Second-order gradient overlap coupling type SQUID current sensor and preparation method

Abstract

The present application relates to a second-order gradient overlapping coupling type SQUID current sensor and a preparation method. The feedback coil and the input coil are both insulated and arranged on the surface of the first loop electrode (part of the SQUID loop), forming an upper and lower overlapping coupling structure, so that the coupling between the input coil and the SQUID loop is more matched, and the coupling coefficient is increased. The first loop electrode, the second loop electrode, the third loop electrode, the fourth loop electrode, the first Josephson junction structure, and the second Josephson junction structure are connected in parallel to form a SQUID loop with a second-order gradient parallel inductance structure, which can effectively offset external magnetic field interference. Therefore, through the second-order gradient overlapping coupling type SQUID current sensor, the overlapping coupling structure has a large coupling coefficient, which is conducive to reducing external magnetic field interference and is conducive to the coupling matching between the input coil and the SQUID loop.

Description

Technical Field

[0001] The present application relates to the field of electronic technology, and in particular to a second-order gradient overlap-coupled SQUID current sensor and a preparation method thereof. Background Art

[0002] Superconducting quantum interference devices (SQUIDs) can be used to read out signals from low-noise detectors such as superconducting transition edge detectors (TES) and magnetic metal microcalorimeters (MMCs). TES detectors have a wide range of applications in astronomy, high-energy physics, quantum information, and photon metrology. They can be used as bolometers for millimeter wave detection, microcalorimeters for X-ray detection, and single-photon detectors for visible light. All TES detectors of different types and wavelengths require SQUID current sensors for signal readout.

[0003] However, SQUID current sensors are highly susceptible to interference from external magnetic fields during operation, and often operate alongside TES detectors in environments with no or poor magnetic shielding. Traditional SQUID current sensors employ a cross-coupling structure between the SQUID loop, input coil, and feedback coil. This results in a low coupling coefficient and a high input coil inductance ranging from nH to μH, hindering proper coupling and matching between the input coil and the SQUID loop. Summary of the Invention

[0004] Based on this, it is necessary to provide a second-order gradient overlapping coupled SQUID current sensor and a preparation method to address the above problems.

[0005] The present application provides a second-order gradient overlap-coupled SQUID current sensor comprising a first loop electrode, an input loop, and a feedback coil. The input loop is disposed on the surface of the first loop electrode. The input loop is insulated from the first loop electrode. The input loop is used to input a superconducting transition edge detector signal. The feedback coil is disposed on the surface of the first loop electrode, spaced apart from the input loop. The feedback coil is insulated from the first loop electrode. The feedback coil is used for magnetic flux locking.

[0006] In one embodiment, the present application provides a method for preparing a second-order gradient overlap coupled SQUID current sensor, comprising:

[0007] Providing a substrate, and preparing a silicon dioxide film on the surface of the substrate;

[0008] Sequentially forming a first superconducting thin film layer, a first insulating layer, and a second superconducting thin film layer on a surface of the silicon dioxide film away from the substrate;

[0009] Etching the second superconducting thin film layer to the first insulating layer to form a second superconducting thin film structure;

[0010] Etching the first insulating layer to the first superconducting thin film to form a first insulating structure, wherein the first insulating structure covers the second superconducting thin film structure;

[0011] Etching the first superconducting thin film layer to the silicon dioxide thin film to form a plurality of loop electrodes with different radii;

[0012] forming a second insulating layer on the surface of the silicon dioxide film, the surfaces of the plurality of loop electrodes with different radii, the surface of the first insulating structure, and the surface of the second superconducting thin film structure;

[0013] Etching the second insulating layer to the loop electrode and the second superconducting thin film structure, respectively, to form a plurality of connecting through holes and the second insulating structure;

[0014] preparing a terminal resistor on the surface of the second insulating structure between the plurality of connecting through holes;

[0015] Depositing a lead superconducting thin film layer on the surface of the plurality of connecting through holes and the second insulating structure;

[0016] The lead superconducting thin film layer is etched to the second insulating structure to form a feedback coil, an input coil and a connection structure.

[0017] In the aforementioned second-order gradient overlap-coupled SQUID current sensor and its preparation method, the input loop can be a polygonal structure, forming the input coil. The input coil is connected to a superconducting transition edge detector (TES) for inputting TES signals. The feedback coil is connected to the test system, specifically the flux-locking loop, for flux locking, providing a stable magnetic field environment for the input coil to prevent interference with the detection process.

