Flux-trapping magnetic films in superconducting circuits.

Abstract

An example includes a superconducting circuit. The circuit includes superconducting circuitry fabricated in a circuit layer. The circuit layer includes a first surface and a second surface opposite the first surface. The circuit also includes a flux moat including a dielectric material formed in the circuit layer. The flux moat can be configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature. The circuit further includes a magnetic film disposed proximate to the flux moat on at least one of the first and second surfaces of the circuit layer. The magnetic film can be configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION This specification relates generally to electronic circuits, and more particularly to flux-trapping magnetic films for superconducting circuits. [Background technology]

[0002] Superconducting circuits operate based on the behavior of superconducting metals in cryogenic environments. For example, at very low cryogenic temperatures (e.g., below 1 K), superconducting metals can exhibit superconductivity, where electrons can propagate with nearly zero resistance. A typical superconducting circuit operates based on the provision of a bias current to a bias input to affect the triggering of Josephson junctions and / or to provide magnetic flux to a superconducting loop. When a superconducting circuit is cooled from a normal ambient temperature environment to a cryogenic temperature, and thus below the superconducting critical temperature of the superconducting device, noise currents can be generated and propagated into the superconducting circuit via the bias input. Such noise currents can generate magnetic flux in the superconducting loop that remains undissipated and can cause flux trapping, which can adversely affect the operation of the superconducting circuit after the superconducting circuit cools to cryogenic temperatures. Summary of the Invention

[0003] An example includes a superconducting circuit. The superconducting circuit includes superconducting circuitry fabricated in a circuit layer. The circuit layer includes a first surface and a second surface opposite the first surface. The superconducting circuit also includes a flux moat including a dielectric material formed in the circuit layer. The flux moat can be configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature. The superconducting circuit further includes a magnetic film disposed on at least one of the first and second surfaces of the circuit layer in proximity to the flux moat. The magnetic film can be configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature.

[0004] Another example described herein includes a method for fabricating a superconducting circuit. The method includes forming superconducting circuitry in a circuit layer. The circuit layer includes a first surface and a second surface opposite the first surface. The method also includes forming a flux moat in the circuit layer, the flux moat including a dielectric material. The flux moat can be configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature. The method further includes depositing a magnetic film on at least one of the first and second surfaces of the circuit layer in proximity to the flux moat. The magnetic film can be configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature.

[0005] Another example described herein includes a superconducting circuit. The superconducting circuit includes a superconducting circuit configuration fabricated in a circuit layer. The circuit layer includes a first surface and a second surface opposite the first surface. The superconducting circuit also includes a flux moat including a dielectric material formed in the circuit layer. The flux moat can be configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature. Furthermore, the superconducting circuit includes a perpendicular magnetic anisotropy (PMA) material film disposed on at least one of the first and second surfaces of the circuit layer and over the flux moat. The magnetic film can be configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a block diagram of an example superconducting circuit. [Figure 2] FIG. 1 is a diagram of an example superconducting circuit. [Figure 3] 1A-1C illustrate a method for fabricating an example superconducting circuit. DETAILED DESCRIPTION OF THE INVENTION

[0007] This specification relates generally to electronic circuits, and more particularly to magnetic flux-trapping magnetic films for superconducting circuits. The superconducting circuits described herein include superconducting circuitry fabricated in a circuit layer including a first surface and a second surface opposite the first surface. As described herein, the term "circuit layer" can refer to a wafer or die layer in which a superconducting circuit is fabricated, the layer being composed of a metal (e.g., a superconducting metal) and a dielectric material. Thus, the first and second surfaces can correspond to opposing surfaces of the wafer or die on which the superconducting circuit is fabricated. The superconducting circuit can also include one or more magnetic flux moats. The magnetic flux moats can be formed as wells of dielectric material extending between the first and second surfaces of the circuit layer and disposed between regions of the circuit layer on which the superconducting circuit is fabricated. The magnetic flux moats can be configured to trap magnetic flux that appears in the superconducting circuitry when the superconducting circuit is cooled to the cryogenic temperatures at which the superconducting circuit operates. As a result, spurious magnetic flux that may appear within the superconducting circuitry is transferred to the flux moat, reducing the adverse effects of magnetic flux within the superconducting circuitry that may degrade device performance during cryogenic operation of the superconducting circuitry.

