BI-DIRECTIONAL RELEASED-BEAM SENSOR

• US 20060138573A1
• Filed: 12/28/2004
• Published: 06/29/2006
• Est. Priority Date: 12/28/2004
• Status: Active Grant

• Current Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Original Assignee: STMicroelectronics Incorporated (STMicroelectronics NV)
• Inventors: McAlexander, Joseph Colby III
• Granted Patent: US 7,179,674 B2
• Time in Patent Office: Days
• US Class Current: 257/415
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2201/032 Bimorph and unimorph actuators, e.g. piezo and thermo
• CPC Class Codes: B81C 1/0015 Cantilevers switches using MEMS H01H1/0036; electrostatic relays using micromechanics H01H59/0009; microelectro-mechanical resonators H03H9/02244
• CPC Class Codes: B81C 2201/019 Bonding or gluing multiple substrate layers
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 15/135 by making use of contacts which are actuated by a movable inertial mass
• CPC Class Codes: G01P 2015/0828 the mass being of the paddle type being suspended at one of its longitudinal ends
• CPC Class Codes: H01H 1/0036 Switches making use of microelectromechanical systems [MEMS] for electromagnetic relays H01H50/005; for electrostatic relays H01H59/0009
• CPC Class Codes: H01H 35/14 Switches operated by change of acceleration, e.g. by shock or vibration, inertia switch wherein the liquid constitutes a contact of the switch H01H29/002

Abstract

An acceleration sensor includes a semiconductor substrate, a first layer formed on the substrate, a first aperture within the first layer, and a beam coupled at a first end to the substrate and suspended above the first layer for a portion of the length thereof. The beam includes a first boss coupled to a lower surface thereof and suspended within the first aperture, and a second boss coupled to an upper surface of the second end of the beam. A second layer is positioned on the first layer over the beam and includes a second aperture within which the second boss is suspended by the beam. Contact surfaces are positioned within the apertures such that acceleration of the substrate exceeding a selected threshold in either direction along a selected axis will cause the beam to flex counter to the direction of acceleration and make contact through one of the bosses with one of the contact surfaces.

Claims

1. A sensor, comprising:

a semiconductor substrate;

a first layer formed on a surface of the substrate;

a first aperture within the first layer;

a beam having first and second ends, the beam being mechanically coupled at the first end to the first layer and suspended above the first layer for at least a portion of the length thereof and the second end having a region above the first aperture;

a first boss coupled to a lower surface of the second end of the beam and suspended at least partially within the first aperture; and

a second boss coupled to an upper surface of the second end of the beam.

2. The sensor of claim 1, further comprising a second layer positioned on the first layer and including a second aperture within which the second boss is at least partially suspended.

3. The sensor of claim 1 wherein the first layer is a dielectric layer.

4. The sensor of claim 1, further comprising a third layer positioned between the first layer and the semiconductor substrate.

5. The sensor of claim 1, further comprising a conductive layer positioned between the semiconductor substrate and the first layer with a portion thereof exposed within the first aperture.

6. The sensor of claim 1 wherein the beam and first and second bosses are electrically conductive.

7. The sensor of claim 1, further comprising a first contact surface positioned on at least one sidewall of the first aperture and a second contact surface positioned on at least one sidewall of the second aperture.

8. The sensor of claim 7 wherein the first contact surface is positioned on a first sidewall of the first aperture, the second contact surface is positioned on a first sidewall of the second aperture, and further comprising third and fourth contact surfaces positioned on second and third sidewalls of the first aperture and fifth and sixth contact surfaces positioned on second and third sidewalls of the second aperture.

9. The sensor of claim 7, further comprising a circuit coupled to the sensor and configured to detect electrical contact between the first or second boss and the first or second contact surface, respectively.

10. The sensor of claim 7, further comprising a circuit coupled to the sensor and configured to detect changes in capacitive coupling between the first and second bosses and the first and second contact surfaces, respectively.

