JP4056575B2 - Superconducting device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a superconducting element using superconducting application technology and a method for manufacturing the same. More specifically, the present invention relates to a superconducting element using an oxide superconductor and a method for manufacturing the same.
[0002]
[Prior art]
When fabricating an element including a Josephson junction, which is the basis of a superconducting electronic device, it is necessary to form a tunnel layer serving as a barrier with good controllability. When forming a superconducting element, the superconducting coherence length is an important parameter at the interface in order to form the tunnel layer with good controllability.
[0003]
The types of superconducting elements comprising Josephson junctions are broadly classified into a stacked type and a flat type. Since the superconducting characteristics of the oxide superconductor constituting the superconducting element are sensitively affected by the crystal structure and composition, a deteriorated layer is generated due to a defect at the junction interface. In this case, if the coherence length is short, good bonding characteristics cannot be obtained. In a c-axis oriented thin film widely used in a laminated type, the coherence length in the c-axis direction is short, making it difficult to produce a tunnel junction, and reproducibility during formation has been a problem.
[0004]
Further, in superconducting elements expected to realize integrated elements, it is known that the matching of characteristics between Josephson junctions affects the sensitivity.
[0005]
[Problems to be solved by the invention]
In view of the above points, research on reproducibility has continued actively. Among these, the flat type using a grain boundary junction fabricated on a bicrystal substrate having a one-dimensional grain boundary on the substrate has good reproducibility, so that a Josephson junction can be fabricated relatively easily. ing. However, since the position where the superconducting element is manufactured is fixed, there is a problem in integration, and both the stacked type and the flat type have practical problems.
[0006]
The present invention has been made to solve the above-described problems in the prior art, and an object of the present invention is to provide a high-quality superconducting element formed with good reproducibility at an arbitrary place on a substrate and a method for manufacturing the same. .
[0007]
[Means for Solving the Problems]
To achieve the object, the superconducting device according to the invention, a processed substrate having a gate electrode made of triangular cross-section convex region on the surface, the oxide thin layer formed on the working board The oxide superconducting film formed on the oxide thin film layer ; and the Josephson coupling part comprising a crystal grain boundary formed inside the oxide superconducting thin film on the tip of the convex region; A drain electrode and a source electrode sandwiching the crystal grain boundary are provided. According to the structure of this superconducting element, it is possible to realize a high-quality superconducting element with good reproducibility at an arbitrary position on the processed substrate by providing a convex region at an arbitrary position on the substrate. .
[0008]
Moreover, in the structure of the superconducting element of the present invention, it is preferable that the convex region is a metal crystallized by orientation. According to this preferred example, an oxide thin film and a superconducting thin film can be formed on the convex region with good crystallinity, and a high-quality superconducting element can be produced relatively easily. In this case, the oriented and crystallized metal is preferably platinum.
[0009]
Moreover, in the structure of the superconducting element of the present invention, it is preferable that the convex region is a thin line .
In the configuration of the superconducting element of the present invention, the oxide thin film layer is preferably an insulating film.
[0010]
According to the superconducting element configured as described above, the metal (metal thin film) can be used as an electrode for applying an electric field by using a metal (metal thin film) crystallized in the linear convex region. Thus, it is possible to configure a field effect element that controls the electric field of carriers at the grain boundary junction.
[0011]
The first method of manufacturing a superconducting device according to the present invention includes the step of forming the oxide superconducting film on a processing substrate having a gate electrode formed on a surface thereof having a triangular section in the cross section, the oxide The oxide superconducting film is oriented and crystallized by annealing the superconducting film, the oxide thin film layer is formed between the processed substrate and the oxide superconducting film, and the convex region Forming a crystal grain boundary inside the oxide superconducting thin film on the tip; and forming the drain electrode and the source electrode so as to sandwich the crystal grain boundary . According to the first manufacturing method of the superconducting element, it is possible to form a crystal grain boundary in the oxide superconducting film on the convex region, and therefore, an element having a Josephson junction is relatively easy. Can be manufactured.
