JPS61264769A - Superconducting device - Google Patents

Abstract

PURPOSE:To obtain a quasi-particle collector having lower leak current and in which a high transmittance and a high impedance can be realized simultaneously, by forming a base layer of a superconductor having a density of electrons lower than those of metals. CONSTITUTION:A superconducting device comprises a base layer 2 which is totally or partially formed of a superconductor having a density of electrons lower than those of ordinary metals (e.g. BaPb1-xBixO3), a means for implanting quasi-particles into the base layer 2 (e.g. an emitter layer 3 of Nb), and a collector for taking out quasi-particles from the base layer 2 (e.g. a semiconductor substrate 1 of InSb). The device having such construction can operate similarly as a bipolar transistor. Further, since the base layer 2 has a lower electron density than those of the metals, the leak current in the semiconductor substrate 1 serving as a collector is decreased and a high electron transmittance can be realized simultaneously with a high impedance.

Description

[Detailed Description of the Invention] [Summary] The present invention provides a superconducting device that uses quasi-particles such as current as carriers and operates in the same way as a transistor, such as signal amplification. The part is formed of a superconductor having a lower electron density than that of ordinary metals, and the base layer is formed with a means for injecting quasiparticles, and furthermore, the quasiparticles are injected from the base layer. By forming a collector junction that extracts , it is possible to realize a quasi-particle collector that has low leakage current, high electron transmittance, and high output impedance.

[Industrial Application Field] □The present invention relates to a superconducting device that uses quasiparticles as carriers and has a signal amplification effect similar to that of a transistor.

[Conventional technology]

Conventionally, quasiparticles were injected into a superconductor from an emitter,
A superconducting device has been proposed that operates similarly to a bipolar transistor in which quasiparticles are taken out from a collector composed of a junction of a superconductor and a semiconductor (see Japanese Patent Application No. 58-224311) ).

[Problem that the invention seeks to solve]

In the superconducting device according to the prior art described above, when a normal metal superconductor such as Nb or PB is used for the base, the following problems occur.

(1) In addition to quasiparticles generated by injection, there are quasiparticles generated by thermal excitation in the base M region. Therefore, a constant leakage current will flow to the output regardless of the presence or absence of injection. Therefore, the value of this leakage current, that is, the value of the collector current ISA4 flowing due to thermal excitation, is an extremely large value at a temperature of 4.2 [K], for example, 500 (A/c++2) when Nb is used. ), and in the case of using Pb, it is as high as 4400 (A/am"), so to avoid this, it is necessary to lower the operating temperature of the device to, for example, about 2 [K].

(2) In addition to quasiparticles, a large number of superconducting electrons exist in the base region. In such a case, increasing the electron transmittance in the collector increases the contribution of superconducting electrons to the current, making collector design difficult.

The present invention provides a superconducting device having a quasiparticle collector that achieves high electron transmittance and low leakage current (high impedance).

[Means for solving problems]

In this type of superconducting device, the collector current I SAT flowing due to thermal excitation is I sat =Nt ed/rmtt
(A/am2)N7: Quasiparticle density at thermal equilibrium d: Base thickness τoff: Given by effective recombination time. That is, the collector current tsAa flowing due to thermal excitation is proportional to the quasiparticle density N at the time of thermal equilibrium. It should be noted that the collector current 1SAT flowing due to thermal excitation is a wasteful current that is unrelated to the transistor operation, as can be seen from the above description.

By the way, the quasiparticle density NY at thermal equilibrium is proportional to the electron density of the superconductor if the gap parameters are approximately the same. Therefore, if a superconductor with a low electron density is used, the quasi-particle density will be reduced, and the collector current ISAT flowing due to thermal excitation, which is a wasteful current, will also be reduced. Furthermore, even when using quasi-particle collectors with the same electron transmittance,
Since the electron density itself is low, it becomes a collector with high impedance.

