3D OLED SUBSTRATE AND FINE METAL MASK

Organic light emitting diode (OLED) backplanes and fine metal masks (FMMs) are described. In an embodiment, an OLED backplane includes an array of raised bottom electrodes, and an FMM includes an array of pixel openings and an array of recesses. The FMM can be positioned over the backplane such that the pixel openings are over the raised bottom electrodes onto which a layer is to be evaporated, and the recesses are over the raised bottom electrodes that are to be protected from the evaporated species.

BACKGROUND

Field

Embodiments described herein relate to organic light emitting diode (OLED) displays and fine metal masks (FMMs) used on OLED production.

Background Information

State of the art displays for phones, tablets, computers, and televisions utilize glass substrates with thin film transistor (TFTs) to control transmission of backlight though pixels based on liquid crystals. More recently emissive displays such as those based on organic light emitting diodes (OLEDs) have been introduced as being more power efficient, and allowing each pixel to be turned off completely when displaying black.

An OLED display includes a matrix of pixels including multiple layers of organic films. For example, each OLED may include an electron transport layer, a hole transport layer, and an organic emission layer between the electron transport layer and the hole transport layer. The multiple layers may additionally include an electron injection layer and hole injection layer. Typically different organic emission layers are deposited for different color emission. A fine metal mask (FMM) is commonly used as a shadow mask during vapor deposition of the organic emission layers within the subpixels of an OLED display.

SUMMARY

OLED backplanes, FMMs, and methods of OLED production are described. In an embodiment, a backplane used for OLED fabrication includes a substrate, an array of raised bottom electrodes on the substrate, and a pixel defining layer (PDL) on the substrate. In an embodiment, the PDL includes an array of openings over the array of raised bottom electrodes, and each raised bottom electrode in the array of raised bottom electrodes is thicker than the PDL.

In an embodiment, a FMM includes a frame with top side and a bottom surface, an array of pixel openings in the frame, and an array of recesses in the bottom surface of the frame laterally between the pixel openings. Each recess may include sidewalls and a top surface.

In an embodiment, a FMM is positioned over the display substrate such that an array of recesses in the FMM is directly over a first array of raised ground contacts, and an array of pixel openings in the FMM is directly over a second array of raised ground contacts. An array of organic emission layers can then be evaporated on the second array of raised contacts, or an intervening layer such as a hole transport layer.

DETAILED DESCRIPTION

The terms “top”, “bottom”, “over”, “to”, “between”, “spanning” and “on” as used herein may refer to a relative position of one layer with respect to other layers. One layer “over”, “spanning” or “on” another layer may be directly in contact with the other layer or may have one or more intervening layers. One layer “between” layers may be directly in contact with the layers or may have one or more intervening layers.

In one aspect, embodiments describe display backplanes and FMMs that may be used to mitigate color mixing between adjacent subpixels, and increase pixel density (pixels per inch, PPI) or aperture ratio. In an embodiment, a backplane includes a pixel defining layer (PDL) and an array of raised bottom electrodes (e.g anodes). The raised bottom electrodes may be thicker than the PDL. In an embodiment, an FMM includes an array of recesses in the bottom surface of the FMM frame laterally between the pixel openings. In operation, the FMM may be positioned over the display backplane so that the array of recesses are positioned over the array of raised electrodes. In such an arrangement, the bottom surface of the FMM can be located below the top surfaces of the raised electrodes (or the top surfaces of any intervening layers on the raised electrodes) during evaporation of the organic emission layers. This may inhibit the migration of the evaporated organic emission layers, and reduce potential color mixing even in the case of FMM misalignment.

Referring now toFIG. 1a cross-sectional side view illustration is provided of a display backplane100. As illustrated, a display backplane100may include an array of pixels104, and an array of spacers110formed on a substrate102. Each pixel102may have a plurality of subpixels106, each designed for a different color emission. The particular pixel104illustrated inFIG. 1includes a blue-emitting subpixel106B, a green-emitting subpixel106G, and a red-emitting subpixel106R for an RGB color arrangement, though this is exemplary and embodiments are not limited to a specific color arrangement.

FIG. 2is a schematic close-up cross-sectional side view illustration of an FMM200positioned over a display backplane100including spacers142. As shown, the display backplane100may include a substrate102. For example, substrate102may include a TFT substrate120and optionally a planarization layer122. An array of electrodes130(e.g. anodes) may be formed on the planarization layer122. A dielectric layer124may optionally separate the electrodes130. A top surface of the electrodes130and dielectric layer124may optionally be planarized. A pixel defining layer (PDL)140including openings144is formed over the array of electrodes130, and a plurality of spacers142may be formed on the PDL140or as part of the PDL. For example, the spacers142and PDL140may be formed of the same layer using a half tone lithography mask.

