JP2624666B2 - Superconducting element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element operating at a very low temperature, and in particular, a current flowing through a channel between two superconducting electrodes at a voltage applied to a control electrode. A superconducting switching device for controlling

[Conventional technology]

The operation principle is to control the value of the superconducting current flowing between two superconducting electrodes provided in contact with the semiconductor by changing the superconducting proximity effect by the voltage applied to the control electrode. For conducting transistors, the Journal of A Applied Physics by TDClark
pplied Physics, 51, 2736 (1980).

[Problems to be solved by the invention]

When fabricating a field-effect type superconducting element, a pair of superconducting electrodes are provided on a semiconductor substrate so as to face each other at a predetermined distance L, and a control electrode is provided on the facing portion. The value of the distance L is selected to 5 to 10 times the coherence length xi] _n in the semiconductor. If the value of L is larger than this range, no superconducting current flows. That is, it is necessary to make the distance close to about 0.5 μm or less, and a high-precision processing technique is required. Further, even when no control voltage is applied, the resistance between the superconducting electrodes is reduced and a current flows, so that the gain of the element cannot be improved.

SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting element suitable for application to an integrated circuit having a high operation speed and a high gain.

[Means for solving the problem]

The above object is achieved by using a film having a super lattice structure in which an ultra thin film is laminated on a channel.

[Action]

When a superconducting thin film having a thickness of about 10 nm and an n-type or p-type semiconductor into which impurities are introduced are laminated and cooled to extremely low temperature in liquid helium, the superconducting element exudes from the superconductor side to the contacted semiconductor side. This is shown in FIG. Thus, the superconducting wave function enters the semiconductor and is attenuated. FIG. 3A shows how the existence probability of superconducting electrons changes when no voltage is applied to the control electrode. In the semiconductor thin film sandwiched between the superconducting thin films 7, superconducting electrons exude from both superconductors. The oozing areas do not overlap each other. Therefore, no supercurrent flows through this superlattice layer. When a voltage is applied to the control electrode, the carrier concentration in the semiconductor thin film increases, and as shown in FIG. 3 (b), the areas oozing out in the semiconductor thin film overlap (shaded portions in the figure), and the superconducting current flows. become. This current flows into the superconducting source / drain electrodes in contact with the superlattice layer.

When the super lattice layer is used in the channel portion in this manner, the resistance in a voltage state increases. For example, when a channel portion composed of a superlattice layer in which nine superconductor thin films and semiconductor thin films are alternately stacked is in a voltage state, the resistance is four times as large as that of a channel composed of only a semiconductor. Become. Therefore, the leakage current when viewed as a device is reduced, and the circuit gain is improved.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to examples.

A first embodiment of the present invention will be described with reference to FIG. After forming a superconductor source electrode 1 made of Nb having a thickness of about 300 nm on a substrate 8 by a molecular beam growth method, the surface is formed to a thickness of about 10 nm while being kept in a vacuum without being exposed to the atmosphere. A superlattice layer 5 is formed by alternately depositing a semiconductor thin film of Si containing a boron impurity concentration of 5 × 10 ²⁴ m ⁻³ and a superconducting thin film of Nb with a thickness of about 1 nm by a molecular beam growth method. Subsequently, a drain electrode 2 made of Nb and having a thickness of about 300 nm is formed on the surface thereof by a molecular beam growth method while keeping a vacuum without taking out the air. Next, this was processed into an angled desired shape by ion etching using a photoresist as a mask, and the surface was oxidized by oxygen plasma to obtain an insulating film 4 of about 15 nm. Finally it is about 500nm deposited Yotsute Nb to DC magnetron spa ivy method, processed this Te cowpea the ion Etsu quenching by CF ₄ gas to obtain a control electrode 3. Thus, a superconducting element having the structure shown in FIG. 1 was manufactured.

When the above superconducting element was operated at a very low temperature in liquid helium, the resistance between the source and drain electrodes in a voltage state was increased, the leakage was reduced, and the gain was improved. In addition, contamination at the interface between the source and drain electrodes and the semiconductor was prevented, and an element having good shot barrier properties was obtained. In addition, since the superconducting electrons pass through the superlattice layer by tunneling, a high-speed switching element was obtained.

