JP2003257709A - Perovskite-containing laminar compound laminate, element using the same, and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique for growing a perovskite-containing laminar compound layer in crystals as the direction of lamination of the compound layer is oriented in parallel with a board. <P>SOLUTION: A rutile-structure crystalline substrate or a conductive or semiconductive spinel-structure crystalline substrate is employed, and a perovskite-containing laminar compound is epitaxially grown on the substrate as the direction of lamination of the laminar compound is oriented in parallel with the surface of the substrate. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a perovskite-containing layered compound laminate and an electronic device and an electronic device using the same, and more particularly to a perovskite-containing layered compound on a conductive substrate in a layered stacking direction (general Direction in which the c-axis direction is parallel to the substrate surface (that is, in general, a or b axis orientation: a or b axis is oriented perpendicular to the substrate surface)
The present invention relates to a laminated body epitaxially grown in, and an electronic element and an electronic device using the structure.

[0002]

BACKGROUND OF THE INVENTION Perovskite-containing layered compounds are a group of substances for which various excellent properties such as ferroelectricity, piezoelectricity, pyroelectricity, superconductivity and thermoelectricity have been reported. It is known that the characteristics are greatly different in the layered stacking direction (generally the c-axis direction) and the direction perpendicular thereto (generally the a-axis and the b-axis direction). However, although many thin films have the c-axis perpendicular to the substrate,
There are limited reports of making thin films with the axis standing perpendicular to the substrate.

For example, since ferroelectrics such as PZT contain lead, they tend to be used in the future because they have a large environmental load. Instead, Bi ₄ Ti ₃ O ₁₂ and SrBi ₂ Ta ₂ O _{9 are used.}
The bismuth layered ferroelectrics such as the above have attracted attention as lead-free ferroelectric substances having excellent characteristics. However, most of the reports about the thin film growth of these lead-free ferroelectrics are basically c-axis oriented growth or a tilted one.

On the other hand, for example, Bi ₄ Ti ₃ O ₁₂ has (110)
There are reports of b-axis oriented growth on MgAl ₂ O ₄ and SrBi ₂ T.
As with a ₂ O ₉ , a- and b-axis oriented growth has been reported as on the (110) MgO substrate, but the number is very limited. Moreover, all of these substrates are insulators.

[0005]

Needless to say, the improvement of the ferroelectric properties is the most important in order for the above-mentioned bismuth layered ferroelectric substance to replace the lead-containing ferroelectric substance, but the bismuth layered ferroelectric substance is required. The ferroelectric properties of the layered direction (c
It is known that the axis) and the direction perpendicular to it (a axis or b axis) differ greatly. Since there are many reports on the growth of c-axis oriented thin films as described above, their properties can be evaluated and they can be put to practical use if necessary, but their properties are not always sufficient. On the other hand, bismuth layered ferroelectrics are generally considered to have better characteristics when they are oriented in the a-axis. There is an example in which it is grown only on the top surface. Therefore, in order to evaluate the characteristics, only the thin film is formed on the substrate, only the thin film is peeled off, and the electrode is formed on the film to evaluate the characteristics.

Therefore, if the bismuth layered ferroelectric substance can be grown on the conductive substrate in the a-axis orientation, the possibility of producing a lead-free ferroelectric element having more excellent characteristics will be opened.

Such a situation is not limited to bismuth layered ferroelectrics but is a problem common to thin films of perovskite-containing layered compounds.

Therefore, in view of the current state of the art, it is an object of the present invention to provide a technique for crystallizing a perovskite-containing layered compound by orienting the layered stacking direction of the compound parallel to the substrate. It was made as.

[0009]

According to the present invention, the above-mentioned objects are
It has been found that the objective can be achieved by: (1) Perovskite inclusion on a crystalline substrate of rutile structure
The layered compound has a layered stacking direction of the compound and the substrate surface.
That it is epitaxially grown in a parallel orientation
A perovskite-containing layered compound laminate characterized by the above. (2) Conductive or semi-conductive spinel structure crystalline substrate
A layer of perovskite-containing layered compound
Epitaxy in the direction in which the stacking direction of the stripes is parallel to the substrate surface.
Containing perovskite characterized by being grown
Layered compound laminate. (3) The layer compound containing perovskite is [(Bi₂O₂)
²⁺] [(A_m-1B_mO_{3m + 1})^2-]) (A is monovalent, divalent or trivalent gold
A group ion or a mixture thereof, where B is Ti ⁴⁺, N
b⁵⁺, Ta⁵⁺, V⁵⁺, W⁶⁺Or a mixture thereof, m
= 1 to 5) (Bi₂O₂)²⁺Layers and perovskites
Of structure (A_m-1B_mO_{3m + 1})^2-Perovska containing units
Ito-containing bismuth layered compound described in (1) and (2)
The layered compound laminate containing the perovskite as described above. (4) The substrate is IrO₂, RuO₂, VO₂, CrO₂, NbO₂, MoO₂,
 WO₂, ReO₂, RhO₂, OsO₂, PtO₂, V₃O_Five, V_nO_2n-1(n = 4-
8), Ti₃O_Five, Ti_nO_2n-1, S_nO_2-x, Na_xTiO₂Selected from
Perovskite according to (1) or (3), which is a conductive substrate
Containing layered compound laminate. (5) The substrate is LiTi₂O_Four, LiM_xTi_2-xO_Four(M = Li, Al, Cr),
Li_1-xM_xTi₂O_Four(M = Mg, Mn), LiV₂O_Four, Fe₃O_FourSelected from
Perovskite according to (2) or (3), which is a conductive substrate
Containing layered compound laminate. (6) The above-mentioned perovskite-containing layered compound layer and substrate
And the substrate is electrically conductive, the perovs
Forming the bottom electrode for the layer of layered compound containing kite
An electronic device characterized in that (7) An electronic device including the electronic device described above.

