JPH03214677A - superconducting device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to superconducting proximity effect (proximj.ty e
The present invention relates to a superconducting device that utilizes the energy gap of a superconductor in a controlled manner by a superconductor, and is particularly suitable for use in a superconducting system LSI.

[Conventional technology]

Conventionally, in order to vary the size of the energy gap of a superconductor within a plane, it was necessary to arrange superconducting materials with energy gaps of different sizes within the plane. That is, it was necessary to arrange multiple superconductors made of different materials in a plane. For example, a quiteron (r) is used as an electronic device by spatially changing the size of the energy gap.
K. E. Gray+Applied Physics
An element called Letter 32 (1978) 392J) is known. This device uses three superconductors with different energy gaps and has a double Josephson junction: one superconductor, one insulator, one superconductor, one fiber, and one superconductor. . Usually, this device is constructed by stacking layers on a substrate, and it is extremely difficult to arrange superconductors with different energy gap sizes within a plane with good controllability. In addition, a Josephson field-effect transistor (Josephson
field effect transistor:
T. D. Clark, et al. , Journa
l of Applied Physjcs 5] (1
980) 2736) is known. However, this does not actively utilize in-plane changes in the size of the energy gap. In other words, it merely controls the overlap of wave functions of Cooper pairs that seep into the semiconductor. Furthermore, in the conventional example, in order to change the size of the energy gap within a plane, the superconductor material itself had to be controlled within the plane. That is, with any conventional superconducting device, it has not been possible to realize a superconducting device in which the energy gap of superconductivity is changed within a plane as intended by the designer. [Problem to be Solved by the Invention] In order to change the size of the energy gap of a superconductor within a plane as described above, superconducting materials having different sizes of energy gaps are arranged in a plane. There must be. However, each superconducting material has its own energy gap, so even if they are arranged in a plane, the change in the energy gap within the plane is discrete and has only a limited value. The problem was that I couldn't get it. Furthermore, since the superconductor material itself must be controlled in-plane, there is a problem in that microfabrication techniques for semiconductors cannot be applied. Furthermore, more fundamental problems from the viewpoint of device integration include the following. -4=1. With a structure of superconductor-insulator-superconductor, it is extremely difficult to make an ultra-thin insulating layer (thickness: 1-3 nm) of good quality and uniformity. In fact, reflecting the variation in film thickness,
In a Josephson junction, the Josephson current varies greatly. Furthermore, holes occur in the insulating layer, which causes gaps between the superconductors, making it difficult to form an LSI with a good yield. 2. Since the potential barrier of an actual insulating layer is as large as several eV, it is essentially difficult to increase the Josephson current. Therefore, if the Josephson junction is made finer, it becomes impossible for current to flow, so that when a highly integrated LSI is fabricated, the operating speed decreases and the advantage of high integration is lost. An object of the present invention is to provide a superconducting device with a planar structure in which a superconducting energy gap can be designed in a plane as intended by the designer and is suitable for high integration.

[Means to solve problems] The problem of the present invention could not be achieved in the past because metals and oxides, the materials of which exhibit superconductivity, were directly used in devices. The present invention is realized by utilizing the fact that a semiconductor that does not originally exhibit superconductivity has properties as a superconductor due to the superconducting proximity effect. In other words, the problem described in item 2 is to form a semiconductor region directly on the surface of a superconductor material or through an insulator or semiconductor heterojunction, and at this time, to form a semiconductor region (conductivity type (P type or N This can be solved by modulating the type (type), impurity concentration, elemental composition, and film thickness). By modulating the properties of the semiconductor in this way, it is possible to modulate the size Δ of the energy gap that seeps into the semiconductor due to the superconducting proximity effect and the depth ξ of the Cooper pair seepage. Furthermore, in order to control the size of the energy gap using semiconductors, it is possible to directly apply the highly developed microfabrication technology for Si and GAAsLSI. The present invention realizes an element with a planar structure suitable for high integration by providing a plurality of semiconductor regions within a junction surface with a superconductor (or insulator) (planar modulation). (effect)

