JPS6134986A - Josephson circuit element - Google Patents

Abstract

PURPOSE:To obtain a Josephson circuit element which can be manufactured easily, by providing two input/output superconductive subloops in a symmetrical relation with respect to an exciting superconductive subloop. CONSTITUTION:Four points of a superconductive main loop SLM are paired connected by means of Josephson junctions J0 and J1, respectively, whereby there are formed two output/input superconductive subloop SL1 and SL2 each having a Josephson junction J1 or J2 and an exciting superconductive subloop SL3 having two Josephson junctions J1 and J2. An input/output line 10L is arranged close to at least one of the input/output superconductive subloops SL1 and SL2, so that it produces magnetic transformer couplings with the input/output superconductive subloops SL1 and SL2. Further, an exciting line EL is arranged close to the exciting subloop SL3, so that it produces a magnetic transformer coupling with the exciting superconductive subloop SL3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a Josephson circuit element having a Josephson junction.

(Traditional technique #f) To better understand the invention, we use the magnetic flux quantum φ.

(= h/2e ) as an information carrier m
Llktlarev circuit element
on ) first i1! I will clarify. As shown in Figure 2, the Tsukura metric cantron is a superconductor Luno SLO with an inductance L and a Josephson junction J with a critical current IM.
. It has a t-containing structure. This is a single loop R
It has the same structure as that called F-3QLIIO, and is described by the following equation expressing the operation.

,” then φ+LIMsln(2) =φ. (1) φO Here, φ is the magnetic flux in the loop fs·LO. This magnetic flux φ is generally not equal to the externally applied magnetic field φ.

The basic operation of Equation (1), in which the following potential energy is derived by Lagranche's undetermined coefficient method, will be explained with reference to FIG. Figure 3 shows the external magnetic flux φ
6 is a graph showing the relationship between 6 and internal magnetic flux φ.

External magnetic flux φ. As φ. /2 bias magnetic flux with human power signal ψ. φ was applied. =φo/2+ψ, (3) For example, a laser beam is used to connect a Josephson junction j.

After putting the superconducting loop fsLo into the 1-open 1 state,
If the irradiation of laser light is stopped and the roof is returned to its original 1i81 state, the magnetic flux φ in the RUG SLO becomes the human input signal φ. 〉O
When φ. So, the input signal ψ. Ku.

When , it becomes O.

However, this kantron is hardly of practical use due to its noise characteristics.

Next, we will explain the pisectron (blsectron).
'Afru. oy is the roof of two superconductors with inductance L as shown in Figure 3.
2 is a junction J with critical current IM. It has a shared structure. In this pisectron, the entire structure is surrounded by one superconducting roof SLM, and this superconducting roof 'SLM has a magnetic flux quantum φ. It is included.

Therefore, the magnetic fluxes φ0.φ2 in the two superconducting roofs ``SLI and SL2'' satisfy the following equation.

φ, +φ2=φ. = const (4) The equation representing the operation of the pisectron is described by the following equation.

Equation (5) is derived from the constraint condition of Equation (4) and the following potential energy by Lagranche's undetermined coefficient method.

If this potential energy is expressed only by φ□, it will be as follows.

It is.

Next, the basic operation of the pisectron will be explained using FIG. FIG. 5 is a graph showing the relationship between the potential energy U given by equation (7) and the internal magnetic flux φ of the superconducting roof SL1.

Josephson junction J functioning as a superconducting switch. For example, by irradiating laser light on the
After reaching the state (1M20), the radiation of Radical light is stopped and the Josephson junction is brought into the 1-closed 1 state again, and the superconducting loop SL1. Input/output close to SL2! External magnetic flux φ given to each superconducting loop SLI, SL2 by li[lOL. 0. When the relationship of φ62 is φ6□−φ82〉00, the magnetic flux quantum φ. is transferred to the seventh superconducting loop fSL1 (point 8 in Fig. 5), φ. , −φ. When 2kuO, the magnetic flux quantum φ. is the second
(point A in FIG. 5).

Josephson junction J. When , the magnetic flux quantum φ. is the first
φ to the superconducting roof 'SL1 and the second superconducting roof SL2. The above operation occurs because the data is never divided and arranged by /2. In this sense/4 isect a
7 can be said to be essentially based on quantum mechanical effects.

