JPH06169112A - Superconducting element and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a three-terminal superconducting element, on which the normal conductive resistance or a zero resistance temperature of a channel layer changes when voltage is applied to a gate electrode, and this change is controlled even after removal of the applied voltage by using the ferroelectric material for the gate electrode and a superconducting element and an oxide superconducting body for a channel layer. CONSTITUTION:An oxide superconducting thin film is used as a channel layer 1, a ferroelectric gate insulating film 2, which is brought into contact with the channel layer 1, a source electrode 4 and a drain electrode 5 are provided, and a gate electrode 3, which comes in contact with the gate insulating film 2, is provided. A Bi oxide superconducting material Bi2-Sr2-Sr1-Cu2-Ox (x indicates an optional natural number) single crystal of 2212 phase cleaved in the thickness of 0.5mm, for example, is used as the channel layer, and a Pb0.9 La0.1TiO3 thin film of 400nm in thickness, which is formed by rf sputtering method, is used as the gate insulating film 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a superconducting application technique,
In particular, the present invention relates to a field effect type superconducting device in which device characteristics are controlled by a voltage applied to a gate electrode.

[0002]

2. Description of the Related Art Conventionally, a superconducting element using a metal-based superconductor includes a weak coupling Josephson element, a tunnel junction Josephson element, a bolometer utilizing superconducting transition of a superconductor, and the like. It was Also, as a superconducting three-terminal element, a Josephson field effect element (JOFET) using a semiconductor-superconductor junction, SUBSIT using a superconducting thin film as a base electrode of a transistor, QUITERON controlling a non-equilibrium superconducting state, etc. Was proposed, and fundamental research and device prototype were made. These elements are expected as elements for ultra-high-speed switches and ultra-high-frequency signal processing, but at present, expected characteristics have not been obtained.

On the other hand, some oxide superconductors recently discovered have a superconducting transition temperature exceeding the liquid nitrogen temperature (77.3 Kelvin), which greatly expands the field of application of superconductors. Became. As for the device application of this oxide superconductor, the Josephson device, which was made by splitting the oxide superconductor into two and making a slight contact again, made a thin film of the oxide superconductor and made a bridge-type Joseph with a small constriction. Most of the prototypes of weak-coupling Josephson devices, such as the Sonson device and the Josephson device in which oxide superconductors are connected by a noble metal such as Au or Ag. Further, although an element based on the same principle as a superconducting three-terminal element using a metal superconductor has been proposed, its characteristics have not been confirmed yet.

[0004]

A superconductor is basically a perfect conductor and cannot apply an electric field (cannot give a potential difference). However, the state near the superconducting transition point is considered to be a mixed state of a superconducting state and a normal conducting state, and an electric field can be applied. When the magnitude of the applied electric field is changed in such a state, the quasi-particles (normal conduction electrons) in the normal conduction state among the mixed states described above may be electrically affected. In the case of metal superconductor (metal),
Since the carrier density is high and it is difficult to obtain the electric field effect unlike ordinary semiconductors, it is considered difficult to realize an element utilizing such a phenomenon. On the other hand, it is considered that the oxide superconductor has a smaller carrier density than a metal superconductor (close to a semiconductor) and an electric field effect is effectively generated. However, there are few examples in which the characteristics of the superconducting device are actually and effectively controlled by voltage control.

On the other hand, in a logic circuit using a superconductor, an element having a memory function is required in addition to a superconducting element having a switching function. Conventionally, a composite superconducting circuit using a plurality of Josephson elements, which uses this function as a magnetic flux holding function, has been proposed. However, in this circuit, the device area is large and high integration is difficult,
There has been a demand for a superconducting device that realizes a memory function by a single device and further by a different principle. Furthermore, a superconducting three-terminal element that has high modulation efficiency and is easy to manufacture has been desired.

In order to solve the above-mentioned conventional problems, the present invention uses a channel layer whose electric characteristics such as superconducting characteristics or normal conducting characteristics can be changed by an external electric field, and a material having ferroelectricity for a gate insulating film. It is an object of the present invention to provide a novel superconducting three-terminal element which can realize a memory function and whose characteristics can be controlled by the electric field effect. Another object of the present invention is to provide a manufacturing method for manufacturing a superconducting three-terminal element having high reproducibility and reliability and high modulation efficiency.

[0007]

In order to achieve the above object, a first superconducting element of the present invention comprises a channel layer, a source electrode and a drain electrode in contact with the channel layer, a gate insulating film, and the gate insulating layer. A superconducting device having at least a gate electrode in contact with the film, wherein the channel layer contains at least an oxide superconductor, and the gate insulating film is a film having ferroelectricity.

