Piezoelectric vibrating reed, piezoelectric vibrator, and oscillator

Abstract

Provided is a piezoelectric vibrating piece in which the shape can be optimized so as to suppress vibration leakage. The piezoelectric plate (30) has a base portion (35), an arm portion (36), and a weight portion (37). Groove portions (60) are formed on both surfaces of the arm portion (36). The width of the weight portion (37) in the X-axis direction is Wh ([mu] m). Lh ([mu] m) is the length of the weight portion (37) in the Y 'direction, t ([mu] m) is the thickness of the piezoelectric plate (30), Lt ([mu] m) is the length of the groove portion (60) in the Y' direction, Wa ([mu] m) is the width of the arm portion (36) in the X-axis direction, Wt ([mu] m) is the width of the groove portion (60) in the X-axis direction, t '([mu] m) is the thickness of the portion of the arm portion (36) corresponding to the groove portion (60), and Ix is a variable satisfying formula (1). When X is a variable satisfying the following formula (2), the width of the base (35) in the X-axis direction is Wb ([mu] m) satisfying the following relational expression (3). Ix = Wt * t '3 / 12 + (Wa-Wt) * t3 / 12 (1) X = Wh * Lh * t * Lt * Wa / Ix (2) Wb > = 197X + 271 (3).

Description

Technical Field

[0001] The present invention relates to a piezoelectric vibrating piece, a piezoelectric vibrator, and an oscillator. Background Art

[0002] For example, piezoelectric vibrators using quartz or other materials are used in electronic devices such as mobile phones and portable information terminals as devices used as time sources, timing sources such as control signals, and reference signal sources. Known piezoelectric vibrators include a piezoelectric vibrating reed hermetically sealed within a package having a cavity. These reeds include a piezoelectric plate formed of a piezoelectric material such as quartz, and two sets of excitation electrodes disposed on the outer surface of the piezoelectric plate to apply a driving voltage for excitation to the piezoelectric plate.

[0003] As a piezoelectric vibrating piece, there is a piezoelectric vibrating piece that includes a piezoelectric plate having a pair of vibrating arms arranged side by side and a base portion connecting the base ends of the pair of vibrating arms. In such a piezoelectric vibrating piece, excitation electrodes are arranged on the outer surfaces of the vibrating arms, and a driving voltage is applied between the two systems of excitation electrodes, so that each vibrating arm vibrates at a predetermined resonant frequency in a direction of approaching or moving away from each other, starting from the connection portion with the base portion. In such a piezoelectric vibrating piece, a wide weight portion is sometimes continuously provided at the front end of the vibrating arm for the purpose of miniaturization, thereby seeking to shorten the overall length (for example, see Patent Documents 1 and 2).

[0004] Furthermore, among the piezoelectric vibrating reeds having the above-mentioned structure, a piezoelectric vibrating reed is known that has a groove formed in the vibrating arm to reduce crystal impedance. In a piezoelectric vibrating reed with a groove formed in the vibrating arm, two systems of excitation electrodes are separately arranged on the side of the vibrating arm and within the groove, thereby improving the electric field efficiency within the vibrating arm when a driving voltage is applied between the two systems of excitation electrodes.

[0005] However, when the pair of vibrating arms of the piezoelectric vibrating reed vibrates, the vibration may be transmitted to the base portion and leak into the package, etc., which is called vibration leakage. Patent Documents 1 and 2 describe techniques for suppressing this vibration leakage.

[0006] In patent document 1, a vibration piece is disclosed, which includes a base, a pair of vibration arms extending from a first end of the base along a first direction, and a protrusion integrally provided with the base, the base having a second end and a width reduction portion on the side opposite to the first end in the first direction, the protrusion being provided at at least one of the third end and the fourth end connecting the two ends of the first end and the two ends of the second end, respectively, and the width reduction portion being provided as follows: a distance along the first direction from a second-direction imaginary line passing between the first end and the second end and along a second direction orthogonal to the first direction to at least one of the first end and the second end becomes shorter as the distance moves away from the first-direction imaginary line passing through the center between the pair of vibration arms and along the first direction.

[0007] Patent document 2 discloses a piezoelectric vibrator comprising: a pair of vibrating arm portions that vibrate in a bending mode and have upper and lower surfaces and side surfaces; a base portion that is integrally formed with one end side of the vibrating arm portion; and a pair of side base portions that are integrally formed with the base portion and extend along the side surfaces of the vibrating arm portion, wherein a second gap that is narrower than the first gap between the vibrating arm portion and the side base portion is continuously formed from the first gap between the base portion and the side base portion, the vibrating arm portion, the base portion, and the side base portion being integrally formed by etching a quartz plate, and the second gap being the minimum width that can be etched through.

