WO2021126143A1

WO2021126143A1 - Oled sub-pixel patterning structure

Info

Publication number: WO2021126143A1
Application number: PCT/US2019/066477
Authority: WO
Inventors: Jungmin Lee; Si-Kyoung Kim; Dieter Haas
Original assignee: Applied Materials, Inc.
Priority date: 2019-12-16
Filing date: 2019-12-16
Publication date: 2021-06-24

Abstract

Disclosed herein is a method for forming a sub-pixel for a display device. The method begins by preparing a glass substrate patterned with indium tin oxide (ITO) layer. The patterned ITO glass substrate is coated with a pixel define layer (PDL). The PDL is developed to form a pattern on the glass substrate. A second metal grid is added on the PDL on the glass substrate. The glass substrate is coated with a photoresist. The photoresist layer is exposed for forming a first OLED sub-pixel. The exposed photoresist layer is developed. An organic layer is added on at least the ITO layer exposed by the photoresist removal and a cathode layer is added on the organic layer.

Description

OLED SUB-PIXEL PATTERNING STRUCTURE

BACKGROUND

Field

[0001] The present disclosure generally relates to a sub-pixel structure. The sub pixel structure may be utilized in a display screen such as an organic light-emitting diode (OLED) display screen.

Description of the Related Art

[0002] Input devices including display devices may be used in a variety of electronic systems. The display resolution tells you how many pixels your screen can display horizontally and vertically. It's written in the form N x M. In this example, the screen can show N pixels horizontally, and M vertically. If you're comparing two screens of the same size but with different resolutions, the screen with the higher resolution (that's the one with more pixels) will be able to show you more of what you're working on, so you don't have to scroll so much. The higher the resolution of the display, the greater degree of detail for clear quality images the display will produce.

[0003] An organic light-emitting diode (OLED) is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of an organic compound that emits light in response to an electric current. OLED devices are classified as bottom emission devices if light emitted passes through the transparent or semi-transparent bottom electrode and substrate on which the panel was manufactured. Top emission devices are classified based on whether or not the light emitted from the OLED device exits through the lid that is added following the fabrication of the device. OLEDs are used to create display devices in many electronics today. Today’s electronics manufacturers are pushing these display devices to shrink in size while providing higher resolution than just a few years ago.

[0004] High-resolution display devices for organic light-emitting diode OLED, having greater than 600 ppi (pixels per inch), require very small pixel sizes. Each pixel may have three or more sub-pixels to set a color at the pixel. With the shrinking pixel sizes in -resolution displays, everything becomes smaller. The circuitry driving the sub-pixel has a plurality of thin-film transistors and capacitors as well as an organic light-emitting diode (OLED) area. However, the pixel footprint is difficult to manufacture inexpensively and reliably.

[0005] As a result, new technology is needed that can inexpensively produce reliable pixels in OLED display devices.

SUMMARY

[0006] Disclosed herein is a method for forming a sub-pixel for a display device. The method begins by preparing a glass substrate patterned with an indium tin oxide (ITO) layer. The patterned ITO glass substrate is coated with a pixel defining layer (PDL). The PDL is developed to form a pattern on the glass substrate. A second metal grid is added to the PDL on the glass substrate. The glass substrate is coated with a photoresist. The photoresist layer is exposed for forming a first OLED sub pixel. The exposed photoresist layer is developed. An organic layer is added on at least the ITO layer exposed by the photoresist removal and a cathode layer is added on the organic layer.

[0007] In another embodiment, a method is disclosed for forming a sub-pixel OLED area in a stack. The method begins by preparing a glass substrate patterned with an indium tin oxide (ITO) layer. The patterned glass substrate is coated with a pixel define layer (PDL). The PDL is developed to form a pattern on the glass substrate. The glass substrate is coated with a photoresist. The photoresist layer is exposed for forming slits between the cathode contact pads. An organic layer is added in the slits and a metal layer is also added in the slits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments, and are therefore not to be considered limiting of inventive scope, as the disclosure may admit to other equally effective embodiments. [0009] FIG. 1 is a schematic of an active matrix organic light-emitting diode (OLED) panel, according to one or more embodiments.

