JPH0714817B2 - Oxide superconducting thin film and method for producing the same - Google Patents
Oxide superconducting thin film and method for producing the sameInfo
- Publication number
- JPH0714817B2 JPH0714817B2 JP1229917A JP22991789A JPH0714817B2 JP H0714817 B2 JPH0714817 B2 JP H0714817B2 JP 1229917 A JP1229917 A JP 1229917A JP 22991789 A JP22991789 A JP 22991789A JP H0714817 B2 JPH0714817 B2 JP H0714817B2
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- Prior art keywords
- thin film
- film
- oxide
- superconducting
- superconducting thin
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
- Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment
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- Inorganic Compounds Of Heavy Metals (AREA)
- Physical Vapour Deposition (AREA)
- Superconductor Devices And Manufacturing Methods Thereof (AREA)
- Containers, Films, And Cooling For Superconductive Devices (AREA)
- Superconductors And Manufacturing Methods Therefor (AREA)
Description
【発明の詳細な説明】 産業上の利用分野 本発明は、100K以上の高臨界温度が期待されるタリウム
を含む酸化物超電導薄膜及びそのの製造方法に関するも
のである。TECHNICAL FIELD The present invention relates to an oxide superconducting thin film containing thallium, which is expected to have a high critical temperature of 100 K or higher, and a method for producing the same.
従来の技術 高温超電導体として、A15型2元系化合物として窒化ニ
オブ(NbN)やゲルマニウムニオブ(Nb3Ge)などが知ら
れていたが、これらの材料の超電導転移温度はたかだか
23Kであった。一方、ペロブスカイト系化合物は、さら
に高い転移温度が期待され、Ba−La−Cu−O系の高温超
電導体が提案された[ジェイ、ジー、ベンドノルツ及び
ケイ、エー、ミューラー(J.G.Bednorz and K.A.Mulle
r),ツァイトシュリフト・フュア・フィジーク(Zetsh
rift Fur Physik B)−コンデンスドマター(Condensed
Matter)Vol.64,189−193(1986)]。Conventional technology As high-temperature superconductors, niobium nitride (NbN) and germanium niobium (Nb 3 Ge) were known as A15 type binary compounds, but the superconducting transition temperature of these materials is at most
It was 23K. On the other hand, perovskite compounds are expected to have even higher transition temperatures, and Ba-La-Cu-O-based high-temperature superconductors have been proposed [JGBednorz and KAMulle.
r), Zeitschrift-Fur-Fizik (Zetsh)
rift Fur Physik B) -Condensed Matter
Matter) Vol. 64, 189-193 (1986)].
さらに、Bi−Sr−Ca−Cu−O系の材料が100K以上の転移
温度を示すことも発見された[エイチ、マエダ、ワイ、
タナカ、エム、フクトミ及びティ、アサノ(H.Maeda,Y.
Tanaka,M.Fukutomi and T.Asano),ジャパニーズ・ジ
ャーナル・オブ・アプライド・フィジックス(Japanese
Journal of Applied Physics)Vol.27,L209−210(198
8)]。加えてこのBi系よりも超電導転移温度の高いTl
−Ba−Ca−Cu−O系の材料が発見されるに至った[ゼッ
ト、ゼット、シェング及びエー、エム、ヘルマン(Z.Z.
Sheng and A.M.Hermann),ネイチャー(Nature)Vol.3
32,138−139(1988).]。この種の材料の超電導機構
の詳細は明らかではないが、転移温度が室温以上に高く
なる可能性があり、高温超電導体として従来の2元系化
合物より、より有望な特性が期待される。Furthermore, it was discovered that Bi-Sr-Ca-Cu-O-based materials exhibit a transition temperature of 100 K or higher [H, Maeda, Wy,
Tanaka, M, Fukutomi and T, Asano (H. Maeda, Y.
Tanaka, M.Fukutomi and T.Asano), Japanese Journal of Applied Physics (Japanese
Journal of Applied Physics) Vol.27, L209-210 (198
8)]. In addition, Tl has a higher superconducting transition temperature than this Bi system.
-Ba-Ca-Cu-O materials have been discovered [Zet, Zet, Sheng and A, M, Hermann (ZZ
Sheng and AMHermann), Nature Vol.3
32,138-139 (1988). ]. Although the details of the superconducting mechanism of this kind of material are not clear, the transition temperature may become higher than room temperature, and more promising properties are expected as a high temperature superconductor than the conventional binary compounds.
さらに超電導体と絶縁物とを交互に積層することによ
り、より高い超電導転移温度が従来から期待されていた
[エム、エイチ、コーエン及びディ、エイチ、ドウグラ
ス、ジュニア(M.H.Cohen and D.H.Douglass,Jr.),フ
ィジカル・レビュー・レターズ(Physical Review Lett
ers)Vol.19,118−121(1967)]。Furthermore, by alternately stacking superconductors and insulators, higher superconducting transition temperatures have been expected from the past [M, H, Cohen and Di, H, Douglas, Jr., (MHCohen and DHDouglass, Jr.), Physical Review Lett
ers) Vol. 19, 118-121 (1967)].
発明が解決しようとする課題 しかしながら、Tl−Ba−Ca−Cu−O系の材料は、現在の
技術では主として焼結という過程でしか形成できないた
め、セラミックの粉末あるいはブロックの形状でしか得
られない。一方、この種の材料を実用化する場合、薄膜
状に加工することが強く要望されているが、従来の技術
では、良好な超電導特性を有する薄膜作製は難しいもの
であった。すなわち、Tl−Ba−Ca−Cu−O系には超電導
転移温度の異なるいくつかの相が存在することが知られ
ているが、特に転移温度が100K以上の相を薄膜の形態で
達成するのは、非常に困難とされていた。DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, since the Tl-Ba-Ca-Cu-O-based material can be formed only in the process of sintering mainly in the present technology, it can be obtained only in the form of ceramic powder or block. . On the other hand, when putting this type of material into practical use, it is strongly demanded to process it into a thin film, but it has been difficult to produce a thin film having good superconducting properties by the conventional techniques. That is, it is known that there are several phases having different superconducting transition temperatures in the Tl-Ba-Ca-Cu-O system. In particular, a phase having a transition temperature of 100 K or more is achieved in the form of a thin film. Was considered very difficult.
