Patent Publication Number: US-11659751-B2

Title: Stacked transparent pixel structures for electronic displays

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of U.S. patent application Ser. No. 15/724,027 filed Oct. 3, 2017 and entitled “Stacked Transparent Pixel Structures for Image Sensors,” now U.S. Pat. No. 10,930,709. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to pixels and more particularly to stacked transparent pixel structures for image sensors. 
     BACKGROUND 
     Pixels are utilized in a variety of electronic displays and sensors. For example, displays used in smartphones, laptop computers, and televisions utilize arrays of pixels to display images. As another example, sensors used in cameras utilize arrays of pixels to capture images. Pixels typically include subpixels of various colors such as red, green, and blue. 
     SUMMARY OF PARTICULAR EMBODIMENTS 
     In one embodiment, a system includes a substrate, a plurality of hexagon-shaped pixels coupled to the substrate, and a plurality of connector columns that electrically couple subpixels to the substrate. Each hexagon-shaped pixel includes a first subpixel formed on the substrate, a second subpixel stacked on top of the first subpixel, and a third subpixel stacked on top of the second subpixel. Each of the first, second, and third subpixels include a photodetector layer located between a transparent cathode layer and a transparent anode layer. Each transparent cathode layer and transparent anode layer of each subpixel is electrically coupled to the substrate through a respective one of the plurality of connector columns. 
     In another embodiment, a pixel for an image sensor includes a first subpixel and a second subpixel stacked on top of the first subpixel. Each of the first and second subpixels include a polygon shape. Each of the first and second subpixels include a photodetector layer, a transparent cathode layer, and a transparent anode layer. 
     In another embodiment, a method of manufacturing a pixel for an image sensor includes creating a first subpixel by performing at least four steps. The first step includes creating a transparent insulating layer by depositing a layer of transparent insulating material and then patterning the layer of transparent insulating material using lithography. The second step includes creating a transparent cathode layer of a subpixel by depositing a layer of transparent conductive material on the patterned transparent insulating layer and then patterning the transparent cathode layer using lithography, wherein patterning the transparent cathode layer comprises forming a portion of the transparent cathode layer into a polygon shape. The third step includes creating a photodetector layer of the subpixel by depositing a layer of photodetecting material on the patterned transparent cathode layer and then patterning the photodetector layer using lithography, wherein patterning the photodetector layer comprises forming a portion of the photodetector layer into the polygon shape. The fourth step includes creating a transparent anode layer of the subpixel by depositing a layer of transparent anode material on the patterned photodetector layer and then patterning the transparent anode layer using lithography, wherein patterning the transparent anode layer comprises forming a portion of the transparent anode layer into the polygon shape. The method further includes creating a second subpixel on top of the first subpixel by repeating the first, second, third, and fourth steps. 
     The present disclosure presents several technical advantages. In some embodiments, three subpixels (e.g., red, green, and blue) are vertically stacked on top of one another to create either display or sensor pixels. By vertically stacking the RGB subpixel components, certain embodiments remove the need for color filters and polarizers which are typically required in pixel technologies such as liquid crystal displays (LCD) and organic light-emitting diode (OLED). This results in smaller pixel areas and greater pixel densities for higher resolutions than typical displays. Some embodiments utilize electroluminescent quantum dot technology that provides more efficient use of power and significantly higher contrast ratios than technologies such as LCD can offer. Additionally, because each subpixel may be controlled directly by voltage, faster response times are possible than with technologies such as LCD. Embodiments that utilize quantum dots that are finely tuned to emit a very narrow band of color provide purer hues and improved color gamut over existing technologies such as OLED and LCD. Thin film design of certain embodiments results in substantial weight and bulk reduction. These and other advantages result in a low-cost, power efficient electronic display/sensor solution capable of high dynamic range output with a small enough pixel pitch to meet the needs of extremely high-resolution applications. 
