JP4796805B2 - Inertial sensor element - Google Patents

Description

  The present invention relates to an inertial sensor element.

In general, an inertia sensor element having an H-shaped structure (hereinafter referred to as “H-shaped structure”) is known.
As shown in FIG. 4, the inertial sensor element 200 having an H-shaped structure includes a base 210, a pair of excitation arms 220 extending from the base 210, and the base on the opposite side of the excitation arms 220. The detection arm portion 230 extends from the pair 210, and the width JWA of the detection arm portion 230 is wider than the width JWB of the excitation arm portion 220. The base portion 210 is provided with a support portion 240 for fixing to the package between a pair of detection arm portions 230 (see, for example, Patent Document 1).

  Ideally, when the excitation arm 220 of the inertial sensor element 200 is vibrated by primary bending vibration (excitation mode) in the XY plane, the detection arm 230 does not vibrate. In order to achieve this, in the conventional inertial sensor element 200, the width JWA of the detection arm 230 is made wider than the width JWB of the excitation arm 220. This avoids coupling between the primary bending vibration mode (excitation mode) in the XY plane of the excitation arm 220 and the primary bending vibration mode in the XY plane of the detection arm 230 during excitation vibration. The vibration is prevented from propagating below the base 210, that is, to the detection arm 230 and the support 240. In other words, the width JWA of the detection arm portion 230 is formed wider than the width JWB of the excitation arm portion 220 because the vibration is propagated to the detection arm portion 230 during the excitation mode operation (no rotation) (hereinafter referred to as “resonance arm”). This may be referred to as “vibration leakage”).

In addition, when the rotational angular velocity Ω around the Y axis is applied in the state of the primary bending vibration, the excitation arm portion 220 applies Coriolis force in the Z axis direction, and vibration in the Z axis direction component occurs. As a result, vibration (distortion) is also generated in the detection arm 230, and the direction and magnitude of the angular velocity can be detected by a detection electrode (not shown) provided on the detection arm 230.
JP 2000-146594 A

However, in the conventional H-type inertial sensor element 200, since the resistance value R1 in the angular velocity detection mode in the equivalent circuit is large and Q is small, the angular velocity detection sensitivity is low.
Further, when distortion occurs in the Z-axis direction due to the Coriolis force, the width JWA of the detection arm 230 is wider than the width JWB of the excitation arm 220, and thus the distortion is small.

  Therefore, an object of the present invention is to provide an inertial sensor element that solves the above-described problems and accurately detects an angular velocity.

In order to solve the above problems, the present invention comprises a piezoelectric element, a base, a pair of excitation arms extending from the base, and a pair of extensions extending from the base opposite to the excitation arms. Each of the excitation arm portions is formed with a predetermined width from the excitation taper portion side, and an excitation taper portion formed to have a width narrowing in a direction away from the base side. And a predetermined width from the first detection taper portion side. The first detection taper portion is formed so that the width of each detection arm portion becomes narrower in a direction away from the base side. A first detection constant width portion formed by the first detection constant width portion, a second detection taper portion formed so as to narrow in a direction away from the first detection constant width portion side, and a predetermined value from the second detection taper portion side. and a second detector constant width portion formed in a width, the width of the second detector constant width portion, the first Narrower than the width of the detector constant width portion, and the formed narrower than the width of the excitation constant width portion, constituting the width of the first detector constant width portion, is more than twice wider the width of the excitation of constant width portion It is characterized by being.

  Further, the present invention may be formed such that a ratio between the length of the second detection constant width portion and the length of the excitation constant width portion is −1% to + 1%.

  According to such an inertial sensor element, the angular velocity can be detected with high accuracy.

Next, the best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described in detail with reference to the drawings as appropriate. FIG. 1 is a diagram showing an example of an inertial sensor element according to the present invention. 2A is an end view taken along the line AA in FIG. 1, and FIG. 2B is an end view taken along the line BB in FIG.
In the present embodiment, the piezoelectric element is described as a crystal. The case where the thickness is constant at a predetermined thickness throughout the element will be described.

  As shown in FIG. 1, an inertial sensor element 100 according to the present invention is formed along a Y ′ axis and a rectangular base 10 having a long side along the X ′ axis, and extending from the base 10. It is mainly comprised from a pair of excitation arm part 20 and the detection arm part 30 extended from the base 10 on the opposite side to this excitation arm part 20. FIG.

