Improved organic light emitting diode (OLED) displays, devices, systems, and methods - Patents.com

Abstract

An apparatus and method for enhancing images on organic light emitting diode (OLED) displays is provided. [Solution] An OLED device is formed with a first light-emitting OLED stack, a charge generation layer (CGL), a second light-emitting OLED stack, and a color filter. The OLED display pixel includes three subpixels, each fabricated with a separate anode and color filter. A dielectric barrier is disposed between the separate anodes of the three subpixels and around the periphery of each separate anode. During operation, when current flows through a desired one of the three subpixels, lateral current flow through the CGL to adjacent subpixels is prevented, resulting in light generation by the desired subpixel and reducing unwanted light generation in subpixels adjacent to the desired subpixel. The OLED device may include microlenses. The microlenses collimate light, thereby reducing the aperture of the emitted light and increasing display brightness.

Description

[Technical field]

[0001] Related Applications This application claims priority from U.S. Provisional Patent Application No. 62 / 847,856, filed May 14, 2019, and entitled “OLED LIGHT ENHANCEMENT,” and this application claims priority from U.S. Provisional Patent Application No. 62 / 911,905, filed October 7, 2019, and entitled “BACKPLANE FOR ORGANIC LIGHT EMITTING DIODE (OLED) DISPLAYS, APPARATUSES, SYSTEMS, AND METHODS.”

[0002] U.S. Provisional Patent Application No. 62 / 847,856 is incorporated herein by reference. U.S. Provisional Patent Application No. 62 / 911,905 is incorporated herein by reference. [Background technology]

[0003] 2. Background of the Invention 1. Field of the invention The present invention relates generally to displays, and more specifically to high brightness organic light emitting diode (OLED) displays and color purity in OLED displays.

[0004] 2.Technical background OLED display technology is advancing at a rapid pace. In particular, the development of highly efficient OLED materials and high-productivity OLED deposition equipment has led to the large-scale commercialization of OLED displays. OLED devices contain an organic semiconductor layer located between two electrodes, an anode and a cathode. The electrodes are usually made of inorganic materials. Holes and electrons are injected into the organic layer from the anode and cathode, respectively. When the electrons and holes recombine in the active organic layer, photons are emitted.

[0005] A subset of OLED displays are micro-OLED displays, which are typically smaller than 1 inch in diagonal size. Micro-OLED displays typically have a backplane integrated circuit fabricated on a single crystal silicon (Si) substrate. Due to the high performance of Si transistors, the pixel size can be very small, typically 15 micrometers (μm) or less, which is used to create high resolution displays at small sizes. The backplane circuitry includes the pixel array, row / column drivers, video input, video processing, and programmable control.

[0006] Due to the small pixel size, full-color micro-OLED displays are typically made using a white-emitting OLED structure with color filters on top. Each pixel is composed of red (R), green (G), and blue (B) sub-pixels. Each sub-pixel has its own separate anode, but all the sub-pixels share a common semi-transparent cathode. Very high resolution displays, up to 2560 x 2560 pixels, have been demonstrated using such OLED configurations.

[0007] Micro-OLED displays are considered the leading display candidates for next-generation wearable products such as virtual reality (VR), augmented reality (AR), and mixed reality (MR) applications due to their small size, high resolution, low power consumption, and high video frame rates. One major performance challenge for micro-OLEDs in these applications is high-brightness operation with acceptable lifetime. Most applications require display brightness above 1000 nits, and in some cases 5000-10,000 nits. Although advances in OLED materials have led to significant improvements in OLED brightness, obtaining such high brightness is very difficult. This can be problematic.

[0008] Attempts to increase OLED display brightness have led to multi-stack OLED structures, such as tandem OLED structure 102, an example of which is shown generally at 100 in FIG. 1. However, white-emitting tandem OLED designs applied to microdisplays have significant drawbacks. Because the subpixel anodes, 110, 112, 114, etc., share a common cathode 116, current flowing from one anode to the common cathode 116 can spread laterally to adjacent pixels, particularly along the highly conductive charge generation layer (CGL) 108 between the two diodes 104 and 106. Lateral current flow manifests as "crosstalk" or light leakage, indicated at 122 / 124 and / or 126 / 128, which can lead to degradation of image sharpness and more seriously degradation of color purity. For example, the red subpixel 120 can be contaminated with some blue 128 and green 124 colors, resulting in a reduction in the color purity of the red. This issue could significantly degrade the color gamut of the display to the point where tandem OLED microdisplays would become unacceptable for most applications.

[0009] Micro OLED display brightness also suffers from the fact that the light output from OLED light emitting elements is Lambertian in nature, meaning that the light output is emitted over a wide output angle, typically greater than plus or minus 50 degrees. As a result, some of the light is not effectively collected by the optics used in wearable products, leading to poor performance. This can be problematic.

