JP6442130B2 - AT cut crystal resonator element - Google Patents

Description

  The present invention relates to an AT-cut crystal resonator element including a crystal piece made of an AT-cut crystal plate and an excitation electrode provided on the crystal piece.

  An AT-cut quartz plate having excellent frequency-temperature characteristics near room temperature is most widely used as a quartz-crystal vibrating element having thickness-shear vibration as a main vibration. The AT-cut quartz plate is cut out so that a plane obtained by rotating a plane including the X-axis and the Z-axis of the quartz crystal about 35 ° counterclockwise around the X-axis becomes the main surface. A thickness-shear vibration mode crystal piece made of an AT-cut crystal plate is generally rectangular.

JP 2014-27592 A

  In the conventional AT-cut crystal resonator element, a rectangular crystal piece is used as described above. In this case, there is a problem that a frequency change called an activity dip is caused by combining the vibration mode of the other sub-vibration with the thickness shear vibration mode of the main vibration.

  Accordingly, an object of the present invention is to provide an AT-cut quartz crystal resonator element that can suppress activity dip.

The AT cut quartz crystal resonator element according to the present invention is
A crystal piece made of an AT-cut crystal plate having a width in a direction perpendicular to the length direction of one direction of the crystal crystal, and
Excitation electrodes provided on the front and back main surfaces of the crystal piece;
A lead electrode and a pad electrode provided on the crystal piece and connected to the excitation electrode;
In an AT-cut crystal resonator element mounted on a package via the pad electrode ,
The width is the widest at least one of both ends in the longitudinal direction, Ri narrowly closer to the center of the length direction,
The pad electrode is formed on the side having the largest width,
It is characterized by that.

  According to the present invention, at least one width at both ends in the length direction is made wider than the width at the center in the length direction, so that the vibration energy in the contour vibration mode is driven to at least one of the both ends in the length direction. Therefore, it is possible to suppress an activity dip that occurs when the thickness vibration mode of the main vibration is combined with the contour vibration mode of the secondary vibration.

1 shows an AT-cut quartz crystal resonator element according to Embodiment 1, in which FIG. 1 [1] is a plan view, FIG. 1 [2] is a cross-sectional view taken along line AA in FIG. 1 [1], and FIG. ] Is a sectional view taken along line BB in FIG. FIG. 2 [1] is a plan view, FIG. 2 [2] is a cross-sectional view taken along line AA in FIG. 2 [1], and FIG. 2 [3] is FIG. 2 [1]. ] Is a sectional view taken along line BB in FIG. 3 is a graph showing the relationship between the width of a crystal piece and the oscillation frequency in the AT-cut crystal resonator element of Embodiment 1. 6 is a graph showing the relationship between the width of a crystal piece and the oscillation frequency in an AT-cut crystal resonator element of Comparative Example 1. FIG. 5 is a plan view illustrating an AT-cut quartz crystal resonator element according to Embodiment 2, in which FIG. 5 [1] is a first example, FIG. 5 [2] is a second example, and FIG. 5 [3] is a third example. FIG. 6 [1] is a plan view, FIG. 6 [2] is a cross-sectional view taken along line AA in FIG. 6 [1], and FIG. 6 [3] is FIG. 6 [1]. It is a BB sectional view.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are used for substantially the same components. The shapes depicted in the drawings are drawn so as to be easily understood by those skilled in the art, and thus do not necessarily match the actual dimensions and ratios.

  Prior to describing an embodiment of the present invention, Related Art 1 (see Patent Document 1) will be described. FIG. 6 shows a contour vibration element of related art 1, FIG. 6 [1] is a plan view, FIG. 6 [2] is a cross-sectional view taken along line AA in FIG. 6 [1], and FIG. 1] is a sectional view taken along line BB in FIG.

  The contour vibration element 30 of the related technique 1 includes a crystal piece 31 made of an elliptical crystal plate having a length L3 and widths W31 and W32, excitation electrodes 32a and 32b provided on the front and back main surfaces of the crystal piece 31, It has. The width W32 at both ends in the length L3 direction is narrower than the center width W31 in the length L3 direction.

  The contour vibration element 30 has a structure in which the crystal piece 31 is sandwiched from both sides in the thickness direction by the excitation electrodes 32a and 32b. When the horizontal AA direction is the longitudinal direction and the vertical BB direction is the short direction, the width in the short direction of the center portion in the AA direction is widened (that is, both ends in the length L3 direction). As it goes to, the width in the short direction is narrowed.

