Semiconductor physical quantity sensor

• US 6,494,096 B2
• Filed: 03/09/2001
• Issued: 12/17/2002
• Est. Priority Date: 03/16/2000
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Sakai, Minekazu, Murata, Minoru
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US09/801,917
• Publication Number:
  US 20010025530A1
• Time in Patent Office: 648 Days
• Field of Search: 735/143.2, 735/040.2, 735/040.3
• 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 semiconductor acceleration sensor, which prevents an adhesion of a movable electrode to a first or second fixed electrode due to an electrostatic attracting force generated therebetween. The sensor has a weight portion and movable electrodes formed on both sides of which, and first and second fixed electrodes each engaging with the each of the movable electrodes. Each of the first and second fixed electrodes is disposed in parallel with each of the movable electrodes so that side faces thereof determine a detection interval and non-detection interval larger than the detection interval with side faces of adjoining two of the movable electrodes. Protrusions are formed on both of the side faces of each of the first and second fixed electrodes. These protrusions prevent the movable electrodes from adhering to the first or second fixed electrode in both of the detection interval and non-detection interval.

Claims

1. A semiconductor physical quantity sensor comprising:

a supporting substrate;

a movable portion supported on the supporting substrate and having a weight portion movable in a displacement direction, and first movable electrodes and second movable electrodes provided on both sides of the weight portion and protruding from the weight portion perpendicularly to the displacement direction;

a fixed portion provided on the supporting substrate and electrically divided from the moving portion by a trench, the fixed portion having first fixed electrodes and second fixed electrodes respectively protruding toward the movable portion and extending in parallel with the first movable electrodes and second movable electrodes and defining first detection intervals and second detection intervals at the both sides of the weight portion;

wherein an applied physical quantity is detected based on changes in capacitances generated between the first movable electrodes and the first fixed electrodes, and between the second movable electrodes and the second fixed electrodes when the first movable electrodes and the second movable electrodes move responsive to the applied physical quantity;

wherein an electrostatic attracting force generated between the first movable electrodes and the first fixed electrodes acts in a direction opposite to that in which an electrostatic attracting force generated between the second movable electrodes and the second fixed electrodes acts;

wherein the first movable electrodes or the first fixed electrodes have protrusions protruding in parallel with the displacement direction from opposing side faces of the first movable electrodes or the first fixed electrodes, and facing in the displacement direction of the movable portion to define the first detection intervals interposed therebetween.

2. A semiconductor physical quantity sensor according to claim 1, wherein the first movable electrodes and the first fixed electrodes include other side faces opposing each other, wherein the other side faces define first non-detection intervals that are larger than the first detection intervals.

3. A semiconductor physical quantity sensor according to claim 1, wherein the second movable electrodes or the second fixed electrodes have protrusions protruding from opposing side faces, the opposing side faces facing in the displacement direction of the movable portion and defining the second intervals interposed therebetween, and the second movable electrodes and the second fixed electrodes include other side faces opposing each other, wherein the other side faces defining second non-detection intervals that are larger than the second detection intervals.

4. A semiconductor physical quantity sensor according to claim 1, wherein the first movable electrodes or the first fixed electrodes have other protrusions protruding in parallel with the displacement direction from the other side faces, the protrusions protruding from the opposing side faces and the other side faces are disposed symmetrically each other with respect to a longitudinal direction of the first movable electrodes or the first fixed electrodes having the protrusions.

5. A semiconductor physical quantity sensor according to claim 1, wherein the first movable electrodes or the first fixed electrodes have other protrusions protruding in parallel with the displacement direction from the other side faces, all of the protrusions being formed on the opposing side faces and on the other side faces to have an identical size and an identical shape.

