PATENT DOCUMENT

Publication Number: US-8692948-B2
Application Number: US-78539510-A
Country: US
Kind Code: B2

Title: Electric field shielding for in-cell touch type thin-film-transistor liquid crystal displays

Abstract:
Displays such as liquid crystal displays may be used in electronic devices. During operation of a display, electrostatic charges on the surface of the display may give rise to electric fields. One or more electric field shielding layers may be provided in the display to prevent the electric fields from disrupting operation of the liquid crystals material in the display. The shielding layers may be formed at a location in the stack of layers that make up the display that is above the liquid crystal material of the display. Touch sensors and thin film transistors may be located below the shielding layer.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 an upper polarizer; 
 a lower polarizer; 
 a liquid crystal layer interposed between the upper polarizer and the lower polarizer; 
 a touch sensor array below the liquid crystal layer; 
 a thin-film-transistor substrate, wherein the touch sensor array is formed on the thin-film-transistor substrate; 
 an electric field shielding layer above the liquid crystal layer; 
 an additional electric field shielding layer above the liquid crystal layer, wherein the upper polarizer is interposed between the electric field shielding layer and the additional electric field shielding layer, and wherein the electric field shielding layer and the additional electric field shielding layer are electrically coupled to a ground contact on the thin-film-transistor substrate; and 
 a dot of conductive paste that electrically couples the additional electric field shield layer to the ground contact on the thin-film transistor substrate. 
 
     
     
       2. The display defined in  claim 1  further comprising a switch that is electrically coupled between the electric field shielding layer and the ground contact. 
     
     
       3. The display defined in  claim 1  further comprising a capacitive touch sensor electrode array below the liquid crystal layer. 
     
     
       4. The display defined in  claim 3  wherein the electric field shielding layer has a resistivity of between 10 M-ohm/square and 10 G-ohm/square. 
     
     
       5. The display defined in  claim 1  wherein the electric field shielding layer comprises a conductive layer with openings that increase resistivity for the conductive layer. 
     
     
       6. The display defined in claim  5 , wherein the electric field shielding layer further comprises an insulating coating that protects the conductive layer. 
     
     
       7. The display defined in  claim 6 , wherein the conductive material comprises a nanomaterial. 
     
     
       8. The display defined in  claim 6 , wherein the insulating coating comprises a polymer resin. 
     
     
       9. The display defined in  claim 5 , wherein the conductive layer comprises carbon nanotubes. 
     
     
       10. The display defined in  claim 5 , wherein the conductive layer comprises conductive adhesive. 
     
     
       11. The display defined in  claim 5 , wherein the conductive layer comprises a conductive doped surface region of a dielectric substrate. 
     
     
       12. The display defined in  claim 5 , wherein the conductive layer comprises a conductive layer in an antistatic polarizer layer. 
     
     
       13. The display defined in  claim 5 , wherein the conductive layer comprises a spray-coated layer. 
     
     
       14. The display defined in  claim 1  further comprising:
 additional conductive paste electrically connected between the electric field shielding layer and a conductive structure. 
 
     
     
       15. A display, comprising:
 an upper polarizer; 
 a lower polarizer; 
 a liquid crystal layer interposed between the upper polarizer and the lower polarizer; 
 a touch sensor array below the liquid crystal layer; 
 a thin-film-transistor substrate, wherein the touch sensor array is formed on the thin-film transistor substrate; 
 an electric field shielding layer above the liquid crystal layer, wherein the electric field shielding layer comprises a conductive polymer; and 
 a conductive paste electrically coupled between the electric field shielding layer and a ground terminal on the thin-film-transistor substrate, wherein the conductive paste comprises a dot of metal paint located at a corner of the electric field shielding layer. 
 
     
     
       16. The display defined in  claim 15  further comprising an additional transparent electric field shielding layer above the liquid crystal layer. 
     
     
       17. The display defined in  claim 16 , wherein the electric field shielding layer is located above the upper polarizer and wherein the additional transparent electric field shielding layer is located below the upper polarizer. 
     
     
       18. The display defined in  claim 15  further comprising a capacitive touch sensor electrode array below the liquid crystal layer. 
     
     
       19. The display defined in  claim 15  wherein the electric field shielding layer has a resistivity of between 10 M-ohm/square and 10 G-ohm/square. 
     
     
       20. A display, comprising:
 an upper polarizer; 
 a lower polarizer; 
 a liquid crystal layer interposed between the upper polarizer and the lower polarizer; 
 a touch sensor array below the liquid crystal layer; 
 an electric field shielding layer above the liquid crystal layer, wherein the electric field shielding layer comprises a conductive polymer; and 
 a switch that is electrically connected between the electric field shielding layer and a ground contact. 
 
