PATENT DOCUMENT

Publication Number: US-11882752-B1
Application Number: US-202117378544-A
Country: US
Kind Code: B1

Title: Electronic devices with through-display sensors

Abstract:
An electronic device display may have an active area with pixels. An optical sensor may be formed under a sensor region in the active area. During operation, ambient light and/or other light associated with the optical sensor may pass through the sensor region. To ensure that the light for the optical sensor can pass through the display, the display may have one or more layers with sensor openings such as a metal layer and a pressure sensitive adhesive layer that attaches the metal layer to the pixels of the display. To help minimize visibility of the openings in the sensor region, the pressure sensitive adhesive layer may be configured to have a reflectivity that matches the appearance of the display in the sensor region to surrounding areas. Undesired light output uniformity can be reduced by ensuring that the substrate material in the display has a low light absorption coefficient.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a housing; 
 a display mounted in the housing, wherein the display has an active area with pixels configured to display an image; and 
 an optical sensor under a sensor region in the active area, wherein the optical sensor is configured to receive light through the sensor region, wherein the display comprises a layer of adhesive having a reflectivity configured to help visually match the sensor region to surrounding portions of the display, and wherein the reflectivity is 5-35%. 
 
     
     
       2. The electronic device defined in  claim 1  wherein the display comprises a metal plate with an opening aligned with the sensor region, wherein the layer of adhesive is between the pixels and the metal plate. 
     
     
       3. The electronic device defined in  claim 2  further comprising a layer of polyimide between the pixels and the layer of adhesive, wherein the layer of polyimide is characterized by an absorption coefficient of less than 5.98×10 4  m -1 . 
     
     
       4. The electronic device defined in  claim 3  wherein the layer of polyimide is characterized by an absorption coefficient of less than 4.31×10 4  m -1 . 
     
     
       5. The electronic device defined in  claim 1  further comprising:
 a substrate layer on which the pixels are formed; 
 a polymer layer between the substrate layer and the layer of adhesive; and 
 an antireflection layer on the polymer layer in the sensor region, wherein the antireflection layer is between the polymer layer and the optical sensor. 
 
     
     
       6. The electronic device defined in claim  1  further comprising:
 a substrate layer on which the pixels are formed; 
 a polymer layer between the substrate layer and the layer of adhesive, wherein the sensor comprises a sensor window formed from clear material; and 
 a layer of index matching material that contacts the polymer layer and that contacts the sensor window. 
 
     
     
       7. The electronic device defined in  claim 1  wherein the adhesive layer comprises a layer of gray pressure sensitive adhesive. 
     
     
       8. The electronic device defined in  claim 7  wherein the optical sensor comprises an ambient light sensor. 
     
     
       9. The electronic device defined in  claim 1  wherein the pixels comprise organic light-emitting diode pixels, wherein the optical sensor comprises an ambient light sensor, and wherein the adhesive layer comprises a layer of pressure sensitive adhesive. 
     
     
       10. The electronic device defined in  claim 1  further comprising a layer of polyimide between the pixels and the layer of adhesive, wherein the layer of polyimide is characterized by an absorption coefficient of less than 4.31×10 4  m -1 . 
     
     
       11. An electronic device, comprising:
 a display having pixels that form an active area in which an image is displayed; 
 a display cover layer that overlaps the pixels, wherein the display has a sensor region within the active area that overlaps some of the pixels; 
 a metal layer configured to support the display, wherein the metal layer has a hole in the sensor region; 
 an adhesive layer with a hole in the sensor region, wherein the adhesive layer is configured to help reduce visibility of the hole in the metal layer; and 
 an ambient light sensor configured to receive ambient light that has passed through the display cover layer, through the pixels in the sensor region, and through the holes in the metal layer and the adhesive layer. 
 
     
     
       12. The electronic device defined in  claim 11  further comprising a polyimide substrate layer between the pixels and the adhesive layer, wherein the polyimide substrate layer has an absorption coefficient of less than 4.31×10 4  m -1 . 
     
