JP5227199B2 - Angular velocity sensor - Google Patents

Description

  The present invention relates to an angular velocity sensor, and more particularly to a technique for improving the detection sensitivity of a vibration gyro type angular velocity sensor.

  As an angular velocity sensor that is small and suitable for mass production, a vibration gyro type sensor is widely used. In this vibration gyro-type angular velocity sensor, the vibrator is moved in the first axial direction among the three axes orthogonal to each other, and at this time, the Coriolis force applied to the vibrator in the second axial direction is measured. As a result, the angular velocity acting around the third axis is detected.

  For example, Patent Documents 1 and 2 listed below disclose a vibration gyro-type angular velocity sensor that uses an annular groove formed in the lower surface of a disk-shaped piezoelectric element and a cylindrical portion surrounded by the annular groove as a vibrator. Has been. In this sensor, by supplying an AC electric signal to a predetermined portion of the piezoelectric element, the vibrator can be vibrated in a predetermined axial direction, and in this state, by measuring a voltage generated in the predetermined portion of the piezoelectric element, The Coriolis force acting on the vibrator can be detected. By using a disk-shaped piezoelectric element, a small angular velocity sensor suitable for mass production can be realized.

  Patent Document 3 below discloses an angular velocity sensor using a structure in which a plate-like piezoelectric element is bonded to the lower surface of a metal diaphragm and a circular through hole is formed at the center thereof. In this sensor, a cylindrical vibrator is disposed in a circular through hole, and an electric signal indicating Coriolis force is taken out from an electrode formed on the piezoelectric element. Since efficient stress concentration occurs at the edge position of the piezoelectric element, detection sensitivity can be increased by extracting a signal from the electrode disposed at the edge position.

Japanese Unexamined Patent Publication No. 08-035981 JP 08-094661 A JP 2002-071705 A

  In order to reduce the size of the angular velocity sensor, it is essential to reduce the mechanical structure including the vibrator. However, the smaller the mechanical structure portion, the smaller the displacement of the vibrator caused by the action of the Coriolis force, and the Coriolis force measurement signal must be reduced. For this reason, in order to realize a small and highly accurate angular velocity sensor, it is important to increase the Coriolis force detection sensitivity.

  However, the vibration gyro-type angular velocity sensor that has been proposed so far cannot sufficiently increase the detection sensitivity of the Coriolis force, and it has been difficult to realize a small and highly accurate angular velocity sensor.

  Accordingly, an object of the present invention is to provide a vibration gyro-type angular velocity sensor that can further increase the detection sensitivity of the Coriolis force.

(1) The first aspect of the present invention is:
A diaphragm part composed of a disk having at least a surrounding part having flexibility; and
A vibrator composed of a cylindrical rigid body arranged concentrically with the diaphragm and the central axis, and joined to the lower surface of the diaphragm,
A rigid body having a cylindrical surface-like inner peripheral surface joined to the outer peripheral surface of the diaphragm portion, and a base portion for fixing the outer peripheral surface of the diaphragm portion to the device housing;
Excitation means for inducing vibration having a motion component in a predetermined vibration axis direction with respect to the vibrator;
A displacement detecting means for detecting a displacement in a predetermined displacement axis direction generated in the vibrator based on the Coriolis force;
With
When an XYZ three-dimensional orthogonal coordinate system is defined in which the origin O is at the center position of the upper surface of the diaphragm and the upper surface of the diaphragm is included in the XY plane, one of the X and Z axes is the vibration axis, and the other In the angular velocity sensor that detects the angular velocity around the Y axis based on the detection value by the displacement detection means,
When the outer diameter of the disk constituting the diaphragm is φ, the outer diameter of the cylinder constituting the vibrator is D, and the height of the cylinder constituting the vibrator is H, the height H of the cylinder is “0”. .2 mm ≦ H ≦ 0.7 mm ”is satisfied, and further, the dimension conditions “ D <φ ”and“ 2.25 ≦ φ / H ≦ 2.54 ”are satisfied.

(2) According to a second aspect of the present invention, in the angular velocity sensor according to the first aspect described above,
The diaphragm portion, the vibrator, and the pedestal portion are constituted by an integral structure made of the same material.

(3) According to a third aspect of the present invention, in the angular velocity sensor according to the second aspect described above,
When a portion having a thickness T on the upper surface side of the substrate is defined as an upper layer portion, and a remaining lower surface portion is defined as a lower layer portion, the lower surface portion on the lower surface side of the substrate has an inner diameter D and an outer diameter φ with the Z axis as the central axis. An annular groove with is formed,
Of the upper layer part, the diaphragm part is constituted by a disk part having an outer diameter φ with the Z axis as the central axis,
Of the lower layer part, the vibrator is constituted by a cylindrical part having a diameter D with the Z axis as the central axis,
The pedestal portion is configured by a portion of the substrate that is not included in a cylinder having a diameter φ with the Z axis as the central axis.

(4) According to a fourth aspect of the present invention, in the angular velocity sensor according to the third aspect described above,
A dimensional condition of T + H <K is satisfied between the thickness T of the diaphragm portion, the height H of the cylindrical vibrator, and the thickness K of the pedestal portion.

(5) According to a fifth aspect of the present invention, in the angular velocity sensor according to the third or fourth aspect described above,
By forming an annular groove on the lower surface of the silicon substrate, a diaphragm portion made of silicon, a vibrator made of silicon, and a pedestal portion made of silicon are formed.

(6) According to a sixth aspect of the present invention, in the angular velocity sensor according to the first to fifth aspects described above,
The excitation means includes an excitation piezoelectric element fixed to a predetermined position on the upper surface of the diaphragm portion, and an excitation electric circuit that applies an AC electric signal to the excitation piezoelectric element;
The displacement detection means includes a detection piezoelectric element fixed to a predetermined position on the upper surface of the diaphragm portion, and a detection electric circuit for detecting a charge generated in the detection piezoelectric element.

(7) According to a seventh aspect of the present invention, in the angular velocity sensor according to the first to fifth aspects described above,
The excitation means includes an excitation displacement electrode formed at a predetermined position of the diaphragm portion or the vibrator, an excitation fixed electrode fixed to the apparatus housing so as to face the excitation displacement electrode, an excitation displacement electrode, and an excitation An excitation electric circuit for applying an AC electric signal between the fixed electrode for use, and
A displacement detection means includes a detection displacement electrode formed at a predetermined location of the diaphragm section or the vibrator, a detection fixed electrode fixed to the apparatus housing so as to face the detection displacement electrode, and a detection displacement electrode. And a detection electric circuit for detecting a capacitance value between the detection fixed electrode and the detection fixed electrode.

(8) According to an eighth aspect of the present invention, in the angular velocity sensor according to the sixth or seventh aspect described above,
An angular velocity sensor, wherein the excitation electric circuit applies an AC electric signal having a frequency equal to a resonance frequency in the vibration axis direction of the vibrator.

  In the angular velocity sensor according to the present invention, the periphery of a diaphragm portion made of a disk having an outer diameter φ is fixed, and a columnar vibrator having a height H is concentrically arranged at the center of the diaphragm portion. A structure is adopted in which the vibrator is vibrated by bending, and further, a design that satisfies the dimensional condition of “2.25 ≦ φ / H ≦ 2.54” is made. When such dimensional conditions are set, the resonance frequency of the vibrator in the axial direction parallel to the upper surface of the diaphragm portion and the resonance frequency of the vibrator in the axial direction perpendicular to the upper surface of the diaphragm portion are very close to each other. Detection sensitivity is significantly improved.

