Sensor for detecting acceleration and angular velocity

• US 20080289417A1
• Filed: 01/23/2008
• Published: 11/27/2008
• Est. Priority Date: 02/02/2007
• Status: Active Grant

• Current Assignee: Wacoh Company
• Original Assignee: Wacoh Company
• Inventors: Okada, Kazuhiro
• Granted Patent: US 7,882,740 B2
• Time in Patent Office: Days
• US Class Current: 73/504.03
• CPC Class Codes: G01C 19/56 Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
• CPC Class Codes: G01P 15/0922 of the bending or flexing mode type
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/084 the mass being suspended at more than one of its sides, e.g. membrane-type suspension, so as to permit multi-axis movement of the mass

Abstract

Static and dynamic acceleration as well as static and dynamic angular velocity are detected with a simple structure. An acceleration detecting section includes a weight body, a pedestal around the weight body, flexible plate-like bridge portions, and piezoresistive elements embedded in the upper surface of the bridge portions. An angular velocity detecting section includes a weight body, a pedestal around the weight body, flexible plate-like bridge portions, and piezoelectric elements fixed to the upper surface of the bridge portions. The pedestals are fixed to a device chassis. When the weight body is displaced by acceleration, the plate-like bridge portions are deflected, so that the acceleration is detected based on the change in the electrical resistances of the piezoresistive elements. When the weight body is displaced by a Coriolis force based on angular velocity while supplying alternating signals to the piezoelectric elements to oscillate the weight body, the plate-like bridge portions are deflected, so that the angular velocity is detected based on charge generation in the piezoelectric elements.

Claims

1. A sensor for detecting acceleration and angular velocity, comprising an acceleration detecting section and an angular velocity detecting section,

the acceleration detecting section comprising:

a weight body for acceleration detection;

a pedestal for acceleration detection arranged in such a manner as to surround the weight body for acceleration detection;

a flexible connection for acceleration detection for connecting the weight body for acceleration detection and the pedestal for acceleration detection;

a piezoresistive element embedded in a surface layer of the flexible connection for acceleration detection; and

an acceleration detecting circuit for detecting an applied acceleration based on a change in an electrical resistance of the piezoresistive element,

the angular velocity detecting section comprising;

a weight body for angular velocity detection;

a pedestal for angular velocity detection arranged in such a manner as to surround the weight body for angular velocity detection;

a flexible connection for angular velocity detection for connecting the weight body for angular velocity detection and the pedestal for angular velocity detection;

a driving piezoelectric element and a detecting piezoelectric element fixed directly or indirectly to a surface of the flexible connection for angular velocity detection; and

an angular velocity detecting circuit for detecting an applied angular velocity based on a signal generated in the detecting piezoelectric element while supplying an alternating signal to the driving piezoelectric element to periodically deform the flexible connection for angular velocity detection and to generate a periodic motion of the weight body for angular velocity detection, wherein

the pedestal for acceleration detection and the pedestal for angular velocity detection form a monolithic structure and are fixed to a device chassis.

2. The sensor for detecting acceleration and angular velocity according to claim 1, wherein

the weight body for acceleration detection, the pedestal for acceleration detection, the flexible connection for acceleration detection, the weight body for angular velocity detection, the pedestal for angular velocity detection, and the flexible connection for angular velocity detection are formed of a single silicon or SOI substrate, and the piezoresistive element is constituted by a silicon layer containing impurities formed in a surface layer of the substrate.

3. The sensor for detecting acceleration and angular velocity according to claim 2, wherein

a pair of first and second annular grooves are formed on a lower surface of the single substrate, a portion surrounded by the first annular groove constituting the weight body for acceleration detection, while a portion surrounded by the second annular groove constituting the weight body for angular velocity detection,

a thinned portion corresponding to the first annular groove constitutes the flexible connection for acceleration detection, while a thinned portion corresponding to the second annular groove constituting the flexible connection for angular velocity detection, and

the piezoresistive element is embedded in an upper surface layer of the flexible connection for acceleration detection, and the driving piezoelectric element and the detecting piezoelectric element are fixed directly or indirectly to an upper surface of the flexible connection for angular velocity detection.

