TRIAXIAL MEMBRANE ACCELEROMETER

• US 20070214891A1
• Filed: 03/14/2007
• Published: 09/20/2007
• Est. Priority Date: 03/14/2006
• Status: Active Grant

• Current Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Original Assignee: Commissariat a L'Energie Atomique (French Alternative Energies and Atomic Energy Commission)
• Inventors: Robert, Philippe, Hentz, Sebastien
• Granted Patent: US 7,600,428 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/0109 Bridges
• CPC Class Codes: B81B 2203/0181 See-saws
• CPC Class Codes: B81B 3/0062 Devices moving in two or more dimensions, i.e. having special features which allow movement in more than one dimension
• CPC Class Codes: G01P 15/0802 Details
• 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 2015/082 for two degrees of freedom of movement of a single mass
• 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

The invention relates to accelerometer structures micro-machined according to micro-electronics technologies. The accelerometer according to the invention comprises a substrate, an elastically deformable thin-layer membrane suspended above the substrate and secured to the substrate at its periphery, a proof mass suspended above the membrane and linked to the latter by a central stud, and capacitive interdigitated combs distributed about the mass, having movable plates secured to the mass and fixed plates secured to the substrate. The fixed plates and movable plates of the various combs are of differentiated heights to help in the discrimination of the upward and downward vertical accelerations.

Claims

1. A micro-machined accelerometer structure, comprising:

a substrate, an elastically deformable thin-layer membrane suspended above the substrate and secured to the substrate at its periphery,

a proof mass suspended above the membrane and linked to the latter by a central stud, and

capacitive interdigitated combs distributed about the mass, having movable plates secured to the mass and fixed plates secured to the substrate.

2. The accelerometer structure according to claim 1, wherein the fixed plates of some of the capacitive combs have a height, measured in the sense perpendicular to the membrane, that is smaller than the height of the movable plates of these combs, and the movable plates of some combs have a height in the sense perpendicular to the membrane that is smaller than the height of the fixed plates of these combs.

3. The accelerometer structure according to claim 2, wherein, on each side of the proof mass there are two combs, one having fixed plates higher than the movable plates and the other having movable plates higher than the fixed plates.

4. The accelerometer structure according to claim 3, wherein the two combs on one and the same side of the proof mass have spacings between plates which vary in opposite senses for one and the same sense of horizontal displacement of the proof mass.

5. The accelerometer structure according to claim 4, wherein two combs facing one another on two opposite sides have, the one, fixed plates higher than the movable plates and, the other, movable plates higher than the fixed plates.

6. The accelerometer structure according to claim 3, wherein two combs facing one another on two opposite sides of the proof mass have spacings between plates which vary in the same sense for one and the same displacement of the proof mass parallel to these sides.

7. The accelerometer structure according to claim 1, wherein the organization of the interdigitated capacitive combs is symmetric in order that the capacitances at rest in the absence of accelerations of all the interdigitated combs are identical.

8. The accelerometer structure according to claim 1, wherein the measurement of the acceleration along a horizontal axis parallel to two sides of the proof mass is done by a linear combination of the capacitance values of four combs situated along these sides.

9. The accelerometer structure according to claim 1, wherein the measurement of the acceleration along a vertical axis perpendicular to the membrane is done by a linear combination of the capacitance values of eight combs, this combination being the difference between the sum of the capacitances of four combs each situated on a respective side of the proof mass and having fixed plates that are lower than the movable plates, and the sum of the capacitances of four other combs also each situated on a respective side of the proof mass and having movable plates that are lower than the fixed plates.

10. The accelerometer structure according to claim 1, wherein the proof mass (M), the interdigitated combs, the membrane and the central stud are made of silicon.

11. The accelerometer structure according to claim 4, wherein two combs facing one another on two opposite sides of the proof mass have spacings between plates which vary in the same sense for one and the same displacement of the proof mass parallel to these sides.

12. The accelerometer structure according to claim 5, wherein two combs facing one another on two opposite sides of the proof mass have spacings between plates which vary in the same sense for one and the same displacement of the proof mass parallel to these sides.

13. The accelerometer structure according to claim 2, wherein the organization of the interdigitated capacitive combs is symmetric in order that the capacitances at rest in the absence of accelerations of all the interdigitated combs are identical.

14. The accelerometer structure according to claim 2, wherein the measurement of the acceleration along a horizontal axis parallel to two sides of the proof mass is done by a linear combination of the capacitance values of four combs situated along these sides.

15. The accelerometer structure according to claim 3, wherein the measurement of the acceleration along a horizontal axis parallel to two sides of the proof mass is done by a linear combination of the capacitance values of four combs situated along these sides.

16. The accelerometer structure according to claim 2, wherein the measurement of the acceleration along a vertical axis perpendicular to the membrane is done by a linear combination of the capacitance values of eight combs, this combination being the difference between the sum of the capacitances of four combs each situated on a respective side of the proof mass and having fixed plates that are lower than the movable plates, and the sum of the capacitances of four other combs also each situated on a respective side of the proof mass and having movable plates that are lower than the fixed plates.

17. The accelerometer structure according to claim 3, wherein the measurement of the acceleration along a vertical axis perpendicular to the membrane is done by a linear combination of the capacitance values of eight combs, this combination being the difference between the sum of the capacitances of four combs each situated on a respective side of the proof mass and having fixed plates that are lower than the movable plates, and the sum of the capacitances of four other combs also each situated on a respective side of the proof mass and having movable plates that are lower than the fixed plates.

18. The accelerometer structure according to claim 4, wherein the measurement of the acceleration along a vertical axis perpendicular to the membrane is done by a linear combination of the capacitance values of eight combs, this combination being the difference between the sum of the capacitances of four combs each situated on a respective side of the proof mass and having fixed plates that are lower than the movable plates, and the sum of the capacitances of four other combs also each situated on a respective side of the proof mass and having movable plates that are lower than the fixed plates.

19. The accelerometer structure according to claim 5, wherein the measurement of the acceleration along a vertical axis perpendicular to the membrane is done by a linear combination of the capacitance values of eight combs, this combination being the difference between the sum of the capacitances of four combs each situated on a respective side of the proof mass and having fixed plates that are lower than the movable plates, and the sum of the capacitances of four other combs also each situated on a respective side of the proof mass and having movable plates that are lower than the fixed plates.

20. The accelerometer structure according to claim 6, wherein the measurement of the acceleration along a vertical axis perpendicular to the membrane is done by a linear combination of the capacitance values of eight combs, this combination being the difference between the sum of the capacitances of four combs each situated on a respective side of the proof mass and having fixed plates that are lower than the movable plates, and the sum of the capacitances of four other combs also each situated on a respective side of the proof mass and having movable plates that are lower than the fixed plates.