It is the perspective view which looked at the basic structure 100 of the angular velocity sensor which concerns on this invention from upper direction. It is the perspective view which looked at the basic structure 100 shown in FIG. 1 from the downward direction. It is a bottom view of the basic structure 100 shown in FIG. It is the sectional side view which cut | disconnected the basic structure 100 shown in FIG. 1 by the XZ plane. FIG. 2 is a side sectional view showing a state in which a vibrator 120 in the basic structure 100 shown in FIG. 1 is displaced in the positive direction of the X axis. FIG. 2 is a side sectional view showing a state in which a vibrator 120 in the basic structure 100 shown in FIG. 1 is displaced in the negative X-axis direction. FIG. 2 is a side sectional view showing a state in which a vibrator 120 in the basic structure 100 shown in FIG. 1 is displaced in the positive Z-axis direction. FIG. 2 is a side sectional view showing a state in which a vibrator 120 in the basic structure 100 shown in FIG. 1 is displaced in the negative Z-axis direction. FIG. 2 is a side sectional view showing an angular velocity sensor configured by adding excitation means and displacement detection means using a piezoelectric element to the basic structure 100 shown in FIG. 1. FIG. 10 is a top view of the angular velocity sensor shown in FIG. 9. FIG. 10 is a side sectional view showing characteristics of a piezoelectric element used in the angular velocity sensor shown in FIG. 9. It is a wave form diagram which shows the alternating current electric signal used in order to drive the angular velocity sensor shown in FIG. FIG. 2 is a side sectional view showing an angular velocity sensor configured by adding excitation means using a capacitive element and displacement detection means to the basic structure 100 shown in FIG. 1. FIG. 14 is a top view of a lower substrate 320 of the angular velocity sensor shown in FIG. 13. It is a graph which shows the vibration frequency characteristic of the basic structure 100 shown in FIG. FIG. 2 is a side sectional view showing dimensions of each part of the basic structure 100 shown in FIG. 1. It is a graph which shows the relationship between dimensional ratio (phi) / H of the basic structure 100 shown in FIG. 1, and the sensitivity of an angular velocity sensor. It is a table | surface which shows the data which became the basis of the graph shown in FIG. It is a sectional side view which shows an example of the basic structure which satisfy | fills the dimension ratio (phi) / H used as the characteristic of this invention. It is a sectional side view which shows another example of the basic structure which satisfy | fills the dimension ratio (phi) / H used as the characteristic of this invention.

  Hereinafter, the present invention will be described based on the illustrated embodiments.

<<< §1. Basic sensor structure >>
First, an example of a mechanical structure portion (hereinafter referred to as a basic structure) including a vibrator of the angular velocity sensor according to the present invention will be described. FIG. 1 is a perspective view of the basic structure 100 as viewed from above, and FIG. 2 is a perspective view of the basic structure 100 as viewed from below. In the example shown here, the basic structure 100 has a shape in which an annular groove G is dug on the lower surface side of a substrate (for example, a silicon substrate) whose upper surface is square. The upper layer portion forming the bottom of the groove G constitutes a flexible diaphragm portion 110, the cylindrical portion surrounded by the groove G constitutes the vibrator 120, and the outer portion of the groove G constitutes the pedestal 130. Configure.

  FIG. 3 is a bottom view of the basic structure 100. As shown in the figure, it is clearly shown that the columnar vibrator 120 and the annular groove G are arranged so as to form a concentric circle. FIG. 4 is a side sectional view of the basic structure 100. Here, for convenience of explanation, as shown in FIG. 1, an XYZ cubic that has an origin O at the center position of the upper surface of the basic structure 100 and the upper surface of the basic structure 100 (the upper surface of the diaphragm portion 110) is included in the XY plane. Define the original Cartesian coordinate system. The X axis and the Y axis are coordinate axes included in the upper surface of the basic structure 100, and the Z axis is a coordinate axis orthogonal to the main surface of the substrate constituting the basic structure 100. FIG. 4 shows a cross section of the basic structure 100 taken along the XZ plane.

  As described above, the basic structure 100 is formed by forming the annular groove G on the lower surface side of the substrate, and the flexible diaphragm portion 110 is formed above the groove G. The diaphragm 120 and the pedestal 130 function as a rigid body, whereas the diaphragm 110 functions as a flexible elastic body because of the difference in thickness. In the case of the illustrated example, a flexible silicon diaphragm portion 110 is formed by preparing a silicon substrate having a thickness of 0.8 mm and digging a groove G from the lower surface side while leaving a portion of the upper layer portion having a thickness of 7 μm. (The dimensional ratio in the figure is different from the actual one for convenience of illustration).

  In this example, the lower surface of the columnar vibrator 120 is raised slightly above the position of the lower surface of the pedestal 130. This is to secure a degree of freedom in which the vibrator 120 is displaced downward when the pedestal 130 is fixed to the apparatus housing (not shown). For example, even when the bottom surface of the pedestal 130 is fixed on a support substrate that constitutes a part of the apparatus housing, a gap is secured between the lower surface of the transducer 120 and the upper surface of the support substrate. 120 can be displaced downward within a predetermined size range.

  In fact, in the basic structure 100 having such a structure, the vibrator 120 can be displaced in any of the X-axis, Y-axis, and Z-axis directions when the diaphragm 110 is bent. For example, if a force + Fx in the positive X-axis direction is applied to the center of gravity of the vibrator 120, the diaphragm 110 is bent as shown in FIG. 5, and the center of gravity of the vibrator 120 is in the positive X-axis direction. Displace. On the other hand, when the force −Fx in the negative X-axis direction is applied, the diaphragm 110 is bent as shown in FIG. 6, and the center of gravity of the vibrator 120 is displaced in the negative X-axis direction.

  As is apparent from the perspective view of FIG. 1, even if this basic structure 100 is rotated 90 ° around the Z-axis, the geometric structure is exactly the same. Therefore, the force + Fx, If a force + Fy, -Fy in the Y-axis direction is applied instead of -Fx, the same displacement can be generated in the Y-axis direction.

  On the other hand, if a force + Fz in the positive Z-axis direction is applied to the center of gravity of the vibrator 120, the diaphragm 110 is bent as shown in FIG. 7, and the center of gravity of the vibrator 120 is in the positive Z-axis direction. Displace. On the other hand, if a force −Fz in the negative Z-axis direction is applied, the diaphragm 110 is bent as shown in FIG. 8, and the center of gravity of the vibrator 120 is displaced in the negative Z-axis direction.

  The angular velocity sensor itself using the basic structure 100 as described in §1 is a known device, and is disclosed in Patent Documents 1 to 3 described above.

<<< §2. Example of angular velocity sensor configuration >>
In general, in a vibration gyro-type angular velocity sensor, a vibrator is moved in a first axial direction among three axes orthogonal to each other, and at this time, a Coriolis force applied to the vibrator in a second axial direction is measured. Thus, the angular velocity acting around the third axis can be detected. As described in §1, the vibrator 120 in the basic structure 100 can be displaced in any of the X-axis, Y-axis, and Z-axis directions. Therefore, in the sensor using the basic structure 100, the angular velocity can be detected by the following six methods.

  <Method 1: Vx, Fy, ωz> The angular velocity ωz around the Z axis is detected by measuring the Coriolis force Fy acting in the Y axis direction in a state where the vibration Vx in the X axis direction is applied to the vibrator.

  <Method 2: Vx, Fz, ωy> The angular velocity ωy around the Y axis is detected by measuring the Coriolis force Fz acting in the Z axis direction in a state where the vibration Vx in the X axis direction is applied to the vibrator.

  <Method 3: Vy, Fx, ωz> The angular velocity ωz around the Z axis is detected by measuring the Coriolis force Fx acting in the X axis direction in a state where the vibration Vy in the Y axis direction is applied to the vibrator.

  <Method 4: Vy, Fz, ωx> The angular velocity ωx around the X axis is detected by measuring the Coriolis force Fz acting in the Z axis direction in a state where the vibration Vy in the Y axis direction is applied to the vibrator.

  <Method 5: Vz, Fx, ωy> The angular velocity ωy around the Y axis is detected by measuring the Coriolis force Fx acting in the X axis direction in a state where the vibration Vz in the Z axis direction is applied to the vibrator.

  <Method 6: Vz, Fy, ωx> The angular velocity ωx around the X axis is detected by measuring the Coriolis force Fy acting in the Y axis direction in a state where the vibration Vz in the Z axis direction is applied to the vibrator.

  Here, an excitation means for electrically inducing vibration having a motion component in a predetermined vibration axis direction with respect to the vibrator 120, or a displacement in a predetermined displacement axis direction generated in the vibrator 120 based on the Coriolis force. As displacement detection means for electrical detection, use of various elements such as a piezoelectric element and a capacitive element has been proposed (for example, see Patent Documents 1 to 3 described above).

