SQUID device and performance regulation and control method

Abstract

The invention discloses an SQUID device performance regulation and control method, and the method comprises the following steps: separating an SQUID chip and a dielectric resonator of an rf SQUID device, and dissolving packaging silicone grease covering the surface of the SQUID chip; the SQUID chip is placed in a focused helium ion microscope, secondary irradiation is carried out on a micro-bridge area, a linear scanning mode is adopted for irradiation, and the irradiation position is kept away from the position of an original Josephson junction; and packaging the cleaned SQUID chip and the dielectric resonator together in an inverted manner by using the vacuum silicone grease through face-to-face bonding, so as to form a regulated rf SQUID device. The invention further comprises the SQUID device obtained through adjustment of the method. The problems that in the prior art, an rf SQUID device is low in yield and performance is degraded are solved.

Description

Technical Field

[0001] The present application relates to the field of superconducting quantum chips, and in particular to a method for continuous and precise control of a high-temperature superconducting radio frequency superconducting quantum interference device. Background Art

[0002] The superconducting quantum interference device (SQUID) is composed of a superconducting ring and a Josephson junction. The magnetic field is based on the magnetic flux quantum (Φ0 = h / 2e = 2.068 × 10 -15 The integer multiples of Wb) pass through the SQUID ring hole and eventually affect the voltage at both ends of the Josephson junction. The flux noise of the SQUID device can be as low as sub-10 -6 Φ0 level (corresponding to 10 -15 T of magnetic field sensitivity), which has significant advantages in detecting weak electromagnetic signals. Due to its high sensitivity to changes in tiny electromagnetic signals, SQUID devices are used as sensors in the circuits of quantum voltage standards and quantum resistance standard devices in metrology.

[0003] High-temperature superconducting rf SQUID uses liquid nitrogen for refrigeration, which has low refrigeration cost, high sensitivity, strong anti-static interference ability, and long device life. It has excellent application prospects in the development of standard devices such as quantum voltage in the future. At present, the practical high-temperature rf SQUID is composed of a SQUID chip containing a Josephson junction and a dielectric resonator flip-chip package. It generally works in the hysteresis mode, and its flux noise is proportional to the critical current of the junction. However, the current high-temperature superconducting SQUID chip generally uses the traditional step-type or bicrystalline Josephson junction preparation technology. The critical current of the junction is very sensitive to the complex step preparation process or the quality of the bicrystalline substrate. Therefore, the parameter error introduced in any step of the preparation process will cause the final device performance to be completely different from the design, and the device yield is low, which limits its wide application in metrology, biomagnetic detection, and non-destructive testing. In addition, during the use of multiple hot and cold cycles, the high-temperature superconducting SQUID device may also have the problem of junction degradation, resulting in increased device noise or even complete failure. Summary of the invention

[0004] In view of the above shortcomings of the prior art and the common problems of the devices, the present application proposes a SQUID device and a performance control method. The present invention is based on helium ion irradiation, a new high-temperature superconducting Josephson junction preparation scheme, and aims to utilize the high-precision helium ion beam spot provided by a helium ion microscope and the characteristics of the irradiation area that can be freely defined to provide a technology that can continuously and accurately control the performance of superconducting quantum interference devices at any time, so as to solve the problems of low yield and performance degradation of rf SQUID devices in the prior art.

[0005] On the one hand, the embodiment of the present application provides a SQUID device performance control method, comprising the following steps:

[0006] Separate the SQUID chip and dielectric resonator of the rf SQUID device, and dissolve the encapsulation silicone grease covering the surface of the SQUID chip;

[0007] The SQUID chip is placed in a focused helium ion microscope, and the microbridge region is subjected to secondary irradiation, wherein the irradiation adopts a line scanning method and the irradiation position avoids the position of the original Josephson junction;

[0008] The cleaned SQUID chip is again packaged face-to-face with the dielectric resonator by flip-chip bonding using vacuum silicone grease to form a regulated rf SQUID device.

