JP3414687B2 - Piezoelectric substrate for surface acoustic wave device and surface acoustic wave device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric substrate for a surface acoustic wave device and a surface acoustic wave device used in a surface acoustic wave device in which interdigital electrodes are provided on a piezoelectric substrate.

[0002]

2. Description of the Related Art In recent years, mobile communication terminals such as mobile phones have rapidly become popular. It is particularly desired that such a terminal device be small and lightweight for convenience of carrying. In order to reduce the size and weight of the terminal, it is required that the electronic components used therein be also small and light. For this reason, surface acoustic wave devices, that is, surface acoustic wave filters, which are advantageous for reduction in size and weight, are often used in the high frequency section and the intermediate frequency section of the terminal. The surface acoustic wave device is one in which interdigital electrodes for exciting, receiving, reflecting or propagating surface acoustic waves are formed on a piezoelectric substrate.

An important characteristic of the piezoelectric substrate used in the surface acoustic wave device is the surface wave velocity of the surface acoustic wave (hereinafter referred to as SAW velocity), the center frequency of the filter or the resonator. In this case, the temperature coefficient of the resonance frequency (hereinafter referred to as the frequency temperature coefficient) and the square of the electromechanical coupling coefficient k ² (hereinafter, k ² is also referred to as electromechanical coupling coefficient) can be mentioned.

FIG. 27 shows the types of substrates that have been widely used as piezoelectric substrates for surface acoustic wave devices and their characteristics. Below, these piezoelectric substrates,
The symbols in FIG. 27 will be used for distinction.

[0005]

From FIG. 27, it can be seen from FIG. 27 that the piezoelectric substrates that have been frequently used so far have 128LN, 64LN, 36 having a large SAW speed and a large electromechanical coupling coefficient.
It can be seen that the LT can be roughly divided into two sets, that is, the LT and the LT112, which has a relatively small SAW speed and a small electromechanical coupling coefficient, and ST crystal. Piezoelectric substrate (128LN, 64L) with large SAW speed and large electromechanical coupling coefficient
N, 36LT) is used, for example, in a surface acoustic wave filter in the high frequency part of a terminal, while a relatively small SA is used.
Piezoelectric substrate (LT with low velocity and small electromechanical coupling coefficient)
112, ST crystal) is used for a surface acoustic wave filter in the intermediate frequency part of a terminal, for example. The reason is as follows.

That is, in the case of the surface acoustic wave filter, the center frequency thereof is almost proportional to the SAW velocity of the piezoelectric substrate used, and is almost inversely proportional to the width of the electrode fingers of the interdigital electrodes formed on the substrate. Therefore, it is preferable to use a substrate having a high SAW speed to form a filter used in the high frequency circuit section. In addition, the filter used in the high frequency part of the terminal is required to have a wide band having a pass band width of 20 MHz or more, and thus it is necessary to have a large electromechanical coupling coefficient.

On the other hand, a frequency band of 70 to 300 MHz is used as an intermediate frequency of mobile terminals.
When a filter having a center frequency in this frequency band is constructed using a surface acoustic wave device, a SAW is used as a piezoelectric substrate.
When a substrate with a high speed is used, the width of the electrode fingers formed on the substrate needs to be made extremely large in accordance with the amount of decrease in the center frequency of the filter used in the high frequency circuit section. There is a problem that the device itself becomes large.

Therefore, as the piezoelectric substrate of the surface acoustic wave filter for intermediate frequency, LT112 or S having a low SAW speed is used.
T-quartz is used. In particular, ST quartz is preferable because the first-order frequency temperature coefficient is zero. Since the ST crystal has a small electromechanical coupling coefficient, only a filter having a narrow pass band can be constructed. However, the role of the intermediate frequency filter is to pass the signal of only one narrow channel, so the fact that this electromechanical coupling coefficient is small means that
It hasn't been a problem so far.

However, in recent years, from the viewpoint of effective use of frequency resources, compatibility with digital data communication, and the like, digital mobile communication systems have been developed, put into practical use, and rapidly spread. The pass bandwidth in this system is very wide, from several 100 kHz to several MHz. When such a wide band intermediate frequency filter is formed by a surface acoustic wave filter, S having a small electromechanical coupling coefficient is used.
It is difficult to realize with a T crystal substrate.

Further, in order to make the mobile terminal more compact and to make it more convenient to carry, it is necessary to reduce the mounting area of the surface acoustic wave filter for intermediate frequency. However, the ST crystal and LT 112, which are conventionally considered to be suitable for the surface acoustic wave filter for the intermediate frequency, have SAW speeds exceeding 3000 m / s (seconds), and there is a limit to miniaturization.

