JP3075147B2 - Superconducting element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device technology, and more particularly to a superconducting device which exhibits a strong non-linearity in current-voltage characteristics of the device and which itself changes in response to a high-frequency electromagnetic field. Things.

[0002]

2. Description of the Related Art Conventionally, as a nonlinear element, a Schottky diode using a semiconductor, a PIN junction diode, a transistor, and an M / I represented by a metal / insulator / metal junction.
/ M element, etc. The Josephson element, which is a superconducting element, is also a non-linear element having non-linearity in current-voltage characteristics.

[0003] Among them, Schottky diode, PIN
In a diode or an M / I / M element, a current flows when electrons jump over an energy barrier formed of a Schottky barrier or an insulator by a voltage applied between the electrodes. Since the current value is not linear with respect to the electric field applied to the barrier, a non-linearity is generated in the current-voltage characteristics.
For example, in the case of a Schottky diode, when the voltage exceeds a certain threshold value, the current easily flows rapidly, and a non-linear current-voltage characteristic is obtained. The transistor is basically a combination of Schottky diodes, and the non-linearity in the current-voltage characteristics can be explained by considering the Schottky diode.

On the other hand, in the Josephson element, non-linearity due to a superconductivity phenomenon, which is a quantum phenomenon, appears on current-voltage characteristics. It should be further noted that despite being a two-terminal element, a high-frequency current flows between its terminals in a voltage state due to the AC Josephson effect.

On the other hand, in recent years, in tunnel type junctions having very small capacitance, various interesting characteristics can be obtained because a large amount of electrostatic energy is stored between electrodes due to tunneling of one electron. It was theoretically derived (for example, Journal of Roten-Hearter Physics, Vol. 62, p. 345 (D.V. Averin, KK Likh).
arev: J. Low Temp. Phys. 6
2 (1983) pp. 345), Fisizuka B, Vol. 152, p. 186 (U. Geigenmuller, G. Sc)
hon: Physica B 152 (1988)
pp. 186) etc.).

This element structure is basically a two-terminal structure, in which electrons (charge e: 1.6) are transferred from one electrode to the other electrode.
× 10 ^-19 coulombs) tunnel one,
A potential difference of e / C occurs between the electrodes. Here, C is the capacitance of the element.

At this time, if C is very small, the potential difference is on the order of observable. For example, if C is 0.1 picofarad (pF: 10 ^-12 farad), the potential difference is 1 microvolt, which is a measurable value. In other words, no current flows below this voltage (because the minimum unit of charge is e).

When a constant current (I) is applied from the outside,
The potential difference between both ends of the element oscillates with time. This vibration can be calculated to be a very high frequency (frequency f = I / e: about 6 terahertz at 1 microampere).

On the other hand, some verification results have been reported experimentally with respect to this theoretical prediction (for example, Shah Nice Nice Off Aphis Physics, Vol. 26, No. 1379).
Page (K. Yoshihiro, et al .: JJ App)
l. Phys. 26 (1987) pp. 137
9, Suppl. 26-3), Sharjah Nice Journal of Affairs Physics, Vol. 26, p. 1387 (LS Kuz)
min, K. K. Likharev: J. J. Ap
pl. Phys. 26 (1987) pp. 138
7, Suppl. 26-3). However, in order to realize a device having a small capacitance, a fine metal particle thin film is used, and there is no example in which a theoretical prediction was confirmed in a practical device structure.

In the tunnel junction having a small capacitance, if the electrode is a superconductor, it is predicted that a negative resistance characteristic appears on the current-voltage characteristic together with the high-frequency oscillation between the electrodes. .

[0011]

The capacity of information communication has been increased,
Along with the digitization, it is expected that the frequency band to be used is raised and a frequency not used at present is used. At present, commercial satellite broadcasts use 10 GHz (G
(Hz), but it is considered that higher frequencies will be required in the future as the number of broadcast channels increases.

Further, as the signal processing frequency increases, there is a demand for a signal processing element having an operating frequency of several tens of GHz or higher, or a high frequency of about several hundred GHz.

In response to these demands, attempts have been made to increase the frequency of semiconductor devices, crystal oscillators and the like conventionally used in the field of communications, but it is clear that there are technical limitations at present. It is getting. Accordingly, it is expected that elements based on different operating principles will solve the limitations.

In the communication field, an oscillator that generates a high-frequency electric field used for a carrier on the transmitting side, a modulator that modulates a carrier by a signal to be transmitted, an oscillator that generates a reference frequency on the receiving side, and a detector that mixes the carrier and the reference radio wave , A specific frequency is selected from the superposed electric field of many frequencies,
Alternatively, a key device is a frequency filter that selects a specific frequency from a signal after detection.

Among them, a high-frequency oscillator and a detector occupy important positions as the frequency of communication increases. Therefore, in the high-frequency communication field, there has been a problem of realizing an element that performs an oscillating operation and an element that performs a detecting operation at a frequency of about 10 GHz to about 1 THz or higher.

Of these, the detection operation can be basically realized if the current-voltage characteristics have nonlinearity. In consideration of the efficiency of the detection operation, the stronger the nonlinearity, the higher the efficiency. Therefore, the realization of an element having strong nonlinearity is an issue in the detector.

An object of the present invention is to provide an oscillating element which oscillates at a frequency of 10 GHz or more, and an element having a detection function and extremely strong nonlinearity. This element is a superconducting element using a superconductor as an electrode, and has an object to provide a non-linear element which responds to a high-frequency electric field and realizes a highly efficient detection operation.

[0018]

According to the present invention, there is provided an element comprising an A electrode and a B electrode made of a superconductor, and a barrier layer in contact with the A electrode and the B electrode and separating the A electrode and the B electrode. In the above, due to various configurations in the barrier layer, (1) the localized portion of the electric conduction carrier, or (2) even if the carrier responsible for electric conduction is uniformly distributed, the carrier is affected. The present invention relates to a junction-type element having a structure including a localized level of a carrier such that the energy potential in a substance is not uniform.

These elements exhibit strong non-linearity in the current-voltage characteristics between the A electrode and the B electrode, and can constitute a detection function at a high frequency or an oscillation element.

