Abstract:
Disclosed herein is method of operating a device that comprises an array of micromirrors. The method comprises a process usable for repairing stuck micromirrors of the micromirror array during the operation. The reparation process applies, at the ON state, two consecutive refresh voltages to the mirror plates of the micromirrors in the array with the pulses being separated in time longer than the characteristic oscillation time of the micromirrors. The reparation process can be applied independently to the micromirrors. Alternatively, the reparation process can be incorporated with a bias inversion process.

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001]     The present invention is related generally to the art of micromirror devices, and more particularly to micromirror devices having light transmissive substrate.  
       BACKGROUND OF THE INVENTION  
       [0002]     In micromirror devices each having a light transmissive substrate, a semiconductor substrate; and a reflective deflectable mirror plate disposed therebetween, incident light to be modulated by the mirror plate travels through the light transmissive substrate and impinges the reflective surface of the mirror plate. The mirror plate switches between the ON and OFF state so as to reflect the incident light into different spatial directions. During switching, the mirror plate may contact the surface of the light transmissive, resulting in electrical short when the light transmissive substrate comprises electrode.  
         [0003]     Therefore, what is needed is a method and apparatus to electrically isolating the mirror plate from the light transmissive substrate.  
       SUMMARY OF THE INVENTION  
       [0004]     In view of the foregoing, the present invention discloses a light optical coating on the light transmissive substrate of micromirror devices. Such optical coating is electrically insulating, but optically transmissive to the incident light such that, electrical short between the deflectable mirror plate and electrode on the light transmissive substrate can be avoided, while the incident light is still able to travel through the light transmissive substrate and impinge the reflecting surface of the mirror plate.  
         [0005]     In one example, the optical coating comprises a titanium dioxide layer, first silicon dioxide layer, an indium-titanium-oxide (ITO) layer, and second silicon dioxide layer.  
         [0006]     In another example, the optical coating comprises a niobium dioxide layer, first silicon dioxide layer, an indium-titanium-oxide (ITO) layer, and second silicon dioxide layer.  
         [0007]     The objects of the invention are achieved in the features of the independent claims attached hereto. Preferred embodiments are characterized in the dependent claims.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]     While the appended claims set forth the features of the present invention with particularity, the invention, together with its objects and advantages, may be best understood from the following detailed description taken in conjunction with the accompanying drawings of which:  
         [0009]      FIG. 1  illustrates an exemplary display system employing a spatial light modulator having an array of micromirrors in which embodiments of the invention can be implemented;  
         [0010]      FIG. 2  illustrates a cross-section of a portion of the spatial light modulator in  FIG. 1 ;  
         [0011]      FIG. 3  illustrates an exploded cross-section view of a micromirror device in  FIG. 2 ;  
         [0012]      FIG. 4  illustrates an exploded cross-section view of the light transmissive substrate having an optical coating thereon in  FIG. 3 ;  
         [0013]      FIG. 5  illustrates an exploded cross-section view of an exemplar optical coating on the light transmissive substrate of  FIG. 4 ;  
         [0014]      FIG. 6   a  illustrates a top view of the optical coating on the light transmissive substrate in  FIG. 5 , and a top view of a plurality of electrical contacting pads on another substrate when the device comprises multiple substrates;  
         [0015]      FIG. 6   b  illustrates a device assembly after then substrates in  FIG. 6   a  are bonded and assembled;  
         [0016]      FIG. 7  is a perspective view of an exemplary micromirror device useable in the spatial light modulator of  FIG. 1 ;  
         [0017]      FIG. 8  schematically illustrates a top view of the deflectable mirror plate of the micromirror device of  FIG. 6 ;  
         [0018]      FIG. 9  is a perspective view of another exemplary micromirror device useable in the spatial light modulator of  FIG. 1 ; and  
         [0019]      FIG. 10  schematically illustrates a top view of the deflectable mirror plate of the micromirror device of  FIG. 8 .  
         [0020]      FIG. 11  is a perspective view of an exemplary spatial light modulator of  FIG. 1 ;  
         [0021]      FIG. 12  is a top view of another exemplary spatial light modulator of  FIG. 1 ;  
         [0022]      FIG. 13  schematically shows a top view of another exemplary micromirror array;  
         [0023]      FIG. 14  schematically shows a top view of yet another exemplary micromirror array; and  
         [0024]      FIGS. 15   a  to  16  schematically show a top view of another exemplary micromirror array device comprising an array of electrodes and circuitry and micromirrors. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0025]     In view of forgoing, the present invention provides a micromirror device that comprises a light transmissive substrate having a light transmissive optical coating formed thereon. The optical coating comprises an electrical conducting layer and an electrical insulating layer. All layers of the optical coating are transmissive to the incident light.  
