HK1103805A - Method and device for manipulating color in a display - Google Patents

Abstract

A method and device for manipulating color in a display includes a display in which one or more of the pixels includes one or more display elements, such as interferometric modulators, configured to output colored light and one or more display elements configured to output white light. Other embodiments include methods of making such displays. In addition, embodiments include color displays configured to provide a greater proportion of the intensity of output light in green portions of the visible spectrum in order to increase perceived brightness of the display.

Description

Method and apparatus for manipulating color in a display

Technical Field

The field of the invention relates to microelectromechanical systems (MEMS).

Background

Microelectromechanical Systems (MEMS) include micromechanical 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 known as 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 in greater detail herein, the position of one plate relative to another can change the optical interference of light incident on the interferometric modulator. These 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.

Disclosure of Invention

The system, method, and devices of the present 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 embodiment comprises a display. The display includes a plurality of pixels. Each of the pixels includes: at least one red subpixel comprising at least one interferometric modulator configured to output red light; at least one green subpixel comprising at least one interferometric modulator configured to output green light; at least one blue subpixel comprising at least one interferometric modulator configured to output blue light; and at least one white subpixel comprising at least one interferometric modulator configured to output colored light.

Another embodiment comprises a display. The display includes a plurality of interferometric modulators. The plurality of interferometric modulators includes: at least one interferometric modulator configured to output red light; at least one interferometric modulator configured to output green light; at least one interferometric modulator configured to output blue light; and at least one interferometric modulator configured to output white light. The at least one interferometric modulator configured to output white light outputs white light having a standardized white point.

Another embodiment comprises a display. The display includes a plurality of display elements. Each of the display elements includes a reflective surface configured to be positioned at a distance from a partially reflective surface. The plurality of display elements includes at least one of the plurality of display elements configured to output colored light and at least one of the plurality of display elements configured to interferometrically output white light.

Another embodiment includes a method of making a display. The method includes forming a plurality of display elements. Each of the plurality of display elements includes a reflective surface configured to be positioned at a distance from a partially reflective surface. Each of the individual distances is selected such that at least one of the plurality of display elements is configured to output colored light and at least another one of the plurality of display elements is configured to interferometrically output white light.

Another embodiment comprises a display comprising means for displaying an image. The display means comprises means for reflecting light and means for partially reflecting light. The reflecting means is configured to be positioned at a distance from the partially reflecting means. The display means includes first means for outputting colored light and second means for interferometrically outputting white light.

Another embodiment comprises a display. The display includes a plurality of pixels, each of which includes red, green, and blue interferometric modulators configured to output red, green, and blue light, respectively. When each of the interferometric modulators is set to output red, green, and blue light, each of the pixels is configured to output green light having a greater intensity than the red light and configured to output green light having a greater intensity than the blue light.

Another embodiment includes a method of making a display. The method includes forming a plurality of pixels. Forming the plurality of pixels includes: forming an interferometric modulator configured to output red light; forming an interferometric modulator configured to output green light; and forming an interferometric modulator configured to output blue light. When each of the interferometric modulators is set to output red, green, and blue light, each of the pixels is configured to output green light having a greater intensity than the red light and configured to output green light having a greater intensity than the blue light.

Another embodiment comprises a display. The display includes a plurality of pixels. Each of the pixels includes red, green, and blue interferometric modulators configured to output red, green, and blue light, respectively. Each of the pixels is configured to output green light having a greater intensity than red light, and is configured to output green light having a greater intensity than blue light. At least one of an interferometric modulator configured to output red light and an interferometric modulator configured to output blue light is configured to output light having a wavelength selected to compensate for the green light having the greater intensity.

Another embodiment includes a display comprising a plurality of means for outputting red light, a plurality of means for outputting green light, and a plurality of means for outputting blue light. The red, green and blue output means form means for displaying image pixels. When the red, green and blue output means are set to output red, green and blue light, each of the pixel display means is configured to output green light having a greater intensity than blue light.

Another embodiment includes a display comprising a plurality of display elements. The plurality of display elements includes at least one color display element configured to output colored light and at least one display element configured to output white light. The at least one display element configured to output white light outputs white light having a standardized white point.

Another embodiment comprises a display comprising means for displaying an image. The display means includes means for outputting colored light and means for outputting white light. The white light output means outputs white light having a standardized white point.

Another embodiment includes a method of making a display comprising forming a plurality of display elements comprising forming at least one color display element configured to output colored light and at least one display element configured to output white light. The at least one display element configured to output white light is configured to output white light having a standardized white point.

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 33 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.

FIG. 5A illustrates one exemplary frame of display data in the 33 interferometric modulator display of FIG. 2.

FIG. 5B illustrates one exemplary timing diagram for row and column signals that may be used to write the frame of FIG. 5A.

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. 8 is a side cross-sectional view of an exemplary interferometric modulator illustrating the spectral characteristics of the output light achieved by positioning the movable mirror within a range of positions.

FIG. 9 is a graph illustrating the spectral response of one embodiment that includes cyan and yellow interferometric modulators for generating white light.

FIG. 10 is a side cross-sectional view of an interferometric modulator illustrating different optical paths through the modulator that result in the reflection of different colors of light.

FIG. 11 is a side cross-sectional view of an interferometric modulator having a layer of material for selectively transmitting light having a particular color.

FIG. 12 is a graph illustrating the spectral response of one embodiment that includes a green interferometric modulator and a "magenta" filter layer for producing white light.

Fig. 13 is a schematic diagram illustrating two pixels of an exemplary pixel array 30. Rows 1-4 and columns 1-4 form a pixel 120 a.

FIG. 14A is a chromaticity diagram illustrating colors that may be produced by an exemplary color display including red, green, and blue display elements.

FIG. 14B is a chromaticity diagram illustrating colors that may be produced by an exemplary color display including red, green, blue, and white display elements.

Detailed Description

The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in many different forms. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be readily 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, displays of camera views (e.g., of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., a display of images for a piece of jewelry). MEMS devices having similar structures to those described herein may also be used in non-display applications such as electronic switching devices.

One embodiment is a display in which each pixel comprises a set of display elements, which may each comprise one or more interferometric modulators. The set of display elements includes display elements configured to output red, green, blue, and white light. In one embodiment, a "white light" display element outputs white light having a broader, higher intensity spectral response than the combined spectral response of "red", "green", and "blue" display elements. In one embodiment, the display includes driver circuitry configured to turn on "white light" display elements upon receiving data for driving pixels. In addition, embodiments include color displays configured to provide a greater proportion of output light intensity in the green portion of the visible spectrum in order to increase the perceived brightness of the display.

