PATENT DOCUMENT

Publication Number: US-10608069-B2
Application Number: US-201815994858-A
Country: US
Kind Code: B2

Title: Displays with redundant bent signal lines and neutral plane adjustment layers

Abstract:
A display may have an array of organic light-emitting diodes that form an active area on a flexible substrate. Display driver circuitry such as a display driver integrated circuit may be coupled to an inactive area of the flexible substrate. Metal traces may extend across a bent region of the flexible substrate between the active area and inactive area. Metal traces may have zigzag shapes to reduce stress when bending. Adjacent pairs of parallel segments in the metal traces may be shorted together by a bridging segment that extends perpendicular to the two parallel segments. The bridging segment may be offset from corners to avoid clusters of stress zones in the metal trace. Neutral plane adjustment layers in the bent region may include a metal layer to help counteract the bending force of the flexible substrate and the relaxation of an upper polymer coating.

Claims:
What is claimed is: 
     
       1. A display, comprising:
 a flexible substrate; 
 an array of pixels that form an active area on the flexible substrate; and 
 zigzag metal traces that extend from the active area to an inactive area on the flexible substrate across a bent region of the flexible substrate, wherein the zigzag metal traces include first and second parallel segments, a third segment that shorts the first segment to the second segment, and a fourth segment that shorts the first segment to the second segment, and wherein the third and fourth segments are perpendicular to the first and second segments such that the first, second, third, and fourth segments surround a rectangular opening. 
 
     
     
       2. The display defined in  claim 1  wherein the rectangular opening is part of an array of rectangular openings in the zigzag metal traces. 
     
     
       3. The display defined in  claim 2  wherein the rectangular openings are different sizes. 
     
     
       4. The display defined in  claim 3  wherein the zigzag metal traces have corners and wherein the rectangular openings include first and second rectangular openings on opposing sides of one of the corners and a third rectangular opening between the first and second rectangular openings, wherein the third rectangular opening is smaller than the first and second rectangular openings. 
     
     
       5. The display defined in  claim 1  wherein the zigzag metal traces have corners and wherein the third segment that shorts the first segment to the second segment is offset from the corners. 
     
     
       6. The display defined in  claim 1  wherein the active area overlaps the inactive area of the substrate. 
     
     
       7. A display, comprising:
 a flexible substrate; 
 an array of pixels that form an active area on the flexible substrate; 
 conductive traces that extend from the active area to an inactive area on the flexible substrate across a bent region of the flexible substrate; and 
 neutral plane adjustment layers that overlap the conductive traces and that align a neutral plane with the conductive traces, wherein the neutral plane adjustment layers include a metal layer. 
 
     
     
       8. The display defined in  claim 7  wherein the metal layer does not carry a signal. 
     
     
       9. The display defined in  claim 7  wherein the neutral plane adjustment layers comprise a polymer coating that overlaps the metal layer. 
     
     
       10. The display defined in  claim 7  wherein the metal layer is formed from the same material as an active display layer in the active area. 
     
     
       11. The display defined in  claim 10  wherein the active display layer is selected from the group consisting of: a signal layer, an anode layer, a cathode layer, and a touch sensor layer. 
     
     
       12. The display defined in  claim 7  wherein the neutral plane adjustment layers comprise an additional metal layer. 
     
     
       13. The display defined in  claim 12  wherein the additional metal layer is formed from the same material as an active display layer in the active area and wherein the active display layer comprises an active display layer selected from the group consisting of: a signal layer, an anode layer, a cathode layer, and a touch sensor layer. 
     
     
       14. The display defined in  claim 7  wherein the metal layer has openings. 
     
     
       15. The display defined in  claim 14  wherein the bent region of the flexible substrate bends around a bend axis, and wherein the openings extend perpendicular to the bend axis. 
     
     
       16. The display defined in  claim 14  wherein the bent region of the flexible substrate bends around a bend axis, and wherein the openings extend parallel to the bend axis. 
     
     
       17. A display, comprising:
 a flexible substrate having first and second flat portions and a bent portion coupled between the first and second flat portions; 
 an array of pixels on the first flat portion of the flexible substrate; 
 touch sensor circuitry on the first flat portion of the flexible substrate; 
 a metal trace on the flexible substrate that extends from the first flat portion to the second flat portion across the bent portion; and 
 a polymer layer and a metal layer that overlap the metal trace on the bent portion of the substrate, wherein the metal layer forms an electromagnetic interference shield between the array of pixels and the touch sensor circuitry. 
 
     
     
       18. The display defined in  claim 17  wherein the metal layer is connected to a ground power supply voltage. 
     
     
       19. The display defined in  claim 17  wherein the polymer layer and the metal layer align a neutral plane with the metal trace. 
     
     
       20. The display defined in  claim 17  wherein the metal trace has sides that are oriented at an angle with respect to an upper surface of the flexible substrate and wherein the angle is between 90 degrees and 180 degrees. 
     
     
       21. The display defined in  claim 17  wherein the metal trace comprises a metal layer interposed between a buffer layer and a passivation layer, wherein the buffer layer and the passivation layer have edges that are oriented at an angle with respect to an upper surface of the flexible substrate, and wherein the angle is between 90 degrees and 180 degrees.