The principle of the present invention will be explained using the basic cross-sectional structure shown in FIG. This is a structure in which a semiconductor region is formed directly on the surface of the superconductor material 5 or via a #@ whole or a semiconductor heterojunction. At this time, regions 1, 2, and 3 having three different properties were created in the semiconductor region. Further, 4 represents an insulator barrier, a Schottky barrier formed by contact between a semiconductor and a metal, or a wide bandgap semiconductor forming a heterojunction with the semiconductors 1, 2, and 3. When such a structure is created, some of the Cooper pairs of the superconductor seep into the semiconductor due to the superconducting proximity effect, causing the semiconductor to exhibit the properties of a superconductor. Figure 2 shows how this seepage occurs. The region x < O in FIG. 2 is a superconductor, and the region x) a is a semiconductor. The region where a > x > O is an insulator barrier, a Schottky barrier, or a heterojunction barrier. The vertical axis represents the size of the energy gap or the size of the pair potential. ΔS is the size of the energy gap at the boundary of the superconductor, which is smaller than the bulk value due to boundary conditions. On the other hand, ΔN is the size of the energy gap at the boundary of the semiconductor, and as it moves away from the boundary with the superconductor, Δ(r) = ΔN−exp
[: (x-a)/ξN], (1) Attenuates in the form of an exponential function. Here, ξN is the coherence length within the semiconductor, and the relationship between ΔS and ΔN is de Genne
The boundary condition of s is given by: Here, DS and DN are the diffusion coefficients of electrons inside each, and NS and NN are the density of states of electrons on each side. The above (ξN
, D.N. NN) or (ξN, ΔN) are quantities determined by the properties of the semiconductor in contact with the superconductor. Therefore, even if the same superconductor is used, the energy gap of the semiconductor that has become a superconductor can be controlled by controlling the properties of the semiconductor it contacts. Therefore, if the elemental composition, type or concentration of impurities is changed in semiconductor 1, semiconductor 2, and semiconductor 3, as shown in FIG.
ξ,, Δ1), (ξ2, Δ2), and (ξ3, Δ3) take different values. At this time, each of the semiconductors 1, 2, and 3 has an effective energy gap of a different size (FIG. 4). Next, consider a cross-sectional structure as shown in FIG. This has a structure in which the three types of semiconductor regions shown in FIG. 1 are separated by insulator regions 9 and 10, respectively. This structure is the same as a double series Josephson junction. At this time, the effective energy gap size in the semiconductor region 6 is assumed to be Δ1, the effective energy gap size in the semiconductor region 7 is assumed to be Δ2, and the effective energy gap size in the semiconductor region 8 is assumed to be Δ3. Then, the properties of each semiconductor are controlled so that the relational expression Δ3×Δ1+Δ2×Δ2+Δ3, (3) is satisfied. The current flowing between terminals AB is ■ΔB
, the voltage is VAB, and the current flowing between terminals BC is IBC.
, the voltage is VBC. The graph shown in Figure 6 shows the current I
This is a BC-voltage VBC characteristic. Graph a in Figure 6 shows the current flow B when the input power P (=I8BXVAB) is zero.
c-voltage VBC characteristics. Graph b in Figure 6 shows the current IBC when the input power P exceeds a certain threshold power Pc.
This is a single voltage VBC characteristic. Therefore, by connecting a load between terminals BC, the operating point v1 when P=0 is set to state (1), and the operating point V when P>P c. and the state (0), the input power is P=
By changing from o to P > P c, the state (1
) to state (0). A feature of this switching operation is that unlike a Josephson junction element, it does not enter a latched state and can therefore be driven with direct current. This corresponds to a device called a quiteron in the prior art. At this time, the semiconductor region 6, the insulator region 9, and the semiconductor region 7 are called an injector junction, and the semiconductor region 7, the insulator region 10, and the semiconductor region 8 are called an acceptor junction. In this way, in the present invention, by using a semiconductor whose physical properties (film thickness, impurity concentration, etc.) are easy to control, the size of the superconducting energy gap Δ and the depth of Cooper pair seepage ξ can be controlled in a plane. We can provide superconducting devices that can be designed. Hereinafter, the present invention will be explained in more detail through Examples.