     
       13. The electronic device defined in  claim 12  wherein the adhesive layer comprises a gray pressure sensitive adhesive layer. 
     
     
       14. The electronic device defined in  claim 13  wherein the adhesive layer has a reflectivity of at least 5%. 
     
     
       15. The electronic device defined in  claim 11  wherein the adhesive layer comprises a pressure sensitive adhesive layer with a reflectivity of at least 7%. 
     
     
       16. The electronic device defined in  claim 11  further comprising:
 a substrate layer on which the pixels are formed; 
 a polymer layer between the substrate layer and the adhesive layer; and 
 an antireflection layer on the polymer layer in the sensor region, wherein the antireflection layer is between the polymer layer and the ambient light sensor. 
 
     
     
       17. An apparatus, comprising:
 a layer of pixels configured to display an image; 
 a sensor configured to measure ambient light passing through the layer of pixels; 
 a metal layer configured to support the layer of pixels; and 
 a pressure sensitive adhesive layer between the metal layer and the layer of pixels that has a reflectivity of at least 7%. 
 
     
     
       18. The apparatus defined in  claim 17  wherein the sensor comprises a color ambient light sensor and wherein the pixels comprise organic light-emitting diode pixels formed on a polyimide substrate. 
     
     
       19. The electronic device defined in  claim 18  wherein the polyimide substrate is between the pixels and the pressure sensitive adhesive layer and wherein the polyimide substrate has an absorption coefficient of less than 5.98×10 4  m -1 . 
     
     
       20. The electronic device defined in  claim 17  further comprising:
 a substrate layer on which the layer of pixels is formed; 
 a polymer layer between the substrate layer and the pressure sensitive adhesive layer; and 
 an antireflection layer on the polymer layer, wherein the antireflection layer is between the polymer layer and the sensor.

Description:
This application claims the benefit of provisional patent application No. 63/071,980, filed Aug. 28, 2020, which is hereby incorporated by reference herein in its entirety. 
    