The present invention has been made in view of the above problems, and an object thereof is to provide a large electromechanical coupling coefficient effective for widening a pass band and a small SAW speed effective for downsizing a surface acoustic wave device. An object of the present invention is to provide a piezoelectric substrate for a surface acoustic wave device having the same, and a surface acoustic wave device capable of widening a band and downsizing.

[0012]

A piezoelectric substrate for a surface acoustic wave device according to the present invention is used in a surface acoustic wave device in which interdigital electrodes are provided on a piezoelectric substrate and belongs to a point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
It has a type crystal structure, the main components of which are Ca, Nb, Ga, Si and O , and a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄ .

According to the piezoelectric substrate for a surface acoustic wave device of the present invention, it is possible to realize a large electromechanical coupling coefficient effective for widening the pass band and a small SAW velocity effective for downsizing the surface acoustic wave device. Will be possible.

The surface acoustic wave device of the present invention is a surface acoustic wave device in which interdigital electrodes are provided on a piezoelectric substrate, and the piezoelectric substrate belongs to the point group 32 and is of Ca ₃ Ga ₂ Ge ₄ O ₁₄ type. Has a crystal structure, the main components of which are Ca, Nb, Ga, Si and O,
It is composed of a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄ .

According to the surface acoustic wave device of the present invention, a piezoelectric substrate having a large electromechanical coupling coefficient effective for widening the pass band and a small SAW velocity effective for downsizing the surface acoustic wave device is used. It becomes possible, and as a result, it becomes possible to widen the band and downsize.

In the piezoelectric substrate for a surface acoustic wave device or the surface acoustic wave device of the present invention, the cut-out angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ). At this time, φ, θ, and ψ may exist in any of the following areas.

[Area 1-1] φ = -5 ° to 5 °, θ = 30 ° to 90 ° and ψ = 0 ° to 75 °

[Area 1-2] φ = -5 ° to 5 °, θ = 110 ° to 155 ° and ψ = 60 ° -80 °

[Area 2-1] φ = 5 ° to 10 ° (not including 5 °), θ = 30 ° -60 ° and ψ = −75 ° to −30 °

[Area 2-2] φ = 5 ° to 10 ° (not including 5 °), θ = 110 ° to 155 ° and ψ = −85 ° to −65 °

[Area 3-1] φ = 10 ° to 20 ° (not including 10 °), θ = 30 ° -60 ° and ψ = −75 ° to −30 °

[Area 3-2] φ = 10 ° to 20 ° (not including 10 °), θ = 110 ° to 155 ° and ψ = −85 ° to −65 °

[Area 4-1] φ = 20 ° to 30 ° (not including 20 °), θ = 30 ° -60 ° and ψ = −80 ° to −40 °

[Area 4-2] φ = 20 ° to 30 ° (not including 20 °), θ = 110 ° to 155 ° and ψ = −75 ° to −55 °

[Area 5] φ = 5 ° to 30 ° (not including 5 °), θ = 30 ° to 90 ° and ψ = −30 ° to 30 °

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing an example of the configuration of a surface acoustic wave device according to an embodiment of the present invention. This surface acoustic wave device includes a piezoelectric substrate 1 and a pair of interdigital electrodes 2 provided on one main surface of the piezoelectric substrate 1. The shape, number and arrangement of the electrodes 2 may be any known form.

The material of the piezoelectric substrate 1 belongs to the point group 32,
It has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main components of which are Ca and N.
A single crystal composed of b, Ga, Si and O and represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄ is used.

The x-axis, y-axis and z-axis shown in FIG. 1 are orthogonal to each other. The x-axis and the y-axis are in the in-plane direction of the substrate 1, and the x-axis defines the propagation direction of the surface acoustic wave. Also,
The z axis is perpendicular to the surface of the substrate 1 and defines the cutting angle (cut surface) of the single crystal substrate. The relationship between these x-axis, y-axis and z-axis and the crystal axes X-axis, Y-axis and Z-axis of the single crystal,
That is, the cut-out angle from the single crystal of the substrate and the surface acoustic wave propagation direction can be expressed by Euler angle display (φ, θ, ψ).

In the surface acoustic wave device according to this embodiment,
The cut-out angle and the propagation direction are displayed in Euler angles (φ,
θ, ψ), φ, θ and ψ are the following regions 1-1, 1-2, 2-1, 2-2, 3-1, 3-2, 4
-1, 4-2 and 5 are present.

