JP2815382B2 - Conductive oxide laminate - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive oxide which can quantitatively control and further fix the oxygen concentration of a conductive oxide such as an oxide superconductor. It relates to a laminate.

(Conventional technology) Conductive oxides are expected to be applied to electronic devices such as sensors and varistors. Above all, oxide superconductors are expected to be used in various applications and have received much attention. On the other hand, the physical properties of these conductive oxides greatly depend on the oxygen concentration in the oxide, and in order to apply conductive oxides, the oxygen concentration must be precisely and stably controlled.
It is said that it is necessary to fix.

As a conventional method of controlling the oxygen concentration of a conductive oxide, a thermal oxidation method in a waste or in an oxygen atmosphere, and an oxidation method by oxygen plasma using sputtering or CVD are generally used. The former is mainly used for controlling the oxygen concentration of a bulk or thick-film conductive oxide, and the latter is mainly used for controlling the oxygen concentration of a thin-film conductive oxide.

Further, as a method of fixing the oxygen concentration of the conductive oxide,
After controlling the oxygen concentration, it is most common to coat the oxide with a material having a high oxygen barrier property.

(Problems to be Solved by the Invention) When the oxygen concentration of the conductive oxide is controlled by using a thermal oxidation method, depending on the type of the conductive oxide, the temperature is high, for example, 800 to 1000 ° C. for the oxide superconductor. Since the conductive oxide must be heated to such a high temperature, it may be difficult to apply the conductive oxide to electronic devices and the like. In addition, when the oxidation method using oxygen plasma is used, the oxygen concentration of the conductive oxide changes greatly depending on the state of the plasma. Therefore, for the purpose of application, a conductive oxide having a predetermined oxygen concentration can be obtained with good reproducibility. If so, the state of the plasma must always be strictly controlled, which is often difficult in practice. Further, with these oxygen concentration control methods, it is difficult to quantitatively evaluate the amount of oxygen taken into the conductive oxide.

Further, if the surface is coated with a material having a high oxygen barrier property after controlling the oxygen concentration to fix the oxygen concentration of the conductive oxide, the oxygen concentration may be changed in the coating process. .

As described above, at present, there is no means capable of accurately controlling the oxygen concentration of the conductive oxide, and no means capable of stably maintaining the oxygen concentration.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a first object of the present invention is to provide a conductive oxide laminate in which the oxygen concentration of the conductive oxide can be accurately controlled, and which can be easily readjusted even with its aging. A second object of the present invention is to provide a conductive oxide laminate which can stably maintain an accurately controlled oxygen concentration and has excellent long-term stability of characteristics.

(Structure and Function of the Invention) The above-mentioned object is achieved by the present invention described below.

That is, the present invention provides a conductive oxide laminate comprising a laminate in which a conductive oxide and a solid electrolyte having oxygen ion conductivity are laminated, and wherein the oxygen concentration of the conductive oxide is controlled via the solid electrolyte. In the body, an electrode that allows oxygen to pass through and ionizes or deionizes the outer surface on the solid electrolyte side of the laminate so as to face the conductive oxide has an oxygen barrier property that does not allow oxygen to permeate the outer surface on the conductive oxide side. A conductive oxide laminate comprising an electrode provided and the conductive oxide covered with an oxygen barrier layer through which oxygen cannot pass so that there is no exposed portion.

The present invention described above is a laminate in which a solid electrolyte having oxygen ion conductivity and a conductive oxide are laminated, and a current is applied by applying a voltage in the laminating direction while maintaining an appropriate temperature. The inventors have found that the oxygen ion conductivity can adjust the oxygen concentration of oxygen in the conductive oxide, and that the oxygen concentration can be precisely controlled by the amount of electric current (coulomb amount).

And, as is apparent from the above-described configuration, the laminate of the present invention can adjust the oxygen concentration in each case by merely arranging electrodes on both sides and flowing current while maintaining an appropriate temperature.
If it is adjusted periodically, stable characteristics can be maintained over a long period of time, and it can be adjusted at a low temperature as will be apparent from the examples described later. it can. In addition, from the viewpoint of periodic adjustment recovery, a configuration in which the electrodes are laminated and fixed to the laminate is preferable.

