JPH08167743A - Superconducting fet element and its manufacture - Google Patents

Abstract

PURPOSE: To provide a superconducting FET element in which a channel layer can be formed very thin and the formation of insulating layers is not required and which can be manufactured easily with less man-hours and a manufacturing method of the element. CONSTITUTION: A superconducting FET element is provided with a (Ba, Bb)BiO3 or (Ba, K)BiO3 channel layer 12 formed on a substrate 11 composed of MgO, SrTiO3 , etc., gate electrode 14 composed of such a metal as In, Al, Cr, etc., which reacts to the channel layer 12 and forms an effected layer 16 having a diode characteristic, and a source electrode 13 and a drain electrode 15 which are separated from the gate electrode 14 and ohmic-contacted with the channel layer 12.

Description

Detailed Description of the Invention

[0001]

The present invention relates to (Ba, Rb) BiO
Superconducting field effect transistor (Superconducting FET: Field Effect Trans) using ₃ (hereinafter BRBO) or (Ba, K) BiO ₃ (hereinafter BKBO).
system].

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, Electric field effect
in high T _c superconducti
ngultratin YBa ₂ Cu ₃ O _7-x fil
ms: X. X. Xi, Q. Li, C.I. Doughty,
C. Kwon, S .; Bhattacharya, A .;
T. Findikoglu and T.M. Venkat
esan, Appl. Phys. Lett. , Vol.
59, No. 26, 23 December (199
1), pp. 3470-3472.

FIG. 3 is a sectional view of such a conventional FET device. Hereinafter, a conventional superconducting FET element will be described. As shown in FIG. 3, the substrate 1 is (100) Sr.
TiO ₃ (hereinafter referred to as STO) is used, and a YBa ₂ Cu ₃ O _7-x (hereinafter referred to as YBCO) film 2 is formed on the substrate 1.
The film is formed with a film thickness of up to 100Å. Furthermore, S of 4000Å
The TO thin film 3 is formed. A source electrode 5 and a drain electrode 6 are provided on the YBCO film 2, and a gate electrode 4 is provided on the STO thin film 3. When a power source is connected between the source / drain and an electric current is passed, if the temperature is below the critical temperature, a superconducting current will flow. The superconducting current is controlled by breaking the superconductivity of the channel by applying a voltage to the gate electrode 4.

FIG. 4 is a diagram showing changes in the resistance of the YBCO channel layer when the YBCO thin film of the FET element thus obtained is 50 Å. Here, the horizontal axis represents the absolute temperature (K), the vertical axis represents the resistance (Ω), and the gate voltage V _G is
0, -2.5V, 20V, drain current I _D 10μ
A, YBCO thin film is 50Å, STO thin film is 4000Å,
The case of the gate electrode Au is shown.

As is apparent from FIG. 4, the gate voltage V _G
It can be seen that the resistance is modulated when is changed from -2.5 to 20V.

[0006]

However, in the structure of the conventional superconducting FET element described above, it is necessary to make the superconducting thin film as the channel layer extremely thin, about 100 Å or less. The number of steps must be increased to form the insulating layer on the superconducting thin film.

In order to form an insulating layer on the superconducting thin film,
It is necessary to lower the film forming temperature of the insulating layer than the film forming temperature of the superconducting thin film. There was such a problem. The present invention eliminates the above-mentioned problems, allows a channel layer to be formed very thin, does not need to form an insulating layer on the channel layer, reduces the number of steps, and is a superconducting FET device that is easy to manufacture. And its manufacturing method.

[0008]

In order to achieve the above object, the present invention provides: (1) In a superconducting FET element, a channel layer made of a superconducting thin film formed on a substrate and reacting with the channel layer, A gate electrode made of a metal forming an altered layer exhibiting a diode characteristic, and a source electrode and a drain electrode which are separated from the gate electrode and are in ohmic contact with each other on the channel layer are provided.

(2) In the superconducting FET element according to claim 1, the superconducting thin film is (Ba, Rb) BiO ₃ or (Ba, K) BiO ₃ . (3) In the superconducting FET element according to claim 1 or 2, the metal forming the altered layer is In, Cr, Al. (4) In the superconducting FET element according to claim 1, 2 or 3, the gate electrode is a comb electrode.