  Here, the BB direction width W31 at the center in the horizontal AA direction can be regarded as half the resonance wavelength λ. This is because the mode in which the vibration frequency of the contour vibration strongly depends on the BB direction width W31 is used. In this related technique 1, since the width in the short direction is narrowed from the center to the end, the vibration frequency can be increased (that is, the vibration wavelength is decreased) from the center to the end. Energy is confined in the part.

  This eliminates unnecessary contour vibration displacement at the end of the crystal piece 31, thereby suppressing vibration inhibition by a support portion (not shown) provided at the end, and as a result, CI (Crystal Impedance). The value can be reduced.

  Next, the AT-cut quartz crystal resonator element (hereinafter simply referred to as “vibrator element”) according to the first embodiment will be described. FIG. 1 shows a resonator element according to the first embodiment, FIG. 1 [1] is a plan view, FIG. 1 [2] is a cross-sectional view taken along line AA in FIG. 1 [1], and FIG. 1] is a sectional view taken along line BB in FIG.

  The resonator element 10 according to the first embodiment includes a crystal piece 11 formed of an AT-cut crystal plate having a direction perpendicular to the length L1 direction as a length L1 direction and a width orthogonal to the length L1 direction, and the front and back main faces of the crystal piece 11. And excitation electrodes 12a and 12b provided on the surface. And the above-mentioned width is the widest at least one of the both ends of the length L1 direction, and becomes narrow as it approaches the center of the length L1 direction. That is, at least one width W12 at both ends in the length L1 direction is wider than the center width W11 in the length L1 direction.

  In the first embodiment, both the widths W12 at both ends in the length L1 direction are wider than the center width W11 in the length L1 direction. The shape of the crystal piece 11 is line symmetric about the AA line and line symmetric about the BB line. The width of the crystal piece 11 is the narrowest at the center width W11 in the length L1 direction, gradually increases toward both ends in the length L1 direction, and becomes the widest width W12 at both ends. The two sides (the upper side 11a and the lower side 11b) that determine the widths W11 and W12 are curved (for example, an arc, an elliptical arc, a hyperbola, a quadratic function, etc.). In the first embodiment, the length L1 direction is the X-axis direction, the width W11 direction is the Y′-axis direction, and the thickness t direction is the Z′-axis direction.

  Next, a method for manufacturing the vibration element 10 will be described. First, an AT-cut quartz wafer is prepared. Then, a pattern made of a corrosion-resistant film and a photoresist is formed, and a large number of crystal pieces 11 are formed on a crystal wafer through wet etching using hydrofluoric acid. Subsequently, a metal film is formed on the quartz wafer by sputtering or vapor deposition, a pattern made of a photoresist is formed, and etching electrodes 12a and 12b are formed on each quartz piece 11 through etching. The crystal piece 11 is also formed with an extraction electrode and a pad electrode (both not shown) connected to the excitation electrodes 12a and 12b, and the vibration element 10 is mounted on the package via the pad electrode.

  Next, the operation and effect of the vibration element 10 will be described based on FIGS. 1 and 2 in addition to Comparative Example 1 shown in FIG.

  2 shows a resonator element of Comparative Example 1, FIG. 2 [1] is a plan view, FIG. 2 [2] is a cross-sectional view taken along line AA in FIG. 2 [1], and FIG. 2 [3] is FIG. 1] is a sectional view taken along line BB in FIG.

  The resonator element 20 of the comparative example 1 includes a crystal piece 21 made of a rectangular crystal plate having a length L2 and a width W2, and excitation electrodes 22a and 22b provided on the front and back main surfaces of the crystal piece 21. Yes. And since it is rectangular shape, the width | variety of the both ends of the length L2 direction is also equal to the center width W2 of the length L2 direction.

  The vibration element 20 has a structure that reduces the CI value by confining the energy of thickness-shear vibration below the excitation electrodes 22a and 22b by disposing the excitation electrodes 22a and 22b substantially at the center of the rectangular crystal piece 21. It has become. At this time, the thickness shear vibration in the crystal piece 21 vibrates in parallel with the X axis of the crystal crystal, has a maximum displacement at the approximate center of the excitation electrodes 22a and 22b, and gradually attenuates outward. .

