PATENT DOCUMENT

Publication Number: US-9329314-B2
Application Number: US-201213549311-A
Country: US
Kind Code: B2

Title: Touch screen display with transparent electrical shielding layer

Abstract:
A polarizer includes a polarizer component having a top surface and an opposite bottom surface. The bottom surface is configured to couple to a color filter layer for a liquid crystal display. The polarizer also includes a transparent conducting layer disposed over the top surface. The transparent conducting layer being configured to electrically shield the LCD from a touch panel. The polarizer further includes a coating layer disposed over the transparent conducting layer.

Claims:
What is claimed is: 
     
       1. A polarizer comprising:
 a polarizer component having a top surface and an opposite bottom surface, the bottom surface being configured to couple to a color filter layer for a liquid crystal display; 
 a transparent conducting layer disposed over the top surface of the polarizer component, the transparent conducting layer being configured to electrically shield the LCD from a touch panel; 
 a first conductive tape contacting the transparent conductive layer at a first position; 
 a second conductive tape contacting the transparent conductive layer at a different second position; and 
 a conductive bar configured to connect the first and second conductive tapes. 
 
     
     
       2. The polarizer of  claim 1 , wherein the transparent conducting layer comprises silver nano wire (AGNW) mesh. 
     
     
       3. The polarizer of  claim 1 , wherein the transparent conducting layer has a sheet resistance ranging from 5 ohm/sq to 600 ohm/sq. 
     
     
       4. The polarizer of  claim 3 , wherein the transparent conducting layer has a sheet resistance ranging from 5 ohm/sq to 150 ohm/sq. 
     
     
       5. The polarizer of  claim 1 , wherein the transparent conducting layer has a transmittance equal to or greater than 97%. 
     
     
       6. The polarizer of  claim 1 , wherein the transparent conducting layer has a reflectance equal to or less than 0.5%. 
     
     
       7. The polarizer of  claim 1 , wherein the transparent conducting layer has a haze equal to or less than 0.3%. 
     
     
       8. The polarizer of  claim 1 , wherein the polarizer component comprises:
 a first adhesive layer; 
 an optical film layer disposed over the adhesive layer, the optical film configured to polarize a light; 
 a second adhesive layer disposed over the optical film layer; and 
 a transparent glass layer disposed over the second adhesive layer. 
 
     
     
       9. The polarizer of  claim 8 , wherein the transparent glass layer comprises a material selected from a group consisting of TAC, COP, PET, and PMMA. 
     
     
       10. The polarizer of  claim 1 , further comprising a coating layer disposed over the transparent conductive layer. 
     
     
       11. An LCD device, the device comprising:
 a front polarizer; 
 a transparent conductive layer on a top surface of the front polarizer; 
 a color filter layer coupled to a bottom surface of the front polarizer; 
 an indium-tin oxide layer between the color filter layer and the bottom surface of the front polarizer; 
 a rear polarizer at a bottom of a stack of the LCD; and 
 a liquid crystal layer between the rear polarizer and the color filter layer. 
 
     
     
       12. The LCD device of  claim 11 , wherein the transparent conductive layer has a substantially rectangular shape. 
     
     
       13. The LCD device of  claim 12 , the device comprising:
 a first conductive tape at a first corner of the transparent conductive layer; 
 a second conductive tape at a second corner of the transparent conductive layer, the second corner being the nearest corner to the first corner; and 
 a conductive bar configured to connect the first and second conductive tapes. 
 
     
     
       14. The LCD device of  claim 13 , further comprising a third conductive tape at a third corner of the transparent layer. 
     
     
       15. The LCD device of  claim 14 , further comprising a fourth conductive tape at a fourth corner of the transparent layer. 
     
     
       16. The LCD device of  claim 15 , further comprising a conductive bar configured to connect the third and fourth conductive tape. 
     
     
       17. The LCD device of  claim 13 , wherein each conductive tape comprises copper. 
     
     
       18. The LCD device of  claim 13 , wherein the conductive bar comprises silver. 
     
     
       19. The LCD device of  claim 11 , wherein the transparent conducting layer comprises silver nano wire (AGNW) mesh. 
     
     
       20. The LCD device of  claim 11 , further comprising a coating layer disposed over the transparent conductive layer, the coating layer being selected from a group consisting of anti-reflection (AR) coating, AG coating, hard coating, and anti-smudge coating. 
     
     
       21. A portable electronic device, the device comprising:
 a touch panel; 
 an LCD (liquid crystal display, wherein the LCD comprises:
 a front polarizer coupled to a bottom surface of the touch panel; 
 a transparent conductive layer on a top surface of the front polarizer; 
 a color filter layer coupled to a bottom surface of the front polarizer; 
 an indium-tin oxide layer between the color filter layer and the bottom surface of the front polarizer; 
 a rear polarizer at a bottom of a stack of the LCD; and 
 a liquid crystal layer between the rear polarizer and the color filter layer. 
 
 
     
     
       22. The portable electronic device of  claim 21 , further comprising a cover glass layer on a top surface of the touch panel. 
     
     
       23. The portable electronic device of  claim 21 , further comprising a first coating layer on a top surface of the transparent conductive layer; a second coating layer on the bottom surface of the touch panel; and an air gap between the touch panel and the LCD. 
     
     
       24. The portable electronic device of  claim 21 , wherein the transparent conductive layer has a substantially rectangular shape. 
     
     
       25. The portable electronic device of  claim 24 , the device comprising:
 a first conductive tape at a first corner of the transparent conductive layer; 
 a second conductive tape at a second corner of the transparent conductive layer, the second corner being the nearest corner to the first corner; and 
 a conductive bar configured to connect the first and second conductive tapes. 
 
