JP2001117059A - Optical switching element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical switching element consisting of a laminated body of aligning thin films which are suitable for the manufacture of electronic elements such as an nonvolatile memory and capacitor, optical modulation elements or the like. SOLUTION: The optical switching element is equipped with a single crystal substrate 1a, a lower electrode 2 consisting of an epitaxial or aligning perovskite ABO3 conductive thin film formed on the substrate, a thin film optical waveguide 3 consisting of an epitaxial or aligning ABO3 ferroelectric material formed on the lower electrode and showing an electro-optic effect when light is introduced, and an upper electrode 4 formed on the thin film optical waveguide. The single crystal substrate has preferably an epitaxial or aligning buffer layer 1' on its surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device such as a nonvolatile memory and a capacitor, and more particularly to an optical switching device having an oriented ferroelectric thin film suitable for manufacturing a light modulation device and the like.

[0002]

2. Description of the Related Art Conventionally, an oxide ferroelectric thin film has a surface acoustic wave, including non-volatile memory, due to many properties of a ferroelectric such as ferroelectricity, piezoelectricity, pyroelectricity, and electro-optic effect. Many applications are expected, such as devices, infrared pyroelectric devices, acousto-optic devices, and electro-optic devices. Among these applications, it is indispensable to produce a single-crystal thin film in order to reduce the optical loss in the thin-film optical waveguide structure and obtain polarization characteristics and electro-optic effects comparable to those of a single crystal. Therefore, BaTiO ₃ , PbTi
O ₃ , Pb _1-x La _x (Zr _1-y Ti _y ) O ₃ (PLZ
T), an epitaxial ferroelectric thin film such as LiNbO ₃ , KNbO ₃ , Bi ₄ Ti ₃ O ₁₂ is formed by Rf-magnetron sputtering, ion beam sputtering,
Laser ablation, metal organic chemical vapor deposition (MOC
VD) and many other methods are formed on an oxide single crystal substrate. Further, for integration with a semiconductor element, it is necessary to form a ferroelectric thin film on a semiconductor substrate. However, epitaxial growth of a ferroelectric thin film on a semiconductor substrate is difficult due to a high growth temperature, interdiffusion between the semiconductor and the ferroelectric, oxidation of the semiconductor, and the like.

[0003] For these reasons, it is necessary to form a capping layer on a semiconductor substrate as a buffer layer, which grows on a semiconductor substrate at a low temperature, assists the epitaxial growth of a ferroelectric thin film, and also functions as a diffusion barrier. It is. The refractive index of a ferroelectric is generally GaAs.
If a buffer layer having a refractive index smaller than s but smaller than a ferroelectric can be obtained, the semiconductor laser light can be confined in the ferroelectric thin-film optical waveguide, and the light can be condensed on the semiconductor laser of the light modulation element. And an optical integrated circuit can be manufactured on a Si semiconductor integrated circuit. In contrast, the present inventor has already proposed that MgO be (100) epitaxially grown on a semiconductor (100) substrate (US Patent Application D / 91626, filing date 1991.1).
1.26. And Japanese Patent Application No. 4-319228). The crystallographic relationship at this time is, for example, for BaTiO ₃ on GaAs, BaTiO ₃ (001) // MgO (100) // Ga
As (100), in-plane orientation BaTiO ₃ [010] // M
A structure of gO [001] // GaAs [001] can be manufactured.

[0004]