[0018] The feedback coil and input coil are both insulated and arranged on the surface of the first loop electrode (part of the SQUID loop), forming an upper and lower overlapping coupling structure. The insulation is used to separate the various structures to prevent crosstalk between the currents flowing between them. At this point, the feedback coil, the input loop (part of the input coil), and the SQUID loop exist independently of each other. Thus, the upper and lower overlapping coupling structure makes the coupling between the input coil and the SQUID loop more compatible, increasing the coupling coefficient. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the conventional technology, the following briefly introduces the drawings required for use in the embodiments or the conventional technology descriptions. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 Schematic diagram of the structure of a second-order gradient overlap-coupled SQUID current sensor provided in one embodiment.

[0021] Figure 2 Schematic diagram of the structure of a second-order gradient overlap-coupled SQUID current sensor provided in one embodiment.

[0022] Figure 3 Schematic diagram of the circuit structure of a second-order gradient overlap-coupled SQUID current sensor provided in one embodiment;

[0023] Figure 4 Schematic cross-sectional view of a second-order gradient overlap-coupled SQUID current sensor provided in one embodiment;

[0024] Figure 5 Schematic cross-sectional view of a second-order gradient overlap-coupled SQUID current sensor provided in one embodiment.

[0025] Description of reference numerals:

[0026] Second-order gradient overlap-coupled SQUID current sensor 100, first loop electrode 20, first input structure 30, first input loop 310, second input loop 320, third input loop 330, feedback coil 40, second loop electrode 50, third loop electrode 60, fourth loop electrode 70, first connecting structure 810, second connecting structure 820, third connecting structure 830, fourth connecting structure 840, first Josephson junction structure 910, second Josephson junction structure 920, fifth connecting structure 850, sixth connecting structure 860, seventh connecting structure 870, eighth connecting structure 880, substrate 10, silicon dioxide film 110, second superconducting thin film structure 120, first insulating structure 130, connecting through hole 140, second insulating structure 150, first superconducting thin film structure 160, terminal resistor 670, resistor connecting structure 671, positive electrode connecting structure 610, and negative electrode connecting structure 921. DETAILED DESCRIPTION

[0027] To facilitate understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings. The accompanying drawings provide embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to make the disclosure of the present application more thorough and comprehensive.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0029] It should be understood that when an element or layer is referred to as being "on," "adjacent to," "connected to," or "coupled to" another element or layer, it can be directly on, adjacent to, connected to, or coupled to the other element or layer, or there can be intervening elements or layers. Conversely, when an element is referred to as being "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers, doping types, and / or portions, these elements, components, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are merely used to distinguish one element, component, region, layer, doping type, or portion from another element, component, region, layer, doping type, or portion. Therefore, without departing from the teachings of the present application, the first element, component, region, layer, doping type or portion discussed below may be represented as a second element, component, region, layer or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0030] Spatially relative terms such as "under," "beneath," "beneath," "under," "above," "above," etc., may be used herein to describe the relationship of an element or feature shown in the figures to other elements or features. It should be understood that in addition to the orientations shown in the figures, spatially relative terms also include different orientations of the device in use and operation. For example, if the device in the drawings is turned over, the element or feature described as "under" or "beneath" or "beneath" the other elements will be oriented as "above" the other elements or features. Thus, the exemplary terms "under" and "under" can include both upper and lower orientations. In addition, the device can also include alternative orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptors used herein are interpreted accordingly.

[0031] As used herein, the singular forms "a," "an," and "the" may also include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include," "comprising," "having," and the like specify the presence of stated features, integers, steps, operations, components, parts, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, components, parts, or combinations thereof. Also, in this specification, the term "and / or" includes any and all combinations of the relevant listed items.

[0032] Embodiments of the present invention are described herein with reference to cross-sectional views that are schematic representations of idealized embodiments (and intermediate structures) of the present invention, and variations in the illustrated shapes due to, for example, manufacturing techniques and / or tolerances are anticipated. Accordingly, embodiments of the present invention should not be limited to the specific shapes of the regions illustrated herein, but rather include deviations in shapes due to, for example, manufacturing techniques. Therefore, the regions shown in the figures are schematic in nature, and their shapes do not represent the actual shapes of the regions of the device and do not limit the scope of the present invention.

[0033] See also Figure 1 The present application provides a second-order gradient overlap coupling type SQUID current sensor 100 including a first loop electrode 20, an input loop 30, and a feedback coil 40. The input loop 30 is disposed on the surface of the first loop electrode 20. The input loop 30 is insulated from the first loop electrode 20. The input loop 30 is used to input a superconducting transition edge detector signal. The feedback coil 40 is spaced apart from the input loop 30 and disposed on the surface of the first loop electrode 20. The feedback coil 40 is insulated from the first loop electrode 20. The feedback coil 40 is used for magnetic flux locking.

