JPH06177443A - Superconducting junction device - Google Patents
Superconducting junction deviceInfo
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- JPH06177443A JPH06177443A JP43A JP32285492A JPH06177443A JP H06177443 A JPH06177443 A JP H06177443A JP 43 A JP43 A JP 43A JP 32285492 A JP32285492 A JP 32285492A JP H06177443 A JPH06177443 A JP H06177443A
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- Prior art keywords
- superconducting
- thin film
- critical current
- weak coupling
- current value
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Abstract
Description
【0001】[0001]
【産業上の利用分野】本発明は超伝導接合素子に係り、
さらに詳しくは臨界電流値の制御が可能な弱結合型超伝
導接合素子に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting junction device,
More specifically, the present invention relates to a weakly coupled superconducting junction element capable of controlling a critical current value.
【0002】[0002]
【従来の技術】液体窒素温度を超える超伝導転移温度を
有する酸化物高温超伝導材料の発見以来、これらの材料
を用いた超伝導エレクトロニクス素子の開発が精力的に
進められている。一般に超伝導エレクトロニクス素子
は、電流−電圧特性上にヒステリシスを示すトンネル型
のジョセフソン接合と、ヒステリシスを示さない弱結合
型のジョセフソン接合の2種を主な基本要素としてい
る。前者は、積層された2つの超伝導薄膜電極間に3n
m以下と非常に薄い絶縁体バリア層を挿入した構造を持
つ。特にこの種の接合は、いわゆるジョセフソンコンピ
ュータなどデジタル演算回路を構成するのに適してい
る。しかしながら、YBa2Cu3Oy(y=6〜7)に
代表される高温超伝導材料は、コヒーレンス長が0.1
〜2.5nmと非常に短く、またCuO面内と、面に垂
直な方向とで大きな電気的異方性を持つため、現在まで
に高品質のトンネル接合は実現されていない(高品質接
合を得るためには、超伝導層−バリア層界面における界
面劣化層の厚みをコヒーレンス長以下に抑制する必要が
ある)。一方、弱結合型ジョセフソン接合は、2つの超
伝導薄膜電極間を、例えば細くくびらせたりなどして、
臨界電流を小さくして超伝導性が弱められた部分で結合
した構造を持つ。高温超伝導材料はキャリア濃度が小さ
く、また大きな電気的異方性を持つため、結晶粒界をよ
ぎる方向では、粒内に比べ臨界電流密度が2、3桁小さ
くなるという性質がある。例えば、SrTiO3単結晶
基板上には臨界電流密度の高い良質のYBa2Cu3Oy
エピタキシャル薄膜が得られるが、2つのSrTiO3
単結晶を結晶軸を傾けて張り合わせた双晶基板を用いる
ことにより双晶粒界上に弱結合接合を容易に形成するこ
とができる。また、SrTiO3単結晶基板上に段差を
形成した後に薄膜を堆積すると、上記段差上に沿って弱
結合接合が形成される。このような方法で形成した高温
超伝導薄膜弱結合接合を利用し、液体窒素温度付近の温
度で動作するDC−SQUID磁束計(超伝導量子干渉
計)や磁束フロートランジスタなどのエレクトロニクス
素子が開発されてきている。これら弱結合型接合を利用
した超伝導接合素子においては、臨界電流密度をある所
定の値に制御することが非常に重要である。例えば、2
つの弱結合型接合を用いるDC−SQUIDは、両者の
臨界電流値Icが等しく、かつループインダクタンスL
とIcの積が量子磁束Φ0の1/2程度の時に最も高感
度になる。Lは、素子の形状で決まるためIcの制御が
重要となるわけである。しかしながら、上述した結晶粒
界を利用する弱結合型接合では、形状や面積を正確に決
めることができないだけでなく、その抵抗値が粒界中の
酸素濃度に非常に敏感であるため、臨界電流値Icを精
密に制御することが困難であるという問題がある。他
方、最近、KudinovあるいはNievaらは、酸素の欠損に
より半導体的な電気抵抗変化や非常に低い超伝導転移温
度Tcを示すLnBa2Cu3Oy(Ln=Y、Gd)薄
膜に、高パワーArイオンレーザ光を照射することによ
り、電気抵抗の減少やTcの上昇が起こること、またそ
の変化が低温において保持されることを報告している
〔Phys. Lett. A151 (1990), p.358 および Appl. Phy
s. Lett.60 (1992), p.2159〕。弱結合型接合の臨界電
流は、一般に薄膜のTcの上昇により増大するため、こ
の効果を利用した臨界電流の制御が可能と考えられる。
しかしながら、数W程度の高パワーレーザが必要なこ
と、また高パワーのため薄膜を液体窒素に直接浸すなど
して温度上昇を防ぐ必要があることなど、エレクトロニ
クス素子への適用を阻害する問題点があった。Since the discovery of high-temperature oxide superconducting materials having a superconducting transition temperature exceeding the liquid nitrogen temperature, development of superconducting electronic devices using these materials has been vigorously pursued. In general, a superconducting electronic device has two main types of elements: a tunnel-type Josephson junction that exhibits hysteresis on a current-voltage characteristic and a weak-coupling Josephson junction that does not exhibit hysteresis. The former is 3n between two stacked superconducting thin film electrodes.