On the other hand, various electronic parts
The thin-film electrodes and thin-film heating resistors used for
In general, metal is used, but metal thin films such as Al and Cr
Vulnerable to oxidation, noble metal thin films such as Pd, Ag, Pt
Strong, but expensive. In addition, using a ferroelectric thin film
In a nonvolatile memory, a metal electrode such as Pt is used.
Then, the fatigue of the ferroelectric is observed with the switching. Nearby
Years, oxide electrode suppresses switching fatigue of ferroelectric thin film
For example, J.I. Lee et al., Appl.
Phys. Lett. ,63, 27 (1993)
YBa_TwoCu_ThreeO_xPb (Zr_{0. 52}Ti_0.48) O_Threeof
The effect on switching fatigue has been reported. But,
YBa, a superconductor_TwoCu_ThreeO_xOxygen concentration for thin film preparation
It is not easy in terms of degree control. JP 4
In -182393, RuO_TwoFerroelectric thin
Although film growth is mentioned, RuO_TwoIs ABO_ThreeType strength
Poor lattice matching with dielectric, RuO _TwoUpper ferroelectric thin
Epitaxial growth of the film is difficult. In addition, Japanese Unexamined Patent Publication No.
In 225711, BaPbO_ThreeConductive oxidation such as
The production of a product is described, but it is a thick film by the paste method.
It is not suitable for an electronic device requiring a thin film. There
Therefore, the present invention has been made in view of the above-mentioned problems.
That is, electronic devices such as nonvolatile memories and capacitors,
Furthermore, oriented ferroelectrics suitable for manufacturing light modulation elements, etc.
Aiming to provide optical switching elements using thin film
Target.

[0005]

The inventor of the present invention has conducted intensive studies on an oriented ferroelectric thin film suitable for manufacturing a nonvolatile memory, a light modulation element, and the like. The present invention has been completed based on the knowledge that a ferroelectric substance can obtain a large remanent polarization value or a large electro-optical constant by forming a body thin film using an epitaxial or oriented conductive thin film. Things. That is, the optical switching element of the present invention is a thin-film optical waveguide in which light is introduced and exerts an electro-optical effect, and a thin-film optical waveguide for applying a voltage in the film-thickness direction positioned above and below the film-thickness direction. It has an upper electrode and a lower electrode. The optical switching element further includes a single crystal substrate, the lower electrode is an epitaxial or oriented conductive thin film provided on the single crystal substrate, and the thin film optical waveguide is an epitaxial or oriented ferroelectric substance. It may be a thin film. Also,
An epitaxial or oriented buffer layer may be provided between the substrate and the lower electrode.

More specifically, the optical switching element of the present invention comprises a single crystal substrate, a lower electrode made of an epitaxial or oriented perovskite ABO ₃ type conductive thin film formed thereon, It comprises a thin film optical waveguide formed of an epitaxial or oriented ABO ₃ type ferroelectric formed thereon and exhibiting an electro-optical effect by introducing light, and an upper electrode provided on the thin film optical waveguide. The single crystal substrate preferably has an epitaxial or oriented buffer layer on its surface.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail. The laminate of the oriented thin films in the optical switching element of the present invention is composed of oxides of MgO, MgAl ₂ O ₄ , S
rTiO ₃ , BaZrO ₃ , LaAlO ₃ , ZnO, A
l ₂ O ₃ , simple semiconductors such as Si, Ge and diamond, and III-V based compound semiconductors such as AlAs and AlS
b, AlP, GaAs, GaSb, InP, InAs,
InSb, AlGaP, AlInP, AlGaAs, A
lInAs, AlAsSb, GaInAs, GaInS
b, GaAsSb, InAsSb, ZnS, ZnSe, ZnTe, CdS, Cd, which are II-VI based compound semiconductors
An epitaxial or oriented perovskite ABO ₃ type conductive thin film is formed on a single crystal substrate selected from Se, CdTe, HgSe, HgTe, etc., or on these single crystal substrates having an epitaxial or oriented buffer layer on the surface. A lower electrode is formed, and a thin film optical waveguide made of an epitaxial or oriented ABO ₃ type ferroelectric thin film is formed thereon. On top of this optical waveguide,
For example, a comb-shaped upper electrode is provided.

