EP2069840A1

EP2069840A1 - Apparatus and method for reducing back reflection from an illumination device

Info

Publication number: EP2069840A1
Application number: EP07852545A
Authority: EP
Inventors: Ion Bita; Gang Xu; Marek Mienko; Russell Wayne Gruhlke
Original assignee: Qualcomm MEMS Technologies Inc
Current assignee: Qualcomm MEMS Technologies Inc
Priority date: 2006-10-06
Filing date: 2007-10-05
Publication date: 2009-06-17
Also published as: WO2008045312A1

Abstract

Embodiments include display devices and devices for illuminating a display. One embodiment includes a display device comprising a plurality of light modulators. The device further includes a light guide panel configured to guide light therein disposed forward of said plurality of light modulators. The device further includes turning microstructure disposed on a surface of said light guide, said turning microstructure configured to direct said light out of said light guide panel onto said plurality of light modulators. The device further includes a plurality of nanostructures disposed on said surface of the light guide panel, said plurality of nanostructures having an effective thickness and effective refractive index so as to reduce reflection of light from said light guide panel. Other embodiments include methods of making such apparatuses.

Description

APPARATUS AND METHOD FOR REDUCING BACK REFLECTION FROM AN

ILLUMINATION DEVICE

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] The field of the invention relates to display systems.

Description of the Related Technology

[0002] Display systems may include light modulators to produce a displayed image by modulating light directed to the light modulators. Such display systems may include a source of illumination to at least partly provide light to the light modulators. One embodiment of a light modulator comprises microelectromechanical systems (MEMS). 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. For example, a need exists for improved illumination sources for light modulator based displays. SUMMARY OF CERTAIN INVENTIVE ASPECTS

[0003] 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 as expressed by the claims which follow, 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 that include improved display contrast.

[0004] One embodiment comprises an illumination apparatus. The illumination apparatus comprises a light guide panel configured to guide light therein. The illumination apparatus further comprises turning microstructure disposed on the light guide panel. The turning microstructure is configured to direct the light out of the light guide panel. The illumination apparatus further comprises a plurality of nanostructures disposed on the light guide panel. The plurality of nanostructures has an effective thickness and effective refractive index so as to reduce reflection of light from the light guide panel.

[0005] One embodiment comprises an illumination apparatus. The illumination apparatus comprises a means for guiding light, means for turning the light guided in the light guiding means and directing the light out of the light guiding means, and means for reducing refractive index mismatch with the light guiding means. The mismatch reducing means is disposed on the light guiding means and has at least one of height, width and length that is less than 1 micron. The mismatch reducing means has an effective thickness and effective refractive index so as to reduce reflection of light from the light guiding means.

[0006] One embodiment comprises a method of manufacturing an illumination apparatus. The method comprises disposing a light guide panel configured to guide light therein. The light guide has (a) turning microstructure thereon configured to direct the light out of the light guide panel, and (b) a plurality of nanostructures disposed thereon. The plurality of nanostructures has an effective thickness and effective refractive index so as to reduce reflection of light from the light guide panel. One embodiment comprises an apparatus manufactured by the method. [0007] One embodiment is a method of manufacturing. The method comprises providing a master comprising a crystalline surface and forming a microstmcture on a surface of the master. The microstructure defines a shape, which when replicated on a light guide panel based on the master, is configured to direct light out of the light guide panel. The method further comprises forming a mold based on the master.

[0008] One embodiment is a method of manufacturing. The method comprises providing a mold that replicates a microstructure formed on a crystalline surface. The microstructure defines a shape, which when replicated on a light guide panel using the mold, is configured to direct light out of the light guide panel. The method further comprises applying the mold to a material so as to form at least part of a light guide panel.

[0009] One embodiment comprises an illumination apparatus. The illumination apparatus comprises a light guide panel configured to guide light therein. The apparatus further comprises a plurality of nanostructures disposed on the light guide panel. The plurality of nanostructures has an effective thickness and effective refractive index so as to reduce reflection of light from said light guide panel. The light guide panel comprises a first section comprising said nanostructures arranged in parallel rows and a second section comprising said nanostructures arranged in parallel rows. The rows in the first section and the rows in the second section are non-parallel. The first and second sections are adjacent.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 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.

[0011] FlG. 2 is a system block diagram illustrating one embodiment of an electronic device incorporating a 3x3 interferometric modulator display.

[0012] FIG. 3 is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of FIG. 1.

[0013] FIG. 4 is an illustration of a set of row and column voltages that may be used to drive an interferometric modulator display. [0014] 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 3x3 interferometric modulator display of FIG. 2.

[0015] FIGS. 6A and 6B are system block diagrams illustrating an embodiment of a visual display device comprising a plurality of interferometric modulators.

[0016] FIG. 7A is a cross-section of the device of FIG. 1.

[0017] FIG. 7B is a cross-section of an alternative embodiment of an interferometric modulator.

[0018] FIG. 7C is a cross-section of another alternative embodiment of an interferometric modulator.

[0019] FIG. 7D is a cross-section of yet another alternative embodiment of an interferometric modulator.

[0020] FIG. 7E is a cross-section of an additional alternative embodiment of an interferometric modulator.

[0021] FlG. 8 is a cross-section of one embodiment of a display device comprising a light guide configured to illuminate an array of light modulators.

[0022] FIG. 9 is a cross-section of one embodiment of a display device similar to that of FIG. 8 that further comprises an anti-reflective coating.

[0023] FIG. 1 OA is a cross-section of one embodiment of a display device comprising a light guide that includes a nanostructure anti-reflective coating on a surface of the light guide.

[0024] FIG. 1 OB is a cross-section illustrating the example anti-reflective coating of FIG. 1 OA in more detail.

[0025] FIG. 1 1 is a perspective view of one embodiment of an anti-reflective coating comprising a two-dimensional array of nano-scale posts such as illustrated in FIG. 1 OB.

[0026] FIG. 12 is a perspective view of another embodiment of an anti-reflective coating comprising a two-dimensional array of pyramid shaped elements

[0027] FIG. 13A is perspective view of one embodiment of an anti-reflective coating comprising a two-dimensional array of inverted nano-scale posts. [0028] FIG. 13B is a perspective view of another embodiment of an anti- reflective coating comprising a two-dimensional array of inverted pyramid shaped elements.

[0029] FIG. 14A is a top view of an example of a nano-structure anti-reflective coating such as illustrated in FlG. 1OA that comprises regions of nanoscale ridges in varying alignments.

[0030] FIG. 14B is a cross-section view of the ridges of a portion of the coating illustrated in FIG. 14A.

[0031] FIG. 14C is top view of the portion of the coating illustrated in FIG. 14B.

[0032] FIG. 15 is a cross-section illustrating the paths of light in an example of a light guide comprising an anti-reflective coating such as illustrated in FIG. 1OA.

[0033] FlG. 16 is a graphical diagram illustrating reflectance characteristics of a light guide without an anti-reflective coating and a light guide comprising an example nanostructure based anti-reflective coating such as illustrated in FIG. 1OA.

[0034] FIG. 17A-171 are cross-sections illustrating one embodiment of a method of making a master or mold for making a light guide with a nanostructure anti-reflective coating such as the light guide illustrated in FIG. 1OA.

[0035] FIG. 18A illustrates a top view of an embodiment of a light guide comprising nonuniformly arranged reflective light turning elements that may also include the anti-reflective coating of FIG. 1 OA.

[0036] FIG. 18B illustrates a top view of a portion of the array of light turning elements of FIG. 18A in more detail.