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 coherently, depending on the position of the movable reflective layer, producing either a fully 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 12 b. 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 16 b.

The optical stacks 16a and 16b (collectively referred to as optical stack 16), as referenced herein, typically include several fused layers, which may include an electrode layer, such as Indium Tin Oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. Thus, the optical stack 16 is 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 a plurality of 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 (orthogonal to the row electrodes 16a, 16b) of a deposited metal layer(s) 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 defined gaps 19. A highly conductive and reflective material such as aluminum may be used for the reflective layer 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. Behaves the same regardless of the polarity of the applied potential difference. In this manner, 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. 2-5B 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 (e.g., ARM, Pentium)^®、Pentium II^®、Pentium III^®、Pentium IV^®、Pentium^®Pro、8051、MIPS^®、Power PC^®、ALPHA^®) Or any special purpose microprocessor such as a digital signal processor, microcontroller, or 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.

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 display array or panel 30. The cross-section of the array illustrated in FIG. 1 is shown by the lines 1-1 in FIG. 2. For MEMS interferometric modulators, the row/column actuation protocol may take advantage of the hysteresis properties of these devices illustrated in FIG. 3. A potential difference of, for example, 10 volts may be required 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 7V 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 window 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 may 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. In this example, each pixel sees a potential difference within the "stability window" of 3-7 volts after being written. 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, if the applied voltage is fixed, no current flows into the pixel.

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 set of asserted 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 process may be repeated for the entire series of rows in a sequential manner to produce a frame. Typically, 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.

Fig. 4, 5A and 5B illustrate one possible activation protocol for forming display frames on the 3 x 3 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-V_biasAnd the appropriate row is set to + deltav, which may correspond to-5 volts and +5 volts, respectively. Relaxing the pixel is by setting the appropriate column to + V_biasAnd the appropriate row is set to the same + av, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, regardless of whether the column is at + V_biasOr is-V_biasThe pixel is stable in whatever state it was originally in. As also illustrated in figure 4 of the drawings,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_biasAnd the appropriate row is set to- Δ V. In this embodiment, the pixel is released by setting the appropriate column to-V_biasAnd the appropriate row is set to the same-av, producing a zero volt potential difference across the pixel.

FIG. 5B is a timing diagram showing a series of row and column signals applied to the 3 x 3 array of FIG. 2 which will result in the display arrangement illustrated in FIG. 5A, wherein 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.

In the frame of fig. 5A, pixels (1, 1), (1, 2), (2, 2), (3, 2), and (3, 3) are activated. 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, since all 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 activates 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 used for arrays having tens 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.

Fig. 6A and 6B are system block diagrams illustrating an embodiment of a display device 40. The display device 40 may 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.

The display device 40 includes a housing 41, a display 30, an antenna 43, a speaker 44, an input device 48, and a microphone 46. The housing 41 is generally formed from any of a variety of manufacturing processes well known to those skilled in the art, including injection molding and vacuum forming. Additionally, 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 combinations 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.

As described herein, the display 30 of exemplary display device 40 may be any of a variety of displays, including a bi-stable display. 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.

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 may include additional components at least partially enclosed in the housing 41. For example, in one embodiment, the exemplary display device 40 includes a network interface 27, the network interface 27 including an antenna 43 coupled to a transceiver 47. The transceiver 47 is connected to the processor 21, and the processor 21 is connected to the conditioning hardware 52. The conditioning hardware 52 may be configured to condition the signal (e.g., filter the 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. A driver controller 29 is coupled to a frame buffer 28 and to an array driver 22, which array driver 22 is in turn coupled to a display array 30. The power supply 50 provides power to all components as required by the particular exemplary display device 40 design.

The network interface 27 includes the antenna 43 and the transceiver 47 so that the exemplary display device 40 can communicate with one or 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 skilled in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 standard, including IEEE 802.11(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 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.

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.

The 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 generally refers to information that identifies the image characteristics at each location within an image. These image characteristics may include color, saturation, and gray-scale level, for example.

In one embodiment, the processor 21 includes a microcontroller, CPU, or logic unit to control the 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.

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. In particular, 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. The driver controller 29 then sends the formatted information to the array driver 22. Although a driver controller 29, such as an LCD controller, is typically associated with the system processor 21 as a stand-alone Integrated Circuit (IC), these 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.

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.

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, the array driver 22 is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, the 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).

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 data is input to the device using the microphone 46, voice commands may be provided by a user for controlling operation of the exemplary display device 40.

The power supply 50 may include a variety of energy storage devices as are well known in the art. For example, in one embodiment, the 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.

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 skilled in the art will appreciate that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.

The structural details 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. 1, wherein a strip of metallic 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 movable reflective layer 14 is suspended from a deformable layer 34, which may comprise a flexible metal. The deformable layer 34 is directly or indirectly connected to the substrate 20 around the perimeter of the deformable layer 34. These connectors are referred to herein as struts. The embodiment illustrated in FIG. 7D has 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 from a planarization material used to form the support post plugs 42. The embodiment illustrated in FIG. 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 additional layer of metal or other conductive material has been used to form the bus structure 44. This allows signals to be sent along the back of the interferometric modulators, eliminating many of the electrodes that may otherwise have had to be formed on the substrate 20.

In embodiments such as those shown in FIG. 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 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 image quality. This separable modulator structure 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 performed 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.

As discussed above with reference to FIG. 1, modulator 12 (i.e., both modulators 12a and 12 b) includes an optical cavity formed between mirrors 14 (i.e., mirrors 14a and 14b) and 16 (mirrors 16a and 16b, respectively). The characteristic distance or effective optical path length d of the optical cavity determines the resonant wavelength λ of the optical cavity and, therefore, of the interferometric modulator 12. The peak resonant visible wavelength λ of the interferometric modulator 12 generally corresponds to the perceived color of light reflected by the modulator 12. Mathematically, the optical path length d is equal to * N λ, where N is an integer. Thus, a given resonant wavelength λ is reflected by the interferometric modulator 12 having an optical path length d of * λ (N ═ 1), λ (N ═ 2), 3/2 λ (N ═ 3), and so on. The integer N may be referred to as the interference order of the reflected light. As used herein, the level of modulator 12 is also referred to as the level N of light reflected by modulator 12 when mirror 14 is in at least one position. For example, the first stage red interferometric modulator 12 may have an optical path length d of about 325nm, which corresponds to a wavelength λ of about 650 nm. Thus, the second stage red interferometric modulator 12 may have an optical path length d of about 650 nm. Typically, higher order modulators 12 reflect light in a narrower wavelength range (e.g., have a higher "Q" value), and thus produce more saturated colored light. The saturation of modulator 12, including the color pixels, affects the properties of the display (e.g., the color gamut and white point of the display). For example, in order to have a display using second level modulator 12 with the same white point or color balance as a display including the same general color of reflected light, second level modulator 12 may be selected to have a different central peak optical wavelength.