     Other technical advantages will be readily apparent to one skilled in the art from  FIGS.  1  through  21   , their descriptions, and the claims. Moreover, while specific advantages have been enumerated above, various embodiments may include all, some, or none of the enumerated advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
         FIG.  1    illustrates a single display pixel with vertically stacked subpixels, according to certain embodiments; 
         FIGS.  2 - 3    illustrate exploded views of the display pixel of  FIG.  1   , according to certain embodiments; 
         FIG.  4    illustrates an array of pixels with stacked subpixels, according to certain embodiments; 
         FIG.  5    is a method of manufacturing a display pixel with stacked subpixels, according to certain embodiments; 
         FIG.  6 A  illustrates a first insulating layer of the pixel of  FIG.  1   , according to certain embodiments; 
         FIG.  6 B  illustrates a portion of a photomask used to manufacture the first insulating layer of  FIG.  6 A , according to certain embodiments; 
         FIG.  7 A  illustrates a cathode layer of the first subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  7 B  illustrates a portion of a photomask used to manufacture the cathode layer of  FIG.  7 A , according to certain embodiments; 
         FIG.  8 A  illustrates an emissive layer of the first subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  8 B  illustrates a portion of a photomask used to manufacture the emissive layer of  FIG.  8 A , according to certain embodiments; 
         FIG.  9 A  illustrates an anode layer of the first subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  9 B  illustrates a portion of a photomask used to manufacture the anode layer of  FIG.  9 A , according to certain embodiments; 
         FIG.  10 A  illustrates a second insulating layer of the pixel of  FIG.  1   , according to certain embodiments; 
         FIG.  10 B  illustrates a portion of a photomask used to manufacture the second insulating layer of  FIG.  10 A , according to certain embodiments; 
         FIG.  11 A  illustrates a cathode layer of the second subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  11 B  illustrates a portion of a photomask used to manufacture the cathode layer of  FIG.  11 A , according to certain embodiments; 
         FIG.  12 A  illustrates an emissive layer of the second subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  12 B  illustrates a portion of a photomask used to manufacture the emissive layer of  FIG.  12 A , according to certain embodiments; 
         FIG.  13 A  illustrates an anode layer of the second subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  13 B  illustrates a portion of a photomask used to manufacture the anode layer of  FIG.  13 A , according to certain embodiments; 
         FIG.  14 A  illustrates a third insulating layer of the pixel of  FIG.  1   , according to certain embodiments; 
         FIG.  14 B  illustrates a portion of a photomask used to manufacture the third insulating layer of  FIG.  14 A , according to certain embodiments; 
         FIG.  15 A  illustrates a cathode layer of the third subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  15 B  illustrates a portion of a photomask used to manufacture the cathode layer of  FIG.  15 A , according to certain embodiments; 
         FIG.  16 A  illustrates an emissive layer of the third subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  16 B  illustrates a portion of a photomask used to manufacture the emissive layer of  FIG.  16 A , according to certain embodiments; 
         FIG.  17 A  illustrates an anode layer of the third subpixel of  FIG.  1   , according to certain embodiments; 
         FIG.  17 B  illustrates a portion of a photomask used to manufacture the anode layer of  FIG.  17 A , according to certain embodiments; 
         FIG.  18    illustrates a single sensor pixel with vertically stacked subpixels, according to certain embodiments; 
         FIGS.  19 - 20    illustrate exploded views of the sensor pixel of  FIG.  18   , according to certain embodiments; and 
         FIG.  21    is a method of manufacturing a sensor pixel with stacked subpixels, according to certain embodiments. 
     
    
    
     DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS 
     Pixels are utilized in a variety of electronic displays and sensors. For example, displays used in smartphones, laptop computers, and televisions utilize arrays of pixels to display images. As another example, sensors used in cameras utilize arrays of pixels to capture images. Pixels may in some instances include subpixels of various colors. For example, some pixels may include red, blue, and green subpixels. Subpixels are typically co-planar and adjacent to each other within a pixel. Having co-planar subpixels may be problematic in some applications, however, due to physical size requirements. For example, some electronic displays require an extremely small pixel pitch (i.e., the distance between each pixel) to provide enough resolution for visual acuity. Doing so with a high dynamic range is problematic given the lower light output due to physical size reduction of the pixels themselves and the circuitry normally surrounding them. 
     To address these and other problems with existing pixel designs, embodiments of the disclosure provide pixels with vertically stacked subpixels that reduces the physical space required for each pixel. For example, some embodiments include three transparent overlapping red, green, and blue subpixels that are vertically stacked on top of one another. By vertically stacking the subpixels instead of locating them within the same plane, a higher number of pixels can be fit into a display or sensor area, thus providing the high pixel densities required by certain applications. 
     In embodiments that emit light (e.g., pixels for electronic displays), light emitted from the vertically stacked subpixels is additively combined to create the full color representation. This is in contrast to existing technologies that utilize subtraction with filters and polarization to create various colors of light. In some embodiments, each individual subpixel structure includes a transparent front emissive plane and a transparent back circuitry plane. The front plane may include transparent conductive film electrodes, charge injection layers, and a tuned color-specific electroluminescent quantum dot layer. Driving circuitry for each subpixel is accomplished by a back plane of layered transparent transistor/capacitor arrays to handle voltage switching and storage for each subpixel. Example embodiments of display pixels are illustrated in  FIGS.  1 - 3   , and a method of manufacturing display pixels is illustrated in  FIG.  5   . 
     In embodiments that sense light (e.g., pixels for sensor arrays), light entering the vertically stacked subpixels passes through to subsequent layers, with narrow bands of light captured by each subpixel layer for accurate color imaging. In some embodiments, each individual subpixel structure is an assembly of transparent layers of tuned color-specific photoelectric quantum dot films, conductive films, and semiconductor films that are patterned to create a phototransistor array. Readout from this array carries voltage from specific pixels only in response to the amount of color present in the light entering a given subpixel layer. Since each layer is tuned to detect only a particular band of light, photoelectric voltage is produced according to the percentage of that band contained within the wavelength of the incoming light. Example embodiments of sensor pixels are illustrated in  FIGS.  18 - 20   , and a method of manufacturing sensor pixels is illustrated in  FIG.  21   . 