    
     FIELD 
     This relates generally to electronic devices, and, more particularly, to electronic devices with displays and sensors. 
     BACKGROUND 
     Electronic devices often have displays. Sensors are sometimes used in electronic devices to gather sensor readings. It can be challenging to accommodate both displays and sensors in electronic devices. 
     SUMMARY 
     An electronic device may be provided with a display. The display may have an active area with pixels configured to display an image for viewing by a user. 
     An optical sensor may be formed under a sensor region in the active area. During operation, ambient light and/or other light associated with the optical sensor may pass through the sensor region. 
     The display may have one or more layers with openings that are aligned with the optical sensor. For example, the display may have a metal plate that helps to support the pixels and may have a pressure sensitive adhesive layer that helps attach the pixels to the metal plate. 
     To ensure that the light for the optical sensor can pass through the display, the metal layer and the pressure sensitive adhesive layer may have openings aligned with the sensor area. 
     To help minimize visibility of the openings in the sensor region, the pressure sensitive adhesive layer may be configured to have a reflectivity that is closely matched to structures in the sensor region. In this way, light such as stray light emitted by the pixels of the display will tend to reflect with equal intensity from the sensor region and the pressure sensitive adhesive, making it difficult or impossible to visually discern any difference in appearance between the sensor region and other portions of the display. 
     Undesired light output variations from the pixels of the display can be reduced and display uniformity enhanced by ensuring that display substrate material in the display has a low 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an illustrative electronic device in accordance with an embodiment. 
         FIG.  2    is a perspective view of an illustrative electronic device in accordance with an embodiment. 
         FIG.  3    is a cross-sectional side view of an illustrative electronic device in accordance with an embodiment. 
         FIG.  4    is a cross-sectional side view of an illustrative display and sensor in accordance with an embodiment. 
         FIG.  5    is a graph in which light transmission through a pair of illustrative display substrate layers has been plotted as a function of wavelength in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may be provided with displays. Displays may be used for displaying images for users. Displays may be formed from arrays of light-emitting diode pixels or other pixels. For example, a device may have an organic light-emitting diode display or a display formed from an array of micro-light-emitting diodes (e.g., diodes formed from crystalline semiconductor dies). The electronic devices may have sensors such as optical sensors that operate through the displays. This helps hide the sensors from view and allows inactive display borders to be minimized. 
     A schematic diagram of an illustrative electronic device having one or more optical sensors that operate through a display is shown in  FIG.  1   . Device  10  may be a cellular telephone, tablet computer, laptop computer, wristwatch device or other wearable device, a television, a stand-alone computer display or other monitor, a computer display with an embedded computer (e.g., a desktop computer), a system embedded in a vehicle, kiosk, or other embedded electronic device, a media player, or other electronic equipment. Configurations in which device  10  is a wristwatch, cellular telephone, tablet computer, or other portable electronic device may sometimes be described herein as an example. This is illustrative. Device  10  may, in general, be any suitable electronic device with a display. 
     Device  10  may include control circuitry  20 . Control circuitry  20  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as 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  20  may be used to gather input from sensors and other input devices and may be used to control output devices. The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors and other wireless communications circuits, power management units, audio chips, application specific integrated circuits, etc. During operation, control circuitry  20  may use a display and other output devices in providing a user with visual output and other output. 
     To support communications between device  10  and external equipment, control circuitry  20  may communicate using communications circuitry  22 . Circuitry  22  may include antennas, radio-frequency transceiver circuitry (wireless transceiver circuitry), and other wireless communications circuitry and/or wired communications circuitry. Circuitry  22 , which may sometimes be referred to as control circuitry and/or control and communications circuitry, may support bidirectional wireless communications between device  10  and external equipment over a wireless link (e.g., circuitry  22  may include radio-frequency transceiver circuitry such as wireless local area network transceiver circuitry configured to support communications over a wireless local area network link, near-field communications transceiver circuitry configured to support communications over a near-field communications link, cellular telephone transceiver circuitry configured to support communications over a cellular telephone link, or transceiver circuitry configured to support communications over any other suitable wired or wireless communications link). Wireless communications may, for example, be supported over a Bluetooth® link, a WiFi® link, a wireless link operating at a frequency between 6 GHz and 300 GHz, a 60 GHz link, or other millimeter wave link, cellular telephone link, wireless local area network link, personal area network communications link, or other wireless communications link. Device  10  may, if desired, include power circuits for transmitting and/or receiving wired and/or wireless power and may include batteries or other energy storage devices. For example, device  10  may include a coil and rectifier to receive wireless power that is provided to circuitry in device  10 . 
