JPH0289380A - Josephson junction element - Google Patents
Josephson junction elementInfo
- Publication number
- JPH0289380A JPH0289380A JP63241502A JP24150288A JPH0289380A JP H0289380 A JPH0289380 A JP H0289380A JP 63241502 A JP63241502 A JP 63241502A JP 24150288 A JP24150288 A JP 24150288A JP H0289380 A JPH0289380 A JP H0289380A
- Authority
- JP
- Japan
- Prior art keywords
- oxide superconductor
- film
- insulating film
- tunnel insulating
- conductive nitride
- 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.)
- Pending
Links
- 239000002887 superconductor Substances 0.000 claims abstract description 39
- 150000004767 nitrides Chemical class 0.000 claims abstract description 20
- 239000000463 material Substances 0.000 abstract description 7
- 238000006243 chemical reaction Methods 0.000 abstract description 5
- 238000009792 diffusion process Methods 0.000 abstract description 5
- 230000000694 effects Effects 0.000 abstract description 5
- 239000013078 crystal Substances 0.000 abstract description 2
- 238000002844 melting Methods 0.000 abstract description 2
- 230000008018 melting Effects 0.000 abstract description 2
- 230000002349 favourable effect Effects 0.000 abstract 1
- 238000010438 heat treatment Methods 0.000 abstract 1
- 238000000034 method Methods 0.000 description 4
- 238000005546 reactive sputtering Methods 0.000 description 4
- 239000000758 substrate Substances 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000004888 barrier function Effects 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 230000006378 damage Effects 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
- 238000010406 interfacial reaction Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 238000001020 plasma etching Methods 0.000 description 1
- 238000001552 radio frequency sputter deposition Methods 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 238000000992 sputter etching Methods 0.000 description 1
- VEALVRVVWBQVSL-UHFFFAOYSA-N strontium titanate Chemical compound [Sr+2].[O-][Ti]([O-])=O VEALVRVVWBQVSL-UHFFFAOYSA-N 0.000 description 1
Landscapes
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
Abstract
Description
【発明の詳細な説明】
［発明の目的］
（産業上の利用分野）
本発明は、酸化物超電導体を用いたトンネル型のジョセ
フソン接合素子に関する。DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a tunnel-type Josephson junction element using an oxide superconductor.
（従来の技術）
最近、高温超電導体として酸化物超電導体が注目されて
いる。酸化物超電導体においては、その組成を選ぶこと
により、液体窒素温度以上の高温で超電導を示すことが
確認されており、材料作製技術の進歩により更に臨界温
度の高い超電導体が得られる可能性がある。(Prior Art) Recently, oxide superconductors have attracted attention as high-temperature superconductors. It has been confirmed that oxide superconductors exhibit superconductivity at temperatures higher than the liquid nitrogen temperature depending on their composition, and it is possible that superconductors with even higher critical temperatures can be obtained with advances in material production technology. be.
この様な酸化物超電導体を電子素子に応用する場合、基
本構成として、二つの超電導体間にトンネル絶縁膜を介
在させた所謂トンネル型ジョセフソン接合を形成するこ
とが不可欠になる。しかし酸化物超電導体は、従来の金
属超電導体と異なり、自己を酸化することで良好な酸化
膜を得ることができない、コヒーレンス長が短いために
特性が絶縁膜厚に大きく依存する、等の問題を有する。When applying such an oxide superconductor to an electronic device, it is essential to form a so-called tunnel-type Josephson junction in which a tunnel insulating film is interposed between two superconductors as a basic structure. However, unlike conventional metal superconductors, oxide superconductors have problems such as the inability to obtain a good oxide film by oxidizing themselves, and the short coherence length, which makes their properties highly dependent on the thickness of the insulating film. has.
