PATENT DOCUMENT

Publication Number: US-9798199-B2
Application Number: US-201514850015-A
Country: US
Kind Code: B2

Title: Liquid crystal display with color motion blur compensation structures

Abstract:
A layer of liquid crystal material may be interposed between display layers. The display layers may include thin-film transistor circuitry having subpixel electrodes for applying electric fields to subpixel portions of the layer of liquid crystal material. Subpixels of different colors may have different shapes and may have different liquid crystal layer thicknesses. These subpixel differences may be configured to slow the switching speed of subpixels of a certain color relative to other subpixels to reduce color motion blur when an object is moved across a black or colored background. The subpixels may have chevron shapes. Subpixels of a first color may have chevron shapes that are less bent than subpixels of second and third colors. In configurations with varying liquid crystal layer thicknesses, the subpixels of the first color may have thicker liquid crystal layers than the subpixels of the second and third colors.

Claims:
What is claimed is: 
     
       1. A liquid crystal display having an array of pixels including red, green, and blue subpixels, the liquid crystal display comprising:
 upper and lower display layers; and 
 a layer of liquid crystal material between the upper and lower display layers, wherein the layer of liquid crystal material has a first thickness that is constant entirely across each of the red subpixels and a second thickness that is smaller than the first thickness and that is constant entirely across each of the green and blue subpixels, wherein the second thickness across the green subpixels is equal to the second thickness across the blue subpixels, wherein the first and second thicknesses extend in a direction perpendicular to the upper and lower display layers, and wherein one of the upper and lower display layers comprises: 
 a substrate; and 
 an overcoat layer on the substrate that completely and continuously overlaps the red, green, and blue subpixels, wherein the overcoat layer has a first thickness in areas overlapping the red subpixels, a second thickness that is larger than the first thickness in areas overlapping the green subpixels, and a third thickness that is equal to the second thickness in areas overlapping the blue subpixels, and wherein the first, second and third thicknesses extend in a direction perpendicular to the upper and lower display layers. 
 
     
     
       2. The liquid crystal display defined in  claim 1  wherein the substrate forms part of the upper display layer, wherein the colored background has a red digital subpixel value, a green digital subpixel value, and a blue digital subpixel value, wherein the red subpixel digital value is larger than the green and blue digital subpixel values, and wherein the liquid crystal display further comprises an array of color filter elements on the substrate. 
     
     
       3. The liquid crystal display defined in  claim 2  wherein the array of color filter elements includes red color filter elements in the red subpixels, green color filter elements in the green subpixels, and blue color filter elements in the blue subpixels. 
     
     
       4. The liquid crystal display defined in  claim 3  further comprising a layer of thin-film transistors in the lower display layer. 
     
     
       5. The liquid crystal display defined in  claim 3  further comprising a layer of thin-film transistors in the upper display layer. 
     
     
       6. The liquid crystal display defined in  claim 2  wherein the overcoat layer is formed on the array of color filter elements. 
     
     
       7. The liquid crystal display defined in  claim 1  wherein the blue and green subpixels have different shapes than the red subpixels. 
     
     
       8. The liquid crystal display defined in  claim 1  wherein the subpixels have chevron shapes and wherein the red subpixels have a chevron shape that is less bent away from a column direction than the chevron shapes of the green and blue subpixels. 
     
     
       9. A liquid crystal display having an array of pixels including red, green, and blue subpixels, the liquid crystal display comprising:
 upper and lower display substrates; 
 an overcoat layer between the upper and lower display substrates; 
 a layer of liquid crystal material between the upper and lower display substrates, wherein the liquid crystal layer has a first thickness that is constant entirely across each of the red subpixels and a second thickness that is smaller than the first thickness and that is constant entirely across each of the green and blue subpixels, wherein the second thickness across the green subpixels is equal to the second thickness across the blue subpixels, and wherein the first and second thicknesses extend in a direction perpendicular to the upper and lower display substrates; and 
 an array of color filter elements on the upper display substrate, wherein the color filter elements all have the same thickness in a direction perpendicular to the upper and lower display substrates. 
 
     
     
       10. The liquid crystal display defined in  claim 9  wherein the overcoat layer is formed on the array of color filter elements. 
     