[0012]
Further, the in the first method of manufacturing a superconducting device of the present invention, after depositing an oxide superconducting film on said processing board, intends line high-temperature annealing. According to which this, not only it is possible to improve the crystallinity and the superconducting properties of the oxide superconducting film, forming an oxide layer of high resistivity at the interface between the oxide superconductor film and the convex regions Therefore, it is possible to easily insulate the metal convex region and the oxide superconducting film. In this case, the oxide film and the oxide superconducting film are preferably films in a polycrystalline state or an amorphous state. According to this preferable example, by performing high-temperature annealing, an element having large crystal grains and high superconducting characteristics and grain boundary resistance can be realized.
[0013]
Further, a second method for manufacturing a superconducting device according to the present invention includes a step of forming the oxide thin film layer on a processed substrate having a gate electrode formed on the surface thereof having a convex region having a triangular cross section. Forming the crystal grain boundary inside the oxide superconducting thin film on the convex region by forming the oxide superconducting film on the oxide thin film layer while heating, and the crystal Forming the drain electrode and the source electrode so as to sandwich the grain boundary. According to is this, for easy control of the thickness and characteristics of the channel layer in the field-effect element, it is possible to easily manufacture the device.
[0014]
The processed substrate having a gate electrode composed of a convex region having a triangular cross section on the surface, an electric field is applied between the tip of the scannable needle and the surface of the substrate to place the convex region on the substrate. It is preferable to obtain by forming.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described more specifically using embodiments. Here, although typical embodiment is described, this invention is not limited by this.
[0016]
(First embodiment)
FIG. 1 is a process cross-sectional view showing a process for manufacturing a superconducting element in the first embodiment of the present invention. Hereinafter, the manufacturing process of the superconducting element will be described with reference to FIGS. 1 (a) to 1 (e).
[0017]
FIG. 1A shows a substrate 11 constituting the superconducting element in the present embodiment. As this substrate 11, for example, a SrTiO ₃ single crystal substrate can be used.
[0018]
In the process shown in FIG. 1B, a platinum thin film 12 having a thickness of about 100 nm was deposited on the substrate 11 under an argon atmosphere of 60 mTorr (about 8.0 Pa) at a temperature of the substrate 11 of 500.degree. The formed platinum thin film 12 was oriented to (100). Hereinafter, the substrate formed in this step (the platinum thin film 12 having a thickness of about 100 nm is formed on the substrate 11) is referred to as a “thin film substrate”.
[0019]
Next, in the process shown in FIG. 1C, a 2 nA tunnel current was passed between the probe 13 and the surface of the thin film substrate using a scanning tunneling microscope, and a bias voltage of -4 V was applied. As a result, atomic groups on the surface of the thin film substrate were induced, and a thin line-shaped convex region 14 was formed on the thin film substrate. The probe 13 of the scanning tunnel microscope used is gold or platinum. By observation with an atomic force microscope (AFM), it was confirmed that a convex portion having a triangular cross section was formed in the processed region (the region processed in this step). The processed convex region 14 had a width of about 250 nm and a height of about 10 nm by scanning with the probe used. Hereinafter, the substrate formed in this process is referred to as a “processed substrate”.
[0020]
Next, in the step shown in FIG. 1D, a polycrystalline or amorphous Bi ₂ Sr ₂ CaCu ₂ O _x oxide superconducting thin film 15 is formed on a processed substrate by sputtering to a thickness of about 200 nm. Formed with. In this state, the oxide superconducting thin film 15 was oriented and crystallized by performing high-temperature annealing at a temperature of about 800 ° C. to 850 ° C. in a mixed atmosphere of oxygen and nitrogen (including 2 to 15% of oxygen). . FIG. 1E shows a state after this process. That is, in FIG. 1E, the oxide superconducting thin film 17 which has been crystallized by orientation is formed by a high temperature annealing process. At this time, it was recognized that a high-resistance oxide thin film layer 16 was formed between the platinum thin film 12 and the oriented crystallized oxide superconducting thin film 17. Moreover, it was recognized that the grain boundary 18 was formed on the convex region 14.