FIG. 8 is a side cross-sectional view of an exemplary interferometric modulator 12 illustrating the spectral characteristics of light that would be output by positioning the movable mirror 14 at a series of positions 61-65. The exemplary modulator includes an Indium Tin Oxide (ITO) conductive layer 52 that serves as a column electrode. In an exemplary modulator, the movable mirror 14 includes a row conductor.

Each of the positions 61-65 of a particular group of the movable mirror 14 is shown by an arrow extending from the fixed mirror 16. The tip of each arrow indicates a particular one of the positions 61-65 of the movable mirror. The color of the light reflected from the interferometric modulator is determined by the optical path length d between the movable mirror 14 and the fixed mirror 16. The distances 61-65 are selected to calculate the thickness and refractive index of the dielectric layer 54 in the optical path length d. Thus, a movable mirror 14 positioned at a different one of positions 61-65 (each corresponding to a different distance d) results in light being output to modulator 12 at viewing position 51 with different spectral responses corresponding to different colors of incident light being reflected by modulator 12. Further, at position 61, the movable mirror 14 is sufficiently close to the fixed mirror 16 that the interference effects can be neglected, and the modulator 12 acts as a mirror that reflects substantially all colors of incident visible light substantially equally, e.g., as white light. The broadband mirror effect is caused because the small distance d is too small for optical resonance in the visible band. The mirror 14 thus acts merely as a reflective surface with respect to visible light.

With mirror 14 positioned at location 62, modulator 12 exhibits a gray shade because the increased gap distance between mirrors 14 and 16 reduces the reflectivity of mirror 14. At position 63, the distance d is such that the cavity operates interferometrically but does not substantially reflect any visible wavelengths of light because the resonant wavelength is outside the visible range.

As the distance d is further increased, the peak spectral response of the modulator 12 shifts into the visible wavelengths. Thus, when the movable mirror 14 is at position 64, the modulator 12 reflects blue light. When the movable mirror 14 is at position 65, the modulator 12 reflects green light. When the movable mirror 14 is in the non-deflected position 66, the modulator 12 reflects red light.

In designing displays using interferometric modulators 12, the modulators 12 may be formed in order to increase the color saturation of the reflected light. Saturation refers to the hue intensity of colored light. Highly saturated hues have lively intense colors, while less saturated hues appear softer and gray. For example, lasers that produce a very narrow range of wavelengths produce highly saturated light. In contrast, a typical incandescent light bulb produces white light that may have an unsaturated red or blue color. In one embodiment, modulator 12 is formed to have a distance d corresponding to a higher order interference (e.g., a second order or a third order) to increase the saturation of the reflected colored light.

An exemplary color display includes red, green, and blue display elements. Other colors are produced in such displays by varying the relative intensities of the light produced by the red, green and blue elements. Such a mixture of primary colors, e.g. red, green and blue, is perceived by the human eye as other colors. The relative values of red, green and blue in such a color system may be referred to as tristimulus values with respect to the excitation of the red, green and blue light sensitive portions of the human eye. In general, the more saturated the primary colors, the greater the range of colors that can be produced by the display. In other embodiments, the display may include a modulator 12 having sets of colors that define other color systems in terms of sets of primary colors other than red, green, and blue.

Another consideration in designing displays incorporating interferometric modulators 12 is the generation of white light. "white" light generally refers to light that is perceived by the human eye as not containing any particular color, i.e., white light is not associated with hue. Black refers to the lack of color (or light), while white refers to light that encompasses a broad spectral range such that a particular color is not perceived. White light may refer to light having a broad spectral range of visible light that is approximately uniform in intensity. However, because the human eye is sensitive to certain wavelengths of red, green, and blue light, white can be produced by mixing the intensities of colored light to produce light having one or more spectral peaks that are perceived by the eye as "white". The color gamut of a display is the range of colors that a device can reproduce, for example, by mixing red, green, and blue light.

In reflective displays, the white light generated using a saturated interferometric modulator tends to have a relatively low intensity to an observer because only a small range of incident wavelengths are reflected at a relatively high intensity to create white light. In contrast, mirrors that reflect broadband white light (e.g., substantially all incident wavelengths) have greater intensity because a greater range of incident wavelengths is reflected. Therefore, designing reflective displays by producing white light using a combination of primary colors typically results in a tradeoff between color saturation and color gamut and the brightness of the white light output by the display.

In one embodiment, the movable mirror 14 is positioned such that in the first position the modulator 12 does not reflect visible light (e.g., position 63 of FIG. 8) and in the second position the distance between the movable mirror 14 and the fixed mirror 16 is too small for interferometric modulation of incident visible light such that the mirror 14 reflects a broadband white color (e.g., position 61 of FIG. 8). In such embodiments, the movable mirror 14 reflects incident light with a broad and relatively uniform spectral response across the visible spectrum. If the incident light comprises white light, the light reflected by modulator 12 in the second position may be substantially similar white light. The spectral response of this "white" reflective state of modulator 12 may be substantially uniform across the visible spectrum. In one embodiment, the spectral response is tuned by selecting the material of the modulator. For example, different materials, such as aluminum or copper, may be used as the reflective surface of the movable mirror 14 in order to tune the spectral response of the modulator 12 when in the white reflective state. In another embodiment, a filter may be used to selectively absorb certain wavelengths of reflected or incident light to achieve the output of such a broadband white modulator.

In one embodiment of pixel array 30, each pixel includes one or more color modulators 12 (e.g., modulators configured to reflect red, green, and blue light) and one or more "white" modulators 12 configured to reflect white light. In this embodiment, light from the red, green, and/or blue modulators 12 in the reflective state combines to output colored light. The light from the white modulator 12 may be used to output white or gray light. Using white in combination with color can increase the brightness or intensity of the pixel.