Prior technical literature

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2014-121039; [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-13910. Summary of the Invention [Problems to be solved by the invention]

[0009] However, conventional methods for evaluating the vibration leakage characteristics of piezoelectric resonators are limited to measuring the vibration leakage characteristics while the resonator is fixed to a package. Consequently, the design and evaluation of piezoelectric resonators is time-consuming, and there is a challenge in efficiently optimizing the shape of the piezoelectric resonator.

[0010] Therefore, the present invention provides a piezoelectric vibrating reed whose shape is optimized so as to suppress vibration leakage, and a piezoelectric vibrator and an oscillator including the piezoelectric vibrating reed.

Solutions to Solve the Problem

[0011] The piezoelectric vibrating piece according to the first embodiment of the present invention includes a piezoelectric plate formed of a quartz substrate, wherein a first direction and a second direction perpendicular to each other are defined in a direction perpendicular to the thickness direction of the piezoelectric plate, the piezoelectric plate having: a base portion; and a pair of vibrating arms extending from the base portion in the first direction and arranged side by side in the second direction, the piezoelectric plate having an arm portion connected to the base portion, and a weight portion connected to the front end of the arm portion and formed wider than the arm portion in the second direction, wherein grooves extending in the first direction are formed on both surfaces of the arm portion in the thickness direction, and when the width of the weight portion in the second direction is set to W h(μm), the length of the hammer portion in the first direction is Lh(μm), the thickness of the piezoelectric plate is t(μm), the length of the groove portion in the first direction is Lt(μm), the width of the arm portion in the second direction is Wa(μm), the width of the groove portion in the second direction is Wt(μm), the thickness of the portion of the arm portion corresponding to the groove portion is t'(μm), Ix is a variable satisfying the following equation (1), X is a variable satisfying the following equation (2), then the width of the base portion in the second direction is Wb(μm) satisfying the following relationship (3). Ix=Wt×t' 3 / 12+(Wa-Wt)×t 3 / 12……(1) X=Wh×Lh×t×Lt×Wa / Ix……(2) Wb≥197X+271……(3)

[0012] According to the first embodiment, the stress generated on the side surfaces of the base facing the second direction can be prevented from reaching 0.41 MPa. Separately evaluating the relationship between the side surfaces of the base and vibration leakage confirmed that when the stress generated on the side surfaces of the base exceeds 0.41 MPa, vibration leakage increases. Therefore, a piezoelectric vibrating reed with an optimized shape that suppresses vibration leakage can be obtained.

[0013] The piezoelectric vibrating piece involved in the second embodiment of the present invention may be the piezoelectric vibrating piece involved in the first embodiment listed above, wherein the piezoelectric plate further includes a pair of support arms extending from the base and extending along the first direction at outer positions of the base in the second direction, and if the spacing between the pair of support arms in the second direction is set to W (μm), the distance between the base and the support arms is Wg (μm) satisfying the following relationship (4). W-Wg≥Wb……(4)

[0014] According to the second aspect, a space of Wg / 2 or more can be ensured between the base and the support arm to prevent an electrical short circuit between the base and the support arm.

[0015] The piezoelectric vibrating piece according to the third aspect of the present invention may be the piezoelectric vibrating piece according to the first aspect or the second aspect listed above, and may satisfy the following relational expression (5). Wb≥207X+274……(5)

[0016] According to the third embodiment, the stress generated on the side surfaces of the base portion is reliably less than 0.35 MPa. Separately evaluating the relationship between the side surfaces of the base portion and vibration leakage confirmed that if the stress generated on the side surfaces of the base portion is 0.35 MPa or less, good vibration leakage characteristics are achieved. This makes it possible to obtain a piezoelectric vibrating reed that more reliably suppresses vibration leakage.

[0017] A piezoelectric vibrator according to a fourth aspect of the present invention includes: the piezoelectric vibrating reed according to any one of the first to third aspects; and a package that hermetically seals the piezoelectric vibrating reed.

[0018] According to the fourth aspect, it is possible to provide a piezoelectric vibrator having excellent vibration characteristics while suppressing vibration leakage of the piezoelectric vibrating reed.

