Monolithic silicon acceleration sensor

• US 6,829,937 B2
• Filed: 06/17/2002
• Issued: 12/14/2004
• Est. Priority Date: 06/17/2002
• Status: Expired due to Term

• Current Assignee: Murata Manufacturing Co Limited
• Original Assignee: VTI Holding Oy
• Inventors: Mahon, Geoffrey L.
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US10/171,616
• Publication Number:
  US 20030230143A1
• Time in Patent Office: 911 Days
• Field of Search: 735/143.3, 735/143.4, 735/143.2, 735/143.6, 735/141.8, 735/142.1, 735/142.3, 735/142.9, 735/10, 735/11
• US Class Current: 73/514.29
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 15/123 by piezo-resistive elements, e.g. semiconductor strain gauges
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends

Abstract

A monolithic silicon acceleration sensor capable of detecting acceleration along multiple orthogonal axes of acceleration is disclosed. The monolithic silicon acceleration sensor is micromachined from silicon to form one or more sensor cells, each sensor cell having an inertial mass positioned by beam members fixed to a silicon support structure. Movement of the inertial mass due to acceleration is detected by either a differential capacitance measurement between opposing surfaces of the inertial mass and electrically conductive layers on a top and a bottom cover plate structure, or by a resistance measurement of piezoresistive elements fixed to the positioning beam members. Embodiments of the invention are capable of detecting acceleration in a plane, along two orthogonal axes of acceleration, or along three orthogonal axis of acceleration.

Claims

1. A monolithic silicon acceleration sensor comprising at least one silicon acceleration sensor cell, the sensor cell comprising a movable silicon inertial mass with a first surface and a second surface, the first and second surfaces being essentially parallel, the inertial mass positioned by beam members fixed to a silicon support structure having a first and opposing second surface, the inertial mass being able to move in response to acceleration along two orthogonal axes of acceleration, a first axis being parallel to the first and second surfaces of the inertial mass and a second axis being perpendicular to the first and second surfaces of the inertial mass, magnitudes of motion of the inertial mass under equal accelerations along the first axis and the second axis being substantially equal, the silicon acceleration sensor cell having means for detecting movement of the inertial mass in response to the acceleration along the first axis and the second axis.

2. The monolithic silicon acceleration sensor according to claim 1, wherein the movable silicon inertial mass is positioned by torsion beam members.

3. The monolithic silicon acceleration sensor according to claim 1, wherein the movable silicon inertial mass is positioned by cantilever beam members.

4. The monolithic silicon acceleration sensor according to claim 1, wherein the means for detecting movement of the movable silicon inertial mass is by measuring a capacitance between the inertial mass and a first cover plate structure spaced from the first surface of the inertial mass and fixed to the first surface of the silicon support structure, and the capacitance between the silicon inertial mass and a second cover plate structure spaced from the second surface of the inertial mass and fixed to the second surface of the silicon support structure.

5. The monolithic silicon acceleration sensor according to claim 1, wherein the means for detecting movement of the inertial mass is by measuring a resistance of piezoresistive devices attached to the beam members.

6. The monolithic silicon acceleration sensor according to claim 1, further comprising a first and second acceleration sensor cell for sensing acceleration along two orthogonal axes of acceleration, the second sensor cell being oriented at a 180 degree angle to the first sensor cell when viewing the first surface of the inertial masses, using the beam members as an angular reference.

7. The monolithic silicon acceleration sensor according to claim 1, further comprising a first, second, and third acceleration sensor cell for sensing acceleration along three orthogonal axes of acceleration, the second sensor cell being oriented at a 90 degree angle to the first sensor cell and the third sensor cell being oriented at a 180 degree angle to the first sensor cell when viewing the first surface of the inertial masses, using the beam members as an angular reference.

8. The monolithic silicon acceleration sensor according to claim 1, further comprising a first, second, third, and a fourth acceleration sensor cell for sensing acceleration along three orthogonal axes of acceleration, the second sensor cell being oriented at a 90 degree angle to the first sensor cell, the third sensor cell being oriented at a 180 degree angle to the first sensor cell, and the fourth sensor cell being oriented at a 270 degree angle to the first sensor cell when viewing the first surface of the inertial masses, using the beam members as an angular reference.

