JP2774713B2 - Superconducting element - Google Patents
Superconducting elementInfo
- Publication number
- JP2774713B2 JP2774713B2 JP3245536A JP24553691A JP2774713B2 JP 2774713 B2 JP2774713 B2 JP 2774713B2 JP 3245536 A JP3245536 A JP 3245536A JP 24553691 A JP24553691 A JP 24553691A JP 2774713 B2 JP2774713 B2 JP 2774713B2
- Authority
- JP
- Japan
- Prior art keywords
- superconductor
- normal conductor
- normal
- junction
- conductor layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 239000002887 superconductor Substances 0.000 claims description 73
- 239000004020 conductor Substances 0.000 claims description 54
- 238000006467 substitution reaction Methods 0.000 claims description 14
- 230000007423 decrease Effects 0.000 claims description 12
- 229910052727 yttrium Inorganic materials 0.000 description 16
- 229910009203 Y-Ba-Cu-O Inorganic materials 0.000 description 13
- 229910002480 Cu-O Inorganic materials 0.000 description 9
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 8
- 238000004544 sputter deposition Methods 0.000 description 5
- 229910002367 SrTiO Inorganic materials 0.000 description 4
- 238000010586 diagram Methods 0.000 description 4
- 239000007788 liquid Substances 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 229910052757 nitrogen Inorganic materials 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- 238000000921 elemental analysis Methods 0.000 description 3
- 239000012535 impurity Substances 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 229920002120 photoresistant polymer Polymers 0.000 description 2
- 206010021143 Hypoxia Diseases 0.000 description 1
- 238000004458 analytical method Methods 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 208000037265 diseases, disorders, signs and symptoms Diseases 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 230000005610 quantum mechanics Effects 0.000 description 1
- 229910052761 rare earth metal Inorganic materials 0.000 description 1
- 238000000992 sputter etching Methods 0.000 description 1
Landscapes
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
Description
【0001】[0001]
【産業上の利用分野】本発明は、超電導近接効果を利用
した超電導素子に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element utilizing a superconducting proximity effect.
【0002】[0002]
【従来の技術】超電導体/常伝導体/超電導体接合で
は、これを構成する常伝導体中に両側の超電導体より及
ぼされる超電導近接効果によって、超電導電流を流すこ
とができる。このような接合を有する素子は、いわゆる
SNS接合型のジョセフソン素子として動作する。近
年、このような超電導体接合において、超電導体として
Y系酸化物超電導体を用いると共に、常伝導体として Y
系酸化物超電導体の Yを一定の割合でPrに置換した電気
伝導性酸化物を用いることが試みられている。2. Description of the Related Art In a superconductor / normal conductor / superconductor junction, a superconducting current can be caused to flow in a normal conductor forming the superconductor by a superconducting proximity effect exerted by superconductors on both sides. An element having such a junction operates as a so-called SNS junction type Josephson element. In recent years, in such superconductor joining, as superconductor
Use a Y-based oxide superconductor, and use Y
Attempts have been made to use an electrically conductive oxide in which Y in a system oxide superconductor is substituted with Pr at a certain ratio.
【0003】このような、超電導体として酸化物高温超
電導体のみを用いた超電導素子は、液体窒素温度での動
作が可能であり、実用化に向けて研究が進められてい
る。その中でも、上述した超電導体として Y系酸化物超
電導体を用い、かつ常伝導体として Y系酸化物超電導体
の Yの一部をPrで置換した電気伝導性酸化物を用いた接
合は、格子定数の差がほとんどなく、界面近傍の格子の
乱れが極めて少ないために、このような材料の組合せで
超電導素子を作製する研究が活発になってきている。[0003] Such a superconducting element using only an oxide high-temperature superconductor as the superconductor can operate at liquid nitrogen temperature, and is being studied for practical use. Among them, a junction using an Y-based oxide superconductor as the above-described superconductor and an electrically conductive oxide in which part of Y of the Y-based oxide superconductor is replaced with Pr as a normal conductor is a lattice. Since there is almost no difference between the constants and the disorder of the lattice near the interface is extremely small, research on fabricating a superconducting element using such a combination of materials has been actively conducted.
