JP2008209215A - Angular velocity sensor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an angular velocity sensor element in which the suppression of diagonal vibration is facilitated to maintain mechanical strength and CI. <P>SOLUTION: The angular velocity sensor element includes a tuning fork-shaped crystal piece, having a pair of tuning fork arms extended from a tuning fork base part; drive electrodes driving tuning fork vibration in a width direction of the tuning fork arms; and sensor electrodes detecting a charge generated due to perpendicular vibration to be in the thickness direction of the tuning fork arms, wherein a cut part preventing the diagonal vibration of the pair of tuning fork arms is provided by a laser in the length direction, with respect to a root part of the tuning fork arms as one of both end sides in the width direction in major surfaces of the tuning fork arms, the cut part comprises a plurality of minute cut parts formed by an ultra-short pulse laser which is irradiated from a femtosecond laser, which sequentially incident thereon along the length direction of the tuning fork arms diagonal to the ridge line parts of the tuning fork arms and which exits therefrom, while cutting the ridge line parts. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an angular velocity sensor element using a tuning-fork type crystal resonator, and more particularly to an angular velocity sensor element that facilitates suppression of oblique vibration and improves angular velocity detection sensitivity.

(Background of the Invention)
The angular velocity sensor element is applied to a vehicle guidance device (car navigation system), camera shake prevention, and the like, and the demand is increasing. One such example is one in which two tuning-fork crystal pieces by the present applicant are bonded together by direct bonding (Patent Document 1).

(Example of conventional technology)
4A and 4B are diagrams for explaining a conventional example. FIG. 4A is an external view of an angular velocity sensor element, and FIG. 4B is a top view showing a connection relationship.

  The angular velocity sensor element includes a tuning-fork crystal piece 3 having a Z-cut shape having a tuning-fork base 1 and a pair of tuning-fork arms 2 (ab) extending therefrom. The tuning fork-shaped crystal piece 3 is formed by directly joining two crystal pieces 3 (ab) in which the ± direction of the X axis in the crystal axis (XYZ) is reversed. These are formed by directly joining two quartz wafers and then etching using photolithography.

  A pair of tuning fork arms 2 (ab) of the tuning fork crystal piece 3 has a drive electrode D, a sensor electrode S, and a monitor electrode M. The drive electrode D is on both main surfaces (D ±) of one tuning fork arm 2a and the other main surface (D−) of the other tuning fork arm 2b, and the sensor electrode S is the inner surface (S− of each tuning fork arm 2 (ab). ) And the outer surface (S +), the monitor electrode M is formed on one main surface of the other tuning fork arm 2b.

  The drive electrodes D− and the sensor electrodes S ± of the same sign in each tuning fork arm 2 (ab) are connected by a wiring path on the surface of the tuning fork not shown. The drive electrode D ± is connected to an oscillation circuit (not shown) and an alternating voltage is applied. The drive electrode (D ±) excites tuning fork vibration (horizontal vibration) in the width direction of the tuning fork arm 2 (ab) by an electric field indicated by a solid line between the drive electrode (D ±) and the sensor electrode S (±).

The sensor electrode S ± is connected to a charge detection circuit (not shown) and set to a reference potential E. Then, an electric charge based on an electric field indicated by a dotted line generated by vertical vibrations (displacements in the vertical direction with respect to the plate surface) in opposite directions that are the thickness direction of the tuning fork arm 2 (ab) due to the Coriolis force is detected. Since the two crystal pieces 3 (ab) by direct bonding have the opposite directions of the ± direction of the X axis, charges of the same sign are generated on the inner side surface and the outer side surface of each tuning fork arm 2 (ab).
Japanese Patent Laying-Open No. 2005-241606, “FIG. 4 (ab)” Japanese Patent Laying-Open No. 2004-93158, “FIG. 3” Japanese Patent Application No. 2006-79442

(Problems of conventional technology)
However, in the angular velocity sensor element having the above-described configuration, the width and thickness are made equal in order to increase the detection sensitivity of the angular velocity by bringing the drive frequency and the sensor frequency close to each other, and for example, each produced from the point of manufacture using etching Due to the asymmetry of the mass between the tuning fork arm and each tuning fork arm, the tuning fork vibration not only includes the horizontal component “arrow A direction in FIG. 5” but also the diagonal component “same arrow C direction” including the vertical component “same arrow B direction”. Direction ".

