JPH08236821A - Superconducting antifuse - Google Patents

Abstract

PURPOSE: To provide a superconducting antifuse which can change a superconducing wiring layer from the state of high resistance or insulation to the superconducting state, after the superconducting wiring layer is formed, regarding a superconducting antifuse wherein, when a voltage higher than or equal to the threshold voltage is applied, the state of high resistance or insulation changes to the superconducting state. CONSTITUTION: At least two superconductor layers 2, 3 are formed on a substrate 1, at an interval. When a voltage lower than or equal to the threshold voltage is applied across the superconductor layers 2, 3, the part between the superconductor layers 2 and 3 is in the state of high resistance. When a voltage higher than or equal to the threshold voltage is applied, the superconductor layers 2, 3 can come into contact with each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting antifuse, and more particularly to a superconducting antifuse that changes from a high resistance state or an insulating state to a superconducting state when a voltage above a threshold value is applied.

[0002]

2. Description of the Related Art Superconducting wiring layers can be used, for example, as wiring for Josephson logic elements or as inter-chip wiring for multi-chip modules (MMC).
It is formed by patterning a superconductor layer of a metal superconducting material such as Nb or Pb or an alloy superconducting material such as NbTi or NbSn formed on a substrate such as.

The superconducting wiring layer of Nb film is made of liquid He, etc.
By cooling below, the electric resistance becomes zero, and a very high speed and low loss signal transmission line can be realized. When such a superconducting wiring layer is used as wiring for Josephson logic elements or wiring between chips of a multi-chip module, mutual signal transmission lines between logic circuits can be sped up and power consumption can be reduced. The system performance can be greatly improved.

[0004]

However, conventionally, a so-called superconducting antifuse that changes from a high resistance state or an insulating state to a superconducting state by applying a voltage above a threshold value has not been realized. Therefore, the superconducting wiring used in the superconducting circuit must be determined at the time of patterning the superconductor layer, and the wiring cannot be connected after the circuit pattern is once created on the substrate. Therefore, in the case of a small amount and a large number of products, it is necessary to change the wiring connection for each product, which causes a problem that the process management becomes complicated.

The present invention was created in view of the above conventional problems, and it is possible to change a superconducting wiring layer from a high resistance state or an insulating state to a superconducting state after forming the superconducting wiring layer. An object is to provide a superconducting antifuse that can be made.

[0006]

The above problem is that at least two superconductor layers on a substrate are in a high resistance state when the voltage below the threshold voltage is applied between the superconductor layers. And a superconducting antifuse, wherein the superconducting layers are formed at intervals such that they can contact each other when a voltage higher than the threshold voltage is applied. A third aspect of the present invention is achieved by the superconducting antifuse according to the first aspect of the invention, characterized in that a coolant is present in the gap between the conductor layers, and thirdly, the substrate has steps. Is achieved by the superconducting antifuse according to the first or second aspect of the present invention, which is formed on the upper and lower steps of the substrate with the step interposed therebetween. In a part of the gap between conductor layers Enmaku, the semiconductor film or the normal conductor layer is achieved by the first to third superconducting antifuse according to any one of the features that it is interposed.

[0007]

According to the superconducting antifuse of the present invention, when a voltage below the threshold voltage is applied between the superconductor layers formed at intervals, the superconductor layers are in an insulating state or a high resistance state, The superconductor layers are formed at intervals such that the superconductor layers can contact each other when a voltage of a threshold voltage or more is applied between the superconductor layers.

Therefore, even if this superconducting antifuse is immersed in a coolant such as liquid helium to cool it to a temperature below the critical temperature of the superconductor layer and to apply a voltage below the threshold voltage between the superconductor layers, The conductor layers are in an insulating state or a high resistance state. At this time, the superconducting antifuse may be exposed to liquid helium, or the entire superconducting antifuse may be covered and not exposed to liquid helium.