The buffer layer is made of MgO, MgA
buffer layer such as l ₂ O ₄ or Pb (Zr _0.53 T
i _0.47 ) Two or more buffer layers such as O ₃ (PZT) / MgO can be used. The above perovskite ABO
_{As the} type ₃ conductive thin film, BaPbO ₃ or (Ba
_{1-2x / m C 2x / m)} (Pb 1-4y / n D 4y / n) conductive oxide thin film represented by O ₃ and the like. Where C is the periodic table I
a represents at least one atom selected from group a, group IIa and group IIIa, and D represents group IIb, group IVa or group IVb of the periodic table
And represents at least one atom selected from the group consisting of Group V, Group Va, Group Vb and Group VIII. Of these atoms, C is Li,
At least one of Na, K, Sr, Y, La, Ce, and Gd is desirable, and D is Si, Ti, V, Fe, Co, Z
At least one of n, Zr, Nb, Sn, Sb, Ta, and Bi is desirable. x and y are 0 <x, y ≦ 1, m means the valence of C, and n means the valence of D. A of the ABO ₃ type ferroelectric thin film is Li, K, S
r, at least one of Ba, La, and Pb, and B is M
g, at least one of Ti, Zr, Nb, and Ta.

The conductive thin film and the ferroelectric thin film are formed by electron beam evaporation, flash evaporation, ion plating, Rf-magnetron sputtering, ion beam sputtering, laser ablation, molecular beam epitaxy (MBE). , Chemical vapor deposition (CVD), plasma CVD, metal organic chemical vapor deposition (M
OCVD) or a wet process such as a sol-gel method or a plurality thereof. Factors affecting epitaxial or oriented thin film growth include differences in lattice constants between materials, differences in crystal structure, differences in crystal symmetry, differences in thermal expansion coefficients, differences in surface electrostatic state, etc. However, lattice matching is one of the most important factors.

Next, several examples of a typical oriented thin film laminate used in the optical switching element of the present invention, in which a ferroelectric layer, a conductor layer, a single crystal substrate, and a buffer layer are combined, are described below. It is listed in the table. 1) Table 1 shows the relationship between the crystal structure and the lattice constant of a ferroelectric layer having a tetragonal or cubic crystal form, a cubic conductor layer, and a cubic oxide single crystal substrate.

[Table 1]

2) Table 2 shows the relationship between the crystal structure and the lattice constant of a ferroelectric layer having a hexagonal crystal structure, a cubic conductor layer, and a hexagonal or cubic oxide single crystal substrate.

[Table 2]

3) Table 3 shows the relationship between the crystal structure and the lattice constant of the ferroelectric layer, the conductive layer, and the oxide single crystal substrate each having the buffer layer formed on the substrate.

[Table 3]

4) Table 4 shows the relationship between the crystal structure and the lattice constant of the ferroelectric layer, the conductor layer, the buffer layer, and the semiconductor single crystal substrate whose substrate is made of a semiconductor.

[Table 4]

5) Table 5 shows the relationship between the crystal structure and the lattice constant of the ferroelectric layer, the conductor layer, the second buffer layer, the first buffer layer, and the semiconductor single crystal substrate in which two buffer layers are formed.

[Table 5]

[0015]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Example 1 Metal alkoxides Ba (OC ₂ H ₅ ) ₂ and P
An equimolar amount of b (OC ₃ H ₇ ) ₂ was dissolved in anhydrous 2-methoxyethanol to obtain a 0.5 M solution. The solution was distilled for 2 hours with stirring, refluxed for another 22 hours, and
The alkoxide BaPb (OC ₂ H ₄ OCH ₃ ) ₄ was obtained. This precursor solution was passed through a 0.2 μm filter, and spin-coated on a MgO (100) single crystal substrate at 2000 rpm. All of the above operations were performed in a nitrogen atmosphere. Prior to spin coating, the substrate was rinsed with solvent, etched with hydrochloric acid, rinsed with deionized water, and finally dried by spin coating with ethanol in a stream of nitrogen.