  When the two crystal pieces 3 (ab) are directly connected, they protrude from the + X-axis surface of each crystal piece (ab), that is, in the diagonal direction of 2 (ab) of each tuning fork arm due to etching anisotropy. 5 (FIG. 6), it is particularly easy to cause oblique vibration. In this case, even if the mass distribution is uniform with respect to the horizontal and vertical centerlines AA and BB of each tuning fork arm 2 (ab), the mass distribution in the diagonal directions opposite to each other is The upward direction is larger than the downward right direction. Therefore, in this case, the vibration is oblique in the upward direction with a large mass distribution.

  For this reason, for example, Patent Document 2 discloses that a laser is applied to the root portion of the tuning fork arm 2 to provide a cutting portion 4 at a corner portion, thereby achieving a mass balance between the pair of tuning fork arms. In this case, the root portion is irradiated with a plurality of lasers from different angles, and cutting is performed according to the amount of the combined portion. The energy that cannot be cut by each single laser is not damaged except for the necessary portion.

  However, with a normal carbon dioxide laser or the like, the beam diameter becomes as large as 100 μm, for example, even if a condensing lens is used, and it becomes difficult to cut locally, so that the corners of the tuning fork arm are cut entirely. Become. For this reason, even if the mass balance that suppresses the oblique vibration by adjusting the root portion by the laser is taken, there is a possibility that the mechanical strength, for example, the drive electrode is damaged and the crystal impedance (CI) is damaged. This becomes more influential as the miniaturization progresses.

(Object of invention)
An object of the present invention is to provide an angular velocity sensor element that facilitates suppression of oblique vibration and maintains mechanical strength and CI.

(Points of interest and prior application)
The present invention focuses on femtosecond lasers having a small beam diameter and large energy, and in the previous application (Patent Document 3), the femtoseconds are applied to the main surface of the edge in the width direction at the root of the tuning fork arm. A configuration in which a circular or arc-shaped hole is provided by irradiating an ultrashort pulse laser from a vertical direction by a laser.

  A femtosecond laser (ultrashort pulse laser) generates a laser having an extremely short pulse signal in units of several femtoseconds (one femto is one thousandth of a trillion). Therefore, the beam diameter is as small as about 3 to 50 μm, the energy is concentrated in a very short time, and the output level is very large. Thereby, the cutting of the minute hole in the cutting part (root part) is facilitated. In addition, because of the ultrashort pulse, there is virtually no thermal effect on the crystal, so there is very little risk of twinning.

  In addition, compared with a laser based on analog time control, the cutting portion of the tuning fork base can be irradiated accurately (pinpoint), and therefore it is easy to suppress oblique vibrations by controlling the number of irradiations, not the time.

(Problems of prior application)
In this case, if the output of the femtosecond laser is reduced, it takes too much cutting time, and if the output is increased, the energy of the ultrashort pulse laser is concentrated (residual) on the bottom surface of the hole. For this reason, there has been a problem that damage such as cracks occurs on the bottom surface of the hole or the crystal structure itself is easily destroyed.

(Solution)
A sensor comprising a tuning fork crystal piece in which a pair of tuning fork arms extends from a tuning fork base, and a drive electrode for driving tuning fork vibration in the width direction of the tuning fork arm, and a sensor for detecting charges due to vertical vibration in the thickness direction of the tuning fork arm A cutting portion that has an electrode and prevents oblique vibration of the pair of tuning fork arms is at least one of both end sides in the width direction of the main surface of the tuning fork arm, and the length direction with respect to the root portion of the tuning fork arm In the angular velocity sensor element provided by the laser, the cutting portion is formed by an ultrashort pulse laser irradiated from a femtosecond laser, and the ultrashort pulse laser is obliquely crossed on the ridge line portion of the tuning fork arm to form the tuning fork. It is configured to include a plurality of minute cutting portions that are sequentially incident along the length direction of the arm and are emitted while cutting the ridge line portion.