[Area 1-1] φ = -5 ° to 5 °, θ = 30 ° to 90 ° and ψ = 0 ° to 75 °

Preferable areas in the area 1-1 are as follows. φ = −5 ° to 5 °, θ = 60 ° to 75 ° and ψ = 0 ° to 10 °

In the area 1-1, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ that is 100 m / s or less, which is smaller than that of ST quartz, and the electromechanical coupling coefficient k ^{2 of} the substrate 1 is 0.2% or more, which is sufficiently large. Area 1
In the above preferable region within −1, there is a combination of φ, θ, and ψ, which has an electromechanical coupling coefficient k ² of 0.3% or more, which is sufficiently larger than that of ST quartz.

[Area 1-2] φ = -5 ° to 5 °, θ = 110 ° to 155 ° and ψ = 60 ° -80 °

In the area 1-2, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ of 200 m / s or less, which is about the same as that of ST quartz, and the electromechanical coupling coefficient k ² of the substrate 1 is 0.2% or more, which is sufficiently large.

[Area 2-1] φ = 5 ° to 10 ° (not including 5 °), θ = 30 ° -60 ° and ψ = −75 ° to −30 °

The preferable areas in the area 2-1 are as follows. φ = 5 ° to 10 ° (not including 5 °), θ = 35 ° to 55 ° and ψ = −60 ° to −35 °

In the area 2-1, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ of 200 m / s or less, which is about the same as that of ST quartz, and the electromechanical coupling coefficient k ² of the substrate 1 is 0.2% or more, which is sufficiently large. The electromechanical coupling coefficient k ² is included in the above-described preferable region in the region 2-1.
Is 0.4% or more, there is a combination of φ, θ, and ψ that is sufficiently larger than that of ST quartz.

[Area 2-2] φ = 5 ° to 10 ° (not including 5 °), θ = 110 ° to 155 ° and ψ = −85 ° to −65 °

The preferred areas within area 2-2 are as follows. φ = 5 ° to 10 ° (not including 5 °), θ = 120 ° to 150 ° and ψ = −80 ° to −70 °

In the area 2-2, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ that is 100 m / s or less, which is smaller than that of ST quartz, and the electromechanical coupling coefficient k ^{2 of} the substrate 1 is 0.2% or more, which is sufficiently large. Area 2
In the above-mentioned preferable region within −2, there is a combination of φ, θ, and ψ, which has an electromechanical coupling coefficient k ² of 0.4% or more, which is sufficiently larger than that of ST quartz.

[Area 3-1] φ = 10 ° to 20 ° (not including 10 °), θ = 30 ° -60 ° and ψ = −75 ° to −30 °

Preferable areas in the area 3-1 are as follows. φ = 10 ° to 20 ° (excluding 10 °), θ = 35 ° to 55 ° and ψ = −65 ° to −40 °

In the area 3-1, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ that is 100 m / s or less, which is smaller than that of ST quartz, and the electromechanical coupling coefficient k ^{2 of} the substrate 1 is 0.2% or more, which is sufficiently large. Area 3
In the above-mentioned preferable region within -1, there is a combination of φ, θ, and ψ that has an electromechanical coupling coefficient k ² of 0.4% or more, which is sufficiently larger than that of ST quartz.

[Area 3-2] φ = 10 ° to 20 ° (not including 10 °), θ = 110 ° to 155 ° and ψ = −85 ° to −65 °

The preferred areas within area 3-2 are as follows. φ = 10 ° to 20 ° (not including 10 °), θ = 125 ° to 150 ° and ψ = −80 ° to −65 °

In the area 3-2, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ of 200 m / s or less, which is about the same as that of ST quartz, and the electromechanical coupling coefficient k ² of the substrate 1 is 0.2% or more, which is sufficiently large. The electromechanical coupling coefficient k ² is included in the above-mentioned preferable region in the region 3-2.
Is 0.4% or more, there is a combination of φ, θ, and ψ that is sufficiently larger than that of ST quartz.

[Area 4-1] φ = 20 ° to 30 ° (not including 20 °), θ = 30 ° -60 ° and ψ = −80 ° to −40 °

Preferable areas in the area 4-1 are as follows. φ = 20 ° to 30 ° (not including 20 °), θ = 30 ° to 55 ° and ψ = −75 ° to −50 °

In the area 4-1, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ of 200 m / s or less, which is about the same as that of ST quartz, and the electromechanical coupling coefficient k ² of the substrate 1 is 0.2% or more, which is sufficiently large. The electromechanical coupling coefficient k ² is included in the above-described preferable region in the region 4-1.
Is 0.5% or more, there is a combination of φ, θ, and ψ that is sufficiently larger than that of ST quartz.

