JPH06196018A - Oriented ferroelectric substance thin film element - Google Patents

Abstract

PURPOSE:To produce an element for a nonvolatile memory, a capacitor, light switch or the like on an Si semiconductor substrate by forming an epitaxial or oriented ferroelectric substance thin film on a singlecrystal Si(100) substrate. CONSTITUTION:An oriented ferroelectric substance thin film element has a structure in which an epitaxial MgO buffer layer is formed on a singlecrystal Si(100) substrate, and further on this buffer layer, an epitaxial or oriented perovskite ABO3 ferroelectric sustance thin film is formed. A crystallographic relation of the singlecrystal Si(100) substrate and the epitaxial MgO buffer layer is MgO(100)//Si(100), in-plane azimuth MgO [100]//Si [100], and the crystallographic relation of the epitaxial MgO buffer layer and the perovskite ABO3 ferroelectric substance thin film is ABO3 (001)//MgO(100) or ABO3(100)//MgO (100), in-plane azimuth ABO3[010]//MgO[001] or ABO3[001]//MgO[001].

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to epitaxial MgO.
Is used as a buffer layer to form an epitaxial or oriented ferroelectric thin film on a single crystal Si (100) substrate, which is a nonvolatile memory, a capacitor,
Further, the present invention relates to an oriented ferroelectric thin film element that can be used when an element such as an optical integrated circuit is formed on a Si semiconductor substrate.

[0002]

2. Description of the Related Art Conventionally, an oxide ferroelectric thin film is a surface acoustic wave device such as a non-volatile memory due to many properties of a ferroelectric substance such as ferroelectricity, piezoelectricity, pyroelectricity and electro-optical effect. Many applications such as infrared pyroelectric elements, acousto-optical elements, and electro-optical elements are expected. Among these applications, the production of single crystal thin films is indispensable in order to achieve low optical loss in thin film optical waveguide structures, polarization characteristics similar to single crystals, and electro-optical effects. Therefore, BaTiO ₃ , PbTi
O ₃ , Pb _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O
₃ (PLZT), LiNbO ₃ , KNbO ₃ , Bi ₄ T
The epitaxial ferroelectric thin film such as i ₃ O ₁₂ is an oxide single crystal substrate by a method such as Rf-magnetron sputtering, ion beam sputtering, laser ablation (laser deposition), and metal organic chemical vapor deposition (MOCVD). Various attempts have been made to form them.

However, it is necessary to form a ferroelectric thin film on a semiconductor substrate for integration with a semiconductor element. Epitaxial growth of a ferroelectric thin film on a Si substrate is difficult because of a high growth temperature, mutual diffusion between Si and a ferroelectric, oxidation of Si, and the like. For these reasons, it is necessary to form a capping layer, which is epitaxially grown on a semiconductor substrate at a low temperature, assists the epitaxial growth of a ferroelectric thin film, and also functions as a diffusion barrier, as a buffer layer on the semiconductor substrate. Further, in the FET element in which the insulator is formed between the ferroelectric substance and the semiconductor, the presence of such a buffer layer makes it possible to prevent the injection of charges from the semiconductor at the time of polarization of the ferroelectric substance. It becomes easy to maintain the polarization state of the dielectric. Also,
The refractive index of the ferroelectric is generally smaller than that of Si, but if a buffer layer having a smaller refractive index than the ferroelectric is obtained, it becomes possible to confine the laser light in the ferroelectric thin film optical waveguide. It becomes possible to fabricate a circuit on a Si semiconductor integrated circuit.

On the other hand, M on Si (100) single crystal
JP-A-61-185808 discloses that a ferroelectric compound is epitaxially grown on a substrate on which gAl ₂ O ₄ (100) or MgO (100) is epitaxially grown.
As disclosed in Japanese Patent Publication No. JP-A-2003-96, Si (100) single crystal and Mg
The crystallographic relationship with O (100) has not been clarified. In fact, in subsequent studies, M with (100) orientation
Even when gO is formed in Si (100) single crystal, Mg
It has been clarified that O has a (100) plane that is parallel to the Si (100) plane, and that the in-plane orientation is oriented polycrystalline MgO (P. Tiwari et a.
l. J. Appl. Phys. 69, 8358 (19
91)). After that, MgO is often used as a substrate for ferroelectrics and high-temperature superconductors due to its lattice constant and thermal stability.
Has been revealed for the first time that it can be epitaxially grown on Si (DK Fork et a.
l. , Appl. Phys. Lett. 58, 22
94 (1991)), and superconducting thin films using the same have been proposed.

