Abstract:
A light modulating Backplane with multi-layer pixel electrodes is disclosed. The light modulating backplane includes a multiple pixel control circuits and multiple pixel electrodes. The pixel electrodes include a first pixel electrode layer coupled to a corresponding pixel control circuit and a second pixel electrode layer. A passivation layer covers the pixel electrodes. The first pixel electrode layer is formed using a first metal such as copper and the second pixel electrode layer is formed using a second metal such as aluminum.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Field of the Invention 
         [0002]    The present invention relates to display technology. More specifically, the present invention relates to digital backplanes that control light modulating elements, spatial light modulators and light sources. 
         [0003]    Discussion of Related Art 
         [0004]    Micro-displays typically include light modulating backplane and a light modulating unit or a light emitting unit. Light modulating units include such technologies as liquid crystal on silicon (LCOS) and digital micro mirrors devices (DMD). Light emitting units include technologies such as Organic light emitting diodes (OLED). The technology used in such micro displays can also be used to make larger display units. 
         [0005]      FIGS. 1A and 1B  illustrate a small portion of a conventional LCOS display  100 . Specifically,  FIG. 1B  only shows 24 pixels of LCOS display  100 . Generally, a LCOS display would have thousands of pixels.  FIG. 1A  is a cross sectional view of display  100  along the A A′ cut shown in  FIG. 1B .  FIG. 1B  shows only one layer of LCOS display  100 . Specifically,  FIG. 1B  shows the top of the reflective pixel electrodes of LCOS display  100 . 
         [0006]    In  FIG. 1A , a substrate  110  supports the active backplane region  120  which includes pixel control circuits PCC_ 1 _ 1 , PCC_ 2 _ 1 , PCC_ 3 _ 1 , PCC_ 4 _ 1 , PCC_ 5 _ 1 , and PCC_ 6 _ 1  and pixel electrodes PE_ 1 _ 1 , PE_ 2 _ 1 , PE_ 3 _ 1 , PE_ 4 _ 1 , PE_ 5 _ 1 , and PE_ 6 _ 1 . The pixel electrodes are located above the pixel control circuits. Each pixel electrode PE_X_Y is coupled to and controlled by pixel control circuit PCC_X_Y. Thus, pixel electrode PE_ 1 _ 1  is coupled to and controlled by pixel control circuit PCC_ 1 _ 1 . Similarly, electrodes PE_ 2 _ 1 , PE_ 3 _ 1 , PE_ 4 _ 1 , PE_ 5 _ 1 , and PE_ 6 _ 1  are coupled to and controlled by pixel control circuits PCC_ 2 _ 1 , PCC_ 3 _ 1 , PCC_ 4 _ 1 , PCC_ 5 _ 1 , and PCC_ 6 _ 1 , respectively. For LCOS display  100 , the pixel electrodes are made of a reflective conductor to reflect incoming light as explained below. As shown in  FIG. 1B , the polarized electrodes are arranged in a rectangular matrix. For clarity the pixel electrodes are PE_X_Y, where X refers to the column location of the pixel electrode and Y refers to the row location of the pixel electrode. 
         [0007]    Active backplane region  120  also includes various, logic circuits to support the operation of the pixel control circuits. For clarity these logic circuits are omitted in the Figures because the omitted logic circuits, which are well known in the art, are not an integral aspect of the present invention. Substrate  110 , the pixel control circuits, the pixel electrodes and the omitted logic circuits form a light modulating backplane  100   b . In addition, a transparent passivation layer (not shown in  FIGS. 1A and 1B ) covers the pixel electrodes. An example of a light modulating backplane is described in U.S. Pat. No. 7,071,908, entitled “Digital Backplane” by Guttag et al., which is included herein by reference. Another example of a light modulating backplane is described in U.S. Pat. No. 8,605,015 entitled “Spatial Light Modulator with Masking Comparators” by Guttag et al., which is incorporated herein by reference. 
