PATENT DOCUMENT

Publication Number: US-9671660-B2
Application Number: US-201213619866-A
Country: US
Kind Code: B2

Title: Display with low reflection electrostatic shielding

Abstract:
An electronic device may be provided with a display such as a liquid crystal display. The display may have a layer of liquid crystal material interposed between upper and lower polarizers. A first substrate such as a thin-film transistor layer may be interposed between the liquid crystal layer and the lower polarizer. A second substrate such as a color filter glass layer may be interposed between the upper polarizer and the liquid crystal layer. The color filter glass layer may have opposing upper and lower surfaces. The lower surface of the color filter glass layer may have an array of color filter elements. To prevent damage to display, an electrostatic shielding layer may be formed on the upper surface of the color filter glass layer under the upper polarizer. Reflections may be minimized by using index-matching dielectric layers in the display or thinning the shielding layer.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a polarizer layer having a first index of refraction; 
 a display layer having a second index of refraction that is different from the first index of refraction; 
 an electrostatic shielding layer having a third index of refraction that is different from the first and second indices of refraction interposed between the polarizer layer and the display layer, wherein the electrostatic shielding layer has a thickness of 30 to 190 angstroms; 
 a first layer of index-matching material having a fourth index of refraction that is between the first index of refraction and the third index of refraction interposed between the polarizer layer and the electrostatic shielding layer; and 
 a second layer of index-matching material having a fifth index of refraction that is between the second index of refraction and the third index of refraction interposed between the electrostatic shielding layer and the display layer. 
 
     
     
       2. The display defined in  claim 1  wherein the display layer comprises a color filter glass layer. 
     
     
       3. The display defined in  claim 2  wherein the electrostatic shielding layer comprises indium tin oxide. 
     
     
       4. The display defined in  claim 2  wherein the electrostatic shielding layer comprises indium tin oxide, wherein the display layer comprises a color filter glass layer having opposing first and second surfaces and color filter elements formed on the second surface, and wherein the indium tin oxide is deposited on the first surface. 
     
     
       5. The display defined in  claim 4  wherein the electrostatic shielding layer has a thickness of between 60 and 120 angstroms. 
     
     
       6. A display, comprising:
 an upper polarizer layer having a first index of refraction; 
 a lower polarizer layer; 
 a liquid crystal layer between the upper polarizer layer and the lower polarizer layer; 
 a color filter glass layer having a second index of refraction between the upper polarizer layer and the liquid crystal layer; 
 a thin-film transistor layer between the liquid crystal layer and the lower polarizer; 
 an electrostatic shielding layer having a third index of refraction between the color filter glass layer and the upper polarizer, wherein the electrostatic shielding layer has a thickness of between 50 and 175 angstroms; 
 a first layer of index-matching material having a fourth index of refraction that is greater than the first index of refraction and less than the third index of refraction interposed between the upper polarizer layer and the electrostatic shielding layer; and 
 a second layer of index-matching material having a fifth index of refraction that is greater than the second index of refraction and less than the third index of refraction interposed between the electrostatic shielding layer and the color filter glass layer. 
 
     
     
       7. The display defined in  claim 6  wherein the electrostatic shielding layer comprises indium tin oxide. 
     
     
       8. The display defined in  claim 6  wherein the electrostatic shielding layer has a thickness of between 50 and 120 angstroms. 
     
     
       9. The display defined in  claim 8  wherein the electrostatic shielding layer comprises a layer of sputtered indium tin oxide on the color filter glass layer.