[Area 4-2] φ = 20 ° to 30 ° (not including 20 °), θ = 110 ° to 155 ° and ψ = −75 ° to −55 °

The preferred areas within area 4-2 are as follows. φ = 20 ° to 30 ° (not including 20 °), θ = 125 ° to 150 ° and ψ = −75 ° to −60 °

In the area 4-2, the SAW speed of the substrate 1 is 3
There is a combination of φ, θ, and ψ of 200 m / s or less, which is about the same as that of ST quartz, and the electromechanical coupling coefficient k ² of the substrate 1 is 0.2% or more, which is sufficiently large. The electromechanical coupling coefficient k ² is included in the above-mentioned preferable region in the region 4-2.
Is 0.4% or more, there is a combination of φ, θ, and ψ that is sufficiently larger than that of ST quartz.

[Region 5] φ = 5 ° to 30 ° (not including 5 °), θ = 30 ° to 90 ° and ψ = −30 ° to 30 °

In the area 5, the SAW speed of the substrate 1 is 310.
There is a combination of φ, θ, and ψ that is 0 m / s or less, which is about the same as that of ST quartz, and the electromechanical coupling coefficient k ² of the substrate 1 is 0.2% or more, which is sufficiently large.

Since the single crystal of Ca ₃ NbGa ₃ Si ₂ O ₁₄ is a trigonal crystal, there are crystallographically equivalent combinations of Euler angles due to the symmetry of the crystal. For example, region 1-
(0 °, 90 °, 17 °) included in 1 is (0 °, 9
0 °, -17 °), (60 °, 90 °, ± 17 °) and (120 °, 90 °, ± 17 °). Furthermore, (0 °, 90 °, 17 °) is (240 °, 90
°, ± 17 °) and (360 °, 90 °, ± 17 °)
Is equivalent to

The Ca ₃ NbGa ₃ Si ₂ O ₁₄ may have oxygen defects. This single crystal also contains inevitable impurities such as Al, Zr, Fe, Ce, Nd, La and P.
It may contain t, Ca and the like.

[0057]

EXAMPLES Examples of the surface acoustic wave device according to this embodiment will be described below. First, a method for manufacturing the surface acoustic wave piezoelectric substrate 1 according to the present embodiment will be described. The material of the piezoelectric substrate 1 belongs to the point group 32, has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, and its main components are Ca, Nb, Ga, Si and O.
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄ . The growth of the single crystal was performed by the CZ method by high frequency heating, that is, the rotary pulling method. From the obtained single crystal,
The substrate was cut at a cutting angle described below to obtain a piezoelectric substrate 1 for a surface acoustic wave device.

Next, a method of manufacturing the surface acoustic wave device for testing will be described. As shown in FIG. 1, the surface acoustic wave device for testing has a piezoelectric substrate 1 cut out from the above single crystal.
The input and output cross-finger electrodes 2 are formed on the surface of. The interdigital electrode 2 was formed by processing an aluminum (Al) film formed by vapor deposition into a predetermined shape by photoetching. The period of the electrode fingers corresponding to the wavelength λ of the surface acoustic wave is 60 μm, and the logarithm is 20.
As a pair, the intersection width (the length of the intersection) is 60λ (3600
μm) and the film thickness was 0.3 μm.

Next, the areas 1-1, 1-2, 2-1, 2-
Tests performed to verify the validity of 2, 3-1, 3-2, 4-1, 4-2 and 5 will be described. In this test, a plurality of surface acoustic wave devices for testing in which the cut-out angle of the substrate 1 and the propagation direction of surface acoustic waves were changed were prepared, and the SAW velocity and electromechanical coupling coefficient k ² of each surface acoustic wave device for testing were examined. It was The SAW velocity was obtained by multiplying the measured value of the center frequency of the filter characteristic by the wavelength of the surface acoustic wave in the surface acoustic wave device having the interdigital electrode 2 having the above-described configuration. The electromechanical coupling coefficient k ² is obtained by measuring the two-terminal admittance of one of the above-mentioned input / output interdigital electrodes 2, for example, the interdigital electrode 2 for input, and the real part (conductance) of this admittance. And the imaginary part (susceptance), were obtained by the method using Smith's equivalent circuit. This method is described, for example, in I.P. of the publication "Surface wave device and its application" (edited by Electronic Material Industries Association, published by Nikkan Kogyo Shimbun, 1978). It is described in detail in the section of basic edition, 4.1.2 Effective electromechanical coupling coefficient of surface wave. The above characteristics were measured with the ambient temperature of the device kept at 25 ° C.

