JPS63261885A - Three-junction dc squid gate - Google Patents

Abstract

PURPOSE:To obtain high sensitivity and the wide operation margin, by specifying the relations of an inductance and a critical current value in a first branch line, a critical current value in a second branch line, and an inductance and a critical current value in a third branch line. CONSTITUTION:A superconducting closed circuit 13 is constituted of a first, a second and a third branch lines which are connected to a gate current line 11 at both ends and in the relation parallel with each other. In the first branch line, the series circuit of an inductance L1 and a Josephson element J having a critical current value Io1 is arranged. In the second branch line, only a Josephson element having a critical current value Io2 is arranged. In the third branch line, the series circuit of an inductance L2 and a Josephson element having a critical current value Io3 is arranged. These inductances L1 and L2 constitute an asymmetrical 3-junction DC SQUID gate 10 with which a control current line 12 is coupled by magnetic induction and equations (1)-(4) are satisfied. A sufficiently wide operation margin can be obtained, while high gain or high sensitivity is maintained.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a pressure junction DC skid gate using the Josephson effect, and is particularly improved to satisfy both high gain (high sensitivity) and wide operating margin. This paper relates to an asymmetric three-junction DC skid gate.

<Prior art> The DC skid gate is known as one of the Josephson switching gates, but in order to achieve a high r, Ik r+” gain, recently, instead of the two-junction mold that was initially developed, a three-junction type, That is, devices using three Josephson elements are now exclusively used.

The basic physical configuration of such a three-junction DC skid gate is shown in Figure 1.2, and the pressure junction DC skid gate IO shown in Figure 1 is called a center foot type in terms of the gate current supply method. The one shown in Figure 2 is called a split foot type.

Both types of skit games 1-10 have their structure and 1
Since the 00-like action itself is well known, simple 7F,
To explain, in the center foot type pressure junction DC skid gate 10 shown in the first diagram, first, regarding the supply line 1+ with a gate current of 1 g, between the circumscribed reading points p, , p2 of the positive electrode side and the negative electrode side (ground side). Inserted superconducting closed circuit 13
This superconducting closed circuit 13 also has points p, , p
Three branch lines inserted in parallel between 2+31
, ]: IC, 13R.

In the figure, the branch line 1''llc shown in the center only contains the Josephson element, I2, but the other two branch lines !3L and 13n, which have a value series relationship with it, contain the Josephson element and I2, respectively. It includes a series circuit of Josephson elements J, , J, and inductances L1, L2, and these inductances L1, L2 are magnetically inductively coupled to inductances Lc+, L(+2) formed in the control current line 12. There is.

However, each inductance L, , L2: Lc,
, I, c2 are generally formed by appropriately setting the length and width of the line, and the inductances L1, L2; l, are shown separately in the figure. l 1Llc
2 are often actually formed as a series of significant line width portions. Note that the resistors R and R2 are damping resistors for suppressing resonance, but may be omitted depending on the case.

In such a pressure junction DC skid gate 10, when a :v control current 1c is passed through the control current line 12 while a gate current +g is passed through the gate current line It, the interaction between the two causes a change in the superconducting closed circuit 13. Motoko Josephson J, ~J
3 switches into a voltage state according to a predetermined sequence, so that the previously zero voltage state as a skid gate transitions to a voltage state, allowing the gate current 1g to be commutated towards the load resistor R,.

This voltage state also changes to iQ and a zero voltage state by returning the control current IC to zero and returning the gate current 1g to zero, and can be reset as a gate.

In the split feed type gate lO shown in FIG. Correspondingly it, (I
Inductive coupling inductance LCI of control current line 12, 1
=C2 is also the divided series inductance LC
After the connection point of the gate current line 11 and the point configured as I l + Lc12 and Lc21 + Lc22 are connected via separation resistors, the inductance L+
l 1LI2: Each connection point PII of L211L22
Although it is different from the center feed type skit gate in that it is +P12, the above explanation can be used as is for the basic operation, and the difference is mainly seen in the threshold characteristics described below.

However, the pressure junction DC skit gate 10 shown in FIG. L2 further includes a built-in Josephson element, 1. ,
J2. Based on the critical current value relationship of J3, it can be classified into symmetric type and asymmetric type.