Next, a second embodiment of the present invention will be described with reference to FIG.

Drain electrode 2 and source electrode 1 above and below superlattice layer 5
, And a control electrode 3 separated by an insulating film 4 is provided on the side wall.

A source electrode 1 made of Nb having a thickness of 300 nm is formed on a substrate 8 by a molecular beam growth method. Superlattice layers 5 are formed by alternately depositing superconducting thin films of Nb having a thickness of about 1 nm. Thereafter, a drain electrode 2 made of Nb having a thickness of about 300 nm is formed by a molecular beam growth method while maintaining a vacuum. Next, after processing into a desired shape by ion etching using a host resist as a mask, the surface of the groove was oxidized by oxygen plasma to obtain an insulating film 4 of about 15 nm. Finally, Nb is reduced to about 50 by DC magnetron spatter method.
This is processed by ion etching with CF ₄ gas to obtain a control electrode 3. As described above, a superconducting element having the structure shown in FIG. 2 was manufactured.

According to this embodiment, the resistance between the source and drain electrodes is increased, and two superconducting elements can be connected in series, so that the output amplitude for a given control voltage can be doubled and the gain is improved. . Also, the number of processes is reduced,
Since the processing is easy, an element suitable for high integration can be obtained. Furthermore, a high-speed switching element having a good shot barrier was obtained.

In the above embodiment, Si was used as the semiconductor material, but GaAs, Ge,
InAs, InP, InSb, GaSb, etc. may be used. The conductivity of the semiconductor portion may be reversed. In addition, Nb
However, similar results were obtained when Nb compounds such as NbN, Nb ₃ Ge, Nb ₃ Sn, and Nb ₃ Al, and Pb alloys such as Pb-Au, Pb-In-Au, and Pb-Bi were used. can get.

〔The invention's effect〕

According to the present invention, a superconducting element controlled by voltage can be manufactured with good reproducibility and uniformity. Further, the use of the superlattice layer and the channel has the effect of improving the gain and realizing a high-speed and highly integrated superconducting integrated circuit.

[Brief description of the drawings]

FIG. 1 is a sectional structural view showing a first embodiment of the present invention, and FIG.
FIG. 3 is a sectional structural view showing a second embodiment, and FIG. 3 is a principle explanatory view showing the operation principle of the present invention. DESCRIPTION OF SYMBOLS 1 ... Source electrode, 2 ... Drain electrode, 3 ... Control electrode, 4 ... Insulating film, 5 ... Superlattice layer formed by alternately laminating semiconductor and superconductor, 6 ... Semiconductor thin film, 7 ...... Superconducting thin film.

Claims (6)

(57) [Claims] 1. A channel having a superlattice structure in which a semiconductor thin film and a superconducting thin film are stacked, a first superconducting electrode provided in contact with an uppermost layer of the channel, and a channel in contact with a lowermost layer of the channel. A superconducting element having a second superconducting electrode provided and a control electrode, wherein the control electrode is in contact with the channel separated by an insulating film, and a surface where the control electrode and the channel contact. A superconducting device having a non-zero angle with a plane including a thin film laminated on the channel. 2. The superconducting device according to claim 1, wherein the semiconductor thin film laminated on the channel is n-type or p-type.
A superconducting element characterized in that the superconducting element is a semiconductor thin film of any one of the following types. 3. A superconducting element according to claim 1, wherein said superconducting thin film laminated on said channel is made of any one of Nb, Nb compound and Pb alloy. . 4. The superconducting device according to claim 1, wherein the control electrode is separated from the first superconducting electrode and the second superconducting electrode by an insulating film. Characterized superconducting element. 5. The superconducting device according to claim 1, wherein a surface where said control electrode and said channel are in contact has a predetermined angle with a surface including a thin film laminated on said channel. A superconducting element, characterized in that: 6. A superconducting device according to claim 1, wherein a surface where said control electrode and said channel are in contact is substantially orthogonal to a surface including a thin film laminated on said channel. Conduction element.