FIG. 2 is an explanatory diagram showing the test results corresponding to the area 1-1. FIG. 11 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. 2. FIG. 12 is a two-dimensional explanatory diagram showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 2, 11 and 12.
If the angle φ is 0 °, the angle θ is 30 ° to 90 °,
When the angle ψ is in the range of 0 ° to 75 °, the electromechanical coupling
A few k ²Is 0.2% or more, SAW speed is 3100m
There are combinations of φ, θ, and ψ that are equal to or less than / s. φ
Even if changes within 0 ± 5 °, the same combination as above
There is a seaweed. When the angle φ is 0 °, the angle θ is 60
It is in the range of 0 ° to 75 ° and the angle ψ in the range of 0 ° to 10 °.
And the electromechanical coupling coefficient k²Is 0.3% or more,
There are combinations of θ and ψ. φ is within the range of 0 ± 5 °
Even if it changes with, there is a combination similar to the above.

Here, it is shown that the characteristics of the substrate 1 and the surface acoustic wave device do not change significantly even if φ is changed to some extent. From FIG. 2, (φ, θ, ψ) = (0 °, 70 °, 0
°), the SAW velocity is 2928 m / s and the electromechanical coupling coefficient k ² is 0.41%. On the other hand, (φ,
When θ, ψ) = (± 5 °, 70 °, 0 °), the SAW velocity is 2929 m / s and the electromechanical coupling coefficient k ² is 0.4.
It was 0%. The same applies to the other areas described below.

FIG. 3 is an explanatory view showing the test results corresponding to the area 1-2. FIG. 13 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. FIG. 14 is a two-dimensional explanatory diagram showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 3, 13 and 14, when the angle φ is 0 °, the angle θ is 110 ° to 155 °.
Then, in the range of the angle ψ from 60 ° to 80 °, the electromechanical coupling coefficient k ² becomes 0.2% or more, and the SAW velocity is 32%.
There are combinations of φ, θ, and ψ that are equal to or less than 00 m / s. Even if φ changes within the range of 0 ± 5 °, the same combination as above exists.

FIG. 4 is an explanatory diagram showing the test results corresponding to the area 2-1. FIG. 15 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. 4. FIG. 16 is a two-dimensional explanatory view showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 4, 15 and 16, when the angle φ is 10 °, the angle θ is 30 ° to 60 °.
Then, there is a combination of φ, θ, and ψ where the electromechanical coupling coefficient k ² becomes 0.2% or more and the SAW velocity becomes 3200 m / s or less in the range of the angle ψ from −75 ° to −30 °. . Even if φ changes within the range of 7.5 ± 2.5 °,
There are similar combinations as above. Also, the angle φ is 10
If °, the angle θ is 35 ° to 55 ° and the angle ψ is −60 °
There is a combination of φ, θ, and ψ in which the electromechanical coupling coefficient k ² is 0.4% or more in the range from −35 °. Even if φ changes within the range of 7.5 ± 2.5 °, the same combination as above exists.

FIG. 5 is an explanatory diagram showing the test results corresponding to the area 2-2. FIG. 17 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. FIG. 18 is a two-dimensional explanatory diagram showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 5, 17 and 18, when the angle φ is 10 °, the angle θ is 110 ° to 155.
There is a combination of φ, θ and ψ such that the electromechanical coupling coefficient k ² becomes 0.2% or more and the SAW velocity becomes 3100 m / s or less in the range of the angle ψ from −85 ° to −65 °. To do. Even if φ changes within the range of 7.5 ± 2.5 °, the same combination as above exists. Further, when the angle φ is 10 °, the electromechanical coupling coefficient k ² becomes 0.4% or more in the range where the angle θ is 120 ° to 150 ° and the angle ψ is −80 ° to −70 °. There are combinations of θ and ψ. Even if φ changes within the range of 7.5 ± 2.5 °, the same combination as above exists.

