Dynamic sensor having capacitance varying according to dynamic force applied thereto

• US 6,694,814 B2
• Filed: 12/28/2001
• Issued: 02/24/2004
• Est. Priority Date: 02/02/2001
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Ishio, Seiichiro
• Primary Examiner(s): KWOK, HELEN C
• Application Number:
  US10/029,025
• Publication Number:
  US 20020104377A1
• Time in Patent Office: 788 Days
• Field of Search: 735/141.6, 735/143.2, 735/143.8, 735/143.6, 735/040.2, 735/040.3, 738/625.2, 738/625.41, 738/626.8, 738/623.81, 738/626.25, 738/626.26, 735/041.4, 361/280, 361/283.3, 361/281
• US Class Current: 73/514.32
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 3/0008 Structures for avoiding electrostatic attraction, e.g. avoiding charge accumulation
• CPC Class Codes: G01P 15/125 by capacitive pick-up
• CPC Class Codes: G01P 2015/0814 for translational movement of the mass, e.g. shuttle type

Abstract

A dynamic sensor includes stationary electrodes and movable electrodes facing each other and forming a capacitance therebetween. The capacitance changes in accordance with a dynamic force such as acceleration imposed on the sensor. Plural projections are formed on the stationary electrodes to avoid or suppress electrode sticking between the movable electrodes and the stationary electrodes due to an excessive impact imposed on the sensor. The projections are formed to have various heights so that higher projections first hit the movable electrodes and thereby protect lower projections. Even after the higher projections are destroyed by the excessive impact, the lower projections remain intact and serve to prevent the electrode sticking by the excessive impact which may occur later.

Claims

1. A dynamic sensor comprising:

a semiconductor substrate;

a stationary member formed on the semiconductor substrate, the stationary member having elongate stationary electrodes;

a movable member anchored on the semiconductor substrate, the movable member having elongate movable electrodes facing the stationary electrodes and forming a capacitance therebetween which varies according to a dynamic force applied to the movable electrodes, wherein;

a plurality of projections are formed on either the stationary electrodes or the movable electrodes, or on both the stationary electrodes and the movable electrodes, the projections having various heights so that the highest ones of the projections first hit ones of the stationary electrodes and/or the movable electrodes facing the projections when an excessive dynamic force is applied to the dynamic sensor.

2. The dynamic sensor as in claim 1, wherein:

the elongate stationary electrodes are supported on the semiconductor substrate at one end thereof, forming cantilevers;

the movable member includes an elongate center rib anchored on the semiconductor substrate at both ends thereof; and

the elongate movable electrodes are connected to the center rib at one end thereof, forming cantilevers.

3. The dynamic sensor as in claim 2, wherein:

the projections are formed on the stationary electrodes.

4. The dynamic sensor as in claim 3, wherein:

the projections are more densely positioned either at a tip portion or at a foot portion of each of the stationary electrodes, or at both the tip portion and the foot portion, than at a center portion thereof.

5. The dynamic sensor as in claim 3, wherein:

the projections are made higher either at a tip portion or at a foot portion of each of the stationary electrodes, or at both the tip portion and the foot portion, than at a center portion thereof.

6. The dynamic sensor as in claim 3, wherein:

the projections are formed on both sides of the stationary electrodes.

7. A dynamic sensor comprising:

a semiconductor substrate;

a stationary member formed on the semiconductor substrate, the stationary member having elongate stationary electrodes;

a movable member anchored on the semiconductor substrate, the movable member having elongate movable electrodes facing the stationary electrodes and forming a capacitance therebetween which varies according to a dynamic force applied to the movable electrodes, wherein;

the elongate stationary electrodes are supported on the semiconductor substrate at one end thereof, forming cantilevers;

the movable member includes an elongate center rib and a flexible beam resiliently swinging according to a dynamic force applied to the dynamic sensor, the elongate center rib being anchored on the semiconductor substrate at both ends thereof, the elongate movable electrodes being connected to the center rib, forming cantilevers; and

a plurality of projections for restricting an excessive swinging motion of the flexible beam are formed on the flexible beam, wherein the projections formed on the flexible beam have various heights so that highest ones of the projections first restrict the excessive swinging motion of the flexible beam.

8. The dynamic sensor as in claim 7, wherein:

a plurality of projections are formed on the stationary electrodes so that the projections hit the movable electrodes when an excessive impact is imposed on the dynamic sensor.

9. The dynamic sensor as in claim 8, wherein:

the projections formed on the stationary electrodes have various heights so that the highest projections first hit the movable electrodes when the excessive impact is imposed on the dynamic sensor.

10. The dynamic sensor as in claim 8, wherein:

the projections formed on the stationary electrodes are positioned more densely either at a tip portion or at a foot portion of the stationary electrodes forming the cantilevers, or at both the tip portion and the foot portion, than at a center portion thereof.