Integrated multi-channel SQUID chip

Abstract

The application provides an integrated multi-channel SQUID chip, which comprises a plurality of channels arranged at intervals, the channels are arranged in an n*n array, and n is greater than or equal to 2; the circuit system in each channel is external feedback mode-based circuit system, a pickup coil, an input coil and a secondary feedback coil are connected in series to form a magnetic flux detection loop, a SQUID device is coupled with the input coil, lead wires at both ends of the SQUID device are connected with two input ends of an operational amplifier, a feedback resistor and a primary feedback coil are sequentially connected with an output end of the operational amplifier, the primary feedback coil is coupled with the secondary feedback coil and used for transmitting a feedback signal. The integrated multi-channel SQUID chip realizes the integration of the chip and the miniaturization of the system, simultaneously achieves the target that the crosstalk rate between the channels is less than 0.1%, and improves the spatial resolution of the whole system.

Description

Technical Field

[0001] This invention relates to the field of SQUID detection technology, and in particular to an integrated multi-channel SQUID chip. Background Technology

[0002] Superconducting quantum interference devices (SQUIDs) are flux sensors that convert magnetic flux into voltage. Their basic principle is based on the superconducting Josephson effect and flux quantization. Due to their advantages such as high sensitivity, wide operating range, and high spatiotemporal resolution, they are widely used in fields such as biomagnetic detection, aeromagnetic detection, and nondestructive testing. Currently, systems used to detect biomagnetic signals are mainly multi-channel, such as the 83-channel magnetocardiograph developed by PTB in Germany [Drung, Dietmar. "The PTB 83-SQUID system for biomagnetic applications in a clinic." IEEE transactions on applied superconductivity 5.2 (1995): 2112-2117], and the 64-channel magnetocardiograph developed by Hitachi in Japan [Itozaki, H. (2003). SQUID application research in Japan. Superconductor Science and Technology, 16(12), 1340.]. Multi-channel magnetocardiograph systems have been installed in Ruijin Hospital and Fuwai Hospital in Shanghai, TEDA Hospital in Tianjin, and 309 Hospital in Beijing. Systems applied to magnetoencephalography (MEG) detection include the 306-channel MEG system developed in Finland [Taulu, S., & Hari, R. (2009). Removal of magnetoencephalographic artifacts with temporal signal-space separation: Demonstration with single-trial audiotory-evoked responses. Human brain mapping, 30(5), 1524-1534.] and the multi-channel atomic magnetometer technology recently developed by the Chinese Academy of Sciences for MEG detection [Li, Jian-Jun, et al. Miniature quad-channel spin-exchange relaxation-free magnetometer for magnetoencephalography. Chinese Physics B28.4 (2019): 040703.]. Therefore, both domestically and internationally, the mainstream detection systems used by SQUID and atomic magnetometers are multi-channel systems based on discrete devices.

[0003] Currently, the distance between channels in multi-channel discrete devices is gradually decreasing, from the centimeter level to the millimeter level and even the micrometer level. This close proximity inevitably leads to mutual interference between channels. For example...Figure 1 As shown, according to Maxwell's equations, when channel 1 detects an external magnetic field, it generates a current. This current will create a mutual inductance with channel 2 (which is close to channel 1), causing the output of channel 2 to contain the signal from channel 1, thus causing crosstalk. Derivation reveals that the crosstalk output in channel 2 is mainly caused by two parts: the mutual inductance between channels and the current generated by the magnetic flux detection circuit when detecting magnetic flux [Brake HJ, Fleuren FH, Ulfrnan JA, et al., Elimination of flux-transformer crosstalk in multichannel SQUID magnetometers[J].Cryogenics:1986,26(12):667-670.].

[0004] In the field of biomagnetic detection, integrated multi-channel chip designs have not been applied, especially integrated multi-channel designs of SQUID chips. Currently, existing technologies can apply superconducting transition edge detectors (TES) and tandem SQUID arrays (SSA) to integrated chip designs, but these are arrays formed by connecting SQUID devices in series, rather than standalone integrated multi-channel designs. This results in low spatial resolution and large system size for biodetection systems, making it difficult to meet high-standard detection requirements. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an integrated multi-channel SQUID chip to solve the problems of easy crosstalk between channels, low spatial resolution of the system, and large size in the prior art.

