JP2005260113A - Superconductor three-terminal device and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a larger quantity of a supercurrent to flow to a superconductor three-terminal device in which the space between two superconductor electrodes are connected by a carbon nanotube, and the supercurrent flowing in the carbon nanotube is controlled by a gate electrode. <P>SOLUTION: The superconductor three-terminal device comprises a substrate 101 composed of silicon, an insulating layer 102 formed on the substrate 101, a carbon nanotube 104 provided on the insulating layer 102, a superconductor source electrode 105 which is ohmic-connected to the end of the carbon nanotube 104 via an alloy layer 115, a superconductor drain electrode 106 which is ohmic-connected to the other end of the carbon nanotube 104 via an alloy layer 116, and a metal electrode layer 107 formed on the back of the substrate 101. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a superconducting three-terminal element used in a quantum computer or the like and a method for manufacturing the same.

A superconducting element having electrical and magnetic unique characteristics operates at high speed and low power consumption, and is a useful element in the electronics field. In particular, superconducting three-terminal devices that control the superconducting current with the gate voltage have been studied for application to quantum computers.
As a superconducting three-terminal element, a Josephson junction field effect transistor (JOFET) using carbon nanotubes has been proposed (see Non-Patent Document 1). For example, it has been confirmed that a maximum superconducting critical current Ic of 2.5 μA flows in a single-walled carbon nanotube having a diameter (width) of about 23 nm (see Non-Patent Document 2). Expected.

  As shown in FIG. 5, the JOFET described above includes carbon nanotubes 504 arranged on a silicon substrate 501 via an insulating layer 502 made of silicon oxide, and both ends of the carbon nanotubes 504 are connected to superconducting source electrodes 505, 505. An electrode layer 507 that is connected to the superconducting drain electrode 506 and serves as a gate electrode on the back surface of the silicon substrate 501 is provided. The carbon nanotube 504 is formed by a well-known CCVD (catalytic chemical vapor deposition) method between the catalytic metal portions 503a and 503b.

The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
AFMorpurgo, J. Kong, M. Marcus, H. Dai, "Gate-Controlled Superconducting Proximity Effect in Carbon Nanotubes" Science, vol.286, pp.263-265, 8 October 1999. A.Yu.Kasumov, R.Deblock, M.Kociak, B.Reulet, H.Bouchiat, IIKhodos, Yu.B.Gorbatov, VTVolkov, C.Journet, and M.Burghard, "Supercurrents Through Single-Walled Carbon Nanotubes" Science, vol.284, pp.1508-1511, 28 May 1999.

  However, the conventional configuration shown in FIG. 5 has a problem that a desired large superconducting current cannot flow between the superconducting source electrode 505 and the superconducting drain electrode 506.

  The present invention has been made in order to solve the above-described problems. A superconducting three-channel structure in which two superconducting electrodes are connected by a carbon nanotube and a superconducting current flowing in the carbon nanotube is controlled by a gate electrode. The purpose is to allow a larger amount of superconducting current to flow through the terminal element.

A superconducting three-terminal element according to the present invention is composed of carbon nanotubes disposed on an insulating layer on a substrate composed of a semiconductor, and made of, for example, niobium nitride, ohmic-connected to both ends of the carbon nanotubes. Two superconducting electrodes, a gate electrode provided on the carbon nanotube via a gate insulating layer, an alloy layer formed at the interface between the carbon nanotube and the superconducting electrode, and composed of a superconducting metal carbon compound; Is provided.
Therefore, the carbon nanotube and the superconducting electrode are in ohmic connection through which a superconducting current flows.

A method of manufacturing a superconducting three-terminal element according to the present invention includes a step of forming an insulating layer on a substrate composed of a semiconductor, a step of disposing carbon nanotubes on the insulating layer, and both ends of the carbon nanotubes. Forming at least two superconducting electrodes in contact with each other and heating an interface where the carbon nanotube and the superconducting electrode are in contact with each other to form an alloy layer composed of a carbon compound of a superconducting metal at the interface. Is.
The superconducting electrode is made of niobium nitride.

  As described above, according to the present invention, since the carbon nanotube is connected to the superconducting electrode made of, for example, niobium nitride in the state where the alloy layer is formed, the superconducting current flowing through the carbon nanotube is The superconducting three-terminal element to be controlled has an excellent effect of allowing more superconducting current to flow.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view (a) and a plan view (b) showing a configuration example of a superconducting three-terminal element in an embodiment of the present invention. The superconducting three-terminal element shown in FIG. 1 includes, for example, a substrate 101 made of silicon, an insulating layer 102 formed on the substrate 101, a carbon nanotube 104 provided on the insulating layer 102, Superconducting source electrode 105 ohmically connected to one end via alloy layer 115, superconducting drain electrode 106 ohmically connected to the other end of carbon nanotube 104 via alloy layer 116, and the back surface of substrate 101 And a metal electrode layer 107 formed. Note that the substrate 101 may be made of another semiconductor material.