【Example】

Embodiment 1 FIG. 7 shows a quateron constructed using a semiconductor that has properties as a superconductor due to the superconducting proximity effect. B is implanted into the N-type Si substrate 18 with an impurity concentration of about 10"cm" as an electrically insulating region with an acceleration energy of about 100keV and a dose of 2X1013cm-2 to form P-type well regions 35-11-2. At this time, the thickness of the P-type well region 35 is 30 mm.
0nm, the impurity concentration is 101''cm-3.Next, As is implanted by normal ion implantation,
N+ regions 13, 14, and 15 are formed. During ion implantation, the ion implantation region is divided into three regions, and As
Change the amount of injection. Furthermore, at this time, the three regions are separated from each other. This can be done using conventional lithography and etching techniques. As a result, three n+ regions 13 having different As concentrations and separated from each other,
14 and 15 are possible. At this time, the As concentration in each region was set to Na. Nb. Let it be Nc. For example, by ion implantation or FIB, As is applied to the 13, 14, and 15 regions with an acceleration energy of 50 keV, and the doses are IXIO15 am'-22X10" cm-2 and 2, respectively.
X101SCm-2 implanted and annealed with SiO2 gap. At this time, each area 13, 14,''. The peak concentrations at 5 are -12Na=5X10"cm"Nb=IX1021cm-"Nc=IX, respectively.
It was 10"cm". Next, these n+ regions are thermally oxidized to form lnm
It is covered with a Si○2 tightening body film 16 of about
The b layer 17 was formed to a thickness of 300 nm by sputtering. When the device thus formed is cooled to below the superconducting transition temperature of Nb, the Nb layer 17 becomes a superconductor, and an energy gap begins to seep into the n0 region due to the superconducting proximity effect. The size of the seeped energy gap depends on the As concentration Na. Nb. In the n+ region 13, Δa.
In the n'' region 14, it becomes Δb, and in the n+ region 15, it becomes 8C. The size of the seeped energy gap increases as the As concentration increases. Therefore, the As concentration in each n+ region is Nc<Na+Nb<Nb+Nc, ( 4)
If the amount of As implanted is controlled to satisfy the relational expression, the size of the energy gap seeping into each n+ region is ΔC〈Δa+Δb Δb+ΔC, (5)
satisfies the condition. The conditions for the above As injection are (4
) and (5) are satisfied. At this time, the n+ region 13 and the n+ region 14 are made into an injector junction, and the n+ region 14 and the n+ region 15
If this is an acceptor junction, the device shown in FIG. 17 becomes a quiteron. The current-voltage characteristics at this time are given in FIG. 6, as explained in the operation section. Although one cuiteron has been constructed above, a system LSI can also be produced by configuring a plurality of cuiterons on the same semiconductor substrate in exactly the same manner. In the above example, a quateron was constructed using an n+ region, but a P-type Si substrate was used instead of an N-type Si substrate, an N-type well was formed instead of a P-type well, and B was used instead of As. If you inject it, p
A Quiteron can be constructed using + regions. ，
The necessary conditions regarding the amount of B note are the same as equation (4), and at this time, the size of the energy gap leaking into the P+ region satisfies equation (5). Further, in place of the above-mentioned Si○2 insulator film 16, a Schottky barrier formed by contact between a metal and a semiconductor may be used. Also, in the above example, Nb was used as the superconductor material, but
Pb. Sn. Nj etc. may also be used. Furthermore, YBa2Cu, which is an oxide high temperature superconductor material,
07-X and B 1 2 S r 2 C a Cu
20 Il+x etc. may also be used. The use of an oxide high temperature superconductor as the superconductor material has the advantage that the present invention can be used in a temperature range of liquefied nitrogen temperature or higher. Further, in the above example, As was implanted to form the n+ region, but other group Ⅰ elements may be used. In addition, when forming the p-domain region, other materials such as boron B and
Group elements may also be used. -16- In particular, it is desirable to use semiconductors in a degenerate state for the semiconductor regions 13, 14, and 15 where Cooper pairs seep out due to the superconducting proximity effect. By placing the Fermi level above the conduction band, many Cooper pairs can be exuded. This point also applies to the following examples. Embodiment 2 FIG. 8 shows a quateron constructed using a semiconductor that has properties as a superconductor due to the superconducting proximity effect. The fabrication of this example is completely the same as that of the first example up to the point where the Sin2 absolute film 22 is formed. This Si0
When forming the Nb layer on the 2M overall film 22, three n+
NbM is divided into three regions 23, 24, and 25 corresponding to semiconductor regions 19, 20, and 21. At this time, three Nb
Insulating regions 26 and 27 are provided between the layers, and the energy gap is made to seep only from the Nb layer 23 into the n+ semiconductor region 19, and the Nb layer 2 into the n+ semiconductor region 20.
Let the energy gap seep out only from 4, and n
+The energy gap is made to seep into the semiconductor region 21 only from the Nb layer 24. The difference between this embodiment and the first embodiment is that the coherence between each superconductor that exerts a superconducting proximity effect on each semiconductor region is weakened. Example 3 Next, an example in which the present invention is implemented using a compound semiconductor will be described. FIG. 9 shows a quiteron constructed using a semiconductor that has superconducting properties due to the superconducting proximity effect. Si is implanted into the semi-insulating GaAs substrate 34 by normal ion implantation (acceleration energy: 25ke
V, dose amount: 5×1 0'3c m-2) L/n
+ regions 29 and 31 are formed, and Be is implanted by normal ion implantation (acceleration energy: 30 keV
, Dose amount: 1×101″cm-”) L/p”
A region 30 is formed to create an npn junction. A high resistance AIGaAs film 32 with a thickness of about 1 nm is formed on these n+ regions 29, 31 and p 4' region 30 by a conventional method. Then, an Nb layer 33 is formed on this high resistance AIGaAs film 32. The amount of Si and Be implanted into each region is determined by Δa, the size of the energy gap leaking from the Nb layer 33 to the n+ region 29, and the amount of Si and Be implanted into each region.
The size of the energy gap that has leaked to 0 is Δb.
When the size of the energy gap leaking into the n+ region 31 is ΔC, adjustment is made so that condition (5) is satisfied. In this device structure, the depletion layer formed by the pn junction serves as a barrier, so that it operates as a quateron below the superconducting transition temperature of Nb. Although an npn junction was formed in the above example, a pnp junction may also be formed. Furthermore, by forming an insulating region between the three semiconductor regions, the entire structure can be made of an n+ semiconductor or a P+ semiconductor. Furthermore, high resistance AI
Instead of the GaAs film 32, a Schmitt key barrier formed by contact between a metal and a semiconductor may be used. Furthermore, when forming the Nb layer, the Nb region may be divided into three regions corresponding to the three semiconductor regions as in the second embodiment. Furthermore, although GaAs was used as the compound semiconductor in this embodiment, a compound semiconductor such as InAs may also be used.