     
     
       21. The display defined in  claim 20  further comprising a thin-film-transistor substrate, wherein the touch sensor array is formed on the thin-film-transistor substrate and wherein the ground contact is located on the thin-film-transistor substrate. 
     
     
       22. The display defined in  claim 21  further comprising a conductive paste electrically coupled between the electric field shielding layer and the ground contact on the thin-film-transistor substrate.

Description:
BACKGROUND 
     This relates generally to displays, and, more particularly, to displays that include protective layers that prevent the operation of the display from being disrupted from electric fields. 
     Displays are widely used in electronic devices to display images. Displays such as liquid crystal displays display images by controlling liquid crystal material associated with an array of image pixels. A typical liquid crystal display has a color filter layer and a thin film transistor layer formed between polarizer layers. The color filter layer has an array of pixels each of which includes color filter subpixels of different colors. The thin film transistor layer contains an array of thin film transistor circuits. The thin film transistor circuits can be adjusted individually for each subpixel to control the amount of light that is produced by that subpixel pixel. A light source such as a backlight may be used to produce light that travels through each of the layers of the display. 
     A layer of liquid crystal material is interposed between the color filter layer and the thin film transistor layer. During operation, the circuitry of the thin film transistor layer applies signals to an array of electrodes in the thin film transistor layer. These signals produce electric fields in the liquid crystal layer. The electric fields control the orientation of liquid crystal material in the liquid crystal layer and change how the liquid crystal material affects polarized light. 
     An upper polarizer is formed on top of the display and a lower polarizer is formed on the bottom of the display. As light travels through the display, the adjustments that are made to the electric fields in the liquid crystal layer are used to control the image that is displayed on the display. 
     In many electronic devices, it is desirable to incorporate touch screen functionality into a display. Touch screens can be used to provide a device with a touch interface. A touch interface may allow users to interact with a device through on-screen touch commands such as finger taps and swipes. 
     A typical touch screen includes a touch panel with an array of touch sensor electrodes. Touch sensor processing circuits can measure capacitance changes on the touch sensor electrodes to determine the position at which a user&#39;s finger is contacting the touch array. 
     When an external object such as a user&#39;s finger comes into contact with a display, there is a potential for electrostatic charges on the user&#39;s finger to create large electric fields in the display. These electric fields may disrupt the operation of the display. For example, the electric fields from an electrostatic charge may interfere with the electric fields created by the electrodes of the thin-film-transistor layer. This can create spots or other visual artifacts on the screen. 
     In some liquid crystal displays that include touch panels, the touch panel may be located above the liquid crystal layer. In this type of situation, the electrodes of the touch sensor array may prevent charge-induced electric fields from reaching the liquid crystal layer. 
     It may sometimes be desirable to construct a display with different touch sensor configurations. For example, it may be desirable to incorporate a touch sensor electrodes into a display at a location that is below the liquid crystal layer. This type of display is sometimes referred to as an in-cell display. If care is not taken, however, the display will be susceptible to disruptions from electrostatic charge, because the touch sensor electrodes will not prevent charge-induced electric fields from reaching the liquid crystal layer. 
     It would therefore be desirable to provide displays such as liquid crystal displays that have improved electric field shielding layers. 
     SUMMARY 
     Displays may be used in electronic devices to display images for a user. A display may include image pixels that are formed from a layer of liquid crystal material. A color filter layer that includes color filter elements may be located above the liquid crystal layer to provide color to the images. The liquid crystal layer may be controlled by electric fields produced using transistors and electrodes in a thin-film-transistor layer. Touch sensor capabilities may be incorporated into the display using an array of touch sensor electrodes. The touch sensor electrodes may be formed on the thin-film-transistor layer or other layer below the liquid crystal layer. 
     When a user or other external object touches the surface of the display, electrostatic charges give rise to electric fields. To ensure that these electric fields do not disturb the liquid crystal layer, one or more transparent electric field shielding layers may be incorporated into the display above the liquid crystal layer. 
     The shielding layers may be formed from conductive adhesive, metal oxides, conductive polymers, materials that include nanostructures such as carbon nanotubes, materials that include metal particles, conductive inks, or other conductive materials. The resistivity of a shielding layer may be small enough to prevent disruptions to the liquid crystal layer and large enough to avoid blocking operation of the touch sensor electrodes. 