[0010] FIG. 2A shows a schematic illustration with a bottom emission OLED display, according to one or more embodiments.

[0011] FIG. 2B shows a schematic illustration with a top emission OLED display, according to one or more embodiments.

[0012] FIG. 3 illustrates a method for manufacturing an OLED area of a sub-pixel, according to one or more embodiments.

[0013] FIG. 4A shows a top isometric view of a pre-patterned ITO glass substrate, according to one or more embodiments.

[0014] FIG. 4B shows a top isometric view of the pre-patterned ITO glass substrate coated with a PDL and developed, according to one or more embodiments.

[0015] FIG. 5 shows a cross-sectional side view through cross-section line 5-5 of FIG. 4A

[0016] FIG. 6A is the cross-sectional side view shown in FIG 3 with a second metal grid added on the PDL.

[0017] FIG. 6B shows a top isometric view of the pre-patterned ITO glass substrate having the second metal grid, according to one or more embodiments.

[0018] FIG. 7 is the cross-sectional side view with a sacrificial or photoresist layer, according to one or more embodiments.

[0019] FIG. 8A is the cross-sectional side view showing the exposure of the photoresist layer, according to one or more embodiments.

[0020] FIG. 8B is the cross-sectional side view showing the development of the exposed photoresist layer, according to one or more embodiments.

[0021] FIG. 9 is the cross-sectional side view showing the addition of an organic layer in a first sub-pixel, according to one or more embodiments. [0022] FIG. 10 is the cross-sectional side view showing the addition of a cathode layer, according to one or more embodiments.

[0023] FIG. 11 is the cross-sectional side view showing the lift-off of the photoresist layer and the addition of an encapsulation layer, according to one or more embodiments.

[0024] FIG. 12 is the cross-sectional side view showing the addition of a second and third OLED sub-pixel, according to one or more embodiments.

[0025] FIG. 13 is the cross-sectional side view showing the addition of a global encapsulation layer, according to one or more embodiments.

[0026] FIG. 14 illustrates another method for manufacturing an OLED area of a sub-pixel, according to one or more embodiments.

[0027] FIG. 15 shows a top side view of a pre-patterned ITO glass substrate, according to one or more embodiments.

[0028] FIG. 16 shows a top side view of the pre-patterned ITO glass substrate coated with a PDL and developed, according to one or more embodiments.

[0029] FIG. 17A shows a top side view with a photoresist, according to one or more embodiments.

[0030] FIG. 17B shows a cross-sectional side view through cross-section line A- A’ of FIG. 17A.

[0031] FIG. 18A shows a top side view with the addition of an organic layer, according to one or more embodiments.

[0032] FIG. 18B shows a cross-sectional side view through cross-section line A- A’ of FIG. 18A.

[0033] FIG. 18C shows a cross-sectional side view through cross-section line B- B’ of FIG. 18A.

[0034] FIG. 19A shows a top side view with the addition of a metal layer, according to one or more embodiments. [0035] FIG. 19B shows a cross-sectional side view through cross-section line A- A’ of FIG. 19A.

[0036] FIG. 19B shows a cross-sectional side view through cross-section line B- B’ of FIG. 19A.

[0037] FIG. 20 shows a top side view showing the arrangement of pixels and subpixels formed from the method of Figure 14.

[0038] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation. The drawings referred to here should not be understood as being drawn to scale unless specifically noted. Also, the drawings are often simplified and details or components omitted for clarity of presentation and explanation. The drawings and discussion serve to explain principles discussed below, where like designations denote like elements.

DETAILED DESCRIPTION

[0039] The following detailed description is merely exemplary in nature and is not intended to limit the disclosure or the application and uses of the disclosure. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding background, summary, or the following detailed description.

[0040] High-resolution display devices for an OLED (i.e. , greater than 600 pixels per inch (ppi)) will have smaller pixel sizes. A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate. A plurality of sub-pixels is formed to produce a red, green, blue (RGB) pixel for the OLED device. The sub-pixels are formed on a pixel defining layer (PDL) which is patterned using a photolithographic process before the deposition of the organic and subsequent layers forming the sub-pixel.