(5) In a method of manufacturing a superconducting FET element, a step of forming a channel layer made of a superconducting thin film on a substrate, and a gate electrode made of metal is vapor-deposited on the channel layer, and the metal becomes the channel layer. A step of reacting to form an altered layer exhibiting diode characteristics and a step of forming a source electrode and a drain electrode separated from the gate electrode and forming ohmic contact on the channel layer are performed.

(6) In the method for manufacturing a superconducting FET element according to claim 5, the superconducting thin film (Ba, R
b) BiO ₃ or (Ba, K) BiO ₃ is used. (7) The method for manufacturing a superconducting FET element according to claim 5 or 6, wherein the metal of the gate electrode is In, Cr,
Al is used. (8) In the method for manufacturing a superconducting FET element according to claim 5, 6 or 7, the gate electrode is formed into a comb-shaped electrode.

[0012]

According to the present invention, since it is configured as described above, BRBO (BKBO) is mainly used for the channel layer, BRBO (BKBO) such as In, Cr, Al or the like is used for the gate electrode, and a metal exhibiting diode characteristics is used. Therefore, when a metal such as these is vapor-deposited on BRBO (BKBO), a reaction occurs and an altered layer can be formed inside BRBO (BKBO).

Therefore, even if the film thickness is, for example, about 1000 Å, the substantial gate thickness can be made sufficiently thin. Further, since a metal such as In penetrates into BRBO (BKBO), an electric field important for the FET can be applied to the inside. (2) Further, by forming the gate electrode as a comb-shaped electrode, in addition to the above effect, it is possible to divide into a part that reacts intentionally and a part that does not react (BRBO (BKBO) channel), and controllability is good. Can be

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view of a superconducting FET element showing a first embodiment of the present invention, and FIG. 2 is a plan view of the superconducting FET element. As shown in these figures, 11 is a substrate, and MgO, SrTiO ₃ (hereinafter referred to as STO) or the like is used. The substrate is selected to be an insulator and a superconducting material (Ba, Rb) BiO ₃ (hereinafter, BRB).
O) or (Ba, K) BiO ₃ (hereinafter BKBO
Is easy to grow and a high quality thin film can be obtained. 12 is a channel BRBO
(BKBO) thin film.

Reference numeral 13 is a source electrode, and BRBO (BK
For example, Au or the like which exhibits ohmic contact with BO) is used.
Reference numeral 14 denotes a gate electrode, which is made of metal such as In, Al, and Cr, which is easily oxidized and exhibits BRBO (BKBO) and diode characteristics. Reference numeral 15 is a drain electrode, and BRBO (BKBO) similar to the source electrode 13 and Au exhibiting ohmic properties are used. 16 is BRBO (BKB
O) In the altered layer, for example, when In is vapor-deposited on the gate electrode 14, it is caused by the reaction between In and BRBO (BKBO).

The basic operation concept is similar to that of the YBCO type FET described above. That is, when a power source is connected between the source and drain and a current is passed through the channel, a superconducting current flows if the temperature is below the critical temperature. The superconducting current is controlled by breaking the superconductivity of the channel by applying a voltage to the gate. Next, a second embodiment of the present invention will be described.

FIG. 5 shows a superconducting F showing a second embodiment of the present invention.
FIG. 6 is a sectional view of the ET element, and FIG. 6 is a plan view of the superconducting FET element. As shown in these figures, 21 is a substrate, and MgO, STO, or the like is used. The selection of the substrate is determined by the fact that it is an insulator, BRBO (BKBO) that is superconducting is easy to grow, and a high quality thin film can be obtained. 22 is a channel BRBO (BKBO)
It is a thin film. Reference numeral 23 is a source electrode, and BRBO (BK
For example, Au or the like that exhibits ohmic contact with BO) is used.

Reference numeral 24 is a gate electrode, which is a comb-shaped electrode 27.
A metal exhibiting ohmic properties (described later) is used. Reference numeral 25 denotes a drain electrode, which is a BRBO similar to the source electrode 23.
Au, which exhibits ohmic contact with (BKBO), is used. Reference numeral 26 is a BRBO (BKBO) altered layer. For example, when In is vapor-deposited on the gate electrode 24, In and BRBO
It is generated by the reaction of (BKBO). 27 is a comb-shaped electrode, which is easily oxidized by In, Al, Cr, etc.,
BRBO (BKBO) and a metal exhibiting diode characteristics are used. Since the junction between In and BRBO (BKBO) is a reaction, in order to improve the controllability, the electrodes are formed in a comb shape, and the part of the altered layer of BRBO (BKBO) and normal BRBO (BKBO) are A method of forming it in any shape is conceivable. The comb-shaped electrode portion and the gap portion should have the best controllability of the gate voltage in the device characteristics.