     
       11. The liquid crystal display defined in  claim 10  wherein the array of color filter elements includes red color filter elements in the red subpixels, green color filter elements in the green subpixels, and blue color filter elements in the blue subpixels. 
     
     
       12. The liquid crystal display defined in  claim 11  further comprising a layer of thin-film transistors on the lower display substrate. 
     
     
       13. The liquid crystal display defined in  claim 9  wherein the blue and green subpixels have different shapes than the red subpixels. 
     
     
       14. The liquid crystal display defined in  claim 9  wherein the red subpixels have a first chevron shape and wherein the green and blue subpixels have a second chevron shape that is different than the first chevron shape. 
     
     
       15. The liquid crystal display defined in  claim 9  wherein the overcoat layer has a first thickness in areas overlapping the red subpixels and a second thickness that is larger than the first thickness in areas overlapping the green subpixels.

Description:
This application claims the benefit of provisional patent application No. 62/128,453 filed on Mar. 4, 2015, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. 
     Liquid crystal displays contain a layer of liquid crystal material. Pixels in a liquid crystal display contain thin-film transistors and electrodes for applying electric fields to the liquid crystal material. The strength of the electric field in a pixel controls the polarization state of the liquid crystal material and thereby adjusts the brightness of the pixel. 
     The speed with which liquid crystal pixels switch can vary as a function of applied voltage. As a result, the amount of time required to switch a black pixel to a gray level will be longer than the amount of time required to switch a black pixel to a white level. In some situations, it may be desirable to move a black object on a screen with a colored background. In this type of scenario, subpixels of different colors may have different target pixel values and may therefore switch at different speeds. This may result in production of unpleasant colored motion blur effects when the black object is moved. 
     It would therefore be desirable to be able to provide improved displays for electronic devices such as displays with reduced color motion blur. 
     SUMMARY 
     A display may have upper and lower display layers. A layer of liquid crystal material may be interposed between the upper and lower display layers. The display may include an upper and lower polarizer and a backlight for providing illumination for the display layer. An array of color filter elements may be used to provide the display with the ability to display color images. The color filter elements may include red, green, and blue elements or color filter elements of different colors. The display may have an array of pixels each of which has subpixels such as red, green, and blue subpixels formed using the red, green, and blue color filter elements. 
     The display layers may include a layer of thin-film transistor circuitry that has subpixel electrodes for applying electric fields to the layer of liquid crystal material for each of the subpixels. The subpixels of different colors may have different electrode shapes (e.g., fingers oriented at different angles) and/or may have different liquid crystal layer thicknesses. These subpixel differences may be configured to slow the switching speed of the subpixels of a certain color relative to other subpixels to reduce color motion blur when an object of one color is moved across a background of another color. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with display structures in accordance with an embodiment. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment. 
         FIG. 6  is a top view of a portion of an array of pixels in a display in accordance with an embodiment. 
         FIG. 7  is a diagram showing how motion of an object against a background has the potential to discolor pixels along the leading and trailing edges of the object and thereby create color motion blur effects. 
         FIG. 8  is a graph showing how red, green, and blue subpixels in a display may have different target pixel values during color transitions such as those associated with movement of the object of  FIG. 7  and therefore have the potential to switch with different speeds in accordance with an embodiment. 
         FIG. 9  is a top view of a portion of a display with an illustrative pixel pattern to reduce color motion blur effects in accordance with an embodiment. 
         FIG. 10  is a graph in which illustrative normalized transmission-versus-applied-pixel-voltage curves have been plotted for different types of subpixels in accordance with an embodiment. 
         FIG. 11  is a top view of an illustrative set of pixel electrodes in which electrode fingers have a chevron shape with center and end kinks in accordance with an embodiment. 
         FIG. 12  is a top view of an illustrative set of subpixels of different colors showing how the electrodes in the subpixels may have fingers with different orientation angles and end kinks in accordance with an embodiment. 