In the above structure, it is preferable that the channel layer, the gate insulating film, and the gate electrode are formed of a thin film and are formed in a laminated structure on the substrate. . Next, a second superconducting element of the present invention comprises an electrically conductive layer, a gate insulating film having ferroelectricity in contact with the electrically conductive layer, a channel layer in contact with the gate insulating film, and a source in contact with the channel layer. A superconducting device including at least an electrode, a drain electrode, and a gate electrode, wherein the channel layer includes at least an oxide superconductor, and the gate insulating film is a film having ferroelectricity. .

In the above structure, it is preferable that the electric conductive layer, the gate insulating film, the channel layer, and the gate electrode are formed of thin films and are formed in a laminated structure on the base. In the above structure, it is preferable that the number of gate electrodes is at least two.

In the above structure, the channel layer is
A ferroelectric or Bi containing an oxide superconductor containing at least Bi and having a gate insulating film containing at least Pb.
It is preferable to include a ferroelectric substance containing.

In the above structure, the channel layer is
The gate insulating film contains at least (Pb _1-x La _x ) (Zr _1-y Ti _y ) _{1 -} containing at least an oxide superconductor or an oxide normal conductor represented by the above formula (Formula 1). _{x / 4} O
It is preferable to include a ferroelectric represented by ₃ (0 ≦ x ≦ 0.2, 0 ≦ y ≦ 1.0) or a ferroelectric represented by Bi ₃ Ti ₄ O ₁₂ .

In the above structure, the channel layer is
An oxide superconductor containing at least Cu and Bi, and Cu and B
It is preferably formed of a laminated film made of an oxide containing i.

Next, in the first method for manufacturing a superconducting device of the present invention, a channel layer is formed on a substrate, a gate insulating film is formed on the channel layer, and a gate electrode is further formed on the gate insulating film. A film is formed and a superconducting element is manufactured using the laminated film.

In the above structure, it is preferable that the film forming temperature of the channel layer is at least 600 ° C. or higher and the film forming temperature of the gate insulating film is 600 ° C. or lower. Further, in the above structure, at least the channel layer, the gate insulating film, and the gate electrode are preferably formed in the same vacuum.

Next, in the second method for manufacturing a superconducting element of the present invention, an electric conductive layer is formed on a substrate, a gate insulating film is formed on the electric conductive layer, and the gate insulating film is formed on the gate insulating film. Forming a channel layer, forming a gate electrode on the channel layer,
It has a structure in which a superconducting element is manufactured using the laminated film.

In the above structure, the film forming temperature of the gate insulating film is 600 ° C. or lower, and after forming the gate insulating film, the substrate temperature is heated to 600 ° C. or higher to form the channel layer. preferable.

Further, in the above structure, it is preferable that the electric conductive layer, the gate insulating film, the channel layer and the gate electrode are formed in the same vacuum.

[0018]

According to the above-described structure of the present invention, a superconducting element including at least a channel layer, a source electrode and a drain electrode in contact with the channel layer, a gate insulating film, and a gate electrode in contact with the gate insulating film is provided. Then, the channel layer contains at least an oxide superconductor, and the gate insulating film is a film having ferroelectricity,
It is possible to realize a superconducting three-terminal device which has a memory function and whose characteristics can be controlled by the field effect. That is, in a superconducting device in which a ferroelectric material is used for the gate electrode to which an electric field is applied and an oxide superconductor is used for the channel layer, when a voltage is applied to the gate electrode, the normal conduction of the channel layer Resistance or zero resistance temperature changes. Moreover, this change continues even after the applied voltage is removed.

Oxide superconductors have a low carrier density, and depending on the size of the carrier density, various superconducting properties such as superconducting transition properties, normal conducting properties such as normal conducting resistance at temperatures higher than the superconducting transition temperature. The characteristics change. The channel layer of the present invention is mainly made of an oxide superconductor, and it is considered that the carrier density and the like are changed by the voltage applied through the gate insulating film, and the electric characteristics are changed. Moreover, it is considered that this change is maintained by the action of the remanent polarization of the ferroelectric even after the applied voltage is removed.

On the other hand, when the electric conductive layer is provided in contact with the gate insulating film (when the electric conductive layer is the ground plane for the gate insulating film), the superconducting element can be manufactured by a simpler manufacturing method. This is because the electrically conductive layer functions as a ground plane, two or more gate electrodes can be formed on the channel layer on the gate insulating film, and in that case, the gate electrode can be manufactured in one manufacturing step. Also, with this configuration,
When thinning the device on an insulating substrate for the purpose of integration, and when several channel layers are arranged in parallel, the manufacturing process is not particularly complicated. Further, since the channel layer is formed on the gate electrode, deterioration of the electrical characteristics, crystallinity and the like of the channel layer can be prevented.

On the other hand, when the above-mentioned superconducting element is thinned and formed on the substrate, the gate electrode can be thinned, and the electric field strength actually applied between the gate insulating films can be applied to the same applied voltage to the gate electrode. Can be increased, and the modulation efficiency of element characteristics can be improved.