  The angular velocity sensor shown in the side sectional view of FIG. 9 is an example in which excitation means and displacement detection means are configured by piezoelectric elements. Here, as described in §1, the basic structure 100 is configured by digging an annular groove G in the lower surface of the silicon substrate. An insulating layer 210, a lower electrode 220, and a piezoelectric element 230 are formed on the upper surface of the basic structure 100, and upper electrodes E11 to E24 are formed on the upper surface.

  FIG. 10 is a top view of the angular velocity sensor. As shown in FIG. 9, the insulating layer 210 (for example, silicon oxide film), the lower electrode 220 (for example, Pt / Ti film), and the piezoelectric element 230 (for example, PZT thin film) all cover the entire upper surface of the basic structure 100. Although it is a covering layer, the upper electrodes E11 to E24 (for example, Au / Pt films) are all fan-shaped electrode layers, and are arranged at predetermined positions on the X axis or the Y axis.

  The piezoelectric element 230 has a property of expanding and contracting in the horizontal direction of FIG. 9 when a voltage is applied between its upper and lower surfaces. FIG. 11 is a side sectional view showing the characteristics of the piezoelectric element 230. The component indicated by the symbol P in the drawing is a part of the piezoelectric element 230 shown in FIG. When the electrodes E1 and E2 are formed on the upper and lower surfaces of the piezoelectric element P, the lower electrode E2 is grounded, and a positive voltage is applied to the upper electrode E1, as shown in FIG. 11 (a). When the piezoelectric element P extends in the horizontal direction and a negative voltage is applied to the electrode E1 on the upper surface side, the piezoelectric element P has a property of contracting in the horizontal direction as shown in FIG. Can be reversed). Also, as shown in FIG. 11 (a), when a stress is applied to extend the piezoelectric element P in the horizontal direction, a positive charge is generated in the electrode E1 on the upper surface side, and the piezoelectric element P is moved as shown in FIG. 11 (b). When a stress that shrinks in the horizontal direction is applied, a negative charge is generated in the electrode E1 on the upper surface side.

  In the configuration shown in FIG. 9, if the piezoelectric element 230 has the properties shown in FIG. 11, the lower electrode 220 is grounded and a positive or negative voltage is applied to any of the upper electrodes E11 to E24. As a result, it is possible to induce bending in a predetermined portion of the diaphragm portion 110 and to displace the vibrator 120 in a desired direction.

  For example, if a negative voltage is applied to the upper electrode E11, a positive voltage is applied to the upper electrode E12, a negative voltage is applied to the upper electrode E13, and a positive voltage is applied to the upper electrode E14, as shown in FIG. The vibrator 120 can be displaced in the positive direction of the X axis. Conversely, a positive voltage is applied to the upper electrode E11, a negative voltage is applied to the upper electrode E12, a positive voltage is applied to the upper electrode E13, and the upper electrode If a negative voltage is applied to E14, the vibrator 120 can be displaced in the negative direction of the X axis as shown in FIG. Accordingly, AC electric signals S1 and S2 having opposite phases as shown in FIG. 12 are prepared (the vertical axis is a voltage axis with the waveform center being the ground potential, and the horizontal axis is the time axis), and the upper electrodes E11 and E13 are applied to the upper electrodes E11 and E13. If the signal S1 is given and the signal S2 is given to the upper electrodes E12 and E14, the vibrator 120 can be vibrated along the X axis.

  Similarly, if the signal S1 is given to the upper electrodes E21 and E23 and the signal S2 is given to the upper electrodes E22 and E24, the vibrator 120 can be vibrated along the Y axis.

  Further, if a negative voltage is applied to the upper electrode E11, a positive voltage is applied to the upper electrode E12, a positive voltage is applied to the upper electrode E13, and a negative voltage is applied to the upper electrode E14, as shown in FIG. The vibrator 120 can be displaced in the positive direction of the Z-axis. Conversely, a positive voltage is applied to the upper electrode E11, a negative voltage is applied to the upper electrode E12, a negative voltage is applied to the upper electrode E13, and the upper electrode If a positive voltage is applied to E14, the vibrator 120 can be displaced in the Z-axis negative direction as shown in FIG. Accordingly, AC electric signals S1 and S2 having opposite phases as shown in FIG. 12 are prepared (the vertical axis is a voltage axis with the waveform center as the ground potential, and the horizontal axis is the time axis), and the upper electrodes E11 and E14 are applied to the upper electrodes E11 and E14. If the signal S1 is given and the signal S2 is given to the upper electrodes E12 and E13, the vibrator 120 can be vibrated along the Z-axis. Alternatively, even if the signal S1 is given to the upper electrodes E21 and E24 and the signal S2 is given to the upper electrodes E22 and E23, the vibrator 120 can also be vibrated along the Z axis.

  On the other hand, in the configuration shown in FIG. 9, if the piezoelectric element 230 has the properties shown in FIG. 11, the lower electrode 220 is grounded and the amount of charge generated in any of the upper electrodes E11 to E24 is measured. By doing so, it is possible to recognize the bending occurring in the predetermined portion of the diaphragm portion 110 and to detect the displacement of the vibrator 120 in the predetermined axial direction. The displacement corresponds to the Coriolis force acting on the vibrator 120 in the predetermined axial direction.

  For example, the sum of the generated charge amounts of the upper electrodes E11 and E13 and the sum of the generated charge amounts of the upper electrodes E12 and E14 are obtained (actually, the sum of the potentials of the respective electrodes with respect to the ground potential may be measured. If the difference between the two is obtained, the difference indicates the amount of displacement of the vibrator 120 in the X-axis direction (the sign is the displacement direction), and indicates the Coriolis force in the X-axis direction applied to the vibrator 120. Become a thing.

  Similarly, the sum of the generated charge amounts of the upper electrodes E21 and E23 and the sum of the generated charge amounts of the upper electrodes E22 and E24 are obtained (actually, even if the sum of the potentials of the respective electrodes with respect to the ground potential is measured). If the difference between the two is obtained, the difference indicates the amount of displacement of the vibrator 120 in the Y-axis direction (the sign is the displacement direction), and the Coriolis force in the Y-axis direction applied to the vibrator 120 is calculated. Will be shown.

  Further, the sum of the generated charge amounts of the upper electrodes E11 and E14 and the sum of the generated charge amounts of the upper electrodes E12 and E13 are obtained (actually, the sum of the potentials of the respective electrodes with respect to the ground potential may be measured. ), The difference between them indicates the amount of displacement of the vibrator 120 in the Z-axis direction (the sign is the displacement direction), and indicates the Coriolis force in the Z-axis direction applied to the vibrator 120. Become a thing. This is to obtain the sum of the generated charge amounts of the upper electrodes E21 and E24 and the sum of the generated charge amounts of the upper electrodes E22 and E23 (actually, even if the sum of the potentials of the respective electrodes with respect to the ground potential is measured). It is the same even if the difference between the two is obtained.

  After all, the angular velocity sensor shown in FIG. 9 grounds the lower electrode 220 and supplies an AC electric signal having a predetermined phase to the predetermined upper electrode, thereby causing the vibration 120 to vibrate in the X-axis direction. The vibration Vy in the Y-axis direction can be given, or the vibration Vz in the Z-axis direction can be given. Further, the Coriolis force Fx in the X-axis direction acting on the vibrator 120 can be obtained by grounding the lower electrode 220 and detecting the amount of charge generated in a predetermined upper electrode, The Coriolis force Fy can be obtained, or the Coriolis force Fz in the Z-axis direction can be obtained.

  As described above, the angular velocity sensor shown in FIG. 9 can implement any of the above-described <Method 1> to <Method 6>, and the angular velocity ωx in the X-axis direction, the angular velocity ωy in the Y-axis direction, and the Z-axis direction. Any angular velocity ωz can be detected. When some of these six methods are carried out, some of the eight upper electrodes E11 to E24 shown in FIG. 10 are used as electrodes for the excitation means and the displacement detection means. However, in such a case, one electrode may be divided into two electrodes that are electrically separated, and the roles may be shared.