  With such a configuration, the mass distribution can be varied and the oblique vibration can be suppressed by the plurality of micro-cut portions provided at the root portion of the tuning fork arm. In this case, the outer peripheral area (contour) of the assembly composed of the minute cutting parts becomes clear as compared with the conventional example. Therefore, unnecessary cutting in the vicinity of the outer periphery of the cutting portion is prevented, so that the mechanical strength and electrical characteristics can be favorably maintained.

  In addition, an ultrashort pulse laser using a femtosecond laser enters and exits while cutting the ridge line portion of the tuning fork arm obliquely. Therefore, the energy of the ultrashort pulse laser does not remain as in the prior application (Patent Document 3) and escapes without being left over, so that damage to the crystal can be prevented.

(Embodiment section)
According to claim 2 of the present invention, in claim 1, adjacent cutting parts of the plurality of cutting parts overlap each other in the cutting part. As a result, a plurality of micro-cut portions by the ultrashort pulse laser are formed in a concentrated manner on the root portion of the tuning fork on the extending start end side of the tuning fork arm, thereby improving the control efficiency of the oblique vibration. This is due to the fact that the closer the cutting part is to the starting end of the tuning fork arm, the more the tuning fork vibration is affected.

  In the said Claim 3, the said cutting part is made flat in Claim 2. According to this, since the ultrashort pulse laser is concentrated at the root portion as compared with the case of claim 2, the control efficiency of the oblique vibration is further increased. Note that the minute cutting portion basically has an arc shape according to the beam shape of the ultrashort pulse laser, and thus becomes flatter as the minute cutting portion approaches. However, since the beam diameter of the ultrashort pulse laser is extremely small, when the adjacent minute cutting parts are overlapped, the cutting parts are almost flat.

  According to the fourth aspect of the present invention, in the first aspect, the cutting portion is separated from the minute cutting portions adjacent to the plurality of minute cutting portions. In this case, since the adjacent minute cutting parts are not separated and overlapped, the irradiation of the ultrashort pulse laser to each minute cutting part is performed only once. Therefore, damage and twinning are further prevented as compared with the case of claims 2 and 3 where the ultrashort pulse laser is overlapped.

  In the fifth aspect of the present invention, in the first, second, third, or fourth aspect, the cutting portion is provided on any one of the pair of tuning fork arms, and is one end side that is the same side in the width direction of the pair of tuning fork arms. . According to this, since a cutting part is provided in any of a pair of tuning fork arms, while suppressing diagonal vibration, the mass of a pair of tuning fork arms is maintained uniformly.

  Therefore, compared with the case where the cutting part is provided only in one of the pair of tuning fork arms, the natural vibration frequency of both tuning fork arms is made uniform, vibration leakage to the tuning fork base is prevented, and the crystal impedance is improved. In order to prevent oblique vibration, providing a cutting portion on only one of the tuning fork arms may cause the natural frequencies of the left and right tuning fork arms to differ.

(First embodiment, equivalent to claims 1 and 4)
FIG. 1 is a partially enlarged view of an angular velocity sensor element (tuning fork-shaped crystal piece) for explaining a first embodiment of the present invention. In addition, the same number is attached | subjected to the same part as a prior art example, and the description is simplified or abbreviate | omitted.

  As described above, the angular velocity sensor element is processed by photo-etching after two quartz wafers 3 (ab) are directly bonded to each other, and each tuning-fork shape in which a pair of tuning fork arms 2 (ab) extends from the tuning fork base 1. Divided into crystal pieces 3. The pair of tuning fork arms 2 (ab) includes a drive electrode D ± that excites tuning fork vibration, a sensor electrode S ± that detects charges due to vertical vibration, and a monitor electrode M that makes the amplitude level of tuning fork vibration constant (front). (See FIG. 4).

  Then, an ultrashort pulse laser (arrow P in the figure) using a femtosecond laser is irradiated to at least one of the tuning fork arms 2 (ab), for example, the root of 2a, and cut to suppress oblique vibration. In this case, the output power (energy) of one pulse in the ultrashort pulse laser is Po μJ, the number of irradiation is N times, and the laser energy Pm (= NPo μJ) which is an integrated value of these is irradiated.

