PATENT DOCUMENT

Publication Number: US-11910654-B1
Application Number: US-202117395381-A
Country: US
Kind Code: B1

Title: Organic light-emitting diode display with active leakage-reducing structures

Abstract:
An organic light-emitting diode (OLED) display may have an array of organic light-emitting diode pixels that each have OLED layers interposed between a cathode and an anode. Voltage may be applied to the anode of each pixel to control the magnitude of emitted light. The conductivity of the OLED layers may allow leakage current to pass between neighboring anodes in the display. To reduce leakage current and the accompanying cross-talk, the display may include active and/or passive leakage-mitigating structures. The passive leakage-mitigating structures may have an undercut that causes discontinuities in the overlying OLED layers. Active leakage-mitigating structures may include a conductive layer (e.g., a conductive ring) that drains leakage current to ground. Alternatively, the active leakage-mitigating structures may include a gate electrode modulator with a variable voltage that stops the current flow laterally.

Claims:
What is claimed is: 
     
       1. A display comprising:
 a substrate; 
 an array of pixels that includes first and second organic light-emitting diode pixels, wherein the first organic light-emitting diode pixel includes a first patterned electrode on the substrate and wherein the second organic light-emitting diode pixel includes a second patterned electrode on the substrate; 
 a pixel definition layer on the substrate that is interposed between the first and second patterned electrodes; 
 a conductive layer formed over the substrate that has a first portion that forms part of the first organic light-emitting diode pixel and a second portion that forms part of the second organic light-emitting diode pixel; 
 a conductive gate that is formed between the first and second patterned electrodes, wherein the conductive gate is coupled to a variable gate voltage and is configured to generate a current that mitigates leakage current through the conductive layer; 
 a metal layer in the substrate; and 
 a via that electrically connects the conductive gate to the metal layer. 
 
     
     
       2. The display defined in  claim 1 , wherein the pixel definition layer has a trench between the first and second patterned electrodes and wherein the conductive gate is formed in the trench. 
     
     
       3. The display defined in  claim 2 , further comprising:
 a gate insulator that is formed over the conductive gate. 
 
     
     
       4. The display defined in  claim 3 , wherein the conductive layer is one of a plurality of organic light-emitting diode layers and wherein the plurality of organic light-emitting diode layers are formed in the trench and directly contact the gate insulator. 
     
     
       5. The display defined in  claim 2 , wherein the conductive gate forms a ring that encloses the first organic light-emitting diode pixel. 
     
     
       6. The display defined in  claim 2 , wherein the conductive gate forms part of a conductive grid that encloses each one of the array of pixels. 
     
     
       7. The display defined in  claim 2 , wherein the array of pixels includes pixels of a first color, pixels of a second color, and pixels of a third color, wherein the pixels of the first color have a first turn-on voltage, wherein the pixels of the second color have a second turn-on voltage that is greater than the first turn-on voltage, wherein the pixels of the third color have a third turn-on voltage that is greater than the first turn-on voltage, wherein each one of the pixels of the first color is laterally surrounded by a respective conductive gate, and wherein none of the pixels of the second and third color are laterally surrounded by a respective conductive gate. 
     
     
       8. The display defined in  claim 1 , wherein the conductive gate is formed on an upper surface of the pixel definition layer. 
     
     
       9. The display defined in  claim 8 , further comprising:
 a gate insulator that is formed over the conductive gate. 
 
     
     
       10. The display defined in  claim 8 , wherein the conductive gate forms a ring that encloses the first organic light-emitting diode pixel. 
     
     
       11. The display defined in  claim 8 , wherein the array of pixels includes pixels of a first color, pixels of a second color, and pixels of a third color, wherein the pixels of the first color have a first turn-on voltage, wherein the pixels of the second color have a second turn-on voltage that is greater than the first turn-on voltage, wherein the pixels of the third color have a third turn-on voltage that is greater than the first turn-on voltage, wherein each one of the pixels of the first color is laterally surrounded by a respective conductive gate, and wherein none of the pixels of the second and third color are laterally surrounded by a respective conductive gate. 
     
     
       12. The display defined in  claim 1 , wherein the first patterned electrode has an extension that is electrically connected to a contact and wherein the conductive gate is routed around the extension and does not overlap the extension. 
     
     
       13. A display comprising:
 a substrate; 
 an array of pixels that includes first and second organic light-emitting diode pixels, wherein the first organic light-emitting diode pixel includes a first patterned electrode on the substrate and wherein the second organic light-emitting diode pixel includes a second patterned electrode on the substrate; 
 a pixel definition layer on the substrate that is interposed between the first and second patterned electrodes; 
 a conductive layer formed over the substrate that has a first portion that forms part of the first organic light-emitting diode pixel and a second portion that forms part of the second organic light-emitting diode pixel; and 
 a conductive gate that is formed between the first and second patterned electrodes, wherein the conductive gate is coupled to a variable gate voltage and is configured to generate a current that mitigates leakage current through the conductive layer, wherein the first patterned electrode has an extension that is electrically connected to a contact and wherein the conductive gate is routed over the extension without overlapping the contact. 
 
     
     
       14. The display defined in  claim 13 , further comprising:
 a metal layer in the substrate; and 
 a via that passes through the substrate and the pixel definition layer to electrically connect the conductive gate to the metal layer. 
 
     
     
       15. The display defined in  claim 13 , further comprising:
 a gate insulator that is formed over the conductive gate. 
 
     
     
       16. The display defined in  claim 13 , wherein the pixel definition layer has a trench between the first and second patterned electrodes and wherein the conductive gate is formed in the trench. 
     
     
       17. The display defined in  claim 13 , wherein the conductive gate is formed on an upper surface of the pixel definition layer. 
     
     
       18. The display defined in  claim 13 , wherein the array of pixels includes pixels of a first color, pixels of a second color, and pixels of a third color, wherein the pixels of the first color have a first turn-on voltage, wherein the pixels of the second color have a second turn-on voltage that is greater than the first turn-on voltage, wherein the pixels of the third color have a third turn-on voltage that is greater than the first turn-on voltage, wherein each one of the pixels of the first color is laterally surrounded by a respective conductive gate, and wherein none of the pixels of the second and third color are laterally surrounded by a respective conductive gate. 
     
     
       19. A display comprising:
 a substrate; 
 an array of pixels that includes first and second organic light-emitting diode pixels, wherein the first organic light-emitting diode pixel includes a first patterned electrode on the substrate and wherein the second organic light-emitting diode pixel includes a second patterned electrode on the substrate; 
 a pixel definition layer on the substrate that is interposed between the first and second patterned electrodes; 
 a conductive layer formed over the substrate that has a first portion that forms part of the first organic light-emitting diode pixel and a second portion that forms part of the second organic light-emitting diode pixel; and 
 a conductive structure that is formed between the first and second patterned electrodes on an upper surface of the pixel definition layer, wherein the conductive structure is coupled to a bias voltage to serve as a current sink for current leaking through the conductive layer. 
 
     
     
       20. The display defined in  claim 19 , wherein the array of pixels includes pixels of a first color, wherein the pixels of the first color have a turn-on voltage, and wherein the bias voltage is within 20% of the turn-on voltage. 
     
     
       21. The display defined in  claim 19 , wherein the array of pixels has a ground voltage and wherein the bias voltage is the ground voltage. 
     
     
       22. The display defined in  claim 19 , wherein the bias voltage is more than 1 volt greater than a ground voltage for the array of pixels. 
     
     
       23. The display defined in  claim 19 , wherein the array of pixels includes pixels of a first color, pixels of a second color, and pixels of a third color, wherein the pixels of the first color have a first turn-on voltage, wherein the pixels of the second color have a second turn-on voltage that is greater than the first turn-on voltage, wherein the pixels of the third color have a third turn-on voltage that is greater than the first turn-on voltage, wherein each one of the pixels of the first color is laterally surrounded by a respective conductive structure that serves as a current sink, and wherein none of the pixels of the second and third color are laterally surrounded by a respective conductive structure that serves as a current sink.

