Abstract:
A pixel includes a primary element and a secondary element. At least a portion of the primary element is deformable between two positions. In one position, the light source is reflected such that the observer observes a dark pixel. In the other position, the light is reflected such that the observer observes a bright pixel. Gray levels of light are viewable by varying between the two positions.

Description:
BACKGROUND 
       [0001]    High definition (HD) television and video renders to a viewer high contrast and fine detailed images in high resolution. The differences between standard definition and HD are so visually apparent that the demand for display devices that have larger screen sizes and higher pixel densities will only continue. 
         [0002]    However, increasing screen size and increasing pixel density exponentially increases the prices of display devices made of conventional monolithic display technologies. Conventional monolithic display technologies utilize a single panel (or chip, etc.), which is responsible for the image the user sees. These characteristics make fabricating large sized displays very tedious and their price extremely high. Modular display devices can decrease the expense of large sized display screens. A modular display device tiles many small panel displays together to form a single large display. Failure of a pixel in a modular display affects only the module that it belongs to, while a failure of a pixel in a monolithic display affects the entire display. 
         [0003]    Modular display devices can solve other limitations of large sized monolithic displays. In particular, pixels can be addressed in an efficient fashion at a modular level. In a modular display, a controller can determine which modules need their data updated based on the sending of a new image. Rather than repainting all of the pixels as would be done in a monolithic display, only those modules that need updating will be repainted. Therefore, a modular display would require a reduced bandwidth and simplified circuitry compared to a monolithic display. 
         [0004]    One problem that has prevented commercialization of the modular display is creating an image that flows seamlessly across the different modules. Although software has been used to blend the seams and make the screen look uniform, there are limitations in the display technologies available for modularizing. Some limitations include light efficiency, contrast, cost and scalability. 
         [0005]    Example types of display technologies include transmissive, reflective and emissive displays. Emissive displays, except for plasma displays, are generally made of unstable materials that have short lives and/or poor color quality. Plasma displays have very large pixels, which can not be scaled down for large pixel density displays. Some reflective displays use ambient light, a very efficient light source, but fail to produce high contrast and full color images. Other reflective displays use MEMS chips, an expensive light source and a projection screen. However, these displays are too expensive for modular fabrication. Transmissive displays, such as liquid crystal displays (LCDs), have extremely low light efficiency. When modularizing LCD displays, the modular display renders even more decreased light efficiency and contrast. Other types of transmissive displays also have very low contrast and color quality or are difficult to control. 
         [0006]    The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. 
       SUMMARY 
       [0007]    This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background. 
         [0008]    A pixel has a primary element that includes a first surface that reflects light received from a light source and a secondary element that includes a first surface that is spaced apart from and faces the first surface of the primary element. At least a portion of the primary element is deformable between a first position and a second position. In the first position, the pixel appears dark to a viewer. In the second position, the primary element focuses reflected light onto the first surface of the secondary element and the pixel appears bright to a viewer. Gray levels of light are viewable between the first position and the second position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  illustrates a schematic diagram of a modular display under one embodiment. 
           [0010]      FIG. 2  illustrates a schematic diagram of a display under one embodiment. 
           [0011]      FIG. 3A  illustrates a schematic diagram of a pixel in a first position under one embodiment. 
           [0012]      FIG. 3B  illustrates a front view representation of the pixel of  FIG. 3A  in the first position. 
           [0013]      FIG. 4A  illustrates a schematic diagram of the pixel of  FIG. 3A  in a second position under one embodiment. 
           [0014]      FIG. 4B  illustrates a front view representation of the pixel of  FIG. 4A  in the second position. 
           [0015]      FIG. 5  illustrates a schematic diagram of a pixel in a first position under one embodiment. 
           [0016]      FIG. 6  illustrates a schematic diagram of the pixel of  FIG. 5  in a second position under one embodiment. 
           [0017]      FIG. 7  illustrates a method of fabricating a pixel under one embodiment. 
           [0018]      FIGS. 8A-8D  illustrate steps in the process of forming a primary structure under one embodiment. 
           [0019]      FIGS. 9A-9B  illustrate steps in the process of forming a secondary structure under one embodiment. 
           [0020]      FIG. 10  illustrates a fabricated pixel as discussed in  FIGS. 7 ,  8 A- 8 D and  9 A- 9 B. 
           [0021]      FIG. 11  illustrates a graphical representation of response of an array of pixels to the modulation signal in the form of a square wave. 
           [0022]      FIG. 12  illustrates a graphical representation of response of an array of pixels in the form of a transfer function. 
       