[0010] BRIEF DESCRIPTION OF THE DRAWINGS The invention may best be understood by reference to the following description and the accompanying drawings, which are used to illustrate embodiments of the invention, and in which: The invention is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which like reference characters indicate similar elements. [Brief description of the drawings]

[0011] [Figure 1] 1 illustrates an existing two-stack tandem OLED display cross-section. [Figure 2A] 1 illustrates various cross-sections corresponding to process stages during the fabrication of a subpixel anode, according to an embodiment of the present invention. [Figure 2B] 1 illustrates various cross-sections corresponding to process stages during the fabrication of a subpixel anode, according to an embodiment of the present invention. [Figure 2C] 1 illustrates various cross-sections corresponding to process stages during the fabrication of a subpixel anode, according to an embodiment of the present invention. [Figure 2D] 1 illustrates various cross-sections corresponding to process stages during the fabrication of a subpixel anode, according to an embodiment of the present invention. [Figure 3A] 1 illustrates, in cross-section, a dielectric barrier according to an embodiment of the present invention. [Figure 3B] 3B illustrates, in cross section, an enlarged view of a portion of the dielectric barrier from FIG. 3A, in accordance with an embodiment of the present invention. [Figure 4A] 1 illustrates, in cross-section, another dielectric barrier according to an embodiment of the present invention. [Figure 4B] 4B illustrates, in cross section, an enlarged view of a portion of the dielectric barrier from FIG. 4A, in accordance with an embodiment of the present invention. [Diagram 5] 1 illustrates a process for improving an image rendered on an OLED display through microstructure fabrication, according to an embodiment of the present invention. [Figure 6] 1 illustrates in cross section the fabrication of a microlens for a subpixel in an OLED display according to an embodiment of the present invention. [Figure 7] 1 illustrates in cross section the fabrication of a microlens for a subpixel in a single stack OLED display according to an embodiment of the present invention. [Figure 8] 1 illustrates a process for improving light collimation from an OLED display according to an embodiment of the present invention. [Figure 9]4A and 4B illustrate in cross section the combination of a microlens for a subpixel in an OLED display with a dielectric barrier as illustrated in FIGS. 3A and 3B, according to an embodiment of the present invention. [Figure 10] 4A and 4B illustrate in cross section the combination of a microlens for a subpixel in an OLED display with a dielectric barrier as illustrated in FIGS. 4A and 4B, according to an embodiment of the present invention. [Figure 11] 1 illustrates a process for improving image quality and brightness from an OLED display according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Detailed Description In the following detailed description of the embodiments of the present invention, reference is made to the accompanying drawings, in which like reference numerals designate similar elements and in which specific embodiments in which the present invention may be practiced are shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure an understanding of the invention. Therefore, the following detailed description should not be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

[0013] Apparatus, methods, and systems are described for providing high brightness OLED displays that produce both sharp images and a wide color gamut with excellent color purity. As used in this description of the embodiments, display and microdisplay should be given a broad meaning and may be used interchangeably. It should be noted that the embodiments of the present invention are applicable to displays of various sizes, including microdisplays measuring 1.5 inches or less across the diagonal of the display to large flat panel displays measuring multiple feet across the diagonal of the display. Thus, the embodiments of the present invention are applicable to displays of any size. Similarly, as used in this description of the embodiments, it should be understood that a pixel of an OLED display can be made of multiple subpixels, each subpixel being used to provide a separate color of light to the pixel. It should be noted that the terms "pixel", "display pixel", "display element", or "OLED device" are used interchangeably, and all of these terms, i.e., "pixel", "display pixel", "display element", or "OLED device", should be distinguished from "subpixel". Additionally, while the subsequent figures will describe one or more OLED pixels for clarity of illustration, it will be understood that such description covers an entire display having many display pixels arranged in a row, and many rows arranged to provide a display having a typical number of m rows and n columns of OLED display elements across which an image is presented to a user.

[0014] 2A-2D illustrate various cross-sections corresponding to process stages during the creation of a subpixel anode according to an embodiment of the present invention. Referring collectively to FIGS. 2A-2D, in various embodiments, a micro-OLED display is fabricated using silicon (Si) semiconductor fabrication techniques for the display backplane. When Si fabrication techniques are utilized for the backplane, it is often desirable to use anode materials commonly used in Si integrated circuit processing. In various embodiments, the anode is fabricated using a thin layer of titanium nitride (TiN) on aluminum (Al). TiN has a high work function (about 4.6 eV) similar to that of indium tin oxide (ITO) (about 4.5 eV), and therefore facilitates hole injection. Making the TiN thin film thin enough, such as 3 nanometers (nm), can make the reflectivity of TiN / Al very high, approaching ninety percent (90%), thereby providing high luminous efficiency. OLED devices using TiN / Al anodes achieve good performance in terms of low OLED diode voltage and high OLED current efficiency.

[0015] In one or more embodiments, a method of forming a TiN anode, as illustrated in any of the figures herein, includes the following.

[0016] 1. A typical complementary metal oxide semiconductor (CMOS) process is used to fabricate a backplane integrated circuit on Si to drive an OLED display. This can consist of six metal processes (not including the anode metal), a representative example of which is illustrated at 226.

[0017] 2. Anode metallization is performed on the processed wafer. Silicon dioxide (SiO 2 A thick dielectric layer 202, such as SiO2, is deposited over the top metal layer and planarized by a chemical mechanical polishing (CMP) step. "Via" holes 206 are etched into the dielectric layer 202 and filled with a metal, such as tungsten.