[0034] In this embodiment, the first loop electrode 20, the feedback coil 40 and the input coil are all made of superconducting thin film materials. The first loop electrode 20 is a regular polygonal structure, such as a regular hexagon, a regular octagon, etc. The first loop electrode 20 forms a geometric center. The structure of the input loop is also a polygonal structure, forming the input coil. The input coil is connected to a superconducting transition edge detector (TES) for inputting TES signals. The feedback coil 40 is used to connect to the test system, that is, to the flux locking loop, for flux locking, to provide a stable magnetic field environment for the input coil to avoid interference during the detection process.

[0035] The feedback coil 40 and the input coil are both insulated and arranged on the surface of the first loop electrode 20 (part of the SQUID loop), forming an upper and lower overlapping coupling structure with the SQUID loop. The insulation setting is used to separate the various structures to prevent crosstalk between the currents flowing between them. At this time, the feedback coil 40, the input loop 30 (part of the input coil), and the SQUID loop exist independently of each other. Therefore, the upper and lower overlapping coupling structure makes the coupling between the input coil and the SQUID loop more matched, increasing the coupling coefficient.

[0036] In one embodiment, the second-order gradient overlap-coupled SQUID current sensor 100 further includes a second loop electrode 50, a third loop electrode 60, and a fourth loop electrode 70. The first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70 are arranged in a clockwise direction. The second loop electrode 50 is rotated 90° relative to the first loop electrode 20. The third loop electrode 60 is rotated 180° relative to the first loop electrode 20. The fourth loop electrode 70 is rotated 270° relative to the first loop electrode 20.

[0037] In this embodiment, the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70 are identical. The first loop electrode 20 and the third loop electrode 60 are arranged on a diagonal line, and the second loop electrode 50 and the fourth loop electrode 70 are arranged on a diagonal line. In this case, the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70 are arranged symmetrically in a clockwise direction, forming a regular quadrilateral. The four loop electrodes are located at the four vertices of the quadrilateral, achieving mutual symmetry. Thus, through the symmetrical structure, the interference generated by each other can be offset.

[0038] In one embodiment, the first loop electrode 20 has a first end and a second end disposed opposite each other. The first end of the first loop electrode 20 and the first end of the second loop electrode 50 are connected via a first connection structure 810. The second end of the first loop electrode 20 and the second end of the second loop electrode 50 are connected via a second connection structure 820. In this case, the first and second connection structures 810 and 820 establish a parallel connection between the first and second loop electrodes 20 and 50.

[0039] The first end of the third loop electrode 60 is connected to the first end of the fourth loop electrode 70 via a third connection structure 830. The second end of the third loop electrode 60 is connected to the second end of the fourth loop electrode 70 via a fourth connection structure 840. At this point, the third loop electrode 60 and the fourth loop electrode 70 are connected in parallel via the third connection structure 830 and the fourth connection structure 840.

[0040] In this embodiment, the first loop electrode 20 has a first end and a second end that are oppositely arranged, which can also be understood as a head end and a tail end. Figure 2 An opening is formed between the first end and the second end, for leading the connection end of the first input loop 310 in each first input structure 30 out through the opening, and connecting multiple first input structures 30 in series to form the input coil.

[0041] The first connection structure 810 and the second connection structure 820 are arranged parallel to each other between the first loop electrode 20 and the second loop electrode 50, and are connected in parallel, forming a symmetrical structure about the vertical direction. The third connection structure 830 and the fourth connection structure 840 are arranged parallel to each other between the third loop electrode 60 and the fourth loop electrode 70, and are connected in parallel, forming a symmetrical structure about the vertical direction. Furthermore, the parallel structure of the third loop electrode 60 and the fourth loop electrode 70 is symmetrically arranged with respect to the horizontal line with the parallel structure formed by the first loop electrode 20 and the second loop electrode 50. Therefore, a mutually symmetrical structure is formed between the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70. Furthermore, the parallel connection of the first loop electrode 20 and the second loop electrode 50, and the parallel connection of the third loop electrode 60 and the fourth loop electrode 70, facilitates the formation of a second-order gradient structure of the SQUID loop, effectively offsetting external magnetic field interference.

[0042] See also Figure 1 and Figure 3In one embodiment, the second-order gradient overlap coupled SQUID current sensor 100 includes a first Josephson junction structure 910 and a second Josephson junction structure 920. The first Josephson junction structure 910 is connected to the first connecting structure 810 and the fourth connecting structure 840 via a fifth connecting structure 850. The second Josephson junction structure 920 is connected to the second connecting structure 820 and the third connecting structure 830 via a sixth connecting structure 860.

