Patent Publication Number: US-8115988-B2

Title: System and method for micro-electromechanical operation of an interferometric modulator

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 11/189,690, filed Jul. 26, 2005, which issued as U.S. Pat. No. 7,567,373 on Jul. 28, 2009 and is hereby incorporated by reference in its entirety. U.S. application Ser. No. 11/189,690 is a continuation-in-part of the following: U.S. application Ser. No. 10/909,228, filed Jul. 29, 2004, now abandoned; and U.S. application Ser. No. 11/048,662, filed Jan. 27, 2005, now abandoned; both of which are hereby incorporated by reference in their entireties. U.S. application Ser. No. 11/189,690 also claims priority to the following: U.S. Provisional Application No. 60/613,466, filed Sep. 27, 2004; U.S. Provisional Application No. 60/613,499, filed Sep. 27, 2004; and U.S. Provisional Application No. 60/658,867, filed Mar. 4, 2005; all of which are hereby incorporated herein by reference in their entireties. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     This invention relates to microelectromechanical systems for use as interferometric modulators. More particularly, this invention relates to systems and methods for improving the micro-electromechanical operation of interferometric modulators. 
     2. Description of the Related Art 
     Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed. 
     SUMMARY 
     The system, method, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description of Certain Embodiments” one will understand how the features of this invention provide advantages over other display devices. 
     One aspect of the invention provides an interferometric modulator, which includes a first layer, a second layer and a member. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion located substantially parallel to the first reflective planar portion. The second layer is movable between a first position and a second position. The first position is located at a first distance from the first layer. The second position is located at a second distance from the first layer. The second distance is greater than the first distance. The member includes a surface that is located between the first layer and second layer. The member defines one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member. 
     Another aspect of the invention provides a microelectromechanical device, which includes a first surface, a second surface and a third surface. The second surface is located substantially parallel to the first surface. The second surface is movable between a first position and a second position. The first position is located at a first distance from the first surface. The second position is located at a second distance from the first surface. The second distance is greater than the first distance. The third surface is located between the first surface and the second surface. The third surface defines one or more gap regions between the first surface and the second surface when the second surface is in the first position, wherein the second surface in the one or more gap regions does not contact either the first surface or the third surface. 
     Another aspect of the invention provides a microelectromechanical device, which includes a first layer; a second layer and a plurality of members. The second layer is located substantially parallel to the first layer. The second layer is movable between a first position and a second position. The first position is a first distance from the first layer. The second position is a second distance from the first layer. The second distance is greater than the first distance. Each of the plurality of members includes a surface located between the first layer and second layer. The plurality of members define one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the plurality of members. 
     Still another aspect of the invention provides a microelectromechanical device, which includes a first surface, a second surface and at least one structure on at least one of the first surface and the second surface. The second surface is located substantially parallel to the first surface. The second surface is movable relative to the first surface between a driven position and an undriven position. The driven position is closer to the first surface than is the undriven position. The at least one structure is compressed by the first surface and the second surface when the second surface is in the driven position. The at least one structure provides a force to the second surface when the second surface is in the driven position. The force assists movement of the second surface from the driven position toward the undriven position. 
     Still another aspect of the invention provides a method of making an interferometric modulator. The method includes: providing a first layer, forming a second layer and forming a member comprising a surface. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion. The second reflective planar portion is located substantially parallel to the first reflective planar portion. The second layer is movable between a first position and a second position. The first position is at a first distance from the first layer. The second position is at a second distance from the first layer. The second distance is greater than the first distance. The surface of the member is located between the first layer and the second layer. The member defines one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member. 
     A further aspect of the invention provides a microelectromechanical device produced by a method. The method includes: providing a first layer, providing a second layer and providing a member comprising a surface. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion. One of the first reflective planar portion and the second reflective planar portion may be partially reflective. The second reflective planar portion is located substantially parallel to the first reflective planar portion. The second layer is movable between a first position and a second position. The first position is at a first distance from the first layer. The second position is at a second distance from the first layer. The second distance is greater than the first distance. The surface of the member is located between the first layer and the second layer. The member defines one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member. 
     A further aspect of the invention provides a method of operating a microelectromechanical device. Here, the device includes a first layer, a second layer and a member. The second layer of the device is located substantially parallel to the first layer. The member includes a surface intervening between the first layer and second layer. The surface of the member is located between only portions of the first layer and the second layer. The method of operating the device includes moving the second layer relative to the first layer from an undriven position to a driven position. The driven position is closer to the first layer than is the undriven position. The method further includes contacting the member with at least one of the first layer and the second layer so as to stop the movement of the second layer at the driven position, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the driven position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member. 
     A further aspect of the invention provides a microelectromechanical device. The device includes first means for partially reflecting and partially transmitting incident light and second means for substantially reflecting incident light. The device further includes means for moving the first means relative to the second means between a driven position and an undriven position. The device further includes means for providing a separation between the first means and the second means when the second means is in the driven position. The driven position is closer to the first means than is the undriven position. The first means may include, for example, a partial mirror surface. The second means may include, for example, a full mirror surface. The means for moving may include, for example, a deformable layer. The means for providing separation may include, for example, at least one of a bump, a landing pad or a spring clip. 
     A further aspect of the invention provides a microelectromechanical device. The device includes: first means for partially reflecting and partially transmitting incident light and second means for substantially reflecting incident light. The device further includes means for moving the first means relative to the second means between a driven position and an undriven position, and means for applying a force on the second means in a direction toward the undriven position when the second means is in the driven position. The first means may include, for example, a partial mirror surface. The second means may include, for example, a full mirror surface. The means for moving may include, for example, a deformable layer. The means for applying force may include, for example, a spring clip, or, as another example, a bump or a landing pad that includes an elastomeric material. 
     A still further aspect of the invention provides an interferometric modulator. The interferometric modulator includes a first layer, a second layer and at least one bump on the at least one of the first layer and the second layer. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion that is located substantially parallel to the first reflective planar portion. The second layer is movable between a driven position and an undriven position. The driven position is closer to the first layer than the undriven position. The at least one bump is configured to prevent the first layer and the second layer from contacting each other. 
     A still further aspect of the invention provides an interferometric modulator, which includes a first layer, a second layer and at least one landing pad located between the first layer and the second layer. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion that is located substantially parallel to the first reflective planar portion. The second layer is movable between a driven position and an undriven position. The driven position is closer to the first layer than the undriven position. The at least one landing pad includes a contact area where one of the first layer and the second layer contacts while not contacting the other when the second layer is in the driven position. 
     A still further aspect of the invention provides an interferometric modulator. The interferometric modulator includes a first layer, a second layer and at least one spring member placed between the at least one of the first layer and the second layer. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion that is located substantially parallel to the first reflective planar portion. One of the first reflective planar portion and the second reflective planar portion may be partially reflective. The second layer is movable between a driven position and an undriven position. The driven position is closer to the first layer than the undriven position. The at least one spring member is compressible by at least one of the first layer and second layer as the second layer moves toward the driven position. The at least one spring member is configured to apply force to the second layer in a direction toward the undriven position when the second layer is in the driven position. 
     Another embodiment provides a display system comprising an interferometric modulator, a display, a processor and a memory device. The processor is in electrical communication with the display and configured to process image data. The memory device is in electrical communication with the processor. 
     Another embodiment provides a method of making a MEMS device, such as a MEMS device that includes an interferometric modulator. The method includes forming a first electrode, depositing a dielectric material over at least a portion of the first electrode, then removing a portion of the dielectric material from over the first electrode, thereby forming a variable thickness dielectric layer. The method further includes forming a second electrode over at least a portion of the variable thickness dielectric layer. In an embodiment, a sacrificial layer is deposited over at least a portion of the dielectric material that is over the first electrode. The sacrificial layer and at least a portion of the dielectric material may be removed during a later etching step. Another embodiment provides an interferometric modulator made by such a method. 
     Another embodiment provides a method of making an interferometric modulator. The method includes forming a first electrode and depositing a dielectric layer over at least a portion of the first electrode. The method further includes removing a portion of the dielectric layer to form a variable thickness dielectric layer, depositing a sacrificial layer over the variable thickness dielectric layer, planarizing the sacrificial layer, and forming a second electrode over the sacrificial layer. Another embodiment provides an interferometric modulator made by such a method. 
     Another embodiment provides a method of making an interferometric modulator. The method includes forming a first electrode and depositing a dielectric layer over at least a portion of the first electrode. The method further includes removing a portion of the dielectric layer to form a variable thickness dielectric layer, depositing a sacrificial layer over the variable thickness dielectric layer, depositing a planarization layer over the sacrificial layer, and forming a second electrode over the planarization layer. Another embodiment provides an interferometric modulator made by such a method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a relaxed position and a movable reflective layer of a second interferometric modulator is in an actuated position. 
         FIG. 2  is a system block diagram illustrating one embodiment of an electronic device incorporating a 3×3 interferometric modulator display. 
         FIG. 3  is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of  FIG. 1 . 
         FIG. 4  is an illustration of a set of row and column voltages that may be used to drive an interferometric modulator display. 
         FIGS. 5A and 5B  illustrate one exemplary timing diagram for row and column signals that may be used to write a frame of display data to the 3×3 interferometric modulator display of  FIG. 2 . 
         FIGS. 6A and 6B  are system block diagrams illustrating an embodiment of a visual display device comprising a plurality of interferometric modulators. 
         FIG. 7A  is a cross section of the device of  FIG. 1 . 
         FIG. 7B  is a cross section of an alternative embodiment of an interferometric modulator. 
         FIG. 7C  is a cross section of another alternative embodiment of an interferometric modulator. 
         FIG. 7D  is a cross section of yet another alternative embodiment of an interferometric modulator. 
         FIG. 7E  is a cross section of an additional alternative embodiment of an interferometric modulator. 
         FIG. 8  is a perspective view of an interferometric modulator array which uses micro-electromechanical system technology. 
         FIG. 9A  is a schematic cross-sectional view of the interferometric modulator array of  FIG. 7  taken along line  8 A- 8 A of  FIG. 7 . 
         FIG. 9B  is a schematic cross-sectional view of another embodiment of the interferometric modulator array utilizing micro-electromechanical system technology. 
         FIG. 10A  is a side cross-sectional view of an embodiment of the interferometric modulator including landing pads with the modulator shown in the undriven state. 
         FIG. 10B  is a side cross-sectional view of the embodiment of  FIG. 9A  in the driven state. 
         FIGS. 10C-10I  are side cross-sectional views of embodiments of the interferometric modulator, illustrating various configurations of landing pads. 
         FIG. 10J  is a top cross-sectional view of an embodiment of the interferometric modulator taken along line  9 J- 9 J of  FIG. 9A  and illustrating various shapes of landing pads. 
         FIG. 11  is a flowchart illustrating a method of manufacturing a MEMS device having a variable thickness dielectric layer. 
         FIG. 12  is a cross-sectional view schematically illustrating an alternative embodiment of a MEMS device having a variable thickness dielectric layer. 
