JPH1028021A - Superconducting amplifier and detector utilizing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an amplifier of high performance with the excellent characteristics of a gain and linearity, etc., by turning the sum of the output voltages of the respective SQUIDs of the serial connection body part of the SQUIDs for which the respective SQUIDs of a SQUID serial connection body are structurally and environmentally in practically the same conditions to the output voltage. SOLUTION: In the SQUID serial connection body 2, the respective SQUIDs 1 are structurally uniformly manufactured and the sum of the voltages of only the serial connection body part of the SQUIDs 1 of the same environment is turned to the output voltage of this superconducting amplifier 9. That is, in the amplifier 9, a DC bias current is made to flow to 1st-7th SQUIDs 1 by using a current source 6. Then, by spirally arranging an input coil 4 through a thin insulation film on the upper surface of a washer coil and magnetically connecting both, signals are inputted from the input coil 4 to the respective SQUIDs 1. Then, a terminal 3 is pulled out so as to measure the voltage generated in 2nd-6th SQUIDs 1 and the voltage generated at the terminal 3 is turned to the output of the amplifier 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a superconducting amplifier, and more particularly, to a low-noise analog superconducting amplifier constituted by connecting three or more analog output SQUIDs in series.

[0002]

2. Description of the Related Art It is known to configure an analog amplifier by connecting a plurality of SQUIDs in series. For example, IEEE TRANSACTIONS ON MAGNETICS (1991)
Volume 27 Number 2, from page 2924 to page 2926
It is described in the page. FIG. 14 shows an example of a circuit of the above-described conventional superconducting amplifier. In this example, a bias current is applied to the SQUID 1 constituting the SQUID series-connected body 2 by using the current source 6 and each coil of the series circuit 4 of the input coil for signal input and each SQUID constituting the series-connected body 2
By magnetically coupling 5 with ID1, SQUID
The output corresponding to the input signal was obtained from each SQUID of the serial connection 2, and the sum of the output voltages of each SQUID was used as the output of the superconducting amplifier 9 from the terminal 3.

FIG. 15 shows the relationship between the input current and the output voltage of each SQUID. In the SQUID, the output voltage is a periodic function whose period is the current input corresponding to the magnetic flux quantum Φ ₀ . Here, for example, if an input current equivalent to 0.25 times the flux quantum Φ ₀ is set as the operating point of the SQUID using the bias current (by the current source 6), the relationship between the input current and the output voltage is as follows: around a point 0.25Φ _0, it shall be increased or decreased. Therefore, when two SQUIDs having substantially the same characteristics are connected in series, the relationship between the input current and the total output voltage is, as shown in FIG. 16, the same input having twice the output of each SQUID. And can be.

[0004]

However, as a practical matter, it is difficult to make characteristics exactly the same,
It is a reality that even if the structures are substantially the same, irregularities may occur due to subtle differences in the environment in which they are placed. FIG. 17 is an extreme example, but shows two S connected in series.
While the QUID is applied with the same input current, each SQUID
D shows the relationship between the input current and the total output voltage in the case where the magnetic flux quantum has an apparently double difference. FIG.
As is apparent from comparison with FIG. 17, in the situation of FIG. 17, the linearity and gain of the superconducting amplifier due to the serial connection of SQUIDs cannot be sufficiently improved.

Therefore, the structure of each SQUID constituting the SQUID series connection unit is made as uniform as possible, and the magnitude of the effect of the signal input to each SQUID on each SQUID is made as equal as possible. It turns out that it is necessary to configure.

However, the SQUID is a magnetic sensor having a very high sensitivity. Therefore, when a circuit or a superconducting wiring composed of a superconductor is provided around the SQUID, mutual interference occurs and the SQUID is generated.
There is a problem that the characteristics of the UID change. Therefore, S
When a plurality of QUIDs are arranged close to each other on the same chip, the SQUIDs cause mutual interference and exhibit different characteristics from the case where they are arranged alone. For example, SQUID
Are arranged in a horizontal line to form a SQUID series connection body, whereas the SQUIDs at both ends are arranged on only one side, while the other SQUIDs are arranged on the left and right.
UID is arranged. Therefore, SQUID at both ends
Has different characteristics from other SQUIDs.

