Angular velocity sensor element, angular velocity sensor and angular velocity sensor unit both using angular velocity sensor element, and signal detecting method for angular velocity sensor unit

Abstract

The An angular velocity sensor of the present invention has one end connected to a holding section and the other another end connected to a weighting section. According to the angular velocity sensor, a driving arm has a dog-leg bent structure of arms extending in a direction perpendicular to a connecting direction of the holding section and the weighting section.

Description

317 3171 and 3172, and a pair of driving arms 305 3051, 3052, 3053 and 3054. The weighting section 3171 can be expressed as “first weighting section 3171”. The weighting section 3172 can be expressed as “second weighting section 3172”. The driving arm 3051 can be expressed as “first arm”. The driving arm 3052 can be expressed as “second arm”. The driving arm 3053 can be expressed as “third arm”. The driving arm 3054 can be expressed as “fourth arm”. Each of supporting arms 316 extends from the mid part of external connection section 315 toward the center of sensor element 301. Weighting sections 317 3171 and 3172 are symmetrically disposed on the both sides of supporting arms 316. Weighting section 3171 is connected with a pair of driving arms 3051, 3052 and weighting section 3172 is connected with a pair of driving arms 305 3053, 3054. Driving Each of driving arms 305 have 3051, 3052, 3053 and 3054 has driving electrode 306, sensing electrode 308, and monitoring electrode 307, which will be described later. The electrodes above are connected via wiring electrode 319 and electrode pad 318 disposed on external connection section 315. Each of driving arms 305 has a dog-leg (bent) structure of arm 305a and extending in the Y-axis direction, arm 305b extending in the Y-axis direction and arm 305c extending in the X-axis direction. Driving arm 305 connects between weighting section 317 sections 3171 and 3172 and the tip of supporting arm 316. The first arm 3051 and the second arm 3052 are surrounded on at least three sides by the holding section and the first weighting section 3171. The third arm 3053 and the fourth arm 3054 are surrounded on at least three sides by the holding section and the second weighting section 3172. A pair of the external connection section 315 and the supporting arm 316 can be expressed as a “holding section”. A space 324 between driving arm 3051 and driving arm 3052 can be expressed as a “continuous space” (or hollow space). A space 326 between driving arm 3053 and driving arm 3054 can be expressed as a “continuous space” (or hollow space). A length between the first arm 3051 and the third arm 3053 in the X-axis direction is shorter than a length of the first arm 3051 or the third arm 3053 in the Y-axis direction. A length between the arm 305a (or the arm 305b) in the Y-axis direction is shorter than a length of the arm 305c in the X-axis direction. The arm 305a can be expressed as “first arm member”. The arm 305b can be expressed as “second arm member”. The arm 305c can be expressed as “third arm member”. The Y-axis direction can be expressed as “first direction”, and the X-axis direction can be expressed as “second direction”.

FIG. 17 schematically shows a fundamental vibration state of the sensor element of the angular velocity sensor unit in accordance with the third exemplary embodiment of the present invention. FIG. 18 schematically shows a detecting vibration state of the sensor element of the angular velocity sensor unit of the embodiment. A driving signal fed from IC 302 is applied, via electrode pad 318 and wiring electrode 319, to driving electrode 306. The application of driving signals allows weighting section 317 sections 3171, 3172 to have fundamental vibration with compression and extension in the X-axis direction, as shown in FIG. 17. In the fundamental vibration state, the angular velocity sensor element undergoes angular velocity with a rotation axis along the Z-axis direction, by which the Coriolis force is produced. The Coriolis force allows driving arms 305 3051, 3052, 3053 and 3054 to vibrate in the Y-axis direction, as shown in FIG. 18. Sensing electrode 308 detects a deflection of driving arms 305 3051, 3052, 3053 and 3054 caused by the vibration in the Y-axis direction, and converts it into an electric signal as a detecting signal. The detecting signal is transmitted to IC 302 via wiring electrode 319 and electrode pads 318. Monitoring electrode 307 controls driving signals; specifically, it detects vibration amplitude and a driving cycle of driving arms 305 3051, 3052, 3053 and 3054 in vibration and feeds the information back to IC 302.

