Micromachined members coupled for relative rotation by torsion bars

• US 6,044,705 A
• Filed: 05/12/1997
• Issued: 04/04/2000
• Est. Priority Date: 10/18/1993
• Status: Expired due to Term

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Xros, Inc. (Nortel Networks Corporation)
• Inventors: Neukermans, Armand P., Slater, Timothy G., Downing, Philip
• Primary Examiner(s): MOLLER, RICHARD ALAN
• Application Number:
  US08/855,883
• Time in Patent Office: 1,058 Days
• Field of Search: 73/504.02, 73/504.12, 73/778, 73/814, 73/504.14, 257/418, 257/417, 257/415, 359/196-199, 359/201-203, 359/212-214, 359/223-226, 359/230
• US Class Current: 73/504.02
• CPC Class Codes: G01C 19/5719 using planar vibrating masses driven in a translation vibration along an axis
• CPC Class Codes: G02B 26/085 the reflecting means being moved or deformed by electromagnetic means
• CPC Class Codes: G02B 26/101 with both horizontal and vertical deflecting means, e.g. raster or XY scanners colour television using laser beams scanning a display screen H04N9/3129

Abstract

Two torsion bars project from a reference member to support at least one plate or frame-shaped first dynamic member for rotation about an axis of the torsion bars. In one embodiment, a frame-shaped first dynamic member and a second pair of torsion bars, oriented non-parallel to the first torsion bars, support a second dynamic member for rotation about an axis that is collinear with the second pair of torsion bars. The vibrational frequency of the principal torsional vibrational mode of the dynamic members are respectively lower by at least 20% than the vibrational frequency of any other vibrational mode thereof. Either an electrostatic or electromagnetic drive means imparts rotary motion to the dynamic members about the collinear torsion bar axis(es). The reference member, the torsion bars and the dynamic member(s) are all monolithically fabricated from a stress-free semiconductor layer of a silicon substrate.

Claims

1. An integrated, micromachined structure comprising:

a reference member;

a first pair of diametrically opposed, axially aligned torsion bars projecting from said reference member;

a first dynamic member that is coupled by said first pair of torsion bars to said reference member to be thereby supported from said reference member for rotation about a first axis that is collinear with said first pair of torsion bars;

said reference member, said first pair of torsion bars and said first dynamic member all monolithically fabricated from a stress-free semiconductor layer of a silicon substrate;

said first dynamic member thus supported within said reference member by said first pair of torsion bars, said first dynamic member;

having a center;

defining a first dynamic member rest plane if no external force is applied to said first dynamic member; and

exhibiting a plurality of vibrational modes including a principal torsional vibrational mode about the first axis that is collinear with said first pair of torsion bars, a vertical shaking vibrational mode, a vertical rocking vibrational mode, a lateral shaking vibrational mode, and a lateral rocking vibrational mode, each vibrational mode of said first dynamic member having a vibrational frequency, the vibrational frequency of the principal torsional vibrational mode being lower by at least 20% than the vibrational frequency of any other vibrational mode of said first dynamic member; and

first drive means for imparting rotary motion to said first dynamic member about the first axis that is collinear with said first pair of torsion bars.

2. The structure of claim 1 wherein said drive means comprises at least a pair of electrodes spaced apart from said first dynamic member, the electrodes being displaced from said first pair of torsion bars.

3. The structure of claim 1 wherein said drive means comprises:

means for applying a magnetic field substantially parallel to the rest plane of said first dynamic member; and

a coil means disposed on said first dynamic member and in the magnetic field.

4. The structure of claim 3 wherein said coil means is formed by a layer of metallic material coated directly onto said first dynamic member.

5. The structure of claim 3 wherein said coil means is formed by a layer of metallic material disposed on a sheet of polymeric material that is adhesively bonded onto said first dynamic member.

6. The structure of claim 1 wherein said semiconductor layer is in a silicon-on-insulator wafer substrate.

7. The structure of claim 1 wherein said semiconductor layer is in a silicon substrate assembled by bonding together two silicon wafers, each of the silicon wafers having both a <

100>

crystallographic direction and a <

110>

crystallographic direction, the two silicon wafers being oriented with respect to each other so the <

110>

crystallographic direction of one wafer coincides with the <

100>

crystallographic direction of the other wafer.

8. The structure of claim 1 further comprising torsion sensing means disposed on one of said first pair of torsion bars for generating a torsion signal that indicates angular deflection of said first dynamic member with respect to said reference member.

9. The structure of claim 8 wherein said torsion sensing means comprises at least three electrical contacts on the one of said first pair of torsion bars, and means for applying an electric current across at least a pair of said electrical contacts, and the torsion signal is sensed from a pair of said electrical contacts.

10. The structure of claim 9 wherein the electric current is applied across the pair of electrical contacts and the torsion signal sensed from the pair of electrical contacts via metallic conductors disposed on the semiconductor layer.

11. The structure of claim 9 wherein the electric current is applied across the pair of electrical contacts and the torsion signal sensed from the pair of electrical contacts via conductive paths established within the semiconductor layer.

12. The structure of claim 9 wherein said torsion sensing means comprises:

at least four electrical contacts disposed on the one of said first pair of torsion bars with a pair of said electrical contacts being disposed along a line that is oriented substantially parallel to the first axis collinear with said first pair of torsion bars; and

means for applying an electric current across a first pair of said electrical contacts while the torsion signal is sensed from a second pair of said electrical contacts oriented perpendicular to a line joining the first pair of said electrical contacts.