[0010]

According to the first aspect of the present invention, it was found that a layer of a perovskite-containing layered compound can be epitaxially grown by using a crystalline substrate having a rutile structure.

The perovskite-containing layered compound used in the present invention means a compound having a layered crystal structure containing a perovskite structure as a constituent layer. Since the perovskite structure itself is not a layered compound, it is not included in the perovskite-containing layered compound in the present invention. For example, the Bi ₄ Ti ₃ O ₁₂ structure known as a ferroelectric is a structure composed of an A-type perovskite unit, a B-type perovskite unit and an oxygen layer as shown in FIG. 1 (written by FS Galassau). Translated by Kato and Uematsu "Illustrated Fine Ceramics Crystal Chemistry" Published by Agne Technical Center, 2
(From page 17). The perovskite structure appears in the compound having a composition formula of ABX ₃ , but the central atoms of the unit cell are A and B.
Depending on how it is represented, it is represented as two types, an A-type perovskite unit and a B-type perovskite unit. In the present invention, a compound having a layered structure having a crystal structure including at least one unit of the A-type perovskite unit and / or the B-type perovskite unit and having another layered structure is referred to as a perovskite-containing layered compound.

[(Bi ₂ O ₂ ) ²⁺ ] is a preferred example of the perovskite-containing layered compound that can be used in the present invention.
[(A _m-1 B _m O _{3m + 1} ) ^2- ]) (A is a monovalent, divalent or trivalent metal ion such as Pb ²⁺ , Ba ²⁺ , Bi ³⁺ , Sr ²⁺ , Ca ^2+, etc.
Or a mixture thereof, and B is Ti ⁴⁺ , Nb ⁵⁺ , Ta ⁵⁺ , V
⁵⁺ , W ⁶⁺ or a mixture thereof, m = 1-5)
Of the (Bi ₂ O ₂ ) ²⁺ layer and the (A _m-1
There are perovskite-containing bismuth layered compounds containing B _m O _{3m + 1} ) ^2- units. Although this perovskite-containing bismuth layered compound is crystallographically referred to as a Bi ₄ Ti ₃ O ₁₂ structure, it is known to exhibit ferroelectricity. Specifically, Bi ₄ Ti ₃ O ₁₂ , SrBi ₂ Ta ₂ O ₉ , Bi ₂ WO ₆ , Bi ₃ TiNbO ₉ , Bi ₃ TiT
aO ₉ , CaBi ₂ NbO ₉ , CaBi ₂ Ta ₂ O ₉ , SrBiNb ₂ O ₉ , CaBi ₄ TiO ₁₅
And so on.

Similarly, another example of the perovskite-containing layered compound that can be preferably used in the present invention is K ₂ NiF ₄
The structure can be mentioned. In the K ₂ NiF ₄ structure, as shown in FIG. 2, two unit cells of the perovskite structure in which the A atom occupies the center are connected to the unit cell of the perovskite structure in which the B atom occupies the center, and then the BX ₃ layer is formed. It is obtained by removing (see above 212-214).
page). That is, the cut A type unit cell is placed above and below the unit cell of the complete B type perovskite structure, and when a is the edge of the unit cell, a tetragonal unit cell of c≈3a is obtained. Be done. The coordination number of B atom is the same as that of perovskite and surrounded by 6 X atoms, but A atom is surrounded by 9 X atoms, which is smaller than the coordination number of 12 A atoms of perovskite. . Specific examples include halides such as K ₂ CoF ₄ , K ₂ CuF ₄ , Rb ₂ NiF ₄ , and Ba ₂
PbO ₄ , Ba ₂ SnO ₄ , Ca ₂ MnO ₄ , Sr ₂ IrO ₄ , Sr ₂ MnO ₄ , SrTiO ₄ ,
La ₂ NiO ₄ and other oxides, La ₂ (Li _0.5 Co _0.5 ) O ₄ , SrLaAlO ₄ ,
Mention may be made of complex oxides such as SrLaCoO ₄ .

