JPS5845193B2 - josephson logic element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a Josephson logic element of the type used as a tunnel gate, and in particular to its signal input circuit.

In conventional Josephson logic devices, the input signal current is arranged to flow through an isolated line from the Josephson junction.

Figure 1 shows the equivalent circuit and structure of a conventional in-line Josephson element, where 10 is a ground plane, 12
14 is a base electrode, 14 is a counter electrode, 16 is a thin insulating layer constituting a tunnel junction, and 18.20 is a rather thick insulating layer made of SiO or the like.

10, 12.14 are made of superconducting materials such as niobium and lead, and 12.degree. 16.14 constitutes a so-called Josephson tunnel gate.

This tunnel gate takes a voltage state and a zero voltage state,
The switching is performed by applying a bias current to the thread path 12-1614, and direct current flowing through the signal line to the tunnel junction 1.
This is done by changing the magnetic field created in step 6 (by changing the strength of the signal current).

The signal line 22 is formed on the insulating layer 22 separately from the tunnel gate.

In FIG. 1, a is an equivalent circuit, b is a sectional view, and C is a plan view.

As is clear from Figures b and fJ), the device with this conventional structure has a multilayer structure 4 with a total thickness of 2 μm. Since it is formed by lift-off of a thin film deposited by vapor deposition or sputtering, there are many disconnections and short circuits at the stepped portions, resulting in a decrease in yield.

Note that in FIG. 1, no paragraphs are shown and the surfaces of the insulating layer 20 and the like are shown as flat, but in reality, the height is high in areas where multiple layers are stacked, and it is low in areas with a small number of stacked layers.

A device that can improve this point is a Josephson device called a current injection type shown in FIG.

In this type of device, the signal line 22 is connected to the base electrode 12 (12, 22 are made integrally), and the signal current flows directly into the Josephson junction 16.

To switch between voltage state and zero voltage state, change element current (■) and critical current (■).

Depending on whether I > Io or I < I O (the former is a voltage state and the latter is a zero voltage state), I due to the magnetic field.

Instead of changing , the element current itself may be changed, and the signal current injected into the tunnel junction by the signal line 22 through the base voltage 12 changes this current .

By doing this, as is clear from FIG. 2, there is no need for multilayer wiring.

For this Dentaki Note large or direct type game 1, press T, R,
, Gheewal a″A 30-Ps Josep
hson Gurr-ent Injection L
ogic (CIL)"IEEE J, 5olid-
8tate C1rc+ Vol, 5C-14+A
5 + PP.

787-793. Oct., 1979 or J.H.M.
agerlein and L, N, Dunklebe
Direct-Cou-pled Jo
sephson ful adder” I EEE
Trans.

Mag, Vol, MAG-13, AI, P
P., 585-588° Jan, 1977.

However, in this type of element, the input signal current and the bias direct current are reflected in the same area and merge, making it difficult to separate the input and output, making circuit design complicated.

That is, the output is taken out from points P, , P2 across the tunnel junctions in Figures 1a and 2a, but in the element in Figure 2, the signal current also flows into the output circuit, making it difficult to separate them. .

The present invention is an attempt to improve this point, and instead of passing a human signal current directly through the tunnel junction, the magnetic field created by the input signal current acts on the tunnel junction, and moreover, the insulating layer is It is an object of the present invention to provide an element that does not require a human power signal line to be placed through the device, and can therefore avoid occurrence of disconnections due to multilayer wiring.

The Josephson element of the present invention is a Josephson logic element in which a base electrode is disposed on a ground plane and an opposing Ti layer facing the base electrode via a tunnel junction, in which a bias current flows from the base electrode to the tunnel junction. G so that the input signal current flows from one extended end of the counter electrode without passing through the tunnel junction.
Next, this will be explained in detail with reference to Examples.

FIG. 3 is a diagram explaining the present invention in detail.

