HK1131216A - Interferometric optical display system with broadband characteristics - Google Patents

Abstract

Broad band white color can be achieved in MEMS display devices by incorporating a material having an extinction coefficient (k) below a threshold value for wavelength of light within an operative optical range of the interferometric modulator. One embodiment provides a method of making the MEMS display device comprising depositing said material (23) over at least a portion of a transparent substrate (20), depositing a dielectric layer (24) over the layer of material, forming a sacrificial layer over the dielectric, depositing an electrically conductive layer (24) on the sacrificial layer, and forming a cavity (19) by removing at least a portion of the sacrificial layer.; The suitable material may comprise germanium, germanium alloy of various compositions, doped germanium or doped germanium-containing alloys, and may be deposited over the transparent substrate, incorporated within the transparent substrate or the dielectric layer.

Description

Interferometric optical display system with broadband characteristics

Technical Field

The present invention relates to microelectromechanical systems used as interferometric modulators (iMoDs). More particularly, the present invention relates to systems and methods for improving the manufacture of interferometric modulators.

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 addition layers thereof to form electrical and electromechanical devices. One type of MEMS device is referred to as an interferometric modulator. As used herein, an 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 include a stationary layer deposited on a substrate and the other plate may include 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. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be used to improve existing products and create new products that have not yet been developed.

Disclosure of Invention

The systems, methods, and devices of the present disclosure each have several aspects, any of which is not capable of separately generating its desired attributes. Without limiting the scope of this invention, its more prominent features will 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.

An embodiment provides a method of manufacturing a MEMS display device, the method comprising: providing a transparent substrate and forming an array of interferometric modulators on the transparent substrate, wherein the interferometric modulators comprise a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulator.

Another embodiment provides a method of forming an array of interferometric modulators, the method comprising: the method includes forming an optical stack on the transparent substrate, depositing a sacrificial layer on the optical stack, forming a conductive layer on the sacrificial layer, and removing at least a portion of the sacrificial layer to form a cavity between the substrate and the conductive layer.

Another embodiment provides a MEMS display device fabricated by a method comprising: providing a transparent substrate and forming an array of interferometric modulators on the transparent substrate, wherein the interferometric modulators comprise a material having a refractive index that increases with increasing wavelength.

Another embodiment provides an interferometric display device comprising means for transmitting light and means for interferometrically reflecting light through the transmitting means, wherein the reflecting means comprises a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulator.

Another embodiment provides a MEMS display device comprising a substrate and an array of interferometric modulators deposited on the substrate, wherein the array comprises a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulators. The display device of this embodiment further includes a processor in electrical communication with the array, the processor configured to process image data; and a memory device in electrical communication with the processor.

These and other embodiments are described in more detail below.

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 flow chart illustrating certain steps in an embodiment of a method of manufacturing an interferometric modulator.

FIG. 9A is a cross section of an embodiment of an interferometric modulator.

FIG. 9B is a cross section of an alternative embodiment of an interferometric modulator.

FIG. 9C is a cross section of another alternative embodiment of an interferometric modulator.

FIG. 9D is a cross section of another embodiment of an interferometric modulator.

FIG. 9E is a cross section of an additional embodiment of an interferometric modulator.

FIG. 10 is a dispersion curve illustrating a material (e.g., Ge) having an increasing index of refraction and a decreasing extinction coefficient (k) as the wavelength increases within the operative optical range of the interferometric modulator.

FIG. 11A is a cross section of one embodiment of an interferometric modulator for spectral response simulation in the bright state.

FIG. 11B is a cross section of one embodiment of an interferometric modulator for simulation of spectral response in the dark state.

FIG. 12 is a simulated spectral response of the modeled interferometric modulator of FIG. 11 utilizing Ge as the absorber, showing broadband white characteristics.

FIG. 13A is a cross section of one embodiment of an unreleased interferometric modulator corresponding to a released interferometric modulator in the bright state.

FIG. 13B is a cross section of one embodiment of an unreleased interferometric modulator corresponding to a released interferometric modulator in the dark state.

FIG. 14 is a deposition 90 on a substrateExperimental dispersion curves for Ge layers.

FIG. 15 is a comparison of experimental and simulated spectral responses of the unreleased interferometric modulator of FIG. 13.

FIG. 16 is another comparison of experimental and simulated spectral responses of the unreleased interferometric modulator of FIG. 13.

FIG. 17 shows simulated spectral responses of two interferometric modulators: (A) an interferometric modulator comprising Ge and (B) an interferometric modulator comprising an absorber with an n: k ratio of 4:1.6, having average n and k values of Ge without dispersion.

FIG. 18 shows simulated spectral responses of (A) an interferometric modulator comprising CuO and (B) an interferometric modulator comprising an absorber with an n: k ratio of 2.5:0.8, which are average n and k values of CuO without dispersion.

FIG. 19 shows a simulated spectral response of an interferometric modulator comprising a partially reflective material with an n: k ratio of 7: 2.4.

