CN113937213A

CN113937213A - Integrated multichannel SQUID chip

Info

Publication number: CN113937213A
Application number: CN202111356064.1A
Authority: CN
Inventors: 孔祥燕; 张志聃; 王海
Original assignee: Ningbo University
Current assignee: Ningbo University
Priority date: 2021-11-16
Filing date: 2021-11-16
Publication date: 2022-01-14

Abstract

The invention provides an integrated multichannel SQUID chip, which comprises a plurality of channels arranged at intervals, wherein the channels are arranged according to an n multiplied by n array, and n is more than or equal to 2; the circuit system in each channel is based on an external feedback mode, a pickup coil, an input coil and a secondary feedback coil are connected in series end to form a magnetic flux detection loop, a SQUID device is coupled with the input coil, leads at two ends of the SQUID device are respectively connected with two input ends of an operational amplifier, the output end of the operational amplifier is sequentially connected with a feedback resistor and a primary feedback coil, and the primary feedback coil is coupled with the secondary feedback coil and used for transmitting feedback signals. The integrated multichannel SQUID chip provided by the invention realizes the integration of the chip and the miniaturization of the system, simultaneously achieves the goal that the crosstalk rate between channels is lower than 0.1%, and improves the spatial resolution of the whole system.

Description

Integrated multichannel SQUID chip

Technical Field

The invention relates to the technical field of SQUID detection, in particular to an integrated multi-channel SQUID chip.

Background

Superconducting quantum interference device (SQUID) is a magnetic flux sensor for converting magnetic flux into voltage, and the basic principle is based on superconducting Josephson effect and magnetic flux quantization phenomenon, and the SQUID has the advantages of high sensitivity, wide working range, high space-time resolution and the like and is widely applied to the fields of biomagnetic detection, aeromagnetic detection, nondestructive detection and the like. Currently, systems for detecting biological magnetic signals are based on multiple channels, such as The 83 channel magnetocardiograph developed by PTB in Germany [ drop, Dietmar. "The PTB 83-SQUID system for biological applications in a clinical." IEEE transactions on applied subconduction 5.2(1995):2112-2117 ], The 64 channel magnetocardiograph developed by Hitachi in Japan [ Itozaki, H. (2003),. SQUID application research in Japan. superconductor Science and Technology,16(12),1340 ]. The multichannel magnetocardiogram instrument system is installed at Shanghai Renjin hospital, Fuweida hospital, Tianjin Taida hospital and Beijing 309 hospital. Systems for magnetoencephalography, such as the 306-channel magnetoencephalography developed in Finland [ tau, S., & Hari, R. (2009). Removal of magnetoencephalic features with temporal signal-space registration: monitoring with single-three-audio-accessed responses. human broad mapping,30 (5); 1524-1534 ], and the latest multichannel atomic magnetometer technology developed in the Central academy for magnetoencephalic detection [ Li, Jian-Jun, et al. "" minimum quality-channel spin-exchange-relaxation-free for magnetoencephalic mapping ] 8928.4 (2019):040703. Therefore, the mainstream detection systems used by SQUIDs and atomic magnetometers, whether domestic or foreign, are multi-channel systems based on discrete devices.

At present, the distance between channels of a multi-channel discrete device is gradually reduced from centimeter magnitude to millimeter magnitude or even micron magnitude, and the channels are inevitably close to each other to cause mutual interference. As shown in fig. 1, the detection of an external magnetic field by channel 1 according to maxwell's equation generates a current that will generate a mutual inductance with channel 2 (which is close to channel 1), so that the signal of channel 1 is present in the output of channel 2, thereby causing crosstalk. It was deduced that the cross-talk output in channel 2 is mainly caused by two components, inter-channel mutual inductance and the current generated by the flux detection circuit due to the detected flux [ Brake H J, Fluuren F H, Ulfrnan J A, et al, excitation of flux-transformer cross in multichannel SQUID magneters [ J ]. Cryogenics:1986,26(12):667-670 ].