         FIG. 13  is a cross-sectional view schematically illustrating the formation of a lower electrode  502  in accordance with an embodiment. 
         FIG. 14  is a cross-sectional view schematically illustrating the formation of a dielectric layer  540  (including a lower portion  550  and an upper portion  560 ) on the stationary layer  502  and over the substrate  500  of  FIG. 13 . 
         FIGS. 15 and 16  are cross-sectional views schematically illustrating the formation of a variable thickness dielectric layer  570  (including “stops”  565 ) on the stationary layer  502  of  FIG. 13  by removing parts of the upper portion  560  of dielectric layer  540  of  FIG. 14 . 
         FIG. 17  is cross-sectional views schematically illustrating the formation of a sacrificial layer  710 , support structures  720 , and an upper electrode  730  of an interferometric modulator. 
         FIG. 18  is a cross-sectional view schematically illustrating the removal of the sacrificial layer  710  and the removal of parts of the lower portion  550  of the dielectric layer  570  of  FIG. 17 . 
         FIG. 19  shows cross-sectional views schematically illustrating an interferometric modulator  1800  comprising a stationary layer  502 , a deformable layer  506 , and a variable thickness dielectric layer  920  that substantially prevents contact between the first electrode  502  and the second electrode  506 . 
         FIG. 20  shows cross-sectional views schematically illustrating the formation of a sacrificial layer  710 , support structures  720 , and an upper electrode  731  of an interferometric modulator. 
         FIG. 21  is a cross-sectional view schematically illustrating an interferometric modulator. 
         FIG. 22A  is a side cross-sectional view of an embodiment of the interferometric modulator with bumps showing the modulator in the undriven state. 
         FIG. 22B  is a side cross-sectional view of the embodiment of  FIG. 22A  in the driven state. 
         FIGS. 22C-22E  are side cross-sectional views of embodiments of the interferometric modulator illustrating various configurations of bumps. 
         FIG. 23A  is a side cross-sectional view of an embodiment of the interferometric modulator with spring clips showing the modulator in the undriven state. 
         FIG. 23B  is a side cross-sectional view of the embodiment of  FIG. 23A  in the driven state. 
         FIGS. 23C-23F  are side cross-sectional views of embodiments of the interferometric modulator illustrating various configurations of spring clips. 
         FIG. 24A  is a side cross-sectional view of one embodiment of a three state interferometric modulator in the undriven state. 
         FIG. 24B  is a side cross-sectional view of the three state interferometric modulator of  FIG. 24A  in the driven state. 
         FIG. 24C  is a side cross-sectional view of the three state interferometric modulator of  FIG. 24A  in the reverse driven state. 
         FIG. 24D  is a side cross-sectional view of another embodiment of the interferometric modulator in the undriven state. 
         FIG. 24E  is a side cross-sectional view of another embodiment of the interferometric modulator in the undriven state. 
         FIG. 25A  is a side cross-sectional view of an alternative embodiment of an interferometric modulator shown in the undriven state. 
         FIG. 25B  is a top plan view of the interferometric modulator of  FIG. 25A , shown in the undriven state. 
         FIG. 25C  is a side view of the interferometric modulator of  FIG. 25A , shown in the driven state. 
         FIG. 25D  is a top plain view of the interferometric modulator of  FIG. 20C , shown in the driven state. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), hand-held or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices. 
     Driving an interferometric modulator may result in contact between a deformable layer and a stationary layer. Such contact may be undesirable and may result in damage to the device, potentially resulting in performance degradation. Various embodiments provides structures (such as landing pads, bumps and spring clips) and methods for reducing such damage. 
     One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in  FIG. 1 . In these devices, the pixels are in either a bright or dark state. In the bright (“on” or “open”) state, the display element reflects a large portion of incident visible light to a user. When in the dark (“off” or “closed”) state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the “on” and “off” states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white. 
       FIG. 1  is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In some embodiments, an interferometric modulator display comprises a row/column array of these interferometric modulators. Each interferometric modulator includes a pair of reflective layers positioned at a variable and controllable distance from each other to form a resonant optical cavity with at least one variable dimension. In one embodiment, one of the reflective layers may be moved between two positions. In the first position, referred to herein as the relaxed position, the movable reflective layer is positioned at a relatively large distance from a fixed partially reflective layer. In the second position, referred to herein as the actuated position, the movable reflective layer is positioned more closely adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel. 
     The depicted portion of the pixel array in  FIG. 1  includes two adjacent interferometric modulators  12   a  and  12   b . In the interferometric modulator  12   a  on the left, a movable reflective layer  14   a  is illustrated in a relaxed position at a predetermined distance from an optical stack  16   a , which includes a partially reflective layer. In the interferometric modulator  12   b  on the right, the movable reflective layer  14   b  is illustrated in an actuated position adjacent to the optical stack  16   b.    
     The optical stacks  16   a  and  16   b  (collectively referred to as optical stack  16 ), as referenced herein, typically comprise of several fused layers, which can include an electrode layer, such as indium tin oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. The optical stack  16  is thus electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the above layers onto a transparent substrate  20 . In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable reflective layers  14   a ,  14   b  may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of  16   a ,  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  14   a ,  14   b  are separated from the optical stacks  16   a ,  16   b  by a defined gap  19 . A highly conductive and reflective material such as aluminum may be used for the reflective layers  14 , and these strips may form column electrodes in a display device. 
     With no applied voltage, the cavity  19  remains between the movable reflective layer  14   a  and optical stack  16   a , with the movable reflective layer  14   a  in a mechanically relaxed state, as illustrated by the pixel  12   a  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  12   b  on the right in  FIG. 1 . The behavior is the same regardless of the polarity of the applied potential difference. In this way, row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies. 
       FIGS. 2 through 5  illustrate one exemplary process and system for using an array of interferometric modulators in a display application. 
       FIG. 2  is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor  21  which may be any general purpose single- or multi-chip microprocessor such as an ARM, Pentium®, Pentium II®, Pentium III®, Pentium IV®, Pentium® Pro, an 8051, a MIPS®, a Power PC®, an ALPHA®, or any special purpose microprocessor such as a digital signal processor, microcontroller, or a programmable gate array. As is conventional in the art, the processor  21  may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application. 
     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 a hysteresis property of these devices illustrated in  FIG. 3 . It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the relaxed state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the exemplary embodiment of  FIG. 3 , the movable layer does not relax completely until the voltage drops below 2 volts. There is thus a range of voltage, about 3 to 7 V in the example illustrated in  FIG. 3 , where there exists a window of applied voltage within which the device is stable in either the relaxed or actuated state. This is referred to herein as the “hysteresis window” or “stability window.” For a display array having the hysteresis characteristics of  FIG. 3 , the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be relaxed are exposed to a voltage difference of close to zero volts. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the “stability window” of 3-7 volts in this example. This feature makes the pixel design illustrated in  FIG. 1  stable under the same applied voltage conditions in either an actuated or relaxed pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or relaxed state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. Essentially no current flows into the pixel if the applied potential is fixed. 
     In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row  1  electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row  2  electrode, actuating the appropriate pixels in row  2  in accordance with the asserted column electrodes. The row  1  pixels are unaffected by the row  2  pulse, and remain in the state they were set to during the row  1  pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention. 
       FIGS. 4 and 5  illustrate one possible actuation protocol for creating a display frame on the 3×3 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 bias , and the appropriate row to +ΔV, which may correspond to −5 volts and +5 volts respectively Relaxing the pixel is accomplished by setting the appropriate column to +V bias , and the appropriate row to the same +ΔV, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at +V bias , or −V bias . As is also illustrated in  FIG. 4 , it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to +V bias , and the appropriate row to −ΔV. In this embodiment, releasing the pixel is accomplished by setting the appropriate column to −V bias , and the appropriate row to the same −ΔV, 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 3×3 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, because all the pixels remain in the 3-7 volt stability window. Row  1  is then strobed with a pulse that goes from 0, up to 5 volts, and back to zero. This actuates the ( 1 , 1 ) and ( 1 , 2 ) pixels and relaxes the ( 1 , 3 ) pixel. No other pixels in the array are affected. To set row  2  as desired, column  2  is set to −5 volts, and columns  1  and  3  are set to +5 volts. The same strobe applied to row  2  will then actuate pixel ( 2 , 2 ) and relax pixels ( 2 , 1 ) and ( 2 , 3 ). Again, no other pixels of the array are affected. Row  3  is similarly set by setting columns  2  and  3  to −5 volts, and column  1  to +5 volts. The row  3  strobe sets the row  3  pixels as shown in  FIG. 5A . After writing the frame, the row potentials are zero, and the column potentials can remain at either +5 or −5 volts, and the display is then stable in the arrangement of  FIG. 5A . It will be appreciated that the same procedure can be employed for arrays of dozens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the systems and methods described herein. 
       FIGS. 6A and 6B  are system block diagrams illustrating an embodiment of a display device  40 . The display device  40  can be, for example, a cellular or mobile telephone. However, the same components of display device  40  or slight variations thereof are also illustrative of various types of display devices such as televisions and portable media players. 
     The display device  40  includes a housing  41 , a display  30 , an antenna  43 , a speaker  45 , an input device  48 , and a microphone  46 . The housing  41  is generally formed from any of a variety of manufacturing processes as are well known to those of skill in the art, including injection molding, and vacuum forming. In addition, the housing  41  may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing  41  includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols. 
     The display  30  of exemplary display device  40  may be any of a variety of displays, including a bi-stable display, as described herein. In other embodiments, the display  30  includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display  30  includes an interferometric modulator display, as described herein. 
     The components of one embodiment of exemplary display device  40  are schematically illustrated in  FIG. 6B . The illustrated exemplary display device  40  includes a housing  41  and can include additional components at least partially enclosed therein. For example, in one embodiment, the exemplary display device  40  includes a network interface  27  that includes an antenna  43  which is coupled to a transceiver  47 . The transceiver  47  is connected to a processor  21 , which is connected to conditioning hardware  52 . The conditioning hardware  52  may be configured to condition a signal (e.g. filter a signal). The conditioning hardware  52  is connected to a speaker  45  and a microphone  46 . The processor  21  is also connected to an input device  48  and a driver controller  29 . The driver controller  29  is coupled to a frame buffer  28 , and to an array driver  22 , which in turn is coupled to a display array  30 . A power supply  50  provides power to all components as required by the particular exemplary display device  40  design. 
     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 of skill in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 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 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. 
     Processor  21  generally controls the overall operation of the exemplary display device  40 . The processor  21  receives data, such as compressed image data from the network interface  27  or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor  21  then sends the processed data to the driver controller  29  or to frame buffer  28  for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level. 
     In one embodiment, the processor  21  includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device  40 . Conditioning hardware  52  generally includes amplifiers and filters for transmitting signals to the speaker  45 , and for receiving signals from the microphone  46 . Conditioning hardware  52  may be discrete components within the exemplary display device  40 , or may be incorporated within the processor  21  or other components. 