Similarly, it can be preferably used in the present invention.
As another example of the perovskite-containing layered compound, Sr₃Ti₂
O₇Structure and Sr_FourTi₃O_TenThe structure can be mentioned. Sr₃Ti₂O
₇As shown in Fig. 3, the structure is B type perovskite.
Two unit cells of the structure are paired, then A type perov
BX from a pair of unit cells of the skyt structure ₃
Remove the layers of and place them above and below the pair of types
It is what is done. Sr_FourTi ₃O_TenStructure is Sr₃Ti₂O₇Similar to structure
However, it has a long c-axis (see above 215).
~ 216). As a specific example, Sr₂TiO_Four, Sr₃Ti₂O₇, S
r_FourTi₃O_Ten, K₃Zn₂F ₇and so on.

FIG. 4 shows Bi ₄ Ti ₃ O ₁₂ as a side view of the layered stacking direction (FIG. 4A) and a bottom view of the layer (FIG. 4I).

Similarly, the result known as superconductor
Crystallographically K₂NiF_FourYBa belonging to the structure₂Cu ₃O_7-xLaminated structure
View of the direction from the side (Fig. 5 (a)) and the layers from the bottom
It is shown as a view (FIG. 5 (i)).

LaSrCo, also known as superconductor
A view of the structure of O ₄ seen from the side in the stacking direction (Fig. 6 (a))
And a layer as viewed from the bottom (FIG. 6 (I)).

4 to 6 also show the lattice constant or the interatomic distance, the interatomic distance is about 3.8Å, about 4.2Å,
It is based on an interval with a component of about 5.4Å, and when the layer structure is viewed from the bottom, the interatomic distance is about 3.
Based on 8Å and about 5.4Å, and the interatomic distances or lattice constants in the biaxial directions are almost evenly spaced, and when the stacked structure is viewed from the side, the interatomic distance different from about 5.4Å (about 4 It can be seen that a large amount of (.2Å, 3.8Å, etc.) Such properties are basically common to the perovskite-containing layered compound. The interatomic distance has a commonality because it is mainly determined by an oxygen atom or a fluorine atom, and generally has a higher commonality in an oxide.

Returning again to Bi ₄ Ti ₃ O ₁₂ , the lattice constants of this perovskite-containing layered compound are 5.44Å on the a axis, 5.41Å on the b axis, and 32.815Å on the c axis, as shown in FIG. Is. That is, the a and b axes are substantially equiaxed, but the c axis (layered stacking direction) has an abnormally different length. On the other hand, many crystal structures have an equiaxed oxygen layer with an interatomic distance of about 5.4Å.
Therefore, when the perovskite-containing layered compound Bi ₄ Ti ₃ O ₁₂ is grown using a crystal having such an oxygen layer as a substrate,
As shown in FIG. 7, since the lattice constant (interatomic distance) of the substrate matches well with the a and b axes of the perovskite-containing layered compound Bi ₄ Ti ₃ O ₁₂ , the stacking direction of the layered crystal is perpendicular to the substrate. It is easily understood to grow into. This is the crystal growth of the conventional perovskite-containing layered compound.

On the other hand, crystals of rutile structure (10
1) When cut out on the plane, the axial length is a = b> c in the rutile structure.
, The minor axis is a = b, the major axis is (ac) ^1/2 , and the lattice constant (interatomic distance) is about 4.5Å and about 5.4Å for TiO ₂ , for example (difference in lattice constant 20%). Thus, on a substrate that matches in the one axis direction but has a large difference in lattice constant (atomic distance) in the other axis direction, the perovskite-containing layered compound Bi ₄ Ti ₃ O ₁₂ is deposited in the layered stacking direction. However, it is difficult to grow epitaxially vertically to the substrate. Moreover, in the rutile structure, the in-plane interatomic distance of the (101) plane of about 5.4Å matches the a-axis or the b-axis, and as shown in FIG. 6, about 4.5Å is 4.5Åx7 = 31.5Å
Therefore, we can roughly match the lattice constant 32.8Å of Bi ₄ Ti ₃ O _{12 on} the c-axis. Generally, there is no problem in matching the lattice constant or the distance between oxygen atoms within 15%, so that this is possible in the rutile structure. What is important here is not to be bound by theory, but one of the lattice constants (interatomic distance) of the substrate matches the lattice constant (interatomic distance) of Bi ₄ Ti ₃ O _{12 in} the layered stacking direction. Rather, one of the lattice constants (interatomic distance) of the substrate matches the lattice constant (interatomic distance) in the layer of Bi ₄ Ti ₃ O ₁₂ while the lattice constant (interatomic distance) in the other direction. Does not match the lattice constant (distance between atoms) in the in-layer direction of Bi ₄ Ti ₃ O ₁₂ , and therefore the layered stacking direction of Bi ₄ Ti ₃ O ₁₂ is prohibited to grow in the direction perpendicular to the substrate surface. Is important,
As a result, the lattice constant (interatomic distance) in the unmatched direction of the substrate becomes relatively matched to the lattice constant (interatomic distance) in the layered stacking direction of Bi ₄ Ti ₃ O ₁₂ , and the perovskite-containing layered layered It is considered that the compound Bi ₄ Ti ₃ O ₁₂ undergoes crystal growth (epitaxial growth) so that its layered stacking direction is parallel to the substrate surface.