It has a structure in which a very thin insulator barrier layer of m or less is inserted. In particular, this type of junction is suitable for forming a digital arithmetic circuit such as a so-called Josephson computer. However, a high temperature superconducting material represented by YBa 2 Cu 3 Oy (y = 6 to 7) has a coherence length of 0.1.
It has a very short length of ~ 2.5 nm, and has a large electrical anisotropy in the CuO plane and in the direction perpendicular to the plane, so high-quality tunnel junctions have not been realized to date (high-quality junctions In order to obtain it, it is necessary to suppress the thickness of the interface deterioration layer at the superconducting layer-barrier layer interface to the coherence length or less). On the other hand, the weak-coupling type Josephson junction is formed by, for example, narrowing between the two superconducting thin film electrodes.
It has a structure in which the superconductivity is weakened by reducing the critical current. Since the high-temperature superconducting material has a low carrier concentration and a large electrical anisotropy, it has a property that the critical current density becomes smaller by a few orders of magnitude in the direction crossing the crystal grain boundaries than in the grain. For example, on a SrTiO 3 single crystal substrate, good quality YBa 2 Cu 3 Oy having a high critical current density is formed.
Epitaxial thin film is obtained, but two SrTiO 3
A weak bond junction can be easily formed on a twin grain boundary by using a twin crystal substrate in which single crystals are bonded with their crystal axes inclined. Further, when a thin film is deposited after forming a step on the SrTiO 3 single crystal substrate, a weak bond bond is formed along the step. Electronic devices such as a DC-SQUID magnetometer (superconducting quantum interferometer) and a magnetic flux flow transistor that operate at a temperature near the liquid nitrogen temperature have been developed by utilizing the high temperature superconducting thin film weak bond junction formed by such a method. Is coming. In the superconducting junction device using these weakly coupled junctions, it is very important to control the critical current density to a certain value. For example, 2
The DC-SQUID using two weak coupling type junctions has the same critical current value Ic and the loop inductance L.
The sensitivity is highest when the product of I and Ic is about 1/2 of the quantum magnetic flux Φ 0 . Control of Ic is important because L is determined by the shape of the element. However, in the weakly-bonded junction utilizing the grain boundaries described above, not only the shape and area cannot be accurately determined, but also the resistance value is very sensitive to the oxygen concentration in the grain boundaries, so that the critical current There is a problem that it is difficult to precisely control the value Ic. On the other hand, recently, Kudinov and Nieva et al. Have reported that high power Ar ions are added to a LnBa 2 Cu 3 Oy (Ln = Y, Gd) thin film showing a semiconductor-like electric resistance change due to oxygen deficiency and a very low superconducting transition temperature Tc. It has been reported that irradiation with laser light causes a decrease in electrical resistance and an increase in Tc, and that the change is maintained at low temperatures [Phys. Lett. A151 (1990), p.358 and Appl. . Phy
s. Lett. 60 (1992), p. 2159]. Since the critical current of a weak bond type junction generally increases with an increase in Tc of the thin film, it is considered possible to control the critical current using this effect.
However, there is a problem that the application to electronic devices is hindered, such as the need for a high power laser of about several W and the need to prevent the temperature rise by directly immersing the thin film in liquid nitrogen because of the high power. there were.
【0003】[0003]
【発明が解決しようとする課題】本発明の目的は、上述
した従来の高温超伝導薄膜を用いた超伝導弱結合型接合
の欠点を解消するものであって、臨界電流値を容易に制
御し得る弱結合型の超伝導接合素子を提供することにあ
る。SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks of the conventional superconducting weak bond type junction using the high temperature superconducting thin film, and to easily control the critical current value. The object is to provide a weakly coupled superconducting junction element.