In the field of biomagnetic detection, the design of an integrated multichannel chip is not applied, in particular to the design of an integrated multichannel SQUID chip. At present, in the prior art, a superconducting transition edge detector (TES) and a Series SQUID Array (SSA) can be applied to integrated chip design, but the SQUID devices are connected in series to form an array, and the array is not a single integrated multi-channel design, so that the spatial resolution of a biological detection system is low, the system volume is large, and the detection requirement of a high standard is difficult to meet.

Disclosure of Invention

In view of the above drawbacks of the prior art, an object of the present invention is to provide an integrated multi-channel SQUID chip, which is used to solve the problems in the prior art that crosstalk is easily generated between channels, the spatial resolution of the system is low, and the volume is large.

In order to achieve the above objects and other related objects, the present invention provides an integrated multichannel SQUID chip, which includes a plurality of channels arranged at intervals, wherein the plurality of channels are arranged in an n × n array, and n is greater than or equal to 2; each circuit system in the passageway is the circuit system based on external feedback mode, the circuit system based on external feedback mode is including picking up coil, input coil, SQUID device, operational amplifier, one-level feedback coil and second grade feedback coil, wherein, pick up coil, input coil and second grade feedback coil end to end series connection form magnetic flux detection circuit, the SQUID device with the input coil coupling, SQUID device both ends lead wire respectively with operational amplifier both ends input is connected, the operational amplifier output connects gradually feedback resistance with one-level feedback coil, one-level feedback coil with second grade feedback coil coupling for transmit feedback signal.

Optionally, the center distance between adjacent channels<5mm, area of the integrated multichannel SQUID chip<10mm²。

Further, the number of the channels is four, the four channels are arranged in a 2 × 2 array, and the center distance between the adjacent channels is 3.43 mm.

Furthermore, the magnetic flux detection loops in the four channels are all of a square structure, the input coil is located at one corner of the square structure, two sets of the secondary feedback coils are located on two sides of the square structure on two sides of the input coil respectively, and the pickup coils are located on the other two sides of the square structure.

Further, the four magnetic flux detection circuits are symmetrically distributed about the center of the array, and the positions of the corresponding four input coils are far away from the center of the array.

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 structures are centrosymmetric structures formed by two mutually connected planar spiral coils, and the directions of currents flowing through the two planar spiral coils are opposite.

Further, the SQUID device is arranged in a double-hole structure corresponding to the input coil and is in overlapped coupling with the input coil; the primary feedback coil is arranged to be of a double-ring reverse structure corresponding to the secondary feedback coil and is in overlapped coupling with the secondary feedback coil.

Furthermore, the structures of the input coil, the SQUID device, the primary feedback coil and the secondary feedback coil are all square structures.

Optionally, an internal feedback mode-based circuit system is further disposed in an area surrounded by the magnetic flux detection loop, and the internal feedback mode-based circuit system is used for comparing a detection result with the external feedback mode-based circuit system and verifying the effectiveness of the external feedback mode-based circuit system.

Further, all lead electrodes within the channel are collectively disposed around the input coil location.

As described above, the integrated multichannel SQUID chip of the present invention has the following beneficial effects:

(1) the SQUID chip of this application adopts the design of integrated form multichannel, and a plurality of passageways are concentrated on same piece of chip to arrange according to nxn array, realize integrating of chip and the miniaturization of system, make the SQUID system that possesses mobility, convenience become possible.

(2) The circuit systems in all the channels are based on an external feedback mode, and the target that the crosstalk rate between the channels is lower than 0.1% is achieved by coupling the primary feedback coil with the secondary feedback coil in the magnetic flux detection loop.

(3) The multiple channels collect signals together, the circuit systems in the channels keep high symmetry and consistency, the working mechanism keeps the same, more noise caused by non-consistency among the channels is avoided, the signals detected by the chip in application have high signal-to-noise ratio, and further the spatial resolution of the whole system is improved.

Drawings

FIG. 1 is a schematic diagram of the four-channel position of the present invention.