     Device  10  may include input-output devices such as devices  24 . Input-output devices  24  may be used in gathering user input, in gathering information on the environment surrounding the user, and/or in providing a user with output. Devices  24  may include one or more displays such as display  14 . Display  14  may be an organic light-emitting diode display, a liquid crystal display, an electrophoretic display, an electrowetting display, a plasma display, a microelectromechanical systems display, a display having a pixel array formed from crystalline semiconductor light-emitting diode dies (sometimes referred to as microLEDs), and/or other display. Configurations in which display  14  is an organic light-emitting diode display or microLED display are sometimes described herein as an example. 
     Sensors  16  in input-output devices  24  may include force sensors (e.g., strain gauges, capacitive force sensors, resistive force sensors, etc.), audio sensors such as microphones, touch and/or proximity sensors such as capacitive sensors (e.g., a two-dimensional capacitive touch sensor integrated into display  14 , a two-dimensional capacitive touch sensor overlapping display  14 , and/or a touch sensor that forms a button, trackpad, or other input device not associated with a display), and other sensors. If desired, sensors  16  may include optical sensors such as optical sensors that emit and detect light, ultrasonic sensors, optical touch sensors, optical proximity sensors, and/or other touch sensors and/or proximity sensors, monochromatic and color ambient light sensors, image sensors, fingerprint sensors, temperature sensors, sensors for measuring three-dimensional non-contact gestures (“air gestures”), pressure sensors, sensors for detecting position, orientation, and/or motion (e.g., accelerometers, magnetic sensors such as compass sensors, gyroscopes, and/or inertial measurement units that contain some or all of these sensors), health sensors, radio-frequency sensors, depth sensors (e.g., structured light sensors and/or depth sensors based on stereo imaging devices that capture three-dimensional images), optical sensors such as self-mixing sensors and light detection and ranging (lidar) sensors that gather time-of-flight measurements, humidity sensors, moisture sensors, gaze tracking sensors, and/or other sensors. In some arrangements, device  10  may use sensors  16  and/or other input-output devices to gather user input. For example, buttons may be used to gather button press input, touch sensors overlapping displays can be used for gathering user touch screen input, touch pads may be used in gathering touch input, microphones may be used for gathering audio input, accelerometers may be used in monitoring when a finger contacts an input surface and may therefore be used to gather finger press input, etc. 
     If desired, electronic device  10  may include additional components (see, e.g., other devices  18  in input-output devices  24 ). The additional components may include haptic output devices, audio output devices such as speakers, light-emitting diodes for status indicators, light sources such as light-emitting diodes that illuminate portions of a housing and/or display structure, other optical output devices, and/or other circuitry for gathering input and/or providing output. Device  10  may also include a battery or other energy storage device, connector ports for supporting wired communication with ancillary equipment and for receiving wired power, and other circuitry. 
       FIG.  2    is a perspective view of electronic device  10  in an illustrative configuration in which device  10  is a portable electronic device such as a wristwatch, cellular telephone, or tablet computer. As shown in  FIG.  2   , device  10  may have a display such as display  14 . Display  14  may cover some or all of the front face of device  10 . Touch sensor circuitry such as two-dimensional capacitive touch sensor circuitry may be incorporated into display  14 . 
     Display  14  may be mounted in housing  12 . Housing  12  may form front and rear housing walls, sidewall structures, and/or internal supporting structures (e.g., a frame, midplate member, etc.) for device  10 . Glass structures, transparent polymer structures, and/or other transparent structures that cover display  14  and other portions of device  10  may provide structural support for device  10  and may sometimes be referred to as housing structures or display cover layer structures. For example, a transparent housing portion such as a glass or polymer housing structure that covers and protects a pixel array in display  14  may serve as a display cover layer for the pixel array while also serving as a housing wall on the front face of device  10 . The portions of housing  12  on the sidewalls and rear wall of device  10  may be formed from transparent structures and/or opaque structures. 
     Device  10  of  FIG.  2    has a rectangular outline (rectangular periphery) with four corners. Device  10  may have other shapes, if desired (e.g., circular shapes, other shapes with curved and/or straight edges, etc.). 