[0008] In a typical superconducting circuit design, the flux moat region may be designed to be energetically favorable for trapping magnetic flux when the superconducting circuit is cooled below the critical superconducting temperature. However, some magnetic flux may be trapped at locations within the superconducting circuit configuration other than the flux moat. Such flux trapping processes may be stochastic, depending on the relative energies of the flux trapping locations when the circuit is cooled to the critical superconducting temperature. Defects in the superconducting material and in certain circuit topologies may inadvertently create locations that are energetically more favorable for flux trapping, thereby competing with the flux moat for advantage in flux trapping.

[0009] As described herein, to provide more deterministic magnetic flux trapping within the flux moats, the superconducting circuit can include a magnetic film formed on at least one of the surfaces of the circuit layer in proximity to (e.g., over) the flux moats. As an example, the magnetic film can be formed from a perpendicular magnetic anisotropic (PMA) material having a magnetization orthogonal to the plane of the respective surfaces of the circuit layer. For example, the superconducting circuit can include multiple magnetic films formed over each of the multiple flux moats on each of the first and second surfaces of the circuit layer. Thus, the magnetic film can provide a higher degree of advantage in trapping magnetic flux within the superconducting circuit configuration into the flux moats when the superconducting circuit is cryogenically cooled.

[0010] FIG. 1 is a block diagram of an example superconducting circuit system 100. The superconducting circuit system 100 can be implemented in any of a variety of superconducting applications, such as a superconducting computer system. The superconducting circuit system 100 includes superconducting circuitry 102, at least one flux moat 104, and at least one magnetic film 106. The superconducting circuitry 102 can be fabricated in a circuit layer including a first surface and a second surface opposite the first surface. The flux moat(s) 104 can be formed as wells of dielectric material extending between the first and second surfaces of the circuit layer and disposed between regions of the circuit layer in which the superconducting circuitry 102 is fabricated. The flux moat(s) 104 can be configured to trap magnetic flux that appears in the superconducting circuitry 102 when the superconducting circuit system 100 is cooled to the cryogenic temperatures at which the superconducting circuit operates. As a result, spurious magnetic flux that may appear within the superconducting circuitry 102 is transferred to the flux moat(s) 104, mitigating the adverse effects of magnetic flux within the superconducting circuitry 102 that may degrade device performance during operation of the superconducting circuitry 102 at cryogenic temperatures.

[0011] The magnetic film(s) 106 are configured to provide a more deterministic, less stochastic process of trapping magnetic flux within the flux moat(s) 104. As an example, the magnetic film(s) 106 may be formed proximate to (e.g., over) the flux moat(s) 104 on at least one of the surfaces of the circuit layer. For example, the magnetic film(s) 106 may be formed from a perpendicular magnetic anisotropy (PMA) material having a magnetization orthogonal to the plane of the respective surfaces of the circuit layer. The superconducting circuit system 100 may include multiple magnetic films 106 formed over each of the flux moat(s) 104 on each of the first and second surfaces of the circuit layer. Thus, the magnetic film(s) 106 can provide greater advantages in trapping magnetic flux within the superconducting circuit configuration 102 into the magnetic flux moat(s) 104 when the superconducting circuit system 100 is cooled to cryogenic temperatures.

[0012] FIG. 2 is a diagram of an example superconducting circuit 200. The superconducting circuit 200 is shown in a cross-sectional view of a circuit layer that may further extend in each of both lateral directions. The circuit layer includes a first surface 202 and a second surface 204 opposite the first surface 202. The circuit layer is shown in the example of FIG. 2 as being fabricated on a substrate 205. The superconducting circuit 200 may correspond to the superconducting circuit system 100 in the example of FIG. 1. Accordingly, the following description of the example of FIG. 2 will refer to the example of FIG. 1.

[0013] 2 , superconducting circuit 200 includes superconducting circuitry 206 distributed at multiple locations within a circuit layer. Superconducting circuit 200 includes a flux moat 208 between each pair of superconducting circuitry 206. Flux moat 208 extends between first surface 202 and second surface 204 of the circuit layer and is shown as part of the circuit layer disposed between or adjacent to a pair of superconducting circuitry 206. By way of example, each of the plurality of flux moats 208 may include only dielectric material within the portion of the respective flux moat 208 between first surface 202 and second surface 204. As described above, each of the plurality of flux moats 208 may be configured to trap magnetic flux that appears within superconducting circuitry 206 when superconducting circuit 200 cools to the cryogenic temperatures at which the superconducting circuit operates.