[0005]

As described above, according to the conventional technique, it is difficult to epitaxially grow the ferroelectric thin film on the single crystal Si substrate. Therefore, the present invention aims to solve this problem. That is, the object of the present invention is to obtain single crystal Si (10
0) To provide an oriented ferroelectric thin film element in which an epitaxial or oriented ferroelectric thin film is formed on a substrate. Another object of the present invention is to provide an oriented ferroelectric thin film element that can be used when a high-performance nonvolatile memory, a capacitor, or an element such as a light modulation element is formed on a semiconductor substrate.

[0006]

The present inventors have found that when MgO is epitaxially grown on a Si (100) substrate by a vapor phase epitaxy method and MgO is used as a buffer layer, the ferroelectric thin film becomes Si (100). It was discovered that epitaxial growth can be performed on a substrate, and the present invention has been completed.
The oriented ferroelectric thin film element of the present invention is a single crystal Si (10
0) An epitaxial MgO buffer layer is formed on a substrate, and an epitaxial or oriented perovskite ABO ₃ type ferroelectric thin film is further formed on the epitaxial MgO buffer layer.

The present invention will be described in detail below. In the present invention, the crystallographic relationship in the oriented ferroelectric thin film is
For example, for BaTiO ₃ , BaTiO ₃ (00
1) // MgO (100) // Si (100), in-plane orientation B
aTiO ₃ [010] // MgO [001] // Si [00
1], it is possible to form a structure in which the polarization direction of the tetragonal ferroelectric is perpendicular to the substrate surface. Regarding the crystallographic relationship between MgO and Si, although the lattice mismatch is 22.5%, the relationship between the crystal orientations of MgO and Si is MgO.
(100) // Si (100), in-plane orientation MgO [00
1] // Si [001]. When observing the interface between MgO and Si with a high resolution transmission electron microscope, about MgO: S
A structure considered to be lattice-matched with i = 4: 3 is formed, and it is recognized that the interface is a steep interface without the generation of SiO ₂ or the like. Considering the lattice matching of 4: 3, MgO (100) // Si (10
0), which has a lattice mismatch of 3.4%, which is smaller than in the case of epitaxial growth of MgO [011] // Si [001],
Despite the apparent large lattice mismatch, M
The in-film stress is relaxed as compared with the case of gO [011] // Si [001], and the film quality of the MgO [001] // Si [001] epitaxial thin film is improved. Therefore, on the Si (100) single crystal, MgAl ₂ O ₄ (10
0) or MgO (100) is epitaxially grown on the substrate, when a ferroelectric compound is epitaxially grown, MgO (100) // Si (100) in MgO and S
The relationship of the in-plane crystal orientation of i is MgO [011] // Si [0
01], but MgO [001] // Si [001] is desirable.

In the present invention, an epitaxial MgO buffer layer is formed on a single crystal Si (100) substrate.
As film forming conditions, a film forming temperature of room temperature to 1200 ° C. and a film forming rate of 0.01 to 10.0 angstrom / sec are adopted, whereby an epitaxial MgO buffer layer can be formed. MgO film thickness is 10
A range of -10 ⁵ Angstroms is preferred. As described above, the epitaxial Mg was formed on the single crystal Si (100) substrate.
By forming the O buffer layer, it becomes possible to form an epitaxial or oriented perovskite ABO ₃ type ferroelectric thin film thereon. Specifically, Ba
TiO ₃ , PbTiO ₃ , Pb _1-x La _x (Zr _y Ti
_1-y ) _{1-x / 4} O ₃ (PLZT), LiNbO ₃ , KNb
An oriented perovskite ABO ₃ type ferroelectric thin film such as O ₃ or Bi ₄ Ti ₃ O ₁₂ is formed. The film thickness is 0.
It is preferably in the range of 01 to 10 μm. These film forming methods include excimer laser deposition,
Rf-magnetron sputtering, ion beam sputtering, electron beam evaporation, flash evaporation,
Ion plating, molecular beam epitaxy (MBE), ionization cluster beam epitaxy, chemical vapor deposition (CVD), metalorganic chemical vapor deposition (MOCVD), plasma CVD and other vapor phase deposition methods are available. It can be used effectively.

