Methods and devices for inhibiting tilting of a mirror in an interferometric modulator Number:7,385,762 from the United States Patent and Trademark Office (PTO) owispatent Interferometric modulators having a separable modulator architecture are disclosed having a reflective layer suspended from a flexible layer over a cavity. The interferometric modulators have one or more anti-tilt members that inhibit undesirable movement of the reflective layer, such as curling and/or tilting. The stabilization of the reflective layer by the anti-tilt members can improve the quality of the optical output of the interferometric modulators, as well as displays comprising such interferometric modulators.<H interferometric, inhibiting, Methods, and, dev, 7385762.html, Patent, pto, 7385762

Title: Methods and devices for inhibiting tilting of a mirror in an interferometric modulator

Abstract: Interferometric modulators having a separable modulator architecture are disclosed having a reflective layer suspended from a flexible layer over a cavity. The interferometric modulators have one or more anti-tilt members that inhibit undesirable movement of the reflective layer, such as curling and/or tilting. The stabilization of the reflective layer by the anti-tilt members can improve the quality of the optical output of the interferometric modulators, as well as displays comprising such interferometric modulators.

Patent Number: 7,385,762 Issued on 06/10/2008 to Cummings

Inventors: Cummings; William J. (Millbrae, CA)
Assignee: IDC, LLC (San Francisco, CA)

Appl. No.: 11/589,582

Filed: October 30, 2006

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
11154283	Jun., 2005	7130104
60613558	Sep., 2004

Current U.S. Class: 359/578 ; 359/223; 359/291; 359/292; 359/295; 359/298; 359/315; 359/584

Field of Search: 359/578,584-589,223,224,290-292,295,298,315-318

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Primary Examiner: Lester; Evelyn A.
Attorney, Agent or Firm: Knobbe, Martens, Olson & Bear LLP

Parent Case Text

RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 11/154,283, entitled "METHODS AND DEVICES FOR INHIBITING TILTING OF A MIRROR IN AN INTERFEROMETRIC MODULATOR", filed Jun. 16, 2005 now U.S. Pat. No. 7,130,104 which claims priority to U.S. Provisional Patent Application No. 60/613,558 entitled "METHOD AND DEVICE FOR INHIBITING TILTING OF A MIRROR," filed on Sep. 27, 2004, both of which are hereby incorporated by reference in their entirety.

Claims

What is claimed is:

1. A device comprising: an array of at least two interferometric modulators, each interferometric modulator comprising: a substrate; an optical layer positioned over the substrate, the optical layer being at least partially transmissive to incident light; a mirror positioned over the substrate and movable between a first position spaced from the optical layer by a first distance and a second position spaced from the optical layer by a second distance, the first distance being greater than the second distance, and the mirror having a surface facing away from the substrate, wherein light reflected by the interferometric modulator is interferometrically modulated; and at least one stationary member contacting the surface of the mirror when the mirror is in the first position, wherein the at least one stationary member is configured to inhibit movement of at least a portion of the mirror when the mirror is in the first position; wherein the stationary members of the at least two interferometric modulators contact the surface of each respective mirror at a different first distance from the optical layer when the mirrors are in the first position.

2. The device of claim 1, further comprising: a display; a processor that is in electrical communication with said display, said processor being configured to process image data; and a memory device in electrical communication with said processor.

3. The device of claim 2, further comprising: a first controller configured to send at least one signal to said display; and a second controller configured to send at least a portion of said image data to said first controller.

4. The device of claim 2, further comprising an image source module configured to send said image data to said processor.

5. The device of claim 4, wherein said image source module comprises at least one of a receiver, transceiver, and transmitter.

6. The device of claim 2, further comprising an input device configured to receive input data and to communicate said input data to said processor.

7. The device of claim 1, wherein the at least one stationary member is located between the at least two interferometric modulators, and the stationary member comprises a shaft segment, a first head segment connected to the shaft segment and contacting the mirror of a first of the at least two interferometric modulators, and a second head segment connected to the shaft segment and contacting the mirror of a second of the at least two interferometric modulators.

