PATENT DOCUMENT

Publication Number: US-12201004-B2
Application Number: US-202017440429-A
Country: US
Kind Code: B2

Title: Methods and configurations for improving the performance of sensors under a display

Abstract:
An electronic device may include a display and a sensor under the display. The display may include an array of subpixels for displaying an image to a user of the electronic device. At least a portion of the array of subpixels may be selectively removed in a pixel removal region to improve optical transmittance to the sensor through the display. The pixel removal region may include a plurality of pixel free regions that are devoid of thin-film transistor structures, that are devoid of power supply lines, that have continuous open areas due to rerouted row/column lines, that are partially devoid of touch circuitry, that optionally include dummy contacts, and/or have selectively patterned display layers.

Claims:
What is claimed is: 
     
       1. An electronic device, comprising:
 a display having first pixels of a first pixel density formed in an active area, wherein the first pixels comprise diodes of a first size; and 
 a sensor under the display, wherein the display comprises a sensing region that at least partially overlaps with the sensor, wherein the sensing region has second pixels of a second pixel density less than the first pixel density, and wherein the second pixels comprise diodes of a second size different than the first size. 
 
     
     
       2. The electronic device of  claim 1 , wherein the sensing region comprises a plurality of pixel free regions each of which is devoid of thin-film transistors, and wherein the plurality of pixel free regions is configured to increase signal transmittance through the display to the sensor. 
     
     
       3. The electronic device of  claim 2 , wherein each of the plurality of pixel free regions is further devoid of power supply lines. 
     
     
       4. The electronic device of  claim 2 , wherein horizontal and vertical control lines in the plurality of pixel free regions are rerouted to provide continuous open areas that reduce an amount of diffraction for light traveling through the display to the sensor. 
     
     
       5. The electronic device of  claim 2 , wherein each of the plurality of pixel free regions comprise rows of continuous open areas within the sensing region. 
     
     
       6. The electronic device of  claim 2 , further comprising:
 an opaque mask with openings aligned to the plurality of pixel free regions. 
 
     
     
       7. The electronic device of  claim 1 , wherein the second pixel density is half of the first pixel density. 
     
     
       8. The electronic device of  claim 1 , wherein the second pixel density is less than half of the first pixel density. 
     
     
       9. The electronic device of  claim 1 , wherein the display comprises an additional sensing region that is physically separated from the sensing region. 
     
     
       10. The electronic device of  claim 9 , wherein the additional sensing region has a different size than the sensing region. 
     
     
       11. The electronic device of  claim 1 , wherein the sensing region overlaps an entire edge of the display. 
     
     
       12. The electronic device of  claim 1 , wherein the sensing region overlaps a corner of the display. 
     
     
       13. The electronic device of  claim 1 , wherein the sensing region overlaps a curved edge of the display. 
     
     
       14. The electronic device of  claim 1 , wherein the sensing region overlaps a recessed notch area in the display. 
     
     
       15. The electronic device of  claim 1 , wherein the sensing region overlaps an entire surface of the display. 
     
     
       16. The electronic device of  claim 1 , wherein the second pixels in the sensing region comprise first subpixels of a first color and second subpixels of a second color, and wherein the density of the first subpixels is different than the density of the second subpixels in the sensing region. 
     
     
       17. The electronic device of  claim 1 , wherein the second pixels in the sensing region comprise blue subpixels and red subpixels, and wherein the density of the blue subpixels is lower than the density of the red subpixels in the sensing region. 
     
     
       18. The electronic device of  claim 1 , wherein the second pixels in the sensing region comprise green subpixels, blue subpixels, and red subpixels, and wherein the density of the blue subpixels is equal to the density of the blue subpixels and is equal to the density of the red subpixels in the sensing region. 
     
     
       19. The electronic device of  claim 1 , wherein the diodes of the second size are larger than the diodes of the first size. 
     
     
       20. The electronic device of  claim 1 , further comprising:
 a conductive touch sensor mesh formed over the display, wherein the conductive touch sensor overlaps with the sensing region. 
 
     
     
       21. The electronic device of  claim 1 , further comprising:
 a conductive touch sensor mesh formed over the display, wherein the conductive touch sensor mesh does not overlap with the sensing region. 
 
     
     
       22. The electronic device of  claim 1 , wherein the sensing region comprises a plurality of pixel free regions each of which lacks dummy contacts. 
     
     
       23. The electronic device of  claim 1 , wherein the sensing region comprises a plurality of pixel free regions each of which includes dummy contacts configured to provide emission current uniformity in the sensing region. 
     
     
       24. The electronic device of  claim 1 , wherein the display comprises a blanket layer that is selectively patterned in the sensing region to increase a transmittance of light through the display to the sensor, and wherein the blanket layer is a display layer selected from the group consisting of: a substrate protection layer, a gate dielectric layer, an inorganic passivation layer, and an organic pixel definition layer. 
     
     
       25. The electronic device of  claim 19 , wherein the second pixels in the sensing region comprise blue subpixels of a first size and green subpixels of a second size that is smaller than the first size. 
     
     
       26. The electronic device of  claim 1 , wherein the second pixels of the sensing region comprise green subpixels of a first subpixel density and blue subpixels of a second subpixel density that is equal to the first subpixel density. 
     
     
       27. The electronic device of  claim 1 , wherein the display comprises a cathode layer that is selectively patterned in the sensing region to increase the transmittance of light through the display to the sensor. 
     
     
       28. A display, comprising:
 first pixels of a first pixel density formed in an active area of the display, wherein the first pixels comprise green subpixels of a first subpixel density and blue subpixels of a second subpixel density different than the first subpixel density; and 
 second pixels of a second pixel density, less than the first pixel density, formed in a given region within the active area, wherein the second pixels comprise green subpixels of a third subpixel density and blue subpixels of a fourth subpixel density equal to the third subpixel density.

