JP2006210585A - New type terahertz oscillator using laminated josephson junction - Google Patents

New type terahertz oscillator using laminated josephson junction Download PDF

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JP2006210585A
JP2006210585A JP2005019662A JP2005019662A JP2006210585A JP 2006210585 A JP2006210585 A JP 2006210585A JP 2005019662 A JP2005019662 A JP 2005019662A JP 2005019662 A JP2005019662 A JP 2005019662A JP 2006210585 A JP2006210585 A JP 2006210585A
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terahertz
terahertz oscillator
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josephson junction
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Kahei O
華兵 王
Takeshi Hatano
毅 羽多野
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National Institute for Materials Science
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a terahertz oscillator using laminated Josephson junction which can generate higher frequency and output intensity. <P>SOLUTION: The terahertz oscillator uses a superconductor single crystal element having laminated Josephson junction where the original Josephson junction is laminated in series between a superconductive layer and an insulating layer. The Josephson junction is small in width and large in depth, and it is comprised so that a magnetic field is applied to its small element width to form rectangular magnetic flux lattices in lines and to generate resonance of standing waves by the small element width. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、超伝導エレクトロニクス及びテラヘルツ応用に関し、特に、テラヘルツ帯連続波を発生させる新原理に基づく積層ジョセフソン接合を用いた新型テラヘルツ発振器に関するものである。その用途は、物性物理・分子科学・生物科学の基礎研究から、画像診断・検査・大気観測・将来の無線通信に至る広範なものである。   The present invention relates to superconducting electronics and terahertz applications, and more particularly to a new terahertz oscillator using a stacked Josephson junction based on a new principle for generating a terahertz band continuous wave. Its applications range from basic research in physical properties physics, molecular science, and biological science to imaging diagnosis, inspection, atmospheric observation, and future wireless communications.

金属系超伝導体では、幅の長いジョセフソン接合が磁束フロー発振器に応用されている。通常、この目的で用いられるジョセフソン接合は直線上に並んだ接合で、言い換えれば、磁界に垂直の幅はジョセフソン侵入長よりも長く、散逸を防ぐため平行な奥行きはジョセフソン侵入長よりも遙かに短く設計される。接合中の磁束がローレンツ力により加速され、素子端から飛び出すところで、放射が起きる。幅が長いため周波数は低く、素子幅との共鳴を使うことができないので出力強度も低い。   In metal-based superconductors, wide Josephson junctions are applied to magnetic flux flow oscillators. Normally, the Josephson junction used for this purpose is a straight-line junction, in other words, the width perpendicular to the magnetic field is longer than the Josephson penetration length, and the parallel depth is greater than the Josephson penetration length to prevent dissipation. Designed much shorter. Radiation occurs where the magnetic flux in the junction is accelerated by the Lorentz force and jumps out of the element end. Since the width is long, the frequency is low, and since the resonance with the element width cannot be used, the output intensity is also low.

さらに、従来の金属系超伝導体を用いた素子では、放射マイクロ波の周波数は磁界強度と磁束フロー速度に比例するが、超伝導エネルギーギャップを越えることは出来ない。金属系では超伝導遷移温度が低いため、超伝導エネルギーギャップもそれに比例して低いため、周波数のカットオフも低くなってしまう。出力パワーは、主に接合の臨界電流と減衰特性に左右される。   Furthermore, in a conventional device using a metallic superconductor, the frequency of the radiation microwave is proportional to the magnetic field strength and the magnetic flux flow speed, but cannot exceed the superconducting energy gap. Since the superconducting transition temperature is low in a metal system, the superconducting energy gap is proportionally low, and the frequency cutoff is also low. The output power depends mainly on the critical current and damping characteristics of the junction.