On the other hand, in these superconducting devices, when two or more gate electrodes are formed, the electrical characteristics of each channel layer in contact with the two gate electrodes can be changed complementarily, which is practically effective. Is.

When all electrodes or thin film layers (electrically conductive layer, channel layer, or gate electrode) in contact with the gate insulating film are formed in the same vacuum, a surface-deteriorated layer having a small relative dielectric constant due to exposure to the atmosphere is formed. Since it is not formed on the gate insulating film, it is effective in improving the reproducibility of element characteristics and the modulation efficiency. Further, by appropriately setting the manufacturing temperature of each thin film material, the reproducibility, reliability and modulation efficiency of the superconducting element can be improved. When constructing a field effect superconducting device as described above, an oxide-based material with a low carrier density is used for the oxide superconductor that constitutes the channel layer, and various element substitutions or the same system as the superconductor are used. Since the superconductivity can be controlled by the laminated structure (combination of various laminating materials, laminating order, laminating period, etc.) with the oxide thin film, the superconducting element that can be operated most efficiently at a specific operating temperature can be designed.

When the laminated film is used for the channel layer,
By selecting materials that have the same type of crystal structure and lattice constants, including each thin film and gate insulating film that are configured, each electrode and thin film layer can be made with good crystallinity, so the characteristics of superconducting devices can be improved. Becomes In particular, since the gate insulating film can be formed thin and with good crystallinity, it has the effect of improving the electrical characteristics of the channel layer (high dielectric constant, improving dielectric strength of the gate insulating film, reducing leak current, etc.). .

The basic structure of an oxide superconductor is perovsk.
It has a skite structure, and if these are used for the channel layer,
In this case, the ferroelectric gate insulating film is the same perovskite.
PbTiO with structure₃System [(Pb_1-xLa_x) (Zr
_1-yTi_y)_{1-x / 4}O₃, Etc.] or Bi layered
Bi, a structural compound₃Ti_FourO₁₂Thin film growth
It is an effective combination from the viewpoints of properties, thin film characteristics, etc.
It Especially for the ferroelectric gate insulating film, PbTiO 3₃system
[(Pb_1-xLa_x) (Zr_1-yTi_y)_{1-x / 4}O ₃Na
And the Bi layered structure compound Bi.₃T
i_FourO₁₂When using a system, the substrate temperature is 600 ° C or less
In that case, compositional deviation (decrease in Pb or Bi ratio) is suppressed.
It is possible to obtain good ferroelectricity. here,
A gate insulating layer on the electrically conductive layer and a channel on it
In a structure in which layers are stacked, the gate insulating film is 600 ° C or less
Film formation at the temperature of, and raise the substrate temperature to 600 ℃ or more
Good ferroelectric gate insulation even when forming a channel layer
A film is obtained and the channel layer has good superconductivity.
Things are obtained. Further, as the channel layer, a Bi-based oxide is used.
Is deposited at 600 ° C or higher, and PbTiO₃System
Or Bi-based ferroelectric as a gate insulating film
At this time, if the substrate temperature is set to 600 ° C. or lower, the channel layer is bonded.
Do not impair crystallinity, superconducting properties, and electrical properties.
In addition, the crystallinity and ferroelectric characteristics of ferroelectrics
With good electrical characteristics such as electrical conductivity and relative permittivity
It From the viewpoints of these thin film growth conditions and thin film characteristics, B
What are i-based oxides, Pb-based ferroelectrics, and Bi-based ferroelectrics?
It is an effective arrangement for the purpose of the invention.

Further, when two gate electrodes are formed on the gate insulating film so as to face each other at a narrow interval, the gap between the electrodes can be reduced, and the electric field is increased by equalization, and the electric field effect is significantly increased.

The thin film laminated type device structure is not only capable of integration but also effective in designing the laminated type channel layer as described above and in producing a thin gate insulating film having high modulation efficiency. Is.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following examples. In the superconducting element of this example, the gate insulating film having ferroelectricity has a function of retaining the electric field effect, and a superconducting element having a memory function can be realized. Since this element independently functions as a memory element, it is very advantageous for high integration. Furthermore, an element having two or more gate electrodes can form an element that works complementarily, which is effective for a logical operation circuit.