[0037] FIG. 19 illustrates a top view of another embodiment of a light guide comprising nonuniformly arranged reflective light turning elements that may also include the anti-reflective coating of the example light guide of FIG. 1OA.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS [0038] 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.

[0039] Light modulator displays may be illuminated using a light guide that directs a pattern of light to the light modulators. The light guide may comprise a light turning (and/or light emissive) elements that directs light onto the array of light modulators. The light guide may comprise film on which the light turning elements are embossed.

[0040] In one embodiment, the light guide comprises a front light, e.g., a light guide positioned between the display modulators and viewing positions. Ambient light incident on such displays may be at least partially reflected to viewing positions by the top or exterior surface of the light guide, thus reducing contrast of the display. One way of improving contrast is to provide an anti-reflective coating (ARC) on the exterior surface of the light guide to reduce such ambient reflections. Application of a separate ARC film or layer adds manufacturing costs and complexity. Moreover, films covering the light turning elements may interfere with the function of the light guide. It has been found that a nanostructure based ARC can also be embossed onto the surface of the light guide as part of the process of forming the light turning elements. Desirably, manufacturing costs and complexity can thereby be reduced. Moreover, in one embodiment, the nanostructure ARC can desirably be formed on portions of the surface of the light guide not comprising the light turning elements. [0041] 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.

[0042] 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.

[0043] 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.

[0044] The optical stacks 16a and 16b (collectively referred to as optical stack 16), as referenced herein, typically comprise of 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.

[0045] 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 FIG.) 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.

[0046] FIGS. 2 through 5 illustrate one exemplary process and system for using an array of interferometric modulators in a display application.

[0047] 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^®, Pentium II^®, Pentium III , Pentium IV^®, Pentium^® Pro, an 8051 , a MIPS^®, a Power PC^®, an ALPHA^®, 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.

[0048] In one embodiment, the processor 21 is also configured to communicate with an array driver 22. In one embodiment, the array driver 22 includes a row driver circuit 24 and a column driver circuit 26 that provide signals to a panel or display array (display) 30. The cross-section of the array illustrated in FIG. 1 is shown by the lines 1-1 in FlG. 2. For MEMS interferometric modulators, the row/column actuation protocol may take advantage of a hysteresis property of these devices illustrated in FIG. 3. It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the relaxed state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the exemplary embodiment of FIG. 3, the movable layer does not relax completely until the voltage drops below 2 volts. There is thus a range of voltage, about 3 to 7 V in the example illustrated in FIG. 3, where there exists a window of applied voltage within which the device is stable in either the relaxed or actuated state. This is referred to herein as the "hysteresis window" or "stability window." For a display array having the hysteresis characteristics of FIG. 3, the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be relaxed are exposed to a voltage difference of close to zero volts. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the "stability window" of 3-7 volts in this example. This feature makes the pixel design illustrated in FIG. 1 stable under the same applied voltage conditions in either an actuated or relaxed pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or relaxed state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. Essentially no current flows into the pixel if the applied potential is fixed.

[0049] In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row 1 electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row 2 electrode, actuating the appropriate pixels in row 2 in accordance with the asserted column electrodes. The row 1 pixels are unaffected by the row 2 pulse, and remain in the state they were set to during the row 1 pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention.

[0050] FIGS. 4 and 5 illustrate one possible actuation protocol for creating a display frame on the 3x3 array of FIG. 2. FIG. 4 illustrates a possible set of column and row voltage levels that may be used for pixels exhibiting the hysteresis curves of FIG. 3. In the FIG. 4 embodiment, actuating a pixel involves setting the appropriate column to -Vb,_as, and the appropriate row to +ΔV, which may correspond to -5 volts and +5 volts respectively Relaxing the pixel is accomplished by setting the appropriate column to +V_b,_as, and the appropriate row to the same +ΔV, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at +V_bιas, or -V_b,_as. As is also illustrated in FIG. 4, it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to +V_b,_as, and the appropriate row to -ΔV. In this embodiment, releasing the pixel is accomplished by setting the appropriate column to -V_b,_aS, and the appropriate row to the same -ΔV, producing a zero volt potential difference across the pixel. [0051) FIG. 5B is a timing diagram showing a series of row and column signals applied to the 3x3 array of FIG. 2 which will result in the display arrangement illustrated in FIG. 5A, where actuated pixels are non-reflective. Prior to writing the frame illustrated in FIG. 5A, the pixels can be in any state, and in this example, all the rows are at 0 volts, and all the columns are at +5 volts. With these applied voltages, all pixels are stable in their existing actuated or relaxed states.

[0052] In the FIG. 5A frame, pixels (1,1), (1 ,2), (2,2), (3,2) and (3,3) are actuated. To accomplish this, during a "line time" for row 1 , columns 1 and 2 are set to -5 volts, and column 3 is set to +5 volts. This does not change the state of any pixels, because all the pixels remain in the 3-7 volt stability window. Row 1 is then strobed with a pulse that goes from 0, up to 5 volts, and back to zero. This actuates the (1 ,1) and (1 ,2) pixels and relaxes the (1 ,3) pixel. No other pixels in the array are affected. To set row 2 as desired, column 2 is set to -5 volts, and columns 1 and 3 are set to +5 volts. The same strobe applied to row 2 will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again, no other pixels of the array are affected. Row 3 is similarly set by setting columns 2 and 3 to -5 volts, and column 1 to +5 volts. The row 3 strobe sets the row 3 pixels as shown in FIG. 5A. After writing the frame, the row potentials are zero, and the column potentials can remain at either +5 or -5 volts, and the display is then stable in the arrangement of FIG. 5A. It will be appreciated that the same procedure can be employed for arrays of dozens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the systems and methods described herein.

[0053] FIGS. 6A and 6B are system block diagrams illustrating an embodiment of a display device 40. The display device 40 can be, for example, a cellular or mobile telephone. However, the same components of display device 40 or slight variations thereof are also illustrative of various types of display devices such as televisions and portable media players.

[0054] The display device 40 includes a housing 41, a display 30, an antenna 43, a speaker 45, an input device 48, and a microphone 46. The housing 41 is generally formed from any of a variety of manufacturing processes as are well known to those of skill in the art, including injection molding, and vacuum forming. In addition, the housing 41 may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing 41 includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols.

[0055] The display 30 of exemplary display device 40 may be any of a variety of displays, including a bi-stable display, as described herein. In other embodiments, the display 30 includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display 30 includes an interferometric modulator display, as described herein.

[0056] The components of one embodiment of exemplary display device 40 are schematically illustrated in FIG. 6B. The illustrated exemplary display device 40 includes a housing 41 and can include additional components at least partially enclosed therein. For example, in one embodiment, the exemplary display device 40 includes a network interface 27 that includes an antenna 43 which is coupled to a transceiver 47. The transceiver 47 is connected to the processor 21 , which is connected to conditioning hardware 52. The conditioning hardware 52 may be configured to condition a signal (e.g. filter a signal). The conditioning hardware 52 is connected to a speaker 45 and a microphone 46. The processor 21 is also connected to an input device 48 and a driver controller 29. The driver controller 29 is coupled to a frame buffer 28 and to the array driver 22, which in turn is coupled to a display array 30. A power supply 50 provides power to all components as required by the particular exemplary display device 40 design.