         [0026]     Turning to the drawings,  FIG. 1  illustrates an exemplary digital display system employing a spatial light modulating having an array of micromirrors in which embodiment of the invention can be implemented. Referring to  FIG. 1 , display system  100  comprises illumination system  116  for producing sequential color light, spatial light modulator  110  that comprises an array of micromirrors, optical element  108  for directing illumination light from the illumination system onto the spatial light modulator, and optical element  112  that projects the reflected illumination light onto display target  114 .  
         [0027]     Illumination system  116  further comprises light source  102 , which can be an arc lamp, lightpipe  104  that can be any suitable integrator of light or light beam shape changer, and color filter  106 , which can be a color wheel. The filter in this particular example is positioned after light pipe  104  at the propagation path of the illumination light. In another example, the color filter can be positioned between the light source and light pipe  104 , which is not shown in the figure.  
         [0028]      FIG. 2  illustrates a cross-section view of an exemplary spatial light modulator in  FIG. 1 . For simplicity purposes, only eight micromirror devices are illustrated therein. In general, the micromirror array of a spatial light modulator consists of thousands or millions of micromirrors, the total number of which determines the resolution of the displayed images. For example, the micromirror array of the spatial light modulator may have 1024×768, 1280×720, 1400×1050, 1600×1200, 1920×1080, or even larger number of micromirrors. In other applications, the micromirror array may have less number of micromirrors.  
         [0029]     In this example, the array of deflectable reflective mirror plates (e.g.  124 ) is disposed between light transmissive substrate  120  and semiconductor substrate  122  having formed thereon an array of addressing electrodes (e.g. addressing electrode  126 ) each of which is associated with a mirror plate for electrostatically deflecting the mirror plate. In operation, the illumination light passes through the light transmissive substrate and illuminates the reflective surfaces of the mirror plates, from which the illumination light is modulated. The reflected illumination light from the mirror plates at the ON state is collected by the projection lens (e.g. projection lens  112  in  FIG. 1 ) so as to generate a “bright” pixel in the display target (e.g. display target  114  in  FIG. 1 ). The reflected illumination from the mirror plates at the OFF state travels away from the projection lens, resulting in the corresponding pixels in the display target to be “dark.” 
         [0030]     The micromirrors in the array can be arranged in many suitable ways. For example, the micromirrors can be arranged such that the center-to-center distance between the adjacent mirror plates can be 10.16 microns or less, such as 4.38 to 10.16 microns. The nearest distance between the edges of the mirror plate can be from 0.1 to 1.5 microns, such as from 0.15 to 0.45 micron, as set forth in U.S. patent application Ser. No. 10/627,302, Ser. No. 10/627,155, and Ser. No. 10/627,303, both to Patel, filed Jul. 24, 2003, the subject matter of each being incorporated herein by reference.  
         [0031]     As a way of example, an exemplary micromirror in  FIG. 2  is schematically illustrated in a cross-section view in  FIG. 3 . Referring to  FIG. 3 , micromirror  118  comprises deflectable mirror plate  124  having a reflective surface for reflecting the illumination light to be modulated. The mirror plate is attached to deformable hinge  129  (e.g. a torsion hinge) via hinge contact  128  with the deformable hinge being held and supported by post  133  on substrate  120  such that the mirror plate can be deflected (rotated) relative to the substrate. The deflection of the mirror plate is achieved by electrostatic field established between the mirror plate and addressing electrode  126 .  
         [0032]     According to the invention, the light transmissive substrate  120  comprises an electrode (e.g. electrode  210 ) for pulling the mirror plate towards the light transmissive substrate. This electrode on the light transmissive substrate is transmissive to the incident light. Specifically, the electrode transmits 90% or more, or 99% or more of the incident light (e.g. visible light). The electrode can be formed as a film, a strip, a grid, or a set of discontinuous segments, as set forth in U.S. patent application Ser. No. 10/437,776 filed May 13, 2003, and Ser. No. 10/947,005 filed Sep. 21, 2004, the subject matter of each being incorporated herein by reference in entirety.  
         [0033]     In accordance with an embodiment of the invention, only one addressing electrode  126  is provided for the micromirror for switching the mirror plate between the ON and OFF state according to the image data of the desired image to be produced by the system. Of course, multiple addressing electrodes can be provided for each micromirror, which will not be discussed in detail herein.  