Symmetrical type means left and right branch lines +3L, l: critical current value I of Josephson element J, , J3 in IR. l+'03
are equal, and the critical current value I of the Josephson element J2 in the central branch line +3C. The asymmetric type is the critical current value of the left and right Josephson elements J, , J3. l+'03 both mean different things. If expressed as a formula, the symmetric type is the following formula (■), and the asymmetric type is the following formula (■).

101:102:[03=1:N:1 ・”-■1
01 :+02 :+03 =1 :N:K
"...-■ In this case, the critical current value I is expressed by the normalized number "1". 1 can be expressed by the unit current value I. That is, ■.l"10... ■It is.

<Problems to be Solved by the Invention> For example, when comparing the center feed type shown in the first figure and the split feed type shown in the second figure, there is no debate as to which one is more practical in terms of physical structure. It's already been done. In conclusion, the center foot type skid gate shown in Figure 1 is considered to be more promising in the future. Second
Although the split feed type skid gate shown in the figure has some advantages in terms of characteristics as described later,
This is because the structure is too complicated and the disadvantage is that it is considerably large.

However, from a different perspective, there are still problems that must be resolved even if the structure of Izuku is adopted.

As is well known, the three-junction DC skid game (3-junction DC skid game) IQ with the configuration shown in L2 adopts a symmetrical configuration according to the formula 0 described above,
For example, each Josephson element? −J, ~J3 critical current value 1
The relationship of G+ = ■02 + 103 is 1:2:1 (N=
When 2) is selected, the threshold characteristic typically becomes as shown in the third diagram.

This property is actually shown in the skid configuration shown in the first diagram as LIO = 0.2: 19 flux quanta;
6.21pH; L2 = 6.21pH; 1o+=Io: IO3-210; 1 (13=10) Many plot points were traced freehand based on the computer simulation results obtained as follows.

However, this tendency of the characteristic curve is not limited to this specific example, but is common to symmetrical types that adopt a critical current value relationship of 1:2:1. However, the overall trend is similar.

The problem common to the symmetrical type motors that can be seen from Fig. 3 is that the slope of the characteristic curve indicated by the point ■ in the figure cannot be very steep.

This shape is exactly like the ridgeline of a gentle mountain, but as is well known, such a gentle slope is disadvantageous in gaining current gain (increasing sensitivity). means.

Therefore, as a method of aiming at improving sensitivity while adopting such a symmetrical type, for example, in the skid gate 10 having the configuration shown in the first diagram, there has been a method of increasing the values of the inductances L+ and L2 in the superconducting closed circuit 13. It was taken.

By doing this, the slope of the slope part ■, which is an important part in terms of dynamic characteristics, certainly became steeper, and it seemed that higher sensitivity could be achieved to some extent, but a new problem occurred, as indicated by the arrow ■. As shown, the distance to the next peak on the control current axis (correctly, the control current ratio Tc/Io axis because it is normalized by the unit current value l) is becoming shorter, and the top of the mountain is indicated by the arrow ■ This resulted in a decrease as shown by , and conversely, the valley part rose as shown by the arrow ■.

The existence of neighboring peaks is, of course, due to the quantum nature of magnetic flux, and they line up repeatedly at predetermined intervals, but when a phenomenon occurs in which the gaps between peaks become narrower, the peaks also fall, and the valleys become shallower. , which continues to narrow the operating margin M1.

The operating margin is well known in itself, but simply put, it is the vector sum of the gate current 1g and the control current [c that crosses the threshold curve part 2 and allows the gate to transition from the zero voltage state to the voltage state. It shows the distribution range of the set of values of 1c, and is generally represented by a rectangular area as shown in the figure, but of course it is better to make it as wide as possible.

However, for example a third
In the illustrated characteristics, the operating margin M1 is only about ±32% to 33% at most.

On the other hand, the split-feed type three-junction DC skid gate IO shown in Figure 2 was actually proposed to improve this point, and the drop in the peak and rise in the valley of the threshold curve due to the increase in inductance are reduced to some extent. It can be suppressed.

However, even in this split-feed type skid gate 10, it is not possible to prevent the peaks from approaching each other as the inductance increases, and the degree of the peak-to-peak approach increases.

Therefore, when viewed as the operating margin Ml, the width in the direction of the arrow {circle around (2)} tends to be extremely narrow, and in the end, only the same operating margin as above was obtained.

In view of these circumstances, a further proposal has been made in the past, which is the asymmetric configuration described above.