また、高温超伝導体の固有接合を用いたテラヘルツ電磁波発振器も公知である（例えば、特許文献１参照）が、従来の金属系超伝導体と同様の設計思想に基づくものであり、接合列の整合した放射や明確な共鳴電流ステップを観測するものではない。
特開２００４−２３５６１４号公報 A terahertz electromagnetic wave oscillator using an intrinsic junction of a high-temperature superconductor is also known (see, for example, Patent Document 1), but is based on the same design concept as a conventional metal-based superconductor. It does not observe matched emission or distinct resonance current steps.
JP 2004-235614 A

特許文献１には、「超伝導層と絶縁層との固有ジョセフソン接合が直列に積層されている超伝導体単結晶メサ構造よりなり、テラヘルツ電磁波を発振できる電磁波発振部」（請求項１）が設けられているが、「前記電磁波発振部の超伝導体単結晶メサ構造は、外部磁場に垂直な方向の長さがジョセフソンの侵入深さより長く構成され」るものである（段落［０００８］、［００３１］）から、従来の金属系超伝導体の場合と同様に素子幅との共鳴を使うことができず、テラヘルツ電磁波の発振は十分ではなく、出力強度を高くすることができないという問題がある。   Patent Document 1 discloses that “an electromagnetic wave oscillation unit that has a superconductor single crystal mesa structure in which intrinsic Josephson junctions of a superconducting layer and an insulating layer are laminated in series and can oscillate terahertz electromagnetic waves” (Claim 1). However, “the superconductor single crystal mesa structure of the electromagnetic wave oscillating part is configured such that the length in the direction perpendicular to the external magnetic field is longer than the depth of penetration of Josephson” (paragraph [0008] ] And [0031]), the resonance with the element width cannot be used as in the case of the conventional metal superconductor, the oscillation of the terahertz electromagnetic wave is not sufficient, and the output intensity cannot be increased. There's a problem.

また、ミリ波の発振器としては、アンダーダンプＮｂジョセフソン接合を２次元に配列する方式がある（例えば、非特許文献１参照）。２次元接合列の共振による、接合列はマイクロ波を整合共振により放射する。敷居値以上では、接合列がマイクロ波の空間波長に達するまで、素子数Ｎの二乗に比例した出力を発生する。この文献によれば、検出された出力は、０．４ｍＷで、周波数は０．１８ＴＨｚであるから、出力強度、周波数は低いものであった。
P. Barbara et al., Phys. Rev. Lett. 82, 1963(1999), and Vasilic, Appl. Phys. Lett. 78, 1137(2001) As a millimeter wave oscillator, there is a system in which under-dump Nb Josephson junctions are two-dimensionally arranged (see, for example, Non-Patent Document 1). Due to the resonance of the two-dimensional junction array, the junction array radiates microwaves by matching resonance. Above the threshold value, an output proportional to the square of the number N of elements is generated until the junction array reaches the spatial wavelength of the microwave. According to this document, since the detected output is 0.4 mW and the frequency is 0.18 THz, the output intensity and frequency are low.
P. Barbara et al., Phys. Rev. Lett. 82, 1963 (1999), and Vasilic, Appl. Phys. Lett. 78, 1137 (2001)

さらに、両面加工法によりコンパクトな集積回路を構成することができる超伝導電子デバイスを製造すること、そのような加工法を用いて単結晶ジョセフソン接合テラヘルツ検出器を得ることも公知であり（例えば、特許文献２及び３参照）、これらの文献には、「この方法を用いて、ａ−ｂ面方向の寸法がサブミクロンから約５００ミクロンまで、ｃ軸方向の厚さが数十から数千オングストロームまで変えることができる超伝導電子デバイス
を製造することができる。」（特許文献２の段落［００２０］）、「典型的なものでは、接合のａ−ｂ面の寸法をサブミクロンまで下げることができ、一方、ｃ軸方向の厚さを数十から数百Åにすることができる。」（特許文献３の段落［００１０］）と記載されているが、ジョセフソン接合を、幅が狭く、奥行きが長い接合とすることは示されていない。
特開２００２−２４６６６５号公報 特開２００２−２４６６６４号公報 Furthermore, it is also known to manufacture a superconducting electronic device capable of forming a compact integrated circuit by a double-sided processing method, and to obtain a single crystal Josephson junction terahertz detector using such a processing method (for example, (See Patent Documents 2 and 3), these documents include: “Using this method, the dimension in the ab plane direction is from submicron to about 500 microns, and the thickness in the c-axis direction is from tens to thousands. A superconducting electronic device that can be changed to angstroms can be manufactured. "(Patent Document 2, paragraph [0020])," Typically, the size of the ab plane of the junction is reduced to submicron. On the other hand, the thickness in the c-axis direction can be made from several tens to several hundreds of millimeters ”(paragraph [0010] of Patent Document 3). Narrow, not been shown that depth and long bonding.
JP 2002-246665 A JP 2002-246664 A

本発明は、上記のような問題を解決しようとするものであり、より高い周波数と出力強度を発生させることができる積層ジョセフソン接合を用いたテラヘルツ発振器を提供することを課題とする。   An object of the present invention is to provide a terahertz oscillator using a stacked Josephson junction that can generate higher frequencies and output intensities.

