CN111724836B - Superconducting magnetic flux storage unit and read-write method thereof - Google Patents

Superconducting magnetic flux storage unit and read-write method thereof Download PDF

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CN111724836B
CN111724836B CN202010493002.4A CN202010493002A CN111724836B CN 111724836 B CN111724836 B CN 111724836B CN 202010493002 A CN202010493002 A CN 202010493002A CN 111724836 B CN111724836 B CN 111724836B
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magnetic flux
loop
josephson junction
current
superconducting
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CN111724836A (en
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陈垒
王镇
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Shanghai Institute of Microsystem and Information Technology of CAS
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Shanghai Institute of Microsystem and Information Technology of CAS
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/14—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements
    • G11C11/15—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using thin-film elements using multiple magnetic layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
    • G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
    • G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
    • G11C11/41—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming static cells with positive feedback, i.e. cells not needing refreshing or charge regeneration, e.g. bistable multivibrator or Schmitt trigger
    • G11C11/413—Auxiliary circuits, e.g. for addressing, decoding, driving, writing, sensing, timing or power reduction
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment

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Abstract

The application relates to a superconducting magnetic flux storage unit and a reading and writing method thereof, wherein the superconducting magnetic flux storage unit comprises a storage loop, an addressing circuit and a reading circuit; the memory loop comprises a first josephson junction; the first Josephson junction has a current phase relationship deviating from a sine function, and stable magnetic flux storage hysteresis is formed by scanning bias current; the addressing circuit is used for adjusting the critical current of the first Josephson junction so as to change the magnetic flux storage hysteresis magnitude of the storage loop; and the reading circuit is used for in-situ reading the magnetic flux state of the storage loop. The offset between the current phase relation of the first Josephson junction in the storage loop and the sine function can be equivalent to the effect of the inductance of the storage loop in forming storage hysteresis, so that the superconducting magnetic flux storage unit can get rid of the minimum area limitation caused by the loop inductance requirement, and the area of the superconducting magnetic flux storage unit can be greatly reduced.

Description

Superconducting magnetic flux storage unit and read-write method thereof
Technical Field
The application relates to the technical field of superconducting electronic information, in particular to a superconducting magnetic flux storage unit and a reading and writing method thereof.
Background
As Moore's law has developed, semiconductor-based integrated circuit feature sizes have approached physical limits, the huge power consumption and heat dissipation problems have become very serious and operating speeds have made it difficult to achieve greater breakthroughs. In the global information age, how to keep the power consumption low while increasing the operating speed of the circuit becomes a major goal of the future development of integrated circuits.
The superconducting single flux quantum circuit (SFQ) based on the Josephson effect and the flux quantization effect is composed of Josephson Junctions (JJ), and a picosecond-magnitude voltage pulse signal is used for transmitting and processing data, so that a large-scale digital integrated circuit with ultrahigh speed and low power consumption can be realized, and an ultrahigh-speed computer and a large-scale data processing center are expected to be constructed. Although superconducting microprocessors based on superconducting SFQ logic have been successful and their operating frequencies have achieved 50GHz, the lack of high speed and high storage density superconducting memory compatible with them has made superconducting computers difficult to implement.
London theory predicts the phenomenon of flux quantization within a superconducting closed loop. The superconducting loop can realize the function of storing magnetic flux quanta, the storage speed of the superconducting loop is in picosecond magnitude, the superconducting loop can be matched with an SFQ integrated circuit, at present, a 4Kb memory with 380ps access speed is realized on the basis of a traditional tunnel type Josephson junction storage unit, and the area of the storage unit is reduced to 9um x 12um through structural optimization. However, such a magnetic flux storage unit is designed based on the magnetic flux hysteresis characteristic of a single junction superconducting loop, the single junction superconducting loop can store different magnetic flux states to satisfy a certain loop inductance value, generally several picohenries (pH), and at present, the fabrication of a high-quality josephson junction with high junction current density is difficult, and these problems make the area of the storage unit difficult to further reduce, and the realization of a high-density magnetic flux storage device is difficult.
Disclosure of Invention
The embodiment of the application provides a superconducting magnetic flux storage unit and a read-write method thereof, which can effectively reduce the area of the superconducting magnetic flux storage unit, thereby improving the problem that the area of the conventional superconducting magnetic flux storage unit is larger.
