Spatial light modulator

• US 5,784,189 A
• Filed: 12/21/1995
• Issued: 07/21/1998
• Est. Priority Date: 03/06/1991
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Rabe, Steven, Bozler, Carl O.
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): BEY, DAWN MARIE
• Application Number:
  US08/569,158
• Time in Patent Office: 943 Days
• Field of Search: 359/230, 359/254, 359/291
• US Class Current: 359/254
• CPC Class Codes: G01J 3/0232 using shutters
• CPC Class Codes: G02B 26/02 for controlling the intensity of light G02B26/004 takes precedence
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: G09F 9/372 the positions of the elements being controlled by the application of an electric field
• CPC Class Codes: H01H 2001/0042 Bistable switches, i.e. having two stable positions requiring only actuating energy for switching between them, e.g. with snap membrane or by permanent magnet
• CPC Class Codes: H01H 2059/0018 Special provisions for avoiding charge trapping, e.g. insulation layer between actuating electrodes being permanently polarised by charge trapping so that actuating or release voltage is altered
• CPC Class Codes: H01H 2059/0081 with a tapered air-gap between fixed and movable electrodes
• CPC Class Codes: H01H 59/0009 making use of micromechanics

Abstract

A spatial light modulator formed of a moveable electrode which is disposed opposite a fixed electrode and is biased to roll in a preferred direction upon application of an electric field across the electrodes to produce a light valve or light shutter. In one embodiment, the moveable electrode is restrained at one end and coils about the fixed end in a preferential roll direction. The bias is achieved by inducing anisotropic stress or anisotropic stiffness.

Claims

1. A device comprising:

a) a fixed electrode;

b) a first high resistance layer on said fixed electrode; and

c) a moveable electrode formed with a stress and affixed at one end and rotationally moveable about a single axis toward said fixed electrode by application of a suitable voltage to the device and rotatable in an opposite direction upon removal of said voltage, said stress biasing said moveable electrode toward movement in said opposite direction, said moveable electrode having a second high resistance layer formed between said moveable electrode and said first high resistance layer.

2. The device of claim 1 wherein the moveable electrode is stiffened to avoid curling transverse the direction of rotation thereof.

3. The device of claim 1 wherein the moveable electrode rotates into a roll and is anisotropically stressed in the direction of roll.

4. The device of claim 1 wherein the moveable electrode is anisotropically stiffened in a direction transverse the direction of rotation.

5. The device of claim 1 wherein the moveable electrode is formed of a film having compressive stress on a side facing the fixed electrode and tensile stress on an opposite side of the film and wherein the net stress of the moveable electrode is low.

6. The device of claim 5 wherein the moveable electrode is formed of outer layers of insulator material and an inner conductive layer.

7. The device of claim 6 wherein the moveable electrode has a thickness of less than about 3000 Angstroms.

8. The device of claim 1 in which the moveable electrode modulates light.

9. The device of claim 1 wherein the moveable electrode switches electricity.

10. The device of claim 1 wherein the moveable electrode forms a light shutter.

11. A device comprising:

a) a substrate;

b) a fixed electrode on the substrate;

c) a first high resistance body covering a surface of the fixed electrode opposite the substrate; and

d) a moveable electrode fixed at one end and stressed, as formed, to roll up in a coil, said moveable electrode having a second high resistance body formed between said moveable electrode and said first high resistance body; and

wherein upon application of an electric potential to the device, the moveable electrode unrolls in a preferential roll direction to cover a substantial portion of the fixed electrode.

12. The device of claim 11 wherein the fixed electrode is comprised of a thin transparent layer of material from the group comprising indium-tin oxide, gold, copper, silver, platinum or tungsten and the moveable electrode, substrate, and high resistance body are transparent and a non-transparent layer is formed over the moveable electrode and the second high resistance body is formed on the moveable electrode on a side of the moveable electrode closest to the fixed electrode.

13. The device of claim 12 wherein the first and second high resistance bodies are formed of material from the group comprising aluminum oxide, silicon dioxide or silicon nitride.

14. The device of claim 11 wherein the moveable electrode is stiffened in a direction transverse the roll direction to cause the moveable electrode to unroll in the preferential roll direction.

15. The device of claim 14 wherein the stiffening is achieved by providing corrugations which extend transverse the roll direction.

16. The device of claim 11 wherein the moveable electrode is formed of three layers comprising a middle layer of metal and outer layers of insulator.

17. The device of claim 16 wherein the net stress of the three layers is low.

18. The device of claim 11 wherein the electrodes switch electricity.

19. The device of claim 16 wherein the two insulator layers are formed of aluminum oxide and the metal layer is formed of aluminum.