In the above, TiO ₂ and Bi ₄ Ti ₃ O having a lattice constant of 4.5Å
_As described with reference to ₁₂ , especially when the lattice constant of the rutile structure is in the range of about 4.2 to 4.8Å, more preferably in the range of about 4.3 to 4.5Å, by using the (101) plane, etc., the perovskite content is preferably contained. Layered compounds (typical c-axis is about 11-32
Å) can be crystal-grown such that the layered stacking direction is parallel to the substrate surface. In the (101) plane of the rutile structure, the minor axis is a≈b and the major axis is (ac) ^1/2 , so
The long axis may preferably be about 5.2-5.6Å, as opposed to 4.2-4.8Å.

Thus, the relationship between the crystal structure of the substrate and the crystal growth of the perovskite-containing layered compound is generally established. The crystal unit is 45% without the perovskite structure being the A type or B type unit described above.
In some cases, the interatomic distance is more important than the lattice constant, because it may be rotated units.

In the above sense, the (101) plane of the rutile structure is generally suitable as a substrate for crystallizing a perovskite-containing layered compound so that its layered stacking direction is parallel to the substrate surface, and The fact is confirmed experimentally.

The rutile structure crystalline substrate used as the substrate in the present invention refers to a compound crystalline substrate having a rutile structure as the crystal structure. As described above, the rutile structure substrate is very suitable for epitaxially growing the perovskite-containing layered compound in which the lattice constant of the crystal of the rutile structure and / or the distance between oxygen atoms is such that the layered stacking direction is parallel to the substrate surface. Compounds having a rutile structure, which are suitable, include a large number of compounds having conductive or semiconductive properties. Therefore, by using the rutile structure substrate, the perovskite-containing layered compound can be epitaxially grown in a direction in which the layered stacking direction is parallel to the substrate surface, and moreover, the substrate is a conductive or semi-conductive substrate. Such growth is possible.

The crystalline substrate having a rutile structure may be a polycrystalline substrate instead of a single crystal substrate.

In addition, since most of the desired perovskite-containing layered compound is an oxide, the substrate is preferably an oxide because of its excellent compatibility with it, but is not limited thereto.

Examples of crystals of rutile structure together with their lattice constants (Å) are as follows. The average, maximum and minimum lattice constants (Å) for these examples are also shown. (Oxide) Compound a-axis lattice constant c-axis lattice constant CrO ₂ 4.41 2.91 GeO ₂ 4.359 2.859 IrO ₂ 4.49 3.14 α-MnO ₂ 4.359 2.86 MoO ₂ 4.86 2.79 NbO ₂ 4.77 2.96 OsO ₂ 4.51 3.19 PbO ₂ 4.964 3.379 RuO ₂ 4.51 3.11 SnO ₂ 4.737 3.185 δ-TaO ₂ 4.709 3.065 TeO ₂ 4.79 3.77 TiO ₂ (rutile type) 4.5929 2.9591 WO ₂ 4.86 2.77 AlAsO ₄ 4.359 2.815 CrVO ₄ 4.551 2.844 Average 4.6178 3.0389 Minimum 4.359 2.77 Maximum 4.946 3.77 (nitride ) Compound a-axis lattice constant c-axis lattice constant Ti ₂ N 4.9452 3.0342 (halide) Compound a-axis lattice constant c-axis lattice constant CoF ₂ 4.695 3.18 MgF ₂ 4.623 3.052 MnF ₂ 4.873 3.31 NiF ₂ 4.651 3.084 PdF ₂ 4.931 3.367 ZnF ₂ 4.703 3.0123 Average 4.739 3.2051 Minimum 4.623 3.052 Maximum 4.931 3.367 Overall average value 4.7011 3.0723 Preferred compounds having a rutile structure are conductive or semiconductive (semiconductor) compounds, and particularly conductive compounds.
Suitable conductive rutile compounds include IrO ₂ , RuO ₂ ,
RhO ₂ , OsO ₂ , VO ₂ , CrO ₂ , NbO ₂ , MoO ₂ , WO ₂ , ReO ₂ , Rh
O ₂ ,, PtO ₂ ,, V ₃ O ₅ ,, V _n O _2n-1 (n = 4-8), Ti ₃ O ₅ ,, Ti _n O _2n-1,, S _{n
O 2-x, Na x TiO} 2, it can be mentioned. Incidentally, the electrical conductivity and the lattice constant of each compound in each axial direction are as follows, and the (101) plane and a plane equivalent thereto may be used.

[0028]

[Table 1]

Examples of the semiconductive rutile structure compound include TiO ₂ , SnO ₂ and GeO ₂ .

