JPH05183200A - Superconducting transistor - Google Patents

Abstract

PURPOSE:To obtain a superconducting transistor having excellent electric characteristics by a simple process without the necessity of complicated interface treatment of surface treatment, by making a first region and a second region composed of ITO layers, and a third region an oxide superconductor layer, and bringing the ITO regions into contact with the oxide superconductor layer directly. CONSTITUTION:An oxide superconductor layer is provided on a substrate 10 as a third region 18 being a base region, and an ITO film is formed on the oxide superconductor layer as a first region 14 being the collector region. On this occasion, it is sufficient if the heating temperature of the first region 14 is set at a temperature of 300-500 deg.C. Consequently, Si is prevented from being oxidized, and oxygen constituting the oxide superconductor is prevented from being mutually diffused with Si. Besides, it becomes possible to form high-quality ITO films having excellent matchability with the oxide superconductor layer, by properly selecting material having a lattice constant approximately equal to that of the ITO as the oxide superconductor layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting transistor, and more particularly to a superconducting transistor having a structure in which a base region is made of an oxide superconducting material.

2. Description of the Related Art A semiconductor transistor in which each electrode region of the transistor is made of a semiconductor material has a problem of high power consumption. Therefore, in recent years, research on a superconducting transistor in which a part of the electrode region is formed by using a superconductor material and high speed operation and low power consumption can be expected has been advanced. Since the oxide superconductor has a high critical temperature T _C and a large energy gap, it is expected that a transistor having a high cutoff frequency can be obtained by forming a superconducting transistor using this material. Therefore, the inventor of the present application discloses in Document I: "JP-A-1-303766" that the emitter and collector regions are semiconductor layers, and the base region between these regions is a superconductor layer.
Moreover, a superconducting base transistor having a structure in which this superconducting layer is sandwiched between metal thin films and interposed between the emitter and collector regions is proposed. Also,
The inventors of the present application have made reference to Document II: “JP-A-1-303
No. 770), a collector and an emitter region are semiconductor layers, and a base region made of an oxide superconductor layer is deposited with constituent elements of the oxide superconductor one atomic layer at a time, without interposing a metal thin film therebetween. Let's make a superconducting base
A method for manufacturing a transistor is proposed. In addition, Frank et al. (DJ Frank et a.
l. ), There is a bipolar transistor having a structure in which a superconductor material is used for a base and an emitter, a semiconductor material is used for a collector, and a tunnel barrier layer is provided between the emitter region and the base region. (Reference I: "IEEE Trans. Magn.,
MAG-21 (1985) p721), the structure and operation of this superconducting transistor are different from those of the superconducting transistor of the present invention described below, and therefore description thereof is omitted. By the way, silicon (Si) as a semiconductor material
Has high reliability, high processability and high reproducibility,
Moreover, since a large-area substrate can be obtained at low cost, it is advantageous if this Si can be used as the substrate, that is, the collector region or the emitter region. Also,
For the same reason, it would be advantageous if quartz glass could also be used.

However, if the superconducting transistor having the above-mentioned conventional structure is to be formed using Si and an oxide superconductor material, there are various problems as described below. In the structures of the superconducting transistors of Documents I and II, it is assumed that silicon (Si) is used for both the collector region and the emitter region and an oxide superconductor material is used for the base region. Normally, when forming a semiconductor layer as an emitter region, the temperature of the lower layer is set to about 800 ° C., so that Si constituting the collector region is oxidized, or Si The constituent elements of the oxide superconductor layer forming the base region, especially oxygen, interdiffuse. For this reason, the underlying Si region may be damaged, and oxygen in the oxide superconductor layer may be deficient to lower the critical temperature T _C. Further, in the structure disclosed in Document II, in order to prevent occurrence of interdiffusion between Si and oxygen, a complicated method of providing a metal thin film between each of the collector region and the emitter region and the superconductor layer is adopted. .. As described above, in the structure of the conventionally proposed superconducting transistor, when Si or another covalently-bonded semiconductor material is used for the emitter or collector region, and when an oxide superconductor material is used for the source region, However, since a problem of interfacial control due to mutual diffusion of oxygen and Si occurs, complicated surface treatment or interfacial treatment must be performed, which complicates the manufacturing process or causes the manufacturing process to be complicated. There was a problem of staying bad. The purpose of this invention is
It is an object of the present invention to provide a superconducting transistor having a structure with a simple manufacturing process, improved manufacturing yield, and low power consumption.