[0019] An oscillator according to a fifth aspect of the present invention includes the piezoelectric vibrator according to the fourth aspect, wherein the piezoelectric vibrator is electrically connected to an integrated circuit as a vibrator.

[0020] According to the fifth aspect, an oscillator that outputs a high-precision frequency signal can be obtained. Effects of the invention

[0021] According to the present invention, it is possible to provide a piezoelectric vibrating piece whose shape is optimized so as to suppress vibration leakage. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a diagram showing an oscillator according to an embodiment. Figure 2 It is a perspective view of the appearance of a piezoelectric vibrator according to the embodiment. Figure 3 It is an exploded perspective view of the piezoelectric vibrator according to the embodiment. Figure 4 It is a plan view of a piezoelectric vibrating piece according to an embodiment. Figure 5 It is along Figure 4 Cross-sectional view of line VV. Figure 6 This is a graph showing the relationship between the width of the base portion in the X-axis direction and the stress generated on the side surfaces of the base portion. Figure 7 This is a graph showing the relationship between the variable X and the width of the base in the X-axis direction. DETAILED DESCRIPTION

[0023] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. In the following description, components having the same or similar functions are denoted by the same reference numerals. In addition, repeated descriptions of these components may be omitted.

[0024] (Oscillator) Figure 1 It is a diagram showing an oscillator according to an embodiment. like Figure 1 As shown, oscillator 100 includes substrate 101, electronic component 102, integrated circuit 103, and piezoelectric vibrator 1. Electronic component 102, such as a capacitor, is mounted on substrate 101. Integrated circuit 103 is an integrated circuit for the oscillator and is mounted on substrate 101. Integrated circuit 103 is electrically connected to piezoelectric vibrator 1 and electronic component 102 via wiring (not shown). Piezoelectric vibrator 1 is mounted on substrate 101, for example, near integrated circuit 103. Piezoelectric vibrator 1 functions as an oscillator. Piezoelectric vibrator 1 will be described later. At least a portion of oscillator 100 may be appropriately molded from a resin (not shown).

[0025] Regarding the oscillator 100, when power is supplied to the piezoelectric vibrator 1, the piezoelectric vibrating piece 3 (see Figure 3 ) vibrates. The vibration of the piezoelectric vibrating piece 3 is converted into an electrical signal due to the piezoelectric characteristics of the piezoelectric vibrating piece 3. The electrical signal is output from the piezoelectric vibrator 1 to the integrated circuit 103. The integrated circuit 103 generates a frequency signal by performing various processes on the electrical signal output from the piezoelectric vibrator 1.

[0026] Oscillator 100 can be applied to, for example, single-function oscillators for timepieces, timing control devices for controlling the timing of operations in various devices such as computers, and devices for providing time or calendar information. Integrated circuit 103 can also be configured to match the functions required of oscillator 100 and include a so-called RTC (real-time clock) module.

[0027] (Piezoelectric Vibrator) Figure 2 It is a perspective view of the appearance of a piezoelectric vibrator according to the embodiment. Figure 3 It is an exploded perspective view of the piezoelectric vibrator according to the embodiment. like Figure 2 and Figure 3As shown, the piezoelectric vibrator 1 is a so-called ceramic-packaged surface-mount vibrator. The piezoelectric vibrator 1 includes a package 2 having an airtightly sealed cavity therein and a piezoelectric vibrating reed 3 housed within the cavity. Furthermore, the piezoelectric vibrator 1 has a rectangular parallelepiped shape. In this embodiment, when viewed from above, the long side direction of the piezoelectric vibrator 1 is referred to as the long side direction L, the short side direction is referred to as the width direction W, and the direction perpendicular to these long side directions L and width direction W is referred to as the thickness direction T.

[0028] The package 2 includes a package body 5 and a sealing plate 6 that is joined to the package body 5 and forms a cavity between the sealing plate 6 and the package body 5 . The package main body 5 includes a first base substrate 10 and a second base substrate 11 which are bonded to each other in a superposed state, and a seal ring 12 bonded to the second base substrate 11 .

[0029] The first base substrate 10 is a ceramic substrate having a rectangular shape when viewed from above in the thickness direction T. The upper surface of the first base substrate 10 forms the bottom of the cavity. A pair of external electrodes 21A and 21B are formed on the lower surface of the first base substrate 10 at a distance along the longitudinal direction L. The external electrodes 21A and 21B are formed, for example, from a single-layer film of a single metal formed by vapor deposition or sputtering, or from a laminated film of different metals.