加えて、良好な超電導特性を得るためには酸化物超電導
体を高温条件下で形成することが必要となり、酸化物超
電導体上に何らかの絶縁膜を形成した後更にこの上に酸
化物超電導体を形成する際に、絶縁膜と酸化物超電導体
の間で組成成分の相互拡散や反応を生じ、絶縁特性が破
壊される、という問題があった。これは、酸化物超電導
体が多くの空格子を有し、他の材料と接合を形成した時
に構成原子の）０互拡散を生じ易いためである。In addition, in order to obtain good superconducting properties, it is necessary to form an oxide superconductor under high temperature conditions. During formation, there was a problem in that mutual diffusion and reactions of compositional components occurred between the insulating film and the oxide superconductor, resulting in destruction of the insulating properties. This is because the oxide superconductor has many vacancies, and when it forms a junction with another material, it tends to cause zero interdiffusion (of its constituent atoms).
（発明が解決しようとする課題）
以上のように、酸化物超電導体を用いて実用に供し得る
電子素子を形成するには、酸化物超電導体−トンネル絶
縁膜−酸化物超電導体という接合を如何にして作るかが
重要な基本的課題となっている。(Problems to be Solved by the Invention) As described above, in order to form a practically usable electronic device using an oxide superconductor, how can the junction of oxide superconductor-tunnel insulating film-oxide superconductor be formed? An important fundamental issue is how to make it.
本発明は上記の点に鑑みなされたもので、酸化物超電導
体を用いて構成した良好な特性を持つトンネル型のジョ
セフソン接合素子を提供することを目的とする。The present invention has been made in view of the above points, and an object of the present invention is to provide a tunnel-type Josephson junction element that is constructed using an oxide superconductor and has good characteristics.
［発明の構成］
（課題を解決するための手段）
本発明にかかるジョセフソン接合素子は、酸化物超電導
体からなる第１．第２の主電極と、これらの間に挟まれ
るトンネル絶縁膜との間に導電性窒化物膜を介在させた
ことを特徴とする。[Structure of the Invention] (Means for Solving the Problems) A Josephson junction element according to the present invention includes a first oxide superconductor made of an oxide superconductor. A feature is that a conductive nitride film is interposed between the second main electrode and the tunnel insulating film sandwiched therebetween.
本発明において用いる導電性窒化物としては、それ自体
ある温度以下で超電導特性を示すＮｂＮやＭｏＮなどが
好ましい。しかしこれら以外にも、超電導特性を示さな
いＷＮなどを用いることが可能である。トンネル障壁部
を構成する絶縁膜は、熱的に安定な材料であることが好
ましく、例えばＭｇ Ｏなどが適している。The conductive nitride used in the present invention is preferably NbN, MoN, or the like, which itself exhibits superconducting properties below a certain temperature. However, in addition to these materials, it is also possible to use WN, which does not exhibit superconducting properties. The insulating film constituting the tunnel barrier section is preferably made of a thermally stable material, and MgO, for example, is suitable.
本発明において、酸化物超電導体電極と導電性窒化物膜
の間に更に金属膜を介在させることも有効である。これ
は、酸化物超電導体と導電性窒化物膜との電気的接触を
良好にするためであり、例えば、Ａｇ、Ａｕなどが挙げ
られる。In the present invention, it is also effective to further interpose a metal film between the oxide superconductor electrode and the conductive nitride film. This is to improve electrical contact between the oxide superconductor and the conductive nitride film, and examples thereof include Ag and Au.
本発明の構造を一層安定化し、特性を改善するためには
、全体をエピタキシャル成長させることが望ましい。そ
のためには、互いに格子整合のとれた材料を用いること
が必要である。In order to further stabilize the structure of the present invention and improve its properties, it is desirable to grow the entire structure epitaxially. For this purpose, it is necessary to use materials that are lattice-matched to each other.
その様な組合わせとして、酸化物超電導体にＹＢａ ２
Ｃｕ ３０．−ａを用い、導電性窒化物としてＮｂＮ
、トンネル絶縁膜としてＭｇ Ｏを用いることが考えら
れる。As such a combination, YBa 2 is added to the oxide superconductor.