[0006] To achieve the above and other related objectives, this invention provides an integrated multi-channel SQUID chip. The integrated multi-channel SQUID chip includes several channels spaced apart from each other, arranged in an n×n array, where n≥2. The circuit system in each channel is an external feedback-based circuit system, which includes a pickup coil, an input coil, a SQUID device, an operational amplifier, a first-stage feedback coil, and a second-stage feedback coil. The pickup coil, the input coil, and the second-stage feedback coil are connected in series to form a flux detection loop. The SQUID device is coupled to the input coil. The leads at both ends of the SQUID device are connected to the two input terminals of the operational amplifier, respectively. A feedback resistor and the first-stage feedback coil are sequentially connected to the output terminal of the operational amplifier. The first-stage feedback coil is coupled to the second-stage feedback coil for transmitting feedback signals.

[0007] Optionally, the center distance between adjacent channels is <5mm, and the area of ​​the integrated multi-channel SQUID chip is <10mm². 2 .

[0008] Furthermore, the number of channels is four, and the four channels are arranged in a 2×2 array, with a center distance of 3.43 mm between adjacent channels.

[0009] Furthermore, the magnetic flux detection circuits in the four channels are all square structures, wherein the input coil is located at one corner of the square structure, there are two sets of secondary feedback coils, which are located on the two sides of the square structure on both sides of the input coil, and the pickup coils are located on the other two sides of the square structure.

[0010] Furthermore, the four magnetic flux detection circuits are symmetrically distributed about the center of the array, and the positions of the four corresponding input coils are all far from the center of the array.

[0011] Furthermore, the structure of the input coil and the structure of the two sets of secondary feedback coils are both double-ring reverse structures. The double-ring reverse structure is a centrally symmetrical structure composed of two interconnected planar spiral coils, and the current flowing through the two planar spiral coils is in opposite directions.

[0012] Furthermore, the SQUID device is configured with a dual-hole structure corresponding to the input coil and is coupled to the input coil in an overlapping manner; the primary feedback coil is configured with a dual-loop reverse structure corresponding to the secondary feedback coil and is coupled to the secondary feedback coil in an overlapping manner.

[0013] Furthermore, the input coil, the SQUID device, the primary feedback coil, and the secondary feedback coil all have a square structure.

[0014] Optionally, a circuit system based on an internal feedback mode is also provided in the area surrounded by the magnetic flux detection loop. The circuit system based on the internal feedback mode is used to compare the detection results with the circuit system based on an external feedback mode to verify the effectiveness of the circuit system based on the external feedback mode.

[0015] Furthermore, all lead electrodes within the channel are concentrated around the location of the input coil.

[0016] As described above, the integrated multi-channel SQUID chip of the present invention has the following beneficial effects:

[0017] (1) The SQUID chip of this application adopts an integrated multi-channel design, with multiple channels concentrated on the same chip and arranged in an n×n array, realizing chip integration and system miniaturization, making it possible to have a portable and convenient SQUID system.

[0018] (2) The circuit system in each channel is a circuit system based on external feedback mode. By coupling the first-level feedback coil with the second-level feedback coil in the magnetic flux detection circuit, the crosstalk rate between channels is less than 0.1%.

[0019] (3) Multiple channels collect signals together, and the circuit systems in each channel maintain high symmetry and consistency. The working mechanism remains the same, avoiding the introduction of more noise due to the inconsistency between channels, ensuring that the signal detected by the chip has a high signal-to-noise ratio when applied, thereby improving the spatial resolution of the entire system. Attached Figure Description

[0020] Figure 1 The diagram shows the four-channel positions of the present invention.

[0021] Figure 2 The diagram shows a circuit system schematic based on an internal feedback mode in the prior art.

[0022] Figure 3 The diagram shown is a schematic of the circuit system based on the external feedback mode of the present invention.

