Piezoelectric diaphragm

Abstract

To provide a piezoelectric diaphragm with excellent characteristics in which spurious vibration is suppressed.SOLUTION: A piezoelectric diaphragm comprises a pair of rectangular excitation electrodes 11, 12 formed opposite to a front and a back surfaces of the piezoelectric diaphragm 1 that operates by thickness shear vibration. Centers of the front and back excitation electrodes are formed to face each other. A parallel side of one of the front and back excitation electrodes is formed along any of an X-axis direction and a Z'-axis direction of the piezoelectric diaphragm. The parallel side of the other of the front and back excitation electrodes is formed so as not to be along the X-axis direction and the Z'-axis direction of the piezoelectric diaphragm. Notch portions 114, 124 in which no excitation electrode is formed are formed at a center of a side of at least one excitation electrode. The notch portions 114, 124 are formed so as to be overlapped with the other excitation electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a piezoelectric diaphragm. [Background technology]

[0002] For example, in a piezoelectric vibration device (e.g., a piezoelectric vibrator, a piezoelectric oscillator, etc.) equipped with a piezoelectric vibration plate that operates by thickness-shear vibration, such as an AT-cut quartz crystal vibration plate, a pair of excitation electrodes are formed opposite each other on the front and back surfaces of the piezoelectric vibration plate, and an AC voltage is applied to the excitation electrodes.

[0003] In recent years, such piezoelectric vibration devices have become increasingly high-frequency (for example, frequencies of 150 MHz or higher), and as a result, there is an increased possibility that spurious signals will occur near the main vibration of the piezoelectric vibration device, which may have a negative impact on the characteristics of the piezoelectric vibration device.

[0004] To address these problems, patent applicants have previously proposed reducing spurious signals by arranging a pair of excitation electrodes of a piezoelectric diaphragm with a staggered arrangement (see, for example, Patent Document 1).

[0005] Furthermore, a piezoelectric diaphragm is known that includes a vibrating portion, an outer frame portion that surrounds the outer periphery of the vibrating portion, and a holding portion that connects the vibrating portion and the outer frame portion, and the patent applicant has also proposed a more desirable reduction in spurious responses in accordance with such a structure (see, for example, Patent Document 2).

[0006] However, the spurious reduction techniques proposed above are insufficient when it comes to stricter specifications or higher frequencies.In addition, there are concerns that conventional spurious reduction techniques alone may affect the characteristics of the main vibration. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 5104867

[0008] [Patent Document 2] WO2020 / 241790 publication Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a more reliable piezoelectric vibration plate that can accommodate higher frequencies in piezoelectric vibration devices while minimizing adverse effects on the main vibration, and can further reduce spurious emissions that accompany higher frequencies. [Means for solving the problem]

[0010] The present invention provides a means for solving the above-described problems as follows: That is, the present invention provides a piezoelectric diaphragm that operates by thickness-shear vibration, wherein a rectangular first excitation electrode is formed on one main surface of the piezoelectric diaphragm, a rectangular second excitation electrode that pairs with the first excitation electrode is formed on the other main surface of the piezoelectric diaphragm, a center of the first excitation electrode and a center of the second excitation electrode are provided at positions that approximately coincide with each other in a plan view, each side of the first excitation electrode is formed along the X-axis direction and the Z'-axis direction of the piezoelectric diaphragm, each side of the second excitation electrode is formed not along the X-axis direction and the Z'-axis direction of the piezoelectric diaphragm, a notch where no excitation electrode is formed or a thickness variation portion that is different in thickness from other regions of the excitation electrode is formed in the center of the side of at least one of the first excitation electrode and the second excitation electrode, and the notch or the thickness variation portion is formed so as to overlap with the other excitation electrode that faces across the piezoelectric diaphragm. It is characterized by:

[0011] According to the above configuration, a directly opposing region that overlaps with each other can be formed in the central portion of the first excitation electrode and the second excitation electrode that are arranged opposite each other on the front and back sides of the piezoelectric vibration plate, and a non-opposing region can be formed near the corners that surround the first excitation electrode and the second excitation electrode, and further, a notch or a thickness increasing / decreasing portion can be formed adjacent to the non-opposing region at a position close to the center of the piezoelectric vibration plate.