     To facilitate a better understanding of the present disclosure, the following examples of certain embodiments are given. The following examples are not to be read to limit or define the scope of the disclosure. Embodiments of the present disclosure and its advantages are best understood by referring to  FIGS.  1 - 21   , where like numbers are used to indicate like and corresponding parts. 
       FIGS.  1 - 4    illustrate various views of a single display pixel  100  with vertically stacked subpixels  110 .  FIG.  1    illustrates an assembled pixel  100 ,  FIGS.  2 - 3    illustrate different exploded views of pixel  100 , and  FIG.  4    illustrates an array of pixels  100 . In general, these figures depict the conductive portions of the illustrated layers. Other insulating areas (e.g., outside and between the subpixel stacks) have been removed for sake of visual clarity. 
     Display pixel  100  may be utilized in any electronic display such as a display of a smartphone, laptop computer, television, a near-eye display (e.g., a head-mounted display), a heads-up display (HUD), and the like. In general, pixel  100  includes multiple subpixels  110  that are vertically stacked on one another. For example, some embodiments of pixel  100  may include three subpixels  110 : first subpixel  110 A formed on a substrate (e.g., backplane driving circuitry), second subpixel  110 B that is stacked on top of first subpixel  110 A, and third subpixel  110 C that is stacked on top of second subpixel  110 B. In a particular embodiment, first subpixel  110 A is a red subpixel (i.e., first subpixel  110 A emits red light), second subpixel  110 B is a green subpixel (i.e., second subpixel  110 B emits green light), and third subpixel  110 C is a blue subpixel (i.e., third subpixel  110 C emits blue light). However, other embodiments may include any other order of red, green, and blue subpixels  110  (e.g., RBG, GRB, GBR, BRG, or BGR). Furthermore, some embodiments may include more or few numbers of subpixels  110  than what is illustrated in  FIGS.  1 - 4    and may include any other appropriate colors of subpixels (e.g., yellow, amber, violet, etc.) or non-visible wavelengths. 
     In some embodiments, pixel  100  is coupled to backplane circuitry  120  which may be formed on a substrate or backplane. In some embodiments, circuitry  120  includes layered transparent transistor/capacitor arrays to handle voltage switching and storage for each subpixel  110 . Various layers of each subpixel  110  (e.g., anode layers  220  and cathode layers  230  as described below) may be electrically coupled to circuitry  120  via connector columns  130  and connection pads  140 . For example, first subpixel  110 A may be coupled to circuitry  120  via connector columns  130 A and  130 B and connection pads  140 A and  140 B, second subpixel  110 B may be coupled to circuitry  120  via connector columns  130 C and  130 D and connection pads  140 C and  140 D, and third subpixel  110 C may be coupled to circuitry  120  via connector columns  130 E and  130 F and connection pads  140 E and  140 F, as illustrated. As a result, each subpixel  110  may be individually addressed and controlled by circuitry  120 . 
     As illustrated in detail in  FIGS.  2 - 3   , each subpixel  110  may include at least three layers: an emissive layer  210 , an anode layer  220 , and a cathode layer  230 . For example, subpixel  110 A may include at least a cathode layer  230 A, an emissive layer  210 A on top of cathode layer  230 A, and an anode layer  220 A on top of emissive layer  210 A. Likewise, subpixel  110 B may include at least a cathode layer  230 B, an emissive layer  210 B on top of cathode layer  230 B, and an anode layer  220 B on top of emissive layer  210 B. Similarly, subpixel  110 C may include at least a cathode layer  230 C, an emissive layer  210 C on top of cathode layer  230 C, and an anode layer  220 C on top of emissive layer  210 C. In other embodiments, subpixels  110  may include additional layers that are not illustrated in  FIGS.  2 - 3   . For example, some embodiments of subpixels  110  may include additional insulating layers  310  that are not specifically illustrated. As a specific example, some embodiments of emissive layers  210  may include multiple sub-layers of OLED emission architectures or electroluminescent quantum dot architectures. 
     Anode layers  220  and cathode layers  230  are formed, respectively, from any appropriate anode or cathode material. For example, anode layers  220  and cathode layers  230  may include simple conductive polymers (or similar materials) used as transparent electrodes. In general, anode layers  220  and cathode layers  230  are transparent so that light may pass from emissive layers  210  and combine with light from subsequent subpixels  110 . 