     A switch may be used to selectively ground the electric field shielding layer. Openings may be formed within an electric field shielding layer to increase resistivity. Protective layers of material may be included in a shielding layer to ensure that a conductive layer portion in the shielding layer is stable. Shielding layers may be formed by incorporating dopant into a thin surface layer in an insulating substrate. Islands of material in an electric field shielding layer may be joined together using an additional layer of conductive material. 
     A shielding layer for a display may be provided by using an antistatic polarizer layer that includes a conductive layer. Shielding layers may also be incorporated into the color filter structures of a display. For example, a black mask in a color filter may be implemented using a conductive material, a conductive layer may be interposed between an overcoat layer and color filter elements in a color filter, or an overcoat layer may be formed using conductive materials. 
     A display may have polyimide layers adjacent to the liquid crystal layer. Conductive shielding layers may be interposed between the polyimide layers and adjacent layers. 
     A conductive ring such as a ring of indium tin oxide may be used to help short the electric field shielding layer to a terminal such as a ground terminal on a thin-film-transistor layer. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device that may be provided with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a cross-sectional side view of an illustrative display in an electronic device in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative array of touch sensor electrodes in a touch sensor in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view showing layers of components that may be used in a liquid crystal display in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of layers in an illustrative display having a thin-film-transistor and touch sensor layer in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of an illustrative display that has a shielding layer above an upper polarizer in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of an illustrative display that has a shielding layer below an upper polarizer in accordance with an embodiment of the present invention. 
         FIG. 8  is a cross-sectional side view of an illustrative display having a conductive peripheral ring that assists in grounding a shielding layer in accordance with an embodiment of the present invention. 
         FIG. 9  is a top view of an illustrative display that has a conductive peripheral ring of the type shown in  FIG. 8  in accordance with an embodiment of the present invention. 
         FIG. 10  is a cross-sectional side view of an illustrative display that has two shielding layers and a conductive peripheral ring that is used to help form a conductive grounding path in accordance with an embodiment of the present invention. 
         FIG. 11  is a cross-sectional side view of an illustrative display that has a spray-coated shielding layer and that uses a masking layer to protect a driver integrated circuit from the spray-coated shielding layer in accordance with an embodiment of the present invention. 
         FIG. 12  is a to view of an illustrative display in which a switch is used to selectively ground a shielding layer in accordance with an embodiment of the present invention. 
         FIG. 13  is a top view of an illustrative shielding layer with openings that reduce the resistivity of the shielding layer in accordance with an embodiment of the present invention. 
         FIG. 14  is a bottom view of an illustrative color filter layer showing how the color filter elements of the color filter layer may be surrounded by an opaque masking layer that serves as a shielding layer in accordance with an embodiment of the present invention. 
         FIG. 15  is a cross-sectional side view of an illustrative display in which a shielding layer that has been formed from a conductive black mask layer is shorted to a ground contact on a thin-film-transistor and touch sensor layer in accordance with an embodiment of the present invention. 
         FIG. 16  is a cross-sectional side view of an illustrative display that has one or more shielding layers formed from a masking layer, an overcoat layer, a layer interposed between an overcoat layer and a masking layer, and a layer adjacent to a polyimide layer in accordance with an embodiment of the present invention. 
         FIG. 17  is a cross-sectional side view of a shielding layer for a display showing how the shielding layer may be formed from a substance that is deposited in a thin layer having islands of material and a coating layer that covers and joins the islands of material in accordance with an embodiment of the present invention. 
         FIG. 18  is a cross-sectional side view of an insulating substrate layer in a display in which the top surface of the substrate layer has been converted into a conductive shielding layer for the display by incorporation of dopant in accordance with an embodiment of the present invention. 
         FIG. 19  is a cross-sectional side view of layers in an illustrative display showing how a protective layer may be deposited on a conductive layer through a shadow mask to form a protected shielding layer with exposed portions for grounding to a ground contact in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An electronic device of the type that may be provided with a display is shown in  FIG. 1 . As shown in  FIG. 1 , electronic device  10  may have a housing  12 . Buttons, input-output ports, and other components  16  may be provided in housing  12 . Display  14  may be mounted in housing  12  on the front surface of device  10  (as shown in  FIG. 1 ) or may be mounted in other suitable locations within housing  12 . If desired, housing  12  may have multiple sections such as first and second sections that are connected with a hinge. 