Magnetic flux quantum φ. However, the Josephson junction J. When closed, λ value logic (or O) can be realized depending on which side of the first and second superconducting roofs SLI and SL2 they are present on. Note that the paysectron described above is an invention by the present inventor who filed a patent application in Japanese Patent Application No. 777J, but as described in the specification of the patent application Sho. Deputy Lou fSLl,
As shown in Figure 6, it is possible to use DC-3QUID as a superconducting switch that splits into SL2, and by using DC-SQUID as a superconducting switch, it can in principle be used as a cane superconducting switch. This has the advantage of being faster than using a method of opening and closing a superconducting switch by irradiating a laser beam. However, with the idea of simply using DC-3QUID as a superconducting switch, there was a difficult problem in manufacturing the device (inability to obtain a sufficient yield during mass production). As shown in the figure, there is also a type (DCFP) in which a superconducting loop having two Josephson junctions is divided by a superconducting wire, but this circuit element will be explained in comparison with the present invention. do.

(Problems to be Solved by the Invention) As shown in FIG. 6, the Josephson circuit element using C-3QUID as a superconducting switch essentially has the characteristics of being able to operate at high speed and with low power. In reality, there are severe manufacturing problems shown in (1m) below.

(2) The first problem is the unevenness of the characteristics of the Josephson junctions that are fabricated, more specifically, the variation in the critical current value 1 of each Josephson junction or the effective critical current value IM in DC-5QυID. This is a problem.

(8) The second problem is to minimize the inductance value, which is one of the four design parameters of superconducting circuit elements, by making the 74 tera of the superconductor thin film as small as possible using microfabrication technology. The problem is that it needs to be created. In other words, the resolution (fine
It is a matter of the mother turn).

The problem with both of the above) and (B) is that the magnetic flux quantum unit φ. (=hC/2e=2.07X/0-'G
-ca"=2.07X10-Wb) is very small.The above problem is caused by the DC
-3QU ID is not a problem specific to biseventrons using ID as a superconducting switch, but a magnetic flux quantum φ. This is a common problem for circuit elements that have information as an information component.

The above problems will be described in more detail below. The lower limit of the critical current value 1rn of a Josephson junction in a logic circuit or a memory circuit is about /00 pA.

Since the liquid helium temperature T = 4A, 2, the noise current related to thermal noise IN = Hiroe kBT /h = 0.3 A
/JA, but the effective noise temperature T is due to the noise given by the lines arranged to drive the circuit elements.
N becomes 1lAjK or more, and the noise current becomes IN equal to 1μA. Therefore, if the critical current value 1m is 10OIIA, the influence of noise is /chi.

On the other hand, the superconducting loop with inductance L is the magnetic flux quantum φ.

In order to include seven items, L must be several times as large as the following values.

φ.

The fact that this value is extremely small is the cause of problems (2) and 0).

For example, even if a hole with d = 2 μm, which is close to the limit of 7 otography, is drilled in a superconductor niobium thin film, the loop of the superconductor is already L = μ. d: Yuj, 2buhenri (2) It has a large value. In general, the resolution of the main hole in photolithography is about 5 times lower than that of line and space or turn, so the loop of an actual superconductor is several times the size of equation (G), and the critical current The lower limit of 1m cannot be achieved.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide a Josephson circuit element that is easy to manufacture.

(Means for Solving the Problems) The Josephson circuit element of the present invention, as shown in FIG. , J□, thereby each connecting one Josephson junction J or J2
Two input/output superconducting sub-loops SLI and S
L2 and seven excitation superconducting subroutes with one Josephson junction J and J2! SL3 is formed. An input/output $I OL is arranged close to at least one of the input/output superconducting sub loops SLI and SL2, and this input/output MI OL is connected to the input/output superconducting sub loop f.
SL1#SL2 and magnetic trans 2 coupling occurs.

Further, an excitation line EL is disposed close to the excitation sub-loop SL3, and this excitation line εL causes magnetic transformer coupling with the excitation superconducting sub-loop SL3.

Here, magnetic transformer coupling is superconducting sub-Lug SL for excitation.
3 and excitation line EL and input/output superconducting side roof “SLI”
, SL2 and the input/output IalOL are magnetically coupled via magnetic flux.