By the way, from the viewpoint of long-term stability, in the present invention described above, after the conductive oxide is provided with an electrode, the conductive oxide is covered with an oxygen barrier layer through which oxygen cannot pass so that there is no exposed portion. With this configuration, after the other electrode is arranged in contact with the surface of the solid electrolyte facing the conductive oxide, the power is turned on, a current flows, and the oxygen concentration of the conductive oxide is adjusted to a desired value. When the power was turned off and the solid electrolyte was cooled to a temperature at which the oxygen electrolyte did not exhibit oxygen ion conduction, the solid electrolyte became an oxygen barrier layer. As a result, a conductive oxide laminate that is stable for a long period of time at a specific oxygen concentration is realized.

Among the electrodes used for controlling the oxygen concentration of the above-described laminate of the present invention, the electrode arranged in contact with the solid electrolyte has a porous structure described later so that the solid electrolyte can exchange oxygen with the atmosphere. used.

 Hereinafter, the present invention will be described in detail.

The conductive oxide used in the laminate of the present invention may be an electron oxide.
As long as it is a conductive oxide having mixed ion conductivity, its type, material, and ratio of the electronic conductivity and the ion conductivity to the total conductivity are not particularly limited. Such conductive oxides include, for example, conductive oxides such as Ti ₂ O ₃ , Ti ₂ O _{5, and} oxide superconductors that have recently attracted attention. The oxide superconductor has a general formula: (La _1-x M _x ) ₂ Cu O
_4-δ (M = Ba, Sr, Ca, X = 0 to 1, δ = 0 to 1) La—Sr—Cu—O-based superconductor represented by the general formula: LnBa ₂ Cu ₃ O
_7−δ (Ln = Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, Lu, δ
Y-Ba-Cu-O system superconductor represented by = 0-1), the general formula; represented by _{n = 1,2,3); Bi 2 Sr} 2 Ca n-1 Cu n O (y ≦ 2n + 4 Bi-Sr-Ca-Cu-O-based superconductor, general formula; Tl ₂ B
a ₂ C a _n-1 C _n O _y (y ≦ 2n + 4; n = 1,2,3) T
l-Ba-Ca-Cu-O-based superconductors and the like. By the way, the present invention can accurately control the oxygen concentration at a low temperature as described above, and furthermore, can have a stable configuration over time. It can be preferably applied to an oxide superconductor. The type and material of the solid electrolyte having oxygen ion conductivity used in the present invention are not particularly limited as long as the solid electrolyte has oxygen ion conductivity. Such solid _{electrolyte, Y 2 O 3 -ZrO 2 (} YSZ), CaO-ZrO 2 (C
SZ), Bi ₂ O ₃ , Bi ₂ O ₃ —Y ₂ O ₃ , Bi ₂ O ₃ —Nb ₂ O ₅ , Bi ₃ O ₃ —WO ₃ , etc. are known. Those having high conductivity, low electron conductivity, a dense structure, and high oxygen barrier properties at temperatures other than the temperature at which oxygen ion conduction is exhibited are preferable. From this point, Y ₂ O ₃ -ZrO ₂ (YSZ), CaO-ZrO ₂
A solid electrolyte of an oxide solid solution type having a fluorite (CaF ₂ ) type crystal structure such as (CSZ) is desirable.

The thickness, size, and shape of the conductive oxide and the solid electrolyte having oxygen ion conductivity are not particularly limited. In addition, the conductive oxide may be an oxide alone, may be formed as a device, or may be formed as a part of an electronic device or the like.

The method for laminating the conductive oxide and the solid electrolyte may be any connection as long as they can exchange oxygen ions. There is no particular limitation, and it is sufficient to simply make the two adhere. However, these conditions must be selected so that the laminate is mechanically stable when the desired laminate is actually formed. For example, as a preferred example, when a thin film of a solid electrolyte having oxygen ion conductivity is laminated on one side of a mechanically stable plate-shaped conductive oxide by physical vapor deposition such as sputtering, a mechanically stable plate-like conductive oxide is obtained. When a conductive oxide thin film is laminated on one side of a solid electrolyte having oxygen ion conductivity by physical vapor deposition such as sputtering, or a mechanically stable flat conductive oxide When a stable and flat plate-like solid electrolyte having oxygen ion conductivity is press-bonded by a mechanical method so that there is no gap, and the like. Above all, a thin film laminate in which a conductive oxide or solid electrolyte thin film is formed on a flat substrate of a conductive oxide or solid electrolyte by a vapor deposition method such as physical vapor deposition (PVD) or chemical vapor deposition (CVD) Those having a structure are preferable because they have excellent electrical connectivity and mechanical adhesiveness.

