PATENT DOCUMENT

Publication Number: US-11700738-B2
Application Number: US-202016888451-A
Country: US
Kind Code: B2

Title: Organic light-emitting diode display with patterned anodes and optical cavities

Abstract:
Pixels in an organic light-emitting diode (OLED) display may be microcavity OLED pixels having optical cavities. The optical cavities may be defined by a partially transparent cathode layer and a reflective anode structure. The anode of the pixels may include both the reflective anode structure and a supplemental anode that is transparent and that is used to tune the thickness of the optical cavity for each pixel. Organic light-emitting diode layers may be formed over the pixels and may have a uniform thickness in each pixel in the display. Pixels may have a conductive spacer between a transparent anode portion and a reflective anode portion, without an intervening dielectric layer. The conductive spacer may be formed from a material such as titanium nitride that is compatible with both anode portions. The transparent anode portions may have varying thicknesses to control the thickness of the optical cavities of the pixels.

Claims:
What is claimed is: 
     
       1. A display comprising:
 a first pixel formed from a first anode, a cathode, and organic light-emitting diode layers, wherein the first anode comprises a first portion in a first layer and a second portion in a second layer, wherein the second portion is electrically connected to the first portion and has a first thickness, wherein the first pixel has an optical cavity defined by a first distance between the first portion and the cathode, and wherein the first pixel includes first and second dielectric layers that are interposed between the first portion of the first anode and the second portion of the first anode; and 
 a second pixel formed from a second anode, the cathode, and the organic light-emitting diode layers, wherein the second anode comprises a third portion and a fourth portion, wherein the fourth portion is electrically connected to the third portion and has a second thickness that is different than the first thickness, wherein the second pixel has an optical cavity defined by a second distance between the third portion and the cathode, and wherein the second distance is different than the first distance. 
 
     
     
       2. The display defined in  claim 1 , wherein the organic light-emitting diode layers have a given thickness over the second portion of the first anode and wherein the organic light-emitting diode layers have the given thickness over the fourth portion of the second anode. 
     
     
       3. The display defined in  claim 1 , wherein the first pixel includes a first via that extends through the first and second dielectric layers to electrically connect the first and second portions of the first anode. 
     
     
       4. The display defined in  claim 3 , wherein the second pixel includes the first and second dielectric layers and wherein the first and second dielectric layers are interposed between the third portion of the second anode and the fourth portion of the second anode. 
     
     
       5. The display defined in  claim 4 , wherein the second pixel includes a second via that extends through the first and second dielectric layers to electrically connect the third and fourth portions of the second anode. 
     
     
       6. The display defined in  claim 5 , wherein the first thickness is greater than the second thickness. 
     
     
       7. The display defined in  claim 6 , wherein the first dielectric layer has a third thickness in the first pixel and a fourth thickness in the second pixel that is the same as the third thickness and wherein the second dielectric layer has a fifth thickness in the first pixel and a sixth thickness in the second pixel that is the same as the fifth thickness. 
     
     
       8. The display defined in  claim 7 , further comprising:
 a third pixel formed from a third anode, the cathode, and the organic light-emitting diode layers, wherein the third anode comprises a fifth portion and a sixth portion, wherein the sixth portion is electrically connected to the fifth portion and has a seventh thickness that is different than the first thickness, wherein the third pixel has an optical cavity defined by a third distance between the fifth portion and the cathode, and wherein the third distance is different than the first and second distances. 
 
     
     
       9. The display defined in  claim 8 , wherein the third pixel includes the first dielectric layer, wherein the first dielectric layer is interposed between the fifth portion of the third anode and the sixth portion of the third anode, wherein the first dielectric layer has an eighth thickness in the third pixel that is the same as the third and fourth thicknesses, wherein the first distance is greater than the second distance, wherein the second distance is greater than the third distance, wherein the organic light-emitting diode layers are white organic light-emitting diode layers, wherein the first pixel is a red pixel, wherein the second pixel is a green pixel, and wherein the third pixel is a blue pixel. 
     
     
       10. The display defined in  claim 1 , further comprising:
 a third pixel formed from a third anode, the cathode, and the organic light-emitting diode layers, wherein the third anode comprises a fifth portion and a sixth portion, wherein the sixth portion is electrically connected to the fifth portion and has a third thickness that is different than the first and second thicknesses, wherein the third pixel has an optical cavity defined by a third distance between the fifth portion and the cathode, and wherein the third distance is different than the first and second distances. 
 
     
     
       11. The display defined in  claim 10 , wherein the first pixel further comprises a first conductive layer that is interposed between and in direct contact with the first portion and the second portion, wherein the second pixel further comprises a second conductive layer that is interposed between and in direct contact with the third portion and the fourth portion, and wherein the third pixel further comprises a third conductive layer that is interposed between and in direct contact with the fifth portion and the sixth portion. 
     