[0043] In this embodiment, the first superconducting thin film structure 160 (lower Nb film) of the first Josephson junction structure 910 is connected to the first connecting structure 810 and the fourth connecting structure 840 respectively. The first superconducting thin film structure 160 (lower Nb film) of the second Josephson junction structure 920 is connected to the second connecting structure 820 and the third connecting structure 830 respectively, forming a SQUID loop formed by two Josephson junctions connected in parallel. The SQUID loop formed by the two Josephson junctions connected in parallel is converted into a circuit structure as shown in FIG. Figure 3 shown.

[0044] Furthermore, the parallel structure formed by the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70 creates a parallel inductance structure between the two Josephson junctions. This increases the coupling area with the input coil and the feedback coil 40 through the parallel inductance of the SQUID loop.

[0045] Therefore, the SQUID loop, formed by the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, the fourth loop electrode 70, the first Josephson junction structure 910, and the second Josephson junction structure 920, with its second-order gradient parallel inductance structure, can effectively offset external magnetic field interference. Furthermore, the SQUID loop is coupled to the input coil and the feedback coil 40 using a top-to-bottom coupling method, which ensures a better match between the input coil and the SQUID loop and increases the coupling coefficient.

[0046] In one embodiment, the first Josephson junction structure 910 and the second Josephson junction structure 920 are spaced apart and arranged at a geometric center position formed by the first ring electrode 20 , the second ring electrode 50 , the third ring electrode 60 and the fourth ring electrode 70 .

[0047] In this embodiment, the four loop electrodes are located at the four vertices of a regular quadrilateral, enclosing a square space. The first Josephson junction structure 910 and the second Josephson junction structure 920 are arranged parallel to each other and spaced apart at the geometric center of the square. The structures formed by the first Josephson junction structure 910, the second Josephson junction structure 920, the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70 are symmetrical, thus offsetting their own effects.

[0048] See also Figure 1 In one embodiment, the feedback coil 40 is disposed near an edge of the first loop electrode 20 away from the symmetric point. The feedback coil 40 is disposed near an edge of the second loop electrode 50 close to the symmetric point. The feedback coil 40 is disposed near an edge of the third loop electrode 60 away from the symmetric point. The feedback coil 40 is disposed near an edge of the fourth loop electrode 70 close to the symmetric point.

[0049] In this embodiment, the feedback coil 40 is Figure 2 The loop coil is marked with a dotted line. The feedback coil 40 is positioned near the edge of the first loop electrode 20 away from the symmetry point. At this point, the feedback coil 40 and the third input loop 330 surround the first loop electrode 20, forming an upper and lower overlapping coupling structure. Simultaneously, the feedback coil 40 and the third input loop 330 form a symmetrical structure. By arranging the feedback coil 40 about the symmetry point, the structure of the current sensor 100 can be made more symmetrical, thereby offsetting the effects of its own structure.

[0050] In one embodiment, the plurality of input loops include a first input loop 310, a second input loop 320, and a third input loop 330. The first input loop 310 is disposed on the first loop electrode 20. The second input loop 320 surrounds the first input loop 310. The third input loop 330 surrounds the second input loop 320. The radius of the second input loop 320 is greater than that of the first input loop 310. The radius of the third input loop 330 is greater than that of the second input loop 320.

[0051] In this embodiment, the geometric centers of the first input loop 310, the second input loop 320, and the third input loop 330 coincide with each other, forming a structure spaced outward from the center point on the surface of the first loop electrode 20. The multiple input loops are connected in series end to end to form an integrated input coil. Thus, the overlapping coupling structure of the input coil and the first loop electrode 20 makes the coupling between the input coil and the SQUID loop more compatible, increasing the coupling coefficient. Furthermore, when the input current in the input coil changes, the SQUID loop can more accurately reflect the change, which is more conducive to reading the TES signal.

[0052] In one embodiment, the first input loop 310, the second input loop 320, and the third input loop 330 are sequentially connected end-to-end in series to form a first input structure 30. The second-order gradient overlap-coupled SQUID current sensor 100 includes a plurality of first input structures 30 sequentially connected end-to-end in series. Each first input structure 30 is disposed on a surface of the first loop electrode 20, a surface of the second loop electrode 50, a surface of the third loop electrode 60, and a surface of the fourth loop electrode 70.

[0053] In this embodiment, each of the first input structures 30 is respectively arranged in a one-to-one correspondence with the first loop electrode 20, the second loop electrode 50, the third loop electrode 60, and the fourth loop electrode 70. A plurality of the first input structures 30 are connected in series end to end to form the input coil. The input coil is connected to the TES for inputting the TES signal. When the TES signal is input, the input current in the input coil changes, causing the magnetic field to change. At this time, the SQUID loop enters a resistive state under the action of the bias magnetic field, and the SQUID loop forms a voltage bias, thereby obtaining the change of the TES signal and realizing the TES detector signal readout.

