JPH0291985A - Superconducting transistor - Google Patents

Abstract

PURPOSE:To obtain a transistor characterized by high current gain by using specified oxide superconductor films as an emitter and a collector, using a required oxide conductor film as a base, and obtaining the heterojunctions of these films. CONSTITUTION:The heterojunctions of an emitter layer 3 and a collector layer 5 comprising oxide superconductor films wherein holes are carriers are formed with a base layer 4 comprising an oxide conductor film wherein electrons are carriers, and a transistor is formed. In this configuration, the reflection of the carrier between a base and a collector can be almost neglected, and the bipolar type superconducting transistor wherein the sufficient current gain is obtained is formed. Furthermore, the same result can be obtained by forming the emitter and the collector with oxide conductor films wherein electrons are carriers and forming a base with an oxide superconductor film wherein holes are carriers.

Description

[Detailed Description of the Invention] [Summary] Regarding a superconducting transistor, for the purpose of realizing a high current gain, two oxide superconductor films that use holes as carriers are formed as an emitter and a collector. , joining the emitter and the collector through a base made of an oxide conductor film using electrons as carriers, or forming two oxide conductor films using electrons as carriers as an emitter and a collector; The emitter and the collector are connected to each other via a base made of an oxide superconductor film using holes as carriers.

(Industrial Application Field) The present invention relates to a superconducting transistor, and more particularly to a bipolar transistor made of an acetate superconductor.

[Conventional technology]

Devices using Gisefson junctions are high-speed and have low power consumption, but because they are two-terminal devices, they have some functions that are difficult to implement. To solve this problem, various transistors made of superconductors have been proposed.

As illustrated in FIG. 6, a conventional superconducting transistor has a collector IIC, a base layer, and an emitter lie made of a superconductor, and barriers N''I, az are interposed between each eyebrow. This is what I did.

The principle of this transistor is explained based on a potential diagram as shown in Fig. 7. Carriers injected from the emitter region to the base region become a state with a certain excitation energy, that is, a real state, and enter the emitter.・Barrier Na between bases! After that, it passes through the base region, and then passes through the barrier layer a1 between the base and the collector to reach the collector region.

In order to provide a sufficient current gain to a transistor having this type of structure, carriers must pass through the base region and the barrier layer a1 between the base and collector without losing energy.

(Problems to be Solved by the Invention) However, in this type of transistor, there are phenomena such as carrier scattering in the base region and part of the carriers being reflected by the barrier layer a1 between the base and the collector. These become problems when trying to provide a gain.

By the way, base Nbl! Since the base layer is made of a superconductor, the resistance will not increase in an atmosphere below the critical temperature even if the base layer is made thinner. Therefore, carrier scattering in the base layer can be reduced by making the base layer thinner. reduced by

On the other hand, when attempting to suppress the reflection of carriers by the barrier layer a between the base and the collector, the energy height El of the barrier layer a1 is lowered by changing the constituent materials to increase the barrier transmittance. However, a new problem arises in that the amount of carrier leakage increases.

Furthermore, if the thickness of the barrier layer is increased while the energy height E of the barrier layer a1 is lowered, the amount of leakage will be reduced, but the time taken for carriers to pass through the barrier layer will increase.
There is a problem that high speed is impaired.

Therefore, in a superconducting transistor using hot carriers, it is difficult to obtain a high current gain for the reasons mentioned above.

The present invention has been made in view of such problems, and an object of the present invention is to provide a superconducting transistor that can realize a high current gain.

[Means to solve the problem]

The above problem was solved by forming two oxide superconductor films that use holes as carriers as an emitter and a collector, and connecting the emitter and the collector via a base made of an oxide conductor film that uses electrons as carriers. Join or
Alternatively, two oxide conductor films that use electrons as carriers are formed as an emitter and a collector, and the emitter and collector are joined via a base made of an oxide superconductor film that uses holes as carriers. This problem is solved by a superconducting transistor featuring the following characteristics.

(Function) In the above invention, it is known that oxide superconductors, which have a much higher superconducting critical temperature than conventional superconductors, generally have carriers in the amount of P; Since the body is doped with an element that becomes n-type, it uses electrons as carriers.

Further, since this transistor is formed of an oxide and the interface between each film is a heterojunction, this transistor is a bipolar type transistor, which is different from the conventional type that uses hot carriers.

In other words, a transistor using two oxide superconductor cavities with holes as carriers and an oxide conductor film with electrons as carriers acts as a pnp bipolar transistor, and also has two oxide superconductor cavities with holes as carriers. A transistor using an oxide conductor film and an oxide superconductor film using holes as carriers functions as an npn bipolar transistor.

According to such a configuration, sufficient current gain can be obtained because the barrier between the base and the collector is such that carrier reflection can be almost ignored.

〔Example〕

(a) Description of one embodiment of the present invention Fig. 1 shows an embodiment of the present invention, in which reference numeral 1 indicates a bipolar transistor using an oxide superconductor. The transistor 1 is constructed by laminating an emitter layer 3, a base layer 4, and a collector layer 5 in order by sputtering or the like on a substrate 2 made of an oxide conductive material. is formed of an oxide superconductor film, and the base layer 5 is formed of a film in which an oxide conductor is doped with an n-type element to use electrons as carriers.