     Electronic device  10  may be a computer monitor for a desktop computer, a kiosk, a table-based computer, a portable computer such as a laptop or tablet computer, a media player, a cellular telephone or other handheld computing device, or may be a somewhat smaller portable device. Examples of smaller portable electronic devices include wrist-watch devices and pendant devices. These are merely examples. In general, display  14  may be incorporated into any suitable electronic device. 
       FIG. 2  is a cross-sectional side view of display  14 . As shown in  FIG. 2 , a cover glass layer such as cover glass  18  may be used to provide display  14  with a robust outer surface. Cover glass layer  18  may be formed from glass, plastic, other suitable materials, or combinations of these materials. 
     Touch sensor and display components  22  may be housed in housing structures  20 . Structures  20  may include plastic chassis members, metal chassis structures, housing structures (e.g., part of housing  12  of  FIG. 1 ), or other suitable mounting or support structures. 
     Touch sensor and display components  22  may include display image pixel structures such as display electrodes and display circuitry for controlling the display electrodes. Touch sensor and display components  22  may also include a touch sensor. The touch sensor may, for example, be formed from touch sensor electrodes. The touch sensor electrodes may be mounted on a dielectric substrate such as plastic or glass to form a touch panel. Display electrodes may be mounted on a display layer such as a thin-film transistor layer or may be mounted on multiple layers of material. If desired, some or all of the touch sensor electrodes and display electrodes may be formed on a common substrate (e.g., as different deposited layers on a thin-film-transistor layer). Other configurations may be used if desired. These touch sensor and display electrode configurations are merely illustrative. 
     A perspective view of a typical touch panel is shown in  FIG. 3 . As shown in  FIG. 3 , panel  24  may include a upper touch sensor electrodes  28  that run perpendicular to lower touch sensor electrodes  30 . Electrodes  28  and  30  may be mounted to the upper and lower surfaces of substrate  26  or may be supported using other arrangements. Electrodes  28  and  30  may be formed from a transparent conductive material such as indium tin oxide (ITO) or other suitable material. Dielectric layer  26  may be formed from glass, plastic, a layer of dielectric material that is deposited using sputtering, spraying, or other deposition techniques, or other suitable materials. 
     When a user&#39;s finger or other external object comes into contact with the touch panel (or is placed in the vicinity of the touch panel) capacitance changes may be detected using electrodes  28  and  30 . These capacitance changes may be used to produce location information. In particular, the square intersections between electrodes  28  and  30  that are shown in  FIG. 3  allow measurement of the point at which a user&#39;s finger or other external object touches panel  24  in terms of lateral dimensions X and Y. If desired, a touch sensor for display  14  may be formed using other touch technologies (resistive touch sensors, acoustic touch sensors, etc.). 
     Display  14  may, in general, be based on any suitable display technology (liquid crystals, organic light-emitting diodes, plasma cells, electronic ink arrays, etc.). Examples that use liquid crystal technology are sometimes described herein as an example. 
     A perspective view of illustrative liquid crystal display structures  32  that may be used in display  14  is shown in  FIG. 4 . As shown in  FIG. 4 , liquid crystal display structures  32  may include color filter (CF) layer  40  and thin-film-transistor (TFT) layer  36 . Color filter layer  40  may include an array of colored filter elements. In a typical arrangement, the pixels of layer  40  each include three colored subpixels (e.g., red, green, and blue subpixels). Liquid crystal (LC) layer  36  includes liquid crystal material and is interposed between color filter layer  40  and thin-film-transistor layer  36 . Thin-film-transistor layer  36  may include electrical components  44  such as transistors coupled to electrodes for controlling the electric fields that are applied to liquid crystal layer  36 . If desired, components  44  may include touch sensor components such as touch sensor electrodes  28  and  30 . 
     Additional optical layers  42  and  34  may be formed above and below color filter layer  30 , liquid crystal layer  38 , and thin-film-transistor layer  36 . Additional optical films  42  and  34  may include polarizing layers, so optical films  42  and  34  are sometimes referred to as polarizing layers or polarizers (“POL”). 
     Touch sensor structures may be incorporated into the layers of display structures  32  (e.g., by including both touch sensor and thin-film-transistor components in components  44  of layer  36  of  FIG. 4 ). This type of arrangement is shown in  FIG. 5 . As shown in  FIG. 5 , thin-film-transistor layer TFT may include layers  36 A and  36 B. Layer  36 B may be formed form a dielectric substrate such as a layer of glass or plastic. Layer  36 A may include both thin-film-transistor structures such as transistors and electrodes for controlling the electric fields in liquid crystal layer  38  and touch sensor electrodes (e.g., capacitive electrodes such as electrodes  28  and  30  of FIG.  3 ). Other configurations may be used if desired. The illustrative arrangement for combining TFT structures and touch structures into layer TFT that is shown in  FIG. 5  is merely illustrative. 
