Superconducting device and method of manufacturing the same

Abstract

To improve the uniformity of characteristics of a Josephson junction.SOLUTION: By depositing a superconducting material using the bridge structures 111 as a mask, the first superconductor layer 102 is formed on the substrate 101 so as to terminate at the first trailer 122 on one end side of the junction formation region 121. A first superconductor layer (102) is formed by depositing (vapor-depositing) a superconducting material on the surface of a substrate (101) from a direction at a first angle of less than 90 ° with respect to a vertical plane (132) on the surface of the substrate (101). After the first superconductor layer 102 is oxidized to form an insulating film, a superconducting material is deposited (vapor-deposited) on the surface of the substrate 101 from the direction of the second angle at which the absolute value of the difference between the second angle and 1 / 2 of the first angle is 45 ° with respect to the vertical plane 132, thereby forming the second superconductor layer 103 and forming a Josephson junction.SELECTED DRAWING: Figure 1D

Description

[Technical Field]

[0001] The present invention relates to a superconducting device and a method for manufacturing the same. [Background technology]

[0002] Since the operating characteristics of superconducting devices that handle quantum information depend heavily on the magnitude of the critical current of the Josephson junction, it is important to align the characteristics of the Josephson junctions. In devices that handle discrete digital information, the information is judged by whether it exceeds a reference value, so some variation in characteristics is acceptable. However, devices that handle quantum information use a continuous superposition of 0 and 1 states, so the tolerance for device variation is narrower, making it important to align the characteristics.

[0003] The method described in Non-Patent Document 1 has been used to fabricate Josephson junctions in superconducting quantum devices. In this method (the Dolan bridge method), a resist material is first applied to a substrate, and a predetermined pattern is then drawn and developed on the applied resist layer to create a bridge structure 201, as shown in Figure 3. Note that the substrate is omitted in Figure 3. Using this bridge structure 201 as a mask, a superconducting material is evaporated from the upper right corner of the page to form a first superconductor 202. At this time, a superconductor 202' is also formed in the bridge structure 201. Next, oxygen is introduced to oxidize the surface of the first superconductor 202, creating an insulating layer 211 for the Josephson junction. Next, using the bridge structure 201 as a mask, a superconducting material is evaporated from the upper left corner of the page to form a second superconductor 203. At this time, a superconductor 203' is also formed in the bridge structure 201.

[0004] When a Josephson junction is fabricated using this method, the area of ​​the insulating layer 211 sandwiched between the first superconductor 202 and the second superconductor 203 generally depends on the thickness of the first superconductor 202. The critical current value of the Josephson junction is proportional to the area of ​​the junction surface on which the insulating layer 211 is formed. Therefore, if there is variation in the thickness of the superconductor layer, there is a problem in that the critical current value of the Josephson junction also varies. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] GJ Dolan, "Offset masks for lift-off photoprocessing", Applied Physics Letters, vol. 31, pp. 337-339, 1977. Summary of the Invention [Problem to be solved by the invention]

[0006] Suppressing the variation in the critical current of Josephson junctions is a challenge for integrating superconducting quantum circuits. However, even when multiple Josephson junctions are fabricated on a wafer under the same conditions to achieve a uniform critical current, variations in the critical current still occur.

[0007] The variation in critical current values ​​with current technology is greater than the uniformity of elements required for the integration of superconducting quantum circuits, which is known to cause problems such as the inability to control the frequency of quantum bits with sufficient precision. In order to put superconducting devices that handle quantum information into practical use, technology is needed to improve the uniformity of the characteristics of the Josephson junctions that are fabricated.

[0008] The present invention has been made to solve the above problems, and has as its object to improve the uniformity of the characteristics of Josephson junctions. [Means for solving the problem]

[0009] A method for manufacturing a superconducting device according to the present invention includes a first step of forming a bridge structure spaced apart from the substrate above a junction formation region of the substrate; a second step of depositing a superconducting material using the bridge structure as a mask to form a first superconductor layer on the substrate so as to terminate at a first termination portion on one end side of the junction formation region; a third step of forming a region acting as an insulating layer for a Josephson junction on the first superconductor layer in the junction formation region including a side surface of the first termination portion of the first superconductor layer; and a third step of depositing a superconducting material using the bridge structure as a mask to form an insulating layer for a Josephson junction between the first termination portion and the second termination portion, extending from the first termination portion onto the first superconductor layer and terminating at a second termination portion. and a fourth step of forming a second superconductor layer so as to overlap the first superconductor layer in the junction formation region where a region acting as an edge layer is formed, wherein the angle is based on a plane perpendicular to the substrate surface, with angles measured clockwise being positive and angles measured counterclockwise being negative, and the second step forms the first superconductor layer by depositing superconducting material on the surface of the substrate from a direction that forms a first angle that is less than 90° with respect to the plane perpendicular to the surface of the substrate, and the fourth step forms the second superconductor layer by depositing superconducting material on the surface of the substrate from a direction that forms a second angle that is such that the absolute value of the difference between the second angle and 1 / 2 of the first angle is 45° with respect to the plane perpendicular to the surface of the substrate.

