Method for an optical switch on a substrate

• US 6,632,373 B1
• Filed: 09/28/2000
• Issued: 10/14/2003
• Est. Priority Date: 09/28/2000
• Status: Expired due to Fees

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Fork, David K., Peeters, Eric, Rosa, Michel A.
• Primary Examiner(s): Kunemund, Robert
• Assistant Examiner(s): Ahmed, Shamim
• Application Number:
  US09/675,093
• Time in Patent Office: 1,111 Days
• Field of Search: 216/24, 216/2, 257/415, 385/12, 385/16, 359/248
• US Class Current: 216/24
• CPC Class Codes: B81B 2201/045 Optical switches
• CPC Class Codes: B81B 2203/04 Electrodes
• CPC Class Codes: B81C 1/00666 Treatments for controlling internal stress or strain in MEMS structures
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G02B 6/3518 the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device MEMS devices in general B81B; manufacture of MEM devices in general B81C; micromechanical devices controlling the direction of light G02B26/0833
• CPC Class Codes: G02B 6/3556 NxM switch, i.e. regular arrays of switches elements of matrix type constellation
• CPC Class Codes: G02B 6/358 Latching of the moving element, i.e. maintaining or holding the moving element in place once operation has been performed; includes a mechanically bistable system
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C

Abstract

Optical cross-connect systems involve the general concept of a two dimensional array of MEMS tilt mirrors being used to direct light coming from a first optical fiber to a second optical fiber. Each MEMS tilt mirror in the two dimensional array can tilt about two non-colinear axes and is suspended by a plurality of suspension arms attached to a substrate.

Claims

1. A method comprising:

providing a substrate;

providing a plurality of suspension arms each comprising an internal stress gradient layer, each of said plurality of suspension arms having a first end and a second end, said first end being attached to said substrate;

providing a polysilicon area having a reflective surface layer, said polysilicon area being attached to said second end of said plurality of suspension arms; and

providing a plurality of electrodes arranged on said substrate adjacent to said plurality of suspension arms to create an electric field for producing deflective movement of said polysilicon area having said reflective surface layer.

2. The method of claim 1 wherein said plurality of suspension arms is three in number.

3. The method of claim 1 wherein said substrate is glass.

4. The method of claim 1 wherein said internal stress gradient layer comprises MoCr.

5. The method of claim 4 wherein an internal stress gradient is on the order of 3 gigapascal across said stress gradient layer.

6. The method of claim 1 wherein said polysilicon area has a substantially square shape.

7. The method of claim 1 wherein said polysilicon area is comprised of two polysilicon layers having internal stress gradients acting in opposite directions.

8. A method of making an array of structures, each structure including:

a polysilicon area having a reflective surface layer;

a plurality of suspension arms to which the polysilicon area is attached; and

a plurality of electrodes to create an electric field for producing deflective movement of the polysilicon area;

the polysilicon area, suspension arms, and electrodes being provided in accordance with claim 1.

9. The method of claim 8 wherein said array is a two dimensional rectilinear array.

10. The method of claim 1 wherein each of said plurality of electrodes is adjacent to and extends underneath one of said plurality of suspension arms.

11. The method of claim 1 wherein each of said plurality of electrodes has a substantially tapered shape.

15. The method of claim 1 in which each of the suspension arms extends away from the substrate to its second end;

each arm'"'"'s internal stress gradient layer moving the arm away from the substrate;

the plurality of electrodes including, for each arm, an electrode that responds to an actuation signal by attracting the arm toward the substrate.

12. A method comprising:

providing a glass substrate;

providing four suspension arms each comprising an internal stress gradient polysilicon layer, each said suspension arm having a first end and a second end, said first end being attached to said substrate;

providing a polysilicon area having a reflective surface layer, said polysilicon area being attached to said second end of each of said four suspension arms; and

providing four electrodes arranged on said glass substrate adjacent to said four metal suspension arms, respectively, to create an electric field for producing deflective movement of said polysilicon area having said reflective surface layer.

13. A method of making an array of structures, each structure including:

a polysilicon area having a reflective surface layer;

four suspension arms to which the polysilicon area is attached; and

four electrodes to create an electric field for producing deflective movement of the polysilicon area;

the polysilicon area, suspension arms, and electrodes being provided in accordance with claim 12.

14. The method of claim 13 wherein said array is a two dimensional rectilinear array.

16. The method of claim 12 in which each of the suspension arms extends away from the substrate to its second end;

each arm'"'"'s internal stress gradient polysilicon layer moving the arm away from the substrate;

the plurality of electrodes including, for each arm, an electrode that responds to an actuation signal by attracting the arm toward the substrate.