Cu 30. -a, and NbN as the conductive nitride.
It is conceivable to use Mg 2 O as the tunnel insulating film.
（作用）
ＮｂＮに代表される導電性窒化物は、結晶構造がち密で
あり、また高融点で耐熱性を有し容易には酸化されない
。従ってこの様な導電性窒化物膜を酸化物超電導体電極
とトンネル絶縁膜の間に介在させると、酸化物超電導体
を形成する際の高温熱工程において酸化物超電導体とト
ンネル絶縁膜との間の相互拡散や反応を防止することが
できる。加えて、Ｎｂ、ＮやＭｏＮ等の導電性窒化物は
高い臨界温度を有する超電導材料であるため、これらの
臨界温度の２倍程度の温度においては酸化物超電導体か
らの近接効果が有効に働き、そのコヒーレンス長が増大
する。従って本発明のジョセフソン接合素子は、例えば
２０〜３０にという簡便な冷凍機で容易に実現できる温
度領域において、酸化物超電導体の大きいギャップ・エ
ネルギーを反映した発生電圧の大きい良好な特性を示す
。(Function) Conductive nitrides represented by NbN have a dense crystal structure, have a high melting point, are heat resistant, and are not easily oxidized. Therefore, if such a conductive nitride film is interposed between the oxide superconductor electrode and the tunnel insulating film, the gap between the oxide superconductor and the tunnel insulating film will be reduced during the high-temperature thermal process when forming the oxide superconductor. mutual diffusion and reactions can be prevented. In addition, since conductive nitrides such as Nb, N, and MoN are superconducting materials with high critical temperatures, the proximity effect from oxide superconductors does not work effectively at temperatures about twice their critical temperatures. , its coherence length increases. Therefore, the Josephson junction device of the present invention exhibits good characteristics with a large generated voltage reflecting the large gap energy of the oxide superconductor in a temperature range of, for example, 20 to 30°C, which can be easily achieved with a simple refrigerator. .
（実施例） 以下、本発明の実施例を図面を参照して説明する。(Example) Embodiments of the present invention will be described below with reference to the drawings.
第１図は、一実施例のジョセフソン接合素子である。１
はチタン酸ストロンチウム（Ｓｒ Ｔ１０３ ）基板で
あり、２．６はそれぞれ第１．第２の主電極となる臨界
温度８４にのＹ Ｂａ ２ Ｃｕ ３０７−ａ膜であり
、４はトンネル絶縁膜としてのＭｇ Ｏ膜である。Ｍｇ
Ｏ膜４とＹ Ｂａ ２ Ｃｕ ３０ｔ−ａ膜２，６の
間にはそれぞれ、導電性窒化物であるＮｂＮ膜３．５が
設けられている。FIG. 1 shows one embodiment of a Josephson junction device. 1
are strontium titanate (Sr T103 ) substrates, and 2.6 are the first . A Y Ba 2 Cu 307-a film at a critical temperature of 84 serves as the second main electrode, and 4 is an Mg O film as a tunnel insulating film. Mg
NbN films 3.5, which are conductive nitrides, are provided between the O film 4 and the Y Ba 2 Cu 30t-a films 2 and 6, respectively.
具体的な製造工程を説明する。基板１上に先ず、第１の
主電極として多元反応性スパッタ法により約５００ ｎ
ｍのＹ Ｂａ ２ Ｃｕ ３０７−Ｊ膜２を形成する。The specific manufacturing process will be explained. First, about 500 nm was deposited on the substrate 1 as a first main electrode by multi-reactive sputtering.
A Y Ba 2 Cu 307-J film 2 of m is formed.
この製膜時の基板温度は約５３０℃である。The substrate temperature during this film formation is approximately 530°C.