Next, it will be explained that the circuit element of the present invention shown in FIG. 1 is the most basic circuit and is the best circuit for solving the above problems and (8).

The following equation can be used to judge whether the circuit is good or bad. The 01st formula is the formula (9) and the 00th formula
This formula is created by combining the formula
This is an equation showing how much resolution d is required when the critical current value 1 m of the Son junction is set to a certain value. K is a variable that is determined in proportion to the size of the circuit constant (inductance), and for the present invention, =l. Therefore, by evaluating the value of K, the quality of the circuit can be determined. It is clear that the larger the value of K, the better.

The value of K can be obtained by performing an equivalent circuit transformation and finding the circuit constant value, but at this time, it is important to note that the problems inherent in equivalent circuit transformation in superconductor circuits can be solved by serial-parallel transformation (Fig. 7). ) and Y-Δ transformation (Figure g)
Explain using. When a closed loop is formed by an equivalent circuit transformation, unlike the case of the inductance of a normal metal, a completely equivalent transformation is not achieved. For example, the circuit of the present invention shown in FIG. 1 is equivalent to the circuit of FIG. 9a, but not the circuit of FIG.

In Figure 8, the outer periphery is entirely made of superconductor disks and forms a superconductor loop, so φ, 1φ2 + φ,
= nl'o = cons t % The condition for magnetic flux quantization is satisfied. In contrast, 11 in Figure 6! Since the outer periphery of the circuit includes a Josephson junction, the condition for magnetic flux quantization in equation (b) does not hold. As shown in this figure, the outer periphery includes the Josephson junction and the (6th)
) for which the condition of formula is not satisfied is D CF P (D
The circuit constant of this 0CFP is determined by the ratio of L' and L as shown in FIGS. 2C to 7F.

In other words, the value of is 4 below. In other words, when a circuit is created at the resolution limit of fine λ wire processing, the circuit constant of the present invention is more than λ times smaller than that of DCFP. Ru. This result was obtained because the present invention shown in FIG. 8 is connected in parallel, and the DCFP shown in FIG. 6 is connected in series.

There are an almost infinite number of circuits that can be transitioned from the present invention in Figure 8 and the DCFP in Figure 6 to the serial/parallel conversion in Figure 7 and the Y-Δ conversion in Figure 1. A typical example is shown in Figure 1o.

FIG. 10c shows the circuit of the present invention, where ji/O8
1 and 1B are circuits that satisfy equation (b) and are similar to the present invention. FIG. 101 is a DCFP, and FIGS. 1Og and 1Oe are circuits similar to DCFPs in which there is a Josephson junction on the outer periphery and the equation (2) does not hold.

The circuits in Figures 1Oc and 1OF are the most basic in the sense that they cannot be made any simpler.

Although the circuit of FIG. 1Oc and the circuit of FIG. 1 are equivalent, this circuit can be said to be the most thorough circuit in terms of parallel connection.

In the circuits of FIG. 1 Oa, FIG. 1 Ob, FIG. 7 Qd, and FIG. 10 e, the values of are all l.

≠ The above description can be collectively represented in FIG.

FIG. 1 is obtained from the value of K and the equation (Ql), and it can be seen at a glance that the present invention is superior to Ike's Josephson circuit.

(Operation) The circuit of the present invention shown in FIG. 1 is the most natural extension of the parametric cantocon shown in FIG. 2 and the pisectron shown in FIG. This means that the Ite/kuyal energy and the condition for quantization of the total magnetic flux φ, 1φ2+φ3=φ. Q4 to RF-
This is clear even when comparing equations (4) and (6) of 3QUl'D.

From the 01st equation and the α◆ equation, the lag 2/shun undetermined coefficient method is 6, which is assumed to be L' (L. This equation is based on the previous equation (5).
It is very similar to the formula. It can be seen that in the first equation (2), 1 and 4 of the equation (5) are replaced by the following equation.

The formula Ia (2) in Figure 1j is φ63.
is shown as a parameter.

Both the force/tron shown in FIG. 3 and the pisectron shown in FIG. 5 use statistical mechanical non-equilibrium phenomena, such as applying radar light, to open and close the superconducting switch, so the switching speed is very slow.

