Bistable DMD addressing circuit and method

• US 5,142,405 A
• Filed: 06/29/1990
• Issued: 08/25/1992
• Est. Priority Date: 06/29/1990
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Texas Instruments, Inc.
• Inventors: Hornbeck, Larry J.
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US07/546,271
• Time in Patent Office: 788 Days
• Field of Search: 359/197, 359/198, 359/201, 359/212, 359/236, 359/226, 359/271, 359/298, 358/231, 353/122
• US Class Current: 359/226.1
• 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: H04N 3/12 by switched stationary formation of lamps, photocells or light relays

Abstract

Bidirectional operation of the bistable DMD is preferred over unidirectional operation because it eliminates contrast degradation caused by duty-factor effects and permits lower voltage operation. However, bidirectional addressing requires either two drain lines and two transistors per pixel or one drain line and three transistors per pixel. An addressing scheme for bidirectional operation is disclosed that requires only a single drain line and one transistor per pixel. For megapixel DMDs used for high-definition television applications, this addressing scheme dramatically lowers the transistor count, with expected improvements in chip yield and cost.

Claims

1. A spatial light modulation device, said device comprising:

a multilayered substrate, wherein an upper layer of said substrate contains a defined rotatable beam area;

a first bias electrode positioned in proximity to said rotatable beam and operative for establishing voltage potential thereon; and

circuitry for selectively establishing an address voltage potential on said beam, said voltage potential operative in conjunction with said voltage potential on said bias electrode for selectively enabling said beam to rotate, wherein said circuitry is in contact with at least one area of said beam.

2. The device set forth in claim 1 wherein said address voltage is one of two voltages, said device further comprising:

a second bias electrode positioned in proximity to said rotatable beam and operative for establishing a voltage potential thereon different from the voltage potential established on said first bias electrode so that one or the other of said address voltages on said beam operating in conjunction with said bias voltages controls the direction of said rotation.

3. The device set forth in claim 2 wherein said bias electrode and said second bias electrode are spaced apart and on opposite sides of a pivotal point of said beam, such that a first voltage on said beam causes said beam to rotate around said pivotal point toward said first bias electrode, and said second voltage on said rotatable beam causes said beam to pivot toward said second bias electrode.

4. The device set forth in claim 3 further including

a pair of electrically insulating landing pads for supporting said beam when said beam is pivoted in conjunction with said bias electrode or in conjunction with said second bias electrode.

5. The device set forth in claim 2 further comprising

a base layer;

a layer separate from said base layer defining said controllably rotatable beam area; and

a hinge supported by said base layer and connected to said rotatable area for supporting said rotatable area and for allowing said rotatable are a to move within a defined motion with respect to said base layer, said hinge laying in a plane separate from the plane of said rotatable layer.

6. The device set forth in claim 5 wherein said base layer includes control circuitry defined therein, and wherein said device further includes:

a layer interposed between said base layer and said layer separate from said base layer, said interposed layer having defined therein discrete areas for providing signals for controlling said rotation of said rotatable area; and

interconnection structure for communicating signals from said control circuitry to said discrete thereby controlling said rotatable area.

7. The device set forth in claim 6 wherein said control circuitry is constructed using CMOS technology.

8. The device set forth in claim 2 wherein said two address voltages are 0 and +V_a and wherein said first and second bias voltages are -|V_b | and +|V_b |+|V_a |, respectively.

9. The device set forth in claim 8 wherein V_a =5 volts and V_b =15 volts.

10. An array of spatial with modulation devices, said array comprising:

a multilayered substrate, wherein an upper layer of said substrate contains a plurality of defined controllably rotatable beam areas;

bias electrodes positioned in proximity to said rotatable beams and operative for establishing different voltage on each said bias electrode; and

circuitry for selectively establishing a voltage potential on said beams, said voltage potential operative in conjunction with said voltage potentials on said bias electrodes for selectively enabling said beams to rotate, wherein said circuitry is in contact with at least one area of each of said beams.

11. The array set forth in claim 10 wherein said beam voltage is one of two voltages so that said beam voltages operate in conjunction with said bias voltages to control the direction of said rotation of said beam.

12. The array set forth in claim 11 wherein said bias electrodes for each said beam are spaced apart and on opposite sides of a pivotal point of said beam, such that a first voltage on said beam causes said beam to rotate around said pivotal point toward said one bias electrode, and said second voltage on said rotatable beam causes said beam to pivot toward said second bias electrode.

13. The array set forth in claim 10 further comprising a HDTV system and wherein said array is the visual display in said system.

14. The array set forth in claim 12 wherein all said bias electrodes on one side of said pivotal points are electrically common on all bias electrodes on the other side of said pivotal points are electrically common.

15. The method of establishing a spatial light modulation device having a defined controllably rotatable beam area, said method comprising the steps of:

positioning a first bias electrode in proximity to said rotatable beam;

establishing a voltage potential on said bias electrode;

selectively establishing an address voltage potential on said beam, said voltage potential operative in conjunction with said established voltage potential on said bias electrode for rotating said beam, wherein said address voltage potential is established by addressing circuitry which is in contact with said beam.

16. The method set forth in claim 15 wherein said address voltage establishing step includes the step of

providing one of two voltages.

17. The method set forth in claim 16 further comprising the steps of:

positioning a second bias electrode in proximity to said rotatable beam;

establishing a voltage potential on said second bias electrode different from the voltage potential established in said first bias electrode so that one or the other of said address voltages on said beam operating in conjunction with said bias voltages controls the direction of said rotation.

18. The method set forth in claim 17 wherein said bias electrode positioning steps include the step of

spacing said electrodes apart and on opposite sides of a pivotal point of said beam, such that said first voltage on said beam causes said beam to rotate around said pivotal point toward said first bias electrode, and said second voltage on said rotatable beam causes said beam to pivot toward said second bias electrode.