PATENT DOCUMENT

Publication Number: US-9201276-B2
Application Number: US-201213654256-A
Country: US
Kind Code: B2

Title: Process architecture for color filter array in active matrix liquid crystal display

Abstract:
An active matrix liquid crystal display having an array of pixels is provided. The display includes a thin film transistor (TFT) for each pixel. The TFT has a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode. The display also includes a color filter layer disposed over the TFT. The color filter layer has a first via hole to expose a portion of the drain electrode. The display further includes a metal layer disposed over the color filter layer and covering the gate electrode. The metal layer is configured to connect to the drain electrode through the first via hole. The display also includes an organic insulator layer disposed over the metal layer. The organic insulator layer has a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer.

Claims:
What is claimed is:  
     
       1. A method for fabricating an active matrix liquid crystal display, the method comprising:
 forming a thin film transistor (TFT) over a substrate, the TFT having a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode; 
 depositing a color filter layer over the TFT, the color filter having at least a first via hole to expose a portion of the drain electrode; 
 forming a metal layer over the color filter, the metal layer filling the first via hole to connect to the drain electrode; 
 depositing a black matrix over the metal layer; 
 depositing an organic insulator layer over the black matrix layer such that at least a portion of the black matrix layer is interposed between the organic insulator layer and the metal layer, the organic insulator layer having a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer; 
 forming a common electrode over the organic insulator, the common electrode being connected to the metal layer through the third via hole; 
 depositing a first passivation layer over the common electrode, the second via hole being through the first passivation layer; and 
 forming a pixel electrode over the first passivation layer, the pixel electrode being connected to the metal layer through the second via hole. 
 
     
     
       2. The method of  claim 1 , wherein each of the gate electrode, the source electrode, the drain electrode, and the metal layer comprises one or more layers of a conductive material selected from a group consisting of copper, copper alloy, aluminum, aluminum alloy, titanium, and molybdenum. 
     
     
       3. The method of  claim 1 , the step of forming a TFT further comprising forming a semiconductor layer between the gate electrode and the source/drain electrodes, and forming a gate insulator layer between the gate electrode and the semiconductor layer. 
     
     
       4. The method of  claim 3 , wherein the semiconductor layer comprises an oxide semiconductor selected from a group consisting of indium-gallium-zinc-oxide (IGZO), zinc oxide (ZnO), indium oxide (InO), gallium oxide (GaO), tin oxide (SnO2), indium gallium oxide (IGO), indium zinc oxide (IZO), zinc tin oxide (ZTO), and indium zinc tin oxide (IZTO). 
     
     
       5. The method of  claim 3 , the step of forming a TFT further comprising depositing an etch-stop layer that covers at least a portion of the semiconductor layer and is under at least a portion of the source/drain electrodes. 
     
     
       6. The method of  claim 3 , wherein the semiconductor layer comprises amorphous silicon. 
     
     
       7. The method of  claim 1 , wherein the gate insulator comprises one or more layers of one or more dielectric materials, each material being selected from a group consisting of silicon oxide (SiO 2 ), silicon nitride (SiN x ), aluminum oxide (Al 2 O 3 ), and organic material. 
     
     
       8. The method of  claim 1 , further comprising depositing a second passivation layer over the TFT prior to depositing the color filter layer. 
     
     
       9. The method of  claim 8 , wherein each of the first and second passivation layers comprises a material selected from a group consisting of silicon oxide and aluminum oxide. 
     
     
       10. The method of  claim 1 , wherein the substrate comprises a glass. 
     
     
       11. The method of  claim 1 , wherein the organic insulator layer comprises a photoactive compound (PAC). 
     
     
       12. The method of  claim 1 , wherein each of the common electrode and the pixel electrode comprises indium-tin oxide (ITO). 
     
     
       13. A method for fabricating an active matrix liquid crystal display, the method comprising:
 forming a thin film transistor (TFT) over a substrate, the TFT having a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode; 
 depositing an organic insulator over the TFT, the organic insulator having a first via hole to expose a portion of the drain electrode; 
 forming a metal layer over the organic insulator, the metal layer filling the first via hole; 
 depositing a color filter layer over the metal layer, the color filter having a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer; 
 forming a common electrode over the color filter layer, the common electrode being connected to the metal layer through the third via hole; 
 depositing a first passivation layer over the common electrode, the second via hole being through the first passivation layer; and 
 forming a pixel electrode over the first passivation layer, the pixel electrode being connected to the metal layer through the second via hole. 
 
     
     
       14. The method of  claim 13 , further comprising depositing a second passivation layer between the TFT and the color filter layer. 
     
     
       15. The method of  claim 13 , further comprising depositing a black matrix layer over the metal layer, the black matrix layer configured to block light reflection from the metal layer. 
     
     
       16. The method of  claim 13 , further comprising arranging the TFT outside an active pixel region of the display. 
     
     
       17. The method of  claim 13 , further comprising arranging the first, second and third via holes outside an active region of the display. 
     