Description:
This application claims priority to U.S. patent application Ser. No. 16/825,978, filed on Mar. 20, 2020, and U.S. provisional patent application No. 62/837,628, filed Apr. 23, 2019, which are hereby incorporated by reference herein in their entireties. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and, more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, an electronic device may have an organic light-emitting diode (OLED) display based on organic light-emitting diode pixels. In this type of display, each pixel includes a light-emitting diode and thin-film transistors for controlling application of a signal to the light-emitting diode to produce light. The light-emitting diodes may include OLED layers positioned between an anode and a cathode. 
     There is a trend towards borderless electronic devices with a full-face display. These devices, however, may still need to include sensors such as cameras, ambient light sensors, and proximity sensors to provide other device capabilities. Since the display now covers the entire front face of the electronic device, the sensors will have to be placed under the display stack. In practice, however, the amount of light transmission through the display stack is very low (i.e., the transmission might be less than 20% in the visible spectrum), which severely limits the sensing performance under the display. 
     It is within this context that the embodiments herein arise. 
     SUMMARY 
     An electronic device may include a display and an optical sensor formed underneath the display. A pixel removal region on the display may at least partially overlap with the sensor. The pixel removal region may include a plurality of non-pixel regions each of which is devoid of thin-film transistors. The plurality of non-pixel regions is configured to increase the transmittance of light through the display to the sensor. In one suitable arrangement, half of all display subpixels in the pixel removal region may be removed to increase the transmittance of light through the display to the sensor. In general, 10-90% of all display subpixels in the pixel removal region may be removed to increase the transmittance of light through the display to the sensor. 
     In accordance with an embodiment, a subset of all display subpixels in the pixel removal region may be removed by iteratively eliminating the nearest neighboring subpixels of the same color. The display may include more than one pixel removal region, which are of the same or different size/shape. The pixel removal region may cover an entire edge of the display. The pixel removal region may cover a corner of the display. The pixel removal region may cover a notch area in the display. The pixel removal region may also cover the entire display area. The pixel removal region may optionally cover any portion of the display. 
     The plurality of non-pixel regions may also be devoid of vertical power supply routing traces. If desired, at least some horizontal and vertical control lines in the plurality of non-pixel regions are rerouted to provide continuous open areas that reduce the amount of diffraction for light traveling through the display to the sensor. Each of the plurality of non-pixel regions may also be devoid of dummy contacts or may alternatively include dummy contacts to help provide emission current uniformity in the pixel removal region. 
     The electronic device may further include a conductive touch sensor mesh formed over the display. In one suitable arrangement, the conductive touch sensor mesh is not removed from the pixel removal region. In another suitable arrangement, the conductive touch sensor mesh is completely removed from the pixel removal region. In yet another suitable arrangement, the conductive touch sensor mesh is only partially removed from the pixel removal region. The display may further include a blanket layer that is selectively patterned in the pixel removal region to increase the transmittance of light through the display to the sensor. The blanket layer may be a display layer selected from the group consisting of: a substrate protection layer, a gate dielectric layer, an inorganic passivation layer, and an organic pixel definition layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an illustrative electronic device having a display and one or more sensors in accordance with an embodiment. 
         FIG.  2 A  is a schematic diagram of an illustrative display with light-emitting elements in accordance with an embodiment. 
         FIG.  2 B  is a circuit diagram of an illustrative display pixel in accordance with an embodiment. 
         FIG.  3    is a cross-sectional side view of an illustrative display stack that at least partially covers a sensor in accordance with an embodiment. 
         FIGS.  4 A- 4 D  are top views showing various pixel removal schemes for improving optical transmission in accordance with some embodiments. 
         FIG.  5 A  is a top layout view showing how red subpixels can be systematically removed in accordance with an embodiment. 
         FIG.  5 B  is a top layout view showing how additional red subpixels can be further systematically removed from the arrangement of  FIG.  5 A  in accordance with an embodiment. 
         FIGS.  6 A and  6 B  are diagrams showing an illustrative pixel removal scheme that follows the process illustrated in  FIG.  5 A  in accordance with an embodiment. 
         FIG.  6 C  is a diagram illustrating non-uniform subpixel omission in accordance with an embodiment. 
         FIG.  6 D  is a diagram showing another illustrative pixel removal scheme in accordance with an embodiment. 
         FIG.  6 E  is a diagram showing a vertical pixel removal scheme in accordance with an embodiment. 
         FIG.  6 F  is a diagram of a pixel arrangement after two pixel removal iterations in accordance with an embodiment. 
         FIG.  6 G  is a diagram of a pixel arrangement where more green subpixels have been removed in accordance with an embodiment. 
         FIG.  6 H  is a diagram of a non-pentile pixel arrangement after pixel removal in accordance with an embodiment. 
         FIGS.  7 A- 7 F  are front views of an electronic device display showing how the display may have one or more localized regions in which the pixels are selectively removed using the scheme of  FIGS.  4 - 6    in accordance with some embodiments. 
         FIG.  7 G  is a cross-sectional side view of an electronic device display showing how the display may have one or more localized regions in which the pixels are selectively removed at a curved edge in accordance with an embodiment. 
         FIG.  8 A  is a top layout view showing how subpixel transistors may be selectively removed to increase transmittance in accordance with an embodiment. 
         FIG.  8 B  is a top layout view showing how power lines over the removed transistors may also be omitted to further increase transmittance in accordance with an embodiment. 
         FIG.  8 C  is a top layout view showing how the horizontal and vertical routing lines may be rerouted to provide a larger continuous opening to reduce optical diffraction in accordance with an embodiment. 
         FIG.  8 D  is a top layout view showing how subpixel structures are relocated along a single row in accordance with an embodiment. 
         FIG.  8 E  is a top layout view showing how the size of subpixel structures may be enlarged in accordance with an embodiment. 
         FIG.  8 F  is a top layout view showing how an opaque mask may be used to define an aperture opening in accordance with an embodiment. 
         FIG.  9 A  is a top layout view showing illustrative touch conductive mesh circuitry formed over the pixel removal region in accordance with an embodiment. 
         FIG.  9 B  is a top layout view showing how the touch conductive mesh circuitry may be partially removed over the pixel removal region in accordance with an embodiment. 
         FIG.  10 A  is a top layout view showing how the region where the subpixel transistors have been removed lacks dummy contacts in accordance with an embodiment. 
         FIG.  10 B  is a top layout view showing how the region where the subpixel transistors have been removed includes dummy contacts in accordance with an embodiment. 
         FIG.  10 C  is a plot of emission current versus gate-to-source voltage showing how the presence of dummy contacts can help improve the emission current profile in accordance with an embodiment. 