     Display  14  may overlap one or more sensors  16 . For example, display  14  may overlap optical sensors at locations such as illustrative sensor regions  28  of  FIG.  2   . Sensor regions  28  may be formed within the active area of display  14  (i.e., sensor regions  28  may overlap pixels in display  14  that are used to display images, rather than being located in inactive border regions of display  14 ). 
     The pixel structures of display  14  have gaps (e.g., gaps forming clear regions between metal traces and other opaque structures forming the pixel structures of display  14 ). Light may pass through these gaps in the pixels of display  14 . As a result, the pixel structures in the active area of display  14  do not block light transmission. Display  14  may therefore be configured so that light passes through display  14 . This light may include, for example, light emitted by sensors located under display  14  in regions  28  and ambient light present in the exterior region surrounding device  10 . When displaying images, the pixels of display  14  emit light and some of this light (e.g., stray light) has an opportunity to pass through transparent portions of display  14  (e.g., portions of display  14  in sensor regions  28 ). 
     The light transmission of the pixel array forming display  14  may be, for example, at least 0.2%, at least 1%, at least 2%, at least 25%, at least 50%, at least 75%, less than 99.9%, less than 75%, or other suitable amount. Because the pixels of display  14  do not form a completely opaque light barrier, optical sensors that are located in the interior of device  12  under display  14  may emit light outwardly that passes through display  14  and reaches the exterior region surrounding device  10  and/or may detect light from the exterior region surrounding device  10  that passes through display  14  to the interior of device  10 . These operations may be performed when some or all of the pixels of display  14  have been turned off or have been momentarily placed in a state in which they are not emitting light and/or may be performed when the pixels of display  14  are emitting light. 
     The optical sensors that operate through display  14  in this way may include infrared light-emitting devices (e.g., flood illuminators for infrared light sources), cameras (e.g., visible light image sensors and associated camera flashes, infrared cameras, etc.), optical proximity sensors such as proximity sensors that emit infrared light and detect the infrared light after the infrared light has reflected from external objects, three-dimensional sensors (e.g., infrared structured light sensors that include infrared image sensors and associated infrared light sources), time-of-flight sensors, lidar sensors, and/or other sensors that emit and/or detect light. 
     In an illustrative configuration, which may sometimes be described herein as an example, the optical sensors that are overlapped by display  14  in regions such as regions  28  of  FIG.  2    may be monochrome ambient light sensors or color ambient light sensors. Ambient light sensors such as these may detect the amount of ambient light present in the vicinity of device  10 . This information may be used to adjust screen brightness (e.g., to dim display  14  in dark ambient conditions and to brighten display  14  in bright lighting conditions) and/or to take other suitable action (e.g., adjusting display color cast based on ambient light color measurements, etc.). 
       FIG.  3    is a cross-sectional side view of device  10  of  FIG.  2    taken through one of regions  28 . As shown in  FIG.  3   , display  14  includes an array of pixels P forming display panel  14 P under an inwardly facing surface of display cover layer  14 CG. Display panel  14 P may be, for example, a thin-film organic light-emitting diode display or a microLED display in which light-emitting pixels P are formed on a substrate layer (e.g., a layer of polyimide or a sheet of other polymer). Additional support for the pixel array of display  14  may be provided by a layer of metal (e.g., a housing midplate layer formed from metal or other metal layer that is coupled to the underside of display panel  14 P). The metal supporting layer of display  14 , which may be considered to form part of panel  14 P or a separate layer that is coupled to panel  14 P, may be coupled to the substrate layer of panel  14 P by a layer of adhesive. An opening may be formed in the metal supporting layer and the layer of adhesive to allow light  30  in region  28  to pass through display  14  to or from an optical sensor. The optical sensor may be an optical sensor such as optical sensor  36  of  FIG.  3    that is aligned with region  28  under display  14 . Optical sensor  36  may be a color or monochrome ambient light sensor, image sensor, proximity sensor, and/or other optical sensor (e.g., one or more of sensors  16  of  FIG.  1   ). 
     Display cover layer  14 CG may be formed from polymer, glass, crystalline materials such as sapphire, other materials, and/or combinations of these materials. In the example of  FIG.  3   , housing  12  has a portion on rear face R that forms a rear housing wall and has side portions forming sidewalls  12 W. The rear housing wall of housing  12  may form a support layer for components in device  10 . Housing  12  may also have one or more interior supporting layers (e.g., frame structures) such as a metal midplate layer for supporting the array of pixels P in panel  14 P. In the example of  FIG.  3   , display  14  is mounted on front face F of device  10 . In general, display  14  may be mounted on any suitable portion of device  10 . One or more sensors such as optical sensor  36  may be mounted under an active portion of display  14  (e.g., a portion of display  14  that includes pixels P for displaying images) and can transit and/or receive light  30  that passes through the pixels (e.g., through gaps between opaque metal traces and other opaque structures in the pixels). Electrical components  32  may be mounted in the interior of device  10  (e.g., between display  14  and the rear of housing  12 . Components  32  may include circuitry of the type shown in  FIG.  1    (e.g., control circuitry  20 , communications circuitry  22 , input-output devices  24 , batteries, etc.). 