  An excitation electrode (not shown) is formed on the excitation arm 20, and a detection electrode K is formed on the detection arm 30 as shown in FIG. As a result, when a rotational angular velocity Ω around the Y ′ axis is applied in a state of primary bending vibration in the X′Y ′ plane (hereinafter referred to as “excitation”), Coriolis force is applied to the excitation arm 20. In addition to the 'axis direction, vibration of the Z' axis direction component occurs. Then, vibration (distortion) is also generated in the detection arm 30, and the direction and magnitude of the angular velocity can be detected by the detection electrode provided on the detection arm 30.

  The base portion 10 has a rectangular shape, and the excitation arm portion 20 and the detection arm portion 30 extend to the long side along the X ′ axis. In addition, a support portion 40 is provided between the pair of detection arm portions so that it can be fixed to a package (not shown).

  The pair of excitation arms 20, 20 are each composed of an excitation taper portion 21 and an excitation constant width portion 22, each of which is a length of the base portion 10 opposite to the support portion 40 with a predetermined interval therebetween. It extends along the Y ′ axis so as to be parallel to each other from the side.

The excitation taper portion 21 extends from the base portion 10 and is formed to have a narrow width in a direction away from the base portion 10.
In the present embodiment, the excitation taper portion 21 is formed by dividing the change rate at which the width becomes narrow into two stages. In other words, the taper side of the excitation taper portion 21 is composed of a portion having a gentle slope with respect to the long side of the base portion 10 and a portion having a steep slope, and a gentle slope with respect to the long side of the base portion 10. The part which becomes is located on the base 10 side.

  The excitation constant width portion 22 is formed with a predetermined width W3 and a predetermined length L3 from an end portion on the side where the width of the excitation taper portion 21 is narrowed.

  The pair of detection arm portions 30 and 30 includes a first detection taper portion 31, a first detection constant width portion 32, a second detection taper portion 33, and a second detection constant width portion 34, respectively, with a predetermined interval. Then, with the support portion 40 in between, the Y portion extends from the long side of the base portion 10 opposite to the excitation arm portion 20 so as to be parallel to each other.

The first detection taper portion 31 extends from the base portion 10 and is formed to have a narrow width in a direction away from the base portion 10.
Similar to the excitation taper portion 21, the first detection taper portion 31 is formed by dividing the rate of change in width into two stages. Similarly to the excitation taper portion 21, the second detection taper portion 33 is also formed by dividing the change rate of the width into two stages.

  The first detection constant width portion 32 is formed with a predetermined width W1 and a predetermined length L1 from an end portion on the side where the width of the first detection taper portion 31 is narrow, and vibration from the excitation arm portion 20 Plays a role in preventing the propagation of

Here, the width W1 of the first detection constant width portion 32 is at least twice the width W3 of the excitation constant width portion 22 of the excitation arm portion 20.
Further, the length L1 of the first detection constant width portion 32 is one third of the length L3 of the excitation constant width portion 22 of the excitation arm portion 20.

  That is, when the length L1 of the first detection constant width portion 32 is not one third of the length L3 of the excitation constant width portion 22, the width W1 of the first detection constant width portion 32 is the width of the excitation constant width portion 22. If it is smaller than twice W3, the vibration during excitation is greatly propagated to the detection arm 30 (it cannot be sufficiently suppressed), and vibration leakage increases. Therefore, by forming the first detection constant width portion 32 as described above, vibration leakage at the time of excitation can be suppressed, so that the angular velocity can be detected with high accuracy.

  The second detection taper portion 33 is formed at the end of the first detection constant width portion 32 so that the width is narrowed in the direction away from the base portion 10.

  The second detection constant width portion 34 is formed with a predetermined width W2 and a predetermined length L2 from the end on the side where the width of the second detection taper portion 33 is narrow, and plays a role of improving the angular velocity detection sensitivity. Fulfill.

