JPH07263761A - Shielded superconductor circuit - Google Patents

Abstract

PURPOSE:To provide a circuit that is stable against external noise and with lower crosstalk between circuits by providing shield layers on the upper and lower sides of a superconductor circuit and reinforcing shields. CONSTITUTION:A shield comprises an upper shield layer 1 and a lower shield layer 2 above a superconductor circuit part 3 and shields at least a part of the superconductor circuit 3 from both above and below. The superconductor circuit part and the shield layers are insulated from each other by insulating layers 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting circuit applied to a high speed logic element, a high sensitivity electromagnetic sensor, a high frequency signal amplifier or the like.

[0002]

2. Description of the Related Art The structure of a conventional superconducting circuit is shown in FIGS. To prevent high-speed operation and malfunction of superconducting circuits,
A shield layer was provided above or below the superconducting circuit. FIG. 3 shows an example in which the lower shield layer 2 is provided in the superconducting circuit section 3. FIG. 4 shows an example in which the superconducting circuit portion 3 including the Josephson element 7 is actually formed of a thin film. This is a conventional example corresponding to FIG. 5 described in the embodiment. The shield layer may be a conductor as long as it is an electromagnetic shield, but a superconducting thin film is generally used because a magnetic shield is also necessary in a superconducting circuit. The lower shield layer 2 and the superconducting circuit portion 3 are electrically insulated via the insulating layer 4.

[0003]

When the shield layer is provided only on one of the upper and lower sides of the superconducting circuit,
The noise coming from the side with the shield layer can be prevented, but the part on the opposite side partially goes inside the circuit. Therefore, the performance of the circuit deteriorates, noise increases, and malfunction occurs.
Therefore, an object of the present invention is to provide a superconducting circuit that is strong against external noise and has less crosstalk between circuits by providing shield layers above and below the superconducting circuit portion.

[0004]

Means for Solving the Problems Shield layers are provided both above and below the superconducting circuit section. Since the superconducting circuit section is almost completely shielded by the upper and lower shield layers, it is possible to prevent external noise and prevent malfunction of the circuit. When there are a plurality of superconducting circuit parts and crosstalk between circuits is a problem, it is possible to separate the shield part of the circuit part from which the crosstalk is desired to be eliminated. In the superconducting circuit including the Josephson element, the Josephson element is easily affected by external electromagnetic noise and magnetic field, and thus the effect of the shield layer is very large. Further, when the shield is partially performed, it is possible to accurately and easily use a superconducting thin film for the shield layer.

[0005]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of the superconducting circuit of the present invention, and FIG.
Shows an example of a plan view. FIG. 1 is a sectional view taken along the line AA ′ in FIG. Compared to the conventional structure, the upper shield layer 1 is also provided on the superconducting circuit section 3. Since the shield layers are provided above and below the superconducting circuit section 3, external noise hardly penetrates into the superconducting circuit section 3, and the circuit performance and malfunction can be reduced.

The shield layer may be made of a conductor as long as it is an electromagnetic shield. However, since a magnetic shield is also important in a superconducting circuit, a superconducting film is generally used. In order to completely shield the magnetic field, the shield layer should be thicker than the penetration depth of the magnetic field of the material used, and about 3 times or more is sufficient. Further, in the present invention, the inductance of the line in the superconducting circuit becomes smaller as compared with the conventional method by the amount of the shield layer added, and therefore it is necessary to consider it at the time of design.

A specific example will be described. Examples of the superconducting circuit unit 3 include a transmission line, a filter, a resonator, etc. as passive elements, a processor using the Josephson element 7 as an active element, a memory, a logic circuit such as an A / D converter 24, and a magnetic field. There are sensors for detecting current and current. The manufacturing method includes a method using a bulk material, a method using a thin film material, and a method combining both. Here, an example of deposition of a thin film capable of performing fine processing with high precision and manufacturing by a photolithography process will be described.

As an example of the superconducting circuit section 3, a dc-SQUID, which is widely used as a superconducting element, will be described. FIG. 5 is a plan view of a dc-SQUID made of a thin film that is often used for current detection. BB 'in FIG.
FIG. 6 shows a cross-sectional structure along the line. This dc-SQUID
Is a SQUID loop 1 with two Josephson elements 7.
0, a shunt resistor 8, a damping resistor 9, and first and second input lines. The entire dc-SQUID is covered with the upper shield layer 1 and the lower shield layer 2. The operation is such that when an appropriate bias current 13 is applied, the voltage across the SQUID changes continuously and periodically according to the current flowing in the input line, and the magnitude of the current can be detected as a change in voltage.

