JP2001119262A - Piezoelectric resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric resonator which is made smaller for its resonance frequency and has large terminal-to-terminal capacitance. SOLUTION: Two layers of internal electrodes 12 and 14 are formed among three layers of ceramic piezoelectric substrates 11, 13 and 15, ad the surface electrodes 10 and 16 are formed on both main surface of the laminated substrates 11, 13 and 15 and electrodes 12 and 14, respectively. The center substrate 13 is not polarized and both side electrodes 11 and 15 are polarized in the direction vertical to each principal surface and with their polarizing directions set opposite to each other. Then a connecting electrode 18 is added the side face of the laminated substrates to secure electrical conduction between the electrodes 10 and 14 (the electrode 18 is insulated from the electrode 12 via an insulating material 17). The other connecting electrode 20 secures electrical conduction between the electrodes 16 and 14 and is insulated form the intermediate electrode 12 via an insulating material 19 that is formed on the side face of the laminated substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric resonator used for a piezoelectric oscillation element, a ladder filter, and the like, and more specifically, to a piezoelectric resonator using a bending vibration having a large capacitance between terminals.

[0002]

2. Description of the Related Art Conventionally, as a resonator in the 300 to 800 kHz band, spread vibration of a ceramic piezoelectric body has been used. FIG. 1A is a perspective view showing the structure of the spreading resonator 1,
FIG. 1B is a side view showing the configuration of the polarization axis and the electric field axis. The extended resonator 1 has a single-layer square-shaped piezoelectric substrate 2 having surface electrodes 3 provided on both front and rear main surfaces thereof, and polarization processing of the entire piezoelectric substrate 2 in a direction perpendicular to both main surfaces. Therefore, the direction of the electric field applied between the surface electrodes 3 (electric field axis) is also perpendicular to both main surfaces and parallel to the polarization axis. In such a spreading vibrator 1, when a signal is applied between both surface electrodes 3, the piezoelectric substrate 2 expands and contracts in the direction parallel to both main surfaces in the outer peripheral direction.

In this extended resonator 1, the product of the length Ls of one side and the resonance frequency fr is substantially constant, and Ls × fr = As. Here, As is a constant (frequency constant),
As ≒ 2100 mmkHz. For example, to obtain a resonator having a resonance frequency fr = 450 kHz, the length of one side is Ls = 4.67 mm.

[0004] In the world of electronic components, the lightening, thinning, and miniaturization of the electronic components have been more and more advanced. Therefore, it is difficult to reduce the size and weight of such extended resonators, as well as to reduce the cost. The critical dimensions were unacceptable.

FIG. 2 shows a two-stage ladder filter 6 composed of series resonators 7a and 7b and parallel resonators 8a and 8b, and FIG. 3 shows its attenuation characteristics. As a characteristic of such a ladder filter 6, the guaranteed attenuation Att. Shown in FIG. The capacitance between the terminals of the series resonators 7a and 7b is C1, and the parallel resonator 8
Assuming that the capacitance between the terminals a and 8b is C2, the guaranteed attenuation amount Att. of the two-stage ladder filter 6 is represented by Att. = 2 × 20log (C2 / C1). In order to increase the capacitance, it is necessary to increase the inter-terminal capacitance C2 of the parallel resonators 8a and 8b and to decrease the inter-terminal capacitance C1 of the series resonators 7a and 7b. However, when the above-described extended resonator 1 is used as the parallel resonators 8a and 8b, it is difficult to increase the inter-terminal capacitance C2 for the following reasons.

[0006] The spreading resonator 1 as shown in FIG.
The terminal-to-terminal capacitance Cs of the piezoelectric substrate
Assuming that the relative permittivity is ε and the thickness is t, Cs = (ε · ε₀・ Ls²) / T... Where ε₀Is the dielectric constant in vacuum,
ε₀= 8.854 × 10 ^-12It is.

When the resonance frequency fr of the spreading resonator 1 is determined, the length Ls of one side of the spreading resonator 1 is determined (see the above equation). Therefore, the terminal capacitance Cs is determined by the thickness t of the piezoelectric substrate 2 and the relative permittivity. It is determined only by ε.

In order to increase the inter-terminal capacitance Cs of the spreading resonator 1, it is necessary to increase the relative permittivity ε of the piezoelectric substrate 2 or to reduce its thickness t. However, the relative permittivity ε of the piezoelectric substrate 2 is a constant unique to the material of the piezoelectric substrate 2 and cannot be arbitrarily selected. Changing the material of the piezoelectric substrate also affects other characteristics. Further, when the thickness t of the piezoelectric substrate 2 is reduced, the breaking strength decreases,
Since the expansion resonator 1 is easily damaged, there is a limit to the selection range.