FIG. 20 shows a simulated spectral response of an interferometric modulator comprising a partially reflective material with an n: k ratio of 4:1.

Detailed Description

The following detailed description is directed to certain specific embodiments of the invention. The invention may, however, be embodied in many different forms. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. It will be apparent from the following description that 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 graphical. 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, video cameras, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), in-cabin controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic bulletin boards or symbols, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices having structures similar to those described herein can also be used in non-display applications such as in electronic switching devices.

One embodiment of the present invention is the use of materials having an extinction coefficient (k) below the threshold value for wavelengths of light within the operative optical range of the interferometric modulator. Another embodiment may use materials that increase in refractive index (n) and/or decrease in extinction coefficient (k) as the wavelength increases within the operative optical range. As an example, the material may be germanium or a germanium-based alloy (e.g., Si)_xGe_1-x). A display device comprising this material is capable of reflecting a broadband white color in the "bright" state without affecting the darkness of the device when it is in the "dark" state. In an embodiment, a germanium layer is used within an absorber layer of an interferometric device to provide a means of reflecting broadband white light to a viewer. In another embodimentThe material is combined with a metal in a stacked layered structure. The metal allows for additional fine tuning of the optical performance of the display device. Specifically, adding a metal layer adjacent to the material allows for reduced reflectivity (darkness) in the dark state and thus improves the contrast ratio of the display device. Of course, it should be recognized that embodiments of the present invention are not limited to these or any particular layer thicknesses.

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 opposite. 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 certain 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 an embodiment, one of the reflective layers is movable between two positions. In the first position, which is 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, which is referred to herein as the actuated position, the movable reflective layer is positioned more adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel.

The depicted portion of the pixel array in FIG. 1 includes two adjacent interferometric modulators 12a and 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 referred to herein, typically comprise 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 certain embodiments, the layers are patterned into parallel strips, and may form row electrodes within a display device as described further below. The movable reflective layers 14a, 14b may be formed as a series of parallel strips of one or more deposited metal layers (orthogonal to the row electrodes of 16a, 16 b) deposited on top of posts 18 and an intervening sacrificial material deposited between the posts 18. When the sacrificial material is etched away, the movable reflective layers 14a, 14b are separated from the optical stacks 16a, 16b by a defined gap 19. A highly conductive and reflective material such as aluminum may be used for the reflective 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 of 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 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 in the right portion of fig. 1. The characteristics are 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. 2-5 illustrate one exemplary method and system for using an array of interferometric modulators in a display application.

FIG. 2 is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor 21, which may be any general purpose single-or multi-chip microprocessor, such asOr 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 panel or display array (display) 30. The cross section of the array illustrated in FIG. 1 is shown by line 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. It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the relaxed state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the exemplary embodiment of FIG. 3, the movable layer does not relax completely until the voltage drops below 2 volts. Thus, there is a range of voltage, about 3 to 7V in the example illustrated in FIG. 3, where there is a window of applied voltage within which the device is stable in either the relaxed or actuated state. This is referred to herein as the "hysteresis window" or "stability window". For a display array having the hysteresis characteristics of FIG. 3, the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be relaxed are exposed to a voltage difference of near zero volts. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After writing, each pixel sees a potential difference within the "stability window" of 3-7 volts in this example. This feature makes the pixel design illustrated in FIG. 1 stable under the same applied voltage conditions in either an actuated or relaxed pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or relaxed state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. If the applied potential is fixed, substantially no current flows into the pixel.

In typical applications, a display frame may be formed by determining a set of column electrodes from the desired set of actuated pixels in the first row. A row pulse is then applied to the row 1 electrode, actuating the pixels in response to the asserted column lines. The asserted set of column electrodes then becomes the desired set corresponding to 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 their set state during the row 1 pulse. This may be repeated in a sequential manner across the entire series of rows to produce a frame. In general, 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 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 and 5 illustrate the 3 tab in fig. 23 one possible actuation protocol for forming display frames on the array. Figure 4 illustrates a possible set of column and row voltage levels that may be used for pixels exhibiting the hysteresis curves of figure 3. In the FIG. 4 embodiment, actuating a pixel involves setting the appropriate column to-V_biasAnd the appropriate row is set to + Δ V, which may correspond to-5 volts and +5 volts, respectively. Relaxing the pixels is accompanied by setting the appropriate column to + V_biasAnd the appropriate row is set to + Δ V, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at + V_biasor-V_bias. As also illustrated in FIG. 4, it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to + V_biasAnd the appropriate row is set to- Δ V. In this embodiment, releasing the pixel is accompanied 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, where actuated pixels are non-reflective. Prior to writing the frame illustrated in FIG. 5A, the pixels can be in any state, and in this example, all the rows are at 0 volts, and all the columns are at +5 volts. With these applied voltages, all pixels are stable in their existing actuated or relaxed states.