As described above, the ability to epitaxially grow the perovskite-containing layered compound on the conductive substrate in the layer-by-layer direction parallel to the substrate surface can be utilized as a base electrode for drawing out the high characteristics of the perovskite-containing layered compound, and therefore is extremely important in the present invention. Is an advantage. For the purpose of use as an electrode, it is sufficient for the conductive rutile structure compound to be present only on the surface of another substrate, for example, a substrate such as alumina. A technique for growing a desired crystal plane of a conductive rutile structure compound on the surface of another substrate, for example, a substrate such as alumina is known.

In the present invention, the method for epitaxially growing the perovskite-containing layered compound on the surface of the crystalline substrate having a rutile structure is not particularly limited. Although a metalorganic chemical vapor deposition method (MOCVD) is a preferred method, various CVD methods and PVD methods other than the sputtering method can be adopted, or a liquid phase method is also possible. This is because the present invention is based on matching of the crystal lattices of the substrate and the perovskite-containing layered compound.

In the second aspect of the present invention, it was found that the same effect as in the first aspect can be obtained even when a conductive or semiconductive spinel structure crystalline substrate is used as the substrate. That is, not only in the rutile structure, but in the spinel structure compound, from the completely same consideration as described in the case of the rutile structure, the perovskite-containing layered compound is subjected to lattice matching in which the layered stacking direction is grown parallel to the substrate surface. I've confirmed that there is something that makes it possible. As a result, by using a conductive or semi-conductive spinel structure crystalline substrate, a perovskite-containing layered compound is formed on a substrate having a conductive or semi-conductive property so that the layered lamination direction is parallel to the substrate surface. Since it can be grown, it becomes possible to manufacture an electronic device having a layer structure having a high property such as ferroelectricity of a perovskite-containing layered compound, and an electronic device including such an electronic device.

Even when a substrate having a spinel structure is used, the (110) plane is used as the crystal plane. A for spinel structure
≈b≈c, so the minor axis is a, b or c, the major axis is (ab) ^1/2 ,
It is (ac) ^1/2 or ^{(bc) 1/2 ≒ √2 (a} , b or c). As a result, one of the lattice constant of the in-plane crystal of the perovskite-containing layered compound or the oxygen atom spacing matches the substrate, and the other mismatches and crystal growth occurs in the direction in which the stacking direction is perpendicular to the substrate surface. And the matching in the layered stacking direction results in the growth of the perovskite-containing layered compound parallel to the substrate surface in the layered stacking direction.

When such a conductive or semi-conductive spinel structure crystalline substrate is used, it is particularly desirable that the lattice constant or the distance between oxygen atoms satisfies the above-mentioned conditions. That is, in the substrate used in the present invention, one of the lattice constants (or oxygen atom intervals) on the surface of the substrate has a perovskite-containing layered compound, for example, about ₄ a-axis or b-axis of Bi ₄ Ti ₃ O _12.
While matching 5.4Å, the other lattice constant (oxygen atom spacing) on the surface of the substrate does not match about 5.4Å of the a-axis or b-axis, but rather its integer multiple is the c-axis of the perovskite-containing layered compound. Another lattice constant (oxygen atom spacing) on the surface of the substrate that can be matched to the lattice constant of is the c of the perovskite-containing layered compound.
A crystal structure that matches the oxygen atom spacing in the axial direction is preferable (typically about 4.2 to 4.5Å). In particular, one of the lattice constants (oxygen atom spacing) on the substrate surface matches the a-axis or b-axis of the perovskite-containing layered compound, for example, about 5.4Å, while the other lattice constant (oxygen atom spacing) is about 4.2 to 4.8. Especially preferred are compounds having a crystal plane with a rectangular lattice point oxygen (atomic spacing) of Å, more preferably about 4.3 to 4.8Å. Matching is possible if the lattice constant or the oxygen atom spacing is within about 15%.

Examples of conductive spinel structure oxides include LiTi ₂ O ₄ , LiM _x Ti _2-x O ₄ (M = Li, Al, Cr), Li _1-x M _x Ti ₂ O
₄ (M = Mg, Mn), LiV ₂ O ₄ , Fe ₂ O _{4 and the} like.

The method for growing the perovskite-containing layered compound on these spinel-structured substrates in a direction parallel to the surface of the substrate is not particularly limited as in the case of the rutile structure.