[0041] Described herein is a method for ensuring electrical contact for lithography into induced red/green/blue (RGB) OLED patterning. The method has an improved electrical potential difference (IR) drop between the two ends of a conducting phase during a current flow at the cathode by the formation of a local contact in between the sub-pixel and assistant grid. The method is to a top contact OLED which makes an electrical grid embedded inside on the PDL to secure a local cathode contact during device making process in between sub-pixels and the surrounding electrical grid. The method reduces dead pixels by connection shorts. The device fabrication process is explained in detail in the illustrated figures below.

[0042] A metal grid is embedded or added to the PDL. While making an OLED device, organist deposition is contained within the PDL by angle control from the source side. The cathode deposition is spread over the PDL by a wider angle from the source and the same or lower taper angle of the photoresist layer wherein the photoresist layer acts like a fine metal mask. The angle limiting photoresist layers is removed after pixelated encapsulation is implemented and then the process is repeated to make the next color device. A global encapsulation layer is added after all photoresist processes are done. The overall out of plane depth of the structure is within 0.5 urn max compared with 1.5 urn to about 3.0 urn for a conventional PDL structure. Because of the low-profile structure, adding a planarization layer is not required. The details for making an OLED device are described below with regard to the figures.

[0043] FIG. 1 is a schematic of an active matrix organic light-emitting diode (OLED) panel 100. The OLED panel 100 has an array of pixels 190, i.e. , a first pixel 190i, a second pixel 1902, a third pixel 1903, etc., arranged in rows 160 and columns 180. Each pixel 190 has a plurality of sub-pixels 150 for determining a value of the pixel 190. For example, a first pixel 190i has a first sub-pixel 150IA, a second sub pixel 150IB, and a third sub-pixel 150ic. Each sub-pixel 150 being a single color element of a respective pixel 190. However, the first pixel 190i may have more than three sub-pixels 150, for example, a sub-pixel 150-IN wherein Ί N’ can represent any number of sub-pixels 150 for the first pixel 190i. Each row 160 in the OLED panel 100 can be accessed independently using gate lines 110. Each column 180 in the OLED panel 100 can be accessed using data lines 120. Addressing a first gate line 112 and a first data line 122 accesses the first sub-pixel 150IA in the first pixel 190i of the OLED panel 100. Each sub-pixel 150 may be similarly addressed in the OLED panel 100. In various embodiments, while each sub-pixel 150 is illustrated as being coupled to a single select line, each sub-pixel may be coupled to a plurality of select lines that may be used to control updating each sub-pixel 150. In such embodiments, the select lines may be driven at different times with different select signals to control the update timing of the sub-pixels 150.

[0044] In one or more embodiments, the OLED panel 100 may be an organic light-emitting diode (OLED) display device. In such an embodiment, each of the sub pixels 150 may comprise an anode electrode that is coupled to a corresponding select line or lines and a data line via one or more transistors. A sub-pixel data signal or signals is applied to each activated anode electrode to drive the anode electrode to a specified voltage level. An OLED display device additionally includes a cathode electrode that is driven to a voltage level by a processing system for display updating and one or more organic layers. The supply voltage is applied to each sub-pixel to drive sub-pixel updating. In one embodiment, a positive supply voltage may be referred to as the electroluminescence voltage drain drain (ELVDD) and a negative supply voltage may be referred to as the electroluminescence voltage source source (ELVSS).

[0045] FIG. 2A shows a schematic illustration with a bottom emission OLED display. OLED is positioned on the top of the sub-pixel circuit 220. Light from the OLED cannot pass through the sub-pixel circuit 220 due to the direction of light emission, downward. The single sub-pixel 150 may be the first sub-pixel 150IA. However, the single sub-pixel 150 shown in FIG. 2A is generic to each of the sub pixels 150, such as the first sub-pixel 150IA, and further discussion will be with regard to the generic sub-pixel 150. The sub-pixel 150 has a sub-pixel area 250. A portion of the sub-pixel area 250 is occupied by an organic light-emitting diode (OLED) area 210. The OLED area 210 is the light-emitting element of the sub-pixel 150. The OLED area 210 is a current-driven light-emitting device. The remaining portion of the sub-pixel area 250 is occupied by a sub-pixel circuit 220 that has one or more transistors, capacitors and metal routing connecting the transistors and capacitors for forming the sub-pixel circuit 220. The one or more transistors, capacitors and metal routing may be disposed within a different metal layer of a substrate (device) than another one of the transistors, capacitors and metal routing in forming the sub-pixel circuit 220. The sub-pixel circuit 220 controls the OLED area 210 providing the power needed to drive the sub-pixel 150, i.e. , to emit or not emit light.