Therefore, in the superconducting device of the present invention, the base layer 2 is made entirely or partly of a superconductor (for example, BaPb+-xBlxOl) having a slightly lower electron density than that of ordinary metals, and means for injecting quasi-particles into the layer 2 (e.g. emitter layer 3 made of Nb) and the base layer 2;
It has a structure including a collector (for example, a semiconductor substrate 1 made of InSb) for extracting quasi-particles from the substrate.

[Effect]

According to this means, a quasi-particle collector with low leakage current, high electron transmittance, and high impedance can be obtained, so that a superconducting device that operates as a transistor with good characteristics can be obtained.

〔Example〕

FIG. 1 shows a cutaway side view of essential parts of an embodiment of the present invention.

In the figure, 1 is a semiconductor substrate made of InSb that acts as a collector, and 2 is BaP, a low electron density superconductor.
b, -XBi, a base layer made of 03, 3 a quasi-particle emitter layer made of metal Nb, 4 an insulating layer made of SiO2, 5 a base electrode, 5' an emitter electrode, 6
indicate collector electrodes with ohmic contact.

In addition, the value of X in B a P I)'I-x B't x Ox may be selected to be about 0.3,
In this embodiment, the base electrode 5 is taken out through the quasi-particle emitter layer 3, but in the case of superconducting mode,
Although there is no problem with this configuration, it may be taken out directly from the base layer 2 if necessary.

In the illustrated example, the semiconductor substrate 1 serving as the collector is made of In
Not limited to Sb, but also GaAs, InAs.

In, -, Gax As, InP, HgCdTe, etc. can be substituted, and as the low electron density superconductor constituting the base layer 2, in addition to the exemplified ones, Li, □
Ti,,0. Or M, Mo6Ss (M=Pb, Cu)
Further, as the metal constituting the quasi-particle emitter layer 3, it is possible to use Al, etc. in addition to Nb. Although not shown in FIG. 1, a tunnel barrier is interposed between the base layer 2 and the quasi-particle emitter layer 4.

According to this embodiment, it is possible to perform the same operation as a bipolar transistor, and since the electron density of the base layer 2 is lower than that of metal, the leakage current in the semiconductor substrate 1, which is the collector, is small. , high electron transmittance and high impedance are simultaneously achieved.

FIG. 2 is a side view showing a main part of another embodiment of the present invention, and the same symbols as those used in FIG. 1 represent the same parts or have the same meanings.

This embodiment is different from the embodiment explained with reference to FIG. The emitter layer 3 is formed.

With such a configuration, the quasi-particle emitter layer 3 is made of a superconducting metal layer 2 such as Nb, which has a relatively large energy gap.
′, the nonlinearity of the quasiparticle emitter layer 3 increases, and when the injected quasiparticles move from the superconducting metal layer 2′ to the base layer 2, as shown in FIG. Since it runs at a higher speed than the illustrated embodiment, it has additional effects such as improved operating speed.

〔Effect of the invention〕

The superconducting device according to the present invention employs a structure in which a low electron density superconductor having a value smaller than the electron density of metal is applied to all or part of the base layer.

With this configuration, a quasi-particle collector can be obtained that has low leakage current and simultaneously achieves high electron transmittance and high impedance.

Therefore, when operating the superconducting device of the present invention as a transistor, it operates well without maintaining a very low temperature.
Moreover, the design of the collector is also easy.

[Brief explanation of drawings]

FIGS. 1 and 2 are main part cutaway side views showing different embodiments of the present invention. In the figure, 1 is a semiconductor substrate, 2 is a base layer, 2' is a superconducting metal layer, 3 is an emitter layer, 4 is an insulating layer, 5 is a base electrode, 5' is an emitter electrode, and 6 is a collector electrode. It shows. Patent Applicant: Fujitsu Ltd. Representative Patent Attorney: Akira Aitani Representative Patent Attorney: Hiroshi Watanabe Figure 1: Cutaway side view of essential parts of an embodiment of the present invention

Claims (1)

[Claims] A base layer made entirely or partially of a superconductor having an electron density lower than that of ordinary metals; means for implanting quasiparticles into the base layer; A superconducting device comprising: a collector for extracting quasiparticles from a base layer.