[0054] Each of the first input structures 30 is respectively arranged on the surface of the first loop electrode 20, the surface of the second loop electrode 50, the surface of the third loop electrode 60 and the surface of the fourth loop electrode 70, forming an upper and lower overlapping coupling structure, so that the coupling between the input coil and the SQUID loop is more matched, thereby increasing the coupling coefficient.

[0055] In one embodiment, the current sensor 100 further includes a seventh connecting structure 870 and an eighth connecting structure 880. The seventh connecting structure 870 is disposed between the first connecting structure 810 and the second connecting structure 820. The two first input structures 30 are connected in series via the seventh connecting structure 870. The eighth connecting structure 880 is disposed between the third connecting structure 830 and the fourth connecting structure 840. The two first input structures 30 are connected in series via the eighth connecting structure 880.

[0056] In this embodiment, the first connection structure 810, the seventh connection structure 870, and the second connection structure 820 are symmetrically arranged with the third connection structure 830, the eighth connection structure 880, and the fourth connection structure 840 about a horizontal line. The first input structure 30 disposed on the surface of the first loop electrode 20 and the first input structure 30 disposed on the surface of the second loop electrode 50 are connected in series end to end via the seventh connection structure 870. The first input structure 30 disposed on the surface of the third loop electrode 60 and the first input structure 30 disposed on the surface of the fourth loop electrode 70 are connected in series end to end via the eighth connection structure 880.

[0057] In one embodiment, a plurality of the first input structures 30 are sequentially connected in series to form the input end A of the input coil (eg Figure 1 As shown) and the input end B of the feedback coil 40 are arranged on both sides of the vertical line and are symmetrical about the vertical line.

[0058] See also Figure 2 In one embodiment, the current sensor 100 further includes a plurality of terminal resistors 670 symmetrically arranged about a horizontal line, and respectively arranged on both sides of the first Josephson junction structure 910 and the second Josephson junction structure 920 .

[0059] The two terminal resistors 670 are respectively connected in parallel to the first Josephson junction structure 910. One end of each terminal resistor 670 is connected to the fifth connection structure 850, thereby connecting to the upper Nb film of the first Josephson junction structure 910. The other end of each terminal resistor 670 is connected to the lower Nb film of the first Josephson junction structure 910 via a resistor connection structure 671, forming a parallel connection structure.

[0060] Similarly, the two terminal resistors 670 are respectively connected in parallel to the second Josephson junction structure 920. One end of each terminal resistor 670 is connected to the sixth connection structure 860, thereby connecting to the upper Nb film of the second Josephson junction structure 920. The other end of each terminal resistor 670 is connected to the lower Nb film of the second Josephson junction structure 920 via a resistor connection structure 671, forming a parallel connection structure.

[0061] A complete second-order gradient parallel SQUID loop is formed by the four terminal resistors 670, the first Josephson junction structure 910, the second Josephson junction structure 920, the first loop electrode 20, the second loop electrode 50, the third loop electrode 60 and the fourth loop electrode 70.

[0062] In one embodiment, a positive electrode connection structure 610 is led out through the third loop electrode 60, and a negative electrode connection structure 921 is led out through the first superconducting thin film structure (lower Nb film) of the first Josephson junction structure 910 and the first superconducting thin film structure (lower Nb film) of the second Josephson junction structure 920. The positive and negative electrodes of a power supply can be connected through the positive and negative electrode connection structures 610 and 921 to detect the voltage of the SQUID loop, thereby obtaining changes in the TES signal and realizing TES detector signal readout.

[0063] In one embodiment, an insulating structure is provided between the fifth connecting structure 850 and the seventh connecting structure 870, the eighth connecting structure 880, the second connecting structure 820, and the third connecting structure 830. The feedback coil 40, the input coil, and the SQUID loop are independent of each other.

