the barrier layer of the Josephson junction, the above-described effects can be achieved more efficiently, and a higher speed and a higher gain can be achieved.

According to the invention described in claim 4, in the magnetic flux quantum flow element, the magnetic flux quantum density control line is
With the configuration provided above the magnetic flux quantum traveling region, the control current supply line is provided above the channel, so that the current gain can be increased by improving the degree of magnetic coupling, and the control line occupies the control line. Because the occupation area becomes zero,
The device can be miniaturized, and high-speed operation and high integration can be achieved. .

According to the fifth aspect of the present invention, in the magnetic flux quantum flow element, the bias current from the bias current supply line causes the magnetic flux quantum traveling region formed of the high-temperature superconducting thin film to be substantially perpendicular to the substrate. With the configuration in which the fluid flows in the direction, the above-described effect can be more efficiently achieved, and the stability is good.

[Brief description of the drawings]

FIGS. 1A and 1B are diagrams illustrating an embodiment of a magnetic flux quantum flow element according to the present invention, wherein FIG. 1A is a perspective view and FIG.

FIG. 2 is a cross-sectional view taken along line AA ′ of FIG.

FIG. 3 is a schematic plan view for explaining a conventional example of a flux quantum flow element.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 weak superconducting layer (channel through which flux quantum flows) 1 ′ strong superconducting layer 2 bias current supply line 3 control current supply line 4 superconductor hole 5 channel flux quantum intrusion end 6 interlayer insulating layer 7 Mesa-etched groove of superconducting thin film from surface 8 Thin film of high-temperature superconductor 9 Device pattern 10 Substrate for epitaxial growth of superconducting thin film Q Flux quantum

────────────────────────────────────────────────── ─── Continuation of the front page (72) Minoru Suzuki 1-6-1 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (56) References JP-A-7-131080 (JP, A) JP-A Sho 64-21974 (JP, A) JP-A-8-250776 (JP, A) JP-A-7-58366 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39/22 -39/24 H01L 39/00

Claims (5)

(57) [Claims] 1. A magnetic flux quantum traveling region comprising a high-temperature superconducting thin film, a bias current supply line connected to the region, and a control current supply line provided near the region for controlling the density of magnetic flux quanta. A flux quantum flow element, wherein the axis of the flux quantum traveling in the flux quantum traveling region is substantially parallel to a substrate surface of a substrate serving as a base of the high-temperature superconducting thin film constituting the flux quantum traveling region. 2. A high-temperature superconducting thin film having a layered structure and having a structure in which crystal layers having weak superconductivity and crystal layers having strong superconductivity are alternately repeated is used as the flux quantum traveling region. 2. The magnetic flux quantum flow element according to claim 1, wherein the magnetic flux quantum runs through the crystal layer having a weak superconductivity. 3. A high-temperature superconducting thin film having a layered structure as the magnetic flux quantum traveling region and having a structure in which crystal layers having weak superconductivity and crystal layers having strong superconductivity are alternately repeated. A thin film in which a layer of strong superconductivity forms an intrinsic Josephson junction through a layer of weak superconductivity, and the flux quantum travels through the barrier layer of the Josephson junction. The magnetic flux quantum flow device according to claim 1, wherein: 4. The control current supply line is provided above the magnetic flux quantum traveling region.
7. A magnetic flux quantum flow device according to claim 1. 5. The method according to claim 1, wherein the bias current from the bias current supply line flows through the flux quantum traveling region formed of the high-temperature superconducting thin film in a direction substantially perpendicular to the substrate. Flux quantum flow device.