  In short, if an angular velocity sensor is configured using a piezoelectric element, an excitation piezoelectric element fixed at a predetermined position on the upper surface of the diaphragm 110 (the upper electrode used for excitation is formed in the piezoelectric element 230 shown in FIG. 9). ) And an excitation electric circuit that applies an AC electric signal to the excitation piezoelectric element, and constitutes excitation means, and the detection piezoelectric element (FIG. 9) fixed to a predetermined position on the upper surface of the diaphragm 110. The displacement detecting means may be constituted by the piezoelectric element 230 shown in FIG. 2 (the portion where the upper electrode used for detection is formed) and the detection electric circuit for detecting the charge generated in the detection piezoelectric element.

  In addition, it is preferable that the piezoelectric element functioning as the excitation unit or the displacement detection unit is disposed in a predetermined portion located above the groove G on the upper surface of the diaphragm portion 110. This is because the stress due to the bending of the diaphragm portion 110 is efficiently transmitted to the piezoelectric element disposed at the location. Further, as in the examples disclosed in the above-mentioned Patent Documents 1 and 2, the basic structure 100 itself can be used as a piezoelectric element.

  Of course, the excitation means and the displacement detection means do not necessarily need to be configured using piezoelectric elements. The angular velocity sensor whose side cross-sectional view is shown in FIG. 13 is an example in which excitation means and displacement detection means are configured by electrostatic capacitance elements. Also in this example, the basic structure 100 is configured by digging an annular groove G in the lower surface of the silicon substrate as described in §1. An upper substrate 310 is disposed above the basic structure 100, and a lower substrate 320 is disposed below.

  The lower substrate 320 is a plate-like insulating substrate, and five fixed electrodes E31 to E35 (for example, an aluminum film) are formed on the upper surface thereof as shown in the top view of FIG. The central fixed electrode E35 is a circular electrode having the Z-axis as a central axis, and is arranged so that fan-shaped fixed electrodes E31 to E34 surround it. As shown in the side sectional view of FIG. 13, a gap is formed between each of the fixed electrodes E31 to E35 and the lower surface of the vibrator 120, and the degree of freedom that the vibrator 120 is displaced downward is formed. It is secured.

  On the other hand, the upper substrate 310 has a groove G ′ formed in the central region of the lower surface, and five fixed electrodes E41 to E45 (for example, an aluminum film) are formed at the bottom of the groove G ′. These fixed electrodes E41 to E45 have the same shape as the fixed electrodes E31 to E35 shown in FIG. 14, respectively, and have the same arrangement. That is, the fixed electrodes E41 to E45 are disposed so as to form a mirror image above the fixed electrodes E31 to E35, respectively. As shown in the side sectional view of FIG. 13, gaps are formed by grooves G ′ between the fixed electrodes E41 to E45 and the upper surface of the basic structure 100, and the vibrator 120 moves upward. A degree of freedom of displacement is secured.

  In this example, the basic structure 100 is made of silicon, so that the whole functions as a conductor. Therefore, a total of 10 sets of electrostatic capacitance elements C31 to C45 are formed by each of the fixed electrodes E31 to E45 and the opposing surface of the basic structure 100 (functioning as a displacement electrode). Therefore, in the configuration shown in FIG. 13, by applying a Coulomb force to any one of the capacitive elements C31 to C45, a predetermined portion of the diaphragm portion 110 is caused to bend, and the vibrator 120 can be displaced in a desired direction. Is possible.

  For example, if the basic structure 100 is maintained at the ground level (the displacement electrodes are both at ground potential) and a voltage is applied to the fixed electrodes E41 and E32, a Coulomb attractive force is applied to the capacitive elements C41 and C32. As shown in FIG. 5, the vibrator 120 can be displaced in the positive direction of the X axis. On the other hand, if a voltage is applied to the fixed electrodes E31 and E42, a Coulomb attractive force can be applied to the capacitive elements C31 and C42, and the vibrator 120 can be displaced in the X-axis negative direction as shown in FIG. . If these displacement operations are performed alternately, the vibrator 120 can be vibrated along the X-axis.

  Similarly, if the basic structure 100 is maintained at the ground level and a voltage is applied to the fixed electrodes E43 and E34, a Coulomb attractive force can be applied to the capacitive elements C43 and C34, and a voltage is applied to the fixed electrodes E33 and E44. Since Coulomb attractive force can be applied to the capacitive elements C33 and C44, the vibrator 120 can be vibrated along the Y axis by alternately performing these displacement operations.

  Further, if the basic structure 100 is maintained at the ground level and a voltage is applied to the fixed electrode E45, a Coulomb attractive force can be applied to the capacitive element C45. As shown in FIG. It can be displaced in the axial positive direction. On the other hand, if a voltage is applied to the fixed electrode E35, a Coulomb attractive force can be applied to the capacitive element C35, and the vibrator 120 can be displaced in the negative Z-axis direction as shown in FIG. If these displacement operations are performed alternately, the vibrator 120 can be vibrated along the Z-axis.

  On the other hand, in the configuration shown in FIG. 13, if the capacitance value between the basic structure 100 functioning as a common displacement electrode and a predetermined fixed electrode is electrically detected, the distance between both electrodes is recognized. Therefore, the displacement of the vibrator 120 in the predetermined axis direction can be detected. The displacement corresponds to the Coriolis force acting on the vibrator 120 in the predetermined axial direction.

  For example, the sum of the capacitance value of the capacitive element C41 and the capacitance value of the capacitive element C32 and the sum of the capacitance value of the capacitive element C31 and the capacitance value of the capacitive element C42 are obtained. If the difference is obtained, the difference indicates the amount of displacement of the vibrator 120 in the X-axis direction (the sign is the displacement direction), and indicates the Coriolis force in the X-axis direction applied to the vibrator 120. .

  Similarly, the sum of the capacitance value of the capacitive element C43 and the capacitance value of the capacitive element C34 and the sum of the capacitance value of the capacitive element C33 and the capacitance value of the capacitive element C44 are obtained. If the difference between the two is obtained, the difference indicates the displacement amount of the vibrator 120 in the Y-axis direction (the sign is the displacement direction), and indicates the Coriolis force applied to the vibrator 120 in the Y-axis direction. Become.

  Further, if the difference between the capacitance value of the capacitive element C45 and the capacitance value of the capacitive element C35 is obtained, the difference indicates the amount of displacement of the vibrator 120 in the Z-axis direction (the sign is the displacement direction). Thus, the Coriolis force in the Z-axis direction applied to the vibrator 120 is shown.

  After all, in the angular velocity sensor shown in FIG. 13, the basic structure 100 is grounded, and an AC electric signal having a predetermined phase is supplied to a predetermined fixed electrode, whereby the vibration 120 in the X-axis direction is applied to the vibrator 120. Can be applied, the vibration Vy in the Y-axis direction can be applied, or the vibration Vz in the Z-axis direction can be applied. Further, the basic structure 100 is grounded, and the capacitance value between the predetermined fixed electrode and the basic structure 100 (displacement electrode) is detected, so that the Coriolis in the X-axis direction acting on the vibrator 120 is detected. The force Fx can be obtained, the Coriolis force Fy in the Y-axis direction can be obtained, or the Coriolis force Fz in the Z-axis direction can be obtained.

  As described above, the angular velocity sensor shown in FIG. 13 can implement any one of the above-described <Method 1> to <Method 6>. The angular velocity ωx in the X-axis direction, the angular velocity ωy in the Y-axis direction, and the Z-axis direction. Any angular velocity ωz can be detected. When some of these six methods are performed, it is necessary to use a part of the ten fixed electrodes E31 to E45 as the electrodes for the excitation means and the electrodes for the displacement detection means. However, in such a case, one electrode may be divided into two electrically separated electrodes, and the respective roles may be shared.

