JP3486957B2 - Oriented materials and surface acoustic wave devices - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oriented material or an oriented substrate which can be used for various devices using diamond, and more specifically, formed on a diamond and a surface of the diamond having a specific orientation. The present invention relates to an orientation material or an orientation substrate including a layer made of the other material, and a surface acoustic wave device using the orientation substrate. Such a surface acoustic wave element can be suitably used for, for example, a high frequency filter.

[0002]

2. Description of the Related Art Diamond has the highest sound velocity of any material, and its band gap is 5.5 eV, which is extremely large in existing materials. In addition, since it is transparent to light in the near-ultraviolet region to the near-infrared region, it is expected to be used for improving characteristics and expanding the operating region in fields such as acoustic applications, surface acoustic waves, optical applications, and semiconductors. ing. Further, since diamond has high thermal conductivity, it can be suitably used as a heat sink by itself, and by using diamond, it is stable and does not require temperature compensation for heat. It is also possible to configure a functional element (for example, an optical functional element).

Utilizing such mechanical, electrical or electronic properties, diamond is used in various mechanical, optical, electrical or electronic devices (for example, by Nao Inuzuka). "Diamond thin film" 99-1
See page 15, 1990 (Kyoritsu Shuppan). As one of the devices using diamond, there is a surface acoustic wave element which can be suitably used for a high frequency filter and the like.

As such a surface acoustic wave device, conventionally, for example, Japanese Patent Publication No. 54-38874, and Japanese Patent Laid-Open No. 64-6487.
As disclosed in Japanese Patent Publication No. 62911, there is known one having a structure in which an electrode and a piezoelectric body are combined and laminated on a diamond thin film or the like.

LiTaO _3, which is one type of piezoelectric material, is a ferroelectric material and is characterized by having a high Curie temperature, a large birefringence, a strong piezoelectric effect, a high acousto-optical characteristic, and a large electro-optical effect. LiTaO ₃ has a refractive index, an electro-optical constant, and the like similar to LiNbO _3, and therefore LiNbO 3
It can be used in a surface acoustic wave device, a modulation device, a switching device, a deflection device, an optical waveguide, etc. to which ₃ is applied. Conventionally, a LiTaO ₃ wafer by the pulling method has been used for such an application. L
Compared to LiNbO ₃ , iTaO ₃ can reduce impurities mixed in during crystal growth, and thus can easily be a high-quality wafer. Further, LiTaO ₃ has the advantage that when it is used as an optical waveguide or the like, there is little change in its own refractive index (optical damage) due to the laser.

In addition to the above-mentioned "LiTaO ₃ wafer by the pulling method" which has been conventionally used, a study on thinning of LiTaO ₃ has recently been made for the purpose of functional devices.
The application of thin film LiTaO ₃ to the field that has been used as a bulk substrate has been studied. With the recent improvement of thin film forming technology, a thin film of LiTaO ₃ has been formed by using a vapor deposition technique such as sputtering, and a substrate such as Al ₂ O ₃ and L
Various applications have been studied by stacking with an iTaO ₃ thin film. As an example of epitaxially growing a LiTaO ₃ single crystal thin film on a heterogeneous substrate, for example, Appl. Phys.
Lett., Vol. 63 (No. 23), p3146-3148
An example using (0001) Al ₂ O ₃ described in (1993) is known, but a substrate having excellent physical properties has been demanded in order to obtain a thin film having higher characteristics.

On the other hand, as a surface acoustic wave element, as disclosed in Japanese Patent Application Laid-Open No. 2-299309, a piezoelectric material such as ZnO / diamond, LiTaO ₃ / diamond, etc., which takes advantage of the high acoustic velocity of diamond, is used. Surface acoustic wave devices having a diamond structure have been known.

[0008]

However, in the conventional surface acoustic wave device using such a diamond thin film, the propagation loss of the surface acoustic wave is large when a piezoelectric body is formed on the diamond thin film. There was a problem.

When forming a surface acoustic wave device having a LiTaO ₃ / diamond structure, a piezoelectric thin film having high crystallinity (especially a single crystal thin film) is used in view of reducing the propagation loss of the device.
However, it has been conventionally considered difficult to form a good LiTaO ₃ thin film on diamond.

Also, as in conventional optical waveguides and the like,
When a LiTaO ₃ optical waveguide is formed on a glass substrate or the like, its thermal conductivity is poor, so that temperature changes and refractive index changes occur during light irradiation, and optical switches and optical modulators that utilize the electro-optical effect and the like are generated. The stable operation of such devices has been hindered.

An object of the present invention is to provide a novel orientation material or orientation substrate which can be suitably used for a device using diamond such as a surface acoustic wave element.

Another object of the present invention is to provide a surface acoustic wave device which uses diamond and reduces the propagation loss of surface acoustic waves.

[0013]

As a result of intensive studies, the present inventors have found that LiT on a diamond surface having a specific orientation.
It has been found that when the aO ₃ film is arranged, a specific high axial orientation can be easily obtained in the LiTaO ₃ film.
The present inventors have conducted further research based on this finding,
Such (LiTaO ₃ film having high axial orientation) /
It has been found that the (diamond surface having the above-mentioned orientation) structure provides an orienting material which is extremely effective in achieving the above-mentioned object.

The oriented material of the present invention is based on the above findings, and more specifically, the diamond and the Li arranged on the surface of the diamond having the (111) orientation.
It is characterized by comprising a TaO ₃ film.

According to the present invention, further, composed of a single crystal diamond, the single crystal diamond (111) single crystal LiTaO ₃ film disposed on a surface, said LiTaO ₃
The (001) plane of the film is (11) of the single crystal diamond.
1) An oriented material characterized by being parallel to a plane is provided.

According to the present invention, further, composed of a single crystal diamond, the single crystal diamond (100) single crystal LiTaO ₃ film disposed on a surface, said LiTaO ₃
The (100) plane of the film is (10) of the single crystal diamond.
Oriented materials are provided that are parallel to the 0) plane.

According to the present invention, an oriented substrate is further characterized by having a laminated structure composed of a diamond layer and a LiTaO ₃ film arranged on a surface of the diamond layer having (111) orientation. Will be provided.

According to the present invention, a layer of single crystal diamond and a single crystal LiTaO ₃ film arranged on the (111) plane of the single crystal diamond are further used.
There is provided an oriented substrate, wherein the (001) plane of the iTaO ₃ film is parallel to the (111) plane of the single crystal diamond.

According to the present invention, further, a layer made of single crystal diamond and a single crystal LiTaO ₃ film arranged on the (100) plane of the single crystal diamond are used.
An oriented substrate is provided, wherein the (100) plane of the iTaO ₃ film is parallel to the (100) plane of the single crystal diamond.

According to the present invention, further, a diamond layer, a LiTaO ₃ film arranged on a surface of the diamond layer having a (111) orientation, and a comb-shaped electrode arranged on the LiTaO ₃ film. A surface acoustic wave device is provided.

According to the present invention, further, the diamond layer, the comb-shaped electrode arranged on the surface of the diamond layer having the (111) orientation, and the L-shaped electrode arranged on the comb-shaped electrode.
Provided is a surface acoustic wave device comprising an iTaO ₃ film.

According to the present invention, a diamond layer and a comb-shaped electrode made of conductive diamond and arranged on the surface of the diamond layer having (111) orientation,
There is provided a surface acoustic wave device comprising a LiTaO ₃ film arranged on the comb-shaped electrode.

According to the present invention, further, a diamond layer, a comb-shaped electrode made of a conductive material, which is arranged in a concave portion of a surface of the diamond layer having (111) orientation, and arranged on the comb-shaped electrode. A surface acoustic wave device is provided which is made of a LiTaO ₃ film.

According to the present invention, a diamond layer, a short-circuiting electrode arranged on the surface of the diamond layer having (111) orientation, and a LiTaO ₃ film arranged on the short-circuiting electrode. And a comb-shaped electrode arranged on the LiTaO ₃ film, to provide a surface acoustic wave device.

According to the present invention, further, a diamond layer, a LiTaO ₃ film arranged on the surface of the diamond layer having (111) orientation, and a SiO ₂ film arranged on the LiTaO ₃ film, Provided is a surface acoustic wave device comprising a layer made of at least one kind of material selected from the group consisting of diamond and a diamond-like carbon film, and a comb-shaped electrode arranged on the material layer. To be done.