In the conventional superconducting amplifier using SQUID series-connected bodies, attention is paid to variations in characteristics due to the environment where each SQUID is placed, and all outputs are added as a part of the output of the superconducting amplifier. There was a problem of poor sex.

An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a high-performance superconducting amplifier having good characteristics such as gain and linearity.

[0009]

SUMMARY OF THE INVENTION The object of the present invention is to provide an SKU.
The problem can be solved by using the output voltage as the sum of the output voltages of the SQUIDs of the serially connected portions of the SQUIDs in which the SQUIDs of the ID serial connection are substantially identical structurally and environmentally.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a circuit diagram of a superconducting amplifier showing a first embodiment of the present invention, and FIG. 2 is a schematic top view of a circuit pattern. In this embodiment, seven SQUIDs 1
Are formed on a single substrate by a superconducting circuit fabrication technique, and these are connected in series to form a SQUID series-connected body 2. The first to seventh SQs are formed using a current source 6.
A DC bias current was applied to the UID. As shown in FIG. 2, each SQUID is a Ketchen type SQUID,
One side of the opening of the washer coil 8 was 20 μm, and the critical current value of the Josephson junction 7 was 90 μA. The space between adjacent SQUIDs 1 was 30 μm. SQ constituting SQUID series connection body 2 in this embodiment
UID1 was fabricated using Nb for the superconductor, MoNx for the resistor, and Nb / AlOx / Nb for the Josephson junction. Although not shown in the figure, the shunt resistance was 2Ω and the damping resistance was 6Ω.

As shown in FIG. 2, the input coil 4 is spirally arranged on the upper surface of the washer coil 8 via a thin insulating film, and the two are magnetically coupled to input a signal from the input coil 4 to each SQUID 1. did. In the present embodiment, the input coil 4 is coupled to the first to seventh SQUIDs.

In this embodiment, the terminal 3 is pulled out so as to measure the voltage generated at the second to sixth SQUIDs 1, and the voltage generated at the terminal 3 is used as the output of the superconducting amplifier 9. As a result, an analog amplifier having good linearity with respect to the input signal was realized. Further, the output voltage of the superconducting amplifier 9 described in the first embodiment was almost five times the output voltage of the SQUID 1 constituting the SQUID series connection 2.

That is, in this embodiment, seven SQUIDs, which can be said to be structurally identical, are arranged on a straight line, and the same input current is supplied to each of them to adjust the environmental conditions. SQ of the part to be arranged
This is an example in which the output is obtained only from the UID series connection body and the structure and environmental conditions are substantially the same.

FIG. 3 is a schematic top view of a circuit pattern of an embodiment having another structure having the same idea as that of the first embodiment. As is apparent from comparison with FIG. 2, this embodiment has a structure in which the wiring of the bias current is avoided between the SQUIDs. By avoiding the wiring of the bias current between the SQUIDs, it is possible to reduce the influence of the fluctuation of the bias current value on the SQUID.

FIG. 4 shows a structure substantially similar to that of FIG. In FIG. 3, the top and bottom of each SQUID structure are aligned, whereas in FIG. 4, the top and bottom of each SQUID structure are reversed so that the direction of the bias current flows from the side where the input coil is stacked. It differs from the embodiment of FIG. 3 in that the Josephson junctions are aligned on the side where they exist. In FIG. 3, when an external magnetic field acts on the SQUID series-connected body, the individual SQUIDs are oriented in the same direction, so that the effect of the external magnetic field on each SQUID is highly symmetrical. Has the advantage of good symmetry.