8. The device of claim 7, wherein the at least one stationary member inhibits movement of at least a portion of both the mirrors of each of the first and second interferometric modulators in a direction generally perpendicular to the surfaces of the mirrors when the mirrors are in the first position.

9. The device of claim 7, wherein the at least one stationary member inhibits movement of at least a portion of both the mirrors of each of the first and second interferometric modulators in a direction generally parallel to the surfaces of the mirrors when the mirrors are in the first position.

10. The device of claim 7, wherein the at least one stationary member inhibits rotational movement of at least a portion of both the mirrors of the first and second interferometric modulators when the mirrors are in the first position.

11. The device of claim 1, further comprising a third interferometric modulator, wherein the first distance between the mirror and the optical layer when the mirror is in the first position is different for each of the three interferometric modulators.

12. The device of claim 11, wherein the three different first distances are dimensioned such that different colors of light are reflected by the three interferometric modulators when the mirrors are in the first position.

13. The device of claim 12, wherein the different colors comprise red, green and blue.

14. The device of claim 1, further comprising a mechanical layer attached to the mirror that suspends the mirror over the substrate, wherein the mechanical layer exerts a force on the mirror that facilitates contact between the at least one member and the surface of the mirror when the mirror is in the first position.

15. The device of claim 1, further comprising a mechanical layer having at least one portion that is attached to the mirror and a second portion that is attached to at least one of the stationary members.

16. An array of at least two interferometric modulators, each interferometric modulator comprising: means for supporting at least a portion of the interferometric modulator; means for transmitting light, the transmitting means positioned over the supporting means, the transmitting means at least partially transmissive to incident light; means for reflecting light, the reflecting means positioned over the supporting means and movable between a first position spaced from the transmitting means by a first distance and a second position spaced from the transmitting means by a second distance, the first distance being greater than the second distance, and the reflecting means having a surface away from the supporting means, wherein light reflected by the interferometric modulator is interferometrically modulated; and means for stabilizing the reflecting means, the stabilizing means contacting the surface of the reflecting means when the reflecting means is in the first position, wherein the stabilizing means is configured to inhibit movement of at least a portion of the reflecting means when the reflecting means is in the first position; wherein the stabilizing means of the at least two interferometric modulators contact the surface of each respective reflecting means at a different first distance from the transmitting means when the reflecting means are in the first position.

17. The array of interferometric modulators of claim 16, wherein the reflecting means is at an angle non-parallel to the supporting means in the first position.

18. The array of interferometric modulators of claim 16, wherein the supporting means comprises a substrate.

19. The array of interferometric modulators of claim 16, wherein the transmitting means comprises an optical layer.

20. The array of interferometric modulators of claim 16, wherein the reflecting means comprises a mirror.

21. The array of interferometric modulators of claim 16, wherein the stabilizing means comprises at least one stationary member.

22. An interferometric modulator comprising: a substrate; an optical layer positioned over the substrate, the optical layer being at least partially transmissive to incident light; a mirror positioned over the substrate and movable between a first position and a second position, wherein a portion of the mirror is spaced from the optical layer by a first distance in the first position, and the portion of the mirror is spaced from the optical layer by a second distance in the second position, the first distance being greater than the second distance, and the mirror having a surface away from the substrate, wherein light reflected by the interferometric modulator is interferometrically modulated; and at least one stationary member contacting the surface of the mirror facing away from the substrate when the mirror is in the first position, wherein the at least one stationary member is configured to inhibit movement of at least a portion of the mirror when the mirror is in the first position, and further wherein the mirror is positioned and an angle non-parallel to the substrate in the first position.

23. The interferometric modulator of claim 22, wherein the mirror comprises a second portion and the at least one stationary member contacts the second portion of the mirror when the mirror is in the first position.

24. The interferometric modulator of claim 23, wherein the second portion of the mirror is spaced from the optical layer by a smaller first distance in the first position than the first distance that first portion of the mirror is spaced form the optical layer in the first position.

25. The interferometric modulator of claim 22, further comprising a mechanical layer attached to the mirror that suspends the mirror over the substrate, wherein the mechanical layer exerts a force on the mirror that facilitates contact between the at least one member and the surface of the mirror when the mirror is in the first position.

