JPS602798B2 - superconducting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting logic circuit element whose latched state can be controlled by direct current.

Conventional logic circuits using Josephson junctions are often latching circuits, and when the gate junction is in a voltage state (on),
To reset to zero voltage state, the gate current must be cut off primarily. Figure 1A shows one of the basic circuits of a Josephson junction when there are three inputs. In the figure, V is the power supply, L is the load element, and 1, 12, and 13 are the inputs flowing to the control line. . The x mark indicates a Josephson junction. The figure shows the current-voltage characteristics of the gate, and a shows the operating straight line. Usually, the value P is smaller than the maximum value lo of the Josephson current lc. In the circuit shown in Figure 1A, the input current is 1.
When the maximum value of the Josephson current becomes smaller than Po due to the magnetic field created by , , 12, 13, a voltage state occurs along the arrow in the characteristic curve in the figure, and the intersection with the operating line P,
I settled on. As shown in FIG. 1A, when controlling by current injection instead of magnetic field control, if a current larger than (lo-Po) is injected, the characteristic curve similarly enters a voltage state along the arrow. lm at the beginning of Figure 1 is the current at which the junction is reset to a zero voltage state when the current decreases by 4. Therefore, since the point P is a point where the current is larger than lm,
Unless 1g is set to 0, it cannot be reset to P6 point.
For these reasons, a method of supplying AC power at 1 g has been considered, but in consideration of power supply loss, DC power supply is preferable. Therefore, M. recently announced a non-latch circuit.

This principle is a method in which a resistor is provided in parallel with the gate junction, and equivalently the edge m of the mouth in FIG. 1 is made larger than the point P. However, in this case, the number of parallel resistors increases, and
This has the disadvantage that the circuit cannot be latched freely. In order to eliminate these inconveniences of Josephson junctions, the present invention aims to provide a superconducting device in which latching and non-latching states can be freely selected using a control current.

In order to achieve the above object, the present invention comprises a rectangular superconducting polycrystalline film having Josephson junctions at grain boundaries, a pair of opposing control terminals connected to this, and another pair of opposing gate terminals. By flowing a current higher than the maximum Josephson current to the gate terminal and simultaneously controlling the current flowing to the control terminal, superconductor energy
The gist of the invention is a superconducting device characterized by returning to a deprived voltage state by cutting the latch L or control current to a voltage that is an integral multiple of twice the gap. Next, embodiments of the present invention will be described with reference to the accompanying drawings.

It should be noted that this embodiment is merely an example, and it goes without saying that various changes and improvements may be made without departing from the spirit of the present invention. Figure 2 shows the basic configuration of the present invention. Consisting of a conductor polycrystalline thin film, 3, 3', 4
, 4' are two sets of electrode terminals made of superconductors provided on opposite sides of the thin film.

A superconductor polycrystalline thin film having a Josephson junction between two grain boundaries is produced by forming a thin film of an oxide superconductor BaPbrxBix03 by sputtering or the like, as described in the Japanese Patent Application No. 11821/1983, for example. 500 to 0 in medium or oxygen
It is formed by heat treatment at 650°C for 3-1 hours.

In this case, a structure as shown in FIG. 3A is obtained in which Josephson junctions are formed around crystal grains having an average grain size of 2500 Å. In the figure, 5 indicates a crystal grain of the superconductor. FIG. 4A shows the voltage-current characteristics of the present invention. A current of 1 g is passed in the direction of AA in Fig. 2 (in this case, lc = 0).When the current of 1 g becomes larger than the maximum value L of the Josephson current, the element enters the voltage state (2△/
e) (here, △ is the superconductor energy gap, and e is the electron charge.) The current changes to curve 8 and decreases to 0.
The voltage changes along the curve, and when it reaches the minimum value lm of the voltage state, it returns to the ambient voltage state. If a DC control current lc flows in the BB direction above a certain threshold value lc, the curve 8 in Figure 4A changes to a curve 8', and the current changes to 1'm, returning to the atmospheric voltage state. do.