         [0034]     Stopper  130  can be provided as an alternative feature to limit the rotation of the mirror plate in accordance with the operation states, such as the ON state when the micromirror is operated in a binary mode including the ON and OFF state. The stopper  130  can be formed in many alternative ways, such as those set forth in U.S. patent application Ser. No. 10/437,776 filed Apr. 13, 2003 and Ser. No. 10/613,379 filed Jul. 3, 2003, Ser. No. 10/703,678 filed Nov. 7, 2003, the subject matter of each being incorporated herein by reference.  
         [0035]     In operation, the mirror plate switches between the ON and OFF state according to the image data so as to reflect the incident light into different directions. As an example, the mirror plate is rotated to the ON state by setting the electrical voltage on the addressing electrode  126  to a value such that the rotation torque derived from the voltage difference between the mirror plate and the addressing electrode is sufficient enough to overcome the total resisting torque including the mechanical torque in the deformable hinge and the electrical torque derived from the voltage difference between the mirror plate and the electrode  210  on the light transmissive substrate. When the voltage difference between the mirror plate and addressing electrode is removed, or reduced to a value that can not balance the total resisting torque including the mechanical torque of the deformed hinge and the electrical torque derived from the voltage difference between the mirror plate and electrode  210  on the light transmissive substrate, the mirror plate rotates towards the OFF state.  
         [0036]     At the ON state, or a state wherein the mirror plate is forced to rotate further than the ON state, the mirror plate, especially the end moving towards the light transmissive substrate when the mirror plate rotates towards the ON state, may contact the electrode  210  on the light transmissive substrate, causing electrical short. In order to avoid such electrical short, the electrode  210  on the light transmissive substrate can be covered by an optical coating, as illustrated in  FIG. 4 .  
         [0037]     Referring to  FIG. 4 , mirror plate  120  comprises electrode  210  formed thereon. An electrical insulating layer  209  is deposited on the electrode layer  210  by laminating the electrode layer  210  between the electrical insulating layer  209  and the surface of the light transmissive substrate  120 . The electrical conducting layer  209  is electrically insulating, preferably having a resistivity of 5×10 9  ohm/cm 2  or higher. For allowing the transmission of the incident light therethrough, the electrical insulating layer  209  comprises a material that transmits 90% or more, such as 95% or more, or 99% or more of the incident light. The electrical insulating layer may be deposited to cover the entire surface of the electrode  210 . Alternatively, the electrical insulating layer can be configured and deposited in any suitable ways as long as the contacting area of the mirror plate to the surface of the light transmissive substrate is covered by the electrical insulating patch and insulated thereby. Specifically, the electrical insulating layer can be shaped independently from the shape of the electrode, especially when other constraints need to be balanced or satisfied.  
         [0038]     The electrically conductive and electrically insulating layers ( 209  and  210 ) can be any suitable materials that are transparent at the thickness at which they are provided on the light transmissive substrate. Preferably, though not necessary, this will be an oxide compound.  
         [0039]     For example, the electrically conductive layers may comprise metalloid, metal alloys that comprise two or more elemental metals, intermetallic compounds, and ceramics, organics, and polymers. The intermetallic compound may be composed of a transition metal, including early and late transition metals.  
         [0040]     A ceramic is a compound wherein a metal (or metalloid) is bonded to a non-metal. The ceramics for the light transmissive and electrically conductive layers can be oxides, nitrides or carbides of metals or metalloids, preferably a metal oxide or metalloid oxide binary or ternary compound.  
         [0041]     For example, the transparent and electrically conductive layer may comprise: indium-titanate-oxide, TiO x , doped ZnO x  (such as ZnO x  doped with aluminum, gallium, fluorine, boron, and indium), SnO 2 , doped SnO 2  (such as SnO 2  doped with fluorine and antimony), GdIn x O y , doped InO x  (such InO x  doped with fluorine, tin and other suitable conductive organics and polymers, such as Baytron® conductive polymers (e.g. Baytron®)). Other transparent and conductive materials may also be used, such as CdSn x O y  (e.g. Cd 2 SnO 4 , CdSnO 3  and CdIn 2 O 4 ), An 2 SnO 4 , MgIn 2 O 4 , Y doped CdSb 2 O 3 , ZnSnO 3 , GaINO 3 , Zn 2 In 2 O 5 , and In 4 Sn 3 O 12 , indium doped CdO, CuAIO 2 , Cu 2 SrO 2 , and CuGaO 2  doped Ga 2 O 3 , Ti 2 O 3 , PbO 2 , Sb 2 O 5 .  
