Temperature-compensated surface micromachined angular rate sensor

• US 5,872,313 A
• Filed: 04/07/1997
• Issued: 02/16/1999
• Est. Priority Date: 04/07/1997
• Status: Expired due to Fees

• Current Assignee: Google Inc. (Alphabet Inc.)
• Original Assignee: Delco Electronics Corporation (General Motors Company)
• Inventors: Johnson, Jack Daniel, Putty, Michael William, Zarabadi, Seyed Ramezan
• Primary Examiner(s): ODA, CHRISTINE K
• Application Number:
  US08/833,438
• Time in Patent Office: 680 Days
• Field of Search: 73/497, 73/DIG. 1, 73/514.32, 73/504.12, 73/504.13, 73/862.041, 73/862.626, 73/1.37, 73/1.82, 361/283.4
• US Class Current: 73/497
• CPC Class Codes: G01C 19/5684 the devices involving a micromechanical structure

Abstract

A motion sensor having a micromachine sensing element and electrodes formed on a silicon chip. The sensing element includes a ring supported above a substrate so as to have an axis of rotation normal to the substrate. Surrounding the ring is at least one pair of diametrically-opposed electrode structures. The sensing ring and electrode structures are configured to include interdigitized members whose relative placement to each other enables at least partial cancellation of the effect of differential thermal expansion of the ring and electrodes. As a result, the performance of the motion sensor is, to first order, insensitive to temperature variation. The sensor further includes circuitry for creating and detecting an electrostatic force between the interdigitized members of the sensing ring and electrode structures. The circuitry operates to sum the electrostatic forces such that, on the occurrence of a temperature change, a corresponding decrease in the electrostatic force between one pair of interdigitized members will at least partially cancel a corresponding increase in electrostatic force between a second pair of interdigitized members. Accordingly, the net effect is that a temperature change will have a reduced effect on the sensing performance of the sensor, because the effects of thermal expansion will be at least partially canceled.

Claims

1. A motion sensor comprising:

a substrate;

a sensing ring supported above the substrate so as to have an axis of rotation normal to the substrate;

at least one pair of diametrically-opposed electrode structures around the sensing ring, each electrode structure comprising;

a base member extending radially from the sensing ring;

first and second members extending perpendicularly from the base member;

a first electrode adjacent the first member such that the first electrode is a distance "d₁ " from the first member, the distance d₁ increasing with a change "Δ

T" in temperature of the sensing ring due to thermal expansion thereof; and

a second electrode adjacent the second member such that the second electrode is a distance "d₂ " from the second member, the distance d₂ decreasing with the change Δ

T in temperature of the sensing ring due to thermal expansion thereof; and

circuitry for detecting an electrostatic force "F₁ " between the first electrode and the first member and an electrostatic force "F₂ " between the second electrode and the second member of at least one electrode structure of the at least one pair of diametrically-opposed electrode structures, the circuitry further summing the electrostatic forces F₁ and F₂ such that, on occurrence of the change Δ

T in temperature of the sensing ring, a corresponding decrease in the electrostatic force F₁ across the distance d₁ at least partially cancels a corresponding increase in the electrostatic force F₂ across the distance d₂.

2. A motion sensor as recited in claim 1, wherein at least one electrode structure of the at least one pair of diametrically-opposed electrode structures is a drive electrode structure, and wherein the circuitry causes the first and second electrodes of the drive electrode structure to induce vibration in the sensing ring near a resonant frequency of the sensing ring.

3. A motion sensor as recited in claim 1, wherein at least one electrode structure of the at least one pair of diametrically-opposed electrode structures is a sensing electrode structure, and wherein the circuitry detects the electrostatic forces F₁ and F₂ through the first and second electrodes of the sensing electrode structure.

4. A motion sensor as recited in claim 1, wherein at least one electrode structure of the at least one pair of diametrically-opposed electrode structures is a balance electrode structure, and wherein the circuitry causes the first and second electrodes of the balance electrode structure to induce stiffness in the sensing ring.

5. A motion sensor as recited in claim 1, further comprising at least a second pair of diametrically-opposed electrode structures around the sensing ring such that there are at least two pairs of electrode structures around the sensing ring, the at least two pairs of electrode structures being located equi-angularly around the sensing ring.