また、従来このTl系において良好な超電導特性を示す薄
膜を形成するためには少なくとも600℃以上の熱処理あ
るいは形成時の加熱が必要であり、そのため高い超電導
転移温度が期待される絶縁膜との周期的な積層構造を得
ることは極めて困難と考えられ、またこの構造を利用し
た集積化デバイスを構成することもたいへん困難である
とされていた。Further, in the past, in order to form a thin film showing good superconducting properties in this Tl system, it is necessary to perform heat treatment at least 600 ° C or heating during formation, and therefore the cycle with the insulating film expected to have a high superconducting transition temperature. It has been considered that it is extremely difficult to obtain a typical laminated structure, and it is also very difficult to form an integrated device using this structure.
課題を解決するための手段 本発明者らによる第1の発明の酸化物超電導薄膜は、主
体成分が少なくともタリウム(Tl)、銅(Cu),および
アルカリ土類(IIa族)を含む層状酸化物超電導薄膜
と、主体成分が少なくともBiとタングステン(W)を含
む層状酸化物薄膜が交互に積層された構造を持つことを
特徴とする酸化物超電導薄膜である。Means for Solving the Problems The oxide superconducting thin film of the first invention by the present inventors is a layered oxide whose main components include at least thallium (Tl), copper (Cu), and alkaline earth (IIa group). An oxide superconducting thin film having a structure in which a superconducting thin film and a layered oxide thin film whose main components are at least Bi and tungsten (W) are alternately laminated.
さらに第2の発明の酸化物超電導薄膜の製造方法は、基
体上に、少なくともTlを含む酸化物と少なくとも銅およ
びアルカリ土類(IIa族)を含む酸化物とを周期的に積
層させて形成する酸化物薄膜と、少なくともBiを含む酸
化物と少なくともWを含む酸化物を周期的に積層させて
形成する酸化物薄膜とを、さらに交互に積層させて得る
ことを特徴とする酸化物超電導薄膜の製造方法である。Furthermore, in the method for producing an oxide superconducting thin film of the second invention, an oxide containing at least Tl and an oxide containing at least copper and an alkaline earth (Group IIa) are periodically laminated on a substrate. An oxide superconducting thin film, characterized by being obtained by further alternately stacking an oxide thin film and an oxide thin film formed by periodically stacking an oxide containing at least Bi and an oxide containing at least W. It is a manufacturing method.
ここでアルカリ土類は、IIa族元素のうちの少なくとも
一種あるいは二種以上の元素を示す。Here, the alkaline earth refers to at least one element or two or more elements of the IIa group elements.
作用 本発明者らによる第1の発明においては、Tl2O2酸化膜
層またはこれを主体とした層によりともに覆われた結晶
構造となっているところのTl系超電導薄膜と、Tl系超電
導体とその結晶における格子定数(a軸)がほぼ等し
く、また安定なBi2O2酸化膜層またはこれを主体とした
層によりともに覆われた結晶構造となっているところの
BiとWとを含む酸化物層状構造の絶縁膜薄膜とが、交互
に積層された成分をとることによって、超電導膜と絶縁
膜との間での相互拡散の少ない積層が可能となり、その
結果Tl系超電導薄膜における超電導転移温度の上昇が実
現されたものである。Action In the first invention by the present inventors, a Tl-based superconducting thin film and a Tl-based superconductor having a crystal structure covered by a Tl 2 O 2 oxide film layer or a layer mainly composed of the Tl 2 O 2 oxide film layer. And its crystal lattice constants (a-axis) are almost equal, and the crystal structure is covered by a stable Bi 2 O 2 oxide layer or a layer mainly composed of this.
Since the insulating film thin film having an oxide layered structure containing Bi and W has an alternatingly stacked component, it is possible to form a stack with less interdiffusion between the superconducting film and the insulating film. This is the realization of an increase in the superconducting transition temperature in the superconducting thin film.
さらに第2の発明においては上記構造を達成するため、
少なくともTlを含む酸化物、少なくともBiを含む酸化物
と、少なくとも銅およびアルカリ土類(IIa族)含む酸
化物あるいは少なくともWを含む酸化物とを、周期的に
積層させて分子レベルの制御による薄膜の作製を行うこ
とによって、再現性良くTl系超電導薄膜と絶縁膜との積
層を得ることに成功したものである。Further, in order to achieve the above structure in the second invention,
A thin film formed by periodically stacking an oxide containing at least Tl, an oxide containing at least Bi, an oxide containing at least copper and an alkaline earth (group IIa), or an oxide containing at least W, and controlling at the molecular level. We have succeeded in obtaining a stack of a Tl-based superconducting thin film and an insulating film with good reproducibility.
実施例 以下に、本発明の実施例について図面を参照しながら説
明する。Embodiments Embodiments of the present invention will be described below with reference to the drawings.
まず、本発明者らはTl系超電導薄膜と絶縁膜との周期的
な積層構造を実現するため、Tl系超電導薄膜と種々の絶
縁膜との相互作用について検討した。First, the present inventors examined the interaction between the Tl-based superconducting thin film and various insulating films in order to realize a periodic laminated structure of the Tl-based superconducting thin film and the insulating film.
通常、Tl系超電導薄膜は400〜600℃に加熱した基体上に
蒸着して得る。蒸着後、そのままでも薄膜は超電導特性
を示すが、その後850〜950℃の熱処理を施し、超電導特
性を向上させる。Usually, a Tl-based superconducting thin film is obtained by vapor deposition on a substrate heated to 400 to 600 ° C. After vapor deposition, the thin film shows superconducting properties as it is, but it is then heat-treated at 850-950 ℃ to improve the superconducting properties.
