JPH04306011A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To realize the piezoelectric resonator in which the structure for facilitating processing for mass-production is adopted and a fundamental wave can be utilized. CONSTITUTION:An insulation resin 6 of a lower dielectric constant than that of a piezoelectric substrate 2 is provided to both front and rear sides of the piezoelectric substrate 2 made of a piezoelectric ceramics in this piezoelectric resonator except a part 6a on which a vibration electrode is to be formed in a way that the parts 6a are opposite to each other while the piezoelectric substrate 2 is inserted between them. Moreover, an electrode member 8 is provided to the parts 6a on which the vibration electrode is to be formed while being extended over its surrounding insulation resin 6.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy trapping type piezoelectric resonator which is used as a piezoelectric filter, for example, and which utilizes longitudinal vibration in the thickness.

0002

2. Description of the Related Art Conventional examples of this type of piezoelectric resonator are shown in FIGS. 5 and 6.

The piezoelectric resonator shown in FIG. 5 is of a frequency increasing type, and has a structure in which a recess is formed in a piezoelectric substrate 2 made of piezoelectric ceramics, and a vibrating electrode 4 is provided on the opposite side of the recess. The piezoelectric resonator shown in FIG. 6 is of a frequency drop type, and vibrating electrodes 4 are placed opposite each other with a piezoelectric substrate 2 in between.
has been established. In both figures, f1, f2, and inequality symbols indicate the frequency and magnitude relationship of the vibrations of the portions.

In the case of a piezoelectric substrate 2 that utilizes thickness longitudinal vibration and is made of a piezoelectric ceramic having a Poisson's ratio (σ) of 1/3 or less, such as PbTiO3-based material having good temperature characteristics and aging characteristics, the piezoelectric substrate 2 shown in FIG. It is known that the energy of the fundamental wave can only be confined in the frequency increasing type (for example, Tanaka, Shimizu: Journal of the Institute of Electronics and Communication Engineers J62-A).
477 (1979)).

However, in the case of the frequency increasing type, as shown in FIG. 5, it is necessary to form a recess in the piezoelectric substrate 2 and install the vibrating electrode 4 there, which is difficult to process. The piezoelectric resonator is a piezoelectric resonator in which the substrate 2 is a flat plate, has a frequency-dropping structure that is easy to process, and can trap energy, and uses three or five times higher order waves.

[0006]

[Problems to be Solved by the Invention] However, since the frequency-drop type piezoelectric resonator as shown in Fig. 6 uses high-order waves, it has only a small electromechanical coupling coefficient (k) and a narrow bandwidth. It is not possible, ■The thickness of the piezoelectric resonator 2 is thicker than when using the fundamental wave, and the capacitance between the two vibrating electrodes 4 is small, so it is easily affected by floating capacitance, and the matching impedance is also high, making it difficult to use.■ Since the piezoelectric substrate 2 is thick, a large amount of piezoelectric ceramic material is required, which increases the cost.

Therefore, the main object of the present invention is to provide a piezoelectric resonator that can utilize a fundamental wave and has a structure that is easy to mass-produce.

[0008]

[Means for Solving the Problems] In order to achieve the above object, the piezoelectric resonator of the present invention includes an insulating resin having a lower dielectric constant than the piezoelectric substrate and a vibrating electrode formed on both sides of the piezoelectric substrate made of piezoelectric ceramics. The electrode material is applied at least from the part where the vibrating electrode is to be formed to the surrounding insulating resin, and the electrode material is applied so that the parts are opposite to each other with the piezoelectric substrate in between. It is characterized by

[0009]

[Function] According to the above structure, the electrode material applied to the portion where the vibrating electrode is to be formed without the insulating resin becomes the vibrating electrode. Then, when a voltage is applied between the upper and lower electrode materials, the applied voltage is distributed to the piezoelectric substrate in the part where the insulating resin is applied according to the dielectric constant ratio of that and the piezoelectric substrate, and the applied voltage is applied to the vibrating electrode part where the insulating resin is not applied. is applied to the piezoelectric substrate as it is, so a difference occurs in the piezoelectric characteristics of the piezoelectric substrate between the two.

Moreover, in the insulating resin application section, the sound velocity is slow (that is, the vibration frequency is low) due to its mass load effect.
On the other hand, in the vibrating electrode portion to which no insulating resin is applied, the speed of sound becomes faster (that is, the frequency of vibration becomes higher), and as a result, energy confinement of the frequency increasing type is achieved, and the fundamental wave can be confined.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view showing a piezoelectric resonator according to an embodiment of the present invention, and FIG. 2 is a plan view showing the piezoelectric resonator of FIG. 1 with electrode materials removed.

[0012] This piezoelectric resonator has a piezoelectric substrate 2 made of, for example, PbTiO3-based piezoelectric ceramics.
An insulating resin 6 having a lower dielectric constant (for example, 1/2 or less than that of the piezoelectric substrate 2) is applied by coating, etc., except for the parts described below, and then, in this embodiment, almost the entire surface is coated with silver, etc. The electrode material 8 is deposited by vapor deposition, sputtering, or the like.

The insulating resin 6 is placed on both the front and back surfaces of the piezoelectric substrate 2.
In this embodiment, as shown in FIG. 2, a portion 6a at the center where the vibrating electrode is to be formed, a portion 6b at the end where the external connection electrode is to be formed, and a portion 6c connecting the two are provided. Furthermore, the portions 6a where the upper and lower vibrating electrodes are to be formed are arranged to face each other with the piezoelectric substrate 2 in between, as shown in FIG.

According to the above structure, the portions of the electrode material 8 attached to the portions 6a and 6b to which the insulating resin 6 is not applied become the vibrating electrode and the external connection electrode, respectively.

In such a piezoelectric resonator, when a voltage is applied between the upper and lower electrode materials 8, the applied voltage is distributed to the piezoelectric substrate 2 at the portion where the insulating resin 6 is applied, depending on the dielectric constant ratio of that and the piezoelectric substrate 2. In the vibrating electrode portion to which the insulating resin 6 is not applied, the applied voltage is directly applied to the piezoelectric substrate 2, so a difference occurs in the piezoelectric characteristics of the piezoelectric substrate 2 between the two.

Furthermore, in the part where the insulating resin 6 is coated, the sound velocity is slow (that is, the vibration frequency is low) due to its mass load effect, whereas in the vibrating electrode part where the insulating resin 6 is not coated, the sound velocity is fast. (i.e. the frequency of vibration becomes higher),
That is, when the former frequency is f2 and the latter frequency is f1, f1 > f2, and as a result, frequency-increasing energy confinement is achieved, and the fundamental wave is confined.

[0017] To explain this using an impedance waveform,
In the conventional piezoelectric resonator having the structure shown in FIG. 6, the resonance response of the fundamental wave was small and the energy confinement of the fundamental wave was insufficient, as shown in FIG. As shown in Figure 3, the resonance response of the fundamental wave has a large and sharp waveform, indicating that sufficient energy confinement has been achieved.

Note that the peripheral edge of the piezoelectric substrate 2 does not directly affect vibration, so the insulating resin 6 and electrode material 8 are also applied to that area.
It is not fundamental and is arbitrary as to how to provide externally connected electrode portions, etc.

Further, the piezoelectric substrate 2 is made of Pb (Zr,
Ti)O3-based piezoelectric ceramics having a Poisson's ratio of 1/3 or less may be used.

[0020]

As described above, according to the piezoelectric resonator of the present invention, the energy of the fundamental wave can be confined by increasing the frequency, so that the fundamental wave can be used. Moreover, since it is easier to process by applying an insulating resin than forming a recess in a piezoelectric substrate as in a conventional frequency increasing type piezoelectric resonator, it is easier to mass-produce the resonator.

Furthermore, since the fundamental wave can be used, the piezoelectric substrate can be made thinner, and costs can be reduced by downsizing the piezoelectric resonator and reducing the amount of piezoelectric ceramic material. It also facilitates the production of low frequency piezoelectric resonators.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a piezoelectric resonator according to an embodiment of the present invention.

FIG. 2 is a plan view showing the piezoelectric resonator of FIG. 1 with electrode materials removed.

3 is a diagram showing an example of an impedance waveform of the piezoelectric resonator of FIG. 1. FIG.

4 is a diagram showing an example of an impedance waveform of the piezoelectric resonator of FIG. 6. FIG.

FIG. 5 is a cross-sectional view showing an example of a conventional frequency increasing type piezoelectric resonator.

FIG. 6 is a cross-sectional view showing an example of a conventional frequency drop type piezoelectric resonator.

[Explanation of symbols]

2 Piezoelectric substrate 6 Insulating resin 6a Part where the vibrating electrode should be formed 8 Electrode material

Claims (1)

[Claims] [Claim 1] An insulating resin having a lower dielectric constant is applied to both the front and back surfaces of a piezoelectric substrate made of piezoelectric ceramics, except for the part where the vibrating electrode is to be formed, and furthermore, the said parts are opposite to each other with the piezoelectric substrate in between. A piezoelectric resonator characterized in that an electrode material is further applied from at least a portion where the vibrating electrode is to be formed to an insulating resin around the portion.