JPS63239990A - Superconducting transistor - Google Patents

Abstract

PURPOSE:To obtain a superconducting transistor able to be sufficiently cooled with liquid nitrogen while shortened its manufacturing process, a flat surface and no change with the lapse of time due to oxidation by using a superconductor of L-M-Cu-O oxide for the source-drain electrode parts. CONSTITUTION:A Y-Ba-Cu-O film 2 is vacuum-evaporated on an Si wafer 1 by a sputtering method. The sputtering at this time is performed with the gas composition of Ar-10% O2 while causing lack of oxygen concentration inside the film so as to produce a semiconductor. Next, since the superconductive source-drain parts are formed on this Y-Ba-Cu-O semiconductor film, the part except the source-drain parts is covered with a resist film 3 for being given heat treatment for one h at 500 deg.C inside a diffusion furnace in which O2 gas is made to flow. In this treatment, oxygen gets mixed with the part having no resist so that only these source-drain parts 5a and 5b become superconductors. This element can control a superconduction current between the source and the drain with the gate voltage so as to function as a three- terminal transistor element.

Description

【発明の詳細な説明】 〔発明の目的〕 （産業上の利用分野） 本発明は、トランジスタのソース、ドレイン部分に超電
導を用いた超電導トランジスタに関する。DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a superconducting transistor using superconductivity in the source and drain portions of the transistor.

（従来の技術） ８ｉ、ＧａＡｓなどを用いて現在、高密度゛、高速度の
素子が開発されているが、４メガビツト、１６メガビツ
トなどへの高集積密度化が進につれて、特に素子の発熱
が大きな問題に成っている。すなわち、現在の例えば８
ｉ素子においては発熱は数ｍＷもあるため今後の高集積
密度化への大きな障壁になっている。(Prior art) High-density, high-speed devices are currently being developed using 8i, GaAs, etc., but as the integration density continues to increase to 4 megabits, 16 megabits, etc., the heat generation of the devices has become particularly important. It has become a big problem. That is, the current example is 8
Since the i-device generates heat of several milliwatts, it is a major barrier to higher integration density in the future.

この問題を解決するため超電導現象の１つであるジョセ
フソン素子を利用したジョセフソン素子が従来開発され
てきた。このジョセフソン素子では、発熱量はＳｉ素子
に比べて３〜４桁小さく約１μＷである。さらに、スイ
ッチング速度も数ｐ〜１０ｐｓｅｅとＳｉ素子に比べて
、３〜４桁速い。In order to solve this problem, a Josephson device using a Josephson device, which is one of the superconducting phenomena, has been developed. In this Josephson element, the amount of heat generated is about 1 μW, which is three to four orders of magnitude smaller than that of a Si element. Furthermore, the switching speed is several p to 10 psee, which is three to four orders of magnitude faster than that of a Si element.

現在このジョセフソン素子に利用されている材料として
はＮｂ、ＮｂＮがある。しかし、Ｎｂ−４？ＮｂＮ膜は
非常に活性であるため酸素と結つきやすく、ジョセフソ
ン素子に必要な数十人の厚さの絶縁膜（障壁膜）を均質
に作ることが出来ず、また酸化のため大気中で不安定な
素子であった。Materials currently used for this Josephson element include Nb and NbN. But Nb-4? The NbN film is very active and easily combines with oxygen, making it impossible to homogeneously form an insulating film (barrier film) several tens of times thick, which is required for Josephson devices, and due to oxidation, it cannot be easily bonded with oxygen in the atmosphere. It was an unstable element.

さらＫ、これらの材料では臨界温度Ｔｃが低いため冷却
に液体Ｈｅを使わねばならなかったためコストの面から
も実用化は難しいとされていた。Furthermore, since these materials have low critical temperatures Tc, liquid He had to be used for cooling, and it was considered difficult to put them into practical use from a cost standpoint.

さらに、ジョセフソン素子は２端子素子であるため、い
まのＳｉ素子の３端子方式（電界制御）に比べて使いに
くい等の欠点があった。Furthermore, since the Josephson element is a two-terminal element, it has drawbacks such as being difficult to use compared to the current three-terminal system (electric field control) of Si elements.

しかるに、最近３端子方式で上記の欠点を無くした超電
導体と半導体を組合わせた超電導トランジスタが開発さ
れつつある。これは、上述のジョセフソン素子と同じ小
さい消費電力、高速のスイッチング速度をもつが、この
場合も冷却材に液体Ｈｅを使う、超電導素子部分が酸化
されやすく不安定である等の理由で未だ実用に至ってい
ないのが現状である。However, recently, a three-terminal type superconducting transistor that eliminates the above-mentioned drawbacks and combines a superconductor and a semiconductor is being developed. This device has the same low power consumption and high switching speed as the above-mentioned Josephson device, but it is still not practical due to the fact that liquid He is used as a coolant, and the superconducting element part is easily oxidized and unstable. The current situation is that this has not been achieved.