On the other hand, when a voltage higher than the threshold voltage is applied between the superconductor layers while being cooled by the refrigerant, the atmospheric gas or helium in the gap causes a dielectric breakdown, and a current is momentarily generated between the superconductor layers. Flowing. Due to this discharge, the opposing portions of the superconductor layer come into contact with each other and the contact portions are welded. Also,
Even if the superconductor layers are formed on the upper and lower substrates with the step formed on the substrate interposed therebetween, the same function can be achieved.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. Before specifically explaining the embodiment of the present invention,
The principle of the present invention will be described. (Explanation of the Principle of the Present Invention) FIGS. 1A and 1B are perspective views schematically showing the principle of the superconducting antifuse of the present invention. FIG. 1A shows the initial high resistance state. FIG. 3B shows the superconducting state.

In the superconducting antifuse shown in FIG. 1A, the first and second superconductor layers 25 and 26 are formed with a gap therebetween. Moreover, the insulating film 27 is sandwiched in a part of the gap. This superconducting antifuse is immersed in liquid helium or the like and cooled to a temperature below the critical temperature at which superconductivity occurs in the superconductor. Regarding the thickness of the insulating film 27, that is, the distance between the first and second superconductor layers 25 and 26, a voltage not higher than a threshold voltage is applied between the first and second superconductor layers 25 and 26. It is sometimes determined that the high resistance state exists between the first and second superconductor layers 25 and 26. At this time, the superconducting antifuse is exposed to liquid helium. Therefore, the gap is filled with liquid helium except where the insulating film 27 is present.

At this time, the first and second superconductor layers 25,
When the voltage between the electrodes 26 exceeds the threshold voltage for the dielectric breakdown of liquid helium, the first and second superconductor layers 25 and 26 are discharged through the liquid helium filled in the gap, and a current flows momentarily. . Due to this discharge, as shown in FIG. 1B, the facing portions of the first and second superconductor layers 25 and 26 are melted and brought into contact with each other, and the contact portions are welded. Thereby, conduction is established between the first and second superconductor layers 25 and 26.

Therefore, the above structure can be made to function as a superconducting antifuse that changes from an insulating state to a connected state by applying a voltage. Next, FIG.
A superconducting antifuse having another structure will be described with reference to (a) and (b). 2 (a) and 2 (b)
It is sectional drawing which represented the initial state of the superconducting antifuse which concerns on this invention, and its connection state typically, the figure (a) shows a high resistance state, and the figure (b) shows a superconducting state.

2 (a) and 2 (b), a superconducting antifuse is formed on a part of the wiring, the first superconductor layer 2 is connected to a terminal 5 for applying a voltage, and The superconductor layer 3 is connected to the ground terminal 6. Also, this superconducting antifuse is dipped in liquid helium, and
It is cooled to 2K. In FIG. 2A, the first and second superconductor layers 2 and 3 are superconductors.
A high resistance state exists between the superconductor layer 2 and the second superconductor layer 3. The resistance value between the first and second superconductor layers 2 and 3 is the resistivity of the substrate 1, the distance between the two superconductor layers 2 and 3, and the contact between the superconductor layers 2 and 3 and the substrate 1. It depends on the resistance and can be controlled from several 100Ω to several GΩ. When the first and second superconductor layers 2 and 3 are in an ideal insulating state, no superconducting current flows between the first and second superconductor layers 2 and 3. The relationship between the superconducting current and the voltage at this time is as shown by the solid line C in the graph of FIG. In this graph, the horizontal axis represents the voltage represented by the linear scale, and the vertical axis represents the current represented by the linear scale.

In FIG. 2B, the first superconductor layer 2
When a voltage equal to or higher than the threshold voltage for dielectric breakdown is applied between the second superconductor layer 3 and the second superconductor layer 3, electric discharge occurs between the first and second superconductor layers 2 and 3, and a current instantaneously flows. As a result, the facing portions of the first and second superconductor layers 2 and 3 are melted and brought into contact with each other to be welded. This discharge voltage is determined by the space between the superconductor layers 2 and 3 and the medium filling the space between the superconductor layers 2 and 3. The value is about several V to several tens V, for example, about 9 V when the medium is liquid helium, the lateral width of the superconductor layers 2 and 3 is 2 μm, and the slit 4 width is 0.1 μm.