[0023] Figure 4 The diagram shown is a single-channel circuit layout of the present invention.

[0024] Figure 5 The diagram shown is a layout of the four-channel circuit structure of the present invention.

[0025] Figure 6 The diagram shows the magnetic flux detection circuit and SQUID device arrangement of the present invention.

[0026] Figure 7 The coil shown is a double-ring reverse structure according to the present invention.

[0027] Figure 8 The diagram shown is a structural schematic of the SQUID device of the present invention.

[0028] Figure 9 The diagram shown is a four-channel simulation schematic of the present invention.

[0029] Figure 10 This diagram illustrates the relationship between the ratio of the gap between adjacent flux detection loops to the side length of the flux detection loop in the four-channel model of this invention and the crosstalk rate.

[0030] Figure 11The diagram shown is a repeating cell layout with multiple channels according to the present invention.

[0031] Component designation explanation

[0032] 1. Magnetic flux detection circuit

[0033] 11 Pick-up coil

[0034] 12 Input Coils

[0035] 13 Secondary feedback coil

[0036] 2 SQUID devices

[0037] 21 Josephson knot

[0038] 22 Superconducting rings

[0039] 3. First-stage feedback coil

[0040] 4 Circuit systems based on internal feedback mode

[0041] 41 Internal pickup coil

[0042] 5. Heating resistance

[0043] 6 lead electrodes Detailed Implementation

[0044] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0045] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity, positional relationship and proportion of each component can be changed at will under the premise of realizing the technical solution, and the layout of the components may also be more complex.

[0046] like Figure 1 As shown, this invention provides an integrated multi-channel SQUID chip, which includes a plurality of channels spaced apart from each other, arranged in an n×n array, where n≥2. This integrated design concentrates multiple channels on the same chip. Preferably, the plurality of channels are arranged in an n×n array on an area less than 10mm². 2On the SQUID chip, the center distance between adjacent channels is less than 5mm, to achieve chip integration and system miniaturization, making a portable and convenient SQUID system possible. Furthermore, several sets of circuit systems are correspondingly arranged in several channels, each set of circuit systems being independent of each other while maintaining the same operating mechanism.

[0047] like Figure 2 The diagram shown is a schematic of an internal feedback circuit in the prior art. When the channel contains a traditional circuit system based on internal feedback, the pickup coil 11 detects the external magnetic field Φ. ex The circuit current I1 is generated, and the input coil 12 is coupled with the SQUID device 2 to generate mutual inductance M. in Simultaneously, an induced current is generated in SQUID device 2 and connected to the input terminal of operational amplifier G. The first-stage feedback coil 3, connected to the output terminal of the operational amplifier, is directly coupled to SQUID device 2, generating a mutual inductance M. fin This is used for internal feedback. At this time, the crosstalk between channel 1 and channel 2 mainly originates from the mutual inductance M between the pickup coils 11. 12 On the other hand, it originates from the mutual inductance generated by the current I1 in the magnetic flux detection circuit.

[0048] like Figure 3 The diagram shows the schematic of the external feedback circuit of the present invention. To weaken the mutual inductance effect caused by the current I1 in the magnetic flux detection loop 1, the circuit system in each channel is configured as an external feedback mode circuit system to suppress crosstalk noise caused by the magnetic flux detection loop 1 in other channels. Specifically, the external feedback mode-based circuit system includes a pickup coil 11, an input coil 12, a SQUID device 2, an operational amplifier G, a first-stage feedback coil 3, and a second-stage feedback coil 13. The pickup coil 11, the input coil 12, and the second-stage feedback coil 13 are connected in series to form the magnetic flux detection loop 1. The SQUID device 2 is coupled to the input coil 12. The leads at both ends of the SQUID device 2 are connected to the two input terminals of the operational amplifier, respectively. The output terminal of the operational amplifier is connected in sequence to a feedback resistor R and the first-stage feedback coil 3. The first-stage feedback coil 3 is coupled to the second-stage feedback coil 13, generating a mutual inductance M. fex It is used to transmit feedback signals.