26. The interferometric modulator of claim 22, further comprising a second stationary member contacting the surface of the mirror when the mirror is in the first position, wherein the second stationary member is configured to inhibit movement of at least a portion of the mirror when the mirror is in the first position, and further wherein the at least one stationary member and the second stationary member contact the mirror at different distances from the substrate.

Description

BACKGROUND

1. Field of the Invention

The invention relates generally to microelectromechanical systems (MEMS), and more particularly to interferometric modulators and display devices comprising such interferometric modulators.

2. Description of Related Art

Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed.

SUMMARY

The system, method, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled "Detailed Description of Certain Embodiments" one will understand how the features of this invention provide advantages over other display devices.

One aspect of the invention is an interferometric modulator comprising a substrate; an optical layer positioned over the substrate, the optical layer being at least partially transmissive to incident light; a mirror positioned over the substrate and movable between a first position spaced from the optical layer by a first distance and a second position spaced from the optical layer by a second distance, the first distance being greater than the second distance and the mirror having a first surface facing toward the substrate and a second surface facing away from the substrate; and at least one stationary member contacting the second surface of the mirror when the mirror is in the first position, wherein the at least one stationary member is configured to inhibit movement of at least a portion of the mirror when the mirror is in the first position. Advantageously, the one or more stationary members are configured to stabilize the mirror in a manner that improves the optical and/or electromechanical performance of the interferometric modulator and display devices incorporating such interferometric modulators.

In certain embodiments, the at least one stationary member inhibits the movement of at least a portion of the mirror in a direction generally perpendicular to the mirror when the mirror is in the first position. The at least one stationary member may also inhibit the movement of the mirror in a rotational manner and/or in a direction generally parallel to the mirror when the mirror is in the first position.

In some aspects, the at least one stationary member inhibits the movement of the mirror in a rotational manner when the mirror is in the second position, and/or when the mirror occupies a position between the first and second positions. The at least one stationary member may also inhibit the movement of the mirror in a direction generally parallel to the mirror when the mirror is in the second position, and/or when the mirror occupies a position between the first and second positions.

In some aspects, the mirror is substantially planar when in the first position, the second position and/or a position between the first and second positions.

In some aspects, the mirror is not impinged by light incident to the interferometric modulator and/or light reflected by the interferometric modulator.

In some aspects, the at least one stationary member contacts at least a portion of the second surface of the mirror when the mirror is in the first position.

In various aspects, the interferometric modulator further comprises a mechanical layer attached to the mirror that suspends the mirror over the substrate. In some embodiments, the mechanical layer exerts a force on the mirror that facilitates contact between the second surface of the mirror and the at least one stationary member when the mirror is in a first position.

The at least one stationary member may be of any shape and/or configuration that is capable of performing the functions described herein. In some aspects, the at least one stationary member comprises a single segment that is substantially curvilinear. In these aspects, the at least one stationary member can be, for example, generally hook-shaped or cane-shaped.

In some aspects the at least one stationary member comprises a shaft segment that is substantially perpendicular to the mirror, and a head segment connected to the shaft segment. The head segment may be substantially parallel to the shaft segment, at an acute angle to the shaft segment, or in any other configuration that allows the at least one stationary member to inhibit at least a portion of the mirror from movement in at least one direction. In some aspects, the shaft segment inhibits lateral movement of at least a portion of the mirror in a direction generally parallel to the mirror when the mirror is in the first position and/or a position between the first and second positions. The shaft segment may also inhibit rotational movement of at least a portion of the mirror when the mirror is in the first position, the second position, and/or a position between the first and second positions. In some aspects, the head segment inhibits movement of at least a portion of the mirror in a direction generally perpendicular to the mirror when the mirror is in the first position. In some aspects, the mirror contacts the head segment when the mirror is in the first position.