Here, the width W2 of the second detection constant width portion 34 is formed to be narrower than the width W1 of the first detection constant width portion 32 and narrower than the width W3 of the excitation constant width portion 22 of the excitation arm portion 20.
The length L2 of the second detection constant width portion 34 is such that the ratio of the length L2 of the second detection constant width portion 34 and the length L3 of the excitation constant width portion 22 of the excitation arm portion 20 is + 1%. It is formed to become.

Thus, the second detection constant width portion 34 has a ratio of ± 1% between the length L2 of the second detection constant width portion 34 and the length L3 of the excitation constant width portion 22 of the excitation arm portion 20. As a result, the vibration node is located at the center of the base 10 during detection vibration, so that erroneous detection of angular velocity is eliminated and detection error can be reduced. The second detection constant width portion 34 is formed so that the ratio of the length L2 of the second detection constant width portion 34 and the length L3 of the excitation constant width portion 22 of the excitation arm portion 20 exceeds ± 1%. Then, the vibration node is not positioned at the center of the base 10 and the vibration balance is deteriorated.
It should be noted that the vibration balance is good when the node of vibration is in the base 10 as described above.

  In such an inertial sensor element 100, since the width W2 of the second detection constant width portion 34 is narrower than the width W3 of the excitation constant width portion 22, the distortion of the second detection constant width portion 34 is increased. However, since stress is applied to the first detection constant width portion 32, the first detection constant width portion 32 is distorted.

Accordingly, electric charges are likely to concentrate on the end portion of the first detection constant width portion 32 on the first detection taper portion 31 side and the end portion of the second detection constant width portion 34 on the second detection taper portion 33 side. Therefore, as shown in FIGS. 2A and 2B, if the detection electrode K is provided in the first detection constant width portion 32 and the second detection constant width portion 34, the effective electrode area of the detection electrode is increased. This increases the angular velocity detection sensitivity.
The detection electrode K is provided with different polarities facing each other in the width direction while arranging different polarities in the thickness direction.

  Here, the first detection constant width portion 32 having the length L1 and the width W1, the second detection constant width portion 34 having the length L2 and the width W2, and the excitation constant width portion 22 having the length L3 and the width W3. Each frequency will be described. FIG. 3 is a graph showing an example of the displacement of the central portion of the base during detection vibration with respect to the ratio of the length of the excitation constant width portion and the length of the second detection width portion.

First, the frequency F3 of the excitation constant width portion 22 at the time of excitation is expressed by equation (1).
F3 = Kf × λ ² × W3 / (L3) ² (1)
Here, Kf is a frequency constant, and λ is a boundary condition.
Further, the frequency F1 of the first detection constant width portion 32 at the time of excitation is expressed by the equation (2).
F1 = Kf × λ ² × W1 / (L1) ² (2)
Moreover, the frequency F2 of the second detection constant width part 34 at the time of excitation is represented by (3) Formula.
F2 = Kf × λ ² × W2 / (L2) ² (3)

  At this time, when making it difficult for the first detection constant width portion 32 and the second detection constant width portion 34 to vibrate during excitation, the vibration F1 of the first detection constant width portion 32 during detection vibration (when detecting vibration) The vibration F2) of the second detection constant width portion 34 is different from the vibration F3 of the excitation constant width portion 22 during excitation. That is, during the excitation as the difference between the vibration F1 of the first detection constant width portion 32 (vibration F2 of the second detection constant width portion 34 during detection vibration) and the vibration F3 of the excitation constant width portion 22 during excitation increases. The first detection constant width portion 32 and the second detection constant width portion 34 are less likely to vibrate.

  Therefore, the width W1 of the first detection constant width portion 32 is twice the width W3 of the excitation constant width portion 22, and the length L1 of the first detection constant width portion 32 is the length L3 of the excitation constant width portion 22. Therefore, the frequency of the first detection constant width portion 32 at the time of excitation is different from that of the excitation constant width portion 22, and the influence of vibration propagation is smaller than that of the conventional case.

  Further, the width W2 of the second detection constant width portion 34 is a half of the width W3 of the excitation constant width portion 22, and the length L1 of the first detection constant width portion 34 is equal to that of the excitation constant width portion 22. Since the length is increased by + 1% of the length L3, the frequency of the first detection constant width portion 32 at the time of excitation is different from that of the excitation constant width portion 22, and the influence of vibration propagation is smaller than in the conventional case.

