Electrostatic bimorph actuator

• US 20030184189A1
• Filed: 03/29/2002
• Published: 10/02/2003
• Est. Priority Date: 03/29/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Sinclair, Michael J.
• Granted Patent: US 7,053,519 B2
• Time in Patent Office: Days
• US Class Current: 310/309
• CPC Class Codes: B81B 2201/032 Bimorph and unimorph actuators, e.g. piezo and thermo
• CPC Class Codes: B81B 2201/038 Microengines and actuators not provided for in B81B2201/031 - B81B2201/037
• CPC Class Codes: B81B 2201/045 Optical switches
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81B 3/0054 For holding or placing an element in a given position

Abstract

An electrostatic bimorph actuator includes a cantilevered flexible bimorph arm that is secured and insulated at one end to a planar substrate. In an electrostatically activated state the bimorph arm is generally parallel to the planar substrate. In a relaxed state, residual stress in the bimorph arm causes its free end to extend out-of-plane from the planar substrate. The actuator includes a substrate electrode that is secured to and insulated from the substrate and positioned under and in alignment with the bimorph arm. An electrical potential difference applied between the bimorph arm and the substrate electrode imparts electrostatic attraction between the bimorph arm and the substrate electrode to activate the actuator. As an exemplary application in which such actuators could be used, a microelectrical mechanical optical display system is described.

Claims

1. A microelectrical mechanical actuator, comprising:

a planar substrate with an anchor secured thereto;

cantilevered flexible bimorph arm secured at one end to the anchor and extending along and over the substrate;

a substrate electrode secured to and insulated from the substrate and positioned under and in alignment with the bimorph arm; and

activation electrical couplings to receive an electrical potential difference between the bimorph arm and the substrate electrode to impart electrostatic attraction between the bimorph arm and the substrate electrode, thereby to activate the actuator.

2. The actuator of claim 1 in which the bimorph arm includes a layer of semiconductor material and a layer of another material having a coefficient of expansion different from that of the semiconductor material to impart a differential residual stress in the bimorph arm.

3. The actuator of claim 2 in which the residual stress induces an inclination for the bimorph arm to curl out-of-plane away from the substrate when the actuator is relaxed.

4. The actuator of claim 1 further including multiple substrate electrodes secured to the substrate and positioned under and in alignment with the bimorph arm.

5. The actuator of claim 1 in which the bimorph arm further comprises a reflective surface positioned at an end of the bimorph arm opposite the end secured to the anchor.

6. The actuator of claim 1 in which the bimorph arm includes a distal end opposite the end secured to the anchor, the actuator further comprising;

a memory electrode secured to and insulated from the substrate and positioned under and in alignment with the distal end of the bimorph arm; and

a memory electrical coupling to receive an electrical potential at the memory electrode relative to the bimorph arm to impart electrostatic attraction between the bimorph arm and the memory electrode separately from the potential difference applied between the bimorph arm and the substrate electrode.

7. The actuator of claim 6 further comprising a source of an electrical potential connected to the memory electrical coupling to provide the potential to the memory electrical coupling relative to the bimorph arm.

8. The actuator of claim 1 further comprising one or more stand-off dimples extending from the bimorph arm toward the substrate to hold the bimorph arm in spaced-apart relation to the substrate when the actuator is activated.

9. The actuator of claim 1 further comprising a source of an electrical potential connected to the activation electrical couplings to provide the potential difference to the activation electrical couplings to activate the actuator.

10. In a microelectrical mechanical actuator formed on a planar semiconductor substrate, the improvement comprising:

a cantilevered flexible bimorph arm that is secured to the planar substrate and selectively postionable in an relaxed state and in an electrostatically activated state, the bimorph arm being generally parallel to the planar substrate in the electrostatically activated state and extending out-of-plane from the planar substrate in the relaxed state.

11. The actuator of claim 10 in which the bimorph arm includes a layer of semiconductor material and a layer of another material having a coefficient of expansion different from that of the semiconductor material to impart a residual stress in the bimorph arm.

12. The actuator of claim 11 in which the residual stress induces an inclination for the bimorph arm to curl out-of-plane away from the substrate when the actuator is relaxed.

13. The actuator of claim 10 in which the bimorph arm is secured at one end to an anchor that is secured to the substrate, the bimorph arm further comprising a reflective surface positioned at an end opposite the end secured to the anchor.