[0030] The second base substrate 11 is a ceramic substrate having the same outer shape as the first base substrate 10 in a plan view, and is integrally bonded to the first base substrate 10 by sintering or the like while being superimposed on the first base substrate 10. Ceramic materials used for the base substrates 10 and 11 include, for example, HTCC (High Temperature Co-Fired Ceramic) made of alumina or LTCC (Low Temperature Co-Fired Ceramic) made of glass ceramic.

[0031] like Figure 3 As shown, the second base substrate 11 has a through portion 11a extending through the second base substrate 11 in the thickness direction T. The through portion 11a has a rounded rectangular shape when viewed from above. Mounting portions 14A and 14B are formed on the inner side of the through portion 11a, on either side in the width direction W. These mounting portions 14A and 14B are located in the center of the second base substrate 11 in the longitudinal direction L.

[0032] A pair of electrode pads 20A and 20B are formed on the mounting portions 14A and 14B, serving as connection electrodes to the piezoelectric vibrating reed 3. Similar to the external electrodes 21A and 21B described above, the electrode pads 20A and 20B are formed from a single-layer film of a single metal, or a laminated film of different metals, formed by vapor deposition or sputtering. The electrode pads 20A and 20B and the external electrodes 21A and 21B are electrically connected to each other via through-wiring (not shown) that penetrates each base substrate 10 and 11 in the thickness direction T.

[0033] At the four corners of each base substrate 10, 11, a quarter-circular arc-shaped cutout 15 is formed across the entire thickness direction T of both base substrates 10, 11 in a plan view. For example, two wafer-shaped ceramic substrates are stacked and bonded, and then a plurality of through-holes are formed in a matrix pattern penetrating the two ceramic substrates. The two ceramic substrates are then simultaneously cut in a grid pattern based on each through-hole. At this point, the through-holes are divided into four sections, forming the aforementioned cutouts 15.

[0034] The sealing ring 12 is a conductive frame-shaped member that is slightly smaller than the outer dimensions of each base substrate 10 or 11. It is bonded to the upper surface of the second base substrate 11. Specifically, the sealing ring 12 is bonded to the second base substrate 11 by welding using a flux material such as silver solder or a solder material, or by welding a metal bonding layer formed on the second base substrate 11. The sealing ring 12, together with the inner side surface of the second base substrate 11 (through portion 11a), forms the side wall of the cavity. In the illustrated example, the inner side surface of the sealing ring 12 is coplanar with the inner side surface of the second base substrate 11.

[0035] As the material of the sealing ring 12, for example, nickel-based alloys are listed, and specifically, materials selected from Kovar, Elinvar, Invar, 42 alloy, etc. are sufficient. In particular, it is preferable to select a material having a thermal expansion coefficient close to that of the ceramic base substrates 10 and 11 as the material of the sealing ring 12. For example, when the thermal expansion coefficient is 6.8×10 -6 When alumina with a thermal expansion coefficient of 5.2×10 / °C is used as the base substrates 10 and 11, it is preferable to use alumina with a thermal expansion coefficient of 5.2×10 -6 / ℃ Kovar alloy or thermal expansion coefficient 4.5 to 6.5×10 -6 / ℃ 42 alloy.

[0036] The sealing plate 6 is formed of a conductive substrate and is bonded to the sealing ring 12 to hermetically seal the interior of the package body 5. The space defined by the sealing ring 12, the sealing plate 6, and the base substrates 10 and 11 forms an hermetically sealed cavity.

[0037] The piezoelectric vibrating piece 3 is housed in the cavity of the airtightly sealed package 2. The piezoelectric vibrating piece 3 includes a piezoelectric plate 30 formed of a piezoelectric material such as quartz, lithium tantalate, or lithium niobate. The piezoelectric plate 30 has a pair of vibrating arms 31 and 32 and a pair of support arms 33 and 34. The piezoelectric vibrating piece 3 is mounted on the package 2 by being supported on the mounting portions 14A and 14B of the package 2 within the cavity by a conductive adhesive. As a result, the piezoelectric vibrating piece 3 is supported within the cavity with the vibrating arms 31 and 32 floating from the base substrates 10 and 11. Two systems of excitation electrodes (not shown) are arranged on the outer surfaces of the vibrating arms 31 and 32, which vibrate the pair of vibrating arms 31 and 32 when a predetermined voltage is applied.