In the fig. 5A frame, pixels (1, 1), (1, 2), (2, 2), (3, 2), and (3, 3) are actuated. To accomplish this, during a "line time" for row 1, columns 1 and 2 are set to-5 volts, and column 3 is set to +5 volts. This does not change the state of any pixels, as 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 actuates the (1, 1) and (1, 2) pixels and relaxes the (1, 3) pixel. Other pixels in the array are not 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). Also, other pixels of the array are not 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 should be appreciated that the same procedure can be employed for arrays of 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 45, a microphone 46, and an input device 48. The housing 41 is generally formed by any of a variety of manufacturing methods well known to those skilled in the art, including injection molding and vacuum forming. Further, the housing 41 may be made of 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.

The display 30 of exemplary display device 40 may be any of a variety of displays, including a bi-stable display as described herein. In other embodiments, display 30 comprises a flat panel display, such as a plasma, EL, OLED, STN LCD, or TFT LCD (as described above), or a non-flat panel display, such as a CRT or other picture tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display 30 comprises 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 therein. 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. The driver controller 29 is coupled to a frame buffer 28 and to the array driver 22, which in turn is coupled to a display array 30. 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 that alleviate the 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 by and further manipulated by the processor 21. The transceiver 47 also processes signals received from the processor 21 so that they may be transmitted from the exemplary display device 40 via the antenna 43.

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 an image 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 determines image characteristics at each location within an image. Such image characteristics may include, for example, color, saturation, and gray scale level.

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 as a stand-alone Integrated Circuit (IC), such a controller may be implemented in a variety of ways. They may be embedded within the processor 21 as hardware, embedded within 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 an 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 an 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 embodiments are 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 the microphone 46 is used to input data to the device, voice commands may be provided by a user to control the 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, power source 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, the control programming capability as described above resides in a driver controller, which may be located in several places in the electronic display system. In some cases, the control programming capability resides in the array driver 22. Those skilled in the art will recognize that the above-described optimizations may be implemented in any number of hardware and/or software components and in various configurations.

The details of the structure of interferometric modulators that operate in accordance with the principles described above may vary widely. For example, figures 7A-7E illustrate five different embodiments of the movable reflective layer 14 and its supporting structures. Fig. 7A is a cross-sectional view of the embodiment of fig. 1, wherein a strip of metallic material 14 is deposited on orthogonally extending support structures 18. In FIG. 7B, the movable 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 material. The deformable layer 34 is directly or indirectly connected to the substrate 20 around the perimeter of the deformable layer 34. These connections may be referred to herein as support posts. The embodiment illustrated in FIG. 7D has a support structure 18 that includes support post plugs 42, with the deformable layer 34 resting on the support post plugs 42. 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 18 by filling holes between the deformable layer 34 and the optical stack 16. Rather, the support posts 18 comprise a planarization material that is 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 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 routed along the back of the interferometric modulators, eliminating a plurality of electrodes that might otherwise 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 certain 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 (FIG. 7E). This allows the shielded areas to be configured and operated upon without adversely affecting image quality. This separable modulator architecture allows the structural design and materials used for the electromechanical aspects and the optical aspects of the modulator to be selected and to function independently of each other. Moreover, the embodiments shown in FIGS. 7C-7E have additional benefits deriving from the decoupling of the optical properties of the reflective layer 14 from its mechanical properties, which is 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.

One embodiment provides a method of manufacturing a MEMS display device comprising providing a transparent substrate and forming an array of interferometric modulators on the transparent substrate, wherein the interferometric modulators comprise a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulator. Forming an array of interferometric modulators includes forming an optical stack on the transparent substrate, depositing a sacrificial layer on the optical stack, forming a conductive layer on the sacrificial layer, and removing at least a portion of the sacrificial layer, thereby forming a cavity between the substrate and the conductive layer.

FIG. 8 illustrates certain steps in an embodiment of a method 800 of manufacturing an interferometric modulator that reflects broadband white light. Such steps may be present in the process of manufacturing interferometric modulators of the general type illustrated in figures 1, 7, and 9, for example, along with other steps not shown in figure 8. Referring to fig. 8 and 9A, the process 800 begins at step 805 by providing a transparent substrate at step 805. In certain embodiments, the transparent substrate 20 is glass, plastic, or other material that is transparent to light, and may also support the fabrication of an array of interferometric modulators. It will be understood by those skilled in the art that the term "transparent" as used herein encompasses materials that are substantially transparent to the operating wavelength of the interferometric modulator, and thus the transparent substrate need not transmit all wavelengths of light and may absorb a portion of the light at the operating wavelength of the interferometric modulator. In certain embodiments, the transparent substrate 20 may be a larger area display.

The process 800 continues at step 810 where the optical stack 16 is formed on the transparent substrate 20 at step 810. Thus, as described above, 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 certain embodiments, the layers are patterned into parallel strips, and may form row electrodes within a display device. In certain embodiments, the optical stack 16 includes a dielectric layer 24 deposited on one or more layers of the partially reflective material 23 (e.g., the material).