On one hand, the embodiment of the application provides a superconducting magnetic flux storage unit, which comprises a storage loop, an address selecting circuit and a reading circuit;
the memory loop comprises a first josephson junction whose current phase relationship deviates from a sine function; the current phase relation of the first Josephson junction, the critical current of the first Josephson junction and the inductance of the storage loop are used for forming a hysteresis curve required by stable magnetic flux storage;
the addressing circuit is used for generating external excitation and adjusting the critical current of the first Josephson junction so as to change the magnetic flux storage hysteresis magnitude of the storage loop;
and the reading circuit is used for in-situ reading the magnetic flux state of the storage loop.
Optionally, the first josephson junction is a superconducting quantum interference device formed by connecting two 3D nanobridge junctions in parallel.
Optionally, the first josephson junction is a superconductor-semiconductor-superconductor structure.
Optionally, the first josephson junction is a superconductor-graphene-superconductor structure.
Optionally, the first josephson junction is a superconductor-non-superconductor metal-superconductor structure.
Optionally, the addressing circuit comprises a coil; and the coil is used for generating a uniform and stable magnetic field and changing the critical current of the first Josephson junction by the action of the magnetic field.
Optionally, the address selecting circuit includes a heating resistor; and a heating resistor for changing the critical current of the first Josephson junction by thermal effect.
Optionally, the address selecting circuit includes a voltage-adjustable gate; and the voltage adjustable grid electrode changes the critical current of the first Josephson junction through an electric field effect.
Optionally, the reading circuit includes a superconducting quantum interference device; the superconducting quantum interference device is inductively coupled with the storage loop; the superconducting quantum interference device consists of two second Josephson junctions connected in parallel, the data readout is realized by applying current bias to the two second Josephson junctions connected in parallel, and the readout addressing is realized by applying magnetic flux bias current to a loop part which does not contain the two second Josephson junctions connected in parallel.
On the other hand, the embodiment of the application provides a data writing method, which is applied to a superconducting magnetic flux storage unit; the superconducting magnetic flux storage unit comprises a storage loop and an addressing circuit; the memory loop comprises a first josephson junction whose current phase relationship deviates from a sine function; the current phase relation of the first Josephson junction, the critical current of the first Josephson junction and the inductance of the storage loop are used for forming a hysteresis curve required by stable magnetic flux storage; the initial bias current of the memory loop is in the middle of the hysteresis curve; the initial bias current is smaller than a first current bias point of the hysteresis curve and larger than a second current bias point of the hysteresis curve; the method comprises the following steps:
generating external excitation through an addressing circuit, adjusting the critical current of the first Josephson junction, and changing the position of the first current bias point and the position of the second current bias point to meet the writing conditions of magnetic flux states of '0' and '1' so as to realize addressing;
adjusting an initial bias current; when the initial bias current is larger than the first current bias point, the writing of the magnetic flux state '1' is realized; writing of a flux state "0" is achieved when the initial bias current is less than the second current bias point.
On the other hand, the embodiment of the application provides a data reading method, which is applied to a superconducting magnetic flux storage unit; the superconducting magnetic flux storage unit comprises a storage loop and a reading circuit; a superconducting quantum interference device; the memory loop comprises a first josephson junction whose current phase relationship deviates from a sine function; the current phase relation of the first Josephson junction, the critical current of the first Josephson junction and the inductance of the storage loop are used for forming a hysteresis curve required by stable magnetic flux storage; the reading circuit comprises a superconducting quantum interference device formed by connecting two second Josephson junctions in parallel and is used for in-situ reading the magnetic flux state of the storage loop; the method comprises the following steps:
applying bias current and loop magnetic flux bias current to the superconducting quantum interference device and the loop thereof respectively to enable the superconducting quantum interference device to be in a magnetic flux sensitive working state and realize reading and address selection of the storage unit;
detecting voltage values at two ends of the superconducting quantum interference device; the magnetic flux state of the sense memory loop is "0" or "1" according to the voltage value.