Next, a procedure for adjusting the oxygen concentration of the conductive oxide of the laminate obtained as described above will be described. After forming a laminate of the conductive oxide and the solid electrolyte having oxygen ion conductivity, electrodes are arranged on the surfaces of the laminated oxide and the solid electrolyte, respectively. On the oxide side, a nonporous electrode having an oxygen barrier property is formed on a part of the surface of the oxide so as not to contact the solid electrolyte. This electrode is a conductive material having high conductivity showing only electron conductivity, and if it is chemically stable, there is no particular limitation on its type, but preferred examples include platinum and gold. . On the solid electrolyte side, a porous electrode is formed on a part of the surface of the solid electrolyte, through which oxygen is passed to ionize or deionize so as not to come into contact with the conductive oxide. The type of the electrode is not particularly limited as long as it is a conductive substance exhibiting electron conductivity and having the same electric conductivity and is chemically stable. Preferable examples include platinum.

Although the thickness and area of each electrode are not particularly limited, it is preferable that the area of the electrode is at least a fraction of the contact area between the oxide and the solid electrolyte.

After the electrodes are formed on the laminate, a DC power supply is connected between the formed nonporous electrode and the porous electrode, and the laminate is heated from room temperature in an atmosphere containing air or oxygen to maintain a constant temperature. This temperature is not particularly limited as long as the oxide and the solid electrolyte used in the laminate are in a temperature range in which oxygen can be injected or discharged in the oxide and the solid electrolyte can conduct oxygen ions. . This temperature varies depending on the solid electrolyte used, the characteristics of the target conductive oxide, and the like, but is usually in the temperature range of about 300 to 900 ° C.

In order to increase the oxygen concentration of the oxide, the cathode of the DC power supply is connected to the electrode on the solid electrolyte side, and the anode is connected to the electrode on the oxide side, and the laminate is heated to a certain temperature within the above temperature range. In the heated state, an appropriate current is applied. Then, in the porous electrode of the solid electrolyte, oxygen molecules and electrons react to generate oxygen ions. The oxygen ions conduct in the solid electrolyte and are injected into the oxide.
The implanted oxygen ions are taken into oxygen vacancies in the oxide and combine with surrounding ions. Inside the oxide,
It emits electrons to keep the charge neutral. The emitted electrons return to the anode of the power supply through the nonporous oxide electrode.
Since a non-porous electrode is made of a conductive material exhibiting only electron conductivity, oxygen ions are blocked and only electrons pass.

Conversely, in order to decrease the oxygen concentration of the oxide, the polarity of the DC power supply is reversed, and a current of an appropriate magnitude is passed while heating to the same temperature as above. Then, inside the oxide of the laminate, a reverse reaction of the above-described reaction proceeds, and ions are discharged from the oxide to the solid electrolyte. The discharged oxygen ions pass through the solid electrolyte, are absorbed by the solid electrolyte porous electrode, that is, are deionized, and are released into the atmosphere as oxygen molecules.

The magnitude of the current flowing through the laminate is not particularly limited, but, needless to say, it must be within a range that does not destroy the laminate.

The oxygen concentration of the conductive oxide can be controlled by flowing a current in the stacking direction of the stacked body and adjusting the direction, magnitude, and duration of the current as described above. Then, when a predetermined oxygen concentration is obtained, the current is stopped, and the laminate is cooled to a temperature at which oxygen ion conduction of the solid electrolyte stops, whereby the oxygen concentration of the conductive oxide can be fixed.

However, after controlling the oxygen concentration of the conductive oxide as described above, if the oxygen partial pressure at the interface between the conductive oxide and the solid electrolyte is different from the oxygen partial pressure in the atmosphere, even after the current is stopped. It is conceivable that a slight amount of oxygen ions move between the conductive oxide and the solid electrolyte, electric polarization occurs in the solid electrolyte according to the difference in oxygen partial pressure, and a slight change occurs in the oxygen concentration. On the other hand, after stopping the current, the temperature at which the oxygen ion conduction of the solid electrolyte stops while applying a voltage of a magnitude necessary and sufficient to maintain the obtained oxygen concentration to the lamination method of the laminate. If the laminate is cooled down, the value of the cooled oxygen concentration can be fixed without changing. Therefore, when it is necessary to more strictly control the oxygen concentration as in the case of an oxide superconductor, such a control method is preferably applied.