    
    
     DETAILED DESCRIPTION 
       [0023]      FIG. 1  illustrates a schematic diagram of a modular display  100  under one embodiment. Modular display  100  includes a plurality of modules (of which four are illustrated in  FIG. 1 )  102 . Each module  102  includes an array of pixels  104 . Each module  102  is projected onto a continuous screen  106  for a viewer  108  to view. Since light diverges after it leaves the pixels  104 , continuous screen  106 , placed at an optimal distance, will look to a viewer like pixels cover the whole screen without empty space between them. In another embodiment and as illustrated in  FIG. 2 , display  200  can include a single module  202  having an array of pixels  204 . In this embodiment, pixels  204  are not tiled together in modules as illustrated in  FIG. 1 , rather, the array of pixels  204  are monolithically positioned together and projected onto a continuous screen  206  for a viewer  208  to view. 
         [0024]      FIGS. 3A and 4A  illustrate schematic diagrams of a pixel  304  for use in modular display  100  of  FIG. 1  or for use in monolithic display  200  of  FIG. 2  under one embodiment.  FIG. 3A  illustrates a first position of pixel  304 , while  FIG. 4A  illustrates a second position of pixel  304 . 
         [0025]    In  FIGS. 3A and 4A , pixel  304  includes a primary element  310  and a secondary element  312 . Primary element  310  is an annular membrane or mirror having an inner diameter  314  and an outer diameter  316 . A portion of primary element  310  that is in proximity to inner diameter  314  is suspended, while a remaining portion of primary element  310  that is in proximity to outer diameter  316  is fixed. Secondary element  312  is a circular mirror having an outer diameter  318 . Although primary element  310  and secondary element  312  are circular in shape, it should be realized that primary element  310  and secondary element  312  can be other shapes. For example, primary element  310  and secondary element  312  can be square or rectangular in shape. 
         [0026]    Primary element  310  is formed with a primary structure  320  and secondary element  312  is formed with a secondary structure  322 . Secondary structure  322  includes a transparent substrate  323 , such as glass, and second element  312  that is only coupled to a portion of secondary structure  323 , while primary structure  320  includes a plurality of different layers. 
         [0027]    Primary structure  320  includes a transparent substrate  324 , such as glass. Coupled to transparent substrate  324  is a transparent conductive material or electrode  326 . While it is possible that electrode  326  can be a transparent conductive polymer, indium tin oxide (ITO) is a suitable material for electrode  326  as it demonstrates a combination of electrical conductivity and optical transparency. A first spacer  328  is positioned between primary element  310  and electrode  326 . The suspended or remaining portion of primary element  310  includes an aperture  327  (illustrated in  FIG. 3B ) that is defined by inner diameter  314 . Aperture  327  is a through hole extending between first surface  330  and an opposing second surface  331  of primary element  310 . Inner diameter  314  is slightly smaller than outer diameter  318  of secondary element  312 . As previously described, a portion of primary element  310  is coupled to first spacer  328 , while a remaining portion of primary element  310  is suspended from primary structure  320 . The suspended or remaining portion of primary element  310  is deformable between a first position as illustrated in  FIG. 3A  and a second position as illustrated in  FIG. 4A . 
         [0028]    Primary element  310  includes a first surface  330  configured to reflect light received from a light source  332 . In  FIGS. 3A and 4A , and in one embodiment, secondary element  312  includes a first surface  334  that is reflective. First surface  334  of secondary element  312  is spaced apart from and faces first surface  330  of primary element  310  In one embodiment, primary element  310  and secondary element  312  comprise a metallic material, such as aluminum, that demonstrate desirable reflective, bending and conductive properties. However, it should be realized that primary element  310  can include non-metallic or dielectric materials that can demonstrate reflective, bending and conductive properties. Such materials provide primary element  310  and secondary element  312  with reflective surfaces. 
         [0029]    As illustrated in the first position of  FIG. 3A , light  336  from light source  332  enters secondary structure  322 . A portion of light  336  proceeds to primary structure  320 , while a remaining portion of light  336  is reflected back to light source  332  by a second surface  338  that opposes first surface  334  of secondary element  312 . The portion of light  336  that proceeds to primary structure  320  reflects from first surface  330  of primary element  310 , back through secondary structure  322  and towards light source  332 . As illustrated in  FIG. 3A , all light provided by light source  332  to pixel  304  is reflected back to light source  332  causing pixel  304  to appear dark to a viewer  308 . Such a dark pixel  304  is represented in  FIG. 3B . 
         [0030]    At least a portion of primary element  310  is deformed into the second position as illustrated in  FIG. 4A . A voltage is simultaneously applied between primary element  310 , which is conductive, and electrode  326 . While the portion of primary element  310  that is fixed to first spacer  328  remains in position, the suspended or remaining portion of primary element  310  is pulled towards electrode  326  by the electrostatic force caused by the application of voltage. The electrostatic force causes the shape of primary element  310  to deform from a planar shape to a parabolic shape. 
