JP6008151B2 - Piezoelectric vibrating piece and piezoelectric vibrator - Google Patents

Description

  The present invention relates to a piezoelectric vibrating piece and a piezoelectric vibrator.

  The AT-cut piezoelectric vibrating piece uses a thickness shear vibration mode having excellent temperature characteristics as a main resonance. Such an AT-cut vibrating piece is processed by machining or photolithography.

  Patent Document 1 discloses a piezoelectric vibrator that performs a so-called mesa-type thickness shear vibration that exhibits an energy confinement effect equivalent to that of a bevel structure or a convex structure.

  In recent years, there has been an increasing tendency to reduce the size of the resonator element, and the need for a vibrator having a small side ratio is increasing. In general, a vibrator having a small side ratio is easily affected by a mode (contour vibration) caused by the contour of the vibrator, and suppresses the thickness-shear mode by coupling with the vibration.

  In Patent Document 2, in the mesa-type AT-cut quartz crystal resonator, the boundary side wall is extended from the excitation electrode at the boundary between the mesa portion and the peripheral thin wall portion at 90 ° with respect to the main surface. It has been made in view of the problem that the extraction electrode (lead electrode) is disconnected, and it is disclosed that the disconnection of the lead electrode can be prevented by making the side wall of the boundary portion inclined or curved. Yes.

  In Patent Document 3, in a mesa-type AT-cut quartz crystal resonator, the side wall portion at the boundary between the mesa portion and the peripheral thin-wall portion is tilted to 63 ° and 35 ° instead of vertical (90 °). Further, it is disclosed that the coupling between the thickness shear vibration, which is the main vibration, and the bending vibration can be suppressed.

  Patent Document 4 discloses that the bending mode vibration, which is a contour vibration, can be suppressed by coupling the thickness-shear mode and the bending mode by setting the mesa dimension and the mesa electrodes at appropriate intervals.

  Patent Document 5 discloses that in a mesa-type AT-cut quartz crystal resonator, an unnecessary mode can be suppressed by setting an appropriate amount of moat at a stepped portion.

  Patent Document 6 discloses that in a mesa-type AT-cut crystal resonator, an unnecessary mode can be suppressed by setting the short side dimension of the piezoelectric substrate and the short side dimension of the vibration part to appropriate values. Yes.

  Patent Document 7 discloses that the energy of the main vibration can be confined more efficiently by providing a multi-stage mesa portion.

  Patent Document 8 discloses a vibrator whose cross-sectional shape is a staircase shape. Such a staircase shape is obtained by performing chemical processing such as etching or sandblasting by changing the resist dimensions for protecting the vibrator portion in stages. It is disclosed that it can be manufactured using mechanical processing such as.

In Patent Document 9, by forming the step between the thick central portion and the thin peripheral portion into a plurality of steps, it becomes easy to form a resist pattern shape and a sufficient thickness of the electrode material, Furthermore, it is disclosed that the energy confinement effect can be enhanced because the central portion of the thick film approaches a convex shape.

  Patent Document 10 discloses that, in a resonator element having a multi-stage mesa structure, the step portion is used as a flow stopper for the conductive adhesive to prevent the adhesive from flowing into the mesa portion.

  Patent Document 11 discloses that an outer shape having a multistage mesa structure is precisely formed by etching a quartz crystal substrate by photolithography.

  Patent Document 12 discloses a method for manufacturing a multi-stage mesa-type AT-cut crystal resonator in which a mesa is formed using a laser.

  As described above, Patent Documents 7 to 12 propose a multi-stage mesa structure in which the number of mesa stages is increased as a structure that suppresses coupling with a bending mode by a strong energy confinement effect.

JP 58-47316 A Japanese Utility Model Publication No. 06-52230 JP 2001-230655 A Japanese Patent No. 4334183 JP 2008-263387 A JP 2010-62723 A Japanese Patent Laid-Open No. 02-57009 Japanese Patent No. 3731348 JP 2008-236439 A JP 2009-130543 A JP 2010-109527 A Japanese Patent No. 4075893

  However, in the thickness-shear piezoelectric vibrating piece having a multistage mesa structure in which the extending direction of the long side is parallel to the X-axis, particularly in the piezoelectric vibrating piece having a small X-side ratio, the thickness-shear vibration and the unnecessary mode such as the contour vibration are not affected. It became clear that CI (Crystal Impedance) value would increase.

  One of the objects according to some aspects of the present invention is to provide a piezoelectric vibrating piece having a multistage mesa structure and capable of reducing the CI value. Another object of some aspects of the present invention is to provide a piezoelectric vibrator including the piezoelectric vibrating piece.