Further, the frequency Fs3 of the excitation constant width portion 22 at the time of detected vibration is expressed by the equation (4).
Fs3 = Kf × λ ² × t / (L3) ² (4)
Here, t is the thickness.
Further, the frequency Fs1 of the first detection constant width portion 32 at the time of the detection vibration is expressed by Expression (5).
Fs1 = Kf × λ ² × t / (L1) ² (5)
Further, the frequency Fs2 of the second detection constant width portion 34 at the time of the detection vibration is expressed by Expression (6).
Fs2 = Kf × λ ² × t / (L2) ² (6)

  When coupling the frequency of the excitation constant width portion 22 and the frequency of the second detection constant width portion 34 at the time of the detection vibration, the node of vibration is set to be in the base portion 10.

As an example, as shown in FIG. 3, when the ratio between the length L2 of the second detection constant width portion 34 and the length L3 of the excitation constant width portion 22 is formed at ± 0.5%, The displacement at the center of the base 10 is almost zero, and the vibration balance is good.
Therefore, since the ratio of the length L2 of the second detection constant width portion 34 and the length L3 of the excitation constant width portion 22 is formed at ± 1%, the vibration balance at the time of detection vibration is improved, and the angular velocity is accurately determined. Can be detected.

  In addition, since the length L1 of the first detection constant width portion 32 is one third of the length L3 of the excitation constant width portion 22, the frequency Fs2 of the second detection constant width portion 34 during detection vibration. And the frequency Fs3 of the excitation constant width portion 22 are not affected.

By configuring the inertial sensor element 100 in this manner, the detection arm 30 is less likely to vibrate during excitation, so that erroneous detection and the like can be eliminated.
Further, since the detection arm 30 can be coupled with the vibration of the excitation arm 20 during the detection vibration, vibration leakage increases, and the angular velocity can be detected with high accuracy.

  An example of the maximum length L including the support portion 40 of the inertial sensor element 100 according to the present invention is, for example, 3.5 mm, and the support portion 40 of the inertial sensor element 100 according to the present invention is also included. An example of the included maximum width W is, for example, 1 mm. Therefore, for example, a package having a size of 50 mm × 32 mm or less that can accommodate such inertial sensor element 100 can be applied.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. For example, in the present embodiment, the piezoelectric element is described as a quartz crystal, but the present invention is not limited to this, and a material having a piezoelectric effect such as lithium niobate or lithium tantalate can be used as appropriate.

It is a figure which shows an example of the inertial sensor element which concerns on this invention. (A) is the AA section end elevation of Drawing 1, (b) is the BB end elevation of Drawing 1. It is a graph which shows an example of the displacement of the base center part at the time of a detection vibration with respect to the ratio of the length of the constant width part for excitation, and the length of the width part for 2nd detection. It is a figure which shows the conventional inertial sensor element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Inertial sensor element 10 Base 20 Excitation arm part 21 Excitation taper part 22 Excitation taper part 30 Detection arm part 31 1st detection taper part 32 1st detection constant width part 33 2nd detection taper part 34 2nd detection constant width Part K Detection electrode W1, W2, W3 Width L1, L2, L3 Length

Claims (2)

A piezoelectric element, comprising a base, a pair of excitation arms extending from the base, and a pair of detection arms extending from the base on the opposite side of the excitation arm,
The excitation taper portion formed so that the width of each of the excitation arm portions becomes narrower in a direction away from the base side,
An excitation constant width portion formed with a predetermined width from the excitation taper portion side,
Each of the detection arms is
A first detection taper portion formed so as to be narrow in a direction away from the base side;
A first detection constant width portion formed with a predetermined width from the first detection taper portion side;
A second detection taper portion formed so that the width becomes narrower in a direction away from the first detection constant width portion side;
A second detection constant width portion formed with a predetermined width from the second detection taper portion side,
The width of the second detection constant width portion is narrower than the width of the first detection constant width portion, and narrower than the width of the excitation constant width portion,
The inertial sensor element, wherein the first detection constant width portion is formed to have a width that is at least twice as wide as the excitation constant width portion . 2. The inertial sensor element according to claim 1, wherein a ratio of a length of the second detection constant width portion and a length of the excitation constant width portion is −1% to + 1%.

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