PATENT DOCUMENT

Publication Number: US-9395583-B2
Application Number: US-201213605918-A
Country: US
Kind Code: B2

Title: Column spacer design for a display incorporating a third metal layer

Abstract:
A display that contains a column spacer arrangement which takes advantage of a protrusion on a TFT substrate is provided. One set of column spacers is disposed on top of the protrusion, while a second set of column spacers of substantially the same height as the first set of column spacers are disposed throughout the display. In this way, the display is adequately protected against deformation from external forces while at the same maintaining enough room to allow for a liquid crystal to spread out during the manufacturing process.

Claims:
What is claimed is: 
     
       1. A display pixel stackup, comprising:
 a top cover; 
 a transistor substrate; 
 a plurality of common electrodes disposed on the transistor substrate; 
 a metal layer in contact with a first common electrode of the plurality of common electrodes, wherein the metal layer forms a protrusion on the transistor substrate; 
 a fluid layer disposed between the top cover and the transistor substrate; and 
 a plurality of column spacers, wherein a first column spacer of the plurality of column spacers is configured to contact the protrusion on the transistor substrate and directly touches the metal layer, 
 wherein the plurality of common electrodes correspond to one or more pixel electrodes for generating an electric field across at least one pixel of the display pixel stackup. 
 
     
     
       2. The display pixel stackup of  claim 1 , wherein the transistor substrate is a TFT substrate, and the protrusion of the transistor substrate is created above a pixel TFT of the TFT substrate. 
     
     
       3. The display pixel stackup of  claim 1 , wherein the first column spacer is disposed on top of a pixel TFT. 
     
     
       4. The display pixel stackup of  claim 1 , wherein the metal layer forms an electrical connection between at least two of the plurality of common electrodes. 
     
     
       5. The display pixel stackup of  claim 1 , wherein the plurality of common electrodes are disposed on the transistor substrate in a common on top arrangement. 
     
     
       6. The display pixel stackup of  claim 1 , wherein the plurality of common electrodes are disposed on the transistor substrate in a common on bottom arrangement. 
     
     
       7. The display pixel stackup of  claim 1 , wherein the first column spacer directly touches the first common electrode. 
     
     
       8. The display pixel stackup of  claim 1 , wherein the first column spacer directly touches a dielectric material disposed on top of the metal layer. 
     
     
       9. A method of arranging a plurality of column spacers on a display pixel stackup, the method comprising:
 disposing a plurality of common electrodes on a transistor substrate of the display pixel stackup; 
 disposing a metal layer in contact with at least one of the plurality of common electrodes, wherein the metal layer forms a protrusion on the transistor substrate; and 
 disposing a first column spacer of the plurality of column spacers such that the first column spacer is configured to contact the protrusion on the transistor substrate and directly touches the metal layer, 
 wherein the plurality of common electrodes correspond to one or more pixel electrodes for generating an electric field across at least one pixel of the display pixel stackup. 
 
     
     
       10. The method of  claim 9 , wherein the transistor substrate is a TFT substrate, and the protrusion on the TFT substrate is disposed above a pixel TFT on the TFT substrate. 
     
     
       11. The method of  claim 9 , wherein the protrusion on the transistor substrate is created above a planarized portion of the transistor substrate. 
     
     
       12. The method of  claim 9 , wherein the metal layer forms an electrical connection between at least two of the plurality of common electrodes. 
     
     
       13. The method of  claim 9 , wherein the plurality of common electrodes are disposed on the transistor substrate in a common on top arrangement. 
     
     
       14. The method of  claim 9 , wherein the plurality of common electrodes are disposed on the transistor substrate in a common on bottom arrangement. 
     
     
       15. The method of  claim 9 , wherein the first column spacer is disposed above the protrusion of the transistor substrate such that the first column spacer directly touches a top edge of the protrusion on the transistor substrate. 
     
     
       16. The method of  claim 9 , wherein the first column spacer directly touches the first common electrode. 
     
     
       17. The method of  claim 9 , wherein the first column spacer directly touches a dielectric material disposed on top of the metal layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit, under 35 U.S.C. §119(e), of U.S. Provisional Patent Application No. 61/656,476, filed Jun. 6, 2012, the contents of which are incorporated by reference herein in their entirety for all purposes. 
    
