JPH0634420B2 - Method for manufacturing oxide superconducting transistor device - Google Patents

Description

Description: TECHNICAL FIELD 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 oxide superconducting devices that can operate at liquid nitrogen temperatures. The present invention relates to a method for manufacturing a transistor device.

[Prior Art] Y-Ba-Cu oxide or Bi-Sr-Ca-Cu
Oxide-based superconducting materials such as oxides have a critical temperature of 90 K or higher and exhibit complete superconductivity at liquid nitrogen temperature. In order to apply these superconducting materials such as Y-Ba-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.

Y-Ba-Cu oxide or Bi-Sr-Ca-Cu
As a superconducting transistor using an oxide, or as a superconducting three-terminal element, a so-called current injection switching element having a current injection electrode made of an Al thin film for a superconducting weak bond made of a Y-Ba-Cu oxide thin film was manufactured. ing. This example is described in the 49th Applied Physics Society Academic Lecture Proceedings, 1st Volume, 151 pages (1988).

[Problems to be Solved by the Invention] The above 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. When the input / output signals are not separated, there is a problem that the input signal current flows through the output line as it is even if the element does not switch. 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 the 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.

Therefore, an object of the present invention is to provide a method for producing a superconducting switching element, particularly a superconducting three-terminal element using an oxide superconducting material having a high critical temperature, which causes a switching operation by a voltage signal.

[Means for Solving the Problems]

In order to achieve the above object, in the present invention, Y-Ba is used.
A field effect superconducting transistor having an oxide superconducting material such as —Cu oxide, Bi—Sr—Ca—Cu oxide, or Tl—Ba—Ca—Cu oxide as source and drain electrodes is formed. In this field effect superconducting transistor, since a part of the elements forming the gate electrode material is included in the oxide superconducting material, a part of the oxide superconducting material is electrically characterized as an insulator and semiconductor. The insulator-characterized portion and the semiconductor-characterized portion are used as an insulating film and a semiconductor layer of a superconducting transistor, respectively. More specifically, a semiconductor such as Si or Ge, or a metal thin wire such as Cu, Ag, or Pd is formed on the above oxide superconducting thin film to serve as a gate electrode. By performing diffusion heat treatment for forming a gate electrode, the components of the gate electrode are made to penetrate into the oxide superconducting thin film. The diffusion reaction proceeds to the back surface of the oxide superconducting thin film.

The interface between the gate electrode film and the oxide superconducting electrode is insulated to form a gate insulating film. Further, the semiconductor property is maintained in the lower part of the gate electrode film from the insulating state part to the conducting part of the oxide superconducting thin film by a diffusion reaction. In this step, the region having the superconducting property of the oxide superconducting thin film is divided into two regions via the thin linear portion having the semiconductor property. The oxide superconducting thin film portions divided into these two regions are used as a source electrode and a drain electrode, respectively.

[Operation] The means described above enables the above purpose, that is, the operation of the superconducting transistor by the field effect using the oxide superconducting material, for the following reasons.

When manufacturing a field effect transistor using an oxide superconducting material, it is possible to use a different material because of the short coherence length of the oxide superconducting material and the large reflection coefficient of the superconducting conductor at the interface. It is difficult to obtain a superconducting weak coupling element having a long distance, that is, a long distance between superconducting electrodes. However, the structure of a conventional field effect MOS transistor made of a semiconductor material such as Si has a complicated structure including a source and drain electrode, an ohmic conductive layer in each semiconductor, a gate portion, a gate insulating film and a gate electrode. There is. When such a MOS transistor type structure is used in a field effect transistor using an oxide superconducting material, the distance between the superconducting source electrode and the drain electrode is restricted to 0.1.
It is extremely difficult to reduce the length to less than μm in terms of pattern forming technology and processing technology. However, in the present invention, the structure and the manufacturing method thereof are very simple, and the distance between the superconducting source and drain electrodes can be shortened corresponding to the reduction of the width of the gate electrode film. That is, if the pattern forming technology has a limit of 0.1 μm, an electrode interval of 0.1 μm can be obtained.