[0010] The superconducting device according to the present invention comprises a junction formation region including a first superconductor layer made of a superconducting material formed so as to terminate at a first termination portion on one end side of a junction formation region of a substrate, a region acting as an insulating layer of a Josephson junction formed on the first superconductor layer in the junction formation region including a side surface of the first termination portion of the first superconductor layer, and a region acting as an insulating layer of a Josephson junction between the first termination portion and the second termination portion, extending from the first termination portion onto the first superconductor layer and terminating at a second termination portion. The device is provided with a second superconductor layer formed to overlap the first superconductor layer, and the angles are based on the perpendicular plane of the substrate surface, with angles measured clockwise being positive and angles measured counterclockwise being negative. The angle formed between the side surface of the first terminal portion of the first superconductor layer and the perpendicular plane of the substrate surface is a first angle that is less than 90°, and the angle formed between the side surface of the second terminal portion of the second superconductor layer and the perpendicular plane of the substrate surface is a second angle that is such that the absolute value of the difference between the second angle and 1 / 2 of the first angle is 45°. [Effects of the Invention]

[0011] As described above, according to the present invention, the uniformity of the characteristics of Josephson junctions can be improved. [Brief explanation of the drawings]

[0012] [Figure 1A] FIG. 1A is a cross-sectional view showing a state in the middle of a process for explaining a method for manufacturing a superconducting device according to an embodiment of the present invention. [Figure 1B] FIG. 1B is a cross-sectional view showing a state in the middle of a process for explaining a method for manufacturing a superconducting device according to an embodiment of the present invention. [Figure 1C] FIG. 1C is a cross-sectional view showing a state in the middle of a process for explaining a method for manufacturing a superconducting device according to an embodiment of the present invention. [Figure 1D] FIG. 1D is a cross-sectional view showing a state in the middle of a process for explaining a method for manufacturing a superconducting device according to an embodiment of the present invention. [Figure 2] FIG. 2 is an explanatory diagram for explaining the effect of the method for manufacturing a superconducting device according to the embodiment of the present invention. [Figure 3] FIG. 3 is an explanatory diagram for explaining a conventional method for manufacturing a superconducting device. DETAILED DESCRIPTION OF THE INVENTION

[0013] A method for manufacturing a superconducting device according to an embodiment of the present invention will be described below with reference to FIGS. 1A to 1D.

[0014] First, as shown in Figure 1A, a bridge structure 111 is formed above the junction formation region 121 of the substrate 101 at a distance from the substrate 101 (first step). For example, the bridge structure 111 can be formed by patterning a photoresist layer using a known photolithography technique. The bridge structure 111 extends from the front to the back of the page in Figure 1A.

[0015] Next, as shown in FIG. 1B, a superconducting material is deposited using the bridge structure 111 as a mask to form a first superconductor layer 102 on the substrate 101 so as to terminate at a first termination portion 122 on one end side of the junction formation region 121 (second step). The superconducting material can be, for example, Al. For example, the first superconductor layer 102 can be formed by depositing a superconducting material such as Al using a well-known vacuum deposition method. At this time, a superconductor layer 102' is also formed on the bridge structure 111.

[0016] In this process, the first superconductor layer 102 is formed by depositing (evaporating) a superconducting material on the surface of the substrate 101 from a direction that forms a first angle of less than 90° with respect to a plane 131 perpendicular to the surface of the substrate 101. For example, evaporation is performed by placing the substrate 101 obliquely so that the above-mentioned angle is formed with respect to the evaporation source (oblique evaporation). In FIG. 1B , the evaporation direction is from the upper right to the lower left of the page. By forming the first superconductor layer 102 in this manner, the angle formed between the first side surface 102a of the first termination portion 122 of the first superconductor layer 102 and the plane 131 perpendicular to the surface of the substrate 101 becomes a first angle. The first angle can be, for example, 30°. Note that in the embodiment, angles are based on the plane perpendicular to the surface of the substrate 101, with clockwise angles being positive and counterclockwise angles being negative. This also applies to the following description.