     
       18. An active matrix liquid crystal display having an array of pixels, the display comprising:
 a thin film transistor (TFT) for each pixel, the TFT having a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode; 
 a color filter layer disposed over the TFT, the color filter layer having a first via hole to expose a portion of the drain electrode; 
 a metal layer disposed over the color filter layer and covering the gate electrode, the metal layer configured to connect to the drain electrode through the first via hole; 
 an organic insulator layer disposed over the metal layer, the organic insulator layer having a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer; and 
 a black matrix layer interposed between the metal layer and the organic insulator layer. 
 
     
     
       19. The display of  claim 18 , further comprising:
 a common electrode disposed over the organic insulator layer, the common electrode configured to connect to the metal layer through the third via hole; 
 a first passivation layer disposed over the common electrode, the first passivation layer having a second via hole aligned with the second via hole of the organic insulator layer; and 
 a pixel electrode disposed over the first passivation layer, the pixel electrode configured to connect to the metal layer in the second via hole through the organic insulator layer and the first passivation layer. 
 
     
     
       20. The display of  claim 19 , wherein the display further comprises a second passivation layer between the TFT and color filter layer. 
     
     
       21. The display of  claim 20 , wherein each of the first and second passivation layers comprises silicon oxide or aluminum oxide. 
     
     
       22. The display of  claim 18 , wherein the TFT further comprises a semiconductor layer between the gate electrode and the source/drain electrodes and a gate insulator layer between the gate electrode and the semiconductor layer. 
     
     
       23. The display of  claim 22 , wherein the semiconductor layer comprises an oxide semiconductor selected from a group consisting of indium-gallium-zinc-oxide (IGZO), zinc oxide (ZnO), indium oxide (InO), gallium oxide (GaO), tin oxide (SnO 2 ), indium gallium oxide (IGO), indium zinc oxide (IZO), zinc tin oxide (ZTO), and indium zinc tin oxide (IZTO). 
     
     
       24. The display of  claim 23 , wherein the TFT further comprises an etch-stop layer between at least a portion of the semiconductor layer and a portion of the source/drain electrodes. 
     
     
       25. The display of  claim 22 , wherein the semiconductor layer comprises amorphous silicon. 
     
     
       26. The display of  claim 22 , wherein the semiconductor layer comprises a material selected from a group consisting of amorphous silicon, indium-gallium-zinc-oxide (IGZO), zinc oxide (ZnO), indium oxide (InO), gallium oxide (GaO), tin oxide (SnO2), indium gallium oxide (IGO), indium zinc oxide (IZO), zinc tin oxide (ZTO), and indium zinc tin oxide (IZTO). 
     
     
       27. The display of  claim 22 , wherein the gate insulator comprises one or more layers of one or more dielectric materials, each material being selected from a group consisting of silicon oxide (SiO 2 ), silicon nitride (SiN x ), aluminum oxide (Al 2 O 3 ), and organic material. 
     
     
       28. The display of  claim 18 , wherein the organic insulator layer comprises a photoactive compound. 
     
     
       29. The display of  claim 18 , wherein the metal layer is configured to minimize light reflection. 
     
     
       30. The display of  claim 18 , wherein the black matrix layer is configured to block light reflection from the metal layer. 
     
     
       31. The display of  claim 18 , wherein the TFT is configured to be outside an active pixel region of the display. 
     
     
       32. The display of  claim 18 , wherein each of the first, second, and third via holes is configured to be outside an active pixel region of the display. 
     
     
       33. The display of  claim 18 , wherein the color filter layer has a dielectric constant higher than the organic insulator layer. 
     
     
       34. The display of  claim 18 , wherein each of the color filter layer and the organic insulator layer has a thickness less than 2.5 μm. 
     
     
       35. The display of  claim 18 , wherein each of the gate electrode, the source electrode, the drain electrode, and the metal layer comprises one or more layers of a conductive material selected from a group consisting of copper, copper alloy, aluminum, aluminum alloy, titanium, and molybdenum. 
     
     
       36. The display of  claim 18 , wherein the substrate comprises a glass. 
     
     
       37. An active matrix liquid crystal display having an array of pixels, the display comprising:
 a thin-film transistor (TFT) for each pixel, the TFT having a gate electrode, a source electrode overlapping a first area with the gate electrode, and a drain electrode overlapping with a second area with the gate electrode; 
 an organic insulator layer disposed over the TFT, the organic insulator layer having a first via hole to expose a portion of the drain electrode; 
 a metal layer disposed over the organic insulator layer and covering the gate electrode, the metal layer configured to connect to the drain electrode through the first via hole; and 
 a color filter layer disposed over the metal layer, the color filter layer having a second via hole to expose a portion of the metal layer and a third via hole to expose a second portion of the metal layer. 
 
     
     
       38. The display of  claim 37 , further comprises a common electrode disposed over the color filter layer, the common electrode configured to connect to the metal layer through the third via hole;
 a first passivation layer disposed over the common electrode, the first passivation layer having a second via hole aligned with the second via hole of the color filter layer; and 
 a pixel electrode disposed over the first passivation layer, the pixel electrode configured to connect to the metal layer in the second via hole through the color filter layer and the first passivation layer. 
 