[0064] See also Figure 4 and Figure 5 In one embodiment, the present application provides a method for preparing a second-order gradient overlap coupled SQUID current sensor, comprising:

[0065] S10, providing a substrate 10, and forming a silicon dioxide film 110 on the surface of the substrate 10;

[0066] S20, sequentially forming a first superconducting thin film layer, a first insulating layer, and a second superconducting thin film layer on a surface of the silicon dioxide film 110 away from the substrate 10;

[0067] S30, etching the second superconducting thin film layer to the first insulating layer to form a second superconducting thin film structure 120;

[0068] S40, etching the first insulating layer to the first superconducting thin film layer to form a first insulating structure 130, wherein the first insulating structure 130 covers the second superconducting thin film structure 120;

[0069] S50, etching the first superconducting thin film layer to the silicon dioxide film 110 to form a loop electrode and a first superconducting thin film structure 160;

[0070] S60, forming a second insulating layer on the surface of the silicon dioxide film 110, the surfaces of the plurality of loop electrodes with different radii, the surface of the first insulating structure 130, and the surface of the second superconducting thin film structure 120;

[0071] S70 , etching the second insulating layer to the loop electrode and the second superconducting thin film structure 120 , respectively, to form a plurality of connecting through holes 140 and a second insulating structure 150 ;

[0072] S80 , preparing a terminal resistor 670 on the surface of the second insulating structure 150 between the plurality of connecting through holes 140 ;

[0073] S90, depositing a lead superconducting thin film layer on the surfaces of the plurality of connecting through holes 140 and the second insulating structure 150;

[0074] S100 , etching the lead superconducting thin film layer to the second insulating structure 150 to form the feedback coil 40 , the input coil and the connection structure.

[0075] In this embodiment, in the step S20, a first superconducting thin film layer (lower Nb film), a first insulating layer (AlO film), and a second insulating layer (AlO film) are sequentially prepared by magnetron sputtering. x ) and the second superconducting thin film layer (upper Nb film), forming Nb / AlO x In the S30 and S40, the second superconducting film and the first insulating layer are etched respectively to form the second superconducting film structure 120 and the first insulating structure 130. In the S40, the first insulating layer is aluminum oxide (AlO x ), wet etching the first insulating layer (aluminum oxide) so that the first insulating structure 130 completely covers the second superconducting thin film structure 120. It can be understood that the area of ​​the first insulating structure 130 is larger than the area of ​​the second superconducting thin film structure 120. By covering the second superconducting thin film structure 120 with the first insulating structure 130, it can be ensured that the formed Nb / AlO x The / Nb Josephson junction region has no side leakage, which is beneficial to the quality stability of the Josephson junction in the SQUID loop.

[0076] In the step S50, the first superconducting thin film layer is etched to form a SQUID loop pattern and a first superconducting thin film structure 160 of a Josephson junction. At this point, it can be understood that the first superconducting thin film structure 160 and the SQUID loop pattern are an integrated structure, both of which are formed by etching the first superconducting thin film layer. Figure 2 The first loop electrode 20, the second loop electrode 50, the third loop electrode 60, the fourth loop electrode 70, the first connection structure 810, the seventh connection structure 870, the second connection structure 820, the third connection structure 830, the eighth connection structure 880, the fourth connection structure 840, etc.

[0077] In the step S70, the plurality of connecting through holes 140 are used to deposit the Nb film. At this time, the Nb film is electrically connected to the loop electrode through the connecting through holes 140. Figure 2 The positive electrode connection structure 610 in the embodiment of the present invention. The Nb film can be electrically connected to the second superconducting thin film structure 120 (the upper Nb film of the Josephson junction) through the connecting through hole 140. Figure 2 The negative electrode connection structure 921 in the embodiment. At the same time, the second insulating structure 150 can be used to realize Figure 2 The isolation and insulation between the overlapping structures. In the S80, the plurality of terminal resistors 670 (see Figure 2 The middle structure) is arranged close to the Josephson junction and serves as the terminal resistance of the current sensor 100.

[0078] In the S90, a lead superconducting film layer is deposited on the surface of the plurality of the connecting through holes 140 and the second insulating structure 150. The lead superconducting film layer is a Nb film. In the S100, the lead superconducting film layer (Nb film) is etched to form the feedback coil 40, the input coil and the connection structure. Figure 1 and Figure 2 The resistor connection structure 671, the fifth connection structure 850, the sixth connection structure 860, etc.

[0079] Therefore, through the fabrication method of the second-order gradient overlap-coupled SQUID current sensor, the first insulating structure 130 covers the second superconducting thin film structure 120, ensuring that the Josephson junction region does not leak sideways, which is beneficial for stabilizing the quality of the Josephson junction in the SQUID. Furthermore, the current sensor 100 fabricated through the fabrication method of the second-order gradient overlap-coupled SQUID current sensor can increase the coupling area, effectively offset external magnetic field interference, reduce parasitic capacitance, and further facilitate TES signal readout.

[0080] In one embodiment, the thickness of the silicon dioxide film 110 is 100 nm to 1000 nm. The thickness of the first superconducting film layer (lower Nb film) is 100 nm to 500 nm. The thickness of the first insulating layer (AlOx) is 5 nm to 30 nm. The thickness of the second superconducting film layer (upper Nb film) is 100 nm to 500 nm. The thickness of the second insulating structure 150 is 200 nm to 600 nm. The thickness of the terminal resistor 670 (PdAu film) is 50 nm to 500 nm. The thickness of the lead superconducting film layer (Nb film) is 300 nm to 800 nm.