[0012] As a result, the configuration that combines the non-facing areas with the cutouts and thickness-increasing / decreasing portions can enhance the effect of inhibiting spurious vibrations that arise from each axial direction of the piezoelectric vibration plate and in which stronger vibration displacement occurs at positions closer to the ends of the piezoelectric vibration plate than the main vibration, thereby more efficiently suppressing spurious vibrations.

[0013] Furthermore, for the main vibration, in which strong vibration displacement occurs near the center of the piezoelectric diaphragm, the formation area of ​​the excitation electrodes in the entire plan view where the first excitation electrode and the second excitation electrode are overlapped is not reduced, so the containment effect of the main vibration generated in the directly opposing area is not reduced and the characteristics of the main vibration are not deteriorated. In particular, as the frequency increases, the vibration displacement of the main vibration is reduced in the area closer to the center of the excitation electrode, so the main vibration is less affected than the spurious vibration, resulting in a more effective configuration. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a highly reliable piezoelectric diaphragm that can accommodate higher frequencies in piezoelectric vibration devices and achieve further reduction in spurious emissions that accompany higher frequencies. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a plan view of the piezoelectric diaphragm according to the embodiment. [Figure 2] FIG. 2 is a bottom view of the piezoelectric diaphragm according to the embodiment. [Figure 3] FIG. 10 is a plan view of a piezoelectric diaphragm according to another embodiment of the present invention. [Figure 4]FIG. 10 is a plan view of a piezoelectric diaphragm according to another embodiment of the present invention. [Figure 5] 10 is a plan view of a piezoelectric diaphragm according to another embodiment of the present invention; DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a plan view of a piezoelectric diaphragm according to an embodiment of the present invention, and Fig. 2 is a bottom view of Fig. 1.

[0017] The piezoelectric vibration plate 1 is made of a rectangular flat quartz vibration plate, for example an AT cut that operates by thickness shear vibration, and has a first excitation electrode 11 that is approximately square in plan view formed in the central region of its front surface, and a second excitation electrode 12 formed in the central region of its back surface.

[0018] In this embodiment, the first excitation electrode 11 and the second excitation electrode 12 are configured to have, for example, the same shape and the same area, and are formed so that their centers 110, 120 directly face each other via the piezoelectric diaphragm 1. The piezoelectric diaphragm 1 is set so that, for example, the X-axis is the long side and the Z'-axis is the short side, and the first excitation electrode 11 has each side formed along the X-axis and the Z'-axis, while the second excitation electrode 12 has each side formed not along the X-axis and the Z'-axis, and one of the features is that the second excitation electrode 12 is rotated relative to the first excitation electrode 11 in a range of 20° to 70° in a plan view (on the main surface).

[0019] With this configuration, substantially octagonal directly facing regions (overlapping regions) 112, 122 that overlap with the other excitation electrode that faces each other on the front and back sides with the piezoelectric diaphragm 1 sandwiched therebetween are formed in one place in the central portions of the first excitation electrode 11 and the second excitation electrode 12, and substantially triangular non-facing regions (non-overlapping regions) 113, 123 that do not overlap with the other excitation electrode that faces each other on the front and back sides with the piezoelectric diaphragm 1 sandwiched therebetween are formed in a total of eight places in the corners 111, 121 that form the periphery of the first excitation electrode 11 and the second excitation electrode 12. Note that in the drawing, these are illustrated as the directly facing region 112 and the non-facing region 113 in the first excitation electrode 11, and as the directly facing region 122 and the non-facing region 123 in the second excitation electrode 12.

[0020] In addition, in this embodiment, by rotating the second excitation electrode 12 relative to the first excitation electrode 11 as described above, the excitation electrodes form a non-facing region, and in addition, a notch 114 where no electrode is partially formed is formed in one place in the center of each of the four sides of the first excitation electrode 11, and a notch 124 where no electrode is partially formed is also formed in one place in the center of each of the four sides of the second excitation electrode 12. Another feature is that by forming the notches in this manner in the center of the sides of each excitation electrode, the four notches 114 of the first excitation electrode 11 are formed overlapping the peripheral areas adjacent to the four non-facing areas 123 of the second excitation electrode 12, which is the other excitation electrode that faces it on the front and back surfaces across the piezoelectric vibration plate 1, and the four notches 124 of the second excitation electrode 12 are formed overlapping the peripheral areas adjacent to the four non-facing areas 113 of the first excitation electrode 11, which is the other excitation electrode that faces it on the front and back surfaces across the piezoelectric vibration plate 1.