In order to achieve this object, according to the superconducting transistor of the present invention, the first and second regions and at least the first region between the first and second regions are provided. In direct contact with at least a third region provided, wherein one or both of the first and second regions are formed of an ITO (tin-doped indium oxide) layer and the third region is oxidized. It is characterized in that it is formed of a superconductor layer.

In carrying out the present invention, it is preferable that the oxide superconductor layer is composed of one or more oxide superconductor thin films.

Further, according to a preferred embodiment of the present invention, the oxide superconductor thin film is preferably composed of a Y (yttrium) -Ba (barium) -Cu (copper) -O (oxygen) thin film.

Further, in implementing the present invention, it is preferable that the first region is a collector region, the second region is an emitter region, and the third region is a base region.

According to the above-described superconducting transistor of the present invention, the first region and the second region are formed of the ITO (tin-doped indium oxide) layer, and the third region is formed of the oxide superconductor layer. The ITO region has a structure in direct contact with the oxide superconductor layer. ITO used here
Is an oxide of In ₂ O ₃ (indium oxide) doped with Sn (tin) by several percent, and has a lattice constant (L
Attic constant: Here, the length of the ridge of the crystal unit cell is 10.12 A ° (A ° is a symbol representing angstrom).

On the other hand, as the oxide superconductor thin film, Y (yttrium) -Ba (barium) -Cu (copper) -O (oxygen) thin film, Bi (bismuth) -Sr (strontium) is used.
Although -ca (calcium) -Cu (copper) -O (oxygen) thin film or the like is typical, 2 ^1/2 (√ these the lattice constants
2) times 5.4A °, ITO lattice constant 10.12A
Approximately 1/2 of the value, that is, 5.1 A °, is approached, and I
It can be said that when the TO film is rotated by 45 ° and formed on these oxide superconductor layers, the matching of the crystal structures of both is excellent. Moreover, this ITO is usually formed on a certain underlying substrate, but at this time, the substrate temperature is set to 300 ° C. to 5 ° C.
A suitable temperature within the range of about 00 ° C. provides good film quality I
A TO thin film can be formed. In addition, after providing the oxide superconductor layer as the third region on the substrate, when forming the ITO film as the first region on the oxide superconductor layer, the heating temperature of the first region is 300 ° C. to 500 ° C. Since it suffices to set the temperature within the range of ° C, there is no possibility that Si will be oxidized during this heating or that oxygen constituting the oxide superconductor will interdiffuse with Si. Furthermore, as an oxide superconductor layer,
By appropriately selecting a material having a lattice constant close to that of ITO, it is possible to form a high quality ITO film having excellent compatibility with the oxide superconductor layer. As a result, the superconducting transistor of the present invention can obtain a superconducting transistor having excellent electric characteristics by a simple process without requiring complicated interface treatment or surface treatment.

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the drawings only schematically show the shapes, dimensions, and arrangement relationships of the respective constituent components to the extent that the present invention can be understood. 1, 2, and 3 are all sectional views showing an embodiment of a superconducting transistor of the present invention.

FIG. 4 is a diagram showing a film forming apparatus used for manufacturing the superconducting transistor of the present invention.

FIG. 5 is a diagram for explaining the laminated state of the oxide superconducting thin films.

<Example 1> First, the film forming process of Example 1 will be outlined with reference to FIG.
The film forming method by the BE method will be described in detail. As the substrate for forming the film in the second region, quartz glass 10 which is easy to obtain at low cost is used. In this embodiment, an emitter region is formed thereon as the second region 16. For that purpose, ITO
(Molecular beam epitaxy) method, for example, 10,000 A °
accumulate. As a raw material of ITO, In ₂ O ₃ or SnO ₂
May be evaporated using a Knudsen cell, but metal In or Sn may be evaporated using a Knudsen cell and an oxide thin film formed with an oxidizing gas such as ozone. In this embodiment, a metal material is used by the latter method and a substrate temperature of 30
0 to 500 ° C., growth rate 0.1 to 10 A ° / sec. The film is formed while adjusting the growth rate within the range. The surface state of the grown thin film is inspected by the reflection high energy electron diffraction method (RHEED).