       FIG.  4    is a side view of a portion of device  10  showing how display panel  14 P may include a stack of display layers such as layers  14 TF. Layers  14 TF may include polarizer layers, thin-film encapsulation layers, layers of thin-film circuitry including pixel circuits for the pixels of panel  14 P, light-emitting diodes for the pixels of panel  14 P, and/or other display circuitry. Touch sensor circuitry may be included in layers  14 TF (e.g., panel  14 P may include a two-dimensional capacitive touch sensor). 
     Layers  14 TF may be formed on substrate layer  14 PI. Layer  14 PI may be formed from polymer such as polyimide. In an illustrative configuration, which may sometimes be described herein as an example, substrate layer  14 PI may include a first polyimide layer such as polyimide layer  54  and a second polyimide layer such as polyimide layer  50 . A thin-film inorganic layer (e.g., a layer of a dielectric such as silicon oxide) may be formed between layers  56  and  54  to help block charge transport between layer  54  and  50 . 
     During fabrication of display panel  14 P, layer  14 PI may be supported by a glass carrier. Following formation of the pixel array for panel  14 P (e.g., the pixels formed from the circuitry of layers  14 TF), a laser lift-off process or other removal process may be used to remove layer  14 PI and layers  14 TF from the glass carrier. These layers may then be attached to clear polymer support layer  56  (e.g., a layer of polyethylene terephthalate) by lamination under heat and/or pressure and/or by using an adhesive layer. Polymer support layer  56  may be attached to a metal support layer such as metal plate  64  using a layer of adhesive such as pressure sensitive adhesive layer  58 . Metal plate  64 , which may be, for example, a housing midplate or other metal supporting layer may be coupled to the inner surface of panel  14 P and may therefore sometimes be considered to form part of panel  14 P. 
     Optical sensor  36  may be mounted in the interior of device  10  in alignment with region  28 . A sensor window opening may be formed in metal plate  64  such as opening  72 . Opening  72  may also be formed in adhesive layer  58 . The outline of opening  72  may be circular, rectangular, etc. By forming openings in pressure sensitive adhesive layer  58  and in metal plate  64 , light may pass through region  28  of display  14  (e.g., light that is emitted by and/or sensed by sensor  36 ). 
     In the illustrative configuration of  FIG.  4   , sensor  36  is an ambient light sensor and includes semiconductor die  70 . Die  70  may contain one or more photodetectors (e.g., photodetectors covered by color filters with different respective pass bands to provide sensor  36  with the ability to make spectral measurements). Die  70  may be formed from silicon and may be coupled to a flexible printed circuit or other signal path (e.g., so that control circuitry  20  of  FIG.  1    may gather sensor data from sensor  36 ). 
     As shown in  FIG.  4   , die  70  may be mounted in package  68 . Package  68  may, as an example, be formed from opaque polymer. Sensor window  66  may include light diffuser layers, filter layers, clear substrate layers and/or other optical films (e.g., clear polymer and/or glass structures, thin-film layers, etc.). Window  66  may be mounted in package  68  over die  70 . During operation, light that is received by device  10  in region  28  (e.g., ambient light from the exterior of device  10 ) may pass into the interior of device  10  through display cover layer  14 CG, through display layers  14 TF, through substrate  14 PI, through support layer  56 , and through opening  72  in pressure sensitive adhesive layer  58  and metal pate  64 . After passing through a gap (e.g., an air gap) between layer  56  and window  66 , this light may then pass through window  66  into the interior of sensor  36  and may be measured by the photodetectors on die  70 . 
     The ambient light that passes through display cover layer  14 CG and light that is emitted by the pixels of layers  14 TF illuminates the surface of pressure sensitive adhesive layer  58  and illuminates opening  72 . The light illuminating these areas of display  14  may potentially exhibit different amounts of reflection. Illumination that reaches the interface between polymer support layer  56  and pressure sensitive adhesive  58  may be reflected at a first level (e.g., reflectivity R1). Illumination that reaches the interface at the lower surface of layer  56  (e.g., the air-to-polymer interface at the innermost surface of polymer support layer  56  in opening  72 ) may be reflected at a second level (e.g., reflectivity R2). If care is not taken, a mismatch between the magnitudes of R1 and R2 may make the presence of opening  72  visible to a user viewing display  14 . For example, opening  72  may appear dark while surrounding portions of display  14  outside of region  28  may appear light or vice versa. 