9. The monolithic silicon acceleration sensor comprising:

an acceleration sensor cell for sensing acceleration along two orthogonal axes, the acceleration sensor cell comprising;

(a) an electrically conductive movable silicon inertial mass having a first surface and a second opposing surface, and positioned by electrically conductive beam members fixed to an electrically conductive silicon support structure having a first and a second surface;

(b) a first cover plate structure comprising a first electrically conductive layer spaced from the first surface of the inertial mass and formed on a first insulator fixed to the first surface of the silicon support structure, the first electrically conductive layer and the first surface of the inertial mass forming a first variable capacitor of a value depending on the position of the inertial mass;

(c) a second cover plate structure comprising a second electrically conductive layer spaced from the second surface of the inertial mass and formed on a second insulator fixed to the second surface of the silicon support structure, the second electrically conductive layer and the second surface of the inertial mass forming a second variable capacitor of a value depending on the position of the inertial mass; and

(d) a means for electrically connecting the inertial mass, the first electrically conductive layer of the first cover plate structure, and the second electrically conductive layer of the second cover plate structure to electronic circuitry capable of measuring the capacitance value of the first and second variable capacitors,

the inertial mass being able to move in response to acceleration alone two orthogonal axes of acceleration, a first axis being parallel to the first and second surfaces of the inertial mass and a second axis being perpendicular to the first and second surfaces of the inertial mass, magnitudes of motion of the inertial mass under equal accelerations along the first axis and the second axis being substantially equal, the silicon acceleration sensor cell having means for detecting movement of the inertial mass in response to the acceleration along the first axis and the second axis.

10. The monolithic silicon acceleration sensor according to claim 9, wherein the inertial mass is positioned by torsion beam members.

11. The monolithic silicon acceleration sensor according to claim 9, wherein the inertial mass is positioned by cantilever beam members.

12. The monolithic silicon acceleration sensor according to claim 9, wherein:

(a) the means for electrically connecting the inertial mass to electronic circuitry is by metallic bonding to the silicon support structure;

(b) the means for electrically connecting the first electrically conductive layer of the first cover plate structure is by a first conductive silicon wafer section mounted to the first insulator, the first conductive silicon wafer section having a first conductive silicon mesa through the first insulator in electrical contact with the first electrically conductive layer and having a metallic bonding pad to which lead wire connected to the electronic circuitry is bonded; and

(c) the means for electrically connecting the second electrically conductive layer of the second cover plate structure is by a second conductive silicon wafer section mounted to the second insulator, the second conductive silicon wafer section having a second conductive silicon mesa through the second insulator in electrical contact with the second electrically conductive layer and having a metallic bonding pad to which lead wire connected to the electronic circuitry is bonded.

13. The monolithic silicon acceleration sensor according to claim 12, wherein the means for electrically connecting the first electrically conductive layer of the first cover plate structure is by forming a hole in the first insulator through the first electrically conductive layer, metallizing the hole to the first electrically conductive layer, and bonding an electrical lead wire to the metallized hole opposite the first electrically conductive layer, and the means for electrically connecting the second electrically conductive layer of the second cover plate structure is by drilling a hole in the second insulator through the second electrically conductive layer, metallizing the hole to the second electrically conductive layer, and bonding an electrical lead wire to the metallized hole opposite the second electrically conductive layer.

14. The monolithic silicon acceleration sensor according to claim 9, wherein the inertial mass is shaped as a rectangular parallelepiped.

15. The monolithic silicon acceleration sensor according to claim 9, wherein the inertial mass is shaped as a cube.

16. The monolithic silicon acceleration sensor according to claim 9, wherein:

(a) the first surface of the inertial mass is slightly depressed from the first surface of the silicon support structure so that a dielectric spacing is provided for the first variable capacitor; and

(b) the second surface of the inertial mass is slightly depressed from the second surface of the silicon support structure so that a dielectric spacing is provided for the second variable capacitor.

17. The monolithic silicon acceleration sensor according to claim 9, wherein:

(a) the first electrically conductive layer of the first cover plate structure is formed on a first insulating layer of glass with electrical connections through the first glass layer; and

(b) the second electrically conductive layer of the second cover plate structure is formed on a second insulating layer of glass with electrical connections through the second glass layer.