[0046] FIG. 2B shows a schematic illustration with a top emission OLED display. For the top emission OLED display, the OLED is positioned on the top of the sub pixel circuit 220. The direction of light from the OLED is upward, so the sub-pixel circuits 220 do not block the light. Therefore, the area of the sub-pixel circuits 220 from top emission OLED display can be comparable with the OLED area 210, which allows higher density than the bottom emission OLED display.

[0047] FIG. 3 illustrates a method 300 for manufacturing the OLED area 210 of the sub-pixel 150, according to one or more embodiments. The description of the method 300 will additionally utilize the illustrations of FIG. 4A through FIG. 13.

[0048] At operation 310, a glass substrate 410 patterned with a first metal layer 420 is prepared for forming the OLED sub-pixel. The glass substrate 410 may be prepared by depositing on the first metal layer 420 on the glass substrate 410 by reactive magnetron sputtering or other suitable technique. An etch operation may form a trench for receiving the first metal layer 420. Alternately, the first metal layer 420 may be deposited directly on the glass substrate 410. The first metal layer 420 is patterned and configured to operate as the anode for the OLED sub-pixel. The first metal layer 420 may be formed from chromium, titanium, gold, silver, copper, aluminum, one of their compounds, indium tin oxide (ITO) or other suitably conductive material. In one example, the first metal layer 420 is formed from ITO. FIG. 4A shows a top isometric view of a pre-patterned ITO glass substrate 400.

[0049] At operation 315, the patterned ITO glass substrate 400 is coated with a pixel defining layer (PDL) 430. The PDL 430 may be formed from a polyimide, SiO, SiN, MgF2 or other suitable material. In one example, the PDL 430 is formed from a single layer of a hydrophilic film such as a photoresist. The thickness of the PDL 430 may be about 100 nm to about 400 nm, such as about 300 nm.

[0050] At operation 320, the PDL 430 is developed to form a pattern on the glass substrate 400. FIG. 4B shows a top isometric view of the pre-patterned ITO glass substrate 400 coated with the PDL 430 and developed. A plurality of openings 424 may be formed in the PDL 430 exposing the first metal layer 420. FIG. 5 shows a cross-sectional side view 500 through cross-section line 5-5 of FIG. 4B. In the cross- section 500, a first PDL 452 is shown adjacent to the anode 462 in the first metal layer 420. A second PDL 454 is shown adjacent to the anode 462 in the first metal layer 420 opposite the first PDL 452. Adjacent the second PDL 454 is yet another opening 424 to the first metal layer 420. It should be appreciated that an alternating pattern of the first metal layer 420 and the PDL 430 repeats itself in each row beginning and ending with the PDL 430.

[0051] At operation 325 a second metal grid 610 is deposited on the PDL 430 on the glass substrate 410. FIG. 6A is the cross-sectional side view shown in FIG 5 with the second metal grid 610 added on the PDL 430. FIG. 6B shows a top isometric view of the pre-patterned ITO glass substrate 400 having the second metal grid 610. The second metal grid 610 is placed on the PDL 430 and not in contact with the first metal layer 420. The second metal grid 610 may be formed by sputtering, or by other suitable deposition techniques, prior to etching. For example, the material of the second metal grid 610 may be sputtered over the ITO glass substrate 400. A phot process may be performed to mask the second metal grid 610. An etch process, such as wet-etching, may be performed to selctively expose the first metal layer 420, i.e. , anode again. The mask is removed to selectively form the second metal grid 610 on the PDL 430. It should be appreciated that the selective formation of the second metal grid 610 on the PDL 430 may be performed in a number of ways using a number of suitable techniques. The second metal grid 610 may be formed from chromium, titanium, gold, silver, copper, aluminum, one of their compounds, indium tin oxide (ITO) or other suitably conductive material.