Fig. 2 is a schematic diagram of a prior art internal feedback mode based circuit system.

Fig. 3 shows a schematic diagram of the external feedback mode based circuitry of the present invention.

Fig. 4 shows a layout of a single-channel circuit structure of the present invention.

Fig. 5 shows a layout of a four-channel circuit structure of the present invention.

Figure 6 shows a schematic layout of the magnetic flux detection circuit and SQUID device of the present invention.

Fig. 7 shows a coil having a double loop reverse structure according to the present invention.

Fig. 8 is a schematic view showing the structure of the SQUID device of the present invention.

FIG. 9 is a diagram illustrating a four-channel simulation according to the present invention.

FIG. 10 is a graph showing the relationship between the ratio of the gap between adjacent flux detection loops (gap) and the side length of the flux detection loop in the four-channel model of the present invention and the crosstalk ratio.

FIG. 11 shows a layout of a repeating cell with multiple channels according to the present invention.

Description of the element reference numerals

1 magnetic flux detection circuit

11 pick-up coil

12 input coil

13 two-stage feedback coil

2 SQUID device

21 josephson junction

22 superconducting ring

3 primary feedback coil

4 circuitry based on internal feedback mode

41 internal pick-up coil

5 heating resistance

6 lead wire electrode

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

It should be noted that the drawings provided in the present embodiment are only for illustrating the basic idea of the present invention, and the drawings only show the components related to the present invention rather than the number, shape and size of the components in actual implementation, and the type, amount, position relationship and proportion of the components in actual implementation can be changed freely on the premise of implementing the technical solution, and the layout of the components may be more complicated.

As shown in figure 1, the invention provides an integrated multichannel SQUID chip, which comprises a plurality of channels arranged at intervals, wherein the channels are arranged according to an n x n array, and n is more than or equal to 2. The integrated design concentrates a plurality of channels on the same chip, and preferably, the channels are distributed in an n × n array with the area less than 10mm²The SQUID chip has a center distance of less than 5mm between adjacent channels, so that the integration of the chip and the miniaturization of the system are realized, and the SQUID system with mobility and convenience becomes possible. In addition, a plurality of groups of circuit systems are correspondingly arranged in the channels, and the circuit systems of each group are mutually independent and the working mechanisms are kept the same.

Fig. 2 shows a schematic diagram of an internal feedback circuit in the prior art, when the channel is a conventional circuit system based on an internal feedback mode, in which the pick-up coil 11 detects an external magnetic field Φ_exGenerating a loop current I₁The input coil 12 is coupled with the SQUID device 2 to generate mutual inductance M_inAnd meanwhile, an induced current is generated in the SQUID device 2 and is connected with the input end of the operational amplifier G. A primary feedback coil 3 connected with the output end of the operational amplifier is directly coupled with the SQUID device 2 to generate mutual inductance M_finFor internal feedback. At this time, the crosstalk between the channel 1 and the channel 2 mainly originates from the mutual inductance M between the pickup coils 11 on the one hand₁₂On the other hand from the current I in the flux-sensing circuit₁The resulting mutual inductance.

FIG. 3 is a schematic diagram of an external feedback circuit of the present invention for attenuating the current I in the magnetic flux detection circuit 1₁The generated mutual inductance influences, and the circuit system in each channel is set as a circuit system based on an external feedback mode and used for suppressing crosstalk noise caused by the magnetic flux detection circuit 1 in other channels. Specifically, the external feedback mode-based circuit system comprises a pickup coil 11, an input coil 12, a SQUID device 2, an operational amplifier G, a primary feedback coil 3 and a secondary feedback coil 13, wherein the pickup coil 11, the input coil 12 and the secondary feedback coil 13 are connected in series end to form a magnetic flux detection loop 1, the SQUID device 2 is coupled with the input coil 12, leads at two ends of the SQUID device 2 are respectively connected with two input ends of the operational amplifier, the output end of the operational amplifier is sequentially connected with a feedback resistor R and the primary feedback coil 3, the primary feedback coil 3 is coupled with the secondary feedback coil 13 to generate mutual inductance M_fexFor transmitting a feedback signal.