  In short, if an angular velocity sensor is configured using a capacitive element, an excitation displacement electrode formed at a predetermined position of the diaphragm 110 or the vibrator 120 and an apparatus housing so as to face the excitation displacement electrode. The excitation fixed electrode fixed to the body and the excitation electric circuit for applying an AC electric signal between the excitation displacement electrode and the excitation fixed electrode constitute excitation means, and the diaphragm unit 110 or the vibrator 120 The detection displacement electrode formed at a predetermined location, the detection fixed electrode fixed to the apparatus housing so as to face the detection displacement electrode, and the electrostatic capacitance between the detection displacement electrode and the detection fixed electrode The displacement detection means may be constituted by a detection electric circuit for detecting the capacitance value.

<<< §3. Factors affecting detection sensitivity >>
Now, in §2, an angular velocity sensor in which excitation means and displacement detection means made of piezoelectric elements are added to the basic structure 100 described in §1, and angular velocity in which excitation means and displacement detection means made of capacitance elements are added. The sensor is illustrated. However, the angular velocity sensor itself that operates on such a principle is a known device, and is disclosed in, for example, the above-mentioned Patent Documents 1 to 3. The feature of the present invention is that in such a sensor, a special condition is set for the structure of the basic structure 100 in order to increase detection sensitivity.

  As described above, in the angular velocity sensor of the vibration gyro type, the vibrator is moved in the first axial direction among the three axes orthogonal to each other, and at this time, the Coriolis force applied to the vibrator in the second axial direction. Is measured to detect the angular velocity acting around the third axis. Here, the measurement of the Coriolis force is performed by detecting a displacement in the second axial direction generated in the vibrator as described in §2.

  Therefore, the first method for increasing the Coriolis force detection sensitivity is to increase the mass of the vibrator. The larger the mass of the vibrator, the greater the acting Coriolis force. However, in order to increase the mass of the vibrator, it is necessary to configure the vibrator with a material having a higher density or to increase the volume of the vibrator. In the case of a mass production type sensor, the material has to be limited, and in order to reduce the size of the sensor, it is not preferable to increase the volume of the vibrator. Therefore, the first method is not adopted in the present invention.

  A second method for increasing the Coriolis force detection sensitivity is to increase the motion speed of the vibrator. In the driving method described in §2, the vibrator reciprocates (single vibration) along a predetermined vibration axis. However, the velocity is zero at both end points of the vibration, and the maximum velocity is obtained at the center point of the vibration. In general, a mechanical structure can define a resonance frequency (natural frequency) unique to the structure, and when the structure is vibrated at the resonance frequency, energy is most efficiently used. It is known that the above vibration mode can be obtained. Therefore, even when the same mechanical structure is vibrated along the same vibration axis, the vibration modes such as amplitude and motion speed differ depending on the vibration frequency, and when the same mechanical structure is vibrated at the resonance frequency, the maximum amplitude is obtained. A stable vibration mode can be obtained.

  Eventually, in the basic structure 100 described in §1, if the vibrator 120 is vibrated at the inherent resonance frequency fr1, the vibrator 120 will vibrate stably with the maximum amplitude, and the maximum motion speed is obtained. Can be obtained. Specifically, for example, when excitation is performed using AC electrical signals S1 and S2 as shown in FIG. 12, the frequency f1 of these signals S1 and S2 relates to a predetermined vibration axis direction of the vibrator 120. If it matches with the resonance frequency fr1, the motion speed of the vibrator 120 can be maximized, and the magnitude of the acting Coriolis force can be maximized.

  A third method for increasing the Coriolis force detection sensitivity is to increase the displacement caused by the action of the Coriolis force. As described above, the angular velocity sensor described in §2 detects the Coriolis force indirectly by measuring the displacement caused by the action of the Coriolis force instead of directly detecting the Coriolis force acting on the vibrator 120. It is carried out. In §2, examples of displacement detection means using a piezoelectric element and displacement detection means using a capacitive element have been described. In either case, the larger the displacement of the vibrator, the larger the electrical signal that can be obtained.

  Here, the resonance frequency inherent to the vibrator 120 is also involved in the magnitude of the displacement caused by the action of the Coriolis force. Since the vibrator reciprocates (single vibration) along a predetermined vibration axis, the movement direction of the vibrator is reversed every half cycle. Accordingly, since the direction of the Coriolis force acting on the vibrator is also reversed every half cycle, the vibrator eventually reciprocates (single vibration) at a predetermined frequency f2 along a predetermined displacement axis. The force will be measured as the amplitude of the reciprocating motion. For this reason, if the vibration frequency f2 in the displacement axis direction of the vibrator due to the action of the Coriolis force matches the resonance frequency fr2 of the vibrator 120 in the displacement axis direction, the magnitude of the displacement caused by the action of the Coriolis force is maximized. Can be.

  By the way, since the Coriolis force is a force generated based on the motion of the vibrator, the “vibration frequency f2 related to the displacement axis direction of the vibrator” caused by the Coriolis force is “the vibration frequency related to the vibration axis direction of the vibrator”. f1 "and f1 = f2. For example, in the detection by <Method 1: Vx, Fy, ωz> described above, when the vibrator is driven to vibrate at a frequency f1 = 10 kHz in the X-axis direction (vibration axis direction), a constant around the Z-axis is obtained. If the angular velocity ωz is acting, the vibrator vibrates at a frequency f2 = 10 kHz in the Y-axis direction (displacement axis direction) by Coriolis force. In the case of the sensor exemplified in §2, the amplitude of vibration in the Y-axis direction is measured with a piezoelectric element or a capacitive element.

  Therefore, in order to increase the displacement caused by the action of the Coriolis force, the design is made such that the resonance frequency fr1 in the vibration axis direction and the resonance frequency fr2 in the displacement axis direction in the basic structure 100 are made as close as possible. May be oscillated at the resonance frequency fr1 (or in the vicinity thereof).

  FIG. 15 is a graph showing the vibration frequency characteristics of the basic structure 100 shown in FIG. The horizontal axis indicates the frequency f, and the vertical axis indicates the Q value indicating the stability of vibration (in a general vibration system, a value obtained by dividing energy accumulated in the system during one period by energy dissipated from the system) Indicates. Here, the graph g1 is a graph showing the frequency characteristics in the first axial direction, and the graph g2 is a graph showing the frequency characteristics in the second axial direction. In any graph, the frequency at which the Q value peaks is the resonance frequency. In the case of the example of this graph, the resonance frequency in the first axial direction is fr1, and the resonance frequency in the second axial direction is fr2.

  In the case of the angular velocity sensor using the basic structure 100 described in §1, as described above, the resonance frequency fr1 in the first axial direction (vibration axis direction) and the resonance in the second axial direction (displacement axis direction). By designing the frequency fr2 as close as possible and driving the vibrator to vibrate at the resonance frequency fr1 (or the vicinity thereof), the Coriolis force detection sensitivity (sensor detection sensitivity) can be increased. It becomes possible.

  Theoretically, the detection sensitivity S when the vibrator is vibrated at a predetermined frequency f is the product of the Q value corresponding to the frequency f in the vibration axis direction and the Q value corresponding to the frequency f in the displacement axis direction. Is proportional to Therefore, in the case of a sensor having a vibration frequency characteristic as shown in the graph of FIG. 15, the vibration direction showing the frequency characteristic as shown in the graph g1 is taken as the vibration axis, and the vibration direction showing the frequency characteristic as shown in the graph g2 is taken as the displacement axis. If the vibrator is vibrated at the resonance frequency fr1 (the peak frequency of the graph g1, that is, the resonance frequency in the vibration axis direction), the peak value Q1 of the graph g1 and the Q value Q2 corresponding to the frequency fr1 of the graph g2 The detection sensitivity S is given by the product of S = k · Q1 · Q2 (k is a proportional constant).

  Of course, when the resonance frequency fr1 related to the vibration axis direction and the resonance frequency fr2 related to the displacement axis direction coincide with each other, the maximum sensitivity S can be obtained. From the viewpoint of improving the sensitivity, fr1 = fr2. It is preferable to design the basic structure 100.