     
     
       39. The display of  claim 37 , wherein the display further comprises a second passivation layer between the TFT and organic insulator layer. 
     
     
       40. The display of  claim 37 , further comprising a black matrix layer disposed over the metal layer, the black matrix layer configured to block light reflection from the metal layer. 
     
     
       41. The display of  claim 37 , wherein the TFT is configured to be outside an active pixel region of the display. 
     
     
       42. The display of  claim 37 , wherein each of the first, second, and third via holes is configured to be outside an active pixel region of the display.

Description:
TECHNICAL FIELD 
     The present invention generally relates to process architecture for color filter array (COA) in active matrix liquid crystal display (AMLCD). More specifically, the invention relates to reducing thickness of color filter array for enhanced performance of the AMLCD. 
     BACKGROUND 
     Liquid crystal displays (LCDs) generally display images by transmitting or blocking light through the action of liquid crystals. LCDs have been used in a variety of computing displays and devices, including notebook computers, desktop computers, tablet computing devices, mobile phones (including smart phones) automobile in-cabin displays, on appliances, as televisions, and so on. LCDs often use an active matrix to drive liquid crystals in a pixel region. In some LCDs, a thin-film transistor (TFT) is used as a switching element in the active matrix. 
     For fabrication of the AMLCD, the conventional manufacturing process selectively uses a relatively thick color filter, because its dielectric constant is normally about twice of the dielectric constant of a photoactive compound (PAC), which has a relatively low dielectric constant. Generally, the color filter array is about 3 μm to 4 μm thick. Such a large thickness of the color filter array (COA) reduces the coupling between common electrode and data line (CD). This CD coupling depends upon the capacitance between common electrode and the data line, and is proportional to the dielectric constant of the color filter, and is inversely proportional to the thickness of the color filter. 
     There are several issues with thicker COA for fringe field switching (FFS) mode. First, it is difficult to coat a thick COA. Second, the large thickness of the COA may require alignment of the color filter array with TFTs, which is an additional step in the process. Third, the large thickness of the color filter array also makes difficult to fill via holes such that the via holes need to be larger to enable completely filling the via holes. Fourth, larger via hole sizes may be required as a result of thicker COA. The larger via holes may reduce a ratio of aperture area to via hole area, which reduces the optical transmission or brightness of the AMLCD. Additionally, the deep via holes may cause non-uniformity in a planarization layer that covers the via holes and the color filter array. Liquid crystal molecules are arranged on the top of the planarization layer. 
     Therefore, it is desirable to develop techniques to reduce the thickness of the COA and to improve optical transmission and performance of the AMLCD. 
     SUMMARY 
     Embodiments described herein may provide a design architecture for the color filter array (COA) in active matrix liquid crystal display (AMLCD). Embodiments also provide a process architecture for fabrication of such AMLCD. 
     In one embodiment, an active matrix liquid crystal display having an array of pixels is provided. The display includes a thin film transistor (TFT) for each pixel. The TFT has a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode. The display also includes a color filter layer disposed over the TFT. The color filter layer has a first via hole to expose a portion of the drain electrode. The display further includes a metal layer disposed over the color filter layer and covering the gate electrode. The metal layer is configured to connect to the drain electrode through the first via hole. The display also includes an organic insulator layer disposed over the metal layer. The organic insulator layer has a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer. 
     In another embodiment, an active matrix liquid crystal display having an array of pixels is provided. The display includes a TFT for each pixel. The TFT has a gate electrode, a source electrode overlapping a first area with the gate electrode, and a drain electrode overlapping with a second area with the gate electrode. The display also includes an organic insulator layer disposed over the TFT. The organic insulator layer has a first via hole to expose a portion of the drain electrode. The display further includes a metal layer disposed over the organic insulator layer and covering the gate electrode. The metal layer is configured to connect to the drain electrode through the first via hole. The display also includes a color filter layer disposed over the metal layer. The color filter layer has a second via hole to expose a portion of the metal layer and a third via hole to expose a second portion of the metal layer. 
     In yet another embodiment, a method for fabricating an active matrix liquid crystal display is provided. The method includes forming a thin film transistor (TFT) over a substrate. The TFT has a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode. The method also includes depositing a color filter layer over the TFT. The color filter has at least a first via hole to expose a portion of the drain electrode. The method further includes forming a metal layer over the color filter. The metal layer fills the first via hole to connect to the drain electrode. The method also includes depositing an organic insulator layer over the metal layer. The organic insulator layer has a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer. The method further includes forming a common electrode over the organic insulator. The common electrode is connected to the metal layer through the third via hole. The method also includes depositing a first passivation layer over the common electrode. The second via hole is through the first passivation layer. The method further includes forming a pixel electrode over the first passivation layer. The pixel electrode is connected to the metal layer through the second via hole. 