Referring to FIG. 9A, which is an example of one embodiment, forming the optical stack 16 includes depositing a partially reflective material 23 (e.g., the material) over at least a portion of the substrate 20 and depositing a dielectric layer 24 over the partially reflective material 23. Typically, the dielectric layer has a thickness of about 100 to about 800 angstroms. The partially reflective material 23 (e.g., the material) has an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulator. In one embodiment, the threshold value of k is about 2.5. In certain embodiments, the partially reflective material 23 may have a K value that remains substantially constant for wavelengths of light within the operative optical range of the interferometric modulator. In certain other embodiments, the k value of the partially reflective material 23 may decrease as the wavelength of light increases within the operative optical range of the interferometric modulator. Certain embodiments may also have partially reflective materials with refractive indices (n) that increase as the wavelength of light increases within the operative optical range of the interferometric modulator. The operative optical range of the interferometric modulator may be from about 300nm to about 800nm wavenumbers, preferably from about 350nm to about 750nm, and more preferably from about 400nm to about 700 nm. In certain embodiments, the partially reflective material 23 (e.g., the material) comprises siliconGermanium alloy (e.g. Si)_xGe_1-x). In another embodiment, the partially reflective material 23 (e.g., the material) may be germanium. The partially reflective layer can have a thickness of about 20 a to aboutPreferably from about 50 to about. In certain embodiments, Si_xGe_1-xVarious components of (x ═ 0-1) can be obtained by varying the values of x and y, and this variation can be used for "fine tuning" of the parameters n and k, which then results in the ability to tune the spectral properties of the high intensity reflected broadband white light. In other embodiments, the n and k properties of partially reflective material 23 (e.g., such material) may be obtained by doping germanium or a germanium-containing alloy (e.g., Si) with impurities having a concentration of about 0.01% to about 10%_xGe_1-x) And tuned. The impurity may be, but is not limited to, B, P, As, C, In, Al, or Ga. In one embodiment, the partially reflective material 23 has an n-to-k ratio of from about 2.5 to about 6. In another embodiment, the partially reflective material 23 has an n-to-k ratio of about 3.

Another embodiment is directed to forming a germanium-rich layer on a transparent substrate with a SiO-like layer on the germanium-rich layer₂Of (2) a layer of (a). In this embodiment, forming the optical stack includes depositing a germanium-containing alloy (e.g., Si) on the substrate_xGe_1-x) And in e.g. O₂、N₂O、O₃Or thermal oxidation of deposited Si in an oxidizing ambient of NO_xGe_1-xAlloys in which Si is preferentially oxidized to form a transparent silicon oxide dielectric layer, leaving behind a layer having the desired n&A layer of k-property germanium-rich partially reflective material. In certain embodiments, the thickness of the deposited germanium-containing alloy may be from about 20 to about

In another embodiment, the partially reflective material 23 is combined with a metal in a stacked layered structure. The metal layer comprises a material selected from the group consisting of chromium, molybdenum, a refractive material, and a refractive alloy. The metalAllowing additional fine-tuning of the optical performance of the display device. In particular, the addition of a metal layer adjacent to the material allows for reduced reflectivity (darkness) in the dark state and thus improves the contrast of the display device. In an embodiment, the chromium layer has a thickness of 1 to 50, 10 to 40, or 25 to 40. In another embodiment, the metal layer has a thickness of 1 to 50, 10 to 40, or 25 to 50 a

The process 800 illustrated in FIG. 8 continues at step 815, where a sacrificial layer is deposited over the optical stack 16 at step 815. The sacrificial layer is then removed (e.g., at step 830) to form the cavity 19 as discussed below, and thus is not shown in the resulting interferometric modulator 12 illustrated in FIGS. 1, 7, and 9. Forming the sacrificial layer on the optical stack 16 may include depositing XeF₂Etchable materials, such as molybdenum, tungsten and amorphous silicon, the deposition thickness being selected to provide (after subsequent removal) a cavity 19 of a desired size. In certain embodiments, the sacrificial layer may be a thermally vaporizable material (e.g., an organic polymer). The thermally vaporizable material can be a material that vaporizes when heated to a vaporization temperature such that substantially all of the polymer (e.g.,>95% by weight) of vaporized solid material. The vaporization temperature range is preferably high enough that the thermally vaporizable material remains intact at normal manufacturing temperatures, but low enough to avoid damage to other materials present during vaporization. In one embodiment, the heat vaporizable material may be a heat vaporizable polymer. A variety of thermally vaporizable polymers can be used. For example, one such thermally vaporizable material is thermally depolymerizable polycarbonate (HDP), such as poly (cyclohexene carbonate), aliphatic polycarbonate, which may be made of CO₂With epoxides, see U.S. Pat. No. 6,743,570B 2. Other HDPs may also be used.

