Electric display device

• US 5,233,459 A
• Filed: 03/06/1991
• Issued: 08/03/1993
• Est. Priority Date: 03/06/1991
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Rabe, Steven, Bozler, Carl O.
• Primary Examiner(s): Bovernick, Rodney B.
• Assistant Examiner(s): Phan, James
• Application Number:
  US07/665,345
• Time in Patent Office: 881 Days
• Field of Search: 359/227, 359/230, 340/763, 340/764
• US Class Current: 359/230
• 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 bistable electrostatic light valve display in which a movable electrode is disposed opposite a fixed electrode and is biased to move 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 movable 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. In another embodiment, the moveable electrode is restrained at both ends and is biased upwardly by anisotropic stress or stiffening.

Claims

1. An electrostatic light valve comprising:

a) a fixed electrode formed on a substrate;

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

c) a movable electrode formed with an anisotropic stress in a predetermined direction and disposed adjacent said fixed electrode with a second high resistive layer formed between the movable electrode and the first high resistance layer; and

d) wherein the fixed electrode, high resistance layers and movable electrode are portions of a monolithic thin film structure and the movable electrode is formed of two layers of metal, one of which is nearer the substrate and is formed with compressive stress and the other of which is formed with tensile stress.

2. The valve of claim 1 wherein the resistive layers have a thickness and the resistance of regions of the resistive layers perpendicular to the thickness is equal.

3. The valve of claim 2 wherein the thickness of the resistive layers is equal.

4. The valve of claim 1 wherein the movable electrode is corrugated.

5. The valve of claim 1 wherein the movable electrode is coiled in a roll after formation and is anisotropically stressed in the direction of roll.

6. The valve of claim 5 further including spacer rails between the fixed and movable electrode.

7. The valve of claim 6 wherein the rails extend along the roll direction.

8. The valve of claim 6 wherein the rails extend transverse the roll direction.

9. The valve of claim 1 wherein the movable 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.

10. The valve of claim 1 wherein the movable electrode is coiled in a roll and unrolls in a first direction when a voltage is applied across the electrodes and has anisotropic stress in the direction of roll.

11. The valve of claim 1 wherein the movable electrode is formed of a conductive film having a thickness of less than about 3000 Angstroms.

12. The valve of claim 1 wherein the fixed electrode is comprised of a thin layer of material from the group comprising indium, tin, gold, silver, platinum or tungsten.

13. The valve of claim 1 wherein the first high resistance layer is formed of material from the group comprising silicon dioxide or silicon nitride.

14. The valve of claim 1 wherein the net stress of the two layers of the movable electrode is low compared with the stress of each of said two layers.

15. The valve of claim 1 wherein the movable electrode is formed into a roll and an electric potential applied across the electrodes unrolls the movable electrode.

16. The valve of claim 1 wherein the two layers are formed of material from the group comprising tungsten, chromium, titanium, magnesium or aluminum.

17. The valve of claim 1 wherein the light valve is a monolithic structure formed of thin films and wherein the movable electrode is formed on the second high resistive layer.

18. An electrostatic light valve comprising:

a) a fixed electrode formed on a substrate;

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

c) a movable electrode formed adjacent said fixed electrode and coiled in a roll after formation and anisotropically stressed in the direction of roll with a second high resistive layer formed between the movable electrode and the first high resistance layer; and

d) wherein the fixed electrode, high resistance layers and movable electrode are portions of a monolithic thin film structure and the movable electrode is formed of two layers of metal, one of which is nearer the substrate and is formed with compressive stress and the other of which is formed with tensile stress.

19. The valve of claim 18 wherein the net stress of the two layers of metal is low compared with the stress of each of said two layers.

20. The valve of claim 18 wherein the two layers are formed of material from the group comprising tungsten, chromium, titanium, magnesium or aluminum.

21. The valve of claim 18 further including spacer rails between the fixed and movable electrode.

22. The valve of claim 21 wherein the rails extend along the roll direction.

23. The valve of claim 21 wherein the rails extend transverse the roll direction.