RU195646U1 - Quantum memory cell based on a superconducting nanostructure - Google Patents

Abstract

Use: to create nanometer-sized memory. The essence of the utility model lies in the fact that a quantum memory cell based on a superconducting nanostructure with a magnetic field source on a chip includes a superconducting thin-film nanostructure on a dielectric substrate in the form of two superconducting contacts for connecting to a current source, interconnected by two superconducting nanostreams of different parallel strips of different sizes that form a closed loop, two strips with two current leads for connecting to a current source to create a magnetic field in the closed loop region of the superconducting nanostructure of the nanostructure. Effect: providing the possibility of creating a superconducting memory cell with the ability to control the magnetic field for an individual cell. 5 cp f-ly, 1 ill.

Description

The utility model relates to nanometer-sized memory devices whose operating principle is based on the phenomenon of superconductivity of thin films. Cooling high-performance processors is one of the main obstacles to the further development of computing devices. The utility model can be used in cryogenic computers as a unit of memory, which will increase processor performance due to the lack of heat generation.

A large number of designs of superconducting quantum devices based on the Josephson effect are known, which are used in various devices of fast single-quantum logic, receivers and magnetometers.

From the beginning of 2000, work began on the creation of compact superconducting memory elements in which applied fields and currents controlled the properties of current transport through a heterostructure with superconducting layers (US Patent No. 6233171 B1, IPC G11C 11/15, published May 15, 2001).

A superconducting spin valve is known, including a superconducting film placed on a substrate and a structure separated from the last layer of the insulator that controls the critical temperature of the superconducting film. The structure consists of two layers of ferromagnetic materials separated by a layer of non-ferromagnetic material (US Patent No. 6414870, IPC G11C 11/18, publ. 02.07.2002). To realize the valve, it is necessary to ensure large values of the magnetic moments in the ferromagnetic layers so that the created magnetic field can significantly change the characteristics of the superconducting film.

To control the flowing current, it is necessary to create large magnetic fields of magnetization reversal, which is a significant drawback of this solution.

Known Josephson phase domain valve, which includes two superconducting electrodes with current leads located on a substrate one below the other and an area of weak coupling between them in the form of a thin-film layered structure containing: an intermediate layer of superconducting material with current leads, the thickness of which lies in the range from 20 to 60 nm separated from the lower superconducting electrode by an insulator layer; a normal metal layer deposited on part of a thin intermediate layer of superconducting material, the thickness of which lies in the range from 1 to 20 nm; a layer of magnetic material deposited on the surface of a thin intermediate layer of a superconducting material that is not covered by a normal metal layer, the thickness of which lies in the range from 1 to 20 nm. EFFECT: provision of the possibility of switching between steady states of the valve without changing magnetization in the layer of magnetic material, which provides a sufficiently short time for the implementation of the write operation (RF Patent No. 2620027, IPC H01L 39/22, publ. 05.22.2017).

A common disadvantage of known implementations of magnetic superconducting memory is the limited speed of recording information. To eliminate it, the process of magnetization reversal is necessary for at least one of the ferromagnetic films present in the structure.

Known high-frequency superconducting memory element having a flat, end surface (bridge geometry), consists of two superconducting electrodes and a weak coupling region, which includes magnetic layers with direct, tunneling or resonant conductivity and a superconducting layer between them (RF Patent No. 2554612, IPC H01L 39/22, publ. 06/27/2015).

The difference from the previously known Josephson structures is that when the direction of magnetization of one of the magnetic layers in the superconducting film is changed, localized in the region of weak coupling between the magnetic layers, a transition occurs from the normal state to the superconducting state or occurs from the superconducting state to the normal state. An increase in the variation in the amplitude of the critical transient current under the action of a small magnetic flux compared with previous geometries provides the possibility of miniaturization of superconducting memory elements while maintaining the properties of the Josephson heterostructure, which leads to an increase in the speed of the memory element based on it.

Known is a superconducting film magnetic flux transformer containing a dielectric substrate, a superconducting squared ring with a narrow active strip, an insulating film placed between the active strip of the magnetic flux transformer and the magnetically sensitive element, the active strip is formed using slots in the form of parallel branches. The technical result of the invention is to increase the multiplication factor of the magnetic flux transformer (RF Patent No. 2455732, IPC H01L 39/16, publ. 10.07.2012).