     
     
       26. The portable electronic device of  claim 25 , further comprising a third conductive tape at a third corner of the transparent layer. 
     
     
       27. The portable electronic device of  claim 26 , further comprising a fourth conductive tape at a fourth corner of the transparent layer. 
     
     
       28. The portable electronic device of  claim 27 , further comprising a conductive bar configured to connect the third and fourth conductive tape. 
     
     
       29. The portable electronic device of  claim 21 , wherein the transparent conducting layer comprises silver nano wire (AGNW) mesh. 
     
     
       30. A portable electronic device, the device comprising:
 a touch panel; 
 an LCD (liquid crystal display, wherein the LCD comprises:
 a front polarizer coupled to a bottom surface of the touch panel; 
 a color filter layer coupled to a bottom surface of the front polarizer; 
 a transparent conductive layer on a top surface of the color filter and coupled between the front polarizer and the color filter; 
 a rear polarizer at a bottom of a stack of the LCD; and 
 a liquid crystal layer between the rear polarizer and the color filter layer. 
 
 
     
     
       31. The portable electronic device of  claim 30 , wherein the transparent conductive layer has a substantially rectangular shape. 
     
     
       32. The portable electronic device of  claim 31 , the device comprising:
 a first conductive tape at a first corner of the transparent conductive layer; 
 a second conductive tape at a second corner of the transparent conductive layer, the second corner being the nearest corner to the first corner; and 
 a conductive bar configured to connect the first and second conductive tapes. 
 
     
     
       33. The portable electronic device of  claim 32 , further comprising a third conductive tape at a third corner of the transparent layer. 
     
     
       34. The portable electronic device of  claim 33 , further comprising a fourth conductive tape at a fourth corner of the transparent layer. 
     
     
       35. The portable electronic device of  claim 34 , further comprising a conductive bar configured to connect the third and fourth conductive tape. 
     
     
       36. The portable electronic device of  claim 30 , wherein the transparent conducting layer comprises silver nano wire (AGNW) mesh. 
     
     
       37. The LCD device of  claim 11 , the device comprising:
 a first conductive tape contacting the transparent conductive layer at a first position; 
 a second conductive tape contacting the transparent conductive layer at a different second location; and 
 a conductive bar configured to connect the first and second conductive tapes. 
 
     
     
       38. The portable electronic device of  claim 21 , the device comprising:
 a first conductive tape contacting the transparent conductive layer at a first position; 
 a second conductive tape contacting the transparent conductive layer at a different second location; and 
 a conductive bar configured to connect the first and second conductive tapes. 
 
     
     
       39. A polarizer comprising:
 a polarizer component having a top surface and an opposite bottom surface, the bottom surface being configured to couple to a color filter layer for a liquid crystal display; 
 a transparent conductive layer disposed over the top surface of the polarizer component; and 
 at least one conductive bar each contacting a portion of the transparent conducting layer adjacent a respective edge of the transparent conducting layer. 
 
     
     
       40. The polarizer of  claim 10 , wherein the coating layer is selected from a group consisting of anti-reflection (AR) coating, anti-glare (AG) coating, anti-fingerprint (AF), hard coating, and anti-smudge coating.