[0014] 2, superconducting circuit 200 includes magnetic films 210 disposed on surfaces 202 and 204 of a circuit layer. As a first example, a single magnetic film 210 may be disposed on either first surface 202 or second surface 204, as generally indicated at 212. As a second example, a magnetic film 210 may be formed on both first surface 202 and second surface 204 over a given flux moat 208, as generally indicated at 214. For example, magnetic film 210 may be formed from a PMA material having a magnetization orthogonal to the plane of each surface 202 and 204 of the circuit layer. For example, the magnetic film may be formed from cobalt-platinum (CoPt), cobalt-palladium (CoPd), terbium-iron (TbFe), or one of a variety of other PMA materials. The magnetization is shown in an exploded view 216, with the magnetization shown as being oriented perpendicular to the respective surfaces 202 and 204. In the example of Figure 2, the direction of magnetization is shown as being oriented away from the substrate 205, but the direction of magnetization may instead be oriented toward the substrate 205. In a second example 214 of the magnetic film 210, the direction of magnetization of the magnetic film 210 may be in the same direction for the aligned polarities.

[0015] Thus, placement of magnetic film 210 in proximity to (e.g., over) flux moat 208 can provide a more deterministic, and therefore less stochastic, process for trapping magnetic flux within flux moat 208. For example, a magnetic film (e.g., formed from a PMA material) can exhibit high magnetocrystalline anisotropy and thus can overcome the demagnetizing fields that normally cause magnetization to lie in the plane of magnetic film 210. Thus, magnetic film 210 provides a greater advantage in trapping magnetic flux within flux moat 208.

[0016] In contrast to typical superconducting circuit systems, magnetic film 210 may provide a greater advantage in flux trapping magnetic flux from superconducting circuit 200 to flux moat 208 when superconducting circuitry 206 is cooled to cryogenic temperatures. Furthermore, by forming magnetic film 210 over flux moat 208, the high permeability material and superconducting circuitry 206 can be confined to separate regions within the circuit layer, thereby minimizing the possibility that the high permeability material will affect the performance of superconducting circuitry 206. Thus, magnetic film 210 of superconducting circuit 200 may be more effective than typical superconducting circuits at mitigating magnetic flux within superconducting circuitry 206 when superconducting circuit 200 is cooled to cryogenic temperatures.

[0017] With the structural and functional features described above in mind, methods according to various aspects of the present invention may be better understood by reference to Figure 3. While, for ease of explanation, the method of Figure 3 is shown and described as being performed sequentially, it should be understood and appreciated that, in accordance with the present invention, some aspects may be performed in a different order and / or simultaneously with other aspects than shown and described herein, and therefore the present invention is not limited by the illustrated order. Furthermore, not all illustrated features may be required to practice a method according to an aspect of the present invention.

[0018] FIG. 3 illustrates an example method 300 for fabricating a superconducting circuit (e.g., superconducting circuit system 100). At 302, superconducting circuitry (e.g., superconducting circuitry 102) is formed in a circuit layer. The circuit layer includes a first surface (e.g., first surface 202) and a second surface (e.g., second surface 204) opposite the first surface. At 304, magnetic flux moats (e.g., flux moats 104) including a dielectric material are formed in the circuit layer. The flux moats may be configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature. At 306, a magnetic film (e.g., magnetic film(s) 106) is deposited on at least one of the first and second surfaces of the circuit layer in proximity to the flux moats. The magnetic film may be configured to direct magnetic flux to the flux moats when the superconducting circuit is cooled below a superconducting critical temperature.