Description:
This application claims the benefit of provisional patent application No. 62/524,224, filed Jun. 23, 2017, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices with displays, and, more particularly, to displays with bent portions. 
     Electronic devices often include displays. Displays such as organic light-emitting diode displays may be formed on flexible substrates. Displays with flexible substrates may be bent. For example, it may be desirable to bend an edge of a display to hide inactive display components along the edge of the display from view. 
     The process of bending a display can create stresses within the structures of the display. For example, bent metal traces may become stressed. Stress-induced damage such as cracks may adversely affect display reliability. 
     It would therefore be desirable to be able to provide improved displays with bent portions. 
     SUMMARY 
     A display may have an array of pixels. The pixels may contain light-emitting diodes such as organic light-emitting diodes and may form an active area that displays images. 
     The pixels may be formed from thin-film layers on a flexible substrate. Conductive traces such as metal traces may extend between the active area and an inactive area of the flexible substrate. Display driver circuitry such as a display driver integrated circuit may be coupled to contacts formed from the metal traces in the inactive area. 
     The metal traces may extend across a bent portion of the flexible substrate. To help enhance reliability for the metal traces, the metal traces may have meandering shapes such as zigzag shapes. Adjacent traces may be shorted together to provide redundancy. For example, each pair of adjacent traces may be shorted together by a series of redundant paths that bridge the gap between the adjacent traces. 
     The bridges between parallel segments may be perpendicular to the parallel segments to help separate neighboring stress zones. The bridges may be offset from corners of the zigzag segments to avoid clusters of stress zones near the corners of the metal trace. 
     The redundant segments in the signal paths may surround rectangular openings. The rectangular openings may have different sizes and may have different or alternating patterns from neighboring signal paths. 
     Neutral plane adjustment layers may include a metal layer to help counteract the bending force of the flexible substrate and the relaxation of an upper polymer coating. The metal layer may be connected to a ground power supply voltage to form an electromagnetic interference shield between pixel circuitry and touch sensor circuitry. 
     The metal layer in the bent region may be formed from the same material as one or more active display layers in the flat portion of the display. For example, the metal layer in the bent region may be formed from the same material as a signal layer, an anode layer, a cathode layer, a touch sensor layer, or other suitable active display layer. 
     Further features will be more apparent from the accompanying drawings and the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 2  is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG. 3  is a top view of an illustrative display in an electronic device in accordance with an embodiment. 
         FIG. 4  is a cross-sectional side view of a portion of an illustrative organic light-emitting diode display in accordance with an embodiment. 
         FIG. 5  is perspective view of an illustrative display with a bent portion in accordance with an embodiment. 
         FIG. 6  is a top view of a portion of a display showing how zigzag signal lines may be used to help accommodate display bending in accordance with an embodiment. 
         FIGS. 7, 8, 9, and 10  are top views of illustrative zigzag signal paths with redundancy and separated stress zones in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of an illustrative bent substrate showing how a neutral plane may be aligned with a layer of signal lines using one or more neutral plane adjustment layers in accordance with an embodiment. 
         FIG. 12A  is a cross-sectional side view of a portion of a display showing how a metal layer may be used to adjust a neutral plane to align with a signal line in accordance with an embodiment. 
         FIG. 12B  is a cross-sectional side view of a portion of a display showing how a signal line may have angled sides to help prevent crack formation in accordance with an embodiment. 
         FIG. 13  is a cross-sectional side view of a portion of a display showing how more than one metal layer may be used to adjust a neutral plane to align with a signal line in accordance with an embodiment. 
         FIG. 14  is a cross-sectional side view of a portion of display showing how a metal layer may include openings that run perpendicular to a bend axis in accordance with an embodiment. 
         FIG. 15  is a cross-sectional side view of a portion of display showing how a metal layer may include openings that run parallel to a bend axis in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG. 1 . Electronic device  10  may be a computing device such as 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, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, 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. In the illustrative configuration of  FIG. 1 , device  10  is a portable device such as a cellular telephone, media player, tablet computer, a watch or other wrist device, or other portable computing device. Other configurations may be used for device  10  if desired. The example of  FIG. 1  is merely illustrative. 
     In the example of  FIG. 1 , device  10  includes a display such as display  14  mounted in housing  12 . Housing  12 , which may sometimes be referred to as an enclosure or case, may be formed of plastic, glass, ceramics, fiber composites, metal (e.g., stainless steel, aluminum, etc.), other suitable materials, or a combination of any two or more of these materials. Housing  12  may be formed using a unibody configuration in which some or all of housing  12  is machined or molded as a single structure or may be formed using multiple structures (e.g., an internal frame structure, one or more structures that form exterior housing surfaces, etc.). 