As described in §2, in the sensor using the basic structure 100, the angular velocity can be detected by the following six methods. Here, Vx, Vy, and Vz indicate that the vibration axis is the X axis, the Y axis, and the Z axis, respectively. Fx, Fy, and Fz indicate that the displacement axis is the X axis, the Y axis, and the Z axis, respectively. Ωx, ωy, and ωz indicate that angular velocities around the X axis, the Y axis, and the Z axis are detected, respectively.
<Method 1: Vx, Fy, ωz>
<Method 2: Vx, Fz, ωy>
<Method 3: Vy, Fx, ωz>
<Method 4: Vy, Fz, ωx>
<Method 5: Vz, Fx, ωy>
<Method 6: Vz, Fy, ωx>

  Here, Method 1 is the X axis for the vibration axis and the Y axis is the displacement axis, and Method 3 is the Y axis for the vibration axis and the X axis is the displacement axis. As long as the basic structure 100 having the structure described above is used, the resonance frequency fr1 related to the vibration axis direction coincides with the resonance frequency fr2 related to the displacement axis direction. This is because, as shown in FIG. 1, even if this basic structure 100 is rotated by 90 ° around the Z axis, the geometric structure is exactly the same, and the frequency characteristic in the X axis direction and the frequency in the Y axis direction are the same. This is because the characteristics are the same.

  Therefore, as long as the above method 1 or 3 is adopted, the maximum sensitivity S can be theoretically obtained with the basic structure 100 having the characteristics described in §1. However, in the method 1 or 3, only the angular velocity ωz around the Z axis can be detected. In order to detect the angular velocity ωx around the X axis, it is necessary to adopt the method 4 or 6, and in order to detect the angular velocity ωy around the Y axis, it is necessary to adopt the method 2 or 5.

  In fact, in the case of a multidimensional angular velocity sensor having a function of detecting angular velocities around a plurality of coordinate axes, Coriolis force acting in two independent displacement axis directions on a vibrator moving along the same vibration axis. Or by changing the vibration direction of the vibrator in various directions (for example, if the vibrator is moved circularly in a plane parallel to the XY plane, vibration in the X-axis direction and in the Y-axis direction). It is necessary to detect a Coriolis force acting in a predetermined displacement axis direction corresponding to each vibration direction.

  In order to be able to cope with such various detection methods, even when the methods 2, 4, 5, and 6 are adopted, it is necessary to devise such that the maximum detection sensitivity can be obtained. . In addition, since the basic structure 100 has geometric commutability between the X-axis and the Y-axis, when considering only the case where the method 2 or 5 is adopted, the case where the method 4 or 6 is adopted. Therefore, only the method 2 or 5 will be considered below.

  Here, Method 2 is the X axis for the vibration axis and Z axis for the displacement axis, and Method 5 is the Z axis for the vibration axis and the X axis for the displacement axis. It is only necessary to realize a structure in which the resonance frequency frx in the X-axis direction and the resonance frequency frz in the Z-axis direction are approximated as much as possible. In such a structure, as a matter of course, an approximate relationship is also obtained between the resonance frequency fry in the Y-axis direction and the resonance frequency frz in the Z-axis direction, and the case where the method 4 or 6 is adopted can be dealt with.

<<< §4. Dimensional conditions for increasing detection sensitivity >>>
Now, based on the theory described in §3, the present inventor uses the prototype in which the dimensional ratio of each part of the basic structure 100 shown in FIG. 1 is changed in various ways to change the detection sensitivity. An experiment was conducted to investigate whether or not. In addition, when these dimensional ratios are changed variously, vibration simulations using a finite element method are also performed, and the dimensional ratios of the respective parts affect the resonance frequency frx in the X-axis direction and the resonance frequency frz in the Z-axis direction. I examined the effect. As a result, the following conclusions could be obtained.

  Here, before describing the conclusion, the following definitions are made for each part of the basic structure 100 with reference to the side sectional view of FIG. The basic structure 100 is practically configured by performing a process of digging a groove on the lower surface of a silicon substrate or the like, and is formed of an integrated structure of the same material (of course, by joining a plurality of parts made of different materials, It is also possible to create the basic structure 100). However, here, for convenience, as shown in FIG. 16, the basic structure 100 will be described by dividing it into three parts: a diaphragm part 110, a vibrator 120, and a pedestal part 130.

  The diaphragm portion 110 is a portion made of a flexible disk. Here, the thickness dimension is T and the outer diameter dimension (diameter) is φ. The vibrator 120 is a cylindrical rigid body disposed at a concentric position having a central axis (Z axis) common to the diaphragm portion 110, and is joined to the lower surface of the diaphragm portion 110. Here, the outer diameter dimension (diameter) of the columnar vibrator 120 is D, and the height is H. Of course, the outer diameter dimension D of the vibrator is smaller than the outer diameter dimension φ of the diaphragm portion 110 and satisfies the condition “D <φ”.

  On the other hand, the pedestal part 130 is a rigid body having a cylindrical surface-like inner peripheral surface joined to the outer peripheral surface of the diaphragm part 110, and has a function of fixing the outer peripheral surface of the diaphragm part 110 to an apparatus housing (not shown). Fulfill. For example, if the bottom surface of the pedestal part 130 is fixed to the apparatus casing, the outer peripheral surface of the diaphragm part 110 is fixed to the apparatus casing via the pedestal part 130. Here, the inner diameter dimension of the pedestal part 130 is the same φ as the outer diameter dimension of the diaphragm part 110. In addition, although the external shape of the base part 130 makes a square shape as shown in FIG. 1, let the dimension of this square one side be ξ here.

  Such a basic structure 100 can be obtained by performing a process of digging a part of the lower surface side of one silicon substrate. That is, when the thickness T portion on the upper surface side of the prepared silicon substrate is defined as the upper layer portion and the remaining lower surface portion is defined as the lower layer portion, the Z axis is centered on the lower layer portion on the lower surface side of the silicon substrate. An annular groove G having an inner diameter D and an outer diameter φ is formed as an axis. Then, the diaphragm part 110 made of silicon is constituted by the disk part having the outer diameter φ with the Z axis as the central axis in the upper layer part. In addition, a vibrator made of silicon is constituted by a cylindrical portion having a diameter D with the Z axis as the central axis in the lower layer portion, and included in a cylinder having a diameter φ with the Z axis as the central axis in the silicon substrate. The pedestal portion 130 made of silicon is constituted by the portion that is not present.

  In the example shown in the drawing, a part of the lower side of the cylindrical portion having the diameter D is cut off, and processing is performed so that the bottom surface of the vibrator 120 is slightly above the bottom surface of the pedestal portion 130. That is, the dimensional condition T + H <K is satisfied among the thickness T of the diaphragm 110, the height H of the columnar vibrator 120, and the thickness K of the pedestal 130. This is a consideration for ensuring the degree of freedom of downward displacement of the vibrator 120.

  The thickness T of the diaphragm portion 110 is set to a sufficiently thin dimension to give flexibility, and therefore, the portion of the diaphragm portion 110 located above the annular groove G is shown in FIGS. As shown in FIG. On the other hand, the height H of the columnar vibrator 120 and the thickness K of the pedestal part 130 are set to dimensions that are sufficiently thick so that the vibrator 120 and the pedestal part 130 behave as a rigid body (the figure shows the figure). For the sake of convenience, the actual dimensional ratio is ignored). The diaphragm 110 is a disk having a thickness T that is thin enough to be flexible. However, since the vibrator 120 made of a rigid body is bonded to the lower surface of the center, The part will behave as a rigid body. In order to displaceably support the vibrator 120, it is sufficient that at least the peripheral portion of the diaphragm portion 110 has flexibility.

  An important conclusion obtained by experiments and simulations conducted by the inventors of the present application is that the dimensional ratio φ / H of the basic structure 100 adopts the method 2 or method 5 described above (method 4 or method 6). This is also the case when it is an important parameter that affects the detection sensitivity. Here, φ is the outer diameter (diameter of the disk) of the diaphragm portion 110 having the thickness T, and H is the height of the columnar vibrator 120 (the height of the column portion having the diameter D). is there.