[0019] The above description is illustrative. Of course, it is not possible to describe every conceivable combination of components or methodologies, but one of ordinary skill in the art will recognize that many more combinations and permutations are possible. Accordingly, this disclosure is intended to embrace all such changes, modifications, and variations that are within the scope of this application, including the appended claims. As used herein, the term "comprising" means including, but not limited to, and the term "comprising" means including, but not limited to. The term "based on" means based at least in part on. Furthermore, when the disclosure or claims recite "a," "an," "a first," "another" element, or the equivalent thereof, this should be construed as including one or more such elements, and does not require or exclude two or more such elements. The technical concepts that can be understood from the above-described embodiment will be described below as supplementary notes. [Appendix 1] A superconducting circuit, superconducting circuitry fabricated in a circuit layer, the circuit layer having a first surface and a second surface opposite the first surface; a flux moat including a dielectric material formed within the circuit layer, the flux moat configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature; a magnetic film disposed on at least one of the first surface and the second surface of the circuit layer proximate to the flux moat, the magnetic film configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature. [Appendix 2] 2. The superconducting circuit according to claim 1, wherein the magnetic film is formed from a perpendicular magnetic anisotropy (hereinafter referred to as PMA) material. [Appendix 3] 3. The superconducting circuit of claim 2, wherein the PMA material has a magnetization orthogonal to each one of the first and second surfaces of the circuit layer. [Appendix 4] 3. The superconducting circuit of claim 2, wherein the PMA material is one of cobalt-platinum (CoPt), cobalt-palladium (CoPd), and terbium-iron (TbFe). [Appendix 5] 2. The superconducting circuit of claim 1, wherein the magnetic film is formed over the flux moat on at least one of the first and second surfaces of the circuit layer. [Appendix 6] The magnetic film is a first magnetic film disposed on the first surface of the circuit layer adjacent to the flux moat; a second magnetic film disposed on the second surface of the circuit layer proximate to the flux moat. [Appendix 7] 5. The superconducting circuit of claim 4, wherein the first magnetic film is disposed over the flux moat on the first surface of the circuit layer, and the second magnetic film is disposed over the flux moat on the second surface of the circuit layer opposite the first magnetic film. [Appendix 8] 2. The superconducting circuit of claim 1, wherein the flux moat is disposed between a first set of superconducting circuitry and a second set of superconducting circuitry within the circuit layer. [Appendix 9] The superconducting circuit comprises: a plurality of flux moats disposed between a plurality of sets of superconducting circuitry, each of the plurality of flux moats including the dielectric material formed within the circuit layer; a plurality of magnetic films, each of the plurality of magnetic films positioned on one of the first and second surfaces of the circuit layer and proximate one of the plurality of magnetic flux moats. [Appendix 10] 1. A method for fabricating a superconducting circuit, comprising: forming superconducting circuitry in a circuit layer, the circuit layer having a first surface and a second surface opposite the first surface; forming a flux moat comprising a dielectric material in the circuit layer, the flux moat configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature; and depositing a magnetic film on at least one of the first surface and the second surface of the circuit layer proximate to the flux moat, the magnetic film being configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature. [Appendix 11] 11. The method of claim 10, wherein the step of depositing a magnetic film includes depositing a perpendicular magnetic anisotropy (hereinafter referred to as PMA) material film. [Appendix 12] 12. The method of claim 11, wherein the PMA material film has a magnetization orthogonal to each one of the first and second surfaces of the circuit layer. [Appendix 13] 11. The method of claim 10, wherein depositing the magnetic film includes depositing the magnetic film on the at least one of the first and second surfaces of the circuit layer and over the flux moat. [Appendix 14] The step of depositing the magnetic film includes: depositing a first magnetic film on the first surface of the circuit layer overlying the flux moat; 11. The method of claim 10, including depositing a second magnetic film on the second surface of the circuit layer over the flux moat. [Appendix 15] 11. The method of claim 10, wherein forming the superconducting circuitry includes forming a first set of superconducting circuitry in the circuit layer and forming a second set of superconducting circuitry in the circuit layer, and forming the flux moat includes forming the flux moat between the first set of superconducting circuitry and the second set of superconducting circuitry in the circuit layer. [Appendix 16] A superconducting circuit, superconducting circuitry fabricated in a circuit layer, the circuit layer having a first surface and a second surface opposite the first surface; a flux moat including a dielectric material formed within the circuit layer, the flux moat configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature; a film of perpendicular magnetic anisotropy (hereinafter PMA) material disposed on at least one of the first and second surfaces of the circuit layer and overlying the flux moat, the PMA material configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature. [Appendix 17] 17. The superconducting circuit of claim 16, wherein the PMA material film has magnetizations orthogonal to one of each of the first and second surfaces of the circuit layer. [Appendix 18] 17. The superconducting circuit of claim 16, wherein the PMA material film is formed from one of cobalt-platinum (CoPt), cobalt-palladium (CoPd), and terbium-iron (TbFe). [Appendix 19] The PMA material film is a first film of PMA material disposed on the first surface of the circuit layer and overlying the flux moat; a second film of PMA material disposed on the second surface of the circuit layer and over the flux moat. [Appendix 20] 17. The superconducting circuit of claim 16, wherein the flux moat is disposed between a first set of superconducting circuitry and a second set of superconducting circuitry in the circuit layer.

