Electromagnetically actuated micromachined flap

• US 5,629,918 A
• Filed: 01/20/1995
• Issued: 05/13/1997
• Est. Priority Date: 01/20/1995
• Status: Expired due to Term

• Current Assignee: California Institute of Technology, Regents of the University of California (University of California)
• Original Assignee: California Institute of Technology, Regents of the University of California (University of California)
• Inventors: Miller, Raanan, Leu, Jeremy Tzong-Shyng, Tai, Yu-Chong, Liu, Chang, Desai, Amish, Miu, Denny K., Ho, Chih-Ming, Tsao, Tom
• Primary Examiner(s): Epps, Georgia Y.
• Assistant Examiner(s): CHU, KIM KWOK
• Application Number:
  US08/377,018
• Time in Patent Office: 844 Days
• Field of Search: 369/126, 369/124, 369/112, 910/309, 910/40 MM, 910/254, 216/13, 216/17, 216/2, 216/22, 60/520, 60/698, 29/598, 250/289
• US Class Current: 310/40.0MM
• CPC Class Codes: H02K 99/00 Subject matter not provided for in other groups of this subclass

Abstract

A surface micromachined micromagnetic actuator is provided with a flap capable of achieving large deflections above 100 microns using magnetic force as the actuating force. The flap is coupled by one or more beams to a substrate and is cantilevered over the substrate. A Permalloy layer or a magnetic coil is disposed on the flap such that when the flap is placed in a magnetic field, it can be caused to selectively interact and rotate out of the plane of the magnetic actuator. The cantilevered flap is released from the underlying substrate by etching out an underlying sacrificial layer disposed between the flap and the substrate. The etched out and now cantilevered flap is magnetically actuated to maintain it out of contact with the substrate while the just etched device is dried in order to obtain high release yields.

Claims

1. A microelectromechanical magnetic actuator comprising:

a substrate having a surface;

a micromachined flap defined from said surface of said substrate and separated therefrom;

at least one micromachined cantilevered beam defined from said surface of substrate coupling said flap to said substrate;

a magnetic layer disposed on said flap; and

a selectively actuatable magnetic field source disposed proximate to said actuator to create a magnetic field in the vicinity of said flap to bend said flap on said cantilevered beam in a predetermined direction to the plane of said surface of said substrate,

whereby a magnetically actuated flap is provided which is selectively disposable out of said surface of said substrate.

2. The actuator of claim 1 wherein said magnetic source is an electromagnet.

3. The actuator of claim 1 wherein said magnetic layer is comprised of a magnetic coil disposed on said flap.

4. The actuator of claim 3 further comprising a current source and wherein said magnetic coil is coupled to said source of current by conductive lines extending from said magnetic coil to said current source, said lines being disposed along said at least one cantilevered beam.

5. The actuator of claim 3 wherein said magnetic source is a permanent magnet.

6. The actuator of claim 3 wherein said magnetic field source comprises at least one magnetic coils disposed on said substrate.

7. The actuator of claim 3 further comprising a plurality of said magnetic coils disposed on said flap.

8. The actuator of claim 7 wherein said magnetic field source comprises at least one magnetic coils disposed on said substrate.

9. The actuator of claim 1 wherein said flap has a plurality of holes defined therein to facilitate separation of said flap from said underlying substrate.

10. The actuator of claim 1 wherein said predetermined direction has at least a component which is out of the plane of said substrate.

11. The actuator of claim 1 wherein said predetermined direction has at least a component which is in the plane of said substrate.

12. The actuator of claim 1 wherein said flap is optically opaque so that said actuator functions as an optical shutter.

13. The actuator of claim 1 wherein at least two cantilevered beams are provided to couple said flap to said substrate.

14. The actuator of claim 1 wherein said flap is optically reflective so that said actuator functions as an optical mirror.