The position of this 1'm is determined by the width of the electrode terminal in the BB' direction, and if the width is equal to or greater than the terminal in the AA' direction, 1'
'm, becomes equal to -lo. Therefore, the width of the electrode in the BB direction is smaller than the width of the electrode in the AA' direction.
This is important. Furthermore, the width of the 0 electrode in the direction of BB' and AA'
By changing the ratio of the width of the electrode in the direction of , the value of the current 1'm, shown in FIG. 4a, can be adjusted. Current 1g is 1' larger than 1g. If you exceed l
When c=0, the voltage at the bottom of Figure 4 is reduced, and when the current is reduced, it changes to curve 9 and returns to the zero voltage state through lm2.

1g>1'.

Then lc>lc, or 1g>lo then lc>lc2(l
When the second threshold (c2>lc) is reached, the curve 9 changes to 9', and as the current decreases it reaches 1'm2, from which it returns to the zero voltage state. At this time, 1'm2 is also rm, and similarly BB
depends on the width of the electrode terminal in the ′ direction. When the current 1g is further increased, the voltage state changes to 6△/e, which is an integral multiple of 2△/e.

If the direction of 1g is reversed, the voltage appearing at the AA' terminal will be reversed, as shown in Figure A and B. Figure 4 A. The characteristics of the mouth are A. A logic switch that allows you to freely choose the sowing state;
It can be applied to Sochi elements.

This will be explained with reference to FIG. 4A. First, set the bias current at the operating point Po, and select the load resistance so that the load Ta line becomes P.

Then, when an input signal is applied to AA' and the current 16 exceeds lo, or the control field causes the Josephson maximum current to be less than lo, the device transitions to the voltage state. l
If c=0, after the input pulse leaves ZO, lm. It is set by Po in the zero voltage state. In other words, a non-latching operation is performed o On the other hand, lc>lc
, then after reaching the voltage state, it changes along the curve 8', settles at the intersection point PI with the load straight line Z, and is latched to the voltage state.

To release from the latched state, lo should be set to 0. If the input current becomes even larger, it is possible to move to the state of voltage 4△/e (curves 9 and 2 and 9') and further to the voltage state of 4△/e as shown in Figure 4B. It is.

It is convenient to determine a specific value of n based on the value of lc. For example, when n=2, lc2<lc<lc3
The voltage is set to 4△/ by the gate bias power supply.
If you make sure that the value is not greater than 2, e will work reliably. The above is an explanation of the operation, and below, the physical basis of this operation will be described with reference to FIG. Figure 3A is an enlarged view of 2 in Figure 2, where 5 is a superconductor crystal grain.

The mouth is a crystal grain that is three times larger, and a Josephson junction is formed around it. Current 1 is applied to the thin film 2 part.
When g and lc are injected, currents ig and ic flow in directions perpendicular to each other in one crystal grain. The positions of the Josephson junctions crossed by ig and lc are different. If la and ib are smaller than the maximum Josephson current ic in each junction, there is no mutual interference between them.

However, for example, when ic becomes more than io, the part 6 in the figure becomes a voltage state, and microwaves with a frequency of 4△/h (△ is the energy gap of the superconductor and h is Planck's constant) are generated. . (B, D, JOSephS.

n''Coupled SuperConductOG
''Rev, ofModemPh$ics, Jan female r
y1964, PP216-22 Foundation). This microwave energy is propagated as shown in Figure C and generates a voltage 2Δ/e in the direction in which the current ig flows. When lc is increased by more than lc, the crystal grains in this state become 2 as shown in Figure 2.
, and as a result, a voltage 2Δ/e is generated in the AA' direction, that is, at the terminals 3 and 3'. l
When c increases to lc2 or more, crystal grains in the voltage state are arranged diagonally in two rows, and Vg becomes 4Δ/e. The voltage at the junction is 2
When Δ/e is an integral multiple, the aforementioned Josephson's theoretical current can take any value between -lc and lc.

This is the reason why the 1g-Vg characteristic of flowing lc at the mouth in Figure 4A changed. However, the second
If the terminal width in the BB' direction in the figure is narrower than in the AA' direction, the absolute value of the lower limit of the current in the voltage state will be smaller than lo. [Example] BaPq~Bix03 (0.25<×
As described in Samurai Application No. Sho 56-11821, which shows an example of 0.35), a thin barrier just like a Josephson junction is formed at the grain boundaries of a polycrystalline thin film of this material. .