【0004】しかし、上記したような Y系酸化物超電導
体/(Y,Pr)系電気伝導性酸化物/ Y系酸化物超電導体に
よるSNS接合は、一般に臨界電流Ic の値は大きくと
れるものの、常伝導抵抗Rn が小さいため、結果的に素
子の出力であるIc ・Rn 積を大きくすることができな
いという問題を有していた。このため、上記した材料の
組合せを超電導素子に応用することは困難であった。However, as described above Y-based oxide superconductor / (Y, Pr) based SNS junction by electrically conductive oxide / Y-based oxide superconductor, although generally the value of the critical current I c is made larger since normal conductive resistance R n is small, there is a problem that it is impossible to increase the I c · R n product is consequently output elements. For this reason, it was difficult to apply the combination of the above-mentioned materials to a superconducting element.
【0005】このような問題を改善するためには、臨界
電流Ic または常伝導抵抗Rn を増やせばよいわけであ
るが、臨界電流密度は超電導現象の特性で最大値が決っ
ており、大幅に増やすことは不可能であることから、I
c ・Rn 積を大きくするためには、常伝導抵抗Rn を大
きくする必要がある。例えば、常伝導体として金属等を
用いる場合には、常伝導体中に不純物を入れる等して、
電子の不純物散乱を増やし、これによって常伝導抵抗R
n を増やす方法が試みられてきた。[0005] In order to solve such a problem, but not may be increased critical current I c or normal conductive resistance R n, the critical current density is maximum determined by the properties of superconductivity, greatly It is impossible to increase to
In order to increase the c · R n product, it is necessary to increase the normal resistance R n . For example, when a metal or the like is used as a normal conductor, an impurity is added to the normal conductor, and the like.
Increases the scattering of electrons by impurities, thereby increasing the normal conduction resistance R
Attempts have been made to increase n .
【0006】しかしながら、上記したような方法は、上
述した(Y,Pr)系の電気伝導性酸化物の場合にはその結晶
性により不純物を入れることが困難であり、適用するこ
とができない。また、Prによる置換率を一様に上げて、
常伝導抵抗Rn を高めることも考えられているが、この
方法では接合の臨界電流Ic が大きく減少してしまうた
め、常伝導抵抗Rn は増えるものの、接合のIc ・Rn
積はかえって減少してしまう。However, in the case of the above-mentioned (Y, Pr) -based electrically conductive oxide, it is difficult to add impurities due to its crystallinity, and thus the above method cannot be applied. Also, by uniformly increasing the substitution rate by Pr,
While also considered to increase the normal conductive resistance R n, since the critical current I c of the joint in this way is reduced greatly, although normal conductive resistance R n is increased, the junction of I c · R n
The product decreases instead.
【0007】[0007]
【発明が解決しようとする課題】上述したように、 Y系
酸化物超電導体とその Yの一部をPrで置換した電気伝導
性酸化物とを用いた、従来の超電導体/常伝導体/超電
導体接合は、その常伝導抵抗Rn が小さいという欠点を
有しており、また常伝導体として金属等を用いた場合に
使用されてきた常伝導抵抗Rn を高める方法も適用でき
ないという問題があった。そこで、常伝導体層として
(Y,Pr)系電気伝導性酸化物を用いる場合に、臨界電流I
c を大きく減少させることなく、常伝導抵抗Rnを大き
くし、接合のIc ・Rn 積を増大させることを可能にす
ることが強く望まれていた。As described above, conventional superconductors / normal conductors / superconductors using a Y-based oxide superconductor and an electrically conductive oxide in which part of Y is replaced with Pr. superconductor junction, a problem that the normal conductive resistance R n has the disadvantage of smaller, also can not be applied a method of increasing the normal conductive resistance R n which have been used in the case of using a metal such as normal conductor was there. So, as a normal conductor layer
When a (Y, Pr) -based electrically conductive oxide is used, the critical current I
It has been strongly desired to be able to increase the normal conduction resistance R n and increase the I c · R n product of the junction without significantly reducing c .
【0008】本発明は、このような課題に対処するため
になされたもので、超電導体としてY系酸化物超電導体
を用い、かつ常伝導体層として Y系酸化物超電導体の Y
の一部をPrに置換した(Y,Pr)系電気伝導性酸化物を用い
る場合に、臨界電流Ic の減少を抑制した上で常伝導抵
抗Rn を増加させ、接合のIc ・Rn 積を増大させた超
電導素子を提供することを目的としている。The present invention has been made to address such a problem, and uses a Y-based oxide superconductor as a superconductor and a Y-based oxide superconductor Y as a normal conductor layer.
