Semiconductor physical quantity sensor

• US 20010025530A1
• Filed: 03/09/2001
• Published: 10/04/2001
• Est. Priority Date: 03/16/2000
• Status: Active Grant

• Current Assignee: DENSO Corporation
• Original Assignee: DENSO Corporation
• Inventors: Sakai, Minekazu, Murata, Minoru
• Granted Patent: US 6,494,096 B2
• Time in Patent Office: Days
• 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 to the supporting substrate and having a weight portion movable in a displacement direction and first 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 and second fixed electrodes respectively protruding toward the movable portion interposed therebetween, extending in parallel with the first 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 and second movable electrodes and the first and second fixed electrodes when the first and second movable electrodes move responsive to the applied physical quantity;

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

wherein one of the first movable electrode and the first fixed electrode has protrusions protruding from opposing side faces thereof in parallel with the displacement direction, one of the side faces facing the first detection interval.

2. A semiconductor physical quantity sensor according to

claim 1

, wherein another one of the side faces facing a first non-detection interval which is larger than the first detection interval.

3. A semiconductor physical quantity sensor according to

claim 1

, wherein one of the second movable electrode and the second fixed electrode has protrusions protruding from opposing side faces thereof in parallel with the displacement direction, one of the side faces facing the first detection interval, and another one of side faces facing a second non-detection interval which is larger than the second detection interval.

4. A semiconductor physical quantity sensor according to

claim 1

, wherein the protrusions of the one of the first movable electrode and the first fixed electrode are disposed symmetrically each other with respect a longitudinal direction of the one of the first movable electrode and the first fixed electrode having the protrusions.

5. A semiconductor physical quantity sensor according to

claim 1

, wherein one of the protrusions formed on one of the opposing side faces has an identical size and an identical shape with respect to another one of the protrusions formed on another one of the side faces.

6. A semiconductor physical quantity sensor according to

claim 1

, wherein a plurality of the protrusions disposed on at least one of the side faces are arranged three and over along a longitudinal direction of the one of the first movable electrode and the first fixed electrode having the protrusions;

wherein an interval between two of the plurality of the protrusions disposed on a tip portion of the one of the first movable electrode and the first fixed electrode having the protrusions is smaller than that between two of the plurality of the protrusions disposed on a root portion of the one of the first movable electrode and the first fixed electrode having the protrusions.

7. A semiconductor physical quantity sensor according to

claim 1

, further comprising:

anchor portions anchoring to the supporting substrate at the outside of both end portions of the weight portion in the displacement direction;

suspension portions each connected each of the anchor portions and suspending the weight portion at the both end portions of the weight portion in the displacement direction, each suspension portion has spring function which enable the weight portion to move along the displacement direction;

wherein each of the both end portions of the weight portion along the displacement direction faces to each of the anchor portions with an interval narrower than the first detection interval disposed between the first movable electrode and the first fixed electrode;

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 excessively 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 lot 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 to the supporting substrate and having a weight portion movable in a displacement direction and first 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 and second fixed electrodes respectively protruding toward the movable portion interposed therebetween, extending in parallel with the first 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 and second movable electrodes and the first and second fixed electrodes when the first and second movable electrodes move responsive to the applied physical quantity;

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

wherein;

the first movable electrode is composed of a plurality of movable electrode members;

the first fixed electrode is composed of a plurality of fixed electrode members engaging with the plurality of movable electrode members, one of the plurality of fixed electrode members defining the first detection interval with a first one of the plurality of movable electrode members, and defining a non-detection interval with a second one of the plurality of movable electrode members, whereby the first and second one of the plurality of movable electrode members are disposed with the one of the plurality of fixed electrode members interposed therebetween;

one of the one of the plurality of fixed electrode members and the first one of the plurality of movable electrode members has a first protrusion protruding to be disposed in the first detection interval; and

one of the one of the plurality of fixed electrode members and the second one of the plurality of movable electrode members has a second protrusion protruding to be disposed in the non-detection interval.

10. A semiconductor physical quantity sensor comprising:

a supporting substrate;

a movable portion having a weight portion and a movable electrode members provided on one side and the other side of the weight portion;

a fixed portion electrically divided from the moving portion, the fixed portion having fixed electrode members each engaging with each of the movable electrode members for forming capacitors;

anchor portions anchoring to the supporting substrate at the outside of both end portions of the weight portion in the displacement direction;

suspension portions each connected each of the anchor portions and suspending the weight portion at the both end portions of the weight portion in the displacement direction, each suspension portion has spring function which enable the weight portion to move along the displacement direction;

wherein each of the both end portions of the weight portion along the displacement direction faces to each of the anchor portions with an interval narrower than the first detection interval disposed between the first movable electrode and the first fixed electrode;

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 excessively 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 a lot 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 protrusions are formed on side faces of one of the weight portion and the anchor portions so as to protrude from the one of the weight portion and the anchor portions to another one of the weight portion and 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 and second movable electrodes protruding from first and second sides of the weight portion and extending perpendicularly to the displacement direction;

first and second fixed electrodes fixed to the supporting substrate at the first side of the weight portion, electrically isolated from the movable portion, and extending in parallel with the first movable electrode at both sides of the first movable electrode in the displacement direction, the first fixed electrode defining an detection interval with the first movable electrode to form a first capacitance that is changed when a physical quantity is applied to the weight portion, the second fixed electrode defining a non-detection interval with the first movable electrode;

third and fourth fixed electrodes fixed to the supporting substrate at the second side of the weight portion, electrically isolated from the movable portion, and extending in parallel with the second movable electrode at both sides of the second movable electrode in the displacement direction, the third fixed electrode defining a detection interval with the second movable electrode to form a second capacitance that is changed in an opposite direction of the first capacitance when the physical quantity is applied to the weight portion; and

first and second stoppers respectively provided in the detection interval between the first fixed electrode and the first movable electrode and in the non-detection interval between the second fixed electrode and the first movable electrode, for preventing the first movable electrode from adhering the first or second fixed electrode, wherein;

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

14. The semiconductor physical quantity sensor according to

claim 13

, wherein the first movable electrode has first and second protrusions as the first and second stoppers respectively protruding from side faces of the first movable electrode to face the first and 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 electrode 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 electrode has at least three protrusions as one of the first and second stoppers, the three protrusions being 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 being smaller than the second interval.

17. The semiconductor physical quantity sensor according to

claim 13

, wherein the first and second fixed electrode respectively have protrusions protruding toward the first movable electrodes.