     Display  14  may be a touch screen display that incorporates a layer of conductive capacitive touch sensor electrodes or other touch sensor components (e.g., resistive touch sensor components, acoustic touch sensor components, force-based touch sensor components, light-based touch sensor components, etc.) or may be a display that is not touch-sensitive. Capacitive touch screen electrodes may be formed from an array of indium tin oxide pads or other transparent conductive structures. 
     Display  14  may include an array of pixels formed from liquid crystal display (LCD) components, an array of electrophoretic pixels, an array of plasma pixels, an array of organic light-emitting diode pixels or other light-emitting diodes, an array of electrowetting pixels, or pixels based on other display technologies. The array of pixels may display images for a user in active area of display  14 . The active area may be surrounded on one or more sides by inactive border regions. 
     Display  14  may be protected using a display cover layer such as a layer of transparent glass or clear plastic. Openings may be formed in the display cover layer. For example, an opening may be formed in the display cover layer to accommodate a button, a speaker port, or other component. Openings may be formed in housing  12  to form communications ports (e.g., an audio jack port, a digital data port, etc.), to form openings for buttons, etc. 
       FIG. 2  is a schematic diagram of device  10 . As shown in  FIG. 2 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may 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. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  18  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 devices  18  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input-output devices  18  and may receive status information and other output from device  10  using the output resources of input-output devices  18 . Input-output devices  18  may include one or more displays such as display  14 . 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14  using an array of pixels in display  14 . 
     Display  14  may have a rectangular shape (i.e., display  14  may have a rectangular footprint and a rectangular peripheral edge that runs around the rectangular footprint), may be circular or oval, may have a shape with both straight and curved edges, or may have other suitable shapes. Display  14  may be planar or may have a curved profile. 
     A top view of a portion of display  14  is shown in  FIG. 3 . As shown in  FIG. 3 , display  14  may have an array of pixels  22 . Pixels  22  may receive data signals over signal paths such as data lines D and may receive one or more control signals over control signal paths such as horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.). There may be any suitable number of rows and columns of pixels  22  in display  14  (e.g., tens or more, hundreds or more, or thousands or more). Each pixel  22  may have a light-emitting diode  26  that emits light  24  under the control of a pixel control circuit formed from thin-film transistor circuitry such as thin-film transistors  28  and thin-film capacitors). Thin-film transistors  28  may be polysilicon thin-film transistors, semiconducting-oxide thin-film transistors such as indium zinc gallium oxide transistors, or thin-film transistors formed from other semiconductors. 
     A cross-sectional side view of a portion of an illustrative organic light-emitting diode display in the vicinity of one of light-emitting diodes  26  is shown in  FIG. 4 . As shown in  FIG. 4 , display  14  may include a substrate layer such as substrate layer  30 . Substrate  30  may be formed from plastic or other suitable materials. One or more sublayers of material may form substrate  30 . Configurations for display  14  in which substrate  30  has been formed from a flexible material such as polyimide, acrylic, or other flexible polymer are sometimes described herein as an example. 
     Thin-film transistor circuitry  44  may be formed on substrate  30 . Thin film transistor circuitry  44  may include layers  32 . Layers  32  may include inorganic layers such as inorganic buffer layers, gate insulator, passivation, interlayer dielectric, and other inorganic dielectric layers. Layers  32  may also include organic dielectric layers such as a polymer layers. Polymer layers may be used, for example, as planarization layers, as interlayer dielectric, and as neutral plane adjustment layers (as examples). Metal layers and semiconductor layers may also be included within layers  32 . For example, semiconductors such as silicon, semiconducting-oxide semiconductors such as indium gallium zinc oxide, or other semiconductor materials may be used in forming semiconductor channel regions for thin-film transistors  28 . Metal in layers  32  may be used in forming transistor gate terminals, transistor source-drain terminals, capacitor electrodes, and metal interconnects. If desired, conductive polymers, conductive nanostructures, and other conductive materials may be included in display  14  (e.g., to form signal traces in a bent portion of display  14 ). 
     As shown in  FIG. 4 , thin-film transistor circuitry  44  may include diode anode structures such as anode  36 . Anode  36  may be formed from a layer of conductive material such as metal on the surface of layers  32  (e.g., on the surface of a planarization layer that covers underlying thin-film transistor structures). Light-emitting diode  26  may be formed within an opening in pixel definition layer  40 . Pixel definition layer  40  may be formed from a patterned photoimageable polymer such as polyimide. In each light-emitting diode, organic emissive material  38  is interposed between a respective anode  36  and cathode  42 . Anodes  36  may be patterned from a layer of metal. Cathode  42  may be formed from a common conductive layer that is deposited on top of pixel definition layer  40  (e.g., a thin layer of metal such as a layer of AgMg). Cathode  42  is transparent so that light  24  may exit light emitting diode  26 . During operation, light-emitting diode  26  may emit light  24 . 