  For example, the pulse width of the ultrashort pulse laser is 70 femtoseconds, the output power Po of one pulse is 10 μJ, the number of pulses N is 10, and the laser energy Pm is 100 μJ.

  The ultrashort pulse laser irradiates obliquely to the outer (right side) ridge line portion of the root portion of one tuning fork arm 2a. The irradiation angle of the ultrashort pulse laser is incident on one main surface of the tuning fork arm 2a as 45 °, for example, and is emitted from the outer surface of the tuning fork arm 2a. In this case, the ridgeline portion is penetrated while being cut in an oblique direction by the energy of the ultrashort pulse laser, and the minute cutting portion 4 is formed in the ridgeline portion.

  Then, the ridge line portion is sequentially irradiated with the ultrashort pulse laser toward the distal end side along the length direction from the extending start end in the root portion of the tuning fork base portion 1 in the tuning fork arm 2a. As a result, a plurality of micro-cut portions 4 along the length direction are formed at the ridge line portion at the root portion of the tuning fork arm 2a. In this case, the angular velocity sensor element is driven each time the base portion of the tuning fork base 1 is irradiated with the ultrashort pulse laser, and the charge due to the vertical component of the oblique vibration is detected by the sensor electrode S ±. This is repeated until the electric charge due to the vertical component becomes equal to or less than the standard value that is almost zero.

  In such a case, as described in the column of the effect of the invention, since the cutting is performed by the ultrashort pulse laser, the gathering area (contour) of the micro-cutting part 4 becomes clear, and unnecessary cutting near the outer periphery of the gathering area is performed. And mechanical strength and electrical characteristics can be maintained well. The ultrashort pulse laser penetrates the ridge line portion of the tuning fork arm 2a while being obliquely cut.

  Therefore, the energy of the ultrashort pulse laser does not remain in the minute cutting part 4 and escapes without being left over, so that damage to the quartz crystal and twinning can be prevented. Furthermore, in this example, since the plurality of micro-cutting parts 4 are formed apart from each other, the ultra-short pulse laser is not repeatedly irradiated as compared with the case where the adjacent micro-cutting parts are overlapped (second embodiment). Therefore, it is possible to further prevent crystal damage and twinning.

(Embodiment 2 corresponds to claims 1, 2, and 3)
FIG. 2 is a partially enlarged view of an angular velocity sensor element for explaining a second embodiment of the present invention. In addition, description of the same part as 1st Embodiment is abbreviate | omitted or simplified.

  Also in the second embodiment, the ultrashort pulse laser by the femtosecond laser is obliquely crossed at the ridge line portion at the root portion of the tuning fork arm 2a and is extended from the extending start end of the tuning fork arm 2a to the distal end side as in the first embodiment. Irradiated towards. And here, the adjacent micro cut parts 4 by the ultrashort pulse laser are formed to overlap each other. In this case, since the beam diameter of the ultrashort pulse laser is μm as described above, the aggregate of the minute cutting portions 4 forms a flat portion 4A that obliquely intersects the ridge line portion.

  In such a case, the flat cutting portion 4A is formed by concentrating the minute cutting portions 4 on the extending start end side of the root portion of the tuning fork arm 2a. Therefore, as compared with the first embodiment in which the minute notches 4 are formed apart from each other, the flat portion 4A by the minute cutting portion 4 is on the extension start end side, so that the suppression effect (adjustment sensitivity) against oblique vibration can be enhanced.

(Other matters)
In the above embodiment, only one tuning fork arm 2a is irradiated with the ultrashort pulse laser to suppress the oblique vibration. However, one main surface on each end side (for example, the right side) in the width direction of the pair of tuning fork arms 2 (ab). You may irradiate the ridgeline part of an ultrashort pulse laser. In these cases, since the ultrashort pulse laser can be irradiated to the extended starting end side in the root portion of the pair of tuning fork arms 2 (ab), the vibration is oblique compared to the case where the root portion of only one tuning fork arm 2a is irradiated. The suppression effect of can be enhanced.

