Acceleration sensor and manufacturing method for the same

• US 20040231422A1
• Filed: 06/29/2004
• Published: 11/25/2004
• Est. Priority Date: 05/13/2002
• Status: Active Grant

• Current Assignee: Wacoh Company
• Original Assignee: Wacoh Company
• Inventors: Okada, Kazuhiro
• Granted Patent: US 6,920,788 B2
• Time in Patent Office: Days
• US Class Current: 73/514.33
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2201/0242 Gyroscopes
• CPC Class Codes: B81B 2203/053 Translation according to an axis perpendicular to the substrate
• CPC Class Codes: B81B 2203/055 Translation in a plane parallel to the substrate, i.e. enabling movement along any direction in the plane
• CPC Class Codes: B81B 2203/056 Rotation in a plane parallel to the substrate
• CPC Class Codes: B81B 2203/058 Rotation out of a plane parallel to the substrate
• 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 15/08 with conversion into electric or magnetic values
• 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 15/125 by capacitive pick-up
• 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
• CPC Class Codes: G01P 2015/0842 the mass being of clover leaf shape
• CPC Class Codes: G01P 2015/0871 using stopper structures for limiting the travel of the seismic mass

Abstract

The present invention easily achieves an accurate control structure for limiting displacement of a weight. An SOI substrate with a trilaminar structure including a silicon layer, a silicon oxide layer, and a silicon layer is prepared, and slits are opened by applying induced coupling plasma etching which can selectively remove only silicon from the upper side. Then, the same etching is applied from the lower side to form grooves, whereby the lower silicon layer is separated into a weight and a pedestal. Next, the structure is immersed in an etchant which can selectively remove only silicon oxide, whereby the vicinities of exposed portions of the silicon oxide layer are removed to form joint layers. A glass substrate is joined to the bottom surface of the pedestal. Piezo resistor elements are formed on the upper surface of the silicon layer to detect bending. The degree of freedom of upward displacements of the weight is accurately set based on the thickness of the joint layer.

Claims

1. An acceleration sensor comprising:

a displacing section;

a fixed section provided adjacent to said displacing section;

a connecting portion for connecting said displacing section to said fixed section so that said displacing section can displace;

a weight connected to said displacing section below;

a pedestal which is disposed adjacent to said weight;

a pedestal joint layer connecting said pedestal and said fixed section; and

a displacement detector for detecting a displacement of said displacing section;

wherein said weight includes an upper surface peripheral portion that opposes a control surface formed on a lower surface of said fixed section so that when an acceleration with a certain degree of magnitude is applied to said weight, said upper surface peripheral portion comes into contact with said control surface to control displacement.

2. The acceleration sensor according to claim 1:

wherein the pedestal joint layer is made of a material different from that of the pedestal and the fixed section.

3. The acceleration sensor according to claim 2:

wherein a material for forming the pedestal joint layer and a material for forming the pedestal and the fixed section are different in etching property from each other.

4. The acceleration sensor according to claim 1:

wherein the fixed section is provided around the displacing section and the pedestal is disposed around the weight.

5. The acceleration sensor according to claim 1:

wherein a thickness of the pedestal joint layer is set to be equal to a distance between the upper surface peripheral portion and the control surface when no acceleration is applied.

6. The acceleration sensor according to claim 1:

wherein a weight joint layer made of the same material as that of the pedestal joint layer is provided between the weight and the displacing section, and said weight and said displacement section are joined together by said weight joint layer.

7. The acceleration sensor according to claim 1:

wherein a distance between a side surface of the weight and a side surface of the pedestal is set so that displacement of the weight is controlled by contact of said side surface of the weight with said side surface of the pedestal when an acceleration with a certain degree of magnitude is applied.

8. The acceleration sensor according to claim 1:

wherein a thickness of the weight is set so that a bottom surface of the weight is located above a bottom surface of the pedestal with a predetermined distance, and when the pedestal is fixed on a control substrate, said predetermined distance is secured between the bottom surface of the weight and the upper surface of said control substrate, said predetermined distance being set so that displacement of the weight is controlled by contact of the bottom surface of the weight with the upper surface of the control substrate when an acceleration with a certain degree of magnitude is applied.

9. The acceleration sensor according to claim 1:

the displacement detector includes piezo resistor elements disposed on the connecting portion and a detecting circuit for detecting electric resistance changes of said piezo resistor elements.