When the first and second superconductor layers 2 and 3 are connected, a superconducting current flows between the superconductor layers 2 and 3. The critical current value of superconducting current by this connection is 10
μA to tens of mA is sufficient for superconducting wiring, and FIG.
The characteristics shown by the dotted line D in FIG. As described above, by disposing the two superconductor layers 2 and 3 on the insulating substrate 1 with the slit 4 interposed therebetween, the superconductor layer is normally in a high resistance state and a voltage higher than a threshold voltage is applied. Two
It is possible to realize the function of a superconducting antifuse in which the three are electrically connected. (Explanation of the first embodiment of the superconducting element) Next, referring to FIG.
(A), (b) shows the superconducting element which concerns on the 1st Example of this invention, The figure (a) is a top view, the figure (b) is the II line of the figure (a). FIG.

4 (a) and 4 (b), on the surface of the insulating substrate 1, a band-shaped first superconductor layer 2 and a second superconductor layer 3 each made of a superconductor material and having a width of 5 μm. Is patterned to form a first superconductor layer 2 and a second superconductor layer 3 with a gap (slit) 4 having a width of about 50 nm interposed therebetween. As the material for the insulating substrate 1, an insulating material, a high-resistance undoped semiconductor material, or a semiconductor material formed on the insulating substrate and not doped with conductive impurities can be used. Here, SrTiO ₃ was used.

After depositing a 100 nm thick Nb film as a superconductor material on the substrate 1, patterning is performed to form a strip-shaped wiring layer. Next, the wiring layer is etched by a focused ion beam (FIB) such as Ga to form the slit 4. As another method, after depositing an Nb film, a resist film is formed and a band-shaped resist mask having slits is formed by electron beam exposure and development. Subsequently, the Nb film may be etched by reactive ion etching using CF ₄ gas based on the resist mask to form a band-shaped superconducting wiring layer having the slit 4. The width of the slit 4 can be widened to about 100 nm depending on the conditions such as the material of the substrate 1.

As described above, the slit 4 is formed on the insulating substrate 1.
By arranging the two superconductor layers 2 and 3 sandwiching between the superconductor layers 2 and 3, the superconductor layers 2 and 3 are electrically connected to each other by applying a voltage equal to or higher than a threshold voltage in a normally high resistance state. The fuse function can be realized. A superconducting current flows through the connected superconducting wiring layers by cooling below the critical temperature. (Description of Second Embodiment) Next, a superconducting antifuse according to a second embodiment of the present invention will be described with reference to FIGS. 5 (a) and 5 (b) are cross-sectional views showing respective manufacturing steps of the laminated superconducting antifuse, and FIG. 5 (c) is a cross-sectional view almost completed as the superconducting antifuse.

First, as shown in FIG. 5A, a first superconductor layer 9 made of an Nb film of a superconducting material and an insulator layer made of a SiO ₂ film are formed on an insulator substrate 8 such as sapphire. 10, Nb
The second superconductor layer 11 made of a film is formed by 100 n
Deposit to a thickness of m, 200 nm, 100 nm. Subsequently, a band-shaped resist mask 12 having a width of 5 μm is formed on the second superconductor layer 11 by the photolithography technique.

Next, as shown in FIG. 5B, the insulating layer 10 and the second superconductor layer 11 are continuously etched using the resist mask 12 to form a strip-shaped pattern having a width of 5 μm. 10 and 11 are formed. Then, after removing the resist mask 12, a band-shaped resist mask 13 having a width of 5 μm is newly formed to cover the band-shaped patterns 10 and 11.

After that, as shown in FIG. 5C, the first superconductor layer 9 is etched by the resist mask 13 to form a band-shaped pattern 9. Thus, the superconducting antifuse in which the first superconductor layer 9 and the second superconductor layer 11 are laminated with the insulator layer 10 sandwiched therebetween is completed. The superconducting antifuse thus produced is immersed in liquid helium and cooled to a temperature of 4.2K. At this time,
When the voltage applied between the first and second superconductor layers 9 and 11 is equal to or lower than the threshold voltage, the superconductor layers 9 and 11 are in a high resistance state, and no superconducting current flows. When a voltage equal to or higher than the threshold voltage is applied between the first and second superconductor layers 9 and 11, discharge occurs via liquid helium filled in the gap 4 between the first and second superconductor layers 9 and 11. Then, the current flows instantaneously. As a result, the first and second superconductor layers 9 and 11 are melted and brought into contact with each other, and the contact portions are welded. Superconducting current will flow through the first and second superconductor layers 9 and 11. (Explanation of Third Embodiment) FIG. 6 is a sectional view showing a third embodiment of the superconducting antifuse of the present invention. A step having a height h is formed on the insulating substrate 17, and a first electrode 18 and a second electrode 19 are formed on the upper surface of each step, so that the liquid He
It is immersed in.