FIG. 5 is a schematic top view of a circuit pattern of an embodiment having another structure having the same idea as that of the first embodiment. In FIG. 5, (1) the bias current wiring is not arranged between the SQUIDs, and (2) the bias current supply direction is the same and the bias current wiring can be shortened. As is apparent from comparison, this embodiment has a structure in which the direction of the SQUID is rotated by 90 ° and the path of the bias current flows linearly via the SQUID. For this reason, the path of the input current is in a form of walking while passing through a position appropriately separated from the SQUID. in this case,
If the distance indicated by the symbol L is not sufficiently set, the input current acts not only as a coil but also through a crossover, which leads to unstable characteristics.

Next, an application of the first embodiment of the present invention will be described with reference to FIG. In this application example, SQUI
The configuration of the D series connection body 2 is the same as that of the first embodiment of the present invention, but additionally includes a sensor SQUI
D10 is provided.

The sensor SQUID 10 is also a Ketjen type S
A bias current is supplied to the SQUID having the Josephson junction 13 using the current source 20. One side of the opening of the washer coil was 20 μm, and the critical current value of the Josephson junction 13 was 90 μA. Shunt resistor 1
5 was 4Ω and the load resistance 11 was 4Ω. Although not shown in the figure, the damping resistance was 6Ω.

The output voltage from the sensor SQUID 10 is converted into a current signal using a load resistor 11 and is supplied to the input coil 4 coupled to the SQUID 1 constituting the SQUID series connection body 2. The inductance of each part 14 of the input coil 4 is approximately The pH was adjusted to 100 pH. In addition, the SQUI
The space between D1 was 30 μm.

SQUID series connection body 2 in this embodiment
SQUID1 and sensor SQUID10
Were formed on a common substrate. Nb for superconductor, MoNx for resistor, Nb / AlOx / Nb for Josephson junction
It was produced using.

When the output from the SQUID is amplified by the SQUID series connection 2 as in this application example, the characteristics of the sensor SQUID 10 and each SQUID 1 constituting the SQUID series connection 2 are equal, and
The magnetic flux of the same amount as the magnetic flux input to UID10 is SQUID
The value of the input coil 4 was designed so that it could be input to each SQUID 1 of the serial connection 2. With this design, the S SUID is independent of the magnitude of the input signal to the sensor SQUID 10.
The amplification factor of the series-connected QUIDs 2 can be kept constant, and the dynamic range can be maximized. The gain of the superconducting amplifier 9 is determined by the SQ
The value of the inductance of the input coil 4 is proportional to the number of UIDs 1 and the SQ
Since it is proportional to the number of UIDs 1, there is also an advantage that the design becomes easy.

In the application of the first embodiment, the SQUID
The D series connection 2 is a series configuration of seven SQUIDs,
As a result of obtaining the output from the series configuration of the five SQUIDs excluding the two sides, the SQUID series connection body 2 has the sensor SQUID.
10 outputs could be amplified 5 times. Also, the sensor SQUI
D10 and S constituting the SQUID series connection body 2
By making the structural characteristics of QUID 1 substantially equal and setting each operating point to 0.25Φ ₀ (Φ ₀ is a magnetic flux quantum), the gain is 5 times, the linearity is good, and ± 0.2 mm. it was possible to realize a superconducting measuring device having a dynamic range of 25Φ _0.

FIG. 7 is a circuit diagram of a superconducting amplifier according to a second embodiment of the present invention, and FIG. 8 is a schematic top view of a circuit pattern. In the present embodiment, twelve SQUIDs 1 are connected in series, and the first to twelfth SQUIDs 1 are
A bias current was applied to the QUID. In this embodiment, S
The SQUID 1 constituting the series-connected QUID 2 was manufactured using the same design values and materials as in the first embodiment. In the present embodiment, as shown in FIG.
The SQUIDs are arranged in rows and the top, bottom, left and right
They were arranged at intervals of 0 μm.