Description:
This application claims the benefit of provisional patent application No. 63/067,261, filed Aug. 18, 2020, and provisional patent application No. 63/067,262, filed Aug. 18, 2020, 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. 
     To emit light from a given pixel in an organic light-emitting diode display, a voltage may be applied to the anode of the given pixel. Ideally, the voltage at the anode of the given pixel would not affect any neighboring pixels. However, the conductivity of the OLED layers between the anodes may allow lateral conduction from the anode of the given pixel to the anodes of adjacent pixels. This may cause pixel cross-talk that allows nominally ‘off’ pixels to emit light due to an adjacent ‘on’ pixel&#39;s leakage. The pixel cross-talk may degrade display performance and cause a color-shift in the resulting image. 
     It may be desirable to reduce the distance between pixels in a display in order to increase the resolution of the display. However, pixel cross-talk due to lateral conduction through OLED layers may worsen as the distance between pixels decreases. 
     It would therefore be desirable to be able to provide improved displays for electronic devices. 
     SUMMARY 
     An electronic device may have a display such as an organic light-emitting diode display. The organic light-emitting diode (OLED) display may have an array of organic light-emitting diode pixels that each have OLED layers interposed between a cathode and an anode. 
     Each organic light-emitting diode pixel may have a respective anode. Voltage may be applied to the anode of each organic light-emitting diode pixel to control how much light is emitted from each organic light-emitting diode pixel. OLED layers formed above the anode (e.g., a hole injection layer, a hole transport layer, an emissive layer, an electron transport layer, an electronic injection layer, an electron blocking layer, a charge generation layer, and/or a hole blocking layer) may be conductive. These conductive layers may be referred to as laterally conductive layers. The conductivity of the OLED layers may allow leakage current to pass between neighboring anodes in the display. 
     To reduce leakage current and the accompanying cross-talk in a display, the display include active and/or passive leakage-mitigating structures. The passive leakage-mitigating structures may be formed in rings around the pixels. A passive leakage-mitigating structure may be formed on the anode of a pixel between the anode and the pixel definition layer. A passive leakage-mitigating structure may be formed on an upper surface of the pixel definition layer. A passive leakage-mitigating structure may be formed on a substrate partially in a trench of the pixel definition layer. The passive leakage-mitigating structure may have an undercut that causes discontinuities in the overlying OLED layers, thus mitigating lateral leakage. 
     Active leakage-mitigating structures may include a conductive layer (e.g., a conductive ring) that drains leakage current to ground. Alternatively, the active leakage-mitigating structures may include a gate electrode modulator with a variable voltage that stops the current flow laterally. The active leakage-mitigating structure may be formed in a trench in the pixel definition layer or on the upper surface of the pixel definition layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a schematic diagram of an illustrative electronic device having a display in accordance with an embodiment. 
         FIG.  2    is a schematic diagram of an illustrative display in accordance with an embodiment. 
         FIG.  3    is a diagram of an illustrative pixel circuit in accordance with an embodiment. 
         FIG.  4    is a cross-sectional side view of an illustrative organic light-emitting diode display showing lateral current leakage between adjacent anodes in accordance with an embodiment. 
         FIG.  5 A  is a cross-sectional side view of an illustrative organic light-emitting diode display showing different layers of the organic light-emitting diodes in accordance with an embodiment. 
         FIG.  5 B  is a cross-sectional side view of an illustrative organic light-emitting diode display showing different layers of a tandem organic light-emitting diode in accordance with an embodiment. 
         FIG.  6    is a cross-sectional side view of an illustrative organic light-emitting diode display having a leakage-mitigating structure that is interposed between an anode and a pixel definition layer in accordance with an embodiment. 
         FIG.  7    is a cross-sectional side view of an illustrative organic light-emitting diode display having a leakage-mitigating structure that is formed on an upper surface of a pixel definition layer in accordance with an embodiment. 
         FIG.  8    is a cross-sectional side view of an illustrative organic light-emitting diode display having a leakage-mitigating structure that is formed on an upper surface of a pixel definition layer and that includes only two layers in accordance with an embodiment. 
         FIG.  9    is a cross-sectional side view of an illustrative organic light-emitting diode display having a leakage-mitigating structure that is formed on a substrate and that has a portion overlapped by a trench in a pixel definition layer in accordance with an embodiment. 
         FIG.  10    is a top view of an illustrative pixel with a leakage-mitigating structure of the type shown in  FIG.  6    in accordance with an embodiment. 
         FIG.  11    is a top view of an illustrative pixel with a leakage-mitigating structure of the type shown in  FIG.  7   ,  FIG.  8   , or  FIG.  9    in accordance with an embodiment. 
         FIG.  12    is a top view of an illustrative display showing how every pixel may be enclosed by a respective leakage-mitigating structure in accordance with an embodiment. 
         FIG.  13    is a top view of an illustrative display showing how only pixels of a given color may be enclosed by a respective leakage-mitigating structure in accordance with an embodiment. 
         FIG.  14    is a top view of an illustrative display showing how a pixel may be enclosed by two respective leakage-mitigating structures in accordance with an embodiment. 
         FIG.  15    is a top view of an illustrative display showing how a pixel may be only partially surrounded by leakage-mitigating structures in accordance with an embodiment. 
         FIG.  16    is a top view of an illustrative display showing how a grid of leakage-mitigating structures may be formed between the array of pixels in accordance with an embodiment. 
         FIG.  17    is a cross-sectional side view of an illustrative organic light-emitting diode display having a guard ring on a substrate that serves as a current sink to mitigate lateral leakage in accordance with an embodiment. 
         FIG.  18    is a cross-sectional side view of an illustrative organic light-emitting diode display having a guard ring on a pixel definition layer that serves as a current sink to mitigate lateral leakage in accordance with an embodiment. 
         FIG.  19    is a top view of an illustrative display showing how only some of the pixels in the array may be enclosed by a respective guard ring in accordance with an embodiment. 
         FIG.  20    is a cross-sectional side view of an illustrative organic light-emitting diode display showing how conductive routing may electrically connect the guard rings in accordance with an embodiment. 
         FIG.  21    is a cross-sectional side view of an illustrative organic light-emitting diode display showing how the guard rings may be omitted between some adjacent anodes in accordance with an embodiment. 
         FIG.  22    is a top view of an illustrative display with each pixel being enclosed by a respective guard ring in accordance with an embodiment. 
         FIG.  23    is a top view of an illustrative display showing some of the pixels enclosed by respective guard rings and routing structures between the guard rings in accordance with an embodiment. 
         FIG.  24    is a cross-sectional side view of an illustrative organic light-emitting diode display having a gate electrode modulator on a substrate that generates a leakage-mitigating current in accordance with an embodiment. 
         FIG.  25    is a cross-sectional side view of an illustrative organic light-emitting diode display having a gate electrode modulator on a pixel definition layer that generates a leakage-mitigating current in accordance with an embodiment. 
         FIG.  26    is a cross-sectional side view of an illustrative organic light-emitting diode display showing how conductive routing may electrically connect conductive gates in accordance with an embodiment. 
         FIGS.  27 A and  27 B  are top views of illustrative displays showing different pixel layouts in accordance with an embodiment. 
         FIGS.  28 A and  28 B  are top views of illustrative pixels having anode extensions and contacts and corresponding leakage-mitigating structures in accordance with an embodiment. 
         FIG.  29    is a cross-sectional side view of an illustrative display showing how an optical sensor may be positioned under the display in accordance with an embodiment. 
         FIG.  30    is a cross-sectional side view of an illustrative display showing how leakage-mitigating structures may disrupt a pixel definition layer waveguide effect in accordance with an embodiment. 
         FIG.  31    is a top view of an illustrative display showing how leakage-mitigating structures may partially surround a respective anode in accordance with an embodiment. 
         FIG.  32    is a cross-sectional side view of an illustrative display showing how cathode continuity is preserved in the opening of a leakage-mitigating structure in accordance with an embodiment. 
         FIG.  33    is a top view of an illustrative display showing how an opaque layer may be formed in an opening in a leakage-mitigating structure that partially surrounds a respective anode in accordance with an embodiment. 
         FIG.  34    is a top view of an illustrative display showing how only pixels of a given color may be partially surrounded by a respective leakage-mitigating structure in accordance with an embodiment. 
         FIG.  35    is a top view of an illustrative display that includes cathode bus lines in accordance with an embodiment. 
         FIG.  36    is a cross-sectional side view of an illustrative display that has an undercut structure and a conductive layer that electrically connects the cathode to a cathode bus line in accordance with an embodiment. 
         FIG.  37    is a cross-sectional side view of an illustrative display that has a single-layer undercut structure in accordance with an embodiment. 
         FIG.  38    is a cross-sectional side view of an illustrative display that has a three-layer undercut structure in accordance with an embodiment. 
         FIG.  39    is a top view of an illustrative display that includes a leakage-mitigating structure and an additional undercut structure in accordance with an embodiment. 
         FIG.  40    is a cross-sectional side view of an illustrative display that has a leakage-mitigating structure and an additional single-layer undercut structure in accordance with an embodiment. 
         FIG.  41    is a cross-sectional side view of an illustrative display that has a leakage-mitigating structure and an additional two-layer undercut structure 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 examples, electronic device  10  may be an augmented reality (AR) headset and/or virtual reality (VR) headset. 
     As shown in  FIG.  1   , electronic device  10  may include control circuitry  16  for supporting the operation of device  10 . The control circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  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-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 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 . 
       FIG.  2    is a diagram of an illustrative display. As shown in  FIG.  2   , display  14  may include layers such as substrate layer  26 . Substrate layers such as layer  26  may be formed from rectangular planar layers of material or layers of material with other shapes (e.g., circular shapes or other shapes with one or more curved and/or straight edges). The substrate layers of display  14  may include glass layers, polymer layers, silicon layers, composite films that include polymer and inorganic materials, metallic foils, etc. 
     Display  14  may have an array of pixels  22  for displaying images for a user such as pixel array  28 . Pixels  22  in array  28  may be arranged in rows and columns. The edges of array  28  may be straight or curved (i.e., each row of pixels  22  and/or each column of pixels  22  in array  28  may have the same length or may have a different length). There may be any suitable number of rows and columns in array  28  (e.g., ten or more, one hundred or more, or one thousand or more, etc.). Display  14  may include pixels  22  of different colors. As an example, display  14  may include red pixels, green pixels, and blue pixels. 
     Display driver circuitry  20  may be used to control the operation of pixels  28 . Display driver circuitry  20  may be formed from integrated circuits, thin-film transistor circuits, and/or other suitable circuitry. Illustrative display driver circuitry  20  of  FIG.  2    includes display driver circuitry  20 A and additional display driver circuitry such as gate driver circuitry  20 B. Gate driver circuitry  20 B may be formed along one or more edges of display  14 . For example, gate driver circuitry  20 B may be arranged along the left and right sides of display  14  as shown in  FIG.  2   . 
     As shown in  FIG.  2   , display driver circuitry  20 A (e.g., one or more display driver integrated circuits, thin-film transistor circuitry, etc.) may contain communications circuitry for communicating with system control circuitry over signal path  24 . Path  24  may be formed from traces on a flexible printed circuit or other cable. The control circuitry may be located on one or more printed circuits in electronic device  10 . During operation, control circuitry (e.g., control circuitry  16  of  FIG.  1   ) may supply circuitry such as a display driver integrated circuit in circuitry with image data for images to be displayed on display  14 . Display driver circuitry  20 A of  FIG.  2    is located at the top of display  14 . This is merely illustrative. Display driver circuitry may be located at both the top and bottom of display  14  or in other portions of device  10 . 
     To display the images on pixels  22 , display driver circuitry  20 A may supply corresponding image data to data lines D while issuing control signals to supporting display driver circuitry such as gate driver circuitry  20 B over signal paths  30 . With the illustrative arrangement of  FIG.  2   , data lines D run vertically through display  14  and are associated with respective columns of pixels  22 . 
     Gate driver circuitry  20 B (sometimes referred to as gate line driver circuitry or horizontal control signal circuitry) may be implemented using one or more integrated circuits and/or may be implemented using thin-film transistor circuitry on substrate  26 . Horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.) run horizontally through display  14 . Each gate line G is associated with a respective row of pixels  22 . If desired, there may be multiple horizontal control lines such as gate lines G associated with each row of pixels. Individually controlled and/or global signal paths in display  14  may also be used to distribute other signals (e.g., power supply signals, etc.). 
     Gate driver circuitry  20 B may assert control signals on the gate lines G in display  14 . For example, gate driver circuitry  20 B may receive clock signals and other control signals from circuitry  20 A on paths  30  and may, in response to the received signals, assert a gate line signal on gate lines G in sequence, starting with the gate line signal G in the first row of pixels  22  in array  28 . As each gate line is asserted, data from data lines D may be loaded into a corresponding row of pixels. In this way, control circuitry such as display driver circuitry  20 A and  20 B may provide pixels  22  with signals that direct pixels  22  to display a desired image on display  14 . Each pixel  22  may have a light-emitting diode and circuitry (e.g., thin-film circuitry on substrate  26 ) that responds to the control and data signals from display driver circuitry  20 . 
     Gate driver circuitry  20 B may include blocks of gate driver circuitry such as gate driver row blocks. Each gate driver row block may include circuitry such output buffers and other output driver circuitry, register circuits (e.g., registers that can be chained together to form a shift register), and signal lines, power lines, and other interconnects. Each gate driver row block may supply one or more gate signals to one or more respective gate lines in a corresponding row of the pixels of the array of pixels in the active area of display  14 . 