     Metal interconnect structures may be used to interconnect transistors and other components in circuitry  44 . Metal interconnect lines may also be used to route signals to capacitors, to data lines D and gate lines G, to contact pads (e.g., contact pads coupled to gate driver circuitry), and to other circuitry in display  14 . As shown in  FIG. 4 , layers  32  may include one or more layers of patterned metal for forming interconnects such as metal traces  74 . Portions of metal traces  74  and other conductive traces may extend from pixels  22  to inactive areas of display  14 . 
     If desired, display  14  may have a protective outer display layer such as cover glass layer  70 . The outer display layer may be formed from a material such as sapphire, glass, plastic, clear ceramic, or other transparent material. Protective layer  46  may cover cathode  42 . Layer  46  may include adhesive, moisture barrier structures and other encapsulation structures, and/or other materials to help protect thin-film transistor circuitry  44 . Functional layers  68  may be interposed between layer  46  and cover layer  70 . Functional layers  68  may include a touch sensor layer, a circular polarizer layer, and other layers. A circular polarizer layer may help reduce light reflections from metal traces in thin-film transistor circuitry  44 . A touch sensor layer may be formed from an array of capacitive touch sensor electrodes on a flexible polymer substrate. The touch sensor layer may be used to gather touch input from the fingers of a user, from a stylus, or from other external objects. Layers of optically clear adhesive may be used to attach cover glass layer  70  and functional layers  68  to underlying display layers such as layer  46 , thin-film transistor circuitry  44 , and substrate  30 . If desired, touch sensor structures for display  14  may be formed from metal layers in thin-film transistor circuitry  44  rather than using a separate touch sensor panel in layer  68 . 
     Display  14  may have an active area in which pixels  22  form images for viewing by a user of device  10 . The active area may have a rectangular shape or other suitable shape. Inactive portions of display  14  may surround the active area. For example, signal traces and other support circuitry such as thin-film display driver circuitry may be formed along one or more of the four edges that run around the rectangular periphery of a rectangular display or may be formed along other peripheral portions of display  14  adjacent to the active area. If desired, one or more display driver integrated circuits may be mounted to substrate  30  in the inactive border (e.g., integrated circuit pads on one or more display driver integrated circuits may be coupled to corresponding contact pads formed at the ends of the signal paths on substrate  30  in the inactive border). This allows the display driver circuitry to supply signals to the data and gate lines on display  14 . If desired, a flexible printed circuit on which one or more display driver integrated circuits have been mounted using solder may be attached to contact pads formed from the end portions of the signal lines in the border of display  14 . 
     To minimize the amount of the inactive border area of display  14  that is visible to a user, one or more edges of display  14  may be bent. As an example, the edge of display  14  to which a display driver circuit or flexible printed circuit has been attached may be folded under the active area of display  14 . This helps minimize visible display borders and reduces the footprint of display  14 . 
     An illustrative display with a bent edge portion is shown in  FIG. 5 . As shown in  FIG. 5 , display  14  has portion  14 A (i.e., a planar active area portion that contains the active area of display  14  that is formed by an array of pixels  22 ), bent portion  14 B, and inactive portion  14 C. If desired, connectors, display driver integrated circuits or other integrated circuits, flexible printed circuits, and/or other components  76  may be mounted to inactive portion  14 C of display  14 . 
     Conductive traces such as metal traces  74  may carry signals between inactive area  14 C of display  14  and active area  14 A of display  14  (i.e., metal traces  74  may traverse bent portion  14 B of display  14 ). When bent portion  14 B is bent around bend axis  72 , portion  14 C may be folded partly or completely under portion  14 A and may therefore be hidden from view by a user such as viewer  80  who is viewing display  14  in direction  82 . As shown in  FIG. 5 , component(s)  76  (e.g., display driver circuitry, etc.) may be mounted on the upper and/or lower surface of display  14  in region  14 C. An optional support structure such as a mandrel with a curved surface may be used to support display  14  in bend region  14 B (e.g., to help establish a desired minimum bend radius in region  14 B) or the mandrel may be omitted to help minimize display thickness (e.g., by allowing portions  14 A and  14 C to be mounted more closely together and by allowing the bend radius for region  14 B to be reduced). 
     When bending display  14  in region  14 B, care should be taken to ensure that sensitive display structures do not become damaged. Stresses can be imparted to display structures in a flexible display when the display is bent. For example, conductive traces such as metal traces  74  of  FIG. 5  that are used to form signal lines that convey signals between display driver circuitry or other circuits in inactive region  14 C and pixels  22  in region  14 A may be subjected to bending stresses in bend region  14 B. 
     To help prevent damage to the signal lines in bend region  14 B, the signal paths of display  14  may be provided with redundancy. For example, pairs of adjacent lines may be shorted together using periodic redundancy connections. Meandering path shapes such as zigzag shapes and serpentine shapes may also be used for the portions of the signal lines traversing region  14 B. Particularly in high-resolution displays, there may be a relatively large number of signal lines passing through region  14 B (e.g., hundreds or thousands or more). 