さらＫ、この従来の超電導トランジスタは、例えばＳｉ
基板上にＮｂやＮｂＮの超電導膜を積層させたものであ
るため、作製に手間もかがシかつ、平坦な構造でないた
めデジタル回路への応用に不向きである。Moreover, this conventional superconducting transistor is made of Si, for example.
Since it is a layered superconducting film of Nb or NbN on a substrate, it is time-consuming to manufacture and does not have a flat structure, making it unsuitable for application to digital circuits.

（発明が解決しようとする問題点） 本発明は、上述の従来の超電導素子がもつ欠点、冷却材
として高価な液体Ｈｅを用いなくてはならないこと、素
子が空気中で酸化されやすく不安定であること、２端子
素子（ジョセフソン素子の場合）であること、および作
製工程が煩雑でかつ平坦構造でないという欠点を改善し
た超電導素子を提供することを目的とする。(Problems to be Solved by the Invention) The present invention solves the above-mentioned drawbacks of conventional superconducting elements, such as the necessity of using expensive liquid He as a coolant, and the fact that the elements are easily oxidized in the air and are unstable. It is an object of the present invention to provide a superconducting element which improves the disadvantages of being a two-terminal element (in the case of a Josephson element), having a complicated manufacturing process, and not having a flat structure.

〔発明の構成〕[Structure of the invention]

（問題点を解決するための手段） 本発明の超電導トランジスタには、そのソース。 (Means for solving problems) The superconducting transistor of the present invention includes a source thereof.

ドレイン電極部分に近年活発に開発が進められているＹ
−Ｂ　ａ−Ｃｕ−０テ代表されるＬ−Ｍ−Ｃｕ−０系酸
化物超電導体（Ｌ＝Ｙ、８ｃ；Ｍ＝Ｂａ、Ｃｒ、Ｃａ　
）を用いる。この超電導体は臨界温度Ｔｃが９０〜１０
０にある。よって、冷却材として液体Ｈｅに比べ格段に
安価な液体窒素を用いることができる。Y, which has been actively developed in recent years for the drain electrode part.
-B a-Cu-0 representative LM-Cu-0 based oxide superconductor (L=Y, 8c; M=Ba, Cr, Ca
) is used. This superconductor has a critical temperature Tc of 90 to 10
It is at 0. Therefore, liquid nitrogen, which is much cheaper than liquid He, can be used as a coolant.

かつ、酸化物であるから、空気中でも安定で、素子の特
性が経年変化で劣化することも危い。さらに、我々はこ
の化合物が、酸素の拡散処理の仕方によって同一元素の
構成物でありながら半導体と超電導体をつくることがで
きるのをつき止めた。Moreover, since it is an oxide, it is stable even in the air, and there is a danger that the characteristics of the element may deteriorate over time. Furthermore, we discovered that this compound can be made into a semiconductor and a superconductor even though it is composed of the same element, depending on how oxygen is diffused.

すなわち、上記化合物の酸素濃度分布を制御することで
、半導体、超電導体をつくることができる。これは、簡
便な酸素の膜中への拡散によシ半導体層中の一部に、ソ
ース、ドレイン電極部分となる超電導体をつくることを
意味する。これにより、ソース、ドレイン部も含めて、
平坦な素子構造が得られる。That is, by controlling the oxygen concentration distribution of the above compound, semiconductors and superconductors can be produced. This means that a superconductor, which will become the source and drain electrode portions, is created in a portion of the semiconductor layer by simple diffusion of oxygen into the film. As a result, including the source and drain parts,
A flat device structure can be obtained.

以上の方法により、本発明は従来の超電導素子がもつ重
大な欠点を解決したものである。Through the method described above, the present invention solves the serious drawbacks of conventional superconducting elements.

（作用） 本発明によれば、安価な液体窒素で冷却して作動させる
ことができ、空気中でも素子が安定で経年変化がなく、
かつ作製方法が簡便で、素子構造も平坦な端子方式の超
電導トランジスタが得られる。(Function) According to the present invention, the device can be operated by cooling with inexpensive liquid nitrogen, and the device is stable even in air and does not change over time.
In addition, a terminal-type superconducting transistor can be obtained which is easy to manufacture and has a flat element structure.

（実施例） Ｓｉ　　ウェハーｆｉｌ上に、スパッタ法によｐＹ−Ｂ
ａ−Ｃｕ−０の膜（２）を３００　ＯＡ蒸着させた。こ
の時のスパッタ条件は、ターゲットがＹ、ＢａＯ，Ｃｕ
Ｏの３種から成るもので、ガス組成Ａｒ　　１０％Ｏｔ
　、ガス圧５Ｘ１０−２Ｔｏｒｒ、高周波パワーは２０
０Ｗである。この条件で作製した膜は、膜中の酸素濃度
が不足しているため半導体であった。(Example) pY-B was deposited on a Si wafer film by sputtering.
A film (2) of a-Cu-0 was deposited at 300 OA. The sputtering conditions at this time were such that the target was Y, BaO, Cu.
Consisting of three types of O, gas composition Ar 10%Ot
, gas pressure 5X10-2 Torr, high frequency power 20
It is 0W. The film produced under these conditions was a semiconductor because the oxygen concentration in the film was insufficient.