When the field effect type superconducting device as described above is constructed, the oxide superconductor constituting the channel layer has a low superconducting transition temperature if it is an oxide material having a low carrier density. Can also be used. Further, an oxide material whose transition temperature can be set by various element substitutions is desirable for designing a superconducting device that can be operated most efficiently at a specific operating temperature. In addition, since the superconductivity of a laminated film of a superconductor and an oxide thin film of the same system can be controlled by the laminated structure (lamination material and combination, lamination order, lamination period, etc.), it is possible to use a single phase for the above reason. Like the channel layer, it is effective for forming the channel layer. In this case, the laminated structure of the laminated film is arbitrary depending on the application, but the combination of materials is preferably those having the same kind of crystal structure. For example, a combination of Y-Ba-Cu-O and Pr-Ba-Cu-O, Bi-Sr-Ca-C
u-O and Bi-Sr-Cu-O (2201 phase), or Bi-Sr-Ca-Cu-O and Bi-Sr-Ln-Cu.
A combination of —O (2212 phase, Ln is Y, or a lanthanoid element) is desirable. Further, it is desirable to select materials having the same type of crystal structure and lattice constant, including each thin film forming the laminated film used for the channel layer and the gate insulating film. For example, a Bi-based oxide superconductor having a crystal structure and a crystal constant very close to each other is used for a channel layer, and a Pb-based ferroelectric material having a perovskite structure is used for a gate insulating film, or a channel layer, a gate insulating film, and When a Bi-based layered structure compound such as a buffer layer, a substrate, and an electroconductive layer is used, each electrode and thin film layer can be formed with good crystallinity, which is advantageous for improving the characteristics of the superconducting device. In particular, since the gate insulating film can be formed thin and with good crystallinity, it is effective in improving the electrical characteristics of the channel layer (high dielectric constant, improvement of dielectric strength of gate insulating film, reduction of leak current, etc.). .

In particular, as a material for the oxide superconducting thin film, a Bi-based oxide superconductor whose main component is 2212 phase, such as (B
_{i 1-y Pb y) 2} -Sr 2 -Ca 1 -Cu 2 -O x ( provided that 0 ≦ y <0.5, x is an arbitrary natural number), or an oxide superconductor of the main component is 2223, for example ( Bi _1-y Pb
_{y) 2 -Sr 2 -Ca 2 -Cu} 3 -O x ( provided that 0 ≦ y
<0.5, x is an arbitrary natural number), and the main component of the oxide thin film is an oxide having a phase of 2212, such as (Bi
_{1-y Pb y) 2 -Sr} 2 -Ln 1 -Cu 2 -O x ( provided that 0 ≦ y <0.5, x is an arbitrary natural number, Ln represents at least one of Y, and lanthanoid element), or A Bi-based oxide whose main component is 2201 phase, such as (Bi
_{1-y Pb y) 2 -Sr} 2 -Cu 1 -O x ( provided that 0 ≦ y
If a combination such as <0.5, x is an arbitrary natural number) is used, a laminated film can be easily formed and a good channel layer can be formed.

Further, when two gate electrodes are formed on the gate insulating film so as to face each other at a narrow interval, the gap between the electrodes can be reduced, and the electric field can be increased by equalization and the electric field effect can be remarkably increased.

In addition, the thin film laminated type device structure is not only capable of integration, but also effective in designing the laminated type channel layer as described above and in producing a thin gate insulating film having high modulation efficiency. Becomes

According to the manufacturing method of forming at least the channel layer, the gate insulating film, the electrically conductive layer, and the gate electrode in the same vacuum, the interface between the gate insulating film and another channel layer, the gate electrode, or the electrically conductive layer is formed. Since a layer having a low dielectric constant is not formed and the interface state can be kept good, it has a remarkable effect in improving the reproducibility of element characteristics, stability, and modulation efficiency.

The present invention will be described below with reference to specific examples.
Will be described in detail. Embodiment 1 An embodiment of the first invention of the present invention will be described with reference to FIG. Figure
1, 1 is a channel layer, 2 is a gate insulating film, 3 is
Gate electrode, 4 is a source electrode, 5 is a drain electrode
It The channel layer 1 is made of a bisected 2212 phase Bi-based oxide.
Superconductor, Bi ₂-Sr₂-Sr₁-Cu₂-O
_x(X is an arbitrary natural number) It is a single crystal and its thickness is about
It is 0.5 mm. Also for later thin film fabrication and device process
At this time, it is fixed to an appropriate base as appropriate to facilitate handling.
It The gate insulating film 2 is formed by rf sputtering.
400 nm thick Pb_0.9La_0.1TiO₃In thin film
It Channel layer during deposition [Bi₂-Sr₂-Sr₁-C
u₂-O_x(X is an arbitrary natural number) Single crystal] is 540 ° C
I kept it. Next, using a metal mask, the gate electrode 3,
The source electrode 4 and the drain electrode 5 are formed by sputtering P
formed at t.

In this element, the conductance between the source electrode 4 and the drain electrode 5 was changed by applying a voltage between the gate electrode 3 and the channel layer 1. Further, the Pb _0.9 La _0.1 TiO ₃ thin film as the gate insulating film 2 exhibited ferroelectricity, and the change in conductance continued even after the voltage was removed. Furthermore, when the amount of oxygen in the single crystal that is the channel layer 1 is reduced or oxidized by heating in vacuum or heating / cooling in oxygen, the operating temperature at which a remarkable electrolytic effect can be obtained could be changed. . Further, the Pb _0.9 La _0.1 TiO ₃ thin film used for the gate insulating film 2 had a perovskite structure and was epitaxially grown on the channel layer 1, and there were almost no defects in the film and it functioned as a good gate insulating film.

