JP2005260692A - Piezoelectric vibrating bar, piezoelectric vibrator and piezo-oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make vibration displacement small at a peripheral end part of a piezoelectric vibrating reed, to improve a CI value and to stabilize an oscillation frequency without inducing other vibration modes by moderately controlling the attenuation of primary vibration in the piezoelectric vibrating reed with thickness-shear vibration defined as primary vibration. <P>SOLUTION: This piezoelectric vibrating reed 10 with thickness-shear vibration defined as as primary vibration is provided with an excitation electrode 20 provided facing the thickness direction of a pair of principal planes 11, a connection electrode 21 connected to the excitation electrode 20 to extend to a peripheral end part of the vibrating reed 10 and protrusions 30 and 31 on the principal planes 11 with thickness being the same as or smaller than that of the excitation electrode 20 with spacing left, surrounding the outer circumference of the excitation electrode 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric vibrating piece, a piezoelectric vibrator, and a piezoelectric oscillator that, in a piezoelectric vibrating piece having a thickness-shear vibration as a main vibration, moderately attenuate the main vibration and reduce a vibration displacement at a peripheral end of the piezoelectric vibrating piece.

  In recent years, piezoelectric vibrators are widely used as reference frequency signal sources in various electronic devices and communication devices. Especially as a piezoelectric resonator, AT-cut quartz resonators have frequency stability over a wide temperature range and are excellent in time-varying characteristics, so they can be used in a wide range of devices such as electronic devices and mobile communication devices. It's being used.

  In general, the AT-cut quartz resonator uses a thickness-shear vibration mode as a main vibration. In this thickness-shear vibration, a standing wave is created directly under the excitation electrode arranged at the center of the vibrating piece, and the vibration is taken out as a resonance frequency. However, the vibration generated at the center of the vibrating piece is attenuated while being attenuated. It is transmitted to the peripheral edge.

  Here, the damped vibration in the outer peripheral portion of the vibrating piece needs to be sufficiently damped in order to ensure the characteristics as the vibrating piece. The vibrating piece is held and fixed to a receiving container such as ceramic via a conductive adhesive or the like at the periphery of the vibrating piece. For this reason, if the vibration at the periphery of the resonator element is not sufficiently damped, the vibration leaks from the fixed part of the periphery of the resonator element to the container, and the vibration at the center of the resonator element is hindered. (Hereinafter referred to as the CI value). In addition, other vibration modes are induced to decrease the stability of the oscillation frequency.

  In order to sufficiently attenuate the damping vibration of the thickness shear vibration at the peripheral end portion of the vibrating piece, configurations as shown in Patent Document 1 and Patent Document 2 are disclosed. According to this configuration, by providing one groove along the outer peripheral edge of the excitation electrode, the vibration at the peripheral end portion of the resonator element is suppressed or the characteristics as a resonator are improved.

JP-A-9-93076 JP 2001-257558 A

  However, in the above-described configuration, in order to form the groove in the resonator element, it is necessary to form the groove by a liquid phase etching method using photolithography. In this method, it is necessary to go through many steps such as resist coating, exposure, development, etching, and washing, and there is a problem that man-hours are required. Etching of the resonator element in the gas phase is also possible, but this is not practical because the apparatus is expensive and large.

  The present invention has been made in view of the above-described problems of the prior art, and ensures a sufficient area of the excitation portion of the vibrating piece without forming a groove in the vibrating piece, and also sufficiently vibrates the peripheral edge of the vibrating piece. An object of the present invention is to provide a piezoelectric vibrating piece, a piezoelectric vibrator, and a piezoelectric oscillator that can be attenuated to obtain good electrical characteristics.

  In order to achieve the above object, a piezoelectric vibrating piece according to the present invention is a piezoelectric vibrating piece having thickness shear vibration as a main vibration, and is formed by exciting electrodes formed oppositely in the thickness direction on a pair of main surfaces. A connection electrode connected to the electrode and extended to a peripheral end of the piezoelectric vibrating piece, and an excitation electrode formed so as to face or surround the excitation electrode with at least one main surface sandwiching the outer periphery of the excitation electrode; And a protrusion formed in the same thickness or a thin thickness.

According to the piezoelectric vibrating piece of the present invention, by forming the protrusion so as to sandwich or surround the excitation electrode of the piezoelectric vibrating piece, the thickness shear vibration generated at the central portion of the main surface is gently attenuated, and the piezoelectric vibrating piece is The vibration displacement at the peripheral end of the vibrating piece can be reduced.
In other words, the CI value can be improved without impeding the main vibration of the piezoelectric vibrator by reducing the attenuation of the main vibration and reducing the leakage of vibration from the piezoelectric vibrating piece to the holding portion. A piezoelectric vibrating piece having a stable oscillation frequency can be obtained without inducing other vibration modes.

  In the piezoelectric vibrating piece of the present invention, the protrusion may be made of the same material as the excitation electrode.

  If it does in this way, the process of forming excitation electrodes and connection electrodes, such as vacuum evaporation and sputtering, and the process of forming a protrusion can be formed in the same process simultaneously. For this reason, it is possible to provide a piezoelectric vibrating piece with excellent mass productivity and good electrical characteristics.

  In the piezoelectric vibrating piece of the present invention, the protrusions may be provided in a plurality of rows at intervals from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece.