Still referring toFIG. 2, the FMM200includes a frame200and an array of pixel openings204in the frame. The pixel openings204may include sloped sidewalls222, and a step220near a bottom surface210of the frame200. As shown, the bottom surface210of the frame200may rest upon the plurality of spacers142during a deposition operation. During such a deposition operation (e.g. evaporation), the deposited species may potentially migrate underneath the bottom surface210of the FMM200and deposit as a shadow zone near the bottom electrodes130that are intended to be covered by the FMM200, potentially causing color mixing. This may be attributed to the total thickness (T) of the PDL140, spacers142, and FMM step220height (S).FIG. 3is a schematic close-up cross-sectional side view illustration of an array of organic emission layers150deposited on a display backplane100including spacers142. As shown, edges152of the organic emission layers150may creep through the gaps between the FMM200and top surface of the PDL140.

Referring now toFIG. 4, in accordance with embodiments an FMM200including recesses235is positioned over a display backplane100including raised bottom electrodes130(e.g. anodes). In the embodiment illustrated, the backplane100may include a substrate102, an array of raised bottom electrodes130on the substrate102, and a PDL140on the substrate102. For example, substrate102may include a TFT substrate120and optionally a planarization layer122. The PDL140includes an array of openings144over the array of raised bottom electrodes130. Each raised bottom electrode130may correspond to a subpixel106(e.g.106R,106G,106B), and be independently addressable. In the embodiment illustrated, each raised bottom electrode130in the array of raised bottom electrodes is thicker than the PDL140.

The raised bottom electrodes130may be formed of a single layer, or a layer stack. For example, the raised bottom electrodes130may be formed of metals, conductive oxides, conductive polymers, and combinations thereof. For example, the raised bottom electrodes130may be formed of indium-tin-oxide (ITO), refractory metal, silver (Ag), or combinations thereof. In an embodiment, the raised bottom electrode130comprise layer stacks of ITO/Ag, ITO/Ag/ITO, ITO/Ag alloy/ITO. These combinations are exemplary, and embodiments are not so limited. For example, ITO may have a uniform work function so that the hold injection barrier is small to the OLED. Ag may function as a mirror layer.

In an embodiment, the raised bottom electrodes130are at least2μm thick, such as3μm thick. The raised bottom electrodes130may include top surfaces132and sidewalls134. In an embodiment, the raised bottom electrodes130are formed by evaporation or sputtering, or a combination of evaporation or sputtering multiple layers. A PDL140may then be formed over the substrate102and patterned to form openings144over the top surfaces132of the raised bottom electrodes130. The openings144may create injection region boundaries for the OLEDs that are formed on the raised bottom electrodes130. In an embodiment, the PDL140is formed of a polymer, such as polyimide (PI), acrylic, or benzocyclobutene (BCB). In an embodiment, the PDL140is formed using a technique such as spin coating, though other techniques may be used. As shown, the coated PDL140is formed on the top surfaces132and sidewalls134of the raised bottom electrodes130and patterned to form openings144. In accordance with embodiments, the PDL140is thinner than the raised bottom electrodes130. For example, the PDL may be less than 1.5 μm thick, such as 1.0 μm thick. Due to the difference in thicknesses of the raised bottom electrodes130and the PDL140, the PDL includes lip regions146around the raised bottom electrodes130on the top surfaces132of the raised bottom electrodes130, and well regions148laterally between adjacent raised bottom electrodes130. In an embodiment, a top surface149of the well regions148is below a top surface132of each raised bottom electrode130.

Still referring toFIG. 4, in accordance with an embodiment an FMM200is positioned over the display backplane100with the recesses235in the FMM positioned directly over the raised bottom electrodes130. The particular embodiment illustrated inFIG. 4illustrates an FMM200positioned over the display backplane100prior to deposition of any of the OLED layers. In application, the formation of the OLED layers may include a number of different FMMs200and deposition operations. For example, the formation of an exemplary OLED may include the deposition of around 10-15 layers. Thus, while the specific embodiment illustrated inFIG. 4shows the bottom surface240of the FMM residing on the top surface149of the PDL140well portions148, this is exemplary and one or more layers may already be formed on top of the underlying structure.

In an embodiment, an FMM200includes a frame202with a top side223and a bottom surface240. An array of pixel openings204are formed in the frame202. For example, the pixel openings204extend between the top side and the bottom surface240. In accordance with embodiments, an array of recesses235is formed in the bottom surface240of the frame202laterally between the pixel openings204. Each recess235may include sidewalls232and a top surface234. The sidewalls232for each recess235may form a complete loop. Each of the pixel openings204may include tapered sidewalls222so that the pixel openings204are wider at the top side223of the frame than at the bottom surface240of the frame202. The tapered sidewalls222for each pixel openings204may additionally span directly over a plurality of recesses235in the bottom surface240of the frame202.

In an embodiment, the FMM200additionally includes legs230(e.g. ridges) between the array of pixel openings204and the array of recesses235. In an embodiment, the legs230(e.g. ridges) include sidewalls220that define the pixel openings204at the bottom surface240. Alternatively, sidewalls222may extend all the way to the bottom surface240. During use, the recesses235can be positioned directly over the raised bottom electrodes130with the legs230(e.g. ridges) laterally surrounding (e.g. completely laterally surrounding) the top surfaces132of the respective raised bottom electrodes130(or top surfaces of any overlying layers that may have already been deposited over the raised bottom electrodes130).

