Patent Publication Number: US-2016226013-A1

Title: Organic Light-Emitting Diode Displays with Tilted and Curved Pixels

Description:
BACKGROUND 
     This relates generally to electronic devices with displays, and, more particularly, to organic light-emitting diode displays. 
     Electronic devices often include displays. Displays such as organic light-emitting diode displays have pixels with light-emitting diodes. The light emitting diodes each have electrodes (i.e., an anode and a cathode). Emissive material is interposed between the electrodes. During operation, current passes between the electrodes through the emissive material, generating light. 
     The electrodes in an organic light-emitting diode display are formed from a photolithographically patterned layer of conductive material such as indium tin oxide and/or metal. Unlike other conductive structures in a display such as signal lines that may be covered with opaque masking material, the light-emitting diode electrodes are exposed. The electrodes may therefore give rise to strong specular light reflections. This may cause ambient light to be reflected towards a viewer. These reflections can make it difficult to view images on the display. Ambient light reflections may be suppressed by covering a display with a circular polarizer, but use of a circular polarizer can significantly reduce light emission efficiency. In some organic light-emitting diode displays, microcavity structures have been used to enhance on-axis efficiency and reduce power consumption. This type of microcavity structure requires optimized organic layer thicknesses with proper electrode reflectivity. Such microcavities will typically result in significant off-axis intensity reductions and color shifts. 
     It would therefore be desirable to be able to provide organic light-emitting diode displays with enhanced specular reflection characteristics and reduced off-axis color and intensity shifts. 
     SUMMARY 
     An organic light-emitting diode display may have an array of light-emitting diodes that form an array of pixels. The array of pixels may be used to display images for a viewer. Each light-emitting diode may have a layer of emissive material interposed between an anode and a cathode. When current is passed between the anode and the cathode through the emissive material, the light-emitting diode will emit light. 
     Thin-film transistor circuitry may be used to form pixel circuits that control the current applied through the light-emitting diode of each pixel. The thin-film transistor circuitry may include transistors and thin-film capacitors and may be formed from semiconductor layers, dielectric layers, and metal layers on a substrate. 
     The substrate on which the thin-film transistor circuitry is formed has a surface. The electrodes that are formed for the light-emitting diodes may have surfaces that are not parallel to the surface of the substrate. The anodes may, for example, have curved surfaces or may have surfaces that are tilted with respect to the surface of the substrate. Tilted anodes may be tilted by an amount that varies across the surface of the display to enhance viewing characteristics for wide displays. Segmented anodes may be provided that have multiple tilted portions joined by connecting portions. Curved and tilted anodes may be used to redirect specular reflections away from a viewer and may help reduce off-axis intensity and color shifts. 
     Anodes that are tilted or curved may be formed by using grayscale masks to fabricate tilted or curved depressions in underlying layers in the thin-film transistor circuitry. Anodes may also be tilted or curved by incorporating tilt-inducing structures such as metal layers into portions of the thin-film transistor circuitry under the anodes. Metal layers or other tilt-inducing structures may, as an example, be formed under a thin polymer layer that becomes tilted due to the presence of the tilt-inducing structures. 
    
    
     
       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 top view of an illustrative display in an electronic device in accordance with an embodiment. 
         FIG. 3  is a cross-sectional side view of a portion of an illustrative organic light-emitting diode display in accordance with an embodiment. 
         FIG. 4  is cross-sectional side view of a portion of an illustrative organic light-emitting diode display with tilted anodes in accordance with an embodiment. 
         FIG. 5  is a diagram showing how the direction of specular reflections from a display may be adjusted by tilting anodes in the display by an appropriate amount in accordance with an embodiment. 
         FIG. 6  is a diagram showing how anodes in a display may be tilted by different amounts as a function of lateral position across the surface of the display in accordance with an embodiment. 
         FIG. 7  is a cross-sectional side view of an illustrative organic light-emitting diode display with curved anodes in accordance with an embodiment. 
         FIG. 8  is a top view of a portion of an illustrative organic light-emitting diode display showing how pixels of different colors may be arranged on the surface of the display in accordance with an embodiment. 
         FIG. 9  is a cross-sectional side view of a pixel in the illustrative organic light-emitting diode display of  FIG. 8  showing how pixels may be provide with tilted anodes that are divided into multiple smaller sections to avoid creating excessive height differences between the edges of the anodes in accordance with an embodiment. 