18. The monolithic silicon acceleration sensor according to claim 9, wherein:

(a) the first cover plate structure comprises a first insulating layer spaced from the first surface of the inertial mass and fixed to the first surface of the silicon support structure;

(b) the second cover plate structure comprises a second insulating layer spaced from the second surface of the inertial mass and fixed to the second surface of the silicon support structure;

(c) piezoresistive elements are attached to the beam members; and

(d) means are provided for connecting the piezoresistive elements to electronic circuitry for measuring a resistance of the piezoresistive elements.

19. The monolithic silicon acceleration sensor according to claim 9, further comprising a second acceleration sensor cell for sensing acceleration along two orthogonal axes, the second acceleration sensor cell comprising

(a) an electrically conductive movable silicon inertial mass having a first surface and a second opposing surface, and positioned by electrically conductive beam members fixed to an electrically conductive silicon support structure having a first and a second surface;

(b) a first cover plate structure comprising a first electrically conductive layer spaced from the first surface of the inertial mass and formed on a first insulator fixed to the first surface of the silicon support structure, the first electrically conductive layer and the first surface of the inertial mass forming a first variable capacitor of a value depending on the position of the inertial mass;

(c) a second cover plate structure comprising a second electrically conductive layer spaced from the second surface of the inertial mass and formed on a second insulator fixed to the second surface of the silicon support structure, the second electrically conductive layer and the second surface of the inertial mass forming a second variable capacitor of a value depending on the position of the inertial mass; and

(d) a means for electrically connecting the inertial mass, the first electrically conductive layer of the first cover plate structure, and the second electrically conductive layer of the second cover plate structure to electronic circuitry capable of measuring the capacitance value of the first and second variable capacitor

the second sensor cell being oriented at either a 90 degree or 180 degree angle to the first sensor cell when viewing first surfaces of inertial masses of the first and second acceleration sensor cells, using the beam members of the first and second acceleration sensor cells as an angular reference.

20. The monolithic silicon acceleration sensor according to claim 19, wherein the inertial mass is positioned by torsion beam members.

21. The monolithic silicon acceleration sensor according to claim 19, wherein the inertial mass is positioned by cantilever beam members.

22. The monolithic silicon acceleration sensor according to claim 19, wherein:

(a) the means for electrically connecting the inertial masses to electronic circuitry is by metallic bonding to the silicon support structure;

(b) the means for electrically connecting the first electrically conductive layers of first cover plate structures is by first conductive silicon wafer sections mounted to first glass insulators, the first conductive silicon wafer sections having first conductive silicon mesas through the first glass insulators in electrical contact with first electrically conductive layers and having metallic bonding pads to which lead wires connected to the electronic circuitry are bonded; and

(c) the means for electrically connecting second electrically conductive layers of second cover plate structures is by second conductive silicon wafer sections mounted to second glass insulators, the second conductive silicon wafer sections having second conductive silicon mesas through the second glass insulators in electrical contact with the second electrically conductive layers and having metallic bonding pads to which lead wire connected to the electronic circuitry are bonded.

23. The monolithic silicon acceleration sensor according to claim 9, further comprising a second acceleration sensor cell and a third acceleration sensor cell, the second acceleration sensor cell and the third acceleration sensor cell comprising

(a) an electrically conductive movable silicon inertial mass having a first surface and a second opposing surface, and positioned by electrically conductive beam members fixed to an electrically conductive silicon support structure having a first and a second surface;

(b) a first cover plate structure comprising a first electrically conductive layer spaced from the first surface of the inertial mass and formed on a first insulator fixed to the first surface of the silicon support structure, the first electrically conductive layer and the first surface of the inertial mass forming a first variable capacitor of a value depending on the position of the inertial mass;

(c) a second cover plate structure comprising a second electrically conductive layer spaced from the second surface of the inertial mass and formed on a second insulator fixed to the second surface of the silicon support structure, the second electrically conductive layer and the second surface of the inertial mass forming a second variable capacitor of a value depending on the position of the inertial mass; and

(d) a means for electrically connecting the inertial mass, the first electrically conductive layer of the first cover plate structure, and the second electrically conductive layer of the second cover plate structure to electronic circuitry capable of measuring the capacitance value of the first and second variable capacitor

the first, second and third acceleration sensor cells of the monolithic silicon acceleration sensor arranged for sensing acceleration along three orthogonal axes of acceleration, the second acceleration sensor cell being oriented at a 90 degree angle to the first acceleration sensor cell and the third acceleration sensor cell being oriented at a 180 degree angle to the first acceleration sensor cell when viewing first surfaces of inertial masses of the first, second and third acceleration sensor cells, using the beam members of the first, second and third acceleration sensor cells as an angular reference.