Some of the substituted Pr (Y, Pr) system when using an electrically conductive oxide, to increase the normal conductive resistance R n on that suppresses decrease of the critical current I c, the junction of I c · R An object is to provide a superconducting element having an increased n product.
【0009】[0009]
【課題を解決するための手段】すなわち本発明の超電導
素子は、 Y系酸化物超電導体と、前記 Y系酸化物超電導
体の Yの少なくとも一部をPrで置換した常伝導体とを用
いて、超電導体/常伝導体/超電導体接合を構成した超
電導素子において、前記常伝導体層内の前記Prによる置
換割合が、前記超電導体層と常伝導体層との界面近傍か
ら該常伝導体層の内部に向けて減少していることを特徴
としている。That is, the superconducting element of the present invention comprises a Y-based oxide superconductor and a normal conductor in which at least a part of Y of the Y-based oxide superconductor is substituted with Pr. In a superconducting element having a superconductor / normal conductor / superconductor junction, the substitution ratio of Pr in the normal conductor layer is set so that the ratio of the normal conductor to the normal conductor layer is changed from the vicinity of the interface between the superconductor layer and the normal conductor layer. It is characterized by a decrease towards the inside of the layer.
【0010】本発明に用いられる Y系酸化物超電導体
は、 Y-Ba-Cu-Oを基本構成元素とし、ペロブスカイト構
造を有する酸化物超電導体であり、実質的に下記の (1)
式で組成が表されるものである。[0010] The Y-based oxide superconductor used in the present invention is an oxide superconductor having a perovskite structure containing Y-Ba-Cu-O as a basic constituent element.
The composition is represented by a formula.
【0011】 式: YBa2 Cu3 O 7-δ ………(1) (式中、δは酸素欠損を表し、通常 1以下の数)ただ
し、各元素の比率は、製造条件等により数モル%程度の
割合で変動可能であり、また超電導特性を劣化させない
範囲で、 Yの一部は他の希土類元素と、またBaの一部は
他のアルカリ土類元素と置換可能である。Formula: YBa 2 Cu 3 O 7-δ (1) (in the formula, δ represents oxygen deficiency, usually a number of 1 or less) However, the ratio of each element is several moles depending on production conditions and the like. %, And within a range that does not deteriorate the superconducting properties, part of Y can be replaced with another rare earth element and part of Ba can be replaced with another alkaline earth element.
【0012】また、本発明に用いられる常伝導体は、上
記した Y系酸化物超電導体の Yの少なくとも一部をPrで
置換した電気伝導性酸化物であり、実質的に下記の (2)
式で組成が表されるものである。The normal conductor used in the present invention is an electrically conductive oxide in which at least a part of Y of the above-mentioned Y-based oxide superconductor is substituted with Pr, and substantially the following (2)
The composition is represented by a formula.
【0013】 式:(Y1-x Prx )Ba2 Cu3 O 7-δ ………(2) (式中、 xは 0.4≦ x≦ 1を満足する数を示す)そし
て、本発明の超電導素子における常伝導体層は、上記
(2)式で実質的に表される(Y,Pr)系電気伝導性酸化物中
のPrによる置換割合を、超電導体層/常伝導体層の界面
近傍から常伝導体層の内部に向けて減少させたものであ
る。このPrの置換率は、一様な勾配をもたせてもよい
し、また段階的に置換率を変化させてもよい。また、Pr
による置換率の勾配は、接合の臨界電流Ic と常伝導抵
抗Rn とを考慮して適宜設定するものであるが、例えば
超電導体層/常伝導体層の界面近傍におけるPrによる置
換割合を最大に設定する部分は、上記 (2)式における x
の値を 0.8〜 1程度とし、常伝導体層内部は xの値を
0.4〜 0.8程度とすることが好ましい。Formula: (Y 1-x Pr x ) Ba 2 Cu 3 O 7-δ (2) (where x is a number satisfying 0.4 ≦ x ≦ 1) The normal conductor layer in the superconducting element is as described above.