         FIG.  11    is a cross-sectional side view of an illustrative display stack showing how at least some of the blanket layers within the display stack can be selectively patterned to improve optical transmittance 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 display, a computer display that contains an embedded computer, 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, or other electronic equipment. Electronic device  10  may have the shape of a pair of eyeglasses (e.g., supporting frames), may form a housing having a helmet shape, or may have other configurations to help in mounting and securing the components of one or more displays on the head or near the eye of a user. 
     As shown in  FIG.  1   , electronic device  10  may include control circuitry  16  for supporting the operation of device  10 . Control circuitry  16  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  12  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  12  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 resources of input-output devices  12  and may receive status information and other output from device  10  using the output resources of input-output devices  12 . 
     Input-output devices  12  may include one or more displays such as display  14 . Display  14  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  14  may be insensitive to touch. A touch sensor for display  14  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. A touch sensor for display  14  may be formed from electrodes formed on a common display substrate with the display pixels of display  14  or may be formed from a separate touch sensor panel that overlaps the pixels of display  14 . If desired, display  14  may be insensitive to touch (i.e., the touch sensor may be omitted). Display  14  in electronic device  10  may be a head-up display that can be viewed without requiring users to look away from a typical viewpoint or may be a head-mounted display that is incorporated into a device that is worn on a user&#39;s head. If desired, display  14  may also be a holographic display used to display holograms. 
     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 . 
     Input-output devices  12  may also include one or more sensors  13  such as 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 associated with a display and/or a touch sensor that forms a button, trackpad, or other input device not associated with a display), and other sensors. In accordance with some embodiments, sensors  13  may include optical sensors such as optical sensors that emit and detect light (e.g., optical proximity sensors such as transreflective optical proximity structures), ultrasonic sensors, and/or other touch and/or proximity sensors, monochromatic and color ambient light sensors, image sensors, fingerprint sensors, temperature sensors, proximity sensors and other 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), 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  13  and/or other input-output devices to gather user input (e.g., 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.). 
     Display  14  may be an organic light-emitting diode display or may be a display based on other types of display technology. Device configurations in which display  14  is an organic light-emitting diode display are sometimes described herein as an example. This is, however, merely illustrative. Any suitable type of display may be used, if desired. In general, 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) 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.  2 A . As shown in  FIG.  2 A , display  14  may have an array of pixels  22  formed on a substrate. 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 include 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 (IGZO) transistors, or thin-film transistors formed from other semiconductors. Pixels  22  may contain light-emitting diodes of different colors (e.g., red, green, and blue) to provide display  14  with the ability to display color images or may be monochromatic pixels. 
     Display driver circuitry may be used to control the operation of pixels  22 . The display driver circuitry may be formed from integrated circuits, thin-film transistor circuits, or other suitable circuitry. Display driver circuitry  30  of  FIG.  2 A  may contain communications circuitry for communicating with system control circuitry such as control circuitry  16  of  FIG.  1    over path  32 . Path  32  may be formed from traces on a flexible printed circuit or other cable. During operation, the control circuitry (e.g., control circuitry  16  of  FIG.  1   ) may supply display driver circuitry  30  with information on images to be displayed on display  14 . 
     To display the images on display pixels  22 , display driver circuitry  30  may supply image data to data lines D while issuing clock signals and other control signals to supporting display driver circuitry such as gate driver circuitry  34  over path  38 . If desired, display driver circuitry  30  may also supply clock signals and other control signals to gate driver circuitry  34  on an opposing edge of display  14 . 
     Gate driver circuitry  34  (sometimes referred to as row control circuitry) may be implemented as part of an integrated circuit and/or may be implemented using thin-film transistor circuitry. Horizontal control lines G in display  14  may carry gate line signals such as scan line signals, emission enable control signals, and other horizontal control signals for controlling the display pixels  22  of each row. There may be any suitable number of horizontal control signals per row of pixels  22  (e.g., one or more row control signals, two or more row control signals, three or more row control signals, four or more row control signals, etc.). 
     The region on display  14  where the display pixels  22  are formed may sometimes be referred to herein as the active area. Electronic device  10  has an external housing with a peripheral edge. The region surrounding the active and within the peripheral edge of device  10  is the border region. Images can only be displayed to a user of the device in the active region. It is generally desirable to minimize the border region of device  10 . For example, device  10  may be provided with a full-face display  14  that extends across the entire front face of the device. If desired, display  14  may also wrap around over the edge of the front face so that at least part of the lateral edges or at least part of the back surface of device  10  is used for display purposes. 
       FIG.  2 B  is a circuit diagram of an illustrative organic light-emitting diode display pixel  22  in display  14 . As shown in  FIG.  2 B , display pixel  22  may include a storage capacitor Cst and associated pixel transistors such as a semiconducting-oxide transistor Toxide, a drive transistor Tdrive, a data loading transistor Tdata, a first emission transistor Tem 1 , second emission transistor Tem 2 , and an anode reset transistor Tar. While transistor Toxide is formed using semiconducting oxide (e.g., a transistor with an n-type channel formed from semiconducting oxide such as indium gallium zinc oxide or IGZO), the other transistors may be thin-film transistors formed from a semiconductor such as silicon (e.g., polysilicon channel deposited using a low temperature process, sometimes referred to as “LTPS” or low-temperature polysilicon). Semiconducting-oxide transistors exhibit relatively lower leakage than silicon transistors, so implementing transistor Toxide as a semiconducting-oxide transistor will help reduce flicker (e.g., by preventing current from leaking away from the gate terminal of drive transistor Tdrive). 
     In another suitable arrangement, transistors Toxide and Tdrive may be implemented as semiconducting-oxide transistors while the remaining transistors Tdata, Tem 1 , Tem 2 , and Tar are LTPS transistors. Transistor Tdrive serves as the drive transistor and has a threshold voltage that is critical to the emission current of pixel  22 . Since the threshold voltage of transistor Tdrive may experience hysteresis, forming the drive transistor as a top-gate semiconducting-oxide transistor can help reduce the hysteresis (e.g., a top-gate IGZO transistor experiences less Vth hysteresis than a silicon transistor). If desired, any of the remaining transistors Tdata, Tem 1 , Tem 2 , and Tar may be implemented as semiconducting-oxide transistors. In general, any one of transistors Tdrive, Tdata, Tem 1 , Tem 2 , and Tar may be either an n-type (i.e., n-channel) or p-type (i.e., p-channel) silicon thin-film transistor. If desired, pixel  22  may include more or less than six transistors and/or may include more or less than one internal capacitor. 