         FIG. 13  is a top view of an illustrative set of subpixels of different colors showing how the fingers in the electrodes may have different orientation angles and may alternate between positive and negative orientation angles in successive rows of a pixel array in a display in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of an illustrative display in which liquid crystal layer thicknesses are different for subpixels of different colors to reduce color motion blur effects in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, 3, and 4 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have openings for components such as button  26 . Openings may also be formed in display  14  to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have an opening to accommodate button  26  (as an example). 
       FIG. 4  shows how electronic device  10  may be a display such as a computer display or may be a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  may be mounted on a support structure such as stand  27  or stand  27  may be omitted (e.g., to mount device  10  on a wall). Display  14  may be mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, 3, and 4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Display  14  for device  10  may include pixels formed from liquid crystal display (LCD) components. A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . The outermost display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     A cross-sectional side view of an illustrative configuration for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 ,  FIG. 4  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     Display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  58  and  56  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of pixel circuits based on thin-film transistors and associated electrodes (pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. Configurations in which color filter elements are combined with thin-film transistor structures on a common substrate layer in the upper or lower portion of display  14  may also be used. 
     During operation of display  14  in device  10 , control circuitry (e.g., one or more integrated circuits on a printed circuit) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed to a display driver integrated circuit such as circuit  62 A or  62 B using a signal path such as a signal path formed from conductive metal traces in a rigid or flexible printed circuit such as printed circuit  64  (as an example). 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . Light source  72  may be located at the left of light guide plate  78  as shown in  FIG. 5  or may be located along the right edge of plate  78  and/or other edges of plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of plastic covered with a dielectric minor thin-film coating. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. If desired, films such as compensation films may be incorporated into other layers of display  14  (e.g., polarizer layers). 
     As shown in  FIG. 6 , display  14  may include an array of pixels  90  such as pixel array  92 . Pixel array  92  may be controlled using control signals produced by display driver circuitry. Display driver circuitry may be implemented using one or more integrated circuits (ICs) and/or thin-film transistors or other circuitry. 
     During operation of device  10 , control circuitry in device  10  such as memory circuits, microprocessors, and other storage and processing circuitry may provide data to the display driver circuitry. The display driver circuitry may convert the data into signals for controlling pixels  90  of pixel array  92 . 
     Pixel array  92  may contain rows and columns of pixels  90 . The circuitry of pixel array  92  (i.e., the rows and columns of pixel circuits for pixels  90 ) may be controlled using signals such as data line signals on data lines D and gate line signals on gate lines G. Data lines D and gate lines G are orthogonal. For example, data lines D may extend vertically and gate lines G may extend horizontally (i.e., perpendicular to data lines D). 
     Pixels  90  in pixel array  92  may contain thin-film transistor circuitry (e.g., polysilicon transistor circuitry, amorphous silicon transistor circuitry, semiconducting oxide transistor circuitry such as InGaZnO transistor circuitry, other silicon or semiconducting-oxide transistor circuitry, etc.) and associated structures for producing electric fields across liquid crystal layer  52  in display  14 . Each display pixel may have one or more thin-film transistors. For example, each display pixel may have a respective thin-film transistor such as thin-film transistor  94  to control the application of electric fields to a respective pixel-sized portion  52 ′ of liquid crystal layer  52 . 
     The thin-film transistor structures that are used in forming pixels  90  may be located on a thin-film transistor substrate such as a layer of glass. The thin-film transistor substrate and the structures of display pixels  90  that are formed on the surface of the thin-film transistor substrate collectively form thin-film transistor layer  58  ( FIG. 5 ). 
