Transflective liquid crystal display

Abstract

A display includes a plurality of pixel circuits, each pixel circuit including a first electrode, a second electrode, a reflective region, and a transmissive region. The reflective region reflects ambient light and includes a first portion of a liquid crystal layer and a polarization dependent reflector. The transmissive region transmits backlight and includes a second portion of the liquid crystal layer. A dielectric layer is between the first and second electrodes in one of the reflective region and the transmissive region, the dielectric layer configured such that when a pixel voltage is applied to the first and second electrodes, the percentage of the pixel voltage applied across the first portion of the liquid crystal layer is different from the percentage of the pixel voltage applied across the second portion of the liquid crystal layer. The display includes a backlight module to generate the backlight.

1 . A display comprising:
 a plurality of pixel circuits each comprising
 a first electrode; 
 a second electrode; 
 a reflective region to reflect ambient light, the reflective region comprising a first portion of a liquid crystal layer between the first and second electrodes, and a polarization dependent reflector that transmits light having a first polarization and reflects light having a second polarization; 
 a transmissive region to transmit backlight, the transmissive region comprising a second portion of the liquid crystal layer between the first and second electrodes; 
 a dielectric layer between the first and second electrodes in one of the reflective region and the transmissive region, the dielectric layer configured such that when a pixel voltage is applied to the first and second electrodes, the percentage of the pixel voltage applied across the first portion of the liquid crystal layer is different from the percentage of the pixel voltage applied across the second portion of the liquid crystal layer; and 
 a backlight module to generate the backlight. 
   
     
     
         2 . The display of  claim 1  wherein the polarization dependent reflector comprises a wire grid polarizer. 
     
     
         3 . The display of  claim 1  wherein the dielectric layer is in the reflective region and configured such that when the pixel voltage is applied to the first and second electrodes, the percentage of the pixel voltage applied across the first portion of the liquid crystal layer is lower than the percentage of the pixel voltage applied across the second portion of the liquid crystal layer. 
     
     
         4 . The display of  claim 3  wherein the liquid crystal layer is between two substrates, and the liquid crystal layer comprises liquid crystal molecules that are substantially aligned along a direction parallel to the surfaces of the substrates when no voltage is applied to the first and second electrodes. 
     
     
         5 . The display of  claim 1  wherein the dielectric layer is in the transmissive region and configured such that when the pixel voltage is applied to the first and second electrodes, the percentage of the pixel voltage applied across the first portion of the liquid crystal layer is higher than the percentage of the pixel voltage applied across the second portion of the liquid crystal layer. 
     
     
         6 . The display of  claim 5  wherein the liquid crystal layer is between two substrates, and the liquid crystal layer comprises liquid crystal molecules that are substantially aligned along a direction normal to the substrates when no voltage is applied to the first and second electrodes. 
     
     
         7 . The display of  claim 1  wherein the dielectric layer has a dielectric constant and a thickness that are selected to reduce a difference between a transmittance of the transmissive region and a reflectance of the reflective region for a given pixel voltage applied to the first and second electrodes. 
     
     
         8 . The display of  claim 1  wherein the dielectric layer functions as a capacitor that is connected in series with the liquid crystal layer between the first and second electrodes. 
     
     
         9 . The display of  claim 1  wherein the dielectric layer comprises at least one of silicon oxide and silicon nitride. 
     
     
         10 . The display of  claim 1  wherein at least one of the first electrode and the second electrode comprises at least one of indium tin oxide, indium zinc oxide, and gallium zinc oxide. 
     
     
         11 . The display of  claim 1 , further comprising a first linear polarizer and a second linear polarizer that both extend over the transmissive and reflective regions, the first and second linear polarizers being at different sides of the liquid crystal layer. 
     
     
         12 . The display of  claim 11  wherein the first linear polarizer is closer to a viewer than the second linear polarizer, and the polarization dependent reflector has a reflective axis that is perpendicular to a transmission axis of the first linear polarizer. 
     
     
         13 . The display of  claim 1  wherein the liquid crystal layer is between two substrates, and the liquid crystal layer comprises liquid crystal molecules that are substantially aligned along a direction normal to the substrates when no voltage is applied to the first and second electrodes. 
     
     
         14 . The display of  claim 1  wherein the liquid crystal layer comprises a negative dielectric anisotropic liquid crystal material. 
     
     
         15 . The display of  claim 1  wherein the liquid crystal layer comprises a positive dielectric anisotropic liquid crystal material. 
     
     
         16 . A display comprising;
 a first substrate;   a second substrate;   pixel circuits between the first and second substrates, each pixel circuit having a transmissive portion and a reflective portion, each pixel circuit comprising a first electrode, a second electrode, a liquid crystal cell, a polarization dependent reflector located at the reflective portion, and a shield capacitor located at one of the reflective and transmissive portions and positioned in series with the liquid crystal cell.   
     