According to the present invention, a diamond layer, a short-circuit electrode arranged on the surface of the diamond layer having (111) orientation, and a LiTaO ₃ film arranged on the short-circuit electrode. A layer made of one or more materials selected from the group consisting of SiO ₂ , diamond, and diamond-like carbon film, arranged on the LiTaO ₃ film, and a comb-shaped electrode arranged on the material layer There is provided a surface acoustic wave device comprising:

According to the present invention, a diamond layer, a LiTaO ₃ film arranged on the surface of the diamond layer having (111) orientation, and a short-circuiting electrode arranged on the LiTaO ₃ film. A layer made of at least one material selected from the group consisting of SiO ₂ , diamond, and diamond-like carbon film, arranged on the short-circuiting electrode, and a comb-shaped electrode arranged on the material layer There is provided a surface acoustic wave device comprising:

According to the present invention, further, the diamond layer, the first LiTaO ₃ film arranged on the surface having the (111) orientation of the diamond layer, and the first LiT.
Provided is a surface acoustic wave device comprising a comb-shaped electrode arranged on an aO ₃ film and a second LiTaO ₃ film arranged on the comb-shaped electrode.

[0029]

In the embodiment of the present invention in which the LiTaO ₃ film is arranged on the diamond surface having the (111) orientation, the LiTaO ₃ thin film is higher than the case where the LiTaO ₃ thin film is formed on the diamond surface having another orientation. L with c-axis orientation
An iTaO ₃ thin film is obtained. Based on the combination of the crystal structure of LiTaO ₃ and this high c-axis orientation, a LiTaO ₃ / diamond structure having good piezoelectricity can be obtained.

Therefore, such c-axis oriented LiTa
When the surface acoustic wave device is constructed by utilizing the O ₃ film / diamond structure, the electromechanical coupling coefficient, which is an index of the conversion efficiency of the device, can be improved. Furthermore, LiTaO ₃
By improving the surface flatness of the film and aligning the c-axis, the L
Since the film quality of iTaO ₃ is also improved, it is possible to reduce the propagation loss as a surface acoustic wave device.

According to the knowledge of the present inventor, the above-mentioned LiTaO
_{In the three} films, the (001) plane {plane perpendicular to the c-axis}
It is assumed that the crystal structure in (1) has a shape similar to the crystal structure of the (111) plane of diamond (compared to the plane having a different orientation from the (111) plane of diamond), and the crystal planes are easily aligned. Therefore, LiTaO ₃ formed on the surface of diamond having (111) orientation
It is estimated that a high c-axis orientation of the film can be obtained.

Further, according to the knowledge of the present inventor, the LiTaO ₃ film having a high c-axis orientation has good crystallinity, the grain boundary scattering of the surface acoustic wave becomes small, and the propagation loss of the surface acoustic wave is reduced. It is estimated that the reduction will be possible.

Further, according to an experiment by the present inventor, Li formed on the surface of diamond having (111) orientation.
It has been found that the surface of the TaO ₃ thin film has higher surface flatness than the LiTaO ₃ thin film formed on the surface of the diamond having a different orientation from the (111) plane. From this point as well, the surface of the LiTaO ₃ thin film formed on the surface of diamond having the (111) orientation has
Li formed on the surface different from (111) of diamond
Compared with the BR> TaO ₃ thin film, it is presumed that the scattering of surface acoustic waves due to surface irregularities can be reduced, which contributes to the reduction of propagation loss.

On the other hand, in the embodiment of the present invention in which the LiTaO ₃ film is arranged on the diamond surface having the (100) orientation, LiT is formed on the diamond surface having another orientation.
A LiTaO ₃ thin film having high a-axis orientation is obtained as compared with the case of forming an aO ₃ thin film. Even in such an embodiment, LiTaO ₃ having good piezoelectricity is obtained based on the combination of the crystal structure of LiTaO ₃ and high a-axis orientation.
₃ / Diamond structure can be obtained. Further, when the surface acoustic wave device is constructed by utilizing the a-axis oriented LiTaO ₃ film / diamond structure, the surface acoustic wave device is formed for the same reason as the case of the c-axis oriented LiTaO ₃ film / diamond structure. It is estimated that it is possible to improve the electromechanical coupling coefficient and to reduce the propagation loss.

When the oriented material or oriented substrate of the present invention is used, even in an optical waveguide, it is possible to reduce the propagation loss by reducing the grain boundary scattering due to the single crystal.

Hereinafter, the present invention will be described in detail with reference to the drawings as necessary.

(Diamond) In the present invention, the crystallinity of the diamond that gives the diamond surface on which the LiTaO ₃ film is to be arranged, and the orientation of the diamond surface are determined by the crystallinity (single crystal / single crystal) of the LiTaO ₃ film. Polycrystal)
It is preferable to use the following combinations depending on the relationship with the orientation (eg, c-axis orientation, a-axis orientation, etc.).

<Diamond><LiTaO ₃ film><Aspect1> Single crystal / (111) plane Single crystal / c-axis orientation ((001) plane of LiTaO ₃ is parallel to (111) plane of diamond) <Aspect 2> Polycrystal / (111) -oriented plane Single crystal / c-axis orientation ((001) plane of LiTaO ₃ is parallel to (111) plane of diamond) <Aspect 3> Single crystal / (100) plane Crystal / a-axis orientation (the (100) plane of LiTaO ₃ is parallel to the (100) plane of diamond) In the present specification, “plane having (111) orientation”
Is used to include both the above-mentioned “(111) plane of single crystal diamond and (111) plane of polycrystalline diamond”.

The method for obtaining the diamond surface is not particularly limited as long as the diamond surface on which the LiTaO ₃ film is to be arranged has the above-mentioned specific orientation. More specifically, for example, as a surface having such a specific orientation,
The surface of the single crystal diamond having the orientation may be used as it is, or a diamond film may be epitaxially grown on another material (base material), and the above-mentioned specific diamond film surface may be used. You may obtain the surface which has orientation.

The shape (planar shape, three-dimensional shape), size, etc. of diamond that gives the surface having the above-mentioned specific orientation are not particularly limited, and can be appropriately selected depending on the use of the orientation material or substrate of the present invention. It is possible.

In the present invention, when the diamond giving the above-mentioned "surface having a specific orientation" is a diamond film or a diamond layer, the diamond (thin)
The method of growing the film or diamond layer is not particularly limited. More specifically, for example, as the growth method, CVD
(Chemical vapor deposition) method, microwave plasma CVD method,
Known methods such as PVD (Physical Vapor Deposition) method, sputtering method, ion plating method, plasma jet method, flame method and hot filament method can be used.

The diamond itself which gives the surface having the above-mentioned orientation may be either insulating diamond or semiconductive diamond. In the present invention, the above-mentioned “insulating diamond” has a volume resistivity of 10 ⁶ Ω · c.
A diamond having a volume resistivity of 10 ⁶ Ω · cm or less is referred to as a “semiconductive diamond”.

The method for forming the semiconductive diamond is not particularly limited, but it is possible to form the semiconductive diamond by, for example, hydrogenating the diamond, doping the diamond with impurities, or introducing lattice defects into the diamond. it can.

(Orientation of Diamond Surface) As described above, the LiTaO ₃ film exhibits the highest orientation when formed on a surface of a single crystal, an epitaxial film or a polycrystalline diamond having (111) orientation. Show.

In the present invention, such (111) orientation of diamond can be compared with the diffraction intensity based on the (111) plane in the diffraction intensity based on X-ray diffraction and the diffraction intensity based on other planes. It is possible to evaluate based on this (for such X-ray diffraction, for example, a usual method using Cu—Kα ray ( 0.154 nm ) as a monochromatic X-ray can be used).

More specifically, in the diffraction intensity based on X-ray diffraction of polycrystalline diamond or the like, the diffraction intensity based on the (111) plane and other planes (for example, the (220) plane,
The diffraction intensity based on the (400) plane was measured, and the obtained intensity of the (111) plane was set to 100, and the diffraction intensity of the other plane was normalized (that is, the intensity of the (111) plane = 1).
When the relative intensity with respect to 00 is obtained), the total of the diffraction intensities obtained from the planes other than the (111) plane with respect to the diffraction intensity 100 of the (111) plane is obtained. In the present invention, the total of the “diffraction intensities other than the (111) plane” thus standardized is 25 or less, which means that the (111) of diamond is
It is preferable from the viewpoint of good c-axis orientation of the LiTaO ₃ film formed on the surface.