[0049] It should be noted that the SQUID device 2 consists of two Josephson junctions and a superconducting ring, wherein the two Josephson junctions are connected in parallel within the superconducting ring. The SQUID device is coupled to the input coil to sense the magnetic flux generated by the input coil and convert it into an electrical signal. Furthermore, this embodiment will be explained using a four-channel configuration arranged in a 2×2 array on the SQUID chip as an example.

[0050] As an example, such as Figure 4-6 As shown, to ensure consistency across channels in the chip, avoid introducing additional noise, and improve the signal-to-noise ratio of the acquired signal, the magnetic flux detection circuits 1 in all four channels are configured as square structures. The input coil 12 is located at one corner of the square structure, and there are two sets of secondary feedback coils 13, located on opposite sides of the square structure on either side of the input coil 12. The pickup coils 11 are located on the other two sides of the square structure. To facilitate subsequent interconnection and to maintain chip symmetry, the two sets of secondary feedback coils 13 are designed identically and are symmetrical about the diagonal of the central input coil 12. To achieve magnetic flux modulation, the pickup coils 11 in each channel are generally designed to be large and maintain consistency. Furthermore, the four magnetic flux detection circuits 1 are symmetrically distributed about the array center, and the positions of the four corresponding input coils 12 are all far from the center of the array. The SQUID devices 2 coupled to the four input coils 12 are positioned accordingly, resulting in a high degree of symmetry in the circuit layout.

[0051] When multiple channels acquire signals together, the circuit systems in each channel maintain high symmetry and consistency, and the working mechanism remains the same. This ultimately improves the spatial resolution of the entire system and increases the signal detection density, which facilitates the application of SQUID, especially in the field of biomagnetic detection, and further promotes its application in clinical diagnosis.

[0052] As an example, such as Figure 4 As shown, the structure of the input coil 12 and the structures of the two sets of secondary feedback coils 13 are both double-loop reverse structures, specifically as follows: Figure 7 As shown, the double-ring reverse structure is a centrally symmetrical structure composed of two interconnected planar spiral coils, with the current flowing through the two planar spiral coils in opposite directions. Specifically, one inner end of the first planar spiral coil is connected to one inner end of the second planar spiral coil. When current flows in from the outer end of the first planar spiral coil, the current spirals inward, flows out through the inner end of the first planar spiral coil, and simultaneously flows into the inner end of the second planar spiral coil, spiraling outward, and flows out through the outer end of the second planar spiral coil. According to the right-hand screw rule, the magnetic fields generated by the currents flowing through the two planar spiral coils in the same plane are in opposite directions. Therefore, at a certain point in the plane, the magnetic fields in different directions can cancel each other out, thus suppressing crosstalk between different channels.

[0053] As an example, such as Figure 4As shown, the SQUID device 2 is configured with a dual-hole structure corresponding to the input coil 12 and is coupled to the input coil 12 in an overlapping manner; the primary feedback coil 3 is configured with a double-loop reverse structure corresponding to the secondary feedback coil 13 and is coupled to the secondary feedback coil 13 in an overlapping manner. Specifically, the input coil 12, the SQUID device 2, the primary feedback coil 3, and the secondary feedback coil 13 all have square structures.

[0054] It should be noted that, in other embodiments, the structural shapes of the input coil 12, the SQUID device 2, the primary feedback coil 3, and the secondary feedback coil 13 can be adjusted as needed, and this should not excessively limit the scope of protection of the present invention.

[0055] Specifically, such as Figure 8 As shown, the SQUID device 2 has two square holes with dimensions (d×d) of 44μm×44μm. The two square holes are connected by a slit with a width (a) of 5μm and a length (l) of 50μm. Two Josephson junctions 21 are located between the two square holes and are respectively disposed on superconducting rings 22 on both sides of the slit. The ring width (w) of the superconducting rings 22 in the SQUID device is 15μm.