  At this time, if the vibration mode of the secondary vibration is combined with the thickness-shear vibration mode of the main vibration, the above-mentioned activity dip occurs, and the CI value increases due to the exchange of energy between the modes.

  The present inventor has conducted experiments and considerations on an activity dip unique to the vibration element 20 using the rectangular crystal piece 21, and as a result, if the secondary vibration causing the activity dip is the contour vibration mode, I came up with the idea that the vibration energy in the contour vibration mode may be confined to the end of the crystal piece by using the structure opposite to that of 1. The present invention has been made based on this finding.

  That is, in the first embodiment, contrary to the related art 1, by increasing the width from the center in the length L1 direction to both ends, the vibration frequency of the contour vibration is decreased from the center to both ends (that is, vibration) Therefore, the energy of the contour vibration is confined at both ends. Therefore, the thickness shear vibration mode increases at the center of the crystal piece 11 while the contour vibration mode decreases, and conversely, the thickness shear vibration mode decreases at both ends of the crystal piece 11 while the contour vibration mode increases. In Comparative Example 1, the thickness-shear vibration mode increases at the center of the crystal piece 21 and the thickness-slip vibration mode decreases at both ends of the crystal piece 21, but the contour vibration mode is about the same at both the center and both ends of the crystal piece 21. It is. Therefore, in the first embodiment, compared with the comparative example 1, the coupling between the thickness-shear vibration mode of the main vibration and the contour vibration mode of the sub vibration can be reduced.

  Therefore, according to the first embodiment, at least one width W12 at both ends in the length L1 direction is made wider than the central width W11 in the length L1 direction, so that the vibration energy in the contour vibration mode is reduced to the length L1. Since it can be driven to at least one of both ends of the direction, it is possible to suppress the activity dip that occurs when the thickness vibration mode of the main vibration is combined with the contour vibration mode of the sub vibration. In addition, since the exchange of energy between the modes due to the coupling of the contour vibration mode of the secondary vibration to the thickness shear vibration mode of the main vibration is reduced, the CI value can be reduced.

  Further, according to the second embodiment, the width W12 at both ends in the length L1 direction is made wider than the width W11 at the center in the length L1 direction, so that the vibration energy in the contour vibration mode is increased at both ends in the length L1 direction. Therefore, it is possible to further suppress the activity dip that occurs when the thickness vibration mode of the main vibration is combined with the contour vibration mode of the secondary vibration.

  Next, the effect of the vibration element 10 will be described more specifically with reference to FIGS. 3 and 4. FIG. 3 is a graph showing the relationship between the width W11 of the crystal piece 11 and the oscillation frequency f1 in the resonator element 10 according to the first embodiment. FIG. 4 is a graph showing the relationship between the width W2 of the crystal piece 21 and the oscillation frequency f2 in the resonator element 20 of Comparative Example 1.

  FIG. 3 shows the variation of the oscillation frequency f1 obtained by simulation using FEM (Finite Element Method) when the length L1 of the crystal piece 11 shown in FIG. 1 is constant at 0.8 mm and the width W11 is changed. It is. Similarly, FIG. 4 shows the change in the oscillation frequency f2 when the length L2 of the crystal piece 21 shown in FIG. 2 is constant at 0.8 mm and the width W2 is changed, by a simulation using FEM. . The horizontal axes of FIGS. 3 and 4 are normalized so that the widths W11 and W2 are each 0.6 mm. The crystal pieces 11 and 21 have the Euler angles (0 °, 125 °, 0 °), and the AT cut plates having the Euler angles (0 °, 35 °, 0 °) are opposite to each other. Except equivalent. The simulation models of the vibration elements 10 and 20 are designed so that the oscillation frequencies f1 and f2 are 35 MHz and in the vicinity thereof.

  In Comparative Example 1 of FIG. 4, the oscillation frequency f2 changes discontinuously when the width W2 is around 0.91 and around 1.01. On the other hand, in the first embodiment of FIG. 3, the oscillation frequency f2 changes substantially continuously in the range of the width W11 from 0.85 to 1.15. As is apparent from this result, the activity dip is improved in the first embodiment. Therefore, according to the first embodiment, it is possible to improve the design freedom of the vibration element and to secure a margin for process variation.

  Next, the resonator element according to the second embodiment will be described. FIG. 5 is a plan view showing the resonator element according to the second embodiment. FIG. 5 [1] is a first example, FIG. 5 [2] is a second example, and FIG. 5 [3] is a third example.