[0057] The network interface 27 includes the antenna 43 and the transceiver 47 so that the exemplary display device 40 can communicate with one ore more devices over a network. In one embodiment the network interface 27 may also have some processing capabilities to relieve requirements of the processor 21. The antenna 43 is any antenna known to those of skill in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.12 standard, including IEEE 802.12(a), (b), or (g). In another embodiment, the antenna transmits and receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS or other known signals that are used to communicate within a wireless cell phone network. The transceiver 47 pre- processes the signals received from the antenna 43 so that they may be received by and further manipulated by the processor 21. The transceiver 47 also processes signals received from the processor 21 so that they may be transmitted from the exemplary display device 40 via the antenna 43.

[0058] In an alternative embodiment, the transceiver 47 can be replaced by a receiver. In yet another alternative embodiment, network interface 27 can be replaced by an image source, which can store or generate image data to be sent to the processor 21. For example, the image source can be a digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data.

[0059] Processor 21 generally controls the overall operation of the exemplary display device 40. The processor 21 receives data, such as compressed image data from the network interface 27 or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor 21 then sends the processed data to the driver controller 29 or to frame buffer 28 for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level.

[0060] In one embodiment, the processor 21 includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device 40. Conditioning hardware 52 generally includes amplifiers and filters for transmitting signals to the speaker 45, and for receiving signals from the microphone 46. Conditioning hardware 52 may be discrete components within the exemplary display device 40, or may be incorporated within the processor 21 or other components.

[0061] The driver controller 29 takes the raw image data generated by the processor 21 either directly from the processor 21 or from the frame buffer 28 and reformats the raw image data appropriately for high speed transmission to the array driver 22. Specifically, the driver controller 29 reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array 30. Then the driver controller 29 sends the formatted information to the array driver 22. Although a driver controller 29, such as a LCD controller, is often associated with the system processor 21 as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor 21 as hardware, embedded in the processor 21 as software, or fully integrated in hardware with the array driver 22.

[0062] Typically, the array driver 22 receives the formatted information from the driver controller 29 and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display's x-y matrix of pixels.

[0063] In one embodiment, the driver controller 29, array driver 22, and display array 30 are appropriate for any of the types of displays described herein. For example, in one embodiment, driver controller 29 is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, array driver 22 is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller 29 is integrated with the array driver 22. Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, display array 30 is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators).

[0064] The input device 48 allows a user to control the operation of the exemplary display device 40. In one embodiment, input device 48 includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone 46 is an input device for the exemplary display device 40. When the microphone 46 is used to input data to the device, voice commands may be provided by a user for controlling operations of the exemplary display device 40. [0065] Power supply 50 can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply 50 is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply 50 is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, power supply 50 is configured to receive power from a wall outlet.

[0066] In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver 22. Those of skill in the art will recognize that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.

[0067] The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example, FIGS. 7A-7E illustrate five different embodiments of the movable reflective layer 14 and its supporting structures. FIG. 7A is a cross-section of the embodiment of FIG. I ₅ where a strip of metal material 14 is deposited on orthogonally extending supports 18. In FIG. 7B, the moveable reflective layer 14 is attached to supports at the corners only, on tethers 32. In FIG. 7C, the moveable reflective layer 14 is suspended from a deformable layer 34, which may comprise a flexible metal. The deformable layer 34 connects, directly or indirectly, to the substrate 20 around the perimeter of the deformable layer 34. These connections are herein referred to as support posts. The embodiment illustrated in FIG. 7D has support post plugs 42 upon which the deformable layer 34 rests. The movable reflective layer 14 remains suspended over the cavity, as in FIGS. 7A-7C, but the deformable layer 34 does not form the support posts by filling holes between the deformable layer 34 and the optical stack 16. Rather, the support posts are formed of a planarization material, which is used to form support post plugs 42. The embodiment illustrated in FlG. 7E is based on the embodiment shown in FIG. 7D, but may also be adapted to work with any of the embodiments illustrated in FIGS. 7A-7C as well as additional embodiments not shown. In the embodiment shown in FIG. 7E, an extra layer of metal or other conductive material has been used to form a bus structure 44. This allows signal routing along the back of the interferometric modulators, eliminating a number of electrodes that may otherwise have had to be formed on the substrate 20.

[0068] In embodiments such as those shown in FlG. 7, the interferometric modulators function as direct-view devices, in which images are viewed from the front side of the transparent substrate 20, the side opposite to that upon which the modulator is arranged. In these embodiments, the reflective layer 14 optically shields some portions of the interferometric modulator on the side of the reflective layer opposite the substrate 20, including the deformable layer 34 and the bus structure 44. This allows the shielded areas to be configured and operated upon without negatively affecting the image quality. This separable modulator architecture allows the structural design and materials used for the electromechanical aspects and the optical aspects of the modulator to be selected and to function independently of each other. Moreover, the embodiments shown in FIGS. 7C-7E have additional benefits deriving from the decoupling of the optical properties of the reflective layer 14 from its mechanical properties, which are carried out by the deformable layer 34. This allows the structural design and materials used for the reflective layer 14 to be optimized with respect to the optical properties, and the structural design and materials used for the deformable layer 34 to be optimized with respect to desired mechanical properties.

|0069] FIG. 8 is a cross-section of one embodiment of a display device 100 comprising a light guide 92 configured to illuminate the display array 30 of light modulators 104 formed on a substrate 90. In one embodiment, the light modulators 104 may comprise interferometric modulators having reflective and partially reflective surfaces as described above with respect to any of Figures 1 to 7A-E. A diffuser 1 14 may also be positioned between the light guide 102 and the array 30 of light modulators 104. It is to be recognized that while the diffuser 1 14 may affect the path of individual light rays, the relevant principles of operation as discussed herein are not substantially affected by the diffuser 1 14. Other layers may be included as well.

|0070] The light guide 92, which may comprise one or more layers, comprises light turning elements 106. The example light turning elements 106 of FlG. 8 each comprise surfaces 107 and 108 that are configured to direct light to the light modulators 104. In the illustrated embodiment, a light source (not shown) provides light 120 that enters through a side surface of the light guide 92. The light guide 92 internally reflects the light 120 (e.g. by total internal reflection) until the light 120 strikes the surfaces 107 and 108 so as to be directed onto one or more of the light modulators 104, which in turn modulate the light 120 and direct a portion of the modulated light to the viewing position 128. In one embodiment, the light guide 92 is configured with respect to the light source so that total internal reflection of the light 120 within the light guide 92 reduces loss of the light 120 except when reflected by the light turning elements 106 towards the light modulators 104 and possible loss to the diffuser 1 14.

[0071] Light 122 from an external light source 123, or ambient light in a viewing environment of the display device, may also be transmitted by the light guide 92 and modulated by the light modulators 104. At least a portion of the light 122 from the light source 123 may pass through the light guide 92 and diffuser 1 14 to the light modulators 104 and may be reflected to the viewing position 128 (see ray 124). A portion 126 of the external or ambient light 122 may be reflected by an upper or external surface 129 of the light guide 92. When received at a viewing position 128 in combination with the modulated light 120 and 124, the reflected light 126 reduces the contrast of the display 100.

|0072] FlG. 9 is a cross-section of one embodiment of the display device 100 that further comprises an anti-reflective coating (ARC) 130. The example ARC 130 of FlG. 9 comprises a film applied to the surface 129 of the light guide 92. In operation, a portion 131 of the incident ambient light 122 that is reflected by the ARC has a lower intensity than the portion 126 that would be reflected by the surface 129 of the light guide 92 without the ARC 130.

