Patent Application
20170163234
This application is based on and claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2015-239045, filed on Dec. 8, 2015, the entire content of which is incorporated herein by reference.
This disclosure relates to a frequency adjustment method of a piezoelectric resonator that vibrates by a coupling of two longitudinal modes and the piezoelectric resonator fabricated by the frequency adjustment method.
A piezoelectric resonator that vibrates by a coupling of two longitudinal modes, for example, a GT-cut crystal resonator attracts attention because it has possibility to show a temperature characteristic equal to or greater than an AT-cut crystal resonator. Some of the examples are disclosed by, for example, Japanese Unexamined Patent Application Publication No. 58-47313 (hereinafter referred to as Patent Literature 1), Japanese Unexamined Patent Application Publication No. 2015-43483 (hereinafter referred to as Patent Literature 2), and similar literature. Patent Literature 1 discloses a crystal resonator having a structure where a vibration attenuation portion is connected to each of two facing sides of a vibrator with a rectangular planar shape, via bridges (FIGS. 1A to 1C of Patent Literature 1 or similar drawing). Furthermore, Patent Literature 1 discloses a frequency adjustment method that does not cause degradation of a temperature characteristic even when a vibration frequency of a main vibration is adjusted. Specifically, Patent Literature 1 adjusts the frequency by adding weights in total four regions that are located in the proximity of each of the four sides of the rectangular vibrator and in the proximity of the center of each side (FIG. 2 of Patent Literature 1 or similar drawing).
Patent Literature 2 discloses a GT-cut crystal resonator that includes the following: a first vibrator with a rectangular planar shape; a second vibrator that has a rectangular planar shape and is connected to one of two facing sides of the first vibrator; and a third vibrator that has a rectangular planar shape and is connected to the other of the two sides of the first vibrator (FIG. 2 of Patent Literature 2 or similar drawing). In the crystal resonator disclosed in Patent Literature 2, it is described that a crystal resonator that has a favorable frequency versus temperature characteristic and enables reduction of an influence such as an outside impact is obtainable by setting the side ratio or the thickness of the vibrator, a thickness of an excitation electrode, and similar dimension to a predetermined range (in paragraph 40 of Patent Literature 2 or similar paragraph).
However, conventionally, a frequency adjustment method that ensures prevention of degradation of a frequency versus temperature characteristic even when performing a frequency adjustment of a piezoelectric resonator that vibrates by a coupling of two longitudinal modes and includes first to third vibrators is not disclosed, to the knowledge of the inventor of the present application.
A need thus exists for a frequency adjustment method of piezoelectric resonator and a piezoelectric resonator which are not susceptible to the drawback mentioned above.
According to an aspect of this disclosure, there is provided a frequency adjustment method for a piezoelectric resonator vibrating by a coupling of a width-longitudinal mode and a length-longitudinal mode. The piezoelectric resonator includes a first vibrator, a second vibrator, a third vibrator, and a supporting portion. The second vibrator connects to one of two ends positioned along a vibration direction of the width-longitudinal mode in the first vibrator. The third vibrator connects to another of the two ends in the first vibrator. The supporting portion is connected to two ends positioned along a vibration direction of the length-longitudinal mode in the first vibrator. The frequency adjustment method includes: setting the second vibrator to a first region, a second region, and a third region from the first vibrator side along the vibration direction of the width-longitudinal mode; setting the third vibrator to a first region, a second region, and a third region from the first vibrator side along the vibration direction of the width-longitudinal mode; and performing the frequency adjustment by reducing or adding mass of at least one of the first region and the third region in each of the second vibrator and the third vibrator.
The foregoing and additional features and characteristics of this disclosure will become more apparent from the following detailed description considered with reference to the accompanying drawings, wherein:
The following describes the embodiments of frequency adjustment methods and piezoelectric resonators according to this disclosure with reference to the attached drawings.
Each drawing used in descriptions are merely illustrated schematically for understanding the disclosure.
In each drawing used in the descriptions, like reference numerals designate corresponding or identical elements, and therefore such elements will not be further elaborated here.
Shapes, dimensions, material, and similar factor described in the following explanations are merely preferable examples within the scope of this disclosure.
Therefore, the disclosure is not limited to only the following embodiments.
The piezoelectric resonator 10 according to the embodiment is a crystal resonator that vibrates by coupling of a width-longitudinal mode and a length-longitudinal mode. Moreover, the piezoelectric resonator 10 includes the following: a first vibrator 11a, a second vibrator 11b, and a third vibrator 11c, where each of them has a rectangular planar shape; supporting portions 13a and 13b; and excitation electrodes 15a and 15b.