         FIG. 10  is a cross-sectional side view of a portion of an illustrative organic light-emitting diode display with an anode that has been tilted due to the presence of a portion of a source-drain metal layer under a polymer layer that supports the anode in accordance with an embodiment. 
         FIG. 11  is a cross-sectional side view of a portion of an illustrative organic light-emitting diode display with an anode that has been tilted due to the presence of a portion of an underlying metal layer located above a portion of a source-drain metal layer and a supplemental planarization layer 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 . As shown in  FIG. 1 , electronic device  10  may have control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for supporting the operation of device  10 . The storage and processing circuitry may include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be used to control the operation of device  10 . The processing circuitry may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, application specific integrated circuits, etc. 
     Input-output circuitry in device  10  such as input-output devices  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. 
     Control circuitry  16  may be used to run software on device  10  such as operating system code and applications. During operation of device  10 , the software running on control circuitry  16  may display images on display  14  using an array of pixels in display  14 . 
     Device  10  may be a tablet computer, laptop computer, a desktop computer, a display, a cellular telephone, a media player, a wristwatch device or other wearable electronic equipment, or other suitable electronic device. 
     Display  14  may be an organic light-emitting diode display or may be a display based on other types of display technology. Configurations in which display  14  is an organic light-emitting diode display are sometimes described herein as an example. This is, however, merely illustrative. Any suitable type of display may be used, if desired. 
     Display  14  may have a rectangular shape (i.e., display  14  may have a rectangular footprint and a rectangular peripheral edge that runs around the rectangular footprint) or may have other suitable shapes. Display  14  may be planar or may have a curved profile. 
     A top view of a portion of display  14  is shown in  FIG. 2 . As shown in  FIG. 2 , display  14  may have an array of pixels  22  formed on substrate  36 . Substrate  36  may be formed from glass, metal, plastic, ceramic, or other substrate materials. Pixels  22  may receive data signals over signal paths such as data lines D and may receive one or more control signals over control signal paths such as horizontal control lines G (sometimes referred to as gate lines, scan lines, emission control lines, etc.). There may be any suitable number of rows and columns of pixels  22  in display  14  (e.g., tens or more, hundreds or more, or thousands or more). Each pixel  22  may have a light-emitting diode  26  that emits light  24  under the control of a pixel control circuit formed from thin-film transistor circuitry such as thin-film transistors  28  and thin-film capacitors). Thin-film transistors  28  may be polysilicon thin-film transistors, semiconducting-oxide thin-film transistors such as indium zinc gallium oxide transistors, or thin-film transistors formed from other semiconductors. Pixels  22  may contain light-emitting diodes of different colors (e.g., red, green, and blue) to provide display  14  with the ability to display color images. 
     Display driver circuitry may be used to control the operation of pixels  22 . The display driver circuitry may be formed from integrated circuits, thin-film transistor circuits, or other suitable circuitry. Display driver circuitry  30  of  FIG. 2  may contain communications circuitry for communicating with system control circuitry such as control circuitry  16  of  FIG. 1  over path  32 . Path  32  may be formed from traces on a flexible printed circuit or other cable. During operation, the control circuitry (e.g., control circuitry  16  of  FIG. 1 ) may supply circuitry  30  with information on images to be displayed on display  14 . 
     To display the images on display pixels  22 , display driver circuitry  30  may supply image data to data lines D while issuing clock signals and other control signals to supporting display driver circuitry such as gate driver circuitry  34  over path  38 . If desired, circuitry  30  may also supply clock signals and other control signals to gate driver circuitry on an opposing edge of display  14 . 
     Gate driver circuitry  34  (sometimes referred to as horizontal control line control circuitry) may be implemented as part of an integrated circuit and/or may be implemented using thin-film transistor circuitry. Horizontal control lines G in display  14  may carry gate line signals (scan line signals), emission enable control signals, and other horizontal control signals for controlling the pixels of each row. There may be any suitable number of horizontal control signals per row of pixels  22  (e.g., one or more, two or more, three or more, four or more, etc.). 
     A cross-sectional side view of an illustrative organic light-emitting diode display is shown in  FIG. 3 . As shown in  FIG. 3 , display  14  may include a substrate layer such as substrate layer  36 . Substrate  36  may be a planar layer or a non-planar layer and may be formed from plastic, glass, ceramic, sapphire, metal, or other suitable materials. The surface of substrate  36  may, if desired, be covered with one or more buffer layers (e.g., inorganic buffer layers such as layers of silicon oxide, silicon nitride, etc.). 