The superconducting magnetic flux storage unit and the read-write method thereof provided by the embodiment of the application have the following beneficial effects:
the superconducting magnetic flux storage unit comprises a storage loop, an addressing circuit and a reading circuit; the memory loop comprises a first josephson junction; the first Josephson junction has a current phase relationship deviating from a sine function, and stable magnetic flux storage hysteresis is formed by scanning bias current; the addressing circuit is used for adjusting the critical current of the first Josephson junction so as to change the magnetic flux storage hysteresis magnitude of the storage loop; and a reading circuit for reading the magnetic flux state of the memory loop. The method comprises the steps that the size of magnetic flux hysteresis in a storage loop is regulated and controlled through an addressing circuit so as to store different magnetic flux states; the offset between the current phase relation of the first Josephson junction in the storage loop and the sine function can be equivalent to the function of the inductance of the storage loop in forming storage hysteresis, so that the superconducting magnetic flux storage unit can get rid of the minimum area limitation caused by the loop inductance requirement, and the area of the superconducting magnetic flux storage unit can be greatly reduced.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a schematic diagram of a superconducting magnetic flux storage unit according to an embodiment of the present application;
fig. 2 is a schematic diagram illustrating a current phase relationship of a first josephson junction J1 according to an embodiment of the present disclosure;
fig. 3 is a schematic structural diagram of a josephson junction of a weak link structure provided in an embodiment of the present application;
FIG. 4 is a graph illustrating the magnitude of magnetic flux storage hysteresis versus offset, critical current, and loop inductance according to an embodiment of the present disclosure;
FIG. 5 is a schematic structural diagram of a 3D nano-bridge junction-based superconducting magnetic flux storage unit according to an embodiment of the present application;
FIG. 6 is a schematic illustration of a magnetic flux storage hysteresis curve provided by an embodiment of the present application;
fig. 7 is a schematic flowchart of a data writing method according to an embodiment of the present application;
fig. 8 is a schematic flowchart of a data reading method according to an embodiment of the present application.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only some embodiments of the present application, and not all embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making creative efforts shall fall within the protection scope of the present application.
It should be noted that the terms "first," "second," and the like in the description and claims of this application and in the drawings described above are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the application described herein are capable of operation in sequences other than those illustrated or described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or server that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
The prior art superconducting magnetic flux storage units all use conventional tunnel type josephson junctions, which are vertical structures of superconductor/insulator/superconductor (SIS), and CPR is a standard sine function. The superconducting storage loop based on the SIS tunnel type Josephson junction is limited by the requirements of junction area, parallel resistance, loop inductance and the like, and at least dozens of micrometers are needed, and the area of the storage unit produced by adopting the most optimized unit design and the most advanced preparation process in the prior art also needs at least 9 micrometers to 12 micrometers, so that the superconducting storage loop is difficult to further reduce and is not beneficial to superconducting integration with high storage density.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a superconducting magnetic flux storage unit according to an embodiment of the present application, including a storage loop 101, an address circuit and a read circuit 102;
the memory loop 101 comprises a first josephson junction J1; the current phase relationship of the first josephson junction J1 deviates from a sine function; the current phase relationship of the first josephson junction J1, the critical current of the first josephson junction J1 and the inductance of the storage loop are used to form a hysteresis curve required for stable magnetic flux storage;
an addressing circuit for generating an external excitation to adjust the critical current of the first josephson junction J1 to change the magnitude of the magnetic flux storage hysteresis of the storage loop 101;
and a read circuit 102 for reading the magnetic flux state of the storage loop 101 in situ.
In the embodiment of the present application, the current phase relationship of the first josephson junction J1, the critical current of the first josephson junction J1, and the inductance of the storage loop are used to form a hysteresis curve required for stable magnetic flux storage; the magnitude of the magnetic flux storage hysteresis in the storage loop 101 is regulated by the addressing circuit to store different magnetic flux states, and the magnetic flux state of the storage loop 101 is read by the reading circuit 102.
Referring to fig. 2, fig. 2 is a schematic diagram of a Current Phase Relationship of a first josephson junction J1 according to an embodiment of the present application, as shown by a solid line, a Current Phase Relationship (CPR) of the first josephson junction J1 deviates from a sine function; and the offset amount Δ θ is defined as the difference between the phase at the maximum and pi/2 or the difference between the phase at the minimum and 3 pi/2.
In the embodiment of the present application, since the first josephson junction J1 has CPR deviating from a sine function, the offset of the CPR can be equivalent to the effect of the inductance of the storage loop 101 in forming storage hysteresis, and the larger the offset is, the smaller the inductance requirement of the storage loop 101 is; in this way, the superconducting magnetic flux storage unit can be freed from the minimum area limitation due to the loop inductance requirement by using the first josephson junction J1 having CPR deviating from the sine function, so that the area of the superconducting magnetic flux storage unit can be greatly reduced.