         [0008]    The light modulating unit  100   a  of LCOS display  100  includes a liquid crystal layer  130 , an alignment layer  140 , a transparent common electrode layer  150 , and a protective glass layer  160 . Protective glass layer  160  protects the rest of LCOS display  100  but typically does not manipulate incoming or reflected light. Transparent common electrode layer  150  works with the pixel electrodes to manipulate the liquid crystals in liquid crystal layer  130 . Alignment layer  140  aligns the liquid crystals in liquid crystal layer  130  to properly manipulate incoming and reflected light. Liquid crystal layer  130  contains liquid crystals that are controlled by the pixel electrodes to selectively pass incoming polarized light through liquid crystal layer  130 . Specifically, when a pixel electrode is charged to an “active state” by the corresponding pixel control circuit polarized light can pass through the area of liquid crystal layer  130  above the pixel electrode and be reflected back by the pixel electrode. However, if the pixel electrode is in an inactive state polarized light is blocked in the area of liquid crystal layer  130  above the pixel electrode. Pulse width modulation is used to create different contrast levels. For color displays, color filters can be included in the light modulating unit or field sequential color schemes (i.e. rapidly cycling through three different colored light sources) can be used. 
         [0009]    The light modulating backplane of conventional LCOS displays are made using a LCOS process on top of structures made with standard CMOS process. Specifically, the pixel control circuits (and supporting circuits) are made using standard CMOS process while the pixel electrodes are made using the LCOS process.  FIG. 2  is a cross sectional view of display  100  along the A A′ cut shown in  FIG. 1B . However  FIG. 2  only shows the portion of the A A′ cut that includes pixel electrodes PE_ 1 _ 1  and PE_ 1 _ 2 .  FIG. 2  shows a very simplified diagram of the various metal layers in a portion active backplane region  120  of light modulating backplane  100   b  of LCOS display  100 . Specifically for light modulating backplane  100   b ,  4  metal layers (typically named M 1 -M 4 ) are used in the CMOS process. However other backplanes can use more or fewer metal layers. In general advanced CMOS processes use copper for the metal layers. In addition a global metal layer (named GM), is used for signals used across the entire display such as power lines, ground lines, and clock lines. In general global metal layer GM is very thick (e.g. 700 to 1300 nanometers) and is made using an additional aluminum layer for light modulating backplanes. An LCOS process is used to fabricate the pixel electrodes and the connection between the pixel electrodes and the metal layers of the pixel control circuits, which were made with the CMOS process. Aluminum is used in conventional LCOS displays for the pixel electrodes. 
         [0010]    In  FIG. 2 , the various conductors and vias only illustrate the relative locations of the metal layers and do not actually form working circuits. Many details and various processing layer, which are well known in the art are omitted for clarity. For additional clarity, aluminum conductors are drawn with light shading, copper conductors are drawn with medium shading, tungsten conductors (vias) are drawn with dark shading, and transparent layers are drawn with no shading. Metal layer M 1  includes copper conductor M 1 _ 1 , M 1 _ 2 , and M 1 _ 3 . Copper conductor M 1 _ 2  is orthogonal to copper conductors M 1 _ 1  and M 1 _ 3  and thus appears very short as compared to copper conductors M 1 _ 1  and M 1 _ 3 . Metal layer M 2  includes copper conductor M 2 _ 1 , M 2 _ 2 , M 2 _ 3 , and M 2 _ 4 . Copper conductor M 2 _ 1  is coupled to copper conductor M 1 _ 1  by a via V 1 . Copper conductor M 2 _ 4  is coupled to copper conductor M 1 _ 3  by a via V 2 . 
         [0011]    Metal layer M 3  includes copper conductor M 3 _ 1  and M 3 _ 2 . Copper Conductor M 3 _ 1  is coupled to copper conductor M 2 _ 2  by a via V 3 . Metal layer M 4  includes copper conductor M 4 _ 1 , M 4 _ 2 , M 4 _ 3 , and M 4 _ 4 . Copper conductor M 4 _ 2  is coupled to copper conductor M 3 _ 1  by a via V 5 . Copper conductor M 4 _ 4  is coupled to copper conductor M 3 _ 2  by a via V 4 . 
         [0012]    Metal conductors M 4 _ 2  is also coupled to pixel electrode PE_ 1 _ 1  by a LCOS via LV_ 1 , a LCOS Stud LS_ 1 , which is formed from the global metal layer, and a LCOS via LV_ 2 . Specifically, LCOS via LV_ 1  couples copper conductor M 4 _ 2  to LCOS stud LS_ 1 , which is part of global metal layer GM. LCOS via LV_ 2  couples LCOS stud LS_ 1  to pixel electrode PE_ 1 _ 1 . Because copper electrodes M 4 _ 2 , M 3 _ 1 , and M 2 _ 2  are coupled to pixel electrode PE_ 1 _ 1 , copper electrodes M 4 _ 2 , M 3 _ 1 , and M 2 _ 2  are components of pixel control circuit PCC_ 1 _ 1  (See  FIG. 1A ). 