The piezoelectric vibrating piece according to the present invention is
Centering on the X axis of an orthogonal coordinate system consisting of an X axis as an electric axis, a Y axis as a mechanical axis, and a Z axis as an optical axis, which are crystal axes of quartz, the Z axis is the Y axis. The axis tilted in the −Y direction is the Z ′ axis, the Y axis is tilted in the + Z direction of the Z axis as the Y ′ axis, and is configured by planes parallel to the X axis and the Z ′ axis. A piezoelectric substrate having a thickness in the direction parallel to the Y ′ axis, and a thickness direction in the direction parallel to the Y ′ axis;
An excitation electrode disposed so as to face the vibration regions of both main surfaces of the piezoelectric substrate on the front and back sides;
Including
The piezoelectric substrate is
A rectangular excitation section having a side parallel to the X axis as a long side and a side parallel to the Z ′ axis as a short side;
A peripheral portion having a thickness smaller than the excitation portion, and formed around the excitation portion;
Have
Each of side surfaces extending in a direction parallel to the X axis of the excitation unit is in one plane,
Each of the side surfaces extending in the direction parallel to the Z ′ axis of the excitation unit has a step.

  According to such a piezoelectric vibrating piece, the coupling between the thickness shear vibration and the unnecessary mode such as the contour vibration in the direction parallel to the Z ′ axis can be suppressed, and the CI value can be reduced (details will be described later).

In the piezoelectric vibrating piece according to the present invention,
When the dimension in the direction parallel to the Z ′ axis of the piezoelectric substrate is Z, the dimension of the short side of the excitation part is Mz, and the thickness of the excitation part is t,
The relationship of 8 ≦ Z / t ≦ 11 and 0.6 ≦ Mz / Z ≦ 0.8 may be satisfied.

  According to such a piezoelectric vibrating piece, the CI value can be further reduced.

In the piezoelectric vibrating piece according to the present invention,
If the dimension of the piezoelectric substrate in the direction parallel to the X axis is X,
The relationship of X / t ≦ 17 may be satisfied.

  According to such a piezoelectric vibrating piece, it is possible to reduce the CI value while reducing the size.

In the piezoelectric vibrating piece according to the present invention,
The excitation unit is
A first portion and a second portion having a thickness smaller than the first portion;
The step on the side surface extending in the Z′-axis direction may be formed by a difference in thickness between the first portion and the second portion.

  According to such a piezoelectric vibrating piece, the CI value can be reduced.

In the piezoelectric vibrating piece according to the present invention,
The excitation unit further includes a third portion having a smaller thickness than the second portion,
The step on the side surface extending in the Z′-axis direction may be formed by a difference in thickness between the first portion, the second portion, and the third portion.

  Such a piezoelectric vibrating piece can have a stronger energy confinement effect.

The piezoelectric vibrator according to the present invention is
A piezoelectric vibrating piece according to the present invention;
A package containing the piezoelectric vibrating piece;
including.

According to such a piezoelectric vibrator, since it has the piezoelectric vibrating piece according to the present invention, it is possible to reduce the CI value.

FIG. 3 is a plan view schematically showing the piezoelectric vibrating piece according to the embodiment. FIG. 3 is a cross-sectional view schematically showing the piezoelectric vibrating piece according to the embodiment. FIG. 3 is a cross-sectional view schematically showing the piezoelectric vibrating piece according to the embodiment. The perspective view which shows an AT cut quartz substrate typically. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view and sectional drawing which show typically the manufacturing method of the piezoelectric vibrating piece which concerns on this embodiment. The top view which shows typically the piezoelectric vibrating piece which concerns on the modification of this embodiment. Sectional drawing which shows typically the piezoelectric vibrating piece which concerns on the modification of this embodiment. Sectional drawing which shows typically the piezoelectric vibrating piece which concerns on the modification of this embodiment. FIG. 3 is a cross-sectional view schematically showing the piezoelectric vibrator according to the embodiment. The top view and sectional drawing which show typically the piezoelectric vibrating piece of a comparative example. The graph which shows distribution of CI value. The graph which shows the relationship between Mz (dimension of the short side of an excitation part) / Z (dimension of the short side of a piezoelectric substrate), and CI value.

  Several embodiments of the present invention will be described below. The embodiments described below illustrate examples of the present invention. The present invention is not limited to the following embodiments at all, and includes various modifications that are carried out within the scope not changing the gist of the present invention. Note that not all of the configurations described in the following embodiments are indispensable constituent requirements of the present invention.