Sensor element 301 has driving electrode 306, sensing electrode 308, and monitoring electrode 307 on the substrate made of Si. As is described in FIG. 26, each of the electrodes has a laminated structure formed of Pt-made lower electrode 3011 disposed on the substrate, PZT-made piezoelectric layer 3009 disposed on lower electrode 3011, and Au-made upper electrode 3010 disposed on piezoelectric layer 3009. When a positive voltage is applied to upper electrode 3010 while lower electrode 3011 is being grounded, compression force 3012 is exerted on the structure in the laminated direction, by which the laminated structure has an extension. When a negative voltage is applied to upper electrode 3010, tensile force 3013 is exerted on the structure in the laminated direction, by which the laminated structure has a compression. Conversely, providing driving arms 305 3051, 3052, 3053 and 3054 with deflection can produce voltage. That is, a negative voltage is obtained by exerting a compression force on the electrode, whereas a positive voltage is obtained by exerting a tensile force on the electrode.

FIG. 19 schematically shows the working state of a driving electrode to provide fundamental vibration of the sensor element of the angular velocity sensor unit in accordance with the third exemplary embodiment of the present invention. To attain the fundamental vibration of sensor element 301, driving electrodes 306 are positioned as follows. First, arm 305b disposed on the side of weighting section 317 sections 3171 and 3172 is divided into four areas with respect to a changing point of deflection shown by dashed lines in FIG. 19. Driving electrodes 306 are disposed in an area close to weighting section 317 sections 3171 and 3172 and in the area diagonal to above. When a positive voltage is applied to the diagonally disposed driving electrodes 306, a compression force is exerted on the electrodes, allowing the electrodes to have extension. As a result, arm 305b has a deflection of an S shape. When a negative voltage is applied to the electrodes, a tensile force is exerted on the electrodes, allowing the electrodes to have compression. As a result, arm 305b has a deflection of an inverted S shape. Repeating the application of voltage allows weighting section 317 sections 3171 and 3172 to have driving vibration in the X-axis direction.

FIG. 20 schematically shows a detecting state in which a monitoring electrode detects the fundamental vibration of the sensor element of the angular velocity sensor unit in accordance with the third exemplary embodiment of the present invention. In the fundamental vibration, arm 305a has a changing point shown by dashed lines at which the direction of deflection is oppositely changed. Monitoring electrode 307 should be disposed in an area of the four areas so as not to extend across the dashed lines. Such positioned monitoring electrode 307 produces voltage corresponding to the deflection of arm 305a and forms a monitoring signal.

FIG. 21 schematically shows a detecting state in which a sensing electrode detects a driving vibration of the sensor element of the angular velocity sensor unit in accordance with the third exemplary embodiment of the present invention. Under the Coriolis force, arm 305a is arched, as shown in FIG. 21. Detecting the deflection of arm 305a, sensing electrode 308 generates a detecting signal corresponding to the deflection. As is shown in FIG. 21, sensing electrode 308 is disposed on arm 305a so as to be offset rightward from the central axis of arm 305a. When arm 305a has a leftward deflection as seen in FIG. 21, sensing electrode 308 disposed in the right half of arm 305a undergoes an extending force, producing a positive voltage. Conversely, when arm 305a has a rightward deflection as seen in FIG. 21, sensing electrode 308 undergoes a compressing force, producing a negative voltage. Sensing electrode 308 thus produces a detecting signal.

To detect angular velocity by the angular velocity sensor unit, it is important that sensor element 301 has fundamental vibration in the X-Y plane. As is described in FIG. 26, driving electrode 306 has a laminated structure of upper electrode 3010, lower electrode 3011, and piezoelectric layer 3009.

In the structure above, the fundamental vibration of driving arms 305 3051, 3052, 3053 and 3054 in the X-axis direction is obtained by compression and extension of driving electrode 306. However, at the same time, compression force 3012 and tensile force 3013 are exerted on driving electrode 306 in the laminated direction, i.e., in the Z-axis direction. The Z-axis vibration has an adversely adverse effect on monitoring electrode 307 that detects fundamental vibration of driving arms 305 3051, 3052, 3053 and 3054. That is, an unwanted signal formed by the Z-axis vibration is mixed into the detecting signal fed from monitoring electrode 307, which has degraded detecting accuracy of the angular velocity sensor unit.