The spin-coated substrate is heated at 10 ° C. in an oxygen atmosphere bubbled in deionized water at room temperature.
After rapidly raising the temperature at a rate of / sec and maintaining the temperature at 300 ° C. for 2 minutes, the temperature was maintained at 650 ° C. for 30 minutes. Finally, the electric furnace was turned off and cooled. As a result, a film thickness of 0.1 μm
Showed an X-ray diffraction pattern in which the BaPbO ₃ thin film was crystallized with (110) orientation. The resistance of the obtained BaPbO ₃ thin film was measured by a four-terminal method.
A low resistance value of × 10 ⁻⁴ Ω · cm was exhibited. BaPbO ₃
Has metallic conductivity due to its small band gap, but is not transparent to visible light. But,
The BaPbO ₃ thin film in this embodiment has an annealing temperature,
Some transparency to visible light was observed depending on the film thickness or composition.

Next, the above BaPbO ₃ (110) / M
0.5M Pb with a Pb concentration of 0.5M on a gO (100) substrate
(Zr _0.53 Ti _0.47 ) O ₃ (PZT)
Spin coating was performed at 000 rpm. This precursor solution has a molar ratio of Pb: Zr: Ti = 1.00: 0.
53: 0.47 Pb (CH ₃ COO) ₂ , Zr (O −
The i-C ₃ H _{7) 4} and _{Ti (O -i-C 3 H} 7) 4 2-
After dissolving in methoxyethanol and distilling for 6 hours, 18
Obtained by refluxing for hours. All of the above operations were performed in a nitrogen atmosphere. The spin-coated substrate is
After the temperature was raised at 10 ° C./sec and pyrolysis was performed at 350 ° C. for 1 minute in an oxygen atmosphere, the substrate was heated at 650 ° C. for 30 minutes to crystallize the PZT thin film. As shown in FIG. 1, the obtained laminate of the oriented thin film is formed on an oxide substrate 1a and a conductor layer 2 composed of BaPbO ₃ (110).
The ferroelectric layer 3 in which the PZT thin film is oriented in (110) is formed. Further, a BaPbO ₃ thin film was formed again on the PZT thin film by the same method as described above. BaPbO ₃ / PZT / BaPbO ₃ / M thus produced
The polarization characteristics of PZT were tested by applying a voltage with BaPbO ₃ as the upper and lower electrodes using the gO element. As a result, the switching characteristics and fatigue characteristics were better than those of the metal electrode.

Example 2 A laminate of an oriented thin film was obtained in the same manner as in Example 1 except that the MgO single crystal substrate was replaced with a SrTiO ₃ (100) single crystal substrate. This thin film is, as shown in FIG.
A conductive layer 2 made of BaPbO ₃ oriented in (100) and a ferroelectric layer 3 made of a PZT thin film oriented in (001) are formed on a. Table 1 shows examples of combinations of ferroelectrics, conductors, and oxide single crystal substrates which are epitaxially or oriented and grown as in Examples 1 and 2. Further, a BaPbO ₃ thin film was formed again on the PZT thin film in the same manner as in Example 1. This BaPbO ₃ /
Using a PZT / BaPbO ₃ / SrTiO ₃ element,
When the polarization characteristics of PZT were tested by applying a voltage using aPbO ₃ as the upper and lower electrodes, as in Example 1, good switching characteristics and fatigue characteristics were exhibited as compared with the metal electrodes.

Example 3 As a raw material, a molar ratio of Ba: Sr: Pb = 0.8: 0.
2: 1.0 Ba (OC_TwoH_Five)_Two, Sr (OC
_TwoH_Five)_TwoAnd Pb (OC_ThreeH₇)_TwoTo anhydrous 2-meth
Dissolved in Toxiethanol, 0.5M solution with Pb concentration
I got The solution was distilled for 2 hours with stirring and a further 22 hours.
After refluxing for an hour, a complex alkoxide was obtained. This precursor solution
Through a 0.2 μm filter, (Ba_0.8Sr
_0.2) Pb (OC _TwoH_FourOCH_Three)_FourAl solution_TwoO_Three
Spin coating on (0001) single crystal substrate at 2000 rpm
I went to the meeting. All of the above operations are performed in a nitrogen atmosphere
And before spin coating, the substrate was the same as in Example 1.
Washing, etching, rinsing and drying were performed in the same manner. S
Pin-coated substrates are placed in a dry oxygen atmosphere
After the temperature was raised at 10 ° C / sec and maintained at 300 ° C, 65
The temperature was kept at 0 ° C., and finally, the electric furnace was turned off and cooled. This
Thereby, (Ba) having (111) orientation is obtained._0.8S
r_0.2) PbO_ThreeA thin film is obtained, which is 5 × 10^-Four
It exhibited a low resistance value of Ω · cm.