  The vibration element according to the second embodiment has the same configuration as that of the vibration element according to the first embodiment except that the shape of the crystal piece is different. The operations and effects of the second embodiment are the same as those of the first embodiment.

  In the crystal piece 41 of the first example shown in FIG. 5 [1], the width W12 at both ends in the length L1 direction is both wider than the center width W11 in the length L1 direction, as in the first embodiment. ing. However, unlike the first embodiment, the two sides (upper side 41a and lower side 41b) that determine the widths W11 and W12 are linear (polygonal). Also in the crystal piece 41 of the first example, the energy of the contour vibration is confined on the width W12 side of both ends, similarly to the crystal piece of the first embodiment.

  In the crystal piece 51 of the second example shown in FIG. 5 [2], unlike the first embodiment, one width W15 at both ends in the length L1 direction is wider than the center width W14 in the length L1 direction, and the length L1. The other width W13 at both ends in the direction is narrower than the central width W14 in the length L1 direction. Two sides (upper side 51a and lower side 51b) that determine the widths W13, W14, and W15 are curved. The energy of contour vibration is confined on the longer width W15 side of both ends. The position where the pad electrode is formed is preferably on the width W15 side in order to release the energy of contour vibration to the package side.

  In the crystal piece 61 of the third example shown in FIG. 5 [3], as in the second example, one width W15 at both ends in the length L1 direction is wider than the center width W14 in the length L1 direction. The other width W13 at both ends in the length L1 direction is narrower than the center width W14 in the length L1 direction. However, unlike the second example, the two sides (the upper side 61a and the lower side 61b) that determine the widths W13, W14, and W15 are linear. As in the second example, the energy of the contour vibration is confined on the longer width W15 side of both ends, and the position where the pad electrode is formed is desirably on the width W15 side.

  Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention. Further, the present invention includes a combination of some or all of the configurations of the above-described embodiments as appropriate.

  For example, the structure of a single crystal of quartz is two-fold symmetric with respect to the Z axis that is the optical axis, and three times symmetric with respect to the X axis that is the electric axis. Therefore, it goes without saying that a plane which is symmetric or equivalent to the plane of the quartz used in the present invention has the same characteristics as the present invention.

  In addition, when the thickness-shear vibration mode crystal piece (that is, the AT-cut crystal plate) is formed so that its thickness is gradually reduced from the center portion toward the end portion, the attenuation amount of the vibration displacement at the end portion increases. Vibration energy is confined in the center, and frequency characteristics such as CI value and Q value are improved. As such a vibration energy confinement structure, there are a bevel shape having a slope between a flat thick central portion and an edge, a mesa type having a thin peripheral portion of the flat thick central portion, and the like. Such a bevel-shaped or mesa-type crystal piece may be used as the crystal piece in the present invention.

<Embodiment 1>
DESCRIPTION OF SYMBOLS 10 Vibration element 11 Crystal piece 12a, 12b Excitation electrode L1 Length W11, W12 Width t Thickness 11a Upper side 11b Lower side <Comparative example 1>
20 Vibrating element 21 Quartz piece 22a, 22b Excitation electrode L2 Length W2 Width <Embodiment 2>
41, 51, 61 Quartz piece W13, W14, W15 Width 41a, 51a, 61a Upper side 41b, 51b, 61b Lower side <Related art 1>
30 Contour vibration element 31 Crystal piece 32a, 32b Excitation electrode L3 Length W31, W32 Width

Claims (3)

A crystal piece made of an AT-cut crystal plate having a width in a direction perpendicular to the length direction of one direction of the crystal crystal, and
Excitation electrodes provided on the front and back main surfaces of the crystal piece;
A lead electrode and a pad electrode provided on the crystal piece and connected to the excitation electrode;
In an AT-cut crystal resonator element mounted on a package via the pad electrode ,
The width is the widest at least one of both ends in the longitudinal direction, Ri narrowly closer to the center of the length direction,
The pad electrode is formed on the side having the largest width,
An AT-cut quartz crystal vibrating element characterized by the above. The widths at both ends in the length direction are both wider than the width at the center in the length direction,
The AT-cut crystal resonator element according to claim 1. The width at one of the ends in the length direction is wider than the width at the center in the length direction,
The other width at both ends of the length direction is narrower than the width at the center in the length direction,
The AT-cut crystal resonator element according to claim 1.

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