The carbon nanotube 104 is formed by a catalytic CVD method between catalytic metal portions 103a and 103b made of a catalytic metal such as Fe or Co and arranged at intervals of several μm.
The superconducting source electrode 105 and the superconducting drain electrode 106 are made of niobium nitride (NbN), which is a superconducting metal. The alloy layers 115 and 116 between the superconducting electrode and the carbon nanotube 104 serving as a channel are made of a carbon compound of a superconducting metal formed by a solid phase reaction between the superconducting metal and the carbon nanotube.

The alloy layers 115 and 116 are considered to be NbC _X N _1-X . When X is 0.1 or less, the superconducting critical temperature of NbC _X N _1-X is 18K. Since the superconducting critical temperature of niobium nitride is about 15K, the alloy layers 115 and 116 can improve the characteristics of the superconducting electrode.
In the three-terminal element shown in FIG. 1, a voltage is applied to the metal electrode layer 107 to change the superconducting current carrier (Cooper pair) concentration in the carbon nanotube 104, thereby controlling the superconducting current flowing through the carbon nanotube 104.

Next, a method for manufacturing the three-terminal element shown in FIG. 1 will be described.
First, SiO ₂ is deposited on the substrate 101 by a known chemical vapor deposition (CVD) method or the like to form an insulating layer 102 having a thickness of about 0.1 to 0.2 μm. Note that the insulating layer 102 may be made of silicon nitride.

  Next, on the insulating layer 102, a mask pattern having an opening is formed in a region where the catalyst metal portions 103a and 103b are to be formed, and then a catalyst metal material is deposited by vacuum evaporation or sputtering to form a catalyst. A metal film is formed. Thereafter, the mask pattern is removed, and the catalyst metal film on the mask pattern is removed, leaving the catalyst metal in the opening portion, and the catalyst metal portions 103a and 103b are formed. In addition, the catalyst metal should just be comprised from either Pd, Fe, Co, and Ni.

  Next, an organic carbon raw material such as methane or acetylene is used as a source gas, the substrate 101 is heated to, for example, about 400 to 500 ° C., and the source gas is circulated over the substrate 101 at a predetermined flow rate to form a catalyst metal. A carbon nanotube is grown between the portions 103a and 103b, and the carbon nanotube 104 is formed. Here, the growth of the carbon nanotube 104 is not limited to the above-described conditions, and various carbon nanotube formation methods by a known catalytic CVD method can be used.

  Next, a new mask pattern having openings is formed in the region where the superconducting source electrode 105 and the superconducting drain electrode 106 are to be formed, and then niobium nitride is deposited by vacuum evaporation or sputtering to superconduct. A metal film is formed. Thereafter, the mask pattern is removed, and the superconducting metal film on the mask pattern is removed, leaving the superconducting metal in the opening, and the superconducting source electrode 105 and the superconducting drain electrode 106 are formed. State. The superconducting metal film may be niobium or a laminated structure of niobium and niobium nitride. However, when niobium nitride is used, the interface (alloy layer) between the superconducting electrode and the carbon nanotube can be formed in a better state by heat treatment. Also, niobium nitride has a higher superconducting current than Nb, which is advantageous in this respect.

Next, the substrate 101 (the carbon nanotube 104, the superconducting source electrode 105, and the superconducting drain electrode 106) is heated so that the alloy layers 115 and 116 are formed at the interfaces thereof. The heat treatment may be performed at about 600 to 700 ° C. for several minutes.
Finally, by setting the metal electrode layer 107 on the back surface of the substrate 101, the superconducting three-terminal element shown in FIG. 1 is formed.

  By the way, it has been reported that, between the multi-walled carbon nanotube (MWCNT) and niobium, NbC is formed at the contacted interface by heat treatment at 650 ° C. for 30 minutes, and ohmic contact in which superconducting current flows can be realized ( Non-patent literature: J. Haruyama, K. Takazawa, S. Miyadai, A. Takeda, N. Hori, I. Takesue, Y. Kanda, N. Sugiyama, T. Akazaki, and H. Takayanagi, "Injection of Cooper pairs into quasidiffusive multiwalled carbon nanotubes with weak localization ", Physical Review B 68, 165420, 2003.). This document shows that a superconducting current flows in a carbon nanotube in a Nb / multi-walled carbon nanotube / Al junction due to a decrease in contact resistance.

As described above, according to the superconducting three-terminal element shown in FIG. 1, since the alloy layers 115 and 116 are formed, the carbon nanotube provided between the superconducting source electrode and the superconducting drain electrode More superconducting current can be passed.
In the superconducting three-terminal element shown in FIG. 1, the gate voltage is applied by the metal electrode layer 107 formed on the back surface of the substrate 101. However, the present invention is not limited to this.

  FIG. 2 is a cross-sectional view (a) and a plan view (b) showing a configuration example of another superconducting three-terminal element in the present embodiment. The superconducting three-terminal element shown in FIG. 2 includes, for example, a substrate 101 made of silicon, an insulating layer 102 formed on the substrate 101, a carbon nanotube 104 provided on the insulating layer 102, A superconducting source electrode 105 ohmically connected to one end via an alloy layer 115 and a superconducting drain electrode 106 ohmically connected to the other end of the carbon nanotube 104 via an alloy layer 116 are provided. These structures are the same as those of the superconducting three-terminal element shown in FIG.