11. The sensor of claim 1 wherein the beam has a cylindrical shape along at least a portion of a length thereof.

12. A sensor, comprising:

a semiconductor substrate;

a first layer of material formed on a surface of the substrate;

a beam having first and second ends, the beam being mechanically coupled at the first end to the first layer and suspended above the first layer such that the second end forms a cantilever above the first layer;

means for increasing a bi-directional sensitivity of the cantilever to acceleration of the substrate along a first axis; and

means for detecting response of the beam to acceleration bi-directionally along the one axis.

13. The sensor of claim 12 wherein the increasing means includes an aperture formed in the first layer and first and second bosses coupled to the second end of the beam, the first boss suspended at least partially within the aperture.

14. The sensor of claim 12 wherein the detecting means includes a second layer positioned above the first layer and including an aperture within which the second boss is at least partially suspended.

15. The sensor of claim 12, comprising:

means for increasing a bidirectional sensitivity of the cantilever to acceleration of the substrate along at least a second axis lying in a plane defined by the first axis the plane lying perpendicular to a longitudinal axis of the beam; and

means for detecting response of the beam to acceleration bi-directionally along at least the second axis.

16. A method, comprising:

forming a first layer on a surface of a semiconductor wafer;

forming a first aperture in the first layer;

forming a second layer over the first layer and within the aperture;

forming a third layer of semiconductor material over the second layer and in the aperture, to form a first plug in the aperture;

forming a fourth layer over the third layer and in contact with the first plug;

patterning the fourth layer to form a beam;

forming a fifth layer over the fourth layer;

forming an aperture in the fifth layer having a shape substantially mirroring the shape of the first plug;

filling the aperture in the fifth layer to form a second plug in contact with the beam;

removing the fifth layer such that the second plug remains on the beam;

forming a sixth layer over the second plug and beam having a thickness substantially equal to a thickness of the second layer;

forming a seventh layer over the sixth layer; and

etching the second and sixth layers to form a cantilever of the beam with one end suspended above the first aperture, the first plug coupled to the beam and suspended at least partially within the first aperture, the second plug coupled to the beam and at least partially suspended within a second aperture formed in the seventh layer by the second plug and the sixth layer.

17. The method of claim 16, further comprising forming an eighth layer of material above the surface of the semiconductor wafer prior to forming the first layer.

18. The method of claim 16, further comprising forming a cylindrical region along at least a portion of a length of the beam.

19. The method of claim 18, further comprising forming a plurality of contact surfaces within each of the first and second apertures.

20. A system, comprising:

a vehicle having a motor, a drive train coupled to the motor, an axle coupled to the drive train, and wheels coupled to the axle for causing movement of the vehicle powered by the motor;

a passenger seat within said vehicle;

an airbag positioned adjacent to the passenger seat;

a sensor coupled to the airbag configured to cause inflation of the airbag, the sensor including a semiconductor material substrate, a first layer above the semiconductor substrate, a beam having first and second ends, the beam being mechanically coupled at the first end to the substrate and positioned above the first layer for a portion thereof to form a cantilever in a plane that is substantially parallel to an upper surface of the substrate, and first and second bosses coupled to upper and lower surfaces, respectively, of the second end of the beam and suspended over the substrate.

21. The system of claim 20 wherein the first layer includes a first aperture positioned underneath the beam such that at least a portion of the first boss is suspended within the first aperture by the beam, and a second layer over the first layer and having a second aperture positioned over the beam such that at least a portion of the second boss is suspended within the second aperture by the beam.

22. A method, comprising:

subjecting a semiconductor substrate to an acceleration;

moving a first and second bosses coupled to an outer end of a cantilevered beam coupled at an inner end to the substrate, in response to the acceleration; and

sending a signal from the cantilevered beam to a sensing circuit if an absolute value of the acceleration exceeds a selected threshold along a selected vector.

23. The method of claim 22 wherein the moving step includes flexing the cantilevered beam such that the first and second bosses move substantially along the selected vector.

24. The method of claim 22, comprising deploying a vehicle airbag if the signal is sent.

25. The method of claim 22 wherein the selected vector is any vector lying in a plane perpendicular to a longitudinal axis of the cantilevered beam.