  In this way, the thickness shear vibration generated at the center of the piezoelectric vibrating piece can be attenuated in stages, and the vibration displacement at the peripheral end of the piezoelectric vibrating piece can be reduced. In addition, abrupt vibration attenuation when a single protrusion is formed can be attenuated in stages by providing a plurality of protrusions, and vibration attenuation can be controlled gently. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece according to the present invention, the thickness of the protrusion may be gradually decreased from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece.

  The thinner the protrusion is, the more effective it is to attenuate vibrations. In this way, it is possible to moderate the attenuation near the main vibration. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece of the present invention, the interval between the protrusions may be formed so as to increase gradually from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece.

  The wider the interval between the protrusions, the more effective the vibration is attenuated. In this way, the attenuation near the main vibration can be moderated. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece of the present invention, the width of the protrusion may be narrowed sequentially from the outer periphery of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece.

  As the width of the protrusion becomes narrower, there is a vibration damping effect. Thus, in this way, it is possible to moderate the damping near the main vibration. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece according to the present invention, the thickness of the protrusion gradually decreases from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the interval at which the protrusion is formed further increases the outer periphery of the excitation electrode. It may be formed so as to gradually increase from the portion toward the peripheral end of the piezoelectric vibrating piece.

  In this way, in addition to the effect of changing the thickness of the protrusions, the effect of changing the interval at which the protrusions are formed is also added, so that the attenuation in the vicinity of the main vibration can be moderated. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece according to the present invention, the thickness of the protrusion gradually decreases from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the width of the protruding portion decreases from the outer peripheral portion of the excitation electrode. You may form narrowly sequentially toward the peripheral edge part of a piezoelectric vibrating piece.

  In this way, in addition to the effect of changing the thickness of the protrusion, the effect of changing the width of the protrusion is added, and the attenuation in the portion close to the main vibration can be moderated. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece according to the present invention, the interval between the protrusions is formed so as to gradually increase from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the width of the protruding portion is further increased. You may form so that it may become narrow sequentially from the outer peripheral part of an electrode toward the peripheral edge part of a piezoelectric vibrating piece.

  In this way, in addition to the effect of changing the interval at which the protrusions are formed, the effect of changing the width of the protrusions is added, so that the attenuation in the portion near the main vibration can be moderated. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  Further, in the piezoelectric vibrating piece according to the present invention, the thickness of the protrusion gradually decreases from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the interval at which the protrusion is formed extends from the outer peripheral portion of the excitation electrode. The width may be gradually increased toward the peripheral end portion of the piezoelectric vibrating piece, and the width of the protrusion may be gradually decreased from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece.

  In this way, in addition to the effect of changing the thickness of the protrusions, the effect of changing the interval and width of the protrusions is added, and the attenuation near the main vibration can be moderated. In this way, the piezoelectric vibrating piece of the present invention can obtain the attenuation of displacement at the periphery of the vibrating piece while sufficiently securing the excitation part area of the main vibration, and has good electrical characteristics as a piezoelectric vibrating piece. Can be obtained.

  It is also possible to provide a piezoelectric vibrator having the above-described piezoelectric vibrating piece according to the present invention, and a holding unit that fixes the piezoelectric vibrating piece at the peripheral end of the piezoelectric vibrating piece and makes electrical connection.

  In this way, the vibration at the end of the piezoelectric vibrating piece is sufficiently damped, and even if the end of the piezoelectric vibrating piece is fixedly held via a conductive adhesive or the like, the vibrating piece is moved to the holding portion. The vibration leakage can be reduced and the main vibration is not hindered. In particular, when a plurality of protrusions are provided on the piezoelectric vibrating piece, attenuation can be further moderated near the main vibration, and inhibition of the main vibration can be reduced. As described above, the piezoelectric vibrator of the present invention can provide the piezoelectric vibrator having excellent electrical characteristics by extracting the effect of forming the protrusion on the main surface of the piezoelectric vibrating piece.

  Further, the above-described piezoelectric vibrating piece according to the present invention, a circuit unit for causing the piezoelectric vibrating piece to oscillate, and holding for fixing and holding the end of the piezoelectric vibrating piece and electrically connecting the piezoelectric vibrating piece and the circuit unit. It is also possible to provide a piezoelectric oscillator having a portion.

  In this way, the vibration at the end of the piezoelectric vibrating piece is sufficiently damped, and even if the end of the piezoelectric vibrating piece is fixedly held via a conductive adhesive or the like, the vibrating piece is moved to the holding portion. The vibration leakage can be reduced and the main vibration is not hindered. In particular, when a plurality of protrusions are provided on the piezoelectric vibrating piece, damping can be further moderated near the main vibration, and inhibition of the main vibration can be reduced. As described above, the piezoelectric oscillator according to the present invention can provide the piezoelectric oscillator with excellent electrical characteristics by extracting the effect of forming the protrusion on the main surface of the piezoelectric vibrating piece.

  Hereinafter, the present invention will be described in detail based on examples, but before that, the principle of the present invention will be described in the case of an AT-cut crystal vibrating piece (hereinafter referred to as a vibrating piece).

  The propagation of thickness shear vibration is expressed by the following formulas 1 to 4. According to Equations 1 to 4, when there are regions having different frequencies on the resonator element, vibration propagation occurs from the higher frequency to the lower frequency. Since β is an imaginary number, propagation of thickness-shear vibration does not occur and is attenuated. That is, the thickness-shear vibration is attenuated without propagation from a portion having a low frequency excitation electrode to a peripheral end portion having no high frequency excitation electrode.