  FIG. 17 is a graph showing the relationship between the dimensional ratio φ / H of the basic structure 100 and the sensitivity of the angular velocity sensor. This graph shows the detection sensitivity when the angular velocity is measured using the method 2 using various prototypes having different dimensional ratios φ / H. More specifically, by supplying a predetermined excitation energy, a constant angular velocity ωy around the Y axis was added in a state where the vibrator was vibrated in the X axis direction at a resonance frequency related to the axial direction. Sometimes, the amplitude value of the vibration in the Z-axis direction generated in the vibrator is measured as the detection sensitivity. The horizontal axis of the graph indicates the dimensional ratio φ / H of the basic structure 100 used in the sensor used for measurement, and the vertical axis indicates the detection sensitivity (normalized so that the maximum value is 1.0). ).

  As a method of obtaining the graph shown in FIG. 17, a method of measuring the detection sensitivity when only the value of H is changed in various ways while maintaining the values of φ, D, T, etc. at a constant value, There is a method of measuring the detection sensitivity when only the value of φ is variously changed while maintaining the values of D, T, etc. at a constant value. The inventor of the present application performed both of these methods, and the same graph shown in FIG. 17 was obtained in any case.

  As shown in the figure, when the dimensional ratio φ / H is between 2 and 3, the detection sensitivity shows a steep rise. FIG. 18 is a table showing data on which the graph shown in FIG. 17 is based. As can be seen from this table, the detection sensitivity increases extremely remarkably in the region that satisfies the dimensional condition “2.25 ≦ φ / H ≦ 2.54”. That is, in the case of the effective number of detection sensitivity shown in the figure (third decimal place), when φ / H is 2 or less or 3 or more, the detection sensitivity is 0.000 (actually, The measurement result of “0.000” in FIG. 3 does not indicate that the sensitivity is zero but indicates that it is buried in a noise component and cannot be measured accurately), “2.25 ≦ φ / H The detection sensitivity of the region satisfying the dimensional condition “≦ 2.54” is remarkable. This is because if the basic structure 100 satisfying such a dimensional condition is designed, the resonance frequency in the X-axis direction and the resonance frequency in the Z-axis direction are very close. This means that extremely good detection sensitivity can be obtained.

  More precisely, since the detection sensitivity is 1.000 (maximum value) when the dimension ratio φ / H is near 2.40, the dimension ratio φ / H = 2 from the viewpoint of improving the detection sensitivity. If the design is such that .40, an ideal basic structure 100 can be obtained.

  The important point here is that even if the thickness T of the diaphragm portion 110 and the diameter D of the vibrator 120 are changed, the results shown in FIGS. 17 and 18 are not changed, and the results have universality. Actually, as a result of measuring the detection sensitivity by adopting the above-described methods 2, 4, 5, and 6, the results equivalent to those shown in FIGS. 17 and 18 were obtained in any case.

  The value φ for determining the dimensional ratio φ / H is the outer diameter of the disk constituting the diaphragm portion 110, and the value H is the height of the cylinder constituting the vibrator 120. The dimension that determines the geometric form of the basic structure 100 shown in FIG. However, according to experiments and simulations conducted by the inventor of the present application, it has been found that factors other than the dimensions φ and H have no significant influence on the peak position of detection sensitivity obtained by the experiments and simulations.

  For example, the thickness T of the diaphragm 110 is a factor that affects the resonance frequency. Actually, by changing the thickness T, the resonance frequency in each coordinate axis direction changes variously. However, the “detection sensitivity” referred to in the present application is the degree of coincidence between the resonance frequency in the vibration axis direction (for example, the resonance frequency in the X axis direction) and the resonance frequency in the displacement axis direction (for example, the resonance frequency in the Z axis direction). It is determined on the basis of the resonance frequency, and is not determined only by the resonance frequency in a specific axial direction.

  The inventor of the present application conducted the above experiments and simulations for various prototypes of basic structures in which the thickness T of the diaphragm portion 110 has a practical range as an angular velocity sensor. As a result, although the absolute value of the sensor sensitivity changes variously, the range in which the mountain-shaped waveform in the graph of FIG. 17 is obtained (the range of the dimension ratio φ / H in which the detection sensitivity becomes remarkable) is “2.25 ≦ φ The point where “/H≦2.54” was not changed. That is, it was confirmed that the value of the dimensional ratio φ / H at which the maximum sensitivity is obtained does not depend on the thickness T of the diaphragm portion 110.

  Similarly, although the outer diameter D of the vibrator 120 is a factor that affects the resonance frequency, it has been confirmed that it does not affect the range of the dimension ratio φ / H that exhibits remarkable detection sensitivity.

  On the other hand, the outer dimension ξ and the thickness K of the pedestal part 130 have no influence on the resonance frequency and the detection sensitivity. In the first place, since the pedestal portion 130 is a rigid body that is assumed to be fixed to the apparatus housing, the shape and thickness of the outer shape do not affect the support structure of the outer peripheral portion of the diaphragm portion 110. Of course, since the inner diameter φ of the pedestal portion 130 is equal to the outer diameter φ of the diaphragm portion 110, it becomes an important factor that affects “detection sensitivity”.

  As described above, regarding the geometric structure of the basic structure 110, the dimension condition “2.25 ≦ φ / H ≦ 2.54” is a universal condition for obtaining good detection sensitivity. However, the dimensional condition has universality with respect to the material of the basic structure 110. The inventor of the present application gave various numerical values to the elastic coefficient of the basic structure 110 and executed a simulation by the finite element method. However, as long as a practical elastic coefficient setting is used, the results shown in FIGS. 17 and 18 are changed. There was no.

  The results shown in FIG. 17 and FIG. 18 indicate that the prototype 120 has a height H of the vibrator 120 within a range of 0.2 mm ≦ H ≦ 0.7 mm (a size that is most demanded industrially). It is the result of having performed analysis by experiment and simulation. At the present stage, verification is not performed in which the height H of the vibrator 120 is set to a range other than the above. However, even when the height H of the vibrator 120 is set to a range other than the above, it is considered that the same result is obtained, and the condition “2.25 ≦ φ / H ≦ 2.54” is Any value of the height H of the vibrator 120 is estimated to be a universal condition for obtaining good detection sensitivity.

  Further, in the actual angular velocity sensor, excitation means for inducing vibration with a motion component in a predetermined vibration axis direction with respect to the vibrator 120 and a predetermined displacement axis direction generated in the vibrator 120 based on the Coriolis force. Displacement detecting means for detecting the displacement is added. For example, in the example shown in FIG. 9, a layered structure such as the insulating layer 210, the lower electrode 220, and the piezoelectric element 230 is formed on the upper surface of the basic structure 100.

  When such a layered structure is formed, the resonance frequency itself changes as when the thickness T of the diaphragm 110 is changed. However, if the basic structure 100 that satisfies the condition that the value of the dimension ratio φ / H is “2.25 ≦ φ / H ≦ 2.54” is prepared in advance, various layered structures can be formed on the upper surface thereof. Even if formed, since the outer diameter φ of the diaphragm portion 110 and the height H of the vibrator 120 are not changed, the value of the dimensional ratio φ / H does not change to satisfy the above condition, and a good detection sensitivity is obtained. Will be obtained.

  Thus, when the outer diameter of the disk constituting the diaphragm portion 110 is φ, the outer diameter of the cylinder constituting the vibrator 120 is D, and the height of the cylinder constituting the vibrator 120 is H, “ If the basic structure 100 is designed so as to satisfy the dimensional condition of “D <φ” and “2.25 ≦ φ / H ≦ 2.54”, the resonance frequency in the X-axis direction of the vibrator and the Z-axis direction of the vibrator The resonance frequency can be approximated, and extremely good detection sensitivity can be obtained. Moreover, the above dimensional conditions are universal conditions that are not affected by the dimensional values and materials of the other parts.

  Therefore, when an XYZ three-dimensional orthogonal coordinate system is defined in which the origin O is at the center position of the upper surface of the diaphragm unit 110 and the upper surface of the diaphragm unit 110 is included in the XY plane, one of the X axis and the Z axis is defined. Designing the basic structure 100 that satisfies the above conditions in an angular velocity sensor that uses the vibration axis and the other as a displacement axis and detects the angular velocity around the Y axis based on the detection value by the displacement detection means increases the detection sensitivity. Very useful. Of course, since this basic structure 100 has a geometric interchangeability between the X-axis and the Y-axis, one of the Y-axis and the Z-axis is a vibration axis and the other is a displacement axis. Even if it is used for an angular velocity sensor that detects an angular velocity around the X axis based on a detection value obtained by the above, it is very useful for increasing detection sensitivity.