[0038] To operate the piezoelectric vibrator 1, a predetermined voltage is applied to the external electrodes 21A and 21B. This causes a current to flow through the excitation electrodes of the piezoelectric vibrating reed 3, generating an electric field between the excitation electrodes. The inverse piezoelectric effect generated by the electric field between the excitation electrodes causes the vibrating arms 31 and 32 to vibrate at a predetermined resonant frequency, for example, in directions of moving toward or away from each other. The vibration of the vibrating arms 31 and 32 can be used as a timing source, a control signal timing source, or a reference signal source.

[0039] (Piezoelectric Vibration Plate) The piezoelectric vibrating reed 3 according to the embodiment will be described in detail. Figure 4 It is a plan view of a piezoelectric vibrating piece according to an embodiment. like Figure 4 As shown, the piezoelectric vibrating reed 3 includes a piezoelectric plate 30 and an electrode film (not shown) arranged on the outer surface of the piezoelectric plate 30 .

[0040] A Lambertian quartz raw stone is sliced ​​at predetermined angles relative to the X-axis (electrical axis), Y-axis (mechanical axis), and Z-axis (optical axis), which are mutually orthogonal to the quartz crystal axes, to form a wafer, which is then shaped by etching to form the piezoelectric plate 30. In the following description, a coordinate system in which the X-axis, Y'-axis, and Z'-axis are mutually orthogonal is used to describe the structure of the piezoelectric vibrating plate 3. The Z'-axis is the axis for rotating the Z-axis around the X-axis within a range of -5° to +10°. The Y'-axis is the axis when the X-axis is used as the rotation axis and the Y-axis is rotated at the same angle as the Z-axis within a plane including the Z-axis and the Y-axis. Regarding the X-axis direction (second direction), the Y'-axis direction (first direction), and the Z'-axis direction, the arrow direction in the figure is set as the + side and the direction opposite to the arrow is set as the - side for description. Moreover, in the piezoelectric plate 30 of this embodiment, the Z'-axis direction coincides with the thickness direction of the piezoelectric plate 30. In addition, the term "width" used in the following description means the size of a portion extending in an arbitrary direction in a plan view as viewed from the Z'-axis direction in a direction perpendicular to the arbitrary direction in a plan view.

[0041] The piezoelectric plate 30 includes a base 35; a pair of vibrating arms 31 and 32 (a first vibrating arm 31 and a second vibrating arm 32) extending from the base 35 toward the positive side in the Y'-axis direction; and a pair of supporting arms 33 and 34 (a first supporting arm 33 and a second supporting arm 34) located on the positive and negative sides in the X-axis direction relative to the base 35. The piezoelectric plate 30 is symmetrical in both front and back directions, excluding any etching residue, and is formed line-symmetrically with respect to an imaginary line extending from the center position in the X-axis direction in the Y'-axis direction when viewed from above.

[0042] The base 35 is formed in a rectangular shape when viewed from above. It includes a first end surface 35a facing the positive side in the Y'-axis direction, a second end surface 35b facing the negative side in the Y'-axis direction, and a pair of side surfaces 35c facing outward in the X-axis direction. The first end surface 35a and the second end surface 35b each extend in the X-axis direction when viewed from above. A recessed portion, which is recessed toward the positive side in the Y'-axis direction when viewed from above, is formed in the middle portion of the second end surface 35b in the X-axis direction. The pair of side surfaces 35c each extend in the Y'-axis direction when viewed from above.

[0043] The pair of vibrating arms 31 and 32 are arranged side by side and parallel to each other in the X-axis direction. The pair of vibrating arms 31 and 32 are connected to the X-axis end of the first end surface 35a of the base 35. Each vibrating arm 31 and 32 vibrates in directions toward and away from each other, with the base end on the base 35 side serving as a fixed end and the tip as a free end. Each vibrating arm 31 and 32 includes an arm portion 36 extending from the first end surface 35a of the base 35 and a weight portion 37 connected to the tip of the arm portion 36 and formed wider than the arm portion 36.

[0044] The arm portion 36 includes: a straight portion 361, which extends with a constant width along the Y'-axis direction; a front end portion 362, which increases in width from the end portion on the + side in the Y'-axis direction of the straight portion 361 toward the + side in the Y'-axis direction, and at the same time extends toward the hammer portion 37 and is connected to the hammer portion 37; and a base end portion 363, which increases in width from the end portion on the - side in the Y'-axis direction of the straight portion 361 toward the - side in the Y'-axis direction, and at the same time extends toward the base portion 35 and is connected to the base portion 35.

