JPS6124289A - Superconducting amplifying element - Google Patents

Abstract

PURPOSE:To extend the margin of operation, and to simplify circuit constitution by connecting a first strip line to a second strip line through a Josephson tunnel junction having parallel relationship with a resistor and controlling the characteristics of the Josephson tunnel junction by injecting quasi-particles to the first strip line. CONSTITUTION:Nb thin-films are evaporated onto a sapphire substrate 10, and a pair of strip lines 12, 14 divided on their midways are formed through dry etching. An electrode 20 for injection quasi-particles crossing at right angles with the strip line 12 is shaped onto the narrow section 16 of the strip line 12. The electrode 20 for injecting quasi-particles is constituted by an Nb evaporating film, and a tunnel barrier 22 is composed of a plasma oxide film in Nb, thus forming a tunnel type Josephson junction. An insulating layer 24 is shaped and windows are formed onto the strip lines 12, 14, and an upper electrode 28 is shaped so as to fill the windows. Current-voltage characteristics between the strip lines 12, 14 are controlled by changing injection currents Ic from the electrode 20 for injecting quasi-particles.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a switching element having an amplification function that can be used in a superconducting integrated circuit.

BACKGROUND OF THE INVENTION Conventional superconducting integrated circuits use tunnel-type Josephson junctions as basic units, which are combined to form logic circuits or memories.

The single tunnel type Josephson junction exhibits current-voltage characteristics with hysteresis as shown in FIG.

That is, it exhibits a DC Josephson current characteristic as indicated by reference number 1 and a quasi-particle tunneling current characteristic as indicated by reference number 2.

Therefore, by providing a load straight line as shown by reference numeral 3 in FIG. 4 and using the transition (switching) from zero voltage state 4 to finite voltage state 5, logical operation is possible. If these two states correspond to the states "0" and "1", it is also possible to use it as a memory.

The time required for transition between two states of this tunnel-type Josephson junction is as short as about 10 psec or less, and therefore it was expected to be used as an element for ultra-high-speed computers.

However, this single tunnel type Josephson junction corresponds to a two-terminal element, that is, a diode in terms of semiconductor elements, and does not have a current or power amplification effect. For this reason, the operating margin of circuits such as logic gates and memory is limited to MOSFETs.
Tunnel-type Josephson junctions are nearly an order of magnitude smaller than semiconductor circuits using ETs or bipolar transistors, and require extremely difficult control of element dimensions and characteristics to realize LSIs, resulting in extremely low manufacturing yields. It was there.

Furthermore, the switching operation of a circuit using a single tunnel Josephson junction is a latching operation, and in order to return from a finite voltage state to a zero voltage state, the current flowing through the circuit must be reset to zero. For this reason, when designing an LSI or the like, there is a drawback that the circuit configuration is more complicated than that of a semiconductor circuit.

On the other hand, as a three-terminal superconducting element that performs non-latching operation and has current and power amplification functions, it has a structure with double stacked tunnel junctions, and quasi-particles are implanted into the intermediate superconductor thin film. QUITBRON which controls the characteristics by
(S. Paris et al: 1131JT
rans.

Magn, MAG-19, 1293 [1983]) has been invented.

However, in this 0UITBRON device, it is necessary to strictly control the crystallinity of the intermediate superconductor thin film and the upper and lower tunnel barrier layers in contact with it. However, the manufacturing yield of devices is low.

Problems to be Solved by the Invention As mentioned above, conventional two-terminal superconducting elements have a small operating margin, no current or power amplification effect, and
A reset operation is required for latching operation.On the other hand, the three-terminal superconducting devices that have recently appeared, which have current and power amplification effects, require only a few materials for the intermediate superconductor; There were problems such as poor manufacturing yield.

Therefore, the present invention has current and power amplification functions, exhibits non-latching switching operation, is not limited to the materials that can be used, and can further expand the operating margin of the circuit and simplify the circuit configuration of integrated circuits. It is an object of the present invention to provide a switching element for a superconducting integrated circuit.

According to the present invention, a means for solving the problem is a strip line made of a first superconducting material and a first strip line connected to the first strip line through a resistor. and a strip line made of a superconducting material of 2, wherein the first IJ tube line connects to the second strip line through a Josephson tunnel junction in parallel relation to the resistor. a superconducting amplification element, wherein the characteristics of the Josephson tunnel junction are controlled by injecting quasiparticles into the first strip line. provided.

In one embodiment of the present invention, the first strip line described above is connected to the quasi-particle injection electrode via a second Josephson tunnel junction formed on the first strip line. The characteristics of the Josephson tunnel junction are controlled by injecting quasiparticles into the first strip line from the quasiparticle injection electrode.