The insulating substrate 17 is made of undoped Sr.
It consists of TiO3. The step of the substrate 17 is formed by applying a resist and patterning it, and then removing it to a depth of about 200 nm by Ar ion beam etching. First
And the second electrodes 18 and 19 are made of Nb of 100 n by the EB vapor deposition method.
deposited to a thickness of m. In the film formation by vapor deposition, since the film does not wrap around, the Nb film is not formed on the side surface of the step of the insulating substrate 17 and the electrodes 18 and 19 are not short-circuited.

In the superconducting antifuse having such a structure, the first electrode 18 and the second electrode 19 are arranged at an interval determined by the step h of the insulating substrate 17, and the voltage applied between both electrodes is predetermined. When the voltage is lower than the voltage, it is in a high resistance state. Then, by applying a voltage pulse equal to or higher than a predetermined voltage, the first and second electrodes 18 and 19 are discharged through the He atmosphere in the step portion of the insulating substrate 17 and the adjacent portions of the electrodes 18 and 19 are removed. It is melted and connected, and superconducting current comes to flow. (Description of Superconducting Circuit According to Fourth Embodiment) Next, referring to FIG.
A superconducting circuit according to a fourth embodiment of the present invention will be described with reference to (a) to (c). FIG. 7 (a) schematically shows the structure of the superconducting circuit of the present invention, FIG. 7 (b) is a partially enlarged plan view thereof, and FIG. 7 (c) is a line of FIG. 7 (b). FIG. 11 is a sectional view taken along line II-II.

As shown in FIG. 7A, vertical superconducting wirings 31a to 31d and horizontal superconducting wirings 32a to 32d.
A matrix-shaped superconducting wiring layer is formed by intersecting d. Superconducting antifuse 33a at each intersection
.About.33p are interposed between the vertical superconducting wiring layer and the lateral superconducting wiring layer. This superconducting antifuse 33a
When about 33p is applied with a voltage equal to or higher than the threshold voltage, the high resistance state changes to the superconducting state.

An enlarged view of a portion A surrounded by a dotted line in FIG. 7A is shown in FIG. 7B. In this figure, a superconducting wiring 31d in the vertical direction is formed on an insulating substrate 34, and a superconducting wiring 32d in the lateral direction crosses over it. In practice, an interlayer insulating film is interposed between the vertical superconducting wire 31d and the horizontal superconducting wire 32d, but it is omitted in the figure. As a part of the lateral superconductor wiring 32d, a superconducting antifuse 33p having a slit is formed in a portion surrounded by a dotted circle, and is connected to the vertical superconductor wiring 31d at a contact portion 35. .

FIG. 7C is a sectional view taken along line II-II of FIG. 7B, in which the superconducting wiring 32d in the lateral direction is formed on the interlayer insulating film 36 laminated on the insulating substrate 34. And a superconducting antifuse 33p having a slit is formed. The interlayer insulating film 36 is made of an undoped semiconductor or the like. In the superconducting circuit having such a configuration, the vertical superconducting wires 31a to 31d and the lateral superconducting wires 32a to
By selecting a set of wiring layers from 32d and applying a voltage equal to or higher than a threshold voltage to the superconducting antifuses 33a to 33p, the superconducting antifuses 33 connected to the intersections are connected.
It is possible to conduct a to 33p.

Therefore, by selecting the wiring layer in the vertical direction and the wiring layer in the horizontal direction and setting any of the superconducting antifuses 33a to 33p in the superconducting antifuses 33a to 33p to the superconducting state, The desired superconducting circuit can be formed by connecting the wiring layer of FIG. This makes it possible to conduct the wiring connection of a specific wiring layer after creating a wiring layer pattern that is interrupted on the way, so it can be used as a wiring layer for Josephson logic gates or low-temperature operation semiconductor logic gates. FPGA (Field Programmable Gate Arrey)
It becomes possible to construct a high-speed logic circuit having wide applicability and low power consumption.