When depositing the ITO thin film 16 on the quartz glass substrate 10, spots and ring patterns appear in the RHEED pattern at the initial stage of film formation. But this is 2,
When it deposits more than 000A °, it gradually changes to a streak pattern. This corresponds to the fact that the fine crystal grains are connected to each other and the surface becomes flat. Film Formation of Third Region (Oxide Superconducting Thin Film) In this embodiment, the third region 18 serves as a base region. I
After confirming that the TO thin film 16 had a streak pattern by RHEED, other portions were masked while leaving only a predetermined necessary portion, and Y-Ba of the oxide superconductor thin film for the third region was masked. The process moves to film formation of the Cu-O thin film 18.

Yttrium (Y), barium (Ba),
Using a Knudsen cell with copper (Cu) as an evaporation material, the substrate temperature is 550 ° C. and the growth rate is 0.1 to 0.5 A ° / s.
ec. In the range of, for example, 100A ° is grown. Deposition of First Region In this embodiment, the first region 20 is the collector region. The ITO thin film 14 for forming the collector region 20 is formed at a necessary position on the formed oxide superconductor thin film 18, for example, 1.0
It was laminated at 00 A °. Electrode formation After lamination, fine processing is performed by the ion sputtering method so that contact resistance is 1 on each of the collector, emitter, and base regions.
The electrodes 20, 22, and 24 are formed by using aluminum (Al) as a metal for wiring so as to have a resistance of 0 ^-6 Ωcm ^-2 or less. Interface state of (Y-Ba-Cu-O thin film) / (ITO thin film) Y-Ba- of the oxide superconducting thin films laminated in this way
The Cu-O thin film 18 is made of ITO in the first region and the second region.
Sandwich with thin films 14 and 16,
The interface is Ba oxide on the ITO thin film, and then C
Since elements having the same ionic valence as the superconducting oxide, such as u oxide and Y oxide, are stacked,
From the beginning of the hetero interface, the conditions for charge neutralization are satisfied for each layer. Therefore, even a hetero interface can be continuously formed, and as a result, a junction having a steep hetero interface in the order of one atom can be formed, and the device characteristics can be significantly improved. <Film Forming Method of Y-Ba-Cu-O and ITO by MBE Method> As shown in FIG. 4, each of the required Knudsen cells (represented by 30) is made of Ba, Y and Cu metals. Are stored separately. The substrate 10 described above is placed on the substrate heating holder 34 provided in the film forming chamber 32, and the inside of the film forming chamber 32 is evacuated to an appropriate vacuum degree by the exhaust pump 36. The knudsen cell 30 is heated to melt the metal inside, and
The shutter of is opened and the metal elements are sequentially evaporated. For example, first, the element Y is evaporated to deposit one atomic layer of Y on the surface of the substrate. Next, close the shutter of this Y cell,
The shutter of the Knudsen cell 30 of the metal element Ba is opened to evaporate Ba, and one atomic layer of Ba atomic layer is deposited on the Y atomic layer. Next, the shutter of this Ba cell is closed, the Knudsen cell 30 of the metallic element Cu is opened, and C
u is evaporated, and at the same time, ozone (O ₃ ) is supplied from the oxidizing gas supply source 38 to deposit a CuO layer on this Ba atomic layer.

By this operation, one Y-Ba-Cu-O thin film 18a is formed as shown in FIG. By repeating the above-mentioned operation, a plurality of Y-Ba-Cu-O thin films, for example, 18b, 18c, ..., 18n are laminated to have a desired thickness as a whole, for example, an oxide superconductor 18 having a thickness of about 100 A °. Can be formed. In addition,
As is well known, the control of the deposition of this one atomic layer is performed by controlling the evaporation supply amount of each element. This control may be performed by controlling the opening / closing time of the shutter with a computer. Also,
The state of deposition may be investigated during film formation by a reflection high-energy electron diffraction (RHEED) method which is usually used. The electron gun 40 and the screen 42 are parts that constitute the RHEED device.