【0004】[0004]
【課題を解決するための手段】上記本発明の目的を達成
するために、基板上に形成された第1および第2の超伝
導薄膜電極と、上記両電極を結ぶ臨界電流のより小さい
超伝導薄膜弱結合部から構成される弱結合型超伝導接合
素子において、上記超伝導薄膜弱結合部に近接し配設さ
れた光ファイバ開放端から、上記超伝導薄膜弱結合部に
可視光を照射して超伝導転移温度を上昇させることによ
り、超伝導薄膜弱結合部の臨界電流値を制御する構成と
するものである。さらに本発明は、上記超伝導接合素子
の超伝導薄膜弱結合部が、一般式LnBa2Cu3Oy
(LnはY、La、Nd、Sm、Eu、Gd、Tb、D
y、Ho、Er、Tm、Yb、Luのうちから選ばれる
少なくとも1種の元素を示し、yは6.35≦y≦6.
9の範囲を表わす。)で示される組成の超伝導接合素子
とするものである。石英系光ファイバは、波長1.3μ
mあるいは1.55μmの赤外光を用いた光通信に広く
用いられているが、短距離であれば可視光をも通すこと
ができ、また液体ヘリウム温度程度の極低温においても
損失はそれほど増大しない。例えば、GI(Graded Ind
ex)マルチモード光ファイバを用いた場合、そのコア径
は50μmであるから、ファイバ開口端を弱結合型接合
に接近して配設すると、直径1mmのレーザビームを空
間伝播で直接照射するのに比べ、約400倍高いパワー
密度の照射を有効に得ることができる。コア径8μmの
単一モード光ファイバでは、さらに大きい約15000
倍ものパワー密度を容易に作り出すことができるため、
小パワーのレーザ光源を用いても大きな効果が期待でき
る。また、通常超伝導エレクトロニクス素子に用いられ
ている接合のサイズは1〜10μmであるから、超伝導
薄膜弱結合部のみを効果的に照射することができ、超伝
導接合素子全体の温度上昇を抑えることができる。In order to achieve the above-mentioned object of the present invention, superconductivity of a first and second superconducting thin film electrodes formed on a substrate and a superconducting current having a smaller critical current connecting the two electrodes. In a weak-coupling type superconducting junction element composed of a thin-film weak-coupling portion, visible light is irradiated to the superconducting thin-film weak-coupling portion from an open end of an optical fiber which is arranged close to the superconducting thin-film weak-coupling portion. By increasing the superconducting transition temperature, the critical current value of the weakly coupled portion of the superconducting thin film is controlled. The invention further superconducting thin weak coupling portion of the superconducting junction device has the general formula LnBa 2 Cu 3 Oy
(Ln is Y, La, Nd, Sm, Eu, Gd, Tb, D
At least one element selected from y, Ho, Er, Tm, Yb, and Lu is shown, and y is 6.35 ≦ y ≦ 6.
Represents a range of 9. ) Is a superconducting junction element having the composition shown in FIG. Quartz optical fiber has a wavelength of 1.3μ
It is widely used for optical communication using infrared light of m or 1.55 μm, but it can also transmit visible light over a short distance, and the loss increases so much even at extremely low temperature such as liquid helium temperature. do not do. For example, GI (Graded Ind)
ex) When a multimode optical fiber is used, its core diameter is 50 μm. Therefore, if the fiber open end is placed close to the weak coupling type junction, it is possible to directly irradiate a laser beam with a diameter of 1 mm by spatial propagation. In comparison, irradiation with a power density about 400 times higher can be effectively obtained. In a single mode optical fiber with a core diameter of 8 μm, it is even larger, about 15,000.
You can easily create double the power density,
A large effect can be expected even if a low-power laser light source is used. In addition, since the size of the junction that is usually used for the superconducting electronic device is 1 to 10 μm, it is possible to effectively irradiate only the weak coupling portion of the superconducting thin film and suppress the temperature rise of the entire superconducting junction device. be able to.