     
       12. A display comprising:
 a pixel that includes:
 an anode comprising a first portion that is formed from a first material and a second portion that is formed from a second material that is different than the first material; 
 a cathode; 
 organic light-emitting diode layers interposed between the second portion of the anode and the cathode; and 
 a conductive spacer, wherein the conductive spacer is formed from a third material that is different than the first and second materials, wherein the conductive spacer is interposed between and electrically connects the first and second portions of the anode, and wherein the pixel has an optical cavity defined by a distance between the first portion of the anode and the cathode. 
 
 
     
     
       13. The display defined in  claim 12 , wherein the pixel is a first pixel, wherein the anode is a first anode, and wherein the display further comprises:
 a second pixel that includes:
 a second anode comprising a third portion and a fourth portion; 
 the cathode; 
 the organic light-emitting diode layers, wherein the organic light-emitting diode layers are interposed between the fourth portion of the second anode and the cathode; and 
 at least one dielectric layer that is interposed between the third and fourth portions of the second anode. 
 
 
     
     
       14. The display defined in  claim 13 , wherein the at least one dielectric layer comprises a first dielectric layer and wherein the first dielectric layer is the only dielectric layer interposed between the third and fourth portions of the second anode. 
     
     
       15. The display defined in  claim 14 , further comprising:
 a third pixel that includes:
 a third anode comprising a fifth portion and a sixth portion; 
 the cathode; 
 the organic light-emitting diode layers, wherein the organic light-emitting diode layers are interposed between the sixth portion of the third anode and the cathode; and 
 two dielectric layers that are interposed between the fifth and sixth portions of the third anode. 
 
 
     
     
       16. The display defined in  claim 15 , wherein the second pixel includes a first via that extends through the first dielectric layer to couple the third portion of the second anode to the fourth portion of the second anode, wherein the third pixel includes a second via that extends through the two dielectric layers to couple the fifth portion of the third anode to the sixth portion of the third anode, and wherein the first pixel does not include any dielectric layers between the first portion of the first anode and the second portion of the first anode. 
     
     
       17. The display defined in  claim 16 , wherein the optical cavity is a first optical cavity and the distance is a first distance, wherein the second pixel has a second optical cavity defined by a second distance between the third portion of the second anode and the cathode, wherein the third pixel has a third optical cavity defined by a third distance between the fifth portion of the third anode and the cathode, wherein the first distance is less than the second distance, and wherein the second distance is less than the third distance. 
     
     
       18. A display comprising:
 first and second pixels having a common cathode formed over organic light-emitting diode layers, wherein each of the first and second pixels comprises:
 a first anode portion; 
 a second anode portion that contacts the organic light-emitting diode layers, wherein the organic light-emitting diode layers have a thickness over the second anode portion of the first pixel and wherein the organic light-emitting diode layers have the thickness over the second anode portion of the second pixel; and 
 at least one dielectric layer interposed between the first and second anode portions, wherein the second anode portion of the first and second pixels have different thicknesses. 
 
 
     
     
       19. The display defined in  claim 18 , wherein the first anode portion of each of the first and second pixels is reflective and wherein the second anode portion of each of the first and second pixels is transparent.

Description:
This application claims the benefit of provisional patent application No. 62/891,142, filed Aug. 23, 2019, which is hereby incorporated by reference herein in its entirety. 
    
    
     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. 
     Some OLED pixels may include microcavity OLED pixels, where OLED layers are covered by a partially transparent layer to form an optical cavity. The thickness of the optical cavity may be tuned so that light of a selected wavelength is emitted with high efficiency. However, if care is not taken, OLED pixels of this type may have non-uniform thicknesses, may have smaller than desired aperture ratios, and/or may require complex manufacturing processes. 
     It is within this context that the embodiments herein arise. 
     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. 
     The pixels in the OLED display may be microcavity OLED pixels having optical cavities. The optical cavities may be defined by a partially transparent cathode layer and a reflective anode structure. The anodes of the pixels may include a supplemental anode that is transparent and that is used to tune the thickness of the optical cavity for each pixel. 
     White organic light-emitting diode layers may be formed over the pixels and may have a uniform thickness in each pixel in the display. The thickness of the optical cavity of each pixel is controlled using the thickness of the transparent anode stack that includes the supplemental anode and additional spacer layers. Blue pixels, green pixels, and red pixels may have increasingly thick optical cavities. 
     Blue pixels may have a conductive spacer between a transparent anode portion and a reflective anode portion. The conductive spacer may be formed from a material such as titanium nitride that is compatible with both of the anode portions. No other dielectric layers may be formed between the anode portions of the blue pixels. This means that no vias are required for the blue pixels, increasing the aperture ratios of the blue pixels. 
     In some arrangements, the transparent anode portions may have varying thicknesses to control the thickness of the optical cavities of the pixels. For example, the transparent anode portions of the red pixels may be thicker than the transparent anode portions of the green or blue pixels. The dielectric layers underneath the transparent anode portions of the red pixels may be thinner in this arrangement, rendering the via through the dielectric layers easier to form. 
    
