Capacitive accelerometer or acceleration switch

• US 7,180,019 B1
• Filed: 06/26/2006
• Issued: 02/20/2007
• Est. Priority Date: 06/26/2006
• Status: Expired due to Fees

• Current Assignee: Temic Automotive of North America, Incorporated (Continental AG)
• Original Assignee: Temic Automotive of North America, Incorporated (Continental AG)
• Inventors: Chiou, Jen-Huang A., Chen, Shiuh-Hui S., Edwards, Arthur J.
• Primary Examiner(s): Friedhofer; Michael A.
• Application Number:
  US11/426,366
• Time in Patent Office: 239 Days
• Field of Search: 200 6145 R- 6145 M, 735/140.1, 735/141.6, 735/142.9, 735/143.1, 735/143.2, 735/143.5, 735/143.6, 735/143.8
• US Class Current: 200/61.45R
• CPC Class Codes: G01P 15/0891 with indication of predetermined acceleration values G01P15/135 takes precedence
• CPC Class Codes: G01P 15/125 by capacitive pick-up

Abstract

An accelerometer or accelerator switch and its method of manufacture are disclosed. The device is fabricated from two substrates: a top substrate having a moveable mass, and a bottom substrate having at least one conductive plate. The top substrate is preferably a SOI substrate, and the mass and its suspending beams are formed in the silicon layer under which the insulator layer has been removed. The bottom substrate is preferably oxide. In one embodiment, the capacitance is formed using the mass as the first capacitor plate the conductive plate as the second plate. As the mass moves, the capacitance is detected to indicate the magnitude of the acceleration, or whether acceleration is above or below a threshold indicting an open or closed switch. The beams which suspend the mass can be serpentines, which make the device compact and render the mass more flexible. Alternatively, the bottom conductive plate can be split into two plates each coupling to the mass. Depending on the capacitance between the two split plates, this configuration allows for the formation of either a normally-open or normally-close acceleration switch.

Claims

1. An accelerometer device or acceleration switch device, comprising:

a moveable mass formed in a first substrate and suspended by a plurality of flexible beams, wherein the mass comprises a first plate of a capacitor and is coupled to a first external terminal; and

a conductive plate formed in a second substrate and spaced from the mass, wherein the conductive plate comprises a second plate of the capacitor, and wherein the conductive plate is coupled to a second external terminal,

wherein the mass is moveable orthogonally to the conductive plate in a presence of an acceleration to change a spacing between the capacitor plates, and wherein the capacitance of the capacitor is sensed at the first and second external terminals and the mass comprises a dielectric layer in the spacing between the first and second capacitor plates.

2. The device of claim 1, wherein the plurality of flexible beams comprise serpentines.

3. The device of claim 1, wherein the first and second substrates are sandwiched together.

4. The device of claim 1, wherein the first substrate comprises a Silicon-On-Insulator (SOI) substrate, and wherein the mass comprises a top crystalline silicon layer of the SOI substrate.

5. The device of claim 1, wherein the mass is formed in a heavily doped crystalline silicon layer.

6. The device of claim 1, wherein the second substrate comprises a dielectric substrate.

7. An accelerometer device or acceleration switch device, comprising:

a moveable mass suspended by a plurality of flexible beams; and

first and second conductive plates in a same plane and underlying the mass and spaced from the mass, wherein the first conductive plate forms a first capacitor with the mass, and wherein the second conductive plate forms a second capacitor with the mass, wherein the first plate is coupled to a first external terminal, and wherein the second plate is coupled to a second external terminal,

wherein the mass moves orthogonally to the first and second conductive plates in a presence of an acceleration to change a spacing in the first and second capacitors, and wherein the capacitance is sensed at the first and second external terminals.

8. The device of claim 7, wherein the plurality of flexible beams comprise serpentines.

9. The device of claim 7, wherein the mass is fabricated on a first substrate, and wherein the first and second conductive plates are fabricated on a second substrate, and wherein the first and second substrates are sandwiched together.

10. The device of claim 9, wherein the first substrate comprises a Silicon-On-Insulator (SOI) substrate, and wherein the mass comprises a top crystalline silicon layer of the SOI substrate.

11. The device of claim 7, wherein the mass is formed in a heavily doped crystalline silicon layer.

12. The device of claim 7, wherein the mass comprises a dielectric layer in the spacing between the first and second capacitor plates.

13. The device of claim 7, wherein the mass is coupled to a fixed potential at a third terminal.

14. The device of claim 7, wherein the first and second plates are inter-digitized.

15. A method of forming an accelerometer device or acceleration switch device, comprising:

suspending a mass in a first substrate by a plurality of flexible beams, wherein the mass is formed in a conductive layer of the first substrate, wherein the mass further comprises a dielectric layer;

forming at least one conductive plate in a second substrate, wherein the dielectric layer faces the at least one conductive plate; and

sandwiching the first and second substrates together to form the device, wherein the mass is moveable orthogonally to the at least one conductive plate in a presence of an acceleration to change the spacing between the at least one conductive plate and the conductive layer, the device including a first external terminal and a second external terminal, wherein the capacitance is sensed at the first and second external terminals.

16. The method of claim 15, wherein the first and second substrates are sandwiched together using anodic bonding.

17. The method of claim 15, wherein the mass is suspended in the first substrate by undercutting the conductive layer.

18. The method of claim 15, wherein the second substrate comprises a dielectric substrate, and wherein at least first and second external terminals are formed in the second substrate.