(LiTaO ₃ Film) In the present invention, the LiTaO ₃ film to be formed on the above-mentioned surface of diamond having a specific orientation may be a single crystal or a polycrystal. It is preferable to use it in combination with the orientation of the diamond surface as shown in the first to third aspects.

As a method of forming a LiTaO ₃ film,
Known methods such as sputtering, vapor deposition method, CVD method, laser annealing method, MOCVD (organic metal CVD) method and MBE (molecular beam epitaxy) method can be used without particular limitation.

The thickness of the LiTaO ₃ film can be appropriately selected depending on the use of the oriented material or oriented substrate of the present invention, and is not particularly limited.

(Orientation of LiTaO ₃ Film) In the present invention, the orientation of the LiTaO ₃ film can be evaluated by, for example, the X-ray rocking pattern method (one of the crystal plane orientation evaluation methods). is there. More specifically, for example, the orientation (in-plane orientation) can be evaluated as follows.

(1) The measurement sample is placed in the sample holder of the X-ray diffractometer.

(2) The plane orientation to be evaluated is measured by using the X-ray diffract pattern method.

(3) The θ axis (measurement sample rotation) and the 2θ axis (X-ray counter) are rotated to fix the θ axis and the 2θ axis to the maximum value of the output in the plane orientation to be evaluated. . LiTa with the c-axis oriented perpendicular to the substrate
In the case of an O ₃ film, 2θ is 39.277 ° and θ is 19.63.
It is 8 °. Further, in the case of a LiTaO ₃ film in which the a-axis is oriented perpendicular to the substrate, 2θ is 62.381 °,
θ is 31.191 °.

(4) Only the sample is rotated (only the θ axis),
Measure the rocking curve.

(5) The measured rocking curve is regarded as a Gaussian distribution, and its standard deviation σ is obtained.

The smaller the standard deviation σ of the rocking curve measured as described above, the better the orientation. In the oriented material, oriented substrate or surface acoustic wave device of the present invention, this σ value is 5 or less (further 4 or less).
Is preferred.

(Electrode Arrangement) In the surface acoustic wave device of the present invention, an electrode arrangement of comb-shaped electrodes (and, if necessary, short-circuiting electrodes) as shown in the schematic sectional views of FIGS. 1 to 4 is preferably used. .

In the structure (electrode arrangement A) shown in FIG. 1, the surface acoustic wave element is composed of diamond, a comb-shaped electrode arranged on the diamond, and a LiTaO ₃ layer arranged on the comb-shaped electrode. Become. The configuration (electrode arrangement C) shown in FIG. 2 is formed by further arranging a short-circuit electrode on the LiTaO ₃ layer of the above-mentioned “electrode arrangement A”.

In the structure (electrode arrangement E) shown in FIG. 3, the surface acoustic wave element is composed of diamond, a LiTaO ₃ layer arranged on the diamond, and a comb-shaped electrode arranged on the LiTaO ₃ layer. Become. The structure (electrode arrangement F) shown in FIG.
A short-circuit electrode is further arranged between the iTaO ₃ layer and the iTaO ₃ layer.

(Comb Type Electrode) The material forming the comb type electrode in the surface acoustic wave device of the present invention is not particularly limited as long as it is a conductive material. From the viewpoint of workability as a comb-shaped electrode and cost, Al (aluminum) can be particularly preferably used.

The thickness of the comb-shaped electrode is not particularly limited as long as the function as the electrode is exhibited, but it is preferably about 10 to 300 nm (more preferably about 10 to 50 nm ). If this thickness is less than 10 nm , the resistivity increases and the loss increases. On the other hand, when the thickness of the electrode exceeds 300 nm , surface acoustic waves (hereinafter referred to as "SA
The mass addition effect that causes the reflection of (W)) becomes significant, and it becomes difficult to obtain the target SAW characteristics.

The planar shape of the comb-shaped electrode is not particularly limited as long as it exhibits the function as the electrode, but it is a so-called single electrode as shown in the schematic plan view of FIG. 5, and the schematic plan view of FIG. A double electrode or the like can be preferably used.

If necessary, the comb-shaped electrode as described above may be embedded in the surface on which the electrode is to be formed (for example, a (111) oriented diamond surface). More specifically, for example, a concave portion having a shape such as a groove is formed (or a predetermined surface is formed so as to give the concave portion in advance), and all or a whole of a conductive material such as Al forming the comb-shaped electrode or A part may be filled in the recess thus formed. By embedding all or part of the comb-shaped electrode in this manner, for example, the height of the comb-shaped electrode can be made substantially equal to the height of the surface on which the electrode is to be formed, and the thickness of the electrode It is possible to reduce the influence of the SAW reflection caused by.

(Short-Circuiting Electrode) In the surface acoustic wave device of the present invention, the short-circuiting electrode provided as required is an electrode having a function of changing the SAW characteristic of the device by setting the electric field to an equal potential. . This electrode is preferably composed of a metal (thin) film (for example, Al, Au, Al-Cu, etc.). Since the short-circuit electrode has a function different from that of the comb-shaped electrode described above, the material forming the short-circuit electrode does not necessarily have to be the same as the material of the comb-shaped electrode.

The thickness of the short-circuit electrode is not particularly limited as long as it exhibits the function as the electrode, but is 10 to 300 nm.
It is preferably about 10 nm to 50 nm. If the thickness is less than 10 nm , it becomes difficult to form an equipotential, while if it exceeds 300 nm , the SAW reflection is likely to be affected.

It is preferable that the short-circuiting electrode has, for example, a planar shape of "solid electrode" having the same occupied area as the comb-shaped electrode.

(SiO ₂ layer, etc.) In the surface acoustic wave device of the present invention, if necessary, SiO ₂ , diamond,
A layer made of one or more kinds of materials selected from the group consisting of and a diamond-like carbon film may be provided. Such a layer can also have a function as a protective layer.

By forming the SiO ₂ (thin) film on the LiTaO ₃ film, the temperature coefficient can be reduced and / or the electromechanical coupling coefficient, which is an index of efficiency, can be increased.

On the other hand, when a diamond thin film or a diamond-like carbon film is laminated on the LiTaO ₃ film as the above layer, it becomes easy to increase the propagation speed and obtain a high electromechanical coupling coefficient.

(Diamond-like carbon) Diamond-like carbon (Diamond-like carbon) forming the diamond-like carbon film
carbon; or DLC) is an amorphous substance having a high hardness, is excellent in stability, and is composed of carbon atoms similar to diamond, so that it is not necessary to substantially consider elemental diffusion and reaction into diamond. It has features. Therefore, diamond-like carbon can be preferably used as an insulating material for forming the insulating film.

The diamond-like carbon (also referred to as i-carbon or amorphous carbon) is a substance having the following properties.

(1) Usually, hydrogen is contained in addition to carbon. In this case, the number of moles of hydrogen is preferably smaller than the number of moles of carbon.

(2) The crystalline state is amorphous. Diamond-like carbon and diamond or graphite can be distinguished by, for example, Raman spectroscopy.
Figure 7 shows diamond-like carbon (amorphous carbon)
(A), graphite (b), diamond (c)
And a typical spectrum is shown. As shown in FIG.
Diamond (c) is 1332 cm ^-1 (derived from sp ³ C-C), and graphite (b) is 1580 cm ^-1 (sp ² C).
-Derived carbon) has sharp peaks, while diamond-like carbon (c) has 1360 cm ^-1 and 1600 c.
A broad peak is shown at m ^-1 .

(3) It has a higher hardness than ordinary metals. The diamond-like carbon used in the present invention has a Vickers hardness Hv (Vickers hardness) of 1,000 to 5.0.
It is preferably about 00 (diamond usually has a Vickers hardness Hv of about 10,000).

(4) It is an insulator electrically.

(5) It has a property of transmitting light.

The diamond-like carbon film having the above-mentioned properties can be used for plasma CV as in the synthesis of diamond.
It can be formed according to a vapor phase process such as D, an ion beam vapor deposition method, and sputtering. More specifically, for example, diamond-like carbon can be obtained by lowering the substrate temperature (for example, a substrate temperature of about 100 ° C.) under the same CVD conditions as diamond formation (for details of diamond-like carbon, see, for example, , Akio Hiraki
Hiroshi Kawarada, "Carbon", 1987 (No. 128), 41-
See page 49 (Japan Carbon Society).