Description:
BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. 
     When touched by a user, a display may be exposed to electrostatic charge. Displays are often provided with electrostatic discharge shielding layers to prevent damage to display structures. An electrostatic shielding layer prevents electrostatic charge from imposing damaging electric fields on underlying display structures and thereby prevents damage to a display during electrostatic discharge events. Electrostatic shielding layers are formed from conductive materials to provide a low-resistance path through which electrostatic charge can be removed from display surfaces. Electrostatic shielding layers are also transparent to allow content on a display to be viewed by a user. 
     A commonly used material that is both transparent and conductive and that can therefore be used in forming an electrostatic discharge shielding layer is indium tin oxide. With one conventional arrangement, a layer of indium tin oxide of about 200-300 angstroms in thickness or more is formed between an upper surface of a display color filter glass layer and a lower surface of an upper polarizer. Indium tin oxide electrostatic shielding layers with this type of conventional configuration may be satisfactory for providing adequate shielding and display transparency, but can give rise to undesirable light reflections from a display. In the presence of excessive reflections, content on a display may appear washed out and difficult to view by a user. 
     It would therefore be desirable to be able to provide improved displays having low reflectivity surfaces with electrostatic discharge shielding. 
     SUMMARY 
     An electronic device may be provided with a display such as a liquid crystal display. The display may have a layer of liquid crystal material and upper and lower polarizers. A first substrate such as a thin-film transistor layer may be interposed between the liquid crystal layer and the lower polarizer. A second substrate such as a color filter glass layer may be interposed between the upper polarizer and the liquid crystal layer. 
     The color filter glass layer may have opposing upper and lower surfaces. An array of color filter elements may be formed on the lower surface of the color filter glass layer. To prevent damage to circuitry in the display and distortion of display images from electrostatic charge, an electrostatic shielding layer may be formed on the upper surface of the color filter glass substrate under the upper polarizer. 
     Display reflections may be minimized by reducing the thickness of the electrostatic shielding layer or by providing dielectric layers such as aluminum oxide layers above and below the electrostatic shielding 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 such as a laptop computer with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment of the present invention. 
         FIG. 4  is a schematic diagram of an illustrative electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 5  is a cross-sectional side view of an illustrative display in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of an illustrative display with a transparent conductive electrostatic discharge shielding layer configured to reduce surface reflections in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of an illustrative display with a transparent conductive electrostatic discharge shielding layer interposed between upper and lower layers of material such as aluminum oxide to reduce surface reflections in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1, 2, and 3 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have a display cover layer or other exterior layer that includes openings for components such as button  26 . Openings may also be formed in a display cover layer or other display layer to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have a cover layer or other external layer with an opening to accommodate button  26  (as an example). 
     The illustrative configurations for device  10  that are shown in  FIGS. 1, 2, and 3  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Displays for device  10  may, in general, include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. In some situations, it may be desirable to use LCD components to form display  14 , so configurations for display  14  in which display  14  is a liquid crystal display are sometimes described herein as an example. It may also be desirable to provide displays such as display  14  with backlight structures, so configurations for display  14  that include a backlight unit may sometimes be described herein as an example. Other types of display technology may be used in device  10  if desired. The use of liquid crystal display structures and backlight structures in device  10  is merely illustrative. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . A display cover layer or other outer display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     Touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide may be formed on the underside of a display cover layer, may be formed on a separate display layer such as a glass or polymer touch sensor substrate, or may be integrated into other display layers (e.g., substrate layers such as a thin-film transistor layer). 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 4 . As shown in  FIG. 4 , electronic device  10  may include control circuitry  29 . Control circuitry  29  may include storage and processing circuitry for controlling the operation of device  10 . Control circuitry  29  may, for example, include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Control circuitry  29  may include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Control circuitry  29  may be used to run software on device  10 , such as operating system software and application software. Using this software, control circuitry  29  may present information to a user of electronic device  10  on display  14 . When presenting information to a user on display  14 , sensor signals and other information may be used by control circuitry  29  in making adjustments to the strength of backlight illumination that is used for display  14 . 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include communications circuitry  32 . Communications circuitry  32  may include wired communications circuitry for supporting communications using data ports in device  10 . Communications circuitry  32  may also include wireless communications circuits (e.g., circuitry for transmitting and receiving wireless radio-frequency signals using antennas). 
     Input-output circuitry  30  may also include input-output devices  34 . A user can control the operation of device  10  by supplying commands through input-output devices  34  and may receive status information and other output from device  10  using the output resources of input-output devices  34 . 
     Input-output devices  34  may include sensors and status indicators  36  such as an ambient light sensor, a proximity sensor, a temperature sensor, a pressure sensor, a magnetic sensor, an accelerometer, and light-emitting diodes and other components for gathering information about the environment in which device  10  is operating and providing information to a user of device  10  about the status of device  10 . 
     Audio components  38  may include speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. 
     Display  14  may be used to present images for a user such as text, video, and still images. Sensors  36  may include a touch sensor array that is formed as one of the layers in display  14 . 
     User input may be gathered using buttons and other input-output components  40  such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as sensors  36  in display  14 , key pads, keyboards, vibrators, cameras, and other input-output components. 
     A cross-sectional side view of an illustrative configuration that may be used for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 , or  FIG. 3  or other suitable electronic devices) is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 5 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted in chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     In a configuration in which display layers  46  are used in forming a liquid crystal display, display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  56  and  58  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter substrate layer on which an array of color filter elements may be formed to provide display  14  with the ability to display color images. The substrate material used in forming layer  56  may be a sheet of transparent material such as glass or plastic. Illustrative configurations in which substrate layer  56  is formed using a layer of glass are sometimes described herein as an example. Color filter elements on glass layer  56  may be formed from polymers colored with dyes or pigments (as examples). 
     During operation of display  14  in device  10 , control circuitry  29  (e.g., one or more integrated circuits such as components  68  on printed circuit  66  of  FIG. 5 ) may be used to generate information to be displayed on display (e.g., display data). The information to be displayed may be conveyed from circuitry  68  to display driver integrated circuit  62  using a signal path such as a signal path formed from conductive metal traces in flexible printed circuit  64  (as an example). 
     Display driver integrated circuit  62  may be mounted on thin-film-transistor layer driver ledge  82  or elsewhere in device  10 . A flexible printed circuit cable such as flexible printed circuit  64  may be used in routing signals between printed circuit  66  and thin-film-transistor layer  58 . If desired, display driver integrated circuit  62  may be mounted on printed circuit  66  or flexible printed circuit  64 . Printed circuit  66  may be formed from a rigid printed circuit board (e.g., a layer of fiberglass-filled epoxy) or a flexible printed circuit (e.g., a flexible sheet of polyimide or other flexible polymer layer). 
