JP2680961B2 - Superconducting field effect device and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting field effect element and a method for manufacturing the same. More specifically, the present invention relates to a superconducting field effect device having a superconducting channel, a superconducting source region, and a superconducting drain region which are integrally formed of an oxide superconducting thin film, and having excellent characteristics, and a method for producing the same.

[0002]

2. Description of the Related Art It is considered that a device utilizing the superconductivity phenomenon has a higher speed, consumes less power, and can achieve a dramatic improvement in performance as compared with a conventional semiconductor device. In particular, by using an oxide superconductor, which has been studied in recent years, it is possible to manufacture a superconducting element that operates at a relatively high temperature. As a superconducting element, a Josephson element is well known, but since the Josephson element is a two-terminal element, the circuit becomes complicated when trying to configure a logic circuit. Therefore, a three-terminal superconducting element is practically advantageous.

[0003] Three-terminal superconducting elements include those utilizing a superconducting proximity effect in which a superconducting current flows through a semiconductor between superconducting regions arranged close to each other, and those controlling a superconducting current flowing in a superconducting channel by a gate electrode. Representative.
Both elements can separate input and output, are voltage-controlled elements, and have a common point in that they have a signal amplifying action. However, in order to obtain the superconducting proximity effect, the superconducting region must be arranged at a distance within several times the coherence length of the superconductor (several nm in the case of an oxide superconductor). Therefore, very precise processing is required. In contrast, a superconducting device channel is superconducting channel, the current density is large, even the manufacturing superconducting territory
There is no need for fine processing of arranging the regions close to each other.

FIG. 2 is a schematic view showing an example of a superconducting field effect element having a superconducting channel. 2 includes a superconducting channel 10 made of an oxide superconductor disposed on a substrate 5, a superconducting source region 2 and a superconducting drain region 3 disposed near both ends of the superconducting channel 10, respectively. A gate electrode 4 disposed on the channel 10 with a gate insulating layer 7 interposed therebetween. A source electrode 12 and a drain electrode 13 are formed on the superconducting source region 2 and the superconducting drain region 3, respectively. This superconducting field effect element has a source electrode
12 and a superconducting channel 10 between the superconducting source region 2 and the superconducting drain electrode 3.
Is controlled by the voltage applied to the gate electrode 4.

In the above superconducting field effect element, the current flowing through superconducting channel 10 is controlled by the voltage applied to gate electrode 4. Therefore, the thickness of the gate portion of the superconducting channel 10 must be about 5 nm, and the thickness of the gate insulating layer 7 must be 10 to 15 nm. on the other hand,
This ultrathin superconducting channel must be composed of an oxide superconducting thin film having good crystallinity and excellent characteristics.

In the above superconducting field effect element,
The superconducting current in the superconducting channel flows in the horizontal direction, and the superconducting current in the superconducting source region and the superconducting drain region flows in the vertical direction. The oxide superconductor has a large critical current density in the direction perpendicular to the c-axis of the crystal. Therefore, it is preferable that the superconducting channel is formed of a c-axis oriented oxide superconducting thin film capable of passing a large current in the horizontal direction, and that the superconducting source region and the superconducting drain region pass a large current in the vertical direction. It is preferable to be composed of an a-axis oriented oxide superconducting thin film.

Therefore, conventionally, after the oxide superconducting thin film having either the a-axis orientation or the c-axis orientation is first formed, an unnecessary portion is etched and the other oxide superconducting thin film is formed again. It was

[0008]

However, in the above conventional superconducting field effect device, the direction of the c-axis of the a-axis oriented oxide superconducting thin film has not been particularly controlled. Therefore, the characteristics of the device may vary greatly depending on the c-axis direction of the a-axis oriented oxide superconducting thin film. This will be described with reference to FIG.

FIG. 3 is a partially enlarged view showing the vicinity of the superconducting source region 2 and the superconducting channel 10 of the superconducting field effect device shown in FIG. 2 in an enlarged manner. In the superconducting field effect device of FIG. 3, it is considered that the superconducting current flows from the source electrode 12 to the middle of the superconducting source region 2 in a substantially vertical direction. However, below the superconducting source region 2, the superconducting current bends toward the superconducting channel 10, and the superconducting current flowing horizontally in the superconducting channel 10 reaches the superconducting drain region 3.