(Use) The oriented material or oriented substrate of the present invention can be applied to various devices utilizing the LiTaO ₃ / diamond structure. Preferred uses of the material or the oriented substrate are as follows.

<Diamond><LiTaO ₃ ><Aspect1> Single crystal / (111) plane Single crystal / c-axis orientation (the (001) plane of LiTaO ₃ is parallel to the (111) plane of diamond) Application: Optical Waveguide, optical splitter, switch, surface acoustic wave device (SAW device) <Aspect 2> Polycrystalline / (111) -oriented plane Single crystal / c-axis oriented (LiTaO ₃ (001) plane is diamond ( (111) plane parallel) Use: Surface acoustic wave device <Aspect 3> Single crystal / (100) plane Single crystal / a-axis orientation ((100) plane of LiTaO ₃ is parallel to (100) plane of diamond) : Optical waveguide, optical branching device, switch, surface acoustic wave device (SAW device) (Application example as optical waveguide) Here, an example in which the oriented substrate of the present invention is applied as an optical waveguide is shown in the schematic sectional view of FIG. Irradiation to now be described.

Referring to FIG. 8, first, a LiTaO ₃ film is grown on diamond. A diamond thermistor and an LD (laser diode) are arranged on both ends of the LiTaO ₃ film to form an external optical modulator on the LiTaO ₃ . In such a mode, since each of these devices is formed on the heat sink having high thermal conductivity of diamond, it becomes possible to form an optical modulator having high thermal stability. At this time, the LiTaO ₃ film to be formed on the diamond is preferably a single crystal from the viewpoint of reducing the propagation loss of light.

More specifically, the above-mentioned preferred LiT
The aO ₃ film can be formed, for example, by epitaxially growing a LiTaO ₃ (001) film on the (111) plane of high-pressure synthetic single crystal diamond. The Li
To form an optical waveguide on the TaO ₃ film, for example,
The proton exchange method is preferably used. This proton exchange method is a kind of optical waveguide forming method that can be suitably used for LiTaO _{3 and the} like. According to this proton exchange method, for example, a waveguide is formed on the surface of a LiTaO ₃ film by using photolithography, and then the LiTaO ₃ film is brought into contact with a proton exchange reagent such as benzoic acid or pyrophosphoric acid to form a LiTaO ₃ film. An exchange reaction between Li of ₃ and H in the acid occurs, and it becomes possible to increase the refractive index of the portion where the proton exchange occurs (for details of such a proton exchange method, see, for example, Hiroshi Nishihara). Other references, "Optical Integrated Circuits", pp. 167-170, Ohmsha (1990) can be referred to).

As other waveguide forming methods, a method of forming a buried type waveguide, a method of forming a protruding ridge type waveguide, and a decrease in the refractive index when a metal electrode is loaded are used to form an electrode. There is a method of forming a loaded type waveguide in which a LiTaO ₃ portion in which there is no is used as a waveguide.

As a method of forming a waveguide which can be preferably combined with an embedded optical modulator, a Ti diffusion method, a proton exchange method and the like are known. When the proton exchange method is used, the Ti diffusion method and the Ti diffusion method are used. In comparison, a higher refractive index difference can be obtained and optical damage can be reduced, so that it is easy to form a low-loss waveguide.

A semiconductor device such as a semiconductor laser or a thermistor may generate heat by itself when used for a long time, and its operating characteristics may change. Especially when the semiconductor laser is used for communication, etc., it is highly likely that problems such as cross-linking and noise increase will occur when the frequency fluctuates. It is preferable to let it escape. When a semiconductor laser is placed on diamond, which has the highest thermal conductivity, and the temperature or temperature change is kept constant by feeding back the change in heat using a thermistor, etc., a stable optical modulator can be formed. Therefore, it is preferable.

Hereinafter, the present invention will be described more specifically with reference to Examples.

[0086]

EXAMPLE 1 LiT type natural diamond and (Ib type) high-pressure synthetic diamond having a (111) plane orientation were each subjected to RF magnetron sputtering to obtain LiT.
An aO ₃ film was formed.

<RF magnetron sputtering conditions> Pressure: 0.665 Pa Substrate temperature: 680 ° C. Ar: O ₂ = 1: 2 RF power: 100 W Film thickness: About 0.6 μm Target: Li: Ta = 3: 2 Sintered body When forming the above LiTaO ₃ film, the substrate temperature is bulk LiT.
Since the temperature is higher than the Curie point (Tc to 620 ° C.) of aO ₃ and the spontaneous polarization has a random orientation of 180 ° C., an electric field is applied to the substrate during sputtering, and after the film formation, the substrate temperature is gradually increased with the electric field applied. The crystal was made to have sufficient piezoelectricity.

[0088] The above Ib high pressure LiTaO ₃ film RHEED formed on a single crystal diamond (reflection high-energy electron diffraction, the incident direction of the electron beam: ^[1 - 10]) was analyzed by, as a photograph in FIG. 9 (replica RHE shown in
ED pattern (appears every 120 °), and FIG.
The RHEED pattern (appears every 60 °) shown in the photograph (shown as a duplicate) was obtained. RH used here
EED is a method of electron beam diffraction and is a method of observing an electron beam diffraction pattern generated by scattering on the surface of a substance with a fluorescent plate at the rear.

Since only spots were obtained as shown in FIGS. 9 and 10, it was confirmed that the LiTaO ₃ film was epitaxially grown.

The two types of LiTaO formed as described above are also used.
_{When three} films were examined by an X-ray diffractometer, it was found that
Also for the O ₃ film, diffraction other than (006) was not observed. That is, the (111) plane of diamond and Li
It was confirmed to be parallel to the (001) plane of the TaO ₃ film. The result of the X-ray diffraction is shown in the graph of FIG.

FIG. 12 shows the single crystal diamond (111)
Result showing the matching state between the plane and the (001) plane of LiTaO ₃ (commercial program MOLGRAPH
The results of simulation using is shown. This FIG.
In, the single crystal diamond is placed on the upper side. 12
The white circles represent C atoms, the black circles represent O atoms, and the gray circles represent Li atoms. As shown in FIG. 12, the interstitial distance between the Li atom and the C atom is about 2: 1, and the C atom is Li.
Every other atom (O is close to C due to matching with Li).

Example 2 LiT type natural diamond and (Ib type) high-pressure synthetic diamond having a (100) plane orientation were each subjected to LiT by RF magnetron sputtering.
An aO ₃ film was formed.

<RF magnetron sputtering conditions> Pressure: 1.33 Pa Substrate temperature: 730 ° C. Ar: O ₂ = 2: 3 RF power: 120 W Film thickness: About 0.7 μm Target: Li: Ta = 3: 2 Sintered body When the two types of LiTaO ₃ films formed above were examined with an X-ray diffractometer, it was found that for any of the LiTaO ₃ films,
No diffraction other than (300) was observed. That is,
(100) face of diamond and (10) of LiTaO ₃ film
It was confirmed to be parallel to the (0) plane. The result of the X-ray diffraction is shown in the graph of FIG.

LiTaO formed on the above diamond
₃ membrane RHEED (incident direction of electron beam: ^[1 - 01])
As a result of analysis, only spots were obtained as in Example 1. That is, it was confirmed that the LiTaO ₃ film was epitaxially grown.

FIG. 14 shows a single crystal diamond (100)
Result showing the matching state between the plane and the (100) plane of LiTaO ₃ (commercial program MOLGRAPH
Is used). In FIG. 14, since the single crystal diamond is on the lower side, some C atoms are hidden. In FIG. 14, the lattice is formed by arranging unit cells based on diamond in the (100) plane. The C atom is located at each lattice point and the center of each lattice. In this figure, the smallest white circle corresponds to the C atom, so that the place where the C atom is not visible (hidden) is the place where matching can be performed. In FIG. 14, black circles represent O atoms and gray circles are Li.
Showing an atom. In this FIG. 14 as well, similar to FIG. 12 described above, the interstitial distance between Li atoms and C atoms is 2:
1 matches, and the O atom exists at a position close to the C atom.

