Method for fabricating five-level microelectromechanical structures and microelectromechanical transmission formed

• US 6,082,208 A
• Filed: 04/01/1998
• Issued: 07/04/2000
• Est. Priority Date: 04/01/1998
• Status: Expired due to Term

• Current Assignee: National Technology & Engineering Solutions Of Sandia LLC (Honeywell International Inc.)
• Original Assignee: Sandia Corporation (Martin Marietta Corporation)
• Inventors: Sniegowski, Jeffry J., Rodgers, M. Steven, McWhorter, Paul J., Miller, Samuel L.
• Primary Examiner(s): FENSTERMACHER, DAVID MORGAN
• Application Number:
  US09/053,569
• Time in Patent Office: 825 Days
• Field of Search: 74/405, 74/406, 310/309, 310/40 MM, 310/DIG. 6
• US Class Current: 74/406
• CPC Class Codes: B81B 2201/035 Microgears
• CPC Class Codes: B81B 2203/06 Devices comprising elements which are movable in relation to each other, e.g. slidable or rotatable
• CPC Class Codes: B81C 1/00198 comprising elements which are movable in relation to each other, e.g. comprising slidable or rotatable elements
• CPC Class Codes: F16H 19/00 Gearings comprising essentially only toothed gears or friction members and not capable of conveying indefinitely-continuing rotary motion with intermittently-driving members F16H27/00 - F16H31/00
• CPC Class Codes: Y10S 310/06 Printed-circuit motors and components
• CPC Class Codes: Y10T 74/19614 Disconnecting means
• CPC Class Codes: Y10T 74/19619 Displaceable elements

Abstract

A process for forming complex microelectromechanical (MEM) devices having five layers or levels of polysilicon, including four structural polysilicon layers wherein mechanical elements can be formed, and an underlying polysilicon layer forming a voltage reference plane. A particular type of MEM device that can be formed with the five-level polysilicon process is a MEM transmission for controlling or interlocking mechanical power transfer between an electrostatic motor and a self-assembling structure (e.g. a hinged pop-up mirror for use with an incident laser beam). The MEM transmission is based on an incomplete gear train and a bridging set of gears that can be moved into place to complete the gear train to enable power transfer. The MEM transmission has particular applications as a safety component for surety, and for this purpose can incorporate a pin-in-maze discriminator responsive to a coded input signal.

Claims

1. A microelectromechanical (MEM) apparatus, comprising:

(a) a plurality of gears on a silicon substrate forming an incomplete gear train; and

(b) a bridging set of gears located on a carriage, with the bridging set of gears and the carriage being moveable on the silicon substrate from a disengaged state to engage the plurality of gears, thereby completing the gear train.

2. The MEM apparatus of claim 1 wherein each gear comprises polycrystalline silicon.

3. The MEM apparatus of claim 1 further comprising a track for guiding motion of the carriage.

4. The MEM apparatus of claim 3 wherein the track comprises a pair of guide rails with the carriage being slidingly engaged with the guide rails of the track.

5. The MEM apparatus of claim 3 wherein the carriage further comprises a linear gear formed on one side thereof to impart linear motion thereto.

6. The MEM apparatus of claim 5 further comprising means for driving the linear gear.

7. The MEM apparatus of claim 1 wherein the plurality of gears comprises a first set of meshed gears and a second set of meshed gears, with the sets of meshed gears being spaced at a distance from each other to prevent mechanical coupling therebetween.

8. The MEM apparatus of claim 7 further comprising a motive source formed on the substrate and operatively connected to an input gear of the first set of meshed gears.

9. The MEM apparatus of claim 8 wherein the motive source comprises an electrostatic motor.

10. The MEM apparatus of claim 8 further comprising a load operatively connected to an output gear of the second set of meshed gears.

11. The MEM apparatus of claim 10 wherein the load comprises a self-assembling structure.

12. The MEM apparatus of claim 10 further including locking means for maintaining the bridging gear set and the first and second sets of meshed gears in an enabled position for uninterrupted power transfer upon engagement of the bridging gear set with the first and second sets of meshed gears.