Ｕ：厚み滑り振動のＸ方向、Ｚ´方向への変位、 Ｂ：振幅強度、
ω、ω_S：メサ部分の角周波数および振動片の角周波数、
α、β：Ｘ、Ｚ´方向それぞれへの伝播定数、Ｃ₅₅、Ｃ₆₆：弾性スティフネス（所定の結晶方向における弾性率を表すマトリックスの中の定数）、
ｓ₁₁、ｓ₁₃、ｓ₃₃：弾性コンプライアンス（所定の結晶方向における弾性率を表すマトリックスの中の定数）、
ｊ：虚数単位、ｔ：時間、ｘ：Ｘ方向の距離、ｚ´：Ｚ´方向の距離。

U: displacement of thickness shear vibration in X direction and Z ′ direction, B: amplitude intensity,
ω, ω _S : angular frequency of the mesa part and angular frequency of the resonator element,
α, β: Propagation constants in the X and Z ′ directions, C ₅₅ , C ₆₆ : Elastic stiffness (a constant in a matrix representing an elastic modulus in a predetermined crystal direction),
s ₁₁ , s ₁₃ , s ₃₃ : elastic compliance (a constant in a matrix representing an elastic modulus in a predetermined crystal direction),
j: imaginary unit, t: time, x: distance in X direction, z ′: distance in Z ′ direction.

The present invention uses the above mathematical formula to create a low frequency portion by forming a protrusion on the vibrating piece, and effectively attenuates the vibration at the peripheral end of the vibrating piece. In addition to the vibration attenuation at the peripheral edge of the resonator element, the impedance was improved by securing a wide excitation part at the center of the resonator element, and the improvement of electrical characteristics was also considered.
That is, the present invention relates to the concave portion sandwiched between the protrusions of the resonator element and sufficiently attenuates the vibration at the periphery of the resonator element, and spurious generation when the low frequency region is completely mechanically separated. In consideration of the above problem, the resonator element having the protrusion structure was analyzed by the finite element method (FEM) using the above formulas 1 to 4.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an AT-cut quartz crystal vibrating piece (hereinafter referred to as a vibrating piece) will be described as an example of the piezoelectric vibrating piece. It should be noted that the scales in the drawings are not the current scales for the sake of explanation, and are appropriately enlarged and reduced.

  FIG. 1 is a schematic diagram for explaining the shape and crystal axis of a vibrating piece used in this embodiment, and FIG. 2 is a schematic view of the vibrating piece for explaining Embodiment 1 of the present invention. 2A is a plan view of the resonator element, FIG. 2B is a cross-sectional view taken along line AA of FIG. 2A, and FIG. 2C is a schematic partial enlarged view of FIG.

As shown in FIG. 1, the resonator element 10 as a piezoelectric resonator element has, for example, a resonance frequency of 27 MHz, an X side ratio (ratio to the thickness of the resonator element in the X-axis direction dimension) 33, and a Z side ratio (Z ′ in the resonator element). The ratio of the dimension in the axial direction to the thickness of the resonator element is 21).
The Y ′ axis and the Z ′ axis of the resonator element 10 are rotated 35.25 degrees clockwise in the + X direction of the X axis in the definition of the crystal axis in accordance with the IEC (International Electro-technical Commission) standard. New coordinate axes. The resonator element 10 is a rectangular flat plate having a thickness 2b in the Y′-axis direction, and has a size 2a in the X-axis direction orthogonal to the Z′-axis and a dimension 2c in the Z′-axis direction orthogonal to the X-axis. It has the surface 11 on both sides.

  Next, as shown in FIG. 2, an excitation electrode 20 is formed at the central portion of the main surface 11 of the resonator element 10, connected to the excitation electrode 20, and a connection electrode 21 extended to the peripheral end of the resonator element 10. Is provided. The excitation electrodes 20 are formed on the front and back surfaces so as to face each other in the thickness direction of the resonator element 10. In addition, the connection electrode 21 is formed on the front and back of the resonator element 10 and is formed so as to be electrically connected to each excitation electrode. The excitation electrode 20 and the connection electrode 21 are formed by a technique such as vacuum deposition or sputtering using Cr as a base and Au as an electrode material.

In addition, a protrusion 30 is formed on the main surface 11 of the resonator element 10 so as to surround the excitation electrode 20. The protrusions 30 are formed on the front and back of the resonator element 10 so as to face each other in the thickness direction of the resonator element 10 like the excitation electrode 20. In the same process as the excitation electrode 20 and the connection electrode 21, the protrusion 30 is simultaneously formed by a technique such as vacuum deposition or sputtering using Cr as a base and Au as an electrode material.
As described above, the protrusion 30 is formed to have the same thickness as that of the excitation electrode 20 and the connection electrode 21. In the present embodiment, the thickness of the excitation electrode 20 is the plate back amount (the percentage obtained by dividing the decrease in the vibration piece main vibration frequency from the vibration piece frequency in the portion where the excitation electrode is formed by the vibration piece frequency in percentage). Value) of 8.8%, and the thickness was about 400 nm on one side. The gap between the protrusion 30 and the excitation electrode 20 was the same as the thickness of the resonator element 10. Further, the protrusion 30 is not electrically connected to others.

Next, the analysis result by the finite element method (FEM) leading to the above-described vibration piece will be described.
FIG. 3 shows the result of analyzing the vibration displacement in the above-mentioned vibrating piece by the finite element method. FIG. 3A shows the analysis result of the vibration displacement of the vibrating piece 10 in the X-axis direction by the finite element method, and FIG. 3B shows the analysis result of the vibration displacement of the vibration piece 10 in the Z′-axis direction by the finite element method. . Note that the vertical axis in FIG. 3 represents the amount of vibration displacement as an arbitrary unit for comparison. Further, the horizontal axis indicates the length of the resonator element 10 in the X-axis direction or the Z′-axis direction.