FIG. 5is a perspective view of the bottom side of an FMM200in accordance with an embodiment. In the embodiment illustrated inFIG. 5, the bottom surface240of the frame202(e.g. bottom surface of the legs/ridges230) may be a planar bottom surface in a grid pattern that is defined by the array of pixel openings204and the array of recesses235. A close up illustration is additionally provided inFIG. 5of a pixel area of the frame202including a recess235B to be positioned over a raised bottom electrode130of a blue-emitting subpixel106B, a recess235G to be positioned over a raised bottom electrode130of a green-emitting subpixel106B, and a pixel opening204R to be positioned over a raised bottom electrode130of a red-emitting subpixel106R. As shown, the arrays of recesses may include a first array of recesses (e.g.235B) with a first top surface234with a first area, and a second array of recesses (e.g.235G) with a second top surface234with a second area that is different from the first area. Similarly, the areas of the corresponding top surfaces132of the raised bottom electrodes130may be different.

Referring now toFIGS. 6-7, in some embodiments the FMM200may include an array of spacers242protruding from the bottom surface240in a direction opposite of the array of recesses235. The spacers242may be formed separately from the frame202, or as part of the frame202.FIG. 6is a perspective view of the bottom side of an FMM200including spacers242in accordance with an embodiment.FIG. 7is a schematic close-up cross-sectional side view illustration of an FMM200including a spacer242positioned over a display backplane100including raised electrodes130in accordance with an embodiment. In accordance with embodiments, the spacers242can be dispersed across the (e.g. planar) bottom surface240of the FMM200. In one embodiment, the thickness of the spacers242is less than thickness of the raised bottom contacts130. In such an arrangement, while a separation distance may be created between the bottom surface240of the FMM and underlying structure on the display backplane100, the relative heights may create a substantial barrier to migration of the evaporated species.

Referring now toFIG. 8a schematic close-up cross-sectional side view illustration is provided of an array of organic emission layers150deposited on a display backplane100including raised electrodes130in accordance with an embodiment. The particular embodiment illustrated inFIG. 8illustrates the formation of the organic emission layers150without other corresponding layers within an OLED. Accordingly, the organic emission layers150illustrated inFIG. 8are illustrative of any layers formed using an FMM200in accordance with embodiments. In the particular embodiment illustrate the deposited organic emission layers150may be formed over the top surfaces132of the raised bottom electrodes130, over the lip regions146and well regions148of the PDL140.

FIG. 9is a schematic close-up cross-sectional side view illustration of multiple layer stack OLEDs in accordance with an embodiment. The particular cross-section illustrated inFIG. 9is exemplary of a cross-section taken along the red-emitting and green-emitting subpixels. As shown, arrays of organic emission layers150R,150G are formed over the array of bottom electrodes130. While only red and green-emitting organic emission layers are illustrated, in an exemplary RGB system, the array of organic emission layers includes a first array of red-emitting organic emission layers, a second array of green-emitting organic emission layers, and a third array of blue-emitting organic emission layers.

In an embodiment, a common hole injection layer followed by common hole transport layer (illustrated together as162) are formed over each of the raised bottom electrodes130. Separate organic emission layers150are the specific raised bottom electrodes130for the corresponding subpixels. A common electron transport layer followed by common electron injection layer (illustrated together as164) are then formed over the arrays of organic emission layers150. A common top electrode layer (e.g. cathode) may then be formed over the common electron injection layer. The top electrode layer may be formed a transparent conductive oxide, such as ITO, or a transparent conductive polymer.

In an embodiment, a method of forming an OLED display comprises positioning an FMM over a display substrate that includes a first array of raised ground contacts and a second array of raised ground contacts. The FMM may include a frame, an array of pixel openings in the frame, and an array of recesses in the bottom surface of the frame laterally between the pixel openings. In the embodiment, positioning the FMM over the display substrate includes positioning the array of recesses directly over the first array of raised ground contacts, and positioning the array of pixel openings directly over the second array of raised ground contacts. An array of organic emission layers is then evaporated on the second array of raised ground contacts.

Prior to positioning the FMM over the display substrate, a PDL may be formed on the display substrate and patterned to form an opening over each raised ground contact. Each raised ground contact may be thicker than the PDL. In an embodiment, the FMM may include an array of spacers on a bottom surface of the FMM. Each raised ground contact may be thicker than each spacer. One or more layers may have already been formed over the arrays of raised ground contacts prior to evaporating the array of organic emission layers. In an embodiment, positioning the FMM over the display substrate includes resting the FMM on a hole transport layer.

In utilizing the various aspects of the embodiments, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for forming a display backplane and FMM. Although the embodiments have been described in language specific to structural features and/or methodological acts, it is to be understood that the appended claims are not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as embodiments of the claims useful for illustration.