    
     FIELD OF THE DISCLOSURE 
     This relates generally to the formation of column spacers on display panels such as liquid crystal display (LCD) panels, and more particularly, to the formation of column spacers on display panels that can utilize a step height difference created by a third metal layer in order to minimize the possibility of damage to a display panel created by applying external forces to the panel. 
     BACKGROUND OF THE DISCLOSURE 
     Display screens of various types of technologies, such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, etc., can be used as screens or displays for a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., cellular telephones, tablet computers, audio and video players, gaming systems, and so forth). LCD devices, for example, typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, LCD devices typically use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage. 
     LCD devices typically include multiple picture elements (pixels) arranged in a matrix. The pixels may be driven by scanning line and data line circuitry to display an image on the display that can be periodically refreshed over multiple image frames such that a continuous image may be perceived by a user. Individual pixels of an LCD device can permit a variable amount light from a backlight to pass through the pixel based on the strength of an electric field applied to the liquid crystal material of the pixel. The electric field can be generated by a difference in potential of two electrodes, a common electrode and a pixel electrode. In some LCDs, such as electrically-controlled birefringence (ECB) LCDs, the liquid crystal can be in between the two electrodes. In other LCDs, such as in-plane switching (IPS) and fringe-field switching (FFS) LCDs, the two electrodes can be positioned on the same side of the liquid crystal. 
     LCDs often require that the liquid crystal be “sandwiched” between two transparent glass substrates. The distance that is maintained between the glass substrates, can determine the thickness of the liquid crystal layer, and the thickness of the liquid crystal layer is correlated with the transmittance of light through the liquid crystal layer. A poor transmittance of light through the liquid crystal layer can have an adverse effect on the quality of an image being displayed. Therefore, maintaining a uniform distance between the glass substrates can be important to maintaining good image fidelity. Column spacers (otherwise known as post spacers) can be used to create a gap between glass substrates, thus maintaining the distance between glass substrates necessary to obtain a desired transmittance of the liquid crystal layer. External forces on the display, however, can cause the column spacers to deform and alter the gap between the glass substrates, thus altering the transmittance of the liquid crystal layer. Column spacers of varying heights can be used to reinforce an LCD panel, so that the gap between the glass substrates is maintained; however, column spacers with varying heights can be difficult to reliably fabricate. 
     SUMMARY OF THE DISCLOSURE 
     This relates to displays with column spacers that take advantage of a protrusion on a Thin Film Transistor (TFT) substrate in order to provide adequate protection to the display from deformation caused by external pressure and forces, while at the same time maintaining enough room in liquid crystal layer to allow the liquid crystal to adequately spread out during fabrication. 
     The protrusion on the substrate can be created for instance by a pixel TFT or a metal layer (M3) deposited onto the TFT substrate. One set of column spacers can be deposited on top of the protrusion, while another set of column spacers of substantially the same height of the first set can be deposited elsewhere. Due to the protrusion, the second set of column spacers will leave a gap between it and the TFT substrate, allowing for enough room for the liquid crystal layer to spread out. Having the two sets of column spacers be of a substantially similar height, can make the fabrication of column spacers easier. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates an example mobile telephone that includes an LCD display screen according to some disclosed embodiments. 
         FIG. 1B  illustrates an example digital media player that includes an LCD display screen according to some disclosed embodiments. 
         FIG. 1C  illustrates an example personal computer that includes an LCD display screen according to some disclosed embodiments. 
         FIG. 2  illustrates an exemplary layer stack up of an LCD panel according to some disclosed embodiments. 
         FIG. 3  illustrates an exemplary cross-section of a layer stack up of an LCD panel while an external force is being exerted on the panel according to some disclosed embodiments. 
         FIG. 4  illustrates an exemplary force-depth curve of an individual column spacer according to some disclosed embodiments. 
         FIG. 5  illustrates an exemplary panel stack up with a reduced column spacer density according to some disclosed embodiments. 
         FIG. 6  illustrates an exemplary force-depth curve for an LCD panel column spacer arrangement according to some disclosed embodiments. 
         FIG. 7 a    illustrates yet another exemplary panel stack up column spacer arrangement according to some disclosed embodiments. 
         FIG. 7 b    illustrates yet another exemplary cross-section of a layer stack up of the LCD panel while an external force is being exerted on the panel according to some disclosed embodiments. 
         FIG. 8  illustrates an example LCD display screen with a magnified view of the two display pixels according to some disclosed embodiments. 
         FIG. 9  illustrates an example arrangement of pixel electrodes deposited on a TFT substrate according to some disclosed embodiments. 
         FIG. 10  illustrates an exemplary cross-sectional view of a partial LCD display layer stackup according to some disclosed embodiments. 
         FIG. 11  illustrates yet another cross-sectional view of a partial LCD display layer stackup according to some disclosed embodiments. 
