JPH0263315B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to improvements in Josephson integrated circuits. In particular, the present invention relates to improvements in improving the sensitivity of multilayer Josephson integrated circuits in which a plurality of Josephson junction devices are stacked.

[Conventional technology]

A Josephson integrated circuit is an integrated circuit that includes a Josephson junction element. A Josephson junction element is a circuit in which two electrodes (base electrode and counter electrode) made of superconducting material are joined through an extremely thin tunnel insulating film. Then, a control current is passed through a separately provided control line to control the critical current of the Josephson junction between the two electrodes (base electrode and counter electrode) made of the above superconducting material, making the Josephson junction superconducting. or non-superconducting state, and utilizes this state change to exhibit a switching function.

A cross-sectional view of an example of a Josephson integrated circuit in the prior art is shown in FIG. In the figure, 1 is a substrate made of silicon or the like. A ground plane 2 is formed by depositing a superconducting material such as niobium or lead alloy over the entire surface of the substrate 1 to a thickness of about 3000 Å. The first function of the ground plane is to form a strip line with the wires wired on it and to transmit signals at high speed. The second function of the ground plane is to increase the sensitivity of the element by concentrating the magnetic field created by the control current between the ground plane and the control line. A dielectric layer 3 is formed by depositing a dielectric layer such as silicon monoxide over the entire surface of the ground plane 2 to a thickness of about 2000 Å. Reference numeral 4 denotes a base electrode, which is formed by depositing the same superconducting material as above to a thickness of about 3000 Å and then patterning it into a linear shape. The linear patterning process can be performed using a photolithography method, a lift-off method, or the like. 5 is a tunnel insulating film, which has an oxide of the material of the base electrode 4.
Form to a thickness of 10 Å. As shown in the figure, the region to be formed is the contact surface between the base electrode 4 and the counter electrode 6, and in order to form this, this region may be selectively oxidized. The counter electrode 6 is formed by depositing the same superconducting material as above to a thickness of about 4000 Å and then patterning it into a linear shape. The patterning method is the same as that for the base electrode 4. Note that the base electrode 4, tunnel insulating film 5, and counter electrode 6 constitute a first layer Josephson junction element A. 7 is a dielectric layer;
A layer made of a dielectric such as silicon monoxide is deposited over the entire surface of the dielectric layer 3 to a thickness of about 6000 Å. Reference numeral 8 denotes a control line, which is formed by depositing the same superconducting material as above to a thickness of about 4000 Å and then patterning it. The reason why the dielectric layer 7 between the base electrode 4, the counter electrode 6 and the control line 8 is thicker than the other dielectric layers 3, and the reason why the thickness of the control line 8 is thicker than the other electrodes. The reason why it is thick is to prevent wire breakage due to the presence of Josephson junction elements A formed in a stepped shape.

A multilayer Josephson integrated circuit is known in which a plurality of Josephson integrated circuits having such a structure are stacked to improve the degree of integration. In order to manufacture a Josephson integrated circuit having this multilayer structure, in the prior art, as shown in FIG. A relatively thick dielectric layer 9 is formed over the entire surface. Since a flat surface of the dielectric layer 9 is advantageous for multilayering, it is advantageous to use a coated film of polymer resin or the like for the dielectric layer 9. Next, a superconductor layer forming the ground plane 10 of the second-layer Josephson integrated circuit is formed on the entire surface of the dielectric layer 9, and as in the case of the first-layer Josephson integrated circuit, the superconductor layer 13 and , a second-layer Josephson junction element B consisting of a base electrode 14, a tunnel insulating film 15, and a counter electrode 16.
, a dielectric layer 17, and a control line 18 to form a second layer Josephson integrated circuit.

[Problem to be solved by the invention]

However, in the Josephson junction element having a multilayer structure as described above, the Josephson junction element A in the first layer is sandwiched between the ground plane 2 in the first layer and the ground plane 10 in the second layer.
The current I _H flowing through the control line 8 that controls the critical current of the Josephson junction element A in the first layer is divided into the upper surface and the lower surface of the control line 8 as shown by the arrow in FIG. The amount of current that directly contributes to controlling the critical current of the first-layer Josephson junction element A decreases, and the first-layer Josephson junction element A cannot obtain a satisfactory level of sensitivity.
On the other hand, the current flowing through the control line 18 that controls the critical current of the Josephson junction element B in the second layer.
As shown by the arrow in FIG. 2, _IH flows only to the lower surface of the control line 18, and the Josephson junction element B in the second layer can obtain a sufficiently satisfactory level of sensitivity. As a result, there is a drawback that the sensitivity of the Josephson junction element A in the first layer and the sensitivity of the Josephson junction element B in the second layer are no longer the same.