[0052] At operation 330, the glass substrate is coated with a photoresist layer 710 and/or sacrificial layer 715. FIG. 7 is the cross-sectional side view showing the sacrificial layer 715 and the photoresist layer 710. It should be appreciated that the operation 330 may involve only one of the photoresist layer 710 or sacrificial layer 715 or both. However, going forward the discussion will utilize the photoresist layer 710 for simplicity and clarity.

[0053] At operation 335, the photoresist layer 710 is exposed as part of forming an opening 850 in the photoresist layer 710. FIG. 8A is the cross-sectional side view showing the exposure of the photoresist layer 710. A mask 810 is used to control the light for exposing the photoresist layer 710. It should be appreciated that the photoresist layer 710 may be formed from a positive photoresist or a negative photoresist and the appropriate mask for the type of photoresist is employed to generate the desired exposure of the photoresist layer 710.

[0054] At operation 340 the exposed photoresist layer 710 is developed. FIG. 8B is the cross-sectional side view showing the development of the exposed photoresist layer 710. The opening 850 is formed in the photoresist layer 710. An overhang structure 833 narrows an entry 832 from a cavity 834 of the opening 850. The overhang structure 833 functions as a metal mask in the operations that follow.

[0055] At operation 345 an organic layer 910 is applied on at least the ITO layer exposed by the photoresist removal. FIG. 9 is the cross-sectional side view showing the addition of the organic layer 910 in a first sub-pixel 901. The organic layer 910 is in contact with the first metal layer 420. In one example, the organic layer 910 is not in contact with the second metal grid 610. Thus, the organic layer 910 does not complete a circuit between the first metal layer 420, i.e. , anode side, and the second metal grid 610, i.e., cathode side. An organic trace 954 illustrates the direction for deposition of the organic layer 910. It should be noted that the organic trace 954 allows the organic layer 910 to be larger than the entry 832. The organic layer 910 is configured to emit a white, red, green, blue or other color light when energized.

[0056] At operation 350, a cathode layer 1010 is added on top of the organic layer. FIG. 10 is the cross-sectional side view showing the addition of the cathode layer 1010. The cathode layer 1010 extends between the second metal grid 610 on both sides of the organic layer 910. The cathode layer 1010 is formed from a conductive material such as a metal. The cathode layer 1010 may be formed from Cr, Ti, Al, ITO, APT, a compound, or other suitably conductive material. A cathode trace 952 (FIG. 9) illustrates the direction for deposition of the cathode layer 1010. It should be noted that the cathode trace 952 direction is different than the organic trace 954 allowing the cathode layer 1010 to be larger than the organic layer 910 when deposited.

[0057] At operation 355, an encapsulation layer 1110 is added on to the cathode layer 1010. FIG. 11 is the cross-sectional side view showing the lift off of the photoresist layer 710 and the additional of an encapsulation layer 1110. The encapsulation layer 1110 extends over the cathode layer 1010 and down to the second metal grid 610 to fully enclose and form the sub-pixel device. At operation 360, the photoresist layer 710 is removed.

[0058] At operation 365, the steps above are repeated to form a second OLED sub-pixel 1202 and third OLED sub-pixel 1203. FIG. 12 is the cross-sectional side view showing the addition of the second sub-pixel 1202 and third OLED sub-pixel 1203. In one example, the organic layer 910 of the first subpixel 901 emits a green light when energized, the organic layer 910 of the second subpixel 1202 emits a red light when energized, and the organic layer 910 of the third subpixel 1203 emits a blue light when energized. The combination of the first subpixel 901 , the second subpixel 1202 and the third subpixel 1203 make a pixel in an OLED display device.