17. A method performed on a substrate, comprising:

producing an array of at least one mirror structure at a surface of the substrate, each mirror structure including;

two or more suspension arms, each arm having an internal stress gradient, each arm further having an end attached to the substrate'"'"'s surface, the arm extending from the substrate'"'"'s surface to an attachment point;

a mirror attached to the attachment points of the suspension arms, the mirror including a polysilicon area and a reflective area on the polysilicon area, the polysilicon area including parts of first and second polysilicon layers, the first and second polysilicon layers having internal stress gradients acting in different directions; and

electrodes operable to deflect the suspension arms, the electrodes being operable together to tilt the mirror by deflecting the suspension arms.

18. The method of claim 17 in which the internal stress gradients of the first and second polysilicon layers act in opposite directions.

19. The method of claim 17 in which each polysilicon area of each mirror includes a first layer part and a second layer part, the act of producing the array comprises:

depositing and patterning the first polysilicon layer, the patterned first polysilicon layer including the first layer parts of the polysilicon areas; and

depositing and patterning the second polysilicon layer over the first polysilicon layer, the patterned second polysilicon layer including the second layer parts of the polysilicon areas.

20. The method of claim 19 in which the first layer parts of the polysilicon areas are exposed when the second polysilicon layer is deposited, each polysilicon area'"'"'s second layer part being over its first layer part.

21. The method of claim 19 in which the act of producing the array further comprises:

depositing and patterning a layer of gold, the layer of gold including, for each mirror, a gold coating over the second layer part of the mirror'"'"'s polysilicon area.

22. The method of claim 17 in which each of the suspension arms includes part of the first polysilicon layer that provides the arm'"'"'s internal stress gradient.

23. The method of claim 22 in which the act of producing the array further comprises:

releasing the mirror structures to allow the internal stress gradients of the suspension arms to raise the mirrors.

24. A method performed on a substrate structure, comprising:

producing an array of at least one optical device on the substrate structure each optical device including;

each arm two or more suspension arms, each including part of a polysilicon layer each arm further extending from a first end attached to the substrate structure to second end not attached to the substrate structure;

the polysilicon layer having a internal stress gradient that moves the arm away from the substrate structure;

an optical element supported on the second ends of the suspension arms; and

for each suspension arm, an electrode that responds to an actuation signal by attracting the suspension arm toward the substrate structure.

25. A method performed on a substrate structure, comprising:

producing an array of optical devices on the substrate structure, each optical device including;

two or more suspension arms, each arm further having a length extending from a first end attached to the substrate structure to a second end that is not attached to the substrate structure;

each arm being movable between a first position in which the arm'"'"'s length has an initial separation from the substrate structure and a second position in which the arm'"'"'s length is drawn toward the substrate structure, decreasing at separation;

each arm having an internal stress gradient polysilicon layer moving the arm'"'"'s length toward the first position;

an optical element supported on the second ends of the suspension arms; and

for each suspension arm, an electrode under the suspension arm, the electrode responding to an actuation signal by deflecting the suspension arm from its first position toward its second position;

the electrodes responding individually to the actuation signals to tilt the optical element around two non-collinear axes.

26. A method performed on a glass substrate structure, comprising:

producing an array of mirror structures on the substrate structure, each mirror structure including;

two or more suspension arms, each arm having a length extending from a first end attached to the substrate structure to a second end that is not attached to the substrate structure;

each arm being movable between a first position in which the arm'"'"'s length has an initial separation from the substrate structure and a second position in which the arm'"'"'s length is drawn toward the substrate structure, decreasing separation;

each arm having an internal stress gradient polysilicon layer moving the arm'"'"'s length toward the first position;

a mirror supported on the second ends of the suspension arms, the mirror including a polysilicon area and a reflective surface layer; and

for each suspension arm, an electrode under the suspension arm, the electrode responding to an actuation signal by creating an electric field that deflects the suspension arm from its first position toward its second position by beginning to decrease separation at the arm'"'"'s first end and proceeding to decrease separation along the length of the arm toward the arm'"'"'s second end;

the electrodes responding individually to the actuation signals to tilt the mirror around two non-collinear axes;

the act of producing the array of mirror structures comprising;

producing first, second, and third patterned layers over the substrate structure;

the first patterned layer including the electrodes of the mirror structures;

the second patterned layer being a polysilicon layer over the first patterned layer and including the internal stress gradient polysilicon layers of the suspension arms and the polysilicon areas of the mirrors;

the third patterned layer being over the second patterned layer and including the reflective surface layers of the mirrors; and

releasing the mirror structures to allow the internal stress gradient polysilicon layer of each suspension arm to move the suspension arm toward its first position.