[0029]

As described above, according to the superconducting antifuse of the present invention, when a voltage below the threshold voltage is applied between the superconductor layers sandwiching the gap, the superconductor layers are in an insulating state or a high resistance state. And the superconductor layers are formed at intervals such that the superconductor layers can contact each other when a voltage higher than the threshold voltage is applied between the superconductor layers.

Therefore, when a voltage equal to or higher than the threshold voltage is applied between the superconductor layers, the medium in the gap causes a dielectric breakdown and discharges, the superconductor layers sandwiching the gap contact each other, and the superconductor layers are separated from each other. Conduct. Further, the same function can be achieved by forming superconductor layers on the upper and lower substrates with the step formed on the substrate interposed therebetween.

Furthermore, in the superconducting circuit of the present invention,
It has a superconducting wiring layer in which the above-mentioned superconducting antifuse is formed. Therefore, only the superconducting wiring layer to be made conductive can be selected and made conductive. Further, at the intersection of the superconducting wiring layers arranged in a matrix, the superconducting antifuse is interposed between the superconducting wiring layers. Therefore, the superconducting antifuse is made conductive by selecting the wiring layers in the vertical and horizontal directions that form the intersections to be connected and applying a voltage equal to or higher than the threshold voltage of the superconducting antifuse. Can be connected.

As described above, after forming the superconducting wiring layer pattern, desired circuit wiring connection can be formed.
Therefore, by using the wiring layer in which the superconducting antifuse is formed as the wiring layer for the Josephson logic gate and the low temperature operation semiconductor logic gate,
It becomes possible to configure a high-speed logic circuit with wide applicability such as GA (Field Programmable Gate Arrey) and low power consumption.

[Brief description of drawings]

FIG. 1 is a perspective view schematically showing the principle of a superconducting antifuse of the present invention, FIG. 1A showing a high resistance state,
The figure (b) shows a superconducting state.

2A and 2B are cross-sectional views schematically showing the principle of a superconducting antifuse having another structure according to the present invention. FIG. 2A shows an initial high resistance state, and FIG. 2B shows a superconducting state. Indicates.

FIG. 3 is a graph showing the relationship between voltage and current of the superconducting antifuse of the present invention.

4A and 4B show a superconducting antifuse according to a first embodiment of the present invention. FIG. 4A is a plan view and FIG. 4B is a sectional view taken along line I-I of FIG. 4A. .

FIG. 5 is a cross-sectional view showing a structure of a superconducting antifuse and a manufacturing method thereof according to a second embodiment of the present invention, and FIGS. 5A to 5C show respective steps.

FIG. 6 is a sectional view showing a schematic structure of a superconducting antifuse according to a third embodiment of the present invention.

FIG. 7 shows a superconducting circuit according to a fourth embodiment of the present invention, FIG. 7A is a circuit diagram, and FIG. 7B is a partially enlarged plan view of the circuit shown in FIG. 7A. FIG. 13C is a sectional view taken along line I-I of FIG.

[Explanation of symbols]

 1, 17 Insulating substrate 2, 9, 18 First superconducting layer, 3, 11, 19 Second superconducting layer, 4 Gap (slit), 5, 6 terminals, 8, 34 Insulator substrate, 10 Insulation Body layer, 12, 13 resist mask, 36 interlayer insulating film, 31a to 31d vertical superconducting wiring, 32a to 32d lateral superconducting wiring, 33a to 33p superconducting antifuse, 35 contact part.

Claims (4)

[Claims] 1. At least two superconductor layers on a substrate, the superconductor layers being in a high resistance state when a voltage not higher than a threshold voltage is applied between the superconductor layers, and a voltage not lower than the threshold voltage. A superconducting antifuse, characterized in that the superconducting layers are formed at intervals such that they can contact each other when a voltage is applied. 2. The superconducting antifuse according to claim 1, wherein a coolant for cooling the superconductor layer is interposed in a gap between the superconductor layers. 3. The substrate according to claim 1, wherein the substrate has a step, and the superconductor layer is formed on each of the upper and lower steps of the substrate with the step interposed therebetween. 2. The superconducting antifuse according to 2. 4. The superconductor according to claim 1, wherein an insulating film, a semiconductor film or a normal conductor film is interposed in a part of the gap between the superconductor layers. Conductive antifuse.