JPH07105533B2 - Superconducting 3-terminal element - Google Patents

Description

The present invention relates to the field of superconducting electronics such as superconducting switching devices that perform switching operations at high speed and low power consumption, and more particularly to a superconducting three-terminal device capable of operating at liquid nitrogen temperature. It is related to the element.

[Conventional technology]

Oxide-based superconducting materials such as Y-Ba-Cu oxides and Bi-Sr-Ca-Cu oxides have a critical temperature of 90K or higher and exhibit complete superconductivity at liquid nitrogen temperature. These Y-Ba
-In order to apply superconducting materials such as Cu oxide to electronics, especially in the field of switching devices, it is necessary to obtain a superconducting transistor which is a basic superconducting active element.

As a superconducting transistor or a superconducting three-terminal device using Y-Ba-Cu oxide or Bi-Sr-Ca-Cu oxide, Y-
So-called current-injection switching devices having a current-injection electrode made of an Al thin film for a superconducting weak bond made of a Ba-Cu oxide thin film have been manufactured. An example of this is described in Proceedings of the 49th Japan Society of Applied Physics Technical Lecture, Volume 1, 151 (1988).

On the other hand, as a superconducting transistor using the field effect, a liquid
Although it uses an Nb-based superconducting material that requires He temperature operation, a three-terminal device using the exuding effect of a superconducting conductor and the electric field effect of GaAs or Si has been obtained. This example is described in Physical Review Letters, Vol. 54, p. 2449, 1985 (Physical Review Letters, Vol. 54, pp. 2449, 1985).

[Problems to be Solved by the Invention]

The above-mentioned first conventional technique controls a superconducting current by adding a third electrode to a current injection type switching element. The switching signal is a current. When the switching signal type is current, it is necessary to separate the input signal current and the output signal current. Even if the input / output signals are not separated, or the element is not switched,
There is a problem that the input signal current flows through the output line as it is. This causes a malfunction in the switching circuit.

As a function of the switching element, it is necessary to perform a switching operation by injecting a switching signal current and to have an input / output current separation action of the element. It is very difficult to impart such a function to a current injection type switching element, and even if such a function is provided, the structure of the element becomes extremely complicated. Therefore, in order to easily achieve the separation of the input / output signals in the switching element, it is necessary to find the input signal other than the current. The easiest method to handle the element is to use a voltage signal like a semiconductor transistor.

A type of element that performs switching operation by a voltage signal, and the element structure that has been conventionally obtained as a field effect superconducting transistor has a source and drain arranged on one side of a semiconductor substrate such as Si or GaAs with a certain gap. To do. The superconducting current flows from the source through the semiconductor substrate to the drain. In order to control this superconducting current, a gate electrode is arranged on the semiconductor in the gap between the source and the drain directly or through an insulating film.

By the way, the superconducting coherence length of Y-Ba-Cu oxide or Bi-Sr-Ca-Cu oxide is a very short value of about 1 nm. Correspondingly, it is necessary to keep the gap between the source and drain at a minute size of at most several tens nm. It is extremely difficult to perform processing of such minute dimensions on an oxide-based high critical temperature superconducting material. Furthermore, it is necessary to dispose a gate electrode on this minute gap. For these reasons, it is extremely difficult in terms of processing technology to obtain a superconducting transistor by applying the structure of a field effect transistor using a metal-based superconducting material to an oxide-based high critical temperature superconducting material.

Therefore, an object of the present invention is to provide an element structure applicable to a field effect superconducting transistor using an oxide-based high critical temperature superconducting material.

[Means for Solving the Problems]

In order to achieve the above object, in the present invention, Y-Ba-Cu
A field-effect superconducting transistor having an oxide or an oxide-based superconducting material such as Bi-Sr-Ca-Cu oxide as a source and drain electrodes is constructed as follows.

An oxide superconducting thin film such as Y-Ba-Cu oxide or Bi-Sr-Ca-Cu oxide is used as one of the source and drain electrodes, and a semiconductor thin film layer is formed on top of this, and further on this semiconductor thin film layer. On the other side of the source and drain electrodes consisting of oxide superconducting thin wire thin film such as Y-Ba-Cu oxide or Bi-St-Ca-Cu oxide, on which the gate insulating film is arranged, In addition, the gate electrode film is provided on the gate insulating film. A part or the whole of the gate electrode film is in contact with the semiconductor thin film, which is expected from the gap of the drain or source thin line on the semiconductor thin film, through the gate insulating film. It is also possible to adopt a structure in which a part of the gate electrode film rides on the source or drain electrode film via the gate insulating film.