         [0013]    Metal conductors M 4 _ 4  is coupled to pixel electrode PE_ 2 _ 1  by a LCOS via LV_ 3 , a LCOS Stud LS_ 2 , and a LCOS via LV_ 4 . Specifically, LCOS via LV 3  couples copper conductor M 4 _ 4  to LCOS stud LS_ 2 , which is part of global metal layer GM. LCOS via LV 4  couples LCOS stud LS_ 2  to pixel electrode PE_ 2 _ 1 . Because copper electrodes M 4 _ 4  and M 3 _ 2  are coupled to pixel electrode PE_ 2 _ 1 , copper electrodes M 4 _ 4  and M 3 _ 2  are components of pixel control circuit PCC_ 2 _ 1  (See  FIG. 1A ). Global metal layer also includes aluminum conductors GM_ 1 , GM_ 2  and GM_ 3 . 
         [0014]    As stated above, pixel electrodes PE_ 1 _ 1  and PE_ 2 _ 1  are formed with aluminum for among other reasons, the high reflectivity of aluminum and the stability of aluminum. In LCOS displays the global metal layer GM can be made using either copper or Aluminum. In LCOS display  100 , global metal layer GM is an aluminum layer. LCOS vias LV_ 1 , LV_ 2 , LV_ 3 , and LV_ 4  are made using tungsten, which can provide good electrical contacts with both copper and aluminum. A transparent passivation layer  210  covers the top of the light modulating backplane. In a light modulating backplane in accordance with one embodiment of the present invention, the pixel electrodes have a thickness of 260 nanometers, a width of 6.2 μm and a length of 6.2 μm. The transparent passivation layer is silicon dioxide with a thickness of 75 nanometers, Global metal layer GM has a thickness between 700 and 1300 nanometers, and metal layers M 1 -M 4  have a thickness between 70 and 500 nanometers. 
         [0015]    Very few microchip fabrication plants (hereinafter fabs or fab) are configured to manufacture the light modulating backplane of a LCOS display primarily due to the difficulties and additional costs of connecting the aluminum pixel electrodes to the copper metal layers of the active backplane region. Thus these few fabs can charge excessive prices to manufacture the light modulating backplanes of LCOS displays. Hence there is a need for a light modulating backplane of a LCOS display that can be manufactured using CMOS processes. 
       SUMMARY 
       [0016]    Accordingly, the present invention provides a novel light modulating backplane having a multiple pixel control circuits and a multiple pixel electrodes. The pixel electrodes, which are multi-layered, include a first pixel electrode layer and a second pixel electrode layer. The first pixel electrode layer is coupled to a corresponding pixel control circuit. Generally, the first pixel electrode layer is formed using a first metal and the second pixel electrode layer is formed using a second metal. In a specific embodiment of the present invention the first metal is copper and the second metal is aluminum. Furthermore, in many embodiments of the present invention the pixel electrodes include a third pixel electrode layer between the first pixel electrode layer and the second pixel electrode layer. For example, in one embodiment of the present invention the third pixel electrode layer is an adhesion layer formed using titanium. 
         [0017]    Some embodiments of the present invention are fabricated using two separate fabs. For example in some embodiments of the present invention, the first pixel electrode layer is formed at a first fab while the second pixel electrode layer is formed at a second fab. For some embodiments a protective layer is formed over the first pixel electrode layer at the first fab. The protective layer is stripped at the second fab prior to forming the second pixel electrode layer. 
         [0018]    The present invention will be more fully understood in view of the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIGS. 1A-1B  illustrate a portion of a conventional LCOS display. 
           [0020]      FIG. 2  is an illustration of a portion of a light modulating backplane in accordance with one embodiment of the present invention. 
           [0021]      FIG. 3  is an illustration of a portion of a light modulating backplane in accordance with one embodiment of the present invention. 
           [0022]      FIG. 4  is an illustration of a portion of a light modulating backplane in accordance with one embodiment of the present invention. 
           [0023]      FIG. 5  is an illustration of a portion of a light modulating backplane in accordance with one embodiment of the present invention. 
           [0024]      FIG. 6  is an illustration of a portion of a light modulating backplane in accordance with one embodiment of the present invention. 