13. A microelectromechanical (MEM) apparatus formed on a silicon substrate for controlling the transfer of power from a motive source to a load, comprising an interruptible gear train formed on the silicon substrate, with the interruptible gear train further comprising:

(a) a first set of meshed gears operatively connected to the motive source;

(b) a second set of meshed gears operatively connected to the load; and

(c) a bridging gear set moveable along a track for engagement with the first and second sets of meshed gears thereby enabling power to be transferred from the motive source to the load.

14. The apparatus of claim 13 wherein the bridging gear set comprises a pair of gears with each gear of the pair having a different number of teeth.

15. The apparatus of claim 13 wherein the motive source comprises an electrostatic motor.

16. The apparatus of claim 13 wherein the load comprises a self-assembling structure.

17. The apparatus of claim 13 wherein each gear comprises polycrystalline silicon.

18. The apparatus of claim 13 wherein the interruptible gear train comprises a reducing gear train for reducing a rotation speed of the motive source.

19. The apparatus of claim 13 wherein the bridging gear set comprises at least one gear formed on a hub secured to a moveable carriage, with the carriage having opposite sides thereof slidingly engaged with guide rails of the track to provide for linear movement of the carriage and bridging gear set along the track.

20. The apparatus of claim 19 wherein the carriage further comprises a linear gear formed on one side thereof to impart linear motion to the carriage and bridging gear set formed thereon.

21. The apparatus of claim 20 wherein the linear gear is operatively connected to another motive source.

22. The apparatus of claim 19 wherein the moveable carriage further includes a capture spring for engagement with a shaped protrusion formed on the substrate to restrain linear movement of the carriage upon engagement of the bridging gear set with the first and second sets of meshed gears.

23. The apparatus of claim 19 wherein the moveable carriage further includes a first interdental stop moveable from an engaged position to a disengaged position, the first interdental stop being initially in the engaged position whereby the first interdental stop is engaged with teeth on at least one gear of the bridging gear set thereby aligning each gear in the bridging gear set to facilitate engagement with the first and second sets of meshed gears.

24. The apparatus of claim 23 further including a second interdental stop proximate to the first and second sets of meshed gears, with the second interdental stop being moveable from an engaged position whereby rotation of the first and second sets of meshed gears is prevented to a disengaged position whereby rotation of the first and second sets of meshed gears is enabled upon engagement of the bridging gear set with the first and second sets of meshed gears.

25. The apparatus of claim 24 further including means for moving each interdental stop from the engaged position to the disengaged position as the bridging gear set is moved into engagement with the first and second sets of meshed gears.

26. The apparatus of claim 25 further including means for locking each interdental stop in the disengaged position upon engagement of the bridging gear set with the first and second sets of meshed gears.

27. A microelectromechanical apparatus, formed on a silicon substrate comprising:

(a) an electrostatic motor comprising a rotatable output gear for providing mechanical power therefrom;

(b) a plurality of sets of meshed gears forming an incomplete gear train with an input gear of the gear train engaging the rotatable output gear of the electrostatic motor for receiving mechanical power therefrom;

(c) at least one gear moveable along a track to engage the plurality of gears and complete the gear train, thereby coupling the mechanical power across the gear train.

28. A method for forming a microelectromechanical (MEM) apparatus, comprising steps for:

(a) depositing and patterning five layers of polysilicon above a silicon substrate, including a first polysilicon layer for forming a voltage reference plane, and four polysilicon layers overlying the first polysilicon layer for forming structural layers wherefrom mechanical elements of the MEM apparatus are formed;

(b) annealing each of the first, second and third structural polysilicon layers prior to patterning each of these layers; and

(c) annealing the fourth structural polysilicon layer after patterning thereof.

29. The method of claim 28 further including a step for depositing a sacrificial layer between each layer of polysilicon.

30. The method of claim 29 wherein the sacrificial layer comprises silicon dioxide or a silicate glass.

31. The method of claim 29 further including a step for planarizing at least one sacrificial layer after deposition thereof.

32. The method of claim 31 wherein the planarization step comprises planarizing the sacrificial layer by chemical-mechanical polishing.

33. The method of claim 29 further including a step for patterning each sacrificial layer after planarization thereof.

34. The method of claim 29 wherein each-patterning step comprises steps for photolithographically defining features to be formed in one of the polysilicon layers and forming the features by etching.

35. The method of claim 34 wherein the etching step comprises reactive ion etching.

36. The method of claim 29 further including a step for releasing the MEM apparatus by removing the sacrificial layers by etching.