Description:
TECHNICAL FIELD 
     The present invention generally relates to touch screen display that includes an in-plane switching (IPS) liquid crystal display (LCD) and a touch panel. More specifically, the invention relates to the touch screen display with a transparent shielding layer to reduce noise coupled from the IPS LCD into the touch panel. 
     BACKGROUND 
     In-plane switching (IPS) LCD uses thin film transistor (TFT) technology to improve image quality. The IPS LCD delivers bright pictures with very good color consistency at a wide viewing angle. IPS LCDs are used in television sets, computer monitors, mobile phones, handheld systems, personal digital assistants, navigation systems, projectors, and many other devices. 
     An IPS LCD includes an array of pixels for displaying images. The pixels are addressed in rows and columns, reducing the connection count from millions for each individual pixel to thousands. The column and row wires attach to transistor switches, one transistor for each pixel. The one-way current passing characteristic of the transistor prevents the charge applied to the pixel from draining between refreshes to the display image. 
     In an IPS LCD, the liquid crystal extends horizontally across the panel and essentially provides a wide viewing angle, fast response speed, and a simple pixel structure. The IPS LCD employs pairs of electrodes at the sides of each cell, applying an electric field horizontally through the material. This approach keeps the liquid crystals parallel to the front of the panel, thereby increasing the viewing angle. 
       FIG. 1A  illustrates a perspective view of an electronic device, such as an IPAD. The electronic device includes a touch screen display  100  enclosed by a housing  138 . The touch screen display  100  includes a touch panel  102  on a front and an LCD display behind the touch panel  102 , although alternative embodiments may employ an OLED layer instead of an LCD. A cross-section is taken along line  2 - 2  in  FIG. 1A .  FIG. 1B  illustrates a simplified cross-section diagram for the touch screen display of  FIG. 1A . Touch screen display  100  includes a touch panel  102  above an IPS LCD  104 . The touch screen display  100  may have an air gap  106  between the touch panel  102  and the IPS LCD  104 . Alternatively, in a full lamination design, an optically clear adhesive (OCA) may connect the touch panel and the LCD such that there is no air gap between the touch panel and display. 
       FIG. 1C  illustrates a cross-section of an embodiment of an IPS LCD of  FIG. 1B . The IPS LCD  104  includes a front polarizer  118 , a rear polarizer  108 , and liquid crystal layer  112  between the front and rear polarizers. The IPS LCD  104  also includes TFT layer arranged between the liquid crystal layer  112  and the rear polarizer  108 . The IPS LCD  104  further includes color filter (CF) layer or glass  114  arranged between the front polarizer  118  and the liquid crystal layer  112 . The IPS LCD  104  further includes a backlight  130  configured to provide white light to the rear polarizer  108 . 
     The IPS LCD usually does not have common electrodes on the color filter (CF) glass, and so is vulnerable to electrostatic discharge (ESD). A conducting coating, for example, indium-tin oxide (ITO) coating, is often put on the top surface of the CF glass to help reduce vulnerability to ESD. 
     The IPS LCD  104  may also include an ITO coating  116  on a top surface of the CF glass  114 , such that the front polarizer  118  is disposed over the ITO coating  116 . The ITO coating  116  also provides shielding to the touch panel  102  from the TFT layer  110 . The front polarizer  118  may include an adhesive layer  136 , one or more optical films and/or compensation films  134 , a polyvinyl alcohol (PVA) with an iodine doping layer  126 , and a plastic film  128 , such as triacetycellulose (TAC), cyclo-olefin polymer (COP), poly(ethylene terephthalate) (PET) or Poly(methyl methacrylate) (PMMA) film. The PVA absorbs light forming particular polarizers. 
     Generally, noise may be coupled from the IPS LCD  104  to the touch panel  102 . When the stackup of the touch panel and the IPS LCD becomes thinner, the noise in the touch panel may increase. In order to provide better shielding, the ITO coating may need to be thicker. However, optical transmittance may be reduced as a result of increasing thickness of the ITO coating. Acquiring both lower noise (or higher shielding) and higher light transmittance (or lower reflection) becomes challenges for thinner touch screen displays. 
     There may be a trade-off between aspects of product design and touch performance. Basically, it may be desirable not only to reduce product thickness, which may result in the touch panel and the LCD being closer to each other, but also to reduce light reflection from the front of the display. However, touch screen performance and operation may be affected by electrical noise. 
     There remains a need for developing techniques to resolve the above issues to meet the customer needs of new touch screen display products. 
     SUMMARY 
     Embodiments described herein may provide an IPS LCD with a transparent conducting layer on a top surface of a front polarizer of the LCD. The conducting layer may include microscopic metal meshes, such as silver nano-wires (AGNW). Compared to the conventional display, the IPS LCD with a metal mesh coated front polarizer may improve display transmittance and reduce light reflection, while still providing adequate electrical shielding for a capacitative touch panel. The improved light transmittance may enable better power efficiency for the LCD, because less power would be required for the backlight of the LCD due to higher transmittance. The IPS LCD may also be thinner than the conventional display, due to replacement of the conventional thick ITO with a transparent AGNW mesh. The IPS LCD may also reduce the manufacturing complexity of a IPS-type of display by removing one post-cell process, as well as reducing the total reflectivity of the display. 
     In one embodiment, a polarizer includes a polarizer component having a top surface and an opposite bottom surface. The bottom surface is configured to couple to a color filter layer for a liquid crystal display. The polarizer also includes a transparent conducting layer disposed over the top surface. The transparent conducting layer being configured to electrically shield the LCD from a touch panel. The polarizer further includes a coating layer disposed over the transparent conducting layer. 
     In another embodiment, an LCD device is provided. The LCD device includes a front polarizer and a transparent conductive layer on a top surface of the front polarizer. The LCD device also includes a color filter layer coupled to a bottom surface of the front polarizer and a rear polarizer at a bottom of a stack of the LCD. The LCD device further includes a liquid crystal layer between the rear polarizer and the color filter layer. 