         [0031]    As illustrated in the second position of  FIG. 4A , light  336  from light source  332  enters transparent substrate  323 . A portion of light  336  proceeds to primary structure  320 , while a remaining portion of light  336  is reflected back to light source  332  by second surface  338  that opposes first surface  334  of secondary element  312 . The portion of light  336  that proceeds to primary structure  320  partially reflects from the fixed portion of primary element  310  back through transparent substrate  323 , towards light source  332  and partially reflects from the deformed portion of primary element  310  that is suspended. The light that reflects from the deformed portion of primary element  310  is focused on first surface  334  of secondary element  312 . Reflected light  340  from first surface  334  of secondary element  312  propagates through aperture  327  (illustrated in  FIG. 4B ) that is defined by inner diameter  314  of primary element  310  such that pixel  304  appears bright to viewer  308 . Such a bright pixel  304  is represented in  FIG. 4B . 
         [0032]    Pixel  304  of  FIGS. 3A ,  3 B,  4 A and  4 B is light efficient and can be brighter than other types of displays that have a similar light source, thus, eliminating the need to darken a room in which the pixel is be used for viewing. In addition, pixel  304  is not sensitive to temperature changes or expensive packaging because it operates in atmospheric conditions. Pixel  304  also deforms between the first position illustrated in  FIG. 3A  and the second position illustrated in  FIG. 4A  at a relatively fast rate (approximately less than  2  ms). Such a rate of change allows pixel  304  to utilize sequential RGB color light sources. In addition, different color shades in accordance with different intensities of light can be realized in a single cycle between the first position and the second position by varying the amount of voltage applied between electrode  326  and primary element  3   10 . 
         [0033]    A plurality of circular shaped primary elements  310  and secondary elements  312  can be stacked in an array of pixels as illustrated in  FIGS. 1 and 2 . Even though a portion of light  336  from light source  332  reflects from second surface  338  of secondary element  312 , reflects from the portion of primary element  310  that is fixed to primary structure  320  and is loss due to reflection on several of the glass and metal surfaces, the light efficiency that viewer  308  is expected to view is approximately 50%, which is 5-10 times more than that of a liquid crystal display. Pixel  304  also solves the problem of a transmissive imager, where the free aperture of each pixel is limited by the opaque backplane circuitry. Pixel  304  can use circuitry that is placed under primary element  310  so as not to block light and achieve a high fill factor. 
         [0034]      FIGS. 5 and 6  illustrate schematic diagrams of a pixel  404  for use in modular display  100  of  FIG. 1  or for use in monolithic display  200  of  FIG. 2  under another embodiment.  FIG. 5  illustrates a first position of pixel  404 , while  FIG. 6  illustrates a second position of pixel  404 . Pixel  404  includes a primary element or mirror  410  and a secondary element  412 . Primary element  410  and secondary element  412  can be any suitable shape, such as circular, rectangular or square. Primary element  410  is deformable between a first position as illustrated in  FIG. 5  and a second position as illustrated in  FIG. 6 . 
         [0035]    Primary element  410  includes a first surface  430  configured to reflect light received from a light source  432 . In  FIGS. 5 and 6 , and in one embodiment, secondary element  412  includes a first surface  434  that is non-reflective or opaque. First surface  434  of secondary element  412  is spaced apart from and faces the first surface  430  of primary element  410 . In one embodiment, primary element  410  comprises a metallic material, such as aluminum, that demonstrates desirable reflective, bending and conductive properties. However, it should be realized that primary element  410  can include non-metallic or dielectric materials that demonstrate reflective, bending and conductive properties. Such materials provide primary element  410  with reflective surfaces. 
         [0036]    At least a portion of primary element  410  is deformed into the first position as illustrated in  FIG. 5 . A voltage is applied causing the shape of primary element  410  to deform from a planar shape to a parabolic shape. As illustrated in the first position of  FIG. 5 , light  436  from light source  432  is reflected from first surface  430  of the deformed primary element  410  at an angle of incidence  442 . Light  444  is reflected from primary element  410  and is focused onto first surface  434  of secondary element  412 . Since first surface  434  of secondary element  412  is non-reflective or opaque, secondary element  412  prevents light  444  from projecting onto screen  406 . In the first position, pixel  404  appears dark to viewer  408 . 
         [0037]    As illustrated in the second position of  FIG. 6 , primary element  410  is deformed into the second position. In the second position, light  436  from light source  432  is reflected from first surface  430  of primary element  410  at an angle of incidence  442 . Light  444  is reflected from primary element  410  and projected onto a screen  406  for viewing by a viewer  408 . In the second position, pixel  404  appears bright to viewer  408 . 
         [0038]    Finding conditions at which primary element  310  ( FIGS. 3 and 4 ) or  410  ( FIGS. 5 and 6 ) deflect enough for efficient light focusing requires careful optimization of various parameters. The more primary element  310  or  410  deflects, the more light can be focused on secondary element  312  ( FIGS. 3 and 4 ) or  412  ( FIGS. 5 and 6 ). For example, the maximum deflection of an annular membrane, such as the annular membrane of primary element  310  having a fixed outer diameter  316  ( FIGS. 3 and 4 ) is described by: 
         [0000]    
       