     Display pixel  22  may include an organic light-emitting diode (OLED)  204 . A positive power supply voltage VDDEL may be supplied to positive power supply terminal  200 , and a ground power supply voltage VSSEL may be supplied to ground power supply terminal  202 . Positive power supply voltage VDDEL may be 3 V, 4 V, 5 V, 6 V, 7 V, 2 to 8 V, or any suitable positive power supply voltage level. Ground power supply voltage VSSEL may be 0 V, −1 V, −2 V, −3 V, −4 V, −5 V, −6V, −7 V, or any suitable ground or negative power supply voltage level. The state of drive transistor Tdrive controls the amount of current flowing from terminal  200  to terminal  202  through diode  204 , and therefore the amount of emitted light from display pixel  22 . Organic light-emitting diode  204  may have an associated parasitic capacitance C OLED  (not shown). 
     Terminal  209  may be used to supply an anode reset voltage Var to assist in turning off diode  204  when diode  204  is not in use. Terminal  209  is therefore sometimes referred to as an anode reset or initialization line. Control signals from display driver circuitry such as row driver circuitry  34  of  FIG.  2 A  are supplied to control terminals such as row control terminals  212 ,  214 - 1 ,  214 - 2 , and  214 - 3 . Row control terminal  212  may serve as an emission control terminal (sometimes referred to as an emission line or emission control line), whereas row control terminals  214 - 1 ,  214 - 2 , and  214 - 3  may serve as first, second, and third scan control terminals (sometimes referred to as scan lines or scan control lines). Emission control signal EM may be supplied to terminal  212 . Scan control signals SC 1 , SC 2 , and SC 3  may be applied to scan terminals  214 - 1 ,  214 - 2 , and  214 - 3 , respectively. A data input terminal such as data signal terminal  210  is coupled to a respective data line D of  FIG.  2 A  for receiving image data for display pixel  22 . Data terminal  210  may also be referred to as a data line. 
     In the example of  FIG.  2 B , transistors Tem 1 , Tdrive, Tem 2 , and OLED  304  may be coupled in series between power supply terminals  200  and  202 . In particular, first emission control transistor Tem 1  may have a source terminal that is coupled to positive power supply terminal  200 , a gate terminal that receives emission control signal EM 2  via emission line  212 , and a drain terminal (labeled as Node 1 ). The terms “source” and “drain” terminals of a transistor can sometimes be used interchangeably and may therefore sometimes be referred to as “source-drain” terminals. Drive transistor Tdrive may have a source terminal coupled to Node 1 , a gate terminal (labeled as Node 2 ), and a drain terminal (labeled as Node 3 ). Second emission control transistor Tem 2  may have a source terminal coupled to Node 3 , a gate terminal that also receives emission control signal EM via emission line  212 , and a drain terminal (labeled as Node 4 ) coupled to ground power supply terminal  202  via light-emitting diode  204 . Configured in this way, emission control signal EM can be asserted to turn on transistors Tem 1  and Tem 2  during an emission phase to allow current to flow through light-emitting diode  204 . 
     Storage capacitor Cst may have a first terminal that is coupled to positive power supply line  200  and a second terminal that is coupled to Node 2 . Image data that is loaded into pixel  22  can be at least be partially stored on pixel  22  by using capacitor Cst to hold charge throughout the emission phase. Transistor Toxide may have a source terminal coupled to Node 2 , a gate terminal configured to receive scan control signal SC 1  via scan line  214 - 1 , and a drain terminal coupled to Node 3 . Signal SC 1  may be asserted to turn on transistor Toxide to short the drain and gate terminals of transistor Tdrive. A transistor configuration where the gate and drain terminals are shorted is sometimes referred to as being “diode-connected.” 
     Data loading transistor Tdata may have a source terminal coupled to data line  210 , a gate terminal configured to receive scan control signal SC 2  via scan line  214 - 2 , and a drain terminal coupled to Node 1 . Configured in this way, signal SC 2  can be asserted to turn on transistor Tdata, which will allow a data voltage from data line  210  to be loaded onto Node 1 . Transistor Tar may have a source terminal coupled to Node 4 , a gate terminal configured to receive scan control signal SC 3  via scan line  214 - 3 , and a drain terminal coupled to initialization line  209 . Configured in this way, scan control signal SC 3  can be asserted to turn on transistor Tar, which drives Node 4  to the anode reset voltage level Var. If desired, the anode reset voltage Var on line  209  can be dynamically biased to different levels during operation of pixel  22 . 
     Device  10  having a full-face display  14  covering the entire front face of the device may have to mount sensor  13  below display  14 .  FIG.  3    is a cross-sectional side view of an illustrative display stack of display  14  that at least partially covers a sensor in accordance with an embodiment. As shown in  FIG.  3   , the display stack may include a backing film  300  and a substrate such as substrate  302  formed on backing film  300 . Substrate  302  may be formed from glass, metal, plastic, ceramic, sapphire, or other suitable substrate materials. In some arrangements, substrate  302  may be an organic substrate formed from polyimide (PI), polyethylene terephthalate (PET), or polyethylene naphthalate (PEN) (as examples). The surface of substrate  302  may optionally be covered with one or more buffer layers (e.g., inorganic buffer layers such as layers of silicon oxide, silicon nitride, etc.). 
     Thin-film transistor (TFT) layers  304  may be formed over substrate  302 . The TFT layers  304  may include thin-film transistor circuitry such as thin-film transistors, thin-film capacitors, associated routing circuitry, and other thin-film structures formed within multiple metal routing layers and dielectric layers. Organic light-emitting diode (OLED) layers  306  may be formed over the TFT layers  304 . The OLED layers  306  may include a diode cathode layer, a diode anode layer, and emissive material interposed between the cathode and anode layers. 
     Circuitry formed in the TFT layers  304  and the OLED layers  306  may be protected by encapsulation layers  308 . As an example, encapsulation layers  308  may include a first inorganic encapsulation layer, an organic encapsulation layer formed on the first inorganic encapsulation layer, and a second inorganic encapsulation layer formed on the organic encapsulation layer. Encapsulation layers  308  formed in this way can help prevent moisture and other potential contaminants from damaging the conductive circuitry that is covered by layers  308 . 
     One or more polarizer films  312  may be formed over the encapsulation layers  308  using adhesive  310 . Adhesive  310  may be implemented using optically clear adhesive (OCA) material that offer high light transmittance. One or more touch layers  316  that implement the touch sensor functions of touch-screen display  14  may be formed over polarizer films  312  using adhesive  314  (e.g., OCA material). For example, touch layers  316  may include horizontal touch sensor electrodes and vertical touch sensor electrodes collectively forming an array of capacitive touch sensor electrodes. Lastly, the display stack may be topped off with a coverglass layer  320  that is formed over the touch layers  316  using additional adhesive  318  (e.g., OCA material). Cover glass  320  may serve as an outer protective layer for display  14 . 
     Still referring to  FIG.  3   , sensor  13  may be formed under the display stack within the electronic device  10 . As described above in connection with  FIG.  1   , sensor  13  may be an optical sensor such as a camera (e.g., an infrared camera), proximity sensor, ambient light sensor, fingerprint sensor, or other light-based sensor. In such scenarios, the performance of sensor  13  depends on the transmission of light traversing through the display stack, as indicated by arrow  350 . A typical display stack, however, has fairly limited transmission properties. For instance, more than 80% of light in the visible spectrum might be lost when traveling through the display stack, which makes sensing under display  14  challenging. 