次いでこのＹ Ｂａ ２ Ｃｕ ３０７−Ｊ膜２上に反
応性スパッタ法によりＮｂＮ膜３を厚さ５０ｎｍＲＦス
パッタ法によりＭｇ Ｏ膜４を１．５ｔ＋ｍ。Next, a NbN film 3 with a thickness of 50 nm was formed on this YBa 2 Cu 307-J film 2 by reactive sputtering, and a MgO film 4 was formed with a thickness of 1.5 t+m by RF sputtering.
再び反応性スパッタによりＮｂＮ膜５を５０ ｎｍ堆積
し、更にこの上に多元反応性スパッタ法により３００
ｎｍのＹ Ｂａ ２ Ｃｕ ３０ｔ−ａ膜６を堆積する
。A 50 nm thick NbN film 5 was deposited again by reactive sputtering, and then a 300 nm thick NbN film 5 was deposited on top of this by multi-reactive sputtering.
A Y Ba 2 Cu 30t-a film 6 is deposited.
その後通常の露光方法でパターン形成したレジストを用
いてＹ Ｂａ ２ Ｃｕ ３０１−ａ膜６をＡ「を用い
たイオンミリング法で加工し、更にＮ、ｂ Ｎ−Ｍｇ
０−Ｎｂ Ｎの積層膜をＣＦ４およびＣＦ４＋０□ガス
を用いた反応性イオンエッチング法により加工して、図
の素子構造を得る。Thereafter, the Y Ba 2 Cu 301-a film 6 was processed by an ion milling method using A' using a resist patterned by a normal exposure method, and further N, b N-Mg
A stacked film of 0-NbN is processed by a reactive ion etching method using CF4 and CF4+0□ gases to obtain the device structure shown in the figure.
第２図は、この実施例のジョセフソン接合素子の温度２
０Ｋにおける電流−電圧特性である。Figure 2 shows the temperature 2 of the Josephson junction element in this example.
This is a current-voltage characteristic at 0K.
図示のように大きい超電導ギャップ（２Δζ１０ｍＶ）
が観測され、良好なジョセフソン接合が形成されている
ことが確認された。酸化物超電導体とトンネル絶縁膜の
間に導電性窒化物膜を介在させることにより、界面反応
のない良好な接合が形成され、また酸化物超電導体から
導電性窒化物膜への近接効果によって導電性窒化物膜内
に大きい超電導ギャップが誘起されていることが理解さ
れる。Large superconducting gap (2Δζ10mV) as shown
was observed, confirming that a good Josephson junction was formed. By interposing a conductive nitride film between the oxide superconductor and the tunnel insulating film, a good bond without interfacial reaction is formed, and the proximity effect from the oxide superconductor to the conductive nitride film increases conductivity. It is understood that a large superconducting gap is induced within the nitride film.
第２図は、本発明の他の実施例のジョセフソン接合素子
である。第１図の実施例と対応する部分には第１図と同
一符号を付して詳細な説明は省略する。この実施例では
、ＹＢａ ２ Ｃｕ ３０ｔ−ａ膜２とＮｂＮ膜３の間
、およびＹ Ｂ ａ ２Ｃｕ３０ を膜６とＮｂＮ膜５
の間にそれぞれＡｇ膜７，８を介在させている。FIG. 2 shows a Josephson junction device according to another embodiment of the present invention. Components corresponding to the embodiment in FIG. 1 are designated by the same reference numerals as in FIG. 1, and detailed explanation thereof will be omitted. In this example, YBa 2 Cu 30 is used between the film 2 and the NbN film 3, and between the film 6 and the NbN film 5.
Ag films 7 and 8 are interposed between them, respectively.
この実施例の素子でも先の実施例と同様、優れたジョセ
フソン接合特性が得られる。またこの実施例の場合、Ｙ
Ｂａ ２ Ｃｕ ３０７−Ｊ膜とＮｂＮ膜の間に金属膜
を介在させることにより、オーミック接触特性が改善さ
れ、この結果近接効果を一層有効に働かせることができ
る。The device of this example also provides excellent Josephson junction characteristics as in the previous example. In addition, in this example, Y
By interposing a metal film between the Ba 2 Cu 307-J film and the NbN film, ohmic contact characteristics are improved, and as a result, the proximity effect can be made more effective.