     A top view of illustrative meandering signal lines of the type that may be used for bent portion  14 B of display  14  is shown in  FIG. 6 . There may be any suitable number of lines  174  (e.g., tens, hundreds, or thousands of lines). Signal lines  174  may be formed from metal traces  74  in layers  32  and/or other conductive traces. Lines (traces)  174  may extend in a direction parallel to axis  100  (i.e., axis  100  may be parallel to the longitudinal axes of lines  174 ). Bend axis  72  ( FIG. 5 ) may extend perpendicular to lines  174  (i.e., bend axis  72  may run parallel to axis  102 ). 
     Lines  174  may have a width W of about 2.5 microns (e.g., more than 1 micron, more than 2 microns, 2-10 microns, less than 10 microns, less than 5 microns, 5-30 microns, 10-75 microns, less than 50 microns, or other suitable width). The separation WB between adjacent lines  174  may be more than 1 micron, more than 2 microns, 2-10 microns, less than 10 microns, less than 5 microns, 5-30 microns, 10-75 microns, less than 50 microns, or other suitable distance. The length L of each segment of line  174  between successive line bends  104  may be about 50-250 microns, more than 40 microns, less than 300 microns, 10-100 microns, less than 25 microns, more than 20 microns, or other suitable length. The thickness of each line may be less than 1 micron, less than 0.5 microns, 0.1 to 0.3 microns, more than 0.01 micron, more than 0.1 microns, 0.05 to 0.5 microns, or other suitable thickness. Corners  104  of lines  174  may be curved to help reduce stress concentration. Curved corners may be produced using curved photolithographic masks and/or using semiconductor fabrication techniques (e.g., wet or dry etching techniques or other patterning techniques) that help create curved edges at bends in lines  174 . As an example, corner edges  104 ′ of lines  174  may have a bending radius of 0.2 mm, 0.1 to 0.3 mm, more than 0.05 mm, less than 0.5 mm, or other suitable bend radius. The separation angle A between successive segments of lines  174  between the bends at corners  104  may be about 120° (i.e., the tilt angle of each segment of line  174  with respect to axis  100  may be about) 60°. Axis  100  runs parallel to the longitudinal axis of zigzagging line  174  (vertically in the orientation of  FIG. 6 ) and crosses bend axis  72  at a right angle. If desired, the value of A may be less than 120° (e.g., 0-120°) or may be more than 120° (e.g., 120° to 180°). The use of a value for A of 120° is merely illustrative. 
     Signal paths in region  14 B may be provided with redundancy by shorting together adjacent lines. Two thin lines that are shorted together may exhibit better immunity to stress-induced damage than one thicker line with a width equal to the widths of the two thin lines added together. As a result, arrangements in which two or more parallel signal lines are shorted together may help ensure that the signal paths in region  14 B operate satisfactorily, even when display  14  is bent tightly in region  14 B. 
     An illustrative configuration for display  14  with zigzag traces in region  14 B that include redundancy structures is shown in  FIG. 7 . In the example of  FIG. 7 , signal path  174 - 1  is formed from parallel adjacent metal lines  174 M- 1  and  174 M- 2 , which are shorted together with redundancy paths  174 ′ and signal path  174 - 2  is formed from parallel adjacent metal lines  174 M- 3  and  174 M- 4 , which are shorted together with redundancy paths  174 ′. Redundancy paths (segments)  174 ′ bridge the gaps separating the adjacent lines. Each of paths  174 - 1  and  174 - 2  contains a pair of adjacent lines. If desired, three or more adjacent lines may be shorted together to provide additional redundancy. 
     In the example of  FIG. 7 , redundancy paths  174 ′ are located in the middle of the zigzagging segments of each line and near the corners of each line. If desired, redundancy paths  174 ′ may be formed at other locations along the lengths of lines  174 , may only be located at corners  104 , or may have any other suitable location. 
     As shown in  FIG. 7 , there is a potential for stress zones such stress zones  188  to develop in bent metal traces. Cracks may form in stress zones  188 . As an example, crack  190  may originate at a sharp bend in the metal traces (e.g., corners  104 - 1  and  104 - 2  of signal paths  174 - 1  and  174 - 2 , respectively), which may exhibit more internal stress than other portions of lines  174 . However, crack  190  tends to stop propagating once it reaches the edges of stress zone  188  because the metal outside of stress zones  188  exhibits low stress. The low stress level in the regions between stress zones  188  can help terminate further propagation of crack  190 . 
     Care must be taken to ensure that stress zones  188  are not so close to one another that they form one combined larger stress zone. For example, if the two stress zones  188  near corner  104 - 2  of  FIG. 7  were closer together, the two stress zones  188  could merge, creating one large stress zone that would allow cracks to potentially propagate longer distances across the metal line. The location and orientation of redundancy paths  174 ′ may be such that stress zones  188  do not cluster together near corners  104  and instead remain separate. For example, paths  174 ′ in signal path  174 - 1  may extend perpendicularly between metal trace  174 M- 1  and metal trace  174 M- 2 , and paths  174 ′ in signal path  174 - 2  may extend perpendicularly between metal trace  174 M- 3  and  174 M- 4 . The perpendicular bridges  174 ′ between traces  174 M- 1  and metal trace  174 M- 2  and between  174 M- 3  and  174 M- 4  creates rectangular slits or openings  186 . Rectangular slits  186  may have curved corners or angled corners with 90 degree angles. 