[0018] 3. In various embodiments, a metal stack consisting of TiN / Al / TiN / Ti (indicated at 218, 216, 214, 212) or TiN / Al / Ti is used as the anode metal layer. 2 A typical metal stack for the anode is shown at 210. The top TiN thickness is in the range of 2-5 nm. The Al thickness is in the range of 30-60 nm. The bottom TiN / Ti or titanium (Ti) layer is an adhesion layer to the oxide underneath the anode metal layer. The bottom TiN thickness is in the range of 5-10 nm and the Ti thickness is in the range of 1-10 nm.

[0019] 4. The metal stack is then patterned by photolithography and etching into individual anodes for the red (R), green (G) and blue (B) sub-pixels 220.

[0020] In various embodiments, existing problems with OLED displays, such as but not limited to luminous efficiency, crosstalk between sub-pixels, reduced color gamut, lack of image sharpness, etc., are resolved by creating a barrier between OLED sub-pixels with a multi-stack OLED structure. For example, a tandem OLED structure consists of two OLED diodes connected in series, where the luminous efficiency measured in candela per ampere of current (Cd / A) can theoretically be doubled compared to a single-junction OLED diode. In a two-stack tandem OLED structure, a highly conductive "charge generation layer" (CGL) is often inserted between the two OLED diodes to minimize the voltage drop between the two diodes when current flows from one diode to the other. Ideally, the voltage of a two-stack tandem OLED should be only twice that of a single-junction OLED. This CGL layer is very important to avoid overvoltage across the tandem OLED device to minimize OLED power consumption.

[0021] FIG. 3A illustrates a dielectric barrier generally at 300 in cross section according to an embodiment of the present invention. FIG. 3B illustrates a detailed view of a portion of FIG. 3A at 350. Referring together to FIG. 3A and FIG. 3B, a cross section of a resulting OLED device resulting from a method of constructing a "barrier" between subpixels to reduce or prevent lateral current flow in a tandem or two-stack OLED device is illustrated. The two-stack OLED device is made of a first light-emitting OLED stack 310, a charge generating layer 312, and a second light-emitting OLED stack 314. As shown in FIG. 3A / FIG. 3B, a dielectric "barrier" is formed between the anodes of each subpixel. Such a structure is formed by dielectric layer deposition followed by a masked etch to expose the anode metal. At 352 h DB The thickness of the dielectric is expressed by 354 h S is selected to be substantially greater than the thickness of the lower OLED stack 310, represented by h DB The thickness range of the CGL layer 312 is between 1000 Angstroms (A) and 5000A, with a preferred range being between 1500A and 3000A. The CGL layer 312 disposed above the lower OLED stack 310 will be significantly "non-planar" above the "barriers" 308a, 308b, 308c, 308d, etc. As a result, the CGL layer 312 may be significantly reduced in thickness, as indicated at 358 / 360 above the "barrier" 308b, relative to the CGL thickness at 356, and may even be discontinuous in these regions. These changes in the CGL layer 312 lead to reduced conductance and reduced lateral current flow. The reduced conductance and reduced lateral current flow reduces and / or eliminates crosstalk between the sub-pixels indicated by 332, 336, and 340 of the OLED structure, thereby improving image clarity and maintaining a proper color gamut. Both of these contribute to high quality image production on an OLED display.

[0022] In various embodiments, the method for producing the cross-section illustrated in FIG. 3A proceeds as follows.

[0023] 1. In various embodiments, a typical CMOS process is used to fabricate a backplane integrated circuit (designated 226) for driving the OLED display elements. This can be composed of six metal processes (not including the anode metal).

[0024] 2. Anode metallization is performed on this processed wafer. SiO 2 A thick dielectric layer 202, such as SiO2, is deposited over the top metal layer and planarized by a chemical mechanical polishing (CMP) step. Via holes 206 are etched in the dielectric layer 202 and filled with a metal, such as tungsten.

[0025] 3. Individual anodes are fabricated for each subpixel by metal deposition and etching. In one or more embodiments, when the display is based on a red, blue, green (RGB) color map and the pixels are implemented with individual subpixels, each subpixel is used to contribute a particular color, i.e., red, blue, or green, to a given pixel. Thus, the anode metal layer 210 can be a stack composed of TiN / Al / TiN / Ti or TiN / Al / Ti, with SiO 2 indicated at 202. 2 (See, e.g., FIG. 2A et al.) The anode metal layer is etched between the sub-pixels by photolithography and dry etching to create the individual sub-pixel anodes 302, 304, 306, etc.

[0026] 4. A dielectric layer made of SiO2 is deposited over the entire surface. The thickness of the dielectric layer ranges from 100 nm to 500 nm, preferably from 200 nm to 300 nm.

[0027] 5. In various embodiments, a photo process is used to define an opening above the anode, and then etching is performed to remove the dielectric and expose the anode metal. The etching can be done by dry etching, wet etching, or a combination of dry and wet etching. The processing results in a dielectric barrier 308b disposed between the subpixel anodes 302 and 304, a dielectric barrier 308c between the subpixel anodes 304 and 306, and so on. A similar structure is repeated for an entire row of pixels, of which Figures 3A / 3B only illustrate a portion. Similarly, a similar structure is repeated for multiple rows of pixels using OLED pixels to create a display with m rows by n columns. Note that each pixel utilizes three unique subpixels to produce the required color.