     To help avoid undesirable visual artifacts such as these as a user is viewing images on display  14 , the reflectivity of pressure sensitive adhesive  58  may be selected so that the values of R1 and R2 are closely matched (e.g., so that R1 differs from R2 by less than 35%, less than 25%, less than 15%, less than 10%, less than 5%, or other suitable amount). Pressure sensitive adhesive  58  may also be provided with a neutral color (e.g., gray rather than a non-neutral color such as blue). In an illustrative embodiment, this may be accomplished by forming pressure sensitive adhesive  58  from a gray polymer material such as a gray pressure sensitive adhesive characterized by a reflectivity R1 of 5-35%, 5-40%, 5-15%, at least 7%, 7-13%, 10-20%, at least 5%, at least 10%, at least 20%, at least 30%, 35%, less than 65%, or other suitable reflectivity value that helps to minimize the difference between the values of R1 and R2. Using dark gray pressure sensitive adhesive in display  14  rather than other colors of pressure sensitive adhesive (e.g., rather than white or black pressure sensitive adhesive as examples) may help enhance the appearance of display  14  by reducing visual artifacts on display  14 . 
     In some configurations, it may be desirable to help minimize the value of R2 in opening  72  (e.g., to allow a darker pressure sensitive adhesive material to be used in forming pressure sensitive adhesive  58  and thereby helping to suppress stray light). This may be accomplished by including antireflection layer  60  on the innermost surface of polymer support layer  56  in opening  72  or by incorporating index-matching material  62  that spans the gap between the lowermost surface of layer  56  and the uppermost layer of window  66 . Incorporating these structures to reduce the reflectivity of region  28  allows the reflectivity of layer  58  to be reduced elsewhere (if desired) while still avoiding undesired visual artifacts. 
     Antireflection layer  60  may be an antireflection coating formed from one or more layers of clear dielectric material (e.g., polymer, inorganic dielectric layer(s), etc.). If desired, antireflection layer  60  may include a stack of thin-film dielectric layers with alternating refractive index values that are configured to form a thin-film interference filter antireflection coating. Index-matching material  62 , which may be, for example, an ultraviolet-light-cured adhesive (e.g., optically clear adhesive) such as an ultraviolet-light-cured epoxy or other transparent polymer adhesive, may have a refractive index value that matched to (or has an intermediate value between) the refractive index values of layer  58  and window  66 . Index matching may be accomplished by ensuring that these index values differ by less than 0.15, less than 0.1, less than 0.05, less than 0.025 or other suitable matching criteria. The use of index-matching material may help suppress reflections at the interface between layer  56  and material  62  and/or at the interface between material  62  and window  66  (e.g., less light will be reflected from these interfaces than in scenarios in which material  62  is not present and the gap between the lower surface of layer  56  and the opposing upper surface of window  66  is filled with air). 
     Because light passes through polyimide layer  14 PI during operation of display  14 , there is a risk that some of this light will be absorbed in layer  14 PI. Light absorbed in layer  14 PI (e.g., light absorbed in layer  50 ) may create photo-induced electrical charge. This charge can create electric fields that affect the voltages on the circuitry of layers  14 TF (e.g., the photo-induced charge may impact the amount of current flowing through transistors in layer  14 TF and the associated amount of light emitted by the light-emitting diodes of the pixels of layer  14 TF). The photo-induced charge may therefore represent a potential source of undesirable variations in the output of the pixels in display panel  14 P across the surface of display  14 . To avoid these undesirable brightness variations while operating display  14 , the amount of light absorption exhibited by layer  14 PI (e.g., the absorption of layer  50 ) may be maintained at a suitably low level. 
     To help increase the light transmission of layer  14 PI and thereby reduce light absorption and photo-induced charge creation in layer  14 PI, layer  14 PI may be configured to exhibit a relatively large amount of light transmission.  FIG.  5    is a graph in which light transmission for an illustrative polyimide layer (e.g., layer  14 PI) with a thickness of 10 microns has been plotted as a function of wavelength for two illustrative types of polyimide. The first type of polyimide is formed using higher-temperature curing temperatures and results in a transmission characteristic of the type shown by curve  80 . The second type of polyimide is formed using reduced-temperature curing (curing for a longer period of time at a temperature below the higher-temperature used in curing the first type of polyimide). The low-temperature-cured polyimide layer may be characterized by a light transmission characteristic of the type shown by curve  82 . In this example, the light transmission T of layer  14 PI at a wavelength of 500 nm is represented by a relatively high value (point  84  on curve  82 ). The light transmission T at point  84  may be, for example, at least 55%, at least 60%, at least 65%, at least 70%, or at least 75% when the polyimide layer thickness is 10 microns. 
     Polyimide layers with different thicknesses will exhibit different amounts of light transmission. Equation 1 represents the intensity I of light after passing through a layer of polyimide of thickness d. In equation 1, intensity I0 is the intensity of light entering the polyimide layer and μ is the absorption coefficient for the polyimide material.
 