Note that the SQUID device 2 is composed of two josephson junctions and a superconducting ring, in which two josephson junctions are disposed in parallel in the superconducting ring. The SQUID device is coupled with the input coil and used for inducing magnetic flux generated by the input coil and converting the magnetic flux into an electric signal. In addition, the present embodiment will be described by taking four channels arranged in a 2 × 2 array on the SQUID chip as an example.

As an example, as shown in fig. 4 to 6, in order to ensure the consistency of each channel in the chip, avoid introducing extra noise, and improve the signal-to-noise ratio of the acquired signal, the magnetic flux detection loops 1 in the four channels are all configured as a square structure, wherein the input coil 12 is located at one corner of the square structure, two sets of the secondary feedback coils 13 are respectively located on two sides of the square structure on two sides of the input coil 12, and the pickup coils 11 are located on the other two sides of the square structure. In order to ensure convenience of the later interconnection lines (Bonding) of the chips and simultaneously ensure the symmetry of the chips, the two sets of secondary feedback coils 13 are designed to be completely the same and are symmetrical based on the diagonal where the middle input coil 12 is located. The pick-up coils 11 in each channel are typically designed larger and are all kept uniform as the flux modulation is done. In addition, the four magnetic flux detection circuits 1 are symmetrically distributed about the center of the array, the positions of the four corresponding input coils 12 are far away from the center of the array, and the SQUID devices 2 coupled with the four input coils 12 are arranged at the corresponding positions, so that the circuit structure layout has high symmetry.

When a plurality of channels collect signals together, due to the fact that circuit systems in the channels keep high symmetry and consistency, working mechanisms are kept the same, the spatial resolution of the whole system is improved finally, the signal detection density is improved, convenience is provided for the application of the SQUID, particularly in the field of biological magnetic detection, and the application of the SQUID in clinical diagnosis is further promoted.

As an example, as shown in fig. 4, the structure of the input coil 12 and the structure of the two sets of secondary feedback coils 13 are both double-loop reverse structures, and specifically, as shown in fig. 7, the double-loop reverse structure is a central symmetry structure composed of two interconnected planar spiral coils, and the directions of currents flowing through the two planar spiral coils are opposite. Specifically, the inside one end of the first planar spiral coil is connected with the inside one end of the second planar spiral coil, and when current flows in from the outside one end of the first planar spiral coil, the current spirals inwards and flows out through the inside one end of the first planar spiral coil, and simultaneously flows into the inside one end of the second planar spiral coil, and the current spirals outwards and flows out through the outside one end of the second planar spiral coil. As can be seen from the right-hand spiral rule, the directions of the magnetic fields excited in the same plane by the currents flowing through the two planar spiral coils are opposite, so that the magnetic fields in different directions can cancel each other at a certain point in the plane, that is, crosstalk between different channels is suppressed.

As an example, as shown in fig. 4, the SQUID device 2 is disposed in a double-hole structure corresponding to the input coil 12, and is overlapped and coupled with the input coil 12; the primary feedback coil 3 is arranged in a double-loop reverse structure corresponding to the secondary feedback coil 13, and is overlapped and coupled with the secondary feedback coil 13. Specifically, the structures of the input coil 12, the SQUID device 2, the primary feedback coil 3, and the secondary feedback coil 13 are all square structures.

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 may be adjusted as needed, and the protection scope of the present invention should not be limited excessively herein.

Specifically, as shown in fig. 8, the double-hole of the SQUID device 2 is a two-sided hole, and the square hole size (d × d) is 44 μm × 44 μm. The two square holes are communicated through a slit, the width (a) of the slit is 5 mu m, and the length (l) of the slit is 50 mu m. Two Josephson junctions 21 are located between the two square holes and are respectively disposed on the superconducting rings 22 on both sides of the slit, and the ring width (w) of the superconducting ring 22 in the SQUID device is 15 μm.