The substitution ratio of Pr in the (Y, Pr) -based electrically conductive oxide substantially represented by the formula (2) is directed from the vicinity of the superconductor layer / normal conductor layer interface to the inside of the normal conductor layer. It has been reduced. The substitution rate of Pr may have a uniform gradient, or the substitution rate may be changed stepwise. Also, Pr
With a gradient of replacement ratio is the critical current I c of the junction and the normal conductive resistances R n is to appropriately set in consideration, for example, the replacement ratio by Pr near the interface of the superconductor layer / normal conductor layer The part to be set to the maximum is x in the above equation (2)
The value of x is about 0.8 to 1, and the value of x is
It is preferred to be about 0.4 to 0.8.
【0014】[0014]
【作用】一般に、超電導体/常伝導体の界面抵抗が増え
ると、超電導体/常伝導体/超電導体接合の臨界電流I
c が減少するため、従来は超電導体/常伝導体の接合部
では臨界電流を減らさないよう、界面抵抗の小さい界面
を作ることが試みられてきた。しかし、図6に見られる
ように、界面抵抗の大きさが適当な範囲内にあれば、界
面抵抗が小さい場合よりも、かえってIc ・Rn 積を大
きくすることができる。具体的な値は、超電導体および
常伝導体の状態密度、フェルミ速度の値、常伝導体層の
厚さによって異なるが、その傾向は同じである。Generally, when the interface resistance between a superconductor and a normal conductor increases, the critical current I of the superconductor / normal conductor / superconductor junction increases.
In order to reduce c , conventionally, an attempt has been made to form an interface having a low interface resistance so as not to reduce the critical current at the junction of the superconductor / normal conductor. However, as can be seen in FIG. 6, if the magnitude of the interface resistance is within an appropriate range, the I c · R n product can be increased rather than when the interface resistance is small. The specific value varies depending on the density of states of the superconductor and the normal conductor, the value of the Fermi velocity, and the thickness of the normal conductor layer, but the tendency is the same.
【0015】この現象は、次のように理解できる。SN
S接合の臨界電流Ic は界面抵抗の小さいうちは、ほぼ
N層の性質で決まるため、界面抵抗を増やしても臨界電
流はあまり減らない。その結果、界面抵抗を増やすこと
により、Ic ・Rn 積を増加させることができる。しか
し、ある値を超えて界面抵抗を大きくしすぎると、臨界
電流Ic が接合面によって大きく抑制されるようにな
り、界面抵抗を増やしても臨界電流の減少分が優って、
結局Ic ・Rn 積は減ってしまうようになる。This phenomenon can be understood as follows. SN
Of S critical current I c of the junction is small interfacial resistance, determined depending on a property of approximately N layer, the critical current is not reduced substantially with increasing the interfacial resistance. As a result, the I c · R n product can be increased by increasing the interface resistance. However, if too large interface resistance exceeds a certain value, it becomes critical current I c is largely suppressed by the bonding surface, and the decrease in the critical current even increasing the interfacial resistance superior,
Eventually, the I c · R n product will decrease.