     Emissive layers  210  generally are formed from any appropriate material capable of emitting light while supporting transparency. In some embodiments, emissive layers  210  may include both electroluminescent capabilities (e.g., a diode converting electric current into light) and photoluminescent capabilities (for down-converting incoming higher-energy light to lower-energy wavelengths). For example, emissive layers  210  may be tuned color-specific electroluminescent quantum dot (QD) layers such as quantum-dot-based light-emitting diode (QLED) layers. In some embodiments, emissive layers  210  may be organic light-emitting diode (OLED) layers. In general, emissive layers  210  may be precisely tuned for narrow band emission of specific wavelengths of light (e.g., red, green, and blue). By using electroluminescent QD emissive layers  210 , certain embodiments provide 1) more efficient use of power than other methods such as liquid crystal displays (LCD), and 2) significantly higher contrast ratios than other technologies such as LCD can offer. And because each subpixel  110  is controlled directly by voltage, faster response times are possible than with technologies such as LCD. Furthermore, implementing quantum dots which are finely tuned to emit a very narrow band of color provides purer hues and improved color gamut over both OLED and LCD technologies. 
     In some embodiments, pixels  100  and subpixels  110  have an overall shape of a polygon when viewed from above. For example, pixels  100  and subpixels  110  may be hexagon-shaped, octagon-shaped, or the shape of any other polygon such as a triangle or quadrangle. To achieve the desired shape, each layer of subpixel  110  may be formed in the desired shape. For example, each of anode layer  220 , emissive layer  210 , and cathode layer  230  may be formed in the shape of the desired polygon. As a result, each side of pixel  100  may be adjacent to a side of another pixel  100  as illustrated in  FIG.  4   . For example, if pixel  100  is in the shape of a hexagon, each pixel  100  in an array of pixels such as array  400  is adjacent to six other pixels  100 . Furthermore, each side of each individual pixel  100  is adjacent to a side of a respective one of the six other hexagon-shaped pixels  100 . In this way, the emissive area of the overall display surface is maximized since only very narrow non-conductive boundaries are patterned between each pixel. This diminishes the percentage of non-emissive “dark” areas within array  400 . 
     Embodiments of pixels  100  include multiple connector columns  130  that electrically connect the various layers of subpixels  110  to circuitry  120  via connection pads  140 . For example, in some embodiments, pixel  100  includes six connector columns  130 : connector column  130 A that couples cathode layer  230 A of subpixel  110 A to circuitry  120 , connector column  130 B that couples anode layer  220 A of subpixel  110 A to circuitry  120 , connector column  130 C that couples cathode layer  230 B of subpixel  110 B to circuitry  120 , connector column  130 D that couples anode layer  220 B of subpixel  110 B to circuitry  120 , connector column  130 E that couples cathode layer  230 C of subpixel  110 C to circuitry  120 , and connector column  130 F that couples anode layer  220 C of subpixel  110 C to circuitry  120 . 
     In general, connector columns  130  are connected only to a single layer of pixel  100  (i.e., a single anode layer  220  or cathode layer  230 ), thereby permitting circuitry  120  to uniquely address each anode layer  220  and cathode layer  230  of pixel  100 . For example, connector column  130 F is coupled only to anode layer  220 C of subpixel  110 C, as illustrated. Connector columns  130  are built up with one or more connector column portions  135 , as illustrated in  FIGS.  6 A- 16 B . Each connector column portion  135  is an island of material that is electrically isolated from the layer on which it is formed, but permits an electrical connection between the various layers of connector column  130 . Connector columns  130  are generally adjacent to a single side of pixel  100  and occupy less than half of the length of a single side of pixel  100  in order to allow enough space for a connector column  130  of an adjacent pixel  100 . For example, as illustrated in  FIG.  4   , connector column  130 E of pixel  100 A occupies one side of pixel  100  but leaves enough space for connector column  130 B of pixel  100 B. In addition, the connector columns  130  of a particular pixel  100  all have unique heights, in some embodiments. In the illustrated embodiment, for example, connector column  130 F is the full height of pixel  100 , while connector column  130 B is only as tall as subpixel  110 A. That is, the height of a particular connector column  130  may depend on the path of the particular connector column  130  to its connection pad  140 . Connector columns  130  may be any appropriate size or shape. For example, connector columns  130  may be in the shape of a square, rectangle, circle, triangle, trapezoid, or any other appropriate shape. 
     Embodiments of pixel  100  may have one or more insulating layers  310 , as illustrated in  FIGS.  2 - 3   . For example, some embodiments of pixel  100  may include a first insulating layer  310 A between cathode layer  230 A of subpixel  110 A and circuitry  120 , a second insulating layer  310 B between cathode layer  230 B of subpixel  110 B and anode layer  220 A of subpixel  110 A, and a third insulating layer  310 C between cathode layer  230 C of subpixel  110 C and anode layer  220 B of subpixel  110 B. Insulating layers  310  may be any appropriate material that electrically isolates adjacent layers of pixel  100 . 