In the magnetic flux detection circuit 1, the input coil 12 is designed to have 6.5 turns × 2 turns, and the line width and the line spacing are designed to be 1 μm in the standard process. The line width of the pickup coil 11 is 10 μm. The line width and the line spacing of the secondary feedback coil 13 are both 1 μm standard width.

As shown in fig. 9, the inner diameter of the square structure of the magnetic flux detection loop is designed to be 3.1mm × 3.1mm, and multiple channels are simulated by software based on the external feedback mode of the circuit system, so as to find the optimal gap (gap) or center distance between adjacent channels for achieving the required crosstalk. Fig. 10 shows the relationship between the ratio of the interval (gap) between adjacent magnetic flux detection loops and the side length of the magnetic flux detection loop and the crosstalk ratio, and the result is obtained by simulating the model by using Maxwell software. In consideration of the error between the simulation result and the actually manufactured chip and the aim of better reducing the crosstalk rate, the invention determines the central distances between four different adjacent channels, namely 3.38mm, 3.43mm, 3.48mm and 3.53 mm. Preferably, the optimal center distance between the adjacent channels is 3.43mm as determined by simulation results, and the crosstalk ratio between the corresponding channels is 0.1%.

As an example, fig. 11 shows a layout of a repeat cell designed by standard processes on an entire wafer. Due to the limitation of the exposure area of the step (stepper) standard process during chip design, the size of the design repeating unit is ensured to be within 22mm multiplied by 22mm, and the chips with the center distances between the four different adjacent channels can be simultaneously designed on the same unit.

As an example, as shown in fig. 4 and 5, the magnetic flux detection circuit 1 is further provided with a circuit system 4 based on an internal feedback mode in which an internal pickup coil 41 is provided, and the position of the internal pickup coil 41 is set corresponding to the position of the pickup coil 11. The circuit system based on the internal feedback mode is selected to be switched on or the circuit system based on the external feedback mode detects an external magnetic field, and the circuit systems in the two modes compare detection results according to different generated electric signals, so that the effectiveness of the circuit system based on the external feedback mode is verified, namely the crosstalk rate of the circuit system based on the external feedback mode is lower. In addition, a heating resistor 5 is further arranged in an area surrounded by the magnetic flux detection loop, and the heating resistor 5 is close to the input coil 12 and the SQUID device 2 and used for changing the ambient temperature of the input coil 12 and the SQUID device 2 and further changing the working states of the input coil 12 and the SQUID device 2 so that the two can be temporarily quenched.

Further, all the lead electrodes 6 in the channel are collectively disposed around the position of the input coil, for example, the lead electrodes at both ends of the primary feedback coil in the external feedback mode-based circuit system, 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 internal feedback mode-based circuit system are collectively disposed around the input coil 12, and the layout thereof has symmetry.

In the present embodiment, the junction area of the thin film designed according to the standard planar process is A_J3 μm × 3 μm, and a critical current density Jc of 100A/cm²Corresponding to the critical current I of the junction₀Empirical unit junction capacitance (square capacitance) C of 9 μ a 40.5F/μm²The square resistance Mo is 2 Ω, and the heating resistance is 100 Ω. The SQUID device has corresponding parameters including critical current Ic of Josephson junction of 18 μ A and bypass resistor R_J17.4 Ω, modulation depth β _L1, coefficient of hysteresis β _C3. In order to improve chip sensitivity, maximize the efficiency of magnetic flux transmission of the circuit system, reduce magnetic flux noise, and improve the signal-to-noise ratio, the input coil 12 and the pickup coil 11 are designed to keep their inductances substantially the same.

In summary, the present invention provides an integrated multichannel SQUID chip, which includes a plurality of channels arranged at intervals, wherein the channels are arranged in an n × n array, and n is greater than or equal to 2; each circuit system in the passageway is the circuit system based on external feedback mode, the circuit system based on external feedback mode is including picking up coil, input coil, SQUID device, operational amplifier, one-level feedback coil and second grade feedback coil, wherein, pick up coil, input coil and second grade feedback coil end to end series connection form magnetic flux detection circuit, the SQUID device with the input coil coupling, SQUID device both ends lead wire respectively with operational amplifier both ends input is connected, the operational amplifier output connects gradually feedback resistance with one-level feedback coil, one-level feedback coil with second grade feedback coil coupling for transmit feedback signal.

