Electrostatic micromotor

• US 4,943,750 A
• Filed: 07/03/1989
• Issued: 07/24/1990
• Est. Priority Date: 05/20/1987
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Howe, Roger T., Schlecht, Martin F., Lang, Jeffrey H., Schmidt, Martin A., Senturia, Stephen D.
• Primary Examiner(s): Budd, Mark O.
• Application Number:
  US07/376,208
• Time in Patent Office: 386 Days
• Field of Search: 310/309, 310/42, 310/90.5
• US Class Current: 310/309
• CPC Class Codes: H02N 1/004 in which a body is moved along a path due to interaction with an electric field travelling along the path

Abstract

An electrostatically driven microactuator is micromachined in a monolithic process. Sacrificial layers are placed between a moving element and stator structural layers. Removal of the sacrificial layers leaves a free standing moving element and micron wide air gaps within a stator. An electric field of about 100 Mv/m and higher is supported across the micron wide gap without breakdown and enables high energy torque densities to be produced between the stator and the moving element. One electrostatic drive scheme involves a series of stator electrodes attached to the stator and a series of electrodes attached to the moving element charged in sequence to attract each other in a direction of movement and to oppose each other in a direction normal to movement. A bearing is aligned with the moving element with the stator during the layering of a sacrificial layer over an edge of the moving element structural layer. The bearing and stator laterally stabilize the moving element. Vertical stability is through aerodynamic shaping of the moving element, electronic circuits, or bushings. Applications of the microactuator include a linearly sliding shutter, an optical modulator, a gyroscope and an air pump.

Claims

1. An electrostatic machine comprising:

a stator formed by surface micromachining sacrificial layers on a substrate surface;

a moveable member positioned for movement relative to the stator free of contact thereto, the moveable member formed and positioned with respect to the substrate surface during the surface micromachining that formed the stator;

means for generating and sustaining an electrostatic field about the moveable member across a gaseous gap between the stator and moveable member, facing surfaces of the surface micromachined stator and moveable member across the gaseous gap being free of contact with each other and sufficiently smooth to support a field strength above about 10⁸ V/m without electrostatic breakdown, the distance between the stator and moveable member across the gaseous gap being about 5 micrometers or less.

2. A machine as claimed in claim 1 wherein the moveable member is of a type which is formed within the stator by supporting the moveable member within the stator by a sacrificial layer and then removing the sacrificial layer to free the moveable member.

3. A machine as claimed in claim 1 wherein the stator comprises a bearing for limiting lateral movement of the moveable member, the bearing being of the type which is aligned with the moveable member by the fabrication steps of:

forming the moveable member;

covering the moveable member, including an edge thereof, with a sacrificial layer;

forming the bearing over the sacrificial layer along the edge of the moveable member; and

removing the sacrificial layer.

4. A machine as claimed in claim 1 wherein the stator includes a series of stator electrode segments on opposite sides of the moveable member, and the moveable member includes a series of member electrode segments, the electrodes of one of the series of electrode segments being charged in sequence to be attracted to the electrodes of the other of the series of electrodes, the attraction toward the electrodes on opposite sides of the moveable member being complementary in a direction of member movement and in opposition in a direction normal to the direction of movement.

5. A machine as claimed in claim 4 wherein the electrodes of the series of member electrode segments are charged in sequence by a series of brushes.

6. A machine as claimed in claim 1 wherein the stator includes a series of stator electrode segments, the electrodes of said series being charged in sequence to induce attracting charge in the movable member.

7. A machine as claimed in claim 1 further comprising means for maintaining separation between the moving member and the stator.

8. A machine as claimed in claim 7 wherein said means include a bushing.

9. A machine as claimed in claim 7 wherein said means includes an electronic circuit for detecting and correcting levitation of the moveable member relative to the stator.

10. A machine as claimed in claim 1 wherein the moveable member is a rotor.

11. A machine as claimed in claim 10 wherein the stator comprises a center bearing for limiting lateral movement of the rotor, the bearing being of the type which is aligned with the rotor by the fabrication step of:

forming a rotor with a circular opening through a center of the rotor to a substrate beneath the rotor;

covering the rotor including an edge of the circular opening with a sacrificial layer;

forming the center bearing over the sacrificial layer along the edge of the circular opening attaching the center bearing to the substrate within the circular opening; and

removing the sacrificial layer.

12. A machine as claimed in claim 11 wherein the bearing is of the type that is aligned with a rotor formed by the steps of:

covering the substrate with one sacrificial film;

depositing a structural film over the one sacrificial film;

covering the structural film with another sacrificial film; and

patterning the rotor to said shape by cutting through said another sacrificial film to said substrate.