     In still yet another embodiment, a method for fabricating an active matrix liquid crystal display is provided. The method includes forming a thin film transistor (TFT) over a substrate. The TFT has a gate electrode, a source electrode overlapping with a first area of the gate electrode, and a drain electrode overlapping with a second area with the gate electrode. The method also includes depositing an organic insulator over the TFT. The organic insulator has a first via hole to expose a portion of the drain electrode. The method further includes forming a metal layer over the organic insulator. The metal layer fills the first via hole. The method also includes depositing a color filter layer over the metal layer. The color filter has a second via hole to expose a first portion of the metal layer and a third via hole to expose a second portion of the metal layer. The method further includes forming a common electrode over the organic insulator. The common electrode is connected to the metal layer through the third via hole. The method also includes depositing a first passivation layer over the common electrode. The second via hole is through the first passivation layer. The method further includes forming a pixel electrode over the first passivation layer. The pixel electrode is connected to the metal layer through the second via hole. 
     Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the invention. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a sample electronic device. 
         FIG. 2  shows a cross-sectional view of the TFT/CF/LC stack of a conventional AMLCD (prior art). 
         FIG. 3A  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a first embodiment of the present disclosure. 
         FIG. 3B  shows a plan view of the TFT/CF stack of the liquid crystal display of  FIG. 3A . 
         FIG. 4  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a second embodiment of the present disclosure. 
         FIG. 5  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a third embodiment of the present disclosure. 
         FIG. 6  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a fourth embodiment of the present disclosure. 
         FIG. 7  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a fifth embodiment. 
         FIG. 8  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a sixth embodiment. 
         FIG. 9  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a seventh embodiment. 
         FIG. 10  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in an eighth embodiment. 
         FIG. 11A  shows a cross-sectional view of an example CD coupling by a photoactive compound (PAC). 
         FIG. 11B  shows a cross-sectional view of an example CD coupling by the COA. 
         FIG. 12  is a flow chart illustrating steps for fabricating the display of  FIGS. 3A-3B  in accordance to embodiments of the present disclosure. 
         FIG. 13  is a flow chart illustrating steps for fabricating the display of  FIG. 5  in accordance to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure may be understood by reference to the following detailed description, taken in conjunction with the drawings as described below. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale. 
     The present disclosure provides a design architecture for the AMLCD, which includes a third metal layer and also an organic insulator layer in the AMLCD. The design architecture allows the thickness of the color filter layer to be reduced. The present disclosure also provides a sample process architecture for fabricating various embodiments. 
       FIG. 1  illustrates a perspective view of a sample electronic device, such as a tablet computer. The electronic device includes a touch screen display  100  enclosed by a housing  138 . The touch screen display  100 A incorporates a cover glass  102  and an LCD  100 B behind the cover glass  102 , although alternative embodiments may employ an organic light-emitting display (OLED) layer instead of an LCD. The LCD  100 B is not shown in  FIG. 1A . 
       FIG. 2  shows a cross-sectional view of a TFT/CF/LC stack of a conventional AMLCD (prior art). TFT/CF/LC stack  200  includes a TFT  238  which includes a gate electrode  206  disposed over a substrate  202 , a source electrode  224 A, and a drain electrode  224 B. The gate electrode  206  is also referred as a first metal layer, and the source/drain electrodes are referred as a second metal layer. The TFT/CF/LC stack  200  also includes a gate insulator  204  disposed over the gate electrode  206 , a semiconductor layer  220 , over the gate insulator  204 . The semiconductor layer  220  connects to the source electrode  224 A and drain electrode  224 B. The TFT/CF/LC stack  200  further includes a first passivation layer  210  over the source electrode  224 A and drain electrode  224 B. 
     The TFT/CF/LC stack  200  further includes a CF layer  214  and a black matrix  228  disposed over the first passivation layer  210 . The CF layer  214  includes a number of sub-color filters (CF), such as red, green and blue colors. The black matrix  228  may be arranged to divide the CF layer  214  into the sub-color filters. Some embodiments may replace one or more of the red, green and blue filters with a yellow filter, a cyan filter, a clear filter, or another color filter. Further, the number of color filters and their arrangement may vary in certain embodiments. 
     The common electrode  208  is disposed over the substrate  202  and is arranged under the color filter  214 . The TFT/CF/LC stack  200  further includes a polyimide layer disposed over the pixel electrode to provide a flat surface of deposition of liquid crystal molecules, and a liquid crystal (LC) layer  242  on top of the polyimide layer  240 . 