Embodiment 2 FIG. 2 is a schematic sectional view showing an embodiment of the second invention of the present invention. 2A is a plan view, and FIG. 2B is A in FIG.
It is a sectional view taken along the line A. First, Nb-doped (100) S
Pb-Zr used as a gate insulating film 2 by an rf magnetron sputtering method using a rTiO ₃ substrate as a substrate.
The -ti-O ₃ film was 400nm deposited. The composition of the deposited thin film of the gate insulating film 2 is approximately Pb (Zr _0.5 T
i _0.5 ) O ₃ is used as the mixed oxide powder compensated. Next, a Bi-based oxide superconductor Bi ₂ -Sr ₂ -Ca ₁ containing an oxide superconductor whose main component is a 2212 phase
-Cu ₂ -O _{x (x} is an arbitrary natural number) using an oxide powder target was adjusted so that is deposited, a thickness of 50nm
Channel layer 1 was deposited. The process of depositing the channel layer 1 was performed in the same vacuum, while keeping the substrate temperature at 650 ° C. Subsequently, the substrate temperature was set to room temperature, and Pt thin films to be the source electrode, the drain electrode, and the gate electrode were formed without breaking the vacuum.

After that, the two gate electrodes 3, the channel layer 1, the source electrode 4, and the drain electrode 5 were patterned by photolithography and ion milling using a negative resist to complete the device.

In this device, the conductance between the source electrode and the drain electrode was changed by applying a voltage between the two gate electrodes. By applying a control voltage to the gate electrode while applying a constant current between the source and drain, the voltage between the source and drain was modulated, and the device operated as a field effect device. Nb-doped SrTiO 3
_{The three} substrates are electrically conductive and also serve as the electrically conductive layer 6. Further, this effect continued even after the voltage applied to the two gate electrodes was removed. This electric field effect is remarkable at a device temperature of 20 Kelvin to 100 Kelvin, and although the operating mechanism has not been clarified, it is explained that it is induction or suppression of superconductivity due to ubiquity of carriers due to electric field effect. Get stuck.

Embodiment 3 FIG. 3 is a schematic view of the manufacturing process of one embodiment of the present invention.
FIG. 3A shows the deposition of a laminated film, and FIG.
Pattern fabrication, same figure (c) etching, same figure (c)
[Fig. 3] is a diagram showing each step of resist removal. The manufacturing method is real
Similar to Example 2, but the substrate 10 is an insulator (10
0) An MgO substrate was used and an electrically conductive layer was formed thereon.
Is the different part. In the same manner as in Example 2, electricity
The conductive layer 6, the gate insulating film 2, the channel layer 1, and the
The contact layer of Pt that becomes the source electrode, the drain electrode, etc.
After manufacturing in the same vacuum, the element manufacturing process was performed.
The electrically conductive layer 6 of this embodiment has a thickness that is deposited on the substrate 10.
Bi-based oxide Bi having a main component of 2201 phase of 300 nm
₂-Sr₂-Cu₁-O_x(X is an arbitrary natural number)
It The substrate temperature was 650 ° C. In addition, the gate insulating film 2
Is 470 nm thick Pb formed by rf sputtering.
-La-Ti-O thin film. The channel layer is on it
Deposited 50 nm thick Bi-based compound whose main component is 2223 phase
Oxide superconductor Bi ₂-Sr₂-Sr₂-Cu₃-O_x
(X is an arbitrary natural number). Substrate temperature is electrical conduction
Layer insulation and gate layer insulation at 650 ° C for gate insulation
The film 3 was deposited at 550 ° C. That is, the electrically conductive layer
After forming the film, lower the substrate temperature by about 100 ° C to remove the gate insulating film.
After film formation, raise the substrate temperature again and deposit the channel layer.
It was The gate insulating film is (Pb_0.9La_0.1) TiO₃To
It is close to the target, and the target is 10% Pb compensated firing.
A knot was used. The gate insulating film shows good ferroelectricity,
At room temperature, the value of coercive field is about 27 KV / cm, remanent polarization
Is about 18 μC / cm²Met. In addition, channel layering
After the film, there is no high temperature film formation process
A good superconducting element without deterioration of superconducting properties of the flannel layer
I was able to make it. The gate electrode 4 has an electrode interval of 2 μm.
Of the opposite type.