FIG. 6 is an explanatory diagram showing the test results corresponding to the area 3-1. FIG. 19 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. 6. FIG. 20 is a two-dimensional explanatory diagram showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 6, 19 and 20, when the angle φ is 15 °, the angle θ is 30 ° to 60 °.
Then, in the range of the angle ψ from −75 ° to −30 °, there is a combination of φ, θ and ψ where the electromechanical coupling coefficient k ² becomes 0.2% or more and the SAW velocity becomes 3100 m / s or less. . Even if φ changes within the range of 15 ± 5 °, the same combination as above exists. When the angle φ is 15 °, the angle θ is 35 ° to 55 °, and the angle ψ is −60 °.
In the range of 40 °, the electromechanical coupling coefficient k ² is 0.4
There are combinations of φ, θ, and ψ that are more than%. Even if φ changes within the range of 15 ± 5 °, the same combination as above exists.

FIG. 7 is an explanatory diagram showing the test results corresponding to the area 3-2. FIG. 21 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. 7. FIG. 22 is a two-dimensional explanatory diagram showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG. 7.

As is apparent from FIGS. 7, 21 and 22, when the angle φ is 15 °, the angle θ is 110 ° to 155.
There is a combination of φ, θ, and ψ at which the electromechanical coupling coefficient k ² becomes 0.2% or more and the SAW velocity becomes 3200 m / s or less in the angle ψ in the range of −85 ° to −65 °. To do. Even if φ changes within the range of 15 ± 5 °, the same combination as above exists. When the angle φ is 15 °, the angle θ is 125 ° to 150 ° and the angle ψ is −80 °.
There is a combination of φ, θ, and ψ in which the electromechanical coupling coefficient k ² is 0.4% or more in the range from −65 °. Even if φ changes within the range of 15 ± 5 °, the same combination as above exists.

FIG. 8 is an explanatory diagram showing the test results corresponding to the area 4-1. FIG. 23 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. 8. FIG. 24 is a two-dimensional explanatory view showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 8, 23 and 24, when the angle φ is 25 °, the angle θ is 30 ° to 60 °.
Then, in the range of the angle ψ from −80 ° to −40 °, there is a combination of φ, θ and ψ where the electromechanical coupling coefficient k ² becomes 0.2% or more and the SAW velocity becomes 3200 m / s or less. . Even if φ changes within the range of 25 ± 5 °, the same combination as above exists. When the angle φ is 25 °, the angle θ is 30 ° to 55 °, and the angle ψ is −75 ° to −.
In the range of 50 °, the electromechanical coupling coefficient k ² is 0.5.
There are combinations of φ, θ, and ψ that are more than%. Even if φ changes within the range of 25 ± 5 °, the same combination as above exists.

FIG. 9 is an explanatory diagram showing the test results corresponding to the area 4-2. FIG. 25 is an explanatory diagram that two-dimensionally represents the relationship between θ and ψ and the SAW speed based on the test results shown in FIG. 9. FIG. 26 is a two-dimensional explanatory diagram showing the relationship between θ and ψ and the electromechanical coupling coefficient k ² based on the test results shown in FIG.

As is apparent from FIGS. 9, 25 and 26, when the angle φ is 25 °, the angle θ is 110 ° to 155.
There is a combination of φ, θ, and ψ at which the electromechanical coupling coefficient k ² becomes 0.2% or more and the SAW velocity becomes 3200 m / s or less in the angle ψ in the range of −75 ° to −55 °. To do. Even if φ changes within the range of 25 ± 5 °, the same combination as above exists. When the angle φ is 25 °, the angle θ is 125 ° to 150 °, and the angle ψ is −75 °.
There is a combination of φ, θ and ψ in which the electromechanical coupling coefficient k ² is 0.4% or more in the range from −60 °. Even if φ changes within the range of 25 ± 5 °, the same combination as above exists.

FIG. 10 is an explanatory diagram showing the test results corresponding to the area 5. As is clear from FIG. 10, the angle φ is 10
-30 °, the angle θ is 30 ° to 90 °, and the angle ψ is -30.
In the range of 30 ° to 30 °, there are combinations of φ, θ and ψ where the electromechanical coupling coefficient k ² is 0.2% or more and the SAW velocity is 3100 m / s or less. φ is 5 ° ~
Even if it changes within the range of 10 °, the same combination as described above exists.

As described above, the cut-out angle from the single crystal of the piezoelectric substrate 1 and the surface acoustic wave propagation direction are in the regions 1-1, 1-
2, 2-1, 2-2, 3-1, 3-2, 4-1, 4-2
It can be seen that when the value is in the range of 5 and 5, a surface acoustic wave device having a sufficiently large electromechanical coupling coefficient and a low SAW velocity can be obtained.