     A schematic diagram of an illustrative pixel circuit of the type that may be used for each pixel  22  in array  28  is shown in  FIG.  3   . As shown in  FIG.  3   , display pixel  22  may include light-emitting diode  38 . A positive power supply voltage ELVDD may be supplied to positive power supply terminal  34  and a negative (ground) power supply voltage ELVSS may be supplied to ground power supply terminal  36 . Diode  38  has an anode (terminal AN) and a cathode (terminal CD). The state of drive transistor  32  controls the amount of current flowing through diode  38  and therefore the amount of emitted light  40  from display pixel  22 . Cathode CD of diode  38  is coupled to ground terminal  36 , so cathode terminal CD of diode  38  may sometimes be referred to as the ground terminal for diode  38 . 
     To ensure that transistor  38  is held in a desired state between successive frames of data, display pixel  22  may include a storage capacitor such as storage capacitor Cst. The voltage on storage capacitor Cst is applied to the gate of transistor  32  at node A to control transistor  32 . Data can be loaded into storage capacitor Cst using one or more switching transistors such as switching transistor  33 . When switching transistor  33  is off, data line D is isolated from storage capacitor Cst and the gate voltage on terminal A is equal to the data value stored in storage capacitor Cst (i.e., the data value from the previous frame of display data being displayed on display  14 ). When gate line G (sometimes referred to as a scan line) in the row associated with display pixel  22  is asserted, switching transistor  33  will be turned on and a new data signal on data line D will be loaded into storage capacitor Cst. The new signal on capacitor Cst is applied to the gate of transistor  32  at node A, thereby adjusting the state of transistor  32  and adjusting the corresponding amount of light  40  that is emitted by light-emitting diode  38 . If desired, the circuitry for controlling the operation of light-emitting diodes for display pixels in display  14  (e.g., transistors, capacitors, etc. in display pixel circuits such as the display pixel circuit of  FIG.  3   ) may be formed using other configurations (e.g., configurations that include circuitry for compensating for threshold voltage variations in drive transistor  32 , etc.). The display pixel circuit of  FIG.  3    is merely illustrative. 
       FIG.  4    is a cross-sectional side view of an illustrative display with organic light-emitting diode display pixels. As shown, display  14  may include a substrate  26 . Substrate  26  may be formed from glass, plastic, polymer, silicon, or any other desired material. Anodes such as anodes  42 - 1 ,  42 - 2 , and  42 - 3  may be formed on the substrate. Anodes  42 - 1 ,  42 - 2 , and  42 - 3  may be formed from conductive material and may be covered by OLED layers  45  and cathode  54 . OLED layers  45  may include one or more layers for forming an organic light-emitting diode. For example, layers  45  may include one or more of a hole-injection layer (HIL), a hole-transport layer (HTL), an emissive layer (EML), an electron-transport layer (ETL), and an electronic-injection layer (EIL). Cathode  54  may be a conductive layer formed on the OLED layers  45 . Cathode layer  54  may form a common cathode terminal (see, e.g., cathode terminal CD of  FIG.  3   ) for all diodes in display  14 . Cathode layer  54  may be formed from a transparent conductive material (e.g., indium tin oxide, a metal layer(s) that is sufficiently thin to be transparent, a combination of a thin metal and indium tin oxide, etc.). Each anode in display  14  may be independently controlled, so that each diode in display  14  can be independently controlled. This allows each pixel  22  to produce an independently controlled amount of light. 
     Anodes  42 - 1 ,  42 - 2 , and  42 - 3  may each be associated with a respective pixel. For example, anode  42 - 1  may be associated with pixel  22 - 1 , anode  42 - 2  may be associated with pixel  22 - 2 , and anode  42 - 3  may be associated with pixel  22 - 3 . To emit light from a pixel, a voltage may be applied to the anode of the respective pixel. Take an example in which it is desired to emit light from pixel  22 - 2  (without emitting light from pixels  22 - 1  and  22 - 3 ). A voltage may be applied to anode  42 - 2 , which causes light  56  to be emitted from pixel  22 - 2 . As previously stated, it would be desirable if no light was emitted from pixels  22 - 1  and  22 - 3  as a result of voltage being applied to anode  42 - 2 . However, as shown, leakage may occur through OLED layers  45  between anode  42 - 2  and anode  42 - 1 , as well as between anode  42 - 2  and anode  42 - 3 . There may be a resistance  58  (i.e., a resistance associated with the OLED layers) between anode  42 - 2  and the adjacent anodes that helps prevent leakage. The greater the resistance, the less leakage current will reach anodes  42 - 1  and  42 - 3 . However, the resistance may not be large enough to totally eliminate leakage between anode  42 - 2  and anodes  42 - 1  and  42 - 3 . As shown, even though pixels  22 - 1  and  22 - 3  are intended to be off, light  56  may be emitted from pixels  22 - 1  and  22 - 3 . The resistance  58  between adjacent anodes may be reduced as the distance  60  between adjacent anodes is reduced. In order to maximize display resolution, it is desirable for the distance  60  between adjacent anodes to be small. However, this reduces the resistance  58  between anodes and increases cross-talk between pixels. 
     Although not shown in  FIG.  4   , display  14  may optionally include a pixel definition layer (PDL). The pixel definition layer may be formed from a dielectric material and may be interposed between adjacent anodes of the display. The pixel definition layer may have openings in which the anodes are formed, thereby defining the area of each pixel. Each of the following embodiments of an organic light-emitting diode display may optionally include a pixel definition layer. 
       FIG.  5 A  is a cross-sectional side view of an illustrative display with organic light-emitting diode display pixels.  FIG.  5 A  shows details of the OLED layers  45  from  FIG.  4   . As shown, OLED layers  45  (sometimes referred to as an organic stack-up, an organic stack, or an organic light-emitting diode (OLED) stack) may include a hole injection layer (HIL)  44 , a hole transport layer (HTL)  46 , an emissive layer (EML)  48 , an electron transport layer (ETL)  50 , and an electron injection layer (EIL)  52  interposed between anodes  42  and cathode  54 . The hole injection layer and hole transport layer may collectively be referred to as a hole layer (i.e., hole layer  62 ). The electron transport layer and the electron injection layer may collectively be referred to as an electron layer (i.e., electron layer  64 ). Emissive layer  48  may include organic electroluminescent material. As shown, hole layer  62  and electron layer  64  may be blanket (common) layers that cover the entire array. 
     Ideally, adjacent diodes in display  14  operate independently. In practice, the presence of common layers such as hole layer  62  present an opportunity for leakage current from one diode to flow laterally into an adjacent diode, thereby potentially biasing the adjacent diode. For example, there is a possibility that the process of applying a drive current between anode  42 - 1  and cathode  54  will give rise to lateral leakage current through hole layer  62  (e.g., a current from anode  42 - 1  to anode  42 - 2 ). In order to reduce leakage between anodes through hole layer  62 , it may be desirable to increase the resistance of the hole layer between adjacent anodes. 
     The examples of layers included between the anodes  42  and the cathode  54  in  FIG.  5 A  are merely illustrative. If desired, additional layers may be included between anodes  42  and cathode  54  (i.e., an electron blocking layer, a charge generation layer, a hole blocking layer, etc.), such as in a tandem organic light-emitting diode. 
       FIG.  5 B  is a cross-sectional side view of a tandem organic light-emitting diode (OLED), with at least two stacked OLED units. As shown in  FIG.  5 B , the tandem OLED may include a hole injection layer (HIL)  44 , a first hole transport layer (HTL)  46 - 1 , a first emissive layer (EML- 1 )  48 , an electron transport layer (ETL)  50 , a first electron injection layer (EIL)  52 - 1 , a charge generation layer (CGL)  53 , a second hole transport layer (HTL)  46 - 2 , an electron blocking layer (EBL)  55 , a second emissive layer (EML- 2 )  48 - 2 , a hole blocking layer (HBL)  57 , and a second electron injection layer (EIL)  52 - 2  interposed between anodes  42  and cathode  54 . This arrangement of layers for a tandem diode is merely illustrative. Other tandem diode stackups may be used if desired. 
     In general, any desired layers may be included in between the anodes and the cathode and any layer that is formed across the display may be considered a common laterally conductive layer. Each layer in light-emitting diode (LED) layers  45  may be formed from any desired material. In some embodiments, the layers may be formed from organic material (optionally including organic or inorganic dopants). However, in some cases one or more layers may be formed from inorganic material. Any or all of the LED layers  45  may be blanket (common) layers that cover the entire array. The display may also include quantum dots (e.g., quantum dot layers) if desired. For example, a display may include OLEDs to produce blue light and quantum dot layers to convert the blue light to red and green light. 
     In the example of  FIGS.  5 A and  5 B , a patterned anode layer is formed below a common cathode layer. This example is merely illustrative. If desired, the organic light-emitting diode may be inverted such that the cathode is patterned per-pixel and the anode is a common layer. In this case, the order of the OLED layers in organic stack  45  may be inverted as well. For example, the electron injection layer may be formed on a patterned cathode, the electron transport layer may be formed on the electron injection layer, the emissive layer may be formed on the electron transport layer, the hole transport layer may be formed on the emissive layer, the hole injection layer may be formed on the hole transport layer, and a common anode layer may be formed on the hole injection layer. 
     In subsequent embodiments, a patterned anode is depicted as being positioned below a common cathode layer. However, it should be understood that in each of these embodiments the anode and cathode may be inverted as previously described. 
     In some cases, a laterally conductive layer may be patterned or otherwise formed with gaps to reduce lateral leakage between pixels. In other words, the laterally conductive layer may be physically interrupted by an air gap or other barrier that prevents lateral leakage from occurring. 
     As one example, a leakage-mitigating structure may be formed directly on the anode of a given pixel. The leakage-mitigating structure may cause a discontinuity in one or more laterally conductive layers that is formed on the leakage-mitigating structure, thus mitigating leakage through the laterally conductive layers. The leakage-mitigating structure may partially or totally enclose the anode (e.g., form a ring around the anode). Because, the leakage-mitigating structure causes a discontinuity (or cut) in a lateral conductive layer, the leakage-mitigating structure may sometimes be referred to as a cutting ring, OLED layer cutting ring, cutting structure, OLED layer cutting structure, laterally conductive layer cutting ring, or laterally conductive layer cutting structure. 
     It may be desirable to create discontinuities in one or more of the organic light-emitting diode layers in the display (to prevent lateral leakage through the organic light-emitting diode layers). However, it may also be desirable to maintain continuity in one or more other layers in the display (e.g., cathode  54 ). Therefore, the shape of the leakage-mitigating structure may be designed such that one or more organic light-emitting diode layers deposited over the leakage-mitigating structure has discontinuities while additional organic light-emitting diode layers and/or cathode  54  deposited over the leakage-mitigating structure do not have discontinuities. 
       FIG.  6    is a cross-sectional side view of a display having a leakage-mitigating structure formed directly on anode  42 . As shown, leakage-mitigating structure  70  is formed over anode  42  and has an undercut  102 . Undercut  102  may sometimes also be referred to as recess  102 , cavity  102 , hole,  102 , indentation  102 , etc. The undercut is a void in the leakage-mitigating structure material that is still covered by a portion of the leakage-mitigating structure. As shown in  FIG.  6   , undercut  102  may have a width  104  and a height  106 . In this arrangement, width  104  is defined as the distance between the edge of portion  70 - 1  of the leakage-mitigating structure and the edge of portion  70 - 2  of the leakage-mitigating structure. Height  106  is defined as the distance between a lower surface of portion  70 - 1  of the leakage-mitigating structure and an upper surface of portion  70 - 3  of the leakage-mitigating structure. Width  104  and height  106  may each be any desired distance (e.g., less than 1 micron, less than 500 nanometers, less than 250 nanometers, less than 150 nanometers, less than 100 nanometers, less than 75 nanometers, less than 50 nanometers, less than 35 nanometers, less than 25 nanometers, less than 20 nanometers, more than 10 nanometers, more than 20 nanometers, between 10 and 100 nanometers, etc.). Height  106  and width  104  may the same or may be different. In one example, height  106  may be less than 50 nanometers and width  104  may be greater than 20 nanometers. 
     In the example of  FIG.  6   , leakage-mitigating structure  70  may be formed from portions  70 - 2 , and  70 - 3  (sometimes referred to as layers  70 - 1 ,  70 - 2 , and  70 - 3 ) that are formed during individual deposition steps. In other words, portions  70 - 1 ,  70 - 2 , and  70 - 3  may be deposited separately when the leakage-mitigating structure is formed. Each portion may be formed from any desired material (e.g., silicon nitride, silicon dioxide, an organic material, etc.). In one example, portions  70 - 1  and  70 - 3  may be formed from silicon dioxide (SiO 2 ) and portion may be formed from silicon nitride (SiN). The materials may be selected to tune the size of the undercut formed during etching. In general, any combination of materials may be used. 
     Portion  70 - 1  may have a thickness  110 , portion  70 - 2  may have a thickness  108 , and portion  70 - 3  may have a thickness  130 . Thicknesses  108 ,  110 , and  130  may each be any desired distance (e.g., less than 1 micron, less than 500 nanometers, less than 250 nanometers, less than 150 nanometers, less than 100 nanometers, less than 75 nanometers, less than 50 nanometers, less than 35 nanometers, less than 25 nanometers, less than 20 nanometers, more than 10 nanometers, more than 20 nanometers, between 10 and 100 nanometers, etc.). Thicknesses  108 ,  110 , and  130  may be the same or may be different. 
     The angles of the edges of portions  70 - 1 ,  70 - 2 , and  70 - 3  may be selected to control the discontinuities of the overlying organic light-emitting diode layers. As shown in  FIG.  6   , portion has an edge surface  126  that is at an angle  128  relative to the planar upper surface of anode  42  (and relative to the planar lower surface of portion  70 - 3 ). Portion  70 - 2  has an edge surface  112  that is at an angle  116  relative to the planar upper surface of anode  42  (and relative to the planar lower surface of portion  70 - 2 ). Portion  70 - 1  has an edge surface  114  that is at an angle  118  relative to the planar upper surface of anode  42  (and relative to the planar lower surface of portion  70 - 1 ). Angles  116 ,  118 , and  128  may be the same or may be different. Each of the angles may be any desired angle (e.g., between 45° and 90°, between 25° and 135°, between 45° and 55°, between 55° and 65°, between 75° and 85°, between 85° and 95° between 45° and 65°, between 70° and 90°, between 10° and 45°, less than 90°, etc.). 