本発明は、上記の課題を解決するために、以下の手段を採用する。
（１）超伝導層と絶縁層との固有ジョセフソン接合が直列に積層されている積層ジョセフソン接合を有する超伝導体単結晶の素子を用いたテラヘルツ発振器において、前記ジョセフソン接合が、幅が狭く、奥行きが長い接合であり、狭い素子幅に磁界を印加して四角形に並んだ磁束格子を形成し、前記狭い素子幅による定在波の共鳴を起こさせるように構成されていることを特徴とするテラヘルツ発振器である。
（２）前記超伝導体単結晶が、ビスマス・ストロンチウム・カルシウム・銅酸化物単結晶であることを特徴とする前記（１）のテラヘルツ発振器である。
（３）前記四角形に並んだ磁束格子の集団的な磁束フローが位相整合状態で実現されることを特徴とする前記（１）又は（２）のテラヘルツ発振器である。
（４）前記素子幅がジョセフソン侵入長の４倍以下であることを特徴とする前記（１）〜（３）のいずれか一のテラヘルツ発振器である。
（５）前記素子幅が１．８μｍ以下であり、前記奥行きが５μｍ以上であることを特徴とする前記（１）〜（４）のいずれか一項に記載のテラヘルツ発振器である。
（６）前記（１）〜（５）のいずれか一のジョセフソン接合を有する素子の上部及び下部電極を超伝導体単結晶で並列に繋いで並列の素子列を構成したことを特徴とするテラヘルツ発振器である。
（７）前記ジョセフソン接合を有する素子が、基板と、該基板上に搭載される両面加工法によりパターン化された超伝導体単結晶からなることを特徴とする前記（１）〜（６）のいずれか一のテラヘルツ発振器である。
（８）前記（１）〜（７）のいずれか一のテラヘルツ発振器を備えていることを特徴とする画像診断・検査装置である。
（９）前記（１）〜（７）のいずれか一のテラヘルツ発振器を備えていることを特徴とする大気観測装置である。
（１０）前記（１）〜（７）のいずれか一のテラヘルツ発振器を備えていることを特徴とする無線通信装置である。
（１１）前記（１）〜（７）のいずれか一のテラヘルツ発振器における磁界の印加方法において、前記狭い素子幅に垂直に磁界を印加することを特徴とする磁界の印加方法である。
（１２）超伝導電磁石、常伝導電磁石又は永久磁石を用いて磁界を印加することを特徴とする前記（１１）の磁界の印加方法である。 The present invention employs the following means in order to solve the above problems.
(1) In a terahertz oscillator using a superconductor single crystal element having a stacked Josephson junction in which intrinsic Josephson junctions of a superconducting layer and an insulating layer are stacked in series, the Josephson junction has a width It is a narrow and long junction, and is configured to apply a magnetic field to a narrow element width to form a square-shaped magnetic flux lattice, and to cause standing wave resonance by the narrow element width. Is a terahertz oscillator.
(2) The terahertz oscillator according to (1), wherein the superconductor single crystal is a bismuth / strontium / calcium / copper oxide single crystal.
(3) The terahertz oscillator according to (1) or (2), wherein a collective magnetic flux flow of the magnetic flux lattices arranged in a quadrangular shape is realized in a phase matching state.
(4) The terahertz oscillator according to any one of (1) to (3), wherein the element width is not more than four times the Josephson penetration length.
(5) The terahertz oscillator according to any one of (1) to (4), wherein the element width is 1.8 μm or less and the depth is 5 μm or more.
(6) The device having the Josephson junction according to any one of the above (1) to (5), wherein the upper and lower electrodes are connected in parallel with a superconductor single crystal to form a parallel device array. It is a terahertz oscillator.
(7) The element having the Josephson junction comprises a substrate and a superconductor single crystal patterned by a double-sided processing method mounted on the substrate. Any one of the terahertz oscillators.
(8) An image diagnostic / inspection apparatus comprising the terahertz oscillator according to any one of (1) to (7).
(9) An atmospheric observation apparatus including the terahertz oscillator according to any one of (1) to (7).
(10) A wireless communication apparatus comprising the terahertz oscillator according to any one of (1) to (7).
(11) The magnetic field application method in the terahertz oscillator according to any one of (1) to (7), wherein the magnetic field is applied perpendicularly to the narrow element width.
(12) The method for applying a magnetic field according to (11), wherein a magnetic field is applied using a superconducting electromagnet, a normal conducting electromagnet, or a permanent magnet.