In the embodiment of the present application, the superconducting weak link structure also has a josephson effect in terms of physical structure. Referring to fig. 3, fig. 3 is a schematic structural diagram of a josephson junction of a weak link structure provided in an embodiment of the present application, where the weak link may be a nanobridge, graphene, a semiconductor and a non-superconducting metal, and CPR of the josephson junction of the weak link structure deviates from a standard sine function. For example, a 3D nano-bridge (3D nano-bridge) is a microbridge type josephson junction, the thickness of which in the bridge region is much smaller than the thickness of the film on both sides of the bridge region; although its CPR deviates from the standard sinusoidal function, it still has a significant josephson effect and can form a closed superconducting loop to store multiple flux states.
According to the existing theoretical model, CPR and critical current of the Josephson junction of the nano-bridge structure are determined by the ratio (L/xi) of the effective length of the bridge junction and the coherent length of the superconducting film; wherein the effective length is determined by the combined dimensions of the length, width and thickness of the nanobridge. For different L/xi CPR, a maximum value point and a limit value point exist in a single period, and the two extreme values are closely related to L/xi; as shown in fig. 2, CPR is a sine function when L/ξ ═ 1, the very large point in CPR is at phase θ ═ π/2; the phase theta of the maximum point of CPR is > pi when L/xi is 6.
In the embodiment of the application, a stable magnetic flux storage hysteresis is formed in the storage loop by combining the working principle of the magnetic flux storage unit, the control of the magnitude of the magnetic flux hysteresis is realized by controlling the critical current of the first Josephson junction, and the switching between different magnetic flux quantum states is realized by changing the bias current in the storage loop. Based on experiments and theories, the magnitude of the magnetic flux storage hysteresis of the storage loop is not only related to the critical current and the loop inductance, but also related to the CPR of the first Josephson junction; referring to fig. 4, fig. 4 is a schematic diagram of a relationship curve between the magnitude of the magnetic flux storage hysteresis and the offset, the critical current, and the loop inductance according to an embodiment of the present application, where when the offset is constant, the larger the product of the critical current and the loop inductance is, the larger the magnetic flux storage hysteresis is; when the product of the critical current and the loop inductance is constant, the flux storage hysteresis increases with an increase in the amount of offset. Thus, an increase in the product of the critical current and the loop inductance of the first josephson junction, or an increase in the offset of the CPR from the sinusoidal function of the first josephson junction, appears to be positive for increasing the flux hysteresis of the memory loop.
Based on the analysis of the physical structure and the working principle of the magnetic flux storage unit, based on the characteristic that the Josephson junction of the nano-bridge structure has CPR deviating from a sine function, the requirement of forming a stable magnetic flux hysteresis curve on loop inductance can be converted into the requirement of the offset of the CPR of the first Josephson junction, so that the area of the storage loop can be reduced by increasing the ratio of the effective length of the bridge junction in the first Josephson junction of the bridge structure to the coherent length of the superconducting thin film to increase the offset aiming at the problem of large area of the storage loop caused by the requirement on the loop inductance; meanwhile, the high dynamic inductance of the bridge junction can further reduce the requirement of the superconducting storage loop on the inductance and further reduce the area of the storage loop; in addition, the 3D nano bridge junction is more beneficial to reducing the area of a storage loop due to the nano junction area.
In an optional implementation manner, based on the advantages of the 3D nano bridge junction that the dynamic inductance is high, the junction area is small, and the joseph effect is obvious, and in combination with the magnetic flux hysteresis phenomenon of a Superconducting Quantum Interference Device (SQUID), the embodiment of the present application provides a Superconducting magnetic flux storage unit based on the 3D nano bridge junction; referring to fig. 5, fig. 5 is a schematic structural diagram of a superconducting magnetic flux storage unit based on a 3D nano bridge junction according to an embodiment of the present application, where a storage loop includes a nano-SQUID formed by connecting two 3D nano bridge junctions in parallel; the critical current of the nano-SQUID can change along with the change of the magnetic flux in the superconducting ring; the addressing circuit comprises a Coil (FC), an external magnetic Field is formed through the Coil FC, and the critical current of the nano-SQUID is changed by changing the magnetic flux in the superconducting ring of the nano-SQUID through the magnetic Field effect; the reading circuit comprises a SQUID, and the SQUID is inductively coupled with the storage loop; the SQUID consists of two second Josephson junctions connected in parallel, data readout is realized by applying current bias to the two second Josephson junctions connected in parallel, and readout addressing is realized by applying magnetic flux bias current to a loop part which does not contain the two second Josephson junctions connected in parallel.