20. The device of claim 11 wherein the moveable electrode modulates light.

21. A light modulator comprising:

a) a fixed electrode;

b) an insulator over the fixed electrode; and

c) a moveable electrode adjacent said fixed electrode and attached at one end to said insulator which moveable electrode is rotatable about said one end and biased, as formed, in a manner which causes said moveable electrode to coil in a direction away from said fixed electrode, wherein

a first resistive layer is formed on a surface of the fixed electrode facing the moveable electrode and a second resistive layer is formed on a surface of said moveable electrode facing the fixed electrode.

22. The modulator of claim 21 wherein the bias is caused by anisotropic stress created in forming the moveable electrode.

23. The modulator of claim 21 wherein the bias is caused by anisotropic stiffening of the moveable electrode.

24. The modulator of claim 21 wherein the bias is caused by anisotropic stiffening provided by corrugations extending transverse the direction of coiling movement.

25. The modulator of claim 21 wherein the corrugations are in the form of non-uniform ridge spacings.

26. A light modulator comprising:

a) a fixed electrode; and

b) a moveable electrode adjacent said fixed electrode which moveable electrode is anisotropically stiffened, as formed, in a manner which tends to cause said moveable electrode to coil in a preferred coil direction.

27. The modulator of claim 26 wherein the movable electrode is stiffened by forming corrugations which extend transverse the preferred roll direction.

28. A light valve comprising:

a) a substrate;

b) a fixed electrode on the substrate; and

c) a moveable electrode fixed at one end and anisotropically biased to roll up in a coil in a preferential direction; and

wherein upon application of an electric potential the moveable electrode unrolls in an opposite direction to cover a substantial portion of the fixed electrode.

29. The valve of claim 28 wherein the fixed electrode is comprised of a thin layer of material from the group comprising indium tin oxide, gold, silver, platinum or tungsten.

30. The valve of claim 28 wherein the moveable electrode is biased by being stiffened in a direction transverse the roll direction to prevent the moveable electrode from curling transverse the roll direction.

31. The valve of claim 28 wherein the stiffening is achieved by providing corrugations which extend transverse the roll direction.

32. The valve of claim 28 wherein the moveable electrode is formed of a middle conductive layer with insulative layers on either side thereof.

33. The valve of claim 32 wherein the net stress of the movable electrode is low.

34. A light valve comprising:

a) a substrate;

b) a fixed electrode on the substrate;

c) a moveable electrode fixed at one end and anisotropically biased to roll up in a coil in a preferential direction; and

wherein one of said electrodes is divided into spaced apart conductive strips and wherein upon application of a first electric potential across said fixed and moveable electrodes the moveable electrode unrolls in an opposite direction to cover a portion of the fixed electrode; and

upon application of a second electric potential across an electrode and one or more conductive strips, the moveable electrode assumes a fixed position.

35. A spatial light modulator comprising:

a) an array of light valves, each valve comprising a fixed electrode and a moveable electrode and wherein the moveable electrode is fixed at one end and anisotropically biased to roll up in a coil in a preferential direction; and

wherein upon application of an electric potential across said electrodes, the moveable electrode unrolls in an opposite direction to cover a substantial portion of the fixed electrode;

b) an array of address pads coupled to a respective one of said valves to apply said potential across said electrodes; and

c) a source of light adjacent said array for projecting light at said array to form a pixel image in space, each pixel thereof formed in response to the respective potentials applied to said electrodes.

36. A microwave switch comprising:

a) a fixed conductive member and a moveable conductive member with an insulator formed therebetween and wherein the moveable member is fixed at one end and is anisotropically biased to roll up in a coil in a preferential direction; and

wherein upon application of an electric potential across said members, the moveable member unrolls in an opposite direction to contact a substantial portion of the fixed electrode;

b) an input lead coupling a source of microwave energy to one member; and

c) an output lead coupled to the remaining member;

whereby when the moveable member unrolls, a large capacitance is formed across the switch, producing low impedance coupling of the microwave energy from the source to the output lead.

37. A DC switch for switching DC voltage comprising:

a) an array of switches, each switch comprising a fixed current carrying electrode on a substrate and a moveable cantilevered electrode fixed at one end with opposed contact areas on said moveable electrode and said fixed electrode;

b) at least one potential supplying electrode; and

wherein upon application of an electric potential to said potential supplying electrode, the moveable electrode moves in a direction to bring the contact areas in contact.

38. The switch of claim 37 in which the potential supplying electrode is formed on the substrate and consists of two spaced apart conductive strips.