Example 3 High Pressure Synthesis (100) Single Crystal Diamond, (111) Single Crystal Diamond, Si (100) Face, and β-Si
A diamond thin film (thickness: 15 μm) was epitaxially grown on each of the C (111) planes, the surface of the diamond film was polished to be flat (thickness: 13 μm), and then a LiTaO ₃ film was formed on the diamond film. The film forming conditions of the LiNbO3 film used at this time were the same as those in Examples 1 and 2.

<Single crystal diamond (100) and S
Formation Condition of Diamond Epitaxial Film on i (100) Surface> Microwave Plasma CVD Power: 350 W Pressure: 3990-5320 Pa CH ₄ / H ₂ = 1-6 (%) <Epitaxial film on single crystal diamond (111) forming conditions> Microwave plasma CVD power of: 350 W _{pressure: 3990~5320Pa CH 4 / H 2 =} 1~2 (%) < conditions of heteroepitaxial on SiC> Microwave plasma CVD method Microwave power: 920W pressure: 1330 _{~399Pa CH 4 / H 2 = 5} / 99.5 substrate temperature: 800 ° C. (applying a DC bias of -180V on the substrate side) was examined four LiTaO ₃ film formed by the X-ray diffractometer , (100) single crystal diamond, Si
In the LiTaO ₃ film formed on the epitaxial diamond thin film on (100), only the diffraction peak of (300) was obtained. That is, diamond (10
It was confirmed that the (0) plane was parallel to the (100) plane of the LiTaO ₃ film.

Further, in the (111) single crystal diamond and the LiTaO ₃ thin film formed on the diamond thin film on (111) SiC, the X-ray diffraction peak was (00
Only 6) was recognized. That is, diamond (1
It was confirmed that the (11) plane was parallel to the (001) plane of the LiTaO ₃ film.

In the RHEED observation, only spots were observed for all of the above four kinds of LiTaO ₃ thin films, and it was confirmed that these LiTaO ₃ thin films were epitaxially grown on the epitaxial diamond thin film.

Example 4 LiTa was deposited on high pressure synthetic single crystal diamond (111).
After forming an O ₃ single crystal thin film (thickness 8 μm) under the same conditions as in Example 1, the LiTaO ₃ surface was patterned by photolithography using photolithography.

Thereafter, pyrophosphoric acid was applied to the surface, and 14
After heating at 0 ° C. for 40 minutes for proton exchange, a waveguide (width of the waveguide: 4 μm, whose schematic perspective view is shown in FIG. 15) is used.
A length of 0.8 mm, θ = 0.02 °) was formed. Furthermore,
An electrode for applying an electric field was formed on the waveguide by using Ti to form an optical branch switch as shown in FIG.

He—Ne laser light (wavelength: 632.8 nm) was applied to the LiTaO ₃ optical waveguide thus formed.
Was introduced by using a rutile prism coupler, and the change of emitted light was examined.

For comparison, Li and sapphire (0001) substrates and a glass substrate, respectively, were used in the same manner as above.
A TaO ₃ thin film was formed, an optical branching switch was formed, and the extinction ratio of emitted light (the ratio between the maximum output light and the minimum output light) was measured. The applied voltage V ₀ was ± 40V.

The measurement results were as follows.

<Substrate><Extinctionratio> (111) diamond 14 dB (0001) sapphire 10 dB glass 8 dB Example 5 c-cut sapphire and (111) single crystal diamond, each having a thickness of 1.0 μm LiTaO ₃ A single crystal thin film was formed. When the LiTaO ₃ thin film was examined by X-ray diffraction, it was confirmed that both the LiTaO ₃ thin film on sapphire and the LiTaO ₃ thin film on diamond were LiTaO ₃ epitaxial films having a (001) orientation.

An Al thin film having a thickness of 50 nm was vapor-deposited on each of the two types of single crystal LiTaO ₃ thin films formed as described above, and then 8 μm was formed by photolithography.
Comb-shaped electrode having a period of (double electrode in FIG. 2, d = 1 μ
m, the number of pairs of input / output electrodes: 40, and the distance between the centers of the input / output electrodes: 640 μm) to form a surface acoustic wave device.

The frequency characteristics of the surface acoustic wave device thus manufactured were evaluated using a network analyzer (Yokogawa Hewlett Packard (YHP) Co., 8719A), and it was found that the surface acoustic wave device using a sapphire substrate operated. The frequency is 651 MHz, while (111)
In a surface acoustic wave device using a diamond single crystal substrate,
The operating frequency was 1.23 GHz. That is, (11
1) A surface acoustic wave device having a structure in which a LiTaO ₃ epitaxial film having (001) orientation is arranged on a single crystal diamond has a higher operating frequency even when a comb-shaped electrode having the same electrode width is used. It was operational.

Example 6 A high-pressure synthetic single crystal diamond was cut in the (110), (331), and (112) directions, and a 1 μm thick LiTaO ₃ thin film was formed on each surface.

<LiTaO ₃ formation conditions> Pressure: 0.665 Pa Substrate temperature: 600 ° C. Ar: O ₂ = 1: 2 RF power: 100 W Target: Li: Ta = 3: 2 Sintered body Formed as described above 3 kinds of single crystal LiTaO ₃
After depositing an Al thin film having a thickness of 50 nm on each thin film, a comb-shaped electrode having a period of 8 μm was formed by a photolithography method to fabricate a surface acoustic wave device. As the comb-shaped electrodes, three types of comb-shaped electrodes having different input / output electrode distances were formed as described below.

Number of electrode pairs (both input and output): 40 pairs (double electrode, normal type) Electrode width: 1.2 μm (center frequency: 1 GHz) Electrode crossing width: 50 × wavelength (wavelength is 8 times the electrode width) Distance between output electrode centers: 50 × wavelength, 80 × wavelength, 11
0 × wavelength The obtained surface acoustic wave device was evaluated based on the operating characteristics using a network analyzer (YHP Co., 8719A) for the above-mentioned three types of devices having different input-output electrode distances. Was measured. This propagation loss includes the propagation loss: the insertion loss (IL) of S21 and the reflection loss: S11, S12 to the conversion loss (TL1), (TL).
2) is calculated, and from the bidirectional loss 6 (dB) essentially obtained by this electrode structure, the propagation loss PL (dB) =
It was determined as IL-TL1-TL2-6. On the other hand, the electromechanical coupling coefficient (K ² ) is K ² = (G / 8) · f ₀ · C · N (based on the measurement of the radiation conductance (real part G) of the comb-shaped electrode using the above network analyzer. f ₀ : center frequency, C: total capacitance of comb-shaped electrodes, N:
The logarithm of the comb-shaped electrode).

Separately from the preparation of the surface acoustic wave device, LiTaO ₃ was epitaxially grown on (100) and (111) diamond single crystal substrates under the following conditions, and then an Al thin film was deposited as described above. Then, a comb-shaped electrode having a period of 8 μm was formed by photolithography to fabricate a surface acoustic wave device. The propagation loss of the surface acoustic wave device thus manufactured was measured in the same manner as above.

<(100) LiTaO ₃ epitaxial film forming condition> Pressure: 1.33 Pa Substrate temperature: 620 ° C. Ar: O ₂ = 2: 3 RF power: 120 W Target: Li: Ta = 3: 2 Sintered body < (111) was the same as the above-mentioned conditions.
> The measurement results of the above propagation loss are shown in Table 1 below.

[0113]

[Table 1]

As shown in Table 1 above, LiTaO ₃ /
It has been found that the propagation loss is reduced in the surface acoustic wave device having the diamond (111) structure and the LiTaO ₃ / diamond (100) structure.

Example 7 High-pressure synthetic single crystal diamonds (110), (331), (1
12) and (111) direction were cut, and a LiTaO ₃ thin film with a thickness of 1 μm was formed on each surface.

<LiTaO ₃ forming conditions> Pressure: 0.665 Pa Substrate temperature: 600 ° C. Ar: O ₂ = 1: 2 RF power: 100 W Target: Li: Ta = 3: 2 Sintered body The above four types of LiTaO ₃ films X-ray diffraction and RHEE
When analyzed by D, the LiTaO ₃ film formed on the (111) plane-oriented diamond single crystal substrate was
Epitaxial growth of a LiTaO ₃ film (c-axis oriented) having a (001) plane was observed. It was found that the LiTaO ₃ film formed on the diamond substrate having other plane orientations was a mixed film containing (110) and (104) directions in addition to the c-axis.