By the way, depending on the type of the conductive oxide, there is a type in which oxygen is exchanged between the exposed portion and the atmosphere in which it is used, and the above-described stacked structure alone controls or fixes the oxygen concentration. It can be difficult. In the case of such an oxide, after the electrodes are formed on the laminate as described above, the portion of the oxide surface that is exposed to the atmosphere has a high oxygen barrier property that blocks oxygen and does not pass through. The object can be achieved by forming a laminated structure covered with a material having high electrical insulation.
The coating material is not particularly limited as long as it has the above-described oxygen barrier property, and a known sealing agent for an electronic device can be applied.However, from the viewpoint of heat resistance, Al ₂ O ₃ , MgO, Al ₂ O ₃ −MgO , SiO ₂ , Si
Ceramic dielectrics ₃ N ₄ or the like are preferable.

As described above, if the exposed portion of the conductive oxide is covered with the above-described oxide barrier or the like as necessary at the stage of forming the stacked body, the entire surface of the oxide is in contact with the oxygen barrier layer and the oxygen barrier property. Below the temperature of high electrode and ionic conductivity, it is coated with a solid or electrolyte exhibiting oxygen barrier properties. In other words, since the entire surface is coated with an oxygen barrier layer, Y-Ba-
Even in the case of a conductive oxide having an unstable oxygen concentration, such as a Cu-O-based oxide superconductor, which directly exchanges oxygen with the atmosphere, it is possible to control and fix the oxygen concentration of the oxide. Will be possible. In addition, oxygen is exchanged with the atmosphere,
In the case of a conductive oxide in which the rate of change of the oxygen concentration is very slow and only the change with time is a problem, the formation of the oxygen barrier layer may be performed after the adjustment of the oxygen concentration. In this case, it is not necessary to withstand the temperature at the time of adjusting the oxygen concentration,
Various synthetic resins known as sealants for electronic devices can be applied to the oxygen barrier layer.

By the way, it is needless to say that the oxygen barrier layer does not need to be composed of the same material.For example, a material having the characteristics is used where electrical insulation is required. Such as using conductive material,
A configuration according to the use of the laminate is adopted. The important point is that
The entire surface of the conductive oxide is coated with an oxygen barrier material.

Note that the formation of the oxygen barrier layer is appropriately selected from known formation methods depending on the material to be used. For example, in the case of the above-described ceramic dielectric, it is preferable to form it into a thin film using a PVD method such as reactive sputtering from the viewpoint of adaptability to various shapes and adhesion, film quality, and the like. Is preferably applied for the following reason.

 Hereinafter, examples of the present invention will be described.

(Example 1) As shown in FIG. 1, the size is 20 mm × 20 mm and the thickness is 1 m.
The YSZ substrate 1 is placed at the center on a solid electrolyte substrate (hereinafter, referred to as “YSZ substrate”) 1 made of a YSZ single crystal having a flat plate shape of m.
While heating to ° C., using an excimer laser sputtering device, the conductive oxide film 2 in the size of 10 mm × 10 mm,
A Y-Ba-Cu-O thin film having a thickness of 1 µm (specifically, Y ₁ Ba ₂ Cu ₃
O _7-δ thin film). YSZ is known as a solid electrolyte having oxygen ion conduction. In addition, Y-Ba-
Cu-O is known as an oxide superconductor having an oxygen vacancy.

As shown in the figure, a porous flat plate-like platinum electrode 3 was previously formed on the surface of the YSZ substrate 1 opposite to the surface on which the conductive oxide film 2 was formed as follows. That is, after the platinum paste was applied to YSZ, it was formed by heating to about 100 ° C. in the air. The porous platinum electrode 3 had a size of 15 mm × 15 mm larger than the conductive oxide film 2 and was formed so as to face the conductive oxide film 2.

Next, an Al ₂ O ₃ -MgO thin film 4a having a thickness of 1 μm as an electrically insulating protective film also serving as the oxygen barrier layer 2 was formed using the above-mentioned YSZ-coated film.
While heating the substrate 1 to 400 ° C., the Y—Ba—Cu—O thin film 2
Y-Ba using an excimer laser sputtering device
−Cu—O thin film 2 is masked and YS is
It was formed on a Z substrate 1.

Similarly, using an excimer laser sputtering device, a width of 1 m, which also served as a resistance measuring terminal as shown in FIG.
m, a four-terminal nonporous flat platinum electrode 5 having a length of 15 mm and a thickness of 1 μm arranged at a predetermined interval was used as a Y-Ba-Cu-
It was formed so as to cross over the O thin film 2 and one end thereof to extend over the Al ₂ O ₃ —MgO thin film 4a.