[0045] The base end portion 363 includes an outer surface 363 a facing the space outside the arm portion 36 in the X-axis direction, and an inner surface 363 b facing the space inside the arm portion 36 in the X-axis direction.

[0046] The outer side surface 363a is connected to the side surface 35c of the base 35. The first half of the outer side surface 363a on the base 35 side is formed coplanar with the side surface 35c of the base 35 and extends in the Y'-axis direction when viewed from above. The second half of the outer side surface 363a on the arm 36 side is a concave curved surface that is recessed inward in the X-axis direction and toward the - side in the Y'-axis direction. After being bent inward in the X-axis direction and toward the + side in the Y'-axis direction from the end of the first half on the straight portion 361 side, the second half extends toward the + side in the Y'-axis direction as it moves inward in the X-axis direction.

[0047] The inner side surface 363b is connected to the first end surface 35a of the base 35. The inner side surface 363b is a concave curved surface that is recessed outward in the X-axis direction and toward the negative side in the Y'-axis direction. The inner side surface 363b extends toward the positive side in the Y'-axis direction as it moves outward from the first end surface 35a of the base 35 in the X-axis direction. In the Y'-axis direction, the positive end of the inner side surface 363b is aligned with the positive end of the outer side surface 363a.

[0048] The straight portion 361 has a pair of side surfaces 361a facing the X-axis direction. The side surfaces 361a are connected one-to-one to the outer side surface 363a and the inner side surface 363b of the base end portion 363. Each side surface 361a is smoothly connected to the outer side surface 363a or the inner side surface 363b of the base end portion 363 in a continuous tangential manner. However, each side surface 361a may be connected to the outer side surface 363a or the inner side surface 363b of the base end portion 363 in a discontinuous tangential manner.

[0049] The front end portion 362 includes an outer side surface 362a facing the space outside the arm portion 36 in the X-axis direction, and an inner side surface 362b facing the space inside the arm portion 36 in the X-axis direction. The outer side surface 362a and the inner side surface 362b are flat surfaces. The outer side surface 362a extends from the end of the side surface 361a of the straight portion 361 outward in the X-axis direction and toward the positive side in the Y'-axis direction. The inner side surface 362b extends from the end of the side surface 361a of the straight portion 361 inward in the X-axis direction and toward the positive side in the Y'-axis direction.

[0050] Plummets 37 are located at the tips of vibrating arms 31 and 32. Plummets 37 extend from the tips of each arm 36 toward the positive side in the Y'-axis direction. Plummets 37 are formed symmetrically with respect to the centerline of straight portion 361 when viewed from above. Plummets 37 are formed larger overall on both sides of the X-axis than the tip 362 of arm 36.

[0051] Each support arm 33 , 34 is L-shaped when viewed from above, surrounding the base portion 35 and the vibrating arms 31 , 32 from outside in the X-axis direction. Specifically, each support arm 33 , 34 includes a base portion 38 that projects outward in the X-axis direction from the negative end of the side surface 35 c of the base portion 35 in the Y'-axis direction, and a terminal portion 39 that extends from the opposite end of the base portion 35 in the Y'-axis direction toward the positive side. The terminal portion 39 extends along the Y'-axis with a constant width. The positive end of the terminal portion 39 in the Y'-axis direction is located closer to the positive side of the base portion 35 in the Y'-axis direction and closer to the negative side of the weight portion 37 in the Y'-axis direction. The first support arm 33 is located on the opposite side of the first vibrating arm 31 from the second vibrating arm 32. The second support arm 34 is located on the opposite side of the second vibrating arm 32 from the first vibrating arm 31.

[0052] Figure 5 It is along Figure 4 Cross-sectional view of line VV. like Figure 4 and Figure 5 As shown, a groove portion 60 is formed in each of the vibration arms 31 and 32. The groove portion 60 is recessed along the Z'-axis direction on the two main surfaces of the piezoelectric plate 30 facing the Z'-axis direction. The groove portion 60 extends along the Y'-axis direction with a constant width in the arm portion 36. In the Y'-axis direction, the positions of the two ends of the groove portion 60 coincide with the positions of the two ends of the arm portion 36. The groove portion 60 extends in a manner such that the center line passing through the center of its width is roughly consistent with the center line of the straight portion 361. In addition, the groove portion 60 can also be formed in a manner such that its center line is offset to the + side in the X-axis direction relative to the center line of the straight portion 361.

