CAPACITIVE SENSOR

• US 20090266164A1
• Filed: 04/25/2007
• Published: 10/29/2009
• Est. Priority Date: 04/28/2006
• Status: Active Grant

• Current Assignee: Mosaid Technologies Incorporated (MOSAID Technologies Inc. (f/k/a Conversant Intellectual Property Management))
• Original Assignee: Panasonic Electric Works Company Limited (Panasonic Holdings Corporation)
• Inventors: Furukubo, Eiichi, Aoki, Ryo, Wakabayashi, Daisuke, Ohbuchi, Masao, Miyajima, Hisakazu
• Granted Patent: US 8,176,782 B2
• Time in Patent Office: Days
• US Class Current: 73/514.320
• CPC Class Codes: G01P 1/023 for acceleration measuring devices
• 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 capacitive sensor includes a fixed electrode and a movable electrode that is movably supported by an anchor portion through a beam portion. The fixed electrode and the movable electrode are opposed to each other with a gap interposed therebetween, thereby constituting a detecting unit. A capacitance suitable for a size of the gap is detected to detect a predetermined physical value. At least one of an end of the beam portion connected to the anchor portion and an end of the beam portion connected to the movable electrode is provided with a stress moderating unit that moderates a stress.

Claims

1. A capacitive sensor comprising a fixed electrode and a movable electrode that is movably supported by a fixed portion of a semiconductor layer through a beam, in which the fixed electrode and the movable electrode are opposed to each other with a gap interposed therebetween, thereby constituting a detecting unit, a capacitance suitable for a size of the gap is detected, thereby detecting a predetermined physical value, wherein at least one of an end of the beam connected to the fixed portion and an end of the beam connected to the movable electrode is provided with a stress moderating unit that moderates a local stress concentration.

2. The capacitive sensor according to claim 1, wherein both the end of the beam connected to the fixed portion and the end of the beam connected to the movable electrode are provided with the stress moderating units.

3. The capacitive sensor according to claim 1, wherein the stress moderating unit includes a frame structure.

4. The capacitive sensor according to claim 1, wherein the stress moderating unit includes a meandering structure.

5. The capacitive sensor according to claim 1, wherein the beam is a torsion beam having substantially a rectangular cross section which is twisted when the movable electrode moves.

6. The capacitive sensor according to claim 5, wherein the movable electrode is rockably supported through the torsion beam, and the detecting unit detects a capacitance suitable for a size of a gap between a surface of the rocking movable electrode and a surface of the fixed electrode opposed to the surface of the movable electrode.

7. A capacitive sensor comprising a first detecting unit that is movably supported by a fixed portion of a semiconductor layer through a beam portion such that asymmetric weight balance is kept, in which a first movable electrode that moves according to displacement of a physical value in a thickness direction of the semiconductor layer and a first fixed electrode formed on a support substrate that supports the semiconductor layer are opposed to each other with a gap interposed therebetween, and the first detecting unit detects the physical value based on a capacitance detected according to sizes of the first movable electrode and the first fixed electrode, the semiconductor layer is a single crystal silicon layer, and the capacitive sensor includes a movable mechanism of the first movable electrode comprising the fixed portion, the beam portion and the first movable electrode formed by vertically etching the single crystal silicon layer.

8. The capacitive sensor according to claim 7, further comprising a region opposed to the first fixed electrode formed on the support substrate, wherein a recess is formed in a surface of the semiconductor layer opposed to the support substrate.

9. The capacitive sensor according to claim 8, wherein the recess is formed by crystal anisotropy etching.

10. The capacitive sensor according to claim 7, wherein using an SOI (Silicon on Insulator) substrate having such a structure that an intermediate oxide film is inserted between a silicon support substrate and a silicon active layer, the semiconductor layer is a silicon active layer of the SOI substrate.

11. The capacitive sensor according to claim 7, wherein a thickness of the beam portion is greater than a width of the beam portion.

12. The capacitive sensor according to claim 11, wherein a thickness of the first movable electrode and a thickness of the beam portion are 10 μ

m or greater.

13. The capacitive sensor according to claim 11, wherein a thickness of the beam portion is 3.16 times or more of a width of the beam portion.

14. The capacitive sensor according to claim 7, wherein the first fixed electrode is independently opposed to a small plate portion that is a member having a small mass of the first movable electrode that is asymmetric mass balance through the beam portion, and opposed to a large plate portion that is a member having a great mass, the first fixed electrode opposed to the small plate portion is disposed such as to be separated away from the beam portion, and the first fixed electrode opposed to the large plate portion is disposed on the support substrate such that it approaches the beam portion.

15. The capacitive sensor according to claim 7, wherein the first fixed electrode is independently opposed to a small plate portion that is a member having a small mass of the first movable electrode that is asymmetric mass balance through the beam portion, and opposed to a large plate portion that is a member having a great mass, the first fixed electrode is not opposed to the fixed portion and a gap provided for forming the beam portion by vertical etching, and the first fixed electrode is formed on the support substrate such that a portion of the first fixed electrode extends along a shape of the gap.

16. The capacitive sensor according to claim 7, further comprising a second movable electrode that is movably supported by the fixed portion of the semiconductor layer through a beam portion, and that is operated according to displacement of physical values in both directions of the semiconductor layer, and a second fixed electrode formed by the semiconductor layer, wherein the second movable electrode and the second fixed electrode are opposed to each other through a gap, the capacitive sensor further comprises a second detecting unit that detects a physical value based on the second movable electrode and a capacitance detected according to the size of the gap with respect to the second movable electrode.

17. The capacitive sensor according to claim 16, wherein a thickness of the semiconductor layer of the first detecting unit and a thickness of the semiconductor layer of the second detecting unit are substantially equal to each other.

18. The capacitive sensor according to claim 16, wherein a thickness of a beam portion of the first detecting unit and a thickness of a beam portion of the second detecting unit are substantially equal to each other.

19. The capacitive sensor according to claim 16, wherein a width of a beam portion of the first detecting unit and a width of a beam portion of the second detecting unit are substantially equal to each other.

20. The capacitive sensor according to claim 16, wherein a gap provided by vertical etching working for forming the beam portion of the first detecting unit, and a gap provided when the second movable electrode and the second fixed electrode of the second detecting unit are opposed to each other are substantially equal to each other.

21. The capacitive sensor according to claim 16, wherein the first movable electrode of the first detecting unit has a shape surrounding the second detecting unit.