JPH0480976A - Substrate crystal material and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductive thin film substrate of excellent crystal free from twin crystal and cracks by a method wherein the oxide of lanthanide and aluminum is formed into a single crystal through their replacement by cerium, neodymium, or europium to a certain extent. CONSTITUTION:A substrate crystal material is formed of lanthanide.aluminum oxide LnAlO3 single crystal composed of lanthanide Ln and aluminum oxide. At this point, 0.01-100 atomic % of lanthanide in the single crystal is replaced by one, two, or all of cerium Ce, neodymium Nd, and europium Eu. A substrate crystal is manufactured using the crystal material 99.99% or above in purity. The temperature distribution on the level of the melt at the growth of a single crystal is so set as to keep temperature gradient/1cm in length in a range of 3O-40 deg.C.

Description

Detailed Description of the Invention A. Object of the Invention [Field of Industrial Application] The present invention relates to a substrate crystal material for an oxide superconducting thin film used for a substrate forming a superconducting thin film in an oxide superconducting device. and its manufacturing method.

[Conventional technology]

Recently, the development of high-temperature oxide superconducting materials has been progressing with the aim of putting them to practical use, and as one example, Josephson elements and superconducting transistors are being developed as high-speed memory elements. It is also expected to be used for wiring on mounting boards. The method for producing such an oxide superconductor is as follows:
There are sputtering methods, vapor deposition methods, CVD methods, etc., and all require high quality substrate materials. The substrate temperature during the formation of a thin film of oxide superconductor needs to be at a high temperature of 600°C or higher, so the substrate material has no reactivity with the oxide superconductor and is compatible below the thin film formation temperature. One that does not metastasize is desired.

It is known that the properties of oxide superconductors vary greatly depending on the crystal orientation, and it is necessary to form them on a substrate oriented in the (001) direction. For this purpose, at least a twin-free substrate is required. Furthermore, in order to form an oxide superconductor thin film with good orientation, a crystal substrate with a small value of lattice constant mismatch is required.

Conventional substrate materials include strontium titanium oxide (SrTi03), lanthanum aluminum oxide (LaAIO:+), lanthanum gallium oxide (LaGa03), neodymium gallium oxide (Nd
Oxide single crystals such as GaO3), magnesium oxide (MgO), and yttrium zirconium oxide (YSZ) have been used. However, LaAlO3, La
Ga03 and NdGaO3 have twinning and phase transition problems, MgO and YSZ have large and insufficient lattice constant mismatches, and 5rTi03 has a large dielectric constant, making it unsuitable for high-speed switching devices. There was no substrate crystal material that satisfied the conditions.

[Problem to be solved by the invention]

The present invention is based on the lanthanide (Ln) element [yttrium (
Y), lanthanum (La), samarium (S), praseodymium (Pr), gadolinium (Gd), dysprosium (Dy)] and LnAl, which is an aluminum oxide.
The lanthanide elements occupied by o are cerium (Ce),
or CeL substituted with 0.01 at% to 100 at% of neodymium (Nd) or europium (Eu)
nAIO3, or NdLnAIOa, or EuLnAI
The object of the present invention is to provide a twin-free oxide superconducting material composed of O:+ and a substrate crystal material forming a high-quality oxide superconductor thin film with little lattice constant mismatch.

B6 Structure of the Invention [Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides lanthanide-based aluminum oxides with cerium (Ce) ions, neodymium (Nd) ions, or europium (Eu) ions. ) ions doped with O, 01 at% or more to replace up to 100% of lanthanide elements (Ln is Y, La, Sm, Pr, Gd, Dy) single crystal.

That is, the present invention provides the following features: 1. Lanthanide (Ln)-based elements [Ln is yttrium (
A substrate made of a lanthanide aluminum oxide (LnAlO3) single crystal of Y), lanthanum (La), samarium (Sm), praseodymium (Pr), gadolinium (Gd), dysprosium (Dy)] and aluminum oxide. In the crystal material, the lanthanide elements in the single crystal are treated with one, two, or three of cerium (Ce), neodymium (Nd), or europium (Eu). % to 10
This is a substrate crystal material characterized in that it is formed with 0 at% substitution.

