JPH0745876A - dc-SQUID element - Google Patents

Abstract

(57) [Abstract] [Purpose] A high-performance high-performance device that does not require any special process for creating damping resistors, does not increase the number of device layers due to the addition of damping resistors, and has little deterioration in device characteristics due to resonance. A dc-SQUID device is provided. [Structure] A second superconductor thin-film electrode 3 is laminated on a loop-shaped first superconductor thin-film electrode 1 via a barrier layer 2 at two locations, and the first and second superconductor thin-film electrodes 3 are laminated at the laminated portion. In a device in which the superconductor thin-film electrodes 1 and 2 are Josephson-junctioned to each other, the barrier layer 2 is integrally formed so as to be continuous between two laminated portions, and the barrier layer 2 functions as a damping resistor. It has a structure with values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a sensor for measuring extremely small magnetic fields such as biomagnetic field measurement and geomagnetic field measurement.
More specifically, the c-SQUID device has a dc-SQUID having a structure in which two Josephson junctions are formed in a superconducting loop by stacking two superconductor thin films on each other via a barrier layer. Regarding the device.

[0002]

2. Description of the Related Art dc-SQ for measuring extremely small magnetic field
In UID, generally, a dc-SQUID element having two Josephson junctions in a superconducting ring, a drive circuit thereof, a pickup coil for picking up a magnetic field to be measured, a dc-SQUID element connected to the pickup coil, and dc-
An input coil magnetically coupled to the SQUID element and a drive circuit, and a dc-SQUI
It is composed of a modulation coil or the like coupled to the ID element.

As the dc-SQUID element, a weak link type element such as a quasi-plane type junction and a tunnel junction type element are known. Among them, the quasi-plane type junction type and the tunnel junction type are known. Then usually
Two superconductor thin film electrodes are laminated on each other via a barrier layer, and a Josephson junction is formed in the laminated portion.

That is, in this type of dc-SQUID element, as shown in FIG. 2 which is a plan view (A) of a quasi-planar junction dc-SQUID and an AA enlarged sectional view (B) thereof, The superconducting thin film electrode 21 of No. 1 is patterned into a loop shape, the barrier layer 22 is formed above the loop of the electrode 21, and the second superconducting thin film electrode 23 is formed on the barrier layer 22. Then, in the two laminated portions of the first and second superconductor thin film electrodes 21 and 23, the superconductor thin film bridges 24a and 24b are formed so as to extend over the surfaces of both electrodes. The electrodes are weakly bonded to each other, and the device structure has two Josephson junctions in the superconducting ring as a whole.

Here, the first and second superconductor thin film electrodes 2
1 and 23, and the bridge 24a, the Nb as the material of 24b, also, as the barrier layer 22, as such is generally a two-layer structure in which the AlO _X and the surface is oxidized to form an Al thin film It is used.

An example of the manufacturing process of such an element will be described. First, by using lift-off with a photoresist,
To create a barrier layer 22 made of Al-ALO _X did this same shape in its upper and first superconducting thin film electrode 21. After that, the second superconducting thin film electrode 23 is similarly formed by the lift-off method, the unnecessary portion of the barrier layer 22 is etched, and then the bridges 24a and 24b are formed.

On the other hand, the tunnel junction device has a device structure which does not have the bridges 24a and 24b shown in FIG.
The superconducting thin film electrodes 21 and 23 are used in a tunnel junction at two locations.

By the way, the above dc-SQUID
In order to prevent the resonance of the inductance of the superconducting ring in the device and the capacitance at the junction from deteriorating the device characteristics, a resistor 25 called a damping resistor (or shunt resistor) is conventionally added to the device. Is commonly practiced.

[0009]

The above-mentioned conventional laminated type dc-SQUID device has a problem that a separate step for forming the damping resistor 25 is required after the device is manufactured. That is, in addition to the above-described element manufacturing process, a film forming and patterning process for forming the resistor 25, and in some cases, an insulating layer addition process and the like are required, which causes a cost increase. Further, since the number of layers of the element increases, there is a problem that the yield decreases.

The present invention has been made in view of the above circumstances, and does not require a special step for producing a damping resistor, and does not cause an increase in the number of layers of elements due to the addition of a damping resistor. It is an object of the present invention to provide a high performance dc-SQUID element without deterioration of element characteristics due to.

[0011]

A structure for achieving the above object will be described with reference to FIG. 1 which is an embodiment drawing, and a dc-SQUID element of the present invention has a loop-shaped first structure. The superconducting thin film electrode 1 of 1 is laminated with the second superconducting thin film electrode 3 via the barrier layer 2 at the two positions, and the first and second superconducting thin film electrodes are laminated at the laminated portion. In an element in which 1 and 3 are Josephson-junctioned to each other, the barrier layer 2 is integrally formed so as to be continuous between the above-mentioned two laminated portions, and the barrier layer 2 has a predetermined function that functions as a damping resistance. It is characterized by having a resistance value.

[0012]

[Function] Weak link type dc- of quasi-plane type joint
SQUID element and tunnel junction type dc-SQUI
In the ID element, as a barrier layer, as described above
Al-ALO _X and or normal conductor such as Hf-HfO _X - insulator film, or a normal conductor film are often used. The present invention utilizes this point to achieve the intended purpose by making the barrier layer also serve as the damping resistance.

That is, the barrier layer 2 laminated between the first and second superconducting thin film electrodes 1 and 3 is formed as a continuous film between two laminated portions, thereby forming a loop shape. The slit portion of the first superconductor thin-film electrode 1 is short-circuited via this barrier layer 2, and by forming this barrier layer 2 with a thin film made of a material such as Al-AlO _x as described above. By having an appropriate resistance value, it will have a function as a damping resistance.