In this device, by applying different voltages or voltages of the same potential to the respective facing gate electrodes,
The conductance between the source electrode and the channel electrode changed. By applying a control voltage to the gate electrode while applying a constant current between the source and drain, the voltage between the source and drain was modulated, and the device operated as a field effect device. This effect persisted even after the voltage applied to the gate electrode was removed, indicating a memory function. This electric field effect is remarkable at a device temperature of 20 Kelvin to 110 Kelvin, and in particular, the modulation effect was larger than when different potentials were applied to the opposing gate electrodes.

When two gate electrodes are formed on one channel layer using this thin film and different voltages are applied to the electrodes, one of the conductances of the channel portion under each gate electrode is large. Then, the other changed so as to become smaller, and a complementary change was made.

Embodiment 4 FIG. 4 (a) is a schematic view showing another embodiment of the present invention.
4B is a partially enlarged view of the channel layer 1 of FIG. 4A. First, the (100) MgO substrate is used as the base 10
Used by the rf magnetron sputtering method,
Bi-based oxide superconductor Bi ₂ -Sr ₂ -Ca ₁ -Cu ₂ -O _x (x
Is an arbitrary natural number), and an oxide superconductor thin film 11 having a thickness of 30 nm was deposited using an oxide powder target adjusted to deposit. Subsequently, in the same vacuum, the Bi-based oxide Bi ₂ —Sr ₂ —Nd containing 2212 phase as the main component was used.
_The oxide thin film 12 is formed from the target of the oxide powder adjusted so that _1- Cu ₂ -O _x (x is an arbitrary natural number) is deposited.
Was deposited to a thickness of 30 nm. With this two-layer film, the channel layer 1
Configured.

Further, PbTiO ₃ which becomes the gate insulating film 2 is formed.
A thin film was deposited to 400 nm. The deposition of the gate insulating film 2 was performed in the same vacuum, and the substrate temperature was lowered to 600 ° C.

After that, the channel layer 1 and the gate insulating film 2 were patterned into a channel layer shape by photolithography using a negative resist and ion milling. Further, after forming contact holes for the source electrode and the drain electrode by the same ion milling, Pt
A thin film was deposited and the gate electrode 3, the source electrode 4, and the drain electrode 5 were patterned to complete the device. The Pt thin film was patterned by the lift-off method.

In this element, the conductance between the source electrode and the drain electrode was changed by applying a voltage to the gate electrode. By applying a control voltage to the gate electrode while applying a constant current between the source and drain,
The voltage between the source and drain was modulated, and the device operated as a field effect device. This electric field effect is remarkable at a device temperature of 20 Kelvin to 100 Kelvin, and although the operating mechanism has not been clarified, it is explained that it is induction or suppression of superconductivity due to ubiquity of carriers due to electric field effect. Get stuck. Further, this effect is remarkable in the laminated film, and it is considered that the effect becomes more effective due to the proximity effect between the oxide superconducting thin film and the oxide thin film.

Embodiment 5 FIG. 5 is a schematic view of still another embodiment of the present invention. Figure 5
5A is a plan view, FIG. 6B is a cross-sectional view taken along line BB in FIG. 5A, and FIG. 5C is a more detailed schematic view of the channel layer 1. The manufacturing method is the same as in Example 4, and the gate insulating film is deposited in the same vacuum, but the configuration of the channel layer 1 is different. The channel layer 1 of this example has a thickness of 30 nm deposited on the substrate 10 and is composed mainly of 2201.
(The x arbitrary natural number) Bi-based oxide Bi ₂ -Sr ₂ -Cu ₁ -O _x phase and the oxide film 12 containing, thick 30nm deposited thereon, Bi-based principal components 2223 oxide superconductor _{Bi 2 -Sr 2 -Sr 2 -Cu 3} -O x (x
Is an oxide superconductor thin film 11 containing an arbitrary natural number. Further, the gate insulating film 2 is a Bi ₃ Ti ₄ O ₁₂ thin film having a thickness of 350 nm formed by the rf sputtering method.
The substrate temperature was kept at 650 ° C during the deposition of the channel layer,
The temperature was set to 550 ° C. when the gate insulating film 3 was deposited. Further, the gate electrode 3 is of a facing type with an electrode interval of 2 μm. In this element, the conductance between the source electrode and the channel electrode was changed by applying different voltages or voltages of the same potential to the facing gate electrodes. By applying a control voltage to the gate electrode while applying a constant current between the source and drain, the voltage between the source and drain was modulated, and the device operated as a field effect device. This electric field effect is remarkable at a device temperature of 20 Kelvin to 110 Kelvin, and in particular, the modulation effect was larger than when different potentials were applied to the opposing gate electrodes.