     In situations such as those in which display  14  does not have a touch panel above its liquid crystal layer, there is a risk that electrostatic charges that are imposed on the cover glass layer of the display will create electric fields in the liquid crystal layer that disrupt proper operation of the display. This risk can be addressed by providing display  14  with one or more electric field shielding layers above liquid crystal layer  38 . 
     To ensure that the electric field shielding layer prevents electrostatic charges on the surface of display  14  from interfering with the operation of liquid crystal layer  38 , this shielding layer should have sufficient conductivity. At the same time, care should be taken that the shielding layer is not too conductive, because this would interfere with the capacitive sensing functions of the touch sensor. Preferably the resistivity of the shielding layer is between 10 M-ohm/square to 10 G-ohm/square. Shielding layer films with a resistivity in this range may sometimes be referred to as having a medium-high resistance. The shielding layer is not insulating (because that would prevent the shielding layer form being effective at blocking the effects of electrostatic charge). At the same time, the shielding layer is only moderately conductive, because a highly conductive conductor would provide too much shielding and would block the touch sensor. 
     In general, the shielding layer may be formed from any suitable material that exhibits a suitable resistivity while exhibiting satisfactory transparency in the visible spectrum. To ensure that the display is efficient at emitting light, it is generally desirable that the shielding layer have a transmittance of about 80% or more, 90% or more, 95% or more, or preferably 96% or more, or 97% or more. Shielding layers with lower values of transmittance may be used, but will tend to dim the display. 
     Examples of materials that may be used in forming the shielding layer include conductive oxides (e.g., indium tin oxide, antimony oxide, tin oxide, zinc oxide, other metal oxides, metal oxides that contain multiple metals, etc.), nanomaterials (e.g., nanotube materials such as carbon nanotube materials), conductive polymers (metallic conductors or semiconductors), conductive inks, conductive mixtures of particles and binders, thin layers of metals, mixtures or chemical combinations of these materials, layered stacks including multiple layers of each of these materials, etc. 
     Shielding layer materials may be deposited on dedicated films (e.g., glass substrates, ceramic substrates, plastic substrates, or other dielectric substrates) or may be deposited on other layers of material in display  14  (e.g., on top of or beneath a color filter substrate, a polarizer layer, a thin-film-transistor substrate, other optical film layers, etc.). 
     Techniques that may be used in depositing the shielding layer include spraying, dipping, dripping, spin-coating, pad printing, evaporation, sputtering, electrochemical deposition, chemical vapor deposition, ion implantation, diffusion, gluing, or other suitable fabrication technique. 
     In discussing the layers that may be used in display  14 , certain layers are sometimes said be “above” or “below” other layers. A layer that is above another structure is higher in the stack than that structure and is therefore closer to the exposed outer surface of display  14 . A layer that is below another structure is lower in the stack of layers in display  14  than the that structure. In general, the shielding layer will be formed above layer  38  (i.e., the shielding layer will be higher in the stack of layers in display  14  than layer  38  and therefore closer to the exposed outer surface of display  14  than layer  38 ). This will help prevent charge-induced fields from disrupting the liquid crystal material of layer  38 . The shielding layer will generally also be above the touch sensor array. Illustrative locations for forming the shielding layer are described in the following examples. 
     In the example shown in  FIG. 6 , electric field shielding layer (“shielding layer”)  46  is formed on top of polarizer  42 . Adhesive  50  may be used to attach cover glass  18  to shielding layer  46  and therefore upper polarizer  42 . A conductive structure such as conductive structure  62  may be used to form an electrical pathway that shorts shielding layer  46  to a terminal such as ground pad  56 . Ground pad  56  may be formed from a conductive trace on thin-film-transistor and touch sensor structures  36  (sometimes referred to herein as “TFT layer  36 ”). Components on the TFT layer  36  such as ground trace  56  and driver integrated circuit  58  may be interconnected using traces such as trace  60 . These traces may be connected to one or more flex circuits (sometimes referred to as “display flex” and “touch flex”) using traces on TFT layer  36 . Flex circuits such as these may be attached to TFT layer  36  using conductive adhesive (sometimes referred to as “anisotropic conductive film” or ACF). The end of a flex circuit that is not attached to TFT layer  36  may be connected to a printed circuit board (e.g., a main logic board). 
     Contacts such as contact  56  on TFT layer  36  may be maintained at a suitable voltage such as a ground voltage and are therefore sometimes referred to as ground contacts or ground. By using conductive structure  62  to connect shielding layer  46  to ground or other suitable potentials, electric fields that are generated by charge on cover glass  18  can be prevented from reaching the layers beneath layer  46 . 
     Conductive structure  62  may be formed from a conductive paste (e.g., a dot of silver or gold paint or other metal paste), conductive adhesive, or any other suitable conductive material. These structures are sometimes referred to herein as conductive dots, because structure  62  may be formed in the shape of a dot (as an example). If desired, conductive structures  62  can be formed in the shape of an elongated line of materials running along the edge of shielding layer  46 . 