     As signal lines  174  are bent around bend axis  72  (parallel to axis  102  of  FIG. 7 ), stress zones  188  may be created near some of the corners of slits  186 . The shape and location of rectangular slits  186  may help ensure that stress zones  188  are separated by low stress zones are not clustered near corners  104 . For example, as shown in  FIG. 7 , by offsetting bridging segments  174  from corners  104 , one rectangular slit  186  extends closer to corner  104  than an adjacent rectangular slit  186 . This may result in one stress zone  188  near corner  104  and another stress zone that is slightly offset from corner  104 . These stress zones  188  are separated by a low stress zone so that cracks in one stress zone  188  do not propagate beyond that stress zone. 
       FIGS. 8, 9, and 10  show illustrative zigzag signal paths with redundancy structures and different patterns of slits. In the example of  FIG. 8 , each slit  186  has one end that extends close to a corner  104  and an opposing end that stops short of the adjacent corner  104 . In the example of  FIG. 9 , adjacent signal paths  174 - 1  and  174 - 2  have slits  186  with alternating locations (e.g., the pattern of slits  186  in signal path  174 - 1  is different from the pattern of slits  186  in signal path  174 - 2 ). In the example of  FIG. 10 , two redundancy paths  174 ′ are formed on either side of each corner  104 , forming a smaller opening  186 ′ between the two redundancy paths  174 ′. The additional redundancy path  174 ′ may increase the signal path&#39;s immunity to stress-induced damage, while maintaining separation between stress zones  188 . 
     It may also be desirable to minimize bending stress and thereby minimize cracks in signal paths  174  and other traces  74  using neutral plane adjustment layers. Neutral plane adjustment layers may be used to align the neutral plane of display  14  in bend region  14 B with traces  74  (e.g., traces  74  that form signal paths  174 ). 
     As shown in  FIG. 11 , when a portion of display  14  is bent in region  14 B, some layers such as layer(s)  88  (e.g., a portion of display  14  that includes substrate  30 ) may be subjected to compressive stress and some layers such as layer(s)  84  (e.g., a coating layer and other layers above the substrate) may be subjected to tensile stress. Neutral plane  86  arises where stress has been eliminated by balancing the compressive stress and tensile stress. The shape of neutral plane  86  may be curved in a curved portion of display  14  such as portion  14 B of  FIG. 5  (i.e., neutral plane  86  may have a curved profile). 
     The relative thicknesses of layers  88  and  84  and the relative modulus of elasticity values for layers  88  and  84  determine the location of the neutral plane within the layers of bent display region  14 B. For example, if the elasticity of layer  88  and layer  84  is the same, neutral plane  86  can be aligned with metal traces  74  between layers  88  and  84  by ensuring that layer  84  has the same thickness as layer  88 . If, on the other hand, layer  84  has an elasticity that is larger than that of layer  88 , layer  84  need not be as thick as layer  88  to balance the compressive and tensile stresses in this way. 
       FIG. 12A  is a cross-sectional side view of a portion of display  14  containing an illustrative signal line (e.g., a signal line such as line  174  of  FIG. 6, 7, 8, 9 , or  10 ). As shown in  FIG. 12A , bend region (bent region)  14 B of display  14  may include substrate  30 . Substrate  30  may include one or more layers of material and may be flexible. With one illustrative configuration, substrate  30  may include upper and lower layers  30 - 1  and  30 - 3  formed from a flexible polymer such as polyimide and an interposed barrier layer  30 - 2 . Barrier layer  30 - 2  may be formed from one or more layers of inorganic material such as silicon oxide and may help block moisture. The thickness of substrate  30  may be 3-20 microns, less than 20 microns, less than 8 microns, less than 7 microns, less than 6 microns, or other suitable thickness. 
     If desired, line  174  may be formed using a strip of buffer layer material such as buffer layer  174 MB. Layer  174 MB, which may sometimes be referred to as a multilayer buffer, may be interposed between substrate  30  and conductive layer  174 M. Layer (trace)  174 M may be formed from metal or other conductive material. Layer  174 MB may help prevent moisture from reaching metal layer  174 M. Layer  174 MB may include one or more layers of material such as alternating layers of inorganic material (e.g., silicon oxide alternated with silicon nitride), other inorganic layer(s) and/or organic layer(s). 
     Layer  174  may be formed form a metal such as aluminum, molybdenum, titanium, copper, silver, gold, other metals, metal alloys, and/or multiple sublayers formed from these metals or other suitable metals. Layer  174  may also be formed from conductive polymers such as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, conductive nanostructures (e.g., silver nanowires, carbon nanotubes, etc.), and other conductive materials (e.g., carbon inks, etc.). Configurations in which conductive traces for display  14  are formed from metal may sometimes be described herein as an example. This is, however, merely illustrative. Any suitable conductive material may be used in forming the signal lines that traverse bend region  14 B of display  14 . 
     Dielectric passivation layer  174 P may be formed on top of layer  174 M. Portions of passivation layer  174 P may extend down the sides of layer  174 M and may contact buffer layer  174 MB. In this way, the metal line formed from layer  174 M may be surrounded by dielectric material that helps prevent moisture from reaching the metal line, thereby helping to avoid corrosion. Passivation layer  174 P may be formed from one or more inorganic layers (e.g., silicon oxide, silicon nitride, silicon oxynitride, etc.) and/or one or more polymer layers. 
     Inorganic layers such as buffer layer  174 MB and passivation layer  174 P may be patterned to match the trace geometry of trace  174  shown in  FIGS. 5, 6, 7, 8, 9, and 10 . Inorganic layers  174 MB and  174 P may match the footprint of metal layer  174 M or may extend beyond the edges of metal layer  174 M (as shown in the example of  FIG. 12A ). Inorganic layers  174 MB and  174 P may be patterned to surround metal layer  174 M and/or other metal layers on substrate  30 . 