1. First, a piezoelectric vibrating piece according to this embodiment will be described with reference to the drawings. FIG. 1 is a plan view schematically showing a piezoelectric vibrating piece 100 according to this embodiment. 2 and 3 are cross-sectional views schematically showing the piezoelectric vibrating piece 100 according to the present embodiment. 2 is a cross-sectional view taken along the line II-II in FIG. 1, and FIG. 3 is a cross-sectional view taken along the line III-III in FIG.

  As shown in FIGS. 1 to 3, the piezoelectric vibrating piece 100 includes a piezoelectric substrate 10 and an excitation electrode 20.

  The piezoelectric substrate 10 is made of an AT cut quartz substrate. FIG. 4 is a perspective view schematically showing the AT cut crystal substrate 101.

Piezoelectric materials such as quartz are generally trigonal and have crystal axes (X, Y, Z) as shown in FIG. The X axis is an electrical axis, the Y axis is a mechanical axis, and the Z axis is an optical axis. The AT-cut quartz substrate 101 is a flat plate cut from a piezoelectric material (for example, artificial quartz) along a plane obtained by rotating the XZ plane around the X axis by an angle θ. Here, θ = 35 ° 15 ′. Note that the Y axis and the Z axis are also rotated by θ around the X axis to be the Y ′ axis and the Z ′ axis, respectively. Therefore, the AT-cut quartz substrate 101 has crystal axes (X, Y ′, Z ′). The AT-cut quartz crystal substrate 101 can vibrate with thickness shear vibration as the main vibration, with the XZ ′ plane orthogonal to the Y′-axis (the plane including the X-axis and Z′-axis) serving as the main surface (excitation surface). The AT-cut quartz substrate 101 can be processed to obtain the piezoelectric substrate 10.

  That is, as shown in FIG. 4, the piezoelectric substrate 10 has an orthogonal coordinate system composed of a crystal axis of quartz, an X axis as an electric axis, a Y axis as a mechanical axis, and a Z axis as an optical axis. The axis tilted in the -Y direction of the Y axis around the X axis is the Z 'axis, the axis tilted in the + Z direction of the Z axis is the Y' axis, and the X axis and the Z 'axis It is composed of an AT-cut quartz substrate that is composed of parallel surfaces and has a thickness in a direction parallel to the Y ′ axis.

  As shown in FIG. 1, the piezoelectric substrate 10 has a direction parallel to the Y-axis (hereinafter also referred to as “Y′-axis direction”) as a thickness direction, and is also referred to as a direction parallel to the X-axis (hereinafter referred to as “X-axis direction”). ) As a long side and a rectangular shape having a short side as a direction parallel to the Z ′ axis (hereinafter also referred to as “Z ′ axis direction”). The piezoelectric substrate 10 has a peripheral part 12 and an excitation part 14.

  As shown in FIG. 1, the peripheral portion 12 is formed around the excitation portion 14. The peripheral portion 12 has a smaller thickness than the excitation portion 14.

  As shown in FIG. 1, the excitation unit 14 is surrounded by the peripheral portion 12 and has a thickness larger than the thickness of the peripheral portion 12 in the Y′-axis direction. That is, the excitation part 14 protrudes in the Y′-axis direction with respect to the peripheral part 12 as shown in FIGS. 2 and 3. In the illustrated example, the excitation unit 14 protrudes toward the + Y ′ side and the −Y ′ side with respect to the peripheral portion 12. The excitation unit 14 (piezoelectric substrate 10) may have, for example, a point (not shown) that is a center of symmetry and a shape that is point-symmetric with respect to the point.

  As shown in FIG. 1, the excitation unit 14 has a rectangular shape having a long side in the X-axis direction and a short side in the Z′-axis direction. That is, the excitation unit 14 has a side parallel to the X axis as a long side and a side parallel to the Z ′ axis as a short side. Therefore, the excitation unit 14 has side surfaces 14a and 14b extending in the X-axis direction and side surfaces 14c and 14d extending in the Z′-axis direction. That is, the longitudinal direction of the side surfaces 14a and 14b extending in the X-axis direction is the X-axis direction, and the longitudinal direction of the side surfaces 14c and 14d extending in the Z′-axis direction is the Z′-axis direction. In the illustrated example, of the side surfaces 14a and 14b, the side surface 14a is the side surface on the + Z ′ side, and the side surface 14b is the side surface on the −Z ′ side. Of the side surfaces 14c and 14d, the side surface 14c is a side surface on the -X side, and the side surface 14d is a side surface on the + X side.

