Z-axis accelerometer with at least two gap sizes and travel stops disposed outside an active capacitor area

• US 20060169043A1
• Filed: 01/28/2005
• Published: 08/03/2006
• Est. Priority Date: 01/28/2005
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: McNeil, Andrew C.
• Granted Patent: US 7,121,141 B2
• Time in Patent Office: Days
• US Class Current: 73/514.10
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0831 the mass being of the paddle type having the pivot axis between the longitudinal ends of the mass, e.g. see-saw configuration

Abstract

An accelerometer includes a pair of conductive plates fixedly mounted on a substrate surface, a structure coupled to the substrate surface and suspended above the conductive plates, and at least one protective shield mounted on the substrate surface. The structure includes two regions of differing total moments disposed above a respective conductive plate and separated by a flexure axis about which the structure rotates during an acceleration normal to the substrate, each region having a substantially planar outer surface and an inner surface having a first corrugation formed thereon. For each of the two regions, an inner gap exists between the first corrugation and an opposing conductive plate, and an outer gap exists between the substantially planar outer surface and the opposing conductive plate, the outer gap being larger than the inner gap. The at least one protective shield is placed apart from either of the conductive plates.

Claims

1. An accelerometer, comprising:

a substrate having a surface;

a pair of conductive capacitor plates fixedly mounted on the substrate surface;

a structure coupled to the substrate surface, and suspended above the conductive capacitor plates, the structure having first and second regions of differing mass that are each disposed above a respective conductive capacitor plate to form a capacitor therewith and are separated by a flexure axis about which the structure rotates during an acceleration normal to the substrate; and

at least one protective shield mounted on the substrate surface, and positioned entirely laterally apart from either of the conductive capacitor plates, and further positioned to limit rotation of the structure and thereby prevent the structure from contacting one of the conductive capacitor plates.

2. The accelerometer of claim 1, wherein the at least one protective shield is a pair of the protective shields mounted on the substrate surface, a fist protective shield from the pair being positioned to oppose the structure first region, and a second protective shield from the pair being positioned to oppose the structure second region.

3. The accelerometer according to claim 1, wherein the structure further comprises at least one stop that opposes, and protrudes toward, the protective shield.

4. The accelerometer according to claim 2, wherein the structure further comprises a fiat stop that opposes, and protrudes toward, the first protective shield, and a second stop that opposes, and protrudes toward, the second protective shield.

5. The accelerometer according to claim 1, wherein the at least one protective shield and the pair of conductive plates are formed from the same material.

6. The accelerometer according to claim 5, wherein the at least one protective shield and the pair of conductive plates are formed directly on the substrate surface.

7. An accelerometer, comprising:

a substrate having a surface;

a pair of conductive plates fixedly mounted on the substrate surface; and

a structure coupled to the substrate surface, and suspended above the conductive plates, the structure comprising;

first and second regions of differing total moments disposed above a respective conductive plate and separated by a flexure axis about which the structure rotates during an acceleration normal to the substrate, each region having a substantially planar outer surface and an inner surface having a fist corrugation formed parallel to the flexure axis formed thereon,

whereby for each of the first and second regions, an inner gap exists between the first corrugation and an opposing conductive plate, and an outer gap exists between the substantially planar outer surface and the opposing conductive plate, the outer gap being larger than the inner gap.

8. The accelerometer according to claim 7, wherein each of the first and second regions further comprises at least one additional corrugation that is formed between the first corrugation and the outer surface, whereby between each additional corrugation and the opposing conductive plate an intermediate gap exists, each intermediate gap being larger than the inner gap and smaller than the outer gap.

9. The accelerometer according to claim 8, wherein from the inner gap to the outer gap, each successive intermediate gap increases in size.

10. The accelerometer according to claim 7, wherein the structure further comprises at least one stop that protrudes a substrate surface area that does not have a conductive plate formed thereon.

11. The accelerometer according to claim 7, wherein the structure further comprises first and second stops that protrude toward respective substrate surface areas that do have a conductive plate formed thereon.

12. An accelerometer, comprising:

a substrate having a surface;

a pair of conductive capacitor plates fixedly mounted on the substrate surface;

a structure coupled to the substrate surface, and suspended above the conductive capacitor plates to form capacitors therewith the structure comprising;

first and second regions of differing total moments disposed above a respective conductive capacitor plate and separated by a flexure axis about which the structure rotates during an acceleration normal to the substrate, each region having a substantially planar outer surface and an inner surface having a first corrugation formed parallel to the flexure axis formed thereon,

whereby for each of the fist and second regions, an inner gap exists between the first corrugation and an opposing conductive capacitor plate, and an outer gap exists between the substantially planar outer surface and the opposing conductive capacitor plate, the outer gap being larger than the inner gap; and

at least one protective shield mounted on the substrate surface, and positioned entirely laterally apart from either of the conductive capacitor plates, and further positioned to limit rotation of the structure and thereby prevent the structure from contacting one of the conductive capacitor plates.

13. The accelerometer of claim 12, wherein the at least one protective shield is a pair of protective shields mounted on the substrate surface, a first protective shield from the pair being positioned to oppose the first region, and the second protective shield from the pair being positioned to oppose the second region.

14. The accelerometer according to claim 12, wherein the structure further comprises at least one stop that opposes, and protrudes toward, the protective shield.

15. The accelerometer according to claim 13, wherein the structure further comprises a first stop that opposes, and protrudes toward, the first protective shield, and a second stop that opposes, and protrudes toward, the second protective shield.

16. The accelerometer according to claim 12, wherein the at least one protective shield and the pair of conductive plates are formed from the same material.

17. The accelerometer according to claim 16, wherein the at least one protective shield and the pair of conductive plates are formed directly on the substrate surface.

18. The accelerometer according to claim 12, wherein each of the fist and second structure regions further comprises at least one additional corrugation that is formed between the first corrugation and the outer surface, whereby between each additional corrugation and the opposing conductive plate an intermediate gap exists, each intermediate gap being larger than the inner gap and smaller than the outer gap.

19. The accelerometer according to claim 12, wherein from the inner gap to the outer gap, each successive intermediate gap increases in size.