     In yet another embodiment, a portable electronic device is provided. The electronic device includes a touch panel and an LCD (liquid crystal display. The LCD includes a front polarizer coupled to a bottom surface of the touch panel, a transparent conductive layer on a top surface of the front polarizer, and a color filter layer coupled to a bottom surface of the front polarizer. The LCD also includes a rear polarizer at a bottom of a stack of the LCD and a liquid crystal layer between the rear polarizer and the color filter layer. 
     In still yet another embodiment, a portable electronic device is provided. The device includes a touch panel and an LCD (liquid crystal display. The LCD includes a front polarizer coupled to a bottom surface of the touch panel, and a color filter layer coupled to a bottom surface of the front polarizer. The LCD also includes a transparent conductive layer on a top surface of the color filter and coupled between the front polarizer and the color filter. The LCD further includes a rear polarizer at a bottom of a stack of the LCD and a liquid crystal layer between the rear polarizer and the color filter layer. 
     Additional embodiments and features are set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the specification or may be learned by the practice of the invention. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings, which forms a part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  illustrates a perspective view of an IPAD. 
         FIG. 1B  illustrates a simplified cross-sectional diagram for a touch screen display (Prior Art). 
         FIG. 1C  illustrates a cross-section of conventional IPS LCD (Prior Art). 
         FIG. 2A  illustrates a stack of an IPS LCD with a transparent conducting layer in a first embodiment. 
         FIG. 2B  illustrates a stack of an IPS LCD with a transparent conducting layer in a second embodiment. 
         FIG. 3A  illustrates a first example touch screen display with a transparent conducting layer as shown in  FIG. 2A or 2B . 
         FIG. 3B  illustrates a second example touch screen display with a transparent conducting layer as shown in  FIG. 2A or 2B . 
         FIG. 4  illustrates sample light reflections from various layers of an IPS LCD with an ITO coating on top of a CF glass. 
         FIG. 5  illustrates a sample total reflection contributed by various reflections from different coatings of area  1  of  FIG. 4 . 
         FIG. 6  illustrates a sample total reflection contributed by various reflections from different coatings of area  2  of  FIG. 4 . 
         FIG. 7  is a simplified system diagram for a touch screen display in an embodiment. 
         FIG. 8A  illustrates LCM noise and the LCM noise coupled into the sense amplifier for the touch screen display of  FIG. 7 . 
         FIG. 8B  shows spectra for the LCM noise of  FIG. 8A . 
         FIG. 9A  illustrates a top view of a first grounding configuration of a front polarizer with ITO as shown in  FIG. 4 . 
         FIG. 9B  illustrates a top view of a second grounding configuration of a front polarizer without any conducting layer and/or grounding. 
         FIG. 9C  illustrates a top view of a third grounding configuration of a front polarizer with AGNW as shown in  FIG. 2A or 2B . 
         FIG. 9D  illustrates a comparison of sample noises of the grounding configurations of  FIGS. 9A-9C . 
         FIG. 10A  illustrates a top view of a grounding configuration for a touch screen display with AGNW as shown in  FIG. 2A or 2B . 
         FIG. 10B  illustrates sample noise curves for the grounding configurations of  FIG. 10A  and  FIG. 9B . 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure may be understood by reference to the following detailed description, taken in conjunction with the drawings as described below. It is noted that, for purposes of illustrative clarity, certain elements in various drawings may not be drawn to scale. 
     The present disclosure provides a thin conducting layer, such as silver nano wire (AGNW) mesh, to shield display noise coupled from a TFT layer of the LCD into a touch panel. The thin conducting layer may be placed at a different location than a conventional ITO layer in a typical IPS LCD. For example, the AGNW may be placed on the top surface of a front polarizer of a LCD. In contrast, the conventional ITO layer is typically placed on a top of a color filter (CF) glass or layer. The present disclosure potentially enables a thinner product design to meet both the shielding requirement and light transmission requirement. 
       FIG. 2A  illustrates a stack of an IPS LCD with a transparent conducting layer in a first embodiment. An IPS LCD  200 A includes a metal mesh coated front polarizer  218  formed from a transparent conducting layer  220 , which may be silver nano wire (AGNW), on the top of a polarizer  118 . Thin layers, such as hard coating, anti-glare (AG) coating, anti-fingerprint (AF) coating, or/and anti-reflection (AR) coating  232 , may be placed on top of the AGNW to meet optical and reliability performance goals. The AGNW  220  may be a mesh. The mesh may be embedded in a dielectric matrix or a polymer matrix to provide more light transmission through the polarizer  218  than a solid film. The nano wires may have a few nanometers in diameter and tens of microns in length. The nano wires create a mesh that may not substantially degrade the light transmittance. A size of the mesh varies with the density of the nano wires in the polymer matrix. When the density of the nano wires increases, the sheet resistance of the AGNW coating may decrease and the mesh size may also decrease. 
     The polarizer  118  may include an adhesive layer  236 , one or more optical films  234 , a PVA with iodine layer  226 , and a plastic film  228 , such as TAC, COP, PET, or PMMA film among others. The plastic film  228  is a base film that protects the polarizer  118 . 
     The IPS LCD  200 A also includes an LCD  204 . The LCD may have a backlight  230 , a rear polarizer  208 , a TFT layer  210 , liquid crystal layer  212 , and a CF layer or glass  214 , similar to the conventional IPS LCD  104 . However, the IPS LCD  200 A does not include an ITO coating in this embodiment. The backlight  230  is configured to provide white light to the rear polarizer  208 . For example, the backlight  230  may include a blue LED emitting blue light and red and green phosphors that emit red and green light when excited by the blue light from the blue LED. When all emitted colors are mixed, a white back light may be produced. Alternatively, the backlight LED  230  may include a blue LED emitting blue light and a yellow phosphor that emit yellow light when excited by blue light from the blue LED, again resulting in a white back light upon mixing. In a further example, the backlight  230  may also include a blue LED and red and green quantum dots to generate a white back light. 