Here, the second vibrator 11b connects to one of two ends positioned along the vibration direction of the width-longitudinal mode in the first vibrator 11a (a direction indicated by fW in
One electrode 15a of the excitation electrodes is arranged in one principal surface of the first to third vibrators 11a to 11c, and the other electrode 15b of the excitation electrodes is arranged in the other principal surface of the first to third vibrators 11a to 11c. However, these excitation electrodes 15a and 15b are disposed in the front and back surfaces of the first to third vibrators 11a to 11c such that the polarity of the excitation electrodes in the front and back surfaces of the second vibrator 11b and the third vibrator 11c is reversed with respect to the polarity of the excitation electrodes in the front and back surfaces of the first vibrator 11a (see
This embodiment employs a crystal element that causes, what is called, a Y-cut plate of a crystal to rotate by 51.5 degrees around the X-axis of the crystal and causes the plate to further rotate by 45.0 degrees inside the surface and has a thickness of 40 μm; however, it is not limited to this. The dimension in fW direction of the first to third vibrators 11a to 11c is set to approximately 0.81 mm, and the dimension in fL direction of the first to third vibrators 11a to 11c is set to approximately 0.86 mm.
In the piezoelectric resonator 10, the second vibrator 11b is divided to be defined as a first region 11ba, a second region 11bb, and a third region 11bc from the first vibrator 11a side along the vibration direction fW of the width-longitudinal mode. Further, the third vibrator 11c is divided to be defined as a first region 11ca, a second region 116, and a third region 11cc from the first vibrator 11a side along the vibration direction fW of the width-longitudinal mode. Then, these first to third regions are, in this embodiment, regions where the vibrator, to which these regions belong, is divided into approximately three equal parts along fW direction. Consequently, when the dimension of each vibrator in fW direction is 0.81 mm as illustrated above, the dimension of each of the first to third regions 11ba, 11ca, 11bb, 11cb, 11bc, 11cc in fW direction is approximately 0.27 mm.
Next, an experiment was performed with the following procedures of a to d with respect to the piezoelectric resonator 10 illustrated in
a. Before performance of a frequency adjustment, a frequency versus temperature characteristic relative to an environmental temperature of the piezoelectric resonator 10 was measured.
b. Next, the frequency adjustment of the piezoelectric resonator 10 was performed with three conditions of a working sample, a comparative example 1, and a comparative example 2, which are described below.
c. Next, the frequency versus temperature characteristic was measured again.
d. By comparing the temperature characteristic before and after the frequency adjustment, the frequency adjustment method that caused smaller-degree degradation of temperature characteristic even when the frequency adjustment was performed, namely, the preferred frequency adjustment method was identified.
First, the frequency versus temperature characteristic of the piezoelectric resonator 10 will be described. The frequency versus temperature characteristic is expressed by the following formula (1) or formula (2). However, an influence of the third-order term in the formula (2) relative to the frequency versus temperature characteristic is small, and focusing on the second-order and first-order terms is effective for evaluation. Thus, the experiment was performed by approximation with the formula (1). Consequently, the frequency versus temperature characteristic before and after the frequency adjustment in this experiment is describable with the schematic diagram illustrated in
Δf=β(t−to)(t−to)+α(t−to)+C (1)
Δf=γ(t−to)(t−to)(t−to)+β(t−to)(t−to)+α(t−to)+C (2)
Here, in the formula (1) and the formula (2), α, β, and γ are coefficients, C is a constant, t is an environmental temperature, and to is any reference temperature.
Next, the detail of the experiment will be described.
First, in the working example, the first region 11ba and the third region 11bc of the second vibrator 11b, and the first region 11ca and the third region 11cc of the third vibrator 11c, which are illustrated in
Varying the frequency of the main vibration varies the frequency of the length-longitudinal-mode vibration (an unwanted response), and thus the frequency of the length-longitudinal-mode vibration was also measured. The amounts of frequency variation of the main vibration and the unwanted response are described in the column of ΔfW and the column of ΔfL in table 1, which is described later, respectively.
In
In the comparative example 1, the whole region of the first to third vibrators 11a to 11c, which are illustrated in
Specifically, as illustrated in
In
In the comparative example 2, a part (a portion of 70% described later) of the first region 11ba and the third region 11bc in the second vibrator 11b and a part (a portion of 70% described later) of the first region 11ca and the third region 11cc in the third vibrator 11c, which are illustrated in
In
Summary and examination will be described with reference to Tables 1 to 3 and
Table 1 summarizes the coefficients α and β of the approximation formula of the frequency versus temperature characteristic, variation amounts Δα and Δβ of the coefficients, and the variation amounts ΔfW and ΔfL of the main vibration and the unwanted response, before and after the adjustment, when the frequency of the piezoelectric resonator 10 was adjusted with each experimental condition of the above-described working example, comparative example 1, and comparative example 2.