On each of the four types of single crystal LiTaO ₃ thin films formed as described above, an Al thin film with a thickness of 50 nm was deposited, and then 8 μm was formed by photolithography.
A comb-shaped electrode having a period of was formed to produce a surface acoustic wave device. As the comb-shaped electrodes, three types of comb-shaped electrodes having different input / output electrode distances were formed as described below.

Number of electrode pairs (both input and output): 40 pairs (double electrode, normal type) Electrode width: 1.2 μm (center frequency: 1 GHz) Electrode crossing width: 50 × wavelength (wavelength is 8 times the electrode width) Distance between output electrode centers: 50 × wavelength, 80 × wavelength, 11
0 × wavelength The obtained surface acoustic wave device was evaluated based on the operating characteristics using a network analyzer (YHP Co., 8719A) for the above-mentioned three types of devices having different input-output electrode distances. , And the electromechanical coupling coefficient, which is an index of efficiency, was measured.

Separately from the preparation of the surface acoustic wave device, a (100) plane of LiTaO ₃ was epitaxially grown on a (100) diamond single crystal substrate under the following conditions, and then an Al thin film similar to the above was formed. A surface acoustic wave device was produced by forming comb-shaped electrodes having a period of 8 μm by vapor deposition and photolithography. With respect to the surface acoustic wave device thus manufactured, the propagation loss and the electromechanical coupling coefficient were measured in the same manner as above.

<(100) LiTaO ₃ epitaxial film forming condition> Pressure: 1.33 Pa Substrate temperature: 620 ° C. Ar: O ₂ = 2: 3 RF power: 120 W Target: Li: Ta = 3: 2 Sintered body Propagation above The measurement results of loss and electromechanical coupling coefficient are shown in Table 2 below.

[0121]

[Table 2]

As shown in Table 2 above, LiTaO ₃ /
It was found that the propagation loss is reduced and the electromechanical coupling coefficient is increased in the surface acoustic wave device having the diamond (111) structure and the LiTaO ₃ / diamond (100) structure. The degree of increase in the electromechanical coupling coefficient was larger in the surface acoustic wave device having the LiTaO ₃ / diamond (111) structure.

Example 8 A Ti thin film (thickness: 50 nm ) was used on an Ia type natural diamond having (311), (110), and (111) plane orientations and an Ib type high-pressure synthetic diamond. A comb-shaped electrode having the same parameters as in 6 was formed, and a LiTaO ₃ thin film was further formed on the comb-shaped electrode by RF magnetron sputtering.

<LiTaO ₃ Thin Film Forming Conditions> Pressure: 2.66 Pa Substrate temperature: 580 ° C. Ar: O ₂ = 1: 2 RF power: 80 W Target: Li: Ta = 3: 2 Sintered body LiTaO formed above _{When the 3} films were analyzed by an X-ray diffractometer to examine the c-axis orientation, no orientation other than the c-axis was observed for the LiTaO ₃ thin film formed on the (111) plane single crystal diamond. On the other hand, it was confirmed that the LiTaO ₃ thin film formed on the (311) and (110) single crystal diamonds was a mixed film having an orientation other than the c-axis.

After evaluating the above-mentioned orientation, a short-circuit electrode (a solid electrode having the same occupied area as the comb-shaped electrode) was formed on the LiTaO ₃ film using an Al film (thickness: 50 nm), and the surface elasticity was improved. A wave element was produced. With respect to the surface acoustic wave element, the propagation loss before and after the formation of the comb-shaped electrode was measured by the same method as in Example 6.

The measurement results of the above propagation loss are shown in Table 3 below.

[0127]

[Table 3]

As shown in Table 1 above, LiTaO ₃ /
It has been found that the propagation loss is reduced in the surface acoustic wave device having the diamond (111) structure.

Example 9 (100), (1 of natural type Ia and high pressure type Ib)
10), (111) diamond single crystal substrate, and S
A diamond thin film (thickness: 15 μm) is epitaxially grown on the i (100) plane and the β-SiC (111) plane, and the surface of the diamond film is polished to be flat (thickness: 13 μm).
μm), and then LiTaO 2 under the same conditions as in Example 7.
_Three films (thickness 1 μm) were formed.

An Al film (with a thickness of 50) is formed on the LiTaO ₃ film.
(nm 2 ) was deposited and then a comb-shaped electrode similar to that of Example 6 was formed by photolithography to obtain a surface acoustic wave device. With respect to the surface acoustic wave device thus obtained, the propagation loss and the electromechanical coupling coefficient were measured in the same manner as in Example 7.

After measuring the above-mentioned propagation loss, SiO ₂ was deposited on the sample.
A film (thickness 300 nm ) was formed and the propagation loss was measured. Further, after this propagation loss measurement, a short-circuit electrode (thickness: 50 nm ) was formed on the SiO ₂ film using Al, and the propagation loss was measured.

<Conditions for forming diamond epitaxial film> Microwave plasma CVD (100), (110) diamond film forming power: 300w Pressure: 3990-5320Pa CH ₄ / H ₂ = 1-6 (%) <( For formation of diamond film on 111), CH
_It was the same as the above except that ₄ / H ₂ = 1 to 2 (%). <Diamond hetero-epitaxial conditions on Si and SiC> Microwave plasma CVD method Microwave power: 900 W Pressure: 1330 to 0.399 Pa CH ₄ / H ₂ = 5 / 99.5 Substrate temperature: 800 ° C. (Substrate side A DC bias of -150 V is applied to the substrate.) <SiO ₂ forming conditions> RF magnetron sputtering apparatus Ar: O ₂ = 1: 1 Pressure: 2.66 Pa RF power: 200 W SiO ₂ target film thickness: 0.3 μm The propagation loss of the surface acoustic wave device was evaluated by the same method as in Example 7. The evaluation results are shown in Table 4 below.

[0133]

[Table 4]

As shown in Table 4 above, LiTaO ₃ /
It has been found that the propagation loss is reduced in the surface acoustic wave device having the diamond (111) structure and the LiTaO ₃ / diamond (100) structure. Above Li
In the surface acoustic wave device having the TaO ₃ / diamond (111) structure, the electromechanical coupling coefficient was further increased.

Example 10 A (100) single crystal Si substrate was mounted in a reaction chamber of a hot filament CVD apparatus, exhausted to 1.33 × 10 ⁻⁴ Pa or less, and then CH ₄ and H ₂ gases were introduced into the reaction chamber. CH ₄ /
It was introduced at a rate of H ₂ = 1 to 8%. The pressure in the reaction chamber is 1
3300 to 26600 Pa , filament temperature 2
The temperature of the substrate surface was set to 950 ° C. by setting the temperature to 100 ° C. and adjusting the distance between the filament and the substrate. Under the above conditions, a diamond film (thickness 17
μm) was formed.

The obtained diamond film was evaluated using an X-ray diffractometer and was found to be polycrystal (40
The plane orientations of 0), (220), and (111) were observed. By simultaneously changing the gas composition ratio and the pressure in the reaction chamber, it was possible to form a polycrystalline diamond film in which the strength ratio of the (111) plane or the (220) plane was changed. In X-ray diffraction, the peak intensity of each plane is different, so the peak intensity of the (111) plane was set to 100 and the peak intensity of other planes was normalized.

Diamond / S thus obtained
i substrate is polished (thickness of diamond after polishing: 15μ
m), a comb-shaped electrode made of Ti (thickness: 50 ) on the substrate.
nm , the same comb-shaped electrode as in Example 7), and a LiTaO ₃ film (thickness 1 μm) were laminated in this order.

The evaluation as a surface acoustic wave device was carried out by using Example 7.
In the same manner as above, the propagation loss was evaluated for the surface acoustic wave device formed by forming comb-shaped electrodes having different electrode intervals. The propagation loss was evaluated in the same manner as in Example 7.

The results of the above evaluations are shown in Table 5 below.

[0140]

[Table 5]

Example 11 In the same manner as in Example 10, a diamond thin film (thickness: 17 μm) was formed on a (100) single crystal Si substrate, and the surface was polished until the diamond film had a thickness of 15 μm. A comb-shaped electrode (thickness: 50 nm , the same comb-shaped electrode as in Example 6) was formed thereon using Ti, and a LiTaO ₃ film (thickness 1 μm) was further formed on the comb-shaped electrode. A surface acoustic wave device was obtained.