The operation of the superconducting magnetic flux storage unit in the above-described alternative embodiment will be explained below. First, a bias current is applied to the memory loop, and the bias current and the total magnetic flux in the memory loop can be expressed by equation (1):
Iwy/Iwy-period＝IcLTf(2πФT/Ф0)/Ф0+ФT/Ф0……(1)
wherein, IwyRepresenting a bias current within the memory loop; i iswy-period＝Ф0/LTRepresenting a period of the bias current corresponding to a periodic variation of one magnetic flux quantum; phi (alpha)TRepresents the total magnetic flux; ic represents the critical current of the first josephson junction; l isTRepresenting the inductance of the storage loop; phi (0Representing magnetic flux quanta, phi0＝h/2e＝2.067×10-15Wb；f(2πФT/Ф0) Representing the current phase relationship function of the first josephson junction. In the prior art, the first josephson junction is a conventional tunnel-type structure with its CPR function f (2 π Φ)T/Ф0) Is a sine function; unlike the prior art, the CPR of the first Josephson junction in the embodiment of the present application deviates from the sine function, i.e., f (2 π φ Φ) in equation (1)T/Ф0) May represent a function deviating from a sinusoidal function.
When the magnitude of the magnetic flux storage hysteresis satisfies the condition of being greater than 0 and less than 1, a magnetic flux storage hysteresis curve as shown in fig. 6 is formed; the magnitude of the flux storage hysteresis can be determined according to equation (2):
ΔIwy/Iwy-period＝2IcLT/Ф0-1/2+(Δθ/π)……(2)
wherein, Delta Iwy/Iwy-periodRepresenting the magnitude of the magnetic flux storage hysteresis; delta IwyRepresenting a difference between the first current bias point and the second current bias point; i iswy-period＝Ф0/LTRepresenting a period of the bias current corresponding to a periodic variation of one magnetic flux quantum; ic represents critical current of nano-SQUID; l isTAn inductance value representing a memory loop; phi (alpha)0Representing magnetic flux quanta, phi0＝h/2e＝2.067×10-15Wb; Δ θ represents the offset of the current phase relationship of the nano-SQUID from the sinusoidal function.
The first josephson junction in the prior art is a standard tunnel type josephson junction, where CPR is a sine function, i.e., Δ θ is 0, then the need to achieve stable flux storage hysteresis will cause IcLTMust be greater than 0.25 phi0This limits the size of the magnetic flux storage unit; however, in this applicationIn the embodiment where CPR at the first Josephson junction is off-sine, IcL is determined when the offset Δ θ is greater than 0.5 πTA stable hysteresis curve of the magnetic flux storage can be formed even if the value is 0, and thus the area of the magnetic flux storage unit can be greatly reduced.
Secondly, a bias current I is applied to the coil FCwxAn external magnetic field is formed, and the critical current of the nano-SQUID is changed through a magnetic flux modulation effect, so that the positions of a first current bias point and a second current bias point of magnetic flux storage hysteresis are changed, the writing conditions of magnetic flux states of 0 and 1 are met, and address selection is realized.
Next, as shown in FIG. 6, the bias current I is swept forward over a periodwyWhen, since phi is unlikely to occurTUnsteady state in the middle of the extremes (dashed portion where the slope of the curve is negative), the flux state will transition from "0" to "1" at the first current bias point; reverse scan bias current, the magnetic flux state will transition from "1" to "0" at the second current bias point; the first current bias point is larger than the second current bias point, and the first current bias point and the second current bias point are both in the same period range.
Secondly, a bias current I is applied to the SQUIDryAnd make IryThe SQUID is in the middle of the SQUID critical current magnetic flux modulation range, so that the SQUID is in a magnetic flux sensitive working state; at the same time, a loop magnetic flux bias current I is applied to the SQUID looprxReading and address selection of the storage unit are realized through control of loop magnetic flux bias; because the SQUID is a very sensitive magnetic moment detection device, the critical current of the SQUID can change along with the change of the magnetic flux in the ring, when two magnetic flux states '0' and '1' in the storage loop are coupled into the SQUID, the critical current of the SQUID can change, the voltage Vr at two ends of the SQUID is detected, and the magnetic flux state in the storage loop can be determined to be '0' or '1' according to the voltage value, so that the SQUID is a non-destructive readout.