         FIG. 12  illustrates an exemplary LCD panel layer stack up with a passivation layer according to some disclosed embodiments. 
         FIG. 13  illustrates an exploded view of display pixel stackups according to some embodiments. 
         FIGS. 14A and 14B  illustrate a close up view of a common electrode with a metal layer disposed on top of it according to some embodiments of the disclosure. 
         FIG. 15  illustrates an exemplary LCD panel stack up with a column spacer arrangement that takes advantage of the step/protrusion created by a metal layer according to some embodiments of the disclosure. 
         FIG. 16  illustrates another exemplary LCD panel stack up with a column spacer arrangement that takes advantage of the step/protrusion created by a metal layer according to some embodiments of the disclosure. 
         FIG. 17  is a block diagram of an example computing system that illustrates one implementation of an example touch screen according to embodiments of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of embodiments, reference is made to the accompanying drawings which form a part hereof, and in which it is shown by way of illustration specific embodiments that can be practiced. It is to be understood that other embodiments can be used and structural changes can be made without departing from the scope of the disclosed embodiments. 
     This relates to the formation of display spacers such as liquid crystal display (LCD) column spacers of a substantially uniform height that adequately protect a gap thickness between glass substrates without impeding the ability of the liquid crystal (or similar material) to spread out. A first set of column spacers can be disposed on top of a raised step portion of a metal layer so that the column spacer touches the substrate. A second of set of column spacers, whose heights are approximately equal to the heights of the first set of column spacers, can be disposed such that a gap is created between the spacer and the substrate. This second set of spacers can be formed such that it provides adequate protection to the first set of column spacers against damage from external pressure, while at the same time maintaining a gap so that the liquid crystal can spread out through the panel. This can be achieved by having the first set of column spacers take advantage of a step height created by a metal layer. 
     Although embodiments disclosed herein may be described and illustrated herein in terms of Fringe Field Switching (FFS) Thin Film Transistor (TFT) LCDs, they can be used in other types of displays such as In Plane Switching (IPS), Electrically Controlled Birefringence (ECB) and Twisted Nematic (TN) LCDs. Furthermore, although embodiments herein may be described in terms of common electrodes made from Indium Tin Oxide (ITO), they can also apply to common electrodes fabricated from any conductive material. Additionally, although embodiments disclosed herein may be described and illustrated herein in terms of LCD displays in a common electrode on top configuration, they are also applicable to LCD display configurations in a common electrode on bottom configuration, or any type of display other than an LCD for which a uniform gap thickness is to be maintained. 
     Display screens of various types of technologies, such as liquid crystal displays (LCDs), organic light emitting diode (OLED) displays, etc., can be used as screens or displays for a wide variety of electronic devices, including such consumer electronics as televisions, computers, and handheld devices (e.g., cellular telephones, tablet computers, audio and video players, gaming systems, and so forth). LCD devices, for example, typically provide a flat display in a relatively thin package that is suitable for use in a variety of electronic goods. In addition, LCD devices typically use less power than comparable display technologies, making them suitable for use in battery-powered devices or in other contexts where it is desirable to minimize power usage. 
       FIGS. 1A-1C  show example systems in which LCD screens (which can be part of touch screens) according to embodiments of the disclosure may be implemented.  FIG. 1A  illustrates an example mobile telephone  136  that includes an LCD display screen  124 .  FIG. 1B  illustrates an example digital media player  140  that includes an LCD display screen  126 .  FIG. 1C  illustrates an example personal computer  144  that includes an LCD display screen  128 . LCD display screens  124 ,  126  and  128  can include numerous layers that are stacked on top of each other and bonded together to form the display. 
       FIG. 2  illustrates an exemplary layer stack up of an LCD panel. LCD Panel  200  can include multiple layers bonded together to form one LCD panel. For instance, LCD panel  200  can consist of a color filter glass  202  and a TFT glass  204  which can be located on opposing ends of the stack up. TFT glass  204  can have a TFT substrate layer  206  disposed immediately on top of it. TFT substrate layer  206  can contain the electrical components necessary to create the electric field that drives the liquid crystal layer  208 . More specifically, TFT substrate  206  can include various different layers that include display elements such as data lines, gate lines, TFTs, common and pixel electrodes, etc. These components can help create a controlled electric field that orients liquid crystals located in liquid crystal layer  208  into a particular orientation, based on the desired color to be displayed at any particular pixel. A set of column spacers  210  can be disposed on color filter glass  202 . The column spacers  210  can maintain a gap between color filter glass  202  and TFT substrate  206 , so that liquid crystal layer  208  can occupy the gap and maintain a desired thickness. Column spacers can be made from a photoresist material and can be fabricated using a photolithography or photoengraving process in which the photoresist material deposited on color filter glass  202  is exposed to ultraviolet light to form a pattern. One skilled in the art will recognize that the thickness of liquid crystal layer  208  can influence the transmittance of light through the liquid crystal layer from a back light (not pictured), which in turn can affect the quality of an image display on the LCD. Therefore, maintaining a uniform liquid crystal layer thickness can be important in maintaining the image quality of a display. Column spacers  210  can work to ensure that the liquid crystal layer  208  is maintained at a uniform thickness. 