     Gate driver circuitry may be used to generate gate signals on gate lines G. The gate driver circuitry may be formed from thin-film transistors on the thin-film transistor layer or may be implemented in separate integrated circuits. The data line signals on data lines D in pixel array  92  carry analog image data (e.g., voltages with magnitudes representing pixel brightness levels). During the process of displaying images on display  14 , a display driver integrated circuit or other circuitry may receive digital data from control circuitry and may produce corresponding analog data signals. The analog data signals may be demultiplexed and provided to data lines D. 
     The data line signals on data lines D are distributed to the columns of display pixels  90  in pixel array  92 . Gate line signals on gate lines G are provided to the rows of pixels  90  in pixel array  92  by associated gate driver circuitry. 
     The circuitry of display  14  may be formed from conductive structures (e.g., metal lines and/or structures formed from transparent conductive materials such as indium tin oxide) and may include transistors such as transistor  94  of  FIG. 6  that are fabricated on the thin-film transistor substrate layer of display  14 . The thin-film transistors may be, for example, silicon thin-film transistors or semiconducting-oxide thin-film transistors. 
     As shown in  FIG. 6 , pixels such as pixel  90  may be located at the intersection of each gate line G and data line D in array  92 . A data signal on each data line D may be supplied to terminal  96  from one of data lines D. Thin-film transistor  94  (e.g., a thin-film polysilicon transistor, an amorphous silicon transistor, or an oxide transistor such as a transistor formed from a semiconducting oxide such as indium gallium zinc oxide) may have a gate terminal such as gate  98  that receives gate line control signals on gate line G. When a gate line control signal is asserted, transistor  94  will be turned on and the data signal at terminal  96  will be passed to node  100  as pixel voltage Vp. Data for display  14  may be displayed in frames. Following assertion of the gate line signal in each row to pass data signals to the pixels of that row, the gate line signal may be deasserted. In a subsequent display frame, the gate line signal for each row may again be asserted to turn on transistor  94  and capture new values of Vp. 
     Pixel  90  may have a signal storage element such as capacitor  102  or other charge storage elements. Storage capacitor  102  may be used to help store signal Vp in pixel  90  between frames (i.e., in the period of time between the assertion of successive gate signals). 
     Display  14  may have a common electrode coupled to node  104 . The common electrode (which is sometimes referred to as the common voltage electrode, Vcom electrode, or Vcom terminal) may be used to distribute a common electrode voltage such as common electrode voltage Vcom to nodes such as node  104  in each pixel  90  of array  92 . As shown by illustrative electrode pattern  104 ′ of  FIG. 6 , Vcom electrode  104  may be implemented using a blanket film of a transparent conductive material such as indium tin oxide, indium zinc oxide, other transparent conductive oxide material, and/or a layer of metal that is sufficiently thin to be transparent (e.g., electrode  104  may be formed from a layer of indium tin oxide or other transparent conductive layer that covers all of pixels  90  in array  92 ). 
     In each pixel  90 , capacitor  102  may be coupled between nodes  100  and  104 . A parallel capacitance arises across nodes  100  and  104  due to electrode structures in pixel  90  that are used in controlling the electric field through the liquid crystal material of the pixel (liquid crystal material  52 ′). As shown in  FIG. 6 , electrode structures  106  (e.g., a display pixel electrode with multiple fingers or other display pixel electrode for applying electric fields to liquid crystal material  52 ′) may be coupled to node  100  (or a multi-finger display pixel electrode may be formed at node  104 ). During operation, electrode structures  106  may be used to apply a controlled electric field (i.e., a field having a magnitude proportional to Vp-Vcom) across pixel-sized liquid crystal material  52 ′ in pixel  90 . Due to the presence of storage capacitor  102  and the parallel capacitances formed by the pixel structures of pixel  90 , the value of Vp (and therefore the associated electric field across liquid crystal material  52 ′) may be maintained across nodes  106  and  104  for the duration of the frame. 
     The electric field that is produced across liquid crystal material  52 ′ causes a change in the orientations of the liquid crystals in liquid crystal material  52 ′. This changes the polarization of light passing through liquid crystal material  52 ′. The change in polarization may, in conjunction with polarizers  60  and  54  of  FIG. 5 , be used in controlling the amount of light  44  that is transmitted through each pixel  90  in array  92  of display  14 . 