    
     
       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 display pixel circuit in accordance with an embodiment. 
         FIG.  4    is a cross-sectional side view of an illustrative display having microcavity organic light-emitting diode pixels including at least one pixel without a via between anode portions in accordance with an embodiment. 
         FIG.  5    is a cross-sectional side view of an illustrative display having microcavity organic light-emitting diode pixels that have respective anode portions with different thicknesses in accordance with an embodiment. 
         FIG.  6    is a cross-sectional side view of an illustrative display having microcavity organic light-emitting diode pixels including pixels of three colors without a via between anode portions in accordance with an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative electronic device of the type that may be provided with a display is shown in  FIG.  1   . Electronic device  10  may be a computing device such as a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, a device embedded in eyeglasses or other equipment worn on a user&#39;s head, or other wearable or miniature device, a display, a computer display that contains an embedded computer, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, or other electronic equipment. Electronic device  10  may have the shape of a pair of eyeglasses (e.g., supporting frames), may form a housing having a helmet shape, or may have other configurations to help in mounting and securing the components of one or more displays on the head or near the eye of a user. 
     As shown in  FIG.  1   , electronic device  10  may include control circuitry  16  for supporting the operation of device  10 . Control circuitry  16  may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application-specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  12  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output devices  12  may include buttons, joysticks, scrolling wheels, touch pads, key pads, keyboards, microphones, speakers, tone generators, vibrators, cameras, sensors, light-emitting diodes and other status indicators, data ports, etc. A user can control the operation of device  10  by supplying commands through input resources of input-output devices  12  and may receive status information and other output from device  10  using the output resources of input-output devices  12 . 
     Input-output devices  12  may include one or more displays such as display  14 . Display  14  may be a touch screen display that includes a touch sensor for gathering touch input from a user or display  14  may be insensitive to touch. A touch sensor for display  14  may be based on an array of capacitive touch sensor electrodes, acoustic touch sensor structures, resistive touch components, force-based touch sensor structures, a light-based touch sensor, or other suitable touch sensor arrangements. A touch sensor for display  14  may be formed from electrodes formed on a common display substrate with the display pixels of display  14  or may be formed from a separate touch sensor panel that overlaps the pixels of display  14 . If desired, display  14  may be insensitive to touch (i.e., the touch sensor may be omitted). Display  14  in electronic device  10  may be a head-up display that can be viewed without requiring users to look away from a typical viewpoint or may be a head-mounted display that is incorporated into a device that is worn on a user&#39;s head. If desired, display  14  may also be a holographic display used to display holograms. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14 . 
       FIG.  2    is a diagram of an illustrative display  14 . 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. Pixels of other colors such as cyan, magenta, and yellow might also be used. 
     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  20  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  20 A 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 across 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 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  32  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 may include additional switching transistors, emission transistors in series with the drive transistor, etc. Capacitor Cst may be positioned at other desired locations within the pixel (e.g., between the source and gate of the drive transistor). 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. Substrate  26  may include thin-film transistor circuitry for applying control signals to the pixels and may therefore sometimes be referred to as a thin-film transistor substrate.  FIG.  4    shows a red pixel  22 -R, a blue pixel  22 -B, and a green pixel  22 -G. 
     Anodes  42  such as anodes  42 -R,  42 -G, and  42 -B may be formed on substrate  26 . Anodes  42 -R,  42 -G, and  42 -B 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 electron-block layer (EBL), an emissive layer (EML), an electron-transport layer (ETL), and an electronic-injection layer (EIL). OLED layers  45  may be formed from white OLED layers (e.g., OLED layers configured to emit white light), combinations of red, green, blue, and/or yellow OLED layers, etc. 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 . 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. 
