Electrostatic discharge protection structures for liquid crystal displays

A liquid crystal display having an outer layer such as a thin-film transistor layer and an inner layer such as a color filter layer may be mounted in a metal device housing. Transparent conductive coating material may be formed on display layers. The transparent conductive coating material may include a layer on the upper surface of the thin-film transistor layer, a layer on the lower surface of the color filter layer, and an edge coating that extends between the upper surface layer and lower surface layer. Electrostatic discharge protection structures for the display may include a conductive elastomeric gasket that couples the upper surface layer to an inner surface of the housing, a conductive tape that couples the lower surface layer to the inner surface, and a conductive material on the inner surface that contacts the edge coating.

BACKGROUND

Electronic devices often include displays. For example, cellular telephones and portable computers include displays for presenting information to users.

Displays such as liquid crystal displays may be disrupted when exposed to electric charge. If care is not taken, a display may not operate properly following exposure to charge in an electrostatic discharge event.

It would therefore be desirable to be able to provide improved displays with electrostatic discharge protection structures.

SUMMARY

An electronic device may be provided with a display. The display may have electrostatic discharge protection structures. The electrostatic discharge protection structures can help prevent electrostatic charge that is deposited on the display during an electrostatic discharge event from disrupting proper operation of the display.

The electronic device may be provided with a housing. A display may be mounted in the housing. The housing may be formed from a conductive material such as metal and may serve as ground during electrostatic discharge events.

The display may be a liquid crystal display having an outer layer such as a thin-film transistor layer and an inner layer such as a color filter layer. Transparent conductive coating material may be formed on the layers of the display. The transparent conductive coating material may be indium tin oxide that is deposited in layers such as a layer on the upper surface of the thin-film transistor layer, a layer on the lower surface of the color filter layer, and an edge coating that extends between the upper surface layer and lower surface layer.

The electrostatic discharge protection structures may electrically couple the transparent conductive coating material to an inner surface of the housing. The electrostatic discharge protection structures may include a conductive elastomeric gasket that couples the upper surface layer to the inner surface, may include conductive tape that couples the lower surface layer to the inner surface, and may include conductive material on the inner surface that contacts the edge coating.

DETAILED DESCRIPTION

Illustrative electronic devices of the types that may be provided with displays are shown inFIGS. 1, 2, 3, and 4.

Electronic device10ofFIG. 1has the shape of a laptop computer and has upper housing12A and lower housing12B with components such as keyboard16and touchpad18. Device10has hinge structures20(sometimes referred to as a clutch barrel) to allow upper housing12A to rotate in directions22about rotational axis24relative to lower housing12B. Display14is mounted in housing12A. Upper housing12A, which may sometimes be referred to as a display housing or lid, is placed in a closed position by rotating upper housing12A towards lower housing12B about rotational axis24.

FIG. 2shows an illustrative configuration for electronic device10based on a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device10, housing12has opposing front and rear surfaces. Display14is mounted on a front face of housing12. Display14may have an exterior layer that includes openings for components such as button26and speaker port28. Device10may, if desired, be a compact device such as a wrist-mounted device or pendant device (as examples).

In the example ofFIG. 3, electronic device10is a tablet computer. In electronic device10ofFIG. 3, housing12has opposing planar front and rear surfaces. Display14is mounted on the front surface of housing12. As shown inFIG. 3, display14has an opening to accommodate button26.

FIG. 4shows an illustrative configuration for electronic device10in which device10is a computer display, a computer that has an integrated computer display, or other display device. Display14is mounted on a front face of housing12. With this type of arrangement, housing12for device10may be mounted on a wall or may have an optional structure such as support stand30to support device10on a flat surface such as a table or desk.

Display14may be a liquid crystal display or a display formed using other suitable display technologies. Display14may be mounted in a watch, equipment in an embedded system, a gaming device, a navigation device, or any other electronic equipment. The examples ofFIGS. 1, 2, 3, and 4are merely illustrative.