  For example, as shown in FIG. 2, the side surface 14 a extending in the X-axis direction is formed on the + Y ′ side and the −Y ′ side with respect to the peripheral portion 12. The same applies to the side surfaces 14b, 14c, and 14d. Each of the side surfaces 14a and 14b extending in the X-axis direction is in one plane as shown in FIG. That is, the side surface 14a on the + Y ′ side is in one plane, and the side surface 14a on the −Y ′ side is in one plane. Similarly, the side surface 14b on the + Y ′ side is in one plane, and the side surface 14b on the −Y ′ side is in one plane.

In the description according to the present invention, “in one plane” includes the case where the side surface of the excitation unit 14 is a flat surface and the case where the crystal part has irregularities corresponding to the crystal anisotropy of quartz. That is, when an AT-cut quartz substrate is processed using a solution containing hydrofluoric acid as an etchant, the side surface of the excitation unit 14 is exposed to the R plane of the quartz crystal and becomes a plane parallel to the XY ′ plane. In some cases, the m-plane is exposed and has irregularities corresponding to the crystal anisotropy of quartz. In the description according to the present invention, the side surface of the quartz crystal having the irregularities due to the m-plane is also “in one plane”. For convenience, in FIG. 1 and FIG. 2, illustration of unevenness by the m-plane is omitted. It is also possible to expose only the R plane of the quartz crystal by processing the AT-cut quartz substrate with a laser.

  Each of the side surfaces 14c and 14d extending in the Z′-axis direction has a step as shown in FIG. The excitation unit 14 includes a first portion 15 and a second portion 16 having a thickness smaller than that of the first portion 15, and the step between the side surfaces 14 c and 14 d is equal to the thickness of the first portion 15 and the second portion 16. Formed by the difference. In the illustrated example, the side surfaces 14 c and 14 d are surfaces parallel to the Y′Z ′ plane of the first portion 15, surfaces parallel to the XZ ′ plane of the second portion 16, and Y′Z ′ of the second portion 16. And a plane parallel to the plane.

  As shown in FIGS. 1 and 3, for example, the second portion 16 is formed so as to sandwich the first portion 15 from the X-axis direction. Therefore, as shown in FIG. 2, the side surfaces 14 a and 14 b extending in the X-axis direction are formed by the side surfaces of the first portion 15. Thus, the excitation unit 14 has two types of portions 15 and 16 having different thicknesses, and it can be said that the piezoelectric vibrating piece 100 has a two-stage mesa structure.

  The excitation unit 14 can vibrate with the thickness shear vibration as the main vibration. Since the excitation unit 14 has a two-stage mesa structure, the piezoelectric vibrating piece 100 can have an energy confinement effect.

Here, the dimension (short side dimension) of the piezoelectric substrate 10 in the Z′-axis direction is Z, the short side dimension of the excitation unit 14 is Mz, and the thickness of the excitation unit 14 (the first portion 15 of the excitation unit 14 is measured). When (thickness) is t, it is preferable to satisfy the relationship of the following formula (1).
8 ≦ Z / t ≦ 11 and 0.6 ≦ Mz / Z ≦ 0.8 (1)

As a result, the coupling between the thickness shear vibration and the unnecessary mode such as the contour vibration can be suppressed, and the CI value can be further reduced (details will be described later). Such coupling between the thickness shear vibration and the unnecessary mode is generally more likely to occur as the piezoelectric vibrating piece is smaller. Therefore, for example, in the small piezoelectric vibrating piece 100 that satisfies the relationship of the following formula (2) when the dimension in the X-axis direction (long side dimension) of the piezoelectric substrate 10 is X, the above formula (1) If it is designed to satisfy this relationship, the coupling between the thickness shear vibration and the unwanted mode can be suppressed more remarkably.
X / t ≦ 17 (2)

  The excitation electrode 20 is formed in the excitation unit 14. In the example shown in FIGS. 2 and 3, the excitation electrode 20 is formed with the excitation unit 14 interposed therebetween. More specifically, the excitation electrode 20 is disposed so as to face the vibration region (excitation unit 14) on both main surfaces (for example, surfaces parallel to the XZ ′ plane) of the piezoelectric substrate 10 on both sides. The excitation electrode 20 can apply a voltage to the excitation unit 14. The excitation electrode 20 is connected to the pad 24 via the extraction electrode 22, for example. The pad 24 is electrically connected to, for example, an IC chip (not shown) for driving the piezoelectric vibrating piece 100. As the material of the excitation electrode 20, the extraction electrode 22, and the pad 24, for example, a material obtained by laminating chromium and gold in this order from the piezoelectric substrate 10 side can be used.

  The piezoelectric vibrating piece 100 according to the present embodiment has the following features, for example.