     In displays such as color displays, color filter layer  56  is used to impart different colors to different pixels. As an example, each pixel  90  in display  14  may contain three (or more than three) different subpixels each with a different respective color. With one suitable arrangement, which may sometimes be described herein as an example, each pixel  90  has a red subpixel, a green subpixel, and a blue subpixel. Each subpixel is driven with an independently selected pixel voltage Vp. The amount of voltage that is supplied to the electrodes of each subpixel is associated with a respective digital pixel value (e.g., a value ranging from 0 to 255 or other suitable digital range). Desired pixel colors may be produced by adjusting the pixel values for each of the three subpixels in a pixel. For example, a black pixel may be associated with a 0 pixel value for the red subpixel, a 0 pixel value for the green subpixel, and a 0 pixel value for the blue subpixel. As another example, an orange pixel may be associated with pixel values of 245, 178, and 66 for the red, green, and blue subpixels. White may be represented by pixel values of 255, 255, and 255. 
     The response times of the pixels in display  14  may vary as a function of the magnitude of the liquid crystal switching voltage applied to electrodes  106 . When switching a black pixel, which has red, green, blue pixel values of (0, 0, 0), to a white pixel (255, 255, 255), each subpixel (red, green, and blue) is provided with the same target pixel value (i.e., 255) and starts from the same initial pixel value (i.e., 0), so the voltage applied across liquid crystal layer  52  during switching is the same for each subpixel. As a result, all subpixels will switch at the same time. This type of switching scenario may arise when moving black text, a black cursor, or other black item against a white background. 
     Other pixel switching scenarios may create color motion blur due to the unequal response times that arise when driving subpixels of different colors with different pixel values. As an example, consider the response of a pixel when switching from black (0, 0, 0) to orange (245, 178, and 66). In this situation, a large voltage drop appears across the red subpixel (i.e., a voltage drop associated with a difference in before and after digital values of 245) and lower voltage drops appear across the green subpixel (a voltage associated with pixel value change of 178) and blue subpixel (a pixel value change of 66). Because the voltage on the red subpixel (and therefore the electric field applied by the red electrode  106  to the liquid crystal layer) is relatively large, the liquid crystal molecules of the red subpixel will rotate more quickly than the liquid crystal molecules of the green and blue subpixels. The red subpixel will therefore change color (from black to red) faster than the green and blue subpixels will switch from black to green and black to blue, respectively. The disparate switching speeds of the subpixels of different colors can lead to unpleasant visual artifacts. In the present example, in which a black item is being moved across an orange background, the relatively faster switching speed of the red subpixels has the potential to create undesirable red motion blur effects. 
     Color motion blur effects can arise both at the leading edge of a moving object and at the trailing edge of a moving object. For example, consider the movement of object  112  across background  110  of display  14  of  FIG. 7 . Object  112  may have a first color (e.g., black) and background  110  may have a second color (e.g., orange). Object  112  may be black text (as an example). Background  110  may have a color that is desirable when presenting electronic books to a user in a warm ambient lighting environment (e.g., indoor lighting). Object  112  may be moved across background  110  up and down during scrolling, right and left when panning, etc. In the example of  FIG. 7 , object  112  is moving to the right in direction  114 . 
     At trailing edge  118 , black pixels (0, 0, 0) are being switched to orange (245, 178, 66). Black-to-white switching speeds (rise times) may vary considerably depending on switching voltage levels. Because the red pixels are provided with a larger switching voltage than the green and blue pixels when switching from black to orange, the red pixels in region  116  may switch from black more quickly than the green and blue pixels, leading to blurred colors in region  118 . In particular, the pixels of display  14  in region  118  have the potential to develop a significant red color due to the enhanced switching speed of the red subpixels relative to the blue and green subpixels. 
     At leading edge  116  of object  112 , pixels are switching from background color  110  to the color of object  112 . For example, pixels in leading edge  116  may be switching from (245, 178, 66) to black (0, 0, 0). The red pixels in this situation may exhibit slightly slower decay times than the green and blue pixels, leading to gray motion blur. 