           [0025]      FIG. 7  is an illustration of a portion of a light modulating backplane in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    As explained above, only a few fabs can manufacture conventional light modulating backplanes for LCOS displays. However light modulating backplanes in accordance with embodiments of the present invention can be manufactured using standard CMOS processes and thus can be manufactured by most CMOS fabs, which can greatly reduce the cost of making LCOS displays using the present invention. 
         [0027]      FIG. 3  is a cross sectional view of a light modulating backplane  300   b  of a display  300 . Display  300  is similar to display  100  ( FIGS. 1A and 1B ), except the LCOS process used to manufacture the light modulating backplane of display  100  are not needed to manufacture the light modulating backplane  300   b  of display  300 . For clarity,  FIG. 3  only shows the same portion of the light modulating backplane as the portion shown in  FIG. 2  of light modulating backplane  100   b  of LCOS display  100 , (i.e. pixel electrodes PE_ 1 _ 1  and PE_ 1 _ 2 ). 
         [0028]    Specifically, light modulating backplane  300   b  of LCOS display  300  uses six copper metal layers (typically named M 1 -M 6 ). As in  FIG. 2 , the various conductors and vias of  FIG. 3  only illustrate the relative locations of the metal layers and do not actually form working circuits. Many details and various processing layer, which are well known in the art are omitted for clarity. Metal layer M 1  includes copper conductor M 1 _ 1 , M 1 _ 2 , and M 1 _ 3 . Copper conductor M 1 _ 2  is orthogonal to copper conductors M 1 _ 1  and M 1 _ 3  and thus appears very short as compared to copper conductors M 1 _ 1  and M 1 _ 3 . Metal layer M 2  includes copper conductor M 2 _ 1 , M 2 _ 2 , M 2 _ 3 , and M 2 _ 4 . Copper conductor M 2 _ 1  is coupled to copper conductor M 1 _ 1  by a via V 1 . Copper conductor M 2 _ 4  is coupled to copper conductor M 1 _ 3  by a via V 2 . 
         [0029]    Metal layer M 3  includes copper conductor M 3 _ 1  and M 3 _ 2 . Copper Conductor M 3 _ 1  is coupled to copper conductor M 2 _ 2  by a via V 3 . Metal layer M 4  includes copper conductor M 4 _ 1 , M 4 _ 2 , M 4 _ 3 , and M 4 _ 4 . Copper conductor M 4 _ 2  is coupled to copper conductor M 3 _ 1  by a via V 5 . Copper conductor M 4 _ 4  is coupled to copper conductor M 3 _ 2  by a via V 4 . 
         [0030]    Metal conductors M 4 _ 2  is also coupled to copper pixel electrode PE_ 1 _ 1 , which is part of metal layer M 6  by a via V 6 , a copper conductor M 5 _ 2 , and a via V 7 . Specifically, via V 6  couples copper conductor M 4 _ 2  to copper conductor M 5 _ 2 , which is part of metal layer M 5 . Via V 6  couples copper conductor M 5 _ 2  to pixel electrode PE_ 1 _ 1 . Because copper electrodes M 4 _ 2 , M 3 _ 1 , and M 2 _ 2  are coupled to pixel electrode PE_ 1 _ 1 , copper electrodes M 4 _ 2 , M 3 _ 1 , and M 2 _ 2  are components of a pixel control circuit PCC_ 1 _ 1  that controls pixel electrode PE_ 1 _ 1 . 
         [0031]    Metal conductors M 4 _ 4  is coupled to a copper pixel electrode PE_ 2 _ 1  by a via V 8 , a copper conductor M 5 _ 4 , and a via V 9 . Specifically, via V 8  couples copper conductor M 4 _ 4  to metal conductor M 5 _ 4 , which is part of metal layer M 5 . Via V 9  couples copper electrode M 5 _ 4  to pixel electrode PE_ 2 _ 1 . Because copper electrodes M 4 _ 4  and M 3 _ 2  are coupled to pixel electrode PE_ 2 _ 1 , copper electrodes M 4 _ 4  and M 3 _ 2  are components of a pixel control circuit PCC_ 2 _ 1  which controls pixel electrode PE_ 2 _ 1 . Metal Layer M 5 _ 1 , which is used in place of Global Metal Layer GM (of  FIG. 2 ) also includes copper conductors M 5 _ 1 , M 5 _ 3 , and M 5 _ 5 . In light modulating backplane  300   b , metal layer M 6  is used for the pixel electrodes of which pixel electrodes PE_ 1 _ 1  and PE_ 2 _ 1  are shown in  FIG. 3 . 