Claims

1. A superconducting circuit, superconducting circuitry fabricated in a circuit layer, the circuit layer having a first surface and a second surface opposite the first surface; a flux moat including a dielectric material formed within the circuit layer, the flux moat configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature; a magnetic film disposed on at least one of the first surface and the second surface of the circuit layer proximate to the flux moat, the magnetic film configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature.

2. 2. The superconducting circuit of claim 1, wherein the magnetic film is made of a perpendicular magnetic anisotropy (hereinafter referred to as PMA) material.

3. 3. The superconducting circuit of claim 2, wherein the PMA material has a magnetization orthogonal to a respective one of the first and second surfaces of the circuit layer.

4. 3. The superconducting circuit of claim 2, wherein the PMA material is one of cobalt-platinum (CoPt), cobalt-palladium (CoPd), and terbium-iron (TbFe).

5. 2. The superconducting circuit of claim 1, wherein the magnetic film is formed over the flux moat on at least one of the first and second surfaces of the circuit layer.

6. The magnetic film is a first magnetic film disposed on the first surface of the circuit layer adjacent to the flux moat; a second magnetic film disposed on said second surface of said circuit layer adjacent said flux moat.

7. 7. The superconducting circuit of claim 6, wherein the first magnetic film is disposed over the flux moat on the first surface of the circuit layer, and the second magnetic film is disposed over the flux moat on the second surface of the circuit layer opposite the first magnetic film.

8. 10. The superconducting circuit of claim 1, wherein the flux moat is disposed between a first set of superconducting circuitry and a second set of superconducting circuitry within the circuit layer.

9. The superconducting circuit comprises: a plurality of flux moats disposed between a plurality of sets of superconducting circuitry, each of the plurality of flux moats including the dielectric material formed within the circuit layer; 10. The superconducting circuit of claim 1, comprising: a plurality of magnetic films, each of said plurality of magnetic films disposed on one of said first and second surfaces of said circuit layer and proximate one of said plurality of magnetic flux moats.

10. 1. A method for fabricating a superconducting circuit, comprising: forming superconducting circuitry in a circuit layer, the circuit layer having a first surface and a second surface opposite the first surface; forming a flux moat comprising a dielectric material in the circuit layer, the flux moat configured to trap magnetic flux when the superconducting circuit is cooled below a superconducting critical temperature; and depositing a magnetic film on at least one of the first surface and the second surface of the circuit layer proximate to the flux moat, the magnetic film being configured to direct magnetic flux to the flux moat when the superconducting circuit is cooled below a superconducting critical temperature.

11. 11. The method of claim 10, wherein the step of depositing a magnetic film includes depositing a perpendicular magnetic anisotropy (hereinafter PMA) material film.

12. The method of claim 11 , wherein the PMA material film has a magnetization orthogonal to a respective one of the first and second surfaces of the circuit layer.

13. 11. The method of claim 10, wherein the step of depositing the magnetic film comprises depositing the magnetic film on the at least one of the first and second surfaces of the circuit layer over the flux moat.

14. The step of depositing the magnetic film includes: depositing a first magnetic film on the first surface of the circuit layer overlying the flux moat; and depositing a second magnetic film on the second surface of the circuit layer over the flux moat.

15. 11. The method of claim 10, wherein forming the superconducting circuitry comprises forming a first set of superconducting circuitry in the circuit layer and forming a second set of superconducting circuitry in the circuit layer, and wherein forming the flux moat comprises forming the flux moat between the first set of superconducting circuitry and the second set of superconducting circuitry in the circuit layer.

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