     Adhesive  48  may be a pressure sensitive adhesive or a liquid adhesive (as examples). When implementing adhesive layer  48  using a layer of pressure sensitive adhesive, it may be desirable to restrict the size of layer  48 . For example, edge  50  of layer  48  may be recessed (cut-back) from edge  52  of polarizer  42  by a distance L. This ensures that pressure sensitive adhesive  48  and cover glass  18  will not exert excess downwards pressure onto conductive dot  62  in region  54 . Excess pressure in this region might lead to the formation of bubbles and other imperfections at the interface between adhesive  48  and cover glass  18  and at the interface between adhesive  48  and polarizer  42 . The cut-back region (recess L) may be formed along the entire edge of polarizer  42  or may only be formed in the corner of polarizer  42 . One, two, three, or four corners (or edges) of display  14  may be provided with conductive structures such as structure  62  and associated recessed adhesive regions. 
     If desired, layer  48  may be regular (non-conducting) pressure sensitive adhesive (or liquid adhesive) and shielding layer  46  may be a layer of transparent conductive pressure sensitive adhesive. Shielding layer  46  may also be formed from other transparent conductive structures (e.g., conductive polymers, metal oxides, conductive inks, conductive nanomaterials, etc.). 
     If desired, shielding layer  46  may be formed under polarizer  42 , as shown in  FIG. 7 . Shielding layer  46  of  FIG. 7  may, for example, be formed from a layer of transparent conductive adhesive that has been applied to the top surface of color filter layer  40  (as an example). As with the other examples presented herein, shielding layer  46  may also be formed from other suitable materials (e.g., conductive polymers, metal oxides, conductive inks, conductive nanomaterials, combinations of these layers, etc.). 
     It may be desirable to form a ring of conductive material around the periphery of color filter layer  40  to help in forming a conductive grounding path between shielding layer  46  and ground  56  on TFT layer  36 . The use of a ring of conductive material may help distribute ground evenly around shielding layer  46 . A cross-sectional side view of a stack of layers in display  14  showing how conductive ring  64  may be formed around the periphery of the top surface of color filter layer  40  is shown in  FIG. 8 . Shielding layer  46  in  FIG. 8  may be a layer of conductive adhesive (as an example). Conductive ring  64  may be formed from a patterned layer of ITO or other conductive materials (e.g., metal, conductive ink, a conductive nanomaterial, etc.). 
       FIG. 9  is a top view showing how conductive ring  64  may have an outer edge  66  and an inner edge  68 . Shielding layer  46  may be electrically connected to conductive dot  62  through conductive ring  64 . Conductive dot  62  may short ring  64  to ground  56  ( FIG. 8 ). 
     If desired, display  14  may be provided with multiple shielding layers. This type of arrangement is shown in  FIG. 10 . As shown in  FIG. 10 , upper shielding layer  46 A may be formed on top of polarizer  42  and lower shielding layer  46 B may be formed beneath polarizer  42 . Conductive structure  62  may include upper conductive dot  62 A and lower conductive dot  62 B. Conductive structure  62 A may electrically connect shielding layer  46 A to conductive ring  64 . Shielding layer  46 B may be electrically connected to conducting ring  64 . Conductive structure  62 B may electrically connect conductive ring  64  and therefore shielding layers  46 A and  46 B to ground contact  56  on TFT layer  36 . Shielding layers  46 A and  46 B may be formed from conductive adhesive, conductive polymers, conductive metal oxides, conductive inks, conductive nanomaterials, or other suitable materials. 
     If desired, polarizer  42  may be an antistatic polarizer layer and the shielding layer (e.g., shielding layer  46 A of  FIG. 10 ) may be a conductive layer that is formed as part of the antistatic polarizer layer. 
     As shown in  FIG. 11 , shielding layer  46  may be deposited using spray coating techniques. For example, shielding layer  46  may be a transparent conductive ink that is sprayed on top of polarizer  42 . To protect display driver integrated circuit  58  and other circuitry on TFT layer  36 , a masking structure such as encapsulant dot  72  may be formed over circuitry  58 . Encapsulant dot  72  may be formed from an insulating polymer mask material or other suitable materials that are able to insulate circuitry  58  from shielding layer  46 . It is possible that shielding layer  46  could develop small breaks or cracks such as break  70 . This might form a open circuit or a high-resistance path between the portion of shielding layer  46  that is on top of polarizer  42  and the portion of shielding layer  46  near ground contact  56 . Conductive ring  64  (e.g., an ITO ring) may therefore be used to provide a redundant circuit pathway and that helps ensure that there is a sufficiently low resistance path between the shielding layer portion on top of polarizer  42  and ground contact  56 , even in the presence of high-resistance features such as break  70 . 