When the superconducting source region 2 is composed of an a-axis oriented oxide superconducting thin film, there is no problem with the superconducting current flowing in the vertical direction. However, when the c-axis of the a-axis oriented oxide superconducting thin film forming the superconducting source region 2 is parallel to the arrow X in FIG. 3, the superconducting current flowing from the superconducting source region 2 into the superconducting channel 10 is The critical current density will flow in the smaller direction, and the size of the superconducting current will be limited in this part. That is, the superconducting source region 2 and the superconducting drain region 3 are preferably composed of an a-axis oriented oxide superconducting thin film in which the c-axis is oriented in the direction parallel to the arrow Y in FIG.

Therefore, an object of the present invention is to provide a superconducting field effect element and a method for manufacturing the same, which solves the problems of the prior art.

[0012]

According to the present invention, a substrate, a superconducting source region and a superconducting drain region formed of an oxide superconductor formed on the substrate, a superconducting source region on the substrate, and a superconducting source region A superconducting channel arranged between the superconducting drain regions and formed of an oxide superconductor, and a gate insulating layer disposed on the superconducting channel via a gate insulating layer, and a gate voltage for controlling a current flowing through the superconducting channel is applied. In a superconducting field effect device including a gate electrode composed of a normal conductor, the superconducting channel has a c-axis orientation, and the superconducting source region and the superconducting drain region have an a-axis with respect to the substrate deposition surface. It is composed of an oxide superconducting thin film in which the c-axis is oriented vertically and perpendicular to the direction of the superconducting current flowing in the superconducting channel. Super-FET, wherein the door is provided.

Further, in the present invention, as a method for producing the superconducting field effect element of the present invention, a substrate formed of a material capable of controlling the c-axis direction of an a-axis oriented oxide superconducting thin film is used. And a step of forming a layer of a material in which a c-axis oriented oxide superconducting thin film grows in a portion to be the superconducting channel to form an oxide superconducting thin film.

[0014]

The superconducting field effect device according to the present invention is an integrated oxide superconducting device having a c-axis orientation in the middle, a-axis orientation at both ends, and a c-axis orientation perpendicular to the direction of superconducting current in a superconducting channel. The thin film constitutes a superconducting channel, a superconducting source region and a superconducting drain region. Therefore, there is no resistance component or unnecessary Josephson junction between the superconducting channel and the superconducting source region and the superconducting drain region. Moreover, since the superconducting current flows only in the direction in which the critical current density of the oxide superconductor is large, the current capacity is large.

In the method of the present invention, a material that can control the direction of the c-axis of an a-axis oriented oxide superconducting thin film is used for the substrate,
A layer of a material on which a c-axis oriented oxide superconducting thin film grows is formed on a portion of the substrate to be a superconducting channel. After that, the oxide superconducting thin film is formed under the condition that the c-axis oriented oxide superconducting thin film grows in the portion to be the superconducting channel.
In the other part, an a-axis oriented oxide superconducting thin film in which the c-axis is oriented perpendicular to the superconducting channel grows. Therefore, according to the method of the present invention, it is possible to manufacture a superconducting element in which there is no resistance component or unnecessary Josephson junction between the superconducting channel and the superconducting source region and the superconducting drain region.

In the method of the present invention, the substrate is made of, for example, SrTiO 3.
It is preferable to use a substrate offset by 5 ° of ₃ (110). What is a SrTiO ₃ (110) 5 ° offset substrate?
The SrTiO ₃ single crystal substrate has a film-forming surface inclined by 5 ° with respect to the (110) surface. Further, it is preferable to use MgO for the layer formed in the portion to be the superconducting channel. When a film is formed on MgO under the condition that a c-axis oriented oxide superconducting thin film grows, on an SrTiO ₃ (110) 5 ° offset substrate, an a-axis oriented oxide superconducting substance in which the c-axis is oriented in a fixed direction is formed. The thin film grows. In addition, SrTiO ₃ is
It does not adversely affect the oxide superconductor more than MgO.

Although any oxide superconductor can be used for the superconducting field effect element of the present invention, the Y ₁ Ba ₂ Cu ₃ O _{7 -X-} based oxide superconductor is stable and has high crystallinity. It is preferable because a good thin film can be obtained. In addition, Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x -based oxide superconductor is particularly preferable because its superconducting critical temperature Tc is high.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the following disclosure is merely an example of the present invention, and does not limit the technical scope of the present invention.

[0019]

EXAMPLES The superconducting field effect element of the present invention was manufactured by the method of the present invention. The process will be described with reference to FIG. First, SrTiO ₃ (110) 5 as shown in FIG.
° The thickness on the offset substrate 5 is 50-100 as shown in Fig. 1 (b).
An MgO film 20 of nm is formed. As a film forming method, various methods such as various sputtering methods and CVD methods can be used.