Table 2 summarizes and indicates the amounts of frequency variation caused by the differences of the temperature characteristic before and after the frequency adjustment of the piezoelectric resonator 10 for each of the working example, the comparative example 1, and the comparative example 2. Specifically, the absolute values of the differences between β (t−to) (t−to) and α (t−to) in the approximation formula (1) when the temperature change is 50° C., for the working example, the comparative example 1, and the comparative example 2, are summarized and indicated. The column of ΔF in Table 2 indicates the absolute values of the differences between β (t−to) (t−to) and α (t−to). The smaller ΔF means the smaller degradation of the temperature characteristic caused by the frequency adjustment.
Table 3 summarizes and indicates the absolute values of the differences between β (t−to) (t−to) and α (t−to) when the temperature change is 100° C., for the working example, the comparative example 1, and the comparative example 2. This is indicated for verification in addition to the case where the temperature change is 50° C.
In the comparative example 2, as illustrated in
Therefore, it is seen that the frequency adjustment method of this disclosure ensures to reduce the degradation of the frequency versus temperature characteristic caused by the frequency adjustment, and thus is a preferred frequency adjustment method. It is seen that the mass-reduction mark is more preferable to extend toward the dimension M by exceeding the dimension 0.7M, centered at the center point M/2 (see
Examining the column of Δα in Table 1 by changing an aspect indicates that while the values of Δα are positive values in the comparative example 1 and the working example, they are negative values in the comparative example 2. In the working example and the comparative example 2, the values of Δα are close to zero, compared with the comparative example 1. In particular, in the working example, the values of Δα are the positive values in addition to the values close to zero. By considering that the values of Δβ in Table 1 indicate the negative values in all conditions, the condition of the working example, where the values of Δα indicate the positive value, means that it has components cancelling Δβ, and the frequency variation in Δα itself is small. Therefore, from this point as well, it is seen that the adjustment method of the working example has an advantage compared with the comparative examples.
Furthermore, as another aspect, a ratio ΔfL/ΔfW between the amount of frequency variation MW of the main vibration and the amount of frequency variation MI of the unwanted response in Table 1 will be examined. ΔfL/ΔfW is in a range of 0.94 to 1.04 in the comparative example 1, is in a range of 0.61 to 0.74 in the working example, and is in a range of 0.08 to 0.14 in the comparative example 2. This indicates that, in the frequency adjustment method of this disclosure, a frequency adjustment region is selected such that ΔfL/ΔfW, which is the ratio of the amount of frequency variation of the unwanted response to the amount of frequency variation of the main vibration, becomes 0.6≦ΔfL/ΔfW≦0.75. Considering conversely, selecting the frequency adjustment region such that ΔfL/ΔfW becomes 0.6≦ΔfL/ΔfW≦0.75 also ensures that the reduced degradation of the frequency versus temperature characteristic caused by the frequency adjustment.
In the above description, the embodiments of the frequency adjustment method of this disclosure have been described; however, this disclosure is not limited to the above-described embodiments. For example, in the above-described examples, the examples that adjusted the first regions and the third regions of the second vibrator and the third vibrator have been described; however, as illustrated in
Furthermore, in the above-described embodiments, the first to third vibrators have the rectangular planar shape; however, this disclosure is applicable even when they have approximately rectangular planar shape with a curved corner portion, a circular planar shape, or an elliptical planar shape.
Further, in the above-described embodiments, the examples that removed the excitation-electrode portions, which correspond to the frequency adjustment regions, with the ion milling method have been described; however, contrary to this, a method that adds mass may be employed. That is, when the original frequency of the piezoelectric resonator 10 is higher than a target frequency, the frequency may be lowered by adding mass to adjust the frequency to the target frequency. A concrete example of such method includes a method that causes a metal film to be deposited on a frequency adjustment region with a vacuum evaporation method or similar method.
According to another aspect of this disclosure, a frequency adjustment method adjusts a frequency of a piezoelectric resonator that vibrates by a coupling of a width-longitudinal mode and a length-longitudinal mode. The piezoelectric resonator includes: a first vibrator; a second vibrator connecting to one of two ends positioned along a vibration direction of the width-longitudinal mode in the first vibrator; a third vibrator connecting to another of the two ends in the first vibrator; and a supporting portion connected to two ends positioned along a vibration direction of the length-longitudinal mode in the first vibrator. When the second vibrator is divided to be defined as a first region, a second region, and a third region from the first vibrator side along the vibration direction of the width-longitudinal mode, and the third vibrator is divided to be defined as a first region, a second region, and a third region from the first vibrator side along the vibration direction of the width-longitudinal mode, the frequency adjustment method is performed by any one of methods (a) to (c) described below.