     Thin-film transistor circuitry  48  may be formed on substrate  36 . Thin film transistor circuitry  48  may include transistors, capacitors, and other thin-film structures. As shown in  FIG. 3 , a transistor such as transistor  28  may be formed from thin-film semiconductor layer  60  in thin-film transistor layers  48 . Semiconductor layer  60  may be a polysilicon layer, a semiconducting-oxide layer such as a layer of indium gallium zinc oxide, or other semiconductor layer. Gate layer  56  may be a conductive layer such as a metal layer that is separated from semiconductor layer  60  by an intervening layer of dielectric such as dielectric  58  (e.g., an inorganic gate insulator layer such as a layer of silicon oxide). Dielectric  62  may also be used to separate semiconductor layer  60  from underlying structures such as shield layer  64  (e.g., a shield layer that helps shield the transistor formed from semiconductor layer  60  from charge in buffer layers on substrate  36 ). 
     Semiconductor layer  60  of transistor  28  may be contacted by source and drain terminals formed from source-drain metal layer  52 . Dielectric layer  54  (e.g., an inorganic dielectric layer) may separate gate metal layer  56  from source-drain metal layer  52 . Source-drain metal layer  52  may be shorted to anode  42  of light-emitting diode  26  using a metal via that passes through dielectric planarization layer  50 . Planarization layer  50  may be formed from an organic dielectric material such as a polymer. 
     Light-emitting diode  26  is formed from light-emitting diode layers  40  on thin-film transistor layers  48 . Each light-emitting diode has a lower electrode and an upper electrode. In a top emission display, the lower electrode may be formed from a reflective conductive material such as patterned metal to help reflect light that is produced by the light-emitting diode in the upwards direction out of the display. The upper electrode (sometimes referred to as the counter electrode) may be formed from a transparent or semi-transparent conductive layer (e.g., a thin layer of transparent or semitransparent metal and/or a layer of indium tin oxide or other transparent conductive material). This allows the upper electrode to transmit light outwards that has been produced by emissive material in the diode. In a bottom emission display, the lower electrode may be transparent (or semi-transparent) and the upper electrode may be reflective. 
     In configurations in which the anode is the lower electrode, layers such as a hole injection layer, hole transport layer, emissive material layer, and electron transport layer may be formed above the anode and below the upper electrode, which serves as the cathode for the diode. In inverted configurations in which the cathode is the lower electrode, layers such as an electron transport layer, emissive material layer, hole transport layer, and hole injection layer may be stacked on top of the cathode and may be covered with an upper layer that serves as the anode for the diode. Both electrodes may reflect light. 
     In general, display  14  may use a configuration in which the anode electrode is closer to the display substrate than the cathode electrode or a configuration in which the cathode electrode is closer to the display substrate than the anode electrode. In addition, both bottom emission and top emission arrangements may be used. Top emission display configurations in which the anode is located on the bottom and the cathode is located on the top are sometimes described herein as an example. This is, however, merely illustrative. Any suitable display arrangement may be used, if desired. 
     In the illustrative configuration of  FIG. 3 , display  14  has a top emission configuration and lower electrode  42  is an anode and upper electrode  46  is a cathode. Layers  40  include a patterned metal layer that forms anodes such as anode  42 . Anode  42  is formed within an opening in pixel definition layer  66 . Pixel definition layer  66  may be formed from a patterned photoimageable polymer. In each light-emitting diode, organic emissive material  44  is interposed between a respective anode  42  and cathode  46 . Anodes  42  may be patterned from a layer of metal on thin-film transistor layers  48  such as planarization layer  50 . Cathode  46  may be formed from a common conductive layer that is deposited on top of pixel definition layer  66 . Cathode  46  is transparent so that light  24  may exit light emitting diode  26  as current is flowing through emissive material  44  between anode  42  and cathode  46 . 
     In the illustrative configuration of  FIG. 3 , surface  68  of planarization layer  50  is flat and is parallel to surface  70  of substrate  36 . Anode  42  and the other layers of light-emitting diode layers  40  are therefore not tilted with respect to substrate  36 . 
     In the illustrative configuration of  FIG. 4 , planarization dielectric layer  50  has a thickness that varies as a function of lateral distance P along the surface of display  14  under diode  26 . As a result, surface  68  of planarization layer  50  in thin-film transistor circuitry  48  is tilted with respect to surface  70  of substrate  36 . Anode  42  is formed on surface  68  of planarization layer  50 , so the tilted orientation of planarization layer surface  68  causes anode  42  to tilt with respect to substrate surface  70 . 