[0073] FIG. 1OA is a cross-section of one embodiment of the display device 100 comprising a light guide 102 that includes a nanostructure anti-reflective coating 140 on the surface 129 of the light guide 102. In the example light guide 102 of FIG. 1OA, the light turning elements 106 comprise the surface portion 107 that is configured to direct internally reflected light toward the light modulators 104. Such light turning elements 106 also include a surface portion 142, which together with the surface portion 107 defines a trough on the light guide 102. Application of the film ARC 130 such as illustrated in FIG. 9 may tend to round off the corners of the facets formed by the surface 107, which can affect performance of the light turning elements 106. Also, formation of the film ARC 130 through wet coating techniques can result in material pooling (i.e. material accumulation) in the troughs defined by the light turning elements 106. Such pooling can also affect the performance of the light turning elements 106 by smoothing out parts of the surface relief structure that is wet coated.

[0074] The nanostructure ARC 140 can be formed as part of the process of forming the light turning elements 106, e.g., as part of an embossing process, thereby reducing manufacturing costs and complexity. Moreover, the ARC 140 may be selectively formed so as to not affect the performance of the light turning elements 106. In one embodiment, the ARC 140 is formed so that the surface portions 107 and 142 are substantially free of the ARC 140. However, in other embodiments, the ARC 140 may be formed across substantially all of the surface 129 of the light guide 102, including all or part of one or both of the surface portions 107 and 142. It is to be understood that in one embodiment, Figure 1OA is not to scale, rather the substantially flat surface 140 covers between 50%-99.9% of the surface area of the guide 102. In one embodiment, the substantially flat surface 140 covers between 95% and 98% or more of the surface area of the guide 102. In one embodiment, the relative density of the surface 140 may vary over the surface of a particular light guide 102, e.g., the light turning elements 106 may comprise less surface area, e.g., the surface 140 may comprise 98% of the surface of the light guide 102 near the light source and the light turning elements 106 may comprise more surface area, e.g., the surface 140 may comprise less, 95% of the surface of the light guide 102, farther from the light source.

[0075] In some embodiments, the nanostructure ARC 140 comprises a film formed on a film comprising the light turning elements 106 formed therein. This film stack may be disposed on the light guide 102. In other embodiments, the nanostructure ARC 140 and the light turning elements 106 may be formed in a same film that is disposed on the light guide 102. In yet other embodiments, the light guide 102 may comprise a monolithic structure with the turning elements 106 and the anti-reflective nanostructure 140 formed therein, for example, by embossing or molding. Accordingly, in certain embodiments the ARC 140 comprises a film separate and distinct from the medium in which the light turning elements 106 and/or light guide are formed while in some embodiments the anti-reflective nanostructure may not be part of a separate medium distinct from the medium or media in which the turning elements 106 or the light guide structure 102 are formed. Nevertheless, the nanostructure may be referred to as forming an ARC or anti-reflective coating in each case.

[0076] FlG. 1OB is an enlarged cross-section 160 of the light guide 102 of FIG. 1OA illustrating the example anti-reflective coating 140 in more detail. The ARC 140 comprises a plurality or an array of sub-wavelength scale features or ARC structures 170. These features are referred to herein as nanostructures because for visible wavelengths, e.g., 400-700 nanometers, the sub-wavelength dimensions results in nanometer scale sized structures (e.g. less than 1 micron). One or more of the dimensions (e.g. height, width, length) may be on the order of nanometers (e.g., about 1-9 nm, about 10-99 nm, or 100-999 nanometers). The nanostructure may also have two or more dimensions that are on the order of nanometers. In many embodiments, the width or length of the nanostructures is less than 800 nm, less than 700 nm, less than 600 nm, less than 500 nm, less than 400 nm, less than 300 nm, less than 200 nm, or less than 100 nm. In many embodiments, the nanostructure has two or more dimensions that are smaller than visible light wavelengths. In one embodiment, the ARC structures 170 comprise a two-dimensional array of solid material posts surrounded by air, or a two-dimensional array of air holes surrounded by a solid material, or similar structures. In one embodiment, the ARC structures 170 comprise groups of lines or ridges arranged substantially in parallel. The plurality of ARC structures 170 defines anti-reflective coating on the surface 129 of the light guide 102.

[0077| Single layer thin film anti-reflective coatings, such as the ARC 140 may be characterized in terms of a thickness, d_eff, and effective index of refraction, n_eff. For nanostructures that are subwavelength in scale, the exact structural details (e.g., shape) are characterized by an effective thickness, d_eff and an effective index of refraction, n_eff, describing the optical response of the effective thin optical layer comprising the nanostructure. Thus, embodiments may comprise nanoposts, nanopyramids, ordered or disordered arrays, or any other suitable nanostructure comprising a nanoscale shaped solid (or even hollow) material surrounded by a material such as air. The shape, size, and density may be selected to provide the appropriate effective thickness, d_eff and effective index of refraction, n_eff to reduce surface reflection. [0078] For example, to reduce reflection at an air/layer interface where the air has an index of refraction of air, n_air, and the layer has an index of refraction of n_L (e.g., light guide without AR coating), the effective index of refraction, n_eff, of the AR coating is preferably an intermediate value between that of the index of refraction of the air, n_a,_r, and the index of refraction of the layer, n^ In particular, n_a,_r < n_etτ < n^ In certain preferred embodiments,

n_clϊ ~ sqrt(n_aιr * n_L) (Eqn. 1),

Additionally, the effective thickness d_cff is about a quarter of a wave of optical path distance. For example, to reduce reflection, the effective thickness d_erτ of the AR coating may be selected to be deff = λ / (4 n_eff ) (Eqn. 2).

[0079] Using target values for thickness, d_eff, and effective index of refraction, n_eff of the AR coating to reduce reflection for a selected wavelength, nanostructures of suitable height to satisfy d_Cff and suitable size and spacing of the structure to satisfy n_eff may be selected for a particular example of the nanostructure ARC 140. The effective index of refraction, n_cff, may be approximated using as the average index of refraction, n_ave, of the nanostructure ARC 140. The average index of refraction, n_ave, may be calculated using effective medium techniques (such as Maxwell-Garnet for low volume fraction, or Bruggeman for comparable volume fractions) that predict the average index of refraction, n_avc, based on composition (volume fraction of air and film material, e.g., plastic). In addition, the calculation may also account for the particular morphology of the nanostructure 140.

[0080] For example, if the film, e.g., the light guide 102, has an index of refraction, Π_L - 1.55, and the target wavelength for reducing reflections is λ = 550 nm, by applying the Equation 1 and Equation 2 above, the AR coating may be designed to have an effective index of refraction, n_etτ ⁼ 1 -24 and effective thickness d_eff =1 10 nm to reduce reflection. For an example nanostructure with a target n_eff = 1.24 to be formed from the light guide material, e.g., plastic, having index of 1.55, the nanostructure 140 has portion of volume average of air to light guide material (e.g., plastic) of about 45 vol. % based on a simple volume averaging based estimation of n_eff. For example, in the case where the nanostructures comprise the same material as the layer beneath having the index n_L, the volume average f_avc can be computed for a desired n_eβ- using the equation n_eff = f_ave*n_L + (1 - f_avc)n_air, where f_ave is the average volume fraction of the ARC 140 that is comprised of the material of the light guide 102. The feature size for a given shape of the nanostructύre elements 170 and for a given spacing (which may be determined by the mask to be used) is selected to provide the coating 140 with a nanostructure having an average volume fraction that is about the target volume fraction.