     
         17 . The display of  claim 16  wherein the shield capacitor is configured to cause a gray scale gamma curve of the transmissive region to more closely match a gray scale gamma curve of the reflective region, as compared to the pixel circuit without the shield capacitor. 
     
     
         18 . The display of  claim 16  wherein the pixel circuits are in dark states when no pixel voltage is applied to the pixel circuits. 
     
     
         19 . The display of  claim 16  wherein the pixel circuits are in bright states when no pixel voltage is applied to the pixel circuits. 
     
     
         20 . A transflective display comprising:
 a first linear polarizer having a first transmission axis;   a second linear polarizer having a second transmission axis, the first linear polarizer located closer to a front side of the display than the second linear polarizer;   pixel circuits each comprising:
 a liquid crystal layer between the first and second linear polarizers, the liquid crystal layer having a first portion and a second portion, the first portion corresponding to a reflective portion of the pixel circuit, the second portion corresponding to a transmissive portion of the pixel circuit; 
 a storage capacitor to store an electric charge corresponding to a pixel voltage; 
 a polarization dependent reflector that is associated with the first portion of the liquid crystal layer, the polarization dependent reflector to reflect a first component of external light and transmit a second component of the external light, the first component having a first polarization substantially perpendicular to the first transmission axis and the second component having a second polarization substantially parallel to the first transmission axis; and 
 means for applying a first percentage of the pixel voltage to the first portion of the liquid crystal layer and a second percentage of the pixel voltage to the second portion of the liquid crystal layer, the first percentage being different from the second percentage. 
   
     
     
         21 . The display of  claim 20  wherein the means for applying the first and second percentages of the pixel voltage is configured to cause the transmissive portion to have a transmittance-voltage characteristic that more closely matches a reflectance-voltage characteristic of the reflective portion, as compared to a pixel circuit that applies the same percentage of the pixel voltage to the first and second portions of the liquid crystal layer. 
     
     
         22 . A method comprising:
 reflecting external light having a first polarization after the external light passes a liquid crystal layer in a reflective region of a pixel of a display, the reflected light being directed toward a viewer of the display;   transmitting external light having a second polarization after the external light passes the liquid crystal layer in the reflective region, the transmitted light being directed away from the viewer;   transmitting backlight through the liquid crystal layer in a transmissive region of the pixel, the transmitted light being directed toward the viewer;   applying a first percentage of a pixel voltage to the liquid crystal layer in the reflective region; and   applying a second percentage of the pixel voltage to the liquid crystal layer in the transmissive region, the second percentage being different from the first percentage.   
     
     
         23 . The method of  claim 22  wherein the first and second percentages are configured to cause the transmittance of the transmissive region to more closely match the reflectance of the reflective region for a given pixel voltage, as compared to applying a same percentage of the pixel voltage to the reflective and transmissive regions. 
     
     
         24 . The method of  claim 22 , further comprising showing a dark state at the pixel when the pixel voltage is below a threshold. 
     
     
         25 . The method of  claim 22 , further comprising showing a bright state at the pixel when the pixel voltage is below a threshold. 
     
     
         26 . The method of  claim 22 , further comprises aligning liquid crystal molecules of the liquid crystal layer along directions substantially normal to surfaces of two substrates when no voltage is applied to the first and second electrodes, the liquid crystal layer being positioned between the two substrates. 
     
     
         27 . The method of  claim 22 , further comprising aligning liquid crystal molecules of the liquid crystal layer along directions substantially parallel to surfaces of two substrates when no voltage is applied to the first and second electrodes, the liquid crystal layer being positioned between the two substrates. 
     
     
         28 . A method comprising:
 forming a polarization dependent reflector in a first region of first substrate, the first region corresponding to a reflective region of a pixel of a display;   forming a first electrode on the first substrate;   forming a second electrode on a second substrate;   forming a dielectric layer on a portion of the first electrode or a portion of the second electrode, the dielectric layer corresponding to either the reflective region of the pixel or a transmissive region of the pixel; and   providing a liquid crystal layer between the first and second substrates, the dielectric layer being positioned in series with the liquid crystal layer between the first and second electrodes.   
     
     
         29 . The method of  claim 28 , further comprising providing alignment layers on the first and second substrates to cause the liquid crystal molecules of the liquid crystal layer to substantially align along a direction normal to the surfaces of the substrates when no voltage is applied to the first and second electrodes. 
     
     
         30 . The method of  claim 28 , further comprising providing alignment layers on the first and second substrates to cause the liquid crystal molecules of the liquid crystal layer to substantially align along a direction parallel to the surfaces of the substrates when no voltage is applied to the first and second electrodes. 
     
     
         31 . The method of  claim 28 , further comprising providing a first linear polarizer at a side of the first substrate facing away from the liquid crystal layer, and providing a second linear polarizer at a side of the second substrate facing away from the liquid crystal layer, the first linear polarizer having a transmission axis that is non-parallel to a transmission axis of the second linear polarizer.