According to the piezoelectric vibrating piece 100, each of the side surfaces 14a and 14b extending in the X-axis direction of the excitation unit 14 is in one plane, and each of the side surfaces 14c and 14d extending in the Z′-axis direction of the excitation unit 14 is Has a step. Accordingly, the CI value can be reduced as compared with a piezoelectric vibrating piece (see FIG. 16 described later) in which each of the side surfaces extending in the X-axis direction of the excitation unit 14 is not in one plane (details will be described later). .

  According to the piezoelectric vibrating piece 100, as described above, the dimension Z of the short side of the piezoelectric substrate 10, the dimension Mz of the short side of the excitation unit 14, and the thickness t of the excitation unit 14 are represented by the relationship of Expression (1). Thus, the CI value can be further reduced.

  According to the piezoelectric vibrating piece 100, as described above, by setting the X side ratio (X / t) to the relationship of Expression (2), it is possible to reduce the CI value while reducing the size.

2. Next, a method for manufacturing a piezoelectric vibrating piece according to this embodiment will be described with reference to the drawings. 5-11 is a figure which shows typically the manufacturing process of the piezoelectric vibrating piece 100 which concerns on this embodiment. 5 to 11, (a) is a plan view, (b) is a sectional view taken along line BB in (a), and (c) is a sectional view taken along line CC in (a). is there.

  As shown in FIG. 5, a corrosion-resistant film 30 is formed on the front and back main surfaces (surfaces parallel to the XZ ′ plane) of the AT-cut quartz crystal vibrating plate 101. The corrosion-resistant film 30 is formed by, for example, laminating chromium and gold in this order by sputtering or vacuum deposition, and then patterning the chromium and gold. The patterning is performed by, for example, a photolithography technique and an etching technique. The corrosion-resistant film 30 has corrosion resistance against a solution containing hydrofluoric acid that becomes an etching solution when the AT-cut quartz crystal substrate 101 is processed.

  As shown in FIG. 6, after applying a positive photoresist film, the photoresist film is exposed and developed to form a resist film 40 having a predetermined shape. The resist film 40 is formed so as to cover a part of the corrosion resistant film 30.

  As shown in FIG. 7, using the mask M, a part of the resist film 40 is exposed again to form a photosensitive portion 42. As shown in FIG. 7A, the mask M is disposed so as to intersect the resist film 40 when viewed from the Y′-axis direction. That is, the dimension of the mask M in the X-axis direction is smaller than the dimension of the resist film 40 in the X-axis direction, and the dimension of the mask M in the Z′-axis direction is larger than the dimension of the resist film 40 in the Z′-axis direction. By exposing using such a mask M, the photosensitive portions 42 can be formed on both sides of the resist film 40 as viewed from the Z′-axis direction as shown in FIG. 7C.

  As shown in FIG. 8, the AT cut quartz crystal substrate 101 is etched using the corrosion resistant film 30 as a mask. Etching is performed using, for example, a mixed liquid of hydrofluoric acid (hydrofluoric acid) and ammonium fluoride as an etching liquid. Thereby, the external shape (shape when viewed from the Y′-axis direction) of the piezoelectric substrate 10 is formed.

  As shown in FIG. 9, after etching the anticorrosion film 30 with a predetermined etching solution using the resist film 40 as a mask, the AT-cut quartz crystal substrate 101 is further half-etched to a predetermined depth using the above mixed solution as an etching solution. . Thereby, the external shape of the excitation part 14 is formed.

  As shown in FIG. 10, the photosensitive portion 42 of the resist film 40 is developed and removed. Thereby, a part of the corrosion-resistant film 30 is exposed. Before developing the photosensitive portion 42, an altered layer (not shown) formed on the surface of the resist film 40 is ashed by, for example, oxygen plasma generated by discharge in a vacuum or reduced pressure atmosphere. Thereby, the photosensitive part 42 can be reliably developed and removed.

  As shown in FIG. 11, after etching the corrosion-resistant film 30 with a predetermined etching solution using the resist film 40 as a mask, the AT-cut quartz crystal substrate 101 is further half-etched to a predetermined depth using the above-mentioned mixed solution as an etching solution. To do. Thereby, each of the side surfaces 14a and 14b extending in the X-axis direction can be formed in one plane. In addition, a step can be formed on each of the side surfaces 14c and 14d extending in the Z′-axis direction.

  Through the above steps, the piezoelectric substrate 10 having the peripheral portion 12 and the excitation portion 14 can be formed.

  As shown in FIGS. 1 to 3, after removing the resist film 40 and the corrosion-resistant film 30, the excitation electrode 20, the extraction electrode 22, and the pad 24 are formed on the piezoelectric substrate 10. The excitation electrode 20, the extraction electrode 22, and the pad 24 are formed by, for example, laminating chromium and gold in this order by sputtering or vacuum deposition, and then patterning the chromium and gold.