Further, as a characteristic action in the present invention, since the superconducting thin film and the semiconductor thin film forming the source and drain electrodes are formed of the same material, a Schottky barrier is formed at the interface between the superconducting electrode and the semiconductor, and the transmittance of the superconducting element is increased. Can be reduced.

As described above, the structure of the transistor device according to the present invention overcomes the problem peculiar to the oxide superconducting material and enables the function of the field effect superconducting transistor of applying the signal voltage by the gate electrode to perform the switching operation. It is something that can be done.

〔Example〕

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

Example 1 The Y-Ba-Cu oxide thin film 2 was formed by the high frequency magnetron sputtering method using the (110) plane oriented single crystal of SrTiO ₃ as the substrate 1. Sputtering was performed by applying a high-frequency power of 100 W using a disk-shaped sintered body of Y-Ba-Cu oxide and having a composition ratio of 1: 2: 4. O ₂ as the discharge gas
Ar + O ₂ mixed gas with a concentration of 50% was used, and the gas pressure was 5
It was mTorr. The substrate temperature during film formation was 700 ° C. According to the above method, the stoichiometric composition of Y-Ba-
Cu oxide thin film 2 was obtained. Y-Ba-Cu oxide thin film 2
Shows an orientation in which the c-axis of the perovskite type crystal is parallel to the substrate surface. The film thickness was 0.1 μm. Furthermore, the superconducting critical temperature is 80K to 85K.

Next, a pattern including a gate for the Y-Ba-Cu oxide thin film 2 and corresponding to the source and drain electrodes is formed by a chemical etching method. Further, an organic resist pattern having a groove having a width of 0.1 μm corresponding to the gate is formed by an electron beam drawing method. A Pt film is formed on this, and then the organic resist film is removed to obtain a Pt thin wire 3 having a width of 0.1 μm.

In this state, in an atmosphere of oxygen at 1 atm,
Heat treatment in the temperature range of 700-900 ℃ from 10min to 2
The thermal diffusion of the Pt layer proceeds in the time range of hr.
Thereby, the metal conductive layer, the barrier layer 4 and the semiconductor layer 5 are obtained in the portion where the Pt thin wire is formed. The metal conductive layer functions as a gate electrode and the barrier layer functions as a gate insulating film.

When Pt is diffused into the Y-Ba-Cu oxide, the relationship between the Pt concentration and the characteristics is as follows. That is, the substitution ratio of Pt with respect to Cu is 10%,
The decrease rate of the critical temperature is about 50%. Substitution ratio 20-
When it is 30%, it is not a superconductor. Therefore, the substitution ratio of Pt to Cu in the semiconductor portion is 30 to 50.
%. Further, when such a Pt diffusion reaction is carried out, an oxide containing Pt and Ba is formed at the interface between the Pt film and the semiconductor layer to form an insulating layer. Pt substitution ratio 30
% Or more is obtained by the condition that the heat treatment temperature after forming the Pt film is 850 ° C. or higher and the heat treatment time is 1 hour or longer.

An oxide superconducting transistor device is obtained by the above steps. This oxide superconducting transistor device can be used as a so-called field effect transistor which performs a switching operation by a voltage signal. That is, as shown in FIG. 2, in the oxide superconducting transistor device, the superconducting current does not flow in the zero voltage state in the state 6 in which the voltage signal is not applied to the gate, but in the case 7 in which the negative voltage is applied, A superconducting current flows and a switching operation is performed. The reason is as follows.
By applying a negative voltage to the gate, the 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.