The white point of a display is a hue that is considered generally neutral (gray or colorless). The white point of a display device can be characterized based on comparing the spectral content of the white light produced by the device to the light emitted by the black body at a particular temperature ("black body radiation"). A black body radiator is an idealized object that absorbs all light incident on the object and that re-emits it with a spectrum that depends on the black body temperature. For example, the black body spectrum at 6,500 ° K may be referred to as white light having a color temperature of 6,500 ° K. This color temperature or white point of approximately 5,000-10,000K is generally considered to be consistent with daylight.

The international association for illumination (CIE) publishes standardized white points for light sources. For example, light source reference "d" refers to daylight. In particular, the normalized white point D correlated with color temperatures of 5,500K, 6,500K, and 7,500K₅₅、D₆₅And D₇₅Is the normalized daylight white point.

Display devices may be characterized by a white point of white light produced by the display. As with light from other light sources, the human perception of the display is determined, at least in part, by the perception of white light from the display. For example, a display or light source having a lower white point (e.g., D55) may be perceived by a viewer as having a yellow hue. A display with a higher temperature white point (e.g., D75) may be perceived by a user as having a "cooler" or bluer tint. Users typically respond more satisfactorily to displays with higher temperature white points. Thus, controlling the white point of the display desirably provides some control over the viewer's response to the display. Embodiments of the interferometric modulator array 30 may be configured to generate white light, with the white point selected to meet the standardized white point for one or more desired lighting conditions.

White light may be generated by the pixel array 30 by including one or more interferometric modulators 12 for each pixel. For example, in one embodiment, the pixel array 30 includes pixels of groups of red, green, and blue interferometric modulators 12. As discussed above, the color of the interferometric modulator 12 may be selected by selecting the optical path length d using the relationship d- * Nλ. In addition, the balance or relative proportion of the colors produced by each pixel in the pixel array 30 may be further affected by the relative reflective area of each of the interferometric modulators 12 (e.g., the red, green, and blue interferometric modulators 12). Furthermore, because the modulator 12 selectively reflects incident light, the white point of the reflected light from the pixel array 30 of the interferometric modulator 12 generally depends on the spectral characteristics of the incident light. In one embodiment, the white point of the reflected light may be configured to be different from the white point of the incident light. For example, in one embodiment, the pixel array 30 may be configured to reflect D75 light when used in D65 sunlight.

In one embodiment, the distance d and area of the interferometric modulators 12 in the pixel array 30 are selected such that the white light produced by the pixel array 30 corresponds to a particular standardized white point under expected lighting conditions (e.g., in sunlight, in fluorescence, or from front light positioned to illuminate the pixel array 30). For example, under certain lighting conditions, the white point of the pixel array 30 may be selected to be D₅₅、D₆₅Or D₇₅. Further, the light reflected by the pixel array 30 may have a different white point than the light of the intended or configured light source. For example, a particular pixel array 30 may be configured to reflect D75 light when viewed in D65 sunlight. More generally, the white point of the display may be selected with reference to an illumination source (e.g., front light) configured with the display or with reference to a particular viewing condition. For example, the display may be configured to have a selected white point (e.g., D55, D65, or D75) when viewed under an expected or typical illumination source such as incandescent, fluorescent, or natural light sources. More particularly, a display used, for example, in a handheld device may be configured to have a selected white point when viewed in sunlight conditions. Or, displays for use in office environmentsCan be configured to have a selected white point (e.g., D75) when illuminated by typical office fluorescent light. In various embodiments, different distances d and regions of modulator 12 may be selected to generate other standardized white point settings for different viewing environments. Furthermore, the red, green and blue modulators 12 may also be controlled so as to be in the reflective or non-reflective state for different amounts of time so as to further change the relative balance of the reflected red, green and blue light, and thus the white point of the reflected light. In one embodiment, the ratio of the reflective areas of each of color modulators 12 may be selected in order to control the white point in different viewing environments. In one embodiment, the optical path length d may be selected so as to correspond to a common multiple of more than one visible resonant wavelength (e.g., the first, second, or third order peaks of red, green, and blue) such that the interferometric modulator 12 reflects white light characterized by three visible peaks in the spectral response. In this embodiment, the optical path length d may be selected such that the white light produced corresponds to a standardized white point.

In addition to the groups of red, green, and blue interferometric modulators 12 in the pixel array 30, other embodiments include other ways of generating white light. For example, one embodiment of the pixel array 30 includes cyan and yellow interferometric modulators 12 (e.g., interferometric modulators 12 having individual separation distances d) in order to generate cyan and yellow light. The combined spectral response of the cyan and yellow interferometric modulators 12 produces light with a broad spectral response that is perceived as "white". The cyan and yellow modulators are positioned in close proximity such that the combined response is perceived by an observer. For example, in one embodiment, the cyan and yellow modulators are arranged in adjacent rows of the pixel array 30. In another embodiment, the cyan and yellow modulators are arranged in adjacent columns of the pixel array 30.

FIG. 9 is a graph illustrating the spectral response of one embodiment that includes cyan and yellow interferometric modulators 12 for generating white light. The horizontal axis represents the wavelength of the reflected light. The vertical axis represents the relative reflectivity of light incident on modulator 12. Trace 80 illustrates the response of the cyan modulator, which is a single peak centered in the cyan portion of the spectrum (e.g., between blue and green). Trace 82 illustrates the response of the yellow modulator, which is a single peak centered in the yellow portion of the spectrum (e.g., between red and green). Trace 84 illustrates the combined spectral response of a pair of cyan and yellow modulators 12. The trace 84 has two peaks at the cyan and yellow wavelengths, but is sufficiently uniform across the visible spectrum that the reflected light from these modulators 12 is perceived as white.

In general, the color of light reflected by the interferometric modulator 12 shifts when the modulator 12 is viewed from different angles. FIG. 10 is a side cross-sectional view of the interferometric modulator 12 illustrating different optical paths through the modulator 12. The color of light reflected from the interferometric modulator 12 may vary for different angles of incidence (and reflection) about an axis AA as illustrated in FIG. 10. For example, for the interferometric modulator 12 of FIG. 10, when the light follows the off-axis path A₁While traveling, light is incident on the interferometric modulator at a first angle, reflects from the interferometric modulator, and travels to an observer. Due to optical interference between a pair of mirrors in the interferometric modulator 12, when light reaches the viewer, the viewer perceives the first color. As the viewer moves or changes his/her position and thus viewing angle, the light received by the viewer follows a different off-axis path A corresponding to a second, different incident (and reflected) angle₂And (4) advancing. The optical interference in the interferometric modulator 12 depends on the optical path length d of the light propagating within the modulator. Different optical paths A₁And A₂Thus producing different outputs of the interferometric modulator 12. With increasing viewing angle, the effective optical path of the interferometric modulator decreases according to the relationship 2dcos β ═ N λ, where β is the viewing angle (the angle between the normal to the display and the incident light). With an increase in viewing angle, the peak resonant wavelength of the reflected light decreases. The user perceives different colors depending on his or her viewing angle. As described above, this phenomenon is referred to as "color shift". Generally with reference to interference when viewed along axis AAThe color shift is identified by the color produced by the modulator 12.