       FIG. 3A  shows an exploded cross-sectional view of a TFT/CF stack of the AMLCD in a first embodiment. TFT/CF stack  300  includes a TFT  338  which includes a gate electrode  306  disposed over a substrate  302 , a source electrode  324 A, and a drain electrode  324 B. The gate electrode  306  is also referred as a first metal layer, and the source/drain electrodes are referred as a second metal layer. The TFT/CF stack  300  also includes a gate insulator  304  disposed over the gate electrode  306 , a semiconductor layer  320 , over the gate insulator  304 . The semiconductor layer  320  connects to the source electrode  324 A and drain electrode  324 B. The TFT/CF stack  300  further includes a first passivation layer  310  over the source electrode  324 A and drain electrode  324 B. The TFT/CF stack  300  further includes a CF layer  314  disposed over the first passivation layer  310 , and a third metal layer  336  over the color filter  314 . 
     The third metal layer  336  covers at least a portion of TFT  338 , such that there is no photo-leakage when the TFT is in an off-current state. The TFT  338  is arranged to be outside the pixel region or aperture area rather than within the aperture area, which further helps improve optical transmission of the AMLCD. 
     The TFT/CF stack  300  further includes a black matrix layer  334  disposed over the third metal layer  336 . The black matrix layer  334  is photo-insensitive and has a low overall dimension. For example, it may be very thin and small in area. The black matrix layer  334  may cover at least a portion of the third metal layer  336  and may block light reflected from the third metal layer. In one embodiment, the black matrix may be made of a polymer, such as polyimide. The black matrix layer  334  may reduce light reflected from the LCD panel by absorbing the light and may also reduce optical transmission of the backlight. Therefore, the black matrix layer  334  may be configured to help block light reflection from the third metal layer while retaining optical transmission of a backlight. Note that this black matrix layer  334  is different from the black matrix  228  which is arranged between two sub-color filters  214 A and  214 B, as shown in  FIG. 2 . The black matrix  228  is also present in the TFT/CF stack  300 , but not shown in  FIG. 3A . 
     The TFT/CF stack  300  further includes an organic insulator layer  332  disposed over the black matrix layer  334 . By including the organic insulator  332 , the color filter layer  314  of the present TFT/CF stack  300  becomes thinner than that of conventional TFT/CF stack  200 , because a combination of the organic insulator and a thinner color filter layer provides equivalent CD coupling to that of a thicker color filter layer of a conventional TFT/CF stack. Additionally, the organic insulator has a lower dielectric constant than the color filter, which also helps make the color filter thinner for the TFT/CF stack  300 . Thickness estimation of the color filter will be described later in details. The organic insulator layer  332  may be formed of a photoactive compound (PAC), among other suitable material to provide a flat surface for forming more layers, such as a common electrode  308  and a pixel electrode  318  among others. 
     The common electrode  308  is disposed over the organic insulator layer  332  for all pixels. By connecting the third metal layer  336  to the drain electrode  324  and covering the gate  306 , common electrode V com    308  is arranged above the color filter  314 . The common electrode  308  includes both an ITO layer and the third metal layer, and has a lower resistivity than the common electrode of the conventional TFT/CF stack  200 . 
     The pixel electrode  318  is disposed over a second passivation layer  316  that is disposed over the common electrode  308  and organic insulator layer  332 . The pixel electrode  318  connects to the third metal  336  above the color filter  314  through via hole CNT2  330 B and thus connects to the drain electrode  324 B or source electrode  324 A (not shown) through via hole CNT1  330 A. The source and drain electrodes may be interchangeable. 
     Via holes formed in the present TFT/CF stack  300  are less deep than that of a conventional TFT/CF stack due to the presence of the third metal layer. The common electrode  308  is now arranged above the color filter layer  314 , as shown in  FIG. 3A , rather than below the color filter layer  214  of a conventional TFT/CF stack, i.e. common electrode  208  as shown in  FIG. 2 . For example, via hole CNT1  330 A formed in the color filter layer of the TFT/CF stack  300  is less deep than conventional via hole CNT1  230 A, as shown in  FIG. 2 . Via hole CNT2  330 B formed in the PAC layer  332  of the TFT/CF stack  300  shown in  FIGS. 3A-B  may also have a shorter depth than the conventional via hole CNT2  230 B, as shown in  FIG. 2 . Via hole CNT3 formed in the PAC layer  332  is also relatively shallow, compared to via holes  220 A and  220 B for the conventional TFT/CF stack  200 . 
       FIG. 3B  shows a plan view of a number of pixel regions with their respective TFTs in a first embodiment. Arrows A-A in  FIG. 3B  illustrate where the cross-sectional view shown in  FIG. 3A  is taken. This cross-section permits depiction of the three via holes CNT1  330 A, CNT2  330 B, and CNT3  330 C in one view. 
     The pixel region includes an active pixel area  350  (also referred to herein as an “aperture area”) above a dashed line and a TFT area below the dashed line. The pixel region edges are defined by first and second data lines  360 A-B and first and second gate lines  370 A-B. The pixel region may be generally rectangular in shape or square in shape. Still other embodiments may have differently-shaped pixel regions. 
     Each gate line  370 A or  370 B may be connected to multiple TFTs. The first data line  360 A may be connected to drain electrode  324 B. The second data line  360 B may be connected to a neighboring drain electrode. The first gate line  370 A may be connected to gate electrode  306  for the pixel regions shown in  FIG. 3B . The second gate line  370 B at the bottom may be connected to the gate electrode for the pixel regions below the gate line  370 B. 
     The TFT  338  switches a respective pixel for each active pixel area  350  on and off. Each active pixel area includes a liquid crystal layer. A voltage between the pixel electrode and the common electrode may be applied to the liquid crystal layer for each active pixel area. The voltage may control the alignment of liquid crystal molecules in the liquid crystal layer and to control light for each pixel of the LCD. 