     Each of the multitude of layers in the display stack contributes to the degraded light transmission to sensor  13 . In particular, the dense thin-film transistors and associated routing structures in TFT layers  304  of the display stack contribute substantially to the low transmission. In accordance with an embodiment, at least some of the display pixels may be selectively removed in regions of the display stack located directly over sensor(s)  13 . Regions of display  14  that at least partially cover or overlap with sensor(s)  13  in which at least a portion of the display pixels have been removed are sometimes referred to as “pixel removal regions.” Each pixel removal region may still have pixels, albeit with a lower density of subpixels. Removing display pixels (e.g., removing transistors and/or capacitors associated with one or more sub-pixels) in the pixel free regions can drastically help increase transmission and improve the performance of the under-display sensor  13 . The pixel removal regions may therefore have a first subpixel density, whereas the rest of the display (often referred to collectively as the active area) may exhibit a second (“native”) subpixel density that is greater than the first subpixel density. The native subpixel density of the active area may be at least two times, three times, four times, 1-5 times, or 1-10 times the subpixel density of the pixel removal regions. 
       FIGS.  4 A- 4 D  are top views showing various pixel removal regions for improving optical transmission in accordance with some embodiments. As an example, display  14  may generally include a repeating pixel group  400  that includes red (R) subpixels, green (G) subpixels, and blue (B) subpixels. As shown in  FIG.  4 A , each pixel group  400  may include two rows of colored subpixels, where the top row includes BGRG subpixels in that order and where the bottom row includes RGBG subpixels in that order. This particular pattern is merely illustrative and is not intended to limit the scope of the present embodiments. If desired, other color display patterns may be implemented in display  14 , which can include subpixels of other colors (e.g., cyan subpixels, magenta subpixels, yellow subpixels, clear subpixels, etc.). 
     In the example of  FIG.  4 A , every other pixel group  400  has been removed in accordance with a checkerboard pattern. The stippled regions illustrate where subpixels would have existed if no removal scheme is implemented but is now at least partially devoid of thin-film transistor circuitry corresponding to the display subpixels that have been removed. Each individual stippled region may be referred to as a non-pixel region, pixel free regions or pixel lacking region. This type of pixel removal scheme may remove up to 50% of all available display subpixels. 
     In  FIG.  4 A , each non-pixel region represents eight removed sub-pixels.  FIG.  4 B  illustrates another pixel removal scheme in which each stippled non-pixel region represents  12  removed subpixels in another checkerboard-like pattern. This type of pixel removal scheme may also remove up to 50% of all available display subpixels.  FIG.  4 C  illustrates yet another pixel removal scheme in which some stippled pixel free regions represent four removed subpixels while other stippled pixel-free regions represent only two removed subpixels in a repeating mosaic-like pattern. This type of pixel removal scheme may also remove up to 50% of all available display subpixels.  FIG.  4 D  illustrates yet another pixel removal scheme in each stippled pixel lacking region represents twelve removed subpixels while removing more than 50% of all available display subpixels from the pixel removal region overall. 
     In general, the amount of pixel removal in the pixel removal region should be carefully chosen so as to maximize optical transmittance through the display stack while ensuring that the effective pixels per inch (PPI) is still sufficiently high such that the user of device  10  will not be able to visually notice any undesired display artifacts in the vicinity of the pixel removal region over which sensor(s)  13  may be located. The exemplary pixel removal regions of  FIGS.  4 A- 4 D  are merely illustrative. If desired, other pixel removal arrangements in which up to 10% of display subpixels have been removed in the pixel removal region, up to 20% of display subpixels have been removed, up to 30% of display subpixels have been removed, up to 40% of display subpixels have been removed, up to 50% of display subpixels have been removed (i.e., the subpixel density of the pixel removal region may be half of the subpixel density of the native active area), 0-50% of display subpixels have been removed, 10-50% of display subpixels have been removed, 20-50% of display subpixels have been removed, 30-50% of display subpixels have been removed, 51-90% of display subpixels have been removed, or more than 50% of display subpixels have been removed (i.e., the subpixel density of the pixel removal region may be less than half of the subpixel density of the native active area) may be implemented to achieve the desired level of optical transmittance through the display stack. 
     The illustrative pixel removal schemes shown in the embodiments of  FIGS.  4 A- 4 D  may not be capable of providing a uniform distribution of subpixels in all directions across the surface of display  14 . To provide a uniform distribution of subpixels across the display surface, an intelligent pixel removal process may be implemented that systematically eliminates the closest subpixel of the same color (e.g., the nearest neighbor of the same color may be removed).  FIG.  5 A  is a top layout view showing how red subpixels can be systematically removed in accordance with an embodiment. The blue and green subpixels are omitted from  FIG.  5 A  to help avoid obscuring the present embodiments. 
     As shown in  FIG.  5 A , display  14  may be initially provided with an array of red subpixels  22 R. The pixel removal process may involve selecting a given subpixel, identifying the closest or nearest neighboring subpixels (in terms of distance from the selected subpixel), and then eliminating/omitting those identified subpixels in the final pixel removal region. For instance, subpixel  22 R- 1  may represent a first selected subpixel. The two closest subpixels may then be marked for elimination (as indicated by markup “X”). Subpixel  22 R- 2  may represent a second selected subpixel. The four closest subpixels (which includes the two previously marked subpixels) may be marked for elimination. This pixel removal process may be performed across the entire display pixel array for subpixels of all colors. 
       FIG.  5 A  illustrates the resulting subpixel array after one iteration of pixel removal has been performed. If desired, additional iterations of subpixel removal may be performed to further increase transmittance at the expense of lower pixel density.  FIG.  5 B  illustrates the resulting subpixel array after another iteration of pixel removal has been performed (e.g., a second order result by again eliminating the closest neighboring subpixels). If desired, any suitable number of iterations may be carried out. Systematically removing subpixels in this way can provide uniform color balance while maintaining a high PPI. 
       FIG.  6 A  shows how subpixels of various colors may be removed using a process of the type described in connection with  FIG.  5 A . As shown in  FIG.  6 A , each pixel group  600  may include two rows of colored subpixels, where the top row includes RGBG subpixels in that order and where the bottom row includes BGRG subpixels in that order. In particular, the red, green, and first green subpixels may be removed from the first row, whereas only the second green subpixel is removed from the second row in each pixel group  600 . The resulting arrangement of the pixel removal region implemented using this method is illustrated in  FIG.  6 B . As shown in  FIG.  6 B , some of the stippled pixel lacking regions represent three consecutive removed subpixels while other pixel lacking regions represent only one removed subpixel. This type of pixel removal scheme may also remove 50% of all available display subpixels in the pixel removal region (e.g., the pixel density of the pixel removal region may be half of the native pixel density of the active area). 