しかしながら、基体温度が高い時に絶縁膜をTl系超電導
薄膜に続いて積層したり、絶縁膜を形成後熱処理を行っ
た場合、超電導膜と絶縁膜との間で、元素の相互拡散が
起こり超電導特性が大きく劣化することが判明した。相
互拡散を起こさないためには、超電導膜、絶縁膜の結晶
性が優れていること、超電導膜・絶縁膜間での格子の整
合性が優れていること、絶縁膜が850〜950℃の熱処理に
対して安定であることが不可欠と考えられる。However, when the substrate temperature is high, if an insulating film is stacked next to the Tl-based superconducting thin film, or if heat treatment is performed after forming the insulating film, mutual diffusion of elements occurs between the superconducting film and the insulating film, resulting in superconducting characteristics. Was found to deteriorate significantly. To prevent mutual diffusion, the superconducting film and insulating film have excellent crystallinity, the lattice matching between the superconducting film and the insulating film is excellent, and the insulating film is heat treated at 850 to 950 ° C. It is considered essential to be stable against.
種々の検討を行った結果、本発明者らは、少なくともW
を含むBi酸化物層状構造の薄膜が絶縁膜として適してい
ることを見いだした。この理由として、Wを含むBi層状
酸化物は、Bi2O2酸化物層がWおよび酸素等の元素から
なる構造体を挟み込んだ層状ペロブスカイトを示すこと
が知られており、このBi2O2層は同種の結晶構造の物質
の界面に対して高温の熱処理においても非常に安定であ
り、またTl系超電導体とBi−W系酸化物との格子の整合
性がきわめて優れていることが考えられる。As a result of various studies, the present inventors found that at least W
It was found that a thin film of Bi oxide layered structure containing Ni is suitable as an insulating film. The reason for this, Bi layered oxide containing W is, Bi 2 O 2 oxide layer are known to exhibit a layered perovskite sandwiched structure consisting of W and elements such as oxygen, the Bi 2 O 2 It is considered that the layer is extremely stable even at a high temperature heat treatment with respect to the interface of substances having the same crystal structure, and that the lattice matching between the Tl-based superconductor and the Bi-W-based oxide is extremely excellent. To be
さらに本発明者らは、Tl系超電導薄膜とBi−W系酸化物
薄膜を周期的に積層した時、Tl系超電導薄膜本来の超電
導転移温度が上昇することを見いだした。Furthermore, the present inventors have found that when the Tl-based superconducting thin film and the Bi-W-based oxide thin film are periodically laminated, the original superconducting transition temperature of the Tl-based superconducting thin film rises.
(実施例1) 本発明者らによる第1の発明の内容を更に深く理解され
るために、第1図を用い具体的な実施例を示す。(Embodiment 1) In order to further understand the content of the first invention by the present inventors, a concrete embodiment will be shown with reference to FIG.
第1図は、本実施例で用いた二元マグネトロンスパッタ
装置内部の概略図であり、11はTl−Ba−Ca−Cu−Oター
ゲット、12はBi−W−Oターゲット、13はシャッター、
14はアパーチャー、15は基体、16は基体加熱用ヒーター
を示す。焼結体をプレス成形加工して作製した2個のタ
ーゲット11、12を用い、第1図に示すように配置させ
た。すなわち、MgO(100)基体15に焦点を結ぶように各
ターゲットが約30゜傾いて設置されている。ターゲット
の前方には回転するシャッター13があり、その中に設け
られたアパーチャー14の回転をパルスモーターで制御す
ることにより、Tl−Ba−Ca−Cu−O→Bi−W−O→Tl−
Ba−Ca−Cu−O→Bi−W−O→Tl−Ba−Ca−Cu−Oのサ
イクルでスパッタ蒸着が行なうことができる。Tl−Ba−
Ca−Cu−O膜、Bi−W−O膜の積層の様子を概念的に第
2図に示す。第2図において、21はTl−Ba−Ca−Cu−O
膜、22はBi−W−O膜を示す。ターゲット11、12への入
力電力、Tl−Ba−Ca−Cu−OおよびBi−W−Oのスパッ
タ時間を制御することにより、基体15上に蒸着するTl−
Ba−Ca−Cu−O膜21、Bi−W−O膜22の膜厚を変えるこ
とができる。基体15をヒーター16で約600℃に加熱し、
アルゴン・酸素(1:1)混合雰囲気0.5Paのガス中で各タ
ーゲットのスパッタリングを行なった。薄膜作製後は酸
素雰囲気中において、850℃の熱処理を10分間施した。
本実施例では、各ターゲットのスパッタ電力を、Tl−Ba
−Ca−Cu−O:100W,Bi−W−O:100Wとし、ターゲット1
1、12のスパッタ時間を制御した。Bi−Ba−Ca−Cu−O
膜21の元素の組成比率がTl:Ba:Ca:Cu=2:2:2:3、Bi−W
−O膜22の元素の組成比率がBi:W=2:1になるよう、タ
ーゲット11、12元素の組成比率を調整した。Tl−Ba−Ca
−Cu−O膜21をBi−W−O膜22と積層せずに基体15上に
形成した場合、すなわちTl−Ba−Ca−Cu−O膜21そのも
のの特性は、125Kで超電導転移を起こし、100Kで抵抗が
ゼロになるものであった。さらに本発明者らによると、
結晶性を維持したまま、薄くできる膜厚の限界はBi−W
−O膜22については約200Aであった。絶縁膜はできるだ
け薄い方が好ましいので、膜厚200AのBi−W−O膜22に
対して、Tl−Ba−Ca−Cu−O膜21の膜厚を変え第2図に
示すような(Tl−Ba−Ca−Cu−O膜→Bi−W−O膜)の
積層構造を20周期作製した。そのときの超電導薄膜の抵
抗の温度特性を第3図に示す。第3図において、Tl−Ba
−Ca−Cu−O膜21の膜厚が100A、300A、500Aのときのを
特性をそれぞれ、特性31、32、33に示す。特性31におい
てはゼロ抵抗温度が約30KとTl−Ba−Ca−Cu−O膜21の
特性が劣化することがわかった。この理由として、Tl−
Ba−Ca−Cu−O膜21とBi−W−O膜22との間で元素の相
互拡散による膜21、22の結晶性の破壊が考えられる。さ
らに特性33においては、Bi−W−O膜22との周期的な積
層なしに基体15上につけたときのTl−Ba−Ca−Cu−O膜
21本来の超電導特性とほとんど同じであり、絶縁膜Bi−
W−O膜22との積層効果は確認されなかった。しかしな
がら、本発明者らは特性32において、超電導転移温度、
ゼロ抵抗温度がともに約5K上昇することを見いだした。
この効果の詳細な理由については未だ不明であるが、Tl
−Ba−Ca−Cu−O膜21とBi−W−O膜22との積層界面で
の元素の相互拡散の影響が少なく、かつ薄いBi−W−O
膜22を介して複数のTl−Ba−Ca−Cu−O膜21を積層する
ことによりTl−Ba−Ca−Cu−O膜21におて超電導機構に
なんらかの変化が引き起こされたことが考えられる。FIG. 1 is a schematic view of the inside of the binary magnetron sputtering apparatus used in this example, 11 is a Tl-Ba-Ca-Cu-O target, 12 is a Bi-W-O target, 13 is a shutter,
Reference numeral 14 is an aperture, 15 is a substrate, and 16 is a heater for heating the substrate. Two targets 11 and 12 prepared by press-molding a sintered body were used and arranged as shown in FIG. That is, each target is installed so as to be tilted by about 30 ° so as to focus on the MgO (100) substrate 15. There is a rotating shutter 13 in front of the target, and by controlling the rotation of the aperture 14 provided therein with a pulse motor, Tl-Ba-Ca-Cu-O->Bi-W-O-> Tl-
Sputter deposition can be performed in the cycle of Ba-Ca-Cu-O->Bi-WO-> Tl-Ba-Ca-Cu-O. Tl-Ba-
FIG. 2 conceptually shows how the Ca—Cu—O film and the Bi—W—O film are laminated. In FIG. 2, 21 is Tl-Ba-Ca-Cu-O.