In other words, the critical current value of the three Josephson elements is 1o+
, roz , I. The relationship of 3 is based on the above-mentioned formula 0, for example, 1:2:2 (N=2.=2).

In this case, the curve tendency of the threshold characteristic is typically as shown in FIG. 4.

As you can immediately see, the slope of part ■ is quite steep. However, the problem is that the top of the mountain is the gate current axis (similarly, more precisely, the gate current ratio Ig/l o'l't
) If it is off the top and along the ITD control current axis as shown in the diagram, it is moving in the stone direction (2).

This ultimately narrows the effective operating margin. This is because the portion above the gate current axis intercept (approximately point 41o in the illustrated case) cannot be used.

Moreover, even with such an asymmetrical configuration, inductance and 2. Similarly, if the values of shi2 are increased, arrows ■, 0. In the split-feed type, the aforementioned problems as shown by arrow (■) occur, and the fundamental problem cannot be solved.

However, in view of the drawbacks of the various conventional examples mentioned above, it can be seen that this is a desirable result. First of all, the slope of the part ■ on the threshold curve is steep, and the mountain is high.
The valley is deep and separated from the neighboring peaks, allowing for a large operating margin.

It is also important not to rely solely on designs that increase inductance in order to satisfy the above conditions. This is because an increase in inductance not only tends to cause the above-mentioned drawbacks, but also leads to an increase in physical and mechanical structure dimensions, which is undesirable.

The present invention was made from this point of view, and its main purpose is to provide a pressure junction DC skid gate that can ensure high sensitivity (high current gain) and a wide operating margin.

Means for Solving the Problems> To achieve the above object, the present invention provides an asymmetric three-junction DC skid gate having the following configuration.

It has a superconducting closed circuit composed of first, second, and third branch lines that are connected to the gate current line at both ends and are in a parallel relationship with each other, and there is an inductance L1 in the first branch line. Critical current value I. Understand that the series circuit of 1 Josephson element has a current value I in the above second branch line. A series circuit of an inductance L2 and a Josephson element with a critical current value of 103 is provided in the third branch line.
, , L2 is an asymmetric three-junction DC skid gate with a control current line or magnetically inductive coupling: Ll>L2 ・
...■101<102 ...
...■101 <103 ...
...■1, +'lo+= L2"103
..."■Asymmetrical three-junction DC skid gate.

<Operations and Effects> Also in the configuration of the present invention described above, equations (1) and (2) are conditions that have already been adopted in the conventional asymmetric three-junction DC skid gate described above.

However, the configuration requirements of Type 0, namely the left and right branch lines 1, . 1
The present invention was the first to propose that the inductances L1 and L2 in 3R themselves have asymmetry, and in the past, 1.1 = L2 in all cases, regardless of the absolute value. .

However, when the present invention is applied to the center-feed type pressure-bonded DC skid gate shown in the first figure, the first
The inductance in the figure is 1. 2 directly corresponds to the inductances L, , L2 in the gist of the present invention.

On the other hand, when the present invention is applied to the split feed type pressure junction DC skid gate shown in FIG.
++ *L12; Since L211L22 are each connected in series, the inductance L in the configuration of the gist of the present invention,
, L2 therefore has the following relationship.

Ll=LIl+L12 ・・・・・・■
L2= L21 + L22
......qΦIn any case, if an asymmetric three-junction DC skit gate is configured according to the conditions introduced by the present invention as described above, the results will also be seen in the representative embodiments described below. Admittedly, it is highly desirable.

To put it simply, the slope of the slope of the threshold curve, which is important in terms of dynamic characteristics, becomes steeper, and despite this, the peak or head is partially high.
Valleys can also be kept to a suitable depth, and above all, it is possible to effectively prevent adjacent mountains from coming close to each other. The position of the peak can also be placed approximately above the gate current level.

As a result, the operating margin becomes sufficiently wide while maintaining high gain or high sensitivity, and even if you choose a modest one from various experimental results that shows a small degree of improvement in characteristics by the present invention, you can earn about ±42%, for example. It has been extremely successful. A 10% improvement over the conventional example is a considerably large improvement, and in reality, a wider operating margin can be obtained.

As described above, the present invention specifies and specifies one direction as this type of asymmetric three-junction DC skid gate, and is a great contribution to the field.