         [0042]     The electrically insulating materials can be materials of high optical indices or materials of low optical indices. For example, the transparent and electrically insulating material with high optical indices can be TiO x  and Nb 2 O 5 , HfO 2 , Ta 2 O 5 , ZrO 2 , Si 3 N 4 , La 2 O 3 , and Nd 2 O 3 . The transparent and electrically insulating materials with low optical indices can be CaF 2 , SiO 2 , MgF 2 , and Al 2 O 3 . Of course, the materials listed above are for demonstration purposes, and is not intend to include all possible transparent and electrically conductive (or insulating) materials that are applicable in the present invention.  
         [0043]     In selecting and applying the transparent and electrically conductive and insulating materials to the light transmissive substrate (e.g. substrate  120 ), the electrically conductive (and/or insulating) layers can themselves be a single or multilayered structures to improve the anti-reflection properties of the layers. Alternatively, the electrically conductive and insulating layers can be alternatively stacked on the light transmissive substrate. For example, a material of high optical index can be stacked closer to the light transmissive substrate than those materials of low optical indices so as to form an optical index gradient from the surface of the light transmissive substrate to the air, which in turn improves the anti-reflection of the incident light.  
         [0044]     In selecting and forming the materials on the light transmissive substrate, other factors may also be included for consideration, such as the compatibility of the Coefficient-of-Thermo Expansion (CTE) and adhesive abilities to the light transmissive substrates, which will not be discussed in detail herein.  
         [0045]     Referring to  FIG. 5 , an exemplary laminated electrode-electrical insulating structure on the light transmissive substrate of the micromirror device is illustrated therein. The laminate comprises niobium oxide layer  212 , silicon oxide layer  214 , indium-titanium-oxide layer  216 , and another silicon oxide layer  218 . These films can be formed using any suitable film fabrication methods, such as chemical-vapor-deposition (CVD), physical-vapor-deposition (PVD), and physical-electro-chemical-vapor phase deposition (PECVD). As a numerical example, the niobium oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 200 angstroms, and more preferably around 100 angstroms. The optical index of this niobium oxide layer is preferably from 1 to 2.7, more preferably from 1.5 to 2.5, and more preferably around 2.3. The first silicon oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 500 angstroms, and more preferably around 400 angstroms. The optical index of this silicon oxide layer is preferably from 1 to 1.7, more preferably from 1.2 to 1.5, and more preferably around 1.46. The indium-titanium-oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 1000 angstroms, and more preferably around 600 angstroms. The optical index of this silicon oxide layer is preferably from 1 to 2.7, more preferably from 1.2 to 1.9, and more preferably around 1.8. The second silicon oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 1500 angstroms, and more preferably around 900 angstroms. The optical index of this silicon oxide layer is preferably from 1 to 1.7, more preferably from 1.2 to 1.5, and more preferably around 1.46.  
         [0046]     The laminate may also comprise a titanium oxide layer, a silicon oxide layer, an indium-titanate-oxide layer, and another silicon oxide layer. These films can be formed using any suitable film fabrication methods, such as chemical-vapor-deposition (CVD), physical-vapor-deposition (PVD), and physical-electro-chemical-vapor phase deposition (PECVD). As a numerical example, the titanium oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 200 angstroms, and more preferably around 100 angstroms. The optical index of this titanium oxide layer is preferably from 1 to 2.7, more preferably from 1.5 to 2.5, and more preferably around 2.4. The first silicon oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 500 angstroms, and more preferably around 400 angstroms. The optical index of this silicon oxide layer is preferably from 1 to 1.7, more preferably from 1.2 to 1.5, and more preferably around 1.46. The indium-titanium-oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 1000 angstroms, and more preferably around 600 angstroms. The optical index of this silicon oxide layer is preferably from 1 to 2.7, more preferably from 1.2 to 1.9, and more preferably around 1.8. The second silicon oxide layer may have a thickness of from 10 angstroms to 5000 angstroms, preferably from 50 angstroms to 1500 angstroms, and more preferably around 900 angstroms. The optical index of this silicon oxide layer is preferably from 1 to 1.7, more preferably from 1.2 to 1.5, and more preferably around 1.46.  