Also, the ITO layer 14 in the first and second regions is formed.
Similarly, when depositing films 16 and 16, In ₂ O ₃ and Sn are added to the Knudsen cell 30 of the above-described film deposition apparatus.
O ₂ may be separately put in, and each may be evaporated individually to form an oxide thin film, or metal In or Sn
It is also possible to deposit these while individually evaporating them, and to deposit them while oxidizing them with an oxidizing gas such as ozone to form an oxide thin film.

<Embodiment 2> FIG. 2 is a sectional view of Embodiment 2 in which a large area and cost-effective silicon is used as a substrate. The method of depositing the ITO and the oxide superconducting thin film is exactly the same as in Example 1.

The reference numerals of common points are the same as those in FIG.

<Embodiment 3> FIG. 3 shows a substrate 10 containing niobium (Nb) -doped strontium titanate (SrT).
This is the case when iO ₃ ) is used. SrT doped with Nb
The iO ₃ substrate 10 is an n-type semiconductor and has a lattice constant of 2
^1/2 times is 5.4 A °, which has the same function as ITO, so that Y-Ba-Cu-O and Bi- of oxide superconducting thin film
It is suitable for directly laminating Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O thereon. Here, Y-Ba-Cu-O was adopted as the oxide superconducting thin film.

The method for forming the oxide superconducting thin film on the SrTiO ₃ substrate and the method for forming the ITO thin film thereon are the same as in the first embodiment.

The method of forming the electrodes is the same for the collector region and the base region, but the emitter electrode is Sr.
It is attached directly to the bottom surface of the TiO ₃ substrate.

As is apparent from the above description, according to the structure of the superconducting transistor of the present invention, the third region of the oxide superconductor is formed between the first region and the second region formed of ITO. The structure has a region. Also,
This ITO can be formed at a temperature lower than 500 ° C., and a film having excellent compatibility with the oxide superconductor material can be obtained.

Therefore, since the superconducting transistor of the present invention does not require complicated surface treatment and interface treatment as in the conventional manufacturing, the manufacturing process is simplified and the manufacturing yield is improved. Also, during the manufacturing process,
Even if heat treatment is performed after the formation of the oxide superconductor layer,
Since there is no risk of surface oxidation of the Si region of the substrate and interdiffusion of Si and oxygen, the electric characteristics of the superconducting transistor formed by using these regions are superior to the conventional ones.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a first embodiment according to the present invention.

FIG. 2 is a sectional view for explaining the second embodiment according to the present invention.

FIG. 3 is a sectional view for explaining a third embodiment according to the present invention.

FIG. 4 is a diagram for explaining a film forming apparatus of the present invention.

FIG. 5 is a diagram for explaining a laminated state of oxide superconducting thin films in the present invention.

[Explanation of symbols]

10: Substrate (eg, quartz glass, silicon, SrTi
O ₃ etc. 14: First region (collector region, ITO layer) 16: Second region (emitter region, ITO layer) 18: Third region (base region, oxide superconductor layer (for example, Y-Ba-Cu) -O layer)) 18a, 18b, ... 18n: oxide superconductor thin film (for example, Y-Ba-Cu-O thin film) 20: collector electrode 22: emitter electrode 24: base electrode

Claims (4)

[Claims] 1. At least a first area and a second area, and a third area provided between the first area and the second area in direct contact with at least the first area.
A superconducting transistor characterized in that both or one of the region and the second region is formed of an ITO (tin-doped indium oxide) layer, and the third region is formed of an oxide superconductor layer. 2. The superconducting transistor according to claim 1, wherein the oxide superconductor layer is composed of one or more oxide superconductor thin films. 3. The superconducting transistor according to claim 1, wherein the oxide superconductor thin film is Y (yttrium).
A superconducting transistor comprising a -Ba (barium) -Cu (copper) -O (oxygen) thin film. 4. The superconducting transistor according to claim 1, wherein the first region is a collector region, the second region is an emitter region, and the third region is a base region.