JP2005123828A - Tuning-fork piezo-electric oscillation piece and piezo-electric device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optimum channel structure which can realize simultaneously with a sufficient balance between a high performance by suppressing a fundamental wave CI value and a high stability assured 1.0 or more CI value ratio (harmonic CI value/fundamental wave CI value) in a tuning-fork piezo-electric oscillation piece of oscillating arm structure with channels which are further size-reduced. <P>SOLUTION: In the tuning-fork piezo-electric oscillation piece 10, a length L1 of channels 14, 15 provided on a main surface is set to 0.7L0 to a length L0 of oscillating arms 12, 13 which are extended from a base 11, and first electrodes 16a, 17a of a drive electrode of the main surface side are formed in the full length of the channels. Second electrodes 16b, 17b of drive electrodes of a side face side are formed on each side face of the oscillating arms. When a predetermined AC voltage is applied to these drive electrodes, stable oscillating characteristics are obtained by eliminating an influence of secondary harmonic waves. Furthermore, the length of the base can be shortened, and the size can be reduced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a piezoelectric device such as a piezoelectric vibrator and a piezoelectric oscillator widely used in various electronic devices, and a piezoelectric vibration gyro used as an angular velocity sensor. More specifically, the present invention relates to a tuning-fork type piezoelectric vibrating piece used for them. .

  2. Description of the Related Art In recent years, piezoelectric devices are required to be further miniaturized along with miniaturization of electronic devices on which they are mounted, and are also required to have high quality and high stability ensuring a low CI (crystal impedance) value. . In order to keep the CI value low, a tuning fork type piezoelectric vibrating piece having a structure in which grooves are provided on the front and back main surfaces of a vibrating arm has been developed (see, for example, Patent Documents 1 and 2). The tuning-fork type piezoelectric vibrating piece having the grooved vibrating arm structure includes a first electrode formed on the side and bottom surfaces of the groove extending linearly along the longitudinal direction on each main surface of the vibrating arm, A drive electrode is constituted by the second electrode formed on each side surface, and when an AC voltage is applied thereto, an electric field parallel to each main surface is generated between the adjacent first electrode and the second electrode. The efficiency is greatly improved, and the CI value can be suppressed low.

  In addition, the tuning fork type piezoelectric resonator element oscillates a signal at the target fundamental frequency due to the vibration, and at the same time, oscillates a similar signal even at a harmonic frequency that is undesirable for the operation of a device such as a vibrator. There is. As a method for preventing the influence of harmonics, a method of designing a tuning fork type piezoelectric vibrating piece based on the CI value ratio (harmonic CI value / fundamental CI value) is known. When the harmonic CI value is larger than the fundamental CI value, that is, when the CI value ratio is 1.0 or more, harmonics are hardly generated. In order to make the CI value ratio 1.0 or more, the length of the drive electrode on the main surface side formed in the groove of the vibrating arm is set to 50% (0.5 L) with respect to the length (L) of the vibrating arm. It is known that it may be set. However, in general, when the harmonic CI value is raised, the fundamental wave CI value is also increased. As the length of the drive electrode on the main surface side is increased, the fundamental wave CI value is lowered, but at the same time the CI value ratio is 1. Since it tends to approach 0, it is not easy to make this 1.0 or more.

  Therefore, the applicant of the present application has a vibrating arm having such a grooved structure, and maintains the CI value ratio constant while keeping the CI value of the fundamental wave low. A tuning fork-type piezoelectric vibrating piece has been proposed (see Patent Document 3) in which the variation in CI value can be reduced, and the entire vibrating piece can be reduced in size. As illustrated in FIGS. 7 and 8, the tuning fork type piezoelectric vibrating piece includes grooves 4 and 5 on the main surfaces of the front and back surfaces of the pair of vibrating arms 2 and 3 protruding from the base 1, and the length of the vibrating arms. (L) is formed with a length of 70% (0.7L), and the drive electrodes 6a and 7a on the main surface side of the groove are 50% with respect to the length (L) of the vibrating arm. The drive electrodes 6b and 7b on the side surface side are formed on the side surfaces of the vibrating arms 2 and 3, respectively. By setting the lengths of the grooves 4 and 5 in this way, the CI value of the fundamental wave can be suppressed to a low level, and by providing the drive electrodes 6a and 7a on the main surface side at such a ratio, the CI value ratio is 1. Since it becomes 0 or more and it becomes difficult to oscillate erroneously with harmonics, a high-performance vibrating piece can be obtained.