In one embodiment, the pixel array 30 includes a first level yellow interferometric modulator and a second level cyan interferometric modulator. When this pixel array 30 is viewed from progressively larger off-axis angles, the light reflected by the first level yellow modulator is shifted toward the blue end of the spectrum, e.g., a modulator at an angle having an effective d equal to that of the first level cyan modulator. At the same time, the light reflected by the second level cyan modulator is shifted to correspond to the light from the first level yellow modulator. Thus, even when the relative peaks of the spectra are shifted, the overall combined spectral response is broad and relatively uniform across the visible spectrum. This pixel array 30 thus produces white light over a relatively large range of viewing angles.

In one embodiment, a display having cyan and yellow modulators may be configured to produce white light having a selected standardized white point under one or more viewing conditions. For example, the spectral responses of the cyan and yellow modulators may be selected such that, under selected lighting conditions including D55, D65, or D75 light (e.g., sunlight) for displays suitable for outdoor use, the reflected light has a white point of D55, D65, D75, or any other suitable white point. In one embodiment, the modulator may be configured to reflect light having a different white point than incident light from an expected or selected viewing condition.

FIG. 11 is a side cross-sectional view of an interferometric modulator 12 having a layer of material 102 for selectively transmitting light having a particular color. In the exemplary embodiment, layer 102 is on the opposite side of substrate 20 from modulator 12. In one embodiment, the layer of material 102 comprises a magenta filter through which the green interferometric modulator 12 is viewed. In one embodiment, the material layer 102 is a dyed material. In one such embodiment, the material is a dyed photoresist material. In one embodiment, the green interferometric modulator 12 is a first stage green interferometric modulator. Filter layer 102 is configured to transmit magenta light when illuminated with a wide range of uniform white light. In the exemplary embodiment, light is incident on layer 20 and the filtered light is transmitted from layer 20 to modulator 12. The modulator 12 reflects the filtered light back through the layer 102. In such embodiments, light passes through layer 102 twice. In such embodiments, the thickness of the material layer 102 may be selected to compensate for and take advantage of this double filtering. In another embodiment, a front light structure may be positioned between layer 102 and modulator 12. In such embodiments, the layer of material 102 only acts on light reflected by the modulator 12. In such embodiments, the layer 102 is selected accordingly.

FIG. 12 is a graph illustrating the spectral response of one embodiment that includes a green interferometric modulator 12 and a "magenta" filter layer 102. The horizontal axis represents the wavelength of the reflected light. The vertical axis represents the relative spectral response of light incident on green modulator 12 and filter layer 102 across the visible spectrum. Trace 110 illustrates the response of the green modulator 12, which is a single peak centered (e.g., near the center of the visible spectrum) in the green portion of the spectrum. Trace 112 illustrates the response of the magenta filter formed by the material layer 102. The trace 112 has two relatively flat portions on either side of a central u-shaped minimum. Trace 112 thus represents the response of a magenta filter that selectively transmits substantially all red and blue light while filtering out light in the green portion of the spectrum. Trace 114 illustrates the combined spectral response of the green modulator 12 paired with the filter layer 102. Trace 114 illustrates that the combined spectral response is at a lower reflectance level than the green modulator 12 due to the filtering of light by the filter layer 102. However, the spectral response is relatively uniform over the entire visible spectrum, so that the filtered reflected light from the green modulator 12 and the magenta filter layer 102 is perceived as white.

In one embodiment, a display having a green modulator 12 and a magenta filter layer 102 may be configured to produce white light having a selected standardized white point under one or more viewing conditions. For example, the spectral responses of the green modulator 12 and the magenta filter layer 102 may be selected such that, under selected lighting conditions including D55, D65, or D75 light (e.g., sunlight) for a display suitable for outdoor use, the reflected light has a white point of D55, D65, D75, or any other suitable white point. In one embodiment, modulator 12 and filter layer 102 may be configured to reflect light having a different white point than incident light from expected or selected viewing conditions.

Fig. 13 is a schematic diagram illustrating two pixels of an exemplary pixel array 30. Rows 1-4 and columns 1-4 form a pixel 120 a. Rows 5-8 and columns 1-4 form a second pixel 120 b. Each pixel 120a and 120b includes at least one modulator 12 configured to reflect red (column 1), green (column 2), blue (column 3), and white (column 4) light. Each pixel of exemplary pixel array 30 includes 4 display elements for each of red, green, blue, and white to form each color display "4-bit", which can output 2 for each of red, green, blue, or white/gray⁴16 shades (2 in total color)¹⁶One shadow).

FIG. 14A is a chromaticity diagram illustrating colors that may be produced by an exemplary color display including red, green, and blue display elements. A wide range of colors is produced in this display by varying the relative intensities of the light produced by the red, green and blue elements. The chromaticity diagram illustrates how the display can be controlled to produce a mixture of primary colors, e.g., red, green and blue, that are perceived by the human eye as other colors. The horizontal and vertical axes of fig. 14 define a chromaticity coordinate system on which color values may be depicted. In particular, point 130 illustrates the color of light reflected by the exemplary red, green, and blue interferometric modulators. The triangular trace 133 encloses a region 134, which region 134 corresponds to a range of colors that can be produced by the light produced at the mixing point 120. This color range may be referred to as the color gamut of the display. In operation, each of the red, green, and blue display elements in a pixel can be controlled to produce a different mix of red, green, and blue light that combine to form each color within a color gamut.