2. Lanthanide (Ln) elements [Ln is yttrium (
A single crystal of lanthanide aluminum oxide (LnAlO3) consisting of Y), lanthanum (La), samarium (Sm), praseodymium (Pr), gadolinium (Gd), dysprosium (Dy)] and aluminum oxide. , cerium (Ce), neodymium (Nd), or europium (Eu), or 0.01 at% to 100 at% of lanthanide elements.
In a method for manufacturing a doped substrate crystal material, the purity of the oxide used is 99.99% or more, and the temperature distribution on the surface of the melt during single crystal growth is determined by a length of 1 c.
This is a method for manufacturing a substrate crystal material, characterized in that the temperature gradient per m is maintained in the range of 30°C to 40°C.

[Effect]

Lanthanide elements and aluminum oxide (LnAlO3
) has a small dielectric constant and a small lattice constant mismatch, but since it is an orthorhombic perovskite crystal, the thermal expansion coefficients of the a-axis, b-axis, and a-axis are somewhat different. Therefore, twin cracks and the like are likely to occur, making it impossible to obtain high-quality crystals with a large area.

NdAlO3, EuAlO3, CeAlO3, etc. are tetragonal or close to tetragonal crystals, and the thermal expansion numbers of the a-axis and b-axis are about the same, so especially on the crystal plane cut in the C-axis direction, twins, cracks, etc. is less likely to occur. Therefore, it is considered that a single crystal material without twins or cracks was obtained by doping LnAIO3 crystal with Nd ions, Eu ions, and Ce ions.

〔Example〕

FIG. 1 is a sectional view showing a crystal growth furnace used in the method for producing a substrate crystal material of the present invention. The iridium crucible 10 contains a raw material melt 4 that has been blended to obtain a desired composition and is melted at a temperature of about 2000°C, and a seed crystal holding rod 1 is placed on the liquid surface.
The seed crystal 2 connected to the seed crystal 2 and the growing single crystal 3 are gently rotated and pulled up by the seed crystal holding rod to produce a defect-free single crystal. The entire growth furnace is housed in a Pelger and sealed in nitrogen gas.

In addition, the iridium crucible 10, the crucible 11, and the heat insulating cylinder 7
, 8 is wound with a high frequency induction heating coil 9 for heating the iridium crucible, and the iridium crucible is induction heated by the high frequency induction heating coil to produce a raw material melt 4.

(Example 1) Next, an example of the present invention will be described. Considering that the optimum segregation coefficient during crystal growth is about 0.25, cerium oxide (Ce204), neodymium oxide (Nd203), and yttrium oxide (Y2O) with a purity of 99.99% or more were used.
3), raw material powder of aluminum oxide (A1203),
2.61 g of Ce2O4 and 3 g of Nd2O:+ each
．． Weighed 02g of Y2O3, 20.13g of Y2O3, and 92.7g of Al2O3, mixed these raw material oxides, and prepared an iridium (Ir) with a diameter of 50mm and a wall thickness of 1.5m installed in a sealed Pel jar. It was charged into a crucible.

After heating the iridium crucible to approximately 2000°C using a high-frequency induction heating coil in a nitrogen gas atmosphere and melting the raw material oxide, a neodymium-doped yttrium aluminum oxide (Nd: YAIO3) seed crystal was immersed in the melt and heated to 2 Orpm. While rotating at a high speed, pull it up at a rate of 3 cm per hour to a diameter of 20 mm and a length of 70 + u.
A yttrium aluminum oxide (NdCe:YAIO:+) single crystal rod doped with neodymium and cerium was obtained. The temperature of the crystal grown at this time is l above the melt surface.
The temperature gradient was controlled to be maintained between 30°C and 40°C per CI. In addition, this single crystal was analyzed and Y was found to have a lat of Ce.
I confirmed that % was replaced. Nd is about 0.9at
It was about %. In the case of conventional YAlO3 crystals without addition of Nd ions, Ce ions, etc., when observing twins and cracks using a crossed Nicol image, defective products occur at a rate of 90% or more, but in the example of the present invention, When grown, the probability of occurrence of twins, cracks, etc. was 1 kneading rate for every 10 plants grown, that is, 10% or less.

(Example 2) In YA103 crystal growth, after mixing Y2O3, Al2O3, Eu2O:+ oxide powder raw materials that were weighed in advance so that Eu ions would replace Y ions by 30 at%, the mixture was sealed. The crucible was charged into an iridium crucible with a diameter of 50 cm and a wall thickness of 1.5 cm placed in a Pel jar.

After heating the iridium crucible to 2000°C with a high-frequency induction heating coil in a nitrogen gas atmosphere and melting the raw material oxide, YAlO3 seed crystals were immersed in the melt and heated for 3 hours while rotating at a rotational speed of 20 rpm. The crystal was pulled up at a speed of 20 m in diameter and 50 mm in length.

At this time, the temperature gradient during the growing crystal on the melt surface is 3 cm per 1 cm in the length direction of the growing crystal.
The temperature was controlled between 0°C and 40°C. After cutting this crystal into rings and mirror-polishing the cut surfaces, the cross Nicol image was observed, and it was confirmed that high-quality crystals without twins and cracks were obtained in this example. Incidentally, the non-defective product rate in this case was 70%.

(Example 3) In YAIO3 crystal growth, Y2O3, Al2O3, Nd2O:+ oxide powder raw materials weighed in advance so that Nd ions would be replaced by lat% with respect to Y ions were mixed, and the mixture was sealed. The mixture was placed in an iridium crucible with a diameter of 50 cm and a wall thickness of 1.5 cm placed in a Pel jar. In a nitrogen gas atmosphere, the iridium crucible was heated to about 2000°C using a high-frequency induction heating coil to melt the raw material oxide, and then a YAlO3 seed crystal was immersed in the melt.
Crystals with a diameter of 20 mm and a length of 50 mm were obtained by rotating at a rotational speed of 1 hour and 3 seconds. Incidentally, the temperature gradient on the surface of the molten liquid of the grown single crystal at this time was controlled to 30° C. to 40° C. per 1 c. When this crystal was cut into small pieces and the cut surfaces were mirror-polished and a crossed Nicol image was observed, a good quality crystal without twins or cracks was obtained.

The non-defective product rate in this example was 80% or more.

In the examples of the present invention, the elements doped into the lanthanide aluminum oxide are cerium (Ce),
Although an example was shown in which neodymium (Nd) and europium (Eu) were added respectively, Ce, Nd, and Eu can also be doped into the same single crystal at the same time, either singly or in a combination of two or in a combination of three. It goes without saying that the same effects as in the embodiments of the invention can be obtained.

C1 Effects of the Invention [Effects of the Invention] As described above, the oxide of lanthanide elements and aluminum according to the present invention can be prepared by adding O,0
By using a single crystal substituted with 1 mm% to 100 at%, it has become possible to provide a high-quality substrate crystal free of twins and cracks as a substrate for an oxide superconducting film.

[Brief explanation of drawings]

FIG. 1 is a front sectional view of a single crystal growth furnace used for growing the substrate crystal material for the oxide superconductor thin film of the present invention. 1... Seed crystal holding rod, 2... Seed crystal, 3... Single crystal, 4... Raw material melt, 6... ZrO2 powder, 7.
8... Heat insulation tube, 9... High frequency induction heating coil, 10
...Iridium crucible, 11...crucible. Patent applicant Tokin Co., Ltd.

Claims (1)

[Claims] 1. Lanthanide (Ln) elements [Ln is yttrium (
A substrate made of a lanthanide aluminum oxide (LnAlO_3) single crystal of Y), lanthanum (La), samarium (Sm), praseodymium (Pr), gadolinium (Gd), disprosium (Dy)] and aluminum oxide. In the crystal material, cerium (Ce), neodymium (Nd),
or one kind, two kinds, or three kinds of europium (Eu)
Depending on the species, lanthanide elements range from 0.01 at% to 1
A substrate crystal material characterized in that it is formed with 00 at% substitution. 2. Lanthanide (Ln) elements [Ln is yttrium (
A single crystal of lanthanide aluminum oxide (LnAlO_3) consisting of Y), lanthanum (La), samarium (Sm), praseodymium (Pr), gadolinium (Gd), disprosium (Dy)] and aluminum oxide. , a type of cerium (Ce), neodymium (Nd), or europium (Eu),
Or 0.01 of lanthanide elements by two or three types
In the method for manufacturing a substrate crystal material doped with at% to 100 at%, the purity of the oxide used is 99.99%.
The temperature distribution on the surface of the melt during single crystal growth is set at 30℃ per 1 cm of purity.
A method for manufacturing a substrate crystal material, characterized by maintaining the temperature in a range of 40 to 40°C.