Common disadvantages of the above technical solutions are the need to implement Josephson junctions in the manufacturing process of the device, which is a complex technological operation. In addition, the use of Josephson junctions limits the possibility of miniaturization of the device.

In the open press (A. Murphy, DV Averin, and A. Bezryadin "Nanoscalesuperconductingmemorybasedonthekineticinductanceofasyirmietri owireloops" NewJ. Phys. 19 (2017) 063015 / A. Murphy, D.V. Averin, A. Bezryadin "Nanometer-sized superconducting quantum memory the asymmetric inductance loop of nanowires "NewJ. Phys. 19 (2017) 063015) describes the possibility of creating a nanometer-sized magnetic memory cell based on the kinetic inductance of superconducting nanowires, which have already shown many remarkable properties. This allows the use of much smaller devices and, naturally, eliminates crosstalk of the magnetic field. The authors showed that helicity, i.e. the number of turns of the order parameter in the complex space when bypassing a closed superconducting loop can be used to implement a nanoscale non-volatile memory device. It is shown how to change the helicity under the control of calibrated current pulses. Demonstrated reliable memory reading. The authors argue that such a memory can function without energy dissipation.

A disadvantage of the known implementation is the inability to create a magnetic field for each memory cell, i.e. when combining several cells into a register, create a separate field for each of the cells in the register.

The closest in technical essence and the achieved technical result to the claimed utility model is the technical solution described in the article by A. Murphy, D.V. Averin, A. Bezryadin "Superconducting quantum memory of nanometer sizes based on the kinetic inductance of an asymmetric loop of nanowires" NewJ. Phys. 19 (2017) 063015. However, in the known device there is no local source of magnetic field. In the known device, a magnetic field is introduced by an external magnet and therefore cannot be applied separately to each memory cell.

The technical problem to which the claimed utility model is directed is to create a superconducting memory cell with the ability to control the magnetic field for an individual cell, which will allow combining such superconducting memory cells into a register.

The stated technical problem is solved in that in a quantum memory cell based on a superconducting nanostructure with a magnetic field source on a chip, including a superconducting thin-film nanostructure on a dielectric substrate in the form of two superconducting contacts for connecting to a current source, interconnected by two superconducting nanostreams parallel to each other different sizes that form a closed loop, according to the proposed utility model, parallel to superconducting two strips with two current leads are formed for the nano-strips to be connected to a current source to create a magnetic field in the closed loop region of the superconducting nanostructure of the nanostructure.

In addition, superconducting nanostrips, contacts to them and strips that create a magnetic field are made of niobium nitride.

In addition, superconducting contacts to nanobands have a length of 2600 micrometers and a width of 800 micrometers with a thickness of less than 4-6 nanometers

In addition, superconducting nanobands have a length of 200 nanometers and a width of 50 and 65 nanometers with a thickness of 4 to 6 nanometers.

In addition, strips for creating a magnetic field in the region of a superconducting nanostructure have a thickness of 500 nanometers, a width of 44 microns and a length of 440 micrometers.

In addition, strips for creating a magnetic field in the region of a superconducting nanostructure are located at a distance not exceeding 35 micrometers from the nanostructure.

In addition, the width of the contact pads of the line creating the magnetic field is 800 micrometers, and the length is 2600 micrometers.

The technical result, the achievement of which is ensured by the implementation of the entire claimed combination of essential features of the utility model, consists in providing the ability to control the number of quanta of magnetic flux penetrating the loop due to the presence of a local source of magnetic field in the immediate vicinity of the loop. This is achieved through the implementation of superconducting nanobridges, forming a superconducting quantum device together with a structure that creates a magnetic field on a single chip in a single technological process.

The essence of the utility model is illustrated in the figure, where in FIG. Figure 1 shows the structure of the cell with the location of the contact pads to the nanobands and strips creating a magnetic field in the loop region.

The figure contains the following positions:

1 - dielectric substrate;

2 - superconducting contacts for connection to a current source;

3 - superconducting nanobands;

4 - strips creating a magnetic field;

5 - conductors.