[0009] Preferably, petroleum ether is used to dissolve the silicone grease.

[0010] In one embodiment, the device is fabricated by helium ion irradiation, and the position of the second irradiation scan should be different from the junction position of the first irradiation.

[0011] In one embodiment, the Josephson junction on the rf SQUID chip is a step grain boundary junction or a double crystal grain boundary junction structure, and the irradiation position should avoid the junction region at the grain boundary position of the step edge.

[0012] In one embodiment, when the rf SQUID fails, an irradiation dose corresponding to a sensitivity within a set range is selected to perform secondary irradiation on the microbridge region.

[0013] In one embodiment, when the noise of the rf SQUID device increases, a secondary irradiation dose greater than or equal to the original irradiation dose is selected to prepare an irradiated junction with a smaller critical current, and the junction is connected in series with the original device junction.

[0014] In one embodiment, the second irradiation uses a larger dose than the first irradiation to prepare an rf SQUID device having two junctions with different critical currents connected in series.

[0015] Preferably, the SQUID device comprises a step grain boundary junction, a twin crystal grain boundary junction, a helium ion irradiation junction or other types of high temperature superconducting Josephson junction.

[0016] Preferably, before separating the SQUID chip and the dielectric resonator, it is determined that the performance of the SQUID device does not meet a set threshold, the noise increases, or the device fails.

[0017] On the other hand, an embodiment of the present application further provides a SQUID device, which is implemented using the method described in any embodiment of the present application, wherein the regulated SQUID device comprises:

[0018] The SQUID chip comprises a first substrate and a superconducting thin film material epitaxially grown thereon, a first ring hole is prepared on the superconducting thin film material by micro-nano processing means, and a microbridge structure is provided on one side of the ring hole;

[0019] The dielectric resonator comprises a second substrate and a superconducting thin film material epitaxially grown thereon, and a second ring hole is prepared on the superconducting thin film material by micro-nano processing means;

[0020] The SQUID chip and the dielectric resonator are bonded and packaged face to face in a flip-chip manner, with the first ring hole and the second ring hole facing each other;

[0021] The microbridge structure is irradiated (line scanned) by focused helium ions to form a Josephson junction, while secondary irradiation forms an ion irradiation junction connected in series with the original (ie previously prepared) Josephson junction.

[0022] Preferably, the focused ions are one of the following: helium ions and neon ions. The performance of the SQUID device composed of the original Josephson structure does not meet the set threshold, the noise increases or the device fails.

[0023] At least one of the above technical solutions adopted in the embodiments of the present application can achieve the following beneficial effects:

[0024] The present invention utilizes the high-precision beam spot of helium ion irradiation and the characteristics of freely defining the irradiation area. Through the scheme of secondary preparation of the junction by helium ion irradiation in the above steps, the continuous and accurate optimization and control of the junction parameters, that is, the final device performance, can be achieved. Helium ion irradiation is a new type of high-temperature superconducting Josephson junction preparation technology. It utilizes the high-precision helium ion beam spot provided by the helium ion microscope and the characteristics of freely defining the irradiation area, so that it has a higher junction parameter control ability and preparation flexibility than the traditional junction preparation technology. In addition, the device itself faces the problem of junction degradation leading to device failure during the multiple cold and hot cycles of measurement. For devices prepared by traditional step or twin crystal technology, work failure means the scrapping of the device. Through the implementation of the key steps in the present invention, the problem of device failure can be fundamentally solved. Therefore, the yield rate of the SQUID device prepared by the multiple focused helium ion irradiation technology in the present invention will be greatly improved compared with the device prepared by the traditional grain boundary junction, which is conducive to the wide use of high-temperature rf SQUID devices in various application fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0026] Figure 1A flow chart of a method provided by an embodiment of the present invention;

[0027] Figure 2.1 It is a schematic diagram of an rf SQUID device packaged in a flip-chip structure provided in the present invention;