         [0032]    By using copper for the pixel electrodes, special LCOS processing steps to form aluminum electrodes and LCOS vias (using Tungsten) are eliminated in the fabrication of light modulating backplane  300   b . Therefore, light modulating backplane  300   b  can be manufactured by most CMOS fabs rather than the just the few fabs that are used for conventional LCOS displays. 
         [0033]    However, copper electrodes have some disadvantages as compared to Aluminum electrodes for LCOS displays. For example, the reflectivity of Copper is less than the reflectivity of aluminum. Accordingly, the brightness of a display using light modulating backplane  300   b  may be lower than conventional LCOS display using the same light sources. Furthermore, Copper has an outdiffussion issue as compared with aluminum. Therefore, passivation layer  310  on light modulating backplane  300   b  must be thicker than passivation layer  210  of light modulating backplane  100   b . A thicker passivation layer may further reduce the brightness of a display using light modulating backplane  300   b . In addition, copper would need additional compensation for white balance as compared to aluminum. 
         [0034]    In a particular embodiment of the present invention, the pixel electrodes have a thickness between 200 and 400 nanometers nanometers, a width of 5 nanometers and a length of 5 nanometers. Passivation layer  310  is silicon dioxide with a thickness between 20 and 100 nanometers. Metal layers M 1 -M 6  have a thickness between 70 and 500 nanometers. 
         [0035]      FIG. 4  shows a light modulating backplane  400   b  that addresses the brightness issues of light modulating backplane  300   b  in accordance with another embodiment of the present invention. Because light modulating backplane  400   b  is very similar to light modulating backplane  300   b , only the differences between light modulating backplane  400   b  and light modulating backplane  300   b  are described. The major difference between light modulating backplane  400   b  and light modulating backplane  300   b  is that light modulating backplane  400   b  uses multilayer pixel electrodes. As shown in  FIG. 400 b   , pixel electrode PE_ 1 _ 1  includes a first pixel electrode layer PEL_ 1 _ 1 _ 1  and a second pixel electrode layer PEL_ 1 _ 1 _ 2  covering first pixel electrode layer PEL_ 1 _ 1 _ 1 . The second pixel electrode layer is the reflective layer of the pixel electrode. Pixel electrode layer PEL_ 1 _ 1 _ 1  is part of metal layer M 6  and made using Copper. However, pixel electrode layer PEL_ 1 _ 1 _ 2  is made using aluminum. In light modulating backplane  400   b , pixel electrode layer PEL_ 1 _ 1 _ 2  is larger than pixel electrode layer PEL_ 1 _ 1 _ 1 . However, in other embodiments of the present invention the various pixel electrode layers can be the same size and in some embodiments the lower pixel electrode layer (e.g. pixel electrode layer PEL_ 1 _ 1 _ 1 ) can be larger than the upper pixel electrode layer (e.g. pixel electrode layer PEL_ 1 _ 1 _ 2 ). Similarly, pixel electrode PE_ 2 _ 1  also includes a first pixel electrode layer PEL_ 2 _ 1 _ 1  and a second pixel electrode layer PEL_ 2 _ 1 _ 2  covering first pixel electrode layer PEL_ 2 _ 1 _ 1 . 
         [0036]    The upper pixel electrode layers (e.g. pixel electrode layers PEL_ 1 _ 1 _ 2  and PEL_ 2 _ 1 _ 2 ) of the pixel electrodes in light modulating backplane  400   b  are made using aluminum to provide better reflectivity than the pixel electrodes of light modulating backplane  300   b . In addition, using aluminum to cover the copper layer of the pixel electrode greatly reduces the outdiffusion issues of the copper layer. Thus, passivation layer  410  (on the top surface of light modulating backplane  400   b ) can be thinner than the passivation layer of light modulating backplane  300   b.    
         [0037]    Light modulating backplane  400   b  can still be manufactures at most CMOS fabs because most CMOS fabs because light modulating backplane does not require special LCOS vias to interconnect aluminum pixel electrodes to lower level metal layers. Most CMOS fabs are capable of depositing and patterning an aluminum layer near the top of the light modulating backplane. In a particular embodiment of the present invention, pixel electrode layer PE_ 1 _ 1 _ 1  has a width of 4 nanometers a length of 4 nanometers, and a thickness of 210 nanometers and pixel electrode layer PE_ 1 _ 1 _ 1 _ 2 , has a width of 5 nanometers a length of 5 nanometers, and a thickness of 260 nanometers, and passivation layer  410  has a thickness of 75 nanometers. 