     The data lines  360 A-B and the gate lines  370 A-B may be controlled by a controller for a LCD (not shown) to change the “on” and “off” states of the TFT. The pixel electrode  318  may be connected to the drain electrode  324 B and may receive a signal from the TFT, such that a voltage between the pixel electrode  318  and the common electrode  310  may be applied to the respective pixel. 
     The third metal layer  336  covers the L-shaped TFT  338 , via holes CNT2  330 B and CNT1  330 A. The TFT  338  may overlap with via hole CNT2 in a particular embodiment, although other embodiments of arrangements of CNT1 and CNT2 are provided and described below, for example, in  FIGS. 7-9 . As shown in  FIG. 3B , the third metal layer  336  is connected to the via hole CNT3 and substantially aligned with the gate line  370  on the top, but is outside the active pixel area  350 . 
     The via holes CNT1  330 A and CNT2  330 B are arranged to be in the TFT area, but beyond the aperture area or the active pixel area. The via holes CNT2 may overlap with a portion of the TFT area. The third metal layer  336  covers the TFT  338  which is illustrated as “L” shaped, via holes CNT1 and CNT2. 
     The first passivation layer  310  in TFT/CF stack  300  is optional, and may be removed.  FIG. 4  shows a TFT/CF stack  400  in accordance with a second embodiment. The TFT/CF stack  500  is similar to the TFT/CF stack  300 , but lacks the first passivation layer  310 . 
     Additionally, the position of color filter layer and the PAC may be exchanged.  FIG. 5  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a third embodiment of the present disclosure. For example, TFT/CF stack  500  includes an organic insulator (OC) or PAC  332  that covers the first passivation layer  310 , which is different from the TFT/CF stack  300 . As shown in  FIG. 5 , via hole CNT1  330 A is formed in the organic insulator  332 . Via hole CNT2  330 B is formed in the color filter layer  314  that covers the third metal layer  336 . Via hole CNT3  330 C is also formed in the color filter layer  314 . V com  connects to the third metal layer  336 . 
     Additionally, the black matrix layer  334  may be removed when the third metal layer  336  is configured to remove reflection of light from the LCD panel.  FIG. 6  shows a cross-sectional view of the TFT/CF stack of the liquid crystal display in a fourth embodiment of the present disclosure. As shown in  FIG. 6 , TFT/CF stack  600  is mostly similar to TFT/CF stack  300 , but does not have the black matrix layer  334 . 
     Various arrangements of the via holes CNT1 and CNT2 are provided.  FIG. 7  shows a plan view of the TFT/CF stack of the liquid crystal display in a fifth embodiment. As shown at the bottom of  FIG. 7 , via hole CNT2 may overlap with the TFT  338 . As shown at the top of  FIG. 7 , the third metal layer  336  (connected to CNT3) may overlap with the gate line. This overlap helps expand the active pixel area, because the third metal layer when overlapping with the gate line does not occupy the active pixel area. 
       FIG. 8  shows a plan view of the TFT/CF stack of the liquid crystal display in a sixth embodiment. As shown a the bottom of  FIG. 8 , via hole CNT2 may be on gate line and via holes CNT1 and CNT2 may be arranged to be substantially parallel to the data line. As shown at the top of  FIG. 8 , the third metal layer  336  does not overlap with the gate line. 
       FIG. 9  shows a plan view of the TFT/CF stack of the liquid crystal display in a seventh embodiment. As shown at the bottom of  FIG. 9 , via hole CNT2 may be formed on the data line, and via holes CNT1 and CNT2 may be arranged to be substantially parallel to the gate line. As shown at the top of  FIG. 9 , the third metal layer  336  may overlap with the gate line. 
     In the various embodiments as shown in  FIGS. 3A ,  4 ,  5 , and  6 , the pixel electrode  318  connects to the third metal layer through via hole CNT2, while the third metal layer  336  connects to the drain electrode  324 B through via hole CNT1  330 A. Each of via holes CNT1  330 A, CNT2  330 B, and CNT3  330 C of these embodiments is shallower than the via holes CNT1  230 A and CNT2  230 B of a conventional design  200 . The color filter layer  314  of the present embodiments is also thinner than conventional color filter layer  214 . 
     The semiconductor layer  320  may be amorphous silicon. Alternatively, the TFT may be an oxide TFT, such as an indium-gallium-zinc oxide (IGZO) TFT. 
       FIG. 10  shows a cross-sectional view of a TFT/CF stack of the AMLCD in an eighth embodiment. Oxide TFT  1000  includes an etch-stop layer  1004  that covers the semiconductor layer  320 , such as IGZO. The etch-stop layer  1004  is positioned to separate the source electrode  324 A and the drain electrode  324 B. The TFT/CF stack  1000  includes gate electrode  306 , a source electrode  324 A, a drain electrode  324 B, a gate insulator  304 , and a semiconductor layer  320 , similar to the TFT/CF stack  300 . The semiconductor layer  320  may be formed of IZGO, which is different from the TFT/CF stack  300  where the semiconductor layer  320  is formed of amorphous silicon. The semiconductor layer  320  connects to the source electrode  324 A and drain electrode  324 B. The TFT/CF stack  1000  further includes a first passivation layer  310 , a color filter (CF) layer  314 , a third metal layer  336 , a black matrix layer  334 , and an organic insulator  332 , a common electrode  308 , a pixel electrode  318 , and a second passivation layer  316 , similar to the TFT/CF stack  300 . 
     By including the organic insulator  332 , the color filter layer  314  of the present TFT/CF stack  300  becomes thinner than that of a conventional TFT/CF stack  200 . The organic insulator and the thinner color filter layer together provide equivalent CD coupling to the capacitance of the thicker color filter layer of the conventional TFT/CF stack. The thickness of the organic insulator  332  (e.g. PAC) may be estimated as follows. As shown in  FIGS. 11A and 11B , the CD coupling between the common electrode and the data line is represented by Equation (1) as follows:
 