[0081] FlG. 1 1 is a perspective view of one embodiment of the anti-reflective coating 140 comprising a two-dimensional array of nanostructures 170, e.g., nano-scale posts. The nanoposts 170 have an effective thickness, d_eff. The volume average of the coating 140 may be determined based on the morphology of the posts relative to the volume of the corresponding portion 200 of the nanostructure coating 140, e.g., the volume of the nanoposts 170 based on their diameter and height, e.g., d_etτ, versus the volume of the region 200. In one embodiment, the posts have a d_cff of about 109 nm, a diameter of about 82 nm, with the posts arranged on a square lattice with a period equal to d_eff. The structure of such an embodiment may comprise a plastic (e.g., polycarbonate) having an index of refraction of about 1.59 and an effective index of refraction, n_eιτ, of about 1.26 for the nanostructured effective layer. The sizes for a particular embodiment may adjusted to compensate for manufacturing factors such as electroforming of the master mold, plastic film embossing, etc.

[0082] FIG. 12 is a perspective view of another embodiment of the anti-reflective coating 140 comprising a two-dimensional array of truncated pyramid shaped elements 170. The volume average of the coating 140 may be determined based on the morphology of the truncated pyramid shaped elements 170 relative to the volume of the corresponding portion 200 of the nanostructure coating 140, e.g., the volume of the pyramid shaped elements 170 based on their top width (e.g., for truncated pyramid structures illustrated in FIG. 12), the bottom width of the pyramid shaped elements 170 and the average height, e.g., d_eff, versus the volume of the region 200. In one embodiment, inverted air truncated nanopyramids created by anisotropic silicon wet etching of the type shown in Fig. 13B, have a height, d_eff, of about 109 nm, with a square base of about 285 nm and an angle of about 70.5° between opposing facets (as given by the angle between (1 1 1) planes of crystalline silicon), and are surrounded by a polycarbonate plastic with refractive index of about 1.59 nm, such that the effective refractive index of this nanostructured layer is 1.26.

(0083] Uniformly (or non-uniformly) arranged nanostructural elements 170 may be formed using etching techniques using appropriate nanostructured etching masks generated by a variety of nanopatterning methods such as optical lithography, self-assembly of nanostructured thin films, etc.. The defined structure may be used to form molds for embossing a plastic film to define the light guide 102. Moreover, while FIGS. 1 1 and 12 illustrate embodiments that include arrays of uniformly arranged posts or pyramids, other embodiments may include two-dimensional randomly arranged items. A wide range of shapes and arrangements are possible. In some embodiments, the elements 170 comprise nanorods, worm-like elements, circular, island like elements or other suitable elements. In one embodiment, such elements 170 may be formed using holography, a stochastic etch mask, e.g., a substrate coated with sol-gel self-assembled nanorod networks or a nanoparticle layer. The elements 170 may also be arranged periodically, non-periodically, aperiodically, nonuniformly, stochastically, or randomly, or combinations thereof.

[0084) FIG. 13A is a perspective view of one embodiment of an anti-reflective coating comprising a two-dimensional array of nano-scale inverted posts. In one embodiment, such an array is fabricated using anisotropic dry etching techniques using a suitable etch mask. As discussed in more detail below, the structure may then be transferred, e.g., via electroforming, to a metal mold configured to emboss the array onto the light guide 102. As described above, the light guide may comprise multiple layers, for example, a light turning film on top of another supporting light guide layer.

[0085] FIG. 13B is a perspective view of another embodiment of an anti- reflective coating comprising a two-dimensional array of inverted pyramid shaped elements. In one embodiment, such an array is fabricated using silicon wet etching techniques and an appropriate etch mask. The structure may then be transferred, e.g., via electroforming, to a metal mold configured to emboss the array onto the light guide 102. As described above, the light guide may comprise multiple layers, for example, a light turning film on top of another supporting light guide layer. In one embodiment, inverted air truncated nanopyramids created by anisotropic silicon wet etching of the type shown in Fig. 13B, have a height, cW, of about 109 nm, a square base of about 285 nm, an angle of about 70.5° between opposing facets (as given by the angle between (1 1 1) planes of crystalline silicon). Such truncated nanopyramids may be surrounded by a polycarbonate plastic with refractive index of about 1.59 nm, such that the effective refractive index of this nanostructured layer is 1.26.

[0086] FIG. 14A is a top view of an example of a nano-structure anti-reflective coating 140 comprising regions 200 of nanoscale structures 170 comprising ridges aligned differently in different regions 200. For example, the angle (e.g., versus the vertical (Y) direction in FlG. 14A) of the ridge structures 170 may vary and/or the spacing of the ridge structures 170 may vary. For sets of linearly parallel ridge structures 170, the anti-reflective effectiveness may be affected by the polarization of incident light relative to the lines (e.g., the reflectance may vary depending on whether the polarization of the incident light is more parallel or more perpendicular to the alignment of the ridge structures 170). By including the regions 200 with varying orientations, the coating 140 desirably reduces reflectance from a wider range of directions and with varying polarizations. Other variations are possible between regions. In one embodiment, the effective index of refraction is substantially the same in each of the regions 200. For example, if one such region 200 has thinner structure 170, those structures 170 are more closely packed to provide the desired effective index.

[0087] FIG. 14B is a cross-section view of one example region 200 of the coating 140 illustrating the ridge shaped elements 170 of FIG. 14A. FIG. 14C is top view of the region 200 of the coating 140 illustrating the ridge shaped elements 170 of FIG. 14A. Although the length may be beyond the nanometer regime, e.g., > 1 micron, the height and width of the structures 170 may be within the nanometer regime, e.g., < 1 micron. Accordingly, the structures 170 would be considered sub-wavelength structures as the individual structures would not diffract or otherwise individually interact with light.

[0088] FIG. 15 is a cross-section illustrating paths of light in an example of the light guide 102 comprising the anti-reflective coating 140 showing that the disclosed ARC layer preserves the light turning function of a front light comprising light turning microstructure and antireflection nanostructure. In FIG. 15, the anti-reflective coating 140 is illustrated functionally. Thus, the nanostructural elements 170 are not shown. FIG. 15 illustrates that the addition of the nanostructure based ARC 140 does not substantially affect operation of the light guide 102, and may improve its function under some circumstances. In particular, the light guide 102 with the ARC 140 guides, via total internal reflection (TIR), illuminating light 181 that is incident on the interface 193 having an angle of incidence within an angular range 180. The extent of the angular range 180, θ!'^~ _R ^ARC , may be expressed as Θ_T'^~ _R ^RC = In₁ ) , where Π_ARC is the index of refraction of ARC 140 (e.g., n_eff), and

Π_L is the index of refraction of the material of the light guide 102. In addition, the ARC 140 may desirably direct internally reflected light 183 incident on the air-ARC surface 129 at a range of angles 182, from θ!^_R ^ARC to Θ!;^~ _R ^mr , at a range of angles 182 into the light guide 102 rather than out of the light guide 102 and into the air. The angular extent of the range 182 of enhanced light guide efficiency may be expressed as θ^_R " = sin^"' («_β)r /n_Λ) , n_a,_r being the index of refraction of air. Light 185 incident on the surface 129 at angles 184 between ®_ΎΪ_R ^{RC an}^ ^tne normal to the interface 193 is transmitted out of the light guide 102 into the air, with or without the ARC 140. Thus, the function of the light guide 102 is not negatively impacted in embodiments that include the ARC 140.

[0089] FIG. 16 is a graphical diagram illustrating reflectance characteristics of an example of the light guide 102 without an anti-reflective coating and the light guide 102 comprising an example of the nanostructure based anti-reflective coating 140. Traces 302, 304, and 306 illustrate the reflectance of light incident at angles of 0°, 30°, and 45°, respectively, at an air-glass (n_gi_ass=l .52) interface such as for one embodiment of the light guide 102 (without the ARC 140) at a range of wavelengths of about 350-800 nm. The traces 302, 304, and 306 show that the reflectance is substantially frequency independent in the illustrated range and has a value of about 0.045, 0.043, and 0.053, respectively.