In another embodiment of the present invention, an optical waveguide is provided to irradiate a part of the first strip line with light, and by irradiating a laser beam through the optical waveguide, the first strip line is irradiated with a laser beam. The properties of the Josephson tunnel junction are controlled by injecting quasiparticles into the stripline of No. 1. and,
The optical waveguide may be an optical fiber or a thin film optical waveguide.

The superconducting amplification element constructed as described above is made by injecting quasi-particles into the first strip line, which includes a resistor connected in parallel to a tunnel-type Josephson junction, to make that part normal conductive. , and as a result, the current-voltage characteristics of the tunnel-type Josephson junction.

This results in a non-latching switch operation and current and power gains not found in conventional single tunnel Josephson junction devices.

Furthermore 1. -1. The materials constituting the strip wire in which It particles are implanted are Nb, Pb-B1 alloy, NbN,
Nb5X (X-Ge.

Ga, A1. Sn, Si), V3Si, BaPb
+-xB+x○3 can be configured, and high-speed switching operation is possible.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Example 1] Fig. 1 is a cross-sectional view of one embodiment of the superconducting amplifying element according to the present invention, and Fig. 2 is a cross-sectional view showing the planar positional relationship of each element forming the superconducting amplifying element. FIG.

As shown in FIG. 1, the illustrated superconducting amplifying element consists of a pair of strips on a sapphire substrate IO with a half-parted shape.
It has IJ tube wires 12 and 14. These strip lines 12 and 14 are formed, for example, by forming a Nb thin film with a thickness of 30 Ωm by vapor deposition, and then dry etching the vapor deposited film.

The separation interval between the strip lines 12 and 14 is 3 μm, and one strip line 12 is separated by 3 μm from the separated portion.
The narrow portion 16 has a width of m and a length of 12 μm, and the other portion has a width of 8 μm. Further, the other strip line 14 has a uniform width of 8 μm from the dividing portion.

A resistor 18 is formed at the divided portion of the strip line, and connects both the strip lines 12 and 14. This resistor 18 is made of, for example, Au formed by lift-off, and has a width of 3 μm, a length of 3 μm, and a resistance value of 0.05Ω.

A quasi-particle injection electrode 20 that is perpendicular to the strip line 12 is formed on the narrow portion 16 of the strip line 12 with a tunnel barrier 22 interposed therebetween.

The quasiparticle injection electrode 20 is made of a Nb vapor deposited film, and the tunnel barrier 22 is made of a Nb plasma oxide film, and has a tunnel type Josephson junction (Josephson current density of 50/cnt) of 3 μm to 84 μm.
) is formed.

An insulating layer 24 made of SiO2, for example, is formed thereon by, for example, lift-off.

Then, the insulation layer 24) IJ tube wires 12 and 1
A barrier layer 26 is formed on the IJ tube wire 12 located in one of the windows. Furthermore, an upper electrode 28 is formed so as to fill these windows.

The barrier layer 26 is formed, for example, by plasma oxidation of Nb, and the upper electrode 28 has a thickness of 0.7 μm.
It is formed by depositing a Pb-B1 alloy of m and lift-off.

Thus, a tunnel-type Josephson junction (
Josephson current density: 50KA/cn),
A junction is formed on the stripline 12 and a contact for contacting the stripline is formed on the stripline 14 .

The current-voltage characteristics between the strip lines 12 and 14 could be controlled by changing the injection current 1c from the quasiparticle injection electrode 20 of the superconducting amplification element configured as described above.

FIG. 3 is a graph showing the current-voltage characteristics of the superconducting amplification element having the above configuration. As shown in Figure 3, the injection current 1
When c is sufficiently small, the current-voltage characteristic of the superconducting amplifying element is a curve in which the tunnel type Josephson junction has a low resistance and does not exhibit shunted hysteresis. When the injection current 1c is increased, the gap parameter of Nb in the strip line 12 under the quasi-particle injection electrode 20 decreases monotonically and eventually becomes normal conductive, resulting in high resistance, and the device characteristics change to normal tunneling. The result is a curve with hysteresis of a Josephson type junction.

Each intersection with the load line in Fig. 3 is in the “0” state,
By making it compatible with the "1" state, the above-described superconducting amplification element can be switched.

Furthermore, when the injection current Ic is returned to zero, the current-voltage characteristic returns to a curve without hysteresis, so this switching becomes a non-latching operation.

The maximum current gain of this superconducting amplifying element is 12, and when using the load line shown in Figure 3, the power gain value of 1.2 can be reduced to 1.
! )is. In addition, when the response time of the superconducting amplification element was measured using Josephson sampling technique, it was 110 ps.
A value of ec was obtained.