[Action]

The means described above enables the above-mentioned purpose, that is, the operation of the superconducting transistor by the field effect using the oxide superconducting material of high critical temperature, for the following reasons.

When manufacturing a field effect transistor using an oxide superconducting material, it is difficult to obtain a superconducting weakly coupled device having a long distance between superconducting electrodes because the coherence length of the oxide superconducting material is short. That is, the distance between the source electrode and the drain electrode must be kept at 0.1 μm or less. If such a condition is not satisfied, the superconducting current cannot flow between the source and the drain due to the seepage effect.

Since the superconducting three-terminal element according to the present invention has a structure in which the source electrode, the semiconductor and the drain electrode are formed into a thin film and stacked in a laminated form, the distance between the source electrode and the drain electrode is set to an arbitrary value depending on the semiconductor film thickness. Can be kept at a value.

Furthermore, the alignment of the gate electrode film pattern is not necessary, and the advanced gate electrode film forming technique such as the self-alignment method as in the conventional superconducting transistor is not required.

As described above, the structure of the superconducting three-terminal element according to the present invention has a small distance between the source and the drain peculiar to the field effect type superconducting transistor, and a gate electrode film of 0.1 μm.
By overcoming the technical difficulties peculiar to the front and rear alignment and the like, the function of the field-effect superconducting transistor of applying a signal voltage by the gate electrode and performing a switching operation is made possible.

〔Example〕

 The present invention will be described based on Examples described below.

As shown in FIGS. 1 and 2, Y-Ba-Cu was prepared by using the (110) -oriented single crystal 1 of SrTiO ₃ as a substrate.
The oxide thin film 2 is formed by a high frequency magnetron sputtering method.

Sputtering is performed by applying a high-frequency power of 100 W using a disc-shaped sintered body of Y-Ba-Cu oxide and a composition ratio of 1: 2: 4. As for discharge, O ₂ concentration of 50%
Ar + O ₂ mixed gas is used, and the gas pressure is 5 mTorr. The substrate temperature during film formation is 700 ° C. The Y-Ba-Cu oxide thin film 2 serving as a source or a drain having a stoichiometric composition is obtained by the above method. The Y-Ba-Cu oxide thin film 2 has an orientation in which the c-axis of the perovskite type crystal is parallel to the substrate surface. The film thickness is 0.1 μm. Furthermore, the superconducting critical temperature is 8
It is in the range of 0K to 85K.

Next, Y in which a part of Cu in the Y-Ba-Cu oxide was replaced by Al
-The Ba-Cu (Al) oxide thin film 3 is formed in a thickness range of 5 to 100 nm. This Y-Ba-Cu (Al) oxide thin film 3 exhibits semiconductor-like properties. In order to perform epitaxial growth on the Y-Ba-Cu oxide thin film 2, the Y-Ba-Cu (Al) oxide thin film 3 was formed at a temperature of 700 ° C. and the Y-Ba-Cu (Al) oxide was sintered. Deposition is performed by a high frequency magnetron sputtering method using a body target. The semiconductor layer is formed by the above method.
On the Y-Ba-Cu oxide 2 and Y-Ba-Cu (Al) oxide 3 bilayer film, a pattern as a lower layer source (or drain) electrode is formed by a chemical etching method. Furthermore Y-Ba
-After forming the electrode pattern of the Cu oxide thin film, fluorine treatment is performed to insulate the end faces.

Furthermore, Y-Ba which becomes drain (or source) on this
-Cu oxide thin film 4 is formed. The film forming method and conditions are the same as those of the lower Y-Ba-Cu oxide thin film 2. Film thickness is 0.1μ
m. Next, a resist pattern having a thin line array with a width of 0.1 μm is formed on the upper Y-Ba-Cu oxide thin film 4, and the Y-Ba-Cu oxide thin film 4 is formed by reactive ion beam etching using Cl ₂ . Perform processing. The processing is performed until the portion of the Y-Ba-Cu oxide thin film 4 which is not covered with the resist film is completely removed.

Next, the MgO thin film 5 to be the gate insulating film is formed by the high frequency magnetron sputtering method. Further, an Au film 6 to be a gate electrode film is formed on this by an evaporation method. Further, etching is performed with an Ar ion beam to obtain a pattern as a gate electrode film.

Through the steps described above, a high critical temperature oxide superconducting three-terminal element including a source, a drain, a gate electrode film, a semiconductor layer and a gate insulating film is obtained. This oxide superconducting three-terminal element can be used as a so-called field effect transistor which performs a switching operation by a voltage signal. That is, in the oxide superconducting transistor device of the present invention, as shown in FIG. 3, the thermoelectric conductive current does not flow in the zero voltage state in the state 7 in which the voltage signal is not applied to the gate, but in the case 8 in which the negative voltage is applied to the gate. A superconducting current flows in the device, and a switching operation is performed.
The reason is as follows. By applying a negative voltage to the gate, the energy band of the semiconductor layer near the gate is bent upward, and the hole concentration is increased. This is because the distance over which the superconducting conductors that exude from the source and drain electrodes to the semiconductor layer spread increases depending on the hole concentration, that is, the concentration of the superconducting conductors, and the superconducting waves exuding from each electrode overlap each other.

Note that the same structure and manufacturing method are also applied to the case where other oxide superconducting materials such as Bi-Sr-Ca-Cu oxide are used as the superconducting electrode material, to produce a field-effect superconducting three-terminal element, Similar superconducting switching characteristics can be obtained. Further, as a semiconductor layer of the superconducting three-terminal element, in addition to a material having the above-mentioned semiconductor characteristics, a semiconductor such as GaAs or Si, a tetragonal perovskite-based superconducting material having a low oxygen concentration
Even if a material having semiconductor characteristics such as Y-Ba-Cu oxide is used, the characteristics as a field-effect superconducting three-terminal element can be obtained.

The superconducting three-terminal element having such characteristics can be applied to a wide range of fields such as digital circuits such as logic circuits and memory circuits, and analog circuits such as analog-digital converters.

〔The invention's effect〕

As described above, the present invention has the following effects regarding the field effect type superconducting three-terminal element using the oxide superconducting material.

(1) Since the source electrode, the semiconductor layer, and the drain electrode are laminated, the distance between the source electrode and the drain electrode can be changed with an accuracy of 1 nm and within a range of 100 nm or less. This makes it extremely easy to manufacture the superconducting three-terminal element and improves the reproducibility of the element characteristics.

(2) The formation of the gate electrode film does not require advanced technology such as self-alignment mint and is 0.1 μm
Fine adjustment is not necessary. It is extremely difficult to obtain the alignment accuracy of 0.1 μm by the optical exposure method. Therefore, it becomes easy to form the gate electrode film, especially the pattern. As a result, the production yield of the superconducting three-terminal element is significantly improved.

[Brief description of drawings]

FIG. 1 is a top view of a superconducting three-terminal element which is an embodiment of the present invention, FIG. 2 is a sectional view taken along the line II of FIG. 1, and FIG. 3 is a voltage-current of the superconducting three-terminal element of the present invention. It is a characteristic diagram. Explanation of symbols 1 …… SrTiO ₃ substrate, 2 …… Y-Ba-Cu oxide superconducting electrode film, 3 …… Y-Ba-Cu (Al) oxide semiconductor layer, 4 …… Y-Ba-
Cu oxide counter electrode film, 5 ... Gate insulating film, 6 ... Gate electrode film, 7 ... Voltage-current characteristics when gate signal voltage is zero, 8 ... Voltage-current characteristics when gate signal voltage is applied.

Claims (3)

[Claims] 1. A semiconductor layer is formed on a first superconducting electrode film of one of a source and a drain made of an oxide-based superconducting material containing a copper element, and a second layer of the other of the source and the drain is formed on the semiconductor layer. In a superconducting three-terminal structure in which a superconducting electrode film is formed, and a gate electrode is formed on the second superconducting electrode film via a gate insulating film, the semiconductor layer has the first and second semiconductor layers. A superconducting three-terminal device characterized by exhibiting semiconductor-like properties by substituting Al for part of the copper element of the elements constituting the superconducting electrode film. 2. The superconducting three-terminal device according to claim 1, wherein the oxide-based superconducting material is Y-Ba-Cu oxide or Bi-Sr-Ca-Cu oxide. 3. The superconducting three-terminal device according to claim 1, wherein at least a part of the gate insulating film is directly arranged on the semiconductor without overlapping the source or drain electrode film.