         [0047]     In operation, the electrical conductive layer, such as the indium-titanate-oxide layer is connected to an external power source for electrostatically deflecting the mirror plates in the direction towards the light transmissive substrate. The electrical potential of the electrically conductive and light transmissive layer may vary over time during operation for many purposes, such as inversing the polarity of the voltages so as to eliminating unexpected charge accumulation, as set forth in U.S. patent application Ser. No. 10/607,687 serial number Jun. 27, 2003, the subject matter being incorporated herein by reference in entirety. For this purpose, the electrical and non-electrical conductive layers are patterned as appropriate. As a way of example,  FIG. 6   a  illustrates in a top view of an exemplary configuration of the transparent layers on the light transmissive substrate.  
         [0048]     Referring to  FIG. 6   a , electrically conductive and light transparent layer, indium-titanate-oxide layer  216 , is deposited and patterned on light transmissive substrate  122 . For simplicity and demonstration purposes, only layer  216  is illustrated. Other layers, such as layers  212 ,  214 , and  218  in  FIG. 5  are removed from the figure. The light transparent and electrically conductive layer  126  is patterned to have electrical contacting pads  222   a  and  222   b , wherein each pad is exposed (e.g. not covered by any other electrically insulating materials). In this example, the electrically conductive layer (layer  126 ) is configured to have two separate contacting pads. In other examples, each electrically conductive and light transmissive layer may be configured to have any suitable number of electric contacting pads. Also shown in the figure are other electrically conducting pads  224   a  and  224   b  for providing electrical contacts to other functional members, such as the reflective and deflectable mirror plates when an array of deflectable reflective mirror plates of a micromirror array device is formed on the light transmissive substrate  122 . Exemplary such micromirrors are shown in FIGS.  7  to  16 , which will be discussed afterwards.  
         [0049]     In an instance when the functional members of the device are formed on separate substrates, the electric contacting pads can be extended to the other substrate of the device, as shown in the figure. Specifically, a group of functional members (e.g. an array of reflective deflectable mirror plates) is formed on light transmissive substrate  122 , and another group of functional members (e.g. an array of addressing electrodes associated with the array of mirror plates) is formed on substrate  190  that can be a standard semiconductor substrate. Electric contacting pads  222   c  and  222   d , (as well as  224   c  and  224   d  if  224   a  and  224   b  are formed on substrate  122 ) are formed at locations such that when the two substrates are aligned or assembled together, electrical contacting pads  222   a  and  222   d  can be directly contacted, so are electric contact pads  222   b  and  222   c  in this way, electrical contacts to pads  222   a  and  222   b , that is to the electrical conductive and light transmissive layer  216  on substrate  122  can be extended to substrate  190  via pads  222   c  and  222   d  on substrate  190 . The electrical contacts to pads  222   c  and  222   d  can be further extended to pads  226  deployed on a surface of substrate  190  that are easy to be managed and handled during installation and operation.  
         [0050]     The assembled device having substrates  120  and  190  in  FIG. 6   a  is illustrated in  FIG. 6   b . It can be seen in the figure that the delicate electric contacting pads  222   a ,  222   b ,  224   a , and  224   b  on substrate  120 , and pads  222   c ,  222   d ,  224   c , and  224   d  on substrate  190 , are securely enclosed with the cell between substrates  120  and  190 . Electrical contacting pads  226  are exposed outside the cell such that external signals and power sources can then be connected to pads  226 , as set forth in US patent application “Electrical Contacts in Micro-electromechanical Devices with Multiple Substrates”, attorney docket number P226-US, filed on the same day as the present patent application, the subject matter being incorporated herein by reference.  
         [0051]     The present invention is applicable to many types of micromirrors. Specifically, the light transparent and electrically conductive layer can be formed on a light transmissive substrate that is a part of or is connected to a micromirror array device. Such transparent and electrically conductive layer can be used as an electrode for pulling the reflective deflectable mirror plates towards the light transmissive substrate.  FIG. 3  illustrates one of the many examples. Referring again to  FIG. 3 , the mirror plate can be attached to the deformable hinge symmetrically or asymmetrically. When the mirror plate is attached to the deformable hinge with the attachment point substantially at or around the geometric (or mass) center of the mirror plate, the mirror plate rotates symmetrically—that is, the maximum angles achievable by the mirror plate rotating in opposite directions are substantially the same. Alternatively, when the attachment point is offset from the geometric (or mass) center of the mirror plate, the mirror plate rotates asymmetrically—that is the maximum angles achievable by the mirror plate in opposite directions are different. The asymmetric rotation of the mirror plate is more advantageous in obtaining higher contrast ratio. The ON state angle of the present invention is preferably 12° degrees or more, such as 14° degrees or more, and 14° degrees or more. The OFF state can be a state where the mirror plate is parallel to the substrate on which the mirror plates are formed, such as substrate  120 . The OFF state angle can be other values, such as −1° degree or less, such as −2° degrees or less, and −4° degrees or less, wherein the minus sign “−” represents the opposite rotation direction in relation to the ON state angle. Such ON and OFF state angles can be achieved by attaching the mirror plate asymmetrically to the deformable hinge. Specifically, the hinge contact ( 128 ) contacts at the mirror plate at a location away from the geometric or mass center of the mirror plate. As a result, the deformable hinge, as well as the rotation axis is not along a diagonal of a diagonal of the mirror plate when viewed from the top of the mirror plate at the non-deflected state. Exemplary micromirrors of asymmetric rotation will be better illustrated in perspective views in FIGS.  7  to  10  afterwards.  