[0028] As used in this description of the embodiment, two light-emitting OLED stacks 310 and 314 are used with a CGL layer 312 disposed between 310 and 314. The embodiments taught herein are easily used with existing OLED stacks and CGL layers. A non-limiting example of an OLED stack, used for illustration only and with no limitations implied thereby, is a stack made of layers including a hole injection layer, a hole transport layer, an emissive layer with a host dopant, and an electron transport layer. The OLED stack 310 can emit primarily in one color, such as red, or two colors, such as red and green. The OLED stack 314 can emit primarily in another color, such as blue, or two colors, such as green and blue. The overall emission from the two OLED stacks 310 and 314 emits in a broad spectrum similar to white. Non-limiting examples of CGL layers, used for illustrative purposes only and with no limitations implied thereby, are CGLs made of n-type doped organic materials and p-type doped organic materials, such as Li:tris(8-quinolinolato)aluminum(III) (Alq3) / FeCl3:4,4'-N,N'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), and 4,7-diphenyl-1,10-phenanthroline (BPhen):Rb2CO3 / NPB:ReO3.

[0029] In various embodiments, three or more OLED stacks are used, for example, a triple-emitting OLED stack is connected in series through two CGL layers. In this case, each OLED stack can emit primarily at one wavelength, such as red, green, and blue. Alternatively, one OLED stack can emit primarily at two wavelengths, such as red and green, and two stacks can emit primarily at blue wavelengths.

[0030] In various embodiments, for an OLED display, contact to the cathode 316 is made from a cathode ring contact placed around the periphery of the display (not shown). During light emission, electrons are transported through the cathode layer to the pixel area. Due to the large undulations in the device structure resulting from the dielectric barrier, a thin metal cathode layer made of silver (Ag) or silver / magnesium (Ag / Mg) may not be continuous beyond the high dielectric barrier 308a, 308b, 308c, 308d, etc. On the other hand, a thicker cathode made of a transparent conductive material such as indium tin oxide (ITO) may form a continuous layer, but its conductance may not be high enough, which may cause a significant voltage drop in the center of the display when the size of the display is larger than 0.5 inches diagonally. A lower effective voltage in the center of the display will result in a lower brightness of the display in that area and a worse uniformity across the display area. A cathode 316 consisting of a combination of a thin layer of metal (Ag or Ag / Mg) and a thicker layer of transparent oxide (ITO or InZnO) can be used to overcome the problem. In various embodiments, the OLED layers are very sensitive to water damage, so layer 317 is needed to protect the OLED layers from moisture penetration. Layer 317 can include a dielectric layer such as silicon nitride or zirconium oxide deposited by atomic layer deposition or chemical vapor deposition, and can include additional organic layers as well. On top of 317, color filters 330, 334, and 338 are fabricated. As described above, the OLED stacks 310 and 314 emit white light.

[0031] Color filters 330, 334, and 338 filter the white light accordingly and emit light of their particular color. In a non-limiting example provided merely for illustration in one or more embodiments, a typical color filter is made by using photopatterning of a photosensitive colored material. The material is generally a negative-tone photoresist mixed with a special color pigment (red, green, blue, etc.). In addition, a transparent material without pigment is also used as an underlayer material for improved adhesion and / or an overlayer material for protection of the color filter layer. The fabrication of the color filter may include the following steps: 1. Spin on a clear photosensitive material, pre-bake, expose with UV light to convert the material into a stable layer, and post-bake. A typical post-bake temperature is 100°C. 2. Spin on a photosensitive material containing a blue dye, pre-bake, expose the material using a photomask for the blue sub-pixel pattern, develop with a solvent to remove unexposed material, post-UV cure and post-bake. 3. Spin on a photosensitive material containing a blue dye, pre-bake, expose the material using a photomask for the green sub-pixel pattern, develop with a solvent to remove unexposed material, post-UV cure and post-bake. 4. Spin on a photosensitive material containing a blue dye, pre-bake, expose the material using a photomask for the red sub-pixel pattern, develop with a solvent to remove unexposed material, post-UV cure and post-bake. 5. Spin on a clear photosensitive material, pre-bake, expose with UV light to convert the material into a stable layer, and post-bake.

[0032] FIG. 4A illustrates another dielectric barrier generally at 400 in cross section according to an embodiment of the present invention. FIG. 4B illustrates a detailed view of a portion of FIG. 4A at 450. Referring together to FIG. 4A and FIG. 4B, a cross section of a resulting OLED device resulting from a method of constructing a "barrier" between subpixels to reduce or prevent lateral current flow in a two-stack OLED device is illustrated. The two-stack OLED device is made of a first white-emitting OLED stack 410, a charge generating layer 412, and a second white-emitting OLED stack 414. As shown in FIG. 4A / FIG. 4B, a dielectric "barrier" is formed between the anodes of each subpixel. Such a structure is formed by dielectric layer deposition followed by a masked etch to expose the anode metal. At 452, DB The thickness of the dielectric is represented by 454 h S is selected to be greater than the thickness of the lower OLED stack 410, represented by h DB h S Lower OLED stack 410 408a / 409a, 408b / 409b, 408c / 409c, 408d / 409d, etc. As a result, the CGL 412 may be significantly reduced in thickness and discontinuous in these regions, as indicated at 458 / 460 above the "barrier" 408b / 409b, relative to the thickness 456 of the CGL above the anode 302. These changes in the CGL 412 lead to reduced conductance and reduced lateral current flow to adjacent subpixels. The reduced conductance and reduced lateral current flow reduces and / or eliminates crosstalk between subpixels, as indicated by 432, 436, and 440 of the OLED structure, thereby improving image clarity and maintaining a proper color gamut, both of which contribute to the creation of high quality images on an OLED display.