本発明によれば、より高い周波数と出力強度を発生するテラヘルツ帯固体連続波発振器を提供することができるという効果を奏する。また、単に固体連続波発振器を提供し、画像診断・検査、大気観測、将来の無線通信を可能にするだけでなく、物性物理、分子科学
、生物科学の基礎研究に貢献するものである。 According to the present invention, it is possible to provide a terahertz solid-state continuous wave oscillator that generates a higher frequency and output intensity. In addition to providing solid-state continuous wave oscillators, it not only enables diagnostic imaging / inspection, atmospheric observation, and future wireless communication, but also contributes to basic research in physical physics, molecular science, and biological science.

通常、定在波はジョセフソン接合では、弱い共鳴しか起こさなかった。従って、その原理から発振器を開発しようという試みはない。よって、定在波の原理に、磁束格子を加えたジョセフソン接合列の発振器は、新原理である。   In general, standing waves caused only weak resonances in Josephson junctions. Therefore, there is no attempt to develop an oscillator based on the principle. Therefore, a Josephson junction oscillator in which a magnetic flux lattice is added to the standing wave principle is a new principle.

また、固有ジョセフソン接合において、明瞭な共鳴発振現象を観測したのは最初である。これは、本発明のの進んだ加工法と磁束フロー運動の深い理解に基づくものである。   It was also the first time that a clear resonance oscillation phenomenon was observed in an intrinsic Josephson junction. This is based on a deep understanding of the advanced processing method and flux flow motion of the present invention.

本発明においては、幅の狭い固有ジョセフソン素子を接合に平行な磁界中に置き、層に垂直な外部電流によるローレンツ力によりジョセフソン磁束を層内でフローさせ、磁束フロー電圧を発生させる。ジョセフソン接合は、電圧に比例する周波数で交流電流が流れる。外部電流を増加させると、フロー電圧が増加し、それに比例した交流電流の周波数が高くなる。即ち、波長が短くなっていく。この交流電流による電磁波の波長が素子の幅と一致すると共鳴が起きる。電磁波の周波数は、素子の幅に反比例することになる。   In the present invention, a narrow intrinsic Josephson element is placed in a magnetic field parallel to the junction, and a Josephson magnetic flux is caused to flow in the layer by a Lorentz force generated by an external current perpendicular to the layer, thereby generating a magnetic flux flow voltage. In the Josephson junction, an alternating current flows at a frequency proportional to the voltage. When the external current is increased, the flow voltage is increased and the frequency of the alternating current is increased in proportion to the flow voltage. That is, the wavelength becomes shorter. Resonance occurs when the wavelength of the electromagnetic wave due to this alternating current matches the width of the element. The frequency of the electromagnetic wave is inversely proportional to the width of the element.

前述したように、従来技術においては、素子の幅を長く、素子の奥行きを短くして、幅の対角線成分を抑制することが必要であるが、本発明では高い磁界により固有ジョセフソン接合素子内部に、四角形に並んだ磁束格子を形成し、その集団的なフローを利用することから、素子の幅を短く、素子の奥行きを長くすることができる。素子の両端面に平行な磁束線により、電磁波の進行方向が磁界と垂直方向に絞られるからである。   As described above, in the prior art, it is necessary to suppress the diagonal component of the width by increasing the width of the element and shortening the depth of the element. In addition, since the magnetic flux lattices arranged in a square are formed and the collective flow is used, the width of the element can be shortened and the depth of the element can be increased. This is because the traveling direction of the electromagnetic wave is narrowed in the direction perpendicular to the magnetic field by the magnetic flux lines parallel to both end faces of the element.