[0021] In this embodiment, the notches 114 and 124 are formed in one location at the center of each of the four sides, allowing the electrode shape to be designed as simply as possible, and the spurious vibration displacement can be suppressed to the greatest extent possible by focusing on the area most susceptible to it. In addition, all four sides are rectangular and symmetrical with respect to the center of the excitation electrode, with approximately the same area. This prevents loss of symmetry and allows for uniform stress distribution within the electrode film.

[0022] This embodiment discloses a configuration rotated by 45°, which maximizes the areas of the non-facing regions 113, 123. In this configuration, the areas of the non-facing regions near the corners of the first excitation electrode 11 and the second excitation electrode 12 are maximized, thereby strengthening the influence on spurious vibrations having a vibration displacement distribution near the ends of the first excitation electrode 11 and the second excitation electrode 12, and enabling efficient suppression.

[0023] Furthermore, by specifying the rotation angle to 45°, the corners 111, 121 and the notches (or thickness change portions) 114, 124 of each excitation electrode are arranged in positions aligned on a straight line passing through the centers 110, 120 of the excitation electrodes. By arranging them in this manner, the notch in one excitation electrode becomes the narrowest part of the directly opposing region of the front and back excitation electrodes, while the corner in the other excitation electrode becomes the widest part of the non-opposing region of the front and back excitation electrodes. By arranging them in the same straight line (alternately), symmetry is not reduced, so spurious vibrations can be suppressed more efficiently and the effect of confining the main vibration is not reduced.

[0024] In this embodiment, notches 114, 124 where no electrodes are formed are formed at the center of each of the four sides of the first excitation electrode 11 and the second excitation electrode 12. These notches overlap the peripheral region of the other excitation electrode and are arranged adjacent to the non-facing region, thereby expanding a portion of the center of the non-facing region toward the center of the piezoelectric diaphragm. This allows the non-facing region to be a region that is more affected by the vibration displacement region of the spurious vibrations caused by each axial direction of the piezoelectric diaphragm 1, thereby more effectively reducing the spurious vibrations. Furthermore, the notches 114, 124 do not reduce the formation region of the excitation electrodes in the overall plan view of the overlapping first excitation electrode 11 and second excitation electrode 12, so the confinement region of the main vibration is not reduced and the characteristics of the main vibration are not deteriorated.

[0025] By combining the excitation electrode configurations of this embodiment as described above, the thickness region of the piezoelectric diaphragm 1 as viewed in cross section can be configured into at least three regions of different thickness. The first region is a thick, directly opposing region 112, 122 where the first excitation electrode 11 and the second excitation electrode 12 overlap, extending from the center of the excitation electrode to the periphery. The second region is a medium-thickness non-opposing region 113, 123 and a region where the notches 114, 124 are formed, each consisting of only the thickness of one of the excitation electrodes. The third region is a non-electrode region where the first excitation electrode 11 and the second excitation electrode 12 do not overlap. By configuring these at least three regions of different thickness, the primary vibration can be confined in a balanced and gradual manner compared to existing piezoelectric vibrators that use only the directly opposing region and the non-electrode region, thereby enhancing the confinement effect. As a result, it is even less likely to cause any adverse effects that would degrade the primary vibration characteristics.

[0026] The first excitation electrode 11 and the second excitation electrode 12 are formed with extraction electrodes (not shown) that extend to the outer peripheral edge of the piezoelectric diaphragm 1. These excitation electrodes and extraction electrodes have a laminated structure in which a main electrode such as Au or Ag is formed on an upper layer of a base electrode such as Cr or Ti, and are formed by vacuum deposition or sputtering. However, there is no limitation on the metal material or laminated structure of the electrodes.

[0027] The above-mentioned piezoelectric vibration plate 1 is electrically and mechanically connected to a first sealing member which serves as a base substrate (not shown), and the piezoelectric vibrator is completed by hermetically sealing it with a second sealing member which serves as a lid (not shown).

[0028] By configuring the piezoelectric vibrator as described above, the two parallel sides of the first excitation electrode 11, among the excitation electrodes on the front and back, are formed along both the X-axis direction and the Z'-axis direction of the piezoelectric vibration plate 1, and a directly opposing area is secured near the center 111 of the first excitation electrode 11 and the center 121 of the second excitation electrode 12, so that the oscillation of the main vibration, which has the strongest vibration displacement distribution near the center of the excitation electrode, is not hindered.