6. A semiconductor physical quantity sensor according to claim 1, wherein the protrusions include at least three protrusions that are arranged along a longitudinal direction of the first movable electrodes or the first fixed electrodes on which the at least three protrusions are disposed;

wherein an interval between two of the at least three protrusions disposed on a tip portion of the first movable electrodes or the first fixed electrodes on which the at least three protrusions are disposed is smaller than that between two of the at least three protrusions disposed on a root portion of the first movable electrodes or the first fixed electrodes on which the at least three protrusions are disposed.

7. A semiconductor physical quantity sensor according to claim 1, further comprising:

anchor portions disposed in the displacement direction of the weight portion for anchoring end portions that are positioned at both sides in the displacement direction of the weight portion;

suspension portions each connected to respective ones of the anchor portions and suspending the weight portion at the end portions of the weight portion in the displacement direction, each suspension portion having a spring function which enables the weight portion to move along the displacement direction;

wherein intervals from each of the end portions to each of the anchor portions are narrower than the first detection intervals disposed between the first movable electrodes and the first fixed electrodes;

wherein a middle part of each suspension portion is folded a plurality of times to have a plurality of folded-back portions at the outside of the weight portion or the anchor portions with respect to the displacement direction;

wherein each of the anchor portions has a portion opposed to the weight portion directly; and

said portion works as a stopper to prevent an excessive displacement of the weight portion.

8. A semiconductor physical quantity sensor according to claim 7, wherein each of the suspension portions has suspension members folded a plurality of times in a direction perpendicular to the displacement direction so as to form a plurality of bending members and at least two resilient folds like an accordion spring;

wherein stopper members are formed on one of the anchor portions and the weight portion to restrict a displacement of the weight portion when an excessively large physical quantity is applied to the weight portion;

wherein the two resilient folds are disposed along a direction perpendicular to the displacement direction so that the one of the at least two resilient folds is disposed away from one of the stopper members and another one of the at least two resilient folds is disposed near the one of the stopper members.

9. A semiconductor physical quantity sensor comprising:

a supporting substrate;

a movable portion supported on the supporting substrate and having a weight portion movable in a displacement direction, and first movable electrodes and second movable electrodes provided on both sides of the weight portion and protruding from the weight portion perpendicularly to the displacement direction;

a fixed portion provided on the supporting substrate and electrically divided from the moving portion by a trench, the fixed portion having first fixed electrodes and second fixed electrodes respectively protruding toward the movable portion and extending in parallel with the first movable electrodes and second movable electrodes and defining first and second detection intervals at the both sides of the weight portion;

wherein an applied physical quantity is detected based on changes in capacitances generated between the first movable electrodes and the first fixed electrodes and between second movable electrodes and the second fixed electrodes when the first movable electrodes and second movable electrodes move responsive to the applied physical quantity;

wherein an electrostatic attracting forces generated between the first movable electrodes and the first fixed electrodes act in a direction opposite to that in which electrostatic attracting forces generated between the second movable electrodes and the second fixed electrodes act;

wherein;

the first movable electrodes are composed of a plurality of movable electrode members;

the first fixed electrodes are composed of a plurality of fixed electrode members opposing the plurality of movable electrode members, the plurality of fixed electrode members define the first detection intervals with the plurality of movable electrode members and define non-detection intervals with the plurality of movable electrode members, whereby the plurality of movable electrode members are disposed with the plurality of fixed electrode members interposed therebetween;

the plurality of fixed electrode members or the plurality of movable electrode members have respective first protrusions protruding in the first detection interval; and

the plurality of fixed electrode members or the plurality of movable electrode members have respective second protrusions protrusion providing in the non-detection interval.