         
           
             
               
                 
                   
                     δ 
                     max 
                   
                   = 
                   
                     
                       δ 
                       center 
                     
                     = 
                     
                       
                         3 
                          
                         
                           
                             Pr 
                             4 
                           
                            
                           
                             ( 
                             
                               1 
                               - 
                               
                                 v 
                                 2 
                               
                             
                             ) 
                           
                         
                       
                       
                         16 
                          
                         
                           Et 
                           3 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where P is pressure, r is the radius of the reflecting surface of primary element  310 , t is the thickness of primary element  310 , v is Poisson ratio and E is Young&#39;s Modulus. In other words, 2r is the reflecting surface diameter of primary element  310 . Pressure can be described by: 
         [0000]    
       
         
           
             
               
                 
                   P 
                   = 
                   
                     
                       
                         F 
                         ei 
                       
                       / 
                       A 
                     
                     = 
                     
                       
                         
                           ɛɛ 
                           0 
                         
                          
                         
                           V 
                           2 
                         
                       
                       
                         2 
                          
                         
                           l 
                           2 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   2 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where F el  is electrostatic force between electrode  326  ( FIGS. 3 and 4 ) and primary element  310 , A is the area of electrode  326 , ε 0  is permittivity of free space, ε is relative permittivity of air, V is the applied voltage and I is the gap between electrode  326  and primary element  310 . In Equation 2, it is assumed that the gap (l) is constant to make a first order approximation. 
         [0039]    It should be realized that deflection can be increased by increasing the applied voltage V or radius r of primary element  310  and decreasing the thickness t of primary element  310  or distance l between electrode  326  and primary element  310 . In general, applied voltage can be kept low in order to minimize power dissipation and simplify the device control. Making the radius r of primary element  310  larger also increases the pixel size. The minimum thickness t of primary element  310  is limited by the reflective properties of the material used for primary element  310 . In an embodiment where aluminum is used, the smallest thickness can be approximately 100 nm. Such a size can be used to easily fabricate structure  320 . The smallest gap l between electrode  326  and primary element  310  is limited by the fabrication procedure as well. In some cases, the gap l can be three times larger than the maximum deflection to avoid any shorting out of the pixel  304 . Furthermore, desired optical properties of the system put additional constraints on the device parameters. The focusing quality depends on the minimum spot size and is calculated by: 
         [0000]      min spotsize=2.4λf#  (3) 
         [0000]    where f is the focal length, f#=f/2r, and the focal length f of the parabolic shaped mirror or element corresponding to the shape of primary element  310  can be described by the following relation: 
         [0000]    
       