         [0052]     In the cross-section view of  FIG. 3 , the deformable hinge and the mirror plate are in different planes. Alternatively, the mirror plate and the deformable hinge can be in the same plane. For example, the mirror plate and the deformable hinge can be fabricated or derived from a single flat substrate, such as a single crystal (e.g. single crystal silicon). Alternatively, the mirror plate and the deformable hinge can be derived from one deposited film by patterning. The stopper (e.g. stopper  130 ) can be in the same plane of the deformable hinge, but can also be in different planes of the deformable hinge.  
         [0053]     In addition to the addressing electrode whose operation state (voltage) depends upon the image data of the desired image, an additional electrode for rotating the mirror plate in the direction opposite to that driven by the addressing electrode can also be provided. For example, the additional electrode can be formed on substrate  120  on which the mirror plate is formed. Alternatively, the additional electrode can be formed on the micromirror on a side opposite to the addressing electrode relative to the rotation axis of the mirror plate.  
         [0054]     In the example as shown in  FIG. 3 , the deflectable mirror plates are formed on substrate  120  that is transmissive to the illumination light to be modulated, such as glass and quartz when the illumination light is visible light. The addressing electrodes and circuitry are formed on substrate  122  that can be a standard semiconductor substrate. In another embodiment of the invention, the mirror plates can be directly derived from the light transmissive substrate, such as by patterning the light transmissive substrate so as to form the deflectable mirror plate. In this instance, the deformable hinge can be single crystal or deposited thin film, which will not be discussed in detail herein. As another example, the mirror plates and the addressing electrodes can be formed on the same substrate, such as semiconductor substrate  122 .  
         [0055]     Addressing electrode  126  is preferably disposed such that the edge of the addressing electrode extending beyond the mirror plate, for example, beyond the furthest point of the mirror plate measured from the deformable hinge, so as to maximize the utilization efficiency of the electrostatic field, as set forth in U.S. patent application Ser. No. 10/947,005 filed Sep. 21, 2004, the subject matter being incorporated herein by reference. In an embodiment of the invention, each mirror plate is addressed and deflected by one single addressing electrode. In this instance, the mirror plate is rotated to the ON state by an electrostatic force derived from the electrostatic field established between the mirror plate and the addressing electrode.  
         [0056]     Referring to  FIG. 7 , a perspective view of an exemplary micromirror device in which embodiments of the invention are applicable is illustrated therein. Micromirror device  180  comprises substrate  190  that is a light transmissive substrate such as glass or quartz and semiconductor substrate  182 . Deflectable and reflective mirror plate  184  is spaced apart and attached to deformable hinge  186  via a hinge contact. The deformable hinge is affixed to and held by posts  188 . The semiconductor substrate has addressing electrode  192  for deflecting the mirror plate. In this particular example, the light transmissive substrate operates as a stopper for stopping the rotation of the mirror plate at the ON state.  
         [0057]     A top view of the micromirror in  FIG. 7  is illustrated in  FIG. 8 . As can be seen in  FIG. 8 , deformable hinge  186  is not along but offset from the symmetrical axis OO′ of the mirror plate such that the mirror plate is operable to rotate asymmetrically. The deformable hinge is located beneath the mirror plate in the direction of the incident light. That is, the mirror plate is located between the light transmissive substrate and the deformable hinge such that the deformable hinge is not illuminated by the incident light so as to prevent unexpected light scattering from the deformable hinge, thereby, increasing the contrast ratio of the produced image. The quality of the produced image is further improved through reduction of the light scattering from the edges of the mirror plate by forming the edges of the mirror plate into zigzagged shape, as shown in the figure.  