[0053] On the outer surface of each vibration arm 31, 32, there are formed two systems of excitation electrodes as part of the electrode film. The two systems of excitation electrodes are electrically insulated from each other. When a predetermined driving voltage is applied between the excitation electrodes, the excitation electrodes generate an electric field in each vibration arm 31, 32, causing each vibration arm 31, 32 to vibrate along the X-axis direction. The excitation electrode is, for example, a laminated film of chromium (Cr) and gold (Au). After a chromium film with good adhesion to quartz is used as a base to form a film, a gold thin film is laminated on the chromium film. However, the film structure of the electrode film is not limited to this. For example, it does not matter if a gold thin film is further laminated on a laminated film of chromium and nickel-chromium alloy (NiCr), or it does not matter if it is a single-layer film of chromium or nickel, aluminum (Al), titanium (Ti), etc. Each excitation electrode is connected to a wiring film not shown in the figure as part of the electrode film. The wiring film is electrically connected to the electrode pads 20A, 20B of the package 2 via a conductive adhesive.

[0054] The dimensions and functions of each part of the piezoelectric vibrating piece 3 according to the embodiment will be described in detail. Here, if Figure 4 and Figure 5 As shown, let the width of plummet 37 in the X-axis direction be Wh (μm), the length of plummet 37 in the Y'-axis direction be Lh (μm), the thickness of piezoelectric plate 30 be t (μm), the length of groove 60 in the Y'-axis direction be Lt (μm), the width of arm 36 in the X-axis direction be Wa (μm), the width of groove 60 in the X-axis direction be Wt (μm), and the thickness of the portion of arm 36 corresponding to groove 60 be t' (μm). Furthermore, let Ix be a variable satisfying the following equation (1), and let X be a variable satisfying the following equation (2). Furthermore, Ix is the second moment of area of ​​arm 36 in the bending direction. Ix=Wt×t' 3 / 12+(Wa-Wt)×t 3 / 12……(1) X=Wh×Lh×t×Lt×Wa / Ix……(2)

[0055] If the width of the base portion 35 in the X-axis direction is Wb (μm), Wb satisfies the following relational expression (3). Wb≥197X+271……(3)

[0056] Furthermore, if the distance between the pair of support arms 33 and 34 in the X-axis direction is set to W (μm), and the distance between the base 35 and the distal end 39 of the support arms 33 and 34 is set to Wg (μm), it is ideal that Wg satisfies the following relationship (4). W-Wg≥Wb……(4)

[0057] Furthermore, it is ideal that Wb satisfies the following relational expression (5). Wb≥207X+274……(5)

[0058] Figure 6 This is a graph showing the relationship between the width of the base portion in the X-axis direction and the stress generated on the side surfaces of the base portion. Figure 6 The horizontal axis shown represents the width of the base portion 35 in the X-axis direction. Figure 6 The vertical axis shown represents the stress generated on the side surface 35 c of the base 35 . like Figure 6As shown, when the variable X is between 0.07 and 0.113, the stress generated on the side surface 35c of the base 35 decreases as the width of the base 35 in the X-axis direction increases. Furthermore, simulations using finite element analysis software manufactured by Ansys confirmed that vibration leakage is insufficiently suppressed when the stress generated on the side surface 35c of the base 35 is 0.41 MPa, but is sufficiently suppressed when the stress is 0.35 MPa or less. However, the location on the side surface 35c of the base 35 where the stress was evaluated was specifically designated as the end portion of the side surface 35c on the support arms 33 and 34.

[0059] Figure 7 This is a graph showing the relationship between the variable X and the width of the base in the X-axis direction. Figure 7 The horizontal axis shown represents the variable X. Figure 7 The vertical axis shown represents the width of the base portion 35 in the X-axis direction. exist Figure 7 The data sets plotted in FIG. 3 are values ​​of the width of the base portion 35 in the X-axis direction when the variable X is changed so that the stress generated on the side surface 35 c of the base portion 35 becomes 0.35 MPa, 0.315 MPa, and 0.41 MPa. Figure 7 The straight lines shown are the results of approximating each data set to a linear function using the least squares method. Specifically, straight line L1 corresponds to the data set with a stress of 0.35 MPa and shows the function of the variable X expressed by the following equation (6). Straight line L2 corresponds to the data set with a stress of 0.315 MPa and shows the function of the variable X expressed by the following equation (7). Straight line L3 corresponds to the data set with a stress of 0.41 MPa and shows the function of the variable X expressed by the following equation (8). Wb=197X+271……(6) Wb=207X+274……(7) Wb=180X+265……(8)

[0060] like Figure 7 As shown, by setting the width of the base portion 35 in the X-axis direction to be greater than the function of the variable X represented by the straight line L1, the stress generated on the side surface 35c of the base portion 35 can be prevented from exceeding 0.41 MPa, which would increase vibration leakage. Therefore, it can be seen that by satisfying the above-mentioned relationship (3), vibration leakage can be suppressed.