The quantum memory cell (Fig. 1) is formed on a dielectric substrate (1) in the form of two superconducting contacts (2) for connecting to a current source, interconnected by two superconducting nanostrips of different sizes parallel to each other

(3) which form a closed loop. To create a magnetic field in the loop area on this planar device, two strips are formed

(4) with two current leads (5) each for connection to a current source. Superconducting nanobands, contacts to them and strips creating a magnetic field are made of niobium nitride. The choice of niobium nitride is due to the fact that thin-film nanostructures with high kinetic inductance can be made from this material.

The superconducting contacts (2) to the nanobands have a length of 2600 micrometers and a width of 800 micrometers with a thickness of less than 6 nanometers. Superconducting nanobands (3) have a length of 200 nanometers and a width of 50 and 65 nanometers with a thickness of 4 to 6 nanometers. The strips (4) for creating a magnetic field in the region of a superconducting nanostructure are parallel to the superconducting nanobands and have a thickness of 500 nanometers, a width of 44 microns and a length of 440 micrometers. They are located at a distance not exceeding 35 micrometers from the nanostructure. The width of the contact pads (5) of the line creating the magnetic field is 800 micrometers, and the length is 2600 micrometers.

The choice of nanoband sizes (3) and the distance between them is due to the need to realize a superconducting loop in which a magnetic flux multiple of several quanta of the magnetic flux can be created in relatively small magnetic fields. The sizes of the strips (4) are optimal for the implementation of magnetic fields from 12 to 32 mT, sufficient to create several quanta of magnetic flux in the loop region. The dimensions of the contact pads (2) and (5) are optimal for the implementation of electrical connections, both with the help of spring contacts, and by ultrasonic welding.

The physical mechanism of the device is based on the following. The information recorded in the memory cell is encrypted in various quantum states of the superconducting loop, each of which is determined by the number of magnetic flux quanta n located “inside” the loop between the two strips. At a certain value of the current passing through the nanobands, the device switches from a superconducting state to a resistive one. Such a current is called critical. In the resistive state, magnetic flux quanta are able to penetrate into the loop and exit from it randomly. To read and write the quantum states of the loop, it is necessary to apply a magnetic field in the range from 12 mT to 32 mT. Such a field is created by the conductive line current from 7.2 mA to 19.1 mA.

In order to record the state, it is necessary to apply alternating current at one of two values of the magnetic field (depending on the state that needs to be recorded). For a fixed magnetic field, the critical current of a device with different quantum states of the loop is different. Therefore, by supplying an alternating current that is higher than the critical current of state n-1, but below the critical current of state n at a certain value of the magnetic field, it is possible to create a state with the number of vortices inside the loop that corresponds to state n. To do this, about 200 iterations should be performed with a frequency of -100 Hz.

The use of a created quantum memory cell in cryogenic computers based on a superconducting nanostructure with a magnetic field source on a chip as a memory unit will increase processor performance due to the lack of heat generation.

Claims (6)

1. A quantum memory cell based on a superconducting nanostructure with a magnetic field source on a chip, including a superconducting thin-film nanostructure on a dielectric substrate in the form of two superconducting contacts for connecting to a current source, interconnected by two superconducting nanostrips of different sizes parallel to each other, which form a closed a loop, characterized in that two strips with two current leads are formed parallel to the superconducting nanostrips for Turning to the current source to create a closed loop in the nanostructure of the superconductor magnetic field. 2. The cell according to claim 1, characterized in that the superconducting nanostrips, contacts to them and strips that create a magnetic field are made of niobium nitride. 3. The cell according to claim 1, characterized in that the superconducting contacts to the nanobands have a length of 2600 micrometers and a width of 800 micrometers with a thickness of less than 4-6 nanometers. 4. The cell according to claim 1, characterized in that the superconducting nanobands have a length of 200 nanometers and a width of 50 and 65 nanometers with a thickness of 4 to 6 nanometers. 5. The cell according to claim 1, characterized in that the strips for creating a magnetic field in the region of the superconducting nanostructure have a thickness of 500 nanometers, a width of 44 microns and a length of 440 micrometers. 6. The cell according to claim 1, characterized in that the strips for creating a magnetic field in the region of the superconducting nanostructure of the nanostructure are located at a distance not exceeding 35 micrometers from the nanostructure.

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