 I=I 0 exp (-μ d )   (1)
 
     Transmission T through the layer of polyimide of thickness d is equal to I/I0. For satisfactory display output uniformity, T is preferably at least 55%, at least 65%, at least 75%, or 55-75% (as examples) in a layer of polyimide where d is equal to 10 microns. Solving for absorption coefficient μ using equation 1, these preferable values correspond to values of μ of less than 5.98×10 4  m -1  (at least 55% transmission), less than 4.31×10 4  m -1  (at least 65% transmission), 2.88×10 4  m -1  (at least 75% transmission), and 5.98 to 2.88×10 4  m -1  (55-75% transmission). 
     Some or all of the polyimide material used in forming layer  14 PI (e.g., polyimide layer  50  and polyimide layer  54 ) may have these preferred optical absorption characteristics to help ensure satisfactorily low levels of photo-induced charge in layer  14 PI and thereby ensure satisfactory display output uniformity. Satisfactory display uniformity characteristics may be achieved by using polyimide with these preferred absorption coefficient values in any suitable displays including displays  14  that include optional antireflection layer  60 , optional index-matching material  62 , and/or that use material such as dark gray polymer for forming pressure sensitive adhesive layer  58  that exhibits a reflectivity R1 of 5-15%, 5-35%, 5-40%, at least 7%, 7-13%, 10-20%, at least 5%, at least 10%, at least 20%, at least 30%, 35%, less than 65%, or other suitable reflectivity value for minimizing appearance differences between region  28  of display  14  and other regions of display  28 . 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20210716
Publication Date: 20240123
Grant Date: 20240123
Priority Date: 20200828
Inventors: WANG, ZHAO
SOYSEVEN, ALEXIS G.
HUM, DAVID S.
WILLIAMS, GRAEME M.
WANG, ING-JYE
CHOI, JAE WON
HUANG, JIMMY H.
XU, MING
LEE, SUNGKI
ELLIS, TIMOTHY H.
CHEN, YU CHENG
CHE, Yuchi
Assignee: APPLE INC
CPC Classifications: [{"code": "G01J1/0233", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01J3/0272", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01J1/0407", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J1/0214", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J3/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01J3/0262", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J3/0205", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J1/4204", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B27/281", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B37/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "G01J1/4204", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2307/416", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B2457/206", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/60", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B27/281", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2457/206", "inventive": false, "first": false, "tree": "[]"}, {"code": "G01J1/4204", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2307/416", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B37/12", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/86", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B7/12", "inventive": true, "first": true, "tree": "[]"}, {"code": "B32B2457/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "B32B27/281", "inventive": true, "first": false, "tree": "[]"}, {"code": "B32B2307/416", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/60", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 89578535