[0017] Next, as shown in FIG. 1C , a region 103 that serves as an insulating layer for the Josephson junction is formed on the first superconductor layer 102 in the junction formation region 121, including the first side surface 102a in the first termination portion 122 of the first superconductor layer 102 (third step). For example, the region 103 that serves as an insulating layer for the Josephson junction can be formed by introducing oxygen onto the first superconductor layer 102 and oxidizing the surface of the first superconductor layer 102 in this region to form an insulating layer. When the first superconductor layer 102 is made of Al, the region 103 that serves as an insulating layer for the Josephson junction can be formed by using aluminum oxide (AlO x ) is composed of

[0018] Next, as shown in FIG. 1D, a superconducting material is deposited using the bridge structure 111 as a mask to form the second superconductor layer 104 (step 4). The superconducting material can be, for example, Al. For example, the second superconductor layer 104 can be formed by depositing a superconducting material such as Al using a well-known vacuum deposition method. At this time, a superconductor layer 104' is also formed on the bridge structure 111. The second superconductor layer 104 extends from the first termination 122 onto the first superconductor layer 102 and terminates at the second termination 123. The second superconductor layer 104 is formed so as to overlap the first superconductor layer 102 at a junction formation region 121 where a region 103 serving as an insulating layer for the Josephson junction between the first termination 122 and the second termination 123 is formed.

[0019] In this process, the second superconductor layer 104 is formed by depositing (evaporating) a superconducting material on the surface of the substrate 101 from a direction at a second angle, where the absolute value of the difference between half of the first angle and the second angle is 45° relative to the plane perpendicular to the surface of the substrate 101. For example, evaporation is performed by placing the substrate 101 obliquely at the above-mentioned angle relative to the evaporation source (oblique evaporation). In FIG. 1D, the evaporation direction is from the upper left to the lower right of the page. By forming the second superconductor layer 104 in this manner, the angle between the second side surface 104a of the second termination portion 123 of the second superconductor layer 104 and the plane perpendicular to the surface of the substrate 101 becomes the second angle. For example, if the first angle is 30°, the second angle can be -30°.

[0020] By the above-described manufacturing method, a Josephson junction consisting of first superconductor layer 102, region 103 serving as an insulating layer for the Josephson junction, and second superconductor layer 104 is formed in junction formation region 121. In this manufacturing method, bridge structure 111 defines junction formation region 121 where a Josephson junction is formed, where first superconductor layer 102 and second superconductor layer 104 overlap. According to the embodiment, the area (junction area) of the region where region 103 serving as an insulating layer for the Josephson junction is formed can be improved in uniformity without being affected by variations in the thickness of first superconductor layer 102.

[0021] A superconducting device manufactured by the above-described manufacturing method first includes a first superconductor layer 102 made of a superconducting material formed so as to terminate at a first termination portion 122 on one end side of a junction formation region 121 of a substrate 101. The superconducting device also includes a region 103 acting as an insulating layer for a Josephson junction formed on the first superconductor layer 102 in the junction formation region 121 including a first side surface 102a of the first termination portion 122 of the first superconductor layer 102. The superconducting device also includes a second superconductor layer 104 formed so as to extend from the first termination portion 122 onto the first superconductor layer 102 and terminate at a second termination portion 123, overlapping with the first superconductor layer 102 in the junction formation region 121 where the region 103 acting as an insulating layer for a Josephson junction between the first termination portion 122 and the second termination portion 123 is formed.

[0022] The angle formed by the first side surface 102a of the first terminal portion 122 of the first superconductor layer 102 and the vertical plane 131 of the surface of the substrate 101 is a first angle that is less than 90°, and the angle formed by the second side surface 104a of the second terminal portion 123 of the second superconductor layer 104 and the vertical plane 132 of the surface of the substrate 101 is a second angle whose absolute value of the difference between the second angle and 1 / 2 of the first angle is 45°.

[0023] As described above, when a Josephson junction is fabricated by evaporating superconducting material using the bridge structure as a mask, the area that acts as the insulating layer of the Josephson junction that makes up the junction is a part that is horizontal to the substrate and a slope (side) at an angle of θ relative to the substrate vertical. Here, if the first superconductor layer becomes thicker, the area of ​​the horizontal part decreases and the area of ​​the side increases. This changes the junction area. If the amount of change in the area of ​​the horizontal part and the amount of change in the area of ​​the slope part can be made the same, the junction area will not change with changes in the thickness of the first superconductor layer.

[0024] Here, first, in forming the first superconductor layer, the bridge structure is used as a mask to deposit (evaporate) the superconducting material at a predetermined angle θ relative to the vertical plane of the substrate plane. Next, in forming the second superconductor layer, the bridge structure is used as a mask to deposit (evaporate) the superconducting material at a predetermined angle φ relative to the vertical plane of the substrate plane. When formed in this way, the cross section of the Josephson junction parallel to the vertical plane is as shown schematically in Figure 2.

[0025] In Figure 2, the inclined plane of the bonding surface is line segment AB, and the plane parallel to the substrate is line segment BC. Therefore, the cross section of the bonding surface is ABC. If the intersection of line segment AD and a line (plane) passing through point B and parallel to line segment CD is taken as E, then line segments ED and BC will be the same length. Here, if triangle ABE is an isosceles triangle with AB = AE, then the length of ABC will be equal to AD. Therefore, if AB = AE, then even if the distance between line segments AD and BC (the thickness of the first superconductor layer) changes, the length of ABC (= AD) will not change. If triangle ABE is an isosceles triangle with AB = AE, then angles ABE and AEB are equal. The condition for this to hold is |θ-2φ| = 90°.