1/ C   PAC =1/ C   CF +1/ C   OC   Equation (1)
 
where C PAC  is the capacitance between common electrode and data line, C CF  is the capacitance for the color filter layer, and C OC  is the capacitance for organic insulator. Assume that the dielectric constant of the PAC is ∈, and the dielectric constant of the color filter is 2∈, based upon Equation (1), the thickness for each of the PAC layer, OC layer, and CF layer can be represented in Equation (2) as follows:
 
 d   PAC   /∈=d   CF /2∈+ d   OC /∈  Equation (2)
 
In a particular example, assuming that d PAC  is about 2.0 μm, d CF  is about 2.2 μm, then d OC  is estimated to be about 0.9 μm based upon Equation (2).
 
     Although conventional color filter material can still be used, a lower dielectric constant for the color filter helps further reduce the CD coupling. The color filter may use transparent color polymer materials, such as polycarbonate or polyester among others. 
     It will be appreciated by those skilled in the art that the source and drain electrodes  324 A and  324 B may be interchangeable. 
     In a particular embodiment, the semiconductor layer may be an indium-gallium-zinc-oxide (IGZO). The IGZO may be replaced by other semiconductors. It will be appreciated by those skilled in the art that the semiconductor layer may include other materials, for example, zinc oxide (ZnO), indium oxide (InO), gallium oxide (GaO), tin oxide (SnO2), indium gallium oxide (IGO), indium zinc oxide (IZO), zinc tin oxide (ZTO), or indium zinc tin oxide (IZTO) among others. 
     The organic insulator layer  332  may be formed of an organic material, such as a photoactive compound (PAC), an acrylate, or an organic-inorganic hybrid like siloxane to provide a flat surface for forming more layers, including the common electrode  308  and the pixel electrode  318 . Furthermore, the photoactive compound (PAC) could be positive tone or negative tone material. The polymer bases may be acrylate, cyclic olefin polymer, or siloxane among others. The PAC has a relatively low dielectric constant, considerably lower than the first and second passivation layers  310  and  316 . The first passivation layer  310  and the second passivation layer  316  may be formed of a dielectric material, such as silicon nitride (g-SiNx) which has a relatively high dielectric constant. 
     The substrate  302  may be transparent, such as a glass substrate. The gate electrode  306 , source electrode  324 A, the drain electrode  324 B, and the third metal layer  336  may be formed of a conductive material having low electrical resistance, such as copper or aluminum and the like. The common electrode  308  and the pixel electrode  318  may be formed of a transparent conductor, such as indium-tin oxide (ITO), indium zinc oxide (IZO) among others. 
     The gate insulator  304  may be formed of an inorganic insulation film including silicon oxide (SiO 2 ), silicon nitride (SiNx), a dielectric oxide film such as aluminum oxide (Al 2 O 3 ), or an organic material, and the like. The gate insulator  304  may be formed by a chemical vapor deposition (CVD) method using a plasma enhanced chemical vapor deposition system or formed by a physical vapor method using a sputtering system. Other deposition processes may also or alternatively be used. The gate insulator  304  may also include multiple layers of the above materials. For example, the gate insulator  304  may include one or more passivation layers. In a particular embodiment, the gate insulator  304  may have a two-layer structure. A silicon nitride layer may be formed as a first insulating layer and a silicon oxide layer may be formed as a second insulating layer. This gate insulator  304  may prevent an impurity such as moisture or alkali metal or copper contamination from diffusing into a TFT element and a display device and may also improve reliability of a semiconductor element formed in an element formation layer, or the like. 
     The disclosure also provides methods for fabricating the color filter array (COA) with back channel etching (BCE).  FIG. 12  is a flow chart illustrating steps for fabricating the display of  FIGS. 3A-3B  in accordance to embodiments of the present disclosure. Method  1200  starts with forming a TFT over a substrate at operation  1202 . The operation of forming the TFT may include gate metal deposition and photo patterning, gate insulate deposition, semiconductor deposition, source/drain metal deposition and photo patterning, and optional deposition of a first passviation layer. The operation of forming the TFT may optionally include active back channel etching prior to deposition of the first passivation layer. 
     For forming the TFT, it may require up to five masks. For example, in the case of forming the TFT according to the first embodiment, at most four masks are used for the depositions of the gate metal, the gate insulator, the semiconductor layer and the source/drain metal as well as the first passivation layer with respective photo patterning. 
     In the case of forming the TFT according to the second embodiment without the first passivation layer, at most three masks may be used for the depositions of the gate metal, the gate insulator, the semiconductor layer or active layer, the source/drain metal and the respective photo patterning as well as active back channel etching. The number of masks is reduced because the first passivation layer is not present in this embodiment. 
     In the case of forming the TFT according to the third embodiment where the color filter and the organic insulator are exchanged, at most four masks may be used for depositions of the gate metal, the gate insulator, the active layer, and the source/drain metal with respective photo patterning, for active back channel photo etching and deposition of the first passivation layer and photo patterning. 