     In some OLED displays, cathode  54  is entirely (or almost entirely) transparent and anodes  42  may be in direct contact with OLED layers  45 . The display of  FIG.  4   , however, uses an optical cavity to enhance efficiency and color purity in the display. Using optical cavities as in  FIG.  4    allows for uniform white OLED layers  45  to provide red, green, and blue light from red pixel  22 -R, green pixel  22 -G, and blue pixel  22 -B respectively. An optical cavity may be formed by reflective layers within the display that are formed on either side of the OLED layers. By tuning the thickness of the optical cavity that includes the OLED layers, each pixel may be optimized to have high emission at a desired wavelength. To form an optical cavity of this type, display  14  in  FIG.  4    includes a partially transparent cathode layer  54  and additional anode portions  44 . 
     Cathode layer  54  may be formed from a partially transparent conductive material. In one illustrative example, cathode layer  54  may be formed from a combination of magnesium (Mg) and silver (Ag). Cathode layer  54  may be formed form any other desired conductive material or combination of conductive materials. Cathode  54  may transmit less than 90% of light, may transmit less than 80% of light, may transmit less than 70% of light, may transmit less than 60% of light, may transmit less than 50% of light, may transmit more than 40% of light, may transmit more than 50% of light, may transmit more than 60% of light, may transmit between 40% and 80% of light, may transmit between 45% and 60% of light, may transmit between 60% and 70% of light, may transmit between 50% and 75% of light, etc. Cathode  54  may reflect more than 10% of light, may reflect more than 20% of light, may reflect more than 30% of light, may reflect more than 40% of light, may reflect more than 50% of light, may reflect more than 60% of light, may reflect less than 50% of light, may reflect less than 60% of light, may reflect between 20% and 60% of light, may reflect between 40% and 55% of light, may reflect between 30% and 40% of light, may reflect between 25% and 50% of light, etc. 
     Cathode layer  54  may define a first boundary for the optical cavity. The other boundary of the optical cavity may be set by anode  42  (sometimes referred to as anode portion  42 ). Anodes  42 -R,  42 -G, and  42 -B may be formed from a highly reflective material such as aluminum, silver or any other desired conductive material. Each anode  42  may reflect more than 70% of light, more than 80% of light, more than 90% of light, more than 95% of light, more than 99% of light, etc. 
     Additional layers may be formed over anodes  42  between the anodes and OLED layers  45 . However, these additional layers may be transparent and therefore do not disrupt the optical cavity. Because the additional layers are transparent, the boundaries of the optical cavity are still determined by the reflective anode  42  and cathode  54 . The presence of the additional transparent layers between anode  42  and cathode  54  may result in an increased distance between the reflective anode  42  and cathode  54  (because the OLED thickness is uniform).  FIG.  4    shows how pixel  22 -R has an optical cavity with thickness  48 -R between anode  42 -R and cathode  54 . Pixel  22 -G has an optical cavity with thickness  48 -G between anode  42 -G and cathode  54 . Pixel  22 -B has an optical cavity with thickness  48 -B between anode  42 -B and cathode  54 . 
     Each optical cavity thickness is tuned to optimize emission of the desired color of light for that pixel. For a given optical cavity thickness, light of a given wavelength will resonate due to multiple reflections off of the walls (e.g., cathode  54  and anode  42 ) of the optical cavity. The increased emission at the given wavelength caused by resonance within the optical cavity may be referred to as a microcavity effect. Pixels that are optimized to induce this effect (such as the pixels in  FIG.  4   ) may be referred to as microcavity OLED pixels. 
     Pixel  22 -R has an optical cavity thickness  48 -R that maximizes emission of red light. Pixel  22 -G has an optical cavity thickness  48 -G that maximizes emission of green light. Pixel  22 -B has an optical cavity thickness  48 -B that maximizes emission of blue light. Blue light has a shorter wavelength than green light, which has a shorter wavelength than red light. Generally, the thickness of the optical cavity may be proportional to the wavelength of the type of light that is intended to be emitted. Therefore, thickness  48 -B is less than thickness  48 -G and thickness  48 -G is less than thickness  48 -R. This example is merely illustrative and does not necessarily hold true for all display designs, as other factors such as the node of the cavity may influence the optical cavity. 
     The thickness of each optical cavity is therefore tuned to optimize emission of light. However, changing the thickness of each optical cavity may present difficulties during manufacturing. To reduce complexity and cost in manufacturing microcavity OLED displays, additional anode portions  44  may be included in each pixel. As shown in  FIG.  4   , red pixel  22 -R has an additional anode portion  44 -R, green pixel  22 -G has an additional anode portion  44 -G, and blue pixel  22 -B has an additional anode portion  44 -B. These additional anode portions  44  (sometimes referred to as supplementary anodes  44 , anodes  44 , etc.) may be formed from a transparent conductive material. The additional anode portions may be formed from indium tin oxide (ITO) or any other desired transparent conductive material. Because the additional anodes are transparent, they may be used to tune the optical cavity thickness  48  of the pixels without disrupting the optical cavity between anode  42  and cathode  54 . 