     A graph showing how pixels with different colors have the potential to switch at different speeds during particular color transitions is shown in the graph of  FIG. 8  in which subpixel transmission T (proportional to subpixel output intensity) has been plotted as a function of time t. In the example of  FIG. 8 , the situation at trailing edge  118  of  FIG. 7  is being illustrated. Initially (at time t 1 ), the pixels are black (0, 0, 0). At time t 3 , object  112  has moved away from edge  118  and each of the subpixels have had sufficient time to acquire their desired target value (i.e., the red subpixel has acquired value 245, the green subpixel has acquired value 178, and the blue subpixel has acquired value 66). The switching progress of the red, green, and blue subpixels in a conventional display at intermediate times between times t 1  and t 3  is illustrated by curves  120  (for red),  122  (for green), and  124  (for blue). These curves (which are not normalized in the graph of  FIG. 8 ) exhibit transitions at different speeds. The green and blue curves  122  and  124  transition relatively slowly. The red curve (curve  120 ) transitions rapidly, because the target value for the red subpixel is relatively high (245). Because red curve  120  rises steeply compared with green curve  122  and blue curve  124 , the color of the pixels in trailing edge  118  (which are associated with time t 2 ) will be overly red in color. 
     To restore the desired balance between the red, green, and blue subpixels in trailing edge  118  and therefore minimize red motion blur effects, the subpixels of display  14  may be configured to equalize the switching speeds of the red, green, and blue subpixels in certain switching scenarios (e.g., when switching from black to orange as described in connection with the present example and/or when switching between other color combinations). In particular, the shape and/or liquid crystal layer thickness of the red subpixel may be configured to slow the red subpixel switching speed relative to the switching speeds of the green and blue subpixels. When configured in this way, display  14  will exhibit a slower red pixel switching characteristic such as curve  126 . At intermediate times such as time t 2  (i.e., for pixels in trailing edge  118 ), the red subpixel pixel value that is associated with curve  126  will not be excessive compared to the pixel values for the green and blue subpixels at time t 2 . As a result, edge  118  will not appear overly reddish and red motion blur effects will be suppressed. 
     Pixel switching characteristics can be influenced by factors such as electrode geometry and pixel cell thickness (i.e., liquid crystal layer thickness). One way in which to selectively adjust the switching speed of the pixels involves changing the layout of electrodes  106  in certain subpixels. This type of arrangement is shown in  FIG. 9 . In the example of  FIG. 9 , display  14  has subpixels of three colors. Each subpixel is associated with a respective chevron-shaped opening in black mask  130  and a corresponding set of electrode fingers  106  that have chevron shapes. If desired, shapes other than chevron shapes may be used for electrodes  106  and the openings of the pixels that contain electrodes  106  (e.g., rectangular shapes, subpixel openings with curved edges, etc.). The use of chevron-shaped electrode fingers and pixel openings openings is merely illustrative. 
     The shape of the subpixels and, in particular, the angular spread of the arms of each chevron-shaped opening and the associated angular spread of the chevron-shaped fingers of the subpixel electrodes can be configured to be different for subpixels of different colors. In the example of  FIG. 9 , red subpixel  90 R has an edge  132  that is angled at an angle A with respect to the X axis and electrode fingers  106  with a parallel longitudinal electrode axis  133  that is likewise angled at angle A with respect to the X axis. Edges  132  and axes  133  of the green subpixel  90 G and the blue subpixel  90 B and their electrodes are each angled at an angle B with respect to the X axis. The value of B may be smaller than the value of A. For example, A may be 85° and B may be 75°, so that the chevrons of red subpixels  90 R (i.e., the chevron-shaped openings and the chevron-shaped electrodes  106 ) are less bent than the chevrons of green subpixels  90 G and blue subpixels  90 B. Other angles may be used, if desired. 
     Within each subpixel, the longitudinal axes  133  of pixel electrodes  106  run parallel to chevron edges  132 , so the different shapes of the subpixels result in different orientations between the electric fields produced by the subpixels and the liquid crystal molecules in the subpixels. 
     The liquid crystal material that makes up liquid crystal layer  52  of display  14  may be either a negative liquid crystal material or a positive liquid crystal material. A negative liquid crystal exhibits a negative dielectric anisotropy, whereas a positive liquid crystal exhibits a positive dielectric anisotropy. The liquid crystal molecules (liquid crystals) in a negative liquid crystal align perpendicularly to applied electric fields (i.e., the longitudinal axis of negative liquid crystal molecules will orient perpendicular to applied electric fields from electrodes  106 ). The liquid crystal molecules in a positive liquid crystal align parallel to applied electric field (i.e., the longitudinal axis of positive liquid crystal molecules will oriented parallel to applied electric fields). 