[0056] In the magnetic flux detection circuit 1, the input coil 12 is designed with 6.5 turns × 2 turns, and the line width and spacing are both designed to be 1μm according to standard manufacturing process. The pickup coil 11 has a line width of 10μm. The secondary feedback coil 13 also adopts a standard width of 1μm for both line width and spacing.

[0057] like Figure 9 As shown, the inner diameter of the square structure of the magnetic flux detection circuit is designed to be 3.1mm × 3.1mm. Based on the external feedback mode of the circuit system, software is used to simulate multiple channels to find the optimal gap or center distance between adjacent channels that ensures the crosstalk meets the requirements. Figure 10 The figure shows the relationship between the ratio of the gap between adjacent flux detection loops to the side length of the flux detection loop and the crosstalk rate. This result was obtained by simulating the model using Maxwell software. Considering the error between the simulation results and the actual fabricated chip, and with the aim of better reducing the crosstalk rate, this invention determined four different center distances between adjacent channels: 3.38 mm, 3.43 mm, 3.48 mm, and 3.53 mm. Preferably, the optimal center distance between adjacent channels, determined by simulation results, is 3.43 mm, at which the corresponding crosstalk rate between channels is 0.1%.

[0058] As an example, such as Figure 11The diagram shows a repeating cell layout designed using standard processes across the entire wafer. Due to the limitations of the exposure area in the standard stepper process during chip design, the size of the repeating cell is guaranteed to be within 22mm × 22mm, allowing chips with the four different center-to-center distances between adjacent channels mentioned above to be designed on the same cell simultaneously.

[0059] As an example, such as Figure 4 and Figure 5 As shown, an internal feedback-based circuit system 4 is also provided within the area surrounded by the magnetic flux detection loop 1. This internal feedback-based circuit system includes an internal pickup coil 41, the position of which corresponds to the position of the pickup coil 11. Selecting either the internal feedback-based circuit system or the external feedback-based circuit system to detect the external magnetic field generates different electrical signals. The detection results of the two circuit systems are compared to verify the effectiveness of the external feedback-based circuit system, i.e., the external feedback-based circuit system has a lower crosstalk rate. Additionally, a heating resistor 5 is provided within the area surrounded by the magnetic flux detection loop. The heating resistor 5 is close to the input coil 12 and the SQUID device 2 to change the ambient temperature of the input coil 12 and the SQUID device 2, thereby changing their operating state and causing them to temporarily lose quench.

[0060] Furthermore, all lead electrodes 6 within the channel are concentrated around the input coil. For example, the lead electrodes at both ends of the first-stage feedback coil in the circuit system based on external feedback mode, the lead electrodes at both ends of the SQUID device, the lead electrodes at both ends of the heating resistor, and the lead electrodes in the circuit system based on internal feedback mode are all concentrated around the input coil 12, and their layout is symmetrical.

[0061] In this embodiment, the junction area of ​​the thin film designed according to the standard planar process is A. J =3μm×3μm, critical current density Jc=100A / cm 2 The corresponding critical current of the junction is I0 = 9 μA, and the empirical unit junction capacitance (sheet capacitance) is C = 40.5 F / μm. 2 The sheet resistance Mo = 2Ω, and the heating resistance is 100Ω. The corresponding parameters for the SQUID device include the Josephson junction critical current Ic = 18μA, and the bypass resistance R... J =17.4Ω, modulation depth β L =1, hysteresis coefficient β C=3. To improve chip sensitivity, maximize the magnetic flux transmission efficiency of the circuit system, reduce magnetic flux noise, and improve the signal-to-noise ratio, the inductance of the input coil 12 and the pickup coil 11 is designed to be basically the same.

[0062] In summary, this invention provides an integrated multi-channel SQUID chip, which includes several channels spaced apart from each other, arranged in an n×n array where n≥2. The circuit system in each channel is based on an external feedback mode, comprising a pickup coil, an input coil, a SQUID device, an operational amplifier, a first-stage feedback coil, and a second-stage feedback coil. The pickup coil, the input coil, and the second-stage feedback coil are connected in series to form a flux detection loop. The SQUID device is coupled to the input coil, and the leads at both ends of the SQUID device are connected to the two input terminals of the operational amplifier. A feedback resistor and the first-stage feedback coil are sequentially connected to the output terminal of the operational amplifier. The first-stage feedback coil is coupled to the second-stage feedback coil for transmitting feedback signals.