The film, 22 is a Bi-W-O film. By controlling the input power to the targets 11 and 12 and the sputtering time of Tl-Ba-Ca-Cu-O and Bi-W-O, Tl- deposited on the substrate 15 is controlled.
The film thickness of the Ba-Ca-Cu-O film 21 and the Bi-W-O film 22 can be changed. The base 15 is heated to about 600 ° C. by the heater 16,
Each target was sputtered in a gas of 0.5 Pa in an argon / oxygen (1: 1) mixed atmosphere. After forming the thin film, heat treatment was performed at 850 ° C. for 10 minutes in an oxygen atmosphere.
In this example, the sputtering power of each target was set to Tl−Ba.
-Ca-Cu-O: 100W, Bi-W-O: 100W, target 1
The sputtering time of 1 and 12 was controlled. Bi-Ba-Ca-Cu-O
The composition ratio of the elements of the film 21 is Tl: Ba: Ca: Cu = 2: 2: 2: 3, Bi-W
The composition ratios of the elements of the targets 11 and 12 were adjusted so that the composition ratio of the elements of the —O film 22 was Bi: W = 2: 1. Tl-Ba-Ca
When the —Cu—O film 21 is formed on the substrate 15 without being laminated with the Bi—W—O film 22, that is, the characteristic of the Tl—Ba—Ca—Cu—O film 21 itself is that the superconducting transition occurs at 125K. The resistance was zero at 100K. Furthermore, according to the inventors,
The limit of the film thickness that can be reduced while maintaining crystallinity is Bi-W
The -O film 22 was about 200A. Since it is preferable that the insulating film be as thin as possible, the film thickness of the Tl-Ba-Ca-Cu-O film 21 is changed with respect to the Bi-W-O film 22 having a film thickness of 200 A as shown in FIG. A laminated structure of —Ba—Ca—Cu—O film → Bi—W—O film) was prepared for 20 cycles. The temperature characteristics of the resistance of the superconducting thin film at that time are shown in FIG. In Figure 3, Tl-Ba
The characteristics when the film thickness of the -Ca-Cu-O film 21 is 100A, 300A, and 500A are shown in characteristics 31, 32, and 33, respectively. It was found that the characteristic 31 has a zero resistance temperature of about 30 K and the characteristics of the Tl-Ba-Ca-Cu-O film 21 deteriorate. The reason for this is that Tl-
It is conceivable that the crystallinity of the films 21 and 22 is destroyed between the Ba—Ca—Cu—O film 21 and the Bi—W—O film 22 due to mutual diffusion of elements. Further, in the characteristic 33, the Tl-Ba-Ca-Cu-O film when applied on the substrate 15 without periodic stacking with the Bi-W-O film 22.
21 It is almost the same as the original superconducting property, and the insulating film Bi-
No stacking effect with the WO film 22 was confirmed. However, in the characteristic 32, the present inventors have found that the superconducting transition temperature,
It was found that the zero resistance temperature increased by about 5K.
The detailed reason for this effect is still unknown, but Tl
-Ba-Ca-Cu-O film 21 and Bi-W-O film 22 have a small effect of mutual diffusion of elements at the laminated interface and are thin Bi-W-O
It is considered that some changes in the superconducting mechanism were caused in the Tl-Ba-Ca-Cu-O film 21 by stacking a plurality of Tl-Ba-Ca-Cu-O films 21 via the film 22. .
なお、超電導転移温度が上昇する効果は、Tl−Ba−Ca−
Cu−O膜21の膜厚が200〜400Aの範囲で有効であること
を、本発明者らは確認した。The effect of increasing the superconducting transition temperature is Tl-Ba-Ca-
The present inventors have confirmed that the Cu-O film 21 is effective in the thickness range of 200 to 400A.
なお、本発明者らは薄膜形成後の熱処理において、Tlガ
スを供給しながら行うと、より再現性よく超電導特性が
得られることを見いだした。このことはTlの蒸気圧が異
常に高く、蒸発しやすいのでこれを供給することによっ
て、結晶性の劣化を防ぐことができたためと考えられ
る。Note that the present inventors have found that, in the heat treatment after the thin film formation, when the Tl gas is supplied, superconducting characteristics can be obtained with better reproducibility. It is considered that this is because the vapor pressure of Tl was abnormally high and it was easy to evaporate, so by supplying it, the deterioration of crystallinity could be prevented.