In the present invention, the single crystal Si (10
0) The crystallographic relationship between the substrate and the epitaxial MgO buffer layer is preferably MgO (100) // Si (100) and in-plane orientation MgO [001] // Si [001]. The crystallographic relationship between the epitaxial MgO buffer layer and the epitaxial or oriented perovskite ABO ₃ type ferroelectric thin film is ABO ₃ (001) // M
gO (100) or ABO ₃ (100) // MgO (1
00), in-plane orientation ABO ₃ [010] // MgO [00
1] or ABO ₃ [001] // MgO [001].

[0010]

Since the oriented ferroelectric thin film element of the present invention has the above-mentioned structure, the ferroelectric thin film can be epitaxially grown on the single crystal Si (100) substrate. That is, the epitaxial MgO buffer layer assists the epitaxial growth of the ferroelectric thin film and also acts as a diffusion barrier. At this time, MgO (10
0) // Si (100), MgO [011] // Si [00
Lattice misalignment smaller than the epitaxial growth of 1] 3.4
%, It is considered that 4: 3 lattice matching is formed at the interface of MgO-Si, which has a large lattice mismatch of 22.5%, but MgO [01
1] // Si [001], the stress in the film is relaxed, and higher quality MgO [001] // Si [001] epitaxial growth is possible. Further, since the orientation of the ferroelectric thin film can be controlled, a large remanent polarization value and a large electro-optical constant can be obtained. In the FET element in which the insulator is formed between the ferroelectric and the semiconductor, the ferroelectric It is possible to prevent injection of charges from the semiconductor during polarization of the body, and it becomes easy to maintain the polarization state of the ferroelectric substance.
Further, although the refractive index of the ferroelectric substance is generally smaller than that of Si,
If a buffer layer having a refractive index smaller than that of a ferroelectric substance can be obtained, laser light can be confined in a ferroelectric thin film optical waveguide, and an optical integrated circuit can be fabricated on a Si semiconductor integrated circuit. Become.

[0011]

Example 1 An epitaxial MgO buffer layer was formed on a single crystal Si substrate by an excimer laser deposition method in which a target surface was instantaneously heated by a UV laser pulse for vapor deposition. Laser is XeCl excimer laser (wavelength 308nm), pulse period 4H
The conditions were z, pulse length 17 ns, and energy 130 mJ (energy density 1.3 J / cm ^{2 on the} target surface). The distance between the target and the substrate is 50 mm. Metal Mg was used as the target because MgO has no absorption at a wavelength of 308 nm. Since MgO has a high binding energy of 10 eV or more, Mg is easily oxidized by introducing O ₂ during the film formation. The Si substrate was heated by a halogen lamp.

As a single crystal Si substrate, n-type or p-type
A mold, a (100) plane, and a 6 × 6 mm wafer were used. These substrates were washed with a solvent and then etched with an HF solution. The substrate was rinsed with deionized water and ethanol, and finally spin-dried with ethanol under a nitrogen stream. After spin-drying, the substrate was immediately introduced into the deposition chamber and heated at a constant temperature, a background pressure of 3 × 10 ⁻⁷ Torr, and 500 ° C. or higher to desorb (sublimate) the H passivation layer on the Si surface Then, MgO is added at 200 to 700 ° C., 1 × 10 ⁻⁶ to 1 × 10 ^−3.
A film of MgO having a thickness of 40 to 300 angstrom was formed under the condition of Torr O ₂ .

When analyzed by X-ray diffraction, the MgO film formed on the Si substrate became an epitaxial film having a single orientation of the (100) plane under a wide range of conditions.
It was confirmed that a good quality thin film was formed under the conditions of 2 ° C ^-6 to 1x10 ^-5 Torr O ₂ . In order to identify the relationship between the in-plane crystal orientations of MgO and Si, X-ray diffraction
Scanned. In the cubic crystal, the phi scan for the (202) plane, which has an angle of 45 ° with respect to the (100) plane, is MgO (100) / Si (100)
Shows a sharp peak with a rotation period of 90 ° with respect to MgO, and this position coincided with the peak position of Si.
From these, the crystallographic relationship between MgO and Si is
Despite the lattice mismatch of 22.5%, the relationship between the crystal orientations of MgO and Si is MgO (100) // Si (1
00), and the in-plane orientation was MgO [001] // Si [001].