10. A semiconductor physical quantity sensor comprising:

a supporting substrate;

a movable portion having a weight portion and movable electrode members provided on both sides of the weight portion, the weight portion including side portions positioned in a displacement direction thereof;

a fixed portion electrically divided from the moving portion, the fixed portion having fixed electrode members each opposing each of the movable electrode members to form capacitors;

anchor portions disposed in the displacement direction of the weight portion for anchoring end portions of the weight portion;

suspension portions each connected to respective ones of the anchor portions and suspending the weight portion at the end portions of the weight portion in the displacement direction, each suspension portion having a spring function which enables the weight portion to move along the displacement direction;

wherein the end portions of the weight portion along the displacement direction face to the anchor portions with intervals narrower than first detection intervals disposed between the first movable electrodes and the first fixed electrodes;

wherein a middle part of each suspension portion is folded a plurality of times to have a plurality of folded-back portions at the outside of the weight portion or the anchor portions with respect to the displacement direction;

wherein each of the anchor portions has a portion opposed to the weight portion directly; and

said portion works as a stopper to prevent an excessive displacement of the weight portion.

11. A semiconductor physical quantity sensor according to claim 10, wherein each of the suspension portions has suspension members folded a plurality of times in a direction perpendicular to the displacement direction so as to form plurality of bending members and at least two resilient folds like an accordion spring;

wherein stopper members are formed on one of the anchor portions and the weight portion to restrict a displacement of the weight portion when an excessively large physical quantity is applied to the weight portion;

wherein the two resilient folds are disposed along a direction perpendicular to the displacement direction so that the one of the at least two resilient folds is disposed away from one of the stopper members and another one of the at least two resilient folds is disposed near the one of the stopper members.

12. A semiconductor physical quantity sensor according to claim 10, wherein the weight portion or the anchor portions have protrusions on side faces thereof so as to protrude from the weight portion or the anchor portions to another one of the weight portion or the anchor portions.

13. A semiconductor physical quantity sensor comprising:

a supporting substrate;

a movable portion disposed on the supporting substrate and movable in a displacement direction, the movable portion having a weight portion, and first movable electrodes and second movable electrodes protruding from first and second sides of the weight portion and extending perpendicularly to the displacement direction;

first fixed electrodes and second fixed electrodes fixed on the supporting substrate, electrically isolated from the movable portion, and extending in parallel with the first movable electrodes to interpose each of the first movable electrodes between each of the first fixed electrodes and each of the second fixed electrodes, the first fixed electrodes define detection intervals with the first movable electrodes to form first capacitances that are changed when a physical quantity is applied to the weight portion, the second fixed electrodes define non-detection intervals with the first movable;

third fixed electrodes and fourth fixed electrodes fixed on the supporting substrate, electrically isolated from the movable portion, and extending in parallel with the second movable electrode to interpose each of the second movable electrodes between each of the third fixed electrodes and each of the fourth fixed electrodes, the third fixed electrodes define detection intervals with the second movable electrodes to form second capacitances that are changed in an opposite direction of the first capacitances when the physical quantity is applied to the weight portion; and

first and second stoppers respectively provided in the detection intervals between the first fixed electrodes and the first movable electrodes and in the non-detection electrodes between the second fixed electrodes and the first movable electrodes, for preventing the first movable electrodes from contacting the first electrodes or the second fixed electrodes, wherein;

each of the first and second stoppers is a protrusion protruding from one of the first fixed electrodes and the second fixed electrodes and the first movable electrodes.

14. The semiconductor physical quantity sensor according to claim 13, wherein the first movable electrodes have first and second protrusions as the first and second stoppers respectively protruding from side faces of the first movable electrodes to face the first fixed electrodes and the second fixed electrodes.

15. The semiconductor physical quantity sensor according to claim 14, wherein the first and second protrusions provided on the side faces of the first movable electrodes are formed to have an identical shape and an identical size with each other.

16. The semiconductor physical quantity sensor according to claim 14, wherein one of the side faces of the first movable electrodes has at least three protrusions as one of the first and second stoppers, the three protrusions are arranged with a first interval at a tip portion of the first movable electrode and a second interval at a root portion of the first movable electrode, the first interval is smaller than the second interval.

17. The semiconductor physical quantity sensor according to claim 13, wherein the first fixed electrodes and the second fixed electrodes respectively have protrusions protruding toward the first movable electrodes.