     A pixel definition layer  66  may be formed between each pixel. The pixel definition layer may be formed from a non-conducting material and may be interposed between adjacent anodes of the display. The pixel definition layer may be formed from a non-conductive material (that is either opaque or transparent) and may have openings in which the anodes are formed, thereby defining the area of each pixel. 
     Additional layers may be included between anode portion  44  and anode portion  42  in each pixel. As shown in  FIG.  4   , first and second dielectric layers  50  and  52  (sometimes referred to as spacers  50  and  52 ) are included in display  14 . Dielectric layer  52  has a portion formed over anode  42 -R in red pixel  22 -R. Dielectric layer  50  has a first portion that is formed over anode  42 -R in red pixel  22 -R and a second portion that is formed over anode  42 -G in green pixel  22 -G. The first portion of dielectric layer  50  is interposed between dielectric layer  52  and supplemental anode  44 -R. The second portion of dielectric layer  50  is interposed between anode  42 -G and supplemental anode  44 -G. 
     Dielectric layers  50  and  52  as well as supplemental anodes  44  may all be transparent or substantially transparent. This allows the layers to serve as spacers that can have thicknesses chosen to tune the thickness of the optical cavity for each pixel. Dielectric layers  50  and  52  as well as supplemental anodes  44  may transmit more than 90% of incident light, more than 95% of incident light, more than 99% of incident light, more than 99.9% of incident light, etc. Dielectric layers  50  and  52  may be formed from silicon dioxide, silicon oxynitride, another desired oxide material, silicon nitride, or any other desired transparent material. 
     Dielectric layers  50  and  52  may serve as spacer structures that allow tuning of cavity thickness  48  for each pixel. For ease of manufacturing, it is desirable for a uniform thickness white OLED layer  45  to be formed over each supplemental anode  44 . This way, OLED layers  45  may be formed in a single deposition step instead of being patterned to have different thicknesses and/or different color OLED material for each pixel. As shown in  FIG.  4   , the OLED thickness  56 -R of pixel  22 -R, the OLED thickness  56 -G of pixel  22 -G, and the OLED thickness  56 -B of pixel  22 -B are approximately (e.g., within 5% of) the same. 
     Without spacer layers  50  and  52 , supplemental anodes  44 , and conductive spacer  68 , having a uniform thickness OLED layer would result in the optical cavity thickness of each pixel being the same. Including dielectric spacers and supplemental anodes as in  FIG.  4    allows for the optical cavity thickness to be tuned for a desired color. 
     Supplemental anodes  44  may be electrically connected to anodes  42 . As shown in  FIG.  4   , a via  60  may be formed that extends through dielectric layers  50  and  52  to electrically connect anode portion  44 -R to anode portion  42 -R. In  FIG.  4   , via  60  includes a conductive portion  62  and a conductive liner  64 . Another via having the same structure (e.g., with a conductive portion and a conductive liner) is also formed through dielectric layer  50  to electrically connect supplemental anode  44 -G to anode  42 -G. 
     Unlike pixels  22 -R and  22 -G, pixel  22 -B may not include a via. Instead, a conductive layer  68  may be interposed between anode portions  42 -B and  44 -B. Conductive layer  68  may electrically connect anode portion  42 -B and anode portion  44 -B and may be in direct contact with both anode portion  42 -B and anode portion  44 -B. Conductive layer  68  (sometimes referred to as conductive spacer  68 ) may be included to avoid incompatibilities between anode portion  44 -B and anode portion  42 -B. Conductive layer  68  may also promote better electrical contact between anode portions  44  and anode portions  42 . For example, transparent anode portion  44 -B may be formed from a material that corrodes when in direct contact with the material of reflective anode portion  42 -B. Transparent anode portion  44 -B may be formed from ITO and reflective anode portion  42 -B may be formed from aluminum, for example. In this example, conductive spacer  68  may be interposed between the anode portions to prevent corrosion. 
     Conductive layer  68  may be formed from titanium nitride (TiN) or another desired conductive material. Conductive layer  68  may be thin enough to be approximately transparent. For example, conductive layer  68  may have a thickness of less than 10 nanometers, less than 5 nanometers, less than 3 nanometers, between 2 and 5 nanometers, between 1 and 6 nanometers, between 2 and 3 nanometers, between 1 and 3 nanometers, etc. Conductive layer  68  may transmit more than 80% of incident light, more than 90% of incident light, more than 95% of incident light, more than 99% of incident light, more than 99.9% of incident light, etc. 