According to the third aspect of the present invention, an electron is obtained by epitaxially growing a perovskite-containing layered compound on a conductive or semi-conductive substrate with the layered stacking direction oriented in a direction parallel to the substrate surface. Devices and electronic devices that include such electronic devices are provided. The perovskite-containing layered compound includes various compound groups having excellent properties such as a ferroelectric substance, a superconductor, a piezoelectric substance, a pyroelectric substance, and a thermoelectric substance. Therefore, in order to utilize its physical properties, the conductive substrate can be used as an electrode by epitaxially growing a perovskite-containing layered compound on a substrate, particularly a conductive substrate. Therefore, an electronic device utilizing the excellent physical properties of the perovskite-containing layered compound For example, it is possible to form a ferroelectric element, a superconductor element, a thermoelectric element, and the like, and according to the present invention, the perovskite-containing layered compound is laminated in a direction parallel to the substrate surface. Since it can be oriented and epitaxially grown, it can be configured as an electronic device having higher physical properties. Thus, according to the present invention, an electronic device obtained by epitaxially growing a perovskite-containing layered compound on a conductive or semi-conductive substrate with the lamination direction of the layered layer oriented in a direction parallel to the substrate surface, and such an electron. An electronic device including an element is provided. The electronic element of the present invention can be incorporated in, for example, a semiconductor device.

[0038]

[Example] (Example 1) As a substrate, RF sputtering method (substrate temperature 400 ~ 600 ℃) and CVD method (substrate temperature 350 ℃)
2) (101) RuO ₂ and (101) IrO ₂ on Al ₂ O ₃ and (101) TiO 2.
_A film of (101) IrO ₂ was formed on top of ₂ . The resulting film was analyzed by X-ray diffraction (10
It was confirmed that the 1) plane was epitaxially grown. The conductivity was also confirmed.

On these substrates, (Bi, Nd) ₄ was formed by MOCVD.
A film of (Ti, V) ₃ O ₁₂ (BNTV) was formed. Using a cold wall type reaction chamber, the raw materials are Bi (CH ₃ ) ₃ , Nd (TMOD) ₃ , Ti (OiC
_{A combination of 3} H ₇ ) ₄ , VO (OC ₂ H ₅ ) ₃ and O ₂ was used. These raw materials were obtained by bubbling a liquid raw material with nitrogen gas at an operating temperature (about 120 to 130 ° C.). However, the Nd raw material is Nd (C ₁₂ H ₂₁ O
₂ ) ₃ (Nd (TMOD) ₃ ) solid was heated to a liquid and bubbled to obtain.

Vertical cold wall system C used in FIG.
2 shows a VD device. In FIG. 9, the substrate 12 placed in the vertical cold wall type reaction chamber 11 can be heated by the heater 13. The above raw materials are contained in a container 14-17 set to a predetermined temperature by an oil bath 21. The containers 18 and 19 are carrier gas nitrogen containers, and the container 20 is an oxygen container. Meter
The reference numeral 22 and the vacuum pump are indicated by 23. The nitrogen gas from the container 18 is first bubbled in the container 14-17 so that the raw material gas is contained in the nitrogen gas, these raw material gases are sent to the reaction chamber together with the oxygen gas 20, and the target BNTV is deposited on the substrate 12. did.

The substrate temperature is 600 ° C., and the deposition time is a film thickness of 30.
It was 3 hours at 0 nm.

The obtained thin film was analyzed by a fluorescent X-ray diffraction method,
(100) (010) BiNdTiVO (BNTV) epitaxial layer on the substrate,
That is, it was confirmed that BNTV crystals with a-axis and b-axis orientation were generated. Figure 10 shows X of BNTV formed on (101) RuO ₂ substrate.
A line diffraction chart is shown. It can be seen that BNTV with a-axis and b-axis orientation is formed on the substrate.

(100) BiNdTiVO 4 grown on the obtained substrate
The electric field-polarization (PE) hysteresis curve of the thin film of (BNTV) is shown in FIG. The remanent polarization was 23.3 μC / cm ² , and the coercive electric field was 249 kV / cm.

For comparison, the electric field-polarization (PE) hysteresis curve of the c-axis oriented BNTV thin film is also shown in FIG. 11. The residual polarization is 1 μC / cm ² , and the coercive electric field is 40 kV / cm. It is recognized that the ferroelectric properties are greatly improved by orienting the a and b axes according to the present invention.

In this embodiment, since conductive RuO ₂ is used as the substrate, the ferroelectric characteristics of the deposited BNTV thin film are as follows.
It was measured as it was without peeling the thin film from the substrate.

Next, the fatigue characteristics of this BNTV thin film were measured. The reversal current amount after reversal of 100 kHz rectangular wave 6 × 10 ⁹ times is shown in FIG. 12, and it is recognized that there is substantially no fatigue, and that it has excellent fatigue characteristics.

Similar results were obtained on the IrO ₂ substrate as on the RuO ₂ substrate.

(Example 2) Another (100) (010) film formed on a (101) RuO ₂ // Al ₂ O ₃ substrate was formed in the same manner as in Example 1 except that the film thickness was changed to 22 μm. (Bi _3.6 Nd _0.4 ) (Ti _2.9 V _0.1 ) O ₁₂ (B
The X-ray diffraction chart of the (NTV) layer is shown in FIG. 13, and excellent remanent polarization of 24 μC / cm ² and coercive electric field of 113 kV / cm are obtained.

FIG. 14 shows the fatigue characteristics, which are 100 k
Even after 1.6 × ^{10 10} times of inversion using the Hz square wave, there is virtually no fatigue, and it is recognized that the fatigue characteristics are superior.