Accordingly, it has been difficult to obtain a wide-spread resonator having a large capacitance between terminals, although a resonator having a large capacitance between terminals is required as a parallel resonator of a ladder filter. On the contrary, if a piezoelectric resonator having a small constant corresponding to the above-described constant Cs is developed and the piezoelectric resonator can be miniaturized, the capacitance between terminals becomes small as a result. As a result, the guaranteed attenuation of the ladder filter becomes worse.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and an object of the present invention is to reduce the size if the same resonance frequency is used. Another object of the present invention is to provide a piezoelectric resonator having a large terminal capacitance.

[0011]

According to a first aspect of the present invention, there is provided a piezoelectric resonator in which at least four layers of electrodes and three or more layers of piezoelectric material are laminated, and at least two of the piezoelectric layers are formed of the electrodes. The piezoelectric resonator is polarized in a direction perpendicular to the direction, an electric field is generated in some piezoelectric layers in the same direction as the polarization direction of the piezoelectric layers, and the electric field is generated in other piezoelectric layers. The electrodes are connected so that an electric field is generated in a direction different from the polarization direction of the piezoelectric layer.

[0012] The piezoelectric resonator according to the second aspect is the first aspect.
In the piezoelectric resonator described in the above, the even number of electrodes and the odd number of piezoelectric layers are stacked, the central piezoelectric layer is not polarized, and the polarization direction and the direction of the electric field are the same on one side, The invention is characterized in that the electrodes are connected to each other so that the polarization direction and the direction of the electric field are opposite to each other.

[0013]

In the piezoelectric resonator according to the first aspect, the piezoelectric layer in which the polarization direction and the electric field direction are in the same direction shrinks in the center direction, and the piezoelectric layer in which the polarization direction and the electric field direction are different from each other. Since the piezoelectric resonator expands in the outer edge direction, the piezoelectric resonator as a whole undergoes bending vibration. In such a bending vibration piezoelectric resonator, the product of the length of one side and the resonance frequency expands and becomes smaller as compared with the resonator. The size of the child can be reduced. In addition, since this piezoelectric resonator has four or more layers of electrodes, a terminal capacitance can be formed between these electrodes, and the terminal capacitance can be increased. In addition, since the piezoelectric layers are stacked, the thickness of each piezoelectric layer can be reduced without lowering the strength, and the capacitance between terminals of the piezoelectric resonator can be further increased.

In the piezoelectric resonator according to the second aspect,
Since the central piezoelectric layer is not polarized, the polarization direction and the direction of the electric field are the same on one side, and the polarization direction and the direction of the electric field are opposite on the other side. Obtainable. Further, by inserting a non-polarized piezoelectric layer, the other piezoelectric layers can be thinned without lowering the strength, and the capacitance between terminals can be further increased.

[0015]

(First Embodiment) FIG. 4 is a perspective view showing a piezoelectric resonator 9 according to an embodiment of the present invention, and FIG. 5 is a cross-sectional view thereof. 300
It is used as a ceramic oscillator in a frequency band of kHz to 800 kHz. This piezoelectric resonator 9
Are three square ceramic piezoelectric layers 11, 1
Sandwiching two layers of internal electrodes 12 and 14 between 3 and 15;
The laminated piezoelectric layers 11, 13, 15 and the internal electrode 1
Surface electrodes 10 and 16 are formed on both the front and back main surfaces of Nos. 2 and 14, respectively. The central piezoelectric layer 13 is not polarized, and the piezoelectric layers 11 and 15 on both sides thereof are subjected to polarization processing in a direction perpendicular to the main surface and in directions opposite to each other. . Note that the polarization direction may be inward with the center piezoelectric layer 13 interposed therebetween, or may be outward with the center piezoelectric layer 13 interposed therebetween, as indicated by solid arrows in FIG. Is also good.

Further, in the piezoelectric resonator 9, connection electrodes 18 and 20 are provided on both side surfaces. The connection electrode 18 is electrically connected to the surface electrode 10 and the internal electrode 14 in every other layer, and is insulated from the intermediate internal electrode 12 by the insulating material 17 formed on the side surface. The other connection electrode 20 is electrically connected to the other surface electrode 16 and the internal electrode 12 and is insulated from the intermediate internal electrode 14 by an insulating material 19 formed on the side surface.