  In the superconducting three-terminal element shown in FIG. 2, a gate electrode 208 is provided on the carbon nanotube 104 via a gate insulating film 207. In the superconducting three-terminal element shown in FIG. 2, the voltage of the gate electrode 208 is applied to change the superconducting current carrier concentration in the carbon nanotube 104, thereby controlling the superconducting current flowing through the carbon nanotube 104.

  In addition, as shown in FIG. 3, gate electrodes 308a and 308b may be provided. In the superconducting three-terminal element shown in FIG. 3, gate electrodes 308a and 308b are formed on the insulating layer 102, and one end thereof is disposed with a predetermined gap from the carbon nanotube 104. In the superconducting three-terminal element shown in FIG. 3, the gap between the gate electrodes 308a and 308b and the carbon nanotube 104 corresponds to the gate insulating layer. Note that either one of the gate electrodes 308a and 308b may be provided.

  Further, as shown in FIG. 4, a high concentration impurity region 408 provided in the substrate 101 may be used as a gate electrode. 4 includes a substrate 101 made of silicon, an insulating layer 102 formed on the substrate 101, a carbon nanotube 104 provided on the insulating layer 102, and one end of the carbon nanotube 104. A superconducting source electrode 105 that is ohmically connected via an alloy layer 115 is provided at a portion, and a superconducting drain electrode 106 that is ohmically connected via an alloy layer 116 to the other end of the carbon nanotube 104. These structures are the same as those of the superconducting three-terminal element shown in FIG.

  In the superconducting three-terminal element shown in FIG. 4, a well region 407 into which, for example, a p-type impurity is introduced is formed on the substrate 101, and an n-type impurity is formed in a region inside the well region 407 and under the carbon nanotube 104. A high concentration impurity region 408 is formed in which is introduced at a high concentration. A wiring 412 is connected to the well region 407 through a contact 411 via the insulating layer 102, and a wiring 414 is connected to the high concentration impurity region 408 through a contact 413 through the insulating layer 102.

  In the superconducting three-terminal element shown in FIG. 4, the superconducting current in the carbon nanotube 104 is applied by applying a gate voltage to the high-concentration impurity region 408 through the wiring 414 while a fixed potential is applied to the well region 407 through the wiring 412. The superconducting current flowing through the carbon nanotubes 104 is controlled by changing the carrier concentration.

  The carbon nanotube 104 may be composed of a single carbon nanotube or a bundle of a plurality of carbon nanotubes. The carbon nanotube 104 may be a single-walled carbon nanotube or a multi-walled carbon nanotube. For example, the state of the growing carbon nanotube can be controlled by controlling the dimensions of the catalytic metal portions 103a and 103b.

  In the above description, the catalytic metal portions 103a and 103b are provided on the substrate 101, and the carbon nanotubes 104 are grown between them by the catalytic CVD method. However, the present invention is not limited to this. Carbon nanotubes formed by other methods may be placed on the insulating layer 102, and then the superconducting source electrode 105 and the superconducting drain electrode 106 may be formed.

It is sectional drawing (a) and top view (b) which show the structural example of the superconducting three-terminal element in embodiment of this invention. It is sectional drawing (a) and top view (b) which show the structural example of the other superconducting three-terminal element in embodiment of this invention. It is a top view which shows the structural example of the other superconducting three-terminal element in embodiment of this invention. It is sectional drawing (a) and top view (b) which show the structural example of the other superconducting three-terminal element in embodiment of this invention. It is sectional drawing which shows the structure of the conventional superconducting three terminal element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Substrate, 102 ... Insulating layer, 103a, 103b ... Catalytic metal part, 104 ... Carbon nanotube, 105 ... Superconducting source electrode, 106 ... Superconducting drain electrode, 107 ... Metal electrode layer, 115, 116 ... Alloy layer.

Claims (4)

A carbon nanotube disposed via an insulating layer on a substrate composed of a semiconductor;
Two superconducting electrodes ohmically connected to both ends of the carbon nanotube,
A gate electrode provided on the carbon nanotube via a gate insulating layer;
A superconducting three-terminal element, comprising: an alloy layer formed at a boundary between the carbon nanotube and the superconducting electrode and made of a carbon compound of a superconducting metal. The superconducting three-terminal element according to claim 1,
A superconducting three-terminal element, wherein the superconducting electrode is made of niobium nitride. Forming an insulating layer on a substrate composed of a semiconductor;
Disposing carbon nanotubes on the insulating layer;
Forming two superconducting electrodes in contact with both ends of the carbon nanotube;
Heating the interface where the carbon nanotube and the superconducting electrode are in contact with each other, and forming an alloy layer composed of a carbon compound of a superconducting metal at the interface. Device manufacturing method. In the manufacturing method of the superconducting three-terminal element according to claim 3,
The method for manufacturing a superconducting three-terminal element, wherein the superconducting electrode is made of niobium nitride.

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