[0021]
Next, in the step shown in FIG. 1 (f), a width of 1 μm and a length are obtained by photolithography and an etching technique using Ar ions so that the grain boundary 18 portion becomes a grain boundary type Josephson junction. After forming a superconducting bridge having a wiring pattern of 10 μm across the convex region, wiring metal electrodes 19a and 19b were formed to produce a superconducting element. Here, the wiring metal electrodes 19a and 19b are formed so as to sandwich the grain boundary 18 formed on the convex region 14, respectively. The wiring metal electrodes 19a and 19b and the convex region 14 of the platinum thin film 12 function as respective electrodes of the superconducting element. For example, the wiring metal electrode 19a is a drain electrode, the wiring metal electrode 19b is a source electrode, and the convex region 14 of the platinum thin film 12 is a gate electrode.
[0022]
FIG. 2 is a plan view showing the element shape of the superconducting element in the present embodiment formed through the above steps. As is apparent from FIG. 2, an oriented supercrystallized thin oxide film 17 is formed on the substrate 11, and the grain boundary 18 portion is a grain boundary type Josephson junction.
[0023]
FIG. 3 is a diagram showing current-voltage characteristics of the superconducting element in the present embodiment. As shown in FIG. 3, in the superconducting device of the present embodiment, a typical Shapiro step was observed when microwaves were irradiated at a temperature of T to 83K. This confirmed that a Josephson junction element was obtained.
[0024]
According to the method for manufacturing a superconducting element according to the present embodiment described above, a crystal grain boundary can be formed in the oxide superconducting thin film on the convex region 14, so that a Josephson junction is provided. Superconducting elements can be manufactured relatively easily. In addition, the oxide superconducting film 17 is deposited on the platinum thin film 12 with the convex region 14 formed thereon, and then high temperature annealing is performed, thereby improving the crystallinity and superconducting characteristics of the oxide superconducting thin film. In addition, since it is possible to form a high-resistance oxide thin film layer 16 between the platinum thin film 12 and the oxide superconducting thin film 17, insulation between the platinum thin film 12 and the oxide superconducting thin film 17 is possible. Can be easily performed.
[0025]
In the present embodiment, the Bi ₂ Sr ₂ CaCu ₂ O _x oxide superconducting thin film 15 in a polycrystalline state or an amorphous state is formed by sputtering on the substrate on which the convex region 14 is formed. The case where a Josephson junction element is manufactured has been described as an example, but the present invention is not necessarily limited to this method. For example, a Josephson junction element can be manufactured as follows. First, a Bi ₂ Sr ₂ CuO _y oxide thin film showing semiconducting conductivity is deposited on a substrate on which a convex region is formed by a sputtering method. Next, the substrate temperature is set to 650 ° C., and c-axis orientation is similarly performed by sputtering without annealing at high temperature under a mixed atmosphere of argon and oxygen (including 10 to 25% oxygen) 7.5 mTorr (about 1.0 Pa). Bi ₂ Sr ₂ CaCu ₂ O _x oxide superconducting thin film is formed. It was confirmed that the Josephson junction device fabricated as described above also exhibits the Josephson effect. However, when comparing I _c · R _n , which is the product of the critical current and the junction resistance, the one that was annealed at a high temperature was about twice as large as about 1.5 mV.
[0026]
(Second Embodiment)
Next, a superconducting element in the second embodiment of the present invention will be described. FIG. 4 is a cross-sectional view showing a superconducting element in the second embodiment of the present invention. The superconducting element in the present embodiment is manufactured as follows.