なお、本発明者らはターゲット11、もしくは12に鉛(P
b)を添加してスパッタしたとき、基体15の温度が上記
実施例よりも約100℃低くても、上記実施例と同等な結
果が得られることを見いだした。The inventors of the present invention used lead (P
It was found that when sputtered by adding b), even if the temperature of the substrate 15 was about 100 ° C. lower than that of the above-mentioned embodiment, the same result as that of the above-mentioned embodiment was obtained.
さらに本発明者らは、Tlの酸化物と、Ba、Ca、Cuの酸化
物を異なる蒸発源から真空中で別々に蒸発させ、基体上
にTl−O→Ba−Cu−O→Ca−Cu−O→Ba−Cu−O→Tl−
Oの順で周期的に積層させた場合、さらにBiの酸化物
と、Wの酸化物を異なる蒸発源から真空中で別々に蒸発
させ、Bi−O→W−O→Bi−Oの順で周期的に積層させ
た場合、(実施例1)に示した積層構造作製方法より極
めて制御性良く、安定した膜質の、しかも膜表面が極め
て平坦なTl−Ba−Ca−Cu−O超電導薄膜およびBi−W−
O絶縁膜が得られることを見いだした。Furthermore, the present inventors separately evaporate the oxide of Tl and the oxides of Ba, Ca, and Cu from different evaporation sources in a vacuum, and Tl-O->Ba-Cu-O-> Ca-Cu on the substrate. -O->Ba-Cu-O-> Tl-
When the layers are periodically stacked in the order of O, the oxide of Bi and the oxide of W are separately evaporated in vacuum from different evaporation sources, and the order of Bi-O->WO-> Bi-O is obtained. When the layers are periodically laminated, the Tl-Ba-Ca-Cu-O superconducting thin film having a much better controllability, a stable film quality, and an extremely flat film surface than the method for producing a laminated structure shown in (Example 1) and Bi-W-
It has been found that an O insulating film can be obtained.
さらに本発明者らは、Tl−O、Ba−Cu−O、Ca−Cu−O,
Bi−O,W−Oを別々の蒸発源から蒸発させ、Tl−Ba−Ca
−Cu−O超電導薄膜とBi−W−O酸化物を周期的に積層
した時、極めて制御性良くm(Tl−Ba−Ca−Cu−O)・
n(Bi−W−O)の周期構造を持つ薄膜を形成できるこ
とを見いだした。ここでm,nは正の整数を示す。さら
に、このm(Tl−Ba−Ca−Cu−O)・n(Bi−W−O)
薄膜は、(実施例1)に示したTl−Ba−Ca−Cu−Oを同
時に蒸着して得る超電導薄膜と、Bi−W−Oを同時に蒸
着して得る酸化物絶縁膜とを周期的に積層して得た薄膜
に比べて、はるかに結晶性が優れ、超電導転移温度、臨
界電流密度等の特性に勝っていることも併せて見いだし
た。さらに本発明者らは、上記の方法で作製したTl−Ba
−Ca−Cu−O超電導薄膜とBi−W−O絶縁膜はともに薄
膜表面が極めて平坦であることを見いだした。Further, the inventors have found that Tl-O, Ba-Cu-O, Ca-Cu-O,
Bi-O and W-O were evaporated from different evaporation sources, and Tl-Ba-Ca
When Cu-O superconducting thin film and Bi-W-O oxide are laminated periodically, m (Tl-Ba-Ca-Cu-O).
It has been found that a thin film having an n (Bi-W-O) periodic structure can be formed. Here, m and n are positive integers. Furthermore, this m (Tl-Ba-Ca-Cu-O) .n (Bi-W-O)
As the thin film, a superconducting thin film obtained by vapor-depositing Tl-Ba-Ca-Cu-O shown in (Example 1) and an oxide insulating film obtained by vapor-depositing Bi-W-O simultaneously were periodically prepared. It was also found that the crystallinity is far superior to that of the thin films obtained by stacking, and it excels in characteristics such as superconducting transition temperature and critical current density. Furthermore, the present inventors have found that the Tl-Ba produced by the above method is
Both the -Ca-Cu-O superconducting thin film and the Bi-W-O insulating film were found to have extremely flat thin film surfaces.
これらのことは第4図に示す積層の概念図を用いて説明
することができる。すなわち、それぞれ層状構造を構成
する異なる元素を別々に順次積層していくことにより、
基体表面に対し平行な面内だけで積層された蒸着元素が
動くだけで、基体表面に対し垂直方向への元素の移動が
ないことによるものと考えられる。さらに、BiとWを含
む酸化物層状ペロブスカイト構造の結晶のa軸の長さ
は、Tl−Ba−Ca−Cu−Oそれとほぼ等しく、連続的にエ
ピタキシャル成長が可能であることによるものと考えら
れる。These can be explained with reference to the conceptual diagram of stacking shown in FIG. That is, by sequentially laminating different elements that respectively form a layered structure,
It is considered that this is because the vapor deposition elements that are stacked move only in the plane parallel to the substrate surface, and there is no movement of the elements in the direction perpendicular to the substrate surface. Further, it is considered that the length of the a-axis of the crystal of the oxide layered perovskite structure containing Bi and W is almost equal to that of Tl-Ba-Ca-Cu-O, and that continuous epitaxial growth is possible.
さらに以外にも、良好な超電導特性を得るに必要な基体
の温度、熱処理温度も、従来より低いことを見いだし
た。In addition to the above, it was found that the temperature of the substrate and the heat treatment temperature required to obtain good superconducting properties are lower than those of the conventional ones.