Note that in the above embodiment, when viewed structurally, the resistor 1
8 and the superconducting strip line including the first Josephson tunnel junction 26 are stacked three-dimensionally, so the parallel parts of the elements can be arranged in a plane. This occupies approximately 1.3 times more area than in the case where the circuit is integrated, and the degree of integration of the circuit can be greatly improved.

[Examples 2 to 9] In the device having the structure shown in FIG.
-=Ge, Ga, 81.5nSSi), V3Si, B
A superconducting amplification device was fabricated using a thin film consisting of aPb,-, Bi, 03.

The following Table 1 shows the manufacturing conditions for each thin film and the TcO values determined by resistance measurement using the four-terminal method.

The strip lines 12 and 14 were formed using the thin films shown in Table 1, and the parameters such as the dimensions of each element and the current density of the tunnel junction were set the same as in [Example 1]. The current and power amplification factors are shown in Table 2 below.

An element using a superconducting strip line made of the materials shown in Table 2 also has the same current and power gain as the superconducting amplifying element using the Nb thin film of [Example 1] for the strip line.
Non-latching switching operation was achieved. Also,
When a pulse with a rising edge of 100 psec was applied to the device and the response was examined, an output waveform with almost the same rise time as the input was observed, and it was found that the response time of the device was 100 psec or less.

[Example IO]

In the superconducting amplification element having the structure of Example 1, a ngle mode is formed in the portion of the superconducting strip line 12 located under the tunnel barrier 22 for quasiparticle injection, the end face of which is brought into close contact with the sapphire substrate 10 from the back surface of the sapphire substrate 10. Semiconductor laser light with a wavelength of 1.3 μm was irradiated using an optical fiber. As a result, 4.6
An output of μW can be taken out through the linear load shown in Figure 3,
A power gain of 1.15 was obtained.

Note that instead of bringing the end surface of the optical fiber into close contact with the back surface of the sapphire substrate 10, an optical integrated circuit is formed on the back surface of the sapphire substrate 10, and the exit of the optical waveguide is connected to a superconducting strip line located under the tunnel barrier 22. It may be made to match directly below the part No. 12.

As described in detail of the invention, the superconducting amplifying element according to the present invention has a current and power amplifying effect that is not found in a conventional single tunnel type Josephson junction. When configured as a logic gate or memory, the circuit can have a large operating margin. Therefore, manufacturing yield is significantly improved.

Furthermore, since the superconducting amplifying element according to the present invention performs a non-latching operation, the circuit configuration when making a logic circuit or a memory circuit using it can be simpler than that of a conventional tunnel-type Josephson junction. It is possible to improve the degree of integration.

Furthermore, since the superconducting amplification device according to the present invention operates by injecting quasi-particles into a part of the superconducting strip line, which can be easily formed with good crystallinity, the device can be formed using various superconductor thin films with good controllability. At the same time, the yield during manufacturing is improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of one embodiment of a superconducting amplification element according to the present invention. FIG. 2 is a plan perspective view showing the planar positional relationship of each element forming the superconducting amplification element shown in FIG. 1. FIG. 3 is a graph showing the current-voltage characteristics of one embodiment of the superconducting amplification element according to the present invention. FIG. 4 is a graph showing current-voltage characteristics of a conventional single tunnel type Josephson junction. [Main reference numbers] 1. DC Josephson current, 2. Quasiparticle tunneling current, 3. Load line, 4. Zero voltage state, 5. Finite voltage state, 10. Sapphire substrate, 12. 14... Strip line, 18... Resistor, 20... Quasiparticle injection electrode, 22...
・Tunnel barrier, 24... Insulating layer, 26... Tunnel barrier layer, 28... Upper electrode Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) A strip line made of a first superconducting material and a strip line made of a second superconducting material connected to the first strip line via a resistor. ,
The first strip line connects to the second strip line via a Josephson tunnel junction in parallel relation to the resistor.
superconducting amplification, characterized in that the characteristics of the Josephson tunnel junction are controlled by injecting quasiparticles into the first strip line, the Josephson tunnel junction being connected to the first strip line. element. (2) The first strip line is connected to a quasiparticle injection electrode via a second Josephson tunnel junction formed on the first strip line, and the first strip line is connected to the quasiparticle injection electrode through a second Josephson tunnel junction formed on the first strip line. 2. The superconducting amplification device according to claim 1, wherein the characteristics of the Josephson tunnel junction are controlled by implanting quasiparticles into the wire. (3) An optical waveguide is provided so that light enters a part of the first strip line, and quasiparticles are injected into the first strip line by irradiating a laser beam through the optical waveguide. 2. The superconducting amplification device according to claim 1, wherein the characteristics of the Josephson tunnel junction are controlled.