本発明は上記実施例に限られるものではない。The present invention is not limited to the above embodiments.
例えば実施例では、酸化物超電導体としてＹＢａ ２
Ｃｕ ３０７−４を用イタカ、臨界温度ノヨり高いＢｉ
系、Ｔｈ系等他の酸化物超電導体を用いることができる
。For example, in the example, YBa 2 is used as the oxide superconductor.
Itaka using Cu 307-4, Bi with high critical temperature
Other oxide superconductors such as Th-based, Th-based, etc. can be used.
［発明の効果］
以上述べたように１本発明によれば、酸化物超電導体電
極とトンネル絶縁膜の間に導電性窒化物膜を介在させる
ことにより、酸化物超電導体とトンネル絶縁膜の間の相
互拡散や反応を防止して、優れた特性を実現したジョセ
フソン接合素子を得ることができる。[Effects of the Invention] As described above, according to the present invention, by interposing the conductive nitride film between the oxide superconductor electrode and the tunnel insulating film, the gap between the oxide superconductor and the tunnel insulating film is It is possible to obtain a Josephson junction element that achieves excellent characteristics by preventing mutual diffusion and reactions.
第１図は本発明の一実施例のジョセフソン接合素子を示
す図、第２図はそのジョセフソン接合素子の電流−電圧
特性を示す図、第３図は他の実施例のジョセフソン接合
素子を示す図である。
１−・・Ｓｒ Ｔ１０３基板、２− Ｙ Ｂ ａ２ Ｃ
０３０ｔ−ａ膜（第１の主電極） ３・・・ＮｂＮ膜（
導電性窒化物膜） ４・・・Ｍｇ Ｏ膜（トンネル絶縁
膜） ５・・・ＮｂＮ膜（導電性窒化物膜）、６・・・
Ｙ Ｂａ ２ Ｃｕ ３０７−ａ膜（第２の主電極）、
７゜８・・・Ａｇ膜。
第１図FIG. 1 is a diagram showing a Josephson junction device according to one embodiment of the present invention, FIG. 2 is a diagram showing the current-voltage characteristics of the Josephson junction device, and FIG. 3 is a diagram showing a Josephson junction device according to another embodiment. FIG. 1-...Sr T103 substrate, 2- Y B a2 C
030t-a film (first main electrode) 3...NbN film (
conductive nitride film) 4...MgO film (tunnel insulating film) 5...NbN film (conductive nitride film), 6...
Y Ba 2 Cu 307-a film (second main electrode),
7゜8...Ag film. Figure 1
Claims (1)
第２の主電極と、これら主電極間に設けられたトンネル
絶縁膜とを有するジョセフソン接合素子において、前記
第１、第２の主電極とトンネル絶縁膜との間に導電性窒
化物膜を介在させたことを特徴とするジョセフソン接合
素子。(1) A first consisting of two oxide superconductors facing each other,
In a Josephson junction element having a second main electrode and a tunnel insulating film provided between these main electrodes, a conductive nitride film is provided between the first and second main electrodes and the tunnel insulating film. A Josephson junction element characterized by interposed.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63241502A JPH0289380A (en) | 1988-09-27 | 1988-09-27 | Josephson junction element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP63241502A JPH0289380A (en) | 1988-09-27 | 1988-09-27 | Josephson junction element |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JPH0289380A true JPH0289380A (en) | 1990-03-29 |
Family
ID=17075279
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP63241502A Pending JPH0289380A (en) | 1988-09-27 | 1988-09-27 | Josephson junction element |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JPH0289380A (en) |
-
1988
- 1988-09-27 JP JP63241502A patent/JPH0289380A/en active Pending
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