  Through the above steps, the piezoelectric vibrating piece 100 according to this embodiment can be manufactured.

  According to the method of manufacturing the piezoelectric vibrating piece 100, the resist film 40 used for forming the outer shape of the excitation unit 14 is developed to remove the photosensitive portion 42, and then the resist film 40 is used again to perform the X-axis direction. The side surfaces 14a and 14b extending in the direction can be exposed. Here, the mask M for forming the photosensitive portion 42 has a dimension in the X-axis direction smaller than the dimension of the resist film 40 and a dimension in the Z′-axis direction larger than the dimension of the resist film 40. Therefore, each of the side surfaces 14a and 14b can be accurately formed in one plane. For example, when a resist film is applied twice to form the excitation portion 14 (for example, after forming the outer shape of the excitation portion using the first resist film, the first resist film is peeled off and a second resist film is newly formed). When the film is applied to expose the side surface of the excitation unit), misalignment occurs between the first resist film and the second resist film, and the side surface of the excitation unit may not be formed in one plane. Such a problem can be solved by the method of manufacturing the piezoelectric vibrating piece 100.

3. Next, a piezoelectric vibrating piece according to a modified example of the present embodiment will be described with reference to the drawings. FIG. 12 is a plan view schematically showing a piezoelectric vibrating piece 200 according to a modification of the present embodiment. 13 and 14 are cross-sectional views schematically showing a piezoelectric vibrating piece 200 according to a modification of the present embodiment. 13 is a sectional view taken along line XIII-XIII in FIG. 12, and FIG. 14 is a sectional view taken along line XIV-XIV in FIG. Hereinafter, in the piezoelectric vibrating piece 200 according to the modified example of the present embodiment, members having the same functions as the constituent members of the piezoelectric vibrating piece 100 according to the present embodiment are denoted by the same reference numerals, and detailed description thereof is omitted. To do.

  In the example of the piezoelectric vibrating piece 100, as shown in FIGS. 1 to 3, the two-stage mesa structure having the first portion 15 and the second portion 16 having different thicknesses has been described.

  On the other hand, the piezoelectric vibrating piece 200 has a three-stage mesa structure as shown in FIGS. That is, the excitation unit 14 of the piezoelectric vibrating piece 200 includes the third portion 17 having a thickness smaller than that of the second portion 16 in addition to the first portion 15 and the second portion 16. In the example shown in FIGS. 12 and 14, the third portion 17 is formed so as to sandwich the first portion 15 and the second portion 16 from the X-axis direction.

The steps of the side surfaces 14c and 14d extending in the Z′-axis direction are formed by the difference in thickness between the first portion 15, the second portion 16, and the third portion 17, as shown in FIG. In the illustrated example, the side surfaces 14 c and 14 d are surfaces parallel to the Y′Z ′ plane of the first portion 15, surfaces parallel to the XZ ′ plane of the second portion 16, and Y′Z ′ of the second portion 16. A plane parallel to the plane, a plane parallel to the XZ ′ plane of the third portion 17, and a plane parallel to the Y′Z ′ plane of the third portion 17 are configured.

  The piezoelectric vibrating piece 200 can be manufactured by applying the method for manufacturing the piezoelectric vibrating piece 100. That is, as shown in FIG. 10, after developing and removing the photosensitive portion 42, the resist film 40 is exposed again to form a second photosensitive portion (not shown) having a predetermined shape. Next, the corrosion-resistant film 30 and the AT-cut quartz substrate 101 are etched using the resist film 40 having the second photosensitive portion as a mask. Next, for example, ashing is performed to remove the deteriorated layer of the resist film 40, and then the second photosensitive portion is developed and removed. Next, the corrosion resistant film 30 and the AT-cut quartz substrate 101 are etched using the resist film 40 from which the second photosensitive portion has been removed as a mask. Through the above steps, the piezoelectric vibrating piece 200 having a three-stage mesa structure can be manufactured.

  According to the piezoelectric vibrating piece 200, it is possible to have a stronger energy confinement effect than the piezoelectric vibrating piece 100 having a two-stage mesa structure.

  In the above-described example, the piezoelectric vibrating piece 200 having a three-stage mesa structure has been described. However, in the invention according to the present application, each side surface extending in the X-axis direction of the excitation unit is 1 in the multi-stage mesa structure. The number of steps of the mesa structure (the number of steps) is not particularly limited as long as it is within one plane.

4). Next, the piezoelectric vibrator according to the present embodiment will be described with reference to the drawings. FIG. 15 is a cross-sectional view schematically showing the piezoelectric vibrator 300 according to the present embodiment.