         
           
             
               
                 
                   f 
                   = 
                   
                     
                       R 
                       / 
                       2 
                     
                     = 
                     
                       
                         r 
                         2 
                       
                       
                         4 
                          
                         
                           δ 
                           max 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
         [0000]    where R is the geometric radius of the reflecting surface of primary element  310  when deformed. 
         [0040]    After optimization utilizing the above equations, it is determined that, in one embodiment, but not by limitation, some device parameters can be: a primary element  310  radius r of 50 μm, a secondary element  312  radius of 25 μm, a radius of aperture  327  of 20 μm, a gap l between primary element  310  and electrode  326  of 6 μm, a maximum deflection δ max  of primary element  310  of 1.8 μm, an applied voltage V of 32V, a focal length f of 350 μm, a distance between primary element  310  and secondary element  312  of 175 μm and a minimum spot size of 4.2 μm. Such parameters render a desirable optical quality. 
         [0041]      FIG. 7  illustrates a method  700  of fabricating pixel  304  under one embodiment. At block  702 , primary structure  320  ( FIG. 3 ) is formed. To form primary structure  320 , a first conductive material or electrode  326  is coated on a first side  350  of first transparent substrate  324 . Such a step is illustrated in  FIG. 8A . As previously discussed, first transparent substrate  324  can include glass. However, other types of transparent substrates can be used. As also previously discussed, electrode  326  can be a conductive material, such as an ITO (indium tin oxide) or polymer that can demonstrate similar characteristics to that of ITO. Deposited on electrode  326  includes first spacer  328  as illustrated in  FIG. 8B . For example, first spacer  328  can be a polyimide, such as HD4000, that is spin-coated on top of electrode  326 . After the example polyimide is post-baked on a hot plate, a layer  352  demonstrating reflective properties is deposited on first spacer  328  to form primary element  310  as illustrated in  FIG. 8C . For example and as previously discussed, layer  352  can be of aluminum that is sputtered onto first spacer  328 . To form primary element  310  from layer  352 , aperture  327  is formed in layer  352  (also illustrated in  FIG. 8C ). For example, positive photoresist, such as AZ1512, can be used for photolithography to form aperture  327  and then can be etched. Finally, first spacer  328  is partially release from layer  352  to form primary element  310  that is suspended as illustrated in  FIG. 8D . For example, a gas can be used to eat first spacer  328  away from aperture  327  of primary element  310  towards an outer diameter  316  of primary element  310 . Removal of first spacer  328  is stopped prior to reaching outer diameter  316  of primary element  310  such that at least a portion of primary element is fixed to structure  320 . 
         [0042]    At block  704  of the method  700  illustrated in  FIG. 7 , secondary structure  322  is formed. To form secondary structure  322 , a layer  354  is deposited on a substrate  356 , such as glass, to form secondary element  312  as illustrated in  FIG. 9A . As previously discussed layer  354  has reflective properties and can be a metallic material, such as aluminum. For example, aluminum can be sputtered onto substrate  356 . To form secondary element  312 , a portion of layer  354  is removed as illustrated in  FIG. 9B . For example, layer  354  can be patterned using photolithography. At block  706  of the method  700  illustrated in  FIG. 7 , primary structure  320  and secondary structure  322  are coupled together with a second spacer  358  and aligned to form pixel  304  as illustrated in  FIG. 10 . 
         [0043]      FIG. 11  illustrates the response of an array of pixels  304  or  404  in the form of a square wave  800 .  FIG. 12  illustrates the response of an array of pixels  304  or  404  in the form of a transfer function  900 . As illustrated in  FIG. 11 , the rise time is 0.625 ms and the fall time is 0.61 ms, which gives response times that are less than 2 ms. This means that pixel  304  or  404  is fast enough to display colors using sequential RGB as previously discussed. Moreover, the pixel transfer function illustrated in  FIG. 12  shows that light intensity can smoothly and monotonically change from 0 to 1. Therefore, color shades can be realized by varying color intensity in a single cycle between a first position ( FIGS. 3A and 5 ) and a second position ( FIGS. 4A and 6 ) in contrast with binary pixels, which use several cycles for every color shadow. In particular, pixel  304  and  404  can experience different light intensities between the first position and the second position by applying different amounts of voltage over the cycle. 
         [0044]    Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.