[0090] Traces 312, 314, and 316 illustrate the reflectance of light incident at angles of 0°, 30°, and 45°, respectively, for air-ARC-glass layer sequence (with an ARC 140 having n_eft = 1 .24 and d_en— 1 10 nm) such as for one embodiment of the light guide 102 at the range of wavelengths of about 350-800 nm. Each of the traces 312, 314, and 316 illustrates the reduced reflectance obtained using the ARC 140. In particular, each of the traces 312, 3 14, and 3 16 defines a single minimum curve having a minimum at wavelengths of about 550 nm, 500 nm, and 450 nm, respectively. The minimum reflectance is much less than 0.005 with maximum values up to about 0.025 at the endpoints of the range of 350-800 nm. In one embodiment, the n_eff and d_efr are selected with reference to a quarter wavelength of visible light that is selected so as to minimize total reflectance (e.g., based on integrating under a reflectance curve such as illustrated by traces 312, 314, and 316) over a selected band of wavelengths, e.g., over visible wavelengths. In various embodiments, the reflectance is less than 0.03, 0.02, or 0.01 in visible wavelengths.

[0091] FIG. 17A-171 are cross-sections illustrating one embodiment of a method of making a surface relief mold that can be subsequently used to mold a light guide 102 with a nanostructure anti-reflective coating 140 and light turning microstructure 106 such as the light guide illustrated in FIG. 1OA. FlG. 17A illustrates a substrate 400, e.g., a silicon (100) substrate prior to processing. FIG. 17B illustrates the substrate 400 following lithographic processing in which the substrate 400 is coated and patterned to form a photoresist etch mask layer 470. FIG. 17C illustrates the substrate 400 following a dry etch (e.g., CF₄ reactive ion etching) process to form recessed areas 472. The recessed areas 472 having a desired depth, e.g., 100 nm, are formed in the portion of the substrate not covered by the layer 470. The portions of the substrate 400 under the layer 470 correspond to a portion of the nanostructure elements 170 of the ARC layer 140 of the light guide 102 discussed above. The mold may be used to injection mold, emboss a film, or otherwise act as a master for forming the light guide 102.

[0092] FIG. 17D illustrates the substrate 400 after the layer 470 is removed. Note that the scale of FIG. 17D is larger so that the nanoscale features are not visible. FIG. 17E illustrates the nanoscale features of a portion 480 of the substrate 400 of FIG. 17D. FIG. 17F illustrates the substrate 400 following another lithographic process to coat and pattern a Si wet etch mask (e.g., SiO₂, or Si₃N₄) thin layer 490. FIG. 17G illustrates the substrate 400 following an anisotropic wet etch of the silicon substrate 400, e.g., KOH, TMAH wet etch to form grooves 472. FIG. 17H illustrates the substrate 400 after the wet etch mask 490 has been removed. The grooves 472 correspond to the light turning elements 106 of the light guide 102. FIG. 171 shows the portion 480 of the substrate 400 at the nanoscale to illustrate the relationship between the nanoscale features 480 and the larger scale grooves 472 that define the nanostructural elements 170 of the ARC 140 and the light turning elements 106 of the light guide 102.

[0093] In one embodiment, the mask 490 may comprise sequences of substantially square shapes that define sequences of pyramid shapes rather than grooves in the substrate 400. In one embodiment, the etching of the grooves or pyramid shapes 472 may be performed such that truncated grooves or pyramids are formed rather than sharp grooves or pyramids.

[0094] In other embodiments, a nanomask pattern for forming the nanostructural elements 170 of the ARC 140 may be transferred to the substrate 400 by a variety of etching methods. For example, isotropic or anisotropic, dry or wet etching techniques may be used depending on the desired shape and the material to be etched. For example, anisotropic dry etching (e.g. RIE with CF₄, CHF₃, etc.), anisotropic wet etching (aqueous KOH), isotropic dry etching (e.g. high pressure plasma etching, CF₄, XeF₂, etc.), or isotropic wet etching (HF+HNO₃+CH₃COOH) may be used to etch a silicon surface. In addition, other process steps may be added or substituted (or steps deleted) to form a mold for nanostructural elements 170 of varying shapes. For example, cylindrical posts may be formed using anisotropic etching via arrays of circular dots as a mask, inverted pyramids may be formed using anisotropic wet etching of silicon, and rounded pockets via isotropic etching. In addition, combinations thereof may be used.

[0095] To form the light guide 102, a plastic film may be embossed using a metal mold or other tool that replicates the structure formed using, for example, the process described with reference to FIGS. 17A- 171. The mold may be formed via suitable technique, such as electroforming, based directly on the formed structure or on a replica of the structure. While 17A- 171 are discussed with reference to silicon, other embodiments may include methods based on germanium (Ge), gallium arsenide (GaAs), gallium phosphide (GaP), gallium nitride (GaN), calcite (CaCO₃), and other crystalline materials.). Particular silicon crystalline orientations, e.g., other than silicon (100), may be used as the substrate in order to control the angle of the light turning faces 472 with reference to the substrate surface. Methods such as illustrated in Figures 17A-17I are desirable for making front lights guides because light features can be made small enough to be substantially invisible to a human observer. In addition, the use of such spaced grooves spaced to cover only a portion, (e.g., 0.1% to 10%) of the surface on substantially flat crystalline surfaces further reduces or eliminates visual artifacts from viewing the display through the front light guide as may occur with light guides that have higher coverage rates for light turning structures (e.g., 50% or greater).

[0096] As described above, in some embodiments, the nanostructure ARC 140 is formed in a first film formed on a second film comprising the light turning elements 106 formed therein. This film stack may be disposed on the light guide 102. In other embodiments, the nanostructure ARC 140 and the light turning elements 106 may be formed in a same film that is disposed on the light guide 102. In yet other embodiments, the light guide 102 may comprise a monolithic structure with the turning elements 106 and the anti- reflective nanostructure 140 formed therein, for example, by embossing or molding. Accordingly, in certain embodiments the ARC 140 comprises a film separate and distinct from the medium in which the light turning elements 106 and/or light guide are formed, while in some embodiments the anti-reflective nanostructure may not be part of a separate medium distinct from the medium or media in which the turning elements 106 or the light guide structure 102 are formed. Nevertheless, the nanostructure may be referred to as forming an ARC or anti-reflective coating in each case.

[0097] In view of the above, one will appreciate that various embodiments of the invention improve contrast in a display that includes a front-light type light guide. For example, embodiments include light guides having a nanostructure-based ARC formed thereon. Embodiments may reduce manufacturing costs and complexity and/or provide an ARC that does not substantially affect the illumination function of the light guide.

(0098) It is to be recognized that the light turning elements 106 of the light guide 102 may be arranged in a variety of ways. For example, FIG. 18A illustrates a top view of an embodiment of the light guide 102 comprising nonuniformly arranged reflective light turning elements 106 that may also include the anti-reflective coating 140 of FIG. 1 OA. Such nonuniform arrangements of light turning elements 106 tends to reduce visible Moire patterns that may be generated by interference between a periodic arrangement of the light turning elements 106 and the period arrangement of the light modulators 104. In the example illustrated in FIG. 18A, the light turning elements 106 comprise regions of the light guide 102 that include reflecting surfaces such as the reflecting surfaces 107 and 140 of Figure 1 OA. The light turning elements 106 of FlG. 18A may be varied in both size and position so that the light guide 102 directs a nonuniformly varying pattern of light to the modulator array 30 (not shown) in one or both of vertical and horizontal dimensions. In the embodiment illustrated in FlG. 18A, a line of the light turning elements 106 is distributed generally along lines X_j X_j+i, ... X_k . In the illustrated embodiment, each of the light turning elements 106 is offset by a random distance in both the vertical (Y) and horizontal (X) from a position along one of the lines X_j1 ... X_k . The vertical and horizontal offsets may be determined in any suitable way, including those discussed with reference to FlG. 14. In one embodiment, the vertical offsets may be zero.

[0099] FIG. 18B illustrates a top view of a portion 600 of the light guide 102 of FlG. 18A in more detail. The example of the portion 600 comprises light turning elements 106a, 106b, and 106c that are each offset in the horizontal direction along an axis X_k, where k is a value between 1 and N, the number of lines in a particular light guide, and where k represents a particular vertical line of light turning elements in the light guide 102. In one embodiment, offset of the reflective surfaces 107 (See FIG. 10A) of each light turning element 106a, 106b, or 106c varies by horizontal offsets that change at positions Y_kJ; where j is a value between 1 and M, the number of light turning elements 106 in a particular line in a particular light guide, and where j represents a particular vertical position of a particular light turning element 106 in the line k of light turning elements 106. The vertical length of the light turning element elements 106, e.g., element 106b is determined by a corresponding vertical position, Y_k0 and the vertical position Y_kj+i of the adjacent element 106c. Each vertical position Y_kj may be selected so that each light turning element 106 has a vertical size or extent within a particular range, e.g., ΔY_mm and ΔY_max. In one embodiment, the vertical size of each light turning element 106 is randomly distributed within the range e.g., ΔY_mιn and ΔY_mav The light turning element 106b at vertical position Y_kj is also offset by an amount ΔX_kj from the line X_k. In one embodiment, the vertical positions Y^ are distributed within a particular or predetermined range of distances, e.g., between ΔX_min and ΔX_max. In one embodiment, the positions Y^ are randomly distributed within the range of distances. It is to be recognized that while in one embodiment, each light turning element 106 is desirably offset in both vertical and horizontal directions, in other embodiments, the light turning element 106 may be offset only in one of the vertical or horizontal directions. The light guide 102 of FIG. I 8A and 18B thus is configured to direct a nonuniformly varying pattern of light to light modulators such as the array 30 of light modulators 104 of FlG. 1OA. The nonuniformly arranged light turning elements 106 may be formed according to suitable variations of the process described above with reference to FIGS. 17A-171. It is to be recognized that randomness selection in the arrangement of light turning elements 106 is generally incorporated at the design or manufacturing stage. During manufacturing, a particular arrangement of light turning elements 106 may be substantially reproduced once or many times.

[0100] FIG. 19 illustrates a top view of another embodiment of the light guide 102 comprising nonuniformly arranged reflective light turning elements 106 that may also include the anti-reflective coating 140 of FIG. 1 OA. In the embodiment illustrated in FIG. 19, the light turning elements 106 of the light guide 102 are also distributed less densely closer to the input location of a light source 650 than at positions on the light guide 102 that are farther from the light source 650. In addition, in the example light guide of FlG. 19, a variety of differently shaped light turning elements 106 are used. For example, light turning elements 106d that have higher levels of efficiency at directing light may to the light modulators 104 may be positioned at distances farther from the light source 650. Moreover, light turning elements such as the light turning element 106e that comprises a single elongated shape may be used in the same light guide 102 as the groups of two-dimensionally offset light turning elements 106f. In the embodiment illustrated in FIG. 19, the two-dimensionally offset light turning elements 106f are closer to the light source 650 and the single, elongated, one- dimensionally offset light turning elements 106e are located farther from the light source 650. While one light source 650 is illustrated in the example light guide 102 shown in FIG. 19, it is to be recognized that other embodiments may include more than one light source. Thus, the positions within the light guide 102 that are farthest from the light sources may be at locations, e.g., the center of the light guide 102, rather than at the end as illustrated in the example of FlG. 19. The example of the light guide 102 illustrated in Figure 19 may optionally comprise an ARC as discussed above.

[0101] A wide variety of variation is possible. Films, layers, components, and/or elements may be added, removed, or rearranged. Additionally, processing steps may be added, removed, or reordered. Also, although the terms film, coating, and layer have been used herein, such terms as used herein include film stacks and multiple layers or multilayers. Such film stacks, multiple layer or multilayers may be adhered to other structures using adhesive or may be formed on other structures using deposition or in other manners. Accordingly, as used herein, the term "on" includes both directly on and over. Thus, a first layer disposed on a second layer can include an intervening layer therebetween.

[0102] While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.

Claims

WHAT IS CLAIMED IS:

1. An illumination apparatus comprising: a light guide panel configured to guide light therein; turning microstructure disposed on said light guide panel, said turning microstructure configured to direct said light out of said light guide panel; and a plurality of nanostructures disposed on said light guide panel, said plurality of nanostructures having an effective thickness and effective refractive index so as to reduce reflection of light from said light guide panel.

2. The apparatus of Claim 1 , wherein each of said nanostructures and said turning microstructure are disposed on a surface of said light guide panel.

3. The apparatus of Claim 2, wherein said nanostructures and said turning microstructure are disposed on an overlapping portion of said surface.

4. The apparatus of Claim 2, wherein said nanostructures and said turning microstructure are disposed on non-overlapping portions of said surface.

5. The apparatus of Claim 1 , further comprising a light source disposed with respect to the light guide panel to inject light therein.

6. The device of Claim 5, wherein the light source comprises a light emitting diode.

7. The apparatus of Claim I , further comprising a plurality of light modulators, wherein said light guide panel is disposed forward of said plurality of light modulators and configured to direct said light out of said light guide panel onto said plurality of light modulators.

8. The apparatus of Claim 7, wherein the plurality of light modulators comprises a plurality of MEMS structures.

9. The apparatus of Claim 8, wherein the plurality of MEMS structures comprises interferometric modulators.

10. The apparatus of Claim 1, wherein the turning microstructure comprises a plurality of faceted features in said light guide panel.

1 1. The apparatus of Claim 1, wherein the turning microstructure comprises a plurality of elongated grooves.

12. The apparatus of Claim 1 1 , wherein the turning microstructure comprises a plurality of triangular grooves having substantially triangular cross-sections.

13. The apparatus of Claim 1 , wherein said turning microstructure is disposed in a film on said light guide panel.

14. The apparatus of Claim 1 , wherein said turning microstructure have a height, width, or spacing greater than 1 micron.

15. The apparatus of Claim 1 , wherein said nanostructures comprise posts, ridges, holes, or a combination thereof.

16. The apparatus of Claim 15, wherein said posts have a cylindrical shape or a pyramidal shape.

17. The apparatus of Claim 15, wherein said posts or ridges have a curved top.

18. The apparatus of Claim 15, wherein said posts, ridges or holes have irregular shapes.

19. The apparatus of Claim 1 , wherein said nanostructures have at least two of height, width, or spacing less than 1 micron.

20. The apparatus of Claim 19, wherein said nanostructures have an average height, width, or spacing that is less than 1 micron.

