JPS6051287B2 - Exclusive OR circuit device using Josephson elements - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a logic circuit device using a Josephson element that is capable of performing an exclusive OR operation with an extremely simple structure.

As is well known, a Josephson junction is a junction in which two superconductors are brought into contact via an insulating thin film thin enough to allow tunneling of superconducting electrons, and the voltage V and current I are as shown in Figure 1. have characteristics.

In other words, even if the voltage V across this junction is 0, a current flows (more specifically, the superconducting current is flowing at this time is i.sin(θ
. −θ, ), so the phase difference between both superconductors θ,
, θ. If current is passed through this junction from the external electrode to make it above the critical value Ic, the superconducting current is insufficient, so a normal current will also flow, and a voltage will be applied to the junction. occurs. This critical value Ic increases or decreases depending on the magnetic field. Therefore, as shown in Fig. 1a, a bias current IB is supplied to the Josephson junction J from a constant current source (not shown), a signal current IH is passed through the signal line, and the magnetic field generated by the current is applied to the Josephson junction J. Thinking about it, if IH■0,1B<1c, the voltage V appearing across the junction is 0, as shown in Figure 1, but when a signal current IH is applied and a magnetic field is applied, Ic becomes I'c. When the voltage is lowered to 1B>1'c, the operating point jumps to point P along the load straight line indicated by the dotted line, and a voltage is generated at junction J. I
H■0 Therefore, Ic remains unchanged and IBf! Even if it is increased to -1'B, the result is the same, the operating point becomes P', and a voltage is generated. The above is an overview of the operation of Josephson logic gates. In a normal Josephson logic gate, the Josephson junction J circuit and the signal current IH circuit are separated and independent, but in this type, they have a multilayer structure (the Josephson junction has a three-layer structure, and an insulating layer is added to this). When the signal line is attached through the
(Adding a ground plane and an insulating layer to effectively provide a 7-layer structure), there are manufacturing difficulties, such as the occurrence of wire breakage.

Therefore, the applicant first directly connected a signal line to one superconductor (counter electrode) of the Josephson junction, and
(the body is used as a signal line), and the counter electrode is directly connected to the ground plane (if a resistor is inserted in this part without being directly connected, a voltage drop due to the signal current will occur in the resistor, and this will change the output terminal potential and reduce the signal current.) He devised a Josephson logic gate with a direct connection to the counter electrode. This is explained in Japanese Patent Application No. 55-20214, and the outline is explained in Fig. 1C and d. 10 is a ground plane,
12, 14, and 16 are superconductor and tunnelable thin layers constituting a Josephson junction, and 18 is an insulating layer. In the Josephson logic gate of the counter electrode direct connection type, the counter electrode 16 is extended and a signal current 1H flows through the extended portion 16a, the other end 16b is dropped to the ground plane 10, and the output voltage is taken out from the base electrode 12. Therefore, the equivalent circuit is as shown in FIG. 1a. This type of Josephson logic gate saves two layers in the signal line section, and is effective in preventing disconnections and improving yield. Furthermore, the signal current circuit and the output current circuit are separated by a junction J, so there is no problem of input current leaking to the output circuit. By the way, as is well known, there are various types of logic gates such as AND, OR, and exclusive OR (hereinafter referred to as EXOR), and these gates are often constructed from semiconductor elements.

Of course, it is also possible to use a Josephson element, but there are very few examples of EXORs using Josephson elements. EXO
R is a logic signal. A4Bl This is (A-B) (A+
Since it can be expanded as B) or (A+B)+(A-B), it can be constructed by a combination of NAND, AND, and OR circuits, or a combination of AND and NOR circuits, but this would make the element considerably complicated. Therefore, the present invention provides EXOR with the simplest possible structure.
A logic circuit using Josephson elements that can execute logic! The device is characterized by a T-shaped base electrode provided on the ground plane via an insulating layer, which extends over the horizontal arm of the T-shape and also serves as a signal line. A counter electrode is provided, and a Josephson junction is formed between the counter electrode and the counter electrode at both ends of the horizontal arm, and the T of the counter electrode is formed between the Josephson junctions.
The protrusion on the opposite side to the vertical leg of the shape is connected to the ground plane, the vertical leg of the base electrode is used as a bias current input and signal output terminal, and both ends of the counter electrode are used as signal input terminals. This is the point.