【Effect of the invention】

According to the present invention, the energy gap of superconductivity can be used in a spatially controlled manner, and thereby an electronic device can be constructed. Furthermore, if it is combined with semiconductor integration technology, it can also be used as a superconducting system LSI.

[Brief Description of the Drawings] Figure 1 is a cross-sectional view showing the basic structure of the present invention, Figure 2 is a diagram explaining the superconducting proximity effect, and Figure 3 is how the energy gap seeps into each semiconductor region. FIG. 4 is a diagram showing the size of the effective energy gap in each semiconductor region, FIG. 5 is a diagram showing the basic structure of the electronic device of the present invention, and FIG. 7 is a cross-sectional view of the first embodiment of the present invention, FIG. 8 is a cross-sectional view of the second embodiment of the present invention, and FIG. 9 is a cross-sectional view of the second embodiment of the present invention. FIG. 3 is a cross-sectional view of the third embodiment. =20- Explanation of symbols] -~3... Semiconductor region, 4... Insulator barrier or Schottky barrier, 5 Superconductor region, 6-8... Semiconductor region, 9, 10... Insulation 11...Insulator barrier or Schottky barrier, 12...Superconductor region, 13-15...n10 semiconductor region, 16...Si
○2 Insulator film, 17...Nb layer, 18...N-type Si
Substrate, 19-21...n ten semiconductor regions, 22...S
in2 insulator film, 23-25...Nb layer, 26.27
...Insulating layer, 29, 31...n10 semiconductor region, 30
...p10 semiconductor region, 3 2-...high resistance AIGaA
s layer, 3 3 ・N b layer, 34... semi-insulating Ga
As substrate, 35...P-type well region. ) 1゛Unexamined Patent Publication No. 3 214677 (8)

Claims (1)

[Claims] 1. By forming a superconductor region near a semiconductor region having a structure composed of a plurality of semiconductors having different properties, a plurality of superconductor regions with different states can be created within the semiconductor region. A superconducting device characterized by being provided with. 2. The superconducting device according to claim 1, wherein the semiconductor region and the superconductor region are separated by a first insulator region, and the superconductor in contact with the semiconductor region is insulated. superconducting device. 3. In the superconducting device according to claim 1 or 2, a thickness is provided between the superconductor region and the semiconductor region that allows Cooper pairs to penetrate from the superconductor region into the semiconductor region due to a superconducting proximity effect. A superconducting device characterized by providing a first insulating layer region having a. 4. In the superconducting device according to claim 1 or 2, a second insulating layer region having a thickness that allows quasiparticle tunneling between the semiconductors is provided between the plurality of semiconductors having different properties. Features of superconducting devices. 5. The superconducting device according to claim 4, wherein the superconductor region and the semiconductor region have a thickness that allows Cooper pairs to penetrate from the superconductor region into the semiconductor region due to a superconducting proximity effect. A superconducting device comprising a first insulating layer region. 6. The superconducting device according to claim 4, wherein each semiconductor region is made of a normal conducting metal. 7. A superconducting device, characterized in that one or more superconducting devices according to claim 1, 2, 3, 4, 5, or 6 are provided on one semiconductor substrate. 8. A superconducting device according to claim 1, 2, 3, 4, 5, 6 or 7, wherein the superconductor region is an oxide high temperature superconductor.