     In the case of forming the oxide TFT with an etch-stop layer according to the eighth embodiment, at most five masks may be used for the depositions of the gate metal, gate insulator, active layer, etch-stop layer, source/drain/metal layer, and the first passivation layer with their respective photo patterning. An additional mask is needed for the deposition of the etch-stop layer. 
     The method  1200  continues with depositing color filter such as red-green-blue (RGB) color filters and patterning at operation  1204 , followed by depositing the third metal layer for common electrode and photo patterning at operation  1206 . The method  1200  also includes depositing a black matrix layer and photo patterning, which may be an optional operation (as shown in dash line)  1208 . The method  1200  further includes depositing organic insulator layer and photo patterning at operation  1210 , depositing common ITO and photo patterning at operation  1212 , depositing a second passivation layer and photo patterning at  1214 , and depositing pixel ITO and photo patterning at operation  1216 . 
     For photo patterning or lithography, a photoresist is first deposited on a surface, and then light is selectively passed through a patterned mask that may block light in certain areas. The exposed photoresist film is developed through the patterned mask to form the photoresist patterns as shown. The exposed photoresist film protects the layers underneath during an etching process, such that the portion exposed by the photoresist may be completely removed by the etching process, such as a wet etching. Portions of underlying layers that are protected by photoresist generally are not removed or otherwise etched. After etching to form a pattern of a deposited layer by using photoresist, the insoluble photoresist is removed prior to the next deposition operation. Different masks may be provided to form various films with different patterns. In alternative embodiments, different photoresist may be used. 
     The photoresist film may be made of a photosensitive material; exposure to light (or particular wavelengths of light) to develop the photoresist. The developed photoresist may be insoluble or soluble to a developer. There may be two types of photoresist, a positive photoresist and a negative photoresist. The positive photoresist is soluble to the photoresist developer. The portion of the positive photoresist that is unexposed remains insoluble to the photoresist developer. The negative resist is a type of photoresist in which the portion of the photoresist that is exposed to light becomes insoluble to the photoresist developer. The unexposed portion of the photoresist is dissolved by the photoresist developer. 
       FIG. 13  is a flow chart illustrating steps for fabricating the display of  FIG. 5  in accordance to embodiments of the present disclosure. Method  1300  starts with forming a TFT over a substrate at operation  1302 . The method  1300  continues with depositing organic insulator and patterning at operation  1304 , followed by depositing the third metal layer for common electrode and photo patterning at operation  1306 . The method  1300  also includes depositing a black matrix layer and photo patterning, which may be an optional operation (as shown in dash line)  1308 . The method  1300  further includes depositing RGB color filter layer and photo patterning at operation  1310 , depositing common ITO and photo patterning at operation  1312 , depositing a second passivation layer and photo patterning at  1314 , and depositing pixel ITO and photo patterning at operation  1316 . 
     The process architecture of the present disclosure provides several benefits over of the conventional COA technology. The benefits include (A) increasing optical transmittance by reducing via hole sizes, and re-arranging the TFT beyond the pixel region compared to the conventional design; (B) simplifying the process by eliminating the operation of the alignment between the COA and TFT due to thinner COA; (C) minimizing color mixing from inter-pixel optical interference for high resolution display by using black matrix on the bottom glass substrate and also low misalignment between pixel and the color filter; (D) reducing CD coupling between data line or data signal and common electrode/pixel electrode by adding the organic passivation layer. Although conventional color filter material with high dielectric constant may still be used, other color filter materials with lower dielectric constant are desirable to further help reduce the CD coupling. 
     Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention. 
     Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.

Metadata:
Filing Date: 20121017
Publication Date: 20151201
Grant Date: 20151201
Priority Date: 20121017
Inventors: YANG YOUNG CHEOL
PARK YOUNG BAE
CHEN CHENG
ZHONG JOHN Z.
Assignee: APPLE INC
CPC Classifications: [{"code": "H10D86/423", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10D86/423", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2001/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133345", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/1225", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136227", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F2001/136222", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136227", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133345", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136227", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136222", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133345", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136222", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/133512", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50475045