     In  FIG.  4   , no dielectric spacer is formed between anode portion  42 -B and anode portion  44 -B. Having supplemental anode portion  44 -B formed directly over anode portion  42 -B with an intervening conductive layer  68  obviates the need for a dielectric layer to be included in the anode stack of pixel  22 -B. This is beneficial as a dielectric spacer in the anode stack of the blue pixel would have to be very thin, presenting manufacturing difficulties. 
     Additionally, having supplemental anode portion  44 -B formed directly over anode portion  42 -B without an intervening dielectric layer allows for via  60  (e.g., through a dielectric layer) to be omitted in pixel  22 -B. Omitting the via in blue pixel  22 -B allows for the aperture ratio of the blue pixel to be increased. A pixel&#39;s aperture is the area from which light is emitted from the pixel. In the display shown in  FIG.  4   , each pixel&#39;s aperture is defined by pixel definition layers  66  (e.g., the aperture corresponds to areas not covered by the opaque pixel definition layer). Aperture ratio refers to the ratio of a pixel&#39;s aperture (e.g., light-emitting area) to the pixel&#39;s non-light-emitting area. In general, having a larger aperture ratio is desirable as larger aperture ratios correspond to higher display efficiency and improved display performance. 
     As shown in  FIG.  4   , vias  60  in pixels  22 -R and  22 -G are non-light-emitting areas that are therefore covered by pixel definition layer  66 . The presence of via  60  reduces the aperture ratio of the pixel. Omitting via  60  in the blue pixel of  FIG.  4    therefore improves the aperture ratio of the blue pixel  22 -B. 
     In some cases, anode portions  42 -B and  44 -B may be formed from materials that are compatible when in direct contact. For example, anode portion  42 -B may be formed from silver and anode portion  44 -B may be formed from ITO. In this example, conductive layer  68  may be omitted and anode portion  42 -B may be formed in direct contact with anode portion  44 -B. 
     Conductive portion  62  of each via  60  may optionally be formed from the same material as supplemental anode portions  44 . For example, if supplemental anode  44 -R for pixel  22 -R is formed from indium tin oxide, conductive portion  62  of via  60  in pixel  22 -R may also be formed from indium tin oxide. However, as discussed in connection with conductive spacer  68 , indium tin oxide may not be placed in direct contact with aluminum anode portion  42 -R to prevent corrosion. Accordingly, conductive liner  64  may be interposed between conductive via portion  62  and anode portion  42 -R. Conductive liner  64  may be formed from the same material as conductive layer  68  (e.g., titanium nitride). Indeed, conductive liner  64  may be formed during the same deposition step as conductive layer  68  during display manufacturing. Similar to how conductive layer  68  may be omitted from the display depending on material compatibility, conductive liner  64  may be omitted if conductive via portion  62  is compatible with anode portions  42 . 
     Each layer in display  14  may have any desired thickness. In some arrangements, supplemental anode portions  44 -R,  44 -G, and  44 -B may have the same thickness. Each supplemental anode portion may have a thickness of less than 100 nanometers, less than 50 nanometers, less than 30 nanometers, less than 20 nanometers, less than 15 nanometers, less than 10 nanometers, greater than 5 nanometers, between 5 and 50 nanometers, between 5 and 100 nanometers, etc. Similarly, each one of dielectric layers  50  and  52  may have any desired thickness (e.g., less than 100 nanometers, less than 50 nanometers, less than 30 nanometers, less than 20 nanometers, less than 15 nanometers, less than 10 nanometers, greater than 5 nanometers, between 5 and 50 nanometers, between 5 and 100 nanometers, etc.). 
     The supplemental anode and underlying layers between the supplemental anode and anode may be referred to as an anode stack. For example, pixel  22 -R has an anode stack that includes supplemental anode  44 -R, dielectric layer  50  (sometimes referred to as oxide layer  50 ), and dielectric layer  52  (sometimes referred to as oxide layer  52 ). The total thickness  70 -R of the anode stack is tuned to determine the total optical cavity thickness  48 -R. Pixel  22 -G has an anode stack that includes supplemental anode  44 -G and dielectric layer  50 . The total thickness  70 -G of the anode stack is tuned to determine the total optical cavity thickness  48 -G. Pixel  22 -B has an anode stack that includes supplemental anode  44 -B and (optionally) conductive spacer  68 . The total thickness  70 -B of the anode stack is tuned to determine the total optical cavity thickness  48 -B. In one arrangement, the thickness  70 -R of the anode stack of red pixel  22 -R may be between 100 and 200 nanometers, the thickness  70 -G of the anode stack of green pixel  22 -G may be between 70 and 100 nanometers, and the thickness  70 -B of the anode stack of blue pixel  22 -B may be between 10 and 30 nanometers. These thickness values are merely illustrative. Each anode stack may have any desired thickness (e.g., greater than 200 nanometers, between 100 nanometers and 150 nanometers, between 50 and 125 nanometers, less than 100 nanometers, less than 50 nanometers, less than 25 nanometers, less than 20 nanometers, etc.). 