13. A machine as claimed in claim 10 wherein the stator includes a series of stator electrode segments on each side of the rotor, and the rotor includes a series of rotor electrode segments, the electrodes of the series of rotor electrode segments being charged in sequence by a series of brushes to be attracted to the electrodes of the series of stator electrode segments, the attraction toward the electrodes to each side of the rotor being complementary in a direction of rotor movement and in opposition in a direction normal to the direction of movement.

14. A machine as claimed in claim 13 wherein the stator comprises a bearing for limiting lateral movement of the rotor and for ensuring frictional contact between the rotor electrode segments and the brushes, the bearing being of the type which is aligned with the rotor by the fabrication steps of:

forming a rotor with a circular opening through a center of the rotor to a substrate beneath the rotor;

covering the rotor including an edge of the circular opening with a sacrificial layer;

forming the center bearing over the sacrificial layer along the edge of the circular opening attaching the center bearing to the substrate within the circular opening; and

removing the sacrificial layer.

15. A machine as claimed in claim 1 wherein the means for generating an electrostatic field generates a field in a manner which elevates the plate and laterally moves the elevated plate.

16. An electrostatic machine comprising:

a stator formed by surface micromachining sacrificial layers on a substrate surface;

a plate formed by the surface micromachining that formed the stator on the substrate surface and positioned for movement relative to the stator free of contact thereto and with a gaseous gap between the stator and plate, the distance across the gap between the stator and plate being short enough and facing surfaces of the stator and plate across the gap being smooth enough to support a field strength above about 10⁸ V/m without electrostatic breakdown, the facing surfaces of the stator and plate being free of contact with each other across the gap, and the gap having a pressure-spacing of less than about 5×

10^-3 bar mm; and

means for generating and sustaining an electrostatic field across the gaseous gap between the stator and plate.

17. An electrostatic machine as claimed in claim 16 wherein said distance across the gap between the stator and the plate is on the order of 1 micrometer or less.

18. A machine as claimed in claim 16 wherein the distance across the gap between the stator and plate causes air within the gap to behave as a viscous fluid such that the air acts as a lubricant between the stator and the plate.

19. A machine as claimed in claim 16 wherein the stator includes a series of stator electrode segments on each side of the plate, and the plate includes a series of plate electrode segments, one of the series of electrode segments being charged in sequence to be attracted to the other of the series of electrodes, the attraction toward the electrodes to each side of the plate being complementary in the direction of plate movement and in opposition in a direction normal to the direction of movement.

20. A machine as claimed in claim 19 further comprising brush means to charge and discharge the series of plate electrode segments.

21. A machine as claimed in claim 19 wherein said series of stator electrode segments are charged in sequence to induce attracting charge in the series of plate electrode segments.

22. A machine as claimed in claim 16 further comprising means for maintaining the position of the plate within the stator.

23. A machine as claimed in claim 22 wherein said means for maintaining plate position include a bushing.

24. A machine as claimed in claim 22 wherein said means for maintaining plate position include an electronic circuit for sensing and correcting a levitation level of the plate relative to the stator.

25. A machine as claimed in claim 16 wherein the means for generating an electrostatic field generates a field in a manner which elevates the plate and laterally moves the elevated plate.

26. An electrostatic machine comprising:

a stator formed on a substrate surface;

a moveable member positioned for movement relative to the stator over the substrate surface in a manner free of contact with the stator, the moveable member formed during the forming of the stator;

means for generating an electrostatic field about the moveable member across a gaseous gap between the stator and moveable member in a manner which elevates the moveable member above the substrate surface and moves the elevated moveable member laterally over the substrate surface, the distance between the stator and moveable member across the gap being about 5 micrometers or less and surfaces of the stator and moveable member facing each other across the gap being free of contact with each other and smooth enough to support a field strength above about 10⁸ V/m without electrostatic breakdown.

27. An electrostatic machine comprising:

a stator formed on a substrate surface;

a plate positioned for movement relative to the stator in a manner free of contact thereto and with a gaseous gap between the stator and plate, the plate formed during the forming of the stator, the distance across the gap between the stator and plate being short enough and surfaces of the stator and plate facing each other across the gap being smooth enough to support a field strength above about 10⁸ V/m without breakdown, the surfaces of the plate and stator facing each other across the gap being free of contact with each other, and the gap having a pressure-spacing less than about 5×

10^-3 bar mm; and

means for generating an electrostatic field across the gap between the stator and plate such that the plate is elevated above the substrate surface and moved laterally while being elevated.