【0005】[0005]
【実施例】以下に本発明の実施例を挙げ、図面を用いて
さらに詳細に説明する。 <実施例1>反応性同時蒸着法を用いて、SrTiO3
(100)単結晶基板上に、厚さ約100nmのYBa
2Cu3Oy薄膜を堆積した。Yは、電子ビームにより蒸
発させ、Ba、Cu源としてはK−cellを用いた。
堆積時の基板温度は約700℃、酸素圧力は1×10~4
mmHg(Torr)とし、約100WのRF(高周
波)パワーを加えることにより酸素の活性化を行った。
薄膜はc軸配向を示し、c軸方向の格子定数は11.6
8Å、Tc(ゼロ抵抗)は90Kであった。これらを高
速アニール炉中で還元処理することにより、酸素の欠損
した薄膜を作製した。雰囲気としては、Ar+0.2〜
2vol%O2混合ガスを用い、温度400〜550℃
における30minのアニール後に、薄膜を150℃程
度の温度にまで急冷した。アニール時の酸素濃度と温度
を変えることにより酸素濃度の異なる薄膜を作製した。
その格子定数〔c0(Å)〕および超伝導転移温度〔T
c(K)〕、また、これらの値から推定される酸素組成
〔y〕および光照射によるTcの上昇量〔δTc
(K)〕の値を表1に示す。Embodiments of the present invention will be described below in more detail with reference to the drawings. <Example 1> SrTiO 3 was prepared using the reactive co-evaporation method.
About 100 nm thick YBa on a (100) single crystal substrate
A 2 Cu 3 Oy thin film was deposited. Y was evaporated by an electron beam and K-cell was used as a source of Ba and Cu.
Substrate temperature during deposition is about 700 ° C, oxygen pressure is 1 × 10 ~ 4
Oxygen was activated by applying RF (high frequency) power of about 100 W in mmHg (Torr).
The thin film shows c-axis orientation, and the lattice constant in the c-axis direction is 11.6.
8Å, Tc (zero resistance) was 90K. Oxygen-deficient thin films were prepared by reducing these in a rapid annealing furnace. The atmosphere is Ar + 0.2-
2vol% O 2 mixed gas, temperature 400-550 ° C.
After annealing for 30 minutes in, the thin film was rapidly cooled to a temperature of about 150 ° C. Thin films with different oxygen concentrations were prepared by changing the oxygen concentration and temperature during annealing.
Its lattice constant [c 0 (Å)] and superconducting transition temperature [T
c (K)], the oxygen composition [y] estimated from these values, and the amount of increase in Tc due to light irradiation [δTc]
The value of (K)] is shown in Table 1.
【0006】[0006]
【表1】 [Table 1]
【0007】上記の手法で作製した薄膜上に、電極取り
出し用のAu薄膜パタンをメタルマスクを用い真空蒸着
で形成した後、フォト工程によるレジストパタンの形成
と、これをマスクとしたArイオンミリングにより、幅
10μm、長さ30μmの弱結合構造の超伝導接合素子
を作製した。次に、出力4mWのHe−Neレーザ(λ
=632.8nm)光源を用い照射効果を調べた。レー
ザ光をレンズ系で絞り、コア系50μmのGIマルチモ
ード光ファイバ内に導入した。光ファイバは低温測定用
のサンプルホルダに通してあり、他方の開口端を図1に
示すようなアルミナ製ガイド6を用い YBa2Cu3O
y薄膜弱結合部3に近接させ、この薄膜弱結合部3全体
が垂直に光照射を受けるように配設した。顕微鏡を用い
た位置合わせ終了後、アルミナ製ガイド6をSrTiO
3(100)基板1に接着し固定した。基板位置での光
パワーは 約2.5mWであった。サンプルホルダを液
体ヘリウムデュワ内に挿入し、液面からの高さを調節す
ることにより薄膜の温度を約100Kに保ち、2.5m
Wの光を弱結合部に8hr照射した後のTcの上昇量
〔δTc(K)〕を表1に示した。元のTcが88Kの
薄膜においてもTcの上昇が観測され、またTcの低い
薄膜ほど大きなTcの上昇量を示す傾向が見られた。ま
た光照射を受けた薄膜は、200K以下の温度に保持し
ている限りTcは上昇したままで、元の低いTcへの緩
和は観測されなかった。一方、325K以上の温度に加
熱し数時間保持すると、最初と全く同じTcを示すよう
になった。さらに、上記のように高温でTcを緩和させ
た表1に示す試料No.4の薄膜を用い、今度は波長の
異なる光源を用い同様の照射実験を行った。用いた光源
は、AlGaAs系LED(λ=850nm)、AlG
aInP系レーザダイオード(λ=670nm)、He
−Neレーザ(λ=543.5nm)、Arイオンレー
ザ(λ=488nm)の4種である。ダイオード電流の
調節あるいはガスレーザではND(Neutral Density)
フィルタの使用により光パワーを減衰させ、試料位置で
のパワーが1.5mWになるようにした。100Kにお
ける8hrの照射により、可視光光源を用いた場合は5
〜6.5KのTcの上昇が観測された。一方、赤外光L
EDではTcの上昇が全く生じなかった。After forming an Au thin film pattern for electrode extraction on the thin film produced by the above method by vacuum deposition using a metal mask, a resist pattern is formed by a photo process and Ar ion milling using this as a mask. A superconducting junction element having a weakly coupled structure with a width of 10 μm and a length of 30 μm was produced. Next, a He-Ne laser (λ
= 632.8 nm) and the irradiation effect was investigated using a light source. The laser light was focused by a lens system and introduced into a GI multimode optical fiber having a core system of 50 μm. The optical fiber is passed through a sample holder for low temperature measurement, and the other open end is made of YBa 2 Cu 3 O using an alumina guide 6 as shown in FIG.