Tl−O,Ba−Cu−O,Ca−Cu−O,Bi−O,W−Oを周期的に積
層させる方法としては、いくつか考えられる。一般に、
MBE装置あるいは多元のEB蒸着装置で蒸発源の前を開閉
シャッターで制御したり、気相成長法で作製する際にガ
スの種類を切り替えたりすることにより、周期的積層を
達成することができる。しかしこの種の非常に薄い層の
積層には従来スパッタリング蒸着は不向きとされてい
た。この理由は、成膜中のガス圧の高さに起因する不純
物の混入およびエネルギーの高い粒子によるダメージと
考えられている。しかしながら、本発明者らは、このTl
系酸化物超電導体に対してスパッタリングにより異なる
薄い層の積層を行なったところ、以外にも良好な積層膜
作製が可能なことを発見した。スパッタ中の高い酸素ガ
ス圧およびスパッタ放電が、Tl系の100K以上の臨界温度
を持つ相の形成、およびBi−W−O絶縁膜の形成に都合
がよいためではなかろうかと考えられる。There are several possible methods for periodically stacking Tl-O, Ba-Cu-O, Ca-Cu-O, Bi-O, and W-O. In general,
Periodic stacking can be achieved by controlling the opening and closing shutters in front of the evaporation source with an MBE device or a multi-source EB evaporation device, and by switching the type of gas during the vapor phase growth method. However, sputtering deposition has hitherto been unsuitable for stacking very thin layers of this type. The reason for this is considered to be contamination of impurities due to high gas pressure during film formation and damage by particles having high energy. However, we found that this Tl
It was discovered that a good laminated film can be produced by laminating different thin layers on a system oxide superconductor by sputtering. It is considered that the high oxygen gas pressure during sputtering and the sputtering discharge are convenient for the formation of a Tl-based phase having a critical temperature of 100 K or higher and the formation of a Bi-W-O insulating film.
スパッタ蒸着で異なる物質を積層させる方法としては、
組成分布を設けた1ケのスパッタリングターゲットの放
電位置を周期的に制御するという方法があるが、組成の
異なる複数個のターゲットのスパッタリングという方法
を用いると比較的簡単に達成することができる。この場
合、複数個のターゲットの各々のスパッタ量を周期的に
制御したり、あるいはターゲットの前にシャッターを設
けて周期的に開閉したりして、周期的積層膜を作製する
ことができる。また基板を周期的運動させて各々ターゲ
ットの上を移動させる方法でも作製が可能である。レー
ザースパッタあるいはイオンビームスパッタを用いた場
合には、複数個のターゲットを周期運動させてビームの
照射するターゲットを周期的に変えれば、周期的積層膜
が実現される。このように複数個のターゲットを用いた
スパッタリングにより比較的簡単にTl系酸化物の周期的
積層が作製可能となる。As a method of stacking different substances by sputter deposition,
There is a method of periodically controlling the discharge position of one sputtering target provided with a composition distribution, but this can be achieved relatively easily by using a method of sputtering a plurality of targets having different compositions. In this case, the sputtering amount of each of the plurality of targets can be periodically controlled, or a shutter can be provided in front of the target to periodically open and close the target to form a periodic laminated film. It can also be manufactured by a method in which the substrate is moved cyclically and moved over each target. When laser sputtering or ion beam sputtering is used, a periodic laminated film is realized by periodically moving a plurality of targets to periodically change the targets irradiated by the beams. As described above, the periodic stacking of Tl-based oxides can be produced relatively easily by sputtering using a plurality of targets.
以下本発明者らによる第2の発明の内容をさらに深く理
解されるために、具体的な実施例を示す。Specific examples will be shown below in order to deepen the understanding of the content of the second invention by the present inventors.
(実施例2) 第5図に本実施例で用いた5元マグネトロンスパッタ装
置の概略図を示す。第5図において、50はBiターゲッ
ト、51はTlターゲット、52はBaCu合金ターゲット、53は
CaCu合金ターゲット、54はWターゲット、55はシャッタ
ー、56はスリット、57は基体、58は基体加熱用ヒーター
を示す。5個のターゲット50、51、52、53、54は第2図
に示すように配置させた。即ち、MgO(100)基体57に焦
点を結ぶように各ターゲットが約30゜傾いて設置されて
いる。ターゲットの前方には回転するシャッター55があ
り、パルスモーターで駆動することによりその中に設け
られたスリット56の回転が制御され、各ターゲットのサ
イクル及びスパッタ時間を設定することができる。基体
57をヒーター58で約600℃に加熱し、アルゴン・酸素
(5:1)混合雰囲気3Paのガス中で各ターゲットのスパッ
タリングを行なった。各ターゲットのスパッタ電流を、
Bi:30mA,Ti:30mA,BaCu:80mA,CaCu:300mA,W:400mAにして
実験を行った。Tl→BaCu→CaCu→Tlのサイクルでスパッ
タし、Tl−Ba−Ca−Cu−O膜の元素の組成比率がTl:Ba:
Ca:Cu=2:2:2:3となるように各ターゲットのスパッタ時
間を調整し、上記サイクルを20周期行った結果、100K以
上の臨界温度を持つ相を作製することができた。このま
まの状態でもこのTl−Ba−Ca−Cu−O薄膜は100K以上の
超電導転移を示したが、さらに酸素中で650℃、1時間
の熱処理を行なうと非常に再現性よくなり、超電導転移
温度125K、抵抗がゼロになる温度は105Kになった。超電
導転移温度が100Kを越す相は金属元素がTl−Ba−Cu−Ca
−Cu−Ca−Cu−Ba−Tlの順序で並んだ酸化物の層から成
り立っているとも言われており、本発明の製造方法がこ
の構造を作るのに非常に役だっているのではないかと考
えられる。また、同様にBi→W→BiのサイクルでBi−W
−O膜の元素の組成比がBi:W=2:1となるように各ター
ゲットのスパッタ時間を調整し、上記サイクルを4サイ
クルまで少なくして、Bi−W−O膜の膜厚を薄くして
も、極めて結晶性に優れたBi−W−O膜が得られた。(Embodiment 2) FIG. 5 shows a schematic view of a five-element magnetron sputtering apparatus used in this embodiment. In FIG. 5, 50 is a Bi target, 51 is a Tl target, 52 is a BaCu alloy target, and 53 is
A CaCu alloy target, 54 is a W target, 55 is a shutter, 56 is a slit, 57 is a substrate, and 58 is a heater for heating the substrate. The five targets 50, 51, 52, 53, 54 were arranged as shown in FIG. That is, each target is installed so as to be focused on the MgO (100) substrate 57 with an inclination of about 30 °. There is a rotating shutter 55 in front of the target, and by driving with a pulse motor, the rotation of the slit 56 provided therein is controlled, and the cycle and sputtering time of each target can be set. Substrate
57 was heated to about 600 ° C. by a heater 58, and each target was sputtered in a gas of an argon / oxygen (5: 1) mixed atmosphere of 3 Pa. The sputtering current of each target is
The experiment was conducted with Bi: 30mA, Ti: 30mA, BaCu: 80mA, CaCu: 300mA, W: 400mA. Sputtering is performed in the cycle of Tl → BaCu → CaCu → Tl, and the composition ratio of elements of the Tl-Ba-Ca-Cu-O film is Tl: Ba:
The sputtering time of each target was adjusted so that Ca: Cu = 2: 2: 2: 3, and the above cycle was repeated 20 times. As a result, a phase having a critical temperature of 100 K or higher could be produced. Even in this state, the Tl-Ba-Ca-Cu-O thin film showed a superconducting transition of 100K or more, but when heat treatment was further performed at 650 ° C for 1 hour in oxygen, the reproducibility became very good and the superconducting transition temperature 125K, the temperature at which resistance becomes zero reached 105K. In the phase where the superconducting transition temperature exceeds 100K, the metallic element is Tl-Ba-Cu-Ca.