     If desired, a switch such as switch  74  of  FIG. 12  may be interposed between shielding layer  46  (i.e., a shielding layer on top of polarizer  42  or other suitable shielding layer) and ground contact  56 . Switch  74  may be formed from passive components (e.g., one or more diodes) or active components (e.g., one or more transistors). Switch  74  may be controlled by control signals on control input  76 . For example, switch  74  can be placed in an open condition when it is desired to isolate the shielding layer and thereby minimize its shielding effect (i.e., during predetermined touch sensing intervals) and can otherwise be placed in a closed condition to maximize the shielding ability of the shielding layer. To reduce the shielding effect of the shielding layer when switch  74  is open, the shielding layer may be divided into small sections (e.g., strips, squares, etc.) each of which can be provided with a respective switch (as an example). 
       FIG. 13  shows how shielding layer  46  may be patterned. In the  FIG. 13  example, shielding layer  46  has a mesh pattern in which rectangular openings  78  are free of shielding layer material. Shielding layer material is present in the other shield regions (i.e., outside of rectangles  78 ). By reducing the amount of shield material that is present, the resistivity of the shielding layer may be increased to within its preferred range (between 10 M-ohm/square and 10 G-ohm/square), even if the shield material that is present has a lower resistivity. This approach for increasing the overall resistivity of the shielding layer by selective removal of shielding layer material may make it possible to use more conductive (and more reliably deposited) shielding layer substances than would otherwise be possible. For example, shielding layer  46  may be formed from a layer of ITO that has a resistivity of less than 10 M-ohm/square in a bulk (unpatterned) film. 
     The shielding layer may be patterned using a shadow mask or using photolithography. After patterning, the modified-area shielding layer will exhibit an increased resistivity (i.e., greater than 10 M-ohm/square). A patterned shielding layer of the type show in  FIG. 13  may be formed on top of polarizer  42  or on top of color filter layer  40  (as examples). Any of the shielding layers in the examples described herein may be provided with removed areas to increase resistivity in this way if desired. 
     In conventional color filter layers, a non-conductive black masking layer is typically used to prevent light leakage between color filter elements (i.e., light leakage elements such as red, green, and blue subpixel filters). 
     If desired, an opaque mask on a color filter such as a patterned layer of black masking material may be formed from a conductive opaque (e.g., black) material and can serve as shielding layer  46 .  FIG. 14  is a top view of a portion of color filter layer  40  showing how shielding layer  46  may be implemented using a patterned conductive mask layer (the portions outside color filter elements  80 ). The patterned conductive mask layer may have a resistivity within the preferred range for shielding layer  46  (i.e., between 10 M-ohm/square and 10 G-ohm/square). Materials that may be used to form conductive mask  46  include chromium, chromium oxide, conductive black ink, and polymer resin (e.g., with added metal particles to lower the resistivity of the mask to a desired level). 
     Conductive mask layer  46  of  FIG. 14  may be electrically connected to ground contact  56  on layer  36  using conductive structures. As shown in  FIG. 15 , conductive structures  82  may be used to electrically connect color filter mask layer  46  to ground contacts  56 . Conductive structures  82  may be formed from conductive ink or, with one particularly suitable arrangement, may be formed from conductive sealant material (e.g., conductive epoxy, non-conductive sealant that is rendered conductive upon application of heat and pressure due to the inclusion of gold-coated plastic balls, or other conductive materials etc.). When structures  82  are implemented using sealant, structures  82  may surround the entire rectangular periphery of color filter layer  40 . This seals liquid crystal layer  38 . At the same time, the conductive nature of seal structures  82  may be used in electrically connecting mask shielding layer  46  to ground  56 . 
     In conventional color filter layers, the color filter elements and black mask regions are coated with a blanket overcoat layer of clear polymer. 
       FIG. 16  shows how a via (via  88 ) may be formed in clear polymer overcoat layer  84  on color filter layer  40  and shows how the via may be filled with a conductive material. Via structure  88  may be, for example, a dot of metal paint (e.g., silver paint) or may be formed from conductive sealant. Conductive via structure  88  may be used to electrically connect conductive opaque patterned masking layer  46  on color filter layer  40  to ground structure  56  on layer  36 . In arrangements of the type shown in  FIG. 16  in which conductive structure  88  is used to short shielding layer  46  to ground  56 , sealant  82  may be formed from conductive sealant material or non-conductive sealant material. 
     Display  14  may include polyimide layers  86  (sometimes referred to as “PI” layers) immediately above and below liquid crystal layer  38 . PI layers  86  help align the liquid crystal material in a desired orientation. If desired, a conductive layer such as conductive layer  90  may be interposed between the upper PI layer and overcoat  84 . Layer  90  may serve as shielding layer  46 . Layer  90  may be formed from a transparent conductive polymer or other conductive material. 
     As indicated by dashed line  92 , an optional blanket coating layer may be provided between black masking layer BM and overcoat layer  84 . Layer  92  may be formed from a conductive material such as a transparent conductive polymer or other suitable shielding layer material and may serve as shielding layer  46 . In this type of configuration, black mask layer BM may, if desired, be formed from insulating black ink. A shielding layer for display  14  may also be implemented by forming substantially all of overcoat layer from a shielding layer material (e.g., a transparent conductive polymer). 
