JPH08330895A - Acoustic wave element - Google Patents

Abstract

PURPOSE: To provide an acoustic wave element high in conversion efficiency between electric energy and mechanical energy. CONSTITUTION: The acoustic wave element 10 includes a piezoelectric substrate 12 consisting of LiNbO3 , e.g. On the entire surface of one main surface of the piezoelectric substrate 12, ZnO layer 14 is formed by a sputtering method, etc., and electrodes 16 and 18 are formed. Electrodes 20 and 22 are formed on one and the other terminal sides of the longitudinal direction of the other main surface side of the piezoelectric substrate 12. The electrodes 18 and 22 are electrically and mechanically connected to each other by etching, etc. An input terminal 26 is connected to the electrode 16 and an output terminal 28 is connected to the electrode 18. A ground terminals 30 and 32 are connected to the electrode 20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic wave element, and more particularly to an acoustic wave element used in piezoelectric bulk wave devices such as piezoelectric resonators, piezoelectric filters and ultrasonic transducers.

[0002]

2. Description of the Related Art Conventionally, as a substrate used for such an acoustic wave device, for example, a ZnO thin film is formed on a Si substrate, a ZnO thin film is formed on a fused silica substrate, and Al ₂ O _{3 is used.} For example, a ZnO thin film is formed on a substrate. However, since the electromechanical coupling coefficient of these various substrates is as small as 0.2 or less, the efficiency is low when used in the acoustic wave device.

On the other hand, as a substrate used for an acoustic wave device, LiNb, which has a large electromechanical coupling coefficient, has recently been used.
O ₃ substrates and LiTaO ₃ substrates have received attention. When using a LiNbO ₃ substrate or the like for an acoustic wave device,
The Euler angle at which the electromechanical coupling coefficient is relatively large, in other words, the cutting direction of the substrate is selected and used.

[0004]

However, LiN
In the case of a substrate formed of bO ₃ or LiTaO ₃ , it is necessary to select the Euler angle, which is troublesome, and at the same time, it is not possible to obtain a sufficiently large electromechanical coupling coefficient. .

That is, since the conventional substrate as described above has a small electromechanical coupling coefficient, the conversion efficiency between electric energy and mechanical energy is low even if various conventional substrates are used for the acoustic wave device. there were.

Therefore, a main object of the present invention is to provide an acoustic wave device having a high conversion efficiency between electric energy and mechanical energy.

[0007]

The invention according to claim 1 includes a LiNbO ₃ substrate, a ZnO layer formed on one main surface of the LiNbO ₃ substrate, and an electrode formed on the surface of the ZnO layer. , An elastic wave device.

According to the second aspect of the present invention, when the thickness of the ZnO layer is a and the thickness of the LiNbO ₃ substrate is b, a ÷ b
The acoustic wave device according to claim 1, wherein> 0.006 is satisfied.

According to the third aspect of the invention, when the thickness of the ZnO layer is a and the thickness of the LiNbO ₃ substrate is b, it is 0.0
The acoustic wave device according to claim 1, wherein 2> a ÷ b ≧ 0.006 is satisfied.

According to a fourth aspect of the present invention, there is provided a LiTaO ₃ substrate, and ZnO formed on one main surface of the LiTaO ₃ substrate.
An acoustic wave device including a layer and an electrode formed on the surface of the ZnO layer.

According to a fifth aspect of the invention, when the thickness of the ZnO layer is a and the thickness of the LiTaO ₃ substrate is b, a / b
The acoustic wave device according to claim 4, wherein> 0.006 is satisfied.

In a sixth aspect of the present invention, when the thickness of the ZnO layer is a and the thickness of the LiTaO ₃ substrate is b, it is 0.
The acoustic wave device according to claim 4, wherein 02> a ÷ b ≧ 0.006 is satisfied.

[0013]

In the invention described in claims 1 to 6, LiNbO _{3 is used.}
Since the ZnO layer is formed on the substrate or the LiTaO ₃ substrate, the electromechanical coupling coefficient becomes large.

[0014]

According to the present invention, since the electromechanical coupling coefficient can be made larger than that of the conventional one, an elastic wave element having a high conversion efficiency between electric energy and mechanical energy can be obtained.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the accompanying drawings.

[0016]

1 is an illustrative view showing one embodiment of the present invention, and FIG. 2 is an illustrative cross sectional view taken along line II-II in FIG. 3 is a sample diagram for measuring the electromechanical coupling coefficient, and FIG. 4 is the electromechanical coupling coefficient of the thickness shear vibration of the acoustic wave device shown in FIG. 3 and the ZnO layer provided on the LiNbO ₃ substrate. 5 is a graph showing the relationship with the thickness of the ZnO layer provided on the LiNbO ₃ substrate and the electromechanical coupling coefficient of the longitudinal stretching vibration of the acoustic wave device shown in FIG. It is a graph shown.