すなわち、本発明は、超伝導層と絶縁層との固有ジョセフソン接合が直列に積層されている積層ジョセフソン接合を有する超伝導体単結晶よりなる素子を用いる点では従来技術と同じであるが、磁界を、狭い素子幅、好ましくはジョセフソン侵入長の４倍以下（ジョセフソン侵入長は、０．２〜１μｍであることが知られており、４倍は０．８〜４μｍに相当する。）、例えば１．８μｍ以下に作製された素子幅に対して印加する。素子幅は、さらに好ましくは、１．５μｍ以下である。逆に奥行きは、出来るだけ長く、例えば５μｍ以上とする。幅が狭く、さらに直線上に並んだ磁束格子が存在するために、定在波がジョセフソン接合内に発生する。   That is, the present invention is the same as the prior art in that an element made of a superconductor single crystal having a stacked Josephson junction in which intrinsic Josephson junctions of a superconductive layer and an insulating layer are stacked in series is used. , The magnetic field is narrow element width, preferably less than 4 times the Josephson penetration length (Josephson penetration length is known to be 0.2-1 μm, 4 times corresponds to 0.8-4 μm ), For example, applied to the element width produced to 1.8 μm or less. The element width is more preferably 1.5 μm or less. Conversely, the depth is as long as possible, for example, 5 μm or more. A standing wave is generated in the Josephson junction due to the presence of narrow and narrow magnetic flux grids.

素子の電流―電圧特性にみられる共鳴に起因する電流ステップが、共鳴する接合数に比例して、徐々に増加することから、各接合の位相が揃った整合放射がおきていることが解る。この発信周波数は接合幅に反比例し、磁界強度とは関係ない。狭い素子幅に起因するエッジ効果により、四角磁束格子が形成され、その集団的な磁束フローが位相整合状態で実現し、ジョセフソン接合列の整合発振が誘起された。そして、素子の幅が１μｍ以下になると、その周波数はテラヘルツにまで達する。   Since the current step due to resonance seen in the current-voltage characteristics of the element gradually increases in proportion to the number of resonant junctions, it can be seen that matched radiation with the phases of each junction aligned occurs. This transmission frequency is inversely proportional to the junction width and is not related to the magnetic field strength. Due to the edge effect due to the narrow element width, a square magnetic flux lattice was formed, and the collective magnetic flux flow was realized in a phase-matched state, and matched oscillation of the Josephson junction array was induced. When the element width becomes 1 μm or less, the frequency reaches terahertz.

このような幅の狭い固有接合を有する素子の上部及び下部電極を超伝導体単結晶で多数並列に繋いで、それらを共振させることにより、ライン幅は狭く、パワーは増大する。これにより、並列固有ジョセフソン接合素子列は、１０μＷを越える出力を発生させることが可能となる。   By connecting a large number of upper and lower electrodes of an element having such a narrow intrinsic junction in parallel with a superconductor single crystal and resonating them, the line width is narrow and the power is increased. Thus, the parallel intrinsic Josephson junction element array can generate an output exceeding 10 μW.

本発明では、超伝導体単結晶として、Ｂｉ2Ｓｒ2ＣａＣｕ2Ｏ8、Ｂｉ2Ｓｒ2Ｃａ2Ｃｕ3Ｏ10等のビスマス・ストロンチウム・カルシウム・銅酸化物、Ｔｌ2Ｂａ2Ｃａ2Ｃｕ3Ｏ10等のタリウム・バリウム・カルシウム・銅酸化物からなる単結晶などを用いることができるが、特に、ビスマス・ストロンチウム・カルシウム・銅酸化物単結晶（ＢＳＣＣＯ）が好ましい。 In the present invention, bismuth, strontium, calcium, copper oxide such as Bi 2 Sr 2 CaCu 2 O 8 and Bi 2 Sr 2 Ca 2 Cu 3 O 10 , Tl 2 Ba 2 Ca 2 Cu 3 are used as the superconductor single crystal. A single crystal composed of thallium, barium, calcium, and copper oxide such as O 10 can be used, and bismuth, strontium, calcium, and copper oxide single crystal (BSCCO) are particularly preferable.