       FIG.  5    illustrates a method  500  of manufacturing a display pixel with stacked subpixels. For example, method  500  may be used to manufacture pixel  100  having stacked subpixels  110 , as described above. Method  500 , in general, utilizes steps  510 - 540  to create layers of a subpixel using lithography. The various layers created by these steps and the photomasks that may be utilized to create the various layers are illustrated in  FIGS.  6 A- 17 B , wherein the insulating material has been removed from the layers to allow a better view of the structure of conductive elements. As described in more detail below, steps  510 - 540  may be repeated one or more times to create stacked subpixels such as subpixels  110  of pixel  100 . For example, steps  510 - 540  may be performed a total of three times to create stacked subpixels  110 A- 110 C, as described above. 
     Method  500  may begin in step  510  where a transparent insulating layer is created by depositing a layer of transparent insulating material and then patterning the layer of transparent insulating material using lithography. In some embodiments, the transparent insulating layer is insulating layer  310 A, which is illustrated in  FIG.  6 A . In some embodiments, the layer of transparent insulating material is deposited on a substrate or backplane that includes circuitry  120 , as described above. In some embodiments, the layer of transparent insulating material is patterned into the transparent insulating layer using photolithography. A portion of a photomask  600  that may be utilized by this step to pattern the layer of transparent insulating material into the transparent insulating layer is illustrated in  FIG.  6 B . 
     At step  520 , a transparent cathode layer of a subpixel is created by depositing a layer of transparent conductive material on the patterned transparent insulating layer of step  510  and then patterning the transparent cathode layer using lithography such as photolithography. In some embodiments, the transparent cathode layer is cathode layer  230 A, which is illustrated in  FIG.  7 A . A portion of a photomask  700  that may be utilized by this step to pattern the layer of transparent conductive material into the transparent cathode layer is illustrated in  FIG.  7 B . In some embodiments, patterning the transparent cathode layer includes forming a portion of the transparent cathode layer into a polygon shape, such as a hexagon or an octagon. For example, as illustrated in  FIG.  7 B , the transparent cathode layer of a single subpixel may have an overall shape of a hexagon when viewed from above and may include a portion of a connector column  130  (e.g., in the shape of a rectangle or a square) coupled to one side of the hexagon shape. 
     At step  530 , an emissive layer of a subpixel is created by depositing a layer of emissive material on the patterned transparent cathode layer of step  520  and then patterning the emissive layer using lithography such as photolithography. In some embodiments, the emissive layer is emissive layer  210 A, which is illustrated in  FIG.  8 A . A portion of a photomask  800  that may be utilized by this step to pattern the layer of emissive material into the emissive layer is illustrated in  FIG.  8 B . In some embodiments, patterning the emissive layer includes forming a portion of the emissive layer into a polygon shape, such as a hexagon or an octagon. For example, as illustrated in  FIG.  8 B , the emissive layer of a single subpixel may have an overall shape of a hexagon when viewed from above. Unlike the transparent cathode layer of step  520 , the sides of the hexagon shape of the emissive layer of this step may be devoid of any portions of connector columns  130 . 
     In some embodiments, the color output of the emissive layers of step  530  are precisely tuned for narrow band emission, resulting in extremely accurate color representation. In some embodiments, high contrast ratios are achievable due to the lack of additional polarizers or filtering necessary to govern the light output of each subpixel. This results in high dynamic range image reproduction with minimal required driving voltage. 
     At step  540 , a transparent anode layer of a subpixel is created by depositing a layer of transparent anode material on the patterned emissive layer of step  530  and then patterning the transparent anode layer using lithography such as photolithography. In some embodiments, the transparent anode layer is anode layer  220 A, which is illustrated in  FIG.  9 A . A portion of a photomask  900  that may be utilized by this step to pattern the layer of transparent anode material into the transparent anode layer is illustrated in  FIG.  9 B . In some embodiments, patterning the transparent anode layer includes forming a portion of the transparent anode layer into a polygon shape, such as a hexagon or an octagon. For example, as illustrated in  FIG.  9 B , the transparent anode layer of a single subpixel may have an overall shape of a hexagon when viewed from above and may include a portion of a connector column  130  (e.g., in the shape of a rectangle or a square) coupled to one side of the hexagon shape. 
     At step  550 , method  500  determines whether to repeat steps  510 - 540  based on whether additional subpixels are to be formed. Using the example embodiment of  FIG.  1   , for example, method  500  would repeat steps  510 - 540  two additional times in order to create second subpixel  110 B on top of first subpixel  110 A and then third subpixel  110 C on top of second subpixel  110 B. To create second subpixel  110 B on top of first subpixel  110 A, method  500  would repeat steps  510 - 540  to create the various layers illustrated in  FIGS.  10 A,  11 A,  12 A , and,  13 A, respectively. Portions of photomasks  1000 ,  1100 ,  1200 , and  1300  that may be utilized by these steps to create second subpixel  110 B are illustrated in  FIGS.  10 B,  11 B,  12 B , and,  13 B, respectively. To create third subpixel  110 C on top of second subpixel  110 B, method  500  would repeat steps  510 - 540  to create the various layers illustrated in  FIGS.  14 A,  15 A,  16 A , and,  17 A, respectively. Portions of photomasks  1400 ,  1500 ,  1600 , and  1700  that may be utilized by these steps to create third subpixel  110 C are illustrated in  FIGS.  14 B,  15 B,  16 B , and,  17 B, respectively. 