The acoustic wave device 10 is made of, for example, LiNbO ₃
It includes a rectangular piezoelectric substrate 12 made of. In this example,
For example, a Y-cut LiNbO ₃ substrate is used, and the piezoelectric substrate 12 is polarized in the thickness direction, for example. Further, in this embodiment, the piezoelectric substrate 12 is formed to have a thickness of 500 μm, for example.

A ZnO layer 14 is formed on the entire surface of the piezoelectric substrate 12 by a method such as a sputtering method, a vacuum deposition method and a chemical vapor deposition method. In this embodiment, the ZnO layer 14 is formed by forming a ZnO thin film on the piezoelectric substrate 12 by the sputtering method.
In this embodiment, a ZnO thin film having a thickness of 10 μm, for example, is formed on the piezoelectric substrate 12.

A ZnO layer 14 is formed on the surface of the piezoelectric substrate 12.
The first electrode 16 is formed on one end side in the upper longitudinal direction, and the second electrode 18 is formed on the other end side in the longitudinal direction. On the back surface side of the piezoelectric substrate 12, a third electrode 20 is formed on one end side in the longitudinal direction thereof so as to face the first electrode 16, and a second electrode is formed on the other end side in the longitudinal direction. The fourth electrode 22 is formed so as to face the electrode 18. further,
The second electrode 18 and the fourth electrode 22 are electrically and mechanically connected by a connecting means 24 such as etching and printing.

A first terminal 26 as an input terminal is connected to the first electrode 16, and a second terminal 28 as an output terminal is connected to the second electrode 18. Furthermore, the third
The third terminal 30 and 32 as a ground terminal is connected to the electrode 20 of.

In this acoustic wave device 10, the first terminal 16
When the drive signal is applied to the piezoelectric substrate 12, the piezoelectric substrate 12 vibrates in its length direction. That is, the elastic wave whose vibration mode is the longitudinal stretching vibration propagates on the piezoelectric substrate 12. Then, the propagated elastic wave is output as an electric signal from the second terminal 28.

In the acoustic wave device 10 according to the present invention, L
Since the ZnO layer 14 is formed on the piezoelectric substrate 12 made of iNbO _3, it is possible to obtain one having a large electromechanical coupling coefficient, as shown in an experimental example described later. Therefore, the elastic wave element 10 has a higher efficiency of conversion between electric energy and mechanical energy, as compared with the conventional elastic wave element, and has high efficiency.

Next, an experimental example showing that the electromechanical coupling coefficient is increased by forming the ZnO layer on the LiNbO ₃ substrate is shown below. In this experimental example, as the measuring acoustic wave element 40 for measuring the electromechanical coupling coefficient,
And those not to form a ZnO thin film on LiNbO ₃ substrate, which was formed ZnO thin film LiNbO ₃ substrate,
Specifically, it was decided to measure and calculate the electromechanical coupling coefficient in the longitudinal stretching vibration mode and the thickness-shear vibration mode for the ZnO thin film having different thickness.

First, for example, Y-cut LiNbO ₃
The substrate is prepared. As shown in FIG. 3, on one main surface of the LiNbO ₃ substrate 42, for example, Z having a film thickness of 2.8 μm is formed.
The nO thin film 44 is formed by sputtering, for example. Furthermore, on the one main surface side of the LiNbO ₃ substrate 42, Zn
An electrode 46 was provided on the ZnO layer 44 made of an O thin film, and another electrode 50 was provided on the other main surface of the LiNbO ₃ substrate 42, so that a sample to be the acoustic wave element 40 for measurement was prepared. Similarly, on the LiNbO ₃ substrate 42, 3.7 μm, 4.8 μm, 6.3 μm, and 8.5 μm, respectively.
ZnO thin film with a thickness of 11 μm,
By providing an electrode on the main surface of the NbO ₃ substrate 42,
Several other samples were made. Then, for these samples, the electromechanical coupling coefficients k ₂₁ and k _S in the longitudinal stretching vibration mode and the thickness shear vibration mode were measured.
Calculations were made and the results are shown in FIGS. 4 and 5.

When the ZnO layer 44 is formed on the LiNbO ₃ substrate 42, as shown in FIG. 4, the electromechanical coupling coefficient k _S is about 0.6 in the thickness shear vibration mode, and the conventional LiNbO ₃ substrate alone is used. The electromechanical coupling coefficient of LiNbO
₃ substrate 42 only, Z on LiNbO ₃ substrate 42
There is not much difference between the nO layer 44 and the nO layer 44.