The present invention provides (1) a composite of at least two substances having different electric conduction carrier densities as a barrier layer,
A junction type element is constituted by a pair of A and B electrodes composed of a pair of superconductors disposed so as to face each other with the barrier layer interposed therebetween. (2) Metal fine particles or semiconductor fine particles are different from these. A thin film of a composite material dispersed in a base substance is used as a barrier layer, and a pair of superconductors, an A electrode and a B electrode, are arranged so as to face each other with the barrier layer interposed therebetween. (3) A junction type element using a layered structure compound in which a layered layer composed of a portion having a large electric conduction carrier density and a layered layer composed of a portion having a small electric conduction period are periodically stacked as a barrier layer. And the average value N of the electric conduction carrier density of the layered structure compound in the substance.
However, the composition is such that 1 × 10 ¹⁵ / cm ³ ≦ N ≦ 5 × 10 ²¹ / cm ^3. (4) Materials having different electric conduction carrier densities are artificially and alternately laminated. A laminated structure material (superlattice structure or multilayer film structure) is used as a barrier layer, and is joined by an A electrode and a B electrode composed of a pair of superconductors arranged so as to face each other with the barrier layer interposed therebetween. (5) The material of the barrier layer is a thin film in which metal fine particles or semiconductor fine particles are aggregated (a thin film in which at least one grain boundary portion exists on a current path), and the metal or semiconductor fine particles are used. An oxide layer, a nitride layer, a sulfide layer, a fluoride layer, which serves as a conduction barrier layer of a conduction carrier between (eg, grain boundaries),
A junction type element is constituted by an A electrode and a B electrode including a pair of superconductors including a layer such as a chloride layer and a bromide layer and arranged so as to face each other with the barrier layer interposed therebetween. ) Doping the oxide superconductor with a different element, or omitting some or all of one constituent element of the oxide superconductor, or removing some or all of one constituent element of the oxide superconductor A junction type superconducting element by various methods, such as replacing the element with other elements, reducing the conduction carrier density, and using a barrier layer that does not exhibit superconductivity at the element operating temperature. By forming, a superconducting element having higher nonlinearity than a conventional element having nonlinearity such as a semiconductor was constituted.

Further, these devices exhibit a video detection function and a heterodyne detection function with respect to a high frequency of 10 GHz or more, and it is possible to constitute a device particularly useful in terms of conversion efficiency.

Further, in the above-mentioned configuration (particularly, (3), (4), (5), (6), etc.), the thickness of the barrier layer is limited to a certain value (resistivity, crystallinity, etc. of each barrier layer). Although it depends, it was found that the element operates as a Josephson element when the thickness is about 150 nm or less, and a high-frequency oscillator based on the AC Josephson effect was constructed.

Further, a negative resistance portion is formed on the current-voltage characteristic, and a superconducting element having a high-efficiency high-frequency detection operation and a high-frequency oscillation operation is constructed by using this portion.

As a result, a high-frequency oscillating element and a high-efficiency high-frequency detecting element, which were problems in the prior art, were realized.

[0025]

[Effect] First of all, K. K. Regarding the small-capacity tunnel junction claimed by Likharev et al., U.S. Pat. Geigen
muller, G .; Analysis of Schon
Vol. 152, p. 186 (U. Geigenmule)
r, G.R. Schon: Physica B 152
(1988) pp. 186)).

In a capacitive junction (a junction capacitance C),
The electrostatic energy Ec of the junction when the charge Q is stored in the junction is given by (Equation 1), and the voltage V between the junctions at that time is given by (Equation 2).

[0027]

(Equation 1)

[0028]

(Equation 2)

Likharev et al. Describe the capacitance C of the junction.
Considering a very small tunnel junction, it is shown that only one electron tunnels between the junctions (charge of the elementary charge e), a very large electrostatic energy is obtained, and the tunneling of the next electron is prevented. (Coulomb blockade).

At this time, a voltage calculated by (Equation 2) is generated between the junctions. Needless to say, this change (change in electrostatic energy and generation of inter-junction voltage) shows a quantized behavior because the current is carried by the electrons.

Considering the current-voltage characteristics when a current flows through this junction, a voltage (V calculated by (Equation 2)) is large enough to be observed just by one electron carrying the current flowing between the junctions. Is generated, the current can be considered to flow out of the voltage V for the first time. Since the current does not flow up to the voltage V (Coulomb blockade) and flows out at a voltage higher than that, the current-voltage characteristic shows nonlinearity such that the current rapidly increases at the voltage V.

Further, when a constant current is passed, electrons tunnel through one by one, so that the voltage between the junctions oscillates (Bloch oscillation: the amplitude is the voltage V calculated by equation (2)). ). This cycle (frequency f) changes depending on the value of the current I flowing, and f = I / e.

In consideration of the above, when the electrode is made of a superconductor, a negative resistance characteristic appears on the current-voltage characteristic. This is an effect that appears in combination with the superconductivity of the electrode and the characteristics of the minute capacitance element.

The present inventors have found that a similar phenomenon occurs not only in a tunnel junction. In other words, if a localized level of conduction electrons is provided on the current path between the junctions, or if an external current is applied while the electrons themselves are localized, the same non-linearity as the small-capacity tunnel junction has the current-voltage characteristic. I found it to appear above.

The physical explanation is still unknown, but at present it is considered as follows. That is, when an electron moves between localized levels or a spatial place and is located at a certain point X, the electrostatic energy of that part or other energy of the system increases, and another electron moves to the position X. Prevents you from reaching a higher level or moving further beyond X. This picture can be considered in contrast to Coulomb blockade.

Further, when a constant current flows from the outside, the conductance on the path changes with the movement of the electrons. This change is also expected to oscillate because the current carrier is a quantized electron. This picture can be contrasted with Bloch oscillation. These are also true when the conduction electrons are holes.

The inventors constructed various junctions by a method of spatially localizing conduction carriers or a method of controlling localization levels of conduction carriers as described below, and showed a non-linearity in current-voltage characteristics. And some of them found to oscillate at high frequencies.