[0033] FIG. 4A illustrates another dielectric barrier generally at 400 in cross section according to an embodiment of the present invention. FIG. 4B illustrates a detailed view of a portion of FIG. 4A at 450. Referring together to FIG. 4A and FIG. 4B, a cross section of a resulting OLED device resulting from a method of constructing a "barrier" between subpixels to reduce or prevent lateral current flow in a two-stack OLED device is illustrated. The two-stack OLED device is made of a first white-emitting OLED stack 410, a charge generating layer 412, and a second white-emitting OLED stack 414. As shown in FIG. 4A / FIG. 4B, a dielectric "barrier" is formed between the anodes of each subpixel. Such a structure is formed by dielectric layer deposition followed by a masked etch to expose the anode metal. At 452, DB The thickness of the dielectric is represented by 454 h S is selected to be greater than the thickness of the lower OLED stack 410, represented by h DB h S 4. The CGL 412 disposed above the lower OLED stack 310 will be significantly "non-planar" above the "barriers" 408a / 409a, 408b / 409b, 408c / 409c, 408d / 409d, etc. As a result, the CGL 412 may be significantly reduced in thickness and discontinuous in these regions, as indicated at 458 / 460 above the "barriers" 408b / 409b, relative to the thickness 456 of the CGL above the anode 302. These changes in the CGL 412 lead to reduced conductance and reduced lateral current flow to adjacent subpixels. The reduced conductance and reduced lateral current flow reduces and / or eliminates crosstalk between subpixels, as indicated by 432, 436, and 440 of the OLED structure, thereby improving image clarity and maintaining a proper color gamut, both of which contribute to the creation of high quality images on an OLED display.

[0034] In various embodiments, the method for producing the cross-section illustrated in Figures 4A-4B proceeds as follows.

[0035] 1. Note that the shape of the barrier in FIGS. 4A-4B differs from that of FIGS. 3A-3B in that the barrier in FIGS. 4A-4B is wider at the top, resembling a "mushroom" shape. As illustrated at 450 in FIG. 4B, the width W of the upper barrier 409b is db2 is the width W of the lower part of the barrier db1 Therefore, W db2 W db1 Greater than.

[0036] 2. The barrier dielectric layer is formed by depositing SiO2 followed by a top layer of SiN. The thickness of SiO2 ranges from 100 to 500 nm and the thickness of SiN ranges from 10 to 100 nm.

[0037] 3. After the SiO2 / SiN dielectric layers are etched, typically by a dry etch, a subsequent wet etch is performed using an oxide etch chemistry such as buffered hydrogen fluoride (BHF) or diluted HF to "undercut" the oxide while leaving the SiN top layer largely unetched, thereby creating features that are wider in the upper regions and narrower in the lower regions.

[0038] 4. This "mushroom" shaped barrier, i.e., 408a / 409a, 408b / 409b, 408c / 409c, 408d / 409d, etc., is very effective in reducing the thickness of the CGL 458 / 460 above the dielectric barrier, thereby making the CGL discontinuous where it crosses over the dielectric barrier fabricated between adjacent subpixel anodes, such as in regions 458, 460.

[0039] In various embodiments, in the case of an OLED display, contact to the cathode 416 is made from a cathode ring contact placed around the periphery of the display (not shown). During light emission, electrons should be transported through the cathode layer to the pixel area. Due to the large undulations of the device structure resulting from the dielectric barrier, a thin metal cathode layer made of silver (Ag) or silver / magnesium (Ag / Mg) may not be continuous over a high barrier, e.g., 408a / 409a, 408b / 409b, 408c / 409c, 408d / 409d, etc. On the other hand, a thicker cathode made of a transparent conductive material such as ITO may form a continuous layer, but its conductance may not be high enough, which may cause a significant voltage drop in the center of the display when the size of the display is larger than 0.5 inches diagonally. A lower effective voltage in the center of the display will result in a lower brightness of the display in that area and a worse uniformity across the entire display area. A cathode composed of a thin layer of metal (Ag or Ag / Mg) in combination with a thicker layer of transparent oxide (ITO or InZnO) can be used to overcome the problem.