As described above, according to the present embodiment, a piezoelectric substrate having a large electromechanical coupling coefficient effective for widening the pass band and a small SAW velocity effective for downsizing the surface acoustic wave device. 1 can be realized. Further, by configuring a surface acoustic wave device using such a piezoelectric substrate 1, it is possible to make the surface acoustic wave device broader in band and downsized.

The present invention is not limited to the above embodiment, and various modifications can be made.

[0081]

As described above, according to the piezoelectric substrate for a surface acoustic wave device of the present invention, a large electromechanical coupling coefficient effective for widening the pass band and a small effective surface acoustic wave device for downsizing. The SAW speed and the effect can be obtained.

According to the surface acoustic wave device of the present invention,
Since a piezoelectric substrate having a large electromechanical coupling coefficient and a small SAW velocity can be used, the surface acoustic wave device can be broadened in band and miniaturized.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a configuration of a surface acoustic wave device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a test result corresponding to a region 1-1 according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a test result corresponding to a region 1-2 according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram showing a test result corresponding to a region 2-1 according to the embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a test result corresponding to a region 2-2 according to the embodiment of the present invention.

FIG. 6 is an explanatory diagram showing test results corresponding to a region 3-1 according to the embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a test result corresponding to a region 3-2 in the embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a test result corresponding to a region 4-1 according to the embodiment of the present invention.

FIG. 9 is an explanatory diagram showing a test result corresponding to a region 4-2 according to the embodiment of the present invention.

FIG. 10 is an explanatory diagram showing a test result corresponding to a region 5 in the embodiment of the present invention.

FIG. 11 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

FIG. 12 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 13 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

FIG. 14 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 15 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

FIG. 16 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 17 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

FIG. 18 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 19 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

FIG. 20 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 21 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

22 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 23 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

24 is a graph showing the results of θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 25 shows θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between and SAW speed two-dimensionally.

FIG. 26 is a graph showing θ and ψ based on the test results shown in FIG.
It is an explanatory view showing the relationship between the electromechanical coupling coefficient and two-dimensionally.

FIG. 27 is an explanatory diagram showing the types of substrates often used as piezoelectric substrates for surface acoustic wave devices and their characteristics.

[Explanation of symbols]

1 ... Piezoelectric substrate, 2 ... Interdigital electrode.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Atsushi Sato 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (56) References B. V. Mill, E.M. L. Belo coneva, T .; Fukuda, New Compounds with a Ca3Ga2Ge2014-Type Strucure: A3XY3Z2014 (A = Ca, Sr, Ba, Pb; X = Sb, Nb, Ta; chemistry, Russia, 1998, Vol.43, No.8, 1168 (58) Fields investigated (Int.Cl. ⁷ , DB name) H03H 9/25 H03H 9/64 CAPLUS (STN) JISST file (JOIS )

Claims (18)