       FIG. 3  illustrates an exemplary cross-section of a layer stack-up of an LCD panel while an external force is being exerted on the panel. When external force  302  is applied to the panel  300 , it can cause color filter glass  202  to compress due to the flexibility and elasticity inherent in the material used to fabricate the color filter glass  202 . Column spacers  210  can help to give support to color filter glass  202 , and can reduce the amount of compression to color filter glass  202  caused by external force  302 . As illustrated in  FIG. 3 , column spacers  210  can be disposed between color filter glass  202  and TFT substrate  206 , so that one side of the column spacer touches the color filter glass and the other side of the column spacer touches the TFT substrate. When external force  302  is applied, column spacers  210  can absorb some of the force. However in doing so, column spacers  210  can compress due to the flexibility and elasticity of the material used to fabricate the column spacer. Column spacer density expressed as a percentage of total surface area of the LCD display panel can represent the amount of column spacers used to maintain the gap between color filter glass  202  and TFT substrate  206 . For instance, a column spacer density of 3% means that 3% of the surface area of the LCD panel is covered by a column spacer. An LCD panel with a column spacer density of 3% has more column spacers than an LCD panel with a column spacer density of 1%. A higher column spacer density can be achieved by placing the column spacers closer to each other, so that more can be deposited on the color filter glass. If column spacers  210  are placed in close proximity to each other as shown in  FIG. 3 , the compression experienced by an individual column spacer can be reduced. 
       FIG. 4  illustrates an exemplary force-depth curve (otherwise known as a modulus curve) of an individual column spacer  210  in a configuration illustrated in  FIG. 3 . The y-axis of the graph is a representation of the amount external force  302  being applied to the panel  300 , with increasing force indicated by the arrow. The x-axis represents the height/depth of column spacer  210  when an external force  302  is being applied to it, with decreasing height/depth indicated by the arrow. As one of ordinary skill in the art will recognize, a force-depth curve actually represents two curves. The first curve, represented by circles  402 , shows the height/depth of column spacer  210  as the external force  302  is increased. As shown, as the external force  302  increases, the height of column spacer  210  is decreased due to the compression experienced by the column spacer as discussed above. The second curve, represented by Xs  404 , which is read from right to left, represents the height/depth of column spacer  210  as the external force  302  is being removed from the column spacer. Since the panel  300  of  FIG. 3  has column spacers  210  which are placed in close proximity to each other, the second curve completely overlaps the first curve, meaning that as the force is removed, the height/depth of the column spacer returns to its original height when no force is being applied. This can mean that the close proximity of column spacers  210  allows for individual column spacers to experience minimal deformation due to an external force being applied to the panel  300 . When the external force  302  is removed from the panel  300 , the column spacers can return to their original height, and the gap between color filter glass  202  and TFT substrate  206  is maintained such that the thickness of liquid crystal layer  208  is maintained, which in turn means that the transmittance of light through the liquid crystal layer is maintained. 
     While placing column spacers  210  in close proximity to one another can minimize the deformation/compression experienced by column spacers, it can cause problems in fabrication of a liquid crystal display, in so far as the liquid crystal may not have adequate room to spread out through the panel. If the liquid crystal layer does not adequately spread out during fabrication of the panels, the LCD display may become inoperable. Thus, while one would place column spacers  210  in close proximity to each other in order to ensure that no individual column spacer becomes deformed when an external force is applied to it, the proximity of column spacers to one another is constrained by the need for a liquid crystal material to adequately spread out during the panel fabrication process. 
       FIG. 5  illustrates an exemplary panel stack up with a reduced column spacer density according to one disclosed embodiment. Column spacers  210  are now placed at a greater distance apart from each other, so as to reduce the total column spacer density of the panel. A reduced column spacer density can provide more space for liquid crystal layer  208  to spread out during the fabrication of the panel. 
       FIG. 6  illustrates an exemplary force-depth curve for the LCD panel column spacer arrangement of  FIG. 5 . As an external force  302  is increased, the column spacer  210  becomes compressed, reducing its height/depth as represented by the first curve  602 . However, since the column spacer density is now lower, each individual column spacer  210  can be required to bear more of the force, meaning that a particular applied force  302  may cause the height/depth of the column spacer to decrease to a greater extent than an LCD panel whose column spacer density is higher. This increased compression on an individual column spacer  210  can permanently deform the column spacer, meaning that even when the force is removed from the panel, the column spacer may no longer return to its original height/depth and instead may become permanently compressed. This phenomenon is expressed by curve  604  which shows that as the force  302  is removed from the panel, the column spacer does not return to its original height of 3.5 μm, but instead returns to a compressed height of 2.0 μm. 