FIG. 6 shows a cross-sectional structure of a dc-SQUID formed of a thin film on a flat substrate 6 such as Si or glass. The upper and lower shield layers 1 and 2, the lower electrode, and the upper electrode can be made of a superconducting material. As an example of the superconducting film, Nb,
Some include NbN or Pb-In deposited by sputtering or vapor deposition. Here, Nb, which can obtain a stable film relatively easily,
Are deposited by DC magnetron sputtering. Each pattern is formed by a photolithography process and etching. As the etching method, dry etching using plasma is generally used, and etching is mainly performed with a CF ₄ gas.

The superconducting film can also be formed of a ceramic material having a high critical temperature. Especially, since the lower shield layer 2 is deposited first, it can be easily applied. There are several types of Josephson element 7, and there are a tunnel type in which thin films are laminated, a bridge type in which a superconductor is narrowed, and the like. Nb / AlOx / N depending on material for tunnel type
b, NbN / MgO / NbN, Nb / Si / Nb, Nb
There are various structures such as / NbOx / Nb, but here, Nb
/ AlOx / Nb structure is sputter deposited. The interlayer insulating layer 4 is made of SiO ₂ , SiO, Si, MgO, AlOx or the like. Any of them can be deposited by sputtering, vapor deposition, CVD or the like.
The deposited film thickness should be such that the underlying film is completely insulated.
Here, SiO ₂ is deposited by RF magnetron sputtering. Both wet and dry etching of SiO ₂ are possible. An example of wet etching is a method using a mixed solution of hydrofluoric acid. An example of dry etching is reactive ion etching (RIE) using a mixed gas of CF ₄ or CHF ₃ and oxygen. Here, SiO ₂ is etched by RIE using a mixed gas of CHF 3 and oxygen.

Examples of resistive films forming the shunt resistor 8, the damping resistor 9, etc. are Mo, MoN, Pd, Au,
There are metals such as Cu, Al, Pd, and Ti, and any of them can be deposited by sputtering or vapor deposition. Here, Al is deposited by DC magnetron sputtering, and patterned into a designed size in a photolithography process. Both wet and dry etching of Al can be performed. As an example of wet etching, there is a method mainly using a mixed solution of phosphoric acid and nitric acid. An example of dry etching is reactive ion etching (RIE) using a Cl-based gas such as CCl ₄ and a mixed gas thereof. Here, Al is wet-etched. FIG. 7 shows an equivalent circuit of dc-SQUID.

FIG. 8 shows the superconducting state and the voltage state, respectively.
Dc-S forming a logic circuit corresponding to 0 "and" 1 "
It is a typical top view of a QUID. It is a structure without the shunt resistor 8 as compared with FIG. The operation becomes a voltage state when the critical current value is exceeded, the output is held, and the bias current 13 is set to 0.
It returns to the superconducting state by making it near. Figure 6 shows the circuit
It is possible in the same process as.

Next, an example of constructing a highly sensitive magnetic sensor by the dc-SQUID will be described with reference to FIG. FIG. 9 is a plan view. The circuit components are the same as the SQUID of FIG. 5, but in order to improve the sensitivity to the input magnetic field, the inductance value of the input coil is increased, and the input magnetic field is linked to the SQUID loop 10 in a large amount. It has a structure in which it is wound in many ways. Input coil and SQUI
The upper and lower shield layers are provided only around the Josephson element 7 so that the magnetic coupling of the D loop 10 is increased. The first input coil 11 is for inputting a magnetic field from the outside. The second input coil 12 is used when driving by feedback or modulation. The number of coils and the value of inductance can be changed by design.

Although three kinds of dc-SQUIDs have been described above, there are many kinds of SQUIDs and superconducting circuits, and it is possible to integrate many kinds of elements. Also, the number of input lines and the shape of the pattern can be variously changed depending on the design. As for the cross-sectional structure, almost all circuits can be manufactured with the structure shown in FIG.

A second embodiment of the present invention is shown in FIGS. 11 is a plan view, and FIG. 10 is a sectional view taken along the line CC ′. In order to make the shield more perfect, a contact hole is formed in the interlayer insulating layer 4 to connect the upper shield layer 1 and the lower shield layer 2 to each other.
Is provided. The side surface of the superconducting circuit portion 3 other than the wiring 5 is also shielded so that the characteristics can be further improved. Also, when it is desired to connect each shield layer to the grounding portion of the superconducting circuit portion 3 or the like, it is possible to open a contact hole in the interlayer insulating layer 4 in the same manner.

Next, an example in which the superconducting circuit section 3 having a plurality of functions is combined will be described. By combining and integrating elements and circuits having several functions, it is possible to construct a more sophisticated circuit system. FIG. 12 shows an example of a system including the sensor unit 20 and the signal processing unit 21 as the superconducting circuit unit 3. A higher-performance system is configured by detecting an input signal from the outside with the circuit of the sensor unit 20, sending the detection signal from the sensor unit 20 to the circuit of the signal processing unit 21, and performing amplification and signal processing. be able to.