(Embodiment 3) In the same manner as in Embodiment 1, (1
A (100) (101) Bi ₄ Ti ₃ O ₁₂ film was formed on a 01) TiO ₂ single crystal substrate.

It was confirmed by electron diffraction that the Bi ₄ Ti ₃ O ₁₂ crystal grown on the substrate was oriented in the a and b axes as described above (FIG. 15).

FIG. 16A shows a transmission electron microscope (TEM) photograph when the Bi layer is viewed from the side. B ₂ O ₂ ²⁻ and Bi ₂ TiO _{10 are shown.}
It is observed that the ²⁺ layered direction is parallel to the substrate. For comparison, a TEM photograph viewed from the direction rotated by 90 ° is shown in FIG.

(Example 4) In the same manner as in Example 1, (10
0) _c CaRuO ₃ // (100) SrTiO ₃ was used as a substrate, on which Bi ₄ Ti ₃ O ₁₂ (BIT) was deposited by MOCVD.

The X-ray diffraction chart of the obtained thin film BIT thin film is shown in FIG. 17. (001) Ba ₄ Ti ₃ O ₁₂ was epitaxially grown on the (100) _c CaRuO ₃ // (100) SrTiO ₃ substrate. It is recognized that

(Example 5) In the same manner as in Example 3, (10
1) A (100) (010) SrBi ₂ Ta ₂ O ₉ film was formed on a TiO ₂ single crystal substrate.

It was confirmed by X-ray diffraction that the SrBi ₂ Ta ₂ O ₉ crystal grown on the substrate was oriented in the a and b axes as described above (FIG. 18). Although FIG. 19 is an X-ray pole figure, it is confirmed that epitaxial growth is performed.

(Example 6) In Example 5, the substrate was
01) RuO ₂ // Change to (110) Al ₂ O ₃ and do the same for (100) (010) S
A film of rBi ₂ Ti ₂ O ₉ was formed.

As shown in the X-ray diffraction chart of FIG. 20, a,
It is confirmed that the b-axis is oriented.

21 and 22 show the results of examining the polarization characteristics and the insulation characteristics by applying a voltage to this thin film. It can be seen that excellent polarization hysteresis characteristics and insulation characteristics are obtained.

Example 7 On a (110) MgAl ₂ O ₄ single crystal substrate, a LiMgTi ₂ O ₄ target was used by a laser ablation method at a substrate temperature of 500 ° C. and a spinel structure of (010) (10
0) A LiMgTi ₂ O ₄ thin film was deposited. The crystal structure of the obtained LiMgTi ₂ O ₄ thin film was confirmed by X-ray diffractometry, and it was also confirmed that the thin film exhibits conductivity.

Using this substrate, in the same manner as in Example 3,
Bi ₄ Ti ₃ O ₁₂ was deposited. Growth temperature 600 ℃, 650 ℃, 700 ℃
3 kinds of.

Under any of the conditions, the spinel structure of (010)
The fact that (100) (010) Bi ₄ Ti ₃ O ₁₂ crystal grows on a (100) LiMgTi ₂ O ₄ substrate and has a, b-axis orientation in the direction perpendicular to the substrate, and that it grows axially is X. Confirmed by line diffraction.

[0063]

According to the present invention, it is possible to epitaxially grow a perovskite-containing layered compound in an orientation in which the layered stacking direction is parallel to the substrate surface, and RuO ₂ , IrO _2, etc. It is possible to grow epitaxially on a flexible substrate in the direction in which the layered direction of the ferroelectric or other layer having excellent characteristic values is parallel to the substrate surface. Therefore, the perovskite-containing layered compound has high ferroelectricity and other properties. There is an effect that an element utilizing the characteristics can be formed.

[Brief description of drawings]

FIG. 1 shows a crystal structure of Bi ₄ Ti ₃ O ₁₂ structure.

FIG. 2 shows a crystal structure of K ₂ NiF ₄ structure.

FIG. 3 shows a crystal structure of Sr ₃ Ti ₂ O ₇ structure.

FIG. 4 is a view of the layered Bi ₄ Ti ₃ O ₁₂ layer viewed from the side (FIG. 4A) and a view of the layer from the bottom (FIG. 4I).
Is.

5 is a view of the structure of YBa ₂ Cu ₃ O _7-x as viewed from the side in the stacking direction (FIG. 5A) and a view of the layers as viewed from the bottom (FIG. 5).
(I)).

6 is a view of the structure of LaSrCoO ₄ as viewed from the side in the stacking direction (FIG. 6A) and a view of the layers as viewed from the bottom (FIG. 6I).
Is.

FIG. 7 is a diagram for explaining how the perovskite-containing layered compound crystal matches the lattice constant of the substrate.

FIG. 8 shows a state in which a perovskite-containing layered compound is epitaxially grown on a substrate in a direction in which the layered stacking direction is parallel to the substrate surface.