     The LCD  204  also includes electrodes (not shown). The electrodes may be combined with the TFT layer. Each pixel of the LCD  204  has a corresponding transistor or switch for controlling voltage applied to the liquid crystal. The liquid crystal layer  212  may include rod-shaped polymers that naturally form into thin layers with a natural alignment. The electrodes may be made of a transparent conductor, such as an indium-tin-oxide material (commonly referred to as “ITO”). The two polarizers  218  and  208  are set at right angles. Normally, the LCD  204  may be opaque. When a voltage is applied across the liquid crystal layer  212 , the rod-shaped polymers align with the electric field and untwist. The voltage controls the light output from the front polarizer  218 . For example, when a voltage is applied to the liquid crystal layer  212 , the liquid crystal layer  212  rotates so that there is light output from the front polarizer  218 . 
     Transistors in the TFT layer  210  may take up only a small fraction of the area of each pixel; the rest of the silicon film may be etched away or essentially removed to allow light to pass through. Polycrystalline silicon may sometimes be used in displays requiring higher TFT performance. However, amorphous silicon-based TFTs are the most common technology due to its lower production cost. The silicon layer for the TFT-LCD is typically deposited over a glass substrate by using a PECVD process. 
       FIG. 2B  shows that a thin ITO coating  216  may be included between the CF glass  214  and the front polarizer  218  in the IPS LCD  200 B in a second embodiment. In this embodiment, the thin ITO coating  216  may be placed on the top of the CF glass  214 . The ITO coating  216  may help with reducing ESD during processing. The ESD may be generated when stacking the front polarizer with the CF glass  214 . The thickness of the ITO coating  216  may be in a range of 10 nm to 30 nm so that the light transmission remains relatively high. Alternatively, an anti-static coating may be added on top of the CF glass  214  during integrating the front polarizer and the CF glass  214  to help reduce ESD. The anti-static coating may be removed prior to stacking the front polarizer on top of the CF glass  214 . 
     In this particular embodiment, the AGNW coating  220  may be placed on a front surface or top surface of the front polarizer  218 , rather than being placed between the front and rear polarizers. The AGNW may degrade a contrast ratio of the LCD, due to depolarization properties of the AGNW. The contrast ratio of a display refers to the ratio of the brightest white to the darkest black that the display may produce. Typically, a higher contrast ratio is associated with better image quality, such as improved clarity and/or brightness. “Light depolarization,” as used herein, refers to the conversion of polarized light into unpolarized light. AGNW has a negative refraction index, which may depolarize light passing therethrough and so negatively impact the display&#39;s contrast ratio. By placing the AGNW coating  220  on the top surface of the front polarizer  218 , such depolarization may be minimized. 
     The AGNW  220  may be pre-coated onto the transparent plastic film  228 , such as triacetycellulose (TAC), cyclo olefin polymer (COP), Poly(methyl methacrylate) (PMMA) or poly(ethylene terephthalate) (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), glass, reinforced glass, polycarbonate (PC), or mixtures of the foregoing thereof. The AGNW coated plastic film may be laminated with polyvinyl alcohol (PVA) which may be iodine doped and/or other optical films or compensation films for the polarizer  218 . The optical films or compensation films may compensate for phase difference. The doped PVA essentially absorbs light having particular directions. The AGNW  220  on the outer surface of the front polarizer  218  also does not de-polarize the light between the crossed polarizers of the LCD. 
     The AGNW  220  may have a sheet resistance ranging from 5 ohm/sq to 600 ohm/sq. The conducting layer, for example, the AGNW  220  may have sheet resistance less than 300 ohm/sq, or less than 150 ohm/sq. The AGNW  220  may have a high light transmittance (e.g. greater than 97% in the stack), a low light reflectance (e.g. less than 0.5%), and a low haze (e.g. less than 0.3%). In a particular embodiment, the AGNW coating  220  may have a light transmittance of 99% at an approximately 150 ohm/sq sheet resistance. In contrast, ITO coatings typically have a sheet resistance ranging from 500 to 1000 ohm/sq for the same transmittance. 
     Although the above example uses AGNW, it will be appreciated by those skilled in the art that the transparent conductive layer may also be nano wires including other metals, such as gold (Au), palladium (Pd), platinum (Pt), nickel (Ni), copper (copper), aluminum (Al), tin (Sn), and titanium (Ti) or a combination of these metals. 
       FIG. 3A  illustrates a first example touch screen display with a transparent conducting layer as shown in  FIG. 2A . Touch screen display  300 A includes a front polarizer  218  that has a transparent conducting layer or AGNW  220  on the top of a conventional front polarizer  118 . Touch screen display  300 A may also include an anti-reflection (AR) coating  312  on the top of the AGNW  220 . Touch screen display  300 A may further include a cover glass  302  bonded to a top surface of a touch panel  306  using a first adhesive  304 . Touch screen display  300 A may also include a plastic film (e.g. TAC)  310  bonded to a bottom surface of the touch panel  306  using a second adhesive  308 . The first adhesive  304  and the second adhesive  308  may be acrylic, polyurethane, epoxy and the like. The adhesives may also be double side adhesive tapes. Touch screen display  300 A may further include an anti-reflective (AR) coating  312 A on a bottom surface of the plastic film (e.g. TAC)  310 .  FIGS. 3A and 3B  show housing  138  coupled to the cover glass  302 . Note that there may be a gap between the housing  138  and the edges of the touch panel  306  and the LCD  204 . Alternatively, the housing  138  may contact the edges of the touch panel and the LCD  204 . 
     Touch screen display  300 A may also include an air gap  316  between two opposite AR coatings, i.e. the AR coating  312 A on the bottom surface of the plastic film  310  and the AR coating  312 B on the top of the transparent conducting layer or AGNW  220 . The AR coatings  312 A and  312 B may help reduce the reflections due to the air gap  316 . A reflection may generally occur at an interface between two materials or two layers with different refractive indexes. The reflection typically increases with the refractive index difference between the two materials. Air has a large difference in refractive index from the plastic film (e.g. TAC)  310 . The AR coating has a refractive index that is in between air and the plastic film, and so may reduce reflections otherwise caused at the air-film junction. The LCD is similar to  200 A or  200 B, as shown in  FIG. 2A  or  FIG. 2B  and described above. 