In FIG. 3A, the curve indicated by the solid line is the X-axis direction vibration displacement when the protrusion 30 is provided on the vibrating piece 10, and the curve indicated by the dotted line is the case where the protrusion is not provided on the vibration piece 10. X-axis direction vibration displacement.
According to this result, a favorable small vibration displacement is ensured on the holding portion side G of the resonator element 10. Further, when comparing the vibration displacement in the X-axis direction of the resonator element 10, it can be seen that the vibration region is wider when the protrusion 30 is provided. This means that by providing the protrusion 30 on the vibrating piece 10, the attenuation of the main vibration can be controlled gently, and the vibration attenuation does not hinder the main vibration and a good vibration is made. This result is equivalent to increasing the effective area of the excitation electrode 20, and has the effect of lowering the CI value.
Conventionally, in order to reduce the CI value, a method of thickening the excitation electrode has been used. However, in this case, since the effective excitation portion due to energy confinement becomes narrow, the equivalent capacitance C ₁ becomes small and the frequency variable amount decreases. There was a problem. According to the present embodiment, even if the thickness of the excitation electrode is increased, the CI value can be lowered without decreasing C ₁ due to the influence of the protrusion on the outer periphery, and the effect that the frequency variable amount is not lowered is produced.

Next, in FIG. 3B, the curve represented by the solid line is the vibration displacement in the Z′-axis direction when the protrusion 30 is provided, and the curve represented by the dotted line is the Z′-axis direction when the protrusion is not provided. It is a vibration displacement.
According to this result, the vibration displacement in the Z′-axis direction of the resonator element 10 can be more moderately attenuated when the protrusion 30 is provided than when the protrusion is not provided, and the vibration attenuation is the main vibration. It turns out that it is not inhibiting.
From the above, the vibration attenuation can be moderated by providing the protrusion 30 on the vibration piece 10, and a good vibration attenuation state is secured. Furthermore, since the vibration region of the resonator element 10 can be widened, the electrical characteristics of the resonator element can be improved.

  The inventor confirmed the effect of suppressing the vibration displacement at the peripheral end of the resonator element even with the excitation electrode having a plate back amount of 1% or more and the thickness of the protrusion. Further, it has been found that when the plate back amount exceeds 15%, contour vibration, which is another vibration mode, is generated, and inhibition of vibration at the peripheral end portion of the vibration piece is hindered.

  FIG. 4 is a schematic view of a resonator element for explaining the second embodiment of the present invention. 4A is a plan view of the resonator element, FIG. 4B is a cross-sectional view taken along the line AA in FIG. 4A, and FIG. 4C is a partially enlarged view of FIG.

The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.
An excitation electrode 20 is formed at the central portion of the main surface 11 of the resonator element 10, and a connection electrode 21 extending to the peripheral end of the resonator element 10 is provided so as to connect to the excitation electrode 20. The excitation electrodes 20 are formed on the front and back surfaces so as to face each other in the thickness direction of the resonator element 10. In addition, the connection electrode 21 is formed on the front and back of the resonator element 10 and is formed so as to be electrically connected to each excitation electrode. The excitation electrode 20 and the connection electrode 21 are formed by a technique such as vacuum deposition or sputtering using Cr as a base and Au as an electrode material.

Further, the first protrusion 30 is formed on the main surface 11 of the resonator element 10 so as to surround the excitation electrode 20 with a space therebetween. Furthermore, the 2nd protrusion 31 is formed at intervals so that the excitation electrode 20 may be enclosed from the outer peripheral side of the 1st protrusion 30. FIG.
The first protrusion 30 and the second protrusion 31 are formed on the front and back of the resonator element 10 so as to face each other in the thickness direction of the resonator element 10 like the excitation electrode 20. The first protrusion 30 and the second protrusion 31 are simultaneously formed by a technique such as vacuum evaporation or sputtering using Cr as a base and Au as an electrode material in the same process as the excitation electrode 20 and the connection electrode 21. Thereafter, the first protrusion 30 and the second protrusion 31 are etched, and the thickness T ₂ of the first protrusion 30 is smaller than the thickness T ₁ of the excitation electrode 20 and the thickness T ₂ of the second protrusion 31. ₃ is formed so as to be thinner than the thickness T ₂ of the first protrusion 30 (relationship T ₁ > T ₂ > T ₃ ). In this etching process, for example, a method such as a plasma etching method or an ion etching method is used. This method is known as a method for adjusting the frequency of the resonator element by etching the excitation electrode.
In the present embodiment, the thickness of the excitation electrode 20 is 8.8% of the plate back amount, and the thickness is about 400 nm. The thickness of the first protrusion 30 was 270 nm, and the thickness of the second protrusion 31 was 200 nm.

Further, the distance L ₂ between the first protrusion 30 and the second protrusion 31 is formed to be equal to the distance L ₁ between the excitation electrode 20 and the first protrusion 30 (relationship L ₁ ≈L _2). ).
Furthermore, the width W ₂ of the second protrusion 31 is formed to be equal to the width W ₁ of the first protrusion 30 (relationship W ₁ ≈W ₂ ).
Note that the first protrusion 30 and the second protrusion 31 are not electrically connected to each other.