When the interface between MgO and Si is observed with a high resolution transmission electron microscope, a structure that appears to be a lattice match of about MgO: Si = 4: 3 is formed, and SiO 2 is present at the interface.
_There was no generation of ₂ etc. and it was a steep interface. Considering the lattice matching of 4: 3, 3.4 in the case of MgO: Si = 4: 3.
%, The stress in the film was relaxed despite having a large lattice mismatch, so that good quality MgO [001] // Si
It is considered that the epitaxial thin film of [001] was obtained.

On the other hand, BaTiO which is a typical ferroelectric substance
The lattice constants of ₃ (tetragonal system, perovskite structure) and Si (cubic system, diamond structure) are greatly different, and the lattice mismatch is 26.4%, but BaTiO ₃ (00
Considering the lattice matching in the in-plane 45 ° rotation of the 1) plane and the Si (100) plane, that is, the orientation relation of BaTiO ₃ [110] // Si [001], the lattice mismatch is 4.0%.
And relatively small. Therefore, BaTiO ₃ was directly grown on GaAs. Upon film formation, during the first 100 laser pulses, and the various O ₂ pressure as described above, was continued deposited by subsequent 1.0mTorrO _2. First 10
Depending on the O ₂ pressure between 0 pulses and the film formation temperature, BaTiO ₃
The crystallinity of was changed, but the obtained one was (110) /
The polycrystalline film had a (101) orientation. Thus, epitaxy was not determined by simple lattice matching.

When BaTiO ₃ was directly grown on Si, epitaxy was not observed as described above, but 600 to 800 ° C., 1 × 10 ⁻⁴ to 1 × 10 ⁻² Tor.
BaTiO 3 with a film thickness of 500 to 2000 angstroms grown in situ on the MgO buffer layer under the condition of r O _2.
No. ₃ had a lattice mismatch of 5.2% with MgO, but all were epitaxially grown. When the X-ray diffraction pattern was analyzed, BaTiO ₃ was c-axis oriented, and BaTiO ₃ and MgO / GaAs were identified by Phi scan.
As shown in FIG. 1, the relationship between the crystal orientations of
₃ (001) // MgO (100) // Si (100), B
aTiO ₃ [010] // MgO [001] // Si [00
1]. In FIG. 1, 1 is a single crystal Si substrate (diamond structure), 2 is a MgO thin film (NaCl structure), and 3 is an epitaxial BaTiO ₃ thin film (perovskite structure).

BaT observed by scanning electron microscope
The surface of iO ₃ was extremely smooth. Further, observing the surface of BaTiO ₃ in an area of 1 × 1 μm ^{2 with} an atomic force microscope, the optically polished glass (50 to 1
The surface roughness was equivalent to 50 angstrom surface roughness). From this fact, it can be expected that this BaTiO ₃ film has a good low light attenuation characteristic as an optical waveguide in terms of its surface smoothness. Also, Cr / 20
B in 00 Angstroms -BaTiO _3/400 Å -MgO / Si capacitors structure
When the polarization characteristics of aTiO ₃ are measured, P
-E characteristic shows a hysteresis loop, and BaTiO ₃
Is a single crystal S with a polarization axis as estimated by structural analysis.
It was found to be a ferroelectric phase (tetragonal) oriented perpendicular to the i substrate.

Example 2 The epitaxial MgO buffer layer was formed on Si in the same manner as in Example 1 above. Si substrate is n type or p
A mold, a (100) plane, and a 6 × 6 mm wafer were used. These substrates were etched, rinsed, and processed in the same manner as in Example 1.
After drying, the substrate was immediately introduced into the deposition chamber at constant temperature and background pressure 3 × 1.
The H passivation layer on the Si surface was desorbed (sublimated) by heating at 0 ⁻⁷ Torr and 500 ° C. or higher. Subsequently, MgO was added at about 30 ° C. under conditions of 600 ° C. and 1 × 10 ⁻⁵ Torr O _2.
A film of MgO of 0 angstrom is formed, and MgO and S
The relationship of the in-plane crystal orientation of i is MgO (100) // Si (1
00), an epitaxial thin film of MgO [001] // Si [001] was obtained. 650 ° C, 1 × 10 ^-2 Torr
PbTiO ₃ having a film thickness of 2000 angstroms grown in situ on the MgO buffer layer under the condition of O ₂ is a
Axial orientation growth was performed. The relationship between the crystal orientations of PbTiO ₃ and MgO / GaAs identified by the X-ray diffraction pattern is P
bTiO ₃ (100) // MgO (100) // Si (10
It was 0).