On the other hand, for the longitudinal stretching vibration mode, by forming the ZnO layer 44 on the LiNbO ₃ substrate 42, the electromechanical coupling coefficient is 0.2.
From the value of 4, the electromechanical coupling coefficient k ₂₁ is 0.25 to 0.31.
And is getting bigger. Moreover, only the LiNbO ₃ substrate 42 (having a ZnO layer thickness of 0 μm) and LiNbO ₃ substrate 42
Comparing with the one in which the ZnO layer 44 is formed on the bO ₃ substrate 42, the substrate in which the ZnO layer 44 is formed is 20%.
It can be seen that the electromechanical coupling coefficient k ₂₁ increases as the amount increases. It is presumed that the electromechanical coupling coefficient is increased in other vibration modes other than the lengthwise vibration mode, such as the lengthwise vibration mode, the radial direction vibration mode, and the thickness direction vibration mode.

In this case, when the thickness of the LiNbO ₃ substrate 42 is a and the thickness of the ZnO layer 44 is b, a / b>
It is preferable to form the thickness b of the ZnO layer 44 that satisfies 0.006, and 0.02> a ÷ b ≧ 0.006
It is more preferable that the thickness b of the ZnO layer 44 satisfying the above condition is formed.

In this example, LiNbO₃Z on the board
By forming the nO layer, the electromechanical coupling coefficient is increased.
I've worked hard, for example, LiTaO₃LiT formed by
aO ₃A ZnO layer may be formed on the substrate.
In this case, LiTiO₃Is LiNbO₃Piezoelectric similar to
Since it is a single crystal material, that is, it has a similar crystal structure,
Similarly to the above-described embodiment, the longitudinal stretching vibration mode, the longitudinal direction
Directional vibration mode, radial vibration mode and thickness vibration mode
Electromechanical coupling coefficient k_{twenty one}, K₃₁, K_rand
k_tIt is easily inferred that an acoustic wave device with a large
Be done. In addition, in this embodiment, Y-cut LiNbO₃Base
Although the description has been given of the case where the ZnO layer is formed on the plate, other
Cut, that is, cut in other orientations
Similarly, when the electromechanical coupling coefficient becomes large,
Guessed.

[Brief description of drawings]

FIG. 1 is an illustrative view showing one embodiment of the present invention;

FIG. 2 is a schematic sectional view taken along line II-II in FIG.

FIG. 3 is a sample diagram for measuring an electromechanical coupling coefficient.

FIG. 4 is a graph showing the relationship between the electromechanical coupling coefficient of thickness shear vibration of the measuring acoustic wave device shown in FIG. 3 and the thickness of the ZnO layer provided on the LiNbO ₃ substrate.

5 is a graph showing the relationship between the electromechanical coupling coefficient of longitudinal vibration of the acoustic wave device for measurement shown in FIG. 3 and the thickness of the ZnO layer provided on the LiNbO ₃ substrate.

[Explanation of symbols]

10 acoustic wave device 12 piezoelectric substrate 14 ZnO layer 16 first electrode 18 second electrode 20 third electrode 22 fourth electrode 24 connection means 26 first terminal 28 second terminal 30 third terminal 32 second 4 terminal 40 elastic wave element for measurement for measuring electromechanical coupling coefficient (sample) 42 LiNbO ₃ substrate 44 ZnO layer 46, 50 electrode

Claims (6)

[Claims] 1. A LiNbO ₃ substrate, ZnO formed on one main surface of the LiNbO ₃ substrate
An acoustic wave device including a layer and an electrode formed on the surface of the ZnO layer. 2. The thickness of the ZnO layer is a, and the LiNb is
The acoustic wave device according to claim 1, wherein a / b> 0.006 is satisfied, where b is the thickness of the O ₃ substrate. 3. The thickness of the ZnO layer is a and the LiNb is
Assuming that the thickness of the O ₃ substrate is b, 0.02> a ÷ b ≧
The acoustic wave device according to claim 1, which satisfies 0.006. 4. A LiTaO ₃ substrate, ZnO is formed on one main surface of the LiTaO ₃ substrate
An acoustic wave device including a layer and an electrode formed on the surface of the ZnO layer. 5. The thickness of the ZnO layer is a, and the LiTa is
The acoustic wave device according to claim 4, wherein a ÷ b> 0.006 is satisfied, where b is the thickness of the O ₃ substrate. 6. The thickness of the ZnO layer is a, and the LiTa is
Assuming that the thickness of the O ₃ substrate is b, 0.02> a ÷ b ≧
The acoustic wave device according to claim 4, which satisfies 0.006.