Next, LiOC having a predetermined molar ratio is used as a raw material.
₂ H ₅ and Nb a (OC ₂ H _{5) 5} was dissolved in 2-methoxyethanol anhydrous give a 0.5M solution. This solution was distilled for 2 hours while stirring, and refluxed for 22 hours to obtain a double alkoxide. Then, add 0.2μ
m and passed through a filter of LiNb (OC ₂ H ₄ OCH
_{3) 6} solution Al ₂ O ₃ (0001) 20 into the single-crystal substrate
Spin coating was performed at 00 rpm. All the above operations were performed in a nitrogen atmosphere, and the substrate was subjected to solvent washing, etching, rinsing, and drying in the same manner as in Example 1 before spin coating. (Ba _0.8 Sr _0.2 ) PbO ₃ is cubic, but the (111) plane of BaPbO ₃ has the same symmetry in the (0001) plane of the hexagonal ferroelectric substance. 000
1) A LiNbO ₃ thin film having an orientation is obtained, and LiNbO _3
3 (0001) / (Ba _0.8 Sr _0.2 ) PbO ₃ (11
1) A thin film structure of / Al ₂ O ₃ (0001) was produced. FIG. 3 shows a stack of oriented thin films having the same layer structure as in Examples 1 and 2. Table 2 shows examples of such combinations of ferroelectrics, conductors and single crystal substrates.

Example 4 In the same manner as in Example 1, the PZT precursor solution was changed to SrTi
The substrate was spin-coated at 2000 rpm on an O ₃ (100) single crystal substrate, heated in an oxygen atmosphere at 10 ° C./sec, thermally decomposed at 350 ° C., and annealed at 650 ° C. to obtain the orientation of (001). Epitaxial P
A ZT thin film was obtained. When this PZT thin film was used as an epitaxial buffer layer and BaPbO ₃ was formed in the same manner as in Example 1, BaPbO ₃ was crystallized epitaxially in the (100) direction. Further, a 0.35 μm-thick (Pb _0.72 L) film was formed thereon in the same manner as in Example 1.
By forming a _0.28 ) TiO ₃ (PLT) thin film, PLT (001) / BaPbO ₃ (100) / PZ
A multilayer epitaxial structure of T (001) / SrTiO ₃ (100) was obtained. FIG. 4 shows a laminate of an oriented thin film composed of a conductor layer 2 and a ferroelectric layer 3 on an oxide substrate 1a having a buffer layer 1 'on the surface. Table 3 shows examples of combinations of such ferroelectrics, conductors, buffer layers, and single-crystal substrates.

Next, by providing a comb-shaped upper Al electrode on the surface of the PLT, laser light was introduced into the PLT thin film optical waveguide by prism coupling. As shown in FIG. 5, when a voltage is applied between Al, which is the upper electrode 4 of the PLT thin film, and BaPbO ₃ (conductor layer), which is the lower electrode 2, Bragg reflection due to the electro-optic effect of the electric flux lines 5 occurs. Switching of the introduced laser light is now possible. At this time, as compared with the general coplanar type element shown in FIG. 6 in which only the comb-shaped electrode 4 'facing the surface of the PLT without forming the lower electrode, the distance between the electrodes is PL.
It is easy to set the thickness to 0.35 μm, which is equal to the thickness of T.