  Further, a tuning fork type piezoelectric vibrating piece that is fixedly supported in a cantilever manner at the base generally has a possibility that the CI value will not be stable and the performance may be lowered unless the length of the base is secured to 40% or more of the length of the vibrating arm. There is. This is because if the length of the vibrating arm is shortened and the width is narrowed, the vibration of the vibrating arm includes a vertical component, and if the vertical vibration leaks to the base of the vibrating piece, Since energy escapes from the fixed region to the package and the vibration becomes unstable, this has been an obstacle to downsizing the resonator element.

  Therefore, the applicant of the present invention has a structure in which cut portions are provided at positions ahead of the fixing region on both sides of the base portion of the tuning fork type piezoelectric vibrating piece so as not to inhibit the vibration of the vibrating arm or affect the fixing to the package. (See also Patent Document 3). Even if the vibration of the vertical component of the vibrating arm leaks to the base, it is difficult for the notch to propagate backward to the fixed area of the base, and therefore it is difficult for energy to escape. It is possible to effectively prevent variation and increase in CI values.

JP-A-56-65517 No. 00-44092 JP 2002-280870 A

  However, the current tuning fork type piezoelectric vibrator is required to be further reduced in size, and accordingly, the second harmonic is strongly acting on the vibration of the vibrating piece due to the support structure of the vibrating piece. There is. The resonating arm usually vibrates in a plane including its main surface, but the CI value of the second harmonic changes in relation to the rigidity of the resonating arm. For example, in this tuning-fork type crystal vibrating piece with a grooved vibrating arm structure, when the fundamental wave is 32.768 kHz, the second harmonic exists at about 250 kHz, and the length of the groove with respect to the length of the vibrating arm is 1300 μm. Is set to 1000 μm, the CI value of the second harmonic is about 10 kΩ, which is smaller than the CI value of the fundamental wave of about 50 kΩ. When the drive voltage (excitation level) is increased by changing the supply voltage to the tuning-fork type crystal vibrating piece, the second harmonic acts on the vibrating piece that has normally vibrated with the fundamental wave, and parametric excitation, that is, intermittent. Abnormal oscillation occurs and the vibration becomes unstable.

  FIG. 13 shows the relationship between the fundamental wave CI value and the CI value ratio in relation to the ratio of the electrode length to the length of the vibrating arm, and the drive (excitation) electrode length varies in FIG. The shorter the length of the arm, the higher the fundamental CI value, and thus the CI value ratio, and conversely, the longer the length of the excitation electrode, the greater the fundamental CI value. The CI value ratio also tends to approach 1.0 at the same time as it falls. However, in the figure, the ratio of the electrode length is limited to the range of 45 to 55%, and the tendency in other ranges is not clear. Similarly, in the above-mentioned Patent Document 3, FIG. 3 showing the relationship between the fundamental wave CI value and the groove length only shows a range where the groove length / tuning fork length (%) is up to 70%.

  Further, in the structure proposed in Patent Document 3, the length of the base portion relative to the vibrating arm is at most about 34%, and on the contrary, it is limited to the presence of the cut portion, making it difficult to further reduce the length of the base portion. ing.

  The present invention has been made in view of the above-described conventional problems, and its purpose is based on the premise that the tuning-fork type piezoelectric vibrating piece having the grooved vibrating arm structure is further miniaturized. Analyzing the relationship between the groove length and electrode length and the fundamental and harmonic (especially second-order) CI values over a wider range and lowering the fundamental CI value to improve performance At the same time, it is to provide an optimum groove structure capable of realizing high stability by increasing the harmonic CI value and maintaining the CI value ratio at 1.0 or more.

  Another object of the present invention is to provide a high-quality and high-stability piezoelectric device using such a tuning-fork type piezoelectric vibrating piece.