     Substrate surface  70  of substrate  36  may be planar and may be characterized by surface normal N (i.e., a surface normal that is oriented parallel to outwardly extending dimension Z in the example of  FIG. 4 ). Anode  42  of  FIG. 4  has upper surface  72 . Anode surface  72  is planar and may be characterized by surface normal N′. Because dielectric layer  50  has a tilted (angled) surface that is not parallel to surface  70 , anode surface normal N′ is oriented at a non-zero angle A with respect to substrate surface normal N. Angle A may be 1-40°, 2-30°, 5-30°, 10-30°, 15-25°, more than 5°, more than 15°, less than 30°, or other suitable non-zero angle. 
     It may be desirable to incorporate display  14  into a device environment with an ambient light source. The ambient light source may be, for example, overhead lighting in an indoor environment, lighting from a laptop computer screen, or other light source. The ambient light source may produce light that has the potential to reflect directly into the eyes of a viewer. By tilting anodes  42  at an appropriate angle A as shown in  FIG. 4 , the reflected ambient light can be directed away from the viewer, so that images on the display are not obscured. The angular intensity of output light from the pixels of display  14  tends to gradually decrease with increasing angle, so an additional benefit of tilting anodes  42  is that this will tend to direct a higher emitting intensity into the eyes of the viewer. 
     Consider, as an example, the configuration of  FIG. 5 . As shown in  FIG. 5 , ambient light source  80  may emit ambient light  82 . Display  14  is lying in a horizontal plane in the illustrative arrangement of  FIG. 5  and viewer  88  is viewing the surface of display  14  at an angle B of about 45°, giving rise to the possibility that ambient light  82  will reflect from the anodes on the surface of display  14  into the eyes of viewer  88  (see, e.g., possible reflected ambient light ray  86 ). This type of layout may arise, for example, in a configuration in which device  10  is a laptop computer, light source  80  is a display mounted in the upper portion of a hinged laptop housing, and display  14  is an ancillary display located in the lower portion of the hinged laptop housing adjacent to the function keys of the laptop computer. This type of layout may also arise in other configurations (e.g., when display  14  is being used as part of a sign or other stationary display and when ambient light source  80  is part of a stationary indoor lighting system). Viewer  88  may also view display  14  at different angles and light source  80  may be located in different positions relative to display  14 . The example of  FIG. 5  in which display  14  is being viewed at a 45° angle so that light  82  has the potential to reflect towards viewer  88  as light  86  is merely illustrative. 
     When display  14  is operating, images will be present on display  14 . Viewer  88  may desire to view the content being displayed by display  14 . If care is not taken, specular reflections from the anodes of display  14  may cause reflected ambient light  86  to shine into the eyes of viewer  88  and obscure the image being displayed on display  14 . To prevent this from occurring, anodes  42  may be tilted at a non-zero angle A with respect to substrate  36 . For example, anodes  42  may be tilted towards viewer  88  by angle A. When anodes  42  are tilted in this way, ambient light  82  will reflect from tilted anodes  42  in the direction of reflected light ray  84  rather than in the direction of reflected light ray  86 . As shown in  FIG. 5 , reflected light ray  84  may be oriented at an angle of B-A with respect to display  14  when anodes  42  are tilted at angle A and may therefore pass by viewer  88 , whereas reflected light ray  86  from anodes that are not tilted would be reflected directly at viewer  88 . The ability of tilted anodes to redirect undesired specular reflections from display  14  so that reflected ambient light  84  is not reflected towards viewer  88  allows display  14  to be used in environments with potentially bright ambient light sources  80  without risk of interference from reflected ambient light. 
     Light  24  is emitted outwards from each anode  42  along surface normal N′. If desired, anodes  42  may be tilted by different angles A at different positions across the surface of display  14 . As shown in  FIG. 6 , for example, anodes near the edge of display  14  such as anode  42 E may be tilted at an angle A that is larger than anodes near the middle of display  14  such as anode  42 M. With this type of configuration, edge diodes will emit light  24 E that is directed towards a viewer such as viewer  88  who is located in front of the center of display  14  and light-emitting diodes in the center of display  14  will emit light  24 M that is directed towards this viewer. This type of tilting arrangement maximizes light-emitting diode emission efficiency while minimizing color shifts due to off-axis viewing. 