     Combinations of these approaches may be used if desired. For example, display  14  may have a conductive overcoat  84  that serves as a shielding layer, a conductive layer such as layer  92  that is interposed between overcoat  84  and black mask  46  that serves as a shielding layer, a conductive black mask that serves as a shielding layer, and one or more layers  90  adjacent to PI layers  86  that serve as shielding layers, or may have any suitable combination of these shielding layers. 
     It can be challenging to deposit indium tin oxide uniformly at thicknesses that are sufficiently thin to form a shielding layer with a desired resistivity (i.e., a resistivity of between 10 M-ohm/square to 10 G-ohm/square). This is because indium tin oxide tends to form isolated areas (sometimes called islands) on a substrate when its thickness is reduced to obtain a resistivity of above 10 M-ohm/square. To ensure that a continuous film is formed for a shielding layer, the shielding layer may be formed using a two-step process. 
     This type of approach is illustrated in  FIG. 17 . Initially, a layer of a first material (material  92 ) is deposited on substrate  40  (i.e., on the surface of the color filter layer). The first material may be, for example, indium tin oxide. To ensure that the resistivity of shielding layer  46  is not too low, the first material is deposited in a thin layer (e.g., hundreds of angstroms thick or less). When indium tin oxide is used as the first material, the resulting deposited layer will be segregated into separate regions such as islands  92 . After the first layer has been deposited, a second layer of material (material  94 ) may be deposited. 
     The second layer of material serves as a bridging layer that electrically connects islands  92  to form a smooth continuous film for shielding layer  46 . The second layer of material may be formed from a conductive polymer, a metal oxide, a conductive ink, nanomaterials or metal particles in a polymer matrix, other materials, or combinations of these materials. 
     Although illustrated in the context of a shielding layer that is formed on color filter layer  40  in the  FIG. 16  example, a two-step process (or a three-step or more than three-step process) may be used when forming any shielding layer for display  14  if desired. 
     Shielding layer  46  may be formed by incorporating dopant into the surface of a substrate such as a glass layer. As shown in  FIG. 18 , for example, dopant (e.g., metal ions) may be implanted into the upper surface of glass substrate  96  using ion implantation (illustrated by arrows  98 ). Dopant may also be incorporated by diffusion (e.g., from a gas or a coating layer). By incorporating sufficient dopant, the top layer of substrate  96  may be provided with a desired resistivity (e.g., between 10 M-ohm/square to 10 G-ohm/square), whereas the remainder of substrate  96  may remain insulating. This allows the top layer of substrate  96  to serve as shielding layer  46 . Glass substrate  96  may be a portion of cover glass  18 , color filter  40 , a polarizer, a separate layer of material, or other suitable layers in display  14 . Shielding layer  46  may be about 1000 angstroms or less, 500 angstroms or less, 200 angstroms thick or less, or may be 100 angstroms thick or less (as examples). 
     Some transparent materials may be deposited in layers that have a suitable resistivity for forming shielding layer  46  (e.g., a resistivity of between 10 M-ohm/square to 10 G-ohm/square), but may not be as stable as desired. To ensure that shielding layer  46  is stable under a variety of environment conditions (e.g., over a wide range of humidity and pressure), one or more protective layers may be incorporated in shielding layer  46 . An example of this type of approach is shown in  FIG. 19 . 
     As shown in  FIG. 19 , shielding layer  46  may be formed from conductive layer  100  and protective layer  102 . Conductive layer  100  may be formed from a metal oxide (e.g., antimony oxide, tin oxide, zinc oxides, or other metal oxides) or other material for which it is desired to provide environmental protection. The resistivity of conductive layer  100  may be, for example, between 10 M-ohm/square and 10 G-ohm/square. In the example of  FIG. 19 , layer  100  has been formed on color filter layer  40 , but this is merely illustrative. Layer  100  may be formed at any suitable location within the stack of layers in display  14 . 
     Protective layer  102  may be formed on top of conductive layer  100  to seal layer  100  from the environment. This may improve the stability of shielding layer  46 . Layer  102  may be formed from silicon oxide, silicon nitride, silicon oxynitrides, or other suitable materials. The material of layer  102  may be insulating. To ensure that conductive structure  62  is able to form an electrical connection with conductive layer  100 , layer  102  may be deposited in direction  108  by sputtering through shadow mask  106 . Shadow mask  106  will block layer  102  from region  104 , thereby allowing conductive structure  62  to form an electrical connection between layer  100  and ground contact  56 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20100521
Publication Date: 20140408
Grant Date: 20140408
Priority Date: 20100521
Inventors: PARK YOUNG-BAE
XU MING
GE ZHIBING
CHEN CHENG
CHANG SHIH CHANG
GETTEMY SHAWN R.
WURZEL JOSHUA G.
ZHONG JOHN Z.
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133334", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/133334", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/13338", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0446", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 44972112