In the angular velocity sensor unit of the embodiment, to address the problem above, correction electrode 320 is disposed on supporting arm 316 at wiring electrode 319 that connects between electrode pad 318 and monitoring electrode 307. Detecting the Z-axis vibration, correction electrode 320 forms a correction signal so as to attenuate the unwanted signal formed in monitoring electrode 307 due to the Z-axis vibration. The structure suppresses the effect on monitoring electrode 307 due to the Z-axis vibration.

For reliably attenuating an unwanted signal caused by the Z-axis vibration, what required for monitoring electrode 320 is—not forming a signal in response to fundamental vibration, but forming a signal with a potential opposite to the unwanted signal generated in monitoring electrode 307 in the Z-axis vibration. That is, correction electrode 320 should be located on a part having less effect of fundamental vibration and having deflection in a direction opposite to deflection that monitoring electrode 307 undergoes in the Z-axis vibration. Specifically, monitoring electrode 307 is disposed on arm 305a on the side of external connection section 315. Correction electrode 320 is disposed on supporting arm 316—which is the axis of symmetry of fundamental vibration and therefore is insusceptible to the vibration—on the side of external connection section 315.

FIG. 22 schematically shows a Z-axis vibration of the sensor element of the angular velocity sensor unit in accordance with the third exemplary embodiment of the present invention. When weighting section 317 moves sections 3171 and 3172 move downward in the Z-axis vibration, arm 305a has a concave deflection at the part on which monitoring electrode 307 is disposed. At that time, monitoring electrode 307 undergoes a compression force, thereby producing a negative voltage. On the other hand, the part on which correction electrode 320 is disposed of supporting arm 316 has a convex deflection. At that time, correction electrode 320 undergoes a tensile force, thereby producing a positive voltage.

An unwanted signal generated in monitoring electrode 307 and a correction signal generated in correction electrode 320, both of which are caused by the Z-axis vibration, are opposite in potential. These signals are transmitted to same electrode pad 318 via wiring electrode 319, as shown in FIG. 16. In this way, electrode pad 318 outputs monitoring signals from which an unwanted signal caused by the Z-axis vibration has been attenuated by a correction signal.

In the Z-axis vibration, an unwanted signal is formed not only in monitoring electrode 307 but also in wiring electrode 319. Employing an improved electrode design capable of attenuating both the unwanted signals by the correction signal from correction electrode 320 enhances detection accuracy of the angular velocity sensor unit.

According to sensor element 301, as described above, correction electrode 320 produces a correction signal to attenuate an unwanted signal generated in monitoring electrode 307 in the Z-axis vibration, without producing a signal in response to the fundamental vibration. By virtue of the proper attenuation, the monitoring signal fed from sensor element 301 to IC 302 has high detection accuracy. That is, the fundamental vibration of sensor element 301 is controlled by the monitoring signal with high detection accuracy, which contributes to enhanced detection accuracy of the angular velocity sensor unit.

By virtue of the structure that suppresses an unwanted signal generated in the Z-axis vibration, TAB tape or other anti-vibration measures against unwanted flexural vibration in the Z-axis direction can be eliminated when sensor element 301 is disposed in package 303.

The present invention provides an angular velocity sensor with enhanced detection level. The angular velocity sensor element of the present invention offers high output sensitivity. Further, the present invention provides an angular velocity sensor unit with enhanced detection accuracy. These advantages are particularly useful for the angular velocity sensor used in electronic equipment that has to meet the needs of having high sensitivity in a compact body, such as a navigation system device.

Claims

1. An angular velocity sensor element comprising:

a driving arm having a first end and a second end opposite to the first end;

a holding section connected to the first end of the driving arm;

a weighting section connected to the second end of the driving arm;

a driving electrode that is disposed on the driving arm and configured to vibrate the weighting section; and

a detecting electrode that is disposed on the driving arm and is configured to detect angular velocity of the driving arm,

wherein, the driving arm is disposed between the holding section and the weighting section,

a length of the driving arm in a first direction from the first end to the second end is shorter than a length of the driving arm in a second direction substantially perpendicular to the first direction, and

the driving arm comprises a first driving arm and a second driving arm,

the driving arm has a continuous space defined between the first driving arm and the second driving arm,

each of the first driving arm and the second driving arm is substantially surrounded on at least three sides by the holding section and the weighting section,

each of the first driving arm and the second driving arm comprises a first arm member, a second arm member and a third arm member,

the first arm member and the second arm member extend in the first direction,

the third arm member extends in the second direction perpendicular to the first direction, and

the weighting section is connected to the first driving arm and the second driving arm.

2. The angular velocity sensor element of claim 1, wherein

the driving arm has arm members extending in the second direction, and

the detecting electrode is disposed on one arm member of the arm members so as to be offset from a central axis of the one arm member in an extending direction.

3. The angular velocity sensor element of claim 2, wherein the detecting electrode has a symmetrical shape in the extending direction of the arm members with respect to a changing point of deflection of the arm members.

4. The angular velocity sensor element of claim 1, wherein

the driving arm is composed of comprises a first third driving arm and a second fourth driving arm,

the first driving arm has first and second arm members extending in the second direction,

the holding section is disposed between the first driving arm and the second third driving arm, and,

the driving electrode is disposed on the first arm member and the detecting electrode is disposed on the second arm member, and the driving electrode is disposed so as to be offset from a central axis of the first arm member in an extending direction.

5. The angular velocity sensor element of claim 4, wherein the driving electrode is divided into two sections and the first arm member is divided into four areas on a vertical axis parallel to the second direction and on a horizontal axis parallel to the first direction of the first arm member, and the divided sections of the driving electrode are disposed in diagonal areas of the four areas.

6. An angular velocity sensor comprising:

an angular velocity sensor element of claim 1;

a driving control circuit that applies configured to apply a driving signal to a the driving electrode disposed on the angular velocity sensor element; and

a detecting circuit that processes configured to process a detecting signal fed from a the detecting electrode disposed on the angular velocity sensor element.

7. The angular velocity sensor element of claim 1, wherein

the driving arm has a dog-leg bent structure of arm members extending in a direction perpendicular to a vibrating direction of the weighting section.

8. The angular velocity sensor element of claim 7, wherein each corner of the dog-leg bent structure of the arm members has fillet geometry.

9. The angular velocity sensor element of claim 1, wherein

the driving electrode has a lower electrode, piezoelectric substrate, and an upper electrode stacked in this order piezoelectric substrate stacked on a lower electrode, and an upper electrode stacked on the piezoelectric substrate.

10. The angular velocity sensor element of claim 1, wherein

the driving arm has an air gap disposed between the first end of driving arm and the second end of the driving arm.

11. The angular velocity sensor element of claim 1, wherein

the holding section is separated into two portions at a center of the holding section.

12. The angular velocity sensor element of claim 1, wherein

the first end of the driving arm is connected to the holding section at a center of the holding section in the second direction substantially perpendicular to the first direction from the first end to the second end.

13. The angular velocity sensor element of claim 1, wherein

the driving arm has a first driving arm and a second driving arm,

the holding section is disposed between the first driving arm and the second driving arm, and

a length between the first driving arm and the second driving arm in the first direction is shorter than a length of the driving arm in the second direction.

14. An angular velocity sensor element comprising:

a driving arm having a first end and a second end opposite to the first end;

a holding section connected to the first end of the driving arm;

a weighting section connected to the second end of the driving arm;

a driving electrode disposed on the driving arm and being configured to vibrate the weighting section; and

a detecting electrode disposed on the driving arm and configured to detect angular velocity of the driving arm,

wherein, the driving arm has a first driving arm and a second driving arm,

the holding section is disposed between the first driving arm and the second driving arm, and

a length of the driving arm in a first direction from the first end to the second end is shorter than a length of the driving arm in a second direction substantially perpendicular to the first direction,

a length between the first driving arm and the second driving arm in the first direction is shorter than a length of the driving arm in the second direction, and

the driving arm is substantially surrounded on at least three sides by the holding section and the weighting section.

15. The angular velocity sensor element of claim 14, wherein

the driving electrode has a lower electrode, piezoelectric substrate, and an upper electrode stacked in this order.

16. The angular velocity sensor element of claim 14, wherein

the holding section is separated into two portions at a center of the holding section.

17. The angular velocity sensor element of claim 14, wherein

the first end of the driving arm is connected to the holding section at a center of the holding section in the direction substantially perpendicular to the direction from the first end to the second end.

18. The angular velocity sensor element of claim 14, wherein

each of the first driving arm and the second driving arm has arm members extending in the second direction, and

the detecting electrode is disposed on one arm member of the arm members so as to be offset from a central axis of the one arm member in the second direction.

19. The angular velocity sensor element of claim 14, wherein

each of the first driving arm and the second driving arm has arm members extending in the second direction, and

the detecting electrode has a symmetrical shape in the second direction with respect to a changing point of deflection of the arm member.

20. The angular velocity sensor element of claim 1, wherein the driving arm has a first driving arm and a second driving arm,

the holding section is disposed between the first driving arm and the second driving arm, and

a shape of the first driving arm is symmetric to a shape of the second driving arm with respect to the holding section.

21. The angular velocity sensor element of claim 20, wherein the holding section is separated into two portions at a center of the holding section.

22. An angular velocity sensor element comprising:

a first arm, a second arm, a third arm and a fourth arm;

a holding section connected to the first arm, the second arm, the third arm and the fourth arm;

a first weighting section connected to the first arm and the second arm;

a second weighting section connected to the third arm and the fourth arm;

driving electrodes configured to vibrate the first weighting section and the second weighting section; and

detecting electrodes configured to detect angular velocity,

wherein,

each of the first arm and the second arm is disposed between the holding section and the first weighting section,

each of the third arm and the fourth arm is disposed between the holding section and the second weighting section,

the first arm and the second arm are surrounded on at least three sides by the holding section and the first weighting section,

the third arm and the fourth arm are surrounded on at least three sides by the holding section and the second weighting section,

each of the first arm and the second arm comprises a first arm member, a second arm member and a third arm member,

the first arm member and the second arm member extend in a first direction, and

the third arm member extends in a second direction perpendicular to the first direction.

23. The angular velocity sensor element of claim 22, wherein

each of the third arm and the fourth arm comprises a first arm member, a second arm member and a third arm member,

the first arm member and the second arm member extend in the first direction,

the third arm member extends in the second direction perpendicular to the first direction, and,

the driving electrodes are disposed on the first arm members and the detecting electrodes are disposed on the second arm members, and the driving electrodes are disposed so as to be offset from a central axis of a respective one of the first arm members.

24. An angular velocity sensor comprising:

an angular velocity sensor element of claim 22;

a driving control circuit configured to apply a driving signal to the driving electrodes disposed on the angular velocity sensor element; and

a detecting circuit configured to process a detecting signal fed from the detecting electrodes disposed on the angular velocity sensor element.

25. The angular velocity sensor element of claim 22, wherein

each of the first arm, the second arm, the third arm and the fourth arm has a bent structure of arm members extending in a direction perpendicular to a vibrating direction of a respective one of the weighting sections.

26. The angular velocity sensor element of claim 25, wherein each corner of the bent structure of the arm members has fillet geometry.

27. The angular velocity sensor element of claim 22, wherein

the driving electrodes have a piezoelectric substrate stacked on a lower electrode, and an upper electrode stacked on the piezoelectric substrate.

28. The angular velocity sensor element of claim 22, wherein

a continuous space is defined between the first arm and the second arm.

29. The angular velocity sensor element of claim 22, wherein

the holding section is separated into two portions at a center of the holding section.

30. The angular velocity sensor element of claim 22, wherein

a continuous space is defined between the third arm and the fourth arm.

31. The angular velocity sensor element of claim 22, wherein

the holding section comprises a connection section and a supporting arm, and

the supporting arm is disposed between the first arm member of the first arm and a first arm member of the third arm.

32. The angular velocity sensor element of claim 22, wherein

a length of the first arm in the first direction from is shorter than a length of the first arm in the second direction substantially perpendicular to the first direction.

33. The angular velocity sensor element of claim 22, wherein

a length between the first arm member or the second arm member in the first direction is shorter than a length of the third arm member in the second direction.