     In  FIG.  6   , a portion of layer  70 - 3  is not covered by layer  70 - 1 . Said another way, layer extends past the edge of layer  70 - 1  (e.g., towards the center of the anode). The width  124  of the portion of layer  70 - 3  that is not covered by layer  70 - 1  may be any desired distance (e.g., less than 1 micron, less than 500 nanometers, less than 250 nanometers, less than 150 nanometers, less than 100 nanometers, less than 75 nanometers, less than 50 nanometers, less than 35 nanometers, less than 25 nanometers, less than 20 nanometers, less than 10 nanometers, more than 10 nanometers, more than 20 nanometers, between 10 and 100 nanometers, etc.). The portion of layer  70 - 3  that is not covered by layer  70 - 1  may be referred to as a step portion or footer of the leakage-mitigating structure. Width  124  may be greater than 40 nanometers. 
       FIG.  6    shows how discontinuities may be formed in the organic light-emitting diodes deposited over the leakage-mitigating structure. As shown in  FIG.  6   , organic light-emitting diode layers  45 - 1 ,  45 - 2 ,  45 - 3 ,  45 - 4 , and  45 - 5  are formed over the leakage-mitigating structure  70  and anode  42 . Cathode layer  54  is formed over the organic light-emitting diode layers. 
     The presence of undercut  102  may result in a void  142  present between the leakage-mitigating structure and organic light-emitting diode layers. In the example of  FIG.  6   , void  142  (sometimes referred to as air-filled void  142 , air-filled region  142 , insulator-filled void  142 , etc.) forms discontinuities between respective portions of organic light-emitting diode layer  45 - 1 . The void may be filled with air or any other desired material. The void also forms discontinuities between respective portions of organic light-emitting diode layer  45 - 2 . Finally, the void forms discontinuities between respective portions of organic light-emitting diode layer  45 - 3 . In this way, lateral leakage through organic light-emitting diode layers  45 - 1 ,  45 - 2 , and  45 - 3  may be prevented. While forming discontinuities in organic light-emitting diode layers  45 - 1 ,  45 - 2 , and  45 - 3 , the void may not form discontinuities between organic light-emitting diode layer  45 - 4 , organic light-emitting diode layer  45 - 5 , and cathode layer  54 . 
     The shape of leakage-mitigating structure  70  may determine how many of the organic light-emitting diode layers are interrupted by void  142 . In  FIG.  6   , three organic light-emitting diode layers ( 45 - 1 ,  45 - 2 , and  45 - 3 ) are interrupted by void  142  whereas two organic light-emitting diode layers ( 45 - 4  and  45 - 5 ) are not interrupted by void  142 . As previously mentioned, in one illustrative arrangement, organic light-emitting diode layer  45 - 1  may be a hole injection layer, organic light-emitting diode layer  45 - 2  may be a hole transport layer, organic light-emitting diode layer  45 - 3  may be an emissive layer, organic light-emitting diode layer  45 - 4  may be an electron transport layer, and organic light-emitting diode layer  45 - 5  may be an electron injection layer. In another illustrative arrangement (e.g., when a tandem diode arrangement is used), organic light-emitting diode layer  45 - 1  may be a hole layer, organic light-emitting diode layer  45 - 2  may be a first emissive layer, organic light-emitting diode layer  45 - 3  may be a charge generation layer, organic light-emitting diode layer  45 - 4  may be a second emissive layer, and organic light-emitting diode layer  45 - 5  may be an electron layer. 
     Organic light-emitting diode layer  45 - 3  (e.g., the last layer interrupted by the void) may have a higher conductivity than organic light-emitting diode layer  45 - 4  (e.g., the first layer that is not interrupted by the void). In other words, the discontinuities in the organic light-emitting diode layers may be propagated to ensure discontinuity of a high conductivity organic light-emitting diode layer. This may effectively reduce lateral leakage between pixels in the display. Continuity in the remaining organic light-emitting diode layers (e.g.,  45 - 4  and  45 - 5 ) may be maintained while still ensuring satisfactory light leakage levels. 
     In general, each of the organic light-emitting diode layers may have any desired conductivity, and discontinuities may be propagated through the organic light-emitting diode layers by leakage-mitigating structure until lateral light leakage is reduced to satisfactory levels (while maintaining continuity of the cathode layer). In other words, in an example where organic light-emitting diode layer  45 - 3  has a low conductivity and organic light-emitting diode layer  45 - 2  has a high conductivity (e.g., higher than layer  45 - 3 ), the discontinuities may only be present in organic light-emitting diode layers  45 - 1  and  45 - 2  (while organic light-emitting diode layers  45 - 3 ,  45 - 4 , and  45 - 5  remain continuous). In yet another example where organic light-emitting diode layer  45 - 2  has a low conductivity and organic light-emitting diode layer  45 - 1  has a high conductivity (e.g., higher than layer  45 - 2 ), the discontinuities may only be present in organic light-emitting diode layer  45 - 1  (while organic light-emitting diode layers  45 - 2 ,  45 - 3 ,  45 - 4 , and  45 - 5  remain continuous). 
     The example of having five OLED layers between cathode  54  and anode  42  is merely illustrative. Additional OLED layers may be incorporated if desired. For example, in  FIG.  5 B  there are 11 OLED layers used to form a tandem diode. In this type of arrangement, leakage-mitigating structure  70  may cause discontinuities in one or more of the OLED layers. In one example, HIL, HTL, EML- 1 , ETL, EIL, CGL, HTL, EBL, and EML- 2  may all have discontinuities caused by leakage-mitigating structure whereas HBL and EIL may not have a discontinuity. In general, discontinuities may be propagated through any desired number of the OLED layers in the tandem diode while maintaining continuity in cathode  54 . 
     As shown in  FIG.  6   , leakage-mitigating structure  70  is formed from a different material than pixel definition layer  76 . Pixel definition layer  76  may be formed from an organic material (that is a different material than any of the materials within leakage-mitigating structure  70 ). In contrast, leakage-mitigating structure  70  may be formed from one or more inorganic materials. Pixel definition layer  76  may be formed over a portion of leakage-mitigating structure  70 . However, the pixel definition layer may be offset from the edge of the leakage-mitigating structure by a distance  74 . This separation between the pixel definition layer and the edge of the leakage-mitigating structure may ensure that the OLED layers  45  are planar (and therefore consistent) at the edge of the leakage-mitigating structure that causes the leakage-mitigating discontinuities in some of the OLED layers. Distance  74  may be greater than 200 nanometers, greater than 300 nanometers, greater than 500 nanometers, greater than 800 nanometers, greater than 1,000 nanometers, less than 5 microns, less than 3 microns, less than 2 microns, less than 1 micron, between 500 nanometers and 5 microns, etc. 
     Leakage-mitigating structure  70  is in direct contact with pixel definition layer  76  (e.g., along an upper surface of portion  70 - 1 ) and is in direct contact with anode  42  (e.g., along a lower surface of portion  70 - 3 ). The upper surface of portion  70 - 1  is also in direct contact with OLED layer  45 - 1 . Said another way, leakage-mitigating structure  70  has first and second opposing surfaces, with the first surface adjacent to (and in direct contact with) pixel definition layer  76  and OLED layer  45 - 1  and the second surface adjacent to (and in direct contact with) anode  42 . 
     Leakage-mitigating structure  70  may conform to an edge surface  78  of anode  42 . Covering edge surface  78  of anode  42  with a portion of leakage-mitigating structure  70  may protect the anode sidewall  78  from damage. Anode  42  (which may be formed from silver or indium tin oxide) may be susceptible to oxidation. Having portion  70 - 3  of leakage-mitigating structure  70  conform to and directly contact sidewall  78  of anode  42  may protect the anode from undesired oxidation during display manufacturing (e.g., caused by subsequent vapor deposition steps). 
     Any of the dimensions of the leakage-mitigating structure may be tuned to impart the desired discontinuities on the organic light-emitting diode layers. For example, thicknesses  108 ,  110 , and  130  of each leakage-mitigating structure portion, the width  104  and height  106  of undercut  102 , angles  116 ,  118 ,  128 , step portion width  124 , PDL separation distance  74 , etc. may all be selected such that desired discontinuities are formed when the organic light-emitting diode layers are deposited. In one illustrative example, width  130  may be between 5 nanometers and 15 nanometers, width  108  (and therefore undercut height  106 ) may be between 30 nanometers and 50 nanometers, and width  110  may be between 15 nanometers and 25 nanometers. The total thickness of leakage-mitigating structure  70  may be less than 80 nanometers. Width  104  may be greater than 50 nanometers (e.g., between 50 and 150 nanometers). Angles  118  and  128  may each be some angle between (or including) 50 degrees and 80 degrees. In one example, angles  118  and  128  are the same. Distance  74  may be greater than 500 nanometers. The pixel definition layer portions and organic light-emitting diode layers may be formed using vapor deposition techniques, photolithography techniques, etc. To modify the dimensions of the pixel definition layer portions, exposure levels, mask profile, deposition pressure, gas composition, and/or other desired manufacturing properties may be tuned. 
     In  FIG.  6   , leakage-mitigating structure  70  is formed directly on anode  42  and underneath pixel definition layer  76 . This example is merely illustrative. In another possible embodiment, shown in  FIG.  7   , leakage-mitigating structure  70  may be formed on an upper surface of pixel definition layer  76 . Leakage-mitigating structure  70  in  FIG.  7    may have the same dimensions and structure as in  FIG.  6    (and these dimensions will therefore not be repeated here). 
     Although only one undercut in the leakage-mitigating structure is necessary to cause discontinuities in the OLED layers and mitigate lateral leakage, the leakage-mitigating structure may have first and second undercuts  102 - 1  and  102 - 2  on first and second opposing sides of the leakage-mitigating structure  70 . Having the leakage-mitigating structure be symmetrical in this way may make the manufacturing of the leakage-mitigating structure  70  less complex and costly. 
     Each undercut may cause discontinuities in one or more layers within OLED layers  45  (as shown in detail in connection with  FIG.  6   ). For example, undercut  102 - 1  may cause first discontinuities in one or more OLED layers  45 . Undercut  102 - 2  may cause second discontinuities in one or more OLED layers  45 . Because undercuts  102 - 1  and  102 - 2  are symmetrical, each undercut may cause discontinuity in the same number of OLED layers. Cathode  54  remains continuous over leakage-mitigating structure  70 . 
     In  FIGS.  6  and  7   , leakage-mitigating structure  70  is formed from three different portions. In one example, portions  70 - 1  and  70 - 3  may be formed from silicon dioxide (SiO 2 ) and portion  70 - 2  may be formed from silicon nitride (SiN). However, it should be noted that portion may optionally be omitted if desired.  FIG.  8    shows an example where leakage-mitigating structure  70  includes only portions  70 - 1  and  70 - 2 . Portions  70 - 1  and  70 - 2  may be formed from the same material or from different materials. For example, portion  70 - 1  may be formed from silicon dioxide and portion  70 - 2  may be formed from silicon nitride. In this case, portion  70 - 2  is formed in direct contact with the upper surface of pixel definition layer  76 . Portion  70 - 3  may be omitted from the leakage-mitigating structure  70  in  FIG.  6 ,  7   , or  9  if desired. 
       FIG.  9    is a cross-sectional side view showing another possible arrangement for leakage-mitigating structure  70 . As shown in  FIG.  9   , there may be a trench  80  within pixel definition layer  76  and leakage-mitigating structure  70  may be partially formed within the trench. Leakage-mitigating structure  70  is symmetric and therefore has first and second undercuts  102 - 1  and  102 - 2  (similar to as in  FIGS.  7  and  8   ). Leakage-mitigating structure  70  is formed on substrate  26  (e.g., not directly on anode  42 ). The first undercut  102 - 1  is filled by pixel definition layer  76  (e.g., the organic material of pixel definition layer  76  conforms to and fills the void left by undercut  102 - 1 ). Undercut  102 - 1  therefore does not cause discontinuities in OELD layers  45 . 
     Pixel definition layer  76  has a trench in which the pixel definition layer is removed. A portion of leakage-mitigating structure  70  is formed in trench  80  and therefore is not covered by pixel definition layer  76 . Undercut  102 - 2  in trench  80  therefore causes discontinuities in one or more of OLED layers  45  (similar to as shown in detail in  FIG.  6   ). Cathode  54  remains continuous over pixel definition layer  76  and leakage-mitigating structure  70 . 
       FIG.  10    is a top view showing a pixel with a leakage-mitigating structure of the type shown in  FIG.  6   . The outline of anode  42  is shown by a dashed line. The anode fills the center of the pixel between the area defined by the dashed line. Leakage-mitigating structure  70  (depicted by two solid lines defining the opposing edges of the structure) partially overlaps anode  42 . As shown, anode  42  and leakage-mitigating structure  70  overlap in region  82 . In the example of  FIG.  10   , leakage-mitigating structure  70  completely laterally surrounds a light emitting area  84  of pixel  22  (e.g., completely surrounds in the XY-plane). Leakage-mitigating structure  70  may sometimes be referred to as a ring because the structure is formed in a ring around the anode and encloses the light-emitting area of the pixel. Said another way, leakage-mitigating structure  70  has a central opening through which light from the pixel is emitted. 
     An edge of pixel definition layer  76  is depicted in  FIG.  10    by a dashed line. The dashed line illustrates the edges of an opening in the pixel definition layer that is occupied by anode  42  and leakage-mitigating structure  70 . The pixel definition layer may include material that laterally surrounds the opening of  FIG.  10   . As shown, the pixel definition layer may at least partially overlap leakage-mitigating structure  70  (as shown in  FIG.  6   ). However, the pixel definition layer may be separated from the edge of the leakage-mitigating structure  70  by distance  74  (similar to as shown in  FIG.  6   ). The pixel definition layer  76  may optionally overlap a portion of the anode or may not overlap any portion of the anode. In  FIG.  10   , leakage-mitigating structure  70  overlaps anode  42  and at least partially defines light-emitting area  84 . 
       FIG.  11    is a top view showing a pixel with a leakage-mitigating structure of the type shown in  FIG.  7   ,  FIG.  8   , or  FIG.  9   . The outline of anode  42  is shown by a dashed line. The anode fills the center of the pixel between the area defined by the dashed line. An edge of pixel definition layer  76  is depicted in  FIG.  11    by a dashed line. The dashed line for pixel definition layer  76  illustrates the edges of an opening in the pixel definition layer that is occupied by anode  42 . In  FIG.  11   , pixel definition layer  76  overlaps anode  42  and at least partially defines light-emitting area  84 . Pixel definition layer  76  overlaps anode  42  in region  86 . The pixel definition layer may include material that laterally surrounds the opening of  FIG.  11   . 
     Leakage-mitigating structure  70  (depicted by two solid lines defining the opposing edges of the structure) is separated from the edge of pixel definition layer  76  and anode  42 . In the example of  FIG.  11   , leakage-mitigating structure  70  completely laterally surrounds a light emitting area  84  of pixel  22  (e.g., completely surrounds in the XY-plane). Leakage-mitigating structure  70  may sometimes be referred to as a ring because the structure is formed in a ring around the anode and encloses the light-emitting area of the pixel. Said another way, leakage-mitigating structure  70  has a central opening through which light from the pixel is emitted. 