[0040] The layers above the cathode 416 follow the order and method described above in connection with Figures 3A and 3B. For example, in various embodiments, the passivation layer 417 and color filters 430, 434, and 438 are fabricated above the cathode 416. As described above, the first and second OLED stacks 410 and 414 are white-emitting structures. The color filters 430, 434, and 438 filter the white light accordingly to emit light of their particular color. Exemplary color filters are fabricated at 430, 434, 438 as described above in connection with Figures 3A and 3B. For a display made with a red, green, blue (RGB) color map, in one embodiment, the color filter 430 filters the white light emitted by the OLED to provide a visible blue light output, the color filter 434 filters the white light emitted by the OLED to provide a visible red light output, and the color filter 438 filters the white light emitted by the OLED to provide a green light output. Each colored subpixel 432, 436, and 440 provides a respective colored light contribution to a given display pixel of which they are a part. In operation, a user views the display pixel output and perceives the overall color of the display pixel. The dielectric barrier provides accurate color generation at the display pixel level by initially providing the correct R, G, and B contributions from the subpixels of the OLED display pixel. In operation, when current flows through a desired subpixel of the three subpixels of any display element, lateral current flow through the charge generation layer (CGL) to adjacent subpixels is prevented, resulting in light generation by the desired subpixel and reducing unwanted light generation in subpixels adjacent to the desired subpixel. The described structure results in accurate reproduction of desired colors by an OLED display.

[0041] FIG. 5 illustrates generally at 500 a process for improving an image rendered on an OLED display through microstructure fabrication, according to an embodiment of the present invention. With reference to FIG. 5, the process begins at block 502. At block 504, OLED subpixels are fabricated. Fabrication of subpixels for OLED displays is described herein with reference to various figures, such as, but not limited to, FIGS. 2A-4B. In various embodiments, the OLED subpixels are fabricated using silicon processing techniques. At block 506, a dielectric barrier is created between the subpixels. In various embodiments, creation of the dielectric barrier between the subpixels is described herein with reference to various figures, such as, but not limited to, FIGS. 3A-4B. The process ends at block 508.

[0042] The light emitted from the OLED stack and output through the color filters has a wide output angle, typically greater than plus or minus 50 degrees. Refractive microlens elements are microfabricated above each color filter to increase the light output and "collimate" it to a narrower angle. The efficiency of the light collimation depends on the light coupling efficiency between the color filter (CF) and the microlens interface, and the shape of the microlens.

[0043] FIG. 6 illustrates in cross section at 600 a microlens fabrication for a subpixel in an OLED display according to an embodiment of the present invention. Referring to FIG. 6, in various embodiments, the microlens fabrication can be accomplished by a thermal flow method or an etch-back method. In the thermal flow method, the lens substrate has a photoresist function. The lens material includes an acrylic resin with a photoinitiator to make it photosensitive. After the lens substrate is patterned into a shape with sharp sidewalls, as indicated at 604, it is transformed into a lens shape by post-curing at high temperature. The post-curing temperature is preferably less than 120° C., preferably less than 100° C. An example of a post-cured lens shape is qualitatively illustrated at 606 for illustrative purposes only. The lens substrate is fabricated on the surface 602 by photolithography and development, similar to the color filter process described above.

[0044] Alternatively, an etch-back process can be used to fabricate the lenses above the color filters, which in various embodiments allows for a higher refractive index material to be utilized for the lenses since the lens substrate does not have photoresist functionality. The fabrication process proceeds as follows:

[0045] 1. A lens material is first coated onto the surface of the OLED microstructure 602 above the color filters.

[0046] 2. Photoresist material is coated on the lens material and formed into a square pattern through exposure and development. A heat flow process is used to make the pattern round.

[0047] The lens material underneath the photoresist is then etched using a dry etching technique, and by deliberately adjusting the etch rates of the photoresist and lens material, a lens shape 606 is formed in the microlens.

[0048] According to the description of the technique above, an array of microlenses is fabricated for a microdisplay having m rows and n columns. Such a display generally includes a pixel array represented by 608. 1,1 Pixels represented by 610 m,n In various embodiments, OLED displays are made with a general number of m rows and n columns. Note that m and n may have the same value or may have different values. Thus, displays can be made with values ​​of m and / or n less than, equal to, or greater than 2560.

[0049] Figure 7 illustrates in cross section generally at 700 microlens fabrication for subpixels in a single stack OLED display according to an embodiment of the invention. With reference to Figure 7, microlenses 702, 704, 706, etc. are fabricated over color filters 330, 334, 338, etc. in the OLED display. As before, in this description of the embodiment, one pixel having three subpixels is used for clarity of illustration. The OLED device includes a white-emitting OLED single stack 310 fabricated over subpixel anodes 302, 304, 306, etc. A common cathode is designated 316.

[0050] To achieve maximum light output from the OLED display, a vacuum cavity or a cavity filled with an inert gas is used above the microlenses 702, 704, 706, etc. Such a cavity is designated 708. In various embodiments, the cavity 708 can be filled with an inert gas or a vacuum can be created. Alternatively, the microlenses can be manufactured using a material with a higher refractive index (about 1.6 or higher) and a resin with a lower refractive index (about 1.5 or lower) is used to fill the gap between the microlenses and the cover 710. The cover 710 is made of a transparent material such as, but not limited to, glass. In operation, light emitted from the subpixels 712, 714, 716, etc. is collimated by structures above the color filters (various combinations of microlenses and gap-filling materials in various embodiments) to enhance the OLED display brightness.