     Anodes  42  may be tilted (rotated) in one dimension or two dimensions. For example, each anode  42  may be rotated by a different angle A about axis Y as a function of the position of that anode  42  along lateral dimension X or each anode  42  may be rotated by different angles about both axes X and Y as a function of the position of that anode  42  in both lateral dimension X and lateral dimension Y (e.g., to accommodate large displays  14  in which the upper and lower edges of the display are far apart from each other as well as the left and right edges). In the example of  FIG. 6 , anodes  42  are have been rotated by varying amounts about axis Y. As shown in  FIG. 6 , anodes  42  to the left of viewer  88  are tilted inwardly to the right and anodes  42  to the right of viewer  88  are tilted inwardly to the left. Emitted light  24  is therefore directed towards viewer  88 , regardless of the location of the light-emitting diode producing that emitted light. For example, light that is emitted from diodes along the left edge of display  14  such as emitted light  24 E will be directed towards viewer  88  (or at least more towards viewer  88  than in a display without tilted anodes) even though these diodes are not located in the center of display  14  such as the diode associated with anode  42 M. 
     Another way in which to minimize intensity and color shifts when viewing off-axis pixels involves the use of curved anode structures of the type shown in  FIG. 7 . As shown in  FIG. 7 , anode  42  may have a curved cross-sectional shape. Anode  42  may, for example, be bowed inwardly towards the underlying thin-film transistor structures on display  14  and towards display substrate  36 . Configurations in which anodes  42  bow outwardly and/or have more complex non-planar surfaces may also be used. The inwardly curved shape of anode  42  in the configuration of  FIG. 7  is merely an example. 
     As shown in  FIG. 7 , dielectric layer  50  may have a curved surface  68  under anode  42 . Anode  42  may be formed in an opening in pixel definition layer  66  and may be supported on curved surface  68  of dielectric layer  50  under the opening in pixel definition layer  66 . This gives anode  42  a curved upper surface such as curved surface  72 . Emissive material  44  and cathode  46  will likewise be curved when deposited on curved surface  72 . The amount of curvature of anode  42  may be characterized by the ratio R of its depth to width. The value of R may be 0.1, 0.2, 0.3, 0.05-0.4, 0.01 to 0.5, 0.1 to 0.3, less than 0.4, more than 0.1, 0.1 to 0.35, or other suitable value. Larger values of R (e.g.,  0 . 3 ) may exhibit lower specular reflections and better off-axis intensity shift and color shift performance than lower values of R (e.g.,  0 . 1 ), but lower values of R may be used, if desired (e.g., to help minimize process complexity). Curved anodes may be implemented by forming dielectric layer  50  from a photoimageable polymer (e.g., by forming curved surface  68  using a graytone photomask and photolithographic patterning techniques). Curved depressions and, if desired, tilted depressions in the surface of dielectric layer  50  may also be formed using other fabrication techniques. The use of graytone masks and photolithographic fabrication techniques to form pixels with anodes  42  that are not parallel with the surface of substrate  36  is merely illustrative. 
     Pixels  22  may include pixels of different colors. For example, pixels  22  may include red pixels having red light-emitting diodes that emit red light, green pixels that have green light-emitting didoes that emit green light, and blue pixels that have blue light-emitting diodes that emit blue light.  FIG. 8  is a top view of a portion of display  14  showing how an illustrative set of red RD, blue BL, and green GR light-emitting diodes may be arranged on the surface of display  14 . This type of configuration may be used to provide the blue diodes with more anode area (e.g., to lower blue diode current levels to accommodate blue emissive material that is more sensitive to aging effects than red and green emissive material). 
     When tilting anodes  42 , it may be desirable to limit the maximum amount of tilt in each anode, thereby helping to maintain planarity in display  14 . Consider, as an example, a configuration in which it is desired to tilt the anodes of the red, green, and blue pixels of  FIG. 8  about tilt axis TL. In this type of configuration, tilt axis TL runs perpendicular to the longitudinal axes of the green and red anodes, so the green and red anodes will potentially exhibit a large amount of height difference between their lowest and highest portions when tilted. To limit the maximum amount of vertical height between the lowest and highest portions of the green and red anodes as the green and red anodes are tilted about tilt axis TL, the green and red anodes may be provided with multiple tilted segments.  FIG. 9  is a cross-sectional side view of a diode with this type of segmented anode configuration. The cross-sectional side view of  FIG. 9  is taken along line  90  of  FIG. 8  as viewed in direction  92 . 