  The inventor of the present application has a 1.300 mm (about 80%) shorter than the 1.644 mm in which the length of the vibrating arm of the tuning fork type crystal vibrating piece having the grooved vibrating arm structure is “short” in Patent Document 3 above. ) And the drive electrode on the main surface side is provided over the entire length of the groove of the vibrating arm, the change in the fundamental wave CI value with respect to the groove length (= electrode length) is expressed as: groove length / vibrating arm Analysis was performed over a range of length ratios of about 50-100%. FIG. 1 shows the fundamental wave CI value obtained by the FEM (finite element method) analysis and experiment. The fundamental CI value decreases as the groove length (= electrode length) increases, and the amount of change decreases as the groove length approaches 50% of the vibration arm length. .

  Furthermore, the inventor of the present application analyzed the relationship between the fundamental wave CI value and the second harmonic CI value related to the groove length over a range of the groove length / vibrating arm length ratio of about 60 to 80%. FIG. 2 shows the result of the FEM analysis. When the groove length (= electrode length) exceeds about 70% of the length of the vibrating arm, the fundamental CI value becomes larger than the second harmonic CI value, and the CI value ratio is 1.0 or less. I understand that

From the analysis results of FIG. 1 and FIG. 2, the following determination is made.
(1) If the groove length (= electrode length) is about 70% or less with respect to the length of the vibrating arm, the CI value of the fundamental wave can be suppressed sufficiently low.
(2) Actually, considering that there is some variation in the CI value of the fundamental wave for each resonator element, if the second harmonic CI value is 100 kΩ or more, a CI of 1.0 or more A value ratio can be secured.

  The present invention has been made based on such knowledge, and according to one aspect thereof, a base, a pair of vibrating arms extending from the base, and first and second main surfaces of each vibrating arm are provided. A driving electrode comprising the electrode and a second electrode provided on the side surface thereof, and a groove extending along the longitudinal direction from the base side end of the vibrating arm on at least one main surface of the vibrating arm; A tuning-fork type piezoelectric element in which the length L1 is 0.7L0 with respect to the length L0 of the vibrating arm and the first electrode provided on the at least one main surface is formed on the inner surface of the groove portion over the entire length thereof. A vibrating piece is provided. As the piezoelectric material, quartz that has been generally employed is preferable.

  As can be seen from the above analysis result, by setting the length of the groove and the length of the drive electrode with respect to the length of the vibrating arm in this way, the tuning-fork type piezoelectric vibrating piece can be further reduced in size, and the fundamental wave CI It is possible to obtain an optimum groove structure capable of simultaneously realizing a high performance by suppressing the value and a high stability by securing a CI value ratio of 1.0 or more in a balanced manner.

  Furthermore, according to the tuning-fork type piezoelectric vibrating piece of the present invention, even if the base portion is not provided with a notch, unstable vibration due to leakage of vibration energy from the fixed region of the base portion to the package side is eliminated, and the length of the vibrating arm is reduced. It has been found that the length of the base relative to the thickness can be further reduced. In one embodiment, the base length Lb can be set to 0.2 to 0.25L0 with respect to the vibrating arm length L0, thereby making it possible to further reduce the size of the tuning fork type piezoelectric vibrating piece. It is.

  In another embodiment, the tuning fork type piezoelectric vibrating piece further includes another pair of vibrating arms extending in a direction opposite to the pair of vibrating pieces from a base, so that the tuning fork type piezoelectric vibrating piece is used in a piezoelectric vibrating gyroscope. Can do.

  According to another aspect of the present invention, a piezoelectric device comprising the above-described tuning-fork type piezoelectric vibrating piece of the present invention, and a package that fixes and supports the tuning-fork type piezoelectric vibrating piece at its base and seals the inside. A piezoelectric device in which an IC element is further mounted on the package is provided.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 3 schematically shows a preferred embodiment of a tuning-fork type crystal vibrating piece to which the present invention is applied. The tuning fork type crystal vibrating piece 10 has a pair of vibrating arms 12 and 13 extending in parallel upward from the base 11 in the figure, and the main surfaces of the front and back surfaces are respectively from the base side end, that is, the tuning fork crotch. Linear grooves 14 and 15 extending in the longitudinal direction toward the distal end are formed.