Next, the analysis result by the finite element method (FEM) leading to the above-described vibration piece will be described.
FIG. 5 shows the result of analyzing the vibration displacement of the vibrating piece by the finite element method when the protruding pieces having the same thickness as the excitation electrode are formed in two rows at the same interval on the vibrating piece. FIG. 5A shows an analysis result of the vibration displacement in the X-axis direction of the resonator element 10 by the finite element method, and FIG. 5B shows an analysis result of the vibration displacement in the Z′-axis direction by the finite element method. Note that the vertical axis in FIG. 5 represents the amount of vibration displacement as an arbitrary unit for comparison. Further, the horizontal axis indicates the length of the resonator element 10 in the X-axis direction or the Z′-axis direction.

In FIG. 5A, the curve represented by the solid line is the X-axis direction vibration displacement when the first protrusion 30 and the second protrusion 31 that are two rows of protrusions are provided on the resonator element 10. The curve shown represents the vibration displacement in the X-axis direction when no protrusion is provided on the resonator element 10.
According to this result, a favorable small vibration displacement is ensured on the holding portion side G of the resonator element 10. Further, the vibration displacement in the X-axis direction of the resonator element 10 is greater in the center of the resonator element 10 when the two rows of the first protrusions 30 and the second protrusions 31 are provided than when the protrusions are not provided. It becomes clear that the vibration region is widened. In addition, even when two rows of protrusions are formed on the vibrating piece in FIG. 3A, the vibration displacement at the center of the vibrating piece 10 is larger when the two rows of protrusions are formed. This is because the vibration piece 10 is provided with the first protrusion 30 and the second protrusion 31 so that the attenuation of the main vibration can be controlled gently, and the vibration attenuation does not disturb the main vibration, and a good vibration is made. Means that That is, this result is equivalent to increasing the effective area of the excitation electrode 20 and has the effect of lowering the CI value.
Conventionally, in order to reduce the CI value, a method of thickening the excitation electrode has been used. However, in this case, the effective excitation part due to energy confinement is narrowed, so the equivalent capacitance C ₁ is reduced and the frequency variable capacitance is reduced. There was a problem. According to the present embodiment, even if the thickness of the excitation electrode is increased, the CI value can be lowered without decreasing C ₁ due to the influence of the protrusion on the outer periphery, and the effect that the frequency variable amount is not lowered is produced.

Next, in FIG. 5B, the curve represented by the solid line is the vibration displacement in the Z′-axis direction when the first protrusion 30 and the second protrusion 31 that are two rows of protrusions are provided on the resonator element 10. Yes, the curve represented by the dotted line is the vibration displacement in the Z′-axis direction when no protrusion is provided on the resonator element 10.
According to this result, the vibration displacement of the vibrating piece 10 in the Z′-axis direction is more gentle in the case where the two first protrusions 30 and the second protrusions 31 are provided than in the case where the protrusions are not provided. And a good attenuation state can be secured. Further, even when one row of protrusions is formed on the vibrating piece of FIG. 3B, the vibration attenuation is more gentle when the two rows of protrusions are formed.
From the above, the vibration attenuation can be moderated by providing the two rows of the first protrusions 30 and the second protrusions 31 on the resonator element 10, and the vibration attenuation does not hinder the main vibration, and the vibration The vibration at the peripheral edge of the piece can be sufficiently damped. Furthermore, since the vibration displacement at the center of the resonator element 10 can be increased, the electrical characteristics of the resonator element can be improved.

  FIG. 6 shows the result of analyzing the vibration displacement of the vibrating piece by the finite element method when the protruding pieces having a thickness smaller than the excitation electrode are formed in two rows on the vibrating piece. 6A shows the analysis result of the vibration displacement in the X-axis direction of the resonator element 10 by the finite element method, and FIG. 6B shows the analysis result of the vibration displacement in the Z′-axis direction by the finite element method.

In FIG. 6A, the curve represented by the solid line is X in the case where the first protrusion 30 and the second protrusion 31 that are two rows of protrusions having a thickness smaller than that of the excitation electrode 20 are provided on the resonator element 10. This is the axial vibration displacement, and the curve represented by the dotted line is the vibration displacement in the X-axis direction when the first protrusion 30 and the second protrusion 31 in two rows having the same thickness as the excitation electrode 20 are provided on the resonator element 10. is there.
According to this result, by forming the two rows of the first protrusions 30 and the second protrusions 31 thinner than the thickness of the excitation electrode 20, vibration attenuation at the peripheral end of the resonator element 10 is significantly generated. You can see that

Next, in FIG. 6B, Z ′ in the case where the two lines of the first protrusions 30 and the second protrusions 31 in which the curve shown by the solid line is thinner than the excitation electrode 20 is provided on the resonator element 10. Z′-axis direction vibration displacement in the case where the first protrusion 30 and the second protrusion 31 in two rows having the same thickness as that of the excitation electrode 20 are provided on the vibration piece 10. It is.
Also from this result, the vibration attenuation at the peripheral end of the resonator element 10 is significantly generated by forming the two rows of the first protrusions 30 and the second protrusions 31 thinner than the thickness of the excitation electrode 20. I understand that.

  As described above, the thin projections 30 and 31 have a vibration damping effect when the projections 30 and 31 are thin, and the vibration piece 10 is provided with two rows of the first projections 30 and the second projections 31, and these projections are used as excitation electrodes. By forming it thinner than 20, the vibration at the peripheral end of the resonator element 10 can be sufficiently damped. Furthermore, since the vibration displacement at the center of the resonator element 10 can be increased, the electrical characteristics of the resonator element 10 can be improved.