このような高温超伝導体単結晶を用いると超伝導エネルギーギャップが大きいことから、周波数の上限は２０ＴＨｚに達する。我々の研究で、既に０．６ＴＨｚ間での発振を検出している。出力パワーは、接合数の二乗に比例することから、数十μＷを見込んでいる。さらに、個々の接合列にはもっと多くの接合を積層させ、それらを並列素子列として集積することが容易に出来るので、数ｍＷのパワーが期待できる。   When such a high-temperature superconductor single crystal is used, the superconducting energy gap is large, so the upper limit of the frequency reaches 20 THz. Our research has already detected oscillations between 0.6 THz. Since the output power is proportional to the square of the number of junctions, several tens of μW are expected. Furthermore, since it is easy to stack more junctions in individual junction rows and integrate them as parallel element rows, a power of several mW can be expected.

本発明の超伝導体単結晶の加工法としては、基板上に搭載された超伝導体単結晶を両面加工法によりパターン化する方法を採用することができる（例えば、特許文献２及び３参照）。
従来のＮｂ系の技術と比較して、本発明の高温超伝導体を用いた加工法は簡略で、加工コストも安価である。しかも、同じ接合数の集積に対して、１００分ノ１の面積で実現可能である。
また、動作温度も、Ｎｂ系では４．２Ｋであるが、ＢＳＣＣＯでは４０Ｋまで可能である点で有利である。 As a processing method of the superconductor single crystal of the present invention, a method of patterning the superconductor single crystal mounted on the substrate by a double-side processing method can be employed (for example, see Patent Documents 2 and 3). .
Compared with the conventional Nb-based technology, the processing method using the high-temperature superconductor of the present invention is simple and the processing cost is low. Moreover, it is possible to realize the integration with the same number of junctions with an area of 100 minutes.
Also, the operating temperature is 4.2K for the Nb system, but it is advantageous in that it can be up to 40K for BSCCO.

ＢＳＣＣＯ単結晶から両面加工法によりパターン化されている素子を作製した。具体的には、（ａ）基板上に劈開されたＢＳＣＣＯ単結晶を固定する工程と、（ｂ）第１のフォトレジストを前記ＢＳＣＣＯ単結晶表面上にフォトリソグラフィ技術を用いて形成する工程と、（ｃ）第１のイオンミリングにより特定の深さにまで前記ＢＳＣＣＯ単結晶をエッチングする工程と、（ｄ）第２のフォトレジストを前記ＢＳＣＣＯ単結晶表面上にフォトリソグラフィ技術を用いて形成する工程と、（ｅ）前記第２のフォトレジストを用いて第２のイオンミリングを行い、固有ジョセフソン接合素子を形成する工程と、（ｆ）前記第２のフォトレジストを除去し、前記固有ジョセフソン接合素子を劈開し、裏返したＢＳＣＣＯ単結晶片を得る工程と、（ｇ）新たな基板上に前記ＢＳＣＣＯ単結晶片を固定し、フォトリソグラフィ技術を用いて形成する工程と、（ｈ）第３のフォトレジストを前記ＢＳＣＣＯ単結晶片上に形成する工程と、（ｉ）前記第３のフォトレジストを用いたフォトリソグラフィと第３のイオンミリングでＢＳＣＣＯ単結晶素子をパターニングする工程と、（ｊ）前記第３のフォトレジストを剥離してから、下部電極及び上部電極を形成する工程を施すことにより、幅１μｍ、奥行き（長さ）３０μｍのジョセフソン接合を有するＢＳＣＣＯ単結晶からなるテラヘルツ発振器を得た。   A device patterned from a BSCCO single crystal by a double-sided processing method was produced. Specifically, (a) a step of fixing the cleaved BSCCO single crystal on the substrate, (b) a step of forming a first photoresist on the surface of the BSCCO single crystal using a photolithography technique, (C) a step of etching the BSCCO single crystal to a specific depth by first ion milling; and (d) a step of forming a second photoresist on the surface of the BSCCO single crystal using a photolithography technique. (E) performing a second ion milling using the second photoresist to form an intrinsic Josephson junction element; and (f) removing the second photoresist and producing the intrinsic Josephson. A step of cleaving the junction element to obtain an inverted BSCCO single crystal piece, and (g) fixing the BSCCO single crystal piece on a new substrate, (H) a step of forming a third photoresist on the BSCCO single crystal piece, and (i) a photolithography using the third photoresist and third ion milling to form a BSCCO single unit. A step of patterning a crystal element; and (j) a step of forming a lower electrode and an upper electrode after removing the third photoresist, thereby providing a Josephson junction having a width of 1 μm and a depth (length) of 30 μm. A terahertz oscillator composed of a BSCCO single crystal having the following characteristics was obtained.

