JPS63283177A - Superconducting transistor - Google Patents

Abstract

PURPOSE:To obtain a superconducting FET which operates at a high temperature and exhibits stable characteristics by employing a junction structure of an oxide superconductor and an N-type semiconductor exhibiting superconductor- semiconductor phase transfer by applying a voltage thereto. CONSTITUTION:An oxide 2 having a channel layer for causing the phase transfer of a superconductor-semiconductor under the control of carrier concentration is superposed on an n-type Si substrate 1, and a gate electrode G is attached through a source drain electrodes S, D and an SiO2 film 6. A perovskite type oxide superconductor which contains rare earth element having high critical temperature is used for the film 2, and L-M-Cu-O (L is La, Sc, Y, M is at least one of Ba, Sr or Ca) or ABa2CU3O7-8 (A is Y, YbHo, Dy, Eu, Er, Tm or Lu) is selected. Since these oxides are substantially of P-type contracted semiconductor, it forms a junction with an n-type layer 1 to alter hole concentration, and since its critical temperature is largely varied by the carrier concentration, it can operate as the function of an FET and can operate with stable characteristics by a simple refrigerating machine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a superconducting transistor, and more particularly to a superconducting transistor that utilizes a semiconductor-superconductor phase transition.

(Prior Art) Until now, the development of ultra-high-density electronic devices and ultra-high-speed electronic devices has focused on silicon and compound semiconductors. High density and high speed conventional semiconductor devices have been achieved through advanced microfabrication technology, homogeneous and highly perfect crystal manufacturing technology, and device design technology using simulation.

Heat generation is an issue that will become increasingly important in the future as the density and speed of semiconductor devices are further increased. This is considered to be a major factor that limits the ability to increase the density and speed of semiconductor devices, in addition to crystal perfection and microfabrication technology.

Electronic devices are superior to semiconductor devices in terms of heat generation. This is a superconducting device typified by the l*7son junction device. However, superconducting devices have so far
There are no prospects for full-scale practical application. The reason for this is that metals or intermetallic compounds are used as superconducting materials, which are easily oxidized, and in the case of Josephson junction elements, the temporal stability and spatial uniformity of the external metal compound used as the insulating film are poor. First, it is difficult to use because it is essentially a two-terminal device.

In recent years, superconducting transistors combining superconductors and semiconductors have been prototyped to overcome the shortcomings of Josephson junction devices, which are two-terminal devices.

In this method, a pair of superconductor electrodes (source and drain electrodes) are provided on one surface of the semiconductor layer, facing each other with a small distance, and an electrode (gate electrode) that controls the carrier concentration distribution within the semiconductor layer is provided on the other surface. It has a built-in structure. If a bias is applied by the gate electrode in a direction that decreases the carrier concentration near the source and drain, a Joseph non junction will not be formed between the source and drain electrodes, and no superconducting current will flow between the source and drain electrodes. This is the off state of the transistor. On the other hand, if a bias is applied to increase the carrier concentration near the source and drain of the gate electrode, the source will increase above a certain voltage.

A disjunction (superconducting junction) is formed between the drain electrodes, and the transistor is turned on. This is a method in which a pair of superconducting electrodes of a conventional device, which were opposed in the thickness direction, are expanded on a plane, and a superconducting junction is formed by controlling the carrier concentration between the superconducting electrodes. Theoretically, there is no heat generation in a star that controls the temperature.

This superconducting transistor has the advantage of being a three-terminal device, making it easier to use compared to conventional Josephson devices, but its operating temperature is extremely low, at or near liquid helium, and its superconducting electrodes are made of air. It is unstable inside. Unless these difficulties with superconductor devices are resolved, it will be difficult to put them into practical use.

(Problem to be Solved by the Invention 9) As mentioned above, superconducting devices are attracting attention as they do not generate heat and can exceed the limits of conventional semiconductor devices in terms of density and speed. It has not been put into practical use due to restrictions.

It is an object of the present inventor to provide a superconducting transistor that has a new operating principle, can operate at a temperature higher than the liquid nitrogen temperature, and has excellent stability in air. With the goal.

[Structure of the invention]

(Means for solving the problem) The present invention #4 consists of an oxide film having a channel layer that causes a supertransitor-semiconductor phase transition by carrier II degree control, and a predetermined interval between this oxide film. a sauce formed by placing the
A superconducting transistor comprising a drain electrode and a gate electrode for controlling carrier concentration in a channel layer of the oxide film, and an n-type semiconductor layer provided in contact with the channel layer.