6. A motion sensor as recited in claim 5, wherein:

at least one electrode structure of the at least two pairs of electrode structures is a drive electrode structure, and wherein the circuitry causes the first and second electrodes of the drive electrode structure to induce vibration in the sensing ring near a resonant frequency of the sensing ring; and

at least one electrode structure of the at least two pairs of electrode structures is a sensing electrode structure, and wherein the circuitry detects the electrostatic forces F₁ and F₂ through the first and second electrodes of the sensing electrode structure.

7. A motion sensor as recited in claim 6, wherein at least one of the drive and sensing electrode structures further comprises a balance electrode structure, and wherein the circuitry causes the balance electrode structure to induce stiffness in the sensing ring.

8. A motion sensor as recited in claim 1, further comprising at least a second, third and fourth pair of diametrically-opposed electrode structures around the sensing ring such that there are at least four pairs of electrode structures around the sensing ring, the at least four pairs of electrode structures being located equi-angularly around the sensing ring.

9. A motion sensor as recited in claim 8, wherein:

at least two electrode structures of the at least four pairs of electrode structures are drive electrode structures, and wherein the circuitry causes the first and second electrodes of each drive electrode structure to induce vibration in the sensing ring near a resonant frequency of the sensing ring; and

at least two electrode structures of the at least four pairs of electrode structures are sensing electrode structures, and wherein the circuitry detects the electrostatic forces F₁ and F₂ through the first and second electrodes of the sensing electrode structure.

10. A motion sensor as recited in claim 9, wherein at least one of the drive and sensing electrode structures further comprises a balance electrode structure, and wherein the circuitry causes the balance electrode structure to induce stiffness in the sensing ring.

11. A motion sensor as recited in claim 1, wherein the distance d₁ is equal to the distance d₂.

12. An angular rate sensor comprising:

a substrate;

an electrically-conductive sensing ring supported above the substrate so as to have an axis of rotation normal to the substrate;

at least two pairs of diametrically-opposed electrode structures located equi-angularly around the sensing ring, each electrode structure comprising;

a base member extending radially from the sensing ring, the base member having opposing sides;

a first pair of members extending perpendicularly from a first side of the base member;

a second pair of members extending perpendicularly from a second side of the base member opposite the first pair of members;

a first electrode between the first pair of members such that the first electrode is a distance "d_1a " from a first member of the first pair of members and a distance "d_1b " from a second member of the first pair of members, the distance d_1a increasing and the distance d_1b decreasing with a change "Δ

T" in temperature of the sensing ring due to thermal expansion thereof; and

a second electrode between the second pair of members such that the second electrode is a distance "d_2a " from a first member of the second pair of members and a distance "d_2b " from a second member of the second pair of members, the distance d_2a increasing and the distance d_2b decreasing with the change Δ

T in temperature of the sensing ring due to thermal expansion thereof; and

circuitry associated with at least one electrode structure of the at least two pairs of diametrically-opposed electrode structures for detecting electrostatic forces "F_1a " and "F_1b " between the first electrode and the first and second members, respectively, of the first pair of members, and for detecting electrostatic forces "F_2a " and "F_2b " between the second electrode and the first and second members, respectively, of the second pair of members, the circuitry further summing the electrostatic forces F_1a, F_1b, F_2a and F_2b such that, on occurrence of the change Δ

T in temperature of the sensing ring, a corresponding decrease in the electrostatic forces F_1a and F_2a across the distances d_1a and d_2a, respectively, at least partially cancels a corresponding increase in the electrostatic forces F_1b and F_2b across the distances d_1b and d_2b, respectively.

13. An angular rate sensor as recited in claim 12, wherein at least two electrode structures of the at least two pairs of diametrically-opposed electrode structures are drive electrode structures, and wherein the circuitry causes the first and second electrodes of each drive electrode structure to induce vibration in the sensing ring near a resonant frequency of the sensing ring.

14. An angular rate sensor as recited in claim 12, wherein at least two electrode structures of the at least two pairs of diametrically-opposed electrode structures are sensing electrode structures, and wherein the circuitry detects the electrostatic forces F_1a, F_1b, F_2a and F_2b through the first and second electrodes of the sensing electrode structure.

15. An angular rate sensor as recited in claim 12, wherein at least one electrode structure of the at least two pairs of diametrically-opposed electrode structures comprises a balance electrode structure, the balance electrode structure comprising:

a third pair of members extending perpendicularly from opposite sides of the base member;

a third electrode adjacent a first member of the third pair of members such that the third electrode is a distance "d_3a " therefrom, the distance d_3a increasing with the change "Δ

T" in temperature of the sensing ring; and

a fourth electrode adjacent a second member of the third pair of members such that the third electrode is a distance "d_3b " therefrom, the distance d_3b decreasing with the change Δ

T in temperature of the sensing ring;

wherein the circuitry causes the third and fourth electrodes of the balance electrode structure to induce stiffness in the sensing ring.