  As shown in FIG. 15, the piezoelectric vibrator 300 includes a piezoelectric vibrating piece (piezoelectric vibrating piece 100 in the illustrated example) according to the present invention and a package 50.

  The package 50 can accommodate the piezoelectric vibrating piece 100 in the cavity 52. Examples of the material of the package 50 include ceramic and glass. The cavity 52 is a space for the piezoelectric vibrating piece 100 to operate. The cavity 52 can be hermetically sealed and installed in a reduced pressure space or an inert gas atmosphere.

  The piezoelectric vibrating piece 100 is accommodated in the cavity 52 of the package 50. In the illustrated example, the piezoelectric vibrating piece 100 is fixed in the cavity 52 in a cantilevered manner via a conductive adhesive 60. As the conductive adhesive 60, for example, solder or silver paste can be used.

  Although not shown, the package 50 may contain an IC chip for controlling the piezoelectric vibrating piece 100. The IC chip may be electrically connected to the pad 24 via the conductive adhesive 60.

  Since the piezoelectric vibrator 300 includes the piezoelectric vibrating piece according to the present invention, it is possible to reduce the CI value.

5. Experimental Example An experimental example is shown below to describe the present invention more specifically. The present invention is not limited by the following experimental examples.

5.1. Configuration of Piezoelectric Vibrating Piece As Example 1, a piezoelectric vibrating piece 100 having a two-stage mesa structure shown in FIGS. In Example 1, the AT-cut quartz plate was processed by wet etching using a solution containing hydrofluoric acid to form the piezoelectric substrate 10 having the peripheral portion 12 and the excitation portion 14. The piezoelectric substrate 10 was formed point-symmetrically with respect to a point (not shown) serving as the center of symmetry. The thickness t of the excitation unit 14 (first portion 15) was 0.065 mm, and the vibration frequency was set to 24 MHz. Further, the long side dimension X of the piezoelectric substrate 10 is 1.1 mm (ie, the X side ratio X / t is 17), and the short side dimension Z of the piezoelectric substrate 10 is 0.629 mm (ie, the Z side ratio Z / t). t is 9.7), the short side dimension Mz of the excitation unit 12 is 0.43 mm, and each of the side surfaces 14a and 14b extending in the X-axis direction is formed in one plane.

  As a comparative example, a piezoelectric vibrating piece 1000 shown in FIG. 16 was used. In addition, in FIG. 16, (b) is the BB sectional drawing of (a).

  In Comparative Example 1, the excitation unit 1014 is formed in the same shape as the excitation unit 14 of Example 1 except that each side surface extending in the X-axis direction has a step as shown in FIG. . Note that the peripheral portion 1012, the excitation electrode 1020, the extraction electrode 1022, and the pad 1024 shown in FIG. 16 are respectively the peripheral portion 12, the excitation electrode 20, the extraction electrode 22, and the pad shown in FIGS. 24.

5.2. CI Value Distribution Measurement Results 200 pieces of each of the above-described Example 1 and Comparative Example 1 were formed, and these were housed in a package, and the CI value (room temperature) was measured. FIG. 17 is a graph showing the CI value with respect to the measured number, FIG. 17A shows the measurement result of Example 1, and FIG. 17B shows the measurement result of Comparative Example 1. That is, FIG. 17 shows the CI value distribution in Example 1 and Comparative Example 1.

  From FIG. 17, it was found that the CI value was 80Ω or less in all samples in Example 1, and the CI value was lower than that in Comparative Example 1. Furthermore, it was found that the variation in CI value was smaller in Example 1 than in Comparative Example 1. That is, the CI value can be reduced by forming each of the side surfaces extending in the X-axis direction of the excitation unit in one plane. This is presumably because the coupling between the thickness shear vibration in the Z′-axis direction and unnecessary modes such as contour vibration could be suppressed by forming each of the side surfaces extending in the X-axis direction in one plane. .

5.3. CI Value Evaluation for Mz / Z In the piezoelectric vibrating piece of Example 1, the thickness t of the excitation unit 14 is fixed to 0.065 mm, and the dimension Mz of the short side of the excitation unit 14 is fixed to 0.43 mm. The CI value (room temperature) was measured by shaking the side dimension Z as 0.46 mm, 0.5 mm, 0.54 mm, 0.59 mm, 0.65 mm, 0.72 mm, 0.81 mm, and 0.92 mm. The measurement was performed by housing the piezoelectric vibrating piece in a package. FIG. 18 is a graph showing the relationship between Mz / Z and CI value.