In some aspects, at least a portion of the head segment is wider than the width of at least a portion of the shaft segment. The head segment may comprise any shape and/or configuration so long as the anti-tilt member is able to inhibit at least a portion of the mirror from movement in at least one direction. In some aspects the shaft has a shape that is conical, substantially rectangular, substantially triangular, and/or substantially round. In some aspects the head segment has a shape that is substantially rectangular, substantially conical, barbed, substantially spherical, oblong, and/or substantially hook-shaped.

In some aspects the at least one stationary member and/or the mirror is modified to facilitate contact between them and/or aid the at least one stationary member in inhibiting the movement of at least a portion of the mirror. For example, in some aspects, the at least one stationary member further comprises a convex portion that contacts at least a portion of the mirror when the mirror is in the first position, the second position, and/or a position between the first and second positions. The mirror may also further comprise a recessed portion that contacts the at least one stationary member when the mirror is in the first position, the second position, and/or a position between the first and second positions. In some aspects, a surface of the at least one member and/or the mirror is modified, for example by roughening. The at least one stationary member may also further comprise a contact region that contacts the at least one stationary member when the mirror is in the first position, the second position, and/or a position between the first and second positions. The contact region may comprise a different material than the other portions of the at least one stationary member.

In some aspects, the invention relates to a member for reducing the movement of a mirror in an interferometric modulator. In various aspects, the member inhibits movement of at least a portion of a mirror in an interferometric modulator in a direction substantially parallel to the mirror, in a direction generally perpendicular to the mirror, and/or in a rotational direction. The member may inhibit movement of at least a portion of the mirror when the mirror is in the first position, the second position, and/or a position between the first and second positions. In some aspects, the member comprises a shaft segment that is substantially perpendicular to the mirror and a head segment connected to the shaft segment. In some aspects, the member inhibits movement of at least a portion of a first mirror of a first interferometric modulator and inhibits movement of at least a portion of a second mirror of a second interferometric modulator.

In some aspects, the invention relates to a visual display device comprising a plurality of interferometric modulators of the invention. In some embodiments, the visual display device further comprises one or more of the following components: a processor that is in electrical communication with the display, the processor being configured to process image data; a memory device in electrical communication with the processor; a first controller configured to send at least one signal to the display; a second controller configured to send at least a portion of the image data to the first controller; an image source module, which may comprise at least one of a receiver, transceiver, and transmitter, the image source module being configured to send image data to the processor; and/or an input device configured to receive input data and to communicate the input data to the processor.

In some aspects, the invention relates to is an interferometric modulator comprising a substrate; an optical layer positioned over the substrate, the optical layer being at least partially transmissive to incident light; a mirror positioned over the substrate and movable between a first position spaced from the optical layer by a first distance and a second position spaced from the optical layer by a second distance, the first distance being greater than the second distance and the mirror having a first surface facing toward the substrate and a second surface facing away from the substrate; and at least one stationary mirror-stabilizing means configured to maintain the mirror in a desired orientation when the mirror is in the first position, said mirror-stabilizing means contacting the second surface of the mirror when the mirror is in the first position.

In various aspects, the mirror-stabilizing means is configured to maintain the mirror in a substantially planar orientation when the mirror is in the first position and/or to maintain the mirror substantially parallel to the substrate when the mirror is in the first position. In some aspects, the mirror-stabilizing means is configured to stabilize the mirror in a manner that improves the optical and/or electromechanical performance of the interferometric modulator.

In some aspects, the invention relates to a process for manufacturing an interferometric modulator of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a relaxed position and a movable reflective layer of a second interferometric modulator is in an actuated position.

FIG. 2 is a system block diagram illustrating one embodiment of an electronic device incorporating a 3.times.3 interferometric modulator display.

FIG. 3 is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of FIG. 1.

FIG. 4 is an illustration of a set of row and column voltages that may be used to drive an interferometric modulator display.

FIGS. 5A and 5B illustrate one exemplary timing diagram for row and column signals that may be used to write a frame of display data to the 3.times.3 interferometric modulator display of FIG. 2.

FIGS. 6A and 6B are system block diagrams illustrating an embodiment of a visual display device comprising a plurality of interferometric modulators.

FIG. 7A is a cross section of the device of FIG. 1.

FIG. 7B is a cross section of an alternative embodiment of an interferometric modulator.