After that, similarly using an excimer laser sputtering device,
Part of the formed non-porous flat platinum electrode 5 is exposed, and Y-
The Ba—Cu—O thin film 2 has a thickness of 1 μm as an electrically insulating oxygen barrier layer 4 so that the exposed surface is eliminated.
The YSZ thin film 4b was formed to have substantially the same size as the porous platinum electrode 3. When the Y—Ba—Cu—O thin film 2 is exposed to the atmosphere, its oxygen concentration is liable to change. Therefore, it is necessary to cover the Y—Ba—Cu—O thin film 2 with the oxygen barrier layer 4 so that the exposed portion disappears.

Next, the control of the oxygen concentration of the conductive oxide 2 of the laminated body and the state of fixing were confirmed as follows. That is, the cathode of the DC stabilized power supply (not shown) is connected to the porous plate-shaped platinum electrode 3 and the anode is connected to the non-porous plate-shaped platinum electrode 5. While maintaining the temperature at the indicated temperature of 500 ° C, connect the 1mA
It flowed intermittently every second. And each time Y-Ba-Cu-
The resistivity of the O thin film 2 is changed to a four-terminal nonporous flat platinum electrode 5.
Was measured by the DC four-terminal method. Then, as shown by the solid line in FIG. 3, the resistivity decreased as the amount of supplied electricity increased, and eventually became saturated at a constant value. Next, the polarity of the power supply was reversed, and a current of 1 mA was intermittently applied for 10 seconds in the reverse direction. As shown by the broken line in FIG. 3, the resistivity began to increase and eventually returned to the original value. Was. These series of Y
The change of the resistivity of the -Ba-Cu-O thin film 2 was reversible.
In addition, from the measurement of the amount of electricity (clone amount), it was found that there was a correspondence between the amount of electricity and the amount of implanted oxygen ions.

When the current was stopped and the laminate was returned to room temperature, Y-Ba-Cu-O
The resistivity of the thin film 2 was fixed to the value obtained last at 500 ° C., and its characteristics did not change with time even after being left indoors for one week or more.

Y-Ba-Cu-O is an oxygen-deficient oxide superconductor, and it is known that the higher the oxygen concentration, the lower the resistivity. Therefore, the change in the resistivity of the Y-Ba-Cu-O thin film 2 at 500 ° C. described above is caused by oxygen ions being injected and discharged from the YSZ substrate into the Y-Ba-Cu-O thin film 2, This corresponds to the fact that the oxygen concentration of the Ba—Cu—O thin film 2 is controlled. At room temperature, Y-Ba-Cu
The fact that the resistivity of the -O thin film 2 became constant indicates that Y-Ba-Cu
This corresponds to the fact that the oxygen concentration of the -O thin film 2 is fixed.

Example 2 After mixing Y ₂ O ₃ , BaCO ₃ , and CuO in ethanol such that the ratio of the number of atoms of the three elements Y, Ba, and Cu becomes Y: Ba: Cu = 1: 2: 3. ,
By baking at 930 ° C. for 10 hours, a powder of Y—Ba—Cu—O was prepared. Isopropyl alcohol was added to this powder to form a paste.

As shown in Fig. 1, the size is 20mm x 20mm and the thickness is 1mm
The Y-Ba-Cu-O paste is screen-printed on the center of the YSZ substrate 1 and then baked at 900 ° C. for 2 hours.
Y-Ba-Cu-O film 2 having a size of 0 mm × 10 mm and a thickness of 10 μm
Was formed.

However, in the center of the surface of the YSZ substrate 1 opposite to the surface on which the Y-Ba-Cu-O film 2 is formed, a porous flat plate having a size of 15 mm × 15 mm is formed in the same manner as in the first embodiment. The platinum electrode 3 was formed in advance.

As shown in FIGS. 1 and ₂ , an Al ₂ O ₃ —MgO film 4 a, a nonporous plate-like platinum electrode 5, and a YSZ thin film 4 b are laminated with an excimer laser sputtering apparatus in the same lamination structure as in the first embodiment. Each was formed in order.

The Al ₂ O ₃ —MgO film 4a is used as an insulating protective layer also serving as the oxygen barrier layer 4 while heating the YSZ substrate 1 to 400 ° C.
-Formed on the YSZ substrate 1 to a thickness of μm so as to be in contact with the side surface of the Cu-O film 2. The non-porous flat platinum electrode is a four-terminal electrode having a width of 1 mm, a length of 15 mm, and a thickness of 1 μm arranged at predetermined intervals in order to also serve as a resistivity measuring terminal.
The film was formed so as to cross over the Ba—Cu—O film 2 and extend to the Al ₂ O ₃ —MgO film 4a. Further, the YSZ thin film 4b serves as an insulating oxygen barrier layer 4 so as to cover the exposed portion of the Y-Ba-Cu-O film 2 at the center of the laminated body with a size of 15 mm × 15 mm and a thickness of 1 μm.
m.