     The driver controller  29  takes the raw image data generated by the processor  21  either directly from the processor  21  or from the frame buffer  28  and reformats the raw image data appropriately for high speed transmission to the array driver  22 . Specifically, the driver controller  29  reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array  30 . Then the driver controller  29  sends the formatted information to the array driver  22 . Although a driver controller  29 , such as a LCD controller, is often associated with the system processor  21  as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor  21  as hardware, embedded in the processor  21  as software, or fully integrated in hardware with the array driver  22 . 
     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&#39;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, array driver  22  is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller  29  is integrated with the array driver  22 . Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, display array  30  is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators). 
     The input device  48  allows a user to control the operation of the exemplary display device  40 . In one embodiment, input device  48  includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone  46  is an input device for the exemplary display device  40 . When the microphone  46  is used to input data to the device, voice commands may be provided by a user for controlling operations of the exemplary display device  40 . 
     Power supply  50  can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply  50  is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply  50  is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, power supply  50  is configured to receive power from a wall outlet. 
     In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver  22 . Those of skill in the art will recognize that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations. 
     The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example,  FIGS. 7A-7E  illustrate five different embodiments of the movable reflective layer  14  and its supporting structures.  FIG. 7A  is a cross section of the embodiment of  FIG. 1 , where a strip of metal material  14  is deposited on orthogonally extending supports  18 . In  FIG. 7B , the moveable reflective layer  14  is attached to supports at the corners only, on tethers  32 . In  FIG. 7C , the moveable reflective layer  14  is suspended from a deformable layer  34 , which may comprise a flexible metal. The deformable layer  34  connects, directly or indirectly, to the substrate  20  around the perimeter of the deformable layer  34 . These connections are herein referred to as support posts. The embodiment illustrated in  FIG. 7D  has support post plugs  42  upon which the deformable layer  34  rests. The movable reflective layer  14  remains suspended over the cavity, as in  FIGS. 7A-7C , but the deformable layer  34  does not form the support posts by filling holes between the deformable layer  34  and the optical stack  16 . Rather, the support posts are formed of a planarization material, which is used to form support post plugs  42 . The embodiment illustrated in  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 extra layer of metal or other conductive material has been used to form a bus structure  44 . This allows signal routing along the back of the interferometric modulators, eliminating a number of electrodes that may otherwise have had to be formed on the substrate  20 . 
     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 the portions of the interferometric modulator on the side of the reflective layer opposite the substrate  20 , including the deformable layer  34 . This allows the shielded areas to be configured and operated upon without negatively affecting the image quality. Such shielding allows the bus structure  44  in  FIG. 7E , which provides the ability to separate the optical properties of the modulator from the electromechanical properties of the modulator, such as addressing and the movements that result from that addressing. This separable modulator architecture allows the structural design and materials used for the electromechanical aspects and the optical aspects of the modulator to be selected and to function independently of each other. Moreover, the embodiments shown in  FIGS. 7C-7E  have additional benefits deriving from the decoupling of the optical properties of the reflective layer  14  from its mechanical properties, which are carried out by the deformable layer  34 . This allows the structural design and materials used for the reflective layer  14  to be optimized with respect to the optical properties, and the structural design and materials used for the deformable layer  34  to be optimized with respect to desired mechanical properties. 
       FIG. 8  schematically illustrates a portion of an exemplary interferometric modulator array  501 . The interferometric modulator array  501  is formed on a substrate  500 , which is transparent for a predetermined light spectrum and has a bottom surface  400 . Although not limited thereto, the substrate  500  is preferably made of glass. A single layer or stack of layers  502  is formed over the substrate  500 . The single layer  502  or at least one sub-layer (not shown) of the stack of layers  502  is made of a conductive material. The layer  502  or a sub-layer serves as a partial mirror as it both reflects and transmits some of the light incident thereto. For the sake of convenience, the term “stationary layer  502 ” is used to refer to the single layer or stack of layers  502  unless the specific terms are used. Deformable layers  506  are located over the stationary layer  502 . Support posts  504  are formed between the substrate  500  and the layers  506 , separating the deformable layers  506  from the substrate  500  and the stationary layer  502 . The deformable layers  506  lie in a generally parallel plane to that of the stationary layer  502 . The surface of the deformable layers  506  facing the stationary layer  502  is highly reflective of the predetermined light spectrum and serves as a full mirror. 
     This interferometric modulator array  501  is operated by applying or not applying an electric potential difference between the conductive portion of the stationary layer  502  and the deformable layers  506 . By applying a certain electric potential difference between them, for example 7 volts, the deformable layer  506  is driven to deform toward and contact the stationary layer  502  as in the case of the interferometric modulator  501   b . In this driven state, the interferometric modulator  501   b  is, for example, in an induced absorption mode, in which most of the light incident to the substrate  500  is absorbed by the interferometric modulator  501   b . If the interferometric modulator  501   b  is designed to operate in the visible light spectrum, the bottom surface  400  of the substrate  500  corresponding to the area of interferometric modulator  501   b  turns to black at the driven state. 
     The interferometric modulator  501   a , on the other hand, is illustrated in the configuration produced when no voltage is applied between the deformable layer  506  and the stationary layer  502 . This configuration is referred to as “the undriven state.” In this state, the deformable layer  506  is maintained separate from the stationary layer  502 , forming a space  499  referred to as an “interferometric cavity” between them. More accurately, the interferometric cavity  499  is defined as the distance between the reflective surface of the deformable layer  506  and the partial mirror surface of the stationary layer  502 . Light that is incident to the interferometric modulator  501   a  through the substrate  500  is interferometrically modulated via the cavity  499 . Depending on the depth of the cavity  499 , which is the distance between the partial mirror surface of the stationary layer  502  and the full mirror surface of the deformable layer  506 , the interferometric modulation selects a certain wavelength of the light, which is reflected from the bottom surface  400  of the substrate  500 . If the selected wavelength of the light is visible, the bottom surface  400  of the substrate  500  displays a visible light corresponding to the wavelength. One of ordinary skill in the art will well appreciate the interferometric modulation produced in the interferometric modulator  501 . 
       FIG. 9A  is a cross-sectional view of the interferometric modulator  501  of  FIG. 8  taken along lines  9 A- 9 A.  FIG. 9A  illustrates additional interferometric modulators  501   c - 501   e  arranged in the lateral direction of the interferometric modulator  501   b . In the illustrated embodiment, the stationary layer  502  is comprised of three sub-layers, for example, including a dielectric layer  413 , a mirror layer  415  and a conductor layer  417 . As illustrated, the deformable layer  506  is laterally spaced by the posts  504  and substantially parallel with the stationary layer  502 , creating an interferometric cavity  418  between them. Although not illustrated, additional layers may be formed over the deformable layer  506 . The overall micro-structure formed over the substrate  500  constitutes an array of interferometric modulators or array  411 . The interferometric modulator  501   c  is illustrated in an undriven state, which generally reflects a certain light through the substrate  500  depending upon the depth of the interferometric cavity  418 . Again, this depth determines the wavelength of light reflected on the surface  400 . The interferometric modulator  501   b  is illustrated in a driven state, which generally reflects no light on the surface  400 . The operation of the interferometric modulators  501   b  and  501   c  will be well appreciated by one of ordinary skill in the art. 
       FIG. 9B  illustrates the micro-construction of another embodiment of the interferometric modulator  501 . In this embodiment, the deformable layer  506  is connected to a mirror  419 , which is located between the deformable layer  506  and the stationary layer  502 . All of the other features are the same as in the embodiment of  FIG. 9A . In one embodiment, the mirror  419  is substantially rigid and has a highly reflective surface facing the stationary layer  502 . The deformable layer  506  functions to control the location of the mirror  419  with respect to the stationary layer  502 , and the rigid mirror  419  does not experience any significant bending or deformation in this process. In this embodiment, the interferometric cavity  418  is defined by the space between the mirror  419  and the stationary layer  502 , and more accurately the mirror layer  415 . The interferometric modulator  501   c  is illustrated in an undriven state, while the interferometric modulator  501   b  is illustrated in a driven state. 
     In the embodiments illustrated in  FIGS. 9A and 9B , the stationary layer  502  may be formed by a single layer functioning as both a conductor and a mirror. Alternatively, the stationary layer  502  may be formed of two layers, for example the pair of a mirror layer and a conductive layer, the pair of a dielectric layer and a bi-functional layer of electrode and mirror. Further, in other embodiments, one or more additional layers may be formed over the stationary layer  502  or in between the layers  413 ,  415  and  417 . Also, although not illustrated, the deformable layer  506  or the mirror  419  of the embodiments of  FIGS. 9A and 9B  may have a laminated construction. For example, a dielectric layer may be formed on a surface of the deformable layer  506  ( FIG. 9A ) or the mirror  419  ( FIG. 9B ), particularly the surface facing the stationary layer  502 . The dielectric layer on the deformable layer  506  ( FIG. 9A ) or the mirror  419  ( FIG. 9B ) may be useful when the stationary layer  502  has the construction that does not include the dielectric layer  413 . One of ordinary skill in the art will appreciate the formation of various films or layers making the stationary layer  502  and/or the additional layers that can be formed on the deformable layer  506  or mirror  419 . 
     In a typical construction, as illustrated in  FIGS. 8 ,  9 A and  9 B, the deformable layer  506  or the mirror  419  may physically contact the stationary layer  502  during its operation, particularly when the interferometric modulator  501  is in its driven state. Physical contact or interaction between the two layers may cause some adverse results, particularly if it is between the surfaces defining the interferometric cavity, which are mirror surfaces of the stationary layer  502  and the deformable layer  506  (or mirror  419 ). The dielectric layer  413  over the mirror layer  415  is provided to minimize or reduce the mechanical and/or electrical interactions between the surfaces forming the interferometric cavity. For the same reason, a dielectric layer (not shown) can be formed on the surface of the deformable layer  506  or the mirror  419 . However, repeated changes between the driven and undriven states can eventually result in degradation of such dielectric layers mechanically and/or electrically. 
     Also, the dielectric layers may contain some charges in them due to, not limited to, imperfection of the manufacturing processes. The charges in the dielectric layers may create attractive forces between the deformable layer  506  (or mirror  419 ) and the stationary layer  502 . Some additional force may be needed to separate the deformable layer  506  (or the mirror  419 ) from the stationary layer  502  when a unit of the interferometric modulator  501  is operating from its driven state to undriven state. Also, when the dielectric layer  413  contacts the deformable layer  506  (or the mirror  419 ), there may be some other form of attractive force between the materials of the two contacting layers. Furthermore, even in an embodiment where the stationary layer  502  does not contact the deformable layer  506  (or the mirror  419 ) in the driven state, the gap between them is generally very small, for example, in the order of 200 Å (20 nm). In certain conditions, moisture from the surrounding environment may condense in the small gap and form a liquid layer. To separate the layers in that condition, additional force overcoming the surface tension of the liquid layer is needed. 