The n-type semiconductor layer used in the present invention is not particularly limited, and may be any thin film of what is generally known as a Vcn-type semiconductor.

The oxide used in the present invention has a carrier concentration of 107
Any oxide with a size of d or less may be used, and is not particularly limited.

Many oxide superconductors are known, but
It is practically preferable to use a vergeskite-type oxide superconductor containing a rare earth element, which has a high critical temperature. The oxide superconductor containing a rare earth element and having a perovskite structure is sufficient as long as it can realize a superconducting state, and is an ABa2Cua07J system having oxygen vacancies (A is Y, Y
Defect perovskite type, 5r-La-Cu-
0-series, etc., layered perovskite type, etc. Broadly speaking, it is defined as a compound having perovskite structure.

Rare earth elements are also defined broadly and include Sc, Y, and lanthanum. Representative systems and Y-Ba-Cu-0
In addition to the system, Y is Yb, )io, Dy, Eu, Er, Tm
, a system substituted with rare earth elements such as Lu, 5c-Ba-Cu-0
system, 5r-La-Cu-0 system, and further Sr is Ba, C
Examples include threads in which a is substituted. The composition of this material may be slightly different depending on manufacturing conditions and the like. For example, B for ijYlmol in d Y -Ba-Cu-0 yarn
The standard composition is a2 mol and Cu3 mol, but in practice BaZ ± 0.6 mol Cua ± 0.2 mo
A deviation of 18 degrees is not a problem. These oxides can also behave as normal semiconductors depending on their composition. For example, La2CuO4 is known as a p-type semiconductor.

When a predetermined voltage is applied to this, the portion with high carrier density behaves as a superconductor due to a change in the carrier density distribution.The gate electrode part has, for example, an MO8 structure, and the source is formed by the electric field effect.

The configuration may be such that the carrier concentration in the semiconductor layer near the drain electrode is controlled. In the present invention, oxide superconductors may also be used for the source and drain electrodes.

(Function) The present invention provides that the oxide superconductor contains 11 ordinary gold F4,
Unlike intermetallic superconductors, it is essentially a p-type degenerate semiconductor; therefore, 2) by forming a junction with an n-type semiconductor, its hole carrier concentration can be changed. ) This is a superconducting transistor that applies the following three characteristics to its operating principle: critical temperature Tc varies greatly depending on carrier concentration.

Considering a pn heterojunction formed in an oxide superconductor on an n-type semiconductor, the junction formation reduces the hole carrier concentration within the superconductor over a range of several tens of people, and Tc decreases. This phenomenon Fi is a new type of proximity effect that is not observed in ordinary metal superconductors with a large carrier concentration. That is, the carrier concentration in a superconductor thin film with a thickness of several 10 to several tens of OA changes greatly by forming a pn junction and applying an external voltage to it, and as a result, T
c also changes significantly.

For example, when a voltage is applied perpendicular to the junction surface to the pn junction, which exhibits superconductivity at nitrogen temperatures, the junction becomes .

Phase transition to semiconductor. The present invention is a superconducting transistor whose operating principle is such a superconducting-semiconductor switching phenomenon.

In the present invention, for example, the oxide superconductor film is formed on an n-type St substrate, and the gate electrode is connected to the source,
The drain electrode is formed directly on the superconductor film. The switching phenomenon in the gate portion can be used to control the current between the source and drain.

The above-mentioned oxide superconducting film has a critical temperature Tc exhibiting superconductivity.
is extremely high, exceeding 30, and the Y--Ba--Cu--O system exhibits superdegradation even at liquid nitrogen temperatures.

These oxide semiconductors also have superior stability in the atmosphere compared to conventional metal or intermetallic compound superconductors.

As described above, the present invention has a new operating principle,
A superconducting transistor that can operate at temperatures obtained with a simple refrigerator and has stable characteristics with little change in light conditions can be obtained.

Since it is a three-terminal device, it is easy to use, and since it does not generate heat, it is possible to realize ultra-high-speed integrated circuits and ultra-high-speed devices that cannot be obtained with devices using only conventional semiconductor materials.

(Example) Examples of the present invention will be described below with reference to the drawings. Figure 1 shows a superconducting transistor of one example.