[0028] Figure 2.2 is a schematic diagram of the SQUID chip of the present invention after cleaning;

[0029] Figure 2.3 is a schematic diagram of irradiation using a focused helium ion beam;

[0030] Figure 2.4 A top view of a SQUID chip is shown;

[0031] Figure 2.5 Schematic diagram of the SQUID device formed by flip-chip packaging of the precisely controlled SQUID chip and dielectric resonator;

[0032] Figure 3 The relationship between the noise of the rf SQUID device composed of a single focused helium ion irradiation structure and the helium ion irradiation dose is demonstrated;

[0033] Figure 4 (a) and (b) show the comparative measurement results of device noise before and after secondary irradiation with a larger irradiation dose. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present application clearer, the technical solution of the present application will be clearly and completely described below in combination with the specific embodiments of the present application and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0035] The technical solutions provided by various embodiments of the present application are described in detail below in conjunction with the accompanying drawings.

[0036] Figure 1 The method flow chart provided in the first embodiment of the present invention includes steps 10 to 40.

[0037] Step 10: Determine whether the SQUID device performance does not meet a set threshold, the noise increases, or the device fails.

[0038] An rf SQUID device is provided. The device can be prepared by different technologies (step grain boundary junction, twin crystal grain boundary junction or helium ion irradiated junction), and the performance is poor, has been degraded or the device has completely failed.

[0039] Step 20: Separate the SQUID chip and the dielectric resonator of the rf SQUID device, and dissolve the encapsulation silicone grease covering the surface of the SQUID chip.

[0040] The SQUID chip 1 and the dielectric resonator 2 of the device are separated in parallel, as shown in FIG. Figure 2.1 As shown, the arrow direction indicates the direction in which the SQUID chip and the dielectric resonator of the device are separated. Specifically, in this embodiment, the Josephson junction on the chip of the failed SQUID device is prepared by low-dose focused helium ion irradiation, and the device performance is poor. The SQUID chip 1 and the dielectric resonator 2 in the device are separated in a manner parallel to the contact surface.

[0041] The encapsulation silicone grease covering the surface of the rf SQUID chip is dissolved, preferably, petroleum ether is used to dissolve the silicone grease. The silicone grease is dissolved by petroleum ether, and the process does not damage the device.

[0042] Step 30: Place the SQUID chip in a focused helium ion microscope and perform secondary irradiation on the microbridge region. The irradiation adopts a line scanning method, and the irradiation position avoids the original Josephson junction position.

[0043] like Figure 2.3~2.4 As shown, the SQUID chip is placed in a focused helium ion microscope, and the microbridge area 4 is irradiated again by a focused helium ion beam 3. The irradiation adopts a line scanning method, and the irradiation position 5 avoids the position 6 of the previously prepared Josephson junction. Figure 2.4 It is a top view of the SQUID chip. The enlarged view includes a schematic diagram of irradiation at the microbridge area. The irradiation position 5 is different from the original junction area position 6 on the microbridge.

[0044] The line scan direction is along the cross-sectional direction of the microbridge region, parallel to the original irradiated junction direction, and the position is staggered. For example, if the device is prepared by helium ion irradiation, the scanning position should be different from the junction position of the first irradiation. For another example, if the Josephson junction on the rf SQUID chip is a step grain boundary junction or a twin grain boundary junction structure, the irradiation position avoids the junction area at the grain boundary position of the step edge.

[0045] In this implementation case, a specific focused helium ion irradiation dose is used for the second irradiation. Regarding the selection of the secondary irradiation dose, since the specific irradiation dose corresponds to a specific junction critical current, it directly determines the performance level of the device. Therefore, the selection of the irradiation dose is the key to achieving device performance optimization and regulation.

[0046] For example, when the rf SQUID fails completely, a secondary irradiation is performed using an irradiation dose corresponding to the sensitivity within the set range. For a completely failed rf SQUID, this is usually due to the junction critical current being too large, causing the device to deviate from the operable parameter region or the junction superconducting weak connection failing completely. In this case, supplementary materials can be used to Figure 3 The relationship between the medium irradiation dose and the device sensitivity directly selects the optimal dose for secondary irradiation, thereby obtaining a device with a suitable junction critical current again.

[0047] For another example, when the noise of the rf SQUID device increases, a secondary irradiation dose greater than or equal to the original irradiation dose is selected to prepare an irradiated junction with a smaller critical current in series with the original device junction. For rf SQUID devices prepared by helium ion irradiation, since the noise of the rf SQUID working in the hysteresis mode is proportional to the critical current, the degradation of the device noise performance is generally caused by a small increase in the junction critical current. At this time, the original dose or the optimal irradiation dose greater than the original dose can be selected (Supplementary Materials Figure 3 As shown in , a secondary irradiation is performed to prepare a helium ion irradiated junction with a smaller critical current, which is connected in series with the junction prepared on the original device. At this time, the noise of the device is completely determined by the critical current of the irradiated junction.

[0048] Step 40: The cleaned SQUID chip is again packaged together with the dielectric resonator by face-to-face bonding using vacuum silicone grease to form a regulated rf SQUID device.

[0049] The cleaned rf SQUID chip is again packaged together with the dielectric resonator by face-to-face bonding using vacuum silicone grease to form a regulated rf SQUID device.

[0050] Figure 2.1 to 2.5 A SQUID device is represented, which is implemented using any one of the method embodiments of the present application, and the SQUID device comprises:

[0051] The SQUID chip comprises a first substrate and a superconducting thin film material epitaxially grown thereon, a first ring hole is prepared on the superconducting thin film material by micro-nano processing means, a microbridge structure 4 is provided on one side of the ring hole, and a gap extending away from the first ring hole is provided on the outer side of the microbridge, Figure 2.4 .

[0052] The dielectric resonator comprises a second substrate and a superconducting film material epitaxially grown thereon, and a second ring hole is prepared on the superconducting film material by micro-nano processing means.

[0053] The SQUID chip and the dielectric resonator are packaged face to face by flip-chip bonding, and the first ring hole and the second ring hole are opposite to each other.

[0054] Preferably, the SQUID device comprises a step grain boundary junction, a twin grain boundary junction or a helium ion irradiation junction. The microbridge structure is irradiated by focused ions to form a Josephson junction, and secondary irradiation forms an irradiation junction connected in series with the original Josephson junction. The focused ions are one of the following: helium ions, neon ions (helium ions in this case). The performance of the SQUID device formed by the original Josephson structure does not meet the set threshold, the noise increases or the device fails.

[0055] Figure 3 is the relationship between the noise of the rf SQUID device and the helium ion irradiation dose. In order to verify the feasibility and effect of continuous and precise control of the performance of the rf SQUID device, Figure 4 After the rf SQUID device corresponding to the middle dotted line is characterized for its flux-voltage characteristics and noise, the SQUID chip of the device is separated from the dielectric resonator, the encapsulating silicone grease covering the surface of the rfSQUID chip is dissolved, and then the SQUID chip is placed in a focused helium ion microscope and the bridge area is irradiated again. The second irradiation uses a dose of 410ions / nm, which is slightly larger than the first irradiation, thereby preparing a device similar to the step grain boundary junction with two critical current junctions of different sizes connected in series.

[0056] Specifically, in this case, the sensitivity of the rf SQUID device was optimized by implementing the aforementioned device control steps, such as Figure 4 shown.