4. The sensor for detecting acceleration and angular velocity according to claim 1, wherein

the flexible connection for acceleration detection is composed of a plurality of plate-like bridge portions, each of which includes a piezoresistive element arranged on an inner side that is closer to the weight body for acceleration detection and a piezoresistive element arranged on an outer side that is closer to the pedestal for acceleration detection, and

the flexible connection for angular velocity detection is composed of a plurality of plate-like bridge portions, each of which includes a driving piezoelectric element arranged on an inner side that is closer to the weight body for angular velocity detection, a driving piezoelectric element arranged on an outer side that is closer to the pedestal for angular velocity detection, a detecting piezoelectric element arranged on an inner side that is closer to the weight body for angular velocity detection, a detecting piezoelectric element arranged on an outer side that is closer to the pedestal for angular velocity detection.

5. The sensor for detecting acceleration and angular velocity according to claim 1, wherein

a lower electrode and an upper electrode are formed, respectively, on a lower surface and an upper surface of the driving piezoelectric element and the detecting piezoelectric element, a lower surface of the lower electrode is fixed to an upper surface of the flexible connection for angular velocity detection, and

the angular velocity detecting circuit detects an applied angular velocity based on an alternating voltage generated between upper and lower electrodes of the detecting piezoelectric element while applying an alternating voltage between upper and lower electrodes of the driving piezoelectric element to generate a periodic motion of the weight body for angular velocity detection.

6. The sensor for detecting acceleration and angular velocity according to claim 5, wherein

the lower electrodes of the piezoelectric elements are formed of a physically single common metal layer.

7. The sensor for detecting acceleration and angular velocity according to claim 5, wherein

the piezoelectric elements are formed of a physically single common piezoelectric element.

8. A sensor for detecting acceleration and angular velocity, comprising:

a weight body;

a pedestal arranged in such a manner as to surround the weight body and fixed to a device chassis;

a flexible connection for connecting the weight body and the pedestal;

a piezoresistive element embedded in a surface layer of the flexible connection;

a driving piezoelectric element and a detecting piezoelectric element fixed directly or indirectly to a surface of the flexible connection;

an acceleration detecting circuit for detecting an applied acceleration based on a change in an electrical resistance of the piezoresistive element; and

an angular velocity detecting circuit for detecting an applied angular velocity based on a signal generated in the detecting piezoelectric element while supplying an alternating signal to the driving piezoelectric element to periodically deform the flexible connection and to generate a periodic motion of the weight body.

9. The sensor for detecting acceleration and angular velocity according to claim 8, wherein

the acceleration detecting circuit has a low-pass filter circuit for filtering out high-frequency components contained in a signal that indicates the change in the electrical resistance of the piezoresistive element, the acceleration detecting circuit outputting signal components passing through the low-pass filter circuit as a detection value of acceleration, and

the angular velocity detecting circuit has a drive control circuit for supplying an alternating signal to the driving piezoelectric element to control the periodic motion of the weight body, a high-pass filter circuit for filtering out low-frequency components contained in an alternating signal generated in the detecting piezoelectric element, and a synchronous detection circuit for synchronously detecting an alternating signal passing through the high-pass filter circuit at a time point determined by a detection signal supplied from the drive control circuit, the angular velocity detecting circuit outputting a detection result by the synchronous detection circuit as a detected value of angular velocity.

10. The sensor for detecting acceleration and angular velocity according to claim 8, wherein

the weight body, the pedestal, and the flexible connection are formed of a single silicon or SOI substrate, and the piezoresistive element is constituted by a silicon layer containing impurities formed in a surface layer of the substrate.

11. The sensor for detecting acceleration and angular velocity according to claim 10, wherein

an annular groove is formed on a lower surface of the single substrate, a portion surrounded by the annular groove constituting the weight body and a thinned portion corresponding to the annular groove constituting the flexible connection, and

the piezoresistive element is embedded in an upper surface layer of the flexible connection, and the driving piezoelectric element and the detecting piezoelectric element are fixed directly or indirectly to an upper surface of the flexible connection.