Figures 72 and 73 show the magnetic field φ applied to loop SL3.
This shows that the superconducting switch can be opened and closed simply by changing 1!3. This can also be seen from the α→ equation. (Other operations are the same as the above-mentioned pisectron.) In other words, the logic circuit of the present invention shown in Fig. 1 acts as a switch for the statistical mechanical equilibrium phenomenon, causing logic circuits such as Ilnote and Kono to S
upperconductlrlg.

Thermal EquIllbrium Param
It will be named etron (STEP).

(Example) Hereinafter, one aspect of the present invention will be explained in detail.

The first diagram is a plan view showing a first embodiment of the present invention. In this embodiment, the Josephson circuit elements are formed into a lower superconductor layer made of niobium or the like formed into predetermined grooves or turns.
Josephson junction is produced by laminating an upper superconductor layer 2 and an insulator layer 3 made of silicon between the lower superconductor layer 1 and the upper superconductor layer 2. J
L and J2 are formed by weak coupling parts 4 and 5.

FIG. 1j is a plan view showing a second embodiment of the present invention, in which the excitation roof 'EL is formed by upper and lower superconductor layers 1 and 2 sandwiching an insulating spacer 3. It is a three-dimensional object.

FIG. 76 is a plan view showing a third embodiment of the present invention. In this embodiment, the excitation loop EL to which the clock signal is applied is connected to the input/output amount R! S.L.I.

It has a spatially collapsed structure compared to SL2.

In the above explanation, the input and output edges are the first and second input/output superconducting loops! Although the loop is placed close to SLI and SL2, it is possible to operate even if it is placed close to only one loop SLI or SL2.

Further, the signal applied to the excitation MEL can be an irregular signal such as a normal clock signal.

(Effect of the invention) The circuit of the present invention is the most thorough and basic circuit in terms of parallel connection, so it is the smallest circuit with the same microfabrication resolution. It will work even if the critical current of the Josephson junction is made sufficiently large, and it is made as shown in Fig. 3.

The larger the critical current is, the easier it is to adjust the critical current within, for example, 5% during the device fabrication process. This makes it an important device that determines the success or failure of logic circuit prototype production.

[Brief explanation of the drawing]

FIG. 1 shows the Josephson circuit element (STEP) of the present invention.
Figure 2 is a circuit diagram of a lametric cantron, Figure 3 is a diagram explaining the operation of a cantron, Figure ≠ is a circuit diagram of a pisectron, Figure 5 is a diagram explaining the operation of a pisectron, Figure 6 is a diagram explaining the operation of a pisectron. is a circuit diagram using DC-5QUID as a superconducting switch for a pisectron, and Figures 7 and g are for series-parallel conversion and Y
- Explain the △ transformation. Figures 8 to 1 are diagrams explaining the comparison of circuit constants of the present invention and DCFP, Figures 1 Oa to 1 Of are diagrams showing equivalent circuits, and Figure σ1 is a diagram explaining the comparison of the circuit constants of the present invention and DCFP. Figures 72 and 13 are diagrams explaining the operation of the present invention, and Figures 14' to 1
Figure 6 is a plan view of an embodiment of the present invention. □ SLM... superconducting main loop, SLI, SL2... superconducting sub-loop for input/output! , SL3
...Superconducting sub-loop for control, 10...Ota line of force, EL...excitation line. Figure 3 Figure 4 Figure 5 Figure 0 Supervision Φ. Figure 6 Figure 7 Figure 12 Figure 13 Figure 14 Figure 15 &+ 5 Figure 16 Procedure amendment band (method) 1. Indication of case Patent application No. 15505 of 1982
No. 7 No. 2, Title of the invention Josephson circuit element 3,
Relationship with the case of the person making the amendment Applicant name (679) RIKEN 4, Agent

Claims (1)

[Claims] The four points of the main superconducting loop are connected via pairs of Josephson junctions, thereby creating one control superconducting subloop with two Josephson junctions and two superconducting loops with one Josephson junction. an excitation line disposed close to the excitation superconducting sub-loop and coupled to the excitation superconducting loop by a magnetic transformer; An input/output line is provided that is disposed close to at least one of the superconducting sub loops and is coupled to the superconducting sub loop for input/output by a magnetic transformer, and the two superconducting sub loops for input/output are mutually connected to the superconducting sub loop for excitation. A Josephson circuit element characterized by symmetry with respect to a superconducting sub-loop.