It is also said that it is composed of oxide layers arranged in the order of -Cu-Ca-Cu-Ba-Tl, and it seems that the production method of the present invention is very useful for producing this structure. Conceivable. Similarly, in the cycle of Bi → W → Bi, Bi-W
The sputtering time of each target was adjusted so that the composition ratio of elements in the -O film was Bi: W = 2: 1, and the above cycle was reduced to 4 cycles to reduce the thickness of the Bi-W-O film. Even then, a Bi—W—O film having extremely excellent crystallinity was obtained.
さらに本発明者らはm×(Tl→BaCu→CaCu→BaCu→Tl)
→n×(Bi→W→Bi)のサイクルで各ターゲットをスパ
ッタし、m(Tl−Ba−Ca−Cu−O)・n(Bi−W−O)
薄膜を基体57上に作製した。ここでm,nは正の整数を示
す。本発明者らはn=4のとき、mを変化させて周期的
に積層して得た膜の超電導特性を調べた。第6図にm=
2、6、16のときに得た膜の抵抗の温度変化をそれぞれ
特性61、62、63に示す。第6図において、m=6のと
き、最も高い超電導転移温度およびゼロ抵抗温度、すな
わち特性62が得られた。特性62の超電導転移温度、ゼロ
抵抗温度はTl−Ba−Ca−Cu−O膜本来のそれらの値より
も約8K高いものであった。この効果の詳細な理由につい
ては未だ不明であるが、本実施例に示した方法でTl−Ba
−Ca−Cu−O膜とBi−W−O膜とを周期的に積層するこ
とによって、Tl−Ba−Ca−Cu−O膜とBi−W−O膜が互
いにTl2O2層とBi2O2層を介してエピタキシャル成長して
いることにより積層界面での元素の相互拡散の影響がな
く、かつ結晶性に優れた薄いBi−W−O膜を介して同じ
く結晶性に優れたTl−Ba−Ca−Cu−O膜を積層すること
によりTl−Ba−Ca−Cu−O膜において超電導機構になん
らかの変化が引き起こされたことが考えられる。Furthermore, the present inventors have m × (Tl → BaCu → CaCu → BaCu → Tl)
→ n × (Bi → W → Bi) each target is sputtered, m (Tl-Ba-Ca-Cu-O) · n (Bi-W-O)
A thin film was formed on the base 57. Here, m and n are positive integers. The present inventors investigated the superconducting property of the film obtained by periodically changing the value of m when n = 4. In FIG. 6, m =
The characteristics 61, 62 and 63 show the temperature changes of the resistance of the films obtained in the cases of 2, 6 and 16, respectively. In FIG. 6, when m = 6, the highest superconducting transition temperature and zero resistance temperature, that is, the characteristic 62 was obtained. The superconducting transition temperature and zero resistance temperature of characteristic 62 were about 8 K higher than those values originally present in the Tl-Ba-Ca-Cu-O film. Although the detailed reason for this effect is not yet clear, Tl-Ba was obtained by the method shown in this example.
-Ca-Cu-O film and the Bi-W-O film and by periodically laminating, Tl-Ba-Ca-Cu -O film and the Bi-W-O film is mutually Tl 2 O 2 layer and Bi Since it is epitaxially grown through the 2 O 2 layer, there is no effect of interdiffusion of elements at the stacking interface, and through the thin Bi-W-O film, which has excellent crystallinity, Tl- It is considered that the stacking of the Ba-Ca-Cu-O film caused some change in the superconducting mechanism in the Tl-Ba-Ca-Cu-O film.
なお、超電導転移温度が上昇する効果は、Tl→BaCu→Ca
Cu→BaCu→Tlのサイクルが4〜10の範囲で有効であるこ
とを、本発明者らは確認した。The effect of increasing the superconducting transition temperature is Tl → BaCu → Ca.
The present inventors have confirmed that the cycle of Cu → BaCu → Tl is effective in the range of 4 to 10.
さらに、本発明者らは基体の温度は400〜600℃の範囲で
最もTl−Ba−Ca−Cu−O超電導薄膜の結晶性、および超
電導特性がよいことを見いだした。これは蒸気圧が異常
に高いTlの蒸発が600℃以上で起こり、さらに400℃以下
では結晶化が得られないことが考えられる。Furthermore, the inventors have found that the Tl-Ba-Ca-Cu-O superconducting thin film has the best crystallinity and superconducting properties in the temperature range of 400 to 600 ° C. It is considered that the vaporization of Tl, which has an abnormally high vapor pressure, occurs at 600 ° C or higher and that crystallization cannot be obtained at 400 ° C or lower.
なお、本発明者らはターゲット51、もしくは54に鉛(P
b)を超電導してスパッタしたとき、基体57の温度が上
記実施例よりも約100℃低くても、上記実施例と同等な
結果が得られることを見いだした。Note that the present inventors have found that lead (P
It was found that, when b) is superconducting and is sputtered, even if the temperature of the substrate 57 is about 100 ° C. lower than that in the above-mentioned embodiment, the same result as in the above-mentioned embodiment can be obtained.