     As shown in the segmented tilted anode arrangement of  FIG. 9 , anode  42  in diode  26  may have a first portion such as tilted segment  42 A and a second portion such as tilted segment  42 B. Dielectric layer  50  may be patterned to form a first tilted surface such as surface  68 A and a second tilted surface such as surface  68 B. Anode  42  may be formed from metal that is deposited and patterned on surfaces  68 A and  68 B. Anode portion  42 A is formed on tilted surface  68 A so surface  72 A of anode  42  is tilted. Anode portion  42 B is formed on tilted surface  68 B so surface  72 B of anode  42  is also tilted. The angle of tilt of portions  42 A and  42 B may be the same or may be different. 
     By using two tilted segments for anode  42 , the maximum height excursion of anode  42  may be minimized. In the absence of the segmented anode arrangement of  FIG. 9 , upper surface  72 ′ of anode  42  would exhibit a height excursion of HB (i.e., the difference in height between the tallest portion of anode  42  and the lowest portion of anode  42  would be HB). When anode  42  is segmented into portions  42 A and  42 B, each segment is narrower and therefore exhibits a smaller height excursion HL. Because HL is less than HB, the use of a segmented tilted anode arrangement may help reduce surface height excursions and may facilitate fabrication. There may be any suitable number of separately tilted portions of each anode  42 . The use of two tilted portions  42 A and  42 B in the example of  FIG. 9  is merely illustrative. 
     In the example of  FIG. 9 , pixel definition layer  66  has a central portion  66 ′ that lies between first anode segment  42 A and second anode segment  42 B. Segments  42 A and  42 B are connected by central connecting anode portion  42 ′. Central anode portion  42 ′ may have portions that reflect ambient light towards viewer  88 . It may be desirable to suppress these reflections by ensuring that pixel definition layer portion  66 ′ overlaps anode portion  42 ′. Alternatively, light emission may be maximized by omitting portion  66 ′ of pixel definition layer  66 . 
     Tilted anodes  42  may be formed by using a photoimageable polymer for forming dielectric layer  50  and by patterning the photoimageable polymer through a graytone mask, thereby forming tilted (or curved) surfaces such as tilted surfaces  68 A and  68 B of diode  26  of  FIG. 9 . If desired, tilted or curved surfaces such as tilted surfaces  68 A and  68 B of  FIG. 9 , tilted surface  68  of  FIG. 4 , curved surface  68  of  FIG. 7 , etc. may be formed by placing underlying metal structures in locations that cause dielectric layer  50  to exhibit tilted (or curved) surface portions. 
     Consider, as an example, the arrangement of  FIG. 10 . In the configuration of  FIG. 10 , a portion of source-drain layer  52  is being used to form source and drain terminals for transistor  28  and a portion of gate layer  56  is being used to form a gate terminal for transistor  28 . Portion  52 ′ of source-drain layer  52  and portion  56 ′ of gate layer  56  serve at tilt-inducing structures and are being used to create a step in height in the structures of thin-film transistor layers  48 . This step in height gives rise to tilted surface  68  in dielectric layer  50  and thereby tilts anode  42 . 
     In the illustrative configuration of  FIG. 11 , dielectric layer  50  has been formed from two dielectric layers  50 A and  50 B. Layers  50 A and  50 B may be formed from photoimageable polymers or other suitable dielectrics. Layer  50 A may be used as a planarization layer. If desired, metal structures  56 ′ and  52 ′ may be formed under layer  50 A to impart tilt to the surface of layer  50 A. After layer  50 A has been deposited, additional tilt-inducing structures such as structure  100  may be formed on the surface of layer  50 A. Structure  100  may be a photolithographically patterned portion of an additional layer of metal, may be a photolithographically patterned polymer structure, may be a photolithographically patterned dielectric layer, may be a structure that is patterned using non-photolithographic techniques, or may be any additional layer of material that helps impart a desired tilt to surface  68  of polymer layer  50 B. As shown in  FIG. 11 , the tilt in surface  68  that is created by additional structure  100  (and optional structures  52 ′ and/or  56 ′) causes anode  42  to tilt and exhibit tilted surface  72 . 
     Although sometimes described in the context of tilted anode configurations, display  14  may have a lower electrode that is either an anode or a cathode and an upper electrode (counter electrode) that is either a cathode or anode, respectively. Both the anode and the cathode will, in general, be tilted (or curved). The use of configurations in which anode  42  is located below cathode  46  is merely illustrative. 
     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.