     Backlight structures  42  may include a light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of white plastic or other shiny materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 5 , optical films  70  and reflector  80  may have a matching rectangular footprint. 
     To provide display  14  with the ability to withstand damage from electrostatic discharge events, display  14  may be provided with an electrostatic discharge shielding layer such as electrostatic discharge shielding layer  90  of  FIG. 6 . Layer  90  may be formed from a transparent conductive material such as indium tin oxide. A conductive path formed from metal traces, metal paint, conductive adhesive, wires, or other conductive materials may be used to electrically short layer  90  to ground  96  (e.g., layer  90  may be shorted to part of a metal housing such as housing  12  or to ground traces on a printed circuit board in housing  12 ). By grounding electrostatic discharge shielding layer  90  in this way, layer  90  may discharge any electrostatic charge that is deposited on display  14  due to contact with an external object such as a hand of a user. Sputtering, other types of physical vapor deposition, or other types of deposition techniques (e.g., chemical vapor deposition, electrochemical deposition, ink-jet patterning, pad printing, spinning, spraying, etc.) may be used in depositing electrostatic discharge shielding layer  90  on the layers of display  14 . 
     Color filter glass layer  56  may be provided with a layer of color filter elements  56 ′. Color filter elements  56 ′ may, for example, include red, blue, and green polymer color filter elements or other patterned colored structures for providing display  14  with the ability to display color images. As an example, color filter layer  56  may be provided with an array of color filter elements  56 ′ that are each aligned with a corresponding display pixel in an array of display pixels on thin-film transistor layer  58 . The circuitry of display  14  may be damaged when exposed to excessive electric fields of the type that may be produced when electrostatic charge builds up on the surface of display  14 . When indium tin oxide layer  90  is included in display  14 , however, indium tin oxide layer  90  will discharge any electrostatic charge that is deposited on the surface of display  14  to ground  96 , thereby preventing damage to the circuitry within display  14  and distortion of images on display  14 . 
     As shown in  FIG. 6 , indium tin oxide electrostatic discharge shielding layer  90  may be interposed between upper polarizer  54  and color filter glass layer  56 . Layer  90  may, for example, be deposited on the upper surface of color filter glass  56  (e.g., using sputtering or other deposition techniques). Polarizer layer  54  may be attached to the upper surface of layer  90  using adhesive (as an example). 
     During operation of display  14 , ambient light  106  may be directed towards the surface of display  14 . A fraction of light  106  may reflect from display  14  and may be visible to a user such as viewer  48  who is viewing display  14  in direction  50 . Excessive reflection by display  14  can degrade the performance of display  14  (e.g., by lowering contrast, by creating stray images on the display that interfere with the content that is being displayed on the display, etc.). 
     Reflections from display  14  may be at least partly the result of the presence of indium tin oxide layer  90 . Polarizer layer  54  may have an index of refraction of about 1.5. Color filter layer  56  may have a glass substrate or other clear dielectric substrate with an index of refraction of about 1.5. Indium tin oxide layer  90  may, however, have an index of refraction that differs significantly from the indices of refraction of layers  54  and  56 . Indium tin oxide layer  90  may, for example, have an index of refraction of 1.9. 
     Ambient light  106  may be reflected from display  14  due at least partly to index of refraction mismatch between indium tin oxide layer  90  and materials such as polarizer  54  and color filter glass  56 . For example, ambient light rays such as light ray  102  may be reflected from the interface between polarizer layer  54  and indium tin oxide layer  90  to produce reflected light  104  and light rays such as light ray (i.e., the portion of ambient light ray  102  that has been transmitted through the interface between layers  54  and  90 ) may be reflected from the interface between indium tin oxide layer  90  and color filter glass  56  to produce reflected light  100 . 
     The magnitude of light reflection from the interface between layers  54  and  90  and from the interface between layers  90  and  56  can be modeled using equation 1, where n 1  represent the index of refraction of indium tin oxide layer  90  and n 2  represents the index of refraction of layers  54  and  56 .
 