When a current is passed through the signal line 22 in the device shown in FIG. 1, the signal current i1 flows only through the surface layer of the signal line 22 because no magnetic field is generated in the superconductor.

The thickness of this surface layer λ□ is called the London penetration depth.

When the current i1 flows in the signal line 22, the current 11 also flows in the surface layer of the counter electrode 14 so that the magnetic field caused by the current 11 and the like does not occur inside the counter electrode.

This current 12 is called an image current.

For the same reason, the image current also flows to the base electrode 12 and the ground plane 10.

13+14 is the image current flowing through these surface layers.

When a signal current flows through the input signal line in this manner, an image current equal to the signal current flows through the counter electrode and the base electrode.

Here, is equal to v, which depends on the spacing. If the counter electrode and the human signal line were separated with no thickness, they would be completely equal, but there are thousands of holes made of SiO etc. between them. Since the thick insulating layer 20 is present, the image current is slightly smaller than the signal current.

Referring again to FIG. 3, the magnetic fields for the 1-channel junction 16 cancel each other out because the current i1 and the current 12 in the upper surface layer of the counter electrode 14 are opposite in direction and equal in magnitude. Since the current 13 in the lower surface layer and the current i4 in the ground plane have a similar relationship, the current i2 in the lower surface layer of the counter electrode 14 and the current i in the upper surface layer of the base electrode 12 end up
3.

Therefore, if the current 12 can be passed through a part of the surface layer of the counter electrode 14, the signal line 22 may be omitted.

Although the ground plane 10 is necessary to efficiently apply a magnetic field to the tunnel junction 16, the input signal line 22 may be omitted if the above-mentioned current 12 can flow.

The present invention is based on the above idea, and one embodiment thereof is shown in FIG.

As shown in FIG. 4, in the present invention, the counter electrode 1 is connected to the signal line 22.
Connect to 4.

That is, one end of the counter electrode 14 is extended along the base electrode, and this extension is used as the signal line 22.

The other end of the counter electrode 14 is connected to the ground plane 10,
Ground.

Reference numeral 24 indicates a connection portion between this counter electrode 14 and the ground plane 10.

In this element, when a signal current IH flows from the signal line 22, an image current flows through the base electrode 12 and the ground plane 10 as shown by the arrow in the figure, and the magnetic field acting on the tunnel junction 16 is generated by the signal current IH and its image current I
3.

In other words, the same result can be obtained when the signal line 22 is provided on the insulating layer 20 as shown in FIG.

Moreover, since the signal current flows through the line 22-1410 and does not pass through the output terminal P1 like the bias current, there is no possibility that the signal current will flow out to the output circuit.

In this device, it is desirable that the other end of the opposing pole 14 be grounded.

This means that if a resistor is inserted at the other end, the human input signal current IH will flow through the resistor and cause a voltage drop, and this voltage drop will push up the potential at the output end P1: f, which ultimately leads to the input signal This is effective in preventing this from affecting the output circuit.

In addition, in this element, the signal current does not reflect a magnetic field on the tunnel junction 16 via an image current as in the element shown in FIG. It takes the value when the thickness of the insulating layer 20 in is zero, and becomes a dog.

Note that in the above description, one end of the counter current hk is connected to the ground plane, but it may be connected to another common line provided on an insulating layer on the ground plane.

Further, it is not necessarily necessary to connect the end of the counter electrode on the reaction side to the ground plane from the end into which the human power signal current is applied, and it is also possible to connect the counter electrode to the ground plane from the middle.

The present invention is applicable not only to single-junction devices but also to multi-junction quantum interference devices.

FIG. 5 shows another circuit and its structural diagram when applied to a two-junction quantum interference device (SQUID).

In this figure, 16a and 16b are two tunnel junctions,
A counter electrode 14 connects these 1-channel junctions and, according to the invention, is extended at one end to become a signal line 22 and at the other end is connected to the ground plane 10.

In other circuits such as those shown in FIG. 5a, the mark on the coil is the tunnel junction 16a.