PbT observed by scanning electron microscope
The surface of io ₃ was extremely smooth, which can be expected to lead to good low light attenuation characteristics as an optical waveguide. Also,
Similarly, Pb _1-x La _x (Zr _y Ti _1-y ) _{1-x / 4} O
₃ (PLZT) could also be epitaxially grown on Si by using an epitaxial MgO buffer layer.

Example 3 A MgO buffer layer was formed on a Si (100) single crystal substrate by an electron beam evaporation method. MgO is used as the target, and the distance between the target and the substrate is 130 m
m, and the electron beam current was 5 to 20 mA. The Si single crystal substrate is heated by a halogen lamp and the substrate temperature is 3
It was set to 00 ° C to 700 ° C. An n-type or p-type 6 × 6 mm wafer having a (100) plane was used as a Si single crystal substrate. After cleaning these Si single crystal substrates with a solvent, etching was performed with an HF-based solution. Finally, spin drying with ethanol was performed under a nitrogen flow. After spin drying, the Si single crystal substrate was immediately introduced into the deposition chamber and after reaching the background pressure,
The Si single crystal substrate was heated, and MgO film was formed when a certain substrate temperature was reached to form a MgO film having a film thickness of 500 Å. When diffracted by X-ray diffraction,
The MgO film formed by changing the electron beam current to change the film forming speed has a film forming speed of 0.5 angstrom / sec.
It was found that under the conditions that the film forming temperature was 610 ° C., the film forming rate was 0.2 angstrom / sec, and the film forming temperature was 440 ° C., the film had a single orientation of (100) plane.

After the MgO buffer layer was formed on the Si single crystal substrate, PZT was immediately formed on MgO by the sol-gel method. The fabrication of PZT begins with Ti (OiC).
₃ H ₇₎ at ₄ and _{Zr (O-i-C 3} H 7) 4 a predetermined molar ratio of 2-methoxyethanol: CH ₃ OCH ₂ CH ₂
It is dissolved in OH (abbreviated as ROH), and then Pb (C
H ₃ COO) ₂ with Pb: (Zr + Ti) = 1.0: 1.
It was blended and dissolved so that the molar composition ratio was 0. After that, the metal complex P was distilled at 125 ° C. for a certain period of time.
b (Zr, Ti) O ₂ (OR) ₂ was formed and by-products CH ₃ COOCH ₂ CH ₂ OCH ₃ were removed. Next, Pb: H ₂ O: NH ₄ OH =
RO of H ₂ O: NH ₄ OH to be 1: 1: 0.1
The H solution was added and the metal alkoxide was partially hydrolyzed by refluxing for several hours. Then, the solution was concentrated under reduced pressure to finally obtain a stable precursor solution having a Pb concentration of 0.6 M. All of the above operations were performed in an N ₂ atmosphere. This precursor solution was added to Si (1
(00) The substrate was spin-coated at 2000 rpm in a N ₂ atmosphere at room temperature. The spin-coated substrate was heated at 300 ° C. in an O ₂ atmosphere and then 650
It was heated to ℃ and crystallized. This gives a film thickness of 1000
An angstrom thin film was obtained. The obtained tetragonal composition PZT (Zr: Ti = 50: 50) is (100)
The tetragonal PZT exhibited (001) orientation on the plane-oriented MgO and the polarization axis [001] was oriented perpendicular to the substrate surface.