12. The sensor for detecting acceleration and angular velocity according to claim 11, wherein

an XYZ three-dimensional coordinate system having X-axis, Y-axis and Z-axis is defined, an origin O thereof being at a center on an upper surface of the weight body and an XY plane thereof corresponding to an upper surface of the substrate,

Xa and Xb-axes are defined on either side of the X-axis in the XY plane, the Xa and Xb-axes running parallel to the X-axis with a predetermined space dx from the X-axis,

Ya and Yb-axes are defined on either side of the Y-axis in the XY plane, the Ya and Yb-axes running parallel to the Y-axis with a predetermined space dy from the Y-axis,

one of the Xa, Xb, Ya, and Yb-axes is defined as an auxiliar W-axis,

a portion of the flexible connection closer to the weight body is defined as an inner side, while a portion of the flexible connection closer to the pedestal is defined as an outer side,

some of the detecting piezoelectric elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the X-axis,

some of the driving piezoelectric elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the Xa-axis,

some of the driving piezoelectric elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the Xb-axis,

some of the detecting piezoelectric elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the Y-axis,

some of the driving piezoelectric elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the Ya-axis,

some of the driving piezoelectric elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the Yb-axis,

some of the piezoresistive elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the X-axis,

some of the piezoresistive elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the Y-axis, and

some of the piezoresistive elements are arranged, respectively, on the inner and outer sides of the flexible connection along respective positive and negative regions of the auxiliar W-axis.

13. The sensor for detecting acceleration and angular velocity according to claim 8, wherein

the flexible connection is composed of a plurality of plate-like bridge portions, each plate-like bridge portion including piezoresistive elements arranged, respectively, on an inner side that is closer to the weight body and on an outer side that is closer to the pedestal, and each plate-like bridge portion including driving piezoelectric elements arranged, respectively, on the inner and outer sides and detecting piezoelectric elements arranged, respectively, on the inner and outer sides.

14. The sensor for detecting acceleration and angular velocity according to claim 8, wherein

a lower electrode and an upper electrode are formed, respectively, on a lower surface and an upper surface of the driving piezoelectric element and the detecting piezoelectric element, a lower surface of the lower electrode is fixed to an upper surface of the flexible connection, and

the angular velocity detecting circuit detects an applied angular velocity based on an alternating voltage generated between upper and lower electrodes of the detecting piezoelectric element while applying an alternating voltage between upper and lower electrodes of the driving piezoelectric element to generate a periodic motion of the weight body.

15. The sensor for detecting acceleration and angular velocity according to claim 14, wherein

the lower electrodes of the piezoelectric elements are formed of a physically single common metal layer.

16. The sensor for detecting acceleration and angular velocity according to claim 14, wherein

the piezoelectric elements are formed of a physically single common piezoelectric element.

17. The sensor for detecting acceleration and angular velocity according to claim 8, wherein

a piezoresistive element and a piezoelectric element are partially laminated with an insulating layer therebetween.

18. A sensor for detecting acceleration and angular velocity, comprising:

a weight body;

a pedestal arranged to a side of the weight body and fixed to a device chassis;

a flexible connection for connecting the weight body and the pedestal;

a piezoresistive element embedded in a surface layer of the flexible connection;

a driving piezoelectric element and a detecting piezoelectric element fixed directly or indirectly to a surface of the flexible connection;

an acceleration detecting circuit for detecting an applied acceleration based on a change in an electrical resistance of the piezoresistive element; and

an angular velocity detecting circuit for detecting an applied angular velocity based on a signal generated in the detecting piezoelectric element while supplying an alternating signal to the driving piezoelectric element to periodically deform the flexible connection and to generate a periodic motion of the weight body.