From the above description of the first and second embodiments, the vibration piece 10 formed with the excitation electrode 20 is provided with a protrusion so as to surround the excitation electrode 20. The vibration at the peripheral edge of the piece 10 can be sufficiently damped. Furthermore, since the vibration region of the resonator element 10 can be widened, the electrical characteristics of the resonator element 10 can be improved.
Furthermore, if the thickness of the protrusion provided on the resonator element 10 is made thinner than the thickness of the excitation electrode 20, the vibration displacement at the periphery of the resonator element can be controlled to be small.

  In addition, when there are a plurality of protrusions formed on the resonator element, the attenuation of the main vibration propagation intensity depends on the propagation distance from Equations 1 to 4, and therefore, the interval between the protrusions is determined by the distance between the protrusions. It can be seen that the vibration attenuation is more effective when the electrodes are formed so as to gradually increase from the outer periphery of the excitation electrode toward the peripheral edge. Further, for the same reason, the width of the protrusion is more effective for damping vibration if it is formed so as to narrow toward the peripheral end of the resonator element.

  In the case of the protrusions formed in a plurality of rows on the resonator element, the thickness of the protrusions is gradually decreased from the outer periphery of the excitation electrode to the peripheral end, and the interval between the protrusions is set at the peripheral end of the resonator element. It is also possible to carry out a combination of forming the protrusions so that they are gradually widened and the widths of the protrusions are gradually narrowed toward the peripheral edge of the resonator element.

(Modification)
Considering the above, the arrangement and shape of the protrusions can be implemented in other forms as shown in FIGS. 7A, 7B, 7C, and 8, for example.
FIG. 7 is a schematic partial cross-sectional view showing another embodiment in the case where two rows of protrusions are provided on the resonator element as in the second embodiment.
An excitation electrode 20 is formed at the center of the resonator element 10, and a first protrusion 30 and a second protrusion 31 are formed so as to surround the excitation electrode 20 with an interval from the outer peripheral side. The excitation electrode 20, the first protrusion 30, and the second protrusion 31 are formed so as to face each other in the thickness direction of the resonator element 10.

In FIG. 7 (a), the thickness T ₂ of the first projection 30 is thinner than the thickness T ₁ of the excitation electrode 20, the thickness T ₃ of the second projection 31 has a thickness T ₂ of the first projection 30 (A relation of T ₁ > T ₂ > T ₃ ).
Further, the distance L ₂ between the first protrusion 30 and the second protrusion 31 is formed wider than the distance L ₁ between the excitation electrode 20 and the first protrusion 30 (relationship L ₁ <L ₂ ). .
Further, the width W ₂ of the second protrusion 31 is formed to be equal to the width W ₁ of the first protrusion 30 (relationship W ₁ ≈W ₂ ).

In FIG. 7B, the thickness T ₂ of the first protrusion 30 is thinner than the thickness T ₁ of the excitation electrode 20, and the thickness T ₃ of the second protrusion 31 is the thickness T of the first protrusion 30. It is formed thinner than ₂ (relationship T ₁ > T ₂ > T ₃ ).
Further, the distance L ₂ between the first protrusion 30 and the second protrusion 31 is formed to be equal to the distance L ₁ between the excitation electrode 20 and the first protrusion 30 (relationship L ₁ ≈L ₂ ). .
Further, the width W ₂ of the second protrusion 31 is formed narrower than the width W ₁ of the first protrusion 30 (relationship W ₁ > W ₂ ).

In FIG. 7C, the thickness T ₂ of the first protrusion 30 is thinner than the thickness T ₁ of the excitation electrode 20, and the thickness T ₃ of the second protrusion 31 is the thickness T of the first protrusion 30. ₂ (relationship T ₁ > T ₂ ≈T ₃ ).
Further, the distance L ₂ between the first protrusion 30 and the second protrusion 31 is formed wider than the distance L ₁ between the excitation electrode 20 and the first protrusion 30 (relationship L ₁ <L ₂ ). .
Further, the width W ₂ of the second protrusion 31 is formed narrower than the width W ₁ of the first protrusion 30 (relationship W ₁ > W ₂ ).

FIG. 8 is a schematic partial cross-sectional view showing an example in which three rows of protrusions are provided on the resonator element.
An excitation electrode 20 is formed at the center of the resonator element 10, and a first protrusion 30 is formed so as to surround the excitation electrode 20 with an interval from the outer peripheral side, and from the outer peripheral side of the first protrusion 30. A second protrusion 31 is formed so as to surround the excitation electrode 20. Further, a third protrusion 32 is formed so as to surround the excitation electrode 20 from the outer peripheral side of the second protrusion 31. The excitation electrode 20, the first protrusion 30, the second protrusion 31, and the third protrusion 32 are formed so as to face each other in the thickness direction of the resonator element 10.

The thickness T ₂ of the first protrusion 30 is thinner than the thickness T ₁ of the excitation electrode 20, and the thickness T ₃ of the second protrusion 31 is thinner than the thickness T ₂ of the first protrusion 30. . The thickness T ₄ of the third protrusion 32 is formed thinner than the thickness T ₃ of the second protrusion 31 (relationship T ₁ > T ₂ > T ₃ > T ₄ ).
Further, the distance L ₂ between the first protrusion 30 and the second protrusion 31 is formed wider than the distance L ₁ between the excitation electrode 20 and the first protrusion 30. The distance L ₃ between the second protrusion 31 and the third protrusion 32 is formed wider than the distance L ₂ between the first protrusion 30 and the second protrusion 31 (L ₁ <L ₂ < L ₃ the relationship).
Furthermore, the width W ₂ of the second projecting portion 31 is narrower than the width W ₁ of the first projection 30, the width W ₃ of the third projection 32 is narrower than the width W ₂ of the second projection 31 is _{(W 1> W 2> W} 3 the relationship).