A cross-sectional side view of an illustrative configuration for display14of device10(e.g., a liquid crystal display for the devices ofFIG. 1,FIG. 2.FIG. 3,FIG. 4or other suitable electronic devices) is shown inFIG. 5. As shown inFIG. 5, display14may include backlight structures such as backlight unit42for producing backlight44. During operation, backlight44travels outwards (vertically upwards in dimension Z in the orientation ofFIG. 5) and passes through display pixel structures in display layers46. This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight44may illuminate images on display layers46that are being viewed by viewer48in direction50.

Display layers46may 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 housing12or display layers46may be mounted directly in housing12(e.g., by stacking display layers46into a recessed portion of housing12).

Display layers46may include a liquid crystal layer such a liquid crystal layer52. Liquid crystal layer52may be sandwiched between display layers such as display layers58and56. Layers56and58may be interposed between lower (innermost) polarizer layer60and upper (outermost) polarizer layer54.

Layers58and56may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers56and58may 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 layers58and56(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 layers58and56and/or touch sensor electrodes may be formed on other substrates.

With one illustrative configuration, outer substrate layer56may 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 layer52and thereby displaying images on display14. Inner substrate layer58may be a color filter layer that includes an array of color filter elements for providing display14with the ability to display color images.

Backlight structures42may include a light guide plate such as light guide plate78. Light guide plate78may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures42, a light source such as light source72may generate light74. Light source72may be, for example, an array of light-emitting diodes.

Light74from light source72may be coupled into edge surface76of light guide plate78and may be distributed in dimensions X and Y throughout light guide plate78due to the principal of total internal reflection. Light guide plate78may 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 plate78.

Light74that scatters upwards in direction Z from light guide plate78may serve as backlight44for display14. Light74that scatters downwards may be reflected back in the upwards direction by reflector80. Reflector80may be formed from a reflective material such as a layer of white plastic or other shiny materials.

To enhance backlight performance for backlight structures42, backlight structures42may include optical films70. Optical films70may include diffuser layers for helping to homogenize backlight44and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight44. If desired, some of these layers may be combined with other layers in display14. For example, compensation films may be incorporated into polarizers54and/or60. Optical films70may overlap the other structures in backlight unit42such as light guide plate78and reflector80. For example, if light guide plate78has a rectangular footprint in the X-Y plane ofFIG. 5, optical films70and reflector80may have a matching rectangular footprint.

Display14may have an array of display pixels (e.g., a rectangular array having rows and columns) for displaying images to a viewer. Vertical signal lines called data lines may be used to carry display data to respective columns of display pixels. Horizontal signal lines called gate lines may be used to carry gate line signals (sometimes referred to as gate control signals or gate signals) to respective rows of display pixels. The outline of the array of display pixels in display14defines an active area for display14. The active area may have a rectangular shape and may be surrounded by an inactive border region. An inactive border area may, for example, run along one edge, two edges, three edges, or all four edges of the active area.

A cross-sectional side view of an illustrative electronic device having a display such as display14ofFIG. 5is shown inFIG. 6. As shown inFIG. 6, images may be displayed on central active area AA of display14. Inactive area IA may have a rectangular ring shape that runs around the rectangular periphery of active area AA. To avoid unsightly bezel structures in device10, it may be desirable to keep inactive area IA free of overlapping housing structures, bezels, or other potentially unattractive border structures.