Therefore, when a voltage is applied to both the surface electrodes 10 and 16 in the directions indicated by the dashed arrows in FIG. The body layer 11 contracts toward the center, and the electric field direction and the polarization direction are opposite to each other inside the other piezoelectric layer 15, and the piezoelectric layer 15 expands toward the outer edge. As a result, when a signal (high-frequency electric field) is applied between both the surface electrodes 10 and 16, both the piezoelectric layers 11 and 15 expand and vibrate and try to expand and contract in the outer edge direction and the center direction. Are inverted, so that the piezoelectric resonator 9 as a whole is curved and deformed such that both main surfaces alternately repeat irregularities (hereinafter referred to as bending vibration, and the piezoelectric resonator 9 according to the present invention).
Is called a bending resonator).

As described above, in the bending resonator 9 having the three-layer structure,
The length of one side is Lb, the relative permittivity of the piezoelectric layers 11, 13, 15 is ε, and the thickness of each of the piezoelectric layers 11, 13, 15 is t.
Assuming that 1, t2 and t3, the inter-terminal capacitance Cb is represented by the following equation. _{Cb = (ε · ε 0 ·} Lb 2) (1 / ta + 1 / tb + 1 / tc) ... represented by. Here, ε ₀ is a dielectric constant in a vacuum.

Now, for the same piezoelectric material (having the same value of ε),
The dimensions are equal (Lb = Ls) and the thickness is equal (ta + tb +
tc = t) When the expansion resonator 1 is compared with the bending resonator 9, the capacitance between terminals of the expansion resonator 1 is expressed by the following equation. On the other hand, each piezoelectric layer 11, 1
Assuming that the thicknesses 3 and 15 are equal (ta = tb = tc = t
/ 3), and the inter-terminal capacitance is given by the following equation. Therefore, in the bending resonator 9 of the present invention, nine times the inter-terminal capacitance can be obtained as compared with the spreading resonator 1 having the same size and the same thickness. Further, even if the thickness of the piezoelectric layers 11, 13, 15 is reduced, they are laminated and the overall thickness does not change, so that the strength does not change.

Therefore, when the parallel resonators 8a and 8b used in the ladder filter as shown in FIG. 2 are expanded and replaced with the bent resonator 9 having a three-layer structure, the guaranteed attenuation of the ladder filter becomes It is increased by 38.2 dB as expressed by the following equation. ΔAtt. = 2 × 20 log (Cb / Cs) = 38.2 [dB]... A method of selecting a material having a different dielectric constant ε or changing the thickness of the series resonator and the parallel resonator, which is a conventional technique. By combining the above, it becomes possible to design the capacity ratio and the guaranteed attenuation more widely.

Also in this bending resonator 9, the product of the length Lb of one side and the resonance frequency fr is substantially constant, and Lb × fr = Ab. Here, this frequency constant is Ab ≒ 430 mmkHz.

The frequency constant Ab of the bent resonator 9 is about 0.3 times (= A) the frequency constant As of the extended resonator 1.
b / As), for the same resonance frequency fr,
The length Lb of one side of the bending resonator 9 is about 0.3 times the length Ls of one side of the expanding resonator 1. Therefore, when the bending resonator 9 is compared with the expanding resonator 1, the bending resonator 9 is about 1 / 3.3 or less of the expanding resonator 1 by one side length, and is about 1/10 in area. Therefore, if the resonance frequency fr is the same, the size of the resonator can be significantly reduced by using the bending resonator 9 as compared with the expansion resonator 1.

Further, when comparing the spread resonator 1 and the bending resonator 9 of the same resonance frequency fr, as described above, an area of about one-tenth the flexural resonator ^{9 (Lb 2 = Ls 2/} 10) , and the The thickness of each of the piezoelectric layers 11, 13, 15 is 1/3 (t
a = tb = tc = t / 3), the bending resonator 9
Is about 9/10 times as large as the inter-terminal capacitance Cs of the expanded resonator 1, and although the size is reduced to about 1/10, almost the same inter-terminal capacitance can be obtained. Further, even if the thickness is the same, the strength is improved by the reduced size.

Next, a method of manufacturing the bending resonator 9 will be described. First, a green sheet 11 made of a piezoelectric material and internal electrodes 12a and 14a formed by thick-film printing of a conductive paste is used.
a, 13a, and 15a are laminated and fired, and then external electrodes 10a and 16a are formed on both surfaces thereof, whereby FIG.
1A, a parent substrate 21 as shown in FIG. 1A is formed, and a terminal electrode 22 electrically connected to the internal electrodes 12a and 14a is formed on an end surface thereof. In this state, the external electrodes 10a and 16a and the terminal electrode 2
By applying an electric field between the two, the polarization process is performed in the direction shown by the arrow in FIG. Next, FIG.
Then, the master substrate 21 is cut into a strip shape along the arrow line shown in FIG. 6 to obtain a strip-shaped master substrate 23 as shown in FIG. Next, the strip-shaped parent substrate 23 is cut along the arrow line shown in FIG. 6D to obtain a single piezoelectric resonator 24 as shown in FIG. 6E. Next, on the end face of the piezoelectric resonator 24, the ends of the internal electrodes 12 and 14 are covered with insulating materials 17 and 19 as shown in FIG. The electrodes 18 and 20 are formed. Thereby, a large number of bending resonators 9 as shown in FIG. 4 are produced at one time.