     Polymer planarization layer  180  may cover line  174  and may have a planar upper surface (surface  184 ). If desired, one or more additional layers of signal lines such as lines  174  may be formed above the first layer of lines that is shown in  FIG. 12A . 
     Layers  194  may cover layer  180  and any layers formed above layer  180 . Layers  194 , which may sometimes be referred to as neutral plane adjustment layers, may have an overall thickness T and bending stiffness that place neutral plane  86  ( FIG. 11 ) in a desired location. Layers  194  may, for example, be configured to align neutral plane  86  with signal lines  174  in region  14 B to help reduce stress in region  14 B and reduce cracks in signal lines  174 . 
     Neutral plane adjustment layers  194  may include a coating layer such as layer  182  and one or more additional layers such as layer  192 . Coating layer  182  may be formed from an organic material such as polyimide or other polymer. In some configurations, coating layer  182  may be formed from a polymer coating that is more compliant than substrate  30 . If coating layer  182  were the only layer being used to counteract the bending force of substrate  30 , coating layer  182  would need to be thicker than substrate  30 . Care must be taken, however, to ensure that coating  182  is not too thick. If polymer coating  182  is too thick, it will become too difficult to bend in region  14 B. Polymer coating  182  may also relax during and after bending, which can cause the neutral plane to shift downwards. Care must therefore be taken to ensure that the relaxation of polymer coating  182  does not cause neutral plane  86  to shift below traces  174 , which would then place traces  174  under tensile stress. 
     To help counteract the bending force of substrate  30  and avoid a large downward shift of the neutral plane, neutral plane adjustment layers  194  may include layers other than polymer coating  182 . For example, neutral plane adjustment layers  194  may include one or more additional layers such as layer  192 . If desired, layer  192  may be a metal layer. Because metal is generally stiffer than polymer, the use of metal layer  192  in neutral plane adjustment layers  194  may help counteract the bending force of lower substrate  30 . The assistance from metal layer  192  may be such that polymer layer  182  need not be as thick to balance the bending force of lower substrate  30 . For example, the thickness of polymer layer  182  may be about 50 microns or other suitable thickness (e.g., between 30 and 60 microns, between 50 and 100 microns, greater than 100 microns, or less than 100 microns). In addition to allowing for a thinner polymer layer  182 , metal layer  192  may also help to avoid a large downward shift in the neutral plane as layer  182  relaxes. A thinner polymer layer  182  will cause less of a shift in neutral plane as it relaxes (since it is already more flexible to begin with at the reduced thickness), and the stiffness of metal layer  192  will help keep the neutral plane from shifting below traces  174 . The combination of metal layer  192  and polymer layer  182  may ensure that the neutral plane remains aligned with signal lines  74 . 
     Layer  192  may be a metal layer that is formed during an existing display processing step by extending a metal layer in active area  14 A of display  14  to bent region  14 B of display  14 . For example, metal layer  192  may be formed by extending one or more of the materials that are used to form thin-film transistors  44  ( FIG. 4 ) in active area  14 A to bent region  14 B (e.g., layer  192  may be formed from the same material and during the same processing step as signal lines  74 , anode  36 , cathode  42 , touch sensor structures such as a layer of indium tin oxide, other suitable display layers that are extended to bent region  14 B, or a combination of these layers). Although metal layers in stack  194  may be formed from the same material as active display layers (if desired), these metal layers need not carry signals or be actively driven at any voltage in region  14 B. The metal layers need not extend continuously between the active display layers in region  14 A and neutral plane adjustment layers  194  in region  14 B. If desired, there may be gaps in the metal layers between region  14 A and region  14 B. 
     If desired, layer  192  may be used as a shielding layer to shield one or more display layers from electromagnetic interference. For example, layer  192  may be located between thin-film transistor circuitry  44  and touch sensor circuitry in layer  68  of  FIG. 5  and may be used to block electromagnetic interference between the display circuitry below layer  192  and the touch sensor circuitry above layer  192 . Layer  192  may be grounded (e.g., coupled to a power supply source such as power supply source  212 ) or may be floated (e.g., not actively driven at any power supply voltage). 
     In the example of  FIG. 12A , the vertical (side) edges of trace  174  are perpendicular to the upper surface of substrate  30 . If desired, the side edges of trace  174  may be non-perpendicular to the upper surface of substrate  30  to suppress interfacial crack initiation along the interface of layers  174 MB,  174 P,  174 M and planarization layer  180 . An example of this type of arrangement is shown in  FIG. 12B . 
     As shown in  FIG. 12B , the side edges of layers  174 MB,  174 P, and  174 M may be angled relative to the upper surface of substrate  30 . The angle θ1 between the upper surface of substrate  30  (indicated by line  214 ) and the side edge of layers  174 B and  174 P (indicated by line  216 ) may be between 90° and 160°, between 90° and 180°, between 100° and 120°, between 120° and 150°, greater than 90°, etc. The angle θ2 between the upper surface of substrate  30  (indicated by line  214 ) and the side edge of metal layer  174 M (indicated by line  218 ) may be between 90° and 160°, between 90° and 180°, between 100° and 120°, between 120° and 150°, greater than 90°, etc. The taper angle between vertical edges of  174 MB/ 174 P/ 174 M and substrate  30  could vary, say from 90 degree to 160 degree. Angle θ2 may be the same as angle θ1 or may be different from angle θ1. The angled side edges of these layers may help suppress interfacial crack initiation at the interface of layers  174 MB,  174 P,  174 M, and planarization layer  180 . If desired, the distance D by which layers  174 MB and  174 P extend beyond metal layer  174 M may be adjusted to achieve the appropriate level of protection for metal layer  174 M. 