[0014]

1 is a plan view (A) of an embodiment of the present invention and an AA enlarged sectional view thereof. First superconductor thin film electrode 1
Is formed in a loop shape on the surface of the substrate 10, and both end portions thereof are separated by a slit 1a. Then, above the both ends of the first superconductor thin film electrode 1 sandwiching the slit 1a, the barrier layer 2 is formed in the direction crossing the slit 1a.
The second superconductor thin film electrode 3 is laminated and formed via.

The barrier layer 2 has a two-layer structure in which the lower layer is Al and the upper layer is AlO _X , and the lower Al layer 2a is in contact with both surfaces of both ends of the first superconductor thin film 1. Straddles the slit 1a with AlO of the same shape as the Al layer 2a above it.
It has a structure in which the second superconductor thin film electrode 3 is laminated via the _X layer 2b.

In the two laminated portions of the first superconductor thin film electrode 1, the barrier layer 2 and the second superconductor thin film electrode 3,
Bridges 4a and 4b made of a superconductor thin film are formed so as to extend over the surfaces of both the first and second superconductor thin film electrodes 1 and 3, and these bridges 4a and 4b are formed.
The first and second superconductor thin-film electrodes 1 and 3 are weakly bonded by the above, and by such a structure, the dc having two Josephson junctions in the superconducting ring as a whole.
-A SQUID element is formed. The first and second
Superconductor thin film electrodes 1 and 3 and bridges 4a and 4b
Any superconductor thin film can be used as the material of, for example, an Nb thin film.

In the above-described structure of the embodiment of the present invention, the Al layer 2a of the barrier layer 2 causes the superconducting ring to be short-circuited, which functions as a damping resistor, and it is not necessary to add a separate damping resistor. As shown in FIG. 5, the step can be omitted, and at the same time, the number of layers of the element is smaller than that of the conventional element having the damping resistance added.

An example of the manufacturing process of the element of the embodiment of the present invention will be described. First, the first superconductor thin film electrode 1 is patterned on the substrate 10 by a lift-off method using a photoresist. Next, the barrier layer 2 including the Al layer 2a and the AlO _X layer 2b is formed on the entire surface of the substrate 10 from above.
To form a film. The barrier layer 2 may be formed by actually forming an Al layer and oxidizing the surface thereof.

After that, the lift-off method is also used,
Alternatively, the second superconductor thin film electrode 3 is patterned by etching after the film formation on the entire surface, and the unnecessary portion of the barrier layer 2, that is, the second superconductor thin film electrode, is patterned using the second superconductor thin film electrode 3 as a mask. The portion other than the lower part of 3 is etched. Then, bridges 4a and 4b are respectively formed above the two laminated portions of the first and second superconductor thin film electrodes 1 and 3 to obtain the element having the structure of FIG. As described above, according to the structure of the embodiment of the present invention, it is not necessary to add a step for producing the damping resistance.

In the above embodiment, the loop-shaped first
The superconducting thin film 1 of FIG.
The upper layer is a structure, but the vertical relationship can be reversed.

Although the Al—AlO _X film is used as the barrier layer 2, the present invention is not limited to this, and any film can be used as long as it has a resistance value that can be a damping resistance. In addition to the above examples, for example, a Hf-HfO _X film can be used as the normal conductor-insulator two-layer film, and a normal conductor single layer film can also be used.

Furthermore, the present invention is a dc-SQ of quasi-planar junction.
It can be applied not only to the UID element but also to a tunnel junction type element in which the first and second superconductor thin films laminated via the barrier layer are mutually tunnel-joined.

[0023]

As described above, according to the present invention,
A second superconducting thin film electrode is laminated on two loop-shaped first superconducting thin film electrodes with a barrier layer interposed therebetween, and the first and second superconducting thin film electrodes are laminated at the laminated portion. In a device having a structure in which and are bonded to each other by a Josephson junction, a barrier layer is integrally formed so as to be continuous between the above-mentioned two laminated parts, and the barrier layer has a resistance value that functions as a damping resistance. Therefore, it is possible to prevent the characteristic deterioration of the element without forming a separate thin film for the damping resistance, and it is possible to achieve cost reduction by reducing the manufacturing process compared with the element with the conventional damping resistance. At the same time, the yield of devices can be improved by reducing the number of device layers.

Further, according to the structure of the present invention, since one superconductor thin film electrode is laminated above the damping resistor which also serves as the barrier layer, the damping resistor is protected by the electrode. There is also an advantage that the damping resistance can be extremely reduced with deterioration over time.

[Brief description of drawings]

FIG. 1 is a plan view (A) showing the configuration of an embodiment of the present invention and an AA enlarged sectional view (B).

FIG. 2 is a plan view (A) showing a configuration example of a conventional dc-SQUID element and an enlarged cross-sectional view (A) taken along the line AA.

[Explanation of symbols]

1 1st superconductor thin film electrode 1a slit 2 barrier layer 2a Al layer 2b AlO _X layer 3 2nd superconductor thin film electrode 4a, 4b bridge 10 substrate

Claims (1)

[Claims] 1. A first superconducting thin film electrode formed in a loop shape is laminated with a second superconducting thin film electrode via a barrier layer at two locations thereof, and the first superconducting thin film electrode is laminated at the laminated portion with the first superconducting thin film electrode. In a device in which a first superconducting thin film electrode and a second superconducting thin film electrode are joined to each other by Josephson junction, the barrier layer is integrally formed so as to be continuous between the two laminated portions, and the barrier layer has a damping resistance. A dc-SQUID element having a predetermined resistance value that functions as.