In one suitable embodiment, a transparent conductive layer such as a layer of indium tin oxide (ITO)100may be formed on the thin-film transistor (TFT) layer56and/or on color filter (CF) layer58to assist in discharging electrostatic charge to ground (see, e.g.,FIG. 7). As shown inFIG. 7, conductive material such as conductive material110may be formed along the inner surfaces of side walls of housing12to electrically couple ITO layer100to housing12. Material110may be formed from conductive adhesive, metal, ITO, conductive tape, conductive elastomeric material (e.g., conductive rubber), metallic paint, or a coating of other conductive material. ITO layer100may have a first portion on the upper surface of layer56, a second conformal portion along the edges of layers56and58that runs perpendicular to the first portion, and a third portion on the lower surface of layer58. All of these portions of the ITO layer are physically and electrically connected to each other to form a conductive path that is shorted to material110and thereby grounded to housing12. This allows layers100and material110to form electrostatic discharge structures. Configured in this way, electrostatic charge that that has the potential to accumulate in layers56and58may be effectively discharged through layer100and material110to housing12, which serves as a ground discharge path. This is merely illustrative. In some embodiments, conductive layer100need not be formed on CF layer58.

In another suitable arrangement (see,FIG. 8), a first conductive layer such as layer100-1(e.g., a first ITO layer) may be formed on CF layer58, whereas a second conductive layer such as layer100-2(e.g., a second ITO layer that is separate from the first ITO layer) may be formed on TFT layer56. As shown inFIG. 8, sidewall conductive material110may serve to couple ITO layer100-2to housing12. An additional conductive path in the form of a conductive tape112(e.g., a conductive black tape) may serve to electrically couple ITO layer100-1to housing12. For example, tape112may have a first end that is attached to an exposed portion120on ITO layer100-1and a second end that is attached to housing12. Tape112may include one or more layers of material such as metal foil layers, metal coatings, adhesive layers, conductive adhesive layers, polymer layers that serve as carrier layers, etc. Black tape may be used for tape112to help block stray light.

FIG. 9Ashows a top view of display14. As shown inFIG. 9A, an ITO layer100may be formed over and along the sides of TFT layer56. Conductive sidewall material110may be formed along all four edges of TFT layer56. This is merely illustrative. Conductive sidewall material110may be formed along one or more edges of layer56, two or more edges of layer56, three or more edges of layer56, etc.

FIGS. 10 and 11are flow charts of illustrative steps for manufacturing display14of the type described in connection withFIGS. 1-9.

In the arrangement ofFIG. 10, layers56and58may be bonded together and optional ITO layer110-1may be formed on the lower surface of color filter layer58. As shown by line200, color filter layer58may then be scribed (if desired) and an edge portion of layer58may be removed to form a TFT ledge (e.g., a ledge that receives subsequent electrical connections for display driver circuitry). After the ledge has been formed, grinding operations may be performed on the bonded layers (e.g., to smooth and bevel the edges of the layers), as shown by line202. As shown by line204, upper and side layer portions of ITO (i.e., ITO coating100-2) may be then be deposited. ITO layers100-2and100-1may be electrically separate or may be shorted to each other. Following formation of layers100-2and100-1, polarizers54and60may be attached to the upper and lower surfaces of TFT layer56and CF layer58(e.g., using adhesive), as shown by line206.

In the arrangement ofFIG. 11, scribing/grinding operations may be performed after ITO deposition. Initially, layers56and58may be bonded together and optional ITO layer110-1may be formed on the lower surface of color filter layer58. As shown by line300, grinding operations may then be performed to smooth and bevel the edges of the layers. As shown by line302, upper and side layer portions of ITO (i.e., ITO coating100-2) may be then be deposited. ITO layers100-2and100-1may be electrically separate or may be electrically coupled (i.e., layers100-1and100-2may contact each other to form an electrical connection between layers100-1and100-2). Following deposition of coating100-2, scribing and grinding operations may be performed to form a TFT layer ledge, as shown by line304. Following formation of layers100-2and100-1, polarizers54and60may be attached to the upper and lower surfaces of TFT layer56and CF layer58(e.g., using adhesive), as shown by line306.

After forming the display layers for display14using techniques of the types shown inFIGS. 10 and 11or other suitable techniques, the display layers may be installed within housing12so that material110shorts layers110-1and/or110-2to housing12. Housing12may be formed from a conductive material such as metal and can serve as ground for electrostatic discharge.