Embodiment 6 Next, still another embodiment of the present invention will be described. The manufacturing method is the same as in Example 4, but the structure of the channel layer 1 is different. In the channel layer 1 of this example, an oxide thin film 12 containing a Bi-based oxide Bi ₂ —Sr ₂ —Cu ₁ —O _x (x is an arbitrary natural number) of 2201 phase as a main component, and 2212 as a main component.
Bi-based oxide phase superconductor Bi ₂ -Sr ₂ -Sr ₁ -C
It is a multilayer film composed of an oxide superconductor thin film 11 containing u ₂ —O _x (x is an arbitrary natural number), and has a thickness of 3
2212 phase of 2.4 nm and 2201 phase of 2.4 nm are alternately deposited in four layers each. FIG. 6 shows a schematic view of this channel layer. In this embodiment, the top layer is
2201 phase. The gate insulating film is a Bi ₃ Ti ₄ O ₁₂ thin film having a thickness of 400 nm formed by the rf sputtering method. The substrate temperature is 650 ° C. when the channel layer is deposited.
And the gate insulating film was deposited at 520 ° C. Further, the gate electrode was of a facing type with an electrode interval of 2 μm.

Also in this device, the conductance between the source electrode and the drain electrode was changed by applying different voltages or voltages of the same potential to the facing gate electrodes. In particular, an element using this multi-layered film as a channel layer has various characteristics (e.g., stacking period, film thickness of each oxide thin film to be stacked) of the stacked film of the channel layer, resulting in excellent characteristics of the device. It was possible to change the operating temperature at which the effect was obtained. Further, Bi used for the gate insulating film
_{The 3} Ti ₄ O ₁₂ thin film was one of the Bi-based layered structure compounds, was epitaxially grown on the channel layer, had almost no defects in the film, and functioned as a good gate insulating film.

In all of the superconducting devices of the above examples, the channel layer and the gate insulating film were formed in the same vacuum, and the device characteristics were stable and the reproducibility was good. In the superconducting devices of Examples 3, 4, 5, and 6 described above, the channel layer and the gate insulating film are all formed in the same vacuum, and the device characteristics are stable and the reproducibility is good. there were.

As described above, according to the present embodiment, a superconducting device using a ferroelectric material for the gate electrode to which an electric field is applied and an oxide superconductor for the channel layer is provided. Thus, it was confirmed that when a voltage is applied to the gate electrode, the normal conduction resistance or the zero resistance temperature of the channel layer changes, and this change continues even after the applied voltage is removed. It was also confirmed that if an electrically conductive layer was provided in contact with the gate insulating film (when the electrically conductive layer was a ground plane for the gate insulating film), the superconducting element could be manufactured by a simpler manufacturing method.

At present, in the field of telecommunications, due to the spread of automobile telephones, the transmission of digital image information, the spread of information networks, etc., a communication means using a higher frequency has been desired as a means for transmitting a large amount of signals. The superconducting element according to the present embodiment can be used for signal processing and detection of high-frequency radio waves that could not be used conventionally, so that the range of use of radio frequency in the telecommunication field can be expanded. Further, a logical operation circuit can be configured by configuring an element having a memory function and a complementary operation function. This circuit is a digital circuit, and can be applied to computers, high frequency digital communication, and the like.

From these points, the practical effect of the present invention is great in the field of electric information communication.

[0053]

As described above, an oxide superconductor is used for the channel layer to which an electric field is applied, and the electric field is applied through the ferroelectric gate insulating film provided in contact with the laminated film. In this case, the normal resistance or the zero resistance temperature in the vicinity of the superconducting transition point of the laminated film is changed, and there is an effect that a superconducting element can be formed. Further, it is possible to manufacture a device having a memory function in which this effect is maintained even after the applied electric field is removed.

In the above superconducting device, the gate insulating film having ferroelectricity has a function of retaining the electric field effect,
A superconducting device having a memory function can be realized. Since this element independently functions as a memory element, it is very advantageous for high integration. Furthermore, an element having two or more gate electrodes can form an element that works complementarily, which is effective for a logical operation circuit.

When the field effect type superconducting element as described above is constructed, an oxide-based material having a low carrier density is used for the oxide superconductor constituting the channel layer, and various element substitutions or superconducting materials are used. The superconductivity can be controlled by the laminated structure (combination of various laminated materials, lamination order, lamination period, etc.) of the conductor and the oxide thin film of the same system, so that the superconducting element can be operated most efficiently at a specific operating temperature. There is an effect that can be designed.

Further, if materials having the same crystal structure and lattice constant are selected, including the respective thin films constituting the laminated film used for the channel layer and the gate insulating film, the respective electrodes and the thin film layers have good crystallinity. Since it can be manufactured, it is effective in improving the characteristics of the superconducting element. In particular, since the gate insulating film can be formed thin and with good crystallinity, it is effective in improving the electrical characteristics of the channel layer (high dielectric constant, improvement of dielectric strength of gate insulating film, reduction of leak current, etc.). .

Further, when two gate electrodes are formed on the gate insulating film so as to face each other at a narrow interval, the gap between the electrodes can be reduced, and the electric field is increased by equalization, so that the electric field effect is significantly increased.