     In a negative liquid crystal configuration for display  14 , the longitudinal axis of the negative liquid crystal molecules runs along the X axis prior to application of electric field by electrodes  106 . In a positive liquid crystal configuration for display  14 , the longitudinal axis of the positive liquid crystal molecules runs along the Y axis prior to application of electric field by electrodes  106 . Despite having perpendicular initial (unrotated) orientations, the angles made by the liquid crystal dipoles associated with the negative and positive liquid crystal molecules with respect to the edges  132  of the subpixels (and therefore the longitudinal axes  133  of electrodes  106 ) is the same. In the present example, the dipole of a negative liquid crystal, which runs along the Y axis when the negative liquid crystal is unrotated, will make will make an angle of  90 -A with respect to edge  132  of red subpixel  90 R (i.e., the dipole of the unrotated negative liquid crystal to the longitudinal axis of electrodes  106  will be 5° in the present example). The dipole of a positive liquid crystal runs along the Y axis when the positive liquid crystal is unrotated and will therefore make the same angle of  90 -A with respect to edge  132  of red subpixel  90 R (i.e., the dipole of the unrotated positive liquid crystal to the longitudinal axis of electrodes  106  will be 5° in the present example). In subpixels  90 G and  90 B, the angle between the liquid crystal molecule dipole and the longitudinal axis  133  of electrodes  106  will be 15° (i.e., an angle greater than the angle for the red subpixel). 
     The increased angle between the liquid crystal dipole and longitudinal electrode axis for the green and blue subpixels will tend to increase their switching speed relative to the red subpixel in switching scenarios of the type described in connection with  FIG. 7  and will therefore compensate display  14  for red motion blur. Although angles of 5° and 15° have been used for this example, other electrode-axis-to-liquid-crystal-dipole angle values may be used if desired. In a configuration in which the subpixels have chevron shapes, flatter (less bent) chevrons can be used for red subpixels than are used for green and blue subpixels to help slow red subpixel switching and thereby suppress red motion blur effects when a black object is moved against a background with a color such as orange that has more red content than blue and green content. 
       FIG. 10  is a graph of a simulation in which transmission T has been plotted against applied pixel voltage Vp for a subpixel with an unmodified and a modified dipole-to-electrode-axis angle. When the angle is unmodified (e.g., 10°), the subpixel will achieve a transmission level of 245 (the desired level for switching a red subpixel in the present black-to-orange switching example) with an applied voltage of 4.5 volts (curve  140 ), but will achieve this same desired transmission level with an application of only 4 volts when the red subpixel is modified to exhibit a dipole-to-electrode-axis angle of 5° (curve  142 ). The lower value of the pixel voltage required to achieve pixel value 245 with the modified arrangement (e.g., the arrangement with less bent chevrons for the red pixels) will allow the red subpixels to be switched using a lower voltage. The lower switching voltage (i.e., 4 volts instead of 4.5 volts in this example), will cause the red pixel switching speed to be reduced as desired. 
     If desired, electrodes  106  may have chevron shapes with kinks. As shown in the illustrative configuration of  FIG. 11 , for example, electrodes  106  may have a main portion in which the fingers of the electrodes run parallel to each other (and are oriented at an angle such as illustrative angle  90 -A with respect to the Y axis for the illustrative subpixel in  FIG. 11 ). Kinks  106 K in the electrodes may be formed from short segments of the electrodes that have different angles (i.e., angles greater than  90 -A) with respect to the Y axis. Kinks  106 K may, for example, be located in the center of electrodes  106  (i.e., to form a central kinked portion) and/or at the ends of electrodes  106  (i.e., to form end kinks). 
       FIG. 12  is an illustrative layout for electrodes  106  in which electrodes  106  have a non-chevron shape. In the example of  FIG. 12 , electrode fingers  106  (i.e., longitudinal electrode finger axes  133 ) run diagonally across each subpixel. Electrode fingers  106  are oriented at an angle of  90 -A with respect to the Y axis in red subpixel  90 R (so that the electrode finger axis is oriented at angle  90 -A with respect to the liquid crystal dipole). Green subpixel  90 G may have electrode fingers  106  with axes  133  that are oriented at angle  90 -B with respect to the Y axis (and with respect to the liquid crystal dipole). Blue subpixel  90 B may likewise have electrode fingers  106  with axes  133  oriented at angle  90 -B with respect to the liquid crystal dipole or, if desired, blue subpixels  90 B of  FIG. 12  (and any other blue subpixels such as chevron-shaped blue subpixels of  FIG. 9 , etc.) may have a different angle (e.g., an angle  90 -C where C is different than B and is different than A). Configurations in which each subpixel color has fingers oriented at a different angle may provide display  14  with an enhanced ability to combat different types of color motion blur, but may be consume more area than displays in which angles C and B are identical. 