In another alternative embodiment, the first josephson junction may also be a superconductor-graphene-superconductor structure; or; the first josephson junction may also be a superconductor-non-superconductor metal-superconductor structure; or; the first josephson junction may also be a superconductor-semiconductor-superconductor structure. Since the josephson junctions of the weak connection structures have a current phase relationship deviating from a sine function, the area of the superconducting magnetic flux storage unit can be greatly reduced by using the first josephson junction of the weak connection structure.
In the embodiment of the application, in order to further effectively reduce the area of the superconducting magnetic flux storage unit, the critical current of the first josephson junction in the storage loop can be controlled by using a thermal effect.
In an alternative embodiment, the addressing circuit comprises a heating resistor R for changing the critical current of the first josephson junction by thermal effect. Specifically, joule heat is generated by applying current to the heating resistor R to change the critical current of the first josephson junction, so that the magnitude of magnetic flux hysteresis of the storage loop is changed, and address selection is realized; compared with a mode of regulating and controlling the critical current of the first Josephson junction through an external magnetic field, the area of the superconducting magnetic flux storage unit can be further reduced.
In another alternative embodiment, the addressing circuit comprises a voltage adjustable gate for changing the critical current of the first josephson junction by electric field effect.
Referring to fig. 7, fig. 7 is a schematic flow chart of a data writing method according to an embodiment of the present application, which is applied to the superconducting magnetic flux storage unit in any of the above-mentioned alternative embodiments; wherein the current phase relationship of the first josephson junction, the critical current of the first josephson junction and the inductance of the storage loop are used to form a hysteresis curve required for stable magnetic flux storage; meanwhile, the initial bias current of the storage loop is in the middle of the hysteresis curve; the initial bias current is smaller than a first current bias point of the hysteresis curve and larger than a second current bias point of the hysteresis curve; the method can comprise the following steps:
s701: an external excitation is generated through an addressing circuit, the critical current of the first Josephson junction is adjusted, and the position of the first current bias point and the position of the second current bias point are changed to meet the writing conditions of magnetic flux states of '0' and '1', so that addressing is realized.
S703: adjusting an initial bias current; when the initial bias current is larger than the first current bias point, the writing of the magnetic flux state '1' is realized; when the initial bias current is less than the second current bias point, writing of a flux state "0" is achieved.
The data writing method in the embodiment of the present application is based on the same application concept as the embodiment of the superconducting magnetic flux storage unit.
Referring to fig. 8, fig. 8 is a schematic flow chart of a data reading method provided in this embodiment, where the method may be applied to the superconducting magnetic flux storage unit in the alternative embodiment corresponding to fig. 5; the method can comprise the following steps:
s801: and applying bias current and loop magnetic flux bias current to the superconducting quantum interference device and the loop thereof respectively to enable the superconducting quantum interference device to be in a magnetic flux sensitive working state and realize the reading and address selection of the storage unit.
S803: detecting voltage values at two ends of the superconducting quantum interference device; the magnetic flux state of the sense memory loop is "0" or "1" according to the voltage value.
The data reading method in the embodiment of the present application is based on the same application concept as the embodiment of the superconducting magnetic flux storage unit.
It should be noted that: the sequence of the embodiments of the present application is only for description, and does not represent the advantages and disadvantages of the embodiments. And that specific embodiments have been described above. Other embodiments are within the scope of the following claims. In some cases, the actions or steps recited in the claims may be performed in a different order than in the embodiments and still achieve desirable results. In addition, the processes depicted in the accompanying figures do not necessarily require the particular order shown, or sequential order, to achieve desirable results. In some embodiments, multitasking and parallel processing may also be possible or may be advantageous.
All the embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the apparatus embodiment, since it is substantially similar to the method embodiment, the description is relatively simple, and for the relevant points, reference may be made to the partial description of the method embodiment.