     To summarize, in  FIG.  10   , leakage-mitigating structure  70  is formed directly on the anode and at least partially defines the light-emitting area of the pixel. Pixel definition layer  76  is set back from the inner edge of the leakage-mitigating structure. In  FIG.  11   , pixel definition layer  76  is formed directly on the anode and at least partially defines the light-emitting area of the pixel. Leakage-mitigating structure  70  is set back from the inner edge of the pixel definition layer. In both  FIGS.  10  and  11   , leakage-mitigating structure  70  may form a ring that encloses the light-emitting area of the pixel. 
       FIG.  12    is a top view of an illustrative display showing how each pixel  22  may have a corresponding leakage-mitigating structure  70 . As shown, the display may include pixels of different colors such as red pixels (R), green pixels (G), and blue pixels (B). In the example of  FIG.  12   , the pixels of every color have a respective leakage-mitigating structure  70  that forms a ring around that pixel. In other words, there is a 1:1 ratio between pixels and leakage-mitigating structures. 
     It should be noted that different pixels may have different associated OLED stackups with different OLED stackup thicknesses. Accordingly, the discontinuities caused by leakage-mitigating structure  70  may vary depending on the color of the pixel. In one possible embodiment, each color pixel may have a leakage-mitigating structure  70  that is optimized for its particular stackup. In other words, red pixels may have leakage-mitigating structures having first dimensions, green pixels may have leakage-mitigating structures having second dimensions that are different than the first dimensions, and blue pixels may have leakage-mitigating structures having third dimensions that are different than the first and second dimensions. Each color&#39;s leakage-mitigating structure may be optimized for its particular OLED layers. This type of arrangement may, however, increase the manufacturing cost and complexity of the device. Therefore, to mitigate cost and complexity, in other embodiments every pixel may have a leakage-mitigating structure of the same dimensions (regardless of the color of the pixel). The pixels of different colors may have slightly different discontinuities in their respective OLED pixels. However, the leakage-mitigating structure may cause discontinuities that sufficiently reduce lateral leakage in all of the colors of pixel in the display. 
     In another example, shown in  FIG.  13   , only some pixels in the display may have an associated leakage-mitigating structure. As shown in  FIG.  13   , the red pixel has an associated leakage-mitigating structure but the green and blue pixels do not. This pattern may hold across the display. In other words, all of the red pixels in the display may have leakage-mitigating structures while all of the green and blue pixels in the display may not have leakage-mitigating structures. 
     The example of only the red pixels having leakage-mitigating structures is merely illustrative. In other embodiments, only the green pixels may have leakage-mitigating structures or only the blue pixels may have leakage-mitigating structures. As yet another possibility, any two pixel colors may have leakage-mitigating structures while the remaining pixel color does not. 
     Each pixel color may have a corresponding turn-on voltage. The turn-on voltages for different colored pixels may be different. In one example, the turn-on voltage for the red pixels may be lower than the turn-on voltages for the green and blue pixels. The pixels with a low turn-on voltage are more susceptible to visible artifacts caused by leakage current. The leakage-mitigating structures may therefore enclose only pixels of the color having the lowest turn-on voltage (e.g., only the red pixels as in  FIG.  13   ). 
     The arrangements of  FIGS.  12  and  13    may apply to leakage-mitigating structures formed on the anode (as in  FIG.  6   ) or leakage-mitigating structures not formed on the anode (as in  FIG.  7 ,  8   , or  9 ). 
     As show in  FIG.  14   , a single pixel may have two respective leakage-mitigating structures. The red pixel in  FIG.  14    has a first leakage-mitigating structure  70 - 1  that forms a ring around the light-emitting area of the pixel. The pixel also includes a second leakage-mitigating structure  70 - 2  that forms a ring around the light-emitting area of the pixel and the first leakage-mitigating structure  70 - 1 . Forming multiple leakage-mitigating structures around a single pixel may improve leakage reduction in some embodiments. Leakage-mitigating structure  70 - 2  in  FIG.  14    may not be formed on the anode (as in  FIG.  7 ,  8   , or  9 ). Leakage-mitigating structure  70 - 1  in  FIG.  14    may be formed on the anode (as in  FIG.  6   ) or may not be formed on the anode (as in  FIG.  7 ,  8   , or  9 ). 
     In  FIGS.  10 - 14   , examples are shown where the leakage-mitigating structure completely encloses a respective light-emitting area of a pixel. This is merely illustrative. In some embodiments, multiple leakage-mitigating structure segments may be formed around a pixel without completely enclosing the pixel. As shown in  FIG.  15   , the red pixel has discrete leakage-mitigating structures  70 - 1  and  70 - 2  (sometimes referred to as leakage-mitigating structure segments) on first and second opposing sides of the pixel. However, the leakage-mitigating structure segments  70 - 1  and  70 - 2  do not extend along the entire height of the pixel. Additionally, no leakage-mitigating structure segments are formed above or below the pixel (e.g., on third and fourth opposing sides of the pixel between the first and second opposing sides). Therefore, the light-emitting area for the red pixel is not completely enclosed by the leakage-mitigating structures. 
     The green pixel in  FIG.  15    has discrete leakage-mitigating structures  70 - 4  and  70 - 6  (sometimes referred to as leakage-mitigating structure segments) on first and second opposing sides of the pixel. The green pixel also includes leakage-mitigating structures  70 - 3  and  70 - 5  on third and fourth opposing sides of the pixel. However, each one of leakage-mitigating structure segments  70 - 3 ,  70 - 4 ,  70 - 5 , and  70 - 6  does not extend along its entire respective pixel side. Therefore, the light-emitting area for the green pixel is not completely enclosed by the leakage-mitigating structures. 
     The blue pixel in  FIG.  15    has discrete leakage-mitigating structures  70 - 7  and  70 - 8  that each have orthogonal portions that conform to a corner of the pixel. However, leakage-mitigating structures  70 - 7  and  70 - 8  do not extend along the entire pixel to completely enclose the pixel. Therefore, the light-emitting area for the blue pixel is not completely enclosed by the leakage-mitigating structures. 
     Each pixel may have leakage-mitigating structures that completely enclose that pixel or one or more leakage-mitigating structures that only partially enclose that pixel (e.g., as in one of the examples of  FIG.  15   ). Every pixel of the same color may have the same leakage-mitigating structure arrangement. Alternatively, different pixels of the same color may have different leakage-mitigating structure arrangements if desired. The arrangements of  FIG.  15    may apply to leakage-mitigating structures formed on the anode (as in  FIG.  6   ) or leakage-mitigating structures not formed on the anode (as in  FIG.  7 ,  8   , or  9 ). 
     In  FIG.  12   , each pixel is enclosed by a respective leakage-mitigating structure that forms a ring around the pixel. Consequently, there are two leakage-mitigating structures interposed between adjacent pixels (e.g., there are two leakage-mitigating structures between the red and green pixels in  FIG.  12   ). In another alternative, shown in  FIG.  16   , there may be only one leakage-mitigating structure interposed between adjacent pixels. As shown, some leakage-mitigating structures  70 - 1  may extend vertically (e.g., parallel to the Y-axis and columns of pixels in the display) across the display. Some leakage-mitigating structures  70 - 2  may extend horizontally (e.g., parallel to the X-axis and rows of pixels in the display) across the display. The leakage-mitigating structure may combine to form a grid that encloses each pixel with a ring of leakage-mitigating structure portions. However, only one leakage-mitigating structure is interposed between each adjacent pair of pixels. The arrangements of  FIG.  16    may apply to leakage-mitigating structures formed on the anode (as in  FIG.  6   ) and/or leakage-mitigating structures not formed on the anode (as in  FIG.  7 ,  8   , or  9 ). 
     These layout examples is merely illustrative. In some cases, there may be some pixels with dedicated leakage-mitigating structure rings (as in  FIGS.  12  and  13   ) and some pixels that are partially or completely surrounded by leakage-mitigating structures formed by rows and columns of leakage-mitigating structures (as in  FIG.  16   ). 
     In  FIGS.  6 - 9   , examples of passive leakage-mitigating structures are shown. The passive leakage-mitigating structures are simply physical structures that cause discontinuities in one or more overlying OLED layers during deposition of the OLED layers. The passive leakage-mitigating structures require no power consumption or active control during operation of the display. 
     Active leakage-mitigating structures may also be included in the display. The active leakage-mitigating structures may include a conductive layer (e.g., a conductive ring) that drains leakage current to ground. Alternatively, the active leakage-mitigating structures may include a gate electrode modulator with a variable voltage that stops the current flow laterally. 
       FIG.  17    is a cross-sectional side view of a display with a conductive ring  204  that serves as an active leakage-mitigating structure. In  FIG.  17   , a first pixel with a first anode  42 - 1  is positioned adjacent to a second pixel with a second anode  42 - 2 . Each anode may have associated OLED layers  45 . In  FIG.  17   , anode  42 - 1  has associated OLED layers  45 -R configured to emit red light. Anode  42 - 2  has associated OLED layers  45 -B configured to emit blue light. 
     Consider an example where anode  42 - 2  is turned on so that OLED layers  45 -B emit blue light. The red pixel formed by anode  42 - 1  and OLED layers  45 -R, meanwhile, is intended to remain off. A leakage current  202  is generated when anode  42 - 2  is turned on. Without conductive ring  204  (sometimes referred to as guard  204 , current sink  204 , etc.), the leakage current may reach OLED layers  45 -R and cause red light to be (undesirably) emitted. 
     Conductive ring  204  may be coupled to a bias voltage such as ground, such that the conductive ring serves as a current sink. Accordingly, leakage current  202  reaches conductive ring  204  and is drained (instead of causing undesirable leakage emissions). 
     Pixel definition layer  76  may define a light-emitting area associated with each pixel. The pixel definition layer  76  may extend between adjacent pixels. As shown in  FIG.  17   , a trench such as trench  206  may be formed in the pixel definition layer between anodes  42 - 1  and  42 - 2 . Trench  206  (sometimes referred to as opening  206  or recess  206 ) results in a portion of conductive ring  204  not being covered by the pixel definition layer. This results in conductive ring  204  being exposed through the pixel definition layer and directly contacting OLED layers  45 -R/ 45 -B. Including trench  206  such that the OLED layers  45  are directly contacting (shorted to) the conductive ring  204  enables conductive ring  204  to serve as a leakage current sink. 
     Conductive ring  204  may be coupled to a bias voltage to enable the conductive ring to serve as a current sink. The magnitude of the bias voltage may be selected to optimize leakage current mitigation and power requirements. In one embodiment, the bias voltage may be ground (e.g., ELVSS in  FIG.  3   ). In this case, conductive ring  204  may be electrically connected to a negative (ground) power supply line that provides negative (ground) power supply voltage ELVSS. Conductive ring  204  may be connected to the same negative power supply line that provides negative power supply voltage ELVSS to cathode  54 . 
     The example of coupling conductive ring  204  to a ground power supply voltage is merely illustrative. In another possible embodiment, the bias voltage for conductive ring  204  may be greater than ELVSS. The conductive ring may be more effective at reducing lateral leakage as the bias voltage is increased closer to the turn-on voltage for the pixels. For example, the red pixels may have an associated turn-on voltage. The red pixel turn-on voltage may be lower than the green and blue pixel turn-on voltage. The bias voltage for the conductive ring may be approximately equal to (e.g., within 5% of, within 10% of, within 20% of, etc.) the turn-on voltage for the red pixels. Where ground is 0V, the bias voltage of the conductive ring may be equal to (e.g., greater than ground by) 0V, more than 0.2V, more than 0.4V, more than 0.6V, more than 0.8V, more than 1.0V, more than 1.2V, more than 1.4V, more than 1.5V, between 1 and 1.5V, between 1 and 2V, between 1.4V and 1.6V, etc. Increasing the bias voltage relative to ground in this manner may improve leakage mitigation with the tradeoff of increased power consumption. 
     In one example, shown in  FIG.  17   , conductive ring  204  may be coupled to an additional metal layer  208  within substrate  26  using conductive via  210 . Metal layer  208  may provide the bias voltage to conductive ring  204 . Metal layer  208  may be part of a source drain metal layer used to form other portions of the display pixels (e.g., a source or drain terminal for a thin-film transistor for the display). The metal layer  208  may receive the bias voltage from gate driving circuitry and/or display driving circuitry in the display. Metal layer  208  may be a negative power supply line. These examples are merely illustrative. Via  210  may optionally be omitted and conductive ring  204  may be provided the bias voltage without being shorted to metal layer  208 . Conductive ring  204  may be coupled to a power voltage supply line or another signal line (e.g., provided by the display driver circuitry and/or gate driver circuitry) to receive the appropriate bias voltage. In other words, the conductive ring  204  is connected to a signal line at the periphery of the display and no vias are used in the active area. 
     In  FIG.  17   , conductive ring  204  is exposed at a trench portion of pixel definition layer  76 . Portions of the pixel definition layer overlap some but not all of conductive ring  204 . This example is merely illustrative. 
       FIG.  18    shows an alternate embodiment where conductive ring  204  is formed over the pixel definition layer  76 . Conductive ring  204  is formed directly on the upper surface of pixel definition layer  76 . The conductive ring  204  is coupled to a bias voltage (as discussed in connection with  FIG.  17   ) to serve as a current sink for leakage current  202 . Conductive ring  204  is still in direct contact with OLED layers  45 -R and  45 -B in  FIG.  18   . 
     As with  FIG.  17   , the conductive ring  204  in  FIG.  18    may optionally be coupled to metal layer  208  using conductive via  210  to receive the bias voltage. Conductive via  210  in  FIG.  18    passes through both portions of substrate  26  and pixel definition layer  76 . 
     There are many possible layouts for the guard structure  204  of  FIGS.  17  and  18   . Each pixel may be enclosed by a respective guard structure (similar to as shown in  FIG.  12   ), the pixels may have guard structures formed in segments that do not entirely enclose the pixel (similar to as shown in  FIG.  15   ), multiple guard structures may surround a single pixel (similar to as shown in  FIG.  14   ), or the guard structures may form a grid that separates the pixels (similar to as in  FIG.  16   ). In yet another possible embodiment, only some pixels (e.g., pixels of one color but not the other colors) may be enclosed by the guard structures. 
       FIG.  19    is a top view showing how some but not all pixels in the display may be enclosed by guard structures. Each pixel has a corresponding light-emitting area  84 . A first pixel is enclosed by guard structure  204 - 1 . A second pixel is enclosed by guard structure  204 - 2 . The remaining four pixels in  FIG.  19    are not enclosed by a guard structure. 
     In this type of arrangement, it may still be desirable to electrically connect guard structures  204 - 1  and  204 - 2  (so that they may easily be provided the same bias voltage). A conductive layer may optionally be provided to electrically connect the guard structures. 
       FIGS.  17  and  18    show illustrative cross-sectional views taken along line  212  in  FIG.  19   . In other words, these figures show an example of a single guard structure interposed between adjacent anodes in the display.  FIGS.  20  and  21    show illustrative cross-sectional views taken along line  214  in  FIG.  19   . 