  As shown well in FIG. 4, the grooves 14, 15 are formed with first electrodes 16 a, 17 a made of electrode films formed on the side surfaces and the bottom surface, and the side surfaces of the vibrating arms 12, 13 are the first electrodes 16 a, 17 a. Two electrodes 16b and 17b are formed, and the first electrode 16a (17a) of one vibrating arm is electrically connected to the second electrode 17b (16b) of the other vibrating arm, and a tuning fork type crystal vibrating piece is formed. The drive electrode which vibrates 10 is comprised. As will be described later, the base 11 is provided with connection electrodes 18 and 19 drawn from the drive electrodes for connection to the package side. When a predetermined AC voltage is applied from the connection terminals 18 and 19 to the drive electrode, an electric field is alternately generated in the opposite direction between the adjacent first electrodes 16a and 17a and the second electrodes 16b and 17b. Repeatedly perform bending motions in opposite directions.

  In this embodiment, the length L1 of the grooves 14 and 15 is set to 70% or 0.7L0 with respect to the length L0 of the vibrating arms 12 and 13. The first electrodes 16a and 17a are formed over the entire length of the grooves 14 and 15, and their length L2 is made equal to the length L1 of the groove.

  In one embodiment, the length L0 of the vibrating arm is set to 1.300 mm, the length L1 of the groove = the length L2 of the first electrodes 16a and 17a is set to 0.9 mm (= 0.69L0). When a predetermined alternating voltage is applied to the tuning-fork type crystal vibrating piece and vibrated, as described above with reference to FIGS. 1 and 2, the fundamental wave CI value is suppressed to a low level, and at the same time, the second harmonic. It was possible to secure a CI value ratio of 1.0 or more by making the CI value larger than the fundamental wave CI value.

  Moreover, in this embodiment, the base length Lb is 0.28 mm and is set to Lb = 0.21L0 (about 21%) with respect to the length of the vibrating arm, but the operation of the tuning-fork type crystal vibrating piece is stable. Therefore, unstable vibration due to leakage of vibration energy from the fixed region of the base portion to the package side was not recognized.

  In another embodiment, the length L0 of the vibrating arm is 1.040 mm, the length L1 of the groove = the length L2 of the first electrodes 16a and 17a is 0.73 mm (= 0.70L0), and the base length Lb is It was set to 0.26 mm (= 0.25 L0). Also in this example, the fundamental wave CI value was similarly suppressed to a low value, a CI value ratio of 1.0 or more was secured, and a stable operation of the tuning-fork type crystal vibrating piece was obtained.

  FIG. 5 schematically shows the structure of the crystal resonator of the present invention using the tuning-fork type crystal vibrating piece of FIG. The crystal resonator 20 includes a package 23 including a base 21 and a lid 22 each having a substantially rectangular box shape in which a plurality of ceramic thin plates are stacked, and the tuning fork crystal resonator element 10 is hermetically sealed therein. The tuning fork type crystal vibrating piece 10 is cantilevered substantially at the bottom of the space inside the base 21 by connecting the connection electrodes 18 and 19 of the base 11 to the corresponding connection terminals 24 on the bottom of the base 21 with a conductive adhesive 25. Supported and electrically connected. A rectangular thin plate lid 22 made of an insulating material such as glass or ceramics is hermetically bonded to the upper end surface of the base 21 with low melting point glass.

  In another embodiment, a piezoelectric device such as a piezoelectric oscillator or a real-time clock can be configured by further mounting an IC constituting a driving circuit of a tuning fork type crystal vibrating piece in a package similar to FIG. it can.

  In another embodiment, another pair of vibrating arms extending from the base 11 of the tuning fork type crystal vibrating piece 10 in the direction opposite to the vibrating arms 12 and 13 can be further provided. FIG. 6 shows such a tuning-fork type piezoelectric vibrating piece 26. The same pair of vibrating arms 12 and 13 as the piezoelectric vibrating piece 10 of FIG. 3 extend from the central base 27 to one side. A pair of detection arms 28 and 29 extend on the opposite side. As described above with reference to FIG. 3, the vibrating arms 12 and 13 are provided with drive electrodes, and the detection arms 28 and 29 are provided with two pairs of detection electrodes 30a and 30b on their side surfaces. The piezoelectric vibrating piece 26 is mounted in a predetermined package (not shown) by bonding and fixing support portions 31a and 31b provided on the base 27, and a piezoelectric vibration gyro used as an angular velocity sensor or a rotation sensor is mounted. Constitute.