After forming the LiTaO ₃ film, the propagation loss was measured by the same method as in Example 7.

After measuring the propagation loss, a short-circuiting electrode (thickness: 50 nm ) was formed on the LiTaO ₃ film by using Al.
Propagation loss was measured.

After measuring the propagation loss, a plasma CVD method was used to form a diamond-like carbon film (thickness: 40 nm ) on the surface of the short-circuit electrode, and the propagation loss was measured. This diamond-like carbon film introduces methane gas at about 5 sccm into the reaction chamber and the pressure inside the reaction chamber is about 0.266 P.
a , the substrate temperature is set to 25 ° C, and the power density is 2
Discharged at W / cm ² and brought to a plasma state, and a diamond-like carbon film layer having a thickness of 40 nm was formed in about 0.5 hours.

Table 6 below shows the measurement results of the X-ray diffraction intensity and the propagation loss.

[0146]

[Table 6]

Example 12 I having (311), (110) and (111) plane orientations
An Al film (thickness: 50 nm ) was formed on a-type natural diamond and Ib-type high-pressure synthetic diamond, and a pattern inverted from the comb-shaped electrode was formed using photolithography, and this was used as a mask.

The above diamond substrate was set in an ion implantation apparatus, and B (boron) ions were implanted at 4.5 × 10 ²⁰ cm ^-2 at an acceleration voltage of 120 keV.

After the ion implantation, the Al mask is peeled off, the substrate is annealed, and the semiconductive diamond portion produced by the B ion implantation is comb-shaped electrode (comb having the same parameters as in the embodiment). Type electrode).

On the comb-shaped electrode formed as described above, Li
After forming a surface acoustic wave device by forming a TaO ₃ film by liquid phase epitaxy, propagation loss was measured in the same manner as in Example 7.

<LiTaO ₃ film forming conditions> Conditions: liquid phase growth method Solution: 50 mol% LiO ₂ +40 mol% V ₂ O ₅ +
10 mol% Ta ₂ O ₅ (while the substrate was immersed in the liquid, the temperature was raised to 1100 ° C. and then slowly cooled to 700 ° C.) After the above-mentioned propagation loss measurement, a diamond thin film (thickness: 300 nm) was formed on the LiTaO ₃ film. ) Was formed and the propagation loss was evaluated.

<Diamond thin film forming conditions> Apparatus: microwave plasma CVD apparatus Microwave power: 350 W Reaction gas CH ₄ : O ₂ : H ₂ = 0.5: 1: 98.5 Reaction pressure: 3990 Pa Film formation temperature: 500 C film thickness: 0.3 μm The evaluation results of the above-mentioned propagation loss are shown in Table 7 below.

[0153]

[Table 7]

Example 13 An Ib type high pressure single crystal diamond having (311), (110) and (111) planes was prepared, and an Al film (thickness: 50 nm ) was vapor-deposited on the diamond plane, followed by photolithography technique. Was used to form an inverted pattern of the comb-shaped electrodes, which was used as a mask. This was set in an RIE (reactive ion etching) apparatus, the diamond surface was etched, and a groove was formed in a comb-shaped electrode shape. The etching depth was 30 nm.

<Conditions of RIE> Ar: O ₂ = 90: 10 RF power 200 W Pressure: 1.33 Pa A resist is formed on the diamond after the above RIE, and the resist is patterned by using a photolithography technique. The film was peeled off to form a groove in the diamond as an electrode.

Ti is formed on the substrate on which the groove is formed in this way.
A film (thickness: 50 nm ) was formed and the resist was removed to form a comb-type electrode of embedded type on the diamond.

A surface acoustic wave device was prepared by forming a LiTaO ₃ film (thickness: 1 μm) on the substrate thus formed with the comb-shaped electrode, and the propagation loss was measured.

After measuring the propagation loss, a SiO ₂ film (thickness: 300 nm ) was formed on the LiTaO ₃ film, and the propagation loss was measured.

After measuring the propagation loss, the SiO ₂ film was further
A short-circuiting electrode (thickness: 50 nm ) was formed using Al, and the propagation loss was measured. The conditions for forming the LiTaO ₃ film and the SiO ₂ film used at this time were as follows.

<LiTaO ₃ film> RF magnetron sputtering apparatus Gas: Ar: O ₂ = 1: 2 Pressure: 1.33 Pa RF power: 80 W Substrate temperature: 580 ° C. Target: Li: Ta = 3: 2 Sintered body <SiO ₂ film> RF magnetron sputtering device Gas: Ar: O ₂ = 1: 1 Pressure: 1.33 Pa RF power: 250 W Target: SiO ₂ Film thickness: 0.3 μm The measurement results of the above propagation loss are shown in Table 8 below.

[0161]

[Table 8]

[0162] Example 14 (100) polycrystalline Si substrate was set in a reaction chamber of a plasma CVD apparatus, 1.33 × 10 ^-4 was evacuated to Pa or less, CH ₄ in the reaction chamber, H ₂ gas CH ₄ / H ₂ = 1 to
It was introduced at a rate of 8%. The pressure in the reaction chamber is 13300-
The substrate temperature was set to 26600 Pa and the substrate temperature was set to 950 ° C.
Under such conditions, a diamond film (thickness: 17 μm) was formed on the polycrystalline Si substrate.

When the diamond film obtained above was evaluated using an X-ray diffractometer, it was found to be polycrystal (40
The plane orientations of 0), (220), and (111) were observed. By simultaneously changing the gas composition ratio and the pressure in the reaction chamber, it was possible to form a polycrystalline diamond film in which the strength ratio of the (111) plane or the (220) plane was changed. In X-ray diffraction, the peak intensity of each plane is different, so the peak intensity of the (111) plane was set to 100 and the peak intensity of other planes was normalized.

Two kinds of substrates thus obtained were prepared under each condition. The surface of each is polished (thickness of the diamond film after polishing: 15 μm), and a short-circuiting electrode (thickness: 50 nm ) is formed thereon using Ti. A LiTaO ₃ film (thickness: 1 μm) is formed on the short-circuiting electrode. ) Was laminated.

Of the two types of substrates described above, one of the substrates was used to form a comb-shaped electrode using Al (Example 6).
And a propagation loss was evaluated by forming a comb-shaped electrode having the same parameters as described above. The conditions for forming the LiTaO ₃ film and the method for evaluating the propagation loss were the same as in Example 7.

After measuring the above-mentioned propagation loss, a diamond-like carbon film (thickness: 50 nm ) was formed in the same manner as in Example 11.
Propagation loss was measured.

Of the above-mentioned two types of substrates, the other substrate was formed in the same manner as above except that a LiTaO ₃ film was formed, a diamond-like carbon film was formed, and then a comb-shaped electrode was formed. The device was obtained. The propagation loss of this surface acoustic wave device sample was measured in the same manner as above. The measurement results are shown in Table 9 below.

[0168]

[Table 9]

Example 15 High pressure Ib type (311), (110) and (111) diamond thin film (thickness 16) on a (111) diamond single crystal substrate.
μm), the surface of the diamond thin film is polished and flattened to a thickness of 15 μm, then a LiTaO ₃ film (thickness 1 μm) is formed, and three substrates are prepared for each plane orientation described above. did. At this time, the diamond epitaxial conditions and the LiTaO ₃ film forming conditions were the same as in Example 7.

For one of the above-mentioned _three substrates, a comb-shaped electrode (comb-shaped electrode having the same parameters as in Example 6) and a SiO ₂ film (thickness: 3 ) were formed on the LiTaO ₃ film.
00 nm ) and a short-circuit electrode (thickness: 50 nm ) were formed in this order to fabricate a surface acoustic wave device A. At this time, SiO
_The conditions for forming the _two films were the same as in Example 14.

Of the above three substrates, the next one was formed on the above-mentioned surface except that the SiO ₂ film and the comb-shaped electrode were formed in this order on the LiTaO ₃ film and the short-circuit electrode was not formed. A surface acoustic wave device was produced in the same manner as the formation of the acoustic wave device A.

For the remaining one of the _three substrates, a short-circuit electrode and a SiO film were formed on the LiTaO ₃ film.
A surface acoustic wave device was produced in the same manner as in the formation of the surface acoustic wave device A except that the _two films and the comb-shaped electrode were formed in this order.

The propagation loss of each surface acoustic wave device sample obtained above was measured in the same manner as in Example 7. The measurement results are shown in Table 10 below.