16b shows the electrode inductance in the Z=j direction.

Bias current ■ is applied to two 1-Hennel junctions 16a and 16b.
The signal current IH flows from the counter electrode 14 to the ground plane 10 without passing through these tunnel junctions.

Further, the input terminal (Fan-in) of the element of the present invention is the sixth
As shown in the figure, an arbitrary plural number can be used, and AND or OR functions between human input signals can be obtained, similar to the conventional element.

In this case as well, it is desirable that the counter electrode 14 be directly grounded.

Further, although an appropriate number of output terminals (Fan-outs) may be used, it is preferable to arrange them in parallel as shown in FIG. 7 in the present invention.

In this figure, 26, 28, and 30 are load resistances. In the device of FIG. 1, point P1. Normally, a series output format is used in which an output circuit is connected between P2 and the circuit is passed through an arbitrary number of subsequent tunnel junctions, but the present invention method in which the human input signal circuit is grounded is used. This serial format cannot be adopted.

The fan-out number in FIG. 7 can be set to any number within the range that can drive the next stage gate when the output is divided into poles.

Next, an embodiment of a Josephson logic element of the opposed tfM direct connection type according to the present invention will be described.

Figure 8 shows two 5QUIDs as shown in Figure C and other circuits.
FIG. 9 shows the second stage of manufacturing.

First, as shown in FIG. 9a, niobium (Nb) is deposited as a ground brain 10 on a substrate 32-1 made of silicon or glass by vapor deposition or sputtering to a temperature of 2,000 to 2,000 ml.
The niobium film is deposited to a thickness of 3,000 mm, and the niobium film is patterned into the desired shape using an etching or lift-off method.

Next, as shown in FIG. 9, about 2,000 insulating materials such as silicon oxide (Sin) are deposited as an insulating layer 18, and patterned into a required shape.

Next, perform sputter etching with argon, etc.
After removing oxides and contaminants formed on the surface of the ground plane 10, a material that is difficult to oxidize or does not oxidize, such as gold (Au) or its alloy (with a large amount of Au) such as Au T, NF, N, etc. A connecting material layer 34 is formed at the contact portion between the counter electrode and the ground brain as shown in FIG. 9C by using a vapor deposition lift-off method using about 2,000 people.

The reason for creating this layer 34 will be described later.

Next, after sputter etching with argon ζ again, the base electrode 12 is made of gold (for example) as shown in FIG. 9d.
A-u) was evaporated by 80 people and lead indium (Pb-■n, indium was 10 tonne weight %) by 2000 people, and the surface was oxidized by high-frequency plasma oxidation to form a protective film against subsequent defects. After forming, it is patterned into the required shape by a lift-off method or the like.

Next, as shown in FIG. 9e, the insulating layer 20 is made of, for example, Si.
O is vapor-deposited at 3000A and patterned into the desired shape using a lift-off method or the like.

Furthermore, as shown in FIG. 9f, the surface portion of the base electrode 12 exposed in the window portion of the insulating layer 20 is oxidized again using a high frequency plasma oxidation method or the like to form an insulating film 16a with a thickness of about 30 mm.
Make 16b.

These insulating films 16a and 16b are made of Pbo+In2O3, etc., and occupy the aforementioned tunnel junction.

Note that in this plasma oxidation, if the film 34 is not present, the film 34
A portion of the surface of the ground plane 10 (which will naturally be exposed) is also oxidized, creating a tunnel junction.

In this case, the counter electrode cannot be directly grounded.

The reason why the film 34 is provided is to prevent the formation of tunnel junctions, and since the film 34 is made of an oxidation-resistant material such as gold, an oxide film and therefore a tunnel junction will not be formed even by plasma oxidation.

After plasma oxidation, the counter electrode 14 and the signal line 22 are first made of lead (Pb) and then gold (Au).
80A and 2,000 lead are continuously evaporated, and these composite films are patterned into the required shape by a lift-off method or the like.