     If a column spacer  210  becomes permanently compressed/deformed by an excess amount of force, the column spacer may no longer be able to maintain a uniform gap between the color filter glass  202  and the TFT substrate  206 . A non-uniformity in the gap between color filter glass  202  and TFT substrate  206  means that the thickness of liquid crystal layer  208  may no longer be uniform, which in turn can mean that the transmittance of light through liquid crystal layer  208  at the site of the deformation/compression of the column spacer can be altered. An altered transmittance of light at a particular spot on the LCD panel can render a permanent and visible visual defect at the site of the compression. 
       FIG. 7 a    illustrates an exemplary panel stack up column spacer arrangement according to one disclosed embodiment. Panel stack up  700  is arranged similarly to panel stack up  200  of  FIG. 2 . Panel  700  can contain a color filter glass  702  and a TFT glass  704  which can be located on opposing ends of the stack up. TFT glass  704  can have a TFT substrate layer  706  disposed immediately on top of it. TFT substrate layer  706  can contain the electrical components necessary to create the electric field that drives the liquid crystal layer  708 . More specifically, TFT substrate  706  can include various different layers that include display elements such as data lines, gate lines, TFTs, common and pixel electrodes, etc. These components can help to create a controlled electric field that orients liquid crystals located in liquid crystal layer  708  into a particular orientation based on the desired color to be displayed at any particular pixel. Panel  700  differs from the panel illustrated in  FIG. 2 , in so far as it contains two sets of columns spacers  710  and  712 . Column spacers  710  and  712  can differ in height. Column spacers  710  can be of a height so that one end of the column spacer touches the color filter glass  702  and the other end of the column spacer touches the TFT substrate  706 . Column spacers  712  can be of height such that one end of the column spacer touch the color filter glass  702  and the other end leaves a gap between the end of the column spacer and the TFT substrate, which leaves room for the liquid crystal to flow underneath them and spread out. As an example, the gap could be approximately 0.5 μm, meaning that the heights of column spacers  710  and  712  differ by that amount. Furthermore, in some embodiments, the column spacer density of column spacer  710  can be different from the column spacer density of column spacer  712 . 
       FIG. 7 b    illustrates the cross-section of the layer stack up of the LCD panel while an external force is being exerted on the panel according to one disclosed embodiment. When an external force  714  pushes down on panel  700 , column spacers  710 , whose heights are sufficient to span the gap between the color filter glass  702  and TFT substrate  706 , can begin to compress due to the force. The compression can cause the gap  804  between color filter glass  702  and TFT substrate  706  to be reduced. Eventually, as force  714  causes the panel  700  to compress, the gap  804  becomes small enough so that column spacers  712  no longer have a gap between their ends and TFT substrate  706 . When column spacer  712  begins to touch TFT substrate  706 , it can then begin to absorb some of the force  714  being applied, and minimize or reduce the amount of compression being experienced by column spacer  710 . From a force-depth curve point of view, this can mean that column spacer  710  can have a force-depth curve similar to that of  FIG. 4  in that when the force is removed, the column spacer can return to its original height. Column spacer  712  can make this possible by providing additional support to column spacer  710  prior to column spacer  710  compressing to the point where it becomes permanently deformed. This can allow the column spacer density of column spacers  710  to remain lower, allowing for adequate room for the liquid crystal layer  708  to spread out. The column spacer density of column spacers  712  can remain high as compared to column spacers  710 , since it does not impede the liquid crystal layer. Since column spacers  712  are short enough to provide a gap between the column spacer and the TFT substrate  706 , they do not impede the liquid crystal layer; however, when the panel becomes compressed it can provide the necessary support to prevent the main column spacers  710  from becoming permanently deformed. 
     While an LCD panel that incorporates column spacers of different heights can provide various benefits as discussed above, it can provide some disadvantages. One such disadvantage is that the fabrication of the column spacers can become more difficult when the column spacers vary in height. Column spacers can be fabricated by depositing a photoresist layer on a color filter glass and then exposing the photoresist layer to a ultraviolet (UV) light. Portions of the photoresist layer can be masked (covered so that it is not exposed or partially exposed to light) to form a desired pattern. The masking required to generate a pattern of column spacers that vary in height can be more difficult to generate than a pattern in which the column spacers have a uniform height. This difficulty can make the fabrication process of the LCD panel more complex and time consuming. 
     One method of creating a column spacer arrangement as described above and illustrated in  FIG. 7  is to take advantage of various physical properties of the TFT substrate layer. 