The deposition of the optical stack and the sacrificial material may be performed using conventional deposition techniques, such as physical vapor deposition (PVD, e.g., sputtering), Plasma Enhanced Chemical Vapor Deposition (PECVD), thermal chemical vapor deposition (thermal VCD), molecular beam deposition, spin coating, ion implantation, ion beam assisted deposition, electroplating, or Pulsed Laser Deposition (PLD). The sacrificial layer may be deposited at selected locations by, for example, printing techniques, one of which is inkjet deposition. In one embodiment, the sacrificial layer is printed at a location adjacent to the location of the post structure (either the post structure already deposited or the post structure to be deposited).

In certain embodiments, a support structure formation step (not shown in fig. 9) may occur after step 815 and before the formation of conductive layer 14 in step 820. The formation of the post 18 as shown in fig. 1, 7 and 9 may include the steps of: the sacrificial layer is patterned to form support structure holes, followed by deposition of a non-conductive material (e.g., a polymer) into the holes to form pillars 18, using a deposition method such as PECVD, thermal CVD, spin-on coating, ion implantation, ion beam deposition, or PLD. The patterning step may include techniques such as electron beam lithography and image transfer. Step 820 may then form the conductive layer 14 over the sacrificial layer and over the posts such that the conductive layer 14 will be supported after the sacrificial layer is removed in step 825.

In certain embodiments, the support structure holes formed in the sacrificial layer extend through the sacrificial layer and the optical stack 16 to the underlying substrate 20 such that the lower ends of the posts 18 contact the substrate 20, as illustrated in FIG. 7A. In other embodiments, the holes formed in the sacrificial layer extend through the sacrificial layer, but not through the optical stack 16. For example, FIG. 7C illustrates the lower end of the support post plugs 42 in contact with the optical stack 16. In one embodiment, XeF₂An etchable material may be used to form at least part of the pillar structure. XeF for pillar structures₂Etchable materials include molybdenum and silicon-containing materials such as silicon itself (including amorphous, polycrystalline, and crystalline silicon), as well as silicon germanium and silicon nitride. In another embodiment, the posts or post structures may be polymers.

The process 800 illustrated in figure 8 continues at step 820 with the formation of a movable reflective layer, such as the movable reflective layer 14 illustrated in figures 1, 7, and 9, in step 820. The movable reflective layer 14 can be formed by employing one or more deposition steps, such as reflective layer (e.g., aluminum alloy) deposition, and one or more patterning, masking, and/or etching steps. As discussed above, the movable reflective layer 14 is typically electrically conductive, and may be referred to herein as an electrically conductive layer. Since the sacrificial layer is still present in the partially fabricated interferometric modulator formed in step 820 of the process 800, the movable reflective plate 14 is typically not movable at this stage. Partially fabricated interferometric modulators containing sacrificial layers may be referred to herein as "unreleased" interferometric modulators.

The process 800 illustrated in fig. 8 continues at step 825 with the formation of a cavity, e.g., cavity 19 as shown in fig. 1, 7 and 9, at step 825. The cavity 19 may be formed by exposing the sacrificial material (deposited at step 815) to an etchant. For example, an etchable sacrificial material such as molybdenum or amorphous silicon may be removed by dry chemical etching, for example, by exposing the sacrificial layer to a gaseous or vaporized etchant (e.g., from solid xenon difluoride (XeF)₂) The resulting vapor) and for a period of time effective to remove the desired amount of material (typically selectively relative to the structure surrounding the cavity 19). Other etching methods, such as wet etching and/or plasma etching, may also be used. In certain embodiments, the vaporizing step 825 comprises heating. Heating may be performed on a heated plate, in an oven, in a kiln, or by using any heating device capable of achieving and maintaining a temperature sufficient to vaporize the heat vaporizable material for a time sufficient to vaporize substantially all of the sacrificial material. The sacrificial layer is thus removed during step 825 of the process 800, the movable reflective layer 14 typically being removable after this stage. After removal of the sacrificial material, the resulting fully or partially fabricated interferometric modulator may be referred to herein as a "released" interferometric modulator. In certain embodiments, process 800 may include additional steps and the steps may be rearranged from the illustration of FIG. 8.