As a result, since a voltage can be effectively applied in the thickness direction of the PLT, the driving voltage is low, and the width between the electrodes is not restricted by the fine processing technology of the electrodes. It became easy. Thus, since an epitaxial electrode thin film can be formed on an insulating substrate, an epitaxial ferroelectric thin film can be formed on an electrode. Therefore, an element having a capacitor-type electrode structure that could not be conventionally formed on an insulating substrate or an insulating thin film can be manufactured without providing an epitaxial electrode.

Example 5 An epitaxial buffer layer was formed on a GaAs (100) single crystal substrate by an excimer laser deposition method in which the target surface was instantaneously heated and deposited by a UV laser pulse. That is, a XeCl excimer laser having a wavelength of 308 nm is used as the laser, and the pulse period is 4 Hz, the pulse length is 17 ns, and the energy is 130 mJ (the energy density on the target surface is 1.3).
J / cm ² ). MgO was used as a target, and MgO was reacted and grown. The GaAs single crystal substrate was etched with a sulfuric acid-based solution after washing with a solvent. Furthermore,
This 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 a deposition chamber and heated to 350 ° C. to form a 400 Å epitaxial MgO (100) buffer layer. Subsequently, a film thickness of 10 was formed on the MgO buffer layer at 700 ° C.
In-situ epitaxial growth was performed on 00 Å of BaPbO ₃ (100) and further on 2000 Å of BaTiO ₃ (001). FIG. 7 shows the layer structure of the obtained laminate of oriented thin films. In this layer structure, a conductor layer (lower electrode) 2 and a ferroelectric layer (thin film optical waveguide) 3 are formed on a semiconductor substrate 1b having a buffer layer 1 'on the surface. Table 4 shows examples of combinations of such ferroelectrics, conductors, buffer layers, and semiconductor single-crystal substrates.

Example 6 In the same manner as in Example 5, an epitaxial MgO buffer layer was formed on a GaAs (100) single crystal substrate by excimer laser deposition. Next, in the same manner as in the previous example, PZT, BaPb
O ₃ and PLT to form PLT (00
1) / BaPbO ₃ (100) / PZT (001) / M
A multilayer epitaxial structure of gO (100) / GaAs (100) was obtained. FIG. 8 shows that the first buffer layer 1 '
a and a semiconductor substrate 1b having a second buffer layer 1'b
Above, a laminate of an oriented thin film composed of a conductor layer (lower electrode) 2 and a ferroelectric layer (thin film optical waveguide) 3 is shown. Table 5 shows examples of combinations of such ferroelectrics, conductors, second buffer layers, first buffer layers, and semiconductor single crystal substrates. Next, a laser beam was introduced by providing a comb-shaped upper Al electrode on the surface of the PLT. As shown in FIG. 9, when a laser beam introduced into the PLT thin film waveguide is applied with a voltage between Al as the upper electrode 4 and BaPbO ₃ (conductor layer) as the lower electrode 2 of the PLT thin film, The switching of the laser light became possible by the Bragg reflection of the electric lines of force 5 due to the electro-optic effect. Therefore, this element can be used as an optical waveguide as in the fourth embodiment. Further, as compared with the device shown in FIG. 10 in which only the comb-shaped electrode 4 'facing the surface of the PLT is provided.
Since a voltage can be effectively applied in the thickness direction of the PLT, the driving voltage is low, and furthermore, the width between the electrodes is not restricted by the fine processing of the electrodes.

In the above embodiments, the film was formed by the sol-gel method or the excimer laser deposition method, or both of them. However, the film forming process is not limited to these methods. , Flash evaporation, Rf-magnetron sputtering, ion beam sputtering, ion plating, MBE, ionized cluster beam epitaxy, CVD, MOCVD, plasma CVD, etc., and other wet processes other than the sol-gel method However, it is also effective for manufacturing the optical switching element of the present invention.