Next, the MgO film 20 is removed except for the central part.
It is removed by reactive ion etching using a chlorine-based etching gas, Ar ion milling, focused ion beam etching, etc., and underneath the portion that will become the superconducting channel of the superconducting field effect element manufactured as shown in Fig. 1 (c). (100)
The strip-shaped MgO film 21 in the direction is left. The substrate 5 is exposed at the portion where the MgO film 20 is removed. In order to clean the exposed part of the substrate 5, the substrate 5 is pressed at a pressure of 1 × 10 ⁻¹⁰ Tor.
Heat to 350-400 ° C in an ultrahigh vacuum of r or less and hold for 5 minutes. Thereafter, as shown in FIG. 1D, a Y ₁ Ba ₂ Cu ₃ O _{7 -X} oxide superconducting thin film having a thickness of about 300 nm is formed on the substrate 5 by off-axis sputtering. The main film forming conditions are shown below. Substrate temperature 700 ℃ Sputtering gas Ar 90% O ₂ 10% Pressure 10 Pa Film thickness 300nm

The portion of the Y ₁ Ba ₂ Cu ₃ O _7-X oxide superconducting thin film on the MgO film 21 becomes a superconducting channel 10 composed of a c-axis oriented oxide superconducting thin film.
On both sides thereof are a superconducting source region 2 and a superconducting drain region 3 which are composed of an a-axis oriented oxide superconducting thin film. Further, the c-axis of the oxide superconducting thin film forming the superconducting source region 2 and the superconducting drain region 3 is substantially perpendicular to the paper surface. Furthermore, superconducting channel 10
The crystal planes of the superconducting source region 2 and the superconducting drain region 3 are continuous.

Next, Au or the like is vapor-deposited on the superconducting source region 2 and the superconducting drain region 3, as shown in FIG. 1 (e).
A source electrode 12 and a drain electrode 13 are formed respectively. Finally, as shown in FIG. 1 (f), a portion under the gate region is recess-etched if necessary, and then the gate insulating layer 7 is formed on the superconducting channel 10 with MgO, silicon nitride or the like. The gate electrode 4 is also formed on Au by 7 to complete the superconducting field effect device of the present invention.

As described above, in the superconducting field effect element of the present invention manufactured by the method of the present invention, the superconducting channel 10 is c-axis oriented, and the superconducting source region 2 and the superconducting drain region 3 are: It is composed of an integral oxide superconducting thin film in which the a-axis is oriented and the c-axis is oriented perpendicular to the direction of the superconducting current in the superconducting channel. Therefore, there is no resistance component or unnecessary Josephson junction between the superconducting channel 10 and the superconducting source region 2 and the superconducting drain region 3. In addition, the superconducting current flowing from the superconducting source region 2 and the superconducting drain region 3 into and out of the superconducting channel 10 is effectively narrowed down to the superconducting channel, and excellent current-voltage characteristics are exhibited.

[0024]

As described above, according to the present invention,
A superconducting field effect device having a novel structure and a method for manufacturing the same are provided. The superconducting field effect element of the present invention produced by the method of the present invention has no resistance component or unnecessary Josephson junctions between the superconducting channel and the superconducting source region and the superconducting drain region. It exhibits better characteristics than the effect element.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a step of producing a superconducting field effect element of the present invention by a method of the present invention.

FIG. 2 is a diagram illustrating a configuration of a superconducting field effect element.

FIG. 3 is a diagram illustrating a problem of a conventional superconducting field effect device.

[Explanation of symbols]

 2 superconducting source region 3 superconducting drain region 4 gate electrode 5 substrate 7 gate insulating layer 10 superconducting channel

Claims (2)

(57) [Claims] 1. A substrate, a superconducting source region and a superconducting drain region formed of an oxide superconductor formed on the substrate, and a substrate disposed between the superconducting source region and the superconducting drain region, and being oxidized. A superconducting channel composed of a superconducting material and a normal conductor arranged on the superconducting channel via a gate insulating layer and to which a gate voltage is applied to control a current flowing through the superconducting channel. In a superconducting field effect device including an electrode, the superconducting channel is c-axis oriented, and the superconducting source region and the superconducting drain region flow in the superconducting channel with the a-axis perpendicular to the substrate film formation surface. Superconducting field effect type characterized by being composed of an oxide superconducting thin film whose c-axis is oriented perpendicular to the direction of superconducting current. element. 2. The method for producing a superconducting field effect element according to claim 1, wherein a substrate made of a material capable of controlling the c-axis direction of an a-axis oriented oxide superconducting thin film is used.
A method comprising: forming a layer of a material on which a c-axis oriented oxide superconducting thin film grows in a portion to be the superconducting channel to form an oxide superconducting thin film.