[0174]

[Table 10]

[0175]

As described above, according to the present invention, (11
By forming a LiTaO ₃ film as a piezoelectric body on a diamond surface having 1) or (100) orientation,
Higher c-axis or a-axis orientation is obtained as compared with the case where a diamond surface having another orientation is used as a base material.

According to the present invention, further, good crystallinity can be obtained based on such orientation, and L formed into a film can be obtained.
Since it becomes possible to reduce the surface irregularities of the iTaO ₃ film, an oriented material or an oriented substrate that can be suitably used as an element for forming various devices is provided.

When a surface acoustic wave element is formed using such an oriented material or an oriented substrate having a high orientation, the surface acoustic wave having a high efficiency as an element while reducing the propagation loss of the surface acoustic wave is obtained. A wave element is provided.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing one aspect (electrode arrangement A) of electrode arrangement of a surface acoustic wave device of the present invention.

FIG. 2 is a schematic cross-sectional view showing another aspect (electrode arrangement C) of the electrode arrangement of the surface acoustic wave device of the present invention.

FIG. 3 is a schematic cross-sectional view showing still another aspect (electrode arrangement E) of electrode arrangement of the surface acoustic wave device of the present invention.

FIG. 4 is a schematic cross-sectional view showing still another aspect (electrode arrangement F) of the electrode arrangement of the surface acoustic wave device of the present invention.

FIG. 5 is a schematic plan view showing an example (single electrode) of a planar shape of a comb-shaped electrode that constitutes a surface acoustic wave device.

FIG. 6 is a schematic plan view showing an example (double electrode) of a planar shape of a comb-shaped electrode that constitutes a surface acoustic wave device.

FIG. 7 is a graph schematically showing typical examples of Raman spectra of amorphous carbon (diamond-like carbon film) (a), graphite (b), and diamond (c).

FIG. 8 is a schematic cross-sectional view showing an example of an optical modulator using the oriented substrate of the present invention.

9 is the (001) LiTaO ₃ / obtained in Example 1. FIG.
It is a figure which shows the RHEED analysis result (pattern which appears every 120 degrees) of a (111) single crystal diamond.

FIG. 10: (001) LiTaO ₃ obtained in Example 1
It is a figure which shows the RHEED analysis result (pattern which appears every 60 degrees) of / (111) single crystal diamond.

FIG. 11: (001) LiTaO ₃ obtained in Example 1
2 is a graph showing X-ray diffraction data of a / (111) single crystal diamond structure.

FIG. 12 is a schematic diagram showing a result of simulating a matching relationship between (001) LiTaO ₃ and (111) diamond.

FIG. 13: (100) LiTaO ₃ obtained in Example 2
2 is a graph showing X-ray diffraction data of a / (100) single crystal diamond structure.

FIG. 14 is a schematic diagram showing a result of simulating a matching relationship between (100) LiTaO ₃ and (100) diamond.

FIG. 15 is a schematic perspective view showing an example of a branch interference type optical waveguide using the oriented substrate of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenjiro Higaki Kenjiro Higaki 1-1-1 Kunyo Kita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Shinichi Shikada Kuichi Kitaichi, Itami City, Hyogo Prefecture 1-1-1, Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A 64-62911 (JP, A) JP-A 4-358410 (JP, A) JP-A 5-90888 (JP, A) JP-A-2-299309 (JP, A) JP-A-5-83068 (JP, A) JP-A-5-90887 (JP, A) JP-A-6-97760 (JP, A) JP-B-54 -38874 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C30B 1/00-35/00 H03H 9/25 H03H 9/145 EUROPAT (QUESTEL) CA (STN) WPI (DIALOG) ) JIST file (JOIS )

Claims (21)

(57) [Claims] 1. A single crystal diamond and a single crystal LiTaO arranged on the (111) plane of the single crystal diamond.
₃ consists of a film, oriented material characterized by (001) plane of the LiTaO ₃ film is parallel to the (111) plane of the monocrystalline diamond. Wherein alignment material according to claim 1, wherein the monocrystalline diamond is natural or high-pressure synthetic diamond. 3. The single crystal diamond that gives the (111) plane is a diamond thin film epitaxially grown on the (111) plane of another single crystal diamond.
1. The oriented material according to 1 . Wherein said (111) single crystal diamond which gives surfaces, alignment material according to claim 1, wherein a diamond film heteroepitaxially grown. 5. A diamond layer and LiTaO arranged on a surface of the diamond layer having a (111) orientation.
A surface acoustic wave device comprising _three films and comb-shaped electrodes arranged on the LiTaO ₃ film. 6. A diamond layer, a comb-shaped electrode arranged on a surface of the diamond layer having (111) orientation, and a LiTaO ₃ film arranged on the comb-shaped electrode. Surface acoustic wave device. 7. A diamond layer, a comb-shaped electrode made of conductive diamond arranged on a surface of the diamond layer having (111) orientation, and a LiTaO ₃ film arranged on the comb-shaped electrode. A surface acoustic wave device characterized by the above. 8. A diamond layer, a comb-shaped electrode made of a conductive material, which is arranged in a concave portion of a surface of the diamond layer having (111) orientation, and L arranged on the comb-shaped electrode.
A surface acoustic wave device comprising an iTaO ₃ film. 9. On the uppermost layer, further the short-circuiting electrode disposed claims 6, 7 or 8 surface acoustic wave device as claimed. 10. A diamond layer, a short-circuit electrode arranged on a surface of the diamond layer having (111) orientation, and a LiTaO ₃ film arranged on the short-circuit electrode.
A surface acoustic wave device comprising a comb-shaped electrode arranged on the LiTaO ₃ film. 11. A top of the uppermost layer, and further, one of SiO _2, diamond, and claims 5 to 10 in which a layer consisting of one or more materials selected from the group consisting of diamond-like carbon film is disposed The surface acoustic wave device described in 1. 12. A layer made of one or more kinds of materials selected from the group consisting of SiO ₂ , diamond, and diamond-like carbon film is arranged on the uppermost layer, and a layer made of the material is further formed. , The short-circuit electrode is arranged
The surface acoustic wave device according to any one of 5 to 8 . 13. A diamond layer and LiTa disposed on a surface of the diamond layer having a (111) orientation.
An O ₃ film and a Si film disposed on the LiTaO ₃ film.
A layer made of one or more kinds of materials selected from the group consisting of O ₂ , diamond, and diamond-like carbon film;
A surface acoustic wave device comprising a comb-shaped electrode arranged on the material layer. 14. A diamond layer, a short-circuit electrode arranged on a surface of the diamond layer having (111) orientation, and a LiTaO ₃ film arranged on the short-circuit electrode.
A layer made of one or more kinds of materials selected from the group consisting of SiO ₂ , diamond, and a diamond-like carbon film, arranged on the LiTaO ₃ film, and a comb-shaped electrode arranged on the material layer. A surface acoustic wave device comprising: 15. A diamond layer and LiTa arranged on a surface having a (111) orientation of the diamond layer.
An O ₃ film, a short-circuiting electrode arranged on the LiTaO ₃ film, and one or more kinds selected from the group consisting of SiO ₂ , diamond, and diamond-like carbon film arranged on the short-circuiting electrode. A surface acoustic wave device comprising a layer made of a material and a comb-shaped electrode arranged on the material layer. 16. The diamond which provides a surface having a (111) orientation is a single crystal diamond.
The surface acoustic wave device according to any one of 5 to 15 . 17. (111) said diamond which gives a surface having an orientation property, claim 5 is polycrystalline diamond
15. The surface acoustic wave device according to any one of to 15 . 18. The surface acoustic wave device according to claim 16 , wherein the single crystal diamond is either a natural diamond or an artificial diamond. 19. (111) said diamond which gives a surface having an orientation property, claim 1 is a single crystal diamond film epitaxially grown on a single crystal diamond
6. The surface acoustic wave device according to item 6 . 20. The surface acoustic wave device according to claim 5 , wherein the diamond that provides the surface having the (111) orientation is a heteroepitaxially grown diamond film. 21. A diamond layer and a first L arranged on a surface of the diamond layer having a (111) orientation.
iTaO ₃ film, comb-shaped electrode arranged on the first LiTaO ₃ film, and second LiT arranged on the comb-shaped electrode
A surface acoustic wave device comprising an aO ₃ film.