[0081] In one embodiment, Nb / AlO is prepared by magnetron sputtering. x When the AlOx film is a three-layer film, the oxidation pressure of the AlOx film is 100mTorr to 5000mTorr, and the oxidation time is 5 hours to 24 hours. The area of ​​the Josephson junction is 1μm 2 ~100μm 2 .

[0082] Specifically, in one embodiment, the method for preparing the second-order gradient overlap coupling SQUID current sensor includes:

[0083] The Nb / AlO film was deposited on a 2-inch single crystal high-resistance silicon wafer 10 with a 100 nm thick SiO2 film 110 by magnetron sputtering. x / Nb three-layer film with thickness of 100nm, 5nm and 100nm respectively. Among them, AlO was prepared by magnetron sputtering x The membrane was prepared at an oxidation pressure of 100 mTorr and an oxidation time of 5 hours.

[0084] Based on the above steps, the first photolithography is performed and the upper Nb film is etched to obtain an area of ​​1 μm 2 The upper layer pattern 120 of the Josephson junction region.

[0085] Based on the above steps, a second photolithography is performed, and the intermediate AlOx film is etched by wet etching to form AlO x Structure 130. wherein AlO xThe structure 130 completely covers the upper pattern 120 .

[0086] Based on the above steps, a third photolithography is performed to etch the bottom Nb film to obtain a SQUID loop pattern.

[0087] Based on the above steps, a 200nm thick SiO2 film is grown using low-temperature chemical vapor deposition. A third photolithography step is then performed, and the SiO2 film is etched to form a through-hole connection structure 140 between the Nb line layer and the underlying Nb film. The remaining SiO2 film serves as the second insulating structure 150.

[0088] Based on the above steps, a fourth photolithography is performed, and a 50 nm thick PdAu thin film is prepared as a resistor layer by electron beam evaporation, and then peeled off to obtain a PdAu resistor 670.

[0089] Based on the above steps, a 300 nm thick Nb film is deposited by magnetron sputtering, and then a fifth photolithography is performed and the Nb film is etched to obtain the feedback coil 40, the input coil and the connection structure pattern.

[0090] Based on the above steps, the 2-inch sample was sliced ​​to obtain a second-order gradient overlap coupling SQUID current sensor.

[0091] In one embodiment, the method for preparing the second-order gradient overlap coupling SQUID current sensor includes:

[0092] The Nb / AlO film was prepared by magnetron sputtering on a 2-inch single crystal high-resistance silicon wafer 10 with a 1000 nm thick SiO2 film 110. x / Nb three-layer film with thickness of 500nm, 30nm and 500nm respectively. Among them, AlO was prepared by magnetron sputtering. x The membrane was prepared at an oxidation pressure of 5000 mTorr and an oxidation time of 24 hours.

[0093] Based on the above steps, the first photolithography is performed and the upper Nb film is etched to obtain an area of ​​100 μm 2 The upper layer pattern 120 of the Josephson junction region.

[0094] Based on the above steps, a second photolithography is performed to etch the middle layer AlO by wet etching. x film, forming AlO x Structure 130. wherein AlO x The structure 130 completely covers the upper pattern 120 .

[0095] Based on the above steps, a third photolithography is performed to etch the bottom Nb film to obtain a SQUID loop pattern.

[0096] Based on the above steps, a 600nm thick SiO2 film is grown using low-temperature chemical vapor deposition. A third photolithography step is then performed, and the SiO2 film is etched to form a through-hole connection structure 140 between the Nb line layer and the underlying Nb film. The remaining SiO2 film serves as the second insulating structure 150.

[0097] Based on the above steps, a fourth photolithography is performed, and a 500 nm thick PdAu thin film is prepared as a resistor layer by electron beam evaporation, and then peeled off to obtain a PdAu resistor 670.

[0098] Based on the above steps, a Nb film with a thickness of 800 nm is deposited by magnetron sputtering, and then a fifth photolithography is performed and the Nb film is etched to obtain the feedback coil 40, the input coil and the connection structure pattern.

[0099] Based on the above steps, the 2-inch sample was sliced ​​to obtain a second-order gradient overlap coupling SQUID current sensor.

[0100] Throughout this specification, references to terms such as "some embodiments," "other embodiments," and "desired embodiments" indicate that a particular feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present application. The schematic descriptions of these terms throughout this specification do not necessarily refer to the same embodiment or example.