     In some embodiments, method  500  may include forming additional layers that are not specifically illustrated in  FIG.  5   . For example, additional layers such as insulating layers  310  may be formed by method  500  at any appropriate location. As another example, some embodiments may include one or more additional layers of graphene or other similar electrically-enhancing materials in order to improve efficiency and conductivity. 
     As described above, pixels with vertically stacked subpixels may be utilized as either display or sensor pixels. The previous figures illustrated embodiments of display pixels  100  that include emissive layers  210 . The following  FIGS.  18 - 20   , however, illustrate embodiments of sensor pixels  1800  with vertically stacked subpixels  110  that include photodetector layers  1910  in place of emissive layers  210 .  FIG.  18    illustrates an assembled sensor pixel  1800  and  FIGS.  19 - 20    illustrate different exploded views of sensor pixel  1800 . In general, these figures depict the conductive portions of the illustrated layers. Other insulating areas (e.g., outside and between the subpixel stacks) have been removed for sake of visual clarity. 
     Sensor pixel  1800  may be utilized in any electronic devices such as cameras that are used to sense or capture light (e.g., photos and videos). Like display pixel  100 , sensor pixel  1800  includes multiple subpixels  110  that are vertically stacked on top of one another. For example, some embodiments of pixel  1800  may include three subpixels  110 : first subpixel  110 A, second subpixel  110 B that is stacked on top of first subpixel  110 A, and third subpixel  110 C that is stacked on top of second subpixel  110 B. In a particular embodiment, first subpixel  110 A is a red subpixel (i.e., first subpixel  110 A detects red light), second subpixel  110 B is a green subpixel (i.e., second subpixel  110 B detects green light), and third subpixel  110 C is a blue subpixel (i.e., third subpixel  110 C detects blue light). However, other embodiments may include any other order of red, green, and blue subpixels  110 . Furthermore, some embodiments may include more or few numbers of subpixels  110  than what is illustrated in  FIGS.  18 - 20    and may include any other appropriate colors of subpixels (e.g., violet, etc.). 
     Like display pixel  100 , sensor pixel  1800  may be coupled to backplane circuitry  120 . In some embodiments, circuitry  120  includes layered transparent transistor/capacitor arrays to handle voltage switching and storage for each subpixel  110  of pixel  1800 . Various layers of each subpixel  110  (e.g., anode layers  220  and cathode layers  230  as described above) may be electrically coupled to circuitry  120  via connector columns  130  and connection pads  140 . For example, first subpixel  110 A may be coupled to circuitry  120  via connector columns  130 A and  130 B and connection pads  140 A and  140 B, second subpixel  110 B may be coupled to circuitry  120  via connector columns  130 C and  130 D and connection pads  140 C and  140 D, and third subpixel  110 C may be coupled to circuitry  120  via connector columns  130 E and  130 F and connection pads  140 E and  140 F, as illustrated. As a result, each subpixel  110  may be individually addressed and controlled by circuitry  120 . 
     As illustrated in detail in  FIGS.  19 - 20   , each subpixel  110  of sensor pixel  1800  may include at least three layers: a photodetector layer  1910 , an anode layer  220 , and a cathode layer  230 . For example, subpixel  110 A may include at least a cathode layer  230 A, a photodetector layer  1910 A on top of cathode layer  230 A, and an anode layer  220 A on top of photodetector layer  1910 A. Likewise, subpixel  110 B may include at least a cathode layer  230 B, a photodetector layer  1910 B on top of cathode layer  230 B, and an anode layer  220 B on top of photodetector layer  1910 B. Similarly, subpixel  110 C may include at least a cathode layer  230 C, a photodetector layer  1910 C on top of cathode layer  230 C, and an anode layer  220 C on top of photodetector layer  1910 C. In other embodiments, subpixels  110  may include additional layers that are not illustrated in  FIGS.  18 - 20   . For example, some embodiments of subpixels  110  may include additional insulating layers  310  that are not specifically illustrated. As another example, some embodiments may include one or more additional layers of graphene or other similar electrically-enhancing materials in order to improve efficiency and conductivity. 
     As discussed above with respect to  FIGS.  2 - 3   , anode layers  220  and cathode layers  230  are formed, respectively, from any appropriate anode or cathode material. In general, anode layers  220  and cathode layers  230  are transparent so that light may pass through them and into photodetector layers  1910 . Only narrow bands of light are captured by each photodetector layer  1910  for accurate color imaging. 