       FIG. 13  shows how neutral plane adjustment layers  194  may include two or more metal layers to counteract the bending force of substrate  30  and the relaxation of polymer layer  182 . In the example of  FIG. 13 , traces  174  are located on top of a polymer layer such as planarization layer  196  (e.g., a layer of polyimide or other polymer). Additional metal layer  102  may be separated from metal layer  192  by a dielectric layer such as layer  104  (e.g., a planarization layer formed from polymer or other suitable material). Metal layer  102  may, if desired, be an extension of a different metal layer in thin-film transistor circuitry  44 . For example, layer  192  may be an extension of a lower signal trace layer and layer  102  may be an extension of an upper signal trace layer, or layer  192  may be an extension of a signal trace layer and layer  192  may be an extension of an anode layer, a cathode layer, or a touch layer. As with metal layer  192 , metal layer  102  need not carry any electrical signals. One or both of metal layers  192  and  102  may be grounded, or both metal layers  192  and  102  may not be grounded and left floating. One or both of metal layers  192  and  102  may be patterned with gaps, or both metal layers  192  and  102  may not be patterned. If desired, layers  194  may include three or more metal layers. Additional metal layers in layers  194  may be grounded or left floating, and may be patterned with gaps or not patterned. The examples of  FIGS. 12A, 12B, and 13  are merely illustrative. 
     Layer  192  may be a blanket layer without openings or may include one or more openings or slits to facilitate bending in region  14 B.  FIG. 14  shows an example in which metal layer  192  includes gaps such as gaps  198 . Gaps  198  may extend perpendicular to axis  102  (and bend axis  72  of  FIG. 5 ). If desired, metal layer  192  may be patterned to form parallel line segments. The line segments may have meandering shapes (e.g., a zigzag shape of the type shown in  FIG. 6 , a chain shape, or other suitable shape) or may be straight. The presence of gaps  198  may facilitate bending in region  14 B. To ensure that signal paths  174  remain in the neutral plane, the segments of metal layer  192  may overlap signal lines  174 . Segments of metal layer  192  may have the same size and shape as signal lines  174 , may have a slightly larger footprint than signal lines  174 , or may have a smaller footprint than signal lines  174 . If desired, the segments of metal layer  192  may be coupled a ground power supply to provide shielding or may be left floating without being actively driven at any power supply voltage. 
       FIG. 15  shows an example in which layer  194  includes openings  208  that extend parallel to bend axis  72 . Openings  208  may be selectively placed to make region  14 B more flexible in a desired region. Portion  14 C may be bent under portion  14 A and may be secured to the underside of portion  14 A using layers such as layers  202  and  204 . Layer  202  and  204  may be polymer layers (sometimes referred to as backfilms) that are attached to one another using adhesive  206  (e.g., a pressure-sensitive adhesive or other suitable adhesive). The placement of layer  204  relative to layer  202  may be used to control the bend profile of portion  14 B. 
     If care is not taken, kinks in display  14  may occur in regions  210  where display  14  attaches at the edges of layers  202  and  204 , which in turn can lead to damage such as cracks. Kinks can be avoided by increasing flexibility in the portion of display  14  that is furthest from the edges of layers  202  and  204 . Metal layer  192  may be patterned to include one or more openings  208  in bend region  14 B, away from layers  202  and  204  so that kinks do not occur in regions  210 . Openings  208  may be continuous elongated slits or may be segmented smaller openings in metal layer  192 . 
     The foregoing is merely illustrative and various modifications can be made by those skilled in the art without departing from the scope and spirit of the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20180531
Publication Date: 20200331
Grant Date: 20200331
Priority Date: 20170623
Inventors: ZHANG, ZHEN
Lam, Terry C.
DRZAIC, PAUL S.
AHMED, Izhar Z.
Assignee: APPLE INC
CPC Classifications: [{"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04102", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F3/044", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L27/3276", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01L51/5253", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F3/0412", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L51/0097", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01L27/323", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F2203/04107", "inventive": false, "first": false, "tree": "[]"}, {"code": "G06F2203/04102", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01L2251/5338", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/844", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K77/111", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/131", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/131", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K2102/311", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K2102/311", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K77/111", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "Y02E10/549", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/873", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 64692806