The integrated multichannel SQUID chip has the following beneficial effects: the SQUID chip of this application adopts the design of integrated form multichannel, and a plurality of passageways are concentrated on same piece of chip to arrange according to nxn array, realize integrating of chip and the miniaturization of system, make the SQUID system that possesses mobility, convenience become possible. And the circuit systems in all the channels are based on an external feedback mode, and the target that the crosstalk rate between the channels is lower than 0.1% is realized by coupling the primary feedback coil with the secondary feedback coil in the magnetic flux detection loop. The multiple channels collect signals together, the circuit systems in the channels keep high symmetry and consistency, the working mechanism keeps the same, more noise caused by non-consistency among the channels is avoided, the signals detected by the chip in application have high signal-to-noise ratio, and further the spatial resolution of the whole system is improved. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. An integrated multichannel SQUID chip is characterized in that the integrated multichannel SQUID chip comprises a plurality of channels which are arranged at intervals, the channels are arranged according to an n x n array, and n is more than or equal to 2; each circuit system in the passageway is the circuit system based on external feedback mode, the circuit system based on external feedback mode is including picking up coil, input coil, SQUID device, operational amplifier, one-level feedback coil and second grade feedback coil, wherein, pick up coil, input coil and second grade feedback coil end to end series connection form magnetic flux detection circuit, the SQUID device with the input coil coupling, SQUID device both ends lead wire respectively with operational amplifier both ends input is connected, the operational amplifier output connects gradually feedback resistance with one-level feedback coil, one-level feedback coil with second grade feedback coil coupling for transmit feedback signal.

2. The integrated multi-channel SQUID chip of claim 1, wherein: center distance between adjacent channels<5mm, area of the integrated multichannel SQUID chip<10mm²。

3. The integrated multi-channel SQUID chip of claim 2, wherein: the number of the channels is four, the four channels are arranged according to a 2 x 2 array, and the center distance between every two adjacent channels is 3.43 mm.

4. The integrated multi-channel SQUID chip of claim 3, wherein: the magnetic flux detection loops in the four channels are all of a square structure, the input coil is located at one corner of the square structure, two groups of secondary feedback coils are located on two sides of the square structure on two sides of the input coil respectively, and the pickup coils are located on the other two sides of the square structure.

5. The integrated multi-channel SQUID chip of claim 4, wherein: the four magnetic flux detection circuits are symmetrically distributed about the center of the array, and the positions of the corresponding four input coils are far away from the center of the array.

6. The integrated multi-channel SQUID chip of claim 5, wherein: the structure of the input coil and the structure of the two secondary feedback coils are both double-ring reverse structures, the double-ring reverse structures are centrosymmetric structures formed by two mutually connected planar spiral coils, and the directions of currents flowing through the two planar spiral coils are opposite.

7. The integrated multi-channel SQUID chip of claim 6, wherein: the SQUID device is arranged into a double-hole structure corresponding to the input coil and is in overlapped coupling with the input coil; the primary feedback coil is arranged to be of a double-ring reverse structure corresponding to the secondary feedback coil and is in overlapped coupling with the secondary feedback coil.

8. The integrated multi-channel SQUID chip of claim 7, wherein: the structures of the input coil, the SQUID device, the primary feedback coil and the secondary feedback coil are all square structures.

9. The integrated multi-channel SQUID chip of claim 4, wherein: and the circuit system based on the internal feedback mode is used for comparing the detection result with the circuit system based on the external feedback mode and verifying the effectiveness of the circuit system based on the external feedback mode.

10. The integrated multi-channel SQUID chip of claim 9, wherein: all lead electrodes within the channel are centrally disposed about the input coil location.