As illustrated in FIG. 13, in one embodiment, the exemplary display 30 includes pixels having red, green, blue, and white subpixels. One embodiment of a scheme for driving such displays defines each color to be displayed by the pixel in terms of a combination of (i) red, green, and white, (ii) red, blue, and white, and (iii) blue, green, and white chromaticity values that define three different color gamuts. In operation of such embodiments, when the display controller determines that a particular pixel is to be set to a color value expressed in terms of red, green, and blue, the display controller translates the color value into a value expressed in terms of one of (i) red, green, and white, (ii) red, blue, and white, and (iii) blue, green, and white.

Fig. 14B is a chromaticity diagram illustrating the colors that may be produced by such a color display. The overall color gamut of the display is defined by the area defined by traces 140, which traces 140 connect each of the points 130 corresponding to the chromaticity of the display primaries red, green, and blue. In addition, the point 130a corresponds to the chromaticity of light emitted by the white subpixel. This point 130a may be in other positions depending on the white color produced by the white subpixel. Traces 144a, 144b and 144c connect the dot 130a corresponding to the white sub-pixel to each of the dots 130 corresponding to the red, blue and green colors, respectively. Traces 144a, 144b, and 144c, along with trace 140, define three regions 146a, 146b, and 146c within the color gamut of the display that correspond to colors that may be produced by (i) red, green, and white, (ii) red, blue, and white, and (iii) blue, green, and white display elements, respectively. Conceptually, therefore, one embodiment of a driving scheme for such displays includes identifying within which of the three regions 146a, 146b, or 146c the desired color to be displayed falls. The input colors, represented as red, green, and blue values, may then be converted to new chromaticities. This chromaticity coordinate will fall within one of the three identification regions 146a, 146b or 146 c. The new output value is then used to drive each of the three identified display elements ((i) red, green and white, (ii) red, blue and white, or (iii) blue, green and white display elements) of the pixel that bound the area into which the desired chromaticity coordinates fall to output the desired color of light.

In one embodiment, when the chromaticity value is within a selected distance of point 130a of the white display element (e.g., on the chromaticity diagram), both the color and white display elements are actuated in order to produce brighter output from the pixel for these colors.

In another embodiment, to drive such an array of pixels, the driver circuit sets the white modulators in the columns 4 to the respective reflective states when the overall hue of the pixel data is below a threshold value, e.g., the pixel data is gray or substantially gray. In one embodiment, the red, green and blue modulators may also be in their reflective states. When the overall tone of the pixel data is above a threshold, e.g., the pixel data is not substantially gray, the driver circuit sets the white modulators in column 4 to their non-reflective states and sets the color modulators in columns 1-3 to their reflective states.

In some embodiments, a white display element may be actuated in conjunction with a color display element to add additional brightness. For example, if a pixel is to output red light, all red display elements in the pixel may be actuated. In addition, one or more of the white display elements may also be actuated to produce other color combinations.

In certain embodiments, the driver circuit may adjust the input data to compensate for the additional white surface area so that such a display produces an image with a color balance that is not substantially altered by the white reflective area (despite the enhancement of the relative brightness of the display).

In one embodiment, the white interferometric modulators are grouped with other white interferometric modulators in additional columns, such as illustrated in FIG. 13. In another embodiment, the white interferometric modulators are uniformly distributed throughout the pixel, e.g., interleaved between the red, green, and blue display elements. Further, in some embodiments, the number of white display elements in each pixel is different from the number of red, green, or blue display elements, for example.

In addition to using additional interferometric modulators configured to reflect white light to increase the intensity of the reflected white light, embodiments of pixel array 30 may be formed that increase the overall apparent brightness of the system by other means. For example, the human eye is more sensitive to green light than to other hues. Thus, in one embodiment, the apparent brightness of the interferometric modulator system is increased by using an additional green interferometric modulator in each pixel. For example, in some embodiments, there are an equal number of green, red, and blue interferometric modulators per pixel. In one embodiment, a second column of green interferometric modulators may also be included, similar to that illustrated in FIG. 13. In another embodiment, pixel array 30 may include column 4 (such as illustrated in FIG. 13) in which some display elements reflect white light and some reflect green light.

In one embodiment, the additional green interferometric modulators may be grouped with other green interferometric modulators in additional columns, such as illustrated in FIG. 13. In other embodiments, the additional green interferometric modulators may be uniformly distributed throughout the pixel, such as interleaved between the red, green, and blue display elements. Furthermore, in some embodiments, the number of additional green display elements in each pixel may be different from the number of red, green, or blue display elements, for example.

In one embodiment, the display element is an interferometric modulator in which the optical path lengths d of the red and blue modulators are selected to compensate for additional green pixels in the color balance of the display. Furthermore, in one embodiment, the optical path length d of one or both of the red and blue display elements may be selected to produce a more saturated color. In one such embodiment, the optical path length d of the red or blue display elements may be selected to produce reflected light of a higher order (2 nd order or greater). The second stage corresponds to an optical path length d equal to 1 x λ. Because interferometric modulators with more saturated responses reflect a smaller portion of incoming light, such modulators tend to have less intense (darker) outputs. However, by increasing the relative intensity of the reflected green light, such displays can be configured to have a brighter appearance to an observer. In one embodiment, the ratio of red to blue regions is one-to-one, while the ratio of green to red (or blue) regions is greater than one-to-one. For example, in one embodiment, 33-50% of the pixels are green, expressed as a percentage of the total reflective area of each pixel. In one embodiment, 38-44% of the pixels are green.

In one embodiment, the ratio of the surface area of the green interferometric modulator to the total reflective surface area of the pixel may be greater than the ratio of the surface areas of the red and blue interferometric modulators in order to increase the perceived brightness. In another embodiment, the green color is increased by increasing the duration that the green interferometric modulator is in the reflective state relative to the duration that the other color producing interferometric modulator is in the reflective state. In one embodiment, blue and red interferometric modulators are tuned toward the green spectrum to increase the green appearance, and thus the perceived brightness in the system. As will be appreciated by those skilled in the art, the driver circuitry can adjust the input data to compensate for the additional green surface area so that such displays produce images whose color balance is not substantially altered by the additional green reflective area (despite the enhancement of the relative brightness of the display). In one embodiment, an additional green display element is used in display modes where brightness is more important than color accuracy (e.g., text display).

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 understood, 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 (83)

1. A display, comprising:

a plurality of pixels, each of the pixels comprising:

at least one red subpixel comprising at least one interferometric modulator configured to output red light;

at least one green subpixel comprising at least one interferometric modulator configured to output green light;

at least one blue subpixel comprising at least one interferometric modulator configured to output blue light; and at least one white subpixel comprising at least one interferometric modulator configured to output colored light.

2. The display of claim 1, wherein said display is configured to output white light having a standardized white point.

3. The display of claim 2, wherein the standardized white point is one of D55, D65, or D75.

4. The display of claim 1, wherein the at least one interferometric modulator configured to output colored light comprises at least one interferometric modulator configured to output cyan light and at least one interferometric modulator configured to output yellow light, wherein the cyan light and the yellow light combine to produce the white light.

5. The display of claim 1, further comprising:

at least one filter associated with the at least one interferometric modulator configured to output colored light, the at least one filter configured to selectively transmit visible wavelengths associated with magenta light and substantially filter out other visible wavelengths when illuminated with white light; and is

Wherein the at least one interferometric modulator configured to output colored light comprises at least one interferometric modulator configured to selectively reflect green light incident thereon.

6. The display of claim 5, wherein the filter comprises an absorptive filter.

7. A display, comprising:

a plurality of interferometric modulators, the plurality of interferometric modulators comprising:

at least one interferometric modulator configured to output red light;

at least one interferometric modulator configured to output green light;

at least one interferometric modulator configured to output blue light; and

at least one interferometric modulator configured to output white light,

wherein the at least one interferometric modulator configured to output white light outputs white light having a normalized white point.

8. The display of claim 7, wherein said at least one interferometric modulator configured to output red light, said at least one interferometric modulator configured to output green light, said at least one interferometric modulator configured to output blue light, are configured to output light that combines to produce white light having a second normalized white point.

9. The display of claim 8, wherein the normalized white point of the at least one interferometric modulator configured to output white light substantially matches the second normalized white point.

10. The display of claim 7, wherein the standardized white point is one of D55, D65, or D75.

11. The display of claim 7, further comprising an illumination source for said plurality of interferometric modulators, said illumination source having a different white point than said generated white light having said standardized white point.

12. The display of claim 7, wherein the at least one interferometric modulator configured to output white light comprises at least one interferometric modulator configured to output cyan light and at least one interferometric modulator configured to output yellow light, wherein the cyan light and the yellow light combine to produce the white light.

13. The display of claim 7, wherein said at least one interferometric modulator configured to output white light comprises a broadband reflector.

14. A display, comprising:

a plurality of display elements each comprising a reflective surface configured to be positioned at a distance from a portion of the reflective surface, the plurality of display elements comprising at least one of the plurality of display elements configured to output colored light and at least one of the plurality of display elements configured to interferometrically output white light.

15. The display of claim 14, wherein said white light is characterized by a standardized white point.

16. The display of claim 15, wherein the standardized white point is one of D55, D65, or D75.

17. The display of claim 14, further comprising an illumination source for said plurality of display elements.

18. The display of claim 17, wherein said illumination source has a different white point than said light reflected by said display.

19. The display of claim 14, wherein the plurality of display elements comprises at least one display element configured to output red light, at least one display element configured to output green light, and at least one display element configured to output blue light.

20. The display of claim 14, further comprising at least one filter associated with at least one of the plurality of display elements and configured to selectively transmit certain visible wavelengths and substantially filter other visible wavelengths when illuminated with white light.

21. The display of claim 14, wherein the at least one of the plurality of display elements configured to output white light comprises at least one interferometric modulator configured to output cyan light and at least one interferometric modulator configured to output yellow light.

22. The display of claim 14, wherein the plurality of display elements comprises a plurality of interferometric modulators.

23. The display of claim 14, further comprising:

a processor in electrical communication with the plurality of display elements, the processor configured to process image data;

a memory device in electrical communication with the processor.

24. The display of claim 23, further comprising:

a driver circuit configured to send at least one signal to the plurality of display elements.

25. The display of claim 24, further comprising:

a controller configured to send at least a portion of the image data to the driver circuit.

26. The display of claim 23, further comprising:

an image source module configured to send the image data to the processor.

27. The display of claim 26, wherein said image source module comprises at least one of a receiver, a transceiver, and a transmitter.

28. The display of claim 23, further comprising:

an input device configured to receive input data and to communicate the input data to the processor.

29. A method of making a display, comprising:

forming a plurality of display elements, each of the plurality of display elements comprising a reflective surface configured to be positioned at a distance from a partially reflective surface,

wherein each of the individual distances is selected such that at least one of the plurality of display elements is configured to output colored light and at least another one of the plurality of display elements is configured to interferometrically output white light.

30. The method of claim 29, wherein the individual distances are selected such that the white light is characterized by a standardized white point.

31. The method of claim 30, wherein the individual distances are selected such that light reflected by the display has a different white point than light illuminating the display.

32. The method of claim 30, wherein the individual distances are selected such that the white point is one of D55, D65, or D75.

33. The method of claim 29, wherein forming at least one of the plurality of display elements configured to output colored light comprises forming at least one display element configured to output red light, at least one display element configured to output green light, and at least one display element configured to output blue light.

34. A display fabricated by the method of any one of claims 29-33.

35. A display, comprising:

means for displaying an image, the displaying means comprising means for reflecting light and means for partially reflecting light, the reflecting means configured to be positioned at a distance from the partially reflecting means, the displaying means comprising first means for outputting colored light and second means for interferometrically outputting white light.

36. The display of claim 35, wherein said displaying means comprises a plurality of display elements, and said reflecting means and partially reflecting means comprise a reflecting surface and a partially reflecting surface, said reflecting surface configured to be positioned at a distance from said partially reflecting surface.

37. The display of claim 35 or 36, further comprising means for selectively transmitting certain visible wavelengths and substantially filtering other visible wavelengths.

38. The display of claim 38, wherein the selectively transmitting means comprises a filter.

39. The display of claim 35, 36, 37 or 38, wherein said white light outputting means comprises means for outputting white light having a standardized white point.

40. The display of claim 39, wherein said standardized white point is one of D55, D65, or D75.

41. The display of claim 35, 36, 37, 38, 39, or 40, further comprising means for illuminating with a different white point than the white light produced by the first and second light outputting means.

42. The display of claim 41, wherein the illumination means comprises an illumination source.

43. A display, comprising:

a plurality of pixels, each comprising red, green, and blue interferometric modulators configured to output red, green, and blue light, respectively,

wherein when each of the interferometric modulators is set to output red, green, and blue light, each of the pixels is configured to output green light having a greater intensity than the red light and configured to output green light having a greater intensity than the blue light.

44. The display of claim 43, wherein each of the interferometric modulators of each of the plurality of pixels has a reflective area, and wherein the green interferometric modulator of each pixel has an overall larger reflective area than the red interferometric modulator of each pixel and than the blue interferometric modulator of each pixel.

45. The display of claim 43, wherein each of the plurality of pixels comprises more interferometric modulators configured to output green light than interferometric modulators configured to output blue light.

46. The display of claim 43, wherein each of the plurality of pixels comprises more interferometric modulators configured to output green light than interferometric modulators configured to output red light.

47. The display of claim 43, wherein said interferometric modulator configured to output red light is configured to output red light having a wavelength selected to compensate for said greater intensity of green light.

48. The display of claim 43, wherein said interferometric modulator configured to output red light is characterized by an optical path length, and wherein said optical path length of said interferometric modulator configured to output red light is substantially equal to about one wavelength λ associated with red light to produce a second order red reflection.

49. The display of claim 43, wherein said interferometric modulator configured to output blue light is configured to output blue light having a wavelength selected to compensate for said greater intensity of green light.

50. The display of claim 43, wherein said interferometric modulator configured to output blue light is characterized by an optical path length, and wherein said optical path length of said interferometric modulator configured to output blue light is substantially equal to about one wavelength λ associated with blue light to produce a second order blue reflection.

51. The display of claim 43, further comprising:

a processor in electrical communication with the plurality of pixels, the processor configured to process image data;

a memory device in electrical communication with the processor.

52. The display of claim 51, further comprising:

a driver circuit configured to send at least one signal to the display.

53. The display of claim 52, further comprising:

a controller configured to send at least a portion of the image data to the driver circuit.

54. The display of claim 51, further comprising:

an image source module configured to send the image data to the processor.

55. The display of claim 54, wherein said image source module comprises at least one of a receiver, a transceiver, and a transmitter.

56. The display of claim 51, further comprising:

an input device configured to receive input data and to communicate the input data to the processor.

57. A method of making a display, comprising:

forming a plurality of pixels, wherein forming the plurality of pixels comprises:

forming an interferometric modulator configured to output red light;

forming an interferometric modulator configured to output green light;

forming an interferometric modulator configured to output blue light,

wherein when each of the interferometric modulators is set to output red, green, and blue light, each of the pixels is configured to output green light having a greater intensity than the red light and configured to output green light having a greater intensity than the blue light.

58. The method of claim 57, wherein each of the interferometric modulators of each of the plurality of pixels has a reflective area, and wherein the green interferometric modulator of each pixel has a total reflective area greater than the red interferometric modulator of each pixel and greater than the blue interferometric modulator of each pixel.

59. The method of claim 57, wherein each of the plurality of pixels comprises more interferometric modulators configured to output green light than interferometric modulators configured to output blue light.

60. The method of claim 57, wherein each of the plurality of pixels comprises more interferometric modulators configured to output green light than interferometric modulators configured to output red light.

61. The method of claim 57, wherein forming the interferometric modulator configured to output red light comprises forming the interferometric modulator to output red light having a wavelength selected to compensate for the greater intensity of green light.

62. The method of claim 57, wherein forming the interferometric modulator configured to output blue light comprises forming the interferometric modulator to output blue light having a wavelength selected to compensate for the greater intensity of green light.

63. A display, comprising:

a plurality of pixels, each comprising red, green, and blue interferometric modulators configured to output red, green, and blue light, respectively,

wherein each of the pixels is configured to output green light having a greater intensity than red light and is configured to output green light having a greater intensity than blue light, and

wherein at least one of the interferometric modulator configured to output red light and the interferometric modulator configured to output blue light is configured to output light having a wavelength selected to compensate for the greater intensity of green light.

64. The display of claim 63, further comprising a circuit configured to drive each of said red, green and blue interferometric modulators for individual periods of time, and wherein said period of time associated with said green interferometric modulator is greater than said individual periods of time associated with said red and blue interferometric modulators.

65. The display of claim 63, wherein said wavelength is selected to be substantially equal to about one wavelength λ associated with red light to produce a second order red reflection.

66. The display of claim 63, wherein said wavelength is selected to be substantially equal to about one wavelength λ associated with blue light to produce a second order blue reflection.

67. A display, comprising:

a plurality of means for outputting red;

a plurality of means for outputting green light; and

a plurality of means for outputting blue light, said red, green and blue output means forming means for displaying an image pixel;

wherein each of the pixel display means is configured to output green light having a greater intensity than blue light when the red, green and blue output means are set to output red, green and blue light.

68. The display of claim 67, wherein said pixel display means comprises a pixel.

69. The display of claim 68, wherein said red, green and blue output means comprise red, green and blue interferometric modulators configured to output red, green and blue light, respectively.

70. The display of claim 69, wherein an overall reflective area of the green interferometric modulator of each pixel is greater than an overall reflective area of the red interferometric modulator of each pixel, and an overall reflective area of the green interferometric modulator of each pixel is greater than an overall reflective area of the blue interferometric modulator of each pixel.

71. A display, comprising:

a plurality of display elements including at least one color display element configured to output colored light and at least one display element configured to output white light, wherein the at least one display element configured to output white light outputs white light having a standardized white point.

72. The display of claim 71, wherein said at least one display element comprises red, green, and blue display elements configured to output red, green, and blue light, respectively.

73. The display of claim 70 or 71, wherein the plurality of display elements comprises a plurality of interferometric modulators.

74. A display, comprising:

means for displaying an image, said display means comprising means for outputting colored light and means for outputting white light, wherein said white light outputting means outputs white light having a standardized white point.

75. A display as claimed in claim 74, in which the display means comprises a plurality of display elements.

76. The display of claim 75, wherein said plurality of display elements comprises a plurality of interferometric modulators.

77. The display of claim 75 or 76, wherein said colored light output means comprises at least one display element configured to output colored light.

78. The display of claim 77, wherein said white light outputting means comprises at least one display element configured to output white light.

79. A method of making a display, comprising:

forming a plurality of display elements, including forming at least one color display element configured to output colored light and

at least one display element configured to output white light, wherein the at least one display element configured to output white light is configured to output white light having a standardized white point.

80. The display of claim 79, wherein said at least one color display element comprises red, green, and blue display elements configured to output red, green, and blue light, respectively.

81. The display of claim 79, wherein plurality of display elements comprises a plurality of interferometric modulators.

82. A display fabricated by the method of any one of claims 57-62.

83. A display fabricated by the method of any of claims 79 to 81.