JPH0750802B2 - Superconducting magnetic flux quantum logic circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

[Industrial application] Superconducting magnetic flux quantum logic circuits are used in ultra-high speed analog-digital converters, ultra-high speed digital-analog converters, ultra-high speed adders, and the like. In particular, the ultra-high speed adder can be used for signal processing of a multi-channel SQUID magnetometer for measuring brain magnetic fields.

[0002]

2. Description of the Related Art FIG. 6 shows a magnetic flux driving type superconducting magnetic flux quantum logic circuit (see Japanese Patent Laid-Open No. 61-34986). In the figure, L ₁ is the first sub loop, L ₂ is the second sub loop, S is the secondary side of the transformer, P is the primary side of the transformer, T is the transformer and J ₁ , J ₂ Is the Josephson junction. In this superconducting magnetic flux quantum logic circuit, the transformer coupling and the Josephson coupling constitute the switch section. The operation will be described with reference to FIGS. 8 and 9. First, when a clock alternating current is passed through the primary side P of the transformer, an alternating magnetic flux is generated thereby.
The Josephson junction opens and closes according to the change in the amplitude of the magnetic flux. As is apparent from FIG. 9 showing the current-voltage characteristic of the Josephson junction, when the clock AC signal changes from to, the voltage changes in a hysteresis loop from to. From this change, the Josephson junction is not in the superconducting state in the voltage state and the switch is open.
In the state where the switch portion is open, the magnetic flux quantum Φ ₀ = h / 2e (h is Planck's constant, e is the amount of electron charge) is in the main loop as shown in the left diagram of FIG. However, it is not included in any of the left and right sub-loops. When the voltage exceeds the critical point, the voltage becomes zero and the Josephson junction becomes a superconducting state. This state continues until the voltage exceeds the critical point again after passing through, during which the switch part closes and the flux quantum
₀ enters either the left or right sub-loop as shown in the upper right or lower left of FIG. It depends on an external condition (input signal) which one of the left and right sub-loops contains the magnetic flux quantum Φ _{0. According} to the external condition, the state of entering the left or right sub-loop is 0.
Alternatively, by corresponding to 1, it can function as a superconducting magnetic flux quantum logic circuit. The case where the voltage / current characteristics have hysteresis has been described, but it is true that even if the voltage / current characteristics are close to, and if the voltage / current characteristics have no hysteresis, exactly the same operation is possible. As you can see from 9.

Although the magnetic flux drive type superconducting magnetic flux quantum logic circuit of FIG. 6 is satisfactory, since it is a magnetic flux drive type, the inductance on the secondary side of the transformer and the mutual inductance between the primary side and the secondary side of the transformer are high. However, the size of the coil of the switch cannot be reduced, which causes a problem that the circuit becomes large due to difficulty in manufacturing.

FIG. 7 shows a superconducting flux quantum logic circuit including a conventional current injection type switch. In operation, clock current only flows in one of the sub-loops L ₂ . The clock current flowing through this relatively large sub-loop creates a noise magnetic field that causes malfunction of the adjacent logic circuit.

[0005]

In view of the above, it is an object of the present invention to provide a superconducting magnetic flux quantum logic circuit which can be made as small as possible by fine processing technology and which does not leak a noise magnetic field to the surroundings. And

[0006]

The above object of the present invention is achieved by improving the switch portion of a current injection type superconducting flux quantum logic circuit. That is, as shown in FIG. 1, the switch unit includes a second sub-loop L ₂ of the first sub-loop L ₁ .
A pair of Josephson junctions J ₁ and J ₂ connected in series to the part 1 ₁ on the side adjacent to the first sub-loop L ₁ and the part on the side adjacent to the _first sub-loop L ₁ of the _second sub-loop L ₂ a pair of Josephson junctions J ₃ and J ₄ connected in series with l ₂ , clock signal supply means connected to the connection points C ₁ and C ₂ of the _two Josephson junctions of each pair, and Josephson junctions of each pair and Fukuru - and means l _3, l ₄ which connects the connection point between the up mutually. The Josephson junction used here is a quasi-planar Josephson junction, and the configuration thereof is schematically shown in FIG. 1 in the figure
0 is a superconductor (niobium), 12 is an insulating layer,
Reference numeral 11 is a superconductor (niobium), and 13 is a weakly-bonded portion of a normal-conducting metal.
It is 2 × 10 ^-11 cm ² . When this device is heated to liquid helium temperature, it becomes superconducting, and a finite-value current (clock current) with no voltage is applied to the superconductor 11, the normal metal 13,
It flows through the superconductor 10. In this superconducting state, the switch section is closed, the main loop is divided into two sub-loops, and quantum flux is injected into one of the sub-loops.