In particular, when the barrier layer has a layered structure and the direction of the current flows so as to penetrate through the layered structure, a negative resistance characteristic was found on the current-voltage characteristic.

Specifically, the barrier layer is made of a superconductor A
Based on a junction type element sandwiched between an electrode and a B electrode, the following barrier layer and (1) a barrier layer is formed of at least two substances having different electric conduction carrier densities (same or different semiconductor materials having different impurity concentrations, Oxides and nitrides with different electrical conductivities).
(2) The barrier layer is made of metal fine particles such as Au, Ag, Pt, and Pd, or semiconductor fine particles such as Si and Ge, which have a relatively small electric conductivity such as SiO ₂ and Al ₂ O ₃ which do not form a solid solution therewith. (3) the barrier layer is formed by alternately laminating at least materials having different electric conduction carrier densities (GaAs / GaAlAs-based semiconductor superlattice;
(4) a layered material having a layered structure in which a Si / Ge-based semiconductor superlattice, a layered structure obtained by combining a semiconductor material, a metal material, a dielectric material, and the like;
The material of the barrier layer is a thin film in which metal fine particles or semiconductor fine particles are aggregated, and furthermore, impurities are present between the metal fine particles or semiconductor fine particles in a crystal grain boundary, an oxide layer, a nitride layer, and a crystal grain boundary on a crystal grain surface. (5) Different types of oxide superconductors, such as those that are diffused and those that have a very fine contact structure between the fine particles, are provided with a layer that serves as a potential barrier that hinders the conduction of conductive carriers. Doping an element, or at least partially or entirely missing one constituent element of the oxide superconductor, or replacing at least a part or all of one constituent element of the oxide superconductor with another element The barrier layer is made of an oxide that does not exhibit superconductivity by any one of the methods described above. There was found to be able to realize a structure which is localized spatially.

Further, the material of the barrier layer is a layered structure compound containing at least layered portions having different electric conduction carrier densities periodically so that the localized level of the conductive carriers is included in the barrier layer. In addition, the layered structure was artificially designed, and the carriers in any layer were controlled by introducing impurities, replacing atoms, changing the bonding state between constituent atoms, etc., and introducing localized levels. By using such a device, a junction-type device having a strong nonlinearity can be formed, and the device was found to be effective as a high-frequency oscillation device and a detection device.

In particular, the average value N of the electric conduction carrier density of the layered structure compound is 1 × 10 ¹⁵ / cm ³ ≦ N ≦ 5 ×
When it is in the range of 10 ²¹ / cm ³ , under the condition that the nonlinearity is strongly observed, the voltage region where the nonlinearity appears becomes an element of about 10 μV to about 1 V which is easy to handle when actually used. Was found to be useful.

In the above devices, strong nonlinearity or negative resistance characteristic is observed in the current-voltage characteristics in all the devices, and the nonlinearity can be used for high-frequency detection in the 10 GHz band and the conversion efficiency is large. Was obtained. In addition, they have found that they can oscillate at high frequencies and can solve two problems in high-frequency communication.

[0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is a junction type element having a structure having a barrier layer sandwiched between a pair of superconducting electrodes, and has a non-linearity in current-voltage characteristics, and has an oscillation in a high-frequency communication field. The present invention relates to a superconducting element that can be used for an element and a detecting element.

In constructing this superconducting element, the superconducting electrode material is not particularly limited as long as it is a superconductor having a Cooper pair presently found, such as a metallic superconducting material or an oxide superconducting material. It suffices if a good interface can be formed for each barrier layer.

The term "good interface" as used herein means a practical interface as long as there is almost no mutual diffusion of constituent elements and the chemical state of the barrier layer is not impaired by a reaction or the like.

The structure and properties of the barrier layer (that the conductive carriers are spatially localized or the localized level of the conductive carriers are present) are important. There are many possibilities.

Hereinafter, the present invention will be described in more detail with reference to specific examples. (Embodiment 1) FIG. 1 is a schematic view showing an embodiment of the present invention. A description will be given of a superconducting element in which a composite of substances having different electric conduction carrier densities is used as a barrier layer according to this embodiment.

First, a (100) MgO substrate was used for the substrate 3, and a ceramic target prepared so as to mainly deposit Y ₁ Ba ₂ Cu ₃ O _x by rf magnetron sputtering was used. Phase Y-Ba-Cu-O (123 phase YBCO) was deposited as A electrode 1.

The sputtering gas at this time, a mixed gas of Ar and O _2, Ar and O ₂ is 7 in the pressure ratio gas: 3. The substrate was heated to 680 ° C. At this time, 123
The phase YBCO becomes a c-axis oriented thin film. The film thickness is about 200
nm.

Next, Y ₂ B mainly called 211 phase
a ₁ Cu ₁ O _y (211 phase YBCO) is deposited on the ceramic target and the target for depositing the 123 phase YBCO is alternately used. It was opened and closed, and a barrier layer 2 having a thickness of 10 nm was deposited. The sputtering gas and the substrate temperature at this time are the same as those at the time of depositing the A electrode.

Then, a B electrode 3 is deposited to a thickness of about 100 nm under the same conditions as the 123-phase YBCO, and a junction element having a junction area of 10 × 20 μm ² is formed from the laminated film by photolithography and ion sputtering. Produced.

The barrier layer 2 comprises 211-phase YBCO and 12
Although it is a three-phase YBCO complex, each of them is crystallized stably, so that it does not become a solid solution but is formed as a eutectic.
The electric conduction carrier density of each substance is 123 phase Y
While BCO is about 1 × 10 ²⁰ , 211 phase YB
CO takes a smaller value.

The temperature dependence of the resistivity of the composite increases as the temperature decreases, and is considered to be dominated by hopping conduction between localized levels on average. Although the cause of the localized level is not clear, the 211-phase YBCO and 123
Chemical defects, physical defects, at the grain boundaries of phase YBCO,
Further, it is presumed that this is due to oxygen deficiency of each YBCO.