The conductive oxide thus prepared, Y-Ba-Cu-
The resistivity of the O film 2 at a low temperature is cooled by liquid helium,
When measured using the DC four-terminal method, it showed a semiconductor-like behavior as shown in FIG. 4 and did not show superconductivity. Therefore,
The cathode of a DC stabilized power supply (not shown) is connected to the porous plate-shaped platinum electrode 3, the anode is connected to the non-porous plate-shaped platinum electrode 5, and the laminate is heated to 500 ° C. in the atmosphere. After a current of 1 mA was passed for 70 seconds to implant oxygen ions into the Y-Ba-Cu-O film 2, the power was turned off and the laminate was cooled to room temperature to fix the oxygen concentration. The low-temperature resistivity of the Y—Ba—Cu—O film 2 was measured in the same manner as described above. As shown by the solid line A in FIG. Showed conduction.

After the resistivity measurement is completed, the laminate is heated again to 500 ° C. in the air, and in the stacking direction, in the opposite direction to the previous one,
After a current of 1 mA was passed for 50 seconds to discharge oxygen ions from the Y-Ba-Cu-O film 2, the power was turned off, the laminate was cooled, and the oxygen concentration was fixed again. And Y-Ba-
When the low-temperature resistivity of the Cu—O film 2 was measured, the resistivity increased as shown by a dashed line B in FIG. 5, and no superconductivity was exhibited at a temperature of 10 K or more.

After the above operation is completed and the laminate is returned to room temperature,
The resistivity of the Y—Ba—Cu—O film 2 became constant, and no change with time was observed.

(Example 3) As shown in FIG. 1, a size of 20 mm × 20 mm and a thickness of 1 mm
Solid electrolyte substrate (hereinafter referred to as “Y
While heating the YSZ substrate 1 to 200 ° C. in the center on the “SZ substrate” 1, using an RF magnetron sputtering apparatus,
The conductive oxide film 2 has a size of 10 mm × 10 mm and a thickness of 1 mm.
μm Y-Ba-Cu-O thin film (specifically, Y ₁ Ba ₂ Cu ₃ O
After forming the ( _7-δ thin film), a heat treatment was performed at 900 ° C. for 1 hour in an oxygen atmosphere to crystallize the Y—Ba—Cu—O thin film 2. This heat treatment is performed for crystallizing the Y-Ba-Cu-O thin film 2 as described above, and is not performed for the purpose of controlling the oxygen concentration.

As shown in the same drawing as in the first embodiment, the same arrangement and the same arrangement as in the first embodiment is applied to the surface of the YSZ substrate 1 opposite to the surface on which the Y-Ba-Cu-O thin film 2 is formed. A porous flat plate-like platinum electrode 3 having a size was formed in advance.

Next, a 1 μm-thick MgO thin film 4 a as an electrically insulating protective layer also serving as the oxygen barrier layer 4 was applied to the above-mentioned YSZ substrate 1 with a film.
While heating to 400 ° C., the Y—Ba—Cu—O thin film 2 was masked using an excimer laser sputtering apparatus and formed on the YSZ substrate 1 so as to be in contact with the side surface.

Similarly, using an excimer laser sputtering apparatus, as in Example 1, four 1 mm-wide, 15 mm-long and 1 μm-thick, which also served as resistivity measuring terminals as shown in FIG. The YSZ substrate 1 with the MgO thin film 1 is traversed on the Y-Ba-Cu-O thin film 2 with a four-terminal non-porous flat platinum electrode 5 having electrodes arranged at predetermined intervals, and one end of the platinum electrode 5 extends over the MgO thin film 4a. 300 ℃
Formed while heating.

After that, similarly using an excimer laser sputtering device,
A part of the nonporous plate-like platinum electrode 5 formed while heating the YSZ substrate 1 with terminals to 400 ° C. is exposed, and the Y—Ba—Cu—O thin film 2 has no exposed surface. As the electrically insulating oxygen barrier layer 4, an MgO thin film 4 b having a thickness of 1 μm was formed in substantially the same size as the porous platinum electrode 3.