     The display of  FIG.  4    has the aforementioned advantage of omitting the via in pixel  22 -B for improved aperture ratio. Additionally, the number of layers deposited is minimized for reduced manufacturing complexity and cost. Dielectric layer  52 , dielectric layer  50 , a conductive layer for liner  64  and layer  68 , and a conductive layer for supplemental anodes  44  may be deposited with generally uniform thicknesses across the display, reducing the need for additional patterning steps. 
     The example of  FIG.  4    in which white OLED layers  45  are uniformly deposited for pixels  22 -R,  22 -G, and  22 -B is merely illustrative. In some designs, each pixel may have corresponding OLED layers of that color. For example, red pixel  22 -R may have red OLED layers (e.g., OLED layers that emit red light), green pixel  22 -G may have green OLED layers (e.g., OLED layers that emit green light), and blue pixel  22 -B may have blue OLED layers (e.g., OLED layers that emit blue light). This type of arrangement may offer efficiency improvements at the cost of increased manufacturing complexity. 
       FIG.  5    is a cross-sectional side view of a display with microcavity OLED pixels similar to the display of  FIG.  4   . For simplicity, duplicative descriptions that apply to both  FIGS.  4  and  5    will not be repeated herein. In  FIG.  5   , each pixel includes a transparent supplemental anode  44  similar to as in  FIG.  4   . However, in  FIG.  5    the thicknesses of the supplemental anodes vary. For example, supplemental anode  44 -R may have a different (e.g., larger) thickness than supplemental anodes  44 -G and  44 -B. This allows for the combined thickness of dielectric layers  50  and  52  in pixel  22 -R to be reduced while achieving the same anode stack height  70 -R. 
     Reducing the thickness of dielectric layers  50  and  52  may be beneficial because it results in via  60  in pixel  22 -R being shorter. Having via  60  extend through thick dielectric layers may present challenges. Manufacturing a via that is both thin and deep may add to manufacturing cost, may add to manufacturing complexity, and may result in reliability issues. The via may be made wider to make manufacturing easier for the same depth, but this sacrifices aperture ratio of the pixel. 
     By reducing the thickness of dielectric layers  50  and  52  in  FIG.  5   , the via may be shorter and therefore easier to manufacture without sacrificing aperture ratio. Additionally, the thickness of dielectric layers  50  and  52  in pixels  22 -R and  22 -G are the same. Therefore, via  60  in pixel  22 -R has the same depth as via  60  in pixel  22 -G. Consequently, the vias for pixels  22 -R and  22 -G may be manufactured during the same processing step, lowering the cost and complexity of manufacturing. 
     By tuning the supplemental anode thickness, the desired anode stack thicknesses  70  and optical cavity thicknesses  48  may remain unaffected even when the thickness of the dielectric layers are reduced. 
     In  FIG.  5   , blue pixel  22 -B has a supplemental anode  44 -B that is separated from anode  42 -B by a portion of dielectric layer  50 . The blue pixel has a via  60  that extends through the dielectric layer to electrically connect anode portion  44 -B to anode portion  42 -B. This type of arrangement allows for dielectric layer  50  to have the same thickness in pixels  22 -R,  22 -G, and  22 -B. The thickness of dielectric layer  50  may be selected primarily based on the tuning of the anode stack of pixel  22 -B. The thicknesses of dielectric layer  52  and supplemental anodes  44  may then be used to tune the overall thicknesses of the anode stacks for pixels  22 -R and  22 -G. 
     Color filter elements may optionally be formed over the pixels of the displays of  FIGS.  4  and  5    if desired. For example, a red color filter element may be formed over each red pixel  22 -R, a green color filter element may be formed over each green pixel  22 -G, and a blue color filter element may be formed over each blue pixel  22 -B. Color filter elements may not be included in the display if desired. 
     Additionally, in  FIGS.  4  and  5    examples are shown where continuous OLED layers  45  are formed across the display. This example is merely illustrative. It should be understood that pixel definition layers  66  and/or other structures may be used to form discontinuities in one or more of the OLED layers if desired. Forming discontinuities in the OLED layers may prevent light leakage between pixels. 
     It should be understood that the arrangements of  FIGS.  4  and  5    may be combined if desired. For example, the display of  FIG.  5    may have a conductive layer  68  and no via interposed between anode portions  42 -B and  44 -B instead of a dielectric layer with a via (e.g., pixel  22 -B in  FIG.  5    may instead have the structure of pixel  22 -B in  FIG.  4   ). 
     In the example of  FIG.  4   , a conductive spacer  68  is depicted as only being formed in the anode stack of blue pixel  22 -B. This example is merely illustrative. If desired, the red and/or green pixels may also include a conductive spacer between a respective anode portion  42  and supplemental anode portion  44 . In general, any subset of the red, green, and blue pixels may include a conductive spacer between the anode portions (and omit dielectric spacers between the anode portions). 