[0027]
First, a platinum thin film having a thickness of about 150 nm was deposited on the entire surface of the substrate 41 by sputtering under an argon atmosphere of 60 mTorr (about 8.0 Pa) at a temperature of the substrate 41 of 500 ° C. The deposited platinum thin film was oriented to (100). In the present embodiment, the film thickness of the platinum thin film is set to about 150 nm, but this is not necessarily limited to this film thickness, and a film to be formed on the platinum thin film later is appropriately formed. Any film thickness that can be obtained (that is, any film thickness that provides appropriate “wetability”) may be used. Therefore, for example, the thickness of the platinum thin film may be about 80 nm.
[0028]
Thereafter, the platinum thin film is processed into a thin wire shape (thin wire-like platinum thin film 42) having a width of 1 μm and a length of 10 μm by photolithography and an etching technique using Ar ions. As the substrate 41, for example, an MgO single crystal substrate can be used.
[0029]
Next, an SrTiO ₃ thin film 43 having a thickness of 500 nm was formed thereon, and a YBa ₂ Cu ₃ O ₇ oxide superconducting thin film 44 having a thickness of 100 nm was further epitaxially grown thereon by a sputtering method. These thin films were formed at a substrate 41 temperature of 650 ° C. and under a mixed atmosphere of argon and oxygen of 40 mTorr (about 5.3 Pa).
[0030]
Next, a superconducting bridge having a wiring pattern having a width of 1 μm and a length of 10 μm is formed so as to cross the processing region (processed convex region) so as to have a shape substantially similar to that of FIG. It formed by the etching technique using Ar ion.
[0031]
FIG. 4 shows a cross section of the superconducting element manufactured by the above process. In FIG. 4, 41 is a substrate, 42 is a thin platinum film processed into a thin line, 43 is a SrTiO ₃ thin film, 44 is a YBa ₂ Cu ₃ O ₇ oxide superconducting thin film, 45 is a grain boundary portion, and 46 and 47 are electrodes. It is. FIG. 4 shows a case where a thin film-processed platinum thin film 42 is used as a gate electrode, an electrode 46 and an electrode 47 are used as a source electrode and a drain electrode, and an SrTiO ₃ thin film 43 is used as a gate barrier. 1 shows the configuration of a field effect element that controls the superconducting current flowing through the.
[0032]
That is, the superconducting element in FIG. 4 is provided with a convex region (platinum thin film processed into a thin line shape) 42 made of oriented and crystallized metal on a substrate 41 as a gate electrode, and an oxide insulating film (SrTiO 2) thereon. ₃ thin film 43) is deposited, and a YBa ₂ Cu ₃ O ₇ oxide superconducting thin film 44 is further deposited thereon, whereby a grain boundary portion 45 is formed on the convex region 42. A drain electrode 46 and a source electrode 47 are formed on both sides. In this element, the conductance between the drain electrode 46 and the source electrode 47 was changed by applying a voltage to the gate electrode (platinum thin film 42). As a result, a field effect element could be obtained.
[0033]
According to the method for manufacturing a superconducting element according to the present embodiment described above, since the thickness and characteristics of the channel layer of the field effect element can be easily controlled, the element can be manufactured easily.
[0034]
In this embodiment, the case where the gate electrode portion (convex region 42) is formed by an etching technique using photolithography and Ar ions has been described as an example. However, the present embodiment is not necessarily limited to this method. It is not a thing. For example, the gate electrode portion (convex region 42) may be formed by applying an electric field between the probe and the surface of the thin film substrate using a scanning tunneling microscope.
[0035]
【The invention's effect】
As described above, according to the present invention, it is possible to solve the problems of the conventional type using a bicrystal substrate, which is a flat superconducting element, and can be placed anywhere on the substrate. It is possible to provide a high-quality superconducting element formed with good reproducibility and a method for manufacturing the same. Moreover, a field effect element can also be comprised by using the orientation crystallized metal for the processed convex part area | region. Therefore, since the device can be manufactured by a simple manufacturing process, the integration technology can be improved, and a superconducting circuit using a transistor circuit or a single flux quantum device can be obtained, thereby realizing a superconducting electronic device. It becomes the basic technology in doing.