[0027]

According to the optical switching element of the present invention, the distance between the electrodes can be reduced as compared with the conventional coplanar element (FIG. 6) in which opposing electrodes are provided on a thin film having an electro-optical effect. Therefore, a voltage can be effectively applied in the film thickness direction. Also, by making the thin film optical waveguide an epitaxial or oriented ferroelectric thin film,
A large remanent polarization value and a large electro-optic constant of the ferroelectric can be obtained. Further, since an epitaxial or oriented oxide electrode is provided between the ferroelectric and the substrate, a switching element such as a light modulation element which can be driven at a low voltage or a high-performance nonvolatile memory can be manufactured. further,
Since it is possible to produce an epitaxial or oriented oxide electrode on a semiconductor substrate and an epitaxial or oriented ferroelectric thin film using the same, an optical modulator on a GaAs semiconductor laser or an optical integrated circuit on a Si semiconductor integrated circuit Can be manufactured.

[Brief description of the drawings]

FIG. 1. PZT (110) on MgO (100) substrate
2 shows a laminate of the oriented thin film of Example 1 on which / BaPbO ₃ (110) was formed.

FIG. 2 SrTiO_ThreePZT (0) on a (100) substrate
01) / BaPbO _ThreeExample 2 in which (100) was formed
1 shows a laminate of an oriented thin film.

FIG. 3. LiNbO on Al ₂ O ₃ (0001) substrate
₃ (0001) / (Ba _0.8 Sr _0.2 ) PbO ₃ (11
1 shows a laminate of the oriented thin film of Example 3 in which 1) was formed.

FIG. 4 shows an epitaxial PLT (001) / BaPbO ₃ (100) / PZ on a SrTiO ₃ (100) substrate.
The laminate of the oriented thin film having a multilayer structure of Example 4 in which T (001) is formed is shown.

FIG. 5 shows an optical switching element based on the electro-optic effect in which an upper electrode is provided on the PLT surface of the laminate of oriented thin films of Example 4.

FIG. 6 shows an optical switching element based on the electro-optic effect in which electrodes are provided on the surface of a PLT on a substrate without providing a conductor layer.

FIG. 7: BaTiO 3 on GaAs (100) substrate
₃ (001) / BaPbO ₃ (100) / MgO (10
5 shows a laminate of the oriented thin film having a multilayer structure of Example 5 in which No. 0) was formed.

FIG. 8 shows an epitaxial PLT (001) / BaPbO ₃ (100) / PZT on a GaAs (100) substrate.
13 shows a laminate of a multi-layered oriented thin film of Example 6 in which (001) / MgO (100) was formed.

FIG. 9 shows an optical switching element based on the electro-optic effect in which an upper electrode is provided on the PLT surface of the stack of oriented thin films of Example 6.

FIG. 10 shows an optical switching element based on the electro-optic effect in which electrodes are arranged on the surface of a PLT on a substrate and a buffer layer without providing a conductor layer.

[Explanation of symbols]

1a ... oxide substrate, 1b ... semiconductor substrate, 1 '... buffer layer, 1'a ... first buffer layer, 1'b ... second buffer layer, 2 ... conductor layer (lower electrode), 3 ... ferroelectric Layer (thin film optical waveguide), 4 ... upper electrode, 4 '... comb-shaped electrode, 5 ... electric lines of force.

Claims (4)

[Claims] 1. A thin-film optical waveguide for introducing light and exhibiting an electro-optical effect, and an upper electrode and a lower electrode positioned above and below the thickness direction of the thin-film optical waveguide for applying a voltage in the thickness direction. An optical switching element comprising: 2. The optical switching device according to claim 1, further comprising a single crystal substrate, wherein said lower electrode is an epitaxial or oriented conductive thin film provided on said single crystal substrate, and said thin film optical waveguide. Is an optical switching element characterized by being an epitaxial or oriented ferroelectric thin film. 3. The optical switching element according to claim 2, wherein an epitaxial or oriented buffer layer is provided between said substrate and said lower electrode. 4. The lower electrode is made of a perovskite ABO ₃ type conductive thin film, and the dielectric thin film is made of a perovskite ABO.
_3. The optical switching element according to claim 2, comprising a type ₃ ferroelectric.