     It will be appreciated by those skilled in the art that TAC  310  may be replaced with another transparent material, such as cyclo olefin polymer (COP), Poly(methyl methacrylate) (PMMA) or poly(ethylene terephthalate) (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), glass, reinforced glass, polycarbonate (PC), or a mixture thereof. 
       FIG. 3B  illustrates a second example touch screen display with a transparent conducting layer as shown in  FIG. 2A . Touch screen display  300 B includes a cover glass  302 , a first adhesive layer  304 , a touch panel  306 , and a second adhesive layer  308 , similar to touch screen display  300 A. Unlike touch screen display  300 A, there is no air gap in this embodiment such that the second adhesive layer  308  may be placed on the top of the transparent conducting layer (e.g. AGNW)  220 , which is in turn placed on the top surface of the front polarizer  218 . Note that there are no anti-reflection coatings  312 A and  312 B on either the bottom of the adhesive layer  308  or the top of the AGNW  220 . The TAC  310  is also absent in  FIG. 3B  such that the second adhesive layer  308  may directly bond to the AGNW  220 . 
     It is known in the art that the ITO coating has a very high refractive index. Thus, the ITO may contribute a large portion to a total reflection from the front polarizer or the display due to a large difference between the refractive indexes of the ITO and the polarizer and/or display. 
       FIG. 4  illustrates sample light reflections from various layers of an IPS LCD with a relatively thick ITO coating.  FIG. 4  illustrates a similar stack to  FIG. 10 . The ITO coating  416  is similar to the conventional ITO coating  116 , but has a larger thickness than the conventional ITO coating  116 . There may be three main reflections from different surfaces or interfaces. Ray  402  illustrates reflection from a top surface of an anti-reflection (AR) layer  422 . Ray  404  illustrates reflection from the interface between the CF glass  214  and the ITO coating  416 . 
     The CF glass  214  includes a number of color filters  420 B arranged in subpixels, such as a red color filter, a green color filter, and a blue color filter. The red, green, and blue filters transmit a light having a specific wavelength of white light incident from the backlight source  230 . The filters  420 B transmit wavelengths of light corresponding to the color of each filter, and absorb other wavelengths. Accordingly, a light loss is generated in the liquid crystal display by the color filters. Each color filter is separated from another color filter by a black matrix  420 A, which includes ink that absorbs all color, acting like a black body. 
     A large portion of the black matrix  420 A is near an outer end of the CF glass  214 , while the CF filters  420 B and a small portion of the black matrix  420 A between the CF filters  420 B are in the middle portion of the CF glass  214 . 
     Turning to the left side of  FIG. 4 , ray  406  illustrates reflection from the interface between the black matrix  420 A of the CF glass  214  and liquid crystal layer  212 . Now, turning to the right side of  FIG. 4 , ray  408  illustrates reflection from the interface between the color filters  420 B of the CF glass  214  and the liquid crystal layer  212 . 
     The ITO contributes to a large portion of the total reflection of the polarizer. When the ITO becomes thicker, the reflection of the ITO becomes greater. Based upon modeling, reflections are estimated and exemplary results are presented below. 
     In an alternative embodiment, the ITO may be replaced by a transparent conductive layer, such as an AGNW layer, i.e. the AGNW layer on top of the CF glass  214 . The AGNW layer may provide better light transmittance, low reflectance than the ITO while having a low sheet resistance to help shield the noise from the TFT to the touch panel. Unlike the embodiments as shown in  FIGS. 2A-2B, 3A-3B , the image quality, such as clarity and/or brightness, may depend upon the AGNW depolarization properties. 
       FIG. 5  illustrates a sample total reflection contributed by various reflections from different coatings of area  1  of  FIG. 4 . As discussed, earlier, the reflection of the ITO  416  varies with thickness or sheet resistance of the ITO. By using the sheet resistance of about 500 to 600 ohm/sq for the ITO, its reflection is estimated. This sheet resistance may be adequate for a relatively thick product, but not low enough for thinner display products. In a particular embodiment, a total reflection  500 A includes about 65% reflection  502  from the ITO coating  416 , about 10% reflection  504  from the AR coating  422 , about 18% reflection from the black matrix  420 A, and about 7% reflection from the CF filters  420 B. Accordingly, the ITO reflection constitutes a major portion of the total reflection  500 A. 
     As discussed above, the color filters  420 B and the black matrix  420 A are in the middle portion of the display so that a combined reflection from the black matrix and the color filters may represent the reflection for a product of area  2  of  FIG. 4 .  FIG. 6  illustrates a sample total reflection contributed by various reflections from different coatings of area  2  of  FIG. 4 . The reflection is obtained based upon modeling using the sheet resistance of about 500 to 600 ohm/sq for the ITO  416 . The total reflection includes about 46% reflection from the ITO coating  416 , about 33% reflection from the top AR coating  422 , and about 33% reflection from a combination of black matrix  420 A and CF filters  420 B. Note that the reflection from the ITO coating  416  is still the largest contributor to the total reflection. 
     Generally, transmittance increases with sheet resistance for the ITO. The sheet resistance increases with decreasing thickness of the ITO  416 , while the transmittance decreases with the increasing thickness due to light absorption in the ITO coating. In one embodiment, the ITO coating may be about 50 nm thick and have a sheet resistance of about 150 ohm/sq and a light transmittance of about 90%. In another embodiment, the ITO coating may be 20 nm thick and have a sheet resistance of about 300 ohm/sq and a light transmittance of about 92%. In a further embodiment, the ITO coating may be 15 nm thick and have a sheet resistance of about 600 ohm/sq and a light transmittance of about 97%. These values may vary with deposition process. 
     In contrast, the transmittance for the AGNW may not vary substantially with the sheet resistance, and may be above 97% for all the sheet resistances. Compared to the ITO, the AGNW may be thinner, for example about 10 nm or less, which enables to deliver thinner touch screen displays. The AGNW may be embedded in a polymer matrix which may be precoated on a plastic film, such as a TAC film. The AGNW with the polymer matrix may have a thickness less than 1 μm. 