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the storage medium may be a read-only memory, a magnetic disk or an optical disk.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims (11)

1. A superconducting magnetic flux storage unit comprising a storage loop (101), an addressing circuit and a reading circuit (102);
the memory loop (101) comprises a first josephson junction J1, the current phase relationship of the first josephson junction J1 deviating from a sine function; the current phase relationship of the first josephson junction J1, the critical current of the first josephson junction J1 and the inductance of the storage loop are used to form a hysteresis curve required for stable magnetic flux storage;
the addressing circuit is used for generating external excitation and adjusting the critical current of the first Josephson junction J1 so as to change the magnitude of magnetic flux storage hysteresis of the storage loop (101);
the read circuit (102) is used for reading the magnetic flux state of the storage loop (101) in situ.
2. The superconducting magnetic flux storage unit of claim 1, wherein the first josephson junction J1 is a superconducting quantum interference device consisting of two 3D nanobridge junctions connected in parallel.
3. The superconducting magnetic flux storage unit of claim 1, wherein the first josephson junction J1 is a superconductor-graphene-superconductor structure.
4. The superconducting magnetic flux storage unit of claim 1, wherein the first josephson junction J1 is a superconductor-semiconductor-superconductor structure.
5. The superconducting magnetic flux storage unit of claim 1, wherein the first josephson junction J1 is a superconductor-non-superconductor metal-superconductor structure.
6. The superconducting magnetic flux storage unit of claim 1, wherein the addressing circuit comprises a coil;
the coil is used for generating a uniform and stable magnetic field and changing the critical current of the first Josephson junction J1 through the action of the magnetic field.
7. The superconducting magnetic flux storage unit of claim 1, wherein the addressing circuit comprises a heating resistor;
the heating resistor changes the critical current of the first josephson junction J1 by thermal effects.
8. The superconducting magnetic flux storage unit of claim 1, wherein the addressing circuit comprises a voltage-tunable gate;
the voltage tunable gate changes a critical current of the first Josephson junction J1 by an electric field effect.
9. A superconducting magnetic flux storage unit according to claim 1, wherein the read circuit (102) comprises a superconducting quantum interference device; the superconducting quantum interference device is inductively coupled with the storage loop (101);
the superconducting quantum interference device consists of two parallel second Josephson junctions J2, the data readout is realized by applying current bias to the two parallel second Josephson junctions J2, and the readout addressing is realized by applying magnetic flux bias current to a loop part which does not contain the two parallel second Josephson junctions J2.
10. A data writing method is applied to a superconducting magnetic flux storage unit; the superconducting magnetic flux storage unit comprises a storage loop (101) and an addressing circuit; the memory loop (101) comprises a first josephson junction J1, the current phase relationship of the first josephson junction J1 deviating from a sine function; the current phase relationship of the first josephson junction J1, the critical current of the first josephson junction J1 and the inductance of the storage loop are used to form a hysteresis curve required for stable magnetic flux storage; an initial bias current of the memory loop (101) is in the middle of the hysteresis curve; the initial bias current is less than a first current bias point of the hysteresis curve and greater than a second current bias point of the hysteresis curve;
the method comprises the following steps:
generating an external excitation through the addressing circuit, adjusting the critical current of the first Josephson junction J1, and changing the position of the first current bias point and the position of the second current bias point to meet the writing conditions of magnetic flux states '0' and '1' to realize addressing;
adjusting the initial bias current; when the initial bias current is larger than the first current bias point, the writing of a magnetic flux state '1' is realized; when the initial bias current is less than a second current bias point, writing of a magnetic flux state "0" is achieved.
11. A data reading method is characterized by being applied to a superconducting magnetic flux storage unit; the superconducting magnetic flux storage unit comprises a storage loop (101) and a reading circuit (102); the memory loop (101) comprises a first josephson junction J1, the current phase relationship of the first josephson junction J1 deviating from a sine function; the current phase relationship of the first josephson junction J1, the critical current of the first josephson junction J1 and the inductance of the storage loop are used to form a hysteresis curve required for stable magnetic flux storage; the reading circuit (102) comprises a superconducting quantum interference device formed by two second Josephson junctions J2 in parallel and used for in-situ reading the magnetic flux state of the storage loop (101);
the method comprises the following steps:
applying bias current and loop magnetic flux bias current to the superconducting quantum interference device and the loop of the superconducting quantum interference device respectively to enable the superconducting quantum interference device to be in a magnetic flux sensitive working state and achieve reading and address selection of the storage unit;
detecting voltage values at two ends of the superconducting quantum interference device; the magnetic flux state of the memory loop (101) is read to be '0' or '1' according to the voltage value.
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