[0063] The integrated multi-channel SQUID chip of this invention has the following advantages: The SQUID chip of this application adopts an integrated multi-channel design, with multiple channels concentrated on the same chip and arranged in an n×n array, realizing chip integration and system miniaturization, making a portable and convenient SQUID system possible. The circuit systems in each channel are all based on an external feedback mode. By coupling the primary feedback coil with the secondary feedback coil in the flux detection circuit, the crosstalk rate between channels is reduced to less than 0.1%. Multiple channels jointly acquire signals, and the circuit systems in each channel maintain high symmetry and consistency, with identical operating mechanisms, avoiding the introduction of excessive noise due to inconsistencies between channels. This ensures that the signal detected by the chip has a high signal-to-noise ratio during application, thereby improving the spatial resolution of the entire system. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0064] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. An integrated multi-channel SQUID chip, characterized in that, The integrated multi-channel SQUID chip includes several channels spaced apart from each other, arranged in an n×n array where n≥2. The circuitry in each channel is based on an external feedback mode, comprising a pickup coil, an input coil, a SQUID device, an operational amplifier, a first-stage feedback coil, and a second-stage feedback coil. The pickup coil, input coil, and second-stage feedback coil are connected in series to form a flux detection loop. The SQUID device is coupled to the input coil, and the leads at both ends of the SQUID device are connected to the two input terminals of the operational amplifier. A feedback resistor and the first-stage feedback coil are sequentially connected to the output terminal of the operational amplifier. The first-stage feedback coil is coupled to the second-stage feedback coil for transmitting feedback signals. The flux detection loops are all square structures. The input coil is located at one corner of the square structure. There are two sets of second-stage feedback coils, located on opposite sides of the square structure, and the pickup coil is located on the other two sides of the square structure. The two sets of second-stage feedback coils are identical in design and symmetrical about the diagonal of the input coil in the middle.

2. The integrated multi-channel SQUID chip according to claim 1, characterized in that: The center-to-center distance between adjacent channels is <5mm, and the area of ​​the integrated multi-channel SQUID chip is <10mm². 2 .

3. The integrated multi-channel SQUID chip according to claim 2, characterized in that: The number of channels is four, and the four channels are arranged in a 2×2 array, with a center distance of 3.43 mm between adjacent channels.

4. The integrated multi-channel SQUID chip according to claim 3, characterized in that: The four magnetic flux detection circuits are symmetrically distributed about the center of the array, and the positions of the four corresponding input coils are all far away from the center of the array.

5. The integrated multi-channel SQUID chip according to claim 4, characterized in that: The structure of the input coil and the structure of the two sets of secondary feedback coils are both double-ring reverse structures. The double-ring reverse structure is a centrally symmetrical structure composed of two interconnected planar spiral coils, and the current flowing through the two planar spiral coils is in opposite directions.

6. The integrated multi-channel SQUID chip according to claim 5, characterized in that: The SQUID device is configured with a dual-hole structure corresponding to the input coil and is coupled to the input coil in an overlapping manner; the primary feedback coil is configured with a double-loop reverse structure corresponding to the secondary feedback coil and is coupled to the secondary feedback coil in an overlapping manner.

7. The integrated multi-channel SQUID chip according to claim 6, characterized in that: The input coil, the SQUID device, the primary feedback coil, and the secondary feedback coil all have a square structure.

8. The integrated multi-channel SQUID chip according to claim 1, characterized in that: The area surrounded by the magnetic flux detection loop is also equipped with a circuit system based on an internal feedback mode. The circuit system based on the internal feedback mode is used to compare the detection results with the circuit system based on an external feedback mode to verify the effectiveness of the circuit system based on the external feedback mode.

9. The integrated multi-channel SQUID chip according to claim 8, characterized in that: All lead electrodes within the channel are concentrated around the input coil location.

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