Furthermore, the properties of the current flowing in a superconductor are as follows:
When two superconductor layers arranged through a dielectric layer, such as a control line and a base electrode/counter electrode, form a pair, one (control line)
The width of the image current flowing to the other (base electrode/counter electrode) in response to the current flowing to the other (base electrode/counter electrode) is the same as the width of the current flowing to one of the above (control line). It is well known that the width of the return current flowing on the back surface in response to a flowing current is determined by the width of the superconductor and is not constrained by the width of the current flowing on the surface, and this property exists. Therefore, in the Josephson junction element, it is well known that the width of the control line is made narrower than the width of the base electrode/counter electrode in order to improve the sensitivity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a Josephson integrated circuit having a two-layer structure, which can have good sensitivity to the current of a control line for controlling the critical current of a Josephson junction element.

[Means to solve the problem]

The above purpose is to form a first layer control line 28 formed on the substrate 1 and made of a superconducting material, and a dielectric layer 27 on the first layer control line 28.
a first layer base electrode 4 made of a superconducting material, and a first layer base electrode 4 formed on the first layer base electrode 4.
A first layer counter electrode 6 made of a superconducting material formed through a layer tunnel insulation film 5 and a first layer made of a counter electrode 6 made of a superconducting material.
A ground plane 32 made of a superconducting material and formed on the first layer Josephson junction element A with a dielectric layer 23 interposed therebetween.
A dielectric layer 33 is placed on this ground plane 32.
A second layer base electrode 14 made of a superconducting material is formed through the second layer base electrode 14, and a second layer counter made of a superconducting material is formed on the second layer base electrode 14 with a second layer tunnel insulating film 15 interposed therebetween. a second layer Josephson junction element B consisting of an electrode 16;
This is achieved by a Josephson integrated circuit formed on the layer Josephson junction element B via a dielectric layer 37 and having a second layer control line 38 made of superconducting material.

[Effect]

In other words, the Josephson junction element A of the first layer
By reversing the arrangement positions of the ground plane 2 and control line 8, the control line 8 is provided at the position of the ground plane 2 to form a control line 28, and the ground plane 2 is provided at the position of the control line 8 to form a ground plane 32. year,
This ground plane 32 also serves as a ground plane for the second-layer Josephson junction element B, and the second-layer Josephson junction element B has a control line as its upper layer, as in the prior art. In this layer structure, both the Josephson junction element A in the first layer and the Josephson junction element B in the second layer have their control lines 28 and 38.
is not pinched by the ground plane,
In each of the control lines 28 and 38, the current I _H flows only through the surfaces that are in contact with the Josephson junction elements A and B, so the sensitivity is improved, and the sensitivity of the Josephson junction element A in the first layer and the The sensitivity of the two-layer Josephson junction element B is the same.

〔Example〕

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A two-layer Josephson integrated circuit according to an embodiment of the present invention will be described below with reference to the drawings to clarify the structure of the present invention and its unique effects.

Refer to FIG. 3. The figure is a cross-sectional view of a two-layer Josephson integrated circuit according to an embodiment of the present invention. In the figure, 1 is a substrate made of silicon, etc., and 28 is a control line, which is formed by depositing a superconducting material such as niobium or lead alloy on the substrate 1 to a thickness of about 4000 Å, and then patterning it. do. A dielectric layer 27 is formed by depositing a dielectric layer such as silicon monoxide over the entire surface of the substrate 1 to a thickness of about 6000 Å. Since this dielectric layer 27 is also desired to function as a flattening layer, a coated film of polymer resin or the like may be used, as in the case of the prior art. Reference numeral 4 denotes a base electrode, which is formed by depositing the same superconducting material as above to a thickness of about 3000 Å and then patterning it into a linear shape. The linear patterning process can be performed using a photolithography method, a lift-off method, or the like. A tunnel insulating film 5 is formed of an oxide of the material of the base electrode 4 to a thickness of several tens of angstroms. As shown in the figure, the region to be formed is the contact surface between the base electrode 4 and the counter electrode 6, and in order to form this, this region may be selectively oxidized. The counter electrode 6 is formed by depositing the same superconducting material as above to a thickness of about 4000 Å and then patterning it into a linear shape. The patterning method is the same as that for the base electrode 4. Note that the base electrode 4, tunnel insulating film 5, and counter electrode 6 constitute the Josephson junction element A of the first layer. A dielectric layer 23 is formed by depositing a dielectric layer such as silicon monoxide over the entire surface of the dielectric layer 3 to a thickness of about 6000 Å. Since this dielectric layer 3 is also desired to function as a flattening layer, a coated film of polymeric resin or the like may be used as described above. 32 is a ground plane, which is formed by depositing the same superconducting material as above on the entire surface of the dielectric layer 23 to a thickness of about 3000 Å.
The function of the ground plane is as described in the prior art section. A dielectric layer 33 is formed by depositing a dielectric layer such as silicon monoxide over the entire surface of the ground plane 32 . 14, 15, and 16 formed thereon are Josephson junction elements B of the second layer, and the first
The layers are similar to Josephson junction device A. 37
is a dielectric layer, and a layer made of a dielectric such as silicon monoxide is deposited over the entire surface of the dielectric layer 23 to a thickness of about 6000 Å. Since this dielectric layer 23 is also desired to function as a flattening layer, a coated film of polymeric resin or the like may be used as described above. 38
is a control line, which is formed by depositing the same superconducting material as above to a thickness of about 6000 Å and then patterning it.