     The degradation of the dielectric layer(s) and the need for additional forces may be overcome by various techniques and features of embodiments described herein, which include use of components such as landing pads, bumps and springs. Although introduced in light of the degradation of the dielectric layer and the associated need for the additional force, the below-described technical features may be used in any constructions of the interferometric modulator utilizing the MEMS technology without such degradation or need of additional force. For the sake of simplicity, the below-described embodiments of the interferometric modulators have the general architecture illustrated in  FIGS. 8 and 9A . However, all of the features can be applied to any other architecture of the interferometric modulators, including the embodiment illustrated in  FIG. 9B . 
     An embodiment provides an interferometric modulator, comprising: a first layer comprising a first reflective planar portion; a second layer comprising a second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a first position and a second position, the first position being a first distance from the first layer, the second position being a second distance from the first layer, the second distance being greater than the first distance; and a member having a surface located between the first layer and the second layer, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member. Various aspects of this embodiment are described in greater detail below. 
     Landing Pads 
       FIGS. 10A and 10B  illustrate an embodiment of the interferometric modulator  301  which includes landing pads  513 . In the illustrated embodiment, the landing pads  513  extend from the substrate  500  through the stationary layer  502  beyond the top surface of the stationary layer  502 . Accordingly, when the interferometric modulator  301  is driven from its undriven state ( FIG. 10A ) to the driven state ( FIG. 10B ), travel of the deformable layer  506  is interrupted by the landing pads  513 , which operate to prevent further travel of the deformable layer  506  toward the stationary layer  502 , and thus to prevent the physical contact between those layers  502  and  506 , and to maintain a desired separation distance between the layers  506  and  502 . As discussed above with reference to  FIGS. 9A and 9B , the stationary layer  502  can be formed of a single layer or multiple layers. Also, the stationary layer  502  may or may not include a dielectric layer  413 . It will be recognized that the landing pads  513  are examples of members having a surface  514  located between the deformable layer  506  and the stationary layer  502 . The landing pads  513  define a gap region  418   a  between the deformable layer  506  and the stationary layer  502  when the interferometric modulator  301  is in the driven state ( FIG. 10B ). The deformable layer  506  in the gap region  418   a  does not contact either the stationary layer  502  or the landing pads  513 . 
     In another embodiment as illustrated in  FIG. 10C , the landing pads  513  may be formed on the top surface of the stationary layer  502 . In another embodiment as illustrated in  FIG. 10D , the landing pads  513  may extend from a sub-layer  415  of the stationary layer  502  through one or more other sub-layers  413 . In still another embodiment as illustrated in  FIG. 10E , the landing pads  513  may be integrally formed with the substrate  500  and extend through the stationary layer  502 . In a further embodiment, as illustrated in  FIG. 10F , the landing pad  513  may extend from below the interface between the substrate  500  and the stationary layer  502  and through both the substrate  500  and the stationary layer  502 . 
     In another embodiment as illustrated in  FIG. 10G , the landing pads  513  may be formed on the deformable layer  506  or mirror  419  (not shown). In other embodiments as illustrated in  FIGS. 10H and 10I , the landing pads  513  may be formed on both the deformable layer  506  and the stationary layer  502 . In the foregoing embodiments where one or more landing pads  513  are formed on the deformable layer  506 , although not illustrated, the landing pads  513  may extend from various sub-layers, if any, of the deformable layer  506 , as the landing pads  513  may extend from various sub-layers of the stationary layer  502  or substrate  500  illustrated in  FIGS. 10A-10F . 
     The landing pads  513  can be positioned in various locations on the stationary layer  502  or the deformable layer  506 , or both within the interferometric cavity  418 .  FIG. 10J  is a top cross-sectional view of the embodiment of  FIG. 10A  taken along line  10 J- 10 J ( FIG. 10A ). In the illustrated embodiment of  FIG. 10J , for example, the landing pads  513  are located generally on peripheral portions of the stationary layer  502  and/or deformable layer  506  within the interferometric cavity  418 . Optionally, the landing pads  513  are positioned on the portions of the stationary layer  502  and/or deformable layer  506  where the existence of the landing pads  513  would not affect the optical characteristics of the interferometric modulator  301 . In another embodiment (not illustrated), the landing pads  513  can be positioned on a central portion of the stationary layer  502  and/or deformable layer  506  within the interferometric cavity  418 . In still another embodiment (not illustrated), the landing pads  513  can be positioned on both the central and peripheral portions of the stationary layer  502  and/or deformable layer  506  within the interferometric cavity  418 . In a further embodiment (not illustrated), the landing pads  513  can be located where the deformable layer  506  first contacts the stationary layer  502 . 
     Referring again to  FIGS. 10A and 10G , it is seen that the landing pads  513  extend beyond the surface of the stationary layer  502  ( FIG. 10A ) or the deformable layer  506  ( FIG. 10G ) by a height indicated at  519 . In one embodiment, the landing pad height  519  is selected so as to prevent physical contact between the deformable layer  506  and the stationary layer  502 . In another embodiment, the height  519  is selected to not only prevent such contact, but to define the depth of the interferometric cavity  418  in the driven state of the interferometric modulator  301 , and so as to enable production of the desired optical characteristics of the interferometric modulator  301 . In one embodiment, the landing pads  513  are configured to precisely define the distance between the two layers  506  and  502 . Thus, the landing pads  513  can be used to control the minimal size of the interferometric cavity  418  with a high degree of accuracy and precision. 
     In one embodiment of interferometric modulator  301  for use as a display element, the interferometric cavity depth at the driven state is short enough to absorb most, if not all, of the visible light. In another embodiment of interferometric modulator  301  for use as a display element, the interferometric cavity depth at the driven state reflects a selected visible wavelength of incident light. Since the interferometric cavity depth at the driven state is determined by the thickness of various layers and/or structures positioned between the reflective surfaces of the layers  502  and  506 , the height  519  of the landing pad  513  is designed in view of the color to be displayed on the substrate  500 . In such display embodiments, the height  519  is, for example, from about 50 Å to about 1500 Å, and preferably from about 100 Å to about 300 Å. 
     In one embodiment, the landing surface  514  of the landing pads  513  is substantially planar, as illustrated in  FIG. 10A . Also as in the embodiment illustrated in  FIG. 10A , the landing surface  514  may be substantially parallel to the surface of the deformable layer  506  or the stationary layer  502  that lands on the landing surface  514 . In this embodiment, the size of the landing surface  514  is from about 0.1 micron to about 25 microns, and preferably from about 3 microns to about 10 microns. In another embodiment as illustrated in  FIG. 10C , the landing surface  514  of the landing pads  513  may be rough, bumpy or embossed. In another embodiment as illustrated in  FIG. 10F , the landing surface  514  of the landing pads  513  may be tilted from the plane parallel to the counterpart surface landing on the landing surface  514 . In still another embodiment as illustrated in  FIG. 10D , the landing surface  514  may be substantially round. 
     The landing pads  513  can be made from various materials, including, but not limited to, a metal, an alloy, a dielectric material, and an elastomeric material. For example, such materials may include metals including aluminum, semiconductors, oxides of metals or semiconductors, nitrides of metals or semiconductors, and oxynitrides of metals or semiconductors. Preferably, the materials forming landing pads  513  are those that substantially do not or only insignificantly affect the electrical or optical characteristics of the interferometric modulator  301 . 
     In one embodiment, the landing pads  513  are optically transparent for the light spectrum which the interferometric modulator  301  can select. Optionally, in the case where the light spectrum includes visible light, the transparent material that can be used for the landing pads  513  includes, for example, oxides of metals or semiconductors, nitrides of metals or semiconductors, and oxynitrides of metals or semiconductors. In another embodiment, the landing pads  513  may be made of a material that absorbs the light spectrum which the interferometric modulator  301  can select. In another embodiment, the landing pads  513  may be covered with the light absorbing material. Optionally, in the case where the light spectrum includes visible light, the light absorbing material that can be used for the landing pads  513  includes, for example, polymeric materials or metals, such as chrome, nickel, titanium, molybdenum, etc. In still another embodiment, the landing pads  513  may be made of a material that reflects the light spectrum which the interferometric modulator  301  can select. In still another embodiment, the landing pads  513  may be covered with the light reflecting material. Optionally, in the case where the light spectrum includes visible light, the light reflecting material that can be used for the landing pads  513  includes, for example, polymeric materials or metals, such as silver, aluminum, gold, platinum, etc. 
     In a unit of the interferometric modulator  301 , multiple landing pads  513  can be used. Thus, 2, 3, 4, 5, 6 or more landing pads  513  can be fabricated to provide the landing surfaces of the layers of the interferometric modulator  301 . Preferably, the multiple landing pads  513  have substantially the same heights  519 . Optionally, the multiple landing pads  513  are arranged as remote as possible from one another on the stationary layer  502  or the deformable layer  506 . In one embodiment, a single landing pad  513  per unit of the interferometric modulator  301  can be used. 
     The landing pads  513  may be positioned in any cross-sectional shape lying in a plane parallel to the stationary layer  502 . In the embodiment illustrated  FIG. 10J , the cross-sectional shape of the landing pads  513  is substantially circular, oval, rectangular and pentagonal, although not limited thereto. 
     The landing pads  513  can be fabricated in various configurations and made of various compounds as discussed above, utilizing the presently existing techniques of depositing and selectively etching a material. In one embodiment, the landing pads  513  can also be created from deformations of the layers of the interferometric modulator  301 . In another embodiment, the landing pads  513  can be created using conventional semiconductor manufacturing techniques. 
     MEMS devices often comprise an array of individual elements activated by application of a voltage potential. The elements may comprise many different types of structures, including mirrors, switches, gears, motors, etc. The application of the voltage potential may be done by applying the potential directly to the structure, or by manipulation of electrical or magnetic fields around the structure. For example, an element may be activated by electrostatic attraction between the element and another structure to which the voltage is applied. For purposes of this discussion, the structure to which the voltage is applied will be referred to as an electrode. 
     In this type of device, there is generally a gap between the element and the electrode. This gap may give rise to capacitive charge between the element and the electrode. For most MEMS devices with this type of structure, the performance of the device will be improved by lowering the capacitance in the gap. This reduction of capacitance produces more predictable performance, and there is a lowered risk of capacitive discharge, which can damage the element or the neighboring elements. 
     In a bi-chrome display, such as a display that switches between black and white, one interferometric modulator element might correspond to one pixel. In a color display, three or more interferometric modulator elements may make up each pixel, e.g., one each for red, green and blue. The individual interferometric modulator elements are controlled separately to produce the desired pixel reflectivity. Typically, a voltage is applied to the movable wall, or element, of the cavity, causing it to be electrostatically attracted to the other electrode, resulting in a change in the color of the pixel seen by the viewer. 
     The interferometric modulator is merely one type of an active MEMS device that has an element separated from an electrode, where the electrode is used to activate the device. Another example may be a MEMS switch. These devices may suffer from high capacitance that may affect their operation. If a device has high capacitance in the mechanically relaxed state, it may take longer for the attractive charge to activate the device, slowing the device response time. 