(Second Embodiment) FIG. 7A is a diagram showing a polarization process of a piezoelectric resonator 31 according to another embodiment of the present invention, and FIG. 7B is a diagram showing a driving state thereof. . In this piezoelectric resonator 31, five (even seven or more odd layers) piezoelectric layers 33, 35, 37, 39, 41, and 4 are provided.
Internal electrodes 34, 3 (even more than six layers)
6, 38 and 40 are laminated, and the surface electrodes 32, 4
2 are formed. In the polarization process, FIG.
As shown in (a), the surface electrodes 32, 42 and the internal electrodes 36, 38 are electrically connected, and the internal electrodes 34, 40
Are electrically connected to each other, and a voltage is applied between them, so that the central piezoelectric layer 37 is not polarized, and the upper and lower piezoelectric layers 33, 35, 39, and 41 are polarized. Thereafter, as shown in FIG. 7B, the surface electrode 32 and the internal electrodes 36 and 40 are electrically connected by the connection electrode, and the internal electrodes 34 and 38 and the surface electrode 42 are electrically connected by the connection electrode. In the piezoelectric layers 33 and 35 above the central piezoelectric layer 37, the polarization axis and the electric field axis are in the same direction, and in the piezoelectric layers 39 and 41 below the central piezoelectric layer 37, the polarization axes are the same. Since the axis and the electric field axis are in different directions, the piezoelectric resonator 31 bends and vibrates. According to such a structure, an inter-terminal capacitance is generated between the surface electrodes 32, 42 and the internal electrodes 34, 40 and between the internal electrodes 34, 36, 38, 40, so that a larger inter-terminal capacitance is obtained. be able to.

(Third Embodiment) FIG. 8A is a diagram showing a polarization processing step of a piezoelectric resonator 51 according to another embodiment of the present invention, and FIG. 8B is a diagram showing a driving state thereof. . In this piezoelectric resonator 51, even-numbered (for example, four) piezoelectric layers 53, 55, 57, and 59 and odd-numbered (for example, three)
The internal electrodes 54, 56, 58 are laminated, and surface electrodes 52, 60 are formed on both surfaces thereof. In the polarization process, as shown in FIG.
And the internal electrodes 56 are electrically connected.
4 and 58 are electrically connected to each other, and a voltage is applied between them, so that all the piezoelectric layers 53, 55, 57 and 59
Is polarized. Thereafter, as shown in FIG. 8B, the surface electrode 52 and the internal electrodes 56 and 58 are electrically connected by connection electrodes, and the internal electrode 54 and the surface electrode 60 are connected.
Are electrically connected by a connection electrode, the polarization axis and the electric field axis are in the same direction in the upper half piezoelectric layers 53 and 55, and the polarization axis and the electric field axis are different in the lowermost piezoelectric layer 59. Therefore, the piezoelectric resonator 51 undergoes bending vibration.
Even with such a structure, inter-terminal capacitance is generated between the surface electrodes 52, 60 and the internal electrodes 54, 58 and between the internal electrodes 54, 56, 58, so that a large inter-terminal capacitance can be obtained.

In the embodiment shown in FIG. 7 or FIG. 8, the wiring during the polarization processing and the wiring during the driving may be reversed. However, if the wiring is as shown in the figure, a signal can be applied to both surface electrodes at the time of driving, so that the structure of the case or package in which the piezoelectric resonator is housed can be simplified.

FIG. 9 shows a flexural vibration piezoelectric resonator 61 in which internal electrodes 64 are laminated between two piezoelectric layers 63 and 65, and external electrodes 62 and 66 are formed on both surfaces thereof. . This piezoelectric resonator 61 is similar to the piezoelectric resonator of the present invention.
Although the size can be significantly reduced as compared with the piezoelectric resonator due to the spread vibration, the capacitance between terminals is smaller than the piezoelectric resonator of the present invention if the same size, the same thickness, and the same piezoelectric material are used. Therefore, if the piezoelectric resonator 61 is a series resonator and the piezoelectric resonator of the present invention is a parallel resonator to form a ladder filter (three or more stages) as shown in FIG.
A small ladder filter with a large guaranteed attenuation can be manufactured.