テラヘルツ発振器の基本構成要素を図１に示す。層平行磁場を幅の狭い方の側面に印加し、接合にバイアス電流を流すと、磁束はフローし、一方の幅の大きな接合面から入り、もう一方から外へ出る。幅の狭い接合では、磁束の出入りに伴う側面の交流電流が両端面において整合する。このような状態の接合がある一定数を超えると、各接合の定在波が同期し共鳴を起こし、外部に強い電磁波を放出する。強い発振を得るために、このような固有ジョセフソン素子をさらに並列に数十個集積した。   The basic components of a terahertz oscillator are shown in FIG. When a layer parallel magnetic field is applied to the narrow side surface and a bias current is applied to the junction, the magnetic flux flows, enters from one large junction surface, and exits from the other. In the case of a narrow joint, the alternating currents on the side surfaces accompanying the entry and exit of the magnetic flux match at both end surfaces. When the number of junctions in such a state exceeds a certain number, the standing waves of the junctions are synchronized to resonate and emit strong electromagnetic waves to the outside. In order to obtain strong oscillation, dozens of such intrinsic Josephson elements were further integrated in parallel.

図１で示した基本構成要素を集積した素子列を図２に示す。それぞれの上部及び下部電極は超伝導体（ＢＳＣＣＯ単結晶）で並列に繋がれている。この配列では、全ての固有ジョセフソンのスタックが等電圧となり、言い換えれば、周波数の固定状態になる。   An element array in which the basic components shown in FIG. 1 are integrated is shown in FIG. Each upper and lower electrode is connected in parallel with a superconductor (BSCCO single crystal). In this arrangement, all intrinsic Josephson stacks are equivoltage, in other words, the frequency is fixed.

図３に示したのは、４０個の１μｍ幅、３０μｍ長の固有接合を４０個並列に並べた素子の一般的な電流―電圧特性である。３００μＶの等間隔な電流ステップが見られる。ここで重要な点は、電流ステップの高さが、数番めのステップ以降、増加する点にある。振動の２次の高調波に対応するステップも見られ、これは２９０ＧＨｚのマイクロ波に相当する。この振動周波数が素子幅に反比例することから、これまでの最高の共鳴周波数は、素子幅が０．３μｍで６００ＧＨｚに達している。   FIG. 3 shows a general current-voltage characteristic of a device in which 40 unique junctions having a width of 1 μm and a length of 30 μm are arranged in parallel. An equally spaced current step of 300 μV is seen. The important point here is that the height of the current step increases after the few steps. There is also a step corresponding to the second harmonic of vibration, which corresponds to a microwave of 290 GHz. Since this vibration frequency is inversely proportional to the element width, the highest resonance frequency thus far reaches 600 GHz when the element width is 0.3 μm.

テラヘルツ発振器の基本構成要素の概念図である。It is a conceptual diagram of the basic component of a terahertz oscillator. 図１で示した基本構成要素を集積した素子列の概念図である。It is a conceptual diagram of the element row | line | column which integrated the basic component shown in FIG. ４０個の１μｍ幅、３０μｍ長の固有接合を４０個並列に並べた素子の一般的な電流―電圧特性を示す図である。It is a figure which shows the general current-voltage characteristic of the element which arranged 40 intrinsic junctions of 40 1 micrometer width and 30 micrometer length in parallel.