     In  FIG.  20    (taken along line  214  in  FIG.  19   ), a routing portion  204 -R is formed between adjacent anodes  42 - 1  and  42 - 2 . The routing portion  204 -R is formed on substrate  26  and is covered by pixel definition layer  76 . The pixel definition layer  76  may conform to and directly contact the upper surface of routing portion  204 -R. Routing portion  204 -R (which may be conductive and formed from the same metal layer as guard structures  204 - 1  and  204 - 2 ) may be biased to the same bias voltage as guard structures  204 - 1  and  204 - 2  in  FIG.  19   . However, because routing portion  204 -R is covered by pixel definition layer  76  and therefore separated from the OLED layers  45 , the routing portion  204 -R does not serve as a current sink and only routes the bias voltage between guard structures  204 - 1  and  204 - 2 . 
     In another example, shown in  FIG.  21   , the conductive layer  204  is omitted entirely between anodes  42 - 1  and  42 - 2  (i.e., there are neither routing portions or current sink portions present). In this example, pixel definition layer  76  extends between anodes  42 - 1  and  42 - 2  without an intervening portion of conductive layer  204 . 
       FIG.  22    is a top view of a display showing an example where conductive guard  204  is formed as a grid between the pixels. Each pixel is completely laterally enclosed by portions of conductive guard  204 . In  FIG.  23   , only the red pixels are enclosed by the conductive guards. As discussed in connection with  FIG.  13   , the example of red pixels being the only color enclosed is merely illustrative. However, it may be desirable to enclose the pixels having the lowest turn-on voltage with conductive guards. 
     As shown, a first red pixel is enclosed by a respective conductive guard  204 - 1 , a second red pixel is enclosed by a respective conductive guard  204 - 2 , etc. The conductive guards  204 - 1  and  204 - 2  may have a cross-sectional structure of the type shown in  FIG.  17    or  FIG.  18   . Between conductive guards  204 - 1  and  204 - 2  may be a routing portion  204 -R having a cross-sectional structure of the type shown in  FIG.  20   . Alternatively, routing portion  204 -R may be omitted (e.g., as in  FIG.  21   ) and conductive guards  204 - 1  and  204 - 2  may receive the bias voltage through other means (e.g., metal layers within substrate  26 ). 
       FIG.  24    is a cross-sectional side view of a display where the active leakage-mitigating structures include a gate electrode modulator with a variable voltage that stops the current flow laterally.  FIG.  24   , a first pixel with a first anode  42 - 1  is positioned adjacent to a second pixel with a second anode  42 - 2 . Each anode may have associated OLED layers  45 . In  FIG.  24   , anode  42 - 1  has associated OLED layers  45 -R configured to emit red light. Anode  42 - 2  has associated OLED layers  45 -B configured to emit blue light. A conductive gate  222  is formed between anodes  42 - 1  and  42 - 2 . 
     Consider an example where anode  42 - 2  is turned on so that OLED layers  45 -B emit blue light. The red pixel formed by anode  42 - 1  and OLED layers  45 -R, meanwhile, is intended to remain off. A leakage current  202  is generated when anode  42 - 2  is turned on. Without conductive gate  222 , the leakage current may reach OLED layers  45 -R and cause red light to be (undesirably) emitted. 
     Conductive gate  222  may be coupled to a gate voltage such that the conductive gate forms a gate electrode. Applying the gate voltage to conductive gate  222  generates a large electric field and a corresponding mitigating current  226  that prevents leakage current  202  from reaching the red pixel and emitting red light. Conductive gate  222  therefore serves as an active leakage-mitigating structure for the display. 
     Conductive gate  222  may be covered by gate insulator  224 . Gate insulator  224  may conform to and completely cover the conductive gate (e.g., to both the upper surface and sidewalls of conductive gate  222 ). The gate insulator prevents conductive gate  222  from being shorted to OLED layers  45 . Gate insulator may be formed from a thin, high-k dielectric material (e.g., a material having a high dielectric constant). The gate insulator may be formed from silicon dioxide, silicon nitride, hafnium dioxide, aluminum oxide, or any other desired material. 
     Pixel definition layer  76  may define a light-emitting area associated with each pixel. The pixel definition layer  76  may extend between adjacent pixels. As shown in  FIG.  24   , a trench such as trench  206  may be formed in the pixel definition layer between anodes  42 - 1  and  42 - 2 . Trench  206  (sometimes referred to as opening  206  or recess  206 ) results in a portion of gate  222  and gate insulator  224  not being covered by the pixel definition layer. This results in conductive gate  222  being able to create a high electric field in OLED layers  45 . 
     Conductive gate  222  be coupled to a variable voltage to enable the conductive gate to serve as a gate electrode modulator. The variable voltage may optionally switch between two different values. To mitigate leakage current, a high voltage that is higher than the turn-on voltage of the red, blue, and green pixels may be applied to conductive gate  222 . When this high voltage is applied, the gate electrode modulator creates a high electric-field and thus a high potential barrier between pixels, which stops leakage current flow between pixels. The gate voltage applied to conductive gate  222  may be greater than 3V, greater than 5V, greater than 6V, greater than 7V, greater than 8V, between 5V and 8V, less than 10V, less than 8V, less than 7V, between 5V and 7V, etc. A low voltage may also sometimes be provided to conductive gate when a high electric field is not required to mitigate leakage current. 
     Conductive gate  222  may optionally be coupled to metal layer  208  using conductive via  210  to receive the gate voltage. Conductive via  210  in  FIG.  24    passes through portions of substrate  26 . Metal layer  208  may have additional portions that form display pixel components, may be a signal line, etc. (as discussed in connection with  FIG.  17   ) 
       FIG.  25    shows an alternate embodiment where conductive gate  222  is formed over pixel definition layer  76 . Conductive gate  222  is formed directly on the upper surface of pixel definition layer  76 . Gate insulator  224  is formed over conductive gate  222 . The conductive gate is coupled to a variable gate voltage (as discussed in connection with  FIG.  24   ) to serve as a gate electrode modulator. Gate insulator  224  is in direct contact with OLED layers  45 -R and  45 -B in  FIG.  25   . 
     As with  FIG.  24   , the conductive gate  222  in  FIG.  25    may optionally be coupled to metal layer  208  using conductive via  210  to receive the gate voltage. Conductive via  210  in  FIG.  25    passes through both portions of substrate  26  and pixel definition layer  76 . 
       FIG.  26    is a cross-sectional view showing how (similar to as in  FIG.  20   ) the display may include may have conductive routing portions  222 -R between conductive gates  222 . In  FIG.  26   , a routing portion  222 -R is formed between adjacent anodes  42 - 1  and  42 - 2 . The routing portion  222 -R is formed on substrate  26  and is covered by pixel definition layer  76 . The pixel definition layer  76  may conform to and directly contact the upper surface of gate insulator  224  (which may still optionally be included over routing portion  222 -R). Routing portion  222 -R may be biased to the same gate voltage as the conductive gates it connects. However, because routing portion  222 -R is covered by pixel definition layer  76  and therefore separated from the OLED layers  45 , the routing portion  222 -R does not serve as a gate electrode modulator and only routes the gate voltage between other conductive gates. 
     It should be noted that in any of  FIGS.  17 ,  18 ,  24  and  25   , via  210  may optionally be omitted and the conductive structure (ring  204  or gate  222 ) may be provided a voltage without being shorted to metal layer  208 . The conductive structure may be coupled to a power voltage supply line or another signal line (e.g., provided by the display driver circuitry and/or gate driver circuitry) to receive the appropriate bias voltage. In other words, the conductive structure (guard  204  or gate  222 ) is connected to a signal line at the periphery of the display and no vias are used in the active area. 
       FIGS.  27 A and  27 B  are top views showing additional possible pixel layouts for the display. Both  FIGS.  27 A and  27 B  include a repeating unit cell of pixels that includes one red pixel, one blue pixel, and two green pixels. In an alternate nomenclature, the repeating unit cell may be referred to as a pixel that includes one red sub-pixel, one blue sub-pixel, and two green sub-pixels. In  FIG.  27 A , the repeating unit cell  302  has two green pixels, one red pixel, and one blue pixel arranged in a diamond pattern. The green pixels may be smaller than the red and blue pixels. The red pixel may be smaller than the blue pixel. In  FIG.  27 A , the pixels have diamond shapes (e.g., rectangles that rotated relative to the upper edge of the display). The repeating unit cells may extend diagonally across the pixel array. This may be referred to as a pentile arrangement. In  FIG.  27 B , the repeating unit cell  302  has two green pixels, one red pixel, and one blue pixel arranged in a rectangular pattern. The green pixels may be smaller than the red and blue pixels. The red pixel may be smaller than the blue pixel. In contrast with  FIG.  27 A , the repeating unit cells of  FIG.  27 B  may extend horizontally and vertically across the display (e.g., in stripes) instead of diagonally. 
     It should be noted that the gate electrodes  222  may have any of the layouts discussed in connection with the guard structure  204  (e.g., the layout of  FIG.  19   ,  FIG.  22   ,  FIG.  23   , etc.). Additionally the active leakage-mitigating structures of  FIGS.  17 - 26    may have any of the layouts described relative to the passive leakage-mitigating structures (e.g., the active leakage-mitigating structures of  FIGS.  17 - 26    may have any of the layouts of  FIGS.  12 - 16   ). 
       FIGS.  28 A and  28 B  show different options for routing leakage-mitigating structures when a contact hole is present. In  FIG.  28 A , the outline of anode  42  is shown by a dashed line. The anode fills the center of the pixel between the area defined by the dashed line. The anode additionally has an extension  308  (sometimes referred to as tab  308  or protrusion  308 ) that is electrically connected to contact hole  306  (sometimes referred to as contact  306  or via  306 ). Contact  306  may be a via that electrically connects the anode to thin-film transistor circuitry in the substrate. The anode may overlap and be electrically connected to contact  306 . Positioning contact  306  outside of the light-emitting area  84  (as in  FIGS.  28 A and  28 B ) may allow the pixel size to be maximized and improve off-angle uniformity. 
     An edge of pixel definition layer  76  is depicted in  FIG.  28 A  by a dashed line. The dashed line for pixel definition layer  76  illustrates the edges of an opening in the pixel definition layer that is occupied by anode  42 . In  FIG.  28 A , pixel definition layer  76  overlaps anode  42  and at least partially defines light-emitting area  84 . Pixel definition layer  76  overlaps anode  42  in region  86  (e.g., around the periphery of the anode). Pixel definition layer  76  may also overlap extension  308  and contact  306 . The pixel definition layer may include material that laterally surrounds the opening of  FIG.  28 A . 
     Leakage-mitigating structure  304  (depicted by two solid lines defining the opposing edges of the structure) is separated from the edge of pixel definition layer  76  and anode  42 . Leakage-mitigating structure  304  completely laterally surrounds a light emitting area  84  of pixel  22  (e.g., completely surrounds in the XY-plane). Said another way, leakage-mitigating structure  304  has a central opening through which light from the pixel is emitted. In the example of  FIG.  28 A , leakage-mitigating structure  304  is routed around extension  308  such that leakage-mitigating structure  304  and extension  308  (as well as contact  306 ) are non-overlapping. 
     Alternatively,  FIG.  28 B  shows another example where leakage-mitigating structure  304  overlaps extension  308  and is routed between contact  306  and the main portion of anode  42 . A portion of pixel definition layer  76  is interposed between extension  308  and leakage-mitigating structure  304  in the overlap area to electrically isolate extension  308  and leakage-mitigating structure  304 . 
     Leakage-mitigating structure  304  may not directly overlap contact  306  to avoid an undesired morphology or tilt from the contact region and to prevent any potential short between the leakage-mitigating structure  304  and contact  306 . 
     Leakage-mitigating structure  304  in  FIGS.  28 A and  28 B  may be a passive leakage-mitigating structure (e.g., of the type shown in  FIGS.  7 - 9   ) or an active leakage-mitigating structure (e.g., of the type shown in  FIG.  17 ,  18   , or  24 - 26 ). 
     The aforementioned concepts may be applied to pixels having any desired layout. The pixels may be arranged in a pentile layout (as in  FIG.  27 A ), in stripes (e.g., similar to as in  FIG.  16    or in  FIG.  27 B ), similar to as in  FIGS.  22  and  23   , or in any other desired layout. 
     The aforementioned concepts may be applied to pixels having OLED layers that form a single diode (as in  FIG.  5 A ) or OLED layers that form a tandem diode (as in  FIG.  5 B ). 
     The aforementioned concepts may involve depositing additional layers for the display (e.g., to form the leakage-mitigating structures). If desired, a protection layer over the anode may be used during manufacturing to reduce the impact of deposition steps on the anode surface morphology. Plasma related processes such as chemical vapor deposition (CVD) or dry-etching may have the potential to damage the anode surfaces. Therefore, a protection layer (such as a molybdenum layer) may be formed over the anode during processing. The protection layer may be removed by wet etching prior to OLED layer deposition over the anode. However, some of the protection layer (e.g., portions that are interposed between the anode and overlying layers) may remain even after the wet etching removal step. For example, a thin molybdenum layer may be interposed between (and in direct contact with) portion  70 - 3  of leakage-mitigating structure  70  and the anode  42  in  FIG.  6    (e.g., in position  92  in  FIG.  6   ). A thin molybdenum layer may be interposed between (and in direct contact with) pixel definition layer  76  and the anode  42  in  FIGS.  7 - 9 ,  17 ,  18 ,  20 ,  21 ,  24 ,  25 , and  26    (e.g., in position  94  in  FIG.  7   ). 
       FIG.  29    is a cross-sectional side view of an illustrative electronic device showing how a sensor may be positioned below display  14 . The sensor may be, for example, an optical sensor such as an ambient light sensor that senses ambient light  404  through display  14 . Ideally, ambient light sensor  402  would receive only ambient light  404  (to maximize the signal-to-noise ratio of the sensor). However, in practice, ambient light sensor  402  may also receive light generated by the pixels of display  14 . 
     As shown, display  14  may include a substrate  26 . Substrate  26  may be formed from glass, plastic, polymer, silicon, or any other desired material. Anodes such as anodes  42 - 1  and  42 - 2  may be formed on the substrate. In  FIG.  29   , anode  42 - 1  has associated OLED layers  45 -R configured to emit red light. Anode  42 - 2  has associated OLED layers  45 -B configured to emit blue light. Pixel definition layer  76  is formed over substrate  26  between anodes  42 - 1  and  42 - 2 . Pixel definition layer  76  may conform to and overlap the edges of anodes  42 - 1  and  42 - 2 . 
     There are at least two ways in which light from the OLED pixels may (undesirably) reach sensor  402 . First, some of the pixel-generated light may become trapped in pixel definition layer  76 , as shown by path  406 . The pixel definition layer  76  may form a waveguide that traps light in the pixel definition layer until it escapes towards sensor  402 . Second, the pixels may generate back-emission light that travels in direction  408  towards sensor  402 . Lateral leakage current (as discussed in connection with  FIG.  4   , for example), may increase the amount of back emission that reaches sensor  402 . 