FIGS. 9A-9E illustrate various embodiments of a MEMS display device, including a substrate 20 and a layer deposited on the substrateAn array of interferometric modulators on the substrate 20, wherein the array comprises a material 23 having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulators. The substrate 20 may be a large area transparent substrate such as glass, plastic, or other material that is transparent to light. Therefore, the transparent substrate is also a member for transmitting light. Interferometric modulators are also means for interferometrically reflecting light through the transmissive means (e.g., a transparent substrate). The interferometric modulator may include an optical stack 16, a conductive layer 14 (e.g., a movable layer), support structures (e.g., posts or post structures 18), and a cavity 19 separating the optical stack from the conductive layer. The material 23 (e.g., a partially reflective layer) typically has a dispersion/extinction coefficient state that compensates for wavelength variations of the insulating or dielectric layer and air in the cavity. In one embodiment, the material has a dispersion/extinction coefficient curve illustrated in fig. 10. Fig. 10 shows the dispersion/extinction coefficient behavior of germanium with increasing refractive index and decreasing extinction coefficient as the wavelength increases within the operating optical range. Materials with similar dispersion and/or extinction coefficient states allow for higher total reflection without compromising the advantageous higher visible light absorbance in the dark/off state. In certain embodiments, the total reflection may be about 30% to about 70% in the operative optical range. A typical thickness of material layer 23 (e.g., germanium, a germanium alloy, doped germanium, or an alloy layer containing doped germanium) may be from about 50 a to aboutIn the range of (1).

In certain embodiments, a partially reflective material 23 (e.g., the material) may be deposited on the transparent substrate 20. In one embodiment, a transparent conductive material 25 (e.g., ITO or other transparent conductive oxide, such as ZnO) may be deposited on the partially reflective material 23 (see fig. 9A). In another embodiment, the partially reflective material 23 (e.g., the material) may be deposited on the transparent conductive material 25 (see fig. 9B). In this case, the transparent conductive material 25 can be deposited on at least a portion of the substrate prior to depositing the partially reflective material 23 (e.g., the material). The transparent conductive material 25 may beIs any optically transparent conductive material and has a typical thickness of about 100 to. The thickness of the transparent conductive material 25 is determined by the position of the layers and the desired cavity size. In certain embodiments, the transparent conductive material 25 comprises tin-based oxide, antimony-based oxide, or indium-based oxide. In another embodiment shown in fig. 9C, the transparent conductive material 25 (e.g., ITO) may be omitted, as the germanium or germanium-containing alloy layer itself may also be configured to act as a conductive layer, particularly when doped with a group III element (e.g., B, Al or Ga) or a group V element (e.g., P, As or Sb).

In another embodiment illustrated in fig. 9D, a partially reflective material 23 (e.g., the material) can be integrated within the transparent substrate 20. The transparent substrate 20 may be doped with a partially reflective material 23. This may be done by ion implanting the material into the substrate 20 and allowing the material to form a band or layer of partially reflective material 23 within the substrate using any known semiconductor processing techniques. In this embodiment, the portion of the substrate comprising the material may be considered to be part of the optical stack 16. In yet another embodiment shown in fig. 9E, the strip of partially reflective material 23 may be integrated within a dielectric layer 24 (e.g., an insulating layer). For example, thin dielectric layers (e.g., SiO)₂) First, depositing, then depositing a partially reflective material 23 thereon, and finally depositing more SiO on the partially reflective material 23₂. Optionally, a transparent conductive material 25 (e.g., ITO) may be deposited on the substrate as an electrical conductor prior to depositing the insulating or dielectric layer 24.

Example 1

Interferometric modulator device simulations were modeled based on one embodiment of the unreleased interferometric modulator shown in FIG. 11. The modeled structure includes a glass substrate 20, an optical stack 16 on the glass substrate 20, a cavity 19 separating the optical stack 16 from the Al reflective layer 14. The optical stack 16 contains an ITO layer 102 on the substrate 20, a partially reflective material 23 on the ITO layer 102, and a dielectric layer 24 on the partially reflective material 23. For this example, Ge is used as the partially reflective material 23. By varying the thicknesses of the ITO layer, Ge, and dielectric layers, the characteristics of the interferometric modulator (e.g., contrast, reflectivity, white balance, or a combination thereof) can be optimized. The reflectance and transmittance of the stack were calculated based on the thickness, refractive index (n) and extinction coefficient (k) of each layer as a function of wavelength using the PC software program from Thin film center Inc (tusson, arizona).

The optimum input thickness of the layers in this simulation is for the ITO layer 102For the partially reflective material 23, germanium isFor dielectric layer 24, SiO₂Is composed ofAnd Al₂O₃Is composed ofAnd 300 for the Al reflective layer 14. The cavity 19 has in the bright stateHas a spacing of (1) and has a dark stateThe interval (fig. 11B). The simulated spectral response of a broadband white interferometric modulator using Ge as a partially reflective layer (e.g., absorber) exhibits a reflectance of over 50% in its bright state and a 100: 1 contrast between the bright and dark states (fig. 12).

Example 2

Another interferometric modulator device simulation is modeled based on one embodiment of the unreleased interferometric modulator shown in FIG. 11. The modeled structure includes a glass substrate 20, an optical stack 16 on the glass substrate, a cavity 19 separating the optical stack 16 from the Al reflective layer 14. The optical stack 16 contains an ITO layer 102 on the substrate 20, a partially reflective material 23 on the ITO layer 102, and a dielectric layer 24 on the partially reflective material 23. However, in this example a metal layer (e.g., Cr or Mo) is modeled on or under the partially reflective material 23. By varying the thicknesses of the ITO, Ge, metal layers, and dielectric layers, the characteristics of the interferometric modulator (e.g., contrast, reflectivity, white balance, or combinations thereof) can be optimized. The reflectance and transmittance of the stack were calculated as a function of wavelength based on the thickness, refractive index (n), and extinction coefficient (k) of each layer using the eastern Macleod software program from Thin Film Center Inc.