         [0058]     The deflectable and reflective mirror plate can be a multilayered structure. For example, the mirror plate may comprise an electrical conducting layer, a reflective layer that is capable of reflecting 85% or more, or 90% or more, or 85% or more, or 99% or more of the incident light (e.g. incident visible light), a mechanical enhancing layer that enhances the mechanical properties of the mirror plate. For example, the mirror plate may comprise a SiO 2  layer, an aluminum layer, a titanium layer, and a titanium nitride layer. When the aluminum layer is to be deposited on the SiO 2  layer, diffusion between the aluminum layer and SiO x  layer may occur. This can be avoided by depositing a barrier layer therebetween.  
         [0059]     Another exemplary micromirror device having a cross-sectional view of  FIG. 3  is illustrated in its perspective view in  FIG. 9 . Referring to  FIG. 9 , deflectable reflective mirror plate  124  with a substantially square shape is formed on light transmissive substrate  120 , and is attached to deformable hinge  132  via hinge contact  128 . The deformable hinge is held by hinge support  134 , and the hinge support is affixed and held by posts on the light transmissive substrate. For electrostatically deflecting the mirror plate, an addressing electrode (not shown in the figure for simplicity purposes) is fabricated in the semiconductor substrate  122 . For improving the electrical coupling of the deflectable mirror plate to the electrostatic field, extending metallic plate  136  can be formed on the mirror plate and contacted to the mirror plate via post  138 .  
         [0060]     The mirror plate is preferably attached to the deformable hinge asymmetrically such that the mirror plate can be rotated asymmetrically in favor of high contrast ratio. The asymmetric attachment is better illustrated in  FIG. 10 . Referring to  FIG. 10 , mirror plate comprises diagonals BB and CC. Deformable hinge is disposed with its length parallel to a diagonal (e.g. BB) of the mirror plate. However, the length of the deformable is not along any diagonal of the mirror plate in the top view when the mirror plate is parallel to the light transmissive substrate. Of course, the mirror plate can be attached to the deformable hinge symmetrically by placing the attachment point around the geometric or mass center of the mirror plate, which will not be discussed in detail herein.  
         [0061]     Similar to that in  FIG. 7 , the deformable hinge is preferably formed beneath the deflectable mirror plate in the direction of the incident light so as to avoid unexpected light scattering by the deformable hinge. For reducing unexpected light scattering of the mirror plate edge, the illumination light is preferably incident onto the mirror plate along a corner of the mirror plate.  
         [0062]     Referring to  FIG. 11 , an exemplary spatial light modulator having an array of micromirrors of  FIG. 9  is illustrated therein. For simplicity purposes, only 4×4 micromirrors are presented. In this example, micromirror array  148  is formed on light transmissive substrate  142 ; and addressing electrode and circuitry array  146  is formed on semiconductor substrate  144  for deflecting the micromirrors in the micromirror array. The deformable hinges of the micromirrors, as well as the addressing electrodes are hidden from the incident light.  
         [0063]     The micromirrors in the micromirror array of the spatial light modulator can be arranged in alternative ways, another one of which is illustrated in  FIG. 12 . Referring to  FIG. 12 , each micromirror is rotated around its geometric center an angle less than 45° degrees. The posts (e.g.  152  and  154 ) of each micromirror (e.g. mirror  156 ) are then aligned to the opposite edges of the mirror plate. No edges of the mirror plate are parallel to an edge (e.g. edges  160  or  162 ) of the micromirror array. The rotation axis (e.g. axis  158 ) of each mirror plate is parallel to but offset from a diagonal of the mirror plate when viewed from the top of the mirror plate at a non-deflected state.  
         [0064]      FIG. 13  illustrates the top view of another micromirror array having an array of micromirrors of  FIG. 7 . In this example, each micromirror is rotated 45° degrees around its geometric center. For addressing the micromirrors, the bitlines and wordlines are deployed in a way such that each column of the array is connected to a bitline but each wordline alternatively connects micromirrors of adjacent rows. For example, bitlines b 1 , b 2 , b 3 , b 4 , and b 5  respectively connect micromirrors groups of (a 11 , a 16 , and a 21 ), (a 14  and a 19 ), (a 12 , a 17 , and a 22 ), (a 15  and a 20 ), and (a 13 , a 18 , and a 23 ). Wordlines w 1 , w 2 , and w 3  respectively connect micromirror groups (a 11 , a 14 , a 12 , a 15 , and a 13 ), (a 16 , a 19 , a 17 , a 20 , and a 18 ), and (a 21 , a 22 , and a 23 ). With this configuration, the total number of wordlines is less the total number of bitlines.  