The y thin film weakly bonded portion 3 was placed close to the thin film weakly bonded portion 3 so that the entire thin film weakly bonded portion 3 was vertically irradiated with light. After completing the alignment using the microscope, the alumina guide 6 is set to SrTiO.
3 It was adhered and fixed to the (100) substrate 1. The optical power at the substrate position was about 2.5 mW. Insert the sample holder into the liquid helium dewar and maintain the temperature of the thin film at about 100K by adjusting the height from the liquid surface to 2.5m.
Table 1 shows the amount of increase in Tc [δTc (K)] after irradiating the weakly coupled portion for 8 hours with W light. A rise in Tc was also observed in the original thin film having a Tc of 88K, and a tendency was shown that the lower the Tc, the greater the increase in Tc. In addition, the thin film irradiated with light had an increased Tc as long as it was kept at a temperature of 200 K or lower, and no relaxation to the original low Tc was observed. On the other hand, when heated to a temperature of 325 K or higher and held for several hours, the same Tc as at the beginning was exhibited. Furthermore, the sample No. shown in Table 1 in which Tc was relaxed at high temperature as described above. The same irradiation experiment was performed using the thin film of No. 4 and this time using light sources having different wavelengths. The light source used was an AlGaAs LED (λ = 850 nm), AlG
aInP laser diode (λ = 670 nm), He
There are four types: -Ne laser (? = 543.5 nm) and Ar ion laser (? = 488 nm). Adjustment of diode current or ND (Neutral Density) in gas laser
The optical power was attenuated by using a filter so that the power at the sample position was 1.5 mW. 5 hours when using a visible light source by irradiation for 8 hours at 100K
An increase in Tc of ~ 6.5K was observed. On the other hand, infrared light L
ED did not cause any increase in Tc.
【0008】<実施例2>実施例1と同様の同時蒸着装
置を用い、厚さ約100nmの LnBa2Cu3Oy
(Ln=Eu、Gd、Dy、Ho、Er、Tm)薄膜を
ほぼ同一条件でSrTiO3(100)基板上に堆積し
た。堆積した薄膜は、いずれもc軸配向を示し、そのT
cは85〜90Kであった。これらの薄膜をAr+0.
2〜2vol%O2ガスフロー中において430℃で3
0min間アニールした後、急冷し、酸素の欠損した薄
膜を作製した。表2に、還元したLnBa2Cu3Oy
( Ln=Eu、Gd、Dy、Ho、Er、Tm)薄膜
の超伝導転移温度Tc(K)と光照射によるTcの上昇
量δTc(K)を示す。Tcには少しばらつきがある
が、これらTcの値から酸素組成yは、y=0.4〜
0.5と推定された。次に、実施例1と同様の方法によ
り、幅10μm、長さ30μmの弱結合構造を作製し、
マルチモードファイバを近接配設し、上記と同様の光照
射実験を行った。光源としてはAlGaInP系レーザ
ダイオード(λ=670nm)を用い、試料位置での光
パワーは3mWとした。100Kにおける8hrの照射
による薄膜のTcの上昇量δTc(K)を表2に示す。Example 2 Using the same vapor deposition apparatus as in Example 1, LnBa 2 Cu 3 Oy having a thickness of about 100 nm was used.
A (Ln = Eu, Gd, Dy, Ho, Er, Tm) thin film was deposited on a SrTiO 3 (100) substrate under almost the same conditions. Each of the deposited thin films exhibits c-axis orientation, and its T
c was 85 to 90K. Ar + 0.
3 at 430 ° C. in a 2 to 2 vol% O 2 gas flow
After annealing for 0 min, it was rapidly cooled to form a thin film lacking oxygen. Table 2 shows the reduced LnBa 2 Cu 3 Oy.