     Light from both the waveguide effect  406  and back emission  408  may decrease the signal-to-noise ratio of sensor  402 . Moreover, these effects may be transient and difficult to account for using compensation techniques (because there is a delay between the display being updated and the corresponding noise-causing-light reaching sensor  402 ). 
     To prevent display light from undesirably reaching a sensor below the display, first and second leakage-mitigating structures  70  may be positioned on substrate  26  between a first anode  42 - 1  for a first pixel and a second anode  42 - 2  for a second pixel. Each leakage-mitigating structure may be a structure similar to as shown in  FIG.  6    (e.g., a three-layered structure), a structure similar to as shown in  FIG.  8    (e.g., a two-layered structure), or a structure of any other desired shape. 
     In  FIG.  6   , it was shown how leakage-mitigating structure  70  has an undercut  102 . The undercut is a void in the leakage-mitigating structure material that is still covered by a portion of the leakage-mitigating structure. As shown in  FIG.  6   , undercut  102  may have a width  104  and a height  106 . The dimensions of the undercut may be selected to create discontinuities in one or more of the organic light-emitting diode layers in the display (to prevent lateral leakage through the organic light-emitting diode layers). In some cases (such as in  FIG.  6   ), the dimensions of the undercut are selected to ensure continuity of the cathode layer (and, optionally, some of the organic light-emitting diode layers in the display). In  FIG.  30   , each leakage-mitigating structure may only partially encircle each pixel. Therefore, in contrast to  FIG.  6   , the dimensions of the undercut may be selected to cause a discontinuity in the cathode layer in addition to the organic light-emitting diode layers. 
     For example, the height of the undercut of the leakage-mitigating structures  70  in FIG. may be greater than 25 nanometers, greater than 40 nanometers, greater than 60 nanometers, greater than 70 nanometers, less than 70 nanometers, between 45 nanometers and 70 nanometers, etc. The thickness of organic light-emitting diode layers  45  may be greater than 100 nanometers, greater than 150 nanometers, greater than 200 nanometers, greater than 250 nanometers, greater than 300 nanometers, less than 300 nanometers, etc. The height of the undercut in each leakage-mitigating structure  70  may be at least 8% of the thickness of OLED layers  45 , at least 16% of the thickness of OLED layers  45 , at least 30% of the thickness of OLED layers  45 , at least 35% of the thickness of OLED layers  45 , at least 40% of the thickness of OLED layers  45 , at least 45% of the thickness of OLED layers  45 , etc. In general, the greater the height of the undercut relative to the thickness of OLED layers  45 , the more discontinuity (and, accordingly, lateral leakage reduction) imparted onto the layers over the leakage-mitigating structure. 
     As shown in  FIG.  30   , the first leakage-mitigating structure  70  (which partially encircles anode  42 - 1 ) may cause a first discontinuity  410  in OLED layers  45  and cathode  54  and the second leakage-mitigating structure  70  (which partially encircles anode  42 - 2 ) may cause a second discontinuity  412  in OLED layers  45  and cathode  54 . Pixel definition layer  76  is formed between each anode and respective leakage-mitigating structure  70 . As shown in  FIG.  30   , pixel definition layer  76  overlaps (and conforms to) a portion of anode  42 - 1  and corresponding leakage-mitigating structure  70 . In other words, the pixel definition layer is formed on the top surface of the first leakage-mitigating structure  70  for anode  42 - 1 . Similarly, pixel definition layer  76  overlaps (and conforms to) a portion of anode  42 - 2  and corresponding leakage-mitigating structure  70 . In other words, the pixel definition layer is formed on the top surface of the second leakage-mitigating structure  70  for anode  42 - 2 . 
     With the arrangement of  FIG.  30   , the deep discontinuities  410  and  412  prevent lateral leakage of current between anodes  42 - 1  and  42 - 2 . This mitigates back emissions that undesirably reach a sensor below the display (e.g., via path  408  in  FIG.  29   ). Positioning the leakage-mitigating structures closer to the anode minimizes back emissions from reaching the sensor. Moreover, as shown in  FIG.  30   , pixel definition layer  76  is omitted between the first and second leakage-mitigating structures  70  (e.g., only OLED layers  45  are present between the first and second leakage-mitigating structures). The waveguide effect of the pixel definition layer  76  is therefore disrupted, mitigating the amount of light that passes through pixel definition layer  76  to an underlying sensor (e.g., via path  406  in  FIG.  29   ). 
     Creating deep discontinuities in the OLED layers  45  and cathode  54  (as in  FIG.  30   ) may be optimal for mitigating lateral leakage in the display (and improving signal-to-noise ratio in a sensor under the display). However, the portion of the cathode  54  over each anode still needs to be electrically connected to the rest of the common cathode layer to ensure the portion of the cathode  54  over each anode is at the appropriate cathode voltage. To ensure continuity of the cathode, the leakage-mitigating structure  70  is omitted in at least one position around the perimeter of the anode. In this location, the cathode is ensured to be electrically connected between the portion over the anode and the remaining bulk of the cathode. 
       FIG.  31    is a top view of illustrative pixels that are partially surrounded by leakage-mitigating structures  70 . As shown, a first pixel  22 -G is configured to emit green light and a second pixel  22 -R is configured to emit red light. Pixel  22 -G includes an anode  42 -G, a leakage-mitigating structure  70 -G, and a pixel definition layer  76 -G. Pixel definition layer  76 -G is represented in  FIG.  31    by dashed lines. As shown, pixel definition layer  76 -G partially overlaps anode  42 -G and partially overlaps leakage-mitigating structure  70 -G. 
     Leakage-mitigating structure  70 -G does not completely surround anode  42 -G. As shown, leakage-mitigating structure  70 -G has an opening  414 -G in at least one location around the perimeter of pixel  22 -G (and anode  42 -G and its corresponding light-emitting area). The leakage-mitigating structure  70 -G therefore only partially surrounds the light-emitting aperture of pixel  22 -G. Leakage-mitigating structure  70 -G may extend around more than 50% of pixel  22 -G (e.g., anode  42 -G and its corresponding light-emitting area), more than 60% of pixel  22 -G, more than 70% of pixel  22 -G, more than 80% of pixel  22 -G, more than 90% of pixel  22 -G, more than 95% of pixel  22 -G, etc. However, leakage-mitigating structure  70 -G may extend around less than 100% of pixel  22 -G (e.g., only partially encloses pixel  22 -G). 
     The cathode  54  may be formed as a blanket layer over the pixels. Leakage-mitigating structure  70 -G may cause a discontinuity in the cathode. In other words, the cathode may have a discontinuity having the same footprint/outline as the leakage-mitigating structure. However, the cathode may be continuous through opening  414 -G in the leakage-mitigating structure. Therefore, opening  414 -G preserves the required cathode continuity for the pixel. 
     As shown in  FIG.  31   , anode  42 -G may optionally have an extension  416 -G (sometimes referred to as tab  416 -G) that overlaps with opening  414 -G in leakage-mitigating structure  70 -G. Extension  416 -G of anode  42 -G may include an anode-contact where the anode is electrically connected to thin-film transistor circuitry in the underlying substrate  26 . 
     Pixel  22 -R includes an anode  42 -R, a leakage-mitigating structure  70 -R, and a pixel definition layer  76 -R. Pixel definition layer  76 -R is represented in  FIG.  31    by dashed lines. As shown, pixel definition layer  76 -R partially overlaps anode  42 -R and partially overlaps leakage-mitigating structure  70 -R. 
     Leakage-mitigating structure  70 -R does not completely surround anode  42 -R. As shown, leakage-mitigating structure  70 -R has an opening  414 -R in at least one location around the perimeter of pixel  22 -R (and anode  42 -R and its corresponding light-emitting area). The leakage-mitigating structure  70 -R therefore only partially surrounds the light-emitting aperture of pixel  22 -R. Leakage-mitigating structure  70 -R may extend around more than 50% of pixel  22 -R (e.g., anode  42 -R and its corresponding light-emitting area), more than 60% of pixel  22 -R, more than 70% of pixel  22 -R, more than 80% of pixel  22 -R, more than 90% of pixel  22 -R, more than 95% of pixel  22 -R, etc. However, leakage-mitigating structure  70 -R may extend around less than 100% of pixel  22 -R (e.g., only partially encloses pixel  22 -R). 
     The cathode  54  may be formed as a blanket layer over the pixels. Leakage-mitigating structure  70 -R may cause discontinuity in the cathode. In other words, the cathode may have a discontinuity having the same footprint/outline as the leakage-mitigating structure  70 -R. However, the cathode may be continuous through opening  414 -R in the leakage-mitigating structure. Therefore, opening  414 -R preserves the required cathode continuity for the pixel. 
     As shown in  FIG.  31   , anode  42 -R may optionally have an extension  416 -R (sometimes referred to as tab  416 -R) that overlaps with opening  414 -R in leakage-mitigating structure  70 -R. Extension  416 -R of anode  42 -R may include an anode-contact where the anode is electrically connected to thin-film transistor circuitry in the underlying substrate  26 . 
     The cross-sectional side view of  FIG.  30    may be taken along line  418  in  FIG.  31   .  FIG.  32    is a cross-sectional view along line  420  in  FIG.  31   . As shown in  FIG.  32   , discontinuities in OLED layers  45  and/or cathode layer  54  are caused by leakage-mitigating structure  70 -G. However, in opening  414 -G in leakage-mitigating structure  70 -G, the cathode  54  (and OLED layers  45 ) are continuous. This allows the portion of cathode  54  over anode  42 -G to be electrically connected to the rest of the cathode (e.g., through opening  414 -G).  FIG.  32    also shows how anode  42 -G is electrically connected to an underlying thin-film transistor layer  26 -M in substrate  26  through a via in the substrate  26 . The via may be formed in an extension of anode  42 -G that overlaps opening  414 -G. 
     The example in  FIGS.  31  and  32    of the anode extensions  416  overlapping the leakage-mitigating structure openings  414  for each pixel is merely illustrative. If desired, as shown in  FIG.  33   , the anode extension  416  of a given pixel  22  may overlap with leakage-mitigating structure  70 . In this example, the leakage-mitigating structure  70  may be formed on the metal for anode extension  416 , on a pixel definition layer that overlaps anode extension  416 , etc. With this type of arrangement, leakage-mitigating structure  70  may still have an opening  414  to preserve continuity of the cathode. However, the pixel may be susceptible to back emissions in opening  414 . In other words, because no leakage-mitigating structure  70  is present in opening  414 , light may be generated by pixel  22  in this region and/or may end up in this region due to reflections. The light may pass through the underlying substrate  26  and reach a through-display optical sensor, undesirably decreasing the signal-to-noise ratio of the sensor. 
     To mitigate these types of back emissions, an opaque layer  420  may be included that overlaps opening  414  in leakage-mitigating structure  70 . Opaque layer  420  may be formed on an upper surface of substrate  26 , may be embedded within substrate  26 , may be formed on a lower surface of substrate  26 , etc. The opaque layer may block back emissions from reaching an underlying sensor in the device through opening  414 . The opaque layer may be a metal layer or dielectric layer. The opaque layer may be formed from a layer that is already present in the thin-film transistor circuitry in substrate  26  (e.g., a metal layer that is already used for contacts and/or signal routing within the substrate). Opaque layer  420  may have an opacity of greater than 80%, greater than 90%, greater than 95%, greater than 99%, etc. 
     As shown in the example of  FIG.  31   , in one possible arrangement, every pixel may have a corresponding leakage-mitigating structure  70  that partially surrounds the pixel. In other words, there is a 1:1 ratio between pixels and leakage-mitigating structures. 
     It should be noted that different pixels may have different associated OLED stackups with different OLED stackup thicknesses. Accordingly, the discontinuities caused by leakage-mitigating structure  70  may vary depending on the color of the pixel. In one possible embodiment, each color pixel may have a leakage-mitigating structure  70  that is optimized for its particular stackup. In other words, red pixels may have leakage-mitigating structures that partially surround the pixels and that have first dimensions, green pixels may have leakage-mitigating structures that partially surround the pixels and that have second dimensions, and blue pixels may have leakage-mitigating structures that partially surround the pixels and that have third dimensions that are different than the first and second dimensions. Each color&#39;s leakage-mitigating structure may be optimized for its particular OLED layers. This type of arrangement may, however, increase the manufacturing cost and complexity of the device. Therefore, to mitigate cost and complexity, in other embodiments every pixel may have a leakage-mitigating structure of the same dimensions (regardless of the color of the pixel). 
     In another example, shown in  FIG.  34   , only some pixels in the display may have an associated leakage-mitigating structure that partially surrounds the pixel. As shown in  FIG.  34   , the red pixel has an associated leakage-mitigating structure that partially surrounds the pixel but the green and blue pixels do not. This pattern may hold across the display. In other words, all of the red pixels in the display may have leakage-mitigating structures that partially surround the pixels while all of the green and blue pixels in the display may not have leakage-mitigating structures. 
     The example of only the red pixels having leakage-mitigating structures that partially surround the pixels is merely illustrative. In other embodiments, only the green pixels may have leakage-mitigating structures that partially surround the pixels or only the blue pixels may have leakage-mitigating structures that partially surround the pixels. As yet another possibility, any two pixel colors may have leakage-mitigating structures that partially surround the pixels while the remaining pixel color does not. 
     Displays of the type described herein may also sometimes have issues associated with IR drop across the cathode. As previously described, the cathode is formed as a blanket layer across the entire display. The cathode may have one or more contacts distributed around the periphery of the display to hold the cathode at a desired cathode voltage (ELVSS in  FIG.  3   ). Ideally, the cathode would be held at the target voltage across the entire display. However, in practice, the resistance of the cathode causes a voltage drop across the display. To mitigate this issue, the cathode may be formed from a low-resistance material. However, in large displays, the cathode voltage drop may cause brightness variations and require increased power consumption (even when a low-resistance material is used for the cathode). 
     To mitigate the non-uniformity and power consumption issues caused by cathode IR drop, the display may include cathode bus lines that are electrically connected to the cathode for each pixel. This reduces the IR drop for the cathode across the display, ensures the cathode is held at a consistent voltage for each pixel, and mitigates brightness non-uniformities associated with cathode IR drop. 
       FIG.  35    is a top view of an illustrative display that includes cathode bus lines  424 . As shown in  FIG.  35   , a first cathode bus line  424 - 1  may extend adjacent to a first column of pixels and a second cathode bus line  424 - 2  may extend adjacent to a second column of pixels. Bus lines  424  may be incorporated into thin-film transistor substrate  26  (e.g., on an outer surface of substrate  26 , embedded within substrate  26 , etc.). Each bus line may be formed from a low-resistance material and may be held at cathode voltage ELVSS. 