FIG. 7C is a cross section of another alternative embodiment of an interferometric modulator.

FIG. 7D is a cross section of yet another alternative embodiment of an interferometric modulator.

FIG. 7E is a cross section of an additional alternative embodiment of an interferometric modulator.

FIG. 8A is a schematic diagram illustrating an embodiment of a back plane support for a separable interferometric modulator.

FIG. 8B is a schematic diagram illustrating an alternative embodiment of a back plane of a seperable interferometric modulator.

FIG. 9 is a schematic diagram illustrating a layout view of a pixel comprising a 3.times.3 array of interferometric modulators and anti-tilt members.

FIGS. 10A-D are cross-sectional views of several embodiments of anti-tilt members.

FIG. 11 is a cross-sectional view taken along line 11-11 of FIG. 9 showing the anti-tilt members located between the adjacent interferometric modulators of the array in FIG. 9.

FIG. 12 is a diagonal cross-sectional view taken along line 12-12 of FIG. 9 showing the post supports for the interferometric modulators of the array in FIG. 9.

FIG. 13 is a cross-sectional view similar to FIG. 11 that further illustrates the material layers that are applied to manufacture interferometric modulators having the anti-tilt members.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices.

One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in FIG. 1. In these devices, the pixels are in either a bright or dark state. In the bright ("on" or "open") state, the display element reflects a large portion of incident visible light to a user. When in the dark ("off" or "closed") state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the "on" and "off" states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white.

FIG. 1 is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In some embodiments, an interferometric modulator display comprises a row/column array of these interferometric modulators. Each interferometric modulator includes a pair of reflective layers positioned at a variable and controllable distance from each other to form a resonant optical cavity with at least one variable dimension. In one embodiment, one of the reflective layers may be moved between two positions. In the first position, referred to herein as the relaxed position, the movable reflective layer is positioned at a relatively large distance from a fixed partially reflective layer. In the second position, referred to herein as the actuated position, the movable reflective layer is positioned more closely adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacent interferometric modulators 12a and 12b. In the interferometric modulator 12a on the left, a movable reflective layer 14a is illustrated in a relaxed position at a predetermined distance from an optical stack 16a, which includes a partially reflective layer. In the interferometric modulator 12b on the right, the movable reflective layer 14b is illustrated in an actuated position adjacent to the optical stack 16b.

The optical stacks 16a and 16b (collectively referred to as optical stack 16), as referenced herein, typically comprise several fused layers, which can include an electrode layer, such as indium tin oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. The optical stack 16 is thus electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the above layers onto a transparent substrate 20. In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable reflective layers 14a, 14b may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of 16a, 16b) deposited on top of posts 18 and an intervening sacrificial material deposited between the posts 18. When the sacrificial material is etched away, the movable reflective layers 14a, 14b are separated from the optical stacks 16a, 16b by a defined gap 19. A highly conductive and reflective material such as aluminum may be used for the reflective layers 14, and these strips may form column electrodes in a display device.

With no applied voltage, the cavity 19 remains between the movable reflective layer 14a and optical stack 16a, with the movable reflective layer 14a in a mechanically relaxed state, as illustrated by the pixel 12a in FIG. 1. However, when a potential difference is applied to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable reflective layer 14 is deformed and is forced against the optical stack 16. A dielectric layer (not illustrated in this Figure) within the optical stack 16 may prevent shorting and control the separation distance between layers 14 and 16, as illustrated by pixel 12b on the right in FIG. 1. The behavior is the same regardless of the polarity of the applied potential difference. In this way, row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies.

FIGS. 2 through 5 illustrate one exemplary process and system for using an array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor 21 which may be any general purpose single- or multi-chip microprocessor such as an ARM, Pentium.RTM., Pentium II.RTM., Pentium III.RTM., Pentium IV.RTM., Pentium.RTM. Pro, an 8051, a MIPS.RTM., a Power PC.RTM., an ALPHA.RTM., or any special purpose microprocessor such as a digital signal processor, microcontroller, or a programmable gate array. As is conventional in the art, the processor 21 may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application.

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