16. An angular rate sensor as recited in claim 15, wherein each electrode structure of the at least two pairs of diametrically-opposed electrode structures further comprises a balance electrode structure.

17. An angular rate sensor as recited in claim 15, further comprising an annular-shaped conductor on the substrate beneath the sensing ring, wherein the balance electrode structure is electrically interconnected with the conductor.

18. An angular rate sensor as recited in claim 12, further comprising:

an annular-shaped conductor on the substrate beneath the sensing ring; and

balance electrodes equi-angularly spaced around and adjacent the sensing ring, each balance electrode structure being electrically interconnected with the conductor;

wherein the circuitry causes the balance electrodes to induce stiffness in the sensing ring.

19. An angular rate sensor as recited in claim 12, wherein the distance d_1a is equal to the distance d_2b, the distance d_1b is equal to the distance d_2a, and the distances d_1a and d_2b are less than the distances d_1b and d_2a, whereby, on occurrence of the change Δ

T in temperature of the sensing ring, the corresponding decrease in the electrostatic force F_1a across the distance d_1a approximately cancels the corresponding increase in the electrostatic force F_2b across the distance d_2b, and the corresponding increase in the electrostatic force F_1b across the distance d_1b approximately cancels the corresponding decrease in the electrostatic force F_2a across the distance d_2a.

20. An angular rate sensor comprising:

a substrate;

a post supported by the substrate;

spring members extending radially from the post;

an electrically-conductive sensing ring supported above the substrate by the spring members so as to have an axis of rotation through the post;

at least one annular-shaped conductor on the substrate beneath the sensing ring;

at least four pairs of diametrically-opposed electrode structures located equi-angularly around the sensing ring, each electrode structure comprising;

a base member extending radially from the sensing ring, the base member having opposing sides;

a first pair of teeth extending perpendicularly from a first side of the base member;

a second pair of teeth extending perpendicularly from a second side of the base member opposite the first pair of teeth;

a third pair of teeth extending perpendicularly from the first side of the base member;

a fourth pair of teeth extending perpendicularly from the second side of the base member opposite the third pair of teeth;

a first pair of electrodes interdigitized with the first pair of teeth, a distance between a first electrode of the first pair of electrodes and a first tooth of the first pair of teeth increasing and a distance between the first electrode and a second tooth of the first pair of teeth decreasing with a change "Δ

T" in temperature of the sensing ring due to thermal expansion thereof;

a second pair of electrodes interdigitized with the second pair of teeth, a distance between a first electrode of the second pair of electrodes and a first tooth of the second pair of teeth increasing and a distance between the first electrode of the second pair of electrodes and a second tooth of the second pair of teeth decreasing with the change "Δ

T" in temperature of the sensing ring due to thermal expansion thereof;

a third pair of electrodes interdigitized with the third pair of teeth, a distance between a first electrode of the third pair of electrodes and a first tooth of the third pair of teeth increasing and a distance between the first electrode of the third pair of electrodes and a second tooth of the third pair of teeth decreasing with the change "Δ

T" in temperature of the sensing ring due to thermal expansion thereof; and

a fourth pair of electrodes interdigitized with the fourth pair of teeth, a distance between a first electrode of the fourth pair of electrodes and a first tooth of the fourth pair of teeth increasing and a distance between the first electrode of the fourth pair of electrodes and a second tooth of the fourth pair of teeth decreasing with the change "Δ

T" in temperature of the sensing ring due to thermal expansion thereof;

circuitry for detecting electrostatic forces between the first pair of electrodes and the first pair of teeth and between the second pair of electrodes and the second pair of teeth of at least two electrode structures of the at least four pairs of diametrically-opposed electrode structures;

circuitry for applying a voltage to the first and second pair of electrodes of at least one electrode structure of the at least four pairs of diametrically-opposed electrode structures so as to induce vibration in the sensing ring near a resonant frequency of the sensing ring;

electrical interconnects between the annular-shaped conductor and the third and fourth pair of electrodes of each electrode structure of the at least four pairs of diametrically-opposed electrode structures; and

circuitry for applying a voltage to the third and fourth pair of electrodes of each electrode structure of the at least four pairs of diametrically-opposed electrode structures so as to induce stiffness in the sensing ring.