An n-type Sl substrate 1" doped with A3 and to19/c+d is used, and an oxide superconductor ("o
, 5ssru1s)2cuo4-y2 to a thickness of 5OA by sputtering. Source 3. Train 4
, the electrodes were formed by Au evaporation. The gate "it" electrode 5 is made of silicon oxide pancreas (thickness 200 mm) formed by the Q method.
X) Source 3. Gate 5 between electrodes and drain 4. The distance between the gelt 5 electrodes is 0.5 μm.

With this configuration, when zero voltage or negative bias is applied to the gate electrode 5, the source and drain are short-circuited by the superconducting thin film 2. That is, the transistor is in an ON state.

When the gate electrode 5 is positively biased, contrary to the above, n-type S
Electrons are injected into the oxide superconductor film from t, the hole carrier density in this film decreases, the superconducting film near the gate becomes a normal conductor, and the resistance between the source and drain increases.

This is the OFF state of the transistor.

Figure 2 shows the source of the superconducting transistor of this example,
The gate voltage dependence of the resistance between drains is shown. A rapid increase in resistance value is observed at a gate voltage of 500 mV.

FIG. 3 shows a superconducting transistor according to another embodiment. The element of this embodiment is different from that shown in FIG. 1 in that the gate electrode is formed in the gate portion with an n-type Si layer (thin film) 7 interposed therebetween. The thickness of the n-type 81 layer 7 is 50A.

The superconducting transistor of this embodiment basically operates in the same way as the previous embodiment. In this example, when the gate voltage is set to negative polarity, holes are injected from the superconductor layer into SiN2, the superconductor layer becomes an insulator, and the n-type Si layer 7 also has a high resistance. The resistance between the source and drain during off-state can be made higher than when there is no insulating film. The situation is shown in Figure @2. The threshold voltage is approximately 2
．． Although the resistance increases to IV, the resistance when off is increased to 5.2Ω.

The present invention is not limited to the above embodiments.

For example, in the above embodiment, a metal electrode was used for each electrode, but
Oxide superconductors can also be used for the source, drain, and gate electrodes.

This is practically advantageous since it is possible to prevent the wiring from becoming long and generating heat when the element of the present invention is incorporated into a concrete circuit.

Other modifications may be made without departing from the spirit of the present invention.

〔Effect of the invention〕

As described above, according to the present invention, by employing a junction structure of an oxide superconductor and an n-type semiconductor that exhibits a superconductor-semiconductor phase transition by voltage application, it is possible to operate at high temperatures. Furthermore, a superconducting transistor with a new operating principle that exhibits stable characteristics can be obtained.

[Brief explanation of the drawing]

1 and 3 are diagrams showing a superconducting transistor according to one embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the gate voltage and the resistance value between the source and drain of the transistor according to one embodiment. . 1 = n-type S1 substrate, 2 (Lag, sssrg, 1
s) 2Cu04-y film, 3... source electrode, 4...
Drain electrode, 6... silicon oxide film, 7... n-Si layer. Agent Patent Attorney Nori Ken Ken Yuken Mitsuyuki Matsuyama Figure 1 ρ 2 ρ 4 ρ θ ctt mv v Figure 2 Figure 3

Claims (7)

[Claims] (1) An oxide film having a channel layer that causes a superconductor-semiconductor phase transition by carrier concentration control, source and drain electrodes arranged and formed at a predetermined interval on this oxide film, and the oxide film 1. A superconducting transistor comprising: a gate electrode for controlling carrier concentration in a channel layer; and an n-type semiconductor layer provided in contact with the channel layer. (2) The superconducting transistor according to claim 1, wherein the oxide film having the channel layer is a perovskite-type oxide film containing a rare earth element. (3) The oxide film having the channel layer is made of LM-Cu
-O system (L is at least one M of La, Sc, Y)
The superconducting transistor according to claim 1, wherein is a film of at least one of Ba, Sr, and Ca. (4) The oxide film with the channel layer is ABa_2C
u_3O_7_-_δ film (A is Y, Yb, Ho, D
y, Eu, Er, Tm, Lu). (5) The superconducting transistor according to claim 1, wherein the source and drain electrodes are formed of an oxide superconductor film. (6) The superconducting transistor according to claim 1, wherein the source, drain electrode, and gate electrode are formed on the same side of the oxide film. (7) The superconducting transistor according to claim 1, wherein the gate electrode portion has an MIS structure in which a gate electrode is formed on the channel layer of the oxide film with an insulating film interposed therebetween.