This junction exhibits non-linearity in the current-voltage characteristics, and is irradiated with a high frequency of about 10 GHz and irradiated (non-irradiated).
OFF), the current-voltage characteristics changed. As a result, a video detection operation was confirmed using this element. Especially at temperatures lower than 50K, this nonlinearity increases,
Practical detection operation was confirmed.

Various devices having different thicknesses of the barrier layer were manufactured.
A similar non-linear element could be manufactured. In addition, a crystallized YBCO thin film was used for the A electrode and the B electrode, but this was useful for forming a eutectic having good crystallinity when forming a composite as a barrier phase.

However, the A electrode and the B electrode need not be YBCO, and it can be easily analogized that they can be realized by an oxide superconductor in which Y is substituted by a rare earth element. The inventors have
Er, Gd, Ho, Nd,
Similar effects were confirmed for Dy.

Further, it has been confirmed that a superconducting element can be similarly produced by using a material in which the Y portion of the 123, 211 phase YBCO is replaced with another rare earth element in the barrier layer.

Although the barrier layer is deposited alternately by using two targets, a so-called simultaneous deposition or an intermediate composition of a target such that a 123-phase or 211-phase thin film is deposited. It has been confirmed that a similar eutectic can be produced even when a single target having However, the characteristics of the thin film, especially the non-linearity of the junction, largely depend on the relative ratio of each of the 123 phases and 211 phases and the particle size thereof, and from the practical viewpoint of controllability and reproducibility of the device characteristics, It is desirable to form films from different targets.

Further, not only the combination of oxides but also semiconductors having different electric conduction carrier densities (different impurity concentrations) are combined to form a barrier layer, and Nb, NbN, Nb are formed on both sides of the barrier layer so as to face each other. ₃ Ge, Nb ₃ S
It has been found that a good superconducting element can be formed even when the electrode is formed of a metal superconductor electrode such as i, Nb ₃ Ti, MoN, Pb, or PbIn alloy.

(Embodiment 2) FIG. 2 is a schematic view of a barrier layer portion according to another embodiment of the present invention. The configuration of a barrier layer in which a metal or a semiconductor is dispersed in a base material will be described with reference to this embodiment. In this embodiment, quartz glass (Si
A composite in which Au fine particles or Pt fine particles are dispersed in O2) or a composite in which Au fine particles are dispersed using Si as a base will be described.

Since these systems can be formed on a substrate at a temperature of about 200 ° C. or less, the A electrode, the B electrode, etc. were made of ordinary metal superconducting thin films. For example, a NbN thin film is deposited on a quartz glass substrate heated to 200 ° C. as a substrate, and an A electrode is formed. Then, at the same temperature, the quartz glass as the base substance 7 is set to a design value with a thickness of 2 nm to 4 nm. At the same time, a film was formed by sputtering, and then Au as the metal fine particles 6 was similarly formed by sputtering to a thickness of 1 nm in terms of Au film thickness. Under these conditions, Au did not become a continuous thin film but grew like an island.

By repeating this procedure two to five times, it is possible to form a barrier layer in which fine particles of Au are dispersed in a layered manner in quartz glass. FIG. 2 shows a state in which two layers of Au fine particles are distributed for simplicity.

Next, an NbN thin film is formed as a B electrode,
From the laminated film, a junction element having a junction area of 20 × 20 μm ² was manufactured by using a photolithography technique and an ion sputtering technique.

In the barrier layer of this embodiment, electrons are Au
And electrons are tunneled or conducted by field emission through the quartz glass between the Au fine particles.

This junction showed strong non-linearity in the current-voltage characteristics at 10 K or less, and the current-voltage characteristics changed at a high frequency of about 10 GHz. As a result, a video detection operation was confirmed using this element.

Also, a superconducting element could be produced by replacing the quartz glass target used for producing the barrier layer with an Si target and producing a junction by the same method. This A
It has been confirmed that the u / Si system has a large conductance of the device and operates in a more practical current and voltage range.

Embodiment 3 FIG. 3 is a schematic view showing a barrier layer according to another embodiment of the present invention. The structure of a barrier layer using a layered compound having an electric conduction carrier density of 1 × 10 ¹⁷ to 1 × 10 ²¹ will be described with reference to this example.

First, a (12) -phase Bi-based oxide superconductor (Bi _1-y P) was mainly formed by using an (100) MgO substrate as a substrate by rf magnetron sputtering.
_{b y) 2 -Sr 2 -Ca 1} -Cu 2 -O x ( provided that 0 ≦ y <0.
5, x is optional) A 300 nm thick A using an oxide powder target adjusted to deposit (BSCCO)
Electrodes were deposited.

[0069] continuing, in the same vacuum, primarily 2212 phase of Bi-based oxide _{(Bi 1- y Pb y) 2} -Sr 2 -
(Nd, Ca) ₁ -Cu ₂ -O _x (where 0 ≦ y <0.5, x is arbitrary) Multi-source sputtering by molecular beam epitaxy (MBE) or with shutter control to deposit (BSNCO) Using a device, the layered structure compound 5 as a barrier layer was sequentially stacked with each of the constituent elements, and a total thickness of 12 nm was deposited.

[0070] After that, further Bi-based oxide superconductor B electrode to become 2212 _{phase, (Bi 1- y Pb y)} 2 -Sr 2 -
A B electrode was deposited to a thickness of 200 nm using an oxide powder target adjusted to deposit Ca ₁ —Cu ₂ —O _x (where 0 ≦ y <0.5, where x is arbitrary). Finally, a B electrode was deposited as a surface protective layer. Pt was deposited to a thickness of 60 nm.

However, the substrate temperature was 650 ° C. in all cases except for the deposition of Pt on the surface protective layer. The surface protection layer was deposited at room temperature. After that, the barrier layer, the B electrode, and the surface protective layer were 10 × 20 by photolithography and ion milling using a negative resist.
It was patterned to a bonding shape of μm ² .

Each electrode and barrier layer were deposited on a heated substrate and had the same crystal structure, so that good epitaxial growth was achieved. In particular, the (100) MgO substrate exhibited c-axis orientation, and crystallization of the barrier layer was possible under a wide range of conditions. It has been confirmed that this is not only advantageous for the reproducibility and controllability of the characteristics of the barrier layer, but also improves the device characteristics.

In a series of trial productions, the amount of Ca was varied in order to control the carrier density of the barrier layer. However, the ratio of Ca to Nd was 0.6 or less, so that a non-linear element could be produced due to reproducibility. Was.

The thickness of the barrier layer is designed in advance in order to control the resistance value of the element, and the thickness (11 n
m to 125 nm).

In controlling the composition and the film thickness, the MBE method or the multiple sputtering method was a very useful means from the viewpoint of reproducibility.

The barrier layer used in this embodiment is a substance containing a localized level as described later. Crystallographically, between the Bi—O ₂ layers, Sr— (Nd, Ca) —Cu—
O layer is sandwiched, and the carrier is the Sr-
It is localized in the (Nd, Ca) -Cu-O layer.

The carrier density and the local level (binding energy) greatly depend on the ratio between Nd and Ca. For example, without Nd, the carrier density is about 10
²⁰ to 10 ²¹ , and the localized level is hardly reflected in the electrical characteristics.

On the other hand, BSd of only Nd without Ca
In O, the resistivity is two to six orders of magnitude higher, and the localized level is clearly reflected in the electric conduction. The carrier density was in the range of about 10 ¹⁵ to 10 ¹⁹ due to the difference in resistivity.

The current-voltage characteristics of this junction (measurement temperature 4.2
An example of K) is shown in FIG. Each thin film of this device was c-axis oriented, and the ratio of Nd to Ca in the barrier layer was 8: 2.
It is.

This junction exhibited non-linearity in current-voltage characteristics, and exhibited negative resistance characteristics at a current value of about 6 mA or more. This device exhibits the Josephson effect, and is approximately 10
The current-voltage characteristics changed for a high frequency of GHz. This is a phenomenon in which the voltage value of the negative resistance characteristic portion increases with respect to the irradiated high frequency power, together with the AC Josephson effect,
It can be said that it is not a simple exchange Josephson effect. Using these characteristics, high-frequency video detection characteristics were confirmed.

Further, the current value is determined at the point where the negative resistance characteristic starts,
Alternatively, when a bias was applied to the point where the characteristic returned to the normal characteristic again and electromagnetic waves having two different frequencies were irradiated, a signal having a frequency corresponding to the difference frequency could be detected, and heterodyne detection operation was confirmed using this element.

Further, high frequency oscillation other than Josephson oscillation was confirmed in the portion where the element exhibited nonlinearity. This oscillation was confirmed by a change in device characteristics when a high frequency of 40 GHz was applied from the outside.

The BSNCO used here is BSC
This is equivalent to the case where Ca of CO is replaced with Nd, but the carrier density can be similarly controlled with other rare earths, for example, Y, Er, Pr, Nd, Ho, and the like, and a superconducting element can be manufactured. Furthermore, in the element of c-axis orientation, negative resistance characteristics were observed with good reproducibility.

In this embodiment, the constituent materials are deposited by the MBE method or the multi-source sputtering method in the barrier layer deposition. However, the deposition is performed by the sputtering method using a single target, and the oxide superconductor Bi Even if a part of the system layered structure compound is replaced with another element, excessively doped, or deleted, the carrier density can be controlled in the same way, and a superconducting element with nonlinearity can be manufactured. Was. This method is considered to be industrially advantageous in that the manufacturing apparatus is simplified.

At this time, the barrier layer preferably has a degree that does not exhibit superconductivity at the operating temperature of the element, but the operating temperature differs depending on the application field (for example, about 20 K in a refrigerator, and 4 K in liquid helium). .2K), it was necessary to design the composition and the film thickness in accordance with the operating temperature.

Also, the YBCO of 123 phase in which Y was substituted with Pr also had a low carrier density and was effective for a barrier layer of a superconducting element. In this case, the carrier density can be similarly controlled by changing the ratio of Y / Pr,
Practical benefits have been confirmed. In the case of the 123-based electrode, an electrode that is also an oxide-based electrode such as 123-based YBCO and has the same crystal structure is advantageous.

This was confirmed to be effective when improving the crystallinity of the barrier layer, and the nonlinearity of the element was also increased, which was advantageous for improving the conversion efficiency of the detection function.

Further, in terms of negative resistance characteristics, another element is substituted for the oxide superconductor of the layered structure compound.
Or a non-superconductor made by removing it, and c
An element configured so that current was passed in the c-axis direction by using an axis-oriented one as a barrier layer (an element having a current path penetrating through the layered structure) exhibited good negative resistance characteristics.

FIG. 5 shows the temperature dependence of the resistivity of the barrier layer used in this embodiment. At low temperatures, it increases rapidly and shows a negative dependence on temperature. Where BSNCO
(2212) and BSECO (2212)
_{(Bi 1-y Pb y)} 2 -Sr 2 -Nd 1 -Cu 2 -O x ( provided that 0 ≦ y <0.5, x is _{any), (Bi 1-y Pb} y) 2 -Sr 2
—Er ₁ —Cu ₂ —O _x (where 0 ≦ y <0.5, x is arbitrary), and BSNCO (2201), BSECO (220
1) is a Bi-Sr of a Bi-based 2201 structure, respectively.
-Nd-Cu-O, Bi-Sr-Er-Cu-O. This temperature dependence can be explained by variable range hopping conduction between localized levels, and it is considered that the non-linearity of the element is also caused by this characteristic.

(Embodiment 4) In this embodiment, another example of a superconducting element using a layered compound having an electric conduction carrier density of 1 × 10 ¹⁷ to 1 × 10 ²¹ will be described.

First, a (223) phase Bi-based oxide superconductor (Bi _1-y P) was mainly formed by rf magnetron sputtering using a (100) MgO substrate as a substrate.
_{b y) 2 -Sr 2 -Ca 2} -Cu 3 -O x ( provided that 0 ≦ y <0.
5, x is optional) using an oxide powder target adjusted to deposit (2223 phase BSCCO), and having a thickness of 30
A 0 nm A electrode was deposited.