【0016】これらのことから、超電導体/常伝導体の
界面近傍に、適当な大きさの界面抵抗が生じる部分を介
在させれば、接合のIc ・Rn 積を増大させることがで
きることが分かる。一方、量子力学で知られているよう
に、電子はポテンシャルやフェルミ速度等の物理状態が
急激に変化する界面があると、古典力学では反射されな
いような界面においても反射され、界面抵抗を増大させ
る。このように、界面抵抗を増大させるためには、系の
物理的性質を急激に変化させればよい。このためには、
(Y,Pr)-Ba-Cu-O系電気伝導性酸化物の電気伝導度がPrの
置換率の変化と共に 2桁以上も変化することを利用し
て、Prの置換率が高い部分を介在させればよい。しか
し、Prの置換率を一定の割合で高くした常伝導体層を用
いた場合に、臨界電流の著しい減少があることからも明
らかなとおり、望む常伝導抵抗Rn を得ると共に、臨界
電流Ic の減少を抑制するには、その後、Prの置換率を
減少させることが必要となる。これらのことから、本発
明のように、常伝導体層として(Y,Pr)-Ba-Cu-O系電気伝
導性酸化物を用いると共に、常伝導体層内のPrによる置
換割合を超電導体層/常伝導体層の界面近傍から常伝導
体層の内部に向けて減少させることによって、臨界電流
Ic の減少を抑制した上で、常伝導抵抗Rn を増大させ
ることができることが明らかであろう。そして、これに
より接合のIc・Rn 積を増大させることが可能とな
る。From these facts, it is possible to increase the I c · R n product of the junction by providing a portion where an appropriate amount of interface resistance is generated near the superconductor / normal conductor interface. I understand. On the other hand, as known in quantum mechanics, if there is an interface where the physical state such as potential or Fermi velocity changes rapidly, electrons are reflected at the interface that is not reflected by classical mechanics, increasing the interface resistance . As described above, in order to increase the interfacial resistance, the physical properties of the system may be rapidly changed. To do this,
Utilizing the fact that the electrical conductivity of the (Y, Pr) -Ba-Cu-O-based electrically conductive oxide changes by more than two orders of magnitude with the change in the substitution rate of Pr It should be done. However, when a normal conductor layer in which the substitution rate of Pr is increased at a constant rate is used, it is apparent from the remarkable decrease of the critical current that the desired normal conduction resistance R n is obtained and the critical current I In order to suppress the decrease in c , it is necessary to reduce the Pr substitution rate thereafter. From these facts, as in the present invention, the (Y, Pr) -Ba-Cu-O-based electrically conductive oxide is used as the normal conductor layer, and the substitution ratio of Pr in the normal conductor layer is determined by the superconductor. by reducing toward the inside of the normal conductor layer from near the interface of layer / normal conductor layer, after suppressing a decrease of the critical current I c, it is clear that it is possible to increase the normal conductive resistance R n There will be. This makes it possible to increase the I c · R n product of the junction.
【0017】[0017]
【実施例】以下、本発明の実施例について図面を参照し
て説明する。Embodiments of the present invention will be described below with reference to the drawings.
【0018】実施例1 図1は、本発明の一実施例の積層型超電導素子の要部を
示す断面図である。下部超電導体層としては、 SrTiO3
基板1上に多元スパッタ法により成膜したY-Ba-Cu-O系
酸化物超電導体膜2を用いた。その上に常伝導体層とし
て、Prによる置換率を変化させると共に、超電導体/常
伝導体の界面近傍でPrの割合が最も高くなるように設定
した、(Y,Pr)-Ba-Cu-O系電気伝導性酸化物膜3を30nm程
度の厚さで形成した。このように、Prによる置換率を連
続的に変えるためには、例えば多元スパッタ法により、
YとPrのスパッタパワーを連続的に変えて(Y,Pr)-Ba-Cu
-O膜を成膜すればよい。さらに上記常伝導体層3上に、
上部超電導体層としてY-Ba-Cu-O系酸化物超電導体膜4
を多元スパッタ法により成膜した。この後、成膜装置よ
り取り出し、フォトレジスト(図示せず)をマスクと
し、イオンミリング等の方法を用いて、上部 Y-Ba-Cu-O
系酸化物超電導体膜4、(Y,Pr)-Ba-Cu-O系電気伝導性酸
化物膜3を順次エッチングし、下部 Y-Ba-Cu-O系酸化物
超電導体膜2に対する電極を形成した。このようにして
作製したSNS接合の大きさは、この実施例では10μm
×10μm とした。Embodiment 1 FIG. 1 is a sectional view showing a main part of a laminated superconducting element according to an embodiment of the present invention. SrTiO 3 for the lower superconductor layer
A Y-Ba-Cu-O-based oxide superconductor film 2 formed on a substrate 1 by a multi-source sputtering method was used. On top of that, as a normal conductor layer, the substitution rate of Pr was changed, and the ratio of Pr was set to be highest near the superconductor / normal conductor interface. (Y, Pr) -Ba-Cu- The O-based electrically conductive oxide film 3 was formed with a thickness of about 30 nm. Thus, in order to continuously change the substitution rate by Pr, for example, by a multi-source sputtering method,
(Y, Pr) -Ba-Cu by continuously changing the sputtering power of Y and Pr
What is necessary is just to form a -O film. Further, on the normal conductor layer 3,
Y-Ba-Cu-O based oxide superconductor film 4 as upper superconductor layer
Was formed by a multi-source sputtering method. Then, it is taken out from the film forming apparatus, and using a photoresist (not shown) as a mask, the upper Y-Ba-Cu-O
-Based oxide superconductor film 4 and (Y, Pr) -Ba-Cu-O-based electrically conductive oxide film 3 are sequentially etched to form an electrode for lower Y-Ba-Cu-O-based oxide superconductor film 2. Formed. The size of the SNS junction thus manufactured is 10 μm in this embodiment.