15. The actuator of claim 14 further comprising a reflective layer disposed on said magnetic layer of said flap.

16. The actuator of claim 1 wherein said magnetic layer is comprised of a permanent magnet.

17. The actuator of claim 16 wherein said permanent magnet is a layer of Permalloy.

18. The actuator of claim 16 wherein said permanent magnet has an alterable polarity.

19. The actuator of claim 1 wherein said cantilevered beams are linear.

20. The actuator of claim 1 wherein said cantilevered beams are serpentine.

21. An improvement in a method of fabricating a microelectromagnetic magnetic actuator, said improvement comprising:

providing a substantially completed microelectromechanical magnetic actuator on a sacrificial layer disposed on an underlying substrate;

removing said sacrificial layer upon which said microelectromechanical magnetic actuator has been fabricated by etching away said sacrificial layer through at least one opening defined through said microelectromechanical magnetic actuator to expose said underlying sacrificial layer; and

drying said microelectromechanical magnetic actuator while simultaneously actuating said microelectromechanical magnetic actuator to maintain the released portions of said actuator out of contact with said underlying substrate until said drying is complete.

22. The improvement of claim 21 where removal of said sacrificial layer is facilitated by providing a plurality of holes through said microelectromechanical magnetic actuator to increase etchant access to said underlying sacrificial layer.

23. In a method of fabricating a surface micromachine cantilevered layer disposed over an underlying substrate, an improvement comprising:

providing said cantilevered layer on a sacrificial layer which in turn is disposed upon said substrate;

disposing a magnetic layer on said cantilevered layer;

removing said sacrificial layer beneath at least part of said cantilevered layer to release said cantilevered layer from said substrate; and

simultaneously maintaining said cantilevered layer apart from said substrate layer by exposing said magnetic layer to a magnetic field which tends to lift said cantilevered layer away from said substrate, said cantilevered being maintained separate from said substrate until removal of said sacrificial layer is completed and possibility of adhesion of said cantilevered layer to said substrate substantially extinguished.

24. The method of claim 23 where disposing said magnetic layer comprises disposing a Permalloy layer.

25. The improvement of claim 24 further comprising disposing an organic polymer on at least said cantilevered layer prior to disposition of said magnetic layer thereon and selectively removing said organic polymer layer and said magnetic layer disposed thereon after removal of said sacrificial layer is complete.

26. The method of claim 23 where removing said sacrificial layer from underneath at least part of said cantilevered layer comprises wet etching said sacrificial layer away and where simultaneously maintaining said cantilevered layer out of contact with said substrate is performed until said microelectromagnetic device is dried.

27. The improvement of claim 26 further comprising disposing an organic polymer on at least said cantilevered layer prior to disposition of said magnetic layer thereon and selectively removing said organic polymer layer and said magnetic layer disposed thereon after removal of said sacrificial layer is complete.

28. The improvement of claim 27 where removing said organic polymer is performed with a dry plasma etch so that stiction is avoided.

29. In a method of controlling flow of a fluid across a surface of an object an improvement comprising:

disposing a plurality of microelectromechanical actuators on said surface, each having a selectively operable flap extendable in a direction out of said surface into a boundary layer above said surface over which said flow is established; and

selectively actuating at least some of said plurality of microelectromechanical actuators to dispose their corresponding flaps into said boundary layer to thereby affect said flow of said fluid.

30. The method of claim 29 where selectively disposing said corresponding flaps into said boundary layer at a position upstream from expected flow separation and oscillating said flaps to affect flow separation of said fluid at a point downstream from said flaps.

31. The improvement of claim 29 where selectively disposing said corresponding flaps into said boundary layer comprises electromagnetically actuating said flaps to bend said flaps into said boundary layer out to the plane of said actuator to affect turbulent flow.

32. The improvement of claim 29 wherein said surface is an airplane control surface and where selectively disposing said corresponding flaps serve to provide a control force to said airplane control surface.

33. The method of claim 29 where selectively disposing said corresponding flaps into said boundary layer serves to reduce fluid drag of said surface.