SQUI Constituting SQUID Series Connected Body 2
When ID1 is arranged in two rows, as can be seen from FIGS. 7 and 8, portions corresponding to both ends, that is, the first row, the first column, the second row, the first column, the first row, the sixth column, and the second row 6 Since the SQUIDs arranged in the columns have different peripheral structures from the SQUIDs of the other parts, the characteristics in the use environment are different even if the structural characteristics are made to match. Therefore, in this embodiment, SQUID1 arranged in 2 rows and 6 columns is 1
The output voltage of the SQUID from the first row, the second row, the second column, the second row, the second column, the first row, the second column, the first row, the third column, and the second row, the second column to the second row, the fifth column Was drawn out so that the sum of the values would be the output voltage of the superconducting amplifier.

As a result, an analog superconducting amplifier having a good linearity with respect to the input signal can be realized. Also,
In the present embodiment, a superconducting amplifier capable of outputting almost eight times the output voltage of the SQUID 1 constituting the SQUID series-connected body 2 could be realized.

When 12 SQUIDs are arranged in one row and 12 columns to form a series connection of SQUIDs, a maximum of 10
The sum of the voltages of the SQUIDs can be used as the output of the superconducting amplifier. However, when the SQUID series-connected bodies are arranged in two rows and six columns as in this embodiment, the voltage that can be taken out as the output of the superconducting amplifier Is a maximum of 8 SKUs
This is the sum of the ID voltages. However, when the width of the space in which the SQUID series connection bodies can be arranged is narrow, it is an effective method to arrange them in two rows.

FIG. 9 is a schematic top view of a circuit pattern of an embodiment having another structure having the same idea as that of the second embodiment. As is clear from comparison with FIG. 8, in this embodiment, S
This is a structure in which the direction of the QUID is reversed. It is clear that the same effect can be obtained even if the arrangement is performed in this manner.

FIG. 10 shows an example in which the SQUID is oriented in each row so as to have the same structure as in FIG. 8, and the flow path of the bias current is meandering between the SQUIDs.

FIG. 11 shows an example in which the SQUID directions between the rows are aligned, and is essentially the same as the embodiment of FIG. However, in the SQUID in the first row, another SQUID exists on the Josephson junction side, and in the SQUID in the second row, another SQUID exists on the side where the input coil is stacked.
Since the ID exists, the environment is different between the first line and the second line. Therefore, it is necessary to have a space on the first and second lines so that other SQUIDs can be ignored.

FIGS. 12A and 12B are a schematic top view and a schematic rear view of a circuit pattern of an embodiment having another structure having the same idea as the embodiment of FIG. The broken line in (b) indicates
Indicates that the SQUID is formed on another surface. In this embodiment, it is necessary to form a pattern on both sides, so that the number of manufacturing steps is increased. However, since the routing of the signal lines can be separated from the routing of the bias current lines, there is a great advantage in that mutual interference can be reduced.

FIG. 13 is a schematic top view of a circuit pattern showing a third embodiment designed so that all outputs of the created SQUID can be used. In the first and second embodiments, even though the structural uniformity of each SQUID can be improved by devising a manufacturing technique, there is a limit in improving the uniformity in a use environment as long as the SQUIDs are arranged in a straight line. That is, the end part is always present. The embodiment of FIG. 13 is also intended to improve this point, and the SQUID1
Are arranged at equal intervals. Those shown in FIG. 13 with the same reference numerals as the other embodiments are equivalent to them.

The embodiment shown in FIG. 13 is configured with the wiring layout based on the same idea as the arrangement of FIG. 2. However, even if these are the wiring layouts based on the concept as shown in FIG. It will be clear that this can be achieved as follows. Further, as shown in FIG. 12, a double-sided structure can be adopted.

[0034]

As described in detail above, by configuring a superconducting amplifier according to the present invention, a high-performance superconducting amplifier having good gain and linearity can be realized.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a superconducting amplifier showing a first embodiment.

FIG. 2 is a schematic top view showing a circuit pattern of the first embodiment.