[0061] Furthermore, by setting the width of the base portion 35 in the X-axis direction to be greater than or equal to the function of the variable X represented by the straight line L2, the stress generated on the side surface 35c of the base portion 35 is reliably less than 0.35 MPa, which is sufficient for achieving good vibration leakage characteristics. Therefore, it can be seen that by satisfying the above-listed relational expression (5), vibration leakage can be more reliably suppressed.

[0062] By setting the width of the base portion 35 in the X-axis direction so as to satisfy the above-listed relational expression (3) as described above, it is possible to obtain the piezoelectric vibrating piece 3 whose shape is optimized so as to suppress vibration leakage.

[0063] Furthermore, when Wg satisfies the above-listed relational expression (4), a space of Wg / 2 or more can be ensured between the base 35 and the support arms 33 , 34 to prevent an electrical short circuit between the base 35 and the support arms 33 , 34 .

[0064] In addition, the present invention is not limited to the above-mentioned embodiment described with reference to the drawings, and various modifications are conceivable within the technical scope of the present invention. For example, in the above embodiments, the piezoelectric vibrating piece 3 is a so-called side-arm type vibrating piece in which the support arms 33 and 34 are arranged outside the vibrating arms 31 and 32. However, the present invention is not limited to this configuration, and the piezoelectric vibrating piece may be a vibrating piece without support arms.

[0065] Furthermore, the components in the above-listed embodiments can be appropriately replaced with known components without departing from the spirit of the present invention.

Explanation of symbols

[0066] 1 ... piezoelectric vibrator 2 ... package 3 ... piezoelectric vibrating piece 30 ... piezoelectric plate 31 , 32 ... vibrating arms 33 , 34 ... support arms 35 ... base 36 ... arm 37 ... weight 60 ... groove 100 ... oscillator 103 ... integrated circuit

Claims

1. A piezoelectric vibrating piece comprising a piezoelectric plate formed of a quartz substrate, A first direction and a second direction perpendicular to each other are defined in a direction perpendicular to the thickness direction of the piezoelectric plate, The piezoelectric plate has: base; and a pair of vibrating arms extending from the base in the first direction and arranged side by side in the second direction, each comprising an arm portion connected to the base, and a weight portion connected to a front end of the arm portion and formed wider than the arm portion in the second direction; Grooves extending along the first direction are formed on both surfaces of the arm portion in the thickness direction. If the width of the weight portion in the second direction is Wh (μm), The length of the plummet in the first direction is defined as Lh (μm). The thickness of the piezoelectric plate is set to t (μm), The length of the groove in the first direction is Lt (μm). The width of the arm portion in the second direction is Wa (μm). The width of the groove in the second direction is Wt (μm). The thickness of the portion of the arm corresponding to the groove is t' (μm). Let Ix be a variable that satisfies the following equation (1): Let X be a variable that satisfies the following formula (2): Then the width of the base in the second direction is Wb (μm) which satisfies the following relational expression (3): Ix=Wt×t' 3 / 12+(Wa-Wt)×t 3 / 12……(1), X=Wh×Lh×t×Lt×Wa / Ix……(2), Wb≥197X+271……(3).

2. The piezoelectric vibrating piece according to claim 1, wherein The piezoelectric plate further includes a pair of support arms extending from the base portion and extending along the first direction at outer positions of the base portion in the second direction. If the distance between the pair of support arms in the second direction is W (μm), Then the distance between the base and the support arm is Wg (μm) which satisfies the following relationship (4), W-Wg≥Wb……(4).

3. The piezoelectric vibrating piece according to claim 1 or claim 2, wherein: The following relationship (5) is satisfied: Wb≥207X+274……(5).

4. A piezoelectric vibrator comprising: The piezoelectric vibrating piece according to claim 1 or claim 2; and A package hermetically seals the piezoelectric vibrating piece. 5 . An oscillator comprising the piezoelectric vibrator according to claim 4 , wherein the piezoelectric vibrator is electrically connected to an integrated circuit as a vibrator.

Images