× 10 μm.
【0019】このようにした得た積層構造体の深さ方向
への元素分析をイオンマイクロアナライザにより行っ
た。その結果を図2に示す。図2から分かるように、Pr
の割合は、下部超電導体層2/常伝導体層3および常伝
導体層3/上部超電導体層4の界面近傍から常伝導体層
3の内部に向けて減少している。Element analysis in the depth direction of the obtained laminated structure was performed by an ion microanalyzer. The result is shown in FIG. As can be seen from FIG.
Decreases from the vicinity of the interface between the lower superconductor layer 2 / normal conductor layer 3 and the normal conductor layer 3 / upper superconductor layer 4 toward the inside of the normal conductor layer 3.
【0020】また、上記によって得た下部 Y-Ba-Cu-O系
酸化物超電導体層2/(Y,Pr)-Ba-Cu-O系電気伝導性酸化
物層3/上部 Y-Ba-Cu-O系酸化物超電導体層4構造のS
NS接合を有する超電導素子の、液体窒素温度(77K) に
おけるI−V特性を測定した。その結果を図3に示す。
図3から明らかなように、明瞭なジョセフソン特性が得
らた。また、上記接合の臨界電流Ic の値は 1.8mAで、
常伝導抵抗Rn の値は60mΩであり、接合のIc ・Rn
積として 0.108mVを得た。The lower Y-Ba-Cu-O-based oxide superconductor layer 2 / (Y, Pr) -Ba-Cu-O-based electrically conductive oxide layer 3 / upper Y-Ba- S of Cu-O based oxide superconductor layer 4 structure
IV characteristics of a superconducting element having an NS junction at a liquid nitrogen temperature (77 K) were measured. The result is shown in FIG.
As is clear from FIG. 3, clear Josephson characteristics were obtained. The value of the critical current I c of the bonding is 1.8 mA,
The value of the normal conduction resistance R n is 60 mΩ, and the junction I c · R n
0.108mV was obtained as the product.
【0021】また、本発明との比較のために、常伝導体
層として Y-Ba-Cu-O系酸化物超電導体の Yの 80%をPrで
置換したものを用いる以外は、上記実施例と同一条件
で、超電導体/常伝導体/超電導体接合を作製したとこ
ろ、臨界電流Ic の値は 1.9mAで、常伝導抵抗Rn の大
きさは5mΩであり、接合のIc ・Rn 積は0.0095mVであ
った。For comparison with the present invention, the same procedure as in the above embodiment was carried out except that the normal conductor layer used was a Y-Ba-Cu-O-based oxide superconductor in which 80% of Y was replaced with Pr. under the same conditions and, were manufactured superconductor / normal conductor / superconductor junctions, the values of the critical current I c is 1.9 mA, the magnitude of the normal conductive resistance R n is 5 m [Omega, the junction I c · R The n product was 0.0095 mV.
【0022】このように、上記実施例による超電導素子
は、常伝導体層としての(Y,Pr)-Ba-Cu-O系電気伝導性酸
化物膜中のPrによる置換率を連続的に変化させたことに
よって、接合のIc ・Rn積を著しく増大させることが
できた。As described above, in the superconducting element according to the above embodiment, the substitution rate of Pr in the (Y, Pr) -Ba-Cu-O-based electrically conductive oxide film as the normal conductor layer is continuously changed. By doing so, the I c · R n product of the junction could be significantly increased.