The optimum input thickness of the layer in this simulation was for the ITO layerFor the Ge layer isCr is 10 to 10 for the dielectric layerSiO₂Is composed ofAnd Al₂O₃Is 80, and for the Al layer isThe cavity 19 has in the bright stateHas a spacing in the dark stateThe interval of (c). The combination of Ge and a metal (e.g., Cr or Mo) as an absorber can improve the contrast by about 25%.

Example 3

By being atDeposition 90 on glass substrate 20As a partially reflective layer 23 to fabricate the unreleased interferometric modulator shown in figure 13. SiO 2₂An insulating layer 101 is deposited on the Ge layer, and then on the SiO₂On layer 101 at a distance greater thanThe Al reflective layer 14 is deposited. SiO in unreleased interferometric modulators₂The insulating layer 101 represents a cavity in the released interferometric modulator. SiO 2₂The thickness of the insulating layer 101 is equal to the distance of separation between the partially reflective layer 23 and the Al reflective layer 14 (i.e., the movable layer in a released interferometric modulator). Preparation of a composition havingAndSiO₂an arrangement of layers. Has the advantages ofSiO₂The device of the layer (FIG. 13B) is equivalent to a released interferometric modulator in the dark state, and 1080SiO₂The device (FIG. 13A) is equivalent to a released interferometric modulator in the bright state. The spectral responses of both devices were measured and compared to simulated data generated using the eastern millard (Essential mechanical) software program from Thin Film Center Inc (tusson, arizona).

FIG. 14 is a schematic illustration of a deposition by sputteringExperimental dispersion curves for Ge layers demonstrating that Ge is one of the materials with increasing refractive index (n) and/or decreasing extinction coefficient (k) as the wavelength increases within the operating optical range (i.e., 400 to 700 nm).

FIG. 15 is a schematic view of a liquid crystal display deviceGe is used as the spectral response of these unreleased interferometric modulators of the partially reflective layer. Both simulation and experimental data show that the total reflectance range between 400 and 700nm wavelengths is 30% to 70% in the bright state (e.g., withSiO₂Layer) and less than 10% in the dark state (e.g., havingSiO₂Layers).

Example 4

By deposition on glass substratesGe as a partially reflective layer 23 makes a series of unreleased interferometric modulators as shown in figure 13. SiO 2₂An insulating layer 101 is deposited on the Ge layer, and then on the SiO₂Greater than 300 on layer 101The Al reflective layer 14 is deposited. SiO in unreleased interferometric modulators₂The insulating layer 101 represents a cavity in the released interferometric modulator. SiO 2₂The thickness of the insulating layer 101 is equal to the distance of separation between the partially reflective layer 23 and the reflective layer 14 (i.e., the movable layer in a released interferometric modulator). In this example, four different thicknesses of SiO were used₂The insulating layer 101 constitutes four devices. In one of the devices, the first and second electrodes are arranged in a circular shape,SiO₂layers are deposited on the Ge layer to form a device equivalent to a released interferometric modulator in the dark state (figure 13B). Using SiO of different thicknesses₂Three other devices (fig. 13A) were fabricated for spectral response measurement in the bright state with different cavity sizes. For each of these devices, SiO₂Has a thickness ofAnd. FIG. 16 showsGe served as the spectral response of these unreleased interferometric modulators of the partially reflective layer. Both simulation and experimental data show that the total reflectance range is 30% to 70% in the different bright states and below 20% in the dark state.

Example 5

Another interferometric modulator device simulation is modeled based on an embodiment of the unreleased interferometric modulator shown in FIG. 11. The modeled structure includes a glass substrate 20, an optical stack 16 on the glass substrate 20, a cavity 19 separating the optical stack 16 from the Al reflective layer 14. The optical stack 16 contains a partially reflective material 23 on the ITO layer, and a dielectric layer on the partially reflective material 23. The input thickness of the layers in this simulation was for the Ge layerSiO for dielectric layer₂Is composed ofAnd for the Al layer is. The cavity 19 has in the bright stateHas a spacing of (1) and has a dark stateThe interval (fig. 11B).