     The capacitance of the device can be approximated by the capacitance of an idealized parallel-plate capacitor, given by C=∈A/d, where ∈ is the electrical permittivity of the material between the movable wall and the electrode, A is the surface area of the electrode, and d is the gap distance between the movable wall and the electrode. The electrical permittivity of a material is equal to the dielectric constant K of the material multiplied by the electrical permittivity ∈ 0  of vacuum. In various embodiments, the capacitance between the movable wall and the electrode is reduced by increasing the size of the gap between the electrode and the movable wall and/or by lowering the dielectric constant of the material within the gap (that is, by decreasing ∈ in the above equation). For example, the gap can comprise a material with a low dielectric constant, such as a gas or a mixture of gases (e.g., air). This use of a material within the gap with a reduced dielectric constant has the effect of lowering the capacitive charging of the dielectric surface, thereby lowering the capacitance. 
     An embodiment of a processing flow for a MEMS device is shown in  FIG. 11 . In that embodiment, an electrode is formed on a substrate at step  150 . A multilayer dielectric stack is deposited at step  152 , and patterned at step  154 . Portions of the multilayer dielectric stack, e.g., a thin oxide stop layer, are removed at step  156 . The MEMS device then undergoes its appropriate processing at step  158 , where the processing includes the use of a sacrificial layer to form the gap. The sacrificial layer, and portions of the multilayer dielectric stack not under the oxide stops, are removed at step  160 . In another embodiment, a graded dielectric material is deposited at step  152  instead of the multilayer dielectric stack. The remainder of the process illustrated in  FIG. 11  continues in a similar manner, including removing upper portions of the graded dielectric material at step  156 , and removing lower portions of the graded dielectric material at step  160 , along with the sacrificial layer. 
     An embodiment of an interferometric modulator having a multilayer dielectric stack is shown in  FIG. 12 . In this embodiment the portions of the dielectric stack  513  not removed appear across the device  140 , rather than just under the support posts  18 . The process of forming the oxide stops can be modified as desired to leave portions of the dielectric stack wherever desired. 
       FIGS. 13-19  illustrate an embodiment of a process for the fabrication of an interferometric modulator that includes landing pads  513 , using conventional semiconductor manufacturing techniques such as photolithography, deposition, masking, etching (e.g., dry methods such as plasma etch and wet methods), etc. Deposition includes “dry” methods such as chemical vapor deposition (CVD, including plasma-enhanced CVD and thermal CVD) and sputter coating, and wet methods such as spin coating.  FIG. 13  illustrates the formation of a stationary layer  502 , which can be a single layer structure or multiple sub-layer structure as described above. In a single layer structure where the layer  502  functions as both electrode and mirror, the layer  502  is formed by deposition of an electrode material  410  on the substrate  500  and subsequent patterning and etching. The electrode material  410  is conductive and may be a metal or a semiconductor (such as silicon) doped to have the desired conductivity. In one embodiment (not shown in  FIG. 13 ), the electrode layer  410  (and the corresponding first electrode  502 ) is a multilayer structure comprising a transparent conductor (such as indium tin oxide) and a primary mirror (such as chromium). 
       FIG. 14  illustrates the formation of a dielectric layer  540  on the substrate  500  and the stationary layer  502  by deposition, preferably by CVD. The lower or “bulk” portion  550  of the dielectric layer  540  need not be a dielectric material and is preferably a material that may be removed in a later etching step, and thus may be molybdenum, a silicon-containing materials (e.g., silicon, silicon nitride, silicon oxide, etc.), tungsten, or titanium, preferably silicon oxide. The upper or “stop” portion  560  of the dielectric layer  540  is preferably a material that is more resistant to a later etching step than the bulk portion  550 , and may be a metal (e.g., titanium, aluminum, silver, chromium) or a dielectric material, preferably a metal oxide, e.g., an aluminum oxide. Aluminum oxide may be deposited directly or by deposition of an aluminum layer followed by oxidation. The upper and lower portions  550 ,  560  of the dielectric layer  540  may be composed of the same material or may be different materials. Additional layers, e.g., intermediate layers, may also be formed over the stationary layer  502 . For example, in an embodiment (not shown), an intermediate layer is formed over at least a portion of the stationary layer  502 , and the dielectric layer  540  is formed over the intermediate layer and over the stationary layer  502  underlying the intermediate layer. Such intermediate layer(s) formed between the stationary layer  502  and the dielectric layer  540  may be utilized for various purposes. For example, the intermediate layer may be an optical layer, a barrier layer and/or a non-conductive layer (such as a second dielectric layer). In an embodiment, in any particular dielectric layer  540 , at least one of the portions  550 ,  560  is an electrical insulator. 
     The upper portion  560  may be thinner or thicker than the lower portion  550 . For example, in one embodiment the upper portion  560  may have a thickness in the range of about 50 Å to about 500 Å, and the lower portion  550  may have a thickness in the range of about 200 Å to about 3000 Å. As described in greater detail below, the upper or “stop” portion  560  may serve as an etch barrier (e.g., functioning in a manner somewhat analogous to a photomask) during a later process step, and a part of the lower portion  550  may serve as a “sacrificial” layer that is removed. In this embodiment, the upper portion  560  is more resistant to removal (e.g. by etching) than the lower portion  550 . In a particular embodiment, the upper portion  560  is aluminum oxide and the lower portion  550  is silicon oxide. The upper and lower portions  550 ,  560  need not be distinct layers and thus the dielectric layer  540  may be a graded layer. For example, the dielectric layer  540  may be compositionally graded so that the composition varies as a function of position (e.g., as a function of vertical position in  FIG. 14 ) within the dielectric layer. For example, the dielectric layer  540  may be a graded silicon nitride layer in which the relative amounts of silicon and nitrogen vary on going from the upper surface  420 ,  421  to the interface  422 ,  423  with the first electrode layer  502  and the substrate  500 . In one embodiment, for example, the graded silicon nitride layer is enriched in silicon at the interface  421  with the first electrode  502  relative to the overall composition of the graded silicon nitride. In another embodiment, the dielectric layer  540  may be a graded silicon oxide layer in which the relative amounts of silicon and oxygen vary on going from the upper surface  420 ,  421  to the interface  422 ,  423  with the first electrode layer  502  and the substrate  500 . In one embodiment, for example, the graded silicon oxide layer is enriched in silicon at the interface  421  with the first electrode  502  relative to the overall composition of the graded silicon oxide. 
       FIG. 15  shows that parts of the upper portion  560  are then removed to form “stops”  565  by masking the upper portion  560  with a photomask  610 , then etching to selectively remove the exposed part of the upper portion  560  of the dielectric layer  540  to form a variable thickness dielectric layer  570  as illustrated in  FIG. 16 . The etching is carried out to expose part of the lower portion  550  of the dielectric layer  540 . The etching is controlled so that a substantial portion of the lower portion  550  of the dielectric layer  540  remains. For example, a small part of the lower portion  550  may be removed during etching, but most of the lower portion  550  preferably remains until it is removed during subsequent processing as described below, thereby increasing the unevenness of the dielectric layer and increasing the average peak-to-valley surface variation of the dielectric layer. 
     The fabrication process continues as illustrated in  FIG. 17 , including formation of a sacrificial layer  710  (which is later removed to form the interferometric cavity  418 ) by deposition, patterning and etching; formation (and optional planarization) of the posts  504 ; and formation of the deformable layer  506  by deposition, patterning and etching. Sacrificial layer  710  is preferably molybdenum. In an embodiment, the deformable layer  506  is an upper electrode. Because these steps are carried out over variable thickness dielectric layer  570 , the interface between sacrificial layer  710  and deformable layer  506  may not be completely flat. For example, in the illustrated embodiment, the lower surface contour  741 ,  742  of the deformable layer  506  tends to substantially parallel the contours of the layers beneath it, e.g., the steps in the variable thickness dielectric layer  570 . However, those skilled in the art will understand that variable thickness dielectric layer  570  may have a thickness of only 100 Å, and thus  FIG. 17  (not to scale) may exaggerate the undulations in the lower contour  741 ,  742 . 
       FIG. 18  illustrates etching with an etchant to remove the “sacrificial” layers, sacrificial layer  710  and the exposed part of the lower portion  550 . As the etchant, XeF 2 , F 2  or HF may be used alone or in combination. The upper or “stop” portion  565  substantially protects the part of the lower portion  550  that is beneath it from being removed by etching, functioning in a manner somewhat analogous to a photomask. The resulting interferometric modulator  1800  illustrated in  FIG. 19  includes the interferometric cavity  418 , a portion  910  of the stationary layer  502  that is not covered by a variable thickness dielectric layer  920  (comprising the upper variable thickness dielectric layer  565  and a variable thickness lower portion  925 ). The lower portion  550  need not be completely removed by etching, and thus part of the lower portion  550  may remain over the stationary layer  502 , preferably where the stationary layer  502  is a single conductor layer. 
     This invention is not limited by theory, but it is believed that XeF 2  serves as a convenient source of F 2  gas. Other etchants such as F 2  and HF may be used in place of or in addition to XeF 2 . In an embodiment, the etchant removes the lower portion  550  at an etch rate that is higher than an etch rate for removing the upper portion  565 . Thus, in an embodiment, the difference in average thickness variation between the lower surface contour  741 ,  742  of the deformable layer  506  and the upper contour of the variable thickness dielectric layer  570  tends to increase as etching proceeds, e.g., as the variable thickness dielectric layer  570  is etched to form the variable thickness dielectric layer  920 . 
     The variable thickness dielectric layer  920  comprises landing pads  513 . The landing pads  513  project upward from the stationary layer  502  and substantially prevent contact between the stationary layer  502  and the deformable layer  506 , during both the driven and undriven states. The variable thickness dielectric layer may be a discontinuous layer, e.g., as illustrated by dielectric layer  920  in  FIG. 19 , or may be a continuous layer in which the thickness variation is manifested as peaks and valleys on the surface of the layer. 
     It will be appreciated by those skilled in the art that the variable thickness dielectric layer  920  may comprise multiple columns of dielectric material that project upward from the bottom electrode and substantially prevent contact between the first and second electrode, during both the driven and undriven states, e.g., as illustrated in  FIG. 12 . Thus, the remaining surface area of the bottom electrode (e.g., the surface portion  910  not covered by such a column) need not be coated or covered by an insulating layer. A substantial improvement in capacitance is thus obtained, because the dielectric constant of air (about 1) is lower than that of insulating materials such as metal oxides disclosed in U.S. Pat. No. 5,835,255. The variable thickness dielectric layer may be a discontinuous layer, e.g., as illustrated by dielectric layer  920  in  FIG. 15 , or may be a continuous layer in which the thickness variation is manifested as peaks and valleys on the surface of the layer. In either case, the distance between the top of the landing pad  513 , for example, and the bottom of the valley or gap  910 , for example, is preferably about 50 Å or greater, more preferably in the range of about 100 Å to about 3,000 Å. 