       FIG.  6 C  illustrates another suitable arrangement where additional blue subpixels are removed from the configuration of  FIG.  6 A . As shown in  FIG.  6 C , every other pixel group  600  will have all of the blue subpixels removed. In other words, more blue sub-pixels may be removed or omitted relative to the green or red subpixels (i.e., the density of the blue subpixels is lower than the density of the red subpixels in the pixel removal region). This example where the non-uniform subpixel removal/omission is targeted towards blue subpixels is merely illustrative and is not intended to limit the present embodiments. If desired, more green subpixels may be omitted relative to the blue/red subpixels, more red subpixels may be omitted relative to the blue/green subpixels, or other non-uniform subpixel removal scheme may be implemented. In yet other suitable embodiments, the degree of omission of all the different colored subpixels may be different, which will affect the density of each subpixel. As an example, more blue subpixels may be removed than the green subpixels, and more green subpixels may be removed than the red subpixels (i.e., the blue subpixels have the highest removal rate and thus the lowest subpixel density, whereas the red subpixels have the lowest removal rate). As another example, more blue subpixels may be removed than the red subpixels, and more red subpixels may be removed than the green subpixels (i.e., the blue subpixels have the highest removal rate, whereas the green subpixels have the lowest removal rate and thus the highest subpixel density). As yet another example, more green subpixels may be removed than the blue subpixels, and more blue subpixels may be removed than the red subpixels (i.e., the green subpixels have the highest omission rate, whereas the red subpixels have the lowest omission rate). Other permutations may also be implemented. 
     The example of  FIG.  6 B  where each individual subpixel is illustrated as a rectangular region have edges parallel to the display edge is merely illustrative. If desired, each subpixel region may have edges that are angled or rotated relative to the display edge (see, e.g.,  FIG.  6 D ). In  FIG.  6 D , the display edge may be parallel to the X axis or the Y axis. The front face of the display may be parallel to the XY plane such that a user of the device views the front face of the display in the Z direction. Portion  610  of  FIG.  6 D  shows the native subpixel arrangement prior to removal. Portion  612  illustrates how every other subpixel may be removed for each color—the removed subpixels are marked using “X”). Portion  614  shows the resulting pixel configuration with 50% of the subpixels removed. 
     In the example of  FIG.  6 D , the subpixels are removed such that there are horizontal stripes of empty pixel regions (see, e.g., continuous striping regions  615  devoid of subpixels in portion  614 ). This is merely illustrative. If desired, the subpixels may also be removed to create vertical stripes of empty pixel regions (see, e.g.,  FIG.  6 E  having contiguous striping regions  617  devoid of subpixels). 
     As described above in connection with  FIG.  5 B , multiple iterations of pixel removal may be performed.  FIG.  6 F  is a diagram of a pixel arrangement after two pixel removal iterations. Compared to the configuration in portion  614  of  FIG.  6 D , the configuration of  FIG.  6 F  has an even smaller subpixel density (e.g., by again eliminating the closest neighboring subpixels, the second order result may have only half the number of subpixels compared to the first order result). In other words, after two pixel removal iterations, 75% of the original native subpixels may be removed. If desired, any suitable number of iterations may be implemented. Systematically removing subpixels in this way can provide uniform color balance while maintaining a high PPI. 
     As described above in connection with  FIG.  6 C , non-uniform subpixel omission may be implemented.  FIG.  6 G  is a diagram of a pixel arrangement where more green subpixels have been removed (e.g., a second round of removal may be performed only for the green subpixels). Compared to the configuration in portion  614  of  FIG.  6 D , the configuration of  FIG.  6 G  has the same number of blue and red subpixels but has only half the number of green subpixels remaining. Since the native pixel group has two green subpixels for every red and blue subpixel pair, eliminating the nearest green neighbors twice may help balance the total number of green, red, and blue subpixels (e.g., the total number of remaining red, green, and blue subpixels may be the same). In other words, the density of the blue subpixels is equal to the density of the blue subpixels and is equal to the density of the red subpixels in the pixel removal region. If desired, the remaining green subpixels may optionally be enlarged in size to help compensate for the reduction in number. 
     The native RGBG/BGRG subpixel arrangement illustrated in portion  610  of  FIG.  6 D  may sometimes be referred to as having a “pentile” arrangement. If desired, the illustrative pixel removal schemes described herein may also be applied to non-pentile or straight pixel arrangements.  FIG.  6 H  is a diagram of a non-pentile pixel arrangement after pixel removal. As shown in  FIG.  6 H , the number of remaining blue, red, and green subpixels are the same, but the blue region subpixel regions may be larger in size than the green subpixel regions, and the green subpixel regions may be larger in size than the red subpixel regions. This is merely illustrative. In general, the size of the different colored subpixel regions may be tuned for optimal display performance. 
     In general, the display subpixels may be partially removed from any region(s) of display  14 .  FIGS.  7 A- 7 F  are front views showing how display  14  may have one or more localized regions in which the pixels are selectively removed using the scheme of  FIGS.  4 - 6    in accordance with certain embodiments. The example of  FIG.  7 A  illustrates various local pixel removal regions  700  physically separated from one another (i.e., the various pixel removal regions  700  are non-continuous). The term “active area” may refer to regions of display  14  outside of and non-overlapping with the pixel removal regions. The various local areas  700  might for example correspond to three different sensors formed underneath display  14 . The example of  FIG.  7 B  illustrates a continuous pixel removal region  702  formed along the top border of display  14 , which might be suitable when there are many optical sensors positioned near the top edge of device  10 . The example of  FIG.  7 C  illustrates a pixel removal region  704  formed at a corner of display  14 . In some arrangements, the corner of display  14  in which pixel removal region  704  is located may be a rounded corner or a corner having a substantially 90° corner. The example of  FIG.  7 D  illustrates a pixel removal region  706  formed only in the center portion along the top edge of device  10  (i.e., the pixel removal region covers a recessed notch area in the display).  FIG.  7 E  illustrates another example in which pixel removal regions  708  and  710  can have different shapes and sizes.  FIG.  7 F  illustrates yet another suitable example in which the pixel removal region covers the entire display surface. These examples are merely illustrative and are not intended to limit the scope of the present embodiments. If desired, any one or more portions of the display overlapping with optically based sensors or other sub-display electrical components may be designated as a pixel removal region/area. 
     In yet another suitable arrangement, a pixel removal region may be formed at a curved edge portion of the display.  FIG.  7 G  is a cross-sectional side view of display  14  showing a curved or bent peripheral edge region  20 . A user  750  may view the front face of display  14  by looking in the direction of arrow  752  that is parallel to the Z direction. The front face of display  14  is parallel to the XY plane. As shown in  FIG.  7 G , a pixel removal region  714  may be formed in the bent edge portion  20 . In general, one or more edges of the device may be curved or bent, and one or more pixel removal regions may optionally be formed in each curved edge portion. 
       FIG.  8 A  is a top layout view showing how some subpixels may be selectively removed from a pixel group  600  to increase transmittance in accordance with the pixel removal scheme shown in  FIGS.  6 A and  6 B . The regions labeled “sub-pixel removed” correspond to pixel free regions that are completely devoid of thin-film transistors and capacitors that would otherwise be present had those subpixels not been removed. Removing the thin-film transistor structures, which might include active silicon or other semiconducting material, associated source-drain contacts, and also thin-film capacitor terminals, can help improve optical transmittance through the display stack in the pixel free regions. 