13. The structure of claim 12 wherein the electric current is applied across the first pair of electrical contacts and the torsion signal sensed from the second pair of electrical contacts via metallic conductors disposed on the semiconductor layer.

14. The structure of claim 12 wherein the electric current is applied across the first pair of electrical contacts and the torsion signal sensed from the second pair of electrical contacts via conductive paths established within the semiconductor layer.

15. The structure of claim 1 wherein said substrate is a silicon material which has both a <

100>

crystallographic direction and a <

110>

crystallographic direction, and said first pair of torsion bars are oriented in the <

110>

crystallographic direction for an n-type silicon layer.

16. The structure of claim 1 wherein said substrate is a silicon material which has both a <

100>

crystallographic direction and a <

110>

crystallographic direction, and said first pair of torsion bars are oriented in the <

100>

crystallographic direction for a p-type silicon layer.

17. The structure of claim 1 wherein said first dynamic member includes:

a frame;

a second pair of diametrically opposed, axially aligned torsion bars projecting from said frame, said second pair of torsion bars being oriented non-parallel to the first pair of torsion bars; and

a second dynamic member that is coupled by said second pair of torsion bars to said first dynamic member to be thereby supported from said first dynamic member for rotation about a second axis that is collinear with said second pair of torsion bars;

said second pair of torsion bars and said second dynamic member all monolithically fabricated from the silicon substrate together with said reference member, said first pair of torsion bars and said first dynamic member;

said second dynamic member thus supported within said first dynamic member by said second pair of torsion bars, said second dynamic member;

having a center;

defining a second dynamic member rest plane if no external force is applied to said second dynamic member; and

exhibiting a plurality of vibrational modes including a principal torsional vibrational mode about the second axis that is collinear with said second pair of torsion bars, a vertical shaking vibrational mode, a vertical rocking vibrational mode, a lateral shaking vibrational mode, and a lateral rocking vibrational mode, each vibrational mode of said second dynamic member having a vibrational frequency, the vibrational frequency of the principal torsional vibrational mode of said second dynamic member being lower by at least 20% than the vibrational frequency of any other vibrational mode of said second dynamic member.

18. The structure of claim 17 wherein a pre-established oscillation frequency for said second dynamic member:

differs from the vibrational frequency of the vertical rocking vibrational mode of said first dynamic member by at least 20%; and

differs from the vibrational frequency for all vibrational modes of said first dynamic member other than the vertical rocking vibrational mode by at least 10%.

19. The structure of claim 17 wherein a pre-established oscillation frequency for said second dynamic member is the same as the vibrational frequency for the principal torsional vibrational mode of said first dynamic member.

20. The structure of claim 17 further comprising second drive means for imparting rotary motion to said second dynamic member about the second axis that is collinear with said second pair of torsion bars.

21. The structure of claim 20 wherein one of said drive means employs electrostatic force, and the other drive means employs magnetic force.

22. The structure of claim 20 wherein said second drive means for imparting rotary motion to said second dynamic member employs electrostatic force, and said first drive means for imparting rotary motion to said first dynamic member employs magnetic force.

23. The structure of claim 1 wherein said first dynamic member is substantially thinner than said reference member.

24. The structure of claim 1 wherein mass around the center of said first dynamic member is mostly etched away.

25. The structure of claim 1 wherein said first dynamic member has front and back sides, and the front side of said first dynamic member has a reflective mirror coating applied thereto.

26. The structure of claim 1 wherein said first dynamic member has front and back sides, and the back side of said first dynamic member has a reflective mirror coating applied thereto.

27. The structure of claim 1 wherein said first dynamic member has front and back sides, and both the front and back sides of said first dynamic member have a reflective mirror coating applied thereto.

28. The structure of claim 1 wherein said first dynamic member has a lesser width between junctions at which the first pair of torsion bars couple to said first dynamic member than along a line that is parallel to the first axis collinear with said first pair of torsion bars but displaced from said first pair of torsion bars.

29. The structure of claim 1 wherein said first dynamic member includes both a plate and a frame that surrounds the plate and to which said first pair of torsion bars couple, the first dynamic member further including flexures that couple the plate to the frame, the plate exhibiting a plurality of vibrational modes with respect to the frame, all of the vibrational modes of the plate with respect to the frame having a vibrational frequency much higher than a frequency at which said drive means imparts rotary motion to said first dynamic member, whereby the frame and the plate move in unison responsive to the rotary motion imparted by said drive means.

30. The structure of claim 1 further comprising:

a supporting member; and

a second pair of diametrically opposed, axially aligned torsion bars projecting from said supporting member that couple said supporting member to said reference member;

said second pair of torsion bars and said supporting member all monolithically fabricated from the silicon substrate together with said reference member, said first pair of torsion bars and said first dynamic member; and

said second pair of torsion bars permitting said reference member to be mechanically rotated about a second axis that is collinear with said second pair of torsion bars and to be locked at an arbitrarily selectable orientation with respect to said supporting member, whereby the first dynamic member coupled to said reference member is disposed at a arbitrarily selectable angle with respect to said supporting member.