An example of this is shown in FIG. In FIG. 2, a shows a plan view, b shows a side view, and the section taken along the line X--X in a is shown in cross section in b.

10 is a ground plane, 18 is an insulating layer, and 12 is a base electrode.

The base electrode 12 is T-shaped in this example, and a counter electrode 16 that also serves as a signal line extends to the left and right on the horizontal arm portion 12a. The counter electrode 16 forms a Josephson junction with the base electrode at both ends of the horizontal arm 12a, and the counter electrode 16 forms a Josephson junction with the base electrode at both ends of the horizontal arm 12a.
, 14b is the insulating thin film. The extensions 16a and 16b at both ends of the counter electrode serve as input ends for a signal current, and the protrusion 16c of the counter electrode 16 is connected to the ground plane 10. The vertical leg 12b of the T-shaped base electrode serves as a bias current input end and a signal output end. As is clear from comparison with FIG. 1, this has a structure in which two Josephson elements of the opposite electrode directly connected type shown in FIG. 1 are provided side by side. To explain the operation of this device, the bias current 1B is applied to the vertical leg portion 12b of the base electrode 12, the horizontal arm portion 12a1, the insulating thin film 14a,
14b, the counter electrode 16, the protrusion 16c1 and the ground plane 10, and the signal currents 1H1 and IH2 flow in the extensions 16a and 16b1 of the counter electrode, the counter electrode 16, and the protrusion 16C1 through the ground plane.

The value of the bias current 1B is the signal current 1H1, IH2
are both O, Josephson junctions J, , J2 are both chosen to be in a voltage-free state. This has a signal current of 1
When H1 or IH2 flows, the critical current value of the junction decreases due to the magnetic field generated by the current, h>IO, and the junctions Jl and J2 enter a voltage state. Next, signal current 1H1
, IH2 flow together, the directions of these currents in the counter electrode 16 are opposite, so the magnetic fluxes created by these currents cancel each other out, and the state is the same as when the signal currents 1H1 and 1H2 are both 0, and the junction Jl, J2 becomes a no-voltage state. Now, if the state where the signal current flows is 1, the state where it does not flow is 01, the voltage state of the junction is 1, and the state where there is no voltage is O, then the above is 00 or 11, 01 or 10 is 1, and EXOR A logical operation has been performed. Note that the function of the signal current with respect to the critical current 1c in this case is slightly different from that in the case of FIG. 1, and is similar to that of the fraudulent PCSQUID. As is clear from the above description, according to the present invention, an EXOR gate utilizing Josephson can be obtained with an extremely simple structure.

Note that with this device, it is preferable to first apply a signal, then apply a bias current and read the output. This is especially true when signal currents 1H1 and IH2 flow together, and if there is a time difference between them, a voltage state will occur when one signal current flows, and this will be held even when the other signal current flows. Not canceled (cancellation is done by reset)
It is from.

[Brief explanation of the drawing]

FIGS. 1A, b, c, and d are equivalent circuit diagrams, graphs, cross-sectional views, and schematic plan views illustrating a Josephson element with a grounded counter electrode. FIGS. 2A and b are schematic diagrams illustrating an embodiment of the present invention. A plan view and a side view are shown.

Claims (1)

[Claims] 1. A T-shaped base electrode is provided on the ground plane via an insulating layer, a counter electrode is provided that extends above the horizontal arm of the T-shape and also serves as a signal line, and the counter electrode is provided at both ends of the horizontal arm. A Josephson junction is formed between the Josephson junctions, and a protruding part of the opposing electrode opposite to the vertical leg of the T-shape in the middle of these Josephson junctions is connected to the ground plane. 1. An exclusive OR circuit device using a Josephson element, characterized in that the legs serve as bias current input and signal output terminals, and both ends of the counter electrode serve as signal input terminals.