Thus, in the arrangement and shape of the protrusions on the resonator element, the thickness of the protrusions, the interval between the protrusions, and the width of the protrusions can be combined without departing from the spirit of the present invention. It can be changed and implemented.
Further, the shape of the excitation electrode may be any shape, and the protrusion may be any shape. The protrusion may have a continuous shape or a discontinuous shape.

In this embodiment, the protrusion is formed on the vibrating piece with the same metal material as that of the excitation electrode. However, it may be formed with a metal different from that of the excitation electrode in a separate process.
Further, the protrusion may be formed of a nonconductive material such as SiO ₂ , TiO ₂ , ZnO, Al ₂ O ₃ or the like. By doing so, it is possible to prevent a short circuit between the protrusion and the conductive adhesive and a short circuit between the protrusion and the conductive adhesive when the vibration piece is fixed with the conductive adhesive in the manufacturing process.

  FIG. 9 is a schematic view showing an example of a piezoelectric vibrator using the piezoelectric vibrating piece of the present invention. 9A is a perspective view of the piezoelectric vibrator, and FIG. 9B is a cross-sectional view taken along the line BB in FIG.

  The piezoelectric vibrator 50 according to the present embodiment, for example, holds the piezoelectric vibrating piece 10 of the present invention in a ceramic container 51 with a conductive adhesive 52 and holds the upper surface of the container 51. It has the structure which has a cover body sealed to the inside of the container 51 in a vacuum or an inert gas atmosphere. In the piezoelectric vibrating piece 10, an excitation electrode 20 is formed at the center so as to face the thickness direction, and a connection electrode 21 extending from the excitation electrode 20 to the peripheral end of the piezoelectric vibrating piece 10 is formed. The first protrusion 30 and the second protrusion 31 are formed so as to face each other in the thickness direction so as to surround the excitation electrode 20 of the piezoelectric vibrating piece 10. The piezoelectric vibrating piece 10 is fixedly held by the conductive adhesive 52 in the holding portion 53 of the storage container 51 and is electrically connected to the excitation electrode 20 and the wiring (not shown) of the storage container 51.

  Thus, by forming the protrusions 30 and 31 so as to surround the excitation electrode 20 of the piezoelectric vibrating piece 10, the vibration at the end of the piezoelectric vibrating piece 10 is sufficiently damped. Even if the end portion is fixed and held via the conductive adhesive 52, leakage of vibration from the piezoelectric vibrating piece 10 to the holding portion 53 can be reduced, and main vibration is not hindered. In addition, by providing a plurality of protrusions on the piezoelectric vibrating piece 10, the damping can be further moderated near the main vibration, and the inhibition of the main vibration can be reduced. Thus, the piezoelectric vibrator 50 of the present embodiment can bring out the effect of forming the protrusions 30 and 31 on the main surface of the piezoelectric vibrating piece 10 and can provide the piezoelectric vibrator 50 with excellent electrical characteristics.

FIG. 10 is a schematic view of a piezoelectric oscillator using the piezoelectric vibrating piece of the present invention. 10A is a perspective view of the piezoelectric oscillator, and FIG. 10B is a cross-sectional view taken along the line C-C in FIG.

The piezoelectric oscillator 70 of the present embodiment is a circuit unit for fixing and holding the piezoelectric vibrating piece 10 of the present invention to a ceramic container 71 with a conductive adhesive 72, and for oscillating the piezoelectric vibrating piece. 74 is fixed and has a structure that is not shown, but has a lid that is joined to the upper surface of the container 71 and hermetically seals the container 71 in a vacuum or an inert gas atmosphere.
In the piezoelectric vibrator 10, an excitation electrode 20 is formed at the center so as to face the thickness direction, and a connection electrode 21 extending from the excitation electrode 20 to the peripheral end of the piezoelectric vibrator 10 is formed. The first protrusion 30 and the second protrusion 31 are formed so as to face each other in the thickness direction so as to surround the excitation electrode 20 of the piezoelectric vibrating piece 10. The piezoelectric vibrating piece 10 is fixedly held by the conductive adhesive 72 in the holding portion 73 of the storage container 71 and is electrically connected to the excitation electrode 20, the wiring (not shown) of the storage container 71, and the circuit portion 74.

  Thus, by forming the protrusions 30 and 31 so as to surround the excitation electrode 20 of the piezoelectric vibrating piece 10, the vibration at the end of the piezoelectric vibrating piece 10 is sufficiently damped. Even if the end portion is fixedly held via the conductive adhesive 72, leakage of vibration from the piezoelectric vibrating piece 10 to the holding portion 73 can be reduced, and main vibration is not hindered. In addition, by providing a plurality of protrusions on the piezoelectric vibrating piece 10, the damping can be further moderated near the main vibration, and inhibition of the main vibration can be reduced. As described above, the piezoelectric oscillator 70 according to the present embodiment can provide the piezoelectric oscillator 70 having excellent electrical characteristics by extracting the effect of forming the protrusions 30 and 31 on the main surface of the piezoelectric vibrating piece 10.