  From FIG. 18, it was found that the CI value was as low as about 60Ω when Mz / Z was in the range of 0.6 to 0.8. At this time, Z is 0.54 mm or more and 0.72 mm or less, and the Z side ratio (Z / t) is 8 or more and 11 or less. From the above, by setting the range of the Z side ratio (Z / t) to 8 ≦ Z / t ≦ 11 and the range of Mz / Z to 0.6 ≦ M1z / Z ≦ 0.8 (that is, the above) It was found that the CI value can be reduced by satisfying equation (1). This is because, by designing Z / t and Mz / Z so as to satisfy Equation (1), the coupling between the thickness shear vibration in the Z′-axis direction and unnecessary modes such as contour vibration can be further suppressed. Inferred.

A piezoelectric vibrating piece having Mz of 0.4 mm and Z of 0.65 mm (that is, Mz / Z = 0.6), and Mz of 0.48 mm and Z of 0.6 mm (that is, Mz / Z = 0) .8) The CI value of the piezoelectric vibrating piece was measured and found to be about 60Ω. From this, it can be said that the CI value can be reduced as long as the above formula (1) is satisfied without being limited to the case of Mz = 0.43 mm.

  Although the above experimental example was performed on the piezoelectric vibrating piece having the two-stage mesa structure shown in FIGS. 1 to 3, the result of this experiment is, for example, a multi-stage mesa structure as shown in FIGS. The present invention can also be applied to a piezoelectric vibrating piece having

  The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the present invention includes substantially the same configuration (for example, a configuration having the same function, method, and result, or a configuration having the same purpose and effect) as the configuration described in the embodiment. In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that achieves the same effect as the configuration described in the embodiment or a configuration that can achieve the same object. In addition, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

10 piezoelectric substrate, 12 peripheral part, 14 excitation part,
14a, 14b Side surfaces extending in the X-axis direction, 14c, 14d Side surfaces extending in the Z′-axis direction,
15 First part, 16 Second part, 17 Third part, 20 Excitation electrode, 22 Extraction electrode, 24 Pad, 30 Corrosion resistant film, 40 Resist film, 42 Photosensitive part, 50 Package,
52 cavity, 60 conductive adhesive, 100 piezoelectric vibrating piece,
101 AT cut crystal substrate, 200 piezoelectric vibrating piece, 300 piezoelectric vibrator

Claims (8)

Centering on the X axis of an orthogonal coordinate system consisting of an X axis as an electric axis, a Y axis as a mechanical axis, and a Z axis as an optical axis, which are crystal axes of quartz, the Z axis is the Y axis. The axis tilted in the −Y direction is the Z ′ axis, the Y axis is tilted in the + Z direction of the Z axis as the Y ′ axis, and is configured by planes parallel to the X axis and the Z ′ axis. And an AT-cut quartz substrate having a thickness in a direction parallel to the Y ′ axis,
The AT-cut quartz substrate is
An excitation unit having a side along the X-axis and a side along the Z′-axis;
A peripheral portion having a smaller thickness than the excitation portion and surrounding the excitation portion;
Have
An excitation electrode is disposed in the excitation unit,
The excitation unit is
In the direction along the X-axis, there are a plurality of steps between the peripheral part and the center of the excitation part,
A piezoelectric vibrating piece having one step between the peripheral portion and the center of the excitation portion in a direction along the Z ′ axis. In claim 1,
The excitation unit is a piezoelectric vibrating piece in which a side along the X-axis is a long side and a side along the Z′-axis is a short side. In claim 2,
When the dimension in the direction along the Z ′ axis of the AT-cut quartz substrate is Z, the dimension of the short side of the excitation part is Mz, and the thickness of the excitation part is t,
A piezoelectric vibrating piece satisfying a relationship of 8 ≦ Z / t ≦ 11 and 0.6 ≦ Mz / Z ≦ 0.8. In claim 3,
When the dimension in the direction along the X axis of the AT-cut quartz substrate is X,
A piezoelectric vibrating piece that satisfies a relationship of X / t ≦ 17. In any one of Claims 1 thru | or 4,
The excitation part is a piezoelectric vibrating piece having two steps between the peripheral part and the center of the excitation part in a direction along the X-axis. In any one of Claims 1 thru | or 4,
The excitation part is a piezoelectric vibrating piece having three steps between the peripheral part and the center of the excitation part in a direction along the X-axis. In any one of Claims 1 thru | or 6,
The piezoelectric vibrating piece , wherein a side surface in the direction along the X axis of the excitation unit is an R plane or an m plane of a quartz crystal . The piezoelectric vibrating piece according to any one of claims 1 to 7,
A package containing the piezoelectric vibrating piece;
Including a piezoelectric vibrator.