【0023】実施例2 図4は、本発明の他の実施例の超電導素子の要部を示す
断面図である。この実施例では、まず適当な段差を有す
る SrTiO3 基板5上に、多元スパッタ法等により、互い
に電気的に絶縁された Y-Ba-Cu-O系酸化物超電導体膜
6、7を成膜した。これら Y-Ba-Cu-O系酸化物超電導体
膜6、7が下部超電導体および上部超電導体層となる。
これらの上に、上記段差を越えて連続させ、かつその上
方にいくほどPrの割合が減少させた(Y,Pr)-Ba-Cu-O系電
気伝導性酸化物膜8を、50nmの厚さで常伝導体層として
形成した。Embodiment 2 FIG. 4 is a sectional view showing a main part of a superconducting element according to another embodiment of the present invention. In this embodiment, first, Y-Ba-Cu-O-based oxide superconductor films 6 and 7 electrically insulated from each other are formed on a SrTiO 3 substrate 5 having an appropriate step by a multi-source sputtering method or the like. did. These Y-Ba-Cu-O-based oxide superconductor films 6 and 7 become a lower superconductor and an upper superconductor layer.
On top of these, a (Y, Pr) -Ba-Cu-O-based electrically conductive oxide film 8 having a thickness of 50 nm was formed so as to be continuous over the above-mentioned step and to decrease the proportion of Pr as going upward. Thus, a normal conductor layer was formed.
【0024】この後、成膜装置より取り出してフォトレ
ジストをマスクとし、イオンミリング等の方法を用い
て、段差を挟んで10μm 幅を残してエッチングした。さ
らに、Y-Ba-Cu-O系酸化物超電導体膜6、7にそれぞれ
電極を取る目的で、(Y,Pr)-Ba-Cu-O系電気伝導性酸化物
膜8を幅10μm だけ残してエッチングした。After that, the film was taken out of the film forming apparatus and etched using a photoresist as a mask by ion milling or the like, leaving a width of 10 μm across the step. Further, in order to take electrodes on the Y-Ba-Cu-O-based oxide superconductor films 6 and 7, respectively, the (Y, Pr) -Ba-Cu-O-based electrically conductive oxide film 8 is left with a width of 10 µm. And etched.
【0025】このようにした得た接合の常伝導体層から
超電導体層方向への元素分析結果を図5に示す。Prの置
換率は、常伝導体層と超電導体層との界面近傍から常伝
導体層内部に向けて減少していることが分かる。この接
合も液体窒素温度(77K)において、良好なジョセフソン
素子として動作した。また、上記接合の臨界電流Ic の
値は0.53×10-4A で、常伝導抵抗Rn の値は 1.9Ωであ
り、接合のIc ・Rn 積は 100.7μV であった。FIG. 5 shows the results of elemental analysis from the normal conductor layer to the superconductor layer of the thus obtained junction. It can be seen that the substitution ratio of Pr decreases from near the interface between the normal conductor layer and the superconductor layer toward the inside of the normal conductor layer. This junction also operated as a good Josephson device at liquid nitrogen temperature (77 K). The value of the critical current I c of the bonding is 0.53 × 10 -4 A, the value of the normal conductive resistance R n is 1.9Omu, I c · R n product of junction was 100.7MyuV.
【0026】また、本発明との比較のために、常伝導体
層として Y-Ba-Cu-O系酸化物超電導体の Yの 80%をPrで
置換したものを用いる以外は、上記実施例と同一条件
で、超電導体/常伝導体/超電導体接合を作製したとこ
ろ、臨界電流Ic の値は0.67×10-4A で、常伝導抵抗R
n の大きさは 0.2Ωであり、接合のIc ・Rn 積は13.4
μV であった。For comparison with the present invention, the same procedure as in the above embodiment was carried out except that the normal conductor layer used was a Y-Ba-Cu-O-based oxide superconductor in which 80% of Y was replaced with Pr. under the same conditions and, it was manufactured superconductor / normal conductor / superconductor junctions, the values of the critical current I c is 0.67 × 10 -4 a, normal conductive resistance R
The magnitude of n is 0.2Ω, and the product of I c and R n of the junction is 13.4.
μV.