       FIG. 8  illustrates an example LCD display screen with a magnified view of two display pixels. Each display pixel can include pixel electrodes  857 . Each display pixel can include a common electrode (Vcom)  859  that can be used in conjunction with pixel electrodes  857  to create an electrical potential across a pixel material (not shown). Varying the electrical potential across the pixel material can correspondingly vary an amount of light emanating from the pixel. In some embodiments, for example, the pixel material can be liquid crystal. A common electrode voltage can be applied to a Vcom  859  of a display pixel, and a data voltage can be applied to a pixel electrode  857  of a sub-pixel of the display pixel through the corresponding data line  855 . A voltage difference between the common electrode voltage applied to Vcom  859  and the data voltage applied to pixel electrode  857  can create the electrical potential through the liquid crystal of the pixel. The electrical potential can generate an electric field through the liquid crystal, which can cause inclination of the liquid crystal molecules to allow polarized light from a backlight (not shown) to emanate from the sub-pixel with a luminance that depends on the strength of the electric field (which can depend on the voltage difference between the applied common electrode voltage and data voltage). In other embodiments, the pixel material can include, for example, a light-emitting material, such as can be used in organic light emitting diode (OLED) displays. 
       FIG. 9  illustrates an example arrangement of pixel electrodes  901  deposited on a TFT substrate in an example display screen  900 . Pixel electrodes  901  can have an arrangement similar to pixel electrodes  857  in  FIG. 8 , for example, in which the pixel electrodes can be arranged in horizontal lines, such as rows  903 . For the purpose of clarity, other pixel electrodes in rows  903  of display screen  900  are not shown in this figure. Pixel electrodes  901  shown in  FIG. 9  can each be associated with a data line  905 , such as data line  855  in  FIG. 8 . Each pixel TFT  907  can include a source  909  connected to data line  905 , a gate  911 , and a drain  913  connected to pixel electrode  901 . Each pixel TFT  907  in one row  903  of pixels can be switched on by applying an appropriate gate line voltage to a gate line  915  corresponding to the row. During a scanning operation of display screen  900 , a target voltage of each pixel electrode  901  in one row  903  can be applied individually to the pixel electrode by switching on pixel TFTs  907  of the of the row with the corresponding gate line  915  while the target voltages of each pixel electrode in the row are being applied to data lines  905 . 
       FIG. 10  illustrates a cross-sectional view of a partial LCD display layer stackup according to some disclosed embodiments. As previously illustrated, a TFT glass  1002  can have a TFT substrate deposited on top of it. The TFT substrate layer can contain the pixel electronics described in  FIG. 9 . In this particular view, only the pixel TFT  907  is shown. The pixel TFT  907  can be composed of gate line  1006 , data line  1010 , gate insulator  1012  and dielectric layer  1014 . As illustrated, the pixel TFT  907  can create a protrusion or step on the TFT substrate layer. 
       FIG. 11  illustrates the cross-sectional view of  FIG. 10  with the color filter glass  1102 , liquid crystal layer  1108  and column spacers  1104  and  1106  disposed on top. As illustrated, the first set of column spacers  1104  are now disposed on top of the protrusion on the TFT substrate created by pixel TFT  907 . The fact that the first set of column spacers  1104  sits on top of a step created by the pixel TFT  907  can mean that the second set of column spacers  1106  can be of the same or substantially the same height as the first set of column spacers  1104 , while still maintaining a gap between the bottom of the column spacer  1106  and the TFT substrate. By taking advantage of a step/protrusion created pixel TFT  907 , a second set of column spacers  1106  can be created to provide adequate support to the first set of columns spacers  1104 , while maintaining a gap, so that the liquid crystal layer  1108  can have adequate room to spread out. Since the step created by pixel TFT  907  allows for the second set of column spacers  1106  to be of equal or substantially equal height as the first set of column spacers  1104 , the column spacers can be more easily fabricated than if the heights were different as discussed above. 
     As one skilled in the art will recognize, any RC time constant delay on the conductive components of a pixel TFT  907  can constrain the refresh rate of an LCD display by slowing down the speed in which voltage on data lines can change. One way to reduce an RC delay of the pixel electrode  901  or pixel TFT  907  is to place a passivation layer on top the pixel TFT. A passivation layer can help to electrically isolate the pixel TFT so that any stray capacitances caused by external conductors to the TFT don&#39;t increase the total capacitance of the TFT, thus keeping the RC time delay of the TFT smaller.  FIG. 12  illustrates an LCD stackup with a passivation layer. As illustrated, passivation layer  1202  is disposed on top of the TFT substrate in order to reduce RC delay. In doing so however, the passivation layer  1202  can cause a planarization of the TFT substrate, which can remove the step/protrusion created by the pixel TFT  907 . With the step created by the pixel TFT  907  removed by the planarization, the second set of column spacers  1106  can no longer be the same height or substantially the same height as the first set of column spacers  1104  and still maintain a gap to allow the liquid crystal layer  1108  to spread out. In order to maintain a gap, a second set of column spacers  1204  can be fabricated. The height of column spacers  1204  can be shorter than column spacers  1104  in order to maintain the gap necessary for the liquid crystal layer  1108  to spread out. However, as discussed above, an LCD panel with column spacers of varying heights can be difficult to fabricate. 