     Photodetector layers  1910  generally are formed from any appropriate material capable of detecting light while supporting transparency. For example, photodetector layers  1910  may be tuned color-specific electroluminescent QD layers such as QLED layers. In some embodiments, photodetector layers  1910  may be OLED layers. In some embodiments, photodetector layers  1910  may be precisely tuned for narrow band detection of specific wavelengths of light (e.g., red, green, and blue). By using electroluminescent QD photodetector layers  1910 , certain embodiments provide 1) improved color gamut in the resulting imagery since precisely-tuned photoelectric quantum dot films are used to capture only the band of light necessary for a given subpixel, and 2) greatly improved shutter speeds over traditional CMOS image sensors due to very fast response times of quantum dot photoelectric materials. 
     In some embodiments, photodetector layers  1910  utilize any transparent photodetector material in combination with unique color filtering instead of QD photodetectors. For example, as depicted in  FIG.  19   , full spectrum light may first enter sensor pixel  1800  from the top (i.e., through third subpixel  110 C). Third subpixel  110 C may include a specific color filter as an additional “sub-layer” (e.g., within photodetector layer  1910 ) to allow only certain wavelengths of light to pass through. Second subpixel  110 B may include a color filter of a different specific color to allow only other certain wavelengths of light to pass through to first subpixel  110 A beneath it. By mathematically subtracting the readout signals from each of these subpixels  110 , sensor pixel  1800  may be able to isolate specific colors from the upper two subpixels (e.g.,  110 C and  110 B), thus outputting a full RGB signal. 
     In some embodiments, sensor pixels  1800  and subpixels  110  have an overall shape of a polygon when viewed from above. For example, pixels  1800  and subpixels  110  may be hexagon-shaped, octagon-shaped, or the shape of any other polygon. To achieve the desired shape, each layer of subpixel  110  may be formed in the desired shape. For example, each of anode layer  220 , photodetector layer  1910 , and cathode layer  230  may be formed in the shape of the desired polygon. As a result, each side of pixel  1800  may be adjacent to a side of another pixel  1800 , similar to pixels  100  as illustrated in  FIG.  4   . For example, if pixel  1800  is in the shape of a hexagon, each pixel  1800  in an array of pixels such as array  400  is adjacent to six other pixels  1800 . Furthermore, each side of each individual pixel  1800  is adjacent to a side of a respective one of the six other hexagon-shaped pixels  1800 . In this way, the sensitive area of the overall display surface is maximized since only very narrow non-conductive boundaries are patterned between each pixel. This diminishes the percentage of non-emissive “dark” areas within an array of pixels  1800 . 
     Like display pixels  100 , embodiments of sensor pixels  1800  include multiple connector columns  130  that electrically connect the various layers of subpixels  110  to circuitry  120  via connection pads  140 . For example, in some embodiments, pixel  1800  includes six connector columns  130 : connector column  130 A that couples cathode layer  230 A of subpixel  110 A to circuitry  120 , connector column  130 B that couples anode layer  220 A of subpixel  110 A to circuitry  120 , connector column  130 C that couples cathode layer  230 B of subpixel  110 B to circuitry  120 , connector column  130 D that couples anode layer  220 B of subpixel  110 B to circuitry  120 , connector column  130 E that couples cathode layer  230 C of subpixel  110 C to circuitry  120 , and connector column  130 F that couples anode layer  220 C of subpixel  110 C to circuitry  120 . 
       FIG.  21    illustrates a method  2100  of manufacturing a sensor pixel with stacked subpixels. For example, method  2100  may be used to manufacture pixel  1800  having stacked subpixels  110 , as described above. Method  2100 , in general, utilizes steps  2110 - 2140  to create layers of a subpixel using lithography. The various layers created by these steps and the photomasks that may be utilized to create the various layers are illustrated in  FIGS.  6 A- 17 B , except that emissive layers  210  are replaced by photodetector layers  1910 . As described in more detail below, steps  2110 - 2140  may be repeated one or more times to create stacked subpixels such as subpixels  110  of pixel  1800 . For example, steps  2110 - 2140  may be performed a total of three times to create stacked subpixels  110 A- 110 C, as described above. 
     Method  2100  may begin in step  2110  where a transparent insulating layer is created by depositing a layer of transparent insulating material and then patterning the layer of transparent insulating material using lithography. In some embodiments, the transparent insulating layer is insulating layer  310 A, which is illustrated in  FIG.  6 A . In some embodiments, the layer of transparent insulating material is deposited on a substrate or backplane that includes circuitry  120 , as described above. In some embodiments, the layer of transparent insulating material is patterned into the transparent insulating layer using photolithography. A portion of a photomask  600  that may be utilized by this step to pattern the layer of transparent insulating material into the transparent insulating layer is illustrated in  FIG.  6 B . 
     At step  2120 , a transparent cathode layer of a subpixel is created by depositing a layer of transparent conductive material on the patterned transparent insulating layer of step  2110  and then patterning the transparent cathode layer using lithography such as photolithography. In some embodiments, the transparent cathode layer is cathode layer  230 A, which is illustrated in  FIG.  7 A . A portion of a photomask  700  that may be utilized by this step to pattern the layer of transparent conductive material into the transparent cathode layer is illustrated in  FIG.  7 B . In some embodiments, patterning the transparent cathode layer includes forming a portion of the transparent cathode layer into a polygon shape, such as a hexagon or an octagon. For example, as illustrated in  FIG.  7 B , the transparent cathode layer of a single subpixel may have an overall shape of a hexagon when viewed from above and may include a portion of a connector column  130  (e.g., in the shape of a rectangle or a square) coupled to one side of the hexagon shape. 