(Ln = Eu, Gd, Dy, Ho, Er, Tm) The superconducting transition temperature Tc (K) of the thin film and the increase amount Tc (K) of Tc due to light irradiation are shown. Although there is some variation in Tc, the oxygen composition y is y = 0.4-
It was estimated to be 0.5. Next, a weakly coupled structure having a width of 10 μm and a length of 30 μm was produced by the same method as in Example 1,
The multimode fibers were arranged close to each other, and the same light irradiation experiment as above was performed. An AlGaInP laser diode (λ = 670 nm) was used as the light source, and the optical power at the sample position was 3 mW. Table 2 shows the amount δTc (K) of increase in Tc of the thin film due to irradiation for 8 hours at 100K.
【0009】[0009]
【表2】 [Table 2]
【0010】表2に示すごとく、実施例1のYBa2C
u3Oy薄膜の場合と同程度のTcの上昇があることが
分かる。なお、LnBa2Cu3Oy(Ln=Y、La、
Nd、Sm、Eu、Gd、Tb、Dy、Ho、Er、T
m、Yb、Lu)薄膜とは同じ構造であり、約90Kと
同程度の超伝導転移温度を有することから、他のランタ
ノイドに対しても同様の効果が期待できる。As shown in Table 2, YBa 2 C of Example 1
It can be seen that the Tc rises to the same extent as in the case of the u 3 Oy thin film. Note that LnBa 2 Cu 3 Oy (Ln = Y, La,
Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
(m, Yb, Lu) thin film has the same structure and has a superconducting transition temperature of about 90 K, so that similar effects can be expected for other lanthanoids.
【0011】<実施例3>図2に示すごとく、SrTi
O3(100)基板1上に、フォト工程でレジストパタ
ンを形成した後、これをマスクとし、Arイオンミリン
グによって高さ100nmの段差7を形成した。レジス
ト除去後、上記の基板上に、化学量論組成の焼結体ター
ゲットを用いたDCマグネトロンスパッタ法により、厚
さ約150nmのYBa2Cu3Oy薄膜2を堆積した。
この際、10PaのAr+5vol%O2ガスを用い基
板温度は650℃とした。この薄膜を、フォト工程とイ
オンミリングにより加工し、図2に示すような幅5μ
m、長さ30μmで、段差を横切る形のYBa2Cu3O
y薄膜弱結合部3を作製した。この弱結合型超伝導接合
素子は、72K以下の温度で超伝導(ゼロ電圧)電流を
示し、より低温では、図3に示すようなRSJ(Resist
ively Shunted Junction)モデルによく従う典型的な弱
結合型ジョセフソン接合の電流−電圧特性が観測され
た。上記の手順で作製した弱結合型超伝導接合素子に、
実施例1と同様のマルチモード光ファイバ5を近接して
配設し、65KにおけるHe−Neレーザ光(λ=63
2.8nm)照射の効果を調べた。ファイバ内に結合さ
れた光パワーは最大で2.5mWであり、またファイバ
への導入部の前にND(Neutral Density)フィルタを
挿入することにより、パワーを−10dB(デシベル)
あるいは−20dB減衰させた光照射も行った。規格化
した臨界(ゼロ抵抗)電流値の光照射時間依存性を示
す。どの光パワーに対しても、臨界電流は時間の対数に
比例する形で増加していく。また、−10dBおよび−
20dBのパワーで0dBと同じ増加量を得るために
は、それぞれ10倍、100倍の時間を要することが分
かる。これらは、臨界電流値がパワーと時間の積、すな
わちフォトンのドーズ量で制御できること、また高パワ
ー密度の光照射により電流値制御に要する時間を著しく
短縮できることを意味する。次に、上記と同じ弱結合型
ジョセフソン接合を、ガスフロー型のクライオスタット
内の銅ブロックヘッドに低温用グリースを用い張り付
け、ブロックからの熱伝導で65Kに冷却した。この場
合、YBa2Cu3Oy薄膜は真空中に置かれている。1
WパワーのArイオンレーザ光(λ=514.5nm、
ビーム径1mm)を1/10に減衰させ、クライオスタ
ットの石英窓を通してYBa2Cu3Oy薄膜弱結合部付
近に照射し、臨界電流値の時間変化を調べた。図5に示
すように、光照射中は、0.25mWのパワーのHe−
Neレーザ光を、光ファイバを通して照射した場合に比
べて臨界電流値の増加は小さい。ところが、100mi
n後に光照射をやめると、臨界電流値はファイバを通し
た場合と同程度のレベルにまで突然増加した(一方、フ
ァイバを用いた場合の臨界電流の変化はほとんど見られ
なかった)。これは、ファイバを通さない場合、光照射
時にYBa2Cu3Oy薄膜の温度が著しく上昇したため
であると考えられる。<Embodiment 3> As shown in FIG. 2, SrTi
After forming a resist pattern on the O 3 (100) substrate 1 by a photo process, using this as a mask, a step 7 having a height of 100 nm was formed by Ar ion milling. After removing the resist, a YBa 2 Cu 3 Oy thin film 2 having a thickness of about 150 nm was deposited on the above substrate by a DC magnetron sputtering method using a sintered body target having a stoichiometric composition.
At this time, the substrate temperature was set to 650 ° C. using Ar + 5 vol% O 2 gas of 10 Pa. This thin film is processed by a photo process and ion milling, and the width is 5 μm as shown in FIG.
m, length 30 μm, cross-stepped YBa 2 Cu 3 O
y The thin film weakly bonded portion 3 was produced. This weak-coupling type superconducting junction element exhibits a superconducting (zero voltage) current at a temperature of 72 K or lower, and at lower temperatures, RSJ (Resist) as shown in FIG.
The current-voltage characteristics of a typical weakly coupled Josephson junction that closely follows the shunted junction model were observed. To the weakly coupled superconducting junction element manufactured by the above procedure,
The same multimode optical fiber 5 as that of the first embodiment is arranged close to each other, and the He—Ne laser light (λ = 63) at 65K is arranged.
The effect of irradiation (2.8 nm) was investigated. The maximum optical power coupled into the fiber is 2.5 mW, and by inserting an ND (Neutral Density) filter in front of the introduction part to the fiber, the power is -10 dB (decibel).
Alternatively, light irradiation with -20 dB attenuation was also performed. The light irradiation time dependence of the normalized critical (zero resistance) current value is shown. The critical current increases proportionally to the logarithm of time for any optical power. Also, −10 dB and −
It can be seen that it takes 10 times and 100 times, respectively, to obtain the same increase amount as 0 dB with the power of 20 dB. These mean that the critical current value can be controlled by the product of power and time, that is, the dose amount of photons, and that the time required for current value control can be significantly shortened by light irradiation with high power density. Next, the same weak-bonding type Josephson junction as that described above was attached to a copper block head in a gas flow type cryostat using low temperature grease and cooled to 65K by heat conduction from the block. In this case, the YBa 2 Cu 3 Oy thin film is placed in a vacuum. 1
W power Ar ion laser light (λ = 514.5 nm,
The beam diameter (1 mm) was attenuated to 1/10, and the vicinity of the YBa 2 Cu 3 Oy thin film weakly coupled portion was irradiated through a quartz window of a cryostat, and the time change of the critical current value was examined. As shown in FIG. 5, during light irradiation, He − with a power of 0.25 mW.
The increase in the critical current value is small as compared with the case where the Ne laser light is irradiated through the optical fiber. However, 100 mi
When the light irradiation was stopped after n, the critical current value suddenly increased to a level comparable to that through the fiber (while the change in the critical current with the fiber was hardly observed). It is considered that this is because the temperature of the YBa 2 Cu 3 Oy thin film remarkably increased during light irradiation without passing through the fiber.
【0012】[0012]
【発明の効果】以上詳細に説明したごとく、本発明の超
伝導接合素子によれば、光ファイバを超伝導薄膜弱結合
部に近接して配設した構造を取ることにより、小パワー
の可視光レーザを用いても、非常に高いパワー密度の照
射を実現することができ、このため光照射による超伝導
薄膜のTcの上昇および超伝導薄膜弱結合部の臨界電流
値の上昇量を短時間に制御することができる。また、超
伝導薄膜弱結合部のみの光照射が可能であるため、超伝
導薄膜接合部の温度上昇が抑制でき、臨界電流値をより
正確に制御できる効果がある。As described in detail above, according to the superconducting junction element of the present invention, a structure in which an optical fiber is disposed close to the superconducting thin film weakly coupled portion allows the visible light of small power to be emitted. Irradiation with a very high power density can be realized even by using a laser. Therefore, the increase in Tc of the superconducting thin film and the increase in the critical current value of the weak junction of the superconducting thin film due to light irradiation can be reduced in a short time. Can be controlled. Further, since it is possible to irradiate light only on the weakly coupled portion of the superconducting thin film, it is possible to suppress an increase in temperature of the superconducting thin film joint portion and to control the critical current value more accurately.
【図1】本発明の実施例1で例示した弱結合型超伝導接
合素子の構成を示す模式図。FIG. 1 is a schematic diagram showing the configuration of a weakly coupled superconducting junction element exemplified in Example 1 of the present invention.
【図2】本発明の実施例3で例示した弱結合型超伝導接
合素子の構成を示す模式図。FIG. 2 is a schematic diagram showing a configuration of a weakly coupled superconducting junction element exemplified in Example 3 of the present invention.
【図3】本発明の実施例3で例示した弱結合型超伝導接
合素子の電流−電圧特性を示す図。FIG. 3 is a diagram showing current-voltage characteristics of the weak coupling type superconducting junction element exemplified in Example 3 of the present invention.
【図4】本発明の実施例3で例示した弱結合型超伝導接
合素子のHe−Neレーザ光照射に対する臨界電流値の
時間変化を示す図。FIG. 4 is a diagram showing a change with time of a critical current value of a weakly coupled superconducting junction element illustrated in Example 3 of the present invention with respect to He—Ne laser light irradiation.
【図5】本発明の実施例3で例示した弱結合型超伝導接
合素子に光ファイバを通したHe−Neレーザ光の照射
の場合と、光ファイバを通さないでArイオンレーザ光
を直接照射した場合の臨界電流値の時間変化を示す図。FIG. 5 is a case of irradiating a He—Ne laser beam through an optical fiber to the weakly coupled superconducting junction element illustrated in Example 3 of the present invention, and a case of directly irradiating an Ar ion laser beam without passing through the optical fiber. The figure which shows the time change of the critical current value at the time of doing.
1…SrTiO3(100)基板 2…YBa2Cu3Oy薄膜 3…YBa2Cu3Oy薄膜弱結合部 4…Au電極パタン 5…マルチモード光ファイバ 6…アルミナ製ガイド 7…段差1 ... SrTiO 3 (100) substrate 2 ... YBa 2 Cu 3 Oy thin film 3 ... YBa 2 Cu 3 Oy thin film weakly-bonded portion 4 Au electrode pattern 5 multimode optical fiber 6 alumina guide 7 step
───────────────────────────────────────────────────── フロントページの続き (72)発明者 鈴木 実 東京都千代田区内幸町一丁目1番6号 日 本電信電話株式会社内 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Minoru Suzuki 1-16, Uchisaiwaicho, Chiyoda-ku, Tokyo Nihon Telegraph and Telephone Corporation
Claims (2)
導薄膜電極と、上記第1および第2の超伝導薄膜電極間
を結ぶ臨界電流のより小さい超伝導薄膜弱結合部によっ
て構成される弱結合型超伝導接合素子において、上記超
伝導薄膜弱結合部に近接して配設された光ファイバ開放
端から超伝導薄膜弱結合部に可視光を照射して超伝導転
移温度を上昇させることにより臨界電流値を制御する手
段を有することを特徴とする超伝導接合素子。1. A structure comprising first and second superconducting thin-film electrodes formed on a substrate, and a superconducting thin-film weak-coupling part connecting between the first and second superconducting thin-film electrodes having a smaller critical current. In the weak coupling type superconducting junction element, the superconducting transition temperature is raised by irradiating the weak coupling portion of the superconducting thin film with visible light from the open end of the optical fiber arranged close to the weak coupling portion of the superconducting thin film. A superconducting junction device, characterized in that it has means for controlling a critical current value by controlling.
超伝導薄膜弱結合部が、一般式 LnBa2Cu3Oy (式中、LnはY、La、Nd、Sm、Eu、Gd、T
b、Dy、Ho、Er、Tm、Yb、Luのうちから選
ばれる少なくとも1種の元素を示し、yは6.35≦y
≦6.9の範囲を表わす。)で示される組成からなるこ
とを特徴とする超伝導接合素子。2. The superconducting junction element according to claim 1, wherein
The superconducting thin film weakly-bonded part has the general formula LnBa 2 Cu 3 Oy (wherein Ln is Y, La, Nd, Sm, Eu, Gd, T
at least one element selected from b, Dy, Ho, Er, Tm, Yb, and Lu, and y is 6.35 ≦ y
It represents a range of ≦ 6.9. ) A superconducting junction element characterized by comprising a composition shown in FIG.
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