     As shown in  FIG.  8 A , the red, green, and blue subpixels have been removed from the upper portion of pixel group  600 , whereas only the rightmost green subpixel has been removed from the lower portion of pixel group  600 .  FIG.  8 A  also shows various gate (G) lines (e.g., horizontal or row control lines) and data (D) lines (e.g., vertical or column control lines) that are routed over the thin-film transistors associated each display subpixel. Moreover, power supply lines carrying power supply voltages ELVDD might also be routed in the vertical column-wise direction. If desired, the power supply lines may also or alternatively be routed in the horizontal direction or in a diagonal fashion across the surface of the display. 
     If desired, the pixel structure of  FIG.  8 A  may optionally be rotated or angled relative to a display edge that is parallel to the X axis or the Y axis. As an example, the pixel arrangement of  FIG.  8 A  may be rotated at a 45° angle relative to the X axis. If desired, the pixel structures may be rotated by other suitable angles (e.g., by 30°, by 60°, by 90°, by 1-89°, etc.). 
     In the example of  FIG.  8 A , the power supply lines (see, e.g., the wider vertical routing traces) are still routed over the non-pixel regions, which contributes to the reduction in overall optical transmittance. In accordance with another suitable arrangement illustrated in  FIG.  8 B , the power supply lines may be selectively removed or omitted from the pixel free regions such as regions  850  and  851  (e.g., from each region where subpixels should be removed). As shown in  FIG.  8 B , the wider ELVDD routing traces are absent and no longer routed through non-pixel regions  850  and  851 . Even though the ELVDD routing lines are shown as being broken into various segments in the vertical direction, the different power segments are still connected together using a conductive power mesh  810  formed in a higher routing layer than the ELVDD routing lines. Interconnecting the separate power line segments using power mesh  810  allows all of the remaining subpixels to be properly supplied with power. Selectively eliminating the power supply routing traces from the non-pixel areas can help further improve transmittance in the overall pixel removal region. In the example of  FIG.  8 B , there are still horizontal gate lines and vertical data lines that are routed over non-pixel regions  850  and  851 , which may contribute to diffraction for light traveling through these regions. In certain embodiments, these conductive traces may be rerouted to provide a larger continuous opening in the non-pixel regions (see, e.g.,  FIG.  8 C ). As shown in  FIG.  8 C , gate lines G′ and data lines D′ may be routed in a more circuitous manner to achieve a larger open area. Routing the control signals in this way reduces diffraction albeit at the expense of decreased transmission. 
     In both  FIGS.  8 A and  8 B , the diamond-shaped regions correspond to the OLEDs of each colored subpixel. In  FIG.  8 B , the thin-film transistors associated with the blue, green, and red subpixels may be formed in region  856  overlapping with the corresponding OLEDs, whereas the thin-film transistors associated with the green subpixel to the right may be formed in region  858 . Since TFT regions  856  and  858  are not continuous with one another, the non-pixel regions  850  and  851  are also non-continuous with each other. 
       FIG.  8 D  illustrates another suitable arrangement in which the thin-film transistors associated with the lone green subpixel (i.e., the upper right green subpixel in pixel group  600 ) is shifted or relocated into region  851  such that the pixel group  600  can have a continuous pixel free region  860 . The OLED of the green subpixel may remain unchanged. In other words, all the TFT structures are formed in row region  862 , whereas row region  860  may be substantially devoid of TFT structures to help attain a larger continuous opening for improved transmittance. 
     The amount of current flowing through the drive transistor (e.g., transistor Tdrive in  FIG.  2 B ) may be relatively high for remaining subpixels within a pixel removal region. To help mitigate potentially aging effects associated with the high drive current levels, the size of the remaining subpixels may be enlarged (e.g., the OLED and/or some of the associated transistors may be increased in size). In the example of  FIG.  8 E , the OLEDs of remaining blue subpixel B′, green subpixels G′, and red subpixel R′ may be relatively larger than the OLEDs in other parts of the display with native subpixel density (i.e., relative to display pixels in the normal active area). Enlarging the OLEDs reduces current density, which can help prolong the lifetime of the diodes. If enlarging the pixel transistors, transistors such as the drive transistor may have its width increased and/or gate length decreased to help mitigate any potential accelerated aging effects due to the high drive current levels. 
       FIG.  8 F  illustrates another suitable arrangement showing how an opaque mask such as mask  870  may be used to define an aperture opening. Mask  870  may be formed using existing metal routing layers, a pixel definition layer (e.g., a black pixel defining layer), and/or other suitable opaque layer. As shown in  FIG.  8 F , opaque mask  870  may have openings such as opening  872  aligned with a corresponding pixel free region (i.e., a continuous region where subpixels have been removed below). In general, opening  872  may have a predetermined shape (e.g., a rectangular window, a circular window, an oval window, an elliptical window, etc.) configured to help control the diffraction pattern for light traversing through the opening. 
     In additional to the thin-film transistor structures, touch based circuitry such as touch-sensor traces within the touch layers  316  ( FIG.  3   ) might also contribute substantially to the low transmission through the display stack.  FIG.  9 A  is a top layout view showing illustrative touch conductive mesh circuitry  900  formed over the pixel removal region in accordance with an embodiment. As shown in  FIG.  9 A , none of the touch mesh  900  is removed (i.e., touch mesh  900  completely overlaps with the pixel removal region), so there is no reduction in touch functionality. On the other extreme, all of touch mesh  900  may be removed from the entire pixel removal region (i.e., the touch mesh and the pixel removal region are non-overlapping), which offers the highest optical transmission while sacrificing the loss of touch functionality in the pixel removal region. Completely removing mesh  900  might, however, result in a noticeable difference in contrast between the pixel removal region and the surrounding normal display region. For instance, the pixel removal region where touch mesh  900  is completely eliminated might appear more reflective than the surrounding regions, which may or may not be acceptable. 
       FIG.  9 B  is a top layout view showing how touch conductive mesh circuitry  900 ′ may be partially removed over the pixel removal region in accordance with another suitable arrangement. As shown in  FIG.  9 B , touch mesh  900 ′ may be present over actual display subpixels but may be absent over the pixel free regions where the subpixels have been intelligently removed. This partial removal of the touch circuitry in the pixel removal region can provide improved optical transmittance while offering partial touch functionality and reduced contrast between the pixel removal region and the surrounding areas. 
       FIG.  10 A  is a top layout view showing how the pixel free region such as region  1000  where subpixel transistor structures have been removed lacks dummy contacts in accordance with an embodiment. A complete lack of dummy contacts in region  1000  helps maximize optical transmittance since the presence of dummy contacts can still block some amount of light. In accordance with another suitable arrangement, non-pixel region  1000  might actually include some dummy contacts even though the underlying transistor(s) have been removed. While the presence of dummy contacts slightly reduces transmittance, including dummy contacts (which may be formed from polysilicon material) helps to provide better polysilicon uniformity during manufacturing. 
     Polysilicon uniformity may affect the transistor current profile, which is illustrated in  FIG.  10 C .  FIG.  10 C  is a plot of emission current (I) versus gate-to-source voltage (Vgs). Curve  1002  may represent the current profile for active p-channel transistors adjacent to region  1000  in  FIG.  10 A , whereas curve  1004  may represent the current profile for active p-channel transistors adjacent to region  1000  in  FIG.  10 B . Curve  1004  offers a more ideal current behavior while curve  1002  offers a shifted version of the ideal profile. Thus, including dummy contacts in the pixel free regions can help maintain transistor current uniformity across the display. 
       FIG.  11    is a cross-sectional side view of an illustrative display stack showing how at least some of the blanket layers within the display stack can be selectively patterned to further improve optical transmittance.  FIG.  11    is similar to the cross-section of  FIG.  3   , but expands upon the TFT layers  304 . For example,  FIG.  11    shows how TFT layers  304  may include a TFT gate dielectric layer  1100 , inorganic passivation layers  1102  formed over the TFT gate dielectric layer  1100 , one or more organic planarization layers  1104  formed over inorganic passivation layers  1102 , and organic pixel definition layers  1106  formed over organic planarization layers  1104 . Moreover, a protection layer such as substrate inorganic protection film  303  may be formed between substrate  302  and TFT layers  304 . In certain embodiments, at least layers  303 ,  1100 ,  1102 , and/or  1106  (which are typically blanket layers that cover the entire display surface) may be selectively patterned or thinned in the pixel removal region to further improve optical transmittance. If desired, other blanket display layers may also be selectively patterned/thinned to help increase the transmittance of light through the display stack. 
     In accordance with an embodiment, an electronic device is provided that includes a display having pixels formed in an active area and a sensor under the display, the display includes a pixel removal region that at least partially overlaps with the sensor, the active area has a first pixel density, and the pixel removal region has a second pixel density that is less than the first pixel density. 
     In accordance with another embodiment, the pixel removal region includes a plurality of pixel free regions each of which is devoid of thin-film transistors, and the plurality of pixel free regions is configured to increase signal transmittance through the display to the sensor. 
     In accordance with another embodiment, each of the plurality of pixel free regions is further devoid of power supply lines. 
     In accordance with another embodiment, horizontal and vertical control lines in the plurality of pixel free regions are rerouted to provide continuous open areas that reduce the amount of diffraction for light traveling through the display to the sensor. 
     In accordance with another embodiment, each of the plurality of pixel free regions include rows of continuous open areas within the pixel removal region. 
     In accordance with another embodiment, the electronic device includes an opaque mask with openings aligned to the plurality of pixel free regions. 
     In accordance with another embodiment, the second pixel density is half of the first pixel density. 
     In accordance with another embodiment, the second pixel density is less than half of the first pixel density. 
     In accordance with another embodiment, the display includes an additional pixel removal region that is physically separated from the pixel removal region. 
     In accordance with another embodiment, the additional pixel removal region has a different size than the pixel removal region. 
     In accordance with another embodiment, the pixel removal region overlaps an entire edge of the display. 
     In accordance with another embodiment, the pixel removal region overlaps a corner of the display. 
     In accordance with another embodiment, the pixel removal region overlaps a curved edge of the display. 
     In accordance with another embodiment, the pixel removal region overlaps a recessed notch area in the display. 
     In accordance with another embodiment, the pixel removal region overlaps the entire surface of the display. 
     In accordance with another embodiment, the pixel removal region includes first subpixels of a first color and second subpixels of a second color, and the density of the first subpixels is different than the density of the second subpixels in the pixel removal region. 
     In accordance with another embodiment, the pixel removal region includes blue subpixels and red subpixels, and the density of the blue subpixels is lower than the density of the red subpixels in the pixel removal region. 
     In accordance with another embodiment, the pixel removal region includes green subpixels, blue subpixels, and red subpixels, and the density of the blue subpixels is equal to the density of the blue subpixels and is equal to the density of the red subpixels in the pixel removal region. 
     In accordance with another embodiment, the pixels in the active area includes first subpixels, and the pixel removal region includes second subpixel having larger diodes than the first subpixels of the active area to mitigate aging. 
     In accordance with another embodiment, the electronic device includes a conductive touch sensor mesh formed over the display, the conductive touch sensor overlaps with the pixel removal region. 
     In accordance with another embodiment, the electronic device includes a conductive touch sensor mesh formed over the display, the conductive touch sensor mesh does not overlap with the pixel removal region. 
     In accordance with another embodiment, the pixel removal region includes a plurality of pixel free regions each of which lacks dummy contacts. 
     In accordance with another embodiment, the pixel removal region includes a plurality of pixel free regions each of which includes dummy contacts configured to provide emission current uniformity in the pixel removal region. 
     In accordance with another embodiment, the display includes a blanket layer that is selectively patterned in the pixel removal region to increase the transmittance of light through the display to the sensor, and the blanket layer is a display layer selected from the group consisting of: a substrate protection layer, a gate dielectric layer, an inorganic passivation layer, and an organic pixel definition layer. 
     In accordance with an embodiment, a display is provided that includes pixels formed in an active area and pixels formed in a given region within the active area, the pixels in the active area are formed at a first pixel density, and the pixels in the given region are formed at a second pixel density that is less than the first pixel density to increase the transmittance of light through the given region. 
     In accordance with an embodiment, an apparatus is provided that includes a display stack having a plurality of blanket display layers and an optical sensor at least partially covered by the display stack, at least some of the blanket display layers are patterned to increase light transmittance through the display stack to the optical sensor. 
     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: 20200408
Publication Date: 20250114
Grant Date: 20250114
Priority Date: 20190423
Inventors: RIEUTORT-LOUIS, WARREN S.
JUNG, WOO SHIK
JAMSHIDI ROUDBARI, ABBAS
YEH, SHIN-HUNG
GLAZOWSKI, CHRISTOPHER E.
GUILLOU, Jean-Pierre S.
CHE, Yuchi
Assignee: APPLE INC
CPC Classifications: [{"code": "H10K59/353", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/131", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/121", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/65", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/831", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3208", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/65", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/122", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/121", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/60", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2300/0426", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/20", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/65", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/30", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/88", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/40", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/353", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/131", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/121", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/65", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 70416597