These emitters It! 3. The base layer 4 and the collector layer 5 are formed by MBE method, sputtering method, etc., and form a heterojunction.

To specifically explain an example of the material used for the above-mentioned transistor l, an oxide conductive material such as strontium titanate (SrTi(h)) is used as the substrate 2, and an oxide material forming the emitter layer 3 and collector layer 5 is used. For material superconductivity, barium yttrium copper oxygen (BaYCuO,
X is a number of about 6.8)), and a 5rTiOs oxide conductor is used for the base electrode 4, and it is used as a dopant for the superconducting material to make it n-type. An element such as niobium (Nb) is used and the doping amount is about 1.5×IQ16/C−. To illustrate the thickness of each layer in this case, the emitter layer 3 is 1 μm, the base layer 4 is 1100 nm, and the collector layer 5 is 0.3 μm.

In addition, the reference numeral 6 in the figure indicates a gold terminal connected to each layer 3, 4, and 5 in order to connect the emitter layer 3, base layer 4, and collector layer 5 to the outside, and 7 indicates a gold terminal connected to each layer 3, 4, and 5 to connect the emitter layer 3, base layer 4, and collector layer 5 to the outside. The protective film formed by the above method is shown.

A schematic diagram and a potential diadam of the transistor configured in this way are shown in FIG. 2.3.
The Fermi level E, of the iOs film is above the lower end of the upper energy band, and the emitter J! ! 3 and collector layer 4
Since the Fermi level E of BazYCuJx, which constitutes the Since it can be changed depending on the doping amount, it is necessary to adjust this so that a tunnel effect does not occur between bands at the junction surface.

Next, the operation of one embodiment of the present invention will be explained.

In the embodiment described above, the emitter layer 3 and the collector layer 5
It is known that the oxide superconductor constituting the base N4 generally has p-committed carriers, and the oxide conductor constituting the base N4 is doped with an element that becomes n-type, so electrons are used as carriers. .

Further, since the emitter layer 3, base layer 4, and collector N5 are made of oxide and form a heterojunction, the transistor is of a bipolar type, which is different from the conventional type using hot carriers.

Therefore, the Fermi level of the emitter layer 3 decreases and the Fermi level E of the collector layer 5 increases.
When a bias is applied between the bases and between the base and collector, holes and electrons move as shown in Figure 4, resulting in bipolar behavior and a high current gain, whose characteristics are shown in Figure 5. It will be something like this.

(b) Description of other embodiments of the present invention In the embodiments described above, Ba-YCu-0 was used as the oxide high temperature superconductor constituting the emitter N3 and the collector layer 5, but other materials, such as lanthanum, were used.・Strontium・Copper・Oxygen (La-3r-Cu-0), Bismuth・
Strontium, calcium, copper, oxygen (Bi-5r-
It is also possible to apply materials such as Ca-Cu-0).

In addition, in the above embodiment, a pnp type transistor was obtained by sandwiching an oxide conductive material film doped with an element such as Nb between two oxide superconductor films. It is also possible to form an npn type transistor by sandwiching an oxide superconductor film between body films.

Note that the transistor described above is not limited to the sandwich-like structure.

(Effects of the Invention) As described above, the present invention can bond an oxide conductor film that uses electrons as carriers to two oxide superconductor films, or bond two oxide conductor films that use electrons as carriers. Since the transistor is constructed by bonding the body layer to the oxide superconductor layer, there is no need to consider hot carrier diffusion or reflection, and a bipolar transistor can be formed, achieving high current gain. can do.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a device showing an embodiment of the present invention. FIG. 2 is a schematic diagram of a device showing an embodiment of the present invention. FIG. 3 is a potential of the device showing an embodiment of the present invention.・Diadarum diagram, FIG. 4 is an explanatory diagram of the operation of the device showing one embodiment of the present invention, FIG. 5 is a characteristic diagram showing an example of the voltage/current gain according to the present invention, and FIG. 6 is a diagram of the conventional device. FIG. 7, which is a sectional view showing an example, is a potential diaphragm diagram in an example of a conventional device. (Explanation of symbols) 1...Transistor, 2...Substrate, 3...Emitter layer, 4...Base layer, 5...Collector layer, 6...Electrode. Patent Applicant Fujitsu Limited Patent Attorney Kei Okamoto Figure 1: Cross-sectional view of a device showing an embodiment of the present invention Figure 1: Schematic diagram of a device showing an embodiment of the present invention Figure 2: An embodiment of the present invention FIG. 4: Base-emitter voltage Characteristic diagram showing an example of voltage/current gain according to the present invention FIG. Cross section Z showing an example of a conventional device FIG. 6: Barrier layer q2

Claims (2)

[Claims] (1) Two oxide superconductor films using holes as carriers were formed as an emitter and a collector, and the emitter and collector were joined via a base made of an oxide conductor film using electrons as carriers. A superconducting transistor characterized by: (2) Two oxide conductor films that use electrons as carriers are formed as an emitter and a collector, and the emitter and collector are joined via a base made of an oxide superconductor film that uses holes as carriers. A superconducting transistor characterized by: