JP2862502B2 - Substrate for superconductor crystal thin film growth - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate suitable for use in, for example, a superconducting microstrip line of a microwave circuit capable of growing a superconducting crystal thin film having no crystal defects. In microwave circuits,
A directional coupler, a matching circuit, a frequency filter, and the like are configured using a microstrip line formed on a dielectric substrate. The material of the microstrip line is a metal having a small electric resistance, typically, gold. (Cu) is used, but the volume resistivity of gold is 2.05 × 10 ⁻⁸ ρ / Ω ·
m (0 ° C.), in order to further reduce the loss, it is desired to use a superconductor crystal thin film having much lower electric resistance than metal.

[0002]

2. Description of the Related Art Usually, a superconductor crystal thin film is formed by using a heteroepitaxial growth technique. This technology is
This is one method of epitaxial growth (meaning that crystals having the same orientation are grown on a substrate having a crystal orientation), and is a crystal growth technique of growing a substance having a different crystal structure from the substrate on the substrate.

In FIG. 4, reference numeral 1 denotes a substrate for growing a superconductor crystal thin film (hereinafter abbreviated as “substrate”), and reference numeral 2 denotes a superconductor crystal thin film (hereinafter abbreviated as “thin film”). The substrate 1 includes, for example,
A dielectric single crystal substrate such as MgO or LAO is used.
A thin film 2, for example, a YBCO-based superconductor crystal thin film is grown on a specific crystal plane (a (001) plane with a Miller index) of the substrate 1.

[0004]

However, in such a conventional substrate for growing a superconducting crystal thin film, as shown in FIG. Are equal (a = b = 0.42 nm; however, the value is MgO)
Therefore, in other words, since the (001) plane is a square, each side surface of the crystal unit cell of the superconductor crystal thin film 2 grown using the (001) plane [(100) plane, (010) plane and these planes] [Back surface] is not uniquely determined, and crystal defects are likely to occur.

Accordingly, an object of the present invention is to eliminate crystal defects in a superconductor crystal thin film formed on a substrate by devising a growth surface shape of the substrate.

[0006]

Means for Solving the Problems The present invention provides a substrate for growing a superconductor crystal thin film, forming the substrate
In the crystal structure, the lengths of the a-edge and the b-edge are equal, and the length of the c-edge is
Is longer than the a-edge and the b-edge, and the superconductor crystal
It is a tetragonal crystal corresponding to the length of the c-edge of the thin film, forms a step on the growth surface of the substrate, and sets the step length of the step to an integral multiple of the length of the a-edge or b-edge of the substrate. , And
The rise height of the step portion is set to be an integral multiple of the length of the c-edge .

The substrate is preferably YBa 2 Cu 3 O.
y, the value of y is 6.0 ≦ y ≦ 6.3 . Or,
The present invention relates to a substrate for growing a superconductor crystal thin film.
In this case, the crystal structure constituting the substrate has an a-edge and a b-edge.
It is cubic with the same c-edge length, and
A single-crystal dielectric thin film is formed on the long side,
The crystal structure of the dielectric thin film has the same length of the a-edge and the b-edge,
The c-edge is longer than the a-edge and the b-edge, and
Tetragonal corresponds to the length of the c edges of the conductive crystal film, the
A step is formed on the surface of the single crystal dielectric thin film, and the step
The step length is the length of the a-edge or b-edge of the single-crystal dielectric thin film.
Height of the stairs,
The length of the c-edge is set to an integral multiple of the length of the c-edge . In the present invention, the crystal growth of the superconductor crystal thin film
The crystal growth in the initial stage is governed by the rise surface of the step because it starts from the intersection of the stepping surface and the rise surface of the step. Therefore, among the a and b edges of the superconductor crystal, a specific edge having a value close to the crystal axis length of the rising surface is in contact with the rising surface, so that the direction of each side surface of the superconductor crystal is uniquely determined, A good superconductor crystal thin film without crystal defects can be obtained.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 3 are views showing one embodiment of a substrate for growing a superconductor crystal thin film according to the present invention. In FIG. 1, reference numeral 10 denotes a substrate for growing a superconducting crystal thin film made of MgO (hereinafter abbreviated as “substrate”). On the surface of the substrate 10, a step portion 15 having risers 11, 12 and steps 13, 14 is provided. Are formed. (3) attached in the figure
Digits are Miller indices indicating crystal planes.

The point of this embodiment lies in that a step 15 is formed on the surface of the substrate 10. Further, the height H of the risers 11 and 12 of the step 15 and the steps 13 and 1
The point where the length D is set as follows is also a point. (1) The height H of the rises 11 and 12 is made to correspond to an integral multiple of the length of the c-edge of the crystal unit cell of the superconductor crystal thin film grown on the substrate 10. For example, as shown in FIG. 2, the length of the c-edge of the Y—B—C—O-based superconductor crystal (typically, YBa ₂ Cu ₃ O _7-x ) is 1.17 nm. The height H of the rises 11 and 12 is given by the following equation.

H = 1.17 nm × N where N is an integer. (2) The length D of the steps 13 and 14 is set to an integral multiple of the length of the a-edge or b-edge of the crystal unit cell of the substrate 10.
For example, the lengths of the a-edge and the b-edge of the MgO crystal are both 0.42.
nm (see FIG. 5), the length D of the steps 13, 14 is given by the following equation.

D = 0.42 nm × M where M is an integer. FIG. 3 is a schematic diagram of the crystal structure of the substrate 10 and the superconductor crystal thin film 16 (hereinafter, abbreviated as “thin film”). A dice-shaped cube indicates a crystal unit cell of the substrate 10, and a cube corresponding to approximately three crystal unit cells of the substrate 10 indicates a crystal unit cell of the thin film 16.

In the structural example of FIG. 3, the height H of the rise is equivalent to one crystal unit cell of the thin film 16 (N = 1), and the stepping length D is nine crystal unit cells of the thin film 16. (M = 9), but is not limited to this. N and M may be any integers. In such a structure, the thin film 16
The crystal growth of the substrate 10 is performed at the intersection of the stepping surface of the step portion and the rising surface, that is, in FIG.
It starts from the intersections 10a and 10b of the plane and the (010) plane. Specifically, of the crystal unit cells of the thin film 16 shown in FIG.
The growth starts from 16d).

Therefore, since the initial growth of the thin film 16 is governed by the rising surface [(010) plane] of the step portion, a specific one of the a and b ridges of the superconductor crystal shown in FIG. That is, the length of the crystal axis of the rising surface (0.42 n
As a result, the b ridge (b = 0.39 nm) having a value close to m) is oriented along the rise surface, so that the direction of each side of the superconductor crystal unit cell is uniquely determined, and good superconductivity without crystal defects is obtained. A particularly advantageous effect that a body crystal thin film can be obtained, which is not available in the prior art, is provided.

In the above embodiment, the substrate material is Mg.
Although a dielectric single crystal such as O or LAO is used, it is not limited to this. Any substrate having a Y—B—C—O-based single crystal layer with a reduced oxygen amount y (to the extent that superconductivity is not exhibited) on the surface can be used. A preferable value of the oxygen amount y is, for example, about 6.3 in the case of YBa ₂ Cu ₃ O _y.
It is about 6.0. YBa ₂ Cu ₃ O _{y of} this composition
Since the lengths of the a-edge and the b-edge are equal to each other and the length of the c-edge corresponds to the length of the c-edge of the superconductor crystal as in the case of MgO or LAO, It can be used instead.

[0015]

According to the present invention, the direction of each side surface of a superconductor crystal on a substrate can be uniquely determined, and a good superconductor crystal thin film free from crystal defects can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic surface shape diagram of a substrate according to one embodiment.

FIG. 2 is a schematic diagram of a crystal unit cell of a superconductor crystal thin film.

FIG. 3 is a schematic diagram of a crystal structure of a substrate and a superconductor crystal thin film of an example.

FIG. 4 is a structural view of a conventional example.

FIG. 5 is a schematic diagram of a crystal unit cell of the substrate of FIG. 4;

[Explanation of symbols]

 10: Superconductor crystal thin film growth substrate 11, 12: Lift-up 13, 14: Stepping-off 15: Step portion 16: Superconductor crystal thin film

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yoshiki Ueno 500-1 Minamiyama, Yonegi-cho, Nisshin-shi, Aichi Pref. Mobile Communication Advanced Technology Laboratory Co., Ltd. (56) References JP-A-1-167912 (JP, A) Kaihei 4-271183 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01G 1/00-57/00 C30B 1/00-35/00 H01L 39/00-39/24

Claims (3)

(57) [Claims] 1. A substrate for growing a superconducting crystal thin film, wherein the crystal structure constituting the substrate has the same length of a-edge and b-edge.
The length of c-edge is longer than that of a-edge and b-edge, and
A tetragonal crystal corresponding to the length of the c-edge of the superconductor crystal thin film.
Ri, a stair portion is formed on the growth surface of the substrate, the stepping white head of the stair portion, is equivalent to an integral multiple of the length of a ridge or b crest of the substrate, and the risers height of the stepped portion A substrate for growing a superconductor crystal thin film, wherein the substrate has an integer multiple of the length of the c-edge . 2. The substrate is made of YBa2 Cu3 Oy.
2. The substrate for growing a superconductor crystal thin film according to claim 1, wherein the value satisfies 6.0 ≦ y ≦ 6.3 . 3. A substrate for growing a superconductor crystal thin film, wherein the crystal structure constituting the substrate has a length of a, b, and c edges.
Are cubic and the growth surface side of the substrate
A single-crystal dielectric thin film is formed, and the crystal structure of the single-crystal dielectric thin film has a length of a-edge and a length of b-edge.
Equal, the length of c-edge is longer than a-edge and b-edge, and
A tetragonal crystal corresponding to the length of the c-edge of the superconductor crystal thin film
Forming a step on the surface of the single-crystal dielectric thin film;
The step length of the a-edge or b-edge of the single-crystal dielectric thin film.
Equal to an integral multiple of the length, and the rise height of the stairs
Is set to be an integral multiple of the length of the c-edge .