|(n1−n2)/(n1+n2)|  (1)
 
Because the values of n 1  and n 2  differ considerably, there is a relatively large potential for the presence of indium tin oxide layer  90  to give rise to unwanted amounts of light reflection. Because the phase of reflected light  100  is 180° out of phase with the phase of reflected light  104 , however, light reflection can be minimized by minimizing the thickness T of indium tin oxide layer  90 . When T is relatively large, out-of-phase rays  100  and  104  do not destructively interfere, leading to relatively large amounts of reflected light. When T is relatively small, out-of-phase rays  100  and  104  tend to cancel each other, thereby minimizing reflections.
 
     When, for example, the value of T is relatively thick (e.g., 200 angstroms or more as in conventional displays), the reflectivity of the display may be larger than desired. As an example, if T is formed with a conventional thickness of 300 angstroms, the reflectivity of the display due to the presence of the indium tin oxide electrostatic discharge shielding layer may be about 1.4%. If T is formed with a conventional thickness of 200 angstroms, the reflectivity of the display may be about 0.75%. 
     Modeling results and experimental results using indium tin oxide electrostatic shielding layers of less than 200 angstroms in thickness indicate that further reductions in reflections can be achieved by forming indium tin oxide electrostatic shielding layer  90  with values of thickness T that are less than 200 angstroms. As an example, if T is 100 angstroms, reflectivity may be reduced to about 0.24%. 
     For satisfactory electrostatic shielding, it may be desirable to ensure that T is not too thin. If T is too thin (e.g., less than 10 angstroms), the sheet resistance of layer  90  may become so large (e.g., more than 10,000 ohms per square). When T has a value that is not too small, however, sheet resistance may be maintained at a suitably low value. As an example, if the value of T is about 90 angstroms, the sheet resistance of indium tin oxide electrostatic shield layer  90  may be about 700 ohms per square. When low sheet resistances are present, shielding layer  90  may effectively discharge electrostatic charge to ground  96 . 
     In general, the thickness T of layer  90  may be less than 200 angstroms, less than 175 angstroms, less than 150 angstroms, less than 100 angstroms, more than 50 angstroms, more than 75 angstroms, between 40-180 angstroms, 30-180 angstroms, 30-190 angstroms, 50-120 angstroms, 50-150 angstroms, 60-140 angstroms, 60-120 angstroms, 40-175 angstroms, 50-175 angstroms, 60-175 angstroms, 60-150 angstroms, 70-130 angstroms, 100-170 angstroms, or other suitable thickness. When thickness T has small values such as these, light  140  and out-of-phase light  100  tend to destructively interfere with each other, thereby reducing reflected light and minimizing the reflectivity of display  14  to ambient light so that viewer  48  can better view content on display  14 . 
     If desired, one or more layers of transparent material may be formed adjacent to indium tin oxide electrostatic shielding layer  90  to help minimize light reflection from display  14 . This type of arrangement is shown in  FIG. 7 . As shown in  FIG. 7 , display  14  may include, for example, an upper layer such as layer  92  of thickness T 1  and a lower layer of material such as layer  94  of thickness T 2 . Layers such as upper layer  92  and lower layer  94  may be formed from transparent insulating materials (e.g., oxides, nitrides, or other dielectrics) such as aluminum oxide (Al 2 O 3 ) or other transparent materials. Layers  92  and  94  may be formed by sputtering, other physical vapor deposition techniques, chemical vapor deposition, or other deposition techniques. 
     Layers  92  and  94  may have indices of refraction that differ from those of indium tin oxide electrostatic shielding layer  90 , polarizer layer  54 , and color filter glass  56 . As an example, layer  92  may have an index of refraction that is intermediate between the index of refraction of layer  54  and the index of refraction of layer  90  and layer  94  may have an index of refraction that is intermediate between the index of refraction of glass layer  56  and the index of refraction of layer  90 . In a scenario in which layers  54  and  56  have indices of refraction of 1.5 and layer  90  has an index of refraction of 1.9, for example, layers  92  and  94  may each of an index of refraction of 1.69 (e.g., the index of refraction of aluminum oxide). By suitable selection of the values of thicknesses T 1 , T, and T 2 , an index-matching configuration can be achieved in which layers  110  are effectively index matched to layers  54  and  56 , minimizing reflections. Examples of suitable thickness values that may be used for T 1 , T, and T 2 , respectively include 1250 angstroms, 250 angstroms, and 1250 angstroms (as a first example), 1050 angstroms, 250 angstroms, and 1050 angstroms (as a second example), and 903 angstroms, 250 angstroms, and 926 angstroms (as a third example). 
     Configurations of the type shown in  FIG. 6  in which indium tin oxide electrostatic shielding layer  90  has a small thickness may be advantageous in minimizing reflections from display  14  without introducing color casts or wavelength-dependent reflectivity. Display configurations of the type shown in  FIG. 7  may be characterized by low sheet resistance for layer  90 . To ensure satisfactory grounding for layer  90  in arrangements of the type shown in  FIG. 7 , a shadow mask may be used to prevent layer  90  from being covered by layers such as layer  92  during fabrication. After the shadow mask is removed, an electrical path may be formed between layer  90  and ground  96 . 
     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.

Metadata:
Filing Date: 20120914
Publication Date: 20170606
Grant Date: 20170606
Priority Date: 20120914
Inventors: DROLET JEAN-JACQUES
GU MINGXIA
CHEN WEI
HUANG YI
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133502", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/136204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/136204", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133502", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 50274141