[0101] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features of the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0102] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A second-order gradient overlap coupling SQUID current sensor, characterized in that: include: first loop electrode; An input loop is provided on the surface of the first loop electrode, and the input loop is insulated from the first loop electrode; The input loop is used to input a superconducting transition edge detector signal; as well as A feedback coil is arranged on the surface of the first loop electrode at a distance from the input loop to form an upper and lower overlapping coupling structure. The feedback coil is insulated from the first loop electrode and is used for magnetic flux locking. The second-order gradient overlap coupling SQUID current sensor further includes a second loop electrode, a third loop electrode, and a fourth loop electrode, wherein the first loop electrode, the second loop electrode, the third loop electrode, and the fourth loop electrode are sequentially arranged in a clockwise direction; The second loop electrode is rotated 90° relative to the first loop electrode; The third ring electrode is rotated 180° relative to the first ring electrode; The fourth ring electrode is rotated 270° relative to the first ring electrode; Wherein, the input loop includes: First input loop; a second input loop, wherein the radius of the second input loop is greater than the radius of the first input loop; a third input loop, wherein the radius of the third input loop is greater than the radius of the second input loop; The feedback coil and the third input loop surround the first loop electrode; The first input loop, the second input loop and the third input loop are connected end to end in sequence to form a first input structure; The second-order gradient overlapping coupling SQUID current sensor includes a plurality of first input structures connected end to end in sequence, each of the first input structures being respectively arranged on the surface of the first loop electrode, the surface of the second loop electrode, the surface of the third loop electrode, and the surface of the fourth loop electrode; The first loop electrode has a first end and a second end that are arranged opposite to each other, and an opening is formed between the first end and the second end of the first loop electrode. The opening is used to lead the connection end of the first input loop in each first input structure out from the opening, and connect multiple first input structures in series to form an input coil.

2. The second-order gradient overlap coupled SQUID current sensor according to claim 1, characterized in that: The first end of the first loop electrode is connected to the first end of the second loop electrode via a first connecting structure; The second end of the first loop electrode is connected to the second end of the second loop electrode via a second connecting structure; The first end of the third loop electrode is connected to the first end of the fourth loop electrode via a third connecting structure; The second end of the third loop electrode is connected to the second end of the fourth loop electrode via a fourth connection structure.

3. The second-order gradient overlap coupled SQUID current sensor according to claim 2, characterized in that: The second-order gradient overlap coupling type SQUID current sensor comprises: a first Josephson junction structure, connected to the first connecting structure and the fourth connecting structure respectively through a fifth connecting structure; The second Josephson junction structure is connected to the second connection structure and the third connection structure through a sixth connection structure.

4. The second-order gradient overlap coupled SQUID current sensor according to claim 3, characterized in that: The first Josephson junction structure and the second Josephson junction structure are arranged at intervals at a geometric center position formed by the first loop electrode, the second loop electrode, the third loop electrode, and the fourth loop electrode.

5. The second-order gradient overlap coupled SQUID current sensor according to claim 1, characterized in that: The feedback coil is arranged close to an edge of the first loop electrode away from the symmetry point; The feedback coil is arranged close to the edge of the second loop electrode close to the symmetrical point; The feedback coil is arranged close to an edge of the third loop electrode away from the symmetrical point; The feedback coil is arranged close to an edge of the fourth loop electrode close to the symmetrical point.

6. A method for preparing a second-order gradient overlap coupling SQUID current sensor, characterized in that: include: Providing a substrate, and preparing a silicon dioxide film on the surface of the substrate; Sequentially forming a first superconducting thin film layer, a first insulating layer, and a second superconducting thin film layer on a surface of the silicon dioxide film away from the substrate; Etching the second superconducting thin film layer to the first insulating layer to form a second superconducting thin film structure; Etching the first insulating layer to the first superconducting thin film to form a first insulating structure, wherein the first insulating structure covers the second superconducting thin film structure; Etching the first superconducting thin film layer to the silicon dioxide thin film to form a loop electrode and a first superconducting thin film structure; forming a second insulating layer on the surface of the silicon dioxide film, the surfaces of the plurality of loop electrodes with different radii, the surface of the first insulating structure, and the surface of the second superconducting thin film structure; Etching the second insulating layer to the loop electrode and the second superconducting thin film structure, respectively, to form a plurality of connecting through holes and the second insulating structure; preparing a terminal resistor on the surface of the second insulating structure between the plurality of connecting through holes; Depositing a lead superconducting thin film layer on the surface of the plurality of connecting through holes and the second insulating structure; The lead superconducting thin film layer is etched to the second insulating structure to form a feedback coil, an input coil and a connection structure.

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