Acceleration sensor with protrusions facing stoppers

• US 20070214888A1
• Filed: 02/14/2007
• Published: 09/20/2007
• Est. Priority Date: 03/14/2006
• Status: Abandoned Application

• Current Assignee: Oki Semiconductor Company Limited (ROHM Co., Ltd.)
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Nomura, Akihiko
• Application Number:
  US11/705,763
• Publication Number:
  US 20070214888A1
• Time in Patent Office: Days
• US Class Current: 73/514.10
• 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 15/18 in two or more dimensions
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape

Abstract

An integrally micromachined acceleration sensor has a mass with a surface facing a stopper. At least one protrusion projects from this surface toward the stopper. In the absence of acceleration, the protrusion is spaced apart from the stopper, but by limiting motion of the mass toward the stopper, the protrusion improves the shock resistance of the acceleration sensor. The protrusion also prevents the mass from sticking to the stopper during the fabrication process. The stopper may have a pattern of holes surrounding the protrusion, so that the protrusion is produced naturally during the wet etching process that separates the mass from the stopper. The holes also shorten the wet etching time.

Claims

1. An acceleration sensor comprising:

a patterned layer including a mass attachment section, a peripheral attachment section surrounding and spaced apart from the mass attachment section, at least one beam flexibly linking the mass attachment section to the peripheral attachment section, and at least one stopper connected to the peripheral attachment section and spaced apart from the mass attachment section and the beam;

a mass spaced apart from the stopper, having a surface facing the stopper;

a first joining layer joining the mass to the attachment section;

a frame surrounding and spaced apart from the mass;

a second joining layer joining the frame to the peripheral attachment section; and

at least one protrusion protruding from said surface of the mass toward the stopper, the protrusion being spaced apart from the stopper when acceleration is absent.

2. The acceleration sensor of claim 1, wherein the acceleration sensor has more than one said protrusion, the more than one said protrusion being arranged in a regular two-dimensional array extending over substantially all parts of said surface of the mass.

3. The acceleration sensor of claim 1, wherein each said protrusion has a square pyramidal shape.

4. The acceleration sensor of claim 1, wherein each said protrusion has a triangular pyramidal shape.

5. The acceleration sensor of claim 1, wherein each said protrusion has a hexagonal pyramidal shape.

6. The acceleration sensor of claim 1, wherein each said protrusion has an octagonal pyramidal shape.

7. The acceleration sensor of claim 1, wherein the first joining layer, the second joining layer, and the protrusion are made of mutually identical materials.

8. The acceleration sensor of claim 7, wherein the stopper has a plurality of holes facing respective areas on said surface of the mass, each said protrusion being disposed between at least two of said areas.

9. The acceleration sensor of claim 8, wherein each said protrusion has a polygonal shape with sides facing respective ones of said areas.

10. The acceleration sensor of claim 8, wherein the holes are arranged in a regular two-dimensional array extending over substantially all parts of the stopper that face the mass.

11. The acceleration sensor of claim 8, wherein the holes have diameters of at least three micrometers.

12. The acceleration sensor of claim 11, wherein the holes have diameters of at most four micrometers.

13. The acceleration sensor of claim 8, wherein mutually adjacent ones of the holes have centers mutually separated by a distance of at least 7.5 micrometers.

14. The acceleration sensor of claim 13, wherein mutually adjacent ones of the holes have centers mutually separated by a distance of at most 9.5 micrometers.

15. The acceleration sensor of claim 1, wherein the first joining layer and the second joining layer have a thickness of at least one micrometer.

16. The acceleration sensor of claim 15, wherein the first joining layer and the second joining layer have a thickness of at most three micrometers.