[Brief description of the drawings]
FIG. 1 is a process cross-sectional view showing a manufacturing process of a superconducting element in the first embodiment of the present invention. FIG. 2 is a plan view showing an element shape of the superconducting element in the first embodiment of the present invention. FIG. 3 is a diagram showing current-voltage characteristics of the superconducting element in the first embodiment of the present invention. FIG. 4 is a cross-sectional view showing the superconducting element in the second embodiment of the present invention.
DESCRIPTION OF SYMBOLS 11,41 Substrate 12 Platinum thin film 13 Scanning tunnel microscope probe 14 Convex region 15 Oxide superconducting thin film 16 Oxide thin film layer 17 Oxide superconducting thin film
18 Grain boundary 19a, 19b Metal electrode 42 for wiring Platinum thin film (gate electrode) processed into fine wire shape
43 SrTiO ₃ thin film (gate barrier)
44 Superconducting thin film 45 Grain boundary part 46 Electrode (source electrode)
47 electrode (drain electrode)

Claims (9)

A processed substrate having a gate electrode formed of a convex region having a triangular cross section on the surface ;
An oxide thin film layer formed on the working board,
And the oxide formed on the oxide thin film layer on the superconducting film,
Josephson coupling part consisting of crystal grain boundaries formed inside the oxide superconducting thin film on the tip of the convex region;
A superconducting device comprising a drain electrode and a source electrode sandwiching the crystal grain boundary .   The superconducting device according to claim 1, wherein the convex region is an orientation crystallized metal.   The superconducting element according to claim 2, wherein the orientation-crystallized metal is platinum. The superconducting device according to claim 1, wherein the convex region has a thin line shape . The superconducting element according to claim 1, wherein the oxide thin film layer is an insulating film. A processed substrate having a gate electrode formed of a convex region having a triangular cross section on the surface ;
An oxide thin film layer formed on the working board,
And the oxide formed on the oxide thin film layer on the superconducting film,
Josephson coupling part consisting of crystal grain boundaries formed inside the oxide superconducting thin film on the tip of the convex region;
A drain electrode and a source electrode sandwiching the crystal grain boundary;
A method of manufacturing a superconducting device comprising:
A step of forming the oxide superconducting film on a processing substrate having a gate electrode formed of a convex region having a triangular cross section on the surface;
The oxide superconducting film is annealed to crystallize the oxide superconducting film, form the oxide thin film layer between the processed substrate and the oxide superconducting film, and Forming the crystal grain boundary inside the oxide superconducting thin film on the tip of the partial region; and
Forming the drain electrode and the source electrode so as to sandwich the crystal grain boundary
The manufacturing method of the superconducting element which has this. 7. The method of manufacturing a superconducting element according to claim 6, wherein the oxide thin film layer and the oxide superconducting film are polycrystalline or amorphous films. A processed substrate having a gate electrode formed of a convex region having a triangular cross section on the surface;
An oxide thin film layer formed on the processed substrate;
An oxide superconducting film formed on the oxide thin film layer;
Josephson coupling part consisting of crystal grain boundaries formed inside the oxide superconducting thin film on the tip of the convex region;
A drain electrode and a source electrode sandwiching the crystal grain boundary;
A method of manufacturing a superconducting device comprising:
Forming the oxide thin film layer on a processing substrate having a gate electrode formed of a convex region having a triangular cross section on the surface;
By forming the oxide superconducting film on the oxide thin film layer while heating the processed substrate, the crystal grain boundary is formed inside the oxide superconducting thin film on the tip of the convex region. And the process of
Forming the drain electrode and the source electrode so as to sandwich the crystal grain boundary
A method of manufacturing a superconducting element having A processed substrate having a gate electrode composed of a convex region having a triangular cross section on the surface applies an electric field between the tip of a scannable needle and the surface of the substrate so that the convex region is placed on the substrate. The method of manufacturing a superconducting element according to any one of claims 6 to 8, which is obtained by forming.

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