       FIG.  6    is a cross-sectional side view of an illustrative display where the red, blue, and green pixels all have a conductive spacer between respective anode portions. For simplicity, duplicative descriptions that apply to  FIG.  6    and one or more previous figures will not be repeated herein. In  FIG.  6   , each pixel includes a transparent supplemental anode  44  similar to as in  FIG.  4   . However, in  FIG.  6    the thicknesses of the supplemental anodes vary. For example, supplemental anode  44 -R may have a different (e.g., larger) thickness than supplemental anode  44 -G and supplemental anode  44 -B. Supplemental anode  44 -G may have a different (e.g., larger) thickness than supplemental anode  44 -B. Using supplemental anodes  44  of varying thicknesses allows for the total optical cavity thickness  48  to be optimized for each pixel type (e.g., pixel  22 -R has an optical cavity thickness  48 -R that maximizes emission of red light, pixel  22 -G has an optical cavity thickness  48 -G that maximizes emission of green light, and pixel  22 -B has an optical cavity thickness  48 -B that maximizes emission of blue light) while allowing OLED thicknesses  56 -R,  56 -G, and  56 -B to remain approximately the same. 
     In  FIG.  6   , there is no intervening dielectric layer between transparent supplemental anode portion  44  and anode portion  42  for each pixel. Instead, a conductive layer  68  may be interposed between anode portions  42  and  44 . As shown, a conductive layer  68 -R is interposed between anode portion  44 -R and anode portion  42 -R, a conductive layer  68 -G is interposed between anode portion  44 -G and anode portion  42 -G, and a conductive layer  68 -B is interposed between anode portion  44 -B and anode portion  42 -B. The conductive layers  68  may electrically connect respective anode portions  42  and  44  and may be in direct contact with both anode portion  42  and anode portion  44 . Conductive layers  68 -R,  68 -G, and  68 -B (sometimes referred to as conductive spacers) may be included to avoid incompatibilities between anode portions  44  and anode portions  42 . Conductive layers  68  may also promote better electrical contact between anode portions  44  and anode portions  42 . For example, transparent anode portion  44  may be formed from a material that corrodes when in direct contact with the material of reflective anode portion  42  (e.g., transparent anode portion  44  may be formed from ITO and reflective anode portion  42  may be formed from aluminum). In this example, conductive spacer  68  may be interposed between the anode portions to prevent corrosion. 
     Each one of conductive layers  68 -R,  68 -G, and  68 -B may be formed from titanium nitride (TiN) or another desired conductive material. Each one of conductive layers  68 -R,  68 -G, and  68 -B may be thin enough to be approximately transparent (e.g., may have a thickness of less than 10 nanometers, less than 5 nanometers, less than 3 nanometers, between 2 and 5 nanometers, between 1 and 6 nanometers, between 2 and 3 nanometers, between 1 and 3 nanometers, etc.). Each one of conductive layers  68 -R,  68 -G, and  68 -B may transmit more than 80% of incident light, more than 90% of incident light, more than 95% of incident light, more than 99% of incident light, more than 99.9% of incident light, etc. Conductive layers  68 -R,  68 -G, and  68 -B may have uniform thicknesses (as in  FIG.  6   ) or may have different thicknesses if desired. 
     An arrangement of the type shown in  FIG.  6    has the benefit of omitting deposition steps for the intervening dielectric layers of  FIGS.  4  and  5   . Additionally, no conductive via is required through the intervening dielectric layers, allowing for the pixel aperture ratio to be increased relative to when a via is required. If the conductive materials used to form anode portions  42  and  44  are compatible for direct contact, the conductive spacer  68  may be omitted (e.g., from any of the red, green, and blue pixels). A via-less pixel design (e.g., as in all three pixels in  FIG.  6    where no intervening dielectric layers are present) may be used for all three pixel color types (as in  FIG.  6   ), one pixel color type (as in  FIG.  4   ), or any two pixel color types. 
     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: 20200529
Publication Date: 20230711
Grant Date: 20230711
Priority Date: 20190823
Inventors: WONG, GLORIA
CHOI, JAEIN
KANG, SUNGGU
TANG, HAIRONG
ZHU, XIAODAN
CHANG, Wendi
KUSTRA, KANUO C.
LIU, RUI
CHEN, CHENG
SASAGAWA, TERUO
BAE, WOOKYUNG
Assignee: APPLE INC
CPC Classifications: [{"code": "H10K50/824", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/121", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K50/818", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K50/818", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K2102/351", "inventive": false, "first": false, "tree": "[]"}, {"code": "H10K50/824", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/35", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/121", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/353", "inventive": true, "first": true, "tree": "[]"}, {"code": "H10K59/80515", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/80518", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/876", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/876", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/80515", "inventive": true, "first": false, "tree": "[]"}, {"code": "H10K59/80518", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 74646082