[0059] At operation 370 a global encapsulation layer 1310 is added over the first, second and third OLED sub-pixels 901 , 1202, 1203. FIG. 13 is the cross-sectional side view showing the addition of a global encapsulation layer 1310. The global encapsulation layer 1310 may be formed from the same material as the encapsulation layer 1110. Alternately, the encapsulation layer 1110 may be knitted together, joined end to end, to form the global encapsulation layer 1310.

[0060] FIG. 14 illustrates another method 1400 for manufacturing the OLED area 210 of the sub-pixel 150, according to one or more embodiments. The description of the method 1400 will additionally utilize the illustrations of FIG. 15 through FIG. 20.

[0061] At operation 1410 a glass substrate 1510 is patterned with an indium tin oxide (ITO) layer 1522. FIG. 15 show a top side view of a patterned ITO glass substrate 1500. The glass substrate 1510 is patterned with an anode metal layer 1520 and a cathode metal layer 1530 in preparation for forming the OLED sub-pixel. The anode metal layer 1520 and the cathode metal layer 1530 are both formed on the glass substrate 1510, may be substantially coplanar and are not electrically coupled. The glass substrate 1510 may be prepared by depositing on the anode metal layer 1520 and the cathode metal layer 1530 on the glass substrate 1510 by reactive magnetron sputtering or other suitable technique. An etch operation may form a trench for receiving the anode metal layer 1520 and the cathode metal layer 1530. Alternately, the anode metal layer 1520 and the cathode metal layer 1530 may be deposited directly on the glass substrate 1510. The anode metal layer 1520 and the cathode metal layer 1530 may be formed from chromium, titanium, gold, silver, copper, aluminum, one of their compounds, indium tin oxide (ITO) or other suitably conductive material. In one example, both the anode metal layer 1520 and the cathode metal layer 1530 are formed from ITO. The anode metal layer 1520 formed a plurality of strips spaced apart a distance (1835 in FIG. 18B) of about 0.5 mm to about 1.5 mm such as about 1.0 mm. The anode metal layer 1520 has a plurality of anode contact pads 1521 at the end of each strip along a first and a third outer edge of the glass substrate 1510. The cathode metal layer 1530 has a plurality of cathode contact pads 1531 are positioned along a second and a fourth outer edge of the glass substrate 1510.

[0062] At operation 1415, the patterned glass substrate 1500 is coated with a pixel defining layer (PDL) 1610. The PDL 1610 extends partially onto anode contact pads 1521 and partially onto the cathode contact pads 1531. For example, the PDL 1610 may extend a distance (1851 in FIG. 18B) between about 0.5 mm to about 1.5 mm onto the cathode contact pads 1531 and the anode contact pads 1521. The PDL 1610 may be formed from a polyimide, SiO, SiN, MgF2 or other suitable material. In one example, the PDL 1610 is formed from a single layer of a hydrophilic film such as a photoresist. The thickness of the PDL 1610 may be about 100 nm to about 400 nm, such as about 300 nm.

[0063] At operation 1420, the PDL 1610 is developed to form a pattern 1640 on the glass substrate 1510. FIG. 16 shows a top side view of the pre-patterned ITO glass substrate 1500 coated with the PDL 1610 and developed. A plurality of openings 1624 may be formed in the PDL 1610 exposing the ITO layer 1522 corresponding to the anode metal layer 1520.

[0064] At operation 1425 the glass substrate 1510 is coated with a photoresist layer 1710. At operation 1430, the photoresist layer 1710 is exposed to form a plurality of slits 1720. Alternately, the slits 1720 may be formed by etching or trenching the photoresist layer 1710. The slits 1720 are formed between the cathode contact pads 1531. FIG. 17A shows a top side view with the photoresist layer 170 having the slits 1720. In the slits 1720, the photoresist layer 1710 is removed. A second pattern 1740 of ITO layer 1522 and PDL 1610 remain in the slits 1720. It should be appreciated that the second pattern 1740 is an alternating pattern of the ITO layer 1522 and the PDL 1610 which repeats itself in each row beginning and ending with the ITO layer 1522.