         [0038]    As shown in  FIG. 5 , some embodiments of the present invention also include a third pixel electrode layer. Specifically,  FIG. 5  shows a light modulating backplane  500   b . Because light modulating backplane  500   b  is very similar to light modulating backplane  400   b , for brevity, only the differences are described. Specifically, the pixel electrodes of light modulating backplane  500   b  include a third pixel electrode layer between the first pixel electrode layer and the second pixel electrode layer. The third pixel electrode layer is an adhesion layer that improves the bonding between the first pixel electrode layer and the second pixel electrode layer. The adhesion layer can be formed using Titanium or Titanium Tungsten Alloy. Specifically, as shown in  FIG. 5 , pixel electrode PE_ 1 _ 1  includes a first pixel electrode layer PEL_ 1 _ 1 _ 1 , a second pixel electrode layer PEL_ 1 _ 1 _ 2 , and a third pixel electrode layer PE_ 1 _ 1 _ 3 , that is in between first pixel electrode layer PEL_ 1 _ 1 _ 1  and second pixel electrode layer PE_ 1 _ 1 _ 3 . Similarly, pixel electrode PE_ 2 _ 1  includes a first pixel electrode layer PEL_ 2 _ 1 _ 1 , a second pixel electrode layer PEL_ 2 _ 1 _ 2 , and a third pixel electrode layer PE_ 2 _ 1 _ 3 , that is in between first pixel electrode layer PEL_ 2 _ 1 _ 1  and second pixel electrode layer PE_ 2 _ 1 _ 3 . In a particular embodiment of the present invention, pixel electrode layer PE_ 1 _ 1 _ 1  has a width of 4 nanometers a length of 4 nanometers, and a thickness of 210 nanometers, pixel electrode layer PE_ 1 _ 1 _ 1 _ 2 , has a width of 5 nanometers a length of 5 nanometers, and a thickness of 260 nanometers, and pixel electrode layer PE_ 1 _ 1 _ 1 _ 3 , has a width of 4 nanometers a length of 4 nanometers, and a thickness of 10 nanometers. Passivation layer  510  has a thickness of 75 nanometers. 
         [0039]    Although most CMOS fabs can manufacture light modulating backplanes  400   b  and  500   b , some fabs may not process both copper and aluminum at a reasonable price. Thus some embodiments of the present invention are first processed at a first fab and then later processed at a second fab to add the second pixel electrode layer. As shown in  FIG. 6 , after formation of the first pixel electrode layer of a light modulating backplane  600   b , a protective layer  610  is used to cover the surface of light modulating backplane  600   b  at the first fab. Light modulating backplane is then completed at a second Fab which strips protective layer  610  from light modulating backplane  600   b  prior to formation of the additional pixel electrode layers as shown in  FIG. 4 or 5 . In a particular embodiment of the present invention protective layer  610  is made using PSG (i.e. Phosphosilicate Glass), which can be easily stripped at the second Fab using a conventional acid rinse. Some Fabs can deposit aluminum layers but cannot properly pattern aluminum. For these fabs, protective layer  610  can be made of Aluminum. In which case the second fab can simply pattern the aluminum protective layer to form the second pixel electrode layer rather than removing protective layer  610 . 
         [0040]    In some embodiments of the present invention, the first fab also fabricates the third pixel electrode layer (i.e. the adhesion layer). Thus, as shown in  FIG. 7 , prior to creating protective layer  710 , the third pixel electrode layer is formed over the first pixel electrode layers. Specifically, pixel electrode layers PEL_ 1 _ 1 _ 3  is fabricated over pixel electrode layer PEL_ 1 _ 1 _ 1  and pixel electrode layer PEL_ 2 _ 1 _ 3  is fabricated over pixel electrode layer PEL_ 2 _ 1 _ 1 . 
         [0041]    In the various embodiments of the present invention, novel structures and methods have been described for creating light modulating backplanes. The various embodiments of the structures and methods of this invention that are described above are illustrative only of the principles of this invention and are not intended to limit the scope of the invention to the particular embodiment described. For example, in view of this disclosure those skilled in the art can define other pixel control circuits, pixel electrodes, pixel electrode layers, passivation layers, protective layers, light modulating units, and so forth, and use these alternative features to create a method or system according to the principles of this invention. Thus, the invention is limited only by the following claims.