次に、このＹ−Ｂａ−Ｃｕ−０半導体膜上に、超電導の
ソース、ドレイン部分を作製するため、ンース、ドレイ
ン部以外をレジスト膜（３）でおおい、その後、０！ガ
スを流している拡散炉中で、５００℃で１時間熱処理し
た。この処理で、レジストのない所は酸素が混入するた
め、このソース、ドレイン部（５ａ）、（５ｂ）のみ超
電導体となる。Next, in order to fabricate superconducting source and drain portions on this Y-Ba-Cu-0 semiconductor film, areas other than the source and drain portions are covered with a resist film (3), and then 0! Heat treatment was performed at 500° C. for 1 hour in a diffusion furnace flowing gas. In this process, oxygen is mixed into areas where there is no resist, so only these source and drain parts (5a) and (5b) become superconductors.

さらに１反対側のＳｉ　ウェハー面にはこの時同時にＳ
ｉｎ！の酸化膜（４）ができ、ゲート電極の絶縁になる
。Furthermore, at the same time, S is added to the Si wafer surface on the opposite side.
In! An oxide film (4) is formed, which insulates the gate electrode.

この後、この絶縁層の上にゲート電極（６）になるＡ４
０層を蒸着した。この作製工程及び最終的な素子構造を
第１図に示す。After this, the A4 which will become the gate electrode (6) is placed on this insulating layer.
0 layers were deposited. This manufacturing process and the final device structure are shown in FIG.

第２図は、この素子のゲート電圧−と超電導電流ＩＣの
関係を調べたものである。−が０〜−５０ｍＶまでは、
工。けないが、それ以上では急激なＩ。FIG. 2 shows an investigation of the relationship between the gate voltage of this device and the superconducting current IC. - from 0 to -50mV,
Engineering. However, if it goes beyond that, it becomes a sharp I.

の増加が見られた。すなわち、本発明の素子においてゲ
ート電圧で、ソースとドレイン間の超電導電流を制御で
きることが明らかになり、三端子トランジスタ素子とし
て働くことを確認できた。他の元素を用いた場合、例え
ばＳｃ；Ｂａ、Ｓｒ、Ｃａでも同様な素子が得られた。An increase was seen. That is, it was revealed that the superconducting current between the source and drain can be controlled by the gate voltage in the device of the present invention, and it was confirmed that the device works as a three-terminal transistor device. When other elements were used, for example, Sc; Ba, Sr, and Ca, similar elements were obtained.

〔発明の効果〕〔Effect of the invention〕

本発明によれば、上述の様に液体窒素で十分冷却が可能
となシ、かつ作製工程が短縮され、表面が平坦で、酸化
による経年変化のない超電導トランジスタができる。According to the present invention, as described above, a superconducting transistor that can be sufficiently cooled with liquid nitrogen, has a shortened manufacturing process, has a flat surface, and does not change over time due to oxidation can be produced.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は本発明の素子をつくるための作製工程の順序を
示す工程図、第２図は本発明による超電導トランジスタ
のゲート電圧と超電導電流の関係を示す特性図である。 （Ｉｌ−８ｒ　ウーｒ−バー、（２１−Ｌ　−Ｍ−Ｃｕ
　−ＯｔＤ膜、（３）・・・レジスト膜、（４）・・・
酸化膜、（５ａ）・・・ソース部、（５ｂ）・・・ドレ
イン部、（６）・・・ゲート電標。 代理人　弁理士　則　近　憲　佑 同　　　　竹　花　喜久男 第１図FIG. 1 is a process diagram showing the order of manufacturing steps for manufacturing the device of the present invention, and FIG. 2 is a characteristic diagram showing the relationship between gate voltage and superconducting current of a superconducting transistor according to the present invention. (Il-8r Woolber, (21-L-M-Cu
-OtD film, (3)...resist film, (4)...
Oxide film, (5a)...source part, (5b)...drain part, (6)...gate electrode mark. Agent Patent Attorney Noriyuki Chika Yudo Kikuo Takehana Figure 1

Claims (1)

【特許請求の範囲】[Claims] 半導体上に一定距離で分離された超電導体のソースとド
レイン電極をもつ超電導トランジスタにおいて、上記超
電導体と半導体の構成元素は共にＬ、Ｍ、Ｃｕ、Ｏ（Ｌ
＝Ｙ、Ｓｃ、Ｍ＝Ｂａ、Ｓｒ、Ｃａ）からなり、酸素の
濃度によって超電導体、半導体の区別してなることを特
徴とする超電導トランジスタ。In a superconducting transistor having superconductor source and drain electrodes separated by a certain distance on a semiconductor, the constituent elements of the superconductor and semiconductor are L, M, Cu, O(L
= Y, Sc, M = Ba, Sr, Ca), and is characterized in that it is a superconductor or a semiconductor depending on the oxygen concentration.