     Those skilled in the art will appreciate that, in the illustrated embodiment of  FIG. 18 , the upper or “stop” portion  565  that is patterned above the lower or “bulk” portion  550  prevents the bulk layer from being completely etched away by the XeF 2  (similar to any masking step used to pattern previous layers). The areas of the bulk layer  550  that are not protected by the stop portion  565  form a sacrificial portion that is later removed, and the portions of the bulk material  925  below the stop  565  remain, forming a variable thickness dielectric layer  920  (comprising an upper layer  565  and a lower layer  925 ), e.g., comprising one or more islands or columns of multilayer dielectric material that substantially prevent contact between the first and second electrodes. Although the lower contour  741 ,  742  of the underside of the deformable layer  506  illustrated in  FIG. 18  tends to substantially parallel the upper contour of the variable thickness dielectric layer  570 , it does not substantially parallel the upper contour of the variable thickness dielectric layer  920  illustrated in  FIG. 19  because etching removes at least a part of the lower portion  550  that is not protected by the upper portion  565  of the variable thickness dielectric layer  570 . This etching to remove the exposed part of the lower portion  550  creates extra space between the lower contour  742  of the deformable layer  506  and the surface portion  910  of the stationary layer  502 . 
       FIG. 19  illustrates an actuated interferometric modulator  1801 . During actuation, the lower contour  741  of the actuated deformable layer  506   a  may contact the top of the stops  565 , e.g. at the landing pads  513  in the illustrated embodiment, thereby creating regions in which the lower contour  741  of the deformable layer  506  is spaced from the surface portion  910  of the lower electrode  502 . These regions include a low dielectric constant gap  418   a  between the lower contour  742  of the actuated deformable layer  506   a  and the surface portion  910  of the stationary layer  502 . Thus, as illustrated in  FIG. 19 , the profile of the underside of the actuated deformable layer  506   a  is different from the profile of the upper side of the variable thickness dielectric layer  920 , so that the low dielectric constant gap  418   a  exists between the actuated deformable layer  506   a  and the stationary layer  502  during operation. Thus, the lower surface of the deformable layer  506  has a surface profile variation  741 ,  742  that is less than a surface profile variation of the variable thickness dielectric layer  920 . In certain embodiments, the surface profile variation is equal to the average peak-to-valley surface profile variation. The average peak-to-valley surface profile variation of the lower surface of the upper electrode may be in the range of about 50 Å to about 200 Å. The average peak-to-valley surface profile variation of the variable thickness dielectric layer may be in the range of about 200 Å to about 1000 Å. Average peak-to-valley surface profile variation may be determined by scanning electron microscopy and/or atomic force microscopy. In certain embodiments, the average peak-to-valley surface profile variation is the difference between the average peak heights and the average valley depths of the layer over a selected area. 
     It will be recognized that the landing pads  513  are examples of members having an upper surface located between the deformable layer  506  and the stationary layer  502 . The landing pads  513  define a gap region  418   a  between the deformable layer  506   a  and the stationary layer  502  when the interferometric modulator  1801  is in the driven state ( FIG. 19 ). The lower surface contour  742  of the deformable layer  506   a  in the gap region  418   a  does not contact either the stationary layer  502  or the landing pads  513 . 
       FIG. 20  illustrates another embodiment in which the sacrificial layer is planarized before deposition of the upper electrode. The structure  1900  illustrated in  FIG. 20  may be formed from the structure  1600  illustrated in  FIG. 17  by planarizing the sacrificial layer  710  to produce a relatively planar surface  746 . In an alternative embodiment (not illustrated), the relatively planar surface is formed by depositing a planarization layer over the sacrificial layer  710 , instead of or in addition to planarizing the sacrificial layer  710 . A deformable layer  506  is then formed over the surface  746  as illustrated in  FIG. 16 . In an embodiment, the deformable layer  506  is an upper electrode. The sacrificial layer  710  may then be removed to form a gap  418  as illustrated in  FIG. 21  in a manner generally similar to that illustrated in  FIG. 18 . Removal of the part of the lower portion  550  that is not protected by the upper portion  565  of the variable thickness dielectric layer  570  (as illustrated in  FIG. 18 ) is optional for the configuration illustrated in  FIGS. 20-21  because the lower contour  747  of the deformable layer  506  is relatively planar. Thus, the profile of the underside of the deformable layer  506  is different from the profile of the upper side of the variable thickness dielectric layer  570  (regardless of whether the part of the lower portion  550  that is not protected by the upper portion  565  of the variable thickness dielectric layer  570  is removed or not) so that a low dielectric constant gap(s) exists between the upper deformable layer  506  and lower stationary layer  502  during operation. Thus, the lower contour  747  of the deformable layer  506  has a surface profile variation that is less than a surface profile variation of the variable thickness dielectric layer  570 . 
     In the illustrated embodiments, the variable thickness dielectric layer  920  is formed over the stationary layer  502  (in this context, “over” refers to the relative location for the orientation illustrated in  FIG. 19 ). A variable thickness dielectric layer may be formed elsewhere in the cavity  418 , e.g., under the deformable layer  506 . Thus, for example, a variable thickness dielectric layer may be formed on the first electrode and/or on the second electrode of an interferometric modulator. Those skilled in the art will also appreciate that an interferometric modulator may contain three or more electrodes, and thus may contain two or more variable thickness dielectric layers, e.g., a variable thickness dielectric layer between each of the electrodes. 
     In the illustrated embodiment, portions of the cavity may contain a low dielectric constant material, e.g., some or all of the interior walls of the cavity  418  may optionally be coated or covered with a low dielectric constant material. For example, after etching to form the interferometric modulator illustrated in  FIG. 19 , a layer of low dielectric constant material (not shown) may be formed on the surface portion  910  of the stationary layer  502 . Preferably, any such layer of low dielectric constant material is relatively thin, such that a gap remains between the top electrode and the low dielectric constant material during both the driven and undriven states. Other interior walls of the cavity  418  that may coated with a low dielectric constant material include the deformable layer  506  (which may be an upper electrode) and the variable thickness dielectric layer  565 . 
     Silicon dioxide has a dielectric constant of approximately 3.8. Preferred low dielectric constant materials have a dielectric constant less than that of silicon oxide, i.e., less than 3.8. Exemplary materials compatible with embodiments described herein include, but are not limited to, porous dielectric materials (e.g., aerogels) and modified silicon oxides. See, e.g., U.S. Pat. Nos. 6,171,945 and 6,660,656, both of which describe low dielectric constant materials and methods for making them which are compatible with embodiments described herein. Preferred low dielectric constant materials have a dielectric constant of about 3.3 or less, more preferably about 3.0 or less, and most preferably about 2.0 or less. 
     In another embodiment (not illustrated), a variable thickness dielectric layer is formed by depositing a dielectric layer having a relatively uniform thickness on the first and/or second electrodes (e.g., over the stationary layer  502  as shown in  FIG. 13 ), then continuing the fabrication process as shown in  FIGS. 14-16  but without the masking step shown in  FIG. 15 . Then, during subsequent etching (e.g., as illustrated in  FIGS. 18-19 ), the flow of the etchant is controlled so that the dielectric layer having a relatively uniform thickness is etched to a greater extent in some areas than others, resulting in a variable thickness dielectric layer. 
     It will be appreciated by those skilled in the art that a variable thickness dielectric layer, e.g., comprising multiple columns of dielectric material that project upward from the bottom electrode, may also reduce damping of the interferometric modulator during operation, and thus may provide increased device switching speed by facilitating escape of the damping medium (e.g., air) from the cavity. It will also be appreciated that the variable thickness dielectric layer has a reduced dielectric constant as compared to a comparable uniform thickness dielectric layer of the same overall thickness as the variable thickness dielectric layer. The reduced dielectric constant may advantageously reduce the RC time constant of the interferometric device into which it is incorporated, based on the relationship time =resistance ×capacitance, thus increasing device switching speed. Certain embodiments provide an interferometric modulator made by a process described herein, wherein the interferometric modulator comprises a variable thickness dielectric layer. Such an interferometric modulator may have a lower capacitance than a comparable interferometric modulator having a uniform thickness dielectric layer in place of the variable thickness dielectric layer. Such an interferometric modulator may also have increased performance (e.g., increased switching speed resulting from reduced damping and/or from a reduced RC time constant) than a comparable interferometric modulator having a uniform thickness dielectric layer in place of the variable thickness dielectric layer. It will also be appreciated that use of a variable thickness dielectric layer as described herein may result in reduced contact area between moving parts of the MEMS device, e.g., a reduced contact area between the dielectric layer and the movable electrode. This reduction in contact area may result in increased mechanical reliability and/or reduced wear. Electrical reliability may also be improved by use of a variable thickness dielectric layer that results in reduced electrical contact area with the moveable electrode. Such reduced electrical contact area may result in reduced electrical charging of the dielectric layer. 
     Bumps 
       FIGS. 22A and 22B  illustrate an embodiment of an interferometric modulator  401  that includes bumps  511 . In the illustrated embodiment, a plurality of bumps  511  is formed on the top surface of the stationary layer  502 . Accordingly, when the interferometric modulator  401  is driven from its undriven state ( FIG. 22A ) to the driven state ( FIG. 22B ), the deformable layer  506  contacts the bumps  511 , which act to prevent or minimize the physical contact between the deformable layer  506  and the stationary layer  502 . Further, with the existence of the bumps, the area of contact between the deformable layer  506  and the stationary layer  502  can be reduced. 
     As discussed above with reference to  FIGS. 9A and 9B , the stationary layer  502  includes at least one conductive layer but can be formed of a single layer or multiple layers. In any of the constructions of the stationary layer  502 , the bumps  511  are preferably located on the top surface of the stationary layer  502 . In one embodiment, the top surface is made of a dielectric material and the bumps  511  are located on the dielectric surface. In another embodiment, the top surface of the stationary layer  502  is made of a conductive layer, and the bumps  511  are located on the conductive surface. 
     In another embodiment as illustrated in  FIG. 22C , the bumps  511  may be located on the deformable layer  506  or mirror  419  (not shown). Again, the deformable layer  506  (or mirror  419 ) may include multiple sub-layers. In any of the constructions, the bumps  511  are preferably located on the surface of the deformable layer  506  (or mirror  419 ) facing the stationary layer  502 . In another embodiment as illustrated in  FIG. 22D , the bumps  511  may be located on both the deformable layer  506  and the stationary layer  502 . 
     The plurality of bumps  511  can be positioned in various locations on the stationary layer  502  and/or the deformable layer  506  within the interferometric cavity  418 . In one embodiment, the bumps  511  are located throughout the surface of the stationary layer  502  and/or the deformable layer  506 . In another embodiment, the bumps  511  are located primarily on a central portion of the stationary layer  502  or the deformable layer  506 . In the area where the bumps  511  are located, the bumps  511  may be regularly, sporadically or randomly arranged on the surface of the stationary layer  502  or the deformable layer  506 . 