     The cathode may be formed as a blanket layer over the entire display. Accordingly, the cathode is not explicitly labeled in  FIG.  35   , since the cathode layer covers all of the components in  FIG.  35   . Surrounding each pixel is an undercut structure  422  that causes a discontinuity in the cathode. As shown, undercut structure  422 - 1  completely surrounds respective anode  42 - 1  whereas undercut structure  422 - 2  completely surrounds respective anode  42 - 2 . Each undercut structure may cause a discontinuity in the cathode layer and the OLED layers for the display. Accordingly, the undercut creates a cathode ‘island’ over each pixel. In other words, each pixel is covered by a discrete portion of the cathode layer that is separated from the remaining portions of the cathode layer by the discontinuity caused by undercut structure  422 . 
     To electrically connect each cathode layer island to the desired cathode voltage, each cathode layer island is electrically connected to a respective bus line  424 . As shown in  FIG.  35   , the cathode layer portion over anode  42 - 1  is electrically connected to a contact pad  428 - 1 , which is in turn electrically connected to bus line  424 - 1 . The cathode layer portion over anode  42 - 2  is electrically connected to a contact pad  428 - 2 , which is in turn electrically connected to bus line  424 - 2 . 
     An intervening conductive layer may be used to electrically connect each cathode layer island to contact pads  428 . The intervening conductive layer may be, for example, formed from a blanket layer of transparent conductive material. The intervening conductive layer may be formed from a transparent metal oxide such as indium tin oxide (ITO) or indium zinc oxide (IZO). 
       FIG.  36    is a cross-sectional side view of an illustrative undercut structure that causes a discontinuity in the cathode layer. As shown in  FIG.  36   , undercut structure  422  may be formed in or adjacent to pixel definition layer  76 . The undercut structure causes OLED emissive layers  45  to be separated into two discrete segments: OLED layers  45 - 1  and OLED layers  45 - 2 . OLED layers  45 - 2  may extend over anode  42  and form part of the light-emitting pixel. OLED layers  45 - 1  are separated from OLED layers  45 - 2  by undercut structure  422 . Separating OLED layers  45 - 1  and  45 - 2  may mitigate lateral leakage current, as previously discussed. 
     The undercut structure  422  also causes cathode layer  54  to be separated into two discrete segments: cathode layer portion  54 - 1  and cathode layer portion  54 - 2 . Cathode layer portion  54 - 2  may extend over anode  42  and form part of the light-emitting pixel. Cathode layer portion  54 - 1  is separated from cathode layer portion  54 - 2  by undercut structure  422 . 
     To ensure electrical connection between cathode layer portions  54 - 1  and  54 - 2  (despite the discontinuity from undercut structure  422 ), conductive layer  426  is included in the display. As shown in  FIG.  36   , conductive structure  426  (sometimes referred to as conductive bridge  426 ) may be formed from a blanket layer of transparent conductive material. The conductive layer may be formed from a transparent metal oxide such as indium tin oxide (ITO) or indium zinc oxide (IZO). 
     Conductive layer  426  electrically connects cathode layer portion  54 - 2  to cathode bus line  424 . As shown, conductive layer  426  is adjacent to and in direct contact with both cathode layer portion  54 - 2  and contact pad  428 . Contact pad  428  is in direct contact with (and electrically connects) conductive layer  426  and cathode bus line  424 . Therefore, cathode layer  54 - 2  is provided the appropriate cathode voltage from bus line  424  (using intervening contact pad  428  and conductive layer  426 ). 
     Contact pad  428  may be formed from the same layer as anode  42 . In other words, contact pad  428  and anode  42  may be formed from the same material during a single deposition/patterning step. This example is merely illustrative. Contact pad  428  and anode  42  may be formed from different materials if desired. 
     Because the distance between bus line  424  and cathode layer portion  54 - 2  is short, IR drop is minimized. The distance is sufficiently short that conductive layer  426  may have a higher resistance than cathode layer  54 . Even if the conductive layer  426  has a relatively high resistance (e.g., higher than layer  54 ), the IR drop caused by conductive layer  426  over the short distance between contact pad  428  and cathode layer portion  54 - 2  does not significantly impact the pixel performance. 
     For ease of manufacturing, conductive layer  426  may be formed as a blanket layer across the entire pixel array (e.g., like cathode layer  54 ). This example is merely illustrative. Alternatively, conductive layer  426  may be patterned to be present only in locations necessary to bridge the gap between discrete cathode layer portions (e.g., portions  54 - 1  and  54 - 2  in  FIG.  36   ) and/or in locations necessary to electrically connect the cathode layer to bus lines  424  via contact pads  428 . 
     To ensure high step-coverage (such that the conductive layer conforms to undercut structure  422  and electrically connects adjacent cathode layer portions), conductive layer  426  may be deposited using atomic layer deposition (ALD) at a low temperature (e.g., less than 100 degrees Celsius). This example is merely illustrative. Conductive layer  426  may be formed using other manufacturing techniques if desired. 
     It should be noted that the example in  FIGS.  35  and  36    of undercut structure  422  being included in addition to bus lines  424  and contact pad  428 /conductive layer  426  is merely illustrative. In another possible arrangement, the undercut structure  422  may be omitted. However, bus lines  424  may still be used to mitigate IR drop in the cathode. In this type of arrangement, contact pad  428  and conductive layer  426  may still be used to electrically connect bus lines  424  to cathode layer  54 . 
     There are many ways to form undercut structure  422  to cause discontinuity in the OLED and/or cathode layers. Any of the leakage-mitigating structures  70  shown in connection with  FIGS.  6 - 9    may be used. In general, the undercut structure  422  may include one layer, two layers, three layers, more than three layers, etc.  FIG.  37    is a cross-sectional side view of an illustrative display where the undercut structure includes one layer  430  that conforms to the edge of contact pad  428 . Layer  430  may be formed from a metal material (e.g., molybdenum, copper, etc.) or a dielectric material (e.g., silicon oxide, silicon nitride, etc.). Pixel definition layer  76  may overhang layer  430  to define an undercut (void) that causes discontinuities in OLED layers  45  and cathode layer  54 . 
       FIG.  38    is a cross-sectional side view of an illustrative display where the undercut structure includes three layers. A first layer  430  conforms to the edge of contact pad  428 . A second layer  432  is formed over layer  430  and conforms to layer  430 . A third layer  434  is formed over layer  432  and conforms to layer  432 . Each one of layers  430 ,  432 , and  434  may be formed from a metal material (e.g., molybdenum, copper, etc.) or a dielectric material (e.g., silicon oxide, silicon nitride, etc.). Pixel definition layer  76  may be formed on layer  434 . Layer  434  may overhang layer  432  to define an undercut (void) that causes discontinuities in OLED layers  45  and cathode layer  54 . If desired, one of the three layers (e.g., layer  430 ) may be omitted and a two-layer undercut structure may be used. 
     In  FIG.  35   , each pixel includes an undercut structure that laterally surrounds a corresponding anode. The undercut structure forms a ring around the anode and therefore may sometimes be referred to as an undercut ring. In addition to an undercut ring, each pixel may also include a leakage-mitigating structure  70  that also forms a ring around the anode.  FIG.  39    is a top view of an illustrative display where each pixel includes a leakage-mitigating structure  70  and an additional undercut structure  422 . 
     As shown in  FIG.  39   , a first cathode bus line  424 - 1  may extend adjacent to a first column of pixels and a second cathode bus line  424 - 2  may extend adjacent to a second column of pixels. The cathode may be formed as a blanket layer over the entire display. Accordingly, the cathode is not explicitly labeled in  FIG.  39   , since the cathode layer covers all of the components in  FIG.  39   . 
     Surrounding each pixel is a leakage-mitigating structure that causes a discontinuity in at least one of the OLED layers  45  for that pixel. As shown, leakage-mitigating structure  70 - 1  completely surrounds anode  42 - 1  and leakage-mitigating structure  70 - 2  completely surrounds anode  42 - 2 . Each leakage-mitigating structure may mitigate lateral leakage from the OLED layers (e.g., using any of the passive or active structures previously discussed). 
     Additionally, surrounding each pixel is an undercut structure  422  that causes a discontinuity in the cathode. As shown, undercut structure  422 - 1  completely surrounds respective leakage-mitigating structure  70 - 1  and anode  42 - 1  whereas undercut structure  422 - 2  completely surrounds respective leakage-mitigating structure  70 - 2  and anode  42 - 2 . Each undercut structure  422  may cause a discontinuity in the cathode layer and the OLED layers for the display. Accordingly, the undercut creates a cathode ‘island’ over each pixel. In other words, each pixel is covered by a discrete portion of the cathode layer that is separated from the remaining portions of the cathode layer by the discontinuity caused by undercut structure  422 . Each cathode layer island is electrically connected to a respective bus line using the techniques previously discussed (e.g., using a conductive bridging layer  426  and a contact pad  428 ). 
       FIG.  40    is a cross-sectional side view of an illustrative display with a leakage-mitigating structure  70  and an undercut structure  422 . As shown in  FIG.  40   , leakage-mitigating structure  70  is formed adjacent to (and conforms to) anode  42 . In  FIG.  40   , leakage-mitigating structure  70  is a passive leakage-mitigating structure that includes an undercut to cause discontinuities in at least some of the overlying layers. Leakage-mitigating structure  70  causes a discontinuity in OLED layers  45  to form electrically disconnected layers  45 - 1  and  45 - 2 . Leakage-mitigating structure  70  may also cause a discontinuity in cathode layer  54  to form electrically disconnected cathode layer portions  54 - 1  and  54 - 2 . This example is merely illustrative. Cathode layer  54  may maintain continuity over leakage-mitigating structure  70  if desired. 
     Blanket conductive layer  426  is formed across the entire display. A first ring of pixel definition layer  76  (sometimes referred to as an inner ring) may be formed between the leakage-mitigating structure ring and the undercut structure ring (see  FIG.  39   ). As shown on the right of  FIG.  40   , a second ring of pixel definition layer  76  (sometimes referred to as an outer ring) may be formed adjacent the undercut structure ring. A first undercut structure  422  is formed in the inner pixel definition layer ring. The undercut structure may include a single layer  430  that conforms to contact pad  428  (that is electrically connected to a cathode bus line). The first undercut structure  422  causes a discontinuity in OLED layers  45  to form electrically disconnected layers  45 - 2  and  45 - 3 . The first undercut structure  422  may also cause a discontinuity in cathode layer  54  to form electrically disconnected cathode layer portions  54 - 2  and  54 - 3 . 
     If desired, the undercut structure ring may include a second undercut structure in addition to the first undercut structure. The second undercut structure may be formed in a ring around the first undercut structure. As shown in  FIG.  40   , the second undercut structure  422  may be formed in the outer ring of pixel definition layer  76 . The undercut structure may include a single layer  430  that conforms to contact pad  428  (that is electrically connected to a cathode bus line). The second undercut structure  422  causes a discontinuity in OLED layers  45  to form electrically disconnected layers  45 - 3  and  45 - 4 . The second undercut structure  422  may also cause a discontinuity in cathode layer  54  to form electrically disconnected cathode layer portions  54 - 3  and  54 - 4 . 
     The first and second contact pads  428  in  FIG.  40    may be electrically connected to the same cathode bus line or to different cathode bus lines. 
     The undercut of leakage-mitigating structure  70  may have the same structure as undercut structures  422  or a different structure than undercut structures  422 . In some arrangements, leakage-mitigating structure  70  may have an undercut with a smaller height than undercut structures  422  (to cause less discontinuity in the overlying layers). Similarly, the first and second undercut structures  422  in  FIG.  40    may have the same structure or may have different structures. In  FIG.  40   , the undercut structures  422  have the same height. However, in an alternate arrangement, shown in  FIG.  41   , the undercut structures  422  have different heights. 
     As shown in the cross-sectional side view of  FIG.  41   , the first undercut structure has a first height  440 - 1  (defined by a lower surface of layer  432  and an upper surface of contact pad  428 ). The second undercut structure has a second height  440 - 2  (defined by a lower surface of layer  432  and an upper surface of substrate  26 ) that is greater than the first height. To make the second height  440 - 2  greater than the first height, contact pad  428  may be shifted or reduced in size so that the overhang of layer  432  is formed over substrate  26  instead of the contact pad. 
       FIG.  41    also demonstrates how each undercut structure may be formed from two layers instead of one layer (as in  FIG.  40   ). The undercut structure may instead have three layers or any other desired structure. 
     An arrangement of the type shown in  FIG.  41   , where first and second undercut structures with different dimensions are used, may be referred to as asymmetrical. In general, each undercut structure may have any desired dimensions, may be formed from any desired number of layers, etc. The second undercut structure in  FIG.  41    causes a discontinuity in conductive layer  426 . This may further reduce lateral leakage for the pixel. However, this example is merely illustrative. The undercut structure may preserve continuity of one or more OLED layers  45 , conductive layer  426 , and/or cathode  54  if desired. 
     It should be noted that the example in  FIGS.  35  and  39    of each cathode bus line running parallel to a respective column of pixels is merely illustrative. Alternatively, each cathode bus line may run parallel to a respective row of pixels. Additionally, the discontinuities in the cathode layer may be leveraged to provide different cathode voltages to different pixels using the bus lines if desired. The cathodes for each pixel may only be electrically connected to a single bus line, so per-pixel, per-row, or per-column cathode voltage control is possible. For example, a first bus line may provide a first cathode voltage to a first column of pixels and a second bus line may provide a second cathode voltage to a second column of pixels. The first and second cathode voltages may have different magnitudes. 
     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: 20210805
Publication Date: 20240220
Grant Date: 20240220
Priority Date: 20200818
Inventors: YEH, PO-CHUN
CHANG, JIUN-JYE
LEE, DOH-HYOUNG
COBURN, Caleb
Ran, Niva A.
CHUANG, CHING-SANG
AFENTAKIS, THEMISTOKLIS
Lin, Chuan-Jung
HUANG, JUNG YEN
YUAN, LEI
Assignee: APPLE INC
CPC Classifications: [{"code": "H10K59/122", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G3/3291", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/621", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2320/0214", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K59/122", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/0214", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3291", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/00", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K71/621", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/122", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/35", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K71/621", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K71/00", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 89908533