(57) [Claims] 1. A surface acoustic wave device provided with interdigital electrodes on a piezoelectric substrate, belonging to a point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
A piezoelectric substrate for a surface acoustic wave device , which has a type crystal structure and whose main components are Ca, Nb, Ga, Si and O, and which is composed of a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O _14. , cut angle and surface acoustic from a single crystal of the piezoelectric substrate
The wave propagation direction is expressed as (φ, θ, ψ) in Euler angles.
At this time, φ, θ, and ψ are present in the regions of φ = −5 ° to 5 °, θ = 30 ° to 90 °, and ψ = 0 ° to 75 ° , respectively. . 2. Elasticity in which interdigital electrodes are provided on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = -5 ° ~5 °, θ = 110 ° ~155 ° and ψ = 60 ° ~80 ° piezoelectric substrate for a surface acoustic wave device characterized by the presence in the area of. 3. Elasticity in which interdigital electrodes are provided on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = 5 ° (not including 5 °) ~10 °, surface acoustic wave device characterized by the presence in the region of θ = 30 ° ~60 ° and ψ = -75 ° ~-30 ° Piezoelectric substrate. 4. Elasticity provided with interdigital electrodes on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = 5 ° (not including 5 °) ~10 °, θ = 110 ° ~155 for ° and ψ = -85 ° ~-65 ° surface acoustic wave device characterized by the presence in the area of Piezoelectric substrate. 5. Elasticity in which interdigital electrodes are provided on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = 10 ° (not including 10 °) ~20 °, surface acoustic wave device characterized by the presence in the region of θ = 30 ° ~60 ° and ψ = -75 ° ~-30 ° Piezoelectric substrate. 6. Elasticity provided with interdigital electrodes on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is (without 10 °) φ = 10 ° ~20 °, θ = 110 ° ~155 for ° and ψ = -85 ° ~-65 ° surface acoustic wave device characterized by the presence in the area of Piezoelectric substrate. 7. Elasticity provided with interdigital electrodes on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = 20 ° ~30 ° (not including 20 °), for the surface acoustic wave device characterized by the presence in the region of θ = 30 ° ~60 ° and ψ = -80 ° ~-40 ° Piezoelectric substrate. 8. Elasticity provided with interdigital electrodes on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = 20 ° ~30 ° (not including 20 °), θ = 110 ° ~155 for ° and ψ = -75 ° ~-55 ° surface acoustic wave device characterized by the presence in the area of Piezoelectric substrate. 9. Elasticity in which interdigital electrodes are provided on a piezoelectric substrate
Used for surface acoustic wave devices, belonging to the point group 32, Ca ₃ Ga ₂ Ge ₄ O ₁₄
Type crystal structure, the main components of which are Ca, Nb, Ga, Si and
And a single crystal represented by the chemical formula Ca ₃ NbGa ₃ Si ₂ O ₁₄
In the piezoelectric substrate for a surface acoustic wave device, the cutting angle from the single crystal of the piezoelectric substrate and the surface acoustic wave propagation direction are represented by Euler angles as (φ, θ, ψ), φ, θ and [psi is, φ = 5 ° (not including 5 °) ~30 °, θ = 30 ° ~90 ° and [psi = -30 ° piezoelectric surface acoustic wave device characterized by the presence in the to 30 ° in the region substrate. 10. A surface acoustic wave device having crossed finger-shaped electrodes provided on a piezoelectric substrate, wherein the piezoelectric substrate belongs to a point group 32 and has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, The main component is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
Made from a single crystal represented by _14, cut angle and surface acoustic from a single crystal of the piezoelectric substrate
The wave propagation direction is expressed as (φ, θ, ψ) in Euler angles.
At this time, φ, θ, and ψ are present in regions of φ = −5 ° to 5 °, θ = 30 ° to 90 °, and ψ = 0 ° to 75 ° . 11. A bullet provided with interdigital electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in regions of φ = −5 ° to 5 °, θ = 110 ° to 155 ° and ψ = 60 ° to 80 °. 12. A bullet having a crossed finger electrode formed on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in regions of φ = 5 ° to 10 ° (not including 5 °), θ = 30 ° to 60 ° and ψ = −75 ° to −30 °. 13. A bullet provided with interdigital electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in regions of φ = 5 ° to 10 ° (not including 5 °), θ = 110 ° to 155 ° and ψ = −85 ° to −65 °. 14. A bullet provided with interdigital electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in a region of φ = 10 ° to 20 ° (not including 10 °), θ = 30 ° to 60 ° and ψ = −75 ° to −30 °. 15. A bullet provided with interdigital electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in regions of φ = 10 ° to 20 ° (not including 10 °), θ = 110 ° to 155 °, and ψ = −85 ° to −65 °. 16. A bullet provided with interdigital electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in regions of φ = 20 ° to 30 ° (not including 20 °), θ = 30 ° to 60 ° and ψ = −80 ° to −40 °. 17. A bullet provided with interdigitated electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
_When the cutting angle and the surface acoustic wave propagation direction from the single crystal of the piezoelectric substrate are represented by Euler angles as (φ, θ, ψ), φ, θ, and ψ are A surface acoustic wave device characterized by being present in regions of φ = 20 ° to 30 ° (not including 20 °), θ = 110 ° to 155 °, and ψ = −75 ° to −55 °. 18. A bullet provided with interdigital electrodes on a piezoelectric substrate.
Surface acoustic wave device, wherein the piezoelectric substrate belongs to the point group 32.
However, it has a Ca ₃ Ga ₂ Ge ₄ O ₁₄ type crystal structure, the main component of which is C
It consists of a, Nb, Ga, Si and O and has the chemical formula Ca ₃ NbGa ₃ Si ₂ O.
Made from a single crystal represented by _14, the cut-out angle and SAW propagation direction of the single crystal piezoelectric substrate Euler angles when expressed (φ, θ, ψ) and, phi, theta, and [psi is, A surface acoustic wave device characterized by being present in regions of φ = 5 ° to 30 ° (not including 5 °), θ = 30 ° to 90 ° and ψ = −30 ° to 30 °.