Next, the control of the oxygen concentration of the Y-Ba-Cu-O thin film 2 of the laminated body and the confirmation of the fixing state were performed in the same manner as in Example 1 as follows. That is, the cathode of a DC stabilized power supply (not shown) is connected to the porous plate-like platinum electrode 3, the anode is connected to the non-porous plate-like platinum electrode 5, and the laminate is subjected to YS.
A 1 mA current was intermittently applied for 10 seconds while the Z substrate 1 was heated to 500 ° C., which is a temperature at which oxygen ion conductivity was exhibited. Each time, the resistivity of the Y—Ba—Cu—O thin film 2 was measured by a DC four-terminal method using a four-terminal nonporous flat platinum electrode 5. Then, as shown by the solid line in FIG. 6, the resistivity decreased as the amount of supplied electricity increased. Next, when the polarity of the power supply was reversed and the 1 mA electrode was intermittently passed for 10 seconds in the reverse direction, the resistivity began to increase conversely as shown by the broken line in FIG. 6, and eventually returned to the original value. Was. These series of Y-
The change in the resistivity of the Ba—Cu—O thin film 2 shows a reversibility with a smaller hysteresis than that of the first embodiment shown in FIG. There was a certain correlation with a good correlation between the amounts of ions, indicating that accurate and accurate concentration control could be performed.

It should be noted that the excellent correspondence with almost no hysteresis is attributed to the excellent oxygen barrier property of the MgO film used for the oxygen barrier layer. According to the analysis, the MgO film used in this example is a polycrystalline film in which the (111) plane is oriented in the direction perpendicular to the film surface. Therefore, in the above-mentioned point, a polycrystalline or single-crystal MgO film having such an orientation is preferable.

When the current was stopped and the laminate was returned to room temperature, Y-Ba-Cu-O
The resistivity of the thin film 2 was fixed at 50 ° C. to the value obtained last.

Further, after completion of the resistivity measurement, the Y-Ba-Cu-O thin film 2 is transferred from the YSZ substrate 1 to the Y-Ba-Cu-O thin film 2 by using the same method as the low-efficiency measurement while maintaining the laminate at 500 ° C. in the air again. Oxygen ions were implanted, and changes in the characteristics of the Y-Ba-Cu-O thin film 2 were examined. The procedure is described below.

The cathode of the DC stabilized power supply is connected to the porous flat platinum electrode 3,
Connect the anode to the platinum electrode 5 on a non-porous flat plate, and
In the above, a current of 1 mA was applied for 20 seconds, that is, an electric quantity of 2 × 10 ^-2 coulombs was supplied. After completion of the energization, the laminate is immediately cooled to room temperature, the oxygen concentration of the Y-Ba-Cu-O thin film 2 is fixed, and then cooled with liquid helium, and the low-temperature resistance of the Y-Ba-Cu-O thin film 2 is reduced. The ratio was measured, and the C-axis length of the unit cell was measured by X-ray diffraction. Subsequently, the same operation as described above was repeated twice. In other words, the total amount of electricity of 6 × 10 ^-2 coulomb is divided into three times of 2 × 10 ^-2 coulomb and Y-Ba-
Injected into the Cu-O thin film 2, each time the Y-Ba-Cu-O thin film 2
Was measured for the resistivity at low temperature and the length of the C-axis. Also,
After all the above operations were completed, the film was allowed to stand at room temperature for one week or more. However, the resistivity of the Y—Ba—Cu—O thin film 2 did not change with time.

FIG. 7 shows the relationship between the temperature and the resistivity at a low temperature of the Y—Ba—Cu—O thin film 2 at the respective amounts of electricity measured as described above. The curves A, B, and C in the figure represent the cumulative amounts of electricity supplied, and represent the 2 × 10 ^-2 clones (A), 4 × 10 ^-2 coulombs (B), and 6 × 10 ^-2 coulombs (C). Y- in the case
5 shows the low-temperature resistivity of the Ba—Cu—O thin film 2. In the case of A, the superconducting state could not be obtained in the current measurement temperature range of 6 to 273K, but in the case of B and C, the superconducting state was obtained at 10K and 57K, respectively. The superconducting property of the Y-Ba-Cu-O thin film 2 is clearly improved as the amount of supplied electricity, in other words, the amount of injected oxygen increases.

FIG. 8 shows the amount of electricity supplied and Y-
The relationship with the length of the C-axis of the Ba—Cu—O thin film 2 is shown. It can be seen that the length of the C-axis becomes shorter as the amount of supplied electricity increases.