In addition, this invention is not limited to forming the protrusion surrounding the excitation electrode of a vibration piece, You may form a protrusion so that it may oppose on both sides of the longitudinal direction of a vibration piece on both sides of an excitation electrode. In other words, the configuration may be such that there are no protrusions facing each other across the excitation electrode on both sides in the short direction of the resonator element.
In addition, protrusions may be formed on both sides of the resonator element in the short direction so as to face each other with the excitation electrode interposed therebetween. In other words, a configuration may be employed in which there are no protrusions facing each other across the excitation electrode on both sides in the longitudinal direction of the resonator element.

Schematic explaining the shape and crystal axis of the resonator element used in this example. FIG. 3 is a schematic diagram of a resonator element illustrating Example 1 of the invention. The displacement distribution map of the analysis by the finite element method which shows the damping state of thickness shear vibration. FIG. 6 is a schematic diagram of a resonator element for explaining Example 2 of the invention. The displacement distribution map of the analysis by the finite element method which shows the damping state of thickness shear vibration. The displacement distribution map of the analysis by the finite element method which shows the damping state of thickness shear vibration. FIG. 9 is a schematic partial cross-sectional view showing another embodiment when two rows of protrusions are provided on the resonator element. FIG. 6 is a schematic partial cross-sectional view showing an example in which three rows of protrusions are provided on a vibrating piece. The schematic diagram of the piezoelectric vibrator in the present invention. The schematic diagram of the piezoelectric oscillator in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Vibrating piece as a piezoelectric vibrating piece, 11 ... Main surface, 20 ... Excitation electrode, 21 ... Connection electrode, 30 ... 1st protrusion as a protrusion, 31 ... 2nd protrusion as a protrusion, 32 ... Projection Third protrusion as a part, 50... Piezoelectric vibrator, 70... Piezoelectric oscillator, T ₁ ... Thickness of excitation electrode, T ₂ ... Thickness of first protrusion, T ₃ . T ₄ ... thickness of the third protrusion, L ₁ ... distance between the excitation electrode and the first protrusion, L ₂ ... distance between the first protrusion and the second protrusion, L ₃ ... second protrusion and third protrusion The interval between the parts, W ₁ ... the width of the first protrusion, W ₂ ... the width of the second protrusion, W ₃ ... the width of the third protrusion.

Claims (12)

  A piezoelectric vibrating piece having thickness shear vibration as a main vibration, which is formed of a pair of main surfaces opposed to each other in the thickness direction, and connected to the excitation electrode and extended to a peripheral end of the piezoelectric vibrating piece The connection electrode is formed so as to face at least one main surface with the outer peripheral portion of the excitation electrode interposed therebetween or to surround the excitation electrode, and is formed to have the same thickness or a thin thickness as the excitation electrode A piezoelectric vibrating piece comprising a protrusion.   The piezoelectric vibrating piece according to claim 1, wherein the protrusion is made of the same material as the excitation electrode.   3. The piezoelectric vibrating piece according to claim 1, wherein the protrusions are provided in a plurality of rows at intervals from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece. .   4. The piezoelectric vibrating piece according to claim 3, wherein the thickness of the protrusion is formed so as to become gradually thinner from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece.   4. The piezoelectric vibrating piece according to claim 3, wherein an interval for forming the protrusions is formed so as to gradually increase from an outer peripheral portion of the excitation electrode toward a peripheral end portion of the piezoelectric vibrating piece. .   4. The piezoelectric vibrating piece according to claim 3, wherein a width of the projecting portion is formed so as to be gradually reduced from an outer peripheral portion of the excitation electrode toward a peripheral end portion of the piezoelectric vibrating piece.   4. The piezoelectric vibrating piece according to claim 3, wherein the thickness of the protruding portion is formed so as to be gradually decreased from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece, and further, the protruding portion is formed. A piezoelectric vibrating piece characterized in that the interval is formed so as to increase gradually from the outer periphery of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece.   4. The piezoelectric vibrating piece according to claim 3, wherein the thickness of the protrusion gradually decreases from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the width of the protrusion is further reduced. A piezoelectric vibrating piece, wherein the piezoelectric vibrating piece is formed so as to become narrower sequentially from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece.   4. The piezoelectric vibrating piece according to claim 3, wherein an interval at which the protrusion is formed is formed so as to gradually increase from the outer peripheral portion of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the width of the protruding portion. Is formed so as to become narrower sequentially from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece.   The piezoelectric vibrating piece according to claim 3, wherein the thickness of the protrusion is formed so as to gradually decrease from the outer peripheral portion of the excitation electrode toward the peripheral end portion of the piezoelectric vibrating piece, and an interval between the protrusions is formed. It is formed so as to gradually increase from the outer periphery of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece, and the width of the protrusion gradually decreases from the outer periphery of the excitation electrode toward the peripheral end of the piezoelectric vibrating piece. The piezoelectric vibrating piece is formed so as to be.   11. A piezoelectric device comprising: the piezoelectric vibrating piece according to claim 1; and a holding portion that holds the piezoelectric vibrating piece in an electrically connected state at an end thereof. Vibrator. 11. The piezoelectric vibrating piece according to claim 1, a circuit unit for oscillating the piezoelectric vibrating piece, an end portion of the piezoelectric vibrating piece being fixedly held, and the piezoelectric vibrating piece and the circuit A piezoelectric oscillator comprising: a holding portion that electrically connects the portion.

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