Subsequently, in the same vacuum, mainly 2
201 phase of Bi-based oxide _{(Bi 1-y Pb y)} 2 -Sr 2 -C
u ₁ -O _x (where 0 ≦ y <0.5, x is arbitrary) (BSCO)
Beam epitaxy method (MBE method)
Or by using a multi-source sputtering apparatus with shutter control, a layered structure compound is sequentially stacked as a barrier layer on each of the constituent elements, and a total thickness of 6
0 nm was deposited.

At this time, in order to control the carrier density of the barrier layer, some Ca was doped during the deposition of the barrier layer. C
The doping amount of a was about 10% based on Ca in the 2223 phase BSCCO. The thickness of the barrier layer is designed in advance in order to control the resistance value of the element. In controlling these compositions, the MBE method or the multi-source sputtering method was a very useful means from the viewpoint of reproducibility.

[0094] After that, further Bi-based oxide B electrode to become 2223 superconductor _{(Bi 1-y Pb y)} 2 -Sr 2 -C
Using an oxide powder target adjusted to deposit a ₂ —Cu ₃ —O _x (where 0 ≦ y <0.5, x is arbitrary),
A B electrode was deposited to a thickness of 200 nm, and finally Pt as a surface protective layer was deposited to a thickness of 60 nm.

However, the substrate temperature was 650 ° C. in all cases except for the deposition of Pt on the surface protective layer. The surface protection layer was deposited at room temperature.

Thereafter, the barrier layer, the B electrode, and the surface protective layer were patterned into a junction shape of 10 × 20 μm ² by photolithography and ion milling using a negative resist.

Each electrode and barrier layer were deposited on a heated substrate, and the thin films had similar crystal structures, and had substantially the same lattice constant in the ab direction. The (100) MgO substrate exhibited c-axis orientation, and crystallization of the barrier layer was possible under a wide range of conditions. This is considered to be advantageous not only for reproducibility and controllability of the characteristics of the barrier layer but also for improvement of device characteristics.

It is unknown whether or not the barrier layer used in this example is a substance containing a localized level as described above. However, the conduction carrier is Cu-
It is considered that the carrier is localized on the O plane, and the carrier is relatively strongly bound to each plane. Incidentally, the carrier density in the barrier layer was about 10 ²⁰ to 10 ²¹ .

The current-voltage characteristics of this junction (measurement temperature 4.2
An example of K) is shown in FIG. Each thin film of this element is c-axis oriented. This junction exhibited non-linearity in current-voltage characteristics, and exhibited negative resistance characteristics at a current value of about 30 mA or more.

This element exhibited the Josephson effect, and the current-voltage characteristics were changed at a high frequency of about 10 GHz. This is due to the phenomenon that the voltage value of the negative resistance characteristic portion increases with respect to the irradiated high-frequency power together with the AC Josephson effect, which indicates that it is not a simple AC Josephson effect. Using these characteristics, high-frequency video detection characteristics were confirmed. When the current value is biased at the point where the negative resistance characteristic starts or returns to the normal characteristic again, and when electromagnetic waves of two different frequencies are irradiated, a signal of the frequency corresponding to the difference frequency can be detected. Heterodyne detection operation was confirmed using the device.

(Embodiment 5) FIG. 7 is a schematic view of a barrier layer portion showing another embodiment of the present invention. Example 1 In this example, a configuration of a barrier layer having a stacked structure of substances having different electric conduction carrier densities will be described.

First, a (100) MgO substrate was used as a substrate, and a 2212-phase Bi-based oxide superconductor (Bi _1-y P) was mainly formed by rf magnetron sputtering.
_{b y) 2 -Sr 2 -Ca 1} -Cu 2 -O x ( provided that 0 ≦ y <0.
5, x is optional) A 300 nm thick A using an oxide powder target adjusted to deposit (BSCCO)
Electrodes were deposited.

Subsequently, in the same vacuum, mainly 2
212 phase of Bi-based oxide _{(Bi 1-y Pb y)} 2 -Sr 2 -N
d ₁ -Cu ₂ -O _x (where 0 ≦ y <0.5, x is arbitrary) (BS
And target adjusted oxide powder as NCO) is deposited mainly Bi-based oxide superconductor of 2201 phase _{(Bi 1-y Pb y)} 2 -Sr 2 -Cu 1 -O x ( provided that 0 ≦ y <
0.5, x is optional) A barrier layer is deposited by repeating a BSCO (2 unit lattice) / BSNCO (2 unit lattice) stacked film four times using an oxide powder target adjusted to deposit (BSCO). I let it. At this time, the barrier layer is c
It is axially oriented, and the length of the two single lattices is defined to be equal to the c-axis length. This portion is the first substance 8 and the second substance 9 described in FIG.

[0104] After that, further Bi-based oxide B electrode to become 2212 phase superconductor _{(Bi 1-y Pb y)} 2 -Sr 2 -C
a ₁ -Cu ₂ -O _x (where 0 ≦ y <0.5, x is arbitrary) using an oxide powder target adjusted to deposit,
A B electrode was deposited to a thickness of 200 nm, and finally Pt as a surface protective layer was deposited to a thickness of 60 nm.

However, the substrate temperature was 650 ° C. in all cases except for the deposition of Pt on the surface protective layer. The surface protection layer was deposited at room temperature.

Thereafter, the barrier layer, the B electrode, and the surface protective layer were patterned into a junction shape of 10 × 10 μm ² by photolithography and ion milling using a negative resist.

The electrodes and barrier layers are deposited on a heated substrate and have the same crystal structure, so that good epitaxial growth can be achieved. In particular, the (100) MgO substrate exhibited c-axis orientation, and crystallization of the barrier layer was possible under a wide range of conditions. It has been confirmed that this is not only advantageous for the reproducibility and controllability of the characteristics of the barrier layer, but also improves the device characteristics.

The barrier layer used in this embodiment has a laminated structure of 2201 phase and 2212 phase Bi-based oxide containing Nd, but the carrier is relatively more localized in the 2201 phase BSCO layer. I have. At this time, the binding energy of carriers in the BSCO layer is determined by the distance between adjacent BSCO layers (BSNCO
Layer thickness) and the carrier density of each of the BSCO and BSNCO layers. Therefore, the characteristics of the device could be changed by changing the lamination cycle of BSCO / BSNCO or replacing Nd and Ca in BSNCO at a certain ratio.