In FIG. 1, the clock current is C ₁ -J _2-
through l ₄ -J ₄ -C ₂ and C ₁ -J ₁ -l ₃ -J _3-
Flows through the C _2, any Fukuru - flop also not flow, does not occur the noise magnetic field to the adjacent circuit.
Further, this switch portion has a simple structure, is easy to manufacture as an integrated circuit, can be reduced to the limit of the fine processing technology, and accordingly the degree of integration can be increased.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention is shown in FIG. 2 and its switch section is shown in FIG. 10 is a niobium film formed on a quartz substrate (corresponding to the paper surface of the figure), J ₁ , J ₂ ,
J ₃ and J ₄ are Josephson junctions shown in FIG. 5, and as shown in FIG. 5, a niobium film 11 is formed on the niobium film 10 with an insulating layer 12 interposed therebetween, and a weakly bonded portion 13 of a normal conductive metal is formed. Form. The flow of clock current is shown in FIG.

A second embodiment of the present invention is shown in FIG.
An example of the above is shown in FIG. Both are easier to manufacture than the first embodiment.

[0010]

By constructing the switch section according to the present invention, the clock current flows in a very limited central area, and magnetic flux does not leak to a wide area which becomes a noise source to the surroundings. Further, the switch portion has a very small structure, which is advantageous for forming an integrated circuit having a high density.

[Brief description of drawings]

FIG. 1 shows a circuit configuration of a superconducting flux quantum logic circuit of the present invention.

FIG. 2 shows a first embodiment of the present invention.

FIG. 3 shows a second embodiment of the present invention.

FIG. 4 shows a third embodiment of the present invention.

FIG. 5 is a perspective view schematically showing a quasi-planar Josephson junction.

FIG. 6 shows a circuit configuration of a conventional superconducting flux quantum logic circuit.

FIG. 7 shows a circuit configuration of another conventional superconducting flux quantum logic circuit.

FIG. 8 is an operation explanatory diagram of a superconducting flux quantum logic circuit.

FIG. 9 is a graph showing voltage-current characteristics of a Josephson junction.

FIG. 10 is an enlarged perspective view of a switch unit according to the first embodiment of this invention.

[Explanation of symbols]

J ₁ , J ₂ , J ₃ , and J ₄ are Josephson junctions 10 and 11 are niobium films 12 are insulating layers 13 are normal-conducting metals L ₁ is a first subloop L ₂ is a second subloop l ₁ is the first Fukuru - second Fukuru the flop L ₁ - part l ₂ adjacent side to flop L ₂ second Fukuru - first Fukuru the flop L ₂ - flop L ₁ The portions C ₁ and C ₂ on the side adjacent to the connection points l ₃ and l ₄ are means for mutually connecting the connection points of the sub-loop and the Josephson junction.

Claims (2)

[Claims] 1. A superconducting flux quantum device comprising one superconducting main loop and a switch section for dividing the superconducting main loop into two adjacent first and second sub-loops. In the logic circuit, the switch unit includes a second sub-loop of the first sub-loop.
Pair of Josephson junctions connected in series to the portion adjacent to the first sub-loop and a pair of Josephson junctions connected in series to the portion adjacent to the first sub-loop of the second sub-loop And a clock signal supply means connected to the connection point of the two Josephson junctions of each pair, and a means for mutually connecting the connection points of the Josephson junction and the sub-loop of each pair. Superconducting magnetic flux quantum logic circuit. 2. The superconducting flux quantum logic circuit according to claim 1, wherein the electrode portion of the Josephson junction is an oxide high temperature superconductor.