The basic operation concept is the above YBCO type F
Similar to ET. That is, when a power source is connected between the source and drain and a current is passed through the channel, a superconducting current flows if the temperature is below the critical temperature. The superconducting current is controlled by breaking the superconductivity of the channel by applying a voltage to the gate. This superconducting FET element
Since the channel is in the superconducting state, it has the effect of zero resistance. In this respect, it is considered suitable for power devices such as electric power. Further, from the viewpoint of a transistor using superconductivity, it can be used for amplification related to a device to be used after cooling, for example, an infrared sensor.

The present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0021]

【The invention's effect】

(1) According to the invention described in claims 1 to 8, BRBO (BKBO) is mainly used for the channel layer, and In, Cr, and
By using BRBO (BKBO) such as Al and a metal exhibiting diode characteristics, a metal such as
When vapor-deposited on RBO (BKBO), a reaction occurs and B
An altered layer can be formed inside the RBO (BKBO).

Therefore, the substantial gate thickness can be made sufficiently thin even if the film thickness is, for example, about 1000 Å.
In addition, since a metal such as In penetrates into BRBO (BKBO), an important electric field can be applied to the inside of the FET. (2) Further, according to the invention of claim 4 or 8, by forming the gate electrode in a comb shape, in addition to the above effect, a portion that intentionally reacts and a BRBO (BKB) that does not react
O) It is possible to improve the controllability by dividing it into the channel part.

[Brief description of drawings]

FIG. 1 is a sectional view of a superconducting FET device showing a first embodiment of the present invention.

FIG. 2 is a plan view of a superconducting FET device showing the first embodiment of the present invention.

FIG. 3 is a sectional view of a conventional FET device.

FIG. 4 is a diagram showing a change in resistance of a YBCO channel layer when the YBCO thin film of a conventional FET element has a thickness of 50 Å.

FIG. 5 is a sectional view of a superconducting FET device showing a second embodiment of the present invention.

FIG. 6 is a plan view of a superconducting FET device showing a second embodiment of the present invention.

[Explanation of symbols]

11, 21 Substrate (MgO, STO) 12, 22 BRBO (BKBO) thin film (channel layer) 13, 23 Source electrode 14, 24 Gate electrode (In, Al, Cr) 15, 25 Drain electrode 16, 26 BRBO (BKBO) Altered layer 27 Comb electrode

Claims (8)

[Claims] 1. A channel layer made of a superconducting thin film formed on a substrate, (b) a gate electrode made of a metal which reacts with the channel layer to form an altered layer exhibiting diode characteristics, and (c) ) A superconducting FET device comprising a source electrode and a drain electrode which are separated from the gate electrode and are in ohmic contact with each other on the channel layer. 2. The superconducting FET element according to claim 1, wherein the superconducting thin film is (Ba, Rb) BiO ₃ or (B).
a, K) BiO ₃ superconducting FET
element. 3. The superconducting FET element according to claim 1, wherein the metal forming the altered layer is In, Cr, A.
A superconducting FET device characterized in that it is 1. 4. The superconducting FET according to claim 1, 2 or 3.
A superconducting FET device, wherein the gate electrode is a comb-shaped electrode. 5. A step of (a) forming a channel layer made of a superconducting thin film on a substrate, and (b) depositing a gate electrode made of a metal on the channel layer, the metal reacting with the channel layer, A superconducting FET device comprising: a step of forming an altered layer exhibiting a diode characteristic; and (c) a step of forming a source electrode and a drain electrode which are separated from the gate electrode and form ohmic junction on the channel layer. Manufacturing method. 6. The method of manufacturing a superconducting FET element according to claim 5, wherein the superconducting thin film is (Ba, Rb) B.
A method for manufacturing a superconducting FET element, which comprises using iO ₃ or (Ba, K) BiO ₃ . 7. The method for manufacturing a superconducting FET element according to claim 5, wherein the metal of the gate electrode is I.
Superconducting FET characterized by using n, Cr, Al
Device manufacturing method. 8. The superconducting FET according to claim 5, 6 or 7.
A method for manufacturing a superconducting FET element, characterized in that the gate electrode is formed as a comb-shaped electrode.