Partially reflective materials 23 (e.g., absorbers) of different n: k ratios were simulated to show the effect of tuning the n and k parameters. FIG. 17 shows and compares the simulated spectral responses of two interferometric modulators: (A) an interferometric modulator comprising Ge and (B) an interferometric modulator comprising an absorber with an n: k ratio of 4:1.6, having average n and k values of Ge without dispersion. FIG. 18 shows simulated spectral responses of (A) an interferometric modulator comprising CuO and (B) an interferometric modulator comprising an absorber with an n: k ratio of 2.5:0.8, which is the average n and k values of CuO without dispersion. Simulations using the average n and k values of certain partially reflective materials can predict how an actual material responds within the operative optical range of the interferometric modulator. FIG. 19 shows a simulated spectral response of an interferometric modulator comprising a partially reflective material with an n: k ratio of 7: 2.4. FIG. 20 shows a simulated spectral response of an interferometric modulator comprising a partially reflective material with an n: k ratio of 4:1. The results of these simulations suggest that the preferred n to k ratio is from about 2.5 to about 6, and more preferably about 3.

Claims (33)

1. A method of manufacturing a MEMS display device, comprising:

providing a transparent substrate; and

an array of interferometric modulators is formed on the transparent substrate, wherein the interferometric modulators comprise a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulators.

2. The method of claim 1, wherein the threshold value is about 2.5.

3. The method of any of claims 1-2, wherein forming an array of interferometric modulators includes:

forming an optical stack on the transparent substrate;

depositing a sacrificial layer over the optical stack;

forming a conductive layer on the sacrificial layer; and

at least a portion of the sacrificial layer is removed, thereby forming a cavity between the substrate and the conductive layer.

4. The method of claim 3, wherein the optical stack further comprises a transparent conductive material.

5. The method of any of claims 3-4, wherein the optical stack further comprises a dielectric layer.

6. The method of claim 5, wherein the material is integrated within the dielectric layer.

7. The method of any one of claims 1-5, further comprising integrating the material within a transparent substrate.

8. The method of any of claims 1-7, wherein the extinction coefficient (k) decreases or remains substantially constant as the wavelength of light increases within the operative optical range of the interferometric modulator.

9. The method of any of claims 1-8, wherein the material has a refractive index (n) that increases as the wavelength of light increases within the operative optical range of the interferometric modulator.

10. The method of claim 9, wherein the material has an n-to-k ratio from about 2.5 to about 6.

11. The method of any one of claims 1-10, wherein the operative optical range is from about 400nm to about 700 nm.

12. A MEMS display device manufactured by the method of any one of claims 1-11.

13. An interferometric display device, comprising:

means for transmitting light; and

means for interferometrically reflecting light through the transmissive means, wherein the reflecting means comprises a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulator.

14. The interferometric display device of claim 13, wherein said threshold value is about 2.5.

15. The interferometric display device of any one of claims 13-14, wherein said layer of material is integrated in said transmissive means.

16. The interferometric display device of any one of claims 13-15, wherein said transmitting means comprises a transparent substrate.

17. The interferometric display device of any one of claims 13-16, wherein said extinction coefficient (k) remains substantially constant or decreases as the wavelength of light increases within the operative optical range of the interferometric modulator.

18. The interferometric display device of any one of claims 13-17, wherein said material has a refractive index (n) that increases as the wavelength of light increases within the operative optical range of the interferometric modulator.

19. The interferometric display device of claim 18, wherein said material has an n-to-k ratio from about 2.5 to about 6.

20. A MEMS display device, comprising:

a substrate; and

an array of interferometric modulators deposited on the substrate, wherein the array comprises a material having an extinction coefficient (k) below a threshold value for wavelengths of light within an operative optical range of the interferometric modulators.

21. The MEMS display device of claim 20, wherein said threshold value is about 2.5.

22. The MEMS display device of any one of claims 20-21, wherein said material is integrated in a transparent substrate.

23. The MEMS display device of any one of claims 20-22, wherein the extinction coefficient (k) remains substantially constant or decreases as the wavelength of light increases over the operative optical range of the interferometric modulator.

24. The MEMS display device of any one of claims 20-23, wherein said material has a refractive index (n) that increases as the wavelength of light increases within the operative optical range of the interferometric modulator.

25. The MEMS display device of claim 24, wherein said material has an n-to-k ratio from about 2.5 to about 6.

26. The MEMS display device of any one of claims 20-25, wherein said operative optical range is from about 400nm to about 700 nm.

27. The MEMS display device of any one of claims 20-26, wherein said MEMS device comprises a cellular telephone.

28. The MEMS display device of any one of claims 20-27, further comprising:

a processor in electrical communication with the array, the processor configured to process image data; and

a memory device in electrical communication with the processor.

29. The MEMS display device of claim 28, further comprising a driver circuit configured to send at least one signal to said array.

30. The MEMS display device of claim 29, further comprising a controller configured to send at least a portion of said image data to said driver circuit.

31. The MEMS display device of any one of claims 28-30, further comprising an image source module configured to send said image data to said processor.

32. The MEMS display device of claim 31, wherein said image source module comprises at least one of a receiver, transceiver, and transmitter.

33. The MEMS display device of any one of claims 28-32, further comprising an input device configured to receive input data and to communicate said input data to said processor.