This junction exhibited non-linearity in the current-voltage characteristics, and the current-voltage characteristics changed at a high frequency of about 10 GHz. In addition, when electromagnetic waves having two different frequencies were irradiated, a signal having a frequency corresponding to the difference frequency could be detected, and heterodyne detection operation was confirmed using this element. In addition, high-frequency oscillation was confirmed in a portion where the nonlinearity of the element appeared. This oscillation was confirmed by a change in device characteristics when a high frequency of 40 GHz was applied from the outside.

The BSNCO used here is BSC
This is equivalent to the case where Ca of CO is replaced with Nd, but the carrier density can be similarly controlled with other rare earth elements, for example, Y, Er, or Ho, and a superconducting element can be manufactured.

Further, as a barrier layer, 123-phase YBCO
In which Y is replaced by Pr, and the other YBCO
System material (Er-Ba-Cu-O, Nd-Ba-Cu-
O, Ho-Ba-Cu-O, etc.) were similarly effective for the barrier layer of the superconducting element. In this case, Y / P
The carrier density can be controlled by changing the ratio of r,
Practical benefits have been confirmed.

In the case of the 123 system, it is advantageous that the electrode is also an oxide system such as YBCO of the 123 system and has the same crystal structure. This was confirmed to work effectively when improving the crystallinity of the barrier layer, and the nonlinearity of the element was also increased, which was advantageous for improving the conversion efficiency of the detection function.

Further, Pb having a perovskite structure
-Ti-O-based material or Bi-Ti-O-based material, C
a-Ti-O based material, Ba-Ti-O based material and BSCO
Similarly, a laminated film serving as a barrier layer could be formed, and a good superconducting element could be manufactured. Also in these elements, the current-voltage characteristics change at a high frequency of about 10 GHz, and when electromagnetic waves of two different frequencies are irradiated, a signal of a frequency corresponding to the difference frequency has been detected. In addition, high-frequency oscillation was also confirmed in a portion where the nonlinearity of the element appeared.

(Embodiment 6) FIG. 8 is a schematic view showing a barrier layer portion according to another embodiment of the present invention. In this embodiment, a configuration of a barrier layer including a grain boundary will be described.

First, a (12) -phase Bi-based oxide superconductor (Bi _1-y P) was mainly formed by rf magnetron sputtering using a (100) MgO substrate as a substrate.
_{b y) 2 -Sr 2 -Ca 1} -Cu 2 -O x ( provided that 0 ≦ y <0.
5, x is optional) A 300 nm thick A using an oxide powder target adjusted to deposit (BSCCO)
Electrodes were deposited.

Next, a Pt thin film was deposited to a thickness of 20 nm. At this time, the Pt thin film was (100) oriented.

Next, a 2201-phase Bi-based oxide (Bi-oxide) was mainly formed by rf magnetron sputtering.
_{1-y Pb y) 2 -Sr} 2 -Cu 1 -O x ( provided that 0 ≦ y <0.5,
x is optional) a target of oxide powder adjusted to deposit (BSCO), or mainly 2212 phase B
i based oxide _{(Bi 1-y Pb y)} 2 -Sr 2 -Nd 1 -Cu 2 -
O _x (provided that 0 ≦ y <0.5, x is any) (BSNCO) using an oxide powder target was adjusted so that is deposited,
A barrier layer having a thickness of 30 nm to 100 nm was deposited.
At this time, the substrate temperature was set at 730 ° C.

Under these conditions, the oxide thin film on Pt became a polycrystalline thin film including many crystal grain boundary portions 10. In addition, the particle size of the polycrystal changed depending on the thickness of the deposited film.
BSCCO to become B electrode in the same vacuum
Was deposited to a thickness of 200 nm.

Thereafter, the barrier layer and the B electrode were patterned into a junction shape of 10 × 10 μm ² by photolithography and ion milling using a negative resist.

Although the barrier layer used in this embodiment is a Bi-based oxide of 2201 phase or 2212 phase, the crystal grain boundary functions as a potential barrier for carriers, and functions to hinder the movement of conductive carriers between grain boundaries. . Carriers localized in each oxide crystal can move to an adjacent crystal only after receiving a certain activation energy from the outside. At this time, the binding energy of the carrier is affected by the distance between adjacent crystal grains and the chemical state of the crystal grain boundaries. It was confirmed that the characteristics of the device were changed by changing the oxygen concentration in the atmosphere after the deposition of the barrier layer.

This junction exhibited non-linearity in the current-voltage characteristics, and the current-voltage characteristics changed at a high frequency of about 10 GHz.

The BSNCO used here is BSCC
This is equivalent to O obtained by substituting Ca for Nd with Nd, but the carrier density can be similarly controlled with other rare earth elements, for example, Y, Er, or Ho, and a superconducting element can be manufactured.

Further, as a barrier layer, 123-phase YBCO
In which Y is replaced by Pr, and other YBCs in the 123 phase
O, Er-Ba-Cu-O, Nd-Ba-Cu-O, H
A polycrystalline thin film such as o-Ba-Cu-O was similarly effective for a barrier layer of a superconducting element.

In this case, the carrier density can be controlled by changing the ratio of Y / Pr, and practical advantages have been confirmed.

Further, transition metals (for example, Nb, Mo, T
a, Ti, etc.) or Al for the barrier layer, and before depositing the B electrode, exposing it to oxygen plasma, fluorine plasma, nitrogen plasma, S vapor, chlorine plasma, etc. It has been confirmed that a superconducting device that responds to high frequency can be manufactured by providing a potential barrier of a conductive carrier such as a nitride phase, a nitride phase, a sulfide phase, and a chloride phase.

[0126]

As described above, the A electrode and the B electrode made of a superconductor, and the conduction carrier which is in contact with the A electrode and the B electrode and is located so as to separate both the electrodes are localized. Alternatively, a superconducting element exhibiting non-linearity in current-voltage characteristics can be realized by forming a junction-type element from a barrier layer in which a localized level of a conduction carrier exists. There is an effect that an oscillation element can be formed.