19. The sensor for detecting acceleration and angular velocity according to claim 18, wherein

the acceleration detecting circuit has a low-pass filter circuit for filtering out high-frequency components contained in a signal that indicates the change in the electrical resistance of the piezoresistive element, the acceleration detecting circuit outputting signal components passing through the low-pass filter circuit as a detection value of acceleration, and

the angular velocity detecting circuit has a drive control circuit for supplying an alternating signal to the driving piezoelectric element to control the periodic motion of the weight body, a high-pass filter circuit for filtering out low-frequency components contained in an alternating signal generated in the detecting piezoelectric element, and a synchronous detection circuit for synchronously detecting an alternating signal passing through the high-pass filter circuit at a time point determined by a detection signal supplied from the drive control circuit, the angular velocity detecting circuit outputting a detection result by the synchronous detection circuit as a detected value of angular velocity.

20. The sensor for detecting acceleration and angular velocity according to claim 18, wherein

the weight body, the pedestal, and the flexible connection are composed of materials including silicon, and the piezoresistive element is constituted by a silicon layer containing impurities.

21. The sensor for detecting acceleration and angular velocity according to claim 18, wherein

the flexible connection is composed of a plate-like bridge portion connecting an upper part of the weight body and an upper part of the pedestal, a lower part of the pedestal being fixed to the device chassis, and

the piezoresistive element is embedded in an upper surface layer of the flexible connection, and the driving piezoelectric element and the detecting piezoelectric element are fixed directly or indirectly to an upper surface of the flexible connection.

22. The sensor for detecting acceleration and angular velocity according to claim 21, wherein

W-axis is defined for connecting a predetermined point on an upper surface of the weight body and a predetermined point on an upper surface of the pedestal, and Wa and Wb-axes are defined on either side of the W-axis, the Wa and Wb-axes running parallel to the W-axis with a predetermined space dw from the W-axis,

a portion of the flexible connection closer to the weight body is defined as a weight body neighborhood, while a portion of the flexible connection closer to the pedestal is defined as a pedestal neighborhood,

the detecting piezoelectric elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the W-axis,

some of the driving piezoelectric elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the Wa-axis,

some of the driving piezoelectric elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the Wb-axis, and

the piezoresistive elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the W-axis.

23. The sensor for detecting acceleration and angular velocity according to claim 21, wherein

W-axis is defined for connecting a predetermined point on an upper surface of the weight body and a predetermined point on an upper surface of the pedestal, and Wa and Wb-axes are defined on either side of the W-axis, the Wa and Wb-axes running parallel to the W-axis with a predetermined space dw from the W-axis,

a portion of the flexible connection closer to the weight body is defined as a weight body neighborhood, while a portion of the flexible connection closer to the pedestal is defined as a pedestal neighborhood,

the driving piezoelectric elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the W-axis,

some of the detecting piezoelectric elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the Wa-axis,

some of the detecting piezoelectric elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the Wb-axis, and

the piezoresistive elements are arranged, respectively, on the weight body neighborhood and the pedestal neighborhood of the flexible connection along the W-axis.

24. The sensor for detecting acceleration and angular velocity according to claim 18, wherein

a lower electrode and an upper electrode are formed, respectively, on a lower surface and an upper surface of the driving piezoelectric element and the detecting piezoelectric element, a lower surface of the lower electrode is fixed to an upper surface of the flexible connection, and

the angular velocity detecting circuit detects an applied angular velocity based on an alternating voltage generated between upper and lower electrodes of the detecting piezoelectric element while applying an alternating voltage between upper and lower electrodes of the driving piezoelectric element to generate a periodic motion of the weight body.

25. The sensor for detecting acceleration and angular velocity according to claim 24, wherein

the lower electrodes on the piezoelectric elements are formed of a physically single common metal layer.

26. The sensor for detecting acceleration and angular velocity according to claim 24, wherein

the piezoelectric elements are formed of a physically single common piezoelectric element.

27. The sensor for detecting acceleration and angular velocity according to claim 18, wherein

a piezoresistive element and a piezoelectric element are partially laminated with an insulating layer therebetween.