[0029]

According to the first aspect of the present invention, it is possible to manufacture a piezoelectric resonator having a large inter-terminal capacitance and a bending vibration, and to obtain a small-sized piezoelectric resonator having a large inter-terminal capacitance. it can. Therefore, if it is used for a parallel resonator of a ladder filter, the guaranteed attenuation can be increased.

According to the piezoelectric resonator of the second aspect, the central piezoelectric layer is not polarized, and the polarization direction and the direction of the electric field are the same on one side and the polarization direction on the other side. And the direction of the electric field are opposite, a large bending vibration can be obtained.

[Brief description of the drawings]

FIG. 1A is a perspective view showing a structure of a conventional spread resonator, and FIG. 1B is a side view showing directions of a polarization axis and an electric field axis thereof.

FIG. 2 is a diagram illustrating a circuit configuration of a ladder filter.

FIG. 3 is a diagram showing characteristics of the ladder filter according to the first embodiment;

FIG. 4 is a perspective view of a piezoelectric resonator according to an embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view of the above piezoelectric resonator.

6A is a perspective view and a cross-sectional view showing a polarization processing step of a parent substrate, FIG. 6B is a perspective view showing a first cutting step of the parent substrate, and FIG. 6C is a cut parent substrate. FIG. 9D is a perspective view, (d) is a perspective view showing a second cutting step of the parent substrate, and (e) is a perspective view showing the obtained piezoelectric resonator.

FIG. 7A is a diagram illustrating a polarization processing method of a piezoelectric resonator according to another embodiment of the present invention, and FIG. 7B is a diagram illustrating a driving method of the piezoelectric resonator.

FIG. 8A is a diagram illustrating a polarization processing method of a piezoelectric resonator according to still another embodiment of the present invention, and FIG. 8B is a diagram illustrating a driving method of the piezoelectric resonator.

FIG. 9 is a perspective view showing a bending vibration piezoelectric resonator having a two-layer structure.

[Explanation of symbols]

 10, 16 Surface electrode 11, 13, 15 Piezoelectric layer 12, 14 Internal electrode 17, 19 Insulating material 18, 20 Connection electrode

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[Procedure amendment]

[Submission Date] November 5, 1999 (1999.11.
5)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Change

[Correction contents]

(Third Embodiment) FIG. 8A is a diagram showing a polarization processing step of a piezoelectric resonator 51 according to another embodiment of the present invention, and FIG. 8B is a diagram showing a driving state thereof. . In this piezoelectric resonator 51, even-numbered (for example, four) piezoelectric layers 53, 55, 57, and 59 and odd-numbered (for example, three)
The internal electrodes 54, 56, 58 are laminated, and surface electrodes 52, 60 are formed on both surfaces thereof. In the polarization process, as shown in FIG.
And the internal electrodes 56 are electrically connected.
4 and 58 are electrically connected to each other, and a voltage is applied between them, so that all the piezoelectric layers 53, 55, 57 and 59
Is polarized. Thereafter, as shown in FIG. 8B, the surface electrode 52 and the internal electrodes 56 and 58 are electrically connected by connection electrodes, and the internal electrode 54 and the surface electrode 60 are connected.
Are electrically connected by a connection electrode, the polarization axis and the electric field axis are in the same direction in the upper half piezoelectric layers 53 and 55, and the polarization axis and the electric field axis are different in the lowermost piezoelectric layer 59. Therefore, the piezoelectric resonator 51 undergoes bending vibration.
Even with such a structure, inter- terminal capacitance is generated between the surface electrodes 52 and 60 and the internal electrodes 54 and 58 and between the internal electrodes 54 and 56, so that a large inter-terminal capacitance can be obtained.

Claims (2)

[Claims] 1. A piezoelectric resonator in which four or more electrodes and three or more piezoelectric layers are stacked, and at least two of the piezoelectric layers are polarized in a direction perpendicular to the electrodes. In some piezoelectric layers, an electric field is generated in the same direction as the polarization direction of the piezoelectric layer, and in some other piezoelectric layers, an electric field is generated in a direction different from the polarization direction of the piezoelectric layer. A piezoelectric resonator characterized in that the electrodes are connected to each other as described above. 2. An even-numbered electrode layer and an odd-numbered piezoelectric layer are laminated, and a central piezoelectric layer is not polarized. On one side, the polarization direction and the direction of the electric field are the same. The piezoelectric resonator according to claim 1, wherein the electrodes are connected to each other such that the polarization direction and the direction of the electric field are opposite on one side.