Further, if the thin film laminated type element structure is used, not only the integration is possible, but also in the design of the laminated type channel layer as described above and when the thin gate insulating film having a high modulation efficiency is produced, it is extremely large. Have a significant effect.

According to the manufacturing method of forming at least the channel layer, the gate insulating film, the electrically conductive layer and the gate electrode in the same vacuum, the interface between the gate insulating film and another channel layer, the gate electrode or the electrically conductive layer is formed. Since a layer having a low dielectric constant is not formed and the interface state can be kept good, it has a remarkable effect in improving the reproducibility of element characteristics, stability, and modulation efficiency.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a superconducting device of Example 1 of the present invention.

FIG. 2 is a schematic sectional view of a superconducting device of Example 2 of the present invention.

FIG. 3 is a manufacturing process diagram of a superconducting device of Example 3 of the present invention.

FIG. 4 is a schematic cross-sectional view (a) of a superconducting device of Example 4 of the present invention and a schematic view (b) of a channel layer.

FIG. 5 is a schematic cross-sectional view (a) and (b) of a superconducting device of Example 5 of the present invention and a schematic view of a channel layer (c).

FIG. 6 is a schematic diagram of a channel layer according to a sixth embodiment of the present invention.

[Explanation of symbols]

 1 channel layer 2 gate insulating film, 3 gate electrode, 4 source electrode, 5 drain electrode, 6 electric conduction layer 7 contact layer 8 negative resist 10 substrate 11 oxide thin film 12 oxide superconducting thin film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kentaro Setsune 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (14)

[Claims] 1. A superconducting element comprising at least a channel layer, a source electrode and a drain electrode in contact with the channel layer, a gate insulating film, and a gate electrode in contact with the gate insulating film, wherein the channel layer is at least oxidized. 1. A superconducting device comprising a material superconductor, wherein the gate insulating film is a film having ferroelectricity. 2. The superconducting element according to claim 1, wherein the channel layer, the gate insulating film, and the gate electrode are formed of a thin film and are formed in a laminated structure on the substrate. 3. An electrically conductive layer, a ferroelectric gate insulating film in contact with the electrically conductive layer, a channel layer in contact with the gate insulating film, a source electrode, a drain electrode and a gate electrode in contact with the channel layer. A superconducting device comprising at least the above, wherein the channel layer contains at least an oxide superconductor, and the gate insulating film is a film having ferroelectricity. 4. The superconducting device according to claim 3, wherein the electrically conductive layer, the gate insulating film, the channel layer, and the gate electrode are formed of thin films and are formed in a laminated structure on the base. 5. The superconducting device according to claim 1, wherein the number of gate electrodes is at least two. 6. The method according to claim 1, wherein the channel layer contains an oxide superconductor containing at least Bi, and the gate insulating film contains a ferroelectric containing at least Pb or a ferroelectric containing Bi. Superconducting element. 7. The channel layer contains at least an oxide superconductor or an oxide normal conductor represented by the following formula (Formula 1), and the gate insulating film contains at least (Pb _{1 -x} La).
_x ) (Zr _1-y Ti _y ) _{1-x / 4} O ₃ (0 ≦ x ≦ 0.2,
0 ≦ y ≦ 1.0) or a ferroelectric substance represented by Bi ₃ T
The superconducting element according to claim 1, which contains a ferroelectric represented by i ₄ O ₁₂ . [Chemical 1] 8. The superconducting element according to claim 1, wherein the channel layer is formed of a laminated film composed of an oxide superconductor containing at least Cu and Bi and an oxide containing Cu and Bi. 9. A channel layer is formed on a substrate, a gate insulating film is formed on the channel layer, and a gate electrode is formed on the gate insulating film, and a superconducting element is manufactured using the laminated film. Method for manufacturing superconducting device. 10. The film forming temperature of the channel layer is at least 6
The temperature is 00 ° C. or higher, and the gate insulating film formation temperature is 6
The method for producing a superconducting device according to claim 9, wherein the temperature is 00 ° C. or lower. 11. The method for manufacturing a superconducting device according to claim 9, wherein at least the channel layer, the gate insulating film, and the gate electrode are formed in the same vacuum. 12. An electrically conductive layer is formed on a substrate, a gate insulating film is formed on the electrically conductive layer, a channel layer is formed on the gate insulating film, and a gate electrode is formed on the channel layer. A method of manufacturing a superconducting device, comprising forming a film, and manufacturing a superconducting device using the laminated film. 13. The film forming temperature of the gate insulating film is 600 ° C. or lower, and after forming the gate insulating film, the substrate temperature is heated to 600 ° C. or higher to form the channel layer. A method for manufacturing the superconducting device according to. 14. The method for manufacturing a superconducting device according to claim 9, wherein the electrically conductive layer, the gate insulating film, the channel layer, and the gate electrode are formed in the same vacuum.