(a) The frequency adjustment method is performed by reducing mass of or adding mass to the first region in each of the second vibrator and the third vibrator.
(b) The frequency adjustment method is performed by reducing mass of or adding mass to the third region in each of the second vibrator and the third vibrator.
(c) The frequency adjustment method is performed by reducing mass of or adding mass to the first region and the third region in each of the second vibrator and the third vibrator.
In these methods, the method (c) preferably enables taking more amount of the frequency adjustment.
For implementing the disclosure of the frequency adjustment method, an amount of frequency variation Δf relative to an environmental temperature change of the piezoelectric resonator is approximated with a below-described a formula (1) or a formula (2).
It is preferred that the mass reduction region or the mass addition region be selected such that an absolute value of a difference between β (t−to) (t−to) and α (t−to) in the below-described formula (1) or formula (2) becomes equal to or less than a predetermined amount.
Here, the predetermined amount is any value that is selected corresponding to a specification required to the piezoelectric resonator. Considering a practical use, it is preferred that the predetermined amount be, for example, 30 ppm, preferably 15 ppm, and more preferably 10 ppm.
Δf=β(t−to)(t−to)+α(t−to)+C (1)
Δf=γ(t−to)(t−to)(t−to)+β(t−to)(t−to)+α(t−to)+C (2)
Here, in the formula (1) and the formula (2), α, β, and γ are coefficients, C is a constant, t is an environmental temperature, and to is any reference temperature.
Further, for implementing the disclosure of the frequency adjustment method, it is preferred that the first to third regions be, typically, regions where the vibrator, to which the first to third regions belong, is divided into three equal parts along the vibration direction of the width-longitudinal mode. Three equal parts mean including characteristically equal regions, and, for example, dimensions in a range from 0.9 to 1.1, which are dimensions of three equal pacts, are also included.
For implementing the disclosure of the frequency adjustment method, when the dimension along the vibration direction of the length-longitudinal mode in the first and third regions is expressed as M (see
With the disclosure of the piezoelectric resonator according to the present application, the piezoelectric resonator includes: a first vibrator; a second vibrator connecting to one of two ends positioned along a vibration direction of the width-longitudinal mode in the first vibrator; a third vibrator connecting to another of the two ends in the first vibrator, and a supporting portion connected to two ends positioned along a vibration direction of the length-longitudinal mode in the first vibrator. The second vibrator is set to a first region, a second region, and a third region from the first vibrator side along the vibration direction of the width-longitudinal mode, and the third vibrator is set to a first region, a second region, and a third region from the first vibrator side along the vibration direction of the width-longitudinal mode. Only total four regions of the first region and the third region in each of the second vibrator and the third vibrator have mass-reduction marks where the mass of the vibrators has been reduced or mass-addition marks where the mass has been added to the regions.
More specifically, it is preferred that the first to third regions be the regions where the vibrators, to which the first to third regions belong, are divided into three equal parts along the vibration direction of the width-longitudinal mode. The meaning of the three equal parts includes the range described in the frequency adjustment method. Further, it is preferred that the mass-reduction mark or the mass-addition mark be in the regions that have a dimension from 0.7M (see
The piezoelectric resonator according to this disclosure is typically a piezoelectric resonator where, what is called, a Y-cut plate of a crystal is rotated in a range from +40 to 55 degrees around the X-axis of the crystal, and is further rotated in the range from 40 to 50 degrees inside the surface. A typical method for reducing mass includes, for example, a method of ion milling or similar method that removes an excitation electrode provided for the piezoelectric resonator.
With the frequency adjustment method of the piezoelectric resonator and the piezoelectric resonator according to the disclosure, reducing mass or adding mass of the predetermined regions ensures reducing the degree of degradation of the predetermined relationship between the width-longitudinal mode and the length-longitudinal mode of the piezoelectric resonator. Therefore, this prevents the frequency versus temperature characteristic from degrading caused by performance of the frequency adjustment of the piezoelectric resonator.
The principles, preferred embodiment and mode of operation of the present invention have been described in the foregoing specification. However, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. Variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present invention. Accordingly, it is expressly intended that all such variations, changes and equivalents which fall within the spirit and scope of the present invention as defined in the claims, be embraced thereby.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-239045 | Dec 2015 | JP | national |