Such a tendency becomes remarkable when the composition x>0.25. In the example, x: 0.3 was selected. The thickness of the thin film is 2000~7
Although 000A is appropriate, 5000A was chosen here. The superconducting transition temperature Tc is approximately 2△/e at x=0.3
is 2.2hV. The preparation of the superconducting thin film is based on the mother (
Pb ship Bio. 3) 0,. Using a target with a composition of 504, the mixed gas pressure of 50% each of argon and oxygen was 6 x 10.
2Ton, plate voltage 1. Approximately 260q in narrow V
A thin film was formed by sputtering on a No. 0 sapphire substrate, and heat treated in oxygen at 560 oo for about 1 hour.

The average diameter of the crystal grains was 2400A. To etch this thin film, use HC and 04 (60.0 to 62.pi○) as described in Japanese Patent Application No. 56-9569.
Etching with a 0 solution in which 20 to 60% by volume of solution) was added to water, and 1 to 0.3% by volume of HC〆 (35.0 to 37.0% solution) was added to this solution. By doing this, the size is loAm× as part 2 in Figure 1.
Two types of patterns were formed: 10 m and loAm x 20 m. Next, BaP was used for the electrode terminals and wiring patterns.
Bo. 7 is io. A composition of 2503 was selected.

In a thin film with this composition, the critical current density is four times larger than the maximum Josephson current in the thin film 2 portion of FIG.
The electrode terminal and wiring section are maintained at zero voltage. The thin film sputtering conditions and heat treatment conditions are the same as above. To form a pattern in this case, a pattern for the electrode terminal and wiring part is formed using a positive resist with the trade name AZ1350J (a pattern excluding the resist in that area), and the above composition is sputtered on top to remove the resist. The device shown in Figure 2 was completed. In Figure 2, the line width in the direction of AA' is 10 mm.
and 201 m, and the width in the BB direction was 10 m. The maximum Josephson current lo of this element is 10 m
70 Buddha A at 20 m, 140 Buddha A at 20 m, 2△/e is 2.2 hV, lc, = 140 Buddha A (line width 10 Buddha m), l
c2-160muA.

If the structure shown in FIG. 2 is constructed using materials other than those in the example, the characteristics shown in FIG. 4 can be achieved.

As mentioned above, according to the present invention, not only can the latch state of the element be freely controlled by an external current, but also the voltage of the gate voltage state can be freely obtained, which is different from the conventional Josephson method. It provides a greater degree of freedom in circuit design than bonding.

Furthermore, since the manufacturing method of the element of the present invention is very simple, it has the advantage that a device with the above-mentioned sophisticated functions can be manufactured at low cost.

[Brief explanation of the drawing]

Figure 1 shows the characteristics of a conventional Josephson junction; Figure 1A shows the basic circuit of a magnetic field controlled type using a conventional element; Figure 2 shows a superconducting device according to the present invention; Figure 3A-2 show the physical characteristics of the operation. Explanatory drawings, Figure 4 A, and mouth indicate the characteristics of the present invention. 1... Base plate, 2... Superconductor polycrystalline thin film with grain boundary Josephson junction, 3, 3', 4, 4 '... Electrode terminal made of superconductor, 5... Crystal particle ' 6... Crystal grain boundary Josephson microwave generation part, 7... Part that absorbs microwave energy and generates voltage, 1g... Gate Current “lo・
...Maximum Josephson current, Po, P,...Operating point, lc
...control current, 8,8'9,9'...curve, lm,,lm2
, 1'm,, 1'm2...Minimum value of current in voltage state. 1st
Figure 2 Figure 3 Figure 4

Claims (1)

[Scope of Claims] 1. A rectangular superconducting polycrystalline film having Josephson junctions at grain boundaries, a pair of opposing control terminals connected to the rectangular superconducting polycrystalline film, and another pair of opposing gate terminals, By flowing a current higher than the maximum Josephson current to the gate terminal of the
A superconducting device characterized by latching to a voltage that is an integral multiple of twice the superconductor energy gap, or returning to a zero voltage state by cutting off the control current. 2. The length of the side of the thin film of the Josephson junction in the direction of the control current is made smaller than the side in the direction of the gate current,
2. The superconducting device according to claim 1, wherein the minimum current in the voltage state of the gate in the latched state is adjusted by the ratio of the two sides. 3 BaPb in a polycrystalline thin film with grain boundary Josephson junctions
_1_-_xBi_xO_3 (0.1<x≦0.35)
3. The superconducting device according to claim 1, wherein a superconducting electrode material is used as the electrode.