When a barrier layer composed of a composite of two substances having different electric conduction carrier densities as described in Embodiment 1 is used, it is effective to provide a practical device whose barrier layer manufacturing process is simple. There is.

Further, as described in Example 2, when the material of the barrier layer is constituted by a thin film of a composite material in which metal fine particles or semiconductor fine particles are dispersed in a base material, the fine particles can be formed based on the electrical characteristics of the base material. The bound state of the carrier inside can be changed. This change in state is directly related to the element characteristics and is effective in controlling the element characteristics. Although not as large as the MBE method, it is also possible to arrange fine particles relatively easily and with good controllability, and this has a great practical advantage.

Further, as described in Examples 3 and 4, the material of the barrier layer is a layered structure compound containing at least layered portions having different electric conduction carrier densities periodically. The average value N of the electric conduction carrier density is 1 × 10 ¹⁵ / cm ³ ≦ N ≦ 5 ×
If a material having a density of 10 ²¹ / cm ³ is formed by MBE or the like, a barrier layer having an arbitrary carrier density suitable for the purpose can be produced. The number, the level of the level, and the spatial position can be arbitrarily set, and this is effective for improving the non-linear characteristics and the high-frequency characteristics, for example, by periodically arranging the positions where the carriers are easily bound. In addition, a negative resistance characteristic appeared, which was effective for high-frequency efficient detection. This negative resistance characteristic is
The reproducibility was obtained by using the c-axis alignment film.

Further, as described in the fifth embodiment, if the material of the barrier layer is a laminated structure material in which at least substances having different electric conduction carrier densities are alternately laminated, the properties of the barrier can be artificially designed and controlled. Thus, a high-frequency element having desired characteristics or higher performance can be realized. This is not only a very useful method including the reproducibility of element characteristics, but also very effective because it is possible to construct an ideal element that cannot be obtained by a normal method.

Further, negative resistance characteristics appeared as described in Examples 3 and 4, which was effective for efficient high-frequency detection. This negative resistance characteristic was obtained with good reproducibility by using the c-axis oriented film.

On the other hand, a thin film in which the material of the barrier layer is a collection of metal fine particles or semiconductor fine particles is easy to obtain as a polycrystalline material. A conductive barrier layer of a conductive carrier can be provided at (a crystal grain boundary), and a superconducting element capable of easily responding to a high frequency can be manufactured. This is very effective in practice.

In the embodiments described here, in many cases, a combination of an oxide superconductor and an oxide barrier is used, but this combination can form a film continuously at the same temperature, and the manufacturing process is simplified. There are benefits. It is said that the oxide superconductor itself has a localized carrier, and when a different element is doped into the oxide superconductor, or a constituent element is deleted or further substituted, the carrier localization is remarkable. Then, when the non-linear superconducting element is used for the barrier layer, there is an effect that the non-linear superconducting element can be configured with good reproducibility.

At present, in the field of telecommunications, with the spread of automobile telephones, the transmission of digital image information, the spread of information networks, etc., communication means using higher frequencies has been desired as means for transmitting a large amount of signals. Since the superconducting element according to the present invention can be used for generating and detecting high-frequency radio waves that could not be used conventionally, the range of use of radio frequencies in the telecommunications field can be expanded. Further, since the detection efficiency is high, the transmission power may be reduced, and the problem of radio interference may be reduced.

In these respects, the practical effect of the present invention is great in the field of telecommunications.

[Brief description of the drawings]

FIG. 1 is a schematic view of a superconducting element for explaining a first embodiment.

FIG. 2 is a schematic view of a barrier layer of a superconducting element for explaining the second embodiment.

FIG. 3 is a schematic view of a barrier layer of a superconducting element for explaining the third embodiment.

FIG. 4 is a current-voltage characteristic diagram of the third embodiment.

FIG. 5 is a diagram showing the temperature dependence of the resistivity of the material of the channel layer used in the third invention.

FIG. 6 is a current-voltage characteristic diagram of the fourth embodiment.

FIG. 7 is a schematic view of a barrier layer of a superconducting element for explaining the fifth embodiment.

FIG. 8 is a schematic view of a barrier layer of a superconducting element for explaining the sixth embodiment.

[Explanation of symbols]

 Reference Signs List 1 A electrode 2 Barrier layer 3 Base 4 B electrode 5 Layered structure compound 6 Metal or semiconductor fine particle 7 Base substance 8 First substance 9 Second substance 10 Crystal grain boundary portion

Continuation of front page (72) Inventor Kentaro Seto 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-63-102383 (JP, A) JP-A-3-160771 ( JP, A) JP-A-4-192381 (JP, A) JP-A-3-295282 (JP, A) JP-A-4-267569 (JP, A) JP-A-7-15049 (JP, A) JP Hei 8-228029 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 39/22 H01L 39/24 H01L 39/00

Claims (3)

(57) [Claims] And 1. A barrier layer, sandwiching the barrier layer, and the junction element including an A electrode and a B electrode comprising at least a pair of superconductor in contact opposite to each other, before
The material of the barrier layer is metal fine particles or semiconductor fine particles.
A composite in which any of the above particles is dispersed in a layered form in a base substance.
A superconducting element comprising a material . 2. A barrier layer sandwiching said barrier layer, and
It consists of at least one pair of superconductors
In the junction type element including the A electrode and the B electrode,
The barrier layer has at least a different electric conduction carrier density.
Oxide materials are alternately stacked, the barrier layer has a thickness of 11 nm to 125 nm,
And the average value N of the electric conduction carrier density in the barrier layer is 1 × 10 ¹⁵ / cm ³ ≦ N ≦ 5 × 10 ²¹ / c
superconducting device which is a m ^3. 3. The material of the barrier layer is an A electrode or a B electrode.
The superconducting element according to claim 2, wherein the superconducting element comprises an oxide material in which part or all of one constituent element of the oxide superconductor constituting the pole is replaced with another element.