[0065] FIG. 17B shows a cross-sectional side view through cross-section line A- A’ of FIG. 17A. The cross-section is taken through the anode metal layer 1520 electrically coupled to the anode contact pads 1521. The PDL 1610 is disposed on top of the anode metal layer 1520. The PDL 1610 may have slanted sidewalls 1762. The photoresist layer 1710 is disposed on top of the PDL 1610. The photoresist layer 1710 has a T shape 1714. The T shape 1714 has a lower portion 1712 and an upper portion 1718. The lower portion 1712 is attached to an underside 1716 of the upper portion 1718. The lower portion 1712 of the T shape 1714 near the PDL 1610 has a smaller cross-section than an upper portion 1718 of the T shape 1714. For example, the cross-section of the upper portion 1718 may be between about 3.5 mm to about 3.0 mm while the cross-section of the lower portion 1712 may be between 2.5 mm to about 3.3 mm. In this manner, the width slits 1720 formed at the lower portion 1712 are wider than the width of the slits 1720 formed above at the upper portion 1718. In one example, the width of the slits 1720 may be between 3.0 mm and 2.5 mm along the lower portion 1712 of the photoresist layer 1710 and the width of the slits 1720 may be between 3.1 mm and 2.3 mm along the upper portion 1718 of the photoresist layer 1710.

[0066] At operation 1435, an open organic mask 1890 is placed to cover the anode contact pads 1521 and the cathode contact pads 1531. FIG. 18A shows a top side view with the addition of the open organic mask 1890. FIG. 18B shows a cross- sectional side view through cross-section line A-A’ of FIG. 18A. FIG. 18C shows a cross-sectional side view through cross-section line B-B’ of FIG. 18A. The open organic mask 1890 is above the patterned glass substrate 1500 and configured to shield, or mask, portions of the patterned glass substrate 1500 in future operations. The open organic mask 1890 has a center opening 1860. The center opening 1860 having edges 1802. The open organic mask 1890 may cover the anode contact pads 1521 and the cathode contact pads 1531 by a distance 1853 of between about 1 mm to about 2 mm, such as about 1.5 mm. The center opening 1860 of the open organic mask 1890 may have a width 1861 of between 28.50 mm to about 32.0 mm on each of the edges 1802.

[0067] At operation 1440 an organic layer 1810 is added in the slits 1720. The organic layer 1810 may correspond to a color upon electrical activation. For example, each slit 1720 may have a different organic layer 1810 corresponding to a red, green, blue, white or other colors. The organic layer 1810 is deposited through the center opening 1860 of the open organic mask 1890. The areas covered by the open organic mask 1890 remain free of the organic layer 1810. The organic layer 1810 is deposited on the ITO layer 1522 and PDL 1610 visible through the photoresist layer 1710. A small portion 1863 of the organic layer 1810 extends beyond the width 1861 of the center opening 1860 due to the lower portion 1712 of the T shape 1714 of the photoresist layer 1710. The organic layer 1810 extends from the PDL 1610 onto the ITO layer 1522 a distance 1867 of between about 90 urn to about 110 urn, such as about 100 urn.

[0068] At operation 1445, the open organic mask 1890 is removed.

[0069] At operation 1450, a metal mask 1990 is placed to cover the anode contact pads 1521 and the cathode contact pads 1531 . The metal mask 1990 has a larger opening than the open organic mask 1890 exposing a portion of the cathode contact pads 1531. FIG. 19A shows a top side view with the addition of a metal layer. The metal mask 1990 is elevated above the patterned glass substrate 1500 and configured to shield, or mask, portions of the patterned glass substrate 1500 in future operations. FIG. 19B shows a cross-sectional side view through cross-section line A-A’ of FIG. 19A. FIG. 19B shows a cross-sectional side view through cross- section line B-B’ of FIG. 19A.