21. The apparatus of Claim 19, wherein said anti-reflective nanostructure have a height less than about 200 nanometers.

22. The apparatus of Claim 19, wherein said anti-reflective nanostructure have a width less than about 200 nanometers.

23. The apparatus of Claim 19, wherein said nanostructure have a spacing less than about 200 nanometers.

24. The apparatus of Claim 1 , wherein said nanostructures have one or more of a periodic, nonuniform, aperiodic, or random spacing.

25. The apparatus of Claim 1 , wherein said nanostructures are arranged in a two- dimensional array.

26. The apparatus of Claim 1 , wherein said nanostructures are arranged in parallel rows.

27. The apparatus of Claim 1 , further comprising a first section comprising said nanostructures arranged in parallel rows and a second section comprising said nanostructures arranged in parallel rows, said rows in said first section and said rows in said second section being non-parallel, said first and second sections being adjacent.

28. The apparatus of Claim 27, further comprising a third section comprising said nanostructures arranged in parallel rows, said rows in said third section being non-parallel to said rows in said first and second sections, said third sections being adjacent to at least one of said first and second sections.

29. The apparatus of Claim 1 , wherein said plurality of nanostructures are included in a film on said turning microstructure.

30. The apparatus of Claim 29, wherein said turning microstructure is disposed in a film on said light guide panel.

31. The apparatus of Claim 1, wherein said turning microstructure and said plurality of nanostructures are included in a film on said light guide panel.

32. The apparatus of Claim 1 , wherein said turning microstructure and said plurality of nanostructures are formed on said light guide panel.

33. The apparatus of Claim 1 , further comprising material disposed on said plurality of nanostructures.

34. The apparatus of Claim 1 , further comprising: a plurality of light modulators, wherein said light guide panel is disposed forward of said plurality of light modulators and configured to direct said light out of said light guide panel onto said plurality of light modulators; a processor that is in electrical communication with at least one of said a plurality of light modulators, said processor being configured to process image data; and a memory device in electrical communication with said processor.

35. The apparatus of Claim 34, further comprising: a driver circuit configured to send at least one signal to said at least one of said plurality of light modulators.

36. The apparatus of Claim 35, further comprising: a controller configured to send at least a portion of said image data to said driver circuit.

37. The apparatus of Claim 34, further comprising: an image source module configured to send said image data to said processor.

38. The apparatus of Claim 37, wherein said image source module comprises at least one of a receiver, transceiver, and transmitter.

39. The apparatus of Claim 34, further comprising: an input device configured to receive input data and to communicate said input data to said processor.

40. An illumination apparatus comprising: means for guiding light; means for turning said light guided in said light guiding means and directing said light out of said light guiding means; and means for reducing refractive index mismatch with said light guiding means, said mismatch reducing means disposed on said light guiding means and having at least two of height, width and length that is less than 1 micron, said mismatch reducing means having an effective thickness and effective refractive index so as to reduce reflection of light from said light guiding means.

41. The apparatus of Claim 40, wherein each of said mismatch reducing means and said turning means are disposed on a surface of said light guiding means.

42. The apparatus of Claim 41 , wherein said mismatch reducing means and said turning means are disposed on an overlapping portion of said surface.

43. The apparatus of Claim 41 , wherein said mismatch reducing means and said turning means are disposed on non-overlapping portions of said surface.

44. The apparatus of Claim 40, further comprising means for modulating light to form an image, wherein said light guiding means is disposed forward of said modulating means.

45. The apparatus of Claim 44, wherein said modulating means comprises an array of interferometric modulators.

46. The apparatus of Claim 45, wherein said light guiding means comprises a light guide panel.

47. The apparatus of Claim 46, wherein said light turning means comprises light turning microstructure.

48. The apparatus of Claim 47, wherein said mismatch reducing means comprises a plurality of nanostructure.

49. A method of manufacturing an illumination apparatus, said method comprising: disposing a light guide panel configured to guide light therein, wherein said light guide has (a) turning microstructure thereon configured to direct said light out of said light guide panel, and (b) a plurality of nanostructures disposed thereon, said plurality of nanostructures having an effective thickness and effective refractive index so as to reduce reflection of light from said light guide panel.

50. The method of Claim 49, further comprising disposing said light guide panel forward of a reflective light modulator array.

51. The method of Claim 49, further comprising disposing said nanostructures and said turning microstructure on a surface of said light guide panel.

52. The method of Claim 51 , wherein said nanostructures and said turning microstructure are disposed on an overlapping portion of said surface.

53. The method of Claim 51 , wherein said nanostructures and said turning microstructure are disposed on non-overlapping portions of said surface.

54. An apparatus manufactured by the method of Claim 49.

55. A method of manufacturing, said method comprising: providing a master comprising a crystalline surface, said surface having formed thereon a microstructure on said surface of the master, said microstructure defining a shape, which when replicated on a light guide panel using said master, is configured to direct light out of said light guide panel; and forming a mold based on the master.

56. The method of Claim 55, further comprising: applying said mold to a material so as to form at least part of a light guide panel.

57. The method of Claim 56, further comprising: applying said mold to a material comprises embossing a film with said mold.

58. The method of Claim 55, wherein the mold is adapted to form a front light guide panel.

59. The method of Claim 55, wherein the microstructure covers between 0.1% and 10% of the crystalline surface.

60. The method of Claim 55, wherein a plurality of nanostructures are formed on said surface of said master, said plurality of nanostructures defining a shape, which when replicated on said light guide panel using said master, has an effective thickness and effective refractive index so as to reduce reflection of light from the light guide panel light.

61. The method of Claim 60, wherein said nanostructures and said turning microstructure are formed on an overlapping portion of said surface.

62. The method of Claim 60, wherein said nanostructures and said turning microstructure are formed on non-overlapping portions of said surface.

63. The method of Claim 55, wherein the microstructure comprises a plurality of triangular grooves having substantially triangular cross-sections.

64. The method of Claim 55, wherein forming said microstructure comprises disposing a two-dimensional array of faceted features on said substrate, said faceted features defining a plurality of light turning elements when replicated on said light guide panel, wherein the light turning elements are configured to direct light from said light guide panel.

65. The method of Claim 55, wherein forming said microstructure comprises disposing 'microstructured elements on said substrate, said microstructured elements defining a plurality of light turning elements when replicated on said light guide panel, wherein the light turning elements are configured to direct a non-uniformly varying pattern of light from said light guide panel.

66. The method of Claim 63, wherein said crystalline surface comprises at least one of silicon, germanium, gallium arsenide, gallium nitride, gallium phosphide, and calcite.

67. A method of manufacturing, said method comprising: providing a mold that replicates a microstructure formed on a crystalline surface, said microstructure defining a shape, which when replicated on a light guide panel using said mold, is configured to direct light out of said light guide panel; and applying said mold to a material so as to form at least part of a light guide panel.

68. The method of Claim 67, wherein the mold is adapted to form a front light guide panel.

69. The method of Claim 67, wherein the microstructure covers between 0.1% and 10% of the crystalline surface.

70. An illumination apparatus comprising: a layer of material comprising a surface configured to receive light; and a plurality of nanostructures disposed on said surface, said plurality of nanostructures having an effective thickness and effective refractive index so as to reduce reflection of said light from said surface, said surface comprising: a first section comprising said nanostructures arranged in parallel rows; and a second section comprising said nanostructures arranged in parallel rows, said rows in said first section and said rows in said second section being non-parallel, said first and second sections being adjacent.

71. The apparatus of Claim 70, further comprising a third section comprising said nanostructures arranged in parallel rows, said rows in said third section being non-parallel to said rows in said first and second sections, said third sections being adjacent to at least one of said first and second sections.

72. The apparatus of Claim 70, wherein said layer comprises a film.