Thus, the Josephson device shown in FIG. 9f and therefore in FIG.

14' is also made.

The counter electrode 14 is connected to the ground plane 10 through a membrane 34, so that the resistance of this membrane 34 enters the human signal circuit, but since this membrane 34 has a relatively large area and a small thickness, it becomes the resistance of the tunnel junction. It is sufficiently small (about 10-'Ω cold in this example).

This resistance should be at least one order of magnitude smaller than the resistance of the tunnel junction), and even if a current of about 10 mA flows, the voltage generated is three orders of magnitude or more smaller than the voltage generated at the tunnel junction, so there is no problem.

It should be noted that if the load resistor 26 is formed at the same time as the film 34 is formed, there is an advantage that no extra process is required.

As a method of connecting the counter electrode 14 and the ground plane 10, the film 34 is not used, so the step of FIG. 9C is not performed, and the counter electrode 14 is connected to the ground plane 10 in the step of FIG. 9F. The oxidized film or contaminants formed on the Gerando tube 1/- 10 and the counter electrode 14 are removed by sputter etching with argon, etc.
Then, as shown in FIG. 10, another superconducting material such as p
A bAu thin film 36 may be used to connect the counter electrode 14 and the ground plane 10.

As shown in FIG. 11; □, another method is to deposit about 100 metals that are difficult to oxidize, such as gold (Au), by vapor deposition on the ground plane 10 deposited in FIG. After that, the insulating layer 18, the base electrode 12, and the insulating layer 20 are formed, and then the tunnel gates 1 and 16 are formed by oxidizing the base electrode, and the counter electrode 14 and the signal line 22 are formed. You may do so.

Of course, the formation of the film 34 is unnecessary. In this case, the thickness of the metal etc. needs to be sufficiently thinner than the penetration depth of the electromagnetic field (skin depth) for the highest frequency acid component of the signal.

As explained in detail above, in the present invention, the counter electrode is extended and the signal current is supplied manually from the extension part, so multilayering and mixing of input and output currents can be prevented.
Further, there is an advantage that the process is simplified.

[Brief explanation of drawings]

Figure 1 a J b + C and Figure 2 a l ri I
C is a circuit diagram, a cross-sectional view, and a plan view of a conventional element;
Fig. 3 is a detailed diagram of the present invention, Fig. 4 a, b
. C and FIG. 5 a + b + C are other circuit diagrams, cross-sectional views, and plan views showing the first and second embodiments of the present invention,
6 and 1 are input/output circuit diagrams of the device of the present invention,
8a, b, and c are cross-sectional views, plan views, and equivalent UjJ path diagrams of other embodiments of the present invention; FIGS. 9a-f are views explaining the manufacturing process of the device in FIG. 8; and FIG. The figures and FIG. 11 are cross-sectional views showing still another embodiment of the present invention. In the drawing, 10 is a ground plane, 12 is a base electrode, and 14
1 is a counter electrode, 16 is a tunnel junction, 22 is a human signal line, 34 is an oxidation-resistant low resistance thin film, and 38 is an oxidation-resistant low resistance thin film on the ground plane.

Claims (1)

[Claims] 1. In a Josephson logic element in which a base electrode and a counter electrode that opposes the base electrode via a tunnel junction are disposed on a ground plane, a bias current flows from the base electrode to the tunnel junction. The Josephson logic element is characterized in that an input signal current is caused to flow from one extended end of the opposing electrode without passing through the tunnel junction. 2. The Josephson logic element according to claim 1, wherein the other end of the counter electrode is connected to a ground plane via a thin film of an oxidation-resistant, low-resistance material. 3. A thin film of an oxidation-resistant low-resistance material is formed on the ground plane, a base electrode is formed on the thin film-L via an insulating layer, and a counter electrode straddles the tunnel junction on the base electrode and the thin film. The Josephson logic element according to claim 1, characterized in that it is formed by.