SYMMETRICAL DIFFERENTIAL CAPACITIVE SENSOR AND METHOD OF MAKING SAME

• US 20090031809A1
• Filed: 08/03/2007
• Published: 02/05/2009
• Est. Priority Date: 08/03/2007
• Status: Active Grant

• Current Assignee: North Star Innovations Inc. (Wi-LAN Inc.)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Lin, Yizhen, McNeil, Andrew C., Fuhrmann, Marco
• Granted Patent: US 7,578,190 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• 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

A symmetrical differential capacitive sensor (60) includes a movable element (66) pivotable about a geometrically centered rotational axis (70). The element (66) includes sections (86, 88). Each of the sections (86, 88) has a stop (94, 96) spaced equally away from the rotational axis (70). Each of the sections (86, 88) also has a different configuration (104, 108) of apertures (102, 106). The configurations (104, 108) of apertures (102, 106) create a mass imbalance between the sections (86, 88) so that the element (66) pivots about the rotational axis (70) in response to acceleration. The apertures (102, 106) also facilitate etch release during manufacturing and reduce air damping when the element (66) rotates. Apertures (126, 128) are formed in electrodes (78, 80) underlying the apertures (102, 106) to match the capacitance between the two sections (86, 88) of movable element (86) to provide the same bi-directional actuation capability.

Claims

1. A device comprising:

a Micro Electro-Mechanical System (MEMS) sensor, said sensor comprising;

a substrate;

a movable sensing element attached to said substrate, said element being adapted for motion relative to a rotational axis substantially geometrically centered between first and second ends of said movable sensing element to form a first section between said rotational axis and said first end and a second section between said rotational axis and said second end, said first section including first apertures extending through said movable element to produce said first section having a first mass, said second section including second apertures extending through said movable element to produce said second section having a second mass that is less than said first mass; and

at least one electrode positioned on said substrate facing said first and second sections of said movable element.

2. A device as claimed in claim 1 wherein:

said first apertures are displaced from said rotational axis toward said first end; and

said second apertures are displaced from said rotational axis towards said second end.

3. A device as claimed in claim 1 wherein:

said first apertures are arranged in said first section in a first configuration; and

said second apertures are arranged in said second section in a second configuration, said second configuration differing from said first configuration, and each of said first and second configurations describing a size and a quantity of corresponding ones of said first apertures and said second apertures.

4. A device as claimed in claim 3 wherein said at least one electrode comprises:

a first electrode facing said first section, said first electrode having third apertures arranged in said second configuration and opposing said first apertures; and

a second electrode facing said second distal region, said second electrode having fourth apertures arranged in said first configuration and opposing said second apertures.

5. A device as claimed in claim 3 further comprising:

third apertures extending through said first section, said third apertures being arranged in a third configuration; and

fourth apertures extending through said second section, said fourth apertures being arranged in said third configuration, and said third and fourth apertures being substantially symmetrically located on said movable element relative to said rotational axis.

6. A device as claimed in claim 1 wherein:

said first section comprises a first proximal region located adjacent said rotational axis and a first distal region located adjacent to said first end;

said second section comprises a second proximal region located adjacent said rotational axis and a second distal region located adjacent to said second end; and

said at least one electrode comprises a first sense electrode facing said first proximal region and a second sense electrode facing said second proximal region, said first and second sense electrodes being substantially symmetrically arranged relative to said rotational axis.

7. A device as claimed in claim 6 wherein said at least one electrode further comprises:

a first actuation electrode facing said first distal region; and

a second actuation electrode facing said second distal region, said first and second actuation electrodes being substantially symmetrically arranged relative to said rotational axis.

8. A device as claimed in claim 1 wherein said at least one electrode comprises:

a first electrode facing said first section and having a perimeter that is approximately equivalent to a section perimeter of said first section; and

a second electrode facing said second section and having said perimeter that is approximately equivalent to said section perimeter of said second section.

9. A device as claimed in claim 8 wherein:

said first electrode includes third apertures opposing said first apertures in said first section; and

said second electrode includes fourth apertures opposing said second apertures in said second section.

10. A device as claimed in claim 1 further comprising a material disposed on said first section of said proof mass, said material increasing said first mass of said first section relative to said second mass.

11. A device as claimed in claim 1 wherein said sensor further comprises:

a first stop extending from a surface of said movable element proximate said first end, said surface facing said substrate; and

a second stop extending from said surface of said movable element proximate said second end, each of said first and second stops being displaced a substantially equivalent distance from said rotational axis.