     The AGNW may have less than 0.5% reflectance, which is much lower than the ITO. The reflectance for the AGNW may have less dependence upon the sheet resistance. In contrast, the reflectance for the ITO may increase with decreasing sheet resistance or increasing thickness, as the transmittance decreases with the increasing thickness due to absorption. Reflectance for the ITO under polarizer, i.e. for reflections as shown in  FIG. 4  by Ray  404 , may be lower than the ITO, because the reflections may be reduced by the polarizer  218  on top of the ITO or AGNW. 
     In a particular embodiment, the haze may be below 0.5% or even below 0.3%. The reflectance for the AGNW may be below 0.5% or even 0.3%. The transmittance may be above 97%. An extra margin on the shielding to display capacitive noise may be achieved by adding the AGNW  220  on the top of the front polarizer and removal of the ITO coating  416  or reducing the ITO coating  416  to a minimum thickness. 
     Based upon the above results, it is noted that the ITO&#39;s optical properties are not adequate when the shielding requirement is met. Generally, lower sheet resistance provides more effective shielding. Less than 150 ohm/sq sheet resistance may be needed for sufficient shielding to noise for thinner display products. This requires the ITO layer to be relatively thick, such as about 50 nm thick or larger thickness, especially for ITO deposited at lower temperature, such as lower than 150° C. As a result, the thick ITO layer is highly reflective. The thick ITO layer  416  may also absorb blue light and transmit light in more yellow color. The loss of light transmittance may also be as high as 8% to achieve 150 ohm/sq sheet resistance. Practically, the ITO sheet resistance may be kept at a higher level as a trade-off between touch performance, display power, and display optical performance. 
     As demonstrated above, the thinner conducting layer (such as AGNW) may have both a low sheet resistance, such as about 150 ohm/sq or lower, and a very high transmittance, such as about 97% or higher, low reflectance, such as about 0.5% or lower, and a low haze, such as about 0.3% or lower. The AGNW  220  may be about 10 nm thick or even thinner. The AGNW  220  is much better than the conventional ITO layer  416 , because the AGNW is thinner, less reflective, and has higher transmission than the ITO, while having a low sheet resistance. This low sheet resistance provides an extra margin which helps tolerate a higher level of capacitive noise from the display, such that more power saving can be achieved. 
       FIG. 7  is a simplified system diagram for a touch screen display in an embodiment. System  700  includes an LCD  706 , sense electrode  702  and drive electrode  704  for a touch panel (not shown), and a sense amplifier  708 . The touch panel may capacitively sense touch and may have a capacitance C sig  between a sense electrode  702  and a drive electrode  704 . The C sig  may represent a touch signal from a user.  FIG. 7  depicts an exemplary touch node, such as one defined by an intersection of sense electrode  702  and drive electrode  704 . The touch panel may include a number of such nodes. In an alternative embodiment, the node may be defined by other geometries than the intersection. The sense amplifier  708  is an exemplary receiving channel circuitry for the touch panel, which senses the total signal transmitted onto the drive electrode  704  through C sig . 
     A typical active matrix LCD is switched line-by-line, at a line frequency ranging from kHz to MHz. This switching electrical field and its harmonics may be capacitively coupled into sense electrode  702  and drive electrode  704 , which causes inaccurate touch sensing, or total disfunction. The liquid crystal module (LCM) noise from the TFT and the LCM noise coupled into the sense amplifier  708  may be measured or monitored by an oscilloscope. The LCM noise may be coupled by a capacitance C toLCM  existing between the IPS LCD  104  and the touch panel  102 . The sense electrode  702  may coupled to the sense amplifier  708 , which may include an input resistor with an input resistance at least one feedback resistor with a feedback resistance R FB , a feedback capacitor with a feedback capacitance C FB , and operational amplifier  710  in some embodiment. The sense amplifier  708 .  FIG. 7  shows the general case when both resistive and capacitive feedback elements are utilized. The signal is coupled into the operational amplifier  710  as an inverting input. The non-inverting input to the operational amplifier  710  may be coupled to ground or a reference voltage. 
       FIG. 8A  illustrates sample LCM noise from the LCD and the LCM noise coupled into the sense amplifier  708  of  FIG. 7 . The ITO coating is connected to a testing equipment ground. The sheet resistance of the ITO coating varies with the touch panel, and is normally in the range of 400 ohm/sq to 700 ohm/sq. As shown, trace  802  for LCM noise coupled into the sense amplifier  708  has similar noise patterns to trace  804  for LCM noise generated from the TFT source.  FIG. 8B  shows spectra for LCM noise of  FIG. 8A . As shown, the LCM noise may be 0.3 mV rms  in the frequency ranging from 100 kHz to 500 kHz. This is in the same range as the line frequency range. The noise may be much higher than the exemplary 0.3 mV rms , depending upon measurement conditions, the touch panel and display. The noise may be high enough to interfere the drive and thus may need to be reduced. 
     Proper grounding may help reduce the noise. In a particular embodiment, the polarizer may serve as an effective noise shielding layer and may provide ESD protection. The noise may be reduced by use of conductive tapes attached to a conductive layer such as ITO or AGNW. The conductive tapes may include copper. The noise may be further reduced by varying the attachment locations of the copper tapes to the AGNW or ITO. 
       FIG. 9A  illustrates a top view of a first sample grounding configuration of a front polarizer with an ITO as shown in  FIG. 4 . Grounding configuration  900 A includes an ITO layer  908  under a polarizer  912  for grounding. In a particular embodiment, the ITO layer  908  may be on the outer surface of the CF glass of the LCD, as shown in  FIG. 4 . The polarizer  912  and the ITO layer  908  are in a substantially rectangular shape. The ITO layer  908  extends outwardly from the polarizer  912  from each side of the rectangle. In this configuration, a conductive tape  910  may contact the ITO layer  908  along four edges of the ITO layer  908 . 
       FIG. 9B  illustrates a top view of a second sample grounding configuration of a front polarizer. Grounding configuration  900 B removes the ITO layer  910 , and thus has no need for the copper tape. Glass  914  covers the polarizer  912 . This is a configuration without any grounding. 