As an example of FIG. 12, a high-sensitivity magnetic sensor system circuit using dc-SQIUD will be described with reference to FIG. The dc-SQUID of FIG. 9 is used for the sensor unit 20, and the input magnetic field is converted into a voltage with high sensitivity. The coil for detecting the input magnetic field is connected to the first input coil 11. Examples of the circuit configuration of the signal processing unit 21 are shown in FIGS.
A circuit using the dc-SQUID, etc., which includes an SQUID amplifier 22, a feedback circuit 23, and an A / D converter 24. The SQUID amplifier 22 is the dc-S of the sensor unit 20.
The main functions are amplification of the output signal of the QUID and separation of the signals of the sensor unit 20 and the signal processing unit 21. A feedback circuit 23 is provided to drive a part of the analog output to be fed back to the sensor section 20 to stabilize the operation of the system. A / D
The converter 24 can also detect the analog output of the feedback circuit 23 as a digital output.

In this embodiment, dc- of the sensor unit 20
Since SQUID is intended to detect a highly sensitive magnetic field, upper and lower shield layers are provided only around the Josephson element 7. Further, the signal processing unit 21 has a structure in which upper and lower shield layers are provided in order to shield external signals as much as possible. As a result, crosstalk between the sensor unit 20 and the signal processing unit 21 is eliminated, and the performance of the sensor system is improved. In other words, by providing the upper and lower shield layers, there are two effects of shielding external noise and preventing the surrounding signals from being affected by the signal from itself.

Although some examples have been described above, the arrangement of the upper and lower shield layers can be changed or the shield layers can be independently provided and separated in each circuit portion depending on the application and purpose of the superconducting circuit. Is. Therefore, it is possible to configure a circuit system that is more resistant to external noise and has less crosstalk than the conventional one. Further, there are various combinations of circuit configurations of the signal processing unit 21, and all may be manufactured by a superconducting circuit or a part thereof may be configured by a room temperature circuit.

[0020]

EFFECTS OF THE INVENTION Since shield layers are provided above and below the superconducting circuit portion as required, a circuit structure that is resistant to external noise and has less crosstalk becomes possible. When there are a plurality of superconducting circuit parts, it is possible to reduce crosstalk between the circuits by separating the shield part of the circuit part from the others.
When the Josephson element is included in the superconducting circuit, the Josephson element is easily affected by external electromagnetic noise and magnetic field, and therefore the effect of the shield layer is very large.
Further, when it is desired to provide the shield portion only in the peripheral portion of the Josephson device by design, it is possible to easily use the superconducting thin film for the shield layer before and after the manufacturing process of the superconducting circuit portion. Further, since the photolithography process is used, it can be manufactured accurately.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting circuit according to a first embodiment of the present invention.

FIG. 2 is a plan view of the superconducting circuit according to the first embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional superconducting circuit.

FIG. 4 is a sectional view of a conventional dc-SQUID.

FIG. 5 is a plan view of a first example of a dc-SQUID using the present invention.

FIG. 6 is a sectional view of a first example of a dc-SQUID using the present invention.

FIG. 7 is an equivalent circuit diagram of a first example of a dc-SQUID using the present invention.

FIG. 8 is a plan view of a second example of a dc-SQUID using the present invention.

FIG. 9 is a plan view of a third example of a dc-SQUID using the present invention.

FIG. 10 is a sectional view of a superconducting circuit according to a second embodiment of the present invention.

FIG. 11 is a plan view of a superconducting circuit according to a second embodiment of the present invention.

FIG. 12 is an example of a superconducting circuit system using the present invention.

FIG. 13 is an example of a high sensitivity magnetic sensor system using the present invention.

[Explanation of symbols]

 1 Upper Shield Layer 2 Lower Shield Layer 3 Superconducting Circuit Section 4 Insulating Layer 5 Wiring 6 Substrate 7 Josephson Element 8 Shunt Resistor 9 Damping Resistor 10 SQUID Loop 11 First Input Coil 12 Second Input Coil 13 Bias Current 14 Contact Section 20 Sensor unit 21 Signal processing unit 22 SQUID amplifier 23 Feedback circuit 24 A / D converter

Claims (4)

[Claims] 1. A superconducting circuit section comprising a superconductor thin film,
A shielded superconducting circuit comprising a lower shield layer and an upper shield layer, and having a structure in which the superconducting circuit portion and the upper and lower shield layers at least partially overlap each other. 2. A superconducting circuit with a shield having a plurality of the superconducting circuit parts, wherein at least one of the shield parts of each circuit part is electrically insulated from a shield of another circuit part. 3. The shielded superconducting circuit according to claim 1, wherein the superconducting circuit portion includes a Josephson junction, and the shield portion is made of a superconducting thin film. 4. The superconducting circuit with a shield according to claim 1, wherein at least a part of the shield is electrically connected so that the shield portion has the same potential.