発明の効果 以上のように第1の本発明の酸化物超電導薄膜は、Tl系
酸化物超電導薄膜の超電導転移温度を上昇させる構造を
提供するものであり、第2の発明の酸化物超電導薄膜の
製造方法は第1の発明をより効果的に実現し、デバイス
等の応用には必須の低温でのプロセス確立したものであ
り、本発明の工業的価値は大きい。EFFECTS OF THE INVENTION As described above, the oxide superconducting thin film of the first aspect of the present invention provides a structure for increasing the superconducting transition temperature of the Tl-based oxide superconducting thin film. The manufacturing method realizes the first invention more effectively and establishes a process at low temperature which is essential for application of devices and the like, and the industrial value of the present invention is great.
第1図は第1の発明の一実施例における薄膜の製造装置
の概略構造図、第2図は第1の発明の薄膜の構造図、第
3図は第1図の装置により得た薄膜における抵抗の温度
特性図、第4図は第2の発明の構造図、第5図は第2の
発明の実施例における薄膜の製造装置の概略構造図、第
6図は第5図の装置により得た薄膜における抵抗の温度
特性図である。 11、12、50、51、52、53、54……スパッタリングターゲ
ット、13、55……シャッター、14……アパーチャー、56
……スリット、15、57……MgO基体、16、58……ヒータ
ー、21……Tl−Ba−Ca−Cu−O膜、22……Bi−W−O
膜、31、32、33、61、62、63……薄膜の抵抗の温度特
性。FIG. 1 is a schematic structural diagram of a thin film manufacturing apparatus in one embodiment of the first invention, FIG. 2 is a structural diagram of a thin film of the first invention, and FIG. 3 is a thin film obtained by the apparatus of FIG. FIG. 4 is a temperature characteristic diagram of resistance, FIG. 4 is a structural diagram of the second invention, FIG. 5 is a schematic structural diagram of a thin film manufacturing apparatus in the embodiment of the second invention, and FIG. 6 is obtained by the apparatus of FIG. It is a temperature characteristic figure of resistance in a thin film. 11, 12, 50, 51, 52, 53, 54 …… Sputtering target, 13, 55 …… Shutter, 14 …… Aperture, 56
...... Slit, 15, 57 …… MgO substrate, 16,58 …… Heater, 21 …… Tl-Ba-Ca-Cu-O film, 22 …… Bi-W-O
Membrane, 31, 32, 33, 61, 62, 63 ... Temperature characteristics of thin film resistance.
フロントページの続き (51)Int.Cl.6 識別記号 庁内整理番号 FI 技術表示箇所 H01L 39/02 ZAA B 9276−4M 39/24 ZAA B 9276−4M Continuation of the front page (51) Int.Cl. 6 Identification number Office reference number FI technical display location H01L 39/02 ZAA B 9276-4M 39/24 ZAA B 9276-4M
Claims (5)
(Cu),およびアルカリ土類(IIa族)を含む層状酸化
物超電導薄膜と、主体成分が少なくともBiとタングステ
ン(W)を含む層状酸化物薄膜が交互に積層された構造
を持つ(ここでアルカリ土類は、IIa族元素のうち少な
くとも一種あるいは二種以上の元素を示す。)ことを特
徴とする酸化物超電導薄膜。1. A layered oxide superconducting thin film whose main component contains at least thallium (Tl), copper (Cu), and alkaline earth (IIa group), and a layered oxide whose main component contains at least Bi and tungsten (W). An oxide superconducting thin film, characterized in that it has a structure in which the thin films are alternately laminated (wherein alkaline earth represents at least one kind or two or more kinds of elements of group IIa).
なくとも銅およびアルカリ土類(IIa族)を含む酸化物
とを周期的に積層させて形成する酸化物薄膜と、少なく
ともBiを含む酸化物と少なくともWを含む酸化物を周期
的に積層させて形成する酸化物薄膜とを、交互に積層さ
せて得る(ここでアルカリ土類は、IIa族元素のうち少
なくとも一種あるいは二種以上の元素を示す。)ことを
特徴とする酸化物超電導薄膜の製造方法。2. An oxide thin film formed by periodically stacking an oxide containing at least Tl and an oxide containing at least copper and alkaline earth (group IIa) on a substrate, and an oxide containing at least Bi. And an oxide thin film formed by periodically stacking oxides containing at least W are alternately stacked (wherein alkaline earth is at least one or two or more elements of Group IIa elements). The method for producing an oxide superconducting thin film is characterized by:
を特徴とする請求項2記載の酸化物超電導薄膜の製造方
法。3. The method for producing an oxide superconducting thin film according to claim 2, wherein the temperature of the substrate is set in the range of 400 to 600 ° C.
発源で行うことを特徴とする請求項2記載の酸化物超電
導薄膜の製造方法。4. The method for producing an oxide superconducting thin film according to claim 2, wherein evaporation of the laminated material is performed by at least two kinds of evaporation sources.
ことを特徴とする請求項2記載の酸化物超電導薄膜の製
造方法。5. The method for producing an oxide superconducting thin film according to claim 2, wherein the evaporation of the laminated material is performed by sputtering.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP1229917A JPH0714817B2 (en) | 1989-09-05 | 1989-09-05 | Oxide superconducting thin film and method for producing the same |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP1229917A JPH0714817B2 (en) | 1989-09-05 | 1989-09-05 | Oxide superconducting thin film and method for producing the same |
Publications (2)
Publication Number | Publication Date |
---|---|
JPH0393625A JPH0393625A (en) | 1991-04-18 |
JPH0714817B2 true JPH0714817B2 (en) | 1995-02-22 |
Family
ID=16899765
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
JP1229917A Expired - Lifetime JPH0714817B2 (en) | 1989-09-05 | 1989-09-05 | Oxide superconducting thin film and method for producing the same |
Country Status (1)
Country | Link |
---|---|
JP (1) | JPH0714817B2 (en) |
-
1989
- 1989-09-05 JP JP1229917A patent/JPH0714817B2/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
JPH0393625A (en) | 1991-04-18 |
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