       FIG. 9C  illustrates a top view of a third sample grounding configuration of a front polarizer with an AGNW mesh or an AGNW polarizer as shown in  FIG. 2A or 2B . Configuration  900 C includes an AGNW polarizer  916 , which is in a substantially rectangular shape. The AGNW may be placed on the outer surface of the front polarizer so that the AGNW may be easily grounded. Conductive tapes  920 A-D, such as copper tapes, may be placed at the four corners and on top of the AGNW polarizer  916  to contact the AGNW on the outer surface of the polarizer. Although reference is generally made herein to copper tape, it should be appreciated that any suitable conductive tape may be used. 
     Two conductive bars  918 A and  918 B may contact two opposite edges of the AGNW polarizer  916 . For example, conductive bar  918 A may contact an edge of the AGNW polarizer  916  and may connect two conductive tapes  920 A and  920 D at two neighboring corners. Another conductive bar  918 B may contact an opposite edge of the AGNW polarizer  916  and may connect two conductive tapes  920 B and  920 C at two other neighboring corners. The conductive bars  918 A and  918 B may include or be formed from a conductive paste, such as silver paste. The AGNW is coated on the polarizer and thus has the same size as the polarizer 
     The grounding configurations  900 A,  900 B, and  900 C have different grounding effects. To compare the grounding effects, noise may be measured with a spectrum analyzer, for example, Tektronix 3308A Spectrum Analyzer.  FIG. 9D  illustrates comparisons of noise from a polarizer with an ITO (grounding configuration  900 A), an AGNW polarizer (grounding configuration  900 C), and a polarizer without grounding (grounding configuration  900 B) in an embodiment. Note that curve  902  for the polarizer without ITO or AGNW shows the highest noise level, which generally is due to the fact that no grounding was provided to the polarizer. Curve  904  for the polarizer with an ITO on the outer surface of the CF glass reveals higher noise than the AGNW polarizer, but lower noise that the polarizer without ITO. As shown, the ITO coating on the outer-surface of CF glass provides a certain level of shielding to the display capacitive noise, especially when properly grounded. Curve  906  for the AGNW polarizer illustrates the lowest noise level, generally because the AGNW may have a lower sheet resistance than the ITO at a relatively thin coating, such as 10 nm thick. 
       FIG. 10A  illustrates a top view of a grounding configuration for the IPS LCD  200  with AGNW as shown in  FIGS. 2A and 2B . As shown, a glass layer  1014  is at the bottom of an AGNW coating  220  which is below the active area of touch panel  1008 . The glass layer  1014  has a larger area than the active area of the touch panel  1008 . The AGNW coating  220  and the active area of the touch panel  1008  are substantially rectangular in shape. There are four positions  1 ,  2 ,  3 , and  4  at which copper tape is placed at the corner of the rectangle and on top of the AGNW coating  220 . One conductive bar  1012 A on top of the AGNW coating  220  may contact one edge of the AGNW coating  220  and may connect copper tapes  1010  at positions  1  and  2 . Another conductive bar  1012 B may contact an opposite edge of the AGNW coating  220  and may connect copper tapes at positions  3  and  4 . The conductive bars  1012 A and  1012 B may include conductive paste, such as silver paste. 
     The conductive bars and the conductive tapes are located outside the active area of the touch panel, which provides better grounding without impact on optical transmittance of the touch panel. 
       FIG. 10B  shows sample noise curves for several grounding configurations of  FIG. 10A  and  FIG. 9B  illustrating the effect of copper tape and the location of the copper tape on grounding. Typically, lower noise indicates better grounding. As shown, curve  1002  for grounding configuration  900 B shows the highest noise, because there is no grounding without ITO or AGNW as well as copper tapes. 
     Compared to curve  1002 , curve  1004  for grounding configuration  1000  with the copper tapes at corner positions  1  and  2  shows lower noise. Similarly, if copper tapes are placed at positions  3  and  4 , grounding results would be essentially the same as that of positions  1  and  2 . 
     Curve  1006  for the grounding configuration  1000  with the copper tapes at corner positions  1 ,  2 ,  3 , and  4  show the lowest noise. Curve  1008  represents the grounding configuration with copper tapes positioned at three corners, such as at any three of positions  1 ,  2 ,  3  and  4 . This suggests that the grounding configuration  1000  with the copper tape placed at three or four corners of the touch panel provides grounding and may reduce noise. 
     Generally, the ITO is deposited on the CF glass in a vacuum, such as by sputtering. The AGNW may be coated on a plastic film such as a TAC film by using a roll-to-roll process. The roll-to-roll process is usually simpler and cheaper than the sputtering. Additionally, the AGNW may be easier to provide consistent thickness than the ITO during fabrication. For example, the ITO coating may be deposited over the CF glass by sputtering, which would have cause larger variation in a thicker ITO coating. This large variation in thickness may require a post processing to minimize the thickness variation and thus may increase fabrication complexity. 
     One of the benefits of the present disclosure is to enable a thinner display product. The transparent conducting layer may be much thinner than a conventional conducting layer, such as ITO, but provide the same sheet resistance and/or electrical shielding. The transparent conducting layer, such as silver nano-wire, may improve light transmittance and reduce reflection, and thus enable better power efficiency and/or longer battery life. High light transmittance and low sheet resistance may not be simultaneously achieved with the conventional conducting ITO layer. The AGNW layer may also reduce LCM noise from the TFT layer, which is coupled to a number of drive circuits. The AGNW layer may thus demonstrate a better shielding than the conventional conducting ITO layer. 
     Having described several embodiments, it will be recognized by those skilled in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Accordingly, the above description should not be taken as limiting the scope of the invention. 
     Those skilled in the art will appreciate that the presently disclosed embodiments teach by way of example and not by limitation. Therefore, the matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense. The following claims are intended to cover all generic and specific features described herein, as well as all statements of the scope of the present method and system, which, as a matter of language, might be said to fall therebetween.

Metadata:
Filing Date: 20120713
Publication Date: 20160503
Grant Date: 20160503
Priority Date: 20120713
Inventors: CHEN CHENG
DORJGOTOV ENKHAMGALAN
KUWABARA MASATO
CHOI WONJAE
GRUNTHANER MARTIN P.
LIN ALBERT
ZHONG JOHN Z.
CHEN WEI
HOTELLING STEVEN P.
YOUNGS LYNN R.
Assignee: APPLE INC
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Family ID: 49913715