12. A device as claimed in claim 11 wherein said substrate comprises:

a first contact plate facing said movable sensing element, said first stop being selectively contactable with said first contact plate; and

a second contact plate facing said movable sensing element, said second stop being selectively contactable with said second contact plate, and said first and second stops being at a substantially equivalent potential as said first and second contact plates.

13. A method of fabricating a Micro Electro-Mechanical System (MEMS) sensor comprising:

providing a substrate;

forming a static conductive layer on said substrate to include a first electrode and a second electrode, said first electrode being electrically isolated from said second electrode;

forming a sacrificial layer on said first conductive layer;

forming a movable element on said first sacrificial layer adapted for motion relative to a rotational axis geometrically centered between first and second ends of said movable element to form a first section between said rotational axis and said first end and a second section between said rotational axis and said second end;

forming first apertures extending through said first section of said movable element to produce said first section having a first mass;

forming second apertures extending through said second section of said movable element to produce said second section having a second mass, said second mass being less than said first mass; and

selectively removing said sacrificial layer such that said conductive layer is spaced away from said movable element, and said conductive layer being formed such that said first electrode faces said first apertures and second electrode faces said second apertures.

14. A method as claimed in claim 13 further comprising:

forming said first apertures arranged across a first distal region of said first section in a first configuration, said first distal region being located adjacent to said first end; and

forming said second apertures arranged across a second distal region of said second section in a second configuration, said second distal region being located adjacent to said second end, said second configuration differing from said first configuration, and each of said first and second configurations describing a size and a quantity of corresponding ones of said first apertures and said second apertures.

15. A method as claimed in claim 14 wherein:

said forming said first electrode includes positioning said first electrode in facing relation with said first distal region, and forming third apertures in said first electrode arranged in said second configuration; and

said forming said second electrode includes positioning said second electrode in facing relation with said second distal region, and forming fourth apertures in said first electrode arranged in said first configuration.

16. A method as claimed in claim 13 further comprising:

forming third apertures distributed across a first proximal region of said first section in a third configuration, said first proximal region being located adjacent to said rotational axis; and

forming fourth apertures distributed across a second proximal region of said second section in said third configuration, said second proximal region being located adjacent to said rotational axis, and said third and fourth apertures being substantially symmetrically distributed across respective ones of said first and second proximal regions in said third configuration relative to said rotational axis.

17. A Micro Electro-Mechanical System (MEMS) sensor comprising:

a substrate;

a movable sensing element attached to said substrate, said element being adapted for motion relative to a rotational axis substantially geometrically centered between first and second ends of said movable sensing elements to form a first section between said rotational axis and said first end and a second section between said rotational axis and said second end, said first section including first apertures extending through said movable element to produce said first section having a first mass, said second section including second apertures extending through said movable element to produce said second section having a second mass that is less than said first mass, said first apertures are arranged in said first section in a first configuration, said second apertures are arranged in said second section in a second configuration, said second configuration differing from said first configuration, and each of said first and second configurations describing a size and a quantity of corresponding ones of said first apertures and said second apertures;

a first stop extending from said surface of said movable element proximate said first end;

a second stop extending from said surface of said movable element proximate said second end, and each of said first and second stops is displaced a substantially equivalent distance from said rotational axis; and

at least one electrode positioned on said substrate facing said first and second sections of said movable element.

18. A sensor as claimed in claim 17 wherein said at least one electrode comprises:

a first electrode facing said first section, said first electrode having third apertures arranged in said second configuration and opposing said first apertures; and

a second electrode facing said second distal region, said second electrode having fourth apertures arranged in said first configuration and opposing said second apertures.

19. A device as claimed in claim 17 wherein:

said first section comprises a first proximal region located adjacent said rotational axis and a first distal region located adjacent said first end;

said second section comprises a second proximal region located adjacent said rotational axis and a second distal region located adjacent said second end a first sense electrode facing said first proximal region;

a second sense electrode facing said second proximal region, said first and second sense electrodes being substantially symmetrically arranged relative to said rotational axis;

a first actuation electrode facing said first distal region; and

a second actuation electrode facing said second distal region, said first and second actuation electrodes being substantially symmetrically arranged relative to said rotational axis.

20. A device as claimed in claim 17 wherein said at least one electrode comprises:

a first electrode facing said first section and having a perimeter that is approximately equivalent to a section perimeter of said first section, said first electrode including third apertures opposing said first apertures in said first section; and

a second electrode facing said second section and having said perimeter that is approximately equivalent to said section perimeter of said second section, said second electrode including fourth apertures opposing said second apertures in said second section.