Example 4 The formation of the MgO buffer layer on the GaAs substrate was carried out according to Example 3
Similarly to the above, the electron beam evaporation method was used. MgO was used as the target, the distance between the target and the GaAs substrate was 200 mm, and the electron beam current was 5 to 20 mA.
The GaAs substrate was heated by a halogen lamp and the substrate temperature was 200 ° C to 600 ° C. As the GaAs substrate, an n-type (100) ± 0.2 °, 6 × 6 mm wafer was used. These GaAs substrates were etched with a H ₂ SO ₄ based solution after cleaning with a solvent. Further, this GaAs substrate was rinsed with deionized water and ethanol, and finally spin-dried with ethanol under a nitrogen flow. Immediately after spin drying, the substrate was introduced into the deposition chamber, the background pressure was reached, the substrate was heated, and MgO film was formed when the substrate temperature reached a certain value. Was formed.

Formed Mg when analyzed by X-ray diffraction
O has a film forming rate of 0.3 angstrom / sec,
Under the conditions of the film forming temperature of 280 ° C., 370 ° C., 440 ° C., and 500 ° C., the epitaxial film had a (100) plane unidirectional orientation. When observing the interface between MgO and GaAs with a high resolution transmission electron microscope, a lattice match of MgO: GaAs = 4: 3 is formed at the MgO-GaAs interface, and no secondary layer is formed at the interface. It was a steep interface. Considering 4: 3 lattice matching, MgO: GaAs =
At 4: 3, it was 0.7%, and despite the large lattice mismatch, the in-film stress was relaxed and MgO [001]
It is considered that // GaAs [001] epitaxial growth was realized.

Next, B is formed on the (100) plane unidirectionally oriented MgO.
aTiO ₃ was formed into a film at 700 ° C., and BaTiO ₃
Was epitaxially grown. When the X-ray diffraction pattern was analyzed, BaTiO ₃ was tetragonal [001] axis-oriented, and BaTiO ₃ was identified by Phi Scan.
And the crystal orientation of MgO / GaAs is BaTiO ₃
(001) // MgO (100) // GaS (100), B
aTiO ₃ [100] // MgO [001] // GaAs
It was [001].

Furthermore, in Examples 1 to 4, the excimer
Although the laser deposition method or the electron beam evaporation method was used, the film forming process is not limited to this, and Rf-magnetron sputtering, ion beam sputtering, flash evaporation, ion plating, molecular deposition Beam epitaxy (MB
E), ionized cluster beam epitaxy, chemical vapor deposition (CVD), metalorganic chemical vapor deposition (MO)
Similarly, vapor phase growth methods such as CVD) and plasma CVD are effective for producing the MgO layer in the present invention.

[0026]

According to the present invention, it is possible to epitaxially grow a ferroelectric thin film on a single crystal Si (100) substrate which is cheaper than the conventionally used single crystal oxide substrate. Become. Therefore, the oriented ferroelectric thin film element of the present invention is useful for producing a non-volatile memory, a capacitor, an FET element and the like, and can be used for producing an element such as an optical integrated circuit on a Si semiconductor substrate. You can

[Brief description of drawings]

FIG. 1 Epitaxial BaTiO ₃ thin film and Mg
It is explanatory drawing which shows the relationship of the crystal orientation with respect to the single crystal Si substrate of O thin film.

[Explanation of symbols]

1 ... Single crystal Si substrate, 2 ... MgO thin film, 3 ... Epitaxial BaTiO ₃ thin film

Claims (4)

[Claims] 1. An orientation characterized in that an epitaxial MgO buffer layer is formed on a single crystal Si (100) substrate, and an epitaxial or oriented perovskite ABO ₃ type ferroelectric thin film is further formed on the epitaxial MgO buffer layer. Ferroelectric thin film element. 2. The crystallographic relationship between the single crystal Si (100) substrate and the epitaxial MgO buffer layer is MgO.
(100) // Si (100), in-plane orientation MgO [00
1] // Si [001]. The oriented ferroelectric thin film element according to claim 1. 3. The epitaxial MgO buffer layer has a film forming temperature of room temperature to 1200 ° C. and 0.01 to 1
The oriented ferroelectric thin film element according to claim 1, which is formed at a film forming rate of 0.0 angstrom / sec. 4. An epitaxial or oriented perovskite ABO ₃ with the epitaxial MgO buffer layer.
Type ferroelectric thin film has a crystallographic relationship of ABO ₃ (001) /
/ MgO (100) or ABO ₃ (100) // MgO
(100), in-plane orientation ABO ₃ [010] // MgO [0
01] or ABO ₃ [001] // MgO [001]. _3. The oriented ferroelectric thin film element according to claim 1.