Claims (12)

超伝導層と絶縁層との固有ジョセフソン接合が直列に積層されている積層ジョセフソン接合を有する超伝導体単結晶の素子を用いたテラヘルツ発振器において、前記ジョセフソン接合が、幅が狭く、奥行きが長い接合であり、狭い素子幅に磁界を印加して四角形に並んだ磁束格子を形成し、前記狭い素子幅による定在波の共鳴を起こさせるように構成されていることを特徴とするテラヘルツ発振器。   In a terahertz oscillator using a superconductor single crystal element having a stacked Josephson junction in which intrinsic Josephson junctions of a superconducting layer and an insulating layer are stacked in series, the Josephson junction is narrow and deep. The terahertz is characterized in that a long junction is formed by applying a magnetic field to a narrow element width to form a square-shaped magnetic flux lattice and causing resonance of standing waves by the narrow element width. Oscillator. 前記超伝導体単結晶が、ビスマス・ストロンチウム・カルシウム・銅酸化物単結晶であることを特徴とする請求項１に記載のテラヘルツ発振器。   2. The terahertz oscillator according to claim 1, wherein the superconductor single crystal is a bismuth / strontium / calcium / copper oxide single crystal. 前記四角形に並んだ磁束格子の集団的な磁束フローが位相整合状態で実現されることを特徴とする請求項１又は２に記載のテラヘルツ発振器。   3. The terahertz oscillator according to claim 1, wherein a collective magnetic flux flow of the magnetic flux gratings arranged in a quadrangular shape is realized in a phase-matched state. 前記素子幅がジョセフソン侵入長の４倍以下であることを特徴とする請求項１〜３のいずれか一項に記載のテラヘルツ発振器。   The terahertz oscillator according to any one of claims 1 to 3, wherein the element width is not more than four times the Josephson penetration length. 前記素子幅が１．８μｍ以下であり、前記奥行きが５μｍ以上であることを特徴とする請求項１〜４のいずれか一項に記載のテラヘルツ発振器。   5. The terahertz oscillator according to claim 1, wherein the element width is 1.8 μm or less, and the depth is 5 μm or more. 請求項１〜５のいずれか一項に記載のジョセフソン接合を有する素子の上部及び下部電極を超伝導体単結晶で並列に繋いで並列の素子列を構成したことを特徴とするテラヘルツ発振器。   6. A terahertz oscillator comprising a parallel element array in which upper and lower electrodes of an element having a Josephson junction according to claim 1 are connected in parallel with a superconductor single crystal. 前記ジョセフソン接合を有する素子が、基板と、該基板上に搭載される両面加工法によりパターン化された超伝導体単結晶からなることを特徴とする請求項１〜６のいずれか一項に記載のテラヘルツ発振器。   7. The element according to claim 1, wherein the element having the Josephson junction includes a substrate and a superconductor single crystal patterned by a double-side processing method mounted on the substrate. The terahertz oscillator described. 請求項１〜７のいずれか一項に記載のテラヘルツ発振器を備えていることを特徴とする画像診断・検査装置。   An image diagnostic / inspection apparatus comprising the terahertz oscillator according to claim 1. 請求項１〜７のいずれか一項に記載のテラヘルツ発振器を備えていることを特徴とする大気観測装置。   An atmospheric observation apparatus comprising the terahertz oscillator according to any one of claims 1 to 7. 請求項１〜７のいずれか一項に記載のテラヘルツ発振器を備えていることを特徴とする無線通信装置。   A wireless communication apparatus comprising the terahertz oscillator according to claim 1. 請求項１〜７のいずれか一項に記載のテラヘルツ発振器における磁界の印加方法において、前記狭い素子幅に垂直に磁界を印加することを特徴とする磁界の印加方法。   The magnetic field application method in the terahertz oscillator according to claim 1, wherein a magnetic field is applied perpendicularly to the narrow element width. 超伝導電磁石、常伝導電磁石又は永久磁石を用いて磁界を印加することを特徴とする請求項１１に記載の磁界の印加方法。
The magnetic field application method according to claim 11, wherein a magnetic field is applied using a superconducting electromagnet, a normal conducting electromagnet, or a permanent magnet.
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