14. The actuator of claim 10 further comprising:

a substrate electrode secured to the substrate and positioned under and in alignment with the bimorph arm; and

activation electrical couplings to receive an electrical potential difference between the bimorph arm and the substrate electrode to impart electrostatic attraction between the bimorph arm and the substrate electrode, thereby to activate the actuator.

15. The actuator of claim 14 further including multiple substrate electrodes secured to the substrate and positioned under and in alignment with the bimorph arm.

16. The actuator of claim 10 in which the bimorph arm is secured at one end to an anchor that is secured to the substrate, the bimorph arm including a length from the end secured to the anchor to a distal end, the actuator further comprising;

a memory electrode secured to the substrate and positioned under and in alignment with the distal end of the bimorph arm; and

a memory electrical coupling to receive an electrical potential at the memory electrode relative to the bimorph arm to impart electrostatic attraction between the bimorph arm and the memory electrode to maintain the bimorph arm in the activated state.

17. The actuator of claim 10 further comprising one or more stand-off dimples extending from the bimorph arm toward the substrate to hold the bimorph arm in spaced-apart relation to the substrate when the actuator is activated.

18. A microelectrical mechanical actuator array, comprising:

a plurality of electrostatic bimorph microelectrical mechanical actuators that each have cantilevered flexible bimorph arm that is secured to a planar substrate and selectively postionable in an activated state and in a relaxed state, the bimorph arm being generally parallel to the planar substrate in the activated state and extending out-of-plane from the planar substrate in the relaxed state.

19. The actuator array of claim 18 further comprising:

a substrate electrode secured to the substrate and positioned under and in alignment with the bimorph arm of each actuator; and

activation electrical couplings to apply an electrical potential difference between the bimorph arm and the substrate electrode of each actuator, the electrical potential difference activating each actuator with electrostatic attraction between the bimorph arm and the substrate electrode.

20. The actuator array of claim 19 in which each actuator is in a first aligned set of actuators and a second aligned set of actuators, the first and second aligned sets of actuators extending in transverse first and second directions, respectively, and the array including plural first and second aligned sets of actuators.

21. The actuator array of claim 20 in which the bimorph arms of the actuators in each first aligned set of actuators are electrically connected together and the substrate electrodes of the actuators in each second aligned set of actuators are electrically connected together.

22. The actuator array of claim 19 in which each bimorph arm is secured at one end to the substrate and includes a length from the end secured to the substrate to a distal end, each actuator further comprising;

a memory electrode secured to the substrate and positioned under and in alignment with the distal end of the bimorph arm; and

a memory electrical coupling to receive an electrical potential at the memory electrode relative to the bimorph arm to impart electrostatic attraction between the bimorph arm and the memory electrode to maintain the bimorph arm in the activated state.

23. The actuator array of claim 22 in which the memory electrical couplings of all the actuators are electrically connected together.

24. The actuator array of claim 18 in which each actuator is in a first aligned set of actuators and a second aligned set of actuators, the first and second aligned sets of actuators extending in transverse first and second directions, respectively, and the array including plural first and second aligned sets of actuators.

25. The actuator array of claim 24 in which the first and second aligned sets of actuators are generally orthogonal to each other and form respective rows and columns of actuators.

26. A microelectrical mechanical actuator activation control method, comprising:

selectively applying an activation potential difference between a cantilevered flexible bimorph arm that is secured to a planar substrate at one end and a substrate electrode that is secured to the substrate and positioned under and in alignment with the bimorph arm, the potential difference imparting an electrostatic attraction between the bimorph arm and the substrate electrode to hold the bimorph arm generally parallel to the planar substrate against a residual stress in the bimorph arm; and

selectively relaxing at least part of the activation potential difference to allow the residual stress in the bimorph arm to extend a free end out-of-plane and away from the planar substrate.

27. The method of claim 26 further comprising selectively applying a memory potential difference between the bimorph arm and a memory electrode that is secured to and insulated from the substrate and positioned under and in alignment with the free end of the bimorph arm, the potential difference imparting an electrostatic attraction between the bimorph arm and the memory electrode to hold the bimorph arm generally parallel to the planar substrate against the residual stress in the bimorph arm.

28. The method of claim 27 further comprising selectively relaxing at least part of the activation potential difference and at least part of the memory potential difference to allow the residual stress in the bimorph arm to extend the free end out-of-plane and away from the planar substrate.