FIG. 3 is a schematic top view showing a circuit pattern of an embodiment of another structure having the same idea as the first embodiment.

FIG. 4 is a schematic top view showing a circuit pattern of an embodiment of another structure having the same idea as the first embodiment.

FIG. 5 is a schematic top view showing a circuit pattern of an embodiment having another structure having the same idea as that of the first embodiment.

FIG. 6 is a circuit diagram showing an example of an application form of the first embodiment.

FIG. 7 is a circuit diagram of a superconducting amplifier showing a second embodiment.

FIG. 8 is a schematic top view showing a circuit pattern of the superconducting amplifier according to the second embodiment.

FIG. 9 is a schematic top view showing a circuit pattern of an embodiment of another structure having the same idea as the second embodiment.

FIG. 10 is a schematic top view showing a circuit pattern of an example of another structure corresponding to FIG. 8;

11 is a schematic top view showing a circuit pattern of an example of another structure corresponding to FIG.

12A and 12B are a schematic top view and a schematic rear view, respectively, showing a circuit pattern of an embodiment of another structure having the same idea as the embodiment of FIG. 8;

FIG. 13 is a schematic top view showing a circuit pattern according to a third embodiment.

FIG. 14 is a circuit diagram showing an example of a conventional superconducting amplifier.

FIG. 15 is a diagram showing a relationship between an input current and an output voltage of the SQUID.

FIG. 16 is a diagram showing the relationship between the input current and the total output voltage when two SQUIDs having substantially uniform characteristics are connected in series.

FIG. 17 is a diagram showing the relationship between the input current and the total output voltage when two SQUIDs having greatly different characteristics are connected in series.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... SQUID, 2 ... SQUID series connection body, 3 ... Terminal, 4 ... Input coil, 5 ... Magnetic coupling, 6 and 20 ... Current source, 7, 13 ... Josephson junction, 8 ... Washer coil, 9 ... Superconducting amplifier, 10: Sensor SQUID, 11
... load resistance, 14 ... part of the input coil, 15 ... shunt resistance.

Claims (5)

[Claims] 1. An SQUID serially-connected body comprising m (where m is an integer of 3 or more) SQUIDs connected in series,
QUID series connected bias current source, and SQ
And a signal input means to the UID series connection unit, wherein each SQUID of the SQUID series connection unit is structurally and environmentally substantially identical to each other of the SQUID series connection unit. SQUI
A superconducting amplifier, wherein a sum of output voltages of D is used as an output voltage. 2. Each SQUID of the SQUID serially connected body
Are arranged substantially on one or a plurality of straight lines, and the remaining SQUIDs excluding the output voltages of the SQUIDs arranged at both ends or both ends of the SQUID series connection body
2. A superconducting amplifier according to claim 1, wherein the sum of the output voltages of the superconducting amplifiers is an output voltage. 3. An SQUID serially connected body comprising m (where m is an integer of 3 or more) SQUIDs connected in series,
QUID series connected bias current source, and SQ
And a signal input means to the UID series connection unit, wherein each SQUID of the SQUID series connection unit is structurally and environmentally substantially identical to each other of the SQUID series connection unit. SQUI
A superconducting amplifier whose output voltage is the sum of the output voltages of D and a sensor S disposed on the same substrate as the substrate on which the amplifier is formed;
A detector comprising a QUID, wherein an output of the sensor SQUID is used as an input of the amplifier. 4. The method according to claim 1, wherein the SQUID series connection bodies are arranged at substantially equal intervals on one circumference, and the sum of the output voltages of all the SQUIDs is used as the output voltage. Superconducting amplifier. 5. A wiring for routing a bias current of said SQUID series connection between each SQUID and said SQUID.
The input signal to each SQUID of the D series connection
Any of the wiring for routing between D
2. The device according to claim 1, wherein the surface is formed on a surface different from the surface on which the series connection body is formed.
5. The superconducting amplifier according to any one of claims 1 to 4.