FIG. 9 shows a vertical cold wall type CVD apparatus.

FIG. 10 shows an X-ray diffraction chart of the BNTV layer formed on the (101) RuO ₂ substrate obtained in Example 1.

FIG. 11 shows a and b axis orientations obtained in Example 1 (10
The field-polarization (P-E) hysteresis curve of the thin film of 0) (010) BNTV is shown in comparison with that of c-axis oriented BNTV.

FIG. 12 shows the results of measuring the fatigue properties of the BNTV thin film obtained in Example 1.

13 shows an electric field-polarization (PE) hysteresis curve of another thin film of a- and b-axis oriented BNTV obtained in Example 2. FIG.

FIG. 14 shows the results of measuring the fatigue properties of thin films of another a-axis and b-axis oriented BNTV obtained in Example 1.

FIG. 15 is an electron beam diffraction photograph confirming that Bi ₄ Ti ₃ O ₁₂ // (101) TiO ₂ obtained in Example 3 is a- and b-axis oriented.

FIG. 16: a, b-axis oriented Bi ₄ Ti ₃ O ₁₂ / obtained in Example 3
It is a TEM photograph of / (101) TiO ₂ .

FIG. 17: (100) _c CaRuO ₃ // (100) SrT obtained in Example 4
iO ₃ shows the _{Bi 4 Ti 3 O 12 (BIT} ) X -ray diffraction chart of the thin film formed on a substrate.

FIG. 18 is an X-ray diffraction chart of the (100) (010) SrBi ₂ Ta ₂ O ₉ thin film grown on the (101) TiO ₂ single crystal substrate obtained in Example 5.

19 is an X-ray polar diagram of the SBT thin film of FIG.

FIG. 20: (101) RuO ₂ // (110) Al ₂ O ₃ obtained in Example 6
3 is an X-ray diffraction chart of a (100) (010) SrBi ₂ Ta ₂ O ₉ thin film on a substrate.

FIG. 21: (101) RuO ₂ // (110) Al ₂ O ₃ obtained in Example 6
_{2 is} an electric field-polarization hysteresis curve of a (100) (010) SrBi ₂ Ta ₂ O ₉ thin film on a substrate.

FIG. 22 (101) RuO ₂ // (110) Al ₂ O ₃ obtained in Example 6
It is a voltage-leakage current density characteristic of the (100) (010) SrBi ₂ Ti ₂ O ₉ thin film on the substrate.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C30B 29/32 C30B 29/32 WF term (reference) 4G077 AA03 BC41 DB08 ED05 ED06 EF01 HA05 TB05 TK01 TK06 4K030 AA11 AA18 BA42 BB02 BB03 CA01 CA05 FA10 5E034 BB05 DA02 DB03 DE08

Claims (7)

[Claims] 1. A perovskite-containing layered compound laminate, wherein a perovskite-containing layered compound is epitaxially grown on a crystalline substrate having a rutile structure in a direction in which the layered stacking direction of the compound is parallel to the substrate surface. . 2. A perovskite-containing layered compound is epitaxially grown on a conductive or semiconductive spinel structure crystalline substrate in a direction in which the layered stacking direction of the compound is parallel to the substrate surface. Perovskite-containing layered compound laminate. 3. The perovskite-containing layered compound,
[(Bi₂O₂)²⁺] [(A_m-1B _mO_{3m + 1})^2-]) (A is monovalent, divalent or
Trivalent metal ion or mixture thereof, B is T
i⁴⁺, Nb⁵⁺, Ta⁵⁺, V⁵⁺, W⁶⁺Or a mixture of them
And m = 1-5) (Bi₂O₂)²⁺Layers and Perovs
Kite structure (A_m-1B_mO_{3m + 1})^2-Pero containing unit
A bismuth-containing bismuth layered compound containing a skeleton.
Is the perovskite-containing layered compound laminate according to 2. 4. The substrate is IrO ₂ , RuO ₂ , VO ₂ , CrO ₂ , NbO.
₂ , MoO ₂ , WO ₂ , ReO ₂ , RhO ₂ , OsO ₂ , PtO ₂ , V ₃ O ₅ , V _n O
_The conductive substrate selected from _2n-1 (n = 4-8), Ti ₃ O ₅ , Ti _n O _2n-1 , S _n O _2-x and Na _x TiO _2. The perovskite-containing layered compound laminate. 5. The substrate is LiTi ₂ O ₄ , LiM _x Ti _2-x O ₄ (M = Li,
_4. A conductive substrate selected from Al, Cr), Li _1-x M _x Ti ₂ O ₄ (M = Mg, Mn), LiV ₂ O ₄ and Fe ₃ O _4. The layered compound laminate containing perovskite according to the item 1. 6. A structure of a perovskite-containing layered compound layer and a substrate according to any one of claims 1 to 5, wherein the substrate is electrically conductive and forms a bottom electrode for the perovskite-containing layered compound layer. An electronic device characterized by. 7. An electronic device including the electronic device according to claim 5.