[0051] FIG. 8 illustrates a process generally at 800 for improving light collimation from an OLED display according to an embodiment of the present invention. With reference to FIG. 8, the process begins at block 802. At block 804, an OLED device is fabricated. In various embodiments, the OLED device can be fabricated using a single stack white-emitting OLED or a tandem stack of white-emitting OLED layers. It is noted that microlens fabrication can be applied to both OLED microstructures that include a dielectric barrier (FIGS. 3A-4B) and those that do not include a dielectric barrier. At block 806, an array of microlenses is fabricated on the OLED device fabricated at block 804. When the OLED device is in the "on" state, collimation of the light output of the OLED display increases the brightness of the display to a user. The process stops at block 810.

[0052] Figure 9 illustrates in cross section generally at 900 the combination of a microlens for a subpixel in an OLED display with the dielectric barrier described in Figures 3A and 3B according to an embodiment of the present invention. With reference to Figure 9, the microlens fabrication described above is combined with the OLED microstructure described in Figures 3A and 3B. The resulting OLED structure combines the benefits of improved color purity through the application of a dielectric barrier and improved display intensity through improved collimation of the output light, thereby providing an OLED display that produces clear, color-pure, and bright images.

[0053] FIG. 11 illustrates a process generally at 1100 for improving image quality and brightness from an OLED display, according to an embodiment of the present invention. With reference to FIG. 11 , the process begins at block 1102. At block 1104, OLED sub-pixels are fabricated. Fabrication of sub-pixels for OLED displays is described herein with reference to various figures, such as, but not limited to, FIGS. 2A-4B. In various embodiments, the OLED sub-pixels are fabricated using silicon processing techniques. At block 1106, a dielectric barrier is created between the sub-pixels. In various embodiments, fabrication of a dielectric barrier between the sub-pixels is described herein with reference to various figures, such as, but not limited to, FIGS. 3A-4B. 。O OLED processing steps are performed, including LED layer deposition, cathode layer formation, passivation, and color filter steps.

[0054] FIG. 11 illustrates generally at 1100 a process for improving image quality and brightness from an OLED display according to an embodiment of the present invention. With reference to FIG. 11, the process begins at block 1102. At block 1104, OLED sub-pixels are fabricated. Fabrication of sub-pixels for OLED displays is described herein with reference to various figures, such as, but not limited to, FIGS. 2A-4B. In various embodiments, the OLED sub-pixels are fabricated using silicon processing techniques. At block 1106, a dielectric barrier is created between the sub-pixels. In various embodiments, creation of the dielectric barrier between the sub-pixels is described herein with reference to various figures, such as, but not limited to, FIGS. 3A-4B. At block 1107, OLED processing steps are performed, including OLED layer deposition, cathode layer formation, passivation, and color filter steps.

[0055] At block 1108, an array of microlenses is created over the OLED device that was fabricated in blocks 1104 and 1106. The process ends at block 1110. When the OLED device is in the "on" state, collimation of the light output from the OLED display is improved, thereby improving the brightness of the display to a user. The process of Figure 11 provides an OLED display that produces clear, color-pure, and bright images.

[0056] In various embodiments, as with the OLED systems described in the previous figures, the components of the OLED system are implemented in an integrated circuit device, which may include an integrated circuit package containing integrated circuits. In some embodiments, as with the systems, the components of the system are implemented in a single integrated circuit die. In other embodiments, as with the systems, the components of the system are implemented in two or more integrated circuit dies of an integrated circuit device, which may include a multi-chip package containing integrated circuits.

[0057] For purposes of discussing and understanding the embodiments of the present invention, it should be understood that various terms are used by those skilled in the art to describe techniques and procedures. Furthermore, in the description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the embodiments of the present invention may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the embodiments of the present invention. These embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, and it should be understood that other embodiments may be utilized, and that logical, mechanical, electrical, and other changes may be made without departing from the scope of the embodiments of the present invention.

[0058] Thus, embodiments of the present invention can be used to provide high brightness OLED displays. Embodiments of the present invention are similarly used to improve image sharpness and to maintain color gamut. Some non-limiting examples of OLED systems in which embodiments of the present invention are used are, but are not limited to, use in mobile phones, large screen displays, near-to-eye (NTE) displays, or headset computing devices. Other embodiments of the present invention are readily implemented in wearable or head-wearable devices of common configurations, such as, but not limited to, wearable products such as virtual reality (VR), augmented reality (AR), mixed reality (MR), wristbands, watches, glasses, goggles, visors, headbands, helmets, and the like, or the like. As used in this description of the embodiments, wearable encompasses head wearables, wrist wearables, neck wearables, and thus any form of wearable that can be attached to a user.

[0059] While the present invention has been described with respect to several embodiments, those skilled in the art will recognize that the invention is not limited to the described embodiments, but can be practiced with modification and alteration within the spirit and scope of the appended claims. Thus, the description should be regarded as illustrative instead of restrictive.