       FIG. 13  shows an illustrative configuration in which the subpixels in some rows (e.g., row n) have electrode fingers  106  that are rotated slightly clockwise from axis Y (by angles such as angles  90 -A for subpixel  90 R and  90 -B for subpixel  90 G, and optionally another angle  90 -C for blue pixel  90 B) and have other rows (e.g., row n+1) in which electrode fingers  106  are rotated slightly counterclockwise in the same way. 
     In general, subpixels  90 R,  90 G, and  90 B may have electrodes with any suitable shapes (i.e., any suitable electrode finger orientations relative to the liquid crystal dipole of layer  52 ). The electrode configurations of  FIGS. 9, 11, 12, and 13  are merely illustrative. 
     If desired, the switching speed of the red subpixel may be slowed by increasing the cell gap for the red subpixels relative to the blue and green subpixels. This type of configuration is shown in the cross-sectional side view of display  14  of  FIG. 14 . As shown in  FIG. 14 , color filter layer  56  may have a color filter layer substrate  56 A (e.g., a layer of clear material such as transparent glass, plastic, ceramic, etc.). Color filter elements such as red element R, green element G, and blue element B may be patterned onto substrate  56 A (e.g., using photoimageable colored polymer and photolithographic patterning techniques). Black masking layer  130  may have chevron-shaped openings or other suitable openings that are aligned with the color filter elements. 
     Using a halftone mask, multiple masks and multiple deposition steps, or other techniques, a clear overcoat layer with multiple thicknesses such as overcoat layer  56 B (e.g., a clear photoimageable polymer layer or other suitable layer) may be deposited on the array of color filter elements on substrate  56 A. Layer  56 B may have a thickness of T 1  in areas that overlap the red subpixels of display  14  and may have larger thicknesses such as respective thicknesses T 2  and T 3  in the green and blue subpixels of display  14 . Thicknesses T 2  and T 3  may be equal to each other or may be different. As a result, the thickness of liquid crystal layer  52  in the red subpixels will be larger (D 1 ) than in the green and blue subpixels (D 2  and D 3 , respectively). Switching speed is slower for thicker cell gaps (e.g., decay times may be proportional to the square of the liquid crystal thickness and rise times may be similarly increased when liquid crystal layer thickness increases). The larger value of liquid crystal layer thickness D 1  in the red subpixels when compared to the smaller value of liquid crystal layer thicknesses D 2  and D 3  in the blue and green subpixels will therefore slow the red subpixel switching speed relative to the green and blue subpixel switching speed to compensate for red motion blur effects of the type that may otherwise arise when moving an object such as object  112  against a background such as background  110 . 
     If desired, selective pixel gap adjustment schemes of the type shown in  FIG. 14  may be used in combination with the selective electrode axis flattening schemes of the type shown in  FIGS. 9, 11, 12, and 13  and/or other selective adjustments may be made to the subpixel structures for subpixels of particular colors to compensate for color motion blur. The examples of  FIGS. 9, 11, 12, and 13  are merely illustrative. 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20150910
Publication Date: 20171024
Grant Date: 20171024
Priority Date: 20150304
Inventors: CHEN YUAN
GE ZHIBING
HERRANZ ADRIA FORES
TAI CHIA HSUAN
NEMATI HOSSEIN
JIANG JUN
CHEN CHENG
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133753", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2201/52", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133345", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133707", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133371", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/134345", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/133757", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133345", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133757", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134345", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134345", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133512", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133753", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133707", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133757", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133371", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133753", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2201/52", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133707", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133519", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133345", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 56849863