     Common electrodes  859  of  FIG. 8  can be made from Indium Tin Oxide (ITO), which is a clear conductive material that can be used in display screens so as to not obscure an aperture of a display. One skilled in the art will recognize that a large RC delay is inherent in ITO. The RC delay inherent in ITO can be large enough that simply applying a passivation layer may not be sufficient to adequately decrease the delay to a required level. One method to reduce an RC delay of an ITO common electrode is disclosed in “Common Bus Design for a TFT-LCD Display” (Chang et. al, U.S. Patent Publication No. 2010/0123866), incorporated herein by reference in its entirety for all purposes. Chang discloses utilizing a metal layer to create a common bus for the common electrodes  859  so as to reduce their resistivity, thus decreasing the RC time delay caused by the ITO material of the common electrode. 
       FIG. 13  is a three-dimensional illustration of an exploded view (expanded in the z-direction) of example display pixel stackups  1300  showing some of the elements within the TFT substrate of an example display. 
     Stackups  1300  can include elements in a first metal (M1) layer  1301 , a second metal (M2) layer  1303 , a common electrode (Vcom) layer  1305 , and a third metal (M3) layer  1307 . Each display pixel can include a common electrode  1309  that is formed in Vcom layer  1305 . M3 layer  1307  can include connection element  1311  that can electrically connect together common electrodes  1309  in order to form a common bus as disclosed in Chang. M1 layer  1301  can include tunnel lines (also referred to as “bypass lines”)  1319  that can electrically connect together different groups of common electrodes through connections, such as conductive vias  1321 , which can electrically connect tunnel line  1319  to the grouped common electrodes in drive region segment display pixels. M2 layer  1303  can include data lines  1323 , which drive each individual pixel. Only one data line  1323  is shown for the sake of clarity; however, a display can include multiple data lines running through each vertical row of pixels, for example, one multiplexed data line for each red, green, blue (RGB) color sub-pixel in each pixel in a vertical row of an RGB display integrated touch screen.  FIG. 13  shows a “common on top” pixel arrangement for an LCD display that uses a fringe-field switching (FFS) method to a liquid crystal layer. One skilled in the art will recognize that in a common on top arrangement, the pixel electrodes (not shown) will be disposed underneath each common electrode. Thus in a common on top arrangement, the common electrode layer  1305  and the M3 layer  1307  can be disposed closer to the color filter glass than the pixel electrode and the pixel TFT. 
       FIGS. 14A and 14B  illustrate a close up view of a common electrode with an M3 layer disposed on top of it. In  FIG. 14A , the common bus line  1401  is immediately above the common electrode  1400 . In  FIG. 14B , the common bus line  1401  is above the common electrode  1400 , but not immediately above it. Instead, there may be some space between the common electrode and the common bus line. This space may be occupied by another layer, such as a dielectric. Connections  1402  can be used to connect the common electrode to the common bus line instead. The addition of an M3 layer can create a protrusion/step on the common electrode layer. As discussed above, the common electrode layer can be disposed on the top of a TFT layer. Since it is disposed on the top of the TFT active layer, the M3 layer can create a protrusion on the TFT substrate layer. 
       FIG. 15  illustrates an LCD panel stack up with a column spacer arrangement that takes advantage of the step/protrusion created by an M3 layer. The stackup can contain a TFT glass  1502  which has a TFT substrate  1516  disposed on top of it. TFT substrate can consist of a pixel electrode layer  1504  with a passivation layer  1514  disposed on top it. In a common on top arrangement, common electrode  1508  can be disposed above the passivation layer  1514 . An M3 layer  1518  is disposed above the common electrode  1508 . As shown in  FIG. 15 , the M3 layer can cause a protrusion on the TFT substrate layer  1516 . A first set of column spacers  1510  can be disposed on top of the M3 layer such that column spacer  1510  rests on top of the column spacer. As discussed above in reference to  FIG. 11 , when a set of column spacers can be disposed on top of a protrusion or step of a TFT substrate layer, a second set of column spacers whose heights are equal or substantially equal to the first set of column spacers can be disposed on the color filter glass, such that a gap is created that is adequate to allow for the liquid crystal layer to spread out. In this case, the M3 layer  1518  can create the step necessary to allow column spacers  1510  and  1512  to be of the same height, while allowing column spacer  1512  to leave an adequate gap between it and TFT substrate  1516  for the liquid crystal layer to spread out. Furthermore, the step created by M3 layer  1518  can act to prevent scratching of the TFT substrate  1516  when the color filter glass is moved laterally since if the column spacer  1510  becomes misaligned with the step created by the M3 layer, it will not scratch the surface of the TFT substrate because there will be a gap between the spacer and the TFT substrate. This advantage can also be realized in a display that utilizes a protrusion created by a TFT substrate as described in  FIG. 11 . 
     In some embodiments, a first set of column spacers  1510  does not have to directly contact an M3 layer  1518 . As shown in  FIG. 16 , a dielectric layer  1602  can be disposed over the M3 layer  1518 , while still maintaining the step created by the M3 layer. 