  The vibrating arms 12 and 13 bend and vibrate in opposite directions when a predetermined AC voltage is applied to the drive electrode via an electrode pad 32 provided on one support portion 31a. In this state, when the tuning fork type crystal vibrating piece 26 rotates around the Y axis 33 in the figure, the Coriolis force acts in the direction perpendicular to the vibration direction with respect to the rotational angular velocity, and the vibrating arms 12 and 13 vibrate in the Z direction. To do. This vibration is transmitted through the base 27 and vibrates the detection arms 28 and 29 in the Z direction at the resonance frequency, and this is detected as an electric signal from the electrode pad 34 provided on the other support 31b. Then, the rotational angular velocity of the tuning fork type crystal vibrating piece 26 and the rotational direction thereof are obtained.

  The preferred embodiments of the present invention have been described in detail above. However, as will be apparent to those skilled in the art, the present invention can be carried out with various modifications and changes made to the above embodiments within the technical scope thereof. . For example, the tuning fork type piezoelectric vibrating piece of the present invention can use various piezoelectric single crystal materials such as lithium niobate in addition to quartz.

The diagram which shows the change of the fundamental wave CI value regarding a groove length / vibration arm length in the tuning fork type crystal vibrating piece of a vibration arm structure with a groove | channel. The diagram which shows the change of CI value of the fundamental wave regarding a groove length / vibration arm length, and the 2nd harmonic in the tuning fork type crystal vibrating piece of a grooved vibration arm structure. 1 is a plan view of a preferred embodiment of a tuning fork type crystal vibrating piece according to the present invention. Sectional drawing of the vibrating arm in the IV-IV line of FIG. FIG. 4 is a longitudinal sectional view of a crystal resonator using the tuning fork type crystal vibrating piece of FIG. 3. The top view of another Example of the tuning fork type crystal vibrating piece by this invention. The top view of the tuning fork type crystal vibrating piece which has the vibration arm of the conventional grooved structure. Sectional drawing of the vibrating arm in the VIII-VIII line of FIG.

Explanation of symbols

1, 11, 27 ... base, 2, 3, 12, 13 ... vibrating arm, 4, 5, 14, 15 ... groove, 6a, 7a, 16a, 17a ... first electrode, 6b, 7b, 16b, 17b ... first 2 electrodes, 10, 26 ... tuning fork type crystal vibrating piece, 18, 19 ... connection electrode, 20 ... crystal resonator, 21 ... base, 22 ... lid, 23 ... package, 24 ... connection terminal, 25 ... conductive adhesive, 28, 29 ... detection arm, 30a, 30b ... detection electrode, 31a, 31b ... support part, 32, 34 ... electrode pad, 33 ... Y axis.

Claims (4)

A base, a pair of resonating arms extending from the base, a drive electrode comprising a first electrode provided on the front and back main surfaces of each resonating arm and a second electrode provided on the side thereof, and at least the resonating arm One of the main surfaces has a groove extending along the longitudinal direction from the base side end of the vibrating arm, and the length L1 of the groove is 0.7L0 with respect to the length L0 of the vibrating arm. The tuning fork type piezoelectric vibrating piece is characterized in that the first electrode provided on the at least one main surface is formed on the inner surface of the groove portion over the entire length thereof. 2. A tuning-fork type piezoelectric vibrating piece according to claim 1, wherein a length Lb of the base portion is 0.2 to 0.25L0 with respect to a length L0 of the vibrating arm. The tuning fork type piezoelectric vibrating piece according to claim 1, further comprising another pair of vibrating arms extending from the base portion in a direction opposite to the pair of vibrating pieces. 4. A piezoelectric device comprising: the tuning fork type piezoelectric vibrating piece according to claim 1; and a package for fixing and supporting the tuning fork type piezoelectric vibrating piece at the base portion and sealing the inside thereof.

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