         [0065]     For the same micromirror array, the bitlines and wordlines can be deployed in other ways, such as that shown in  FIG. 14 . Referring to  FIG. 14 , each row of micromirrors is provided with one wordline and one bitline. Specifically, bitlines b 1 , b 2 , b 3 , b 4  and b 5  respectively connect column  1  (comprising micromirrors a 11 , a 16 , and a 21 ), column  2  (comprising micromirrors a 14  and a 19 ), column  3  (comprising micromirrors a 12 , a 17 , and a 22 ), column  4  (comprising micromirrors a 15  and a 20 ), and column  5  (comprising micromirrors a 13 , a 18 , and a 23 ). Wordlines WL 1 , WL 2 , WL 3 , WL 4 , and WL 5  respectively connect row  1  (comprising micromirrors a 11 , a 12 , and a 13 ), row  2  (comprising micromirrors a 14  and a 15 ), row  3  (comprising micromirrors a 16 , a 17 , and a 18 ), row  4  (comprising micromirrors a 19  and a 20 ) and row  5  (comprising micromirrors a 21 , a 22 , and a 23 ).  
         [0066]     According to another embodiment of the invention, the mirror plates of the micromirrors in the array can form a plurality of pockets, in which posts can be formed, wherein the pockets are covered by the extended areas of the addressing electrodes when viewed from the top of the micromirror array device, as shown in  FIGS. 15   a  to  16 .  
         [0067]     Referring to  FIG. 15   a , a portion of an array of mirror plates of the micromirrors is illustrated therein. The mirror plates in the array form a plurality of pockets in between. For example, pockets  172   a  and  172   b  are formed in which posts for supporting and holding mirror plate  174  can be formed. For individually addressing and deflecting the mirror plates in  FIG. 15   a , an array of addressing electrodes is provided, a portion of which is illustrated in  FIG. 15   b.    
         [0068]     Referring to  FIG. 15   b , each addressing electrode has an extended portion, such as extended portion  178  of addressing electrode  176 . Without the extended portion, the addressing electrode can be generally square, but having an area equal to or smaller than the mirror plate.  
         [0069]      FIG. 16  illustrates a top view of a micromirror array device after the addressing electrodes in  FIG. 15   b  and the mirror plates in  FIG. 15   a  being assembled together. It can be seen in the figure that each addressing electrode is displaced a particular distance along a diagonal of the mirror plate associated with the addressing electrode. As a result, the pockets presented between the mirror plates are covered by the addressing electrode, specifically by the extended portions of the addressing electrodes. In this way, light scattering otherwise occurred in the substrate having the addressing electrodes can be removed. The quality, such as the contrast ratio of the displayed images can be improved.  
         [0070]     When used in a spatial light modulator of a display system as shown in  FIG. 1 , the incident light beam is directed onto the mirror plates in a direction along the displacement direction of the addressing electrodes when viewed from the top of the addressing electrodes as shown in the figure. For example, the incident light has an angle θ to an edge of the addressing electrode (or the mirror plate) when viewed from the top; and the angle can be 135° degrees.  
         [0071]     The micromirrors in which embodiments of the invention can be implemented may be composed of any suitable materials and fabricated in many ways. According to the invention, the deflectable mirror plate comprises reflective film, preferably composed of a metallic material (e.g. aluminum, gold, silver) having a high reflectivity, deposited on another non-metallic material, such as SiO x , SiN x  and TiN x  for enhancing the mechanical properties of the mirror plate. Alternatively, other materials, such as a barrier layer for preventing diffusion between the metallic reflecting layer and the mechanical enhancing layer, can be deposited between the metallic reflecting layer and the mechanical enhancing layer.  
         [0072]     The deformable hinge preferably comprises an electrically conductive layer. Examples of suitable materials for the hinge layer are Al, Ir, titanium, titanium nitride, titanium oxide(s), titanium carbide, TiSiN x , TaSiN x , or other ternary and higher compounds.  
         [0073]     It will be appreciated by those skilled in the art that a new and useful method and apparatus for transposing pixel data matrices into bitplane data matrices for use in display systems having micromirror arrays have been described herein. In view of many possible embodiments to which the principles of this invention may be applied, however, it should be recognized that the embodiments described herein with respect to the drawing figures are meant to be illustrative only and should not be taken as limiting the scope of invention. For example, those of skill in the art will recognize that the illustrated embodiments can be modified in arrangement and detail without departing from the spirit of the invention. Therefore, the invention as described herein contemplates all such embodiments as may come within the scope of the following claims and equivalents thereof. In the claims, only elements denoted by the words “means for” are intended to be interpreted as means plus function claims under 35 U.S.C. §112, the sixth paragraph.