       FIG. 17  is a block diagram of an example computing system  1700  that illustrates one implementation of an example display with the column spacer design described above integrated with a touch screen  1720  according to embodiments of the disclosure. Computing system  1700  could be included in, for example, mobile telephone  136 , digital media player  140 , personal computer  144 , or any mobile or non-mobile computing device that includes a touch screen. Computing system  1700  can include a touch sensing system including one or more touch processors  1702 , peripherals  1704 , a touch controller  1706 , and touch sensing circuitry. Peripherals  1704  can include, but are not limited to, random access memory (RAM) or other types of memory or storage, watchdog timers and the like. Touch controller  1706  can include, but is not limited to, one or more sense channels  1708 , channel scan logic  1710  and driver logic  1714 . Channel scan logic  1710  can access RAM  1712 , autonomously read data from the sense channels and provide control for the sense channels. In addition, channel scan logic  1710  can control driver logic  1714  to generate stimulation signals  1716  at various frequencies and phases that can be selectively applied to drive regions of the touch sensing circuitry of touch screen  1720 , as described in more detail below. In some embodiments, touch controller  1706 , touch processor  1702  and peripherals  1704  can be integrated into a single application specific integrated circuit (ASIC). 
     Computing system  1700  can also include a host processor  1728  for receiving outputs from touch processor  1702  and performing actions based on the outputs. For example, host processor  1728  can be connected to program storage  1732  and a display controller, such as an LCD driver  1734 . Host processor  1728  can use LCD driver  1734  to generate an image on touch screen  1720 , such as an image of a user interface (UI), and can use touch processor  1702  and touch controller  1706  to detect a touch on or near touch screen  1720 , such a touch input to the displayed UI. The touch input can be used by computer programs stored in program storage  1732  to perform actions that can include, but are not limited to, moving an object such as a cursor or pointer, scrolling or panning, adjusting control settings, opening a file or document, viewing a menu, making a selection, executing instructions, operating a peripheral device connected to the host device, answering a telephone call, placing a telephone call, terminating a telephone call, changing the volume or audio settings, storing information related to telephone communications such as addresses, frequently dialed numbers, received calls, missed calls, logging onto a computer or a computer network, permitting authorized individuals access to restricted areas of the computer or computer network, loading a user profile associated with a user&#39;s preferred arrangement of the computer desktop, permitting access to web content, launching a particular program, encrypting or decoding a message, and/or the like. Host processor  1728  can also perform additional functions that may not be related to touch processing. 
     Integrated display and touch screen  1720  can include touch sensing circuitry that can include a capacitive sensing medium having a plurality of drive lines  1722  and a plurality of sense lines  1723 . It should be noted that the term “lines” is sometimes used herein to mean simply conductive pathways, as one skilled in the art will readily understand, and is not limited to elements that are strictly linear, but includes pathways that change direction, and includes pathways of different size, shape, materials, etc. Drive lines  1722  can be driven by stimulation signals  1716  from driver logic  1714  through a drive interface  1724 , and resulting sense signals  1717  generated in sense lines  1723  can be transmitted through a sense interface  1725  to sense channels  1708  (also referred to as an event detection and demodulation circuit) in touch controller  1706 . In this way, drive lines and sense lines can be part of the touch sensing circuitry that can interact to form capacitive sensing nodes, which can be thought of as touch picture elements (touch pixels), such as touch pixels  1726  and  1727 . This way of understanding can be particularly useful when touch screen  1720  is viewed as capturing an “image” of touch. In other words, after touch controller  1706  has determined whether a touch has been detected at each touch pixel in the touch screen, the pattern of touch pixels in the touch screen at which a touch occurred can be thought of as an “image” of touch (e.g. a pattern of fingers touching the touch screen). 
     In some example embodiments, touch screen  1720  can be an integrated touch screen in which touch sensing circuit elements of the touch sensing system can be integrated into the display pixels stackups of a display. 
     Although the disclosed embodiments have been fully described with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Such changes and modifications are to be understood as being included within the scope of the disclosed embodiments as defined by the appended claims.

Metadata:
Filing Date: 20120906
Publication Date: 20160719
Grant Date: 20160719
Priority Date: 20120606
Inventors: KIM KYUNG-WOOK
CHANG SHIH CHANG
CHEN CHENG
PARK YOUNG-BAE
ZHONG JOHN Z.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/1368", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13439", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134309", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136286", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/136286", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/134363", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1333", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1343", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2201/123", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2201/121", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1339", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133514", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2201/12", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134363", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F2001/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13394", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F2001/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133302", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/134372", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13396", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 48700697