[0057] Figure 4 (a) and (b) show the device measurement results after secondary irradiation (solid curve), which show that the performance of the device is improved compared with that before secondary irradiation (dashed curve). The transfer function and sensitivity level of the device are significantly improved. The transfer function amplitude is increased from 0.26V / Φ0 to 0.82V / Φ0, and the white noise level of the device at 10kHz is also increased from 160μΦ0 / Hz to 1 / 2 Reduced to 74μΦ0 / Hz 1 / 2 , the improved magnetic field sensitivity is 220fT / Hz 1 / 2 The improvement of device performance confirms that the Josephson junction with lower critical current after re-irradiation plays a leading role in the operation of the rf SQUID device. Based on this, the present invention can use the secondary irradiation method to achieve optimized regulation of device performance or performance recovery of failed devices.

[0058] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of further restrictions, the elements defined by the sentence "comprises..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0059] It will be understood by those skilled in the art that, unless otherwise stated, the singular forms "a", "an", "said" and "the" used may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0060] Those skilled in the art will understand that unless otherwise defined, all terms (including technical, technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this invention belongs.

[0061] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A method for controlling the performance of a SQUID device, characterized in that: The following steps are involved: Separate the SQUID chip and dielectric resonator of the rf SQUID device, and dissolve the encapsulation silicone grease covering the surface of the SQUID chip; The SQUID chip is placed in a focused helium ion microscope, and the microbridge region is subjected to secondary irradiation, wherein the irradiation adopts a line scanning method and the irradiation position avoids the position of the original Josephson junction; The cleaned SQUID chip is again packaged face-to-face with the dielectric resonator by flip-chip bonding using vacuum silicone grease to form a regulated rf SQUID device.

2. The SQUID device performance control method according to claim 1, characterized in that: Dissolve the silicone grease with petroleum ether.

3. The SQUID device performance control method according to claim 1, characterized in that: The device is prepared by helium ion irradiation, and the position of the second irradiation scan is different from the junction position of the first irradiation; and / or, If the Josephson junction on the rf SQUID chip is a step grain boundary junction or a twin crystal grain boundary junction structure, the irradiation position should avoid the junction area at the grain boundary position of the step edge.

4. The SQUID device performance control method according to claim 1, characterized in that: When the rf SQUID fails, the microbridge area is irradiated again with an irradiation dose corresponding to the sensitivity within the set range.

5. The SQUID device performance control method according to claim 1, characterized in that: When the noise of the rf SQUID device increases, a secondary irradiation dose greater than or equal to the original irradiation dose is selected to prepare an irradiated junction with a smaller critical current, and the irradiated junction is connected in series with the original device junction.

6. The SQUID device performance control method according to claim 1, characterized in that: The second irradiation used a larger dose than the first irradiation to produce an rf SQUID device with two junctions of different critical current sizes connected in series.

7. The SQUID device performance control method according to claim 1, characterized in that: The SQUID device includes a step grain boundary junction, a twin crystal grain boundary junction, a helium ion irradiation junction or other types of high temperature superconducting Josephson junction. Before separating the SQUID chip and the dielectric resonator, it is determined that the performance of the SQUID device does not meet the set threshold, the noise increases or the device fails.

8. A SQUID device, implemented using the method of claims 1 to 7, characterized in that: The regulated SQUID device comprises: The SQUID chip comprises a first substrate and a superconducting thin film material epitaxially grown thereon, a first ring hole is prepared on the superconducting thin film material by micro-nano processing means, and a microbridge structure is provided on one side of the ring hole; The dielectric resonator comprises a second substrate and a superconducting thin film material epitaxially grown thereon, and a second ring hole is prepared on the superconducting thin film material by micro-nano processing means; The SQUID chip and the dielectric resonator are bonded and packaged face to face in a flip-chip manner, with the first ring hole and the second ring hole facing each other; The microbridge structure is subjected to focused ion irradiation line scanning to form a Josephson junction, and the secondary irradiation forms an ion irradiation junction connected in series with the original Josephson junction.

9. The SQUID device according to claim 8, characterized in that The focused ions are one of the following: helium ions and neon ions.

10. The SQUID device according to claim 8, characterized in that The performance of the original SQUID device composed of Josephson structure does not meet the set threshold, the noise increases or the device fails.

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