  The above-mentioned Patent Documents 1 to 3 disclose a basic structure having a dimensional ratio φ / H of 6 or more. This is because in order to reduce the thickness of the entire sensor, it is advantageous to make the dimension value H sufficiently smaller than the dimension value φ, and it was considered to be a preferable structure for a small angular velocity sensor. However, the aforementioned Patent Documents 1 to 3 are documents disclosing inventions related to the structure and operation principle of a novel sensor, and do not mention anything about the dimensional ratio for obtaining good detection sensitivity. Actually, from the viewpoint of detection sensitivity, the dimensional ratios of the basic structures illustrated in the above-mentioned Patent Documents 1 to 3 are not preferable. In fact, according to the results shown in FIG. 18, if a basic structure with φ / H = 2.40 is used instead of a basic structure with a size ratio φ / H = 6, extremely high detection sensitivity can be obtained. It will be.

  19 and 20 are side sectional views showing an example of a basic structure that satisfies the dimensional ratio φ / H, which is a feature of the present invention. In the basic structure shown in both figures, the height H of the columnar vibrator 120 and the outer diameter φ of the disk-shaped diaphragm 110 are common, and the dimensional ratio φ / H = 2.40 is set. Has been. As shown in the table of FIG. 18, this corresponds to a dimensional ratio that provides the maximum detection sensitivity. In other words, the dimensional ratio is such that the resonance frequency in the X-axis or Y-axis direction and the resonance frequency in the Z-axis direction are completely the same.

  Of course, comparing the example shown in FIG. 19 with the example shown in FIG. 20, other dimensions, for example, the thicknesses T1, T2 of the diaphragm portion 110, the outer diameters D1, D2 of the vibrator 120, and the outer size ξ1 of the pedestal portion 130 are compared. , Ξ2, and thicknesses K1 and K2 of the pedestal portion 130 are different from each other. Therefore, the example shown in FIG. 19 and the example shown in FIG. However, since the dimensional ratio φ / H is all set to 2.40, in each case, the resonance ratios are respectively unique resonance frequencies (common resonance frequencies in the X-axis, Y-axis, and Z-axis directions). If detection is performed by vibrating the vibrator 120, the maximum detection sensitivity can be obtained.

  As described above, when the dimension ratio φ / H = 2.40 is set, the maximum detection sensitivity can be obtained, but generally, the higher the detection sensitivity, the lower the frequency response as a sensor. Therefore, in practice, the value of the dimension ratio φ / H is set to a range of “2.25 ≦ φ / H ≦ 2.40−δ” or “2.40 + δ ≦ φ / H ≦ 2.54”. preferable. Here, as the value of δ, a large value may be set as appropriate when a high response frequency is required, and a small value may be set as appropriate when a low response frequency is sufficient.

100: Basic structure 110: Diaphragm part 120: Vibrator 130: Pedestal part 210: Insulating layer 220: Lower electrode 230: Piezoelectric element 310: Upper substrate 320: Lower substrate D, D1, D2: Outside the columnar vibrator 120 Diameters E1 and E2: Electrodes E11 to E24: Upper electrodes E31 to E45: Fixed electrodes f: Frequency fr1, fr2: Resonance frequency G: Toroidal groove G ′: Grooves g1, g2 formed on the lower surface of the upper substrate 310: Graph H showing vibration frequency characteristics: Height K, K1, K2 of cylindrical vibrator 120: Thickness of basic structure 100 P: Part of piezoelectric element Q1, Q2: Q value S1, S2 of vibration system: AC electric signal T, T1, T2: Disc-shaped diaphragm thickness t: Time XYZ: Each coordinate axis of the three-dimensional orthogonal coordinate system φ: Outer diameter of the disc-shaped diaphragm 110 ξ, ξ1, ξ2: Outer dimensions of the basic structure 100

Claims (8)

A diaphragm part composed of a disk having at least a surrounding part having flexibility; and
A vibrator composed of a cylindrical rigid body arranged at a concentric position having a common center axis with the diaphragm portion, and bonded to the lower surface of the diaphragm portion;
A rigid body having a cylindrical surface-like inner peripheral surface joined to an outer peripheral surface of the diaphragm portion, and a pedestal portion for fixing the outer peripheral surface of the diaphragm portion to an apparatus housing;
Excitation means for inducing vibration having a motion component in a predetermined vibration axis direction with respect to the vibrator;
Displacement detecting means for detecting a displacement in a predetermined displacement axis direction generated in the vibrator based on Coriolis force;
With
When an XYZ three-dimensional orthogonal coordinate system having an origin O at the center position of the upper surface of the diaphragm portion and the upper surface of the diaphragm portion being included in the XY plane is defined, one of the X axis and the Z axis is vibrated. In the angular velocity sensor for detecting the angular velocity around the Y axis based on the detection value by the displacement detection means, with the other axis as the displacement axis,
The outer diameter of the disk constituting the diaphragm portion and phi, the outer diameter of the cylinder constituting the oscillator is D, the height of the cylinder constituting the vibrator is taken as H, the height of the cylinder H satisfies the dimensional condition of “0.2 mm ≦ H ≦ 0.7 mm”, and further satisfies the dimensional condition of “D <φ” and “2.25 ≦ φ / H ≦ 2.54”. Angular velocity sensor. The angular velocity sensor according to claim 1,
An angular velocity sensor, wherein the diaphragm portion, the vibrator, and the pedestal portion are formed of an integral structure made of the same material. The angular velocity sensor according to claim 2,
When the thickness T portion on the upper surface side of the substrate is defined as the upper layer portion and the remaining lower surface portion is defined as the lower layer portion, the lower surface portion on the lower surface side of the substrate has an inner diameter D and an outer diameter with the Z axis as the central axis. An annular groove with φ is formed,
Of the upper layer part, a diaphragm part is constituted by a disk part having an outer diameter φ with the Z axis as the central axis,
Of the lower layer portion, a vibrator is constituted by a cylindrical portion having a diameter D with the Z axis as a central axis,
An angular velocity sensor, wherein a pedestal is formed by a portion of the substrate that is not included in a cylinder having a diameter φ with the Z axis as a central axis. The angular velocity sensor according to claim 3.
An angular velocity sensor in which a dimensional condition of T + H <K is satisfied among a thickness T of a diaphragm portion, a height H of a cylindrical vibrator, and a thickness K of a pedestal portion. The angular velocity sensor according to claim 3 or 4,
An angular velocity sensor comprising: a diaphragm portion made of silicon, a vibrator made of silicon, and a pedestal portion made of silicon by forming an annular groove on a lower surface of the silicon substrate. In the angular velocity sensor according to any one of claims 1 to 5,
The excitation means includes an excitation piezoelectric element fixed to a predetermined position on the upper surface of the diaphragm portion, and an excitation electric circuit that applies an AC electric signal to the excitation piezoelectric element;
An angular velocity sensor, wherein the displacement detection means includes a detection piezoelectric element fixed to a predetermined position on the upper surface of the diaphragm portion, and a detection electric circuit for detecting a charge generated in the detection piezoelectric element. In the angular velocity sensor according to any one of claims 1 to 5,
An excitation means includes an excitation displacement electrode formed at a predetermined position of the diaphragm portion or the vibrator, an excitation fixed electrode fixed to an apparatus housing so as to face the excitation displacement electrode, and the excitation displacement electrode. And an excitation electric circuit for applying an alternating electric signal between the excitation fixed electrode and the excitation fixed electrode,
Displacement detecting means includes a detection displacement electrode formed at a predetermined location of the diaphragm portion or the vibrator, a detection fixed electrode fixed to the apparatus housing so as to face the detection displacement electrode, and the detection displacement. An angular velocity sensor comprising: a detection electric circuit that detects a capacitance value between an electrode and the detection fixed electrode. The angular velocity sensor according to claim 6 or 7,
An angular velocity sensor, wherein the excitation electric circuit applies an AC electric signal having a frequency equal to a resonance frequency in the vibration axis direction of the vibrator.

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