     The bumps  511  may be fabricated in various shapes. In an embodiment as illustrated in  FIG. 22E , the bumps  511  may not have a regular shape and may comprise irregular protrusions from the stationary layer  502  or the deformable layer  506 . In other embodiments, the bumps  511  may have one or more regular shapes as illustrated in  FIGS. 22A-22D . In the embodiments of regularly shaped bumps, the bumps  511  may have a distal surface  512  ( FIG. 22A ). In the illustrated embodiments, the distal surface  512  is substantially planar and parallel to the counterpart surface of the deformable layer  506  (or the stationary layer  502  in the embodiment of  FIG. 22C  or the counterpart bumps in the embodiment of  FIG. 22D ). In another embodiment, the distal surface  512  may be planar but tilted with reference to the counterpart surface (not illustrated). In still another embodiment, the distal surface  512  of the bumps  511  may be round or rough (not illustrated). 
     The bumps  511  protrude from the stationary layer  502  or the deformable layer  506  by a height indicated at  515  of  FIG. 22A . The height  515  of a bump  511  is defined as the distance between the distal end (distal surface  512  in  FIG. 22A ) of the bump  511  and the surface from which the bump  511  protrudes. In some situations where the bumps are formed of the same material as the underlying layer and are shaped irregularly, the reference surface may be difficult to determine. In such cases, the height  515  of a bump  511  is the farthest distance between the distal end of the bump and the surface of the stationary layer  502  and/or the deformable layer  506 . In some embodiments, the bumps  511  have substantially the same height  515 . In other embodiments, each of the bumps  511  may have a different height. 
     In one embodiment, the height  515  is selected so as to prevent physical contact between the deformable layer  506  and the stationary layer  502 . In another embodiment, the height  515  is selected not only to prevent such contact, but to define the depth of the interferometric cavity  418  in the driven state of the interferometric modulator  401 , so as to enable production of the desired optical characteristics of the interferometric modulator  401 . In the embodiments of interferometric modulator  401  for use as a display element, the interferometric cavity depth at the driven state is designed to be short enough to absorb most, if not all, of the visible light. Although not so limited, the height  515  of the bumps  511  can be substantially smaller than the height  519  of the landing pads  513 . The height  511  is from about 50 Å to about 500 Å, and preferably from about 100 Å to about 200 Å. 
     In a unit of the interferometric modulator  401 , a number of bumps  511  can be provided. As noted above, the bumps  511  are provided to prevent the stationary layer  502  and the deformable layer  506  from directly contacting each other, and also to reduce the contact area of the two layers  502  and  506 . The number of the bumps  511  in a unit of the interferometric modulator  401  is determined in view of the height  515  thereof. For example, if the height  515  of the bump  511  is significantly large, only very few bumps  511  are necessary to effectively prevent the contact between the stationary layer  502  and the deformable layer  506  because it is unlikely that the deformable layer  506  in contact with the tall bumps  511  can also contact the stationary layer  502 . On the other hand, when the height  515  of the bumps  511  is small, more bumps  511  may be needed. 
     The plurality of bumps  511  can be fabricated from various materials. In one embodiment, the bumps  511  are made of a dielectric material. If the bumps  511  extend from a dielectric surface of the stationary layer  502  or the deformable layer  506 , the bumps  511  may be made of the same dielectric material. Alternatively, the bumps  511  may be formed of another dielectric material of the surface from which they extend. In another embodiment, the bumps  511  are made of a conductive material. Preferably, the materials used to form for the bumps  511  are those that do not significantly affect the electrical or optical characteristics of the interferometric modulator. For example, materials for the bumps  511  may include oxides, nitrides and oxynitrides. Preferably, the bumps  511  are substantially transparent to predetermined wavelengths of light. 
     The bumps  511  can be produced in a number of ways. In one embodiment, the bumps  511  are formed by the process described above for the production of landing pads  513 . In one embodiment, a material is deposited over the stationary layer  502  or the deformable layer  506 , and the material is etched to form the bumps  511  on the layer  502  or  506 . The layer to be etched to form the bumps may comprise the same material as the top or sole layer of the stationary layer  502  or layer  506 . For example an exposed SiO 2  layer formed over the stationary layer  502  may be etched with an etchant to produce a rough surface, thereby forming bumps  511 . The etching process can be random, or the etching can be further directed into particular shapes through the use of particular etching barriers. This can allow one to control the size and shape of the bumps and create patterns which may be optimized for reducing or preventing the adverse impact created by contact of the deformable layer  506  with the stationary layer  502 . 
     Spring Clips 
       FIGS. 23A-23F  illustrate embodiments of an interferometric modulator  501  including spring clips  509 . In typical constructions of the interferometric modulator e.g., as illustrated in  FIGS. 8 ,  9 A and  9 B, the deformable layer  506  has a tension in its deformed (driven) state  501   b  and has a tendency to return to its non-deformed (undriven) state  501   c  to reduce the tension. The tension of the deformable layer  506  in its deformed state creates a mechanical restoring force that is exerted on that layer  506  in the direction away from the stationary layer  502 . The deformable layer  506  returns from its deformed state  501   b  to the undeformed state  501   c  when the mechanical restoring force overcomes the attractive force created by the electrical potential applied between the deformable layer  506  and the stationary layer  502 . As will be described below in detail, the spring clips  509  are provided to help the recovery of the deformable layer  506  from its driven state to the undriven state by applying an additional element of force onto the deformable layer  506  in the direction away from the stationary layer  502 . When combined with the mechanical restoring force of the deformable layer  502 , the additional element of force can increase the likelihood and/or speed of the return of the deformable layer  506  to the driven state when the return is desired. 
     In the illustrated embodiment of  FIGS. 23A and 23B , the spring clips  509  are provided on the stationary layer  502  of the interferometric modulator  501 . Referring to  FIG. 23A  which illustrates the undriven state, a portion of the spring clip  509  is located on the top surface of the stationary layer  502 , and the tip  510  of the spring clip  509  is bent so as to extend into the interferometric cavity  418  toward the deformable layer  506 . In this undriven state, the spring clips  509  are in their normal configuration as no force is applied thereto. When this interferometric modulator  501  is driven, the deformable layer  506  deforms into the driven state illustrated in  FIG. 23B . As the deformable layer  506  is deforming to its deformed state, the deformable layer  506  first contacts the tip  510  of the clips  509  and compresses the tip  510  into the substantially flat configuration as shown in  FIG. 23B . The spring clips  509  in their flat configuration have a tendency to return to their normal configuration. This tendency produces a force that is exerted by the tips  510  on the deformable layer  506 . When actuating the deformed layer  506  from the deformed state to its flat state, the force of the spring clips  509  exerted on the deformable layer  506  can help the actuation and increase the likelihood and/or speed of the recovery of the deformable layer  506 . 
     The embodiment illustrated in  FIGS. 23C and 23D  is the same as the embodiment of  FIGS. 23A and 23B  except that the spring clips  509  are formed on the deformable layer  506 . In the embodiments of  FIGS. 23A-23D , the spring clips  509  can also serve as the above-described landing pads and/or bumps that maintain a desired distance between the stationary layer  502  and the deformable layer  506 . 
       FIGS. 23E and 23F  illustrate another embodiment of the interferometric modulator  501  that includes the spring clips  509 . Referring to  FIG. 23E  which illustrates the interferometric modulator  501  in the undriven state, the stationary layer  502  has a recess  520  and the spring clip  509  has a portion contained in and attached to the recess  520 . The tip  510  of the spring clip  509  is bent with respect to the portion of the clip  509  contained in the recess  520  and extends upwardly beyond the top surface of the stationary layer  502  into the interferometric cavity  418 . Referring to  FIG. 23F  illustrating the driven state, the tip  510  of the spring clip  509  is substantially flattened by the deformable layer  506  and the stationary layer  502 . Again, this tip  510  has the tendency to return to its normal configuration shown in  FIG. 23E  and thus exerts a force on the deformable layer  506  that is in the direction away from the stationary layer  502 . 
     In the embodiment of  FIGS. 23E and 23F , the thickness  521  of the spring clip  509  is substantially the same as or smaller than the depth of the recess  520 . As a result, the deformable layer  506  contacts the top surface of the stationary layer  502  in the driven state as shown in  FIG. 23F . In another embodiment, the thickness  521  of the spring clip  509  at the tip  510  and/or in the portion contained in the recess  520  may be greater than the depth of the recess  520 . In such an embodiment, in the driven state of the interferometric modulator  501 , the deformable layer  506  contacts the spring clip  509  particularly at the area thereof that has the thickness  521  greater than the depth of the recess  520 , while not contacting the stationary layer  502 . In this configuration, the spring clips  509  serve as the above-described landing pads and/or bumps as well as the spring clips  509  prevent direct contact between the stationary layer  502  and the deformable layer  506 . 
     As will be appreciated by one of skill in the art, the spring clips  509  may not have the exact configuration as illustrated in  FIGS. 23A-23F . Also, many different types of biasing mechanisms and springs may be employed in lieu of the clips  509 . Additionally, materials with biasing characteristics can also be employed. For example a landing pad that includes one or more elastomeric materials may also be employed in lieu of the clips  509 . For the sake of convenience, the term “spring clip” refers to any and all mechanisms having the function of exerting a force on the deformable layer  506  in the direction toward its undriven state. Although two spring clips  509  are illustrated in  FIGS. 23A-23F , a single spring clip or more than two spring clips may be employed. Optionally, two or more spring clips  509  are arranged in the interferometric cavity  418  such that the forces exerted on the deformable layer  506  by the spring clips  509  are substantially balanced with one another, rather than focusing the forces on a local area of the deformable layer  506 . 
     As will be appreciated by one of skill in the art, the size, placement and strength of the spring or biasing elements can all be varied according to the desired characteristics of the interferometric modulator. The stronger the spring, the faster and the more reliably the deformable layer  506  will return to its undriven planar position. Of course, this may also require one to adjust the initial voltage input in order to drive the interferometric modulator  501  to its fully driven state, as the deformable layer  506  will tend to have an increased amount of resistance against the spring clips  509  during its approach towards the stationary layer  502 . 
     In some embodiments, the spring clips  509  are useful in overcoming stictional forces (static friction) that may develop when the deformable layer  506  comes in close proximity to or contacts the stationary layer  502 . These forces can include Van der Waals or electrostatic forces, as well as other possibilities as appreciated by one of skill in the art. The stictional forces in nature hinder the separation of the deformable layer  506  from the stationary layer  502 . Since the spring clips  509  provide additional force to separate the deformable layer  506  from the stationary layer  502 , the force of the spring clips  509  can balance or overcome the stictional forces. 
     In some embodiments, the stictional forces between the deformable layer  506  and the stationary layer  502  can be reduced by coating the layers with a polymer that reduces static friction with or without the spring clips. For example, the layers can be coated by an anti-stiction polymer coating, which can reduce the degree of adhesion between the deformable layer  506  and the stationary layer  502 . In one embodiment, this coating is applied to other aspects of the device, such as the spring clips  509 , bumps  511  or landing pad  513 . 
     As will be appreciated by one of skill in the art, the above features of landing pads  513 , bumps  511  and spring clips  509  may be employed individually or may be employed together in a single embodiment. For example, an interferometric modulator may have one, two or all three of these features. Also, as described, certain features can serve both to assist in the return of the deformable layer  506  to its undriven state and to reduce the likelihood that the deformable layer  506  and the stationary layer  502  adversely contact each other, as landing pads  513  and spring clips  509  might function. 