[0026] Therefore, a Josephson junction that is robust against changes in the thickness of the first superconductor layer can be fabricated by using the bridge structure as a mask to deposit a superconducting material onto the surface of the substrate from a direction that forms a first angle less than 90° with respect to the perpendicular plane of the surface of the substrate, and then depositing a superconducting material onto the surface of the substrate from a direction that forms a second angle with respect to the perpendicular plane of the surface of the substrate such that the absolute value of the difference between the second angle and half the first angle is 45°. Note that one combination in which the absolute values ​​of the deposition angle (first angle) when forming the first superconductor layer and the deposition angle (second angle) when forming the second superconductor layer are equal is when +30° is selected for the first deposition (evaporation) and -30° is selected for the second deposition (evaporation).

[0027] As described above, in the embodiment of the present invention, the bridge structure is used as a mask, and a first superconductor layer is formed by depositing a superconducting material on the surface of the substrate from a direction that forms a first angle less than 90° with respect to the perpendicular plane of the surface of the substrate, and a second superconductor layer is formed by depositing a superconducting material on the surface of the substrate from a direction that forms a second angle with respect to the perpendicular plane of the surface of the substrate such that the absolute value of the difference between the second angle and half the first angle is 45°. As a result, according to the embodiment of the present invention, it is possible to improve the uniformity of the characteristics of the Josephson junction.

[0028] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0029] 101...substrate, 102...first superconductor layer, 102'...superconductor layer, 102a...first side, 103...region acting as insulating layer for Josephson junction, 104...second superconductor layer, 104'...superconductor layer, 104a...second side, 121...junction formation region, 122...first termination portion, 123...second termination portion, 131...vertical surface, 132...vertical surface.

Claims

1. a first step of forming a bridge structure spaced apart from the substrate above a bonding region of the substrate; a second step of depositing a superconducting material using the bridge structure as a mask to form a first superconductor layer on the substrate, the first superconductor layer terminating in a first termination portion on one side of the junction formation region; a third step of forming a region serving as an insulating layer of a Josephson junction on the first superconductor layer in the junction formation region including a side surface of the first termination portion of the first superconductor layer; a fourth step of depositing a superconducting material using the bridge structure as a mask to form a second superconductor layer extending from the first end portion onto the first superconductor layer and terminating at a second end portion, the second superconductor layer overlapping the first superconductor layer in the junction formation region, where a region serving as an insulating layer for a Josephson junction between the first end portion and the second end portion is formed; Equipped with The angle is based on a plane perpendicular to the substrate surface, and angles measured clockwise are positive and angles measured counterclockwise are negative. the second step includes depositing a superconducting material on the surface of the substrate in a direction at a first angle of less than 90° with respect to a plane perpendicular to the surface of the substrate, thereby forming the first superconductor layer; The fourth step forms the second superconductor layer by depositing a superconducting material on the surface of the substrate from a direction at a second angle with respect to a plane perpendicular to the surface of the substrate, the second angle being 45°, the absolute value of the difference between the second angle and half of the first angle. Methods for manufacturing superconducting devices.

2. 2. The method for manufacturing a superconducting device according to claim 1, A method for manufacturing a superconducting device, wherein the angle formed between the side surface of the first termination portion of the first superconductor layer and a plane perpendicular to the surface of the substrate is the first angle.

3. 3. The method for manufacturing a superconducting device according to claim 1 or 2, A method for manufacturing a superconducting device, wherein the first angle is 30°.

4. a first superconductor layer made of a superconducting material formed so as to terminate at a first termination portion on one end side of a junction formation region of the substrate; a region serving as an insulating layer for a Josephson junction formed on the first superconductor layer in the junction formation region including a side surface of the first termination portion of the first superconductor layer; a second superconductor layer extending from the first termination portion onto the first superconductor layer and terminating at a second termination portion, the second superconductor layer being formed so as to overlap the first superconductor layer in the junction forming region where a region serving as an insulating layer for a Josephson junction between the first termination portion and the second termination portion is formed; Equipped with The angle is based on a plane perpendicular to the substrate surface, and angles measured clockwise are positive and angles measured counterclockwise are negative. an angle formed by a side surface of the first termination portion of the first superconductor layer and a plane perpendicular to a surface of the substrate is a first angle that is less than 90°; The angle formed by the side surface of the second termination portion of the second superconductor layer and the perpendicular plane to the surface of the substrate is a second angle, the absolute value of the difference between the second angle and half of the first angle being 45°. Superconducting devices.

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