24. The monolithic silicon acceleration sensor according to claim 23, wherein the inertial mass is positioned by torsion beam members.

25. The monolithic silicon acceleration sensor according to claim 23, wherein the inertial mass is positioned by cantilever beam members.

26. The monolithic silicon acceleration sensor according to claim 23, wherein:

(a) the means for electrically connecting the inertial masses to electronic circuitry is by metallic bonding to the silicon support structure;

(b) the means for electrically connecting first electrically conductive layers of first cover plate structures is by third conductive silicon wafer sections mounted to first glass insulators, first conductive silicon wafer sections having first conductive silicon mesas through the first glass insulators in electrical contact with the first electrically conductive layers and having metallic bonding pads to which lead wires connected to the electronic circuitry are bonded; and

(c) the means for electrically connecting second electrically conductive layers of second cover plate structures is by second conductive silicon wafer sections mounted to second glass insulators, the second conductive silicon wafer sections having second conductive silicon mesas through the second glass insulators in electrical contact with the second electrically conductive layers and having metallic bonding pads to which lead wires connected to the electronic circuitry are bonded.

27. The monolithic silicon acceleration sensor according to claim 9, further comprising a second acceleration sensor cell, a third acceleration sensor cell and a fourth acceleration sensor cell, the second acceleration sensor cell, the third acceleration sensor cell and the fourth acceleration sensor cell comprising

(a) an electrically conductive movable silicon inertial mass having a first surface and a second opposing surface, and positioned by electrically conductive beam members fixed to an electrically conductive silicon support structure having a first and a second surface;

(b) a first cover plate structure comprising a first electrically conductive layer spaced from the first surface of the inertial mass and formed on a first insulator fixed to the first surface of the silicon support structure, the first electrically conductive layer and the first surface of the inertial mass forming a first variable capacitor of a value depending on the position of the inertial mass;

(c) a second cover plate structure comprising a second electrically conductive layer spaced from the second surface of the inertial mass and formed on a second insulator fixed to the second surface of the silicon support structure, the second electrically conductive layer and the second surface of the inertial mass forming a second variable capacitor of a value depending on the position of the inertial mass; and

(d) a means for electrically connecting the inertial mass, the first electrically conductive layer of the first cover plate structure, and the second electrically conductive layer of the second cover plate structure to electronic circuitry capable of measuring the capacitance value of the first and second variable capacitor

the first, second, third and fourth acceleration sensor cells of the monolithic silicon acceleration sensor arranged for sensing acceleration along three orthogonal axes of acceleration, the second acceleration sensor cell being oriented at a 90 degree angle to the first acceleration sensor cell, the third acceleration sensor cell being oriented at a 180 degree angle to the first acceleration sensor cell, and the fourth acceleration sensor cell being oriented at a 270 degree angle to the first sensor cell when viewing first surfaces of inertial masses of the first, second, third and fourth acceleration sensor cells, using the beam members of the first, second, third and fourth acceleration sensor cells as an angular reference.

28. The monolithic silicon acceleration sensor according to claim 27, wherein the inertial mass is positioned by torsion beam members.

29. The monolithic silicon acceleration sensor according to claim 27, wherein the inertial mass is positioned by cantilever beam members.

30. The monolithic silicon acceleration sensor according to claim 27, wherein:

(a) the means for electrically connecting the inertial masses to electronic circuitry is by metallic bonding to the silicon support structure;

(b) the means for electrically connecting first electrically conductive layers of first cover plate structures is by first conductive silicon wafer sections mounted to first glass insulators, the first conductive silicon wafer sections having first conductive silicon mesas through the first glass insulators in electrical contact with the first electrically conductive layers and having metallic bonding pads to which lead wires connected to the electronic circuitry are bonded; and

(c) the means for electrically connecting second electrically conductive layers of second cover plate structures is by second conductive silicon wafer sections mounted to second glass insulators, the second conductive silicon wafer sections having second conductive silicon mesas through the second glass insulators in electrical contact with the second electrically conductive layers and having metallic bonding pads to which lead wires connected to the electronic circuitry are bonded.