  When the ridge line portion of one main surface (for example, the right main surface) on one end side in the width direction of each tuning fork arm 2 (ab) is irradiated with an ultrashort pulse laser, the oblique vibration C shown in FIG. 5 is applied. Return to horizontal vibration A. And when it irradiates to one main surface (left main surface) which becomes the other end side of the width direction in each tuning fork arm 2 (ab), the horizontal vibration A turns into the diagonal vibration C. And when cutting the ridgeline part of the other main surface of a pair of tuning fork arms 2 (ab), it becomes adjustment in the direction opposite to these.

  In short, the inner side of one tuning fork arm 2a and the outer side of the other tuning fork arm 2b exhibit an equivalent effect at the ridge line portion on each main surface side of the pair of tuning fork arms 2 (ab), and the outer side of one tuning fork arm 2a The inside of the other tuning fork arm 2b has an equivalent effect. From this, when the diagonal vibration is suppressed at one end side of one tuning fork arm 2a and the diagonal vibration in the reverse direction is generated, the tuning fork arm 2a or the other tuning side of the other tuning fork arm 2b is extremely short. The original horizontal vibration can be restored by irradiating a pulse laser.

  And when the ultrashort pulse laser is irradiated to the ridge line part of a pair of tuning fork arms 2 (ab) and the minute cutting part 4 is provided, the natural vibration frequency between the tuning fork arms 2 (ab) is made uniform. The vibration characteristics can be maintained well. Further, in the case of suppressing the oblique vibration by irradiating the ultrashort pulse laser from the same main surface side of the pair of tuning fork arms 2 (ab), as shown in FIG. It is useful because it can be adjusted after it is stored. Reference numeral 6 in the figure denotes a pedestal that holds the tuning fork base 1.

Further, although the tuning fork crystal piece 3 is formed by directly joining two crystal pieces 3 (ab), it is needless to say that the tuning fork crystal piece 3 can be applied even if it is a single plate. In this case, protrusions are generated on the + X-axis surface due to the anisotropy of etching, and oblique vibration is generated in the same manner (top view of FIG. 3). In the above embodiment, an example of a tuning fork using quartz has been described. However, the material is not limited to this, and any material such as lithium niobate, lithium tantalate, or silicon with a piezoelectric film formed thereon can be used.

It is a partial enlarged view of the angular velocity sensor element for explaining the first embodiment of the present invention. It is a partial enlarged view of the angular velocity sensor element explaining the second embodiment of the present invention. It is a top view of the angular velocity sensor element accommodated in the container main body which shows the example of application of this invention. It is a figure explaining a prior art example, the figure (a) is an external view of an angular velocity sensor element, and the figure (b) is a top view which shows a connection relation. It is a top view of the angular velocity sensor element explaining a prior art example (diagonal vibration). It is a top view of the angular velocity sensor element explaining a conventional example.

Explanation of symbols

1 tuning fork base, 2 tuning fork arm, 3 tuning fork crystal piece, 4 cutting part 4, 5 container body, 6 pedestal.

Claims (5)

  A sensor comprising a tuning fork crystal piece in which a pair of tuning fork arms extends from a tuning fork base, and a sensor for detecting electric charges caused by vertical vibration in the thickness direction of the tuning fork arm and a driving electrode for driving the tuning fork vibration in the width direction of the tuning fork arm A cutting portion that has an electrode and prevents oblique vibration of the pair of tuning fork arms is at least one of both end sides in the width direction of the main surface of the tuning fork arm, and the length direction with respect to the root portion of the tuning fork arm In the angular velocity sensor element provided by the laser, the cutting portion is formed by an ultrashort pulse laser irradiated from a femtosecond laser, and the ultrashort pulse laser is obliquely crossed on the ridge line portion of the tuning fork arm to form the tuning fork. An angular velocity sensor element comprising a plurality of minute cutting portions that are sequentially incident along the length direction of the arm and are emitted while cutting the ridge line portion.   The angular velocity sensor element according to claim 1, wherein the cutting portion is a superposition of adjacent micro cutting portions of the plurality of micro cutting portions.   The angular velocity sensor element according to claim 2, wherein the cutting portion is flat.   2. The angular velocity sensor element according to claim 1, wherein the cutting portion is an adjacent one of the plurality of minute cutting portions.   5. The angular velocity sensor element according to claim 1, wherein the cutting portion is provided on any one of the pair of tuning fork arms, and is one end side on the same side in the width direction of the pair of tuning fork arms.

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