[0070] At operation 1455 a metal layer 1910 is added in the slits 1720. The metal layer 1910 is deposited through the opening in the metal mask 1990. The areas covered by the metal mask 1990 and photoresist layer 1710 remain free of the metal layer 1910. The metal layer 1910 is deposited on the organic layer 1810 and PDL 1610 visible through the photoresist layer 1710. A small portion of the metal layer 1910 extends beyond the width 1861 of the center opening 1860 due to the lower portion 1712 of the T’ shape 1714 of the photoresist layer 1710. The metal layer 1910 extends beyond the organic layer 1810 onto the PDL 1610. For example, the metal layer 1910 extends beyond the organic layer 1810 a distance 1961 of between about 90 urn to about 110 urn, such as about 100 urn. Additionally, the metal layer 1910 extends onto the cathode contact pads 1531. Thus, the metal mask 1990 electrically couple a pair of cathode contact pads 1531 on either end of each respective slit 1720

[0071] At operation 1460, the metal mask is removed. At operation 1465, the photoresist is removed.

[0072] At operation 1470, a global encapsulation layer is added over the glass substrate. FIG. 20 shows a top side view showing the arrangement of pixels and subpixels formed from the method of Figure 14. The cathode contact pads 1531 in each row may be assigned a color such as red 2010, green 2020, and blue 2030 in forming a pixel 2002. The number of pixels 2002 can be extended to form a display device, such as a TV. Each pixel 2002 can be activated by supplying power across a selection of anode contact pads 1521 and cathode contact pads 1531 combinations for forming a particular color value in an image for presentation on the display.

[0073] Advantageously, the methods provided above generate a top contact RGB OLED with improved IR drop while reducing the number of dead pixels by failed connections or shorts.

[0074] These and other advantages maybe realized in accordance with the specific embodiments described as well as other variations. It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments and modifications within the spirit and scope of the claims will be apparent to those of skill in the art upon reviewing the above description. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Claims

WHAT IS CLAIMED IS:

1. A method for fabricating a sub-pixel circuit for an organic light-emitting diode (OLED) display, the method comprising: preparing a glass substrate deposited with an indium tin oxide (ITO) layer having a first pattern; coating the first patterned ITO glass substrate with a pixel defining layer

(PDL); developing the PDL to form a second pattern on the glass substrate; depositing a second metal grid on the second patterned PDL; coating the glass substrate with a photoresist layer; exposing the photoresist layer for forming a first OLED sub-pixel; developing the exposed photoresist layer; adding an organic layer on at least the ITO layer exposed by the developed photoresist layer corresponding to the first OLED sub-pixel; adding a cathode layer on the organic layer; and adding an encapsulation layer on the cathode layer

2. The method of claim 1 further comprising: repeating the steps above to form a second and third OLED sub-pixel.

3. The method of claim 2, further comprising: adding a global encapsulation layer over the first, second and third OLED sub-pixels.

4. The method of claim 1 , further comprising: removing the photoresist layer after adding the encapsulation layer.

5. The method of claim 1 wherein the photoresist layer is a sacrificial layer.

6. The method of claim 1 wherein the cathode layer extends between the second metal grid on both sides of the organic layer.

7. A method for forming a sub-pixel OLED area in a stack, the method comprising: preparing a glass substrate patterned with an indium tin oxide (ITO) layer; coating the patterned glass substrate with a pixel define layer (PDL); developing the PDL to form a pattern on the glass substrate; coating the glass substrate with a photoresist layer; exposing the photoresist layer for forming slits between the cathode contact pads; adding an organic layer in the slits; and adding a metal layer in the slits.

8. The method of claim 7, wherein the PDL extends onto anode contact pads and cathode contact pads in the ITO layer.

9. The method of claim 7, further comprising: placing an open organic mask to cover the anode contact pads and the cathode contact pads prior to adding the organic layer; and removing the mask organic mask after the organic layer has been added.

10. The method of claim 10, prior to adding the metal layer in the slits, the method further comprising: placing a metal mask to cover the anode contact pads and the cathode contact pads wherein the metal mask has a larger opening than the open organic mask.

11. The method of claim 10, after adding the metal layer in the slits, the method further comprising: removing the metal mask.

12. The method of claim 7, further comprising: removing the photoresist; and adding a global encapsulation layer over the glass substrate.

13. The method of claim 8, wherein the organic layer is deposited on the ITO layer and PDL is visible through the photoresist layer.

14. The method of claim 8, wherein the metal layer extends beyond the organic layer onto the PDL.

15. The method of claim 8, wherein the metal layer extends from a first anode contact pad to a second anode contact pad.