Example 2 The oxide superconducting transistor as shown in FIG. 3 which can be manufactured with the same material structure is as follows. S
Using the (110) plane oriented single crystal of rTiO ₃ as the substrate 1,
An organic resist pattern having a groove having a width of 0.1 μm corresponding to the gate is formed by an electron beam drawing method. A Pt film 3 is also formed on this, and then the organic resist film is removed to obtain a Pt thin wire 3 having a width of 0.1 μm. P
The thickness of the t film is 0.05 μm. Y-Ba-
The Cu oxide thin film 2 is formed by the same method and conditions as in Example 1, and processed for forming source and drain electrode patterns. The pattern formation of the Y-Ba-Cu oxide thin film 2 is performed by chemical etching using dilute nitric acid. Next, in an atmosphere of 1 atm of oxygen, 700 to 900 ° C.
By performing the heat treatment in the temperature range of 10 min to 2 hr, the thermal diffusion of the Pt layer proceeds. Thereby, the barrier layer 4 and the semiconductor layer 5 are obtained at the portion where the Pt thin wire 3 is formed. The metal conductive layer 3 serves as a gate electrode, and the barrier layer 4 serves as a gate insulating film.

The material structure of the semiconductor region is as described in the first embodiment.

An oxide superconducting transistor device is obtained by the above steps. This oxide superconducting transistor device is the first embodiment.
As in the case of the above, it has a function of switching between the superconducting state and the voltage state depending on the presence or absence of an applied signal for the gate voltage.

The superconducting switching characteristics can be obtained by adopting the same structure and manufacturing method when other oxide superconducting materials such as Bi-Sr-Ca-Cu oxide are used as the superconducting electrode material. In addition to Pt, Si, Ge, Ir, R are used as the gate electrode material of the oxide superconducting transistor.
An oxide superconducting transistor device having similar characteristics can be obtained when other metal material such as h, Pd, Ag, Ti, Zr, Hf or a semiconductor material is used. Especially Ir, Rh, Pd, Ag, Ti, Zr, Hf, etc. are Pr
The semiconductor layer can be obtained by the substitution with almost the same concentration as in the above case. The diffusion heat treatment conditions are almost the same. On the other hand, Si, Ge, etc. have a lower heat treatment temperature, that is, 8
The superconducting property can be removed by heat treatment in oxygen at 00 ° C. for 1 hr or more.

〔The invention's effect〕

As described above, the oxide superconducting transistor device according to the present invention has the following effects.

(1) Since the switching signal applied to the gate electrode is a voltage signal, the input / output signals can be sufficiently separated. Therefore, it can be easily applied to arithmetic circuits and the like.

(2) Since the element structure is simple, pattern alignment with submicron resolution is not required. The pattern formation for forming the gate electrode portion can be completed once.

(3) Since the structure of the gate electrode portion is simple, the gate length can be reduced to the limit of the pattern formation dimension. This makes it possible to operate the oxide superconducting transistor at the liquid nitrogen temperature by setting the gate length to 100 nm or less and making it equal to the coherence length of the superconducting conductor.

[Brief description of drawings]

1 is a sectional view of an oxide superconducting transistor device according to a first embodiment of the present invention, FIG. 2 is a voltage-current characteristic diagram of an oxide superconducting transistor of the present invention, and FIG. 3 is an oxidation according to a second embodiment of the present invention. It is a sectional view of a superconducting transistor device. Explanation of symbols 1 ... SrTiO ₃ substrate, 2 ... Y-Ba-Cu oxide superconducting thin film, 3 ... Pt thin film, 4 ... barrier layer, 5 ... semiconductor layer, 6 ... when gate signal voltage is zero Voltage-current characteristics,
7: Voltage-current characteristics when gate signal voltage is applied.

Claims (1)

[Claims] 1. A laminated structure of a semiconductor layer and a barrier layer is formed by forming a superconducting thin film on a substrate and electrically characterizing a part of the superconducting thin film as a semiconductor and an insulator. Forming a source electrode and a drain electrode by dividing the superconducting thin film into two, and forming a gate electrode on the barrier layer.