【0027】[0027]
【発明の効果】以上説明したように、本発明の超電導素
子によれば、超電導体/常伝導体の界面近傍部にPrの割
合が高い部分が存在すると共に、Prの割合を常伝導体層
内部で減少させているため、臨界電流を大きく減らすこ
となく、界面抵抗により常伝導抵抗を増大させることが
できる。よって、再現性よくIc ・Rn 積を増やすこと
が可能となる。As described above, according to the superconducting element of the present invention, a portion having a high Pr ratio exists in the vicinity of the interface between the superconductor and the normal conductor, and the ratio of Pr is reduced by the normal conductor layer. Since it is reduced internally, the normal conduction resistance can be increased by the interface resistance without greatly reducing the critical current. Therefore, it is possible to increase the I c · R n product with good reproducibility.
【図1】本発明の一実施例による超電導素子の要部を示
す断面図である。FIG. 1 is a sectional view showing a main part of a superconducting element according to one embodiment of the present invention.
【図2】図1に示す超電導素子のイオンマイクロアナラ
イザによる深さ方向の元素分析結果を示す図である。FIG. 2 is a diagram showing a result of elemental analysis of the superconducting element shown in FIG. 1 in a depth direction by an ion microanalyzer.
【図3】図1に示す超電導素子の液体窒素温度における
I−V特性を示す図である。FIG. 3 is a diagram showing IV characteristics of the superconducting element shown in FIG. 1 at liquid nitrogen temperature.
【図4】本発明の他の実施例による超電導素子の要部を
示す断面図である。FIG. 4 is a sectional view showing a main part of a superconducting element according to another embodiment of the present invention.
【図5】図4に示す超電導素子のイオンマイクロアナラ
イザによる深さ方向の元素分析結果を示す図である。5 is a diagram showing a result of elemental analysis of the superconducting element shown in FIG. 4 in a depth direction by an ion microanalyzer.
【図6】超電導体/常伝導体/超電導体接合における界
面抵抗を変化させた際のIc ・Rn 積の変化の理論計算
値を示す図である。FIG. 6 is a diagram showing theoretically calculated values of a change in I c · R n product when an interface resistance in a superconductor / normal conductor / superconductor junction is changed.
1…… SrTiO3 基板 2、6…下部 Y-Ba-Cu-O系酸化物超電導体膜 3、8…Prの割合を変化させた(Y,Pr)-Ba-Cu-O系電気伝
導性酸化物膜 4、7…上部 Y-Ba-Cu-O系酸化物超電導体膜 9……段差を有する SrTiO3 基板1 SrTiO 3 substrate 2, 6 Lower Y-Ba-Cu-O-based oxide superconductor film 3, 8… Pr (Y, Pr) -Ba-Cu-O-based electrical conductivity Oxide film 4, 7 ... Upper Y-Ba-Cu-O-based oxide superconductor film 9 ... SrTiO 3 substrate with steps
───────────────────────────────────────────────────── フロントページの続き (72)発明者 水島 公一 神奈川県川崎市幸区小向東芝町1番地 株式会社東芝 総合研究所内 (56)参考文献 特開 平2−21676(JP,A) 特開 平3−196686(JP,A) 特開 平4−192381(JP,A) (58)調査した分野(Int.Cl.6,DB名) H01L 39/22 ZAA H01L 39/24 ZAA H01L 39/00 ZAA──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Koichi Mizushima 1 Tokoba, Komukai Toshiba-cho, Saisaki-ku, Kawasaki-shi, Kanagawa Prefecture (56) References JP-A-2-21676 (JP, A) JP-A-3-196686 (JP, A) JP-A-4-192381 (JP, A) (58) Fields investigated (Int. Cl. 6 , DB name) H01L 39/22 ZAA H01L 39/24 ZAA H01L 39 / 00 ZAA
Claims (1)
超電導体の Yの少なくとも一部をPrで置換した常伝導体
とを用いて、超電導体/常伝導体/超電導体接合を構成
した超電導素子において、 前記常伝導体層内の前記Prによる置換割合が、前記超電
導体層と常伝導体層との界面近傍から該常伝導体層の内
部に向けて減少していることを特徴とする超電導素子。1. A superconductor / normal conductor / superconductor junction is formed using a Y-based oxide superconductor and a normal conductor in which at least a part of Y of the Y-based oxide superconductor is replaced with Pr. In the configured superconducting element, the substitution ratio of the Pr in the normal conductor layer decreases from the vicinity of the interface between the superconductor layer and the normal conductor layer toward the inside of the normal conductor layer. Characteristic superconducting element.
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