In addition, when applying the present invention to a split feed type three-junction DC skid gate, in addition to the above-mentioned requirements according to the present invention, it is preferable that Io+-L++=L+z,
Io2...01oz・L2+=L
By adding the condition z21o:+''...@ as an example, higher sensitivity and wider operating margin can be obtained.

<Example> As an example according to the gist of the present invention, a case will be described in which the center feed type pressure junction DC skid gate IO shown in FIG. 1 is adopted as the physical configuration.

Specific values according to the 0-0 formula described above are as follows.

L [to O= 0.2; L, : 6.21911; L2= 3.1051) II; 1o+=Io; 1.2= 21o; l03=21°= where - magnetic flux quantum @, = 2.07x 1O-15
Wb: This condition indicates that the inductance L2 of the branch line +3H in Fig. 1 is half the inductance of the branch line 13L, but its characteristics are similar to many computer simulation results. This is shown in Figure 5, which is a free hand trace of the plotted points.

The value of the maximum gate current rg that can flow through this skid gate when the control current 1c is zero is determined by the above condition 1o+=To
; 102= 21o; +o*= 21o As is clear from
In the characteristics shown in the figure, the maximum gate current value is extremely close to that value, about 4.6Io, and on the other hand,
The valley is 1 minute deeper, 1.8+. It is kept to a certain extent.

Also, the control current that appears repeatedly as the magnetic flux quantum becomes 2%, 3+o,...! The distance between the peaks of the threshold curve along Il[h (rc/10 axis) is also quite large, and no adjacent peaks appear within the illustrated range.

Therefore, the operating margin M2 is sufficiently wide that the right hand is missing, and the slope of the threshold curve is also at a satisfactory level.

In fact, the effects of the present invention have been confirmed in experimental examples based on other specific numerical values, and at least about ±42% can be secured.

Furthermore, even in the case of the three-junction DC skid gate according to the split feed type configuration shown in FIG. In the case of the feed type, as already mentioned in the section on action, L, = L1, +L, 2...■
L2=L2. +12□ ......In addition to satisfying the conditional expressions ■ to ■ of the present invention as [phase], IO+"Lll"L12.102 ...
・・■I02・L21"L22・ro3・
...If the @ condition is taken into account, collapse of mountains can be particularly effectively suppressed.

In addition, according to the present invention, not only improvements in electrical characteristics as described above but also effects in physical dimensions can be obtained as a result. As seen in the examples above, Ll>
In this example, L2=L,/2)
This is because the area required for forming the inductance for the smaller L2 can be largely saved. In fact, in this type of circuit, the inductance portion occupies the largest area, so this effect is also extremely significant.

[Brief explanation of drawings]

Figure 1 is a basic configuration diagram of a center feed type pressure joint DC skid gate, Figure 2 is a basic configuration diagram of a split foot type pressure joint DC skid gate, and Figure 3 is a conventional symmetrical configuration diagram. A typical threshold characteristic diagram seen in a three-junction DC skid skate; FIG. 4 is a typical threshold characteristic diagram seen in a conventional three-junction DC skid skate configured asymmetrically; FIG. FIG. 2 is a typical characteristic diagram of an I/IA example showing the tendency of the threshold characteristics of the asymmetric pressure-jointed DC skid cage. In the figure, IO is a three-junction DC skid gate, 11 is a gate current line, 12 is M[open current line, 13 is a superconducting closed circuit, J, , +2. , +3 is a Josephson element, L,
, L2 is inductance, Io+ 1102110
:l is the critical 7 current value of each Josephson element. Designated agent Agency of Industrial Science and Technology Figure 3 Ic/I. Figure 5

Claims (1)

[Claims] A superconducting closed circuit is connected to the gate current line at both ends thereof and is configured of first, second, and third branch lines that are in parallel with each other, and the first branch line Inside is a series circuit of a Josephson element with an inductance L_1 and a critical current value I_0_1, and in the second branch line is a series circuit with an understanding current value I.
Only the Josephson element _0_2 is used, and the inductance L_2 and critical current value I_0 are included in the third branch line.
An asymmetric three-junction DC skid gate comprising a series circuit of _3 Josephson elements, and a control current line is magnetically inductively coupled to the inductances L_1 and L_2; L_1>L_2... (1) I_0_1<I_0_2...(2) I_0_1
<I_0_3...(3)L_1・I_0_1=
Asymmetric three-junction DC skid gate with L_2・I_0_3...(4).