     Multi-State Interferometric Modulators 
     In some embodiments, the interferometric modulator provides more than two states (driven and undriven). An example of this is illustrated in the embodiment shown in  FIGS. 24A-24C . In this embodiment, the interferometric modulator is not only capable of a deflection of the deformable layer  506  towards the layer  503 , in the driven state as shown in  FIG. 24B , but the interferometric modulator is also capable of reversing the direction of the deflection of layer  506  in the opposite direction, as illustrated in  FIG. 24C . This “upwardly” deflected state may be called the “reverse driven state.” 
     As will be appreciated by one of skill in the art, this reverse driven state can be achieved in a number of ways. In one embodiment, the reverse driven state is achieved through the use of an additional stationary layer  502 ′ that can pull the deformable layer  506  in the upward direction, as depicted in  FIG. 24C . In this particular embodiment, there are basically two interferometric modulators positioned symmetrically around a single layer  506 . This allows each of the stationary layers  502  and  502 ′ to attract the layer  506  in opposite directions. Thus, while an initial voltage command may send layer  506  into the normal driven state ( FIG. 24B ), the next voltage command can accelerate the recovery of the deformable layer  506  by driving that layer towards the reverse driven state. In this mode, the deformable layer  506  is then attracted in the opposite direction to the stationary layer  502 ′. In this embodiment, the stationary layers  502  and  502 ′ may be in various constructions as described earlier in the disclosure, and do not have to be in the same construction at the same time. For example, the stationary layers  502  and  502 ′ can be in a single layer construction or in multiple sub-layer construction. In the illustrated embodiment, a support surface  500 ′ is maintained some distance above the deformable layer  506  through a second set of supports  504 ′. 
     As will be appreciated by one of skill in the art, not all of these elements will be required in every embodiment. For example, if the precise relative amount of upward deflection, such as that shown in  FIG. 24C  compared to  FIG. 24A  or  24 B, is not relevant in the operation of the device, then the stationary layer  502 ′ can be positioned at various distances from the deformable layer  506 . Thus, there may be no need for support elements  504 ′ or a separate substrate  500 ′. In these embodiments, it is not necessarily important how far upward the deflection of the deformable layer  506  extends, but rather that the stationary layer  502 ′ is configured to attract the deformable layer  506  at the appropriate time. In other embodiments, the position of the deformable layer  506  as shown in  FIG. 24C  may alter optical characteristics of the interferometric modulator. In these embodiments, the precise distance of deflection of layer  506  in the upward direction can be relevant in improving the image quality of the device. 
     As will be appreciated by one of skill in the art, the materials used to produce the stationary layer  502 ′ (or its sub-layers) and substrate  500 ′ need not be similar to the materials used to produce the corresponding layer  502  and substrate  500 . For example, in some embodiments, light need not pass through the layer  500 ′ while it may be necessary for light to be able to pass through the layer  500 . Additionally, if layer  502 ′ is positioned beyond the reach of layer  506  in its deformed upward position, then a dielectric sub-layer may not be needed in the stationary layer  502 ′ as there is little risk of layer  506  contacting the conductive portion of the layer  502 ′. Accordingly, the voltages applied to layers  502 ′ and  506  can be different based on the above differences. 
     As will be appreciated by one of skill in the art, the voltage applied to drive the deformable layer  506  from the driven state shown in  FIG. 24B  to the undriven state shown in  FIG. 24A , may be different from that required to drive the deformable layer  506  from the state shown in  FIG. 24A  to the upward or reverse driven state shown in  FIG. 24C , as the distance between plates  502 ′ and  506  is different in the two states. Thus, the amount of voltage to be applied is determined based upon the desired application and amounts of deflection. 
     In some embodiments, the amount of force or the duration that a force is applied between the layer  502 ′ and the layer  506  is limited to that is necessary to merely increase the rate at which the interferometric modulator transitions between the driven state and the undriven state. Since the deformable layer  506  can be made to be attracted to either the layer  502  or  502 ′ which are located on opposite sides of the layer  506 , a very brief driving force can be provided to weaken the interaction of the layer  506  with the opposite layer. For example, as the layer  506  is driven to interact with the layer  502 , a pulse of energy to the opposite layer  502 ′ can be used to weaken the interaction of the layer  506  with the layer  502 ′ and thereby make it easier for the deformable layer  506  to move to the undriven state. 
     Controlling Offset Voltages 
     Traditionally, interferometric modulator devices have been designed such that there is a minimum, or no, fixed electrical charge associated with each layer. However, as current fabrication techniques have not been able to achieve a “no fixed charge standard,” it is frequently desirable to have the resulting fixed charge considered and compensated for when selecting the operational voltages used to control the deformable layer  506 . 
     Through testing various configurations of layers and various deposition techniques, the amount of fixed electrical charge that is associated with each layer can be modeled and used as design criteria to select materials and layer configurations that minimize the amount of total offset voltage imparted to the interferometric modulator. For example, one or more materials can be replaced in the interferometric modulator layers to change the electrical characteristics of the overall interferometric modulator device. 
     Referring now to  FIG. 24D , in some embodiments, the dielectric sub-layer  413  or another sub-layer of the stationary layer  502  is modified with a charged component in order to obtain a neutrally charged system. In the illustrated embodiment, the stationary layer  502  is in a two sub-layer construction, a dielectric sub-layer  413  is located on a sub-layer  416  that serves as mirror and conductive electrode, and the dielectric sub-layer  413  contains charged components  514 . Again, the stationary layer  502  can be in various constructions as described above. 
     The incorporation of the charged component  514  can be achieved in a number of ways. For example, additional charged components  514  can be added to the dielectric material when the dielectric sub-layer  413  is being formed on the underlying sub-layer  416 . As will be appreciated by one of skill in the art, there are a variety of charged components that can be used, the amount and particular characteristics of these charged components can vary depending upon the desired properties of the interferometric modulator. Examples can include, forming a dielectric layer in a sputter tool (which can be negative) as compared to a chemical vapor deposition process (which can be positive), or altering the amount of hydrogen in the layer. 
     In some embodiments, the control of the amount of charged components  514  in the interferometric modulator can also be achieved through altering the method of deposition of the layers or adding entirely new layers. In another embodiment, one selects particular materials with the goal of optimizing the electrochemical characteristics of the materials. Thus, one can use various work function differences to control the final offset voltage of the interferometric modulator or change the charge accumulation rate within the device during operation of the device. For example, the deformable layer  506  can have a surface that can contact the stationary layer  502 , the surface can have a high work function to minimize the transfer of electrons between the layers. In another embodiment, one can modify a sacrificial material used in the creation of the interferometric modulator so that as the sacrificial material is being removed, one is not imparting charge to the deformable layer  506  and/or the stationary layer  502 . In another embodiment, materials to be used to connect the layers  502  and  506  during processing can be selected on the basis of their work function properties. In another embodiment, the material selected for the connector rod  333  ( FIGS. 25A and 25B ) is based on its work function characteristics. 
     In one embodiment, during the creation of the interferometric modulator, the stationary layer  502  and the deformable layer  506  are electrically connected so as to minimize the charge difference between the two layers. This can allow for higher yield in production and higher reliability in the final interferometric modulator. This electrical connection can be removed to allow the device to properly function. In one embodiment, this connection between the two layers is created from the same material as that from which the deformable layer  506  is created. 
     Reducing the Movement of the Deformable Layer  506   
     In some embodiments, the supports  504  interact with the deformable layer  506  through direct contact of the top end  37  of the supports  504  and the bottom surface of layer  506 . In certain situations, sliding or slippage of the deformable layer  506  along the top  37  of support  504  may occur. This movement can be decreased in a number of ways. In one embodiment, the movement is decreased by altering the surface characteristics of the top  37  of the support  504 . For example, one can roughen the deformable layer  506  and/or the support  504  at the point  505  where the two interact, as shown in  FIGS. 24D and 249E . For example, this can be done by oxygen plasma burn down of the support or by sputter etching before the deposition of the deformable layer  506 . 
     Alternative Forces for Driving Recovery from the Driven State 
     In some embodiments, the manner of deformation of the deformable layer  506  may be altered for improved functionality. In a traditional interferometric modulator  501 , the deformable layer  506  is a single contiguous sheet stretched taut across the support members  504 . Because the layer is stretched taut, the residual stress in the layer allows the layer to “spring” or “snap back” from the driven state to the undriven state. However, this particular arrangement can be sensitive to process variability. 
     Instead of relying upon the tautness of the deformable layer  506  (to create residual stress), one can instead rely upon the elastic modulus of the material, which is a constant based upon the material, rather than on primarily how the material is arranged or processed. Thus, in one aspect, the deformable layer  506  retains and provides its elasticity through a material constant of the material from which it is made. In one embodiment, this is similar to that of a cantilever spring, rather than a taut stretched film. An example of such a design is shown in  FIGS. 25A-25D .  FIG. 25A  shows a side view, and  FIG. 25B  shows a top view of one embodiment of an interferometric modulator  501  in the undriven state.  FIG. 25C  shows a side view and  FIG. 25D  shows a top view of the interferometric modulator  501  in a driven state. 
     In this embodiment, the deformable layer  506  has been divided into two separate parts, a load bearing part  506   a  that is responsible for providing the flexibility and resilience for the movement of the layer through its elastic modulus, and a substantially planar part  506   b , which functions as the secondary mirror for the interferometric modulator. The two parts  506   a  and  506   b  are connected to each other via a connector rod  333 . In one embodiment, the connector rod  333  is made of the same material as the load bearing part  506   a  and/or the substantially planar part  506   b . In another embodiment, the connector rod  333  is made of a material different from the load bearing part  506   a  and the substantially planar part  506   b . In some embodiments, the connector rod  333 , rather than the load bearing structure  506   a , is the part that provides flexibility and resilience to the system. In some embodiments, the load bearing structure  506   a  is thicker than the deformable layer  506  in the previous embodiments. 
     As shown in  FIG. 25B , the load bearing part  506   a  is configured in an “X” shape that is supported at its four corners  70 ,  71 ,  72 , and  73  to provide its elastomeric properties. In the driven state, the load bearing part  506   a  bends downward and towards the stationary layer  502  through the pull from the planar part  506   b  of the deformable layer  506 . As will be appreciated by one of skill in the art, the particular material or materials used to provide the elasticity for the system can vary depending upon the particularly desired characteristics of the system. 
     The above-described modifications can help remove process variability and lead to a more robust design and fabrication. Additionally, while the above aspects have been described in terms of selected embodiments of the interferometric modulator, one of skill in the art will appreciate that many different embodiments of interferometric modulators may benefit from the above aspects. Of course, as will be appreciated by one of skill in the art, additional alternative embodiments of the interferometric modulator can also be employed. The various layers of interferometric modulators can be made from a wide variety of conductive and non-conductive materials that are generally well known in the art of semi-conductor and electromechanical device fabrication. 
     While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.