By the way, when the stoichiometric number (7-δ) of oxygen is in the range of 6 to 7, the YBa ₂ Cu ₃ O _7-δ superconductor has (7-
It is known that the larger the value of δ), the higher the critical temperature Tc at which the resistance becomes zero and the shorter the length of the C-axis.
(For example, Japan Journal of Applied Physics, 26,
(7), (1987), P1156, Solid State Communications,
66, (9), (1988), P953). 7 and 8 shown above.
The results in the figure are consistent with these known findings. Therefore, by the structure of laminating with the solid electrolyte of the present invention, oxygen ions are implanted into the Y-Ba-Cu-O thin film 2 corresponding to the amount of electricity supplied, and the oxygen concentration of the Y-Ba-Cu-O thin film 2 is accurately controlled. Obviously, it can be understood that the present invention has a great effect on improving and stabilizing the characteristics of the oxide superconductor.

(Effects of the Invention) As described above, the present invention has a basic structure of a laminate in which a conductive oxide such as an oxide superconductor and a solid electrolyte are laminated, and a conductive oxide that has been impossible in the past. Above all, it enables precise control of oxygen concentration in oxide superconductors, has the effect of enabling accurate control of the oxygen concentration at relatively low temperatures, and opens applications to various devices. is there. The long-awaited effect that the controlled oxygen concentration can be stably maintained over a long period of time can be obtained by the configuration in which the conductive oxide is covered with the oxygen barrier layer so that there is no exposed portion. The present invention having such an effect,
Among conductive oxides, they make a great contribution to the practical use of oxide superconductors, which are expected to have accurate control of characteristics and long-term stability in practical use, and are industrially very useful.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an embodiment of the present invention, FIG. 2 is a plan view of the embodiment, and FIG. 3 is a graph showing a control situation of an oxygen concentration of a conductive oxide by a current in the embodiment 1. The horizontal axis is the amount of electricity (coulomb) and the vertical axis is the resistivity (Ω · cm).
4 and 5 are graphs showing the results of Example 2, in which the horizontal axis is temperature (K) and the vertical axis is resistivity (Ω · cm).
FIGS. 6, 7, and 8 are graphs showing the results of Example 3, FIG. 6 is a graph showing the relationship between the amount of energized electricity (× 10 ⁻² coulombs) and the resistivity, and FIG. Temperature at low temperature (K)
FIG. 8 is a graph showing the relationship between resistivity and resistivity, and FIG.
It is a graph which shows the relationship with axis length ((triangle | delta)). 1: Solid electrolyte (YSZ) substrate, 2: Conductive oxide (Y-Ba-C)
u-O) thin film, 3: porous plate-like platinum electrode, 4: oxygen barrier layer, 5: non-porous plate-like platinum electrode.

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 39/24 ZAA H01L 39/24 ZAAB (56) References JP-A-63-158452 (JP, A) JP-A-1-148712 (JP, A) JP-A-1-157481 (JP, A) JP-A-2-504259 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 39/00 H01L 39/22-39 / 24 H01L 39/02-39/04 C01B 13/14 H01B 12/02 C01G 1/00 G01N 27/46

Claims (8)

(57) [Claims] 1. A conductive oxide laminate comprising a laminate in which a conductive oxide and a solid electrolyte having oxygen ion conductivity are laminated, wherein the oxygen concentration of the conductive oxide is controlled via the solid electrolyte. In the body, an electrode that allows oxygen to pass through and ionizes or deionizes the outer surface on the solid electrolyte side of the laminate so as to face the conductive oxide has an oxygen barrier property that does not allow oxygen to pass through the outer surface on the conductive oxide side. A conductive oxide laminate comprising an electrode, and the conductive oxide covered with an oxygen barrier layer through which oxygen cannot pass so that there is no exposed portion. 2. The conductive oxide laminate according to claim 1, wherein the electrode on the solid electrolyte side is a porous electrode, and the electrode on the conductive oxide side is a non-porous electrode. Laminate. 3. The conductive oxide laminate according to claim 1, wherein the (111) plane is oriented in the direction perpendicular to the film surface in the oxygen barrier layer. A conductive oxide laminate using a polycrystalline or single-crystal MgO thin film. 4. The conductive oxide laminate according to claim 1, wherein the conductive oxide is an oxide superconductor. 5. The conductive oxide laminate according to claim 4, wherein the conductive oxide is a Y—Ba—Cu—O-based oxide superconductor. 6. The conductive oxide laminate according to claim 1, wherein the solid electrolyte and the conductive oxide are plate-like bodies. 7. The conductive oxide laminate according to claim 6, wherein a conductive oxide thin film is laminated on the solid electrolyte substrate by a vapor deposition method. 8. The conductive oxide laminate according to claim 6, wherein a conductive oxide thin film is laminated on the solid electrolyte substrate by a coating method.