[0029] In particular, when the main vibration of the fundamental wave of the piezoelectric vibrator is a high frequency, for example, 150 MHz or more, spurious vibrations having a vibration displacement distribution near the ends of the excitation electrodes 11 and 12, such as the (1,2,1) mode or (1,1,2) mode, which are second-order modes of the thickness system, or the (1,3,1) mode or (1,1,3) mode, which are third-order modes of the thickness system, tend to appear near the main vibration, adversely affecting the vibration characteristics of the main vibration.

[0030] However, these spurious vibrations are suppressed by the combination of the non-facing regions 112, 122 and the cutouts 114, 124 near the corners of the first excitation electrode 11 and the second excitation electrode 12 on the front and back, which affect the vibration displacement of each spurious and act to inhibit the vibration. Note that it is preferable that the centers of the front and back excitation electrodes 11, 12 are formed at the same position so as to completely face each other, but the same effect can be expected even if there is some misalignment due to manufacturing errors, etc.

[0031] Furthermore, since the first excitation electrode 11 and the second excitation electrode 12 on the front and back are formed to have the same shape, it is possible to reduce the vibration area of ​​each spurious vibration near the end of the excitation electrode while ensuring the vibration area near the center of the excitation electrode without increasing the area of ​​the first excitation electrode 11 and the second excitation electrode 12 formed on the piezoelectric diaphragm 1. In other words, it is possible to reduce the size of the piezoelectric diaphragm and suppress spurious vibrations without interfering with the oscillation of the main vibration.

[0032] In the above embodiment, square excitation electrodes 11 and 12 are disclosed, but rectangular electrodes may also be used. Also, as shown in Fig. 3, instead of the notches, thickness increasing / decreasing portions 115 and 125 that increase or decrease a part of the thickness of the excitation electrodes can be formed, which can have an effect on spurious vibrations and can be expected to have a similar effect.

[0033] The piezoelectric diaphragm of the present invention is not limited to the flat plate-like one shown in the above embodiment, but may be an inverted mesa-shaped one having a thin vibration region 101a in the center of piezoelectric diaphragm 1a and a thick frame region 102a around it, as shown in Fig. 4, or a piezoelectric diaphragm 1b having a vibration portion 101b in the center, penetrating portions 102b around this, and an outer frame portion 103b on the periphery, with holding portions 104b connecting vibration portion 101b and outer frame portion 103b, as shown in Fig. 5. Note that, since the excitation electrodes and other components other than the piezoelectric diaphragm in each of the other embodiments are the same as those in the above embodiment, some of them are numbered the same and their description will be omitted.

[0034] The present invention can be embodied in various other forms without departing from its spirit or essential features. Therefore, the above-described embodiments are merely illustrative in all respects and should not be interpreted as limiting. The scope of the present invention is defined by the claims and is not limited to the text of the specification. Furthermore, all modifications and variations within the scope of the claims are within the scope of the present invention. [Industrial Applicability]

[0035] The present invention can be applied to a piezoelectric diaphragm of a piezoelectric vibration device. [Explanation of symbols]

[0036] 1, 1a, 1b Piezoelectric diaphragm 11 1st excitation electrode 12 Second excitation electrode

Claims

[Claim 1] A piezoelectric diaphragm that operates by thickness shear vibration, a rectangular first excitation electrode is formed on one main surface of the piezoelectric diaphragm, and a rectangular second excitation electrode that pairs with the first excitation electrode is formed on the other main surface of the piezoelectric diaphragm; a center of the first excitation electrode and a center of the second excitation electrode are provided at positions that substantially coincide with each other in a plan view, each side of the first excitation electrode is formed along an X-axis direction and a Z'-axis direction of a piezoelectric diaphragm, and each side of the second excitation electrode is formed not along the X-axis direction and the Z'-axis direction of the piezoelectric diaphragm, a notch where no excitation electrode is formed, or a thickness increasing / decreasing portion having a thickness different from that of other regions of the excitation electrode, is formed in the center of a side of at least one of the first excitation electrode and the second excitation electrode, and the notch or the thickness increasing / decreasing portion is formed so as to overlap with the other excitation electrode that faces the piezoelectric diaphragm therebetween; A piezoelectric diaphragm characterized by:

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