     At step  2130 , a photodetector layer of a subpixel is created by depositing a layer of photodetector material on the patterned transparent cathode layer of step  2120  and then patterning the photodetector layer using lithography such as photolithography. In some embodiments, the photodetector layer is photodetector layer  1910 A, which is illustrated in  FIG.  8 A  (except that emissive layer  210 A is replaced by photodetector layer  1910 A). A portion of a photomask  800  that may be utilized by this step to pattern the layer of photodetector material into the photodetector layer is illustrated in  FIG.  8 B . In some embodiments, patterning the photodetector layer includes forming a portion of the photodetector layer into a polygon shape, such as a hexagon or an octagon. For example, as illustrated in  FIG.  8 B , the photodetector layer of a single subpixel may have an overall shape of a hexagon when viewed from above. Unlike the transparent cathode layer of step  2120 , the sides of the hexagon shape of the photodetector layer of this step may be devoid of any portions of connector columns  130 . 
     At step  2140 , a transparent anode layer of a subpixel is created by depositing a layer of transparent anode material on the patterned photodetector layer of step  2130  and then patterning the transparent anode layer using lithography such as photolithography. In some embodiments, the transparent anode layer is anode layer  220 A, which is illustrated in  FIG.  9 A . A portion of a photomask  900  that may be utilized by this step to pattern the layer of transparent anode material into the transparent anode layer is illustrated in  FIG.  9 B . In some embodiments, patterning the transparent anode layer includes forming a portion of the transparent anode layer into a polygon shape, such as a hexagon or an octagon. For example, as illustrated in  FIG.  9 B , the transparent anode layer of a single subpixel may have an overall shape of a hexagon when viewed from above and may include a portion of a connector column  130  (e.g., in the shape of a rectangle or a square) coupled to one side of the hexagon shape. 
     At step  2150 , method  2100  determines whether to repeat steps  2110 - 2140  based on whether additional subpixels are to be formed for pixel  1800 . Using the example embodiment of  FIG.  18   , for example, method  2100  would repeat steps  2110 - 2140  two additional times in order to create second subpixel  110 B on top of first subpixel  110 A and then third subpixel  110 C on top of second subpixel  110 B. To create second subpixel  110 B on top of first subpixel  110 A, method  2100  would repeat steps  2110 - 2140  to create the various layers illustrated in  FIGS.  10 A,  11 A,  12 A , and,  13 A, respectively. Portions of photomasks  1000 ,  1100 ,  1200 , and  1300  that may be utilized by these steps to create second subpixel  110 B are illustrated in  FIGS.  10 B,  11 B,  12 B , and,  13 B, respectively. To create third subpixel  110 C on top of second subpixel  110 B, method  2100  would repeat steps  2110 - 2140  to create the various layers illustrated in  FIGS.  14 A,  121 A,  16 A , and,  17 A, respectively. Portions of photomasks  1400 ,  12100 ,  1600 , and  1700  that may be utilized by these steps to create third subpixel  110 C are illustrated in  FIGS.  14 B,  121 B,  16 B , and,  17 B, respectively. 
     In some embodiments, method  2100  may include forming additional layers that are not specifically illustrated in  FIG.  21   . For example, additional layers such as insulating layers  310  may be formed by method  2100  at any appropriate location. Furthermore, as previously noted, some steps of some embodiments of method  210  may include additional steps that are not specifically mentioned. For example, some layers (e.g., some insulating layers) may be a combination of both insulating and conductive films. Such layers may be manufactured using standard planar semiconductor techniques: depositing, masking, etching, and repeating as many times as necessary to produce the required pattern of conductive and non-conductive areas within the layer. 
     Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context. 
     Herein, the phrase “on top” when used to describe subpixels  110  and their various layers (e.g., layers  210 ,  220 , and  230 ) refers to a viewing direction for display pixels  100  and a light entry direction for sensor pixels  1800 . As an example, subpixel  110 B of display pixel  100  is described as being stacked “on top” of subpixel  110 A. As illustrated in  FIGS.  2 - 3   , “on top” means that subpixel  110 B is on the side of subpixel  110 A that is towards the location that the combined light that is emitted from display pixel  100  may be viewed. Stated another way, subpixel  110 B is on the opposite side of subpixel  110 A from circuitry  120 . As another example, subpixel  110 C of sensor pixel  1800  is described as being stacked “on top” of subpixel  110 B. As illustrated in  FIGS.  19 - 20   , “on top” means that subpixel  110 C is on the side of subpixel  110 B that is towards the location that the full spectrum light enters sensor pixel  1800 . 
     The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. 
     Although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. 
     Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative.