JPH05218788A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To obtain the piezoelectric resonator with small size and high performance by reducing the response of undesired resonance in the vicinity of the resonance frequency in the thickness longitudinal energy enclosing piezoelectric resonator. CONSTITUTION:An exciting electrode 2 is provided almost in the middle of a piezoelectric substrate 1, only the vicinity of the exciting electrode 2 of the piezoelectric substrate 1 is polarized in the broadwise direction, then part of a lateral wave component of the thickness longitudinal vibration is reflected at a border between a polarized region 5 and a non-polarized region in the piezoelectric substrate 1 toward the polarized region 5. Then the part of the wave is transmitted to the non-polarized region and is reflected to one end face of the piezoelectric substrate 1, and since the reflecting component is reflected in the border face similarly as above, the reflecting component is very small. Thus, the effect of the lateral component reflected at the end face is small and the undesired resonance response in the vicinity of the resonance frequency in the thickness longitudinal vibration caused by the end face reflection is very small and the size of a non-electrode forming part 4 is made small to ensure miniaturization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thickness longitudinal energy trap type piezoelectric resonator utilizing vibration of a piezoelectric body.

[0002]

2. Description of the Related Art Among piezoelectric resonators such as filters using piezoelectric ceramics, piezoelectric single crystals, and oscillators, those having a center frequency and an oscillation frequency of about 1 MHz or more have electrical resonance frequencies. The thickness vibration mode, which is primarily inversely proportional to the thickness (t) of the resonator, is widely used. Particularly, in a resonator having a high center frequency and a high oscillation frequency, thickness longitudinal vibration having a sound velocity of a bulk wave about twice that of thickness shear vibration is used.

FIG. 4 is a plan view of an example of a conventional piezoelectric resonator utilizing thickness longitudinal vibration. In FIG. 4, 11 is a rectangular piezoelectric substrate made of piezoelectric ceramic or the like and uniformly polarized in the thickness direction and having a length of 6 mm and a width of 4 mm, and 12 is a piezoelectric substrate 11
A pair of excitation electrodes, which are provided at approximately the center of the
Reference numeral 13 is an extraction electrode for electrically connecting an external terminal (not shown) to the electrode 12, and a non-electrode forming portion having a large area outside the excitation electrode 12 in order to reduce the influence from the end face of the piezoelectric substrate 11. 14 were provided.

[0004]

However, in the above-mentioned conventional configuration, when the non-electrode forming portion 14 is made smaller in response to the demand for miniaturization of the piezoelectric resonator, the end face of the piezoelectric substrate 11 is affected and the excitation is performed. There is a problem in that the unnecessary resonance response is introduced in the vicinity of the resonance frequency of the thickness extensional vibration confined in the vicinity of the electrode 12, and the piezoelectric substrate 11 cannot be made small.
This is because the thickness longitudinal vibration has a displacement distribution of longitudinal waves and transverse waves, and when the non-electrode forming portion 14 is small, the transverse wave component is not sufficiently attenuated in the non-electrode forming portion 14 and reflected by the end surface of the piezoelectric substrate 11, This is because the reflection component affects thickness longitudinal vibration.

The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a small-sized and high-performance piezoelectric resonator.

[0006]

In order to achieve this object, the present invention provides a pair of excitation electrodes facing the front and back, which are connected to extraction electrodes, at substantially the center of both sides of the piezoelectric substrate. In the configuration, only the vicinity of the excitation electrode is polarized in the thickness direction.

[0007]

With this configuration, the transverse wave component of the thickness longitudinal vibration is
Since only the vicinity of the excitation electrode is polarized, part of it is reflected in the polarized region at the boundary surface between the polarized region and the non-polarized region in the piezoelectric substrate, and part of it is transmitted to the non-polarized region and reflected by the end face of the piezoelectric substrate. Since the reflection component is also reflected on the boundary surface as in the above, the reflection component is extremely small. Therefore, the influence of the end face reflection of the transverse wave component becomes small, and the unnecessary resonance response near the resonance frequency of the thickness longitudinal vibration becomes extremely small. Therefore, in the piezoelectric resonator of the present invention, the non-electrode forming portion of the piezoelectric substrate can be made small, and the piezoelectric resonator as a whole can be miniaturized.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 1A is a plan view of a piezoelectric resonator according to an embodiment of the present invention, FIG. 1B is a front sectional view thereof, and FIG. 2 is a plan view for explaining a manufacturing method thereof.

In FIG. 1, 1 is a piezoelectric substrate, 2 is an excitation electrode facing the front and back sides, 3 is an extraction electrode connected to the excitation electrode 2, 4 is a non-electrode forming portion, and 5 is a polarization region of the piezoelectric substrate 1. And the arrow A indicates the polarization direction of the polarization region 5.

Next, a method for producing this piezoelectric resonator will be described with reference to FIG. First, the excitation electrodes 2 are provided on both sides of the unpolarized strip-shaped piezoelectric substrate 1a whose thickness is polished to a predetermined frequency so as to face each other by plating or vapor deposition.
To form. In this embodiment, the excitation electrode 2 has a circular shape with a diameter of 1.2 mm and is not more than a value determined by the Beckman constant so as not to cause overtone. A lead electrode 3 for electrically connecting the excitation electrode 2 to an external terminal (not shown) is also formed at the same time as the excitation electrode 2.
Next, a DC voltage is applied to the extraction electrode 3 in insulating oil to polarize only the vicinity of the excitation electrode 2 and then the piezoelectric substrate 1
By cutting a, a rectangular piezoelectric resonator having a length of 6 mm and a width of 2.5 mm was prepared. In the rectangular piezoelectric resonator, the excitation electrode 2 is located substantially in the center of the piezoelectric substrate 1, and the polarization is made only in the vicinity of the excitation electrode 2.

As described above, in the piezoelectric resonator of the present embodiment, only the vicinities of the excitation electrodes 2 are polarized, so that the transverse wave component of the thickness longitudinal vibration is reflected and transmitted at the boundary surface between the polarized region and the non-polarized region to cause piezoelectricity. The influence of the end face of the substrate 1 is less likely to occur, so that the unwanted resonance response near the resonance frequency due to the end face reflection component of the transverse wave becomes extremely small. FIG. 3 shows the frequency characteristic of the present embodiment together with that of the comparative example. In FIG. 3, the resonance response in the vicinity of the resonance frequency of the piezoelectric resonator of the present example is shown by a solid line, and the comparative example is shown by a broken line. The comparative example is a piezoelectric resonator using a uniformly polarized piezoelectric substrate having the same width dimensions and electrode dimensions as the piezoelectric substrate 1 of the present embodiment. As is clear from this figure, the unnecessary resonance response appears in the comparative example in which the width of the conventional piezoelectric resonator is simply reduced, but in this embodiment, the unnecessary resonance response does not appear even if the width is small, and the size can be significantly reduced. .

[0012]

As described above, the present invention realizes a piezoelectric resonator which is much smaller than the conventional one without deteriorating the characteristics by polarizing only the vicinity of the excitation electrode of the piezoelectric substrate. .

[Brief description of drawings]

FIG. 1A is a plan view of a piezoelectric resonator according to an embodiment of the present invention, and FIG. 1B is a front sectional view of the same.

FIG. 2 is a plan view for explaining a method for manufacturing the same piezoelectric resonator.

FIG. 3 is a frequency characteristic diagram of the piezoelectric resonator and a conventional piezoelectric resonator.

FIG. 4 is a plan view of a conventional piezoelectric resonator.

[Explanation of symbols]

 1, 1a Piezoelectric substrate 2 Excitation electrode 3 Extraction electrode 4 Non-electrode forming part 5 Polarization region

Claims (1)

[Claims] 1. A piezoelectric resonance in which a pair of excitation electrodes, which are connected to extraction electrodes and are opposed to each other, are provided at substantially central portions on both front and back surfaces of a piezoelectric substrate, and only the vicinity of the excitation electrodes of the piezoelectric substrate is polarized in the thickness direction. Child.