In the Josephson integrated circuit according to the present invention formed as described above, the ground plane 32 functions in common for the two Josephson junction elements A and B. Since the control lines 28 and 38 do not come into contact with other superconductor layers in either the first-layer Josephson integrated circuit or the second-layer Josephson integrated circuit, the control current I _H is As shown in the figure, the control current flows only on the upper surface of the control line 28, and only on the lower surface of the control line 38, and the control current is not shunted to both sides of the control circuit. Therefore, both Josephson junction elements A and B achieve sufficiently high sensitivity to the same extent.

〔Effect of the invention〕

As explained above, in the two-layer Josephson integrated circuit according to the present invention, two Josephson junction elements are formed in opposite directions with the ground plane at the center, and the control unit controls each Josephson junction element. The lines constitute the top layer and the bottom layer, respectively, and each control line does not come into contact with any other superconductor layer, so the current flowing through each control line is connected to the corresponding Josephson junction. It flows only facing the element. Therefore, the current flowing through the control line contributes 100% to the control of the Josephson junction element, realizing a two-layer Josephson integrated circuit with good sensitivity.

It should be noted that since the control line is narrow, there is a high risk of disconnection, and it is well known that the control line is virtually the only place where disconnection may occur in Josephson integrated circuits. Since the Josephson integrated circuit has fewer steps than the conventional Josephson integrated circuit having a two-layer structure, it also has the secondary effect of reducing the possibility of disconnection. Needless to say, this secondary effect can be further enhanced if a polymer resin or the like is used for the dielectric layer to give the dielectric layer a function as a flattening layer.

It goes without saying that any superconducting material can be used as the superconducting material, including niobium and lead alloys, and it goes without saying that the dielectric material is also limited to silicon monoxide. Furthermore, the thickness of each layer shown in the examples is just one example and does not have any particular limiting meaning.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a Josephson integrated circuit according to the prior art. FIG. 2 is a cross-sectional view of a Josephson integrated circuit having a multilayer structure (two-layer structure in the figure) according to the prior art. FIG. 3 is a cross-sectional view of a two-layer Josephson integrated circuit according to an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... First layer ground plane, 3... Dielectric layer, 4... First layer base electrode,
5... First layer tunnel insulating film, 6... First layer counter electrode, A... First layer Josephson junction element, 7... Dielectric layer, 8... First layer control line, 9... Dielectric body layer, 10... second layer ground plane, 13... dielectric layer, 14... second layer base electrode, 15... second layer tunnel insulating film, 1
6... Second layer counter electrode, B... Second layer Josephson junction element, 17... Dielectric layer, 18...
Second layer control line, 28...First layer control line according to the gist of the present invention, 27...Dielectric layer, 23...Dielectric layer, 32...Josephson junction element of first layer and second layer. shared ground plane, 33... dielectric layer, 37... dielectric layer,
38...Second layer control line according to the gist of the present invention.

Claims (1)

[Claims] 1. A first layer control line 28 formed on the substrate 1 and made of a superconducting material, and a dielectric layer 27 formed on the first layer control line 28 and made of a superconducting material. The first
A first layer Josephson junction element A comprising a layer base electrode 4 and a first layer counter electrode 6 made of a superconducting material formed on the first layer base electrode 4 via a first layer tunnel insulating film 5. , a ground plane 32 formed on the first layer Josephson junction element A via a dielectric layer 23 and made of a superconducting material; and a ground plane 32 formed on the ground plane 32 via a dielectric layer 33 and made of a superconducting material. A second layer counter electrode 16 made of a superconducting material is formed on the second layer base electrode 14 via a second layer tunnel insulating film 15. a junction element B, and a second layer formed on the second Josephson junction element B with a dielectric layer 37 interposed therebetween and made of a superconducting material.
layer control line 38.