Claims

1. 1. An organic light emitting diode (OLED) display device, comprising:

1. An OLED device, the OLED device being formed of a first OLED stack, a charge generation layer (CGL), a second OLED stack, and a color filter, the OLED device comprising: Three sub-pixels, each having a separate anode, the three sub-pixels sharing a common cathode, the common cathode comprising: a first layer, the first layer being a thin layer formed of a metal; three sub-pixels, a second layer, the second layer being a thicker layer formed of a transparent oxide, the common cathode having a lower surface proximate the separate anodes and an upper surface remote from the separate anodes, the separate anodes having an outer periphery; a dielectric barrier disposed between the separate anodes of the three sub-pixels and around the periphery of each separate anode, the dielectric barrier extending beyond the separate anodes of the three sub-pixels into both the first OLED stack and the second OLED stack, the dielectric barrier having a particular undulating shape, the particular undulating shape being characterized as follows:

1. The dielectric barrier has a maximum height above the separate anodes that is less than a minimum height of the top surface of the common cathode located above the separate anodes; 2. The maximum height of the dielectric barrier is less than the minimum height of the lower surface of the common cathode located above the separate anodes; a dielectric barrier, which causes the CGL to have the particular contoured shape, such that in operation, when current flows through a desired one of the three sub-pixels, lateral current flow through the CGL to an adjacent sub-pixel is prevented, resulting in light generation by the desired sub-pixel and reducing unwanted light generation in sub-pixels adjacent to the desired sub-pixel; The OLED device further comprises:

1. An organic light emitting diode (OLED) display device comprising:

2. The device of claim 1 , wherein the color filters provide a different color filter for each of the three sub-pixels.

3. The device of claim 2 , wherein the colors of the different color filters are red, blue, and green.

4. a plurality of OLED devices arranged in a row and column arrangement providing at least 2560 rows with 2560 OLED devices in each row; The apparatus of claim 2 , further comprising:

5. The device of claim 3 , wherein the device is a microdisplay.

6. three microlenses, each of the three microlenses positioned above a different sub-pixel of the OLED device, wherein in operation, when light is emitted from the sub-pixel, the microlenses collimate the emitted light; The apparatus of claim 1 further comprising:

7. a cover layer disposed over the microlens to form a gap; The apparatus of claim 6 further comprising:

8. The apparatus of claim 7 , wherein the gap is filled with an inert gas or a vacuum is created in the gap.

9. A cover layer; a filler material disposed between the microlens and the cover layer, the filler material having a refractive index less than a refractive index of the cover layer; and The apparatus of claim 6 further comprising:

10. The apparatus of claim 1 , wherein the CGL is thinned adjacent the dielectric barrier.

11. The apparatus of claim 10 , wherein the dielectric barrier has substantially non-parallel sides.

12. The apparatus of claim 1 , wherein the CGL is discontinuous near the dielectric barrier.

13. 13. The apparatus of claim 12, wherein the dielectric barrier is made of two different materials, a first material extending up from the separate anode and defining a first region characterized by a first width, and a second material affixed to the first material and extending up from the separate anode and defining a second region characterized by a second width, and the two different materials are processed to make the second width wider than the first width.

14. The first material is silicon dioxide (SiO ２ 14. The apparatus of claim 13, wherein the first material is made of silicon mononitride (SiN).

15. 1. An organic light emitting diode (OLED) pixel microstructure, comprising: A plurality of pixel elements, each of the plurality of pixel elements comprising: Three sub-pixels, each of which is vertically stacked above a substrate in the following order: An anode; a first OLED stack; and a charge generating layer (CGL); a second OLED stack; and a cathode having a lower surface proximate the anode and an upper surface distal to the anode; a dielectric barrier disposed between the anodes and around a periphery of each anode, the dielectric barrier extending beyond the anodes into both the first OLED stack and the second OLED stack, the dielectric barrier being of a particular undulating shape, the particular undulating shape being characterized as follows:

1. The dielectric barrier has a maximum height above the anode that is less than the minimum height of the top surface of the cathode located above the anode; 2. The maximum height of the dielectric barrier is less than the minimum height of the lower surface of the cathode located above the anode; a dielectric barrier, which causes the CGL to have the particular contoured shape, such that in operation, when current flows through a desired one of the three sub-pixels, lateral current flow through the CGL to an adjacent sub-pixel is prevented, resulting in light generation by the desired sub-pixel and reducing unwanted light generation in sub-pixels adjacent to the desired sub-pixel; The three sub-pixels further include The plurality of pixel elements further comprises:

1. An organic light emitting diode (OLED) pixel microstructure comprising:

16. 16. The apparatus of claim 15, wherein the dielectric barrier is made of two different materials, the first material extending up from the anode and defining a first region characterized by a first width, the second material being affixed to the first material and the second material extending up and defining a second region characterized by a second width, and the two different materials being processed to make the second width wider than the first width.

17. The cathode is a first layer, the first layer being a thin layer formed of a metal; 16. The apparatus of claim 15, further comprising: a second layer, said second layer being a thicker layer formed of a transparent oxide.

18. 20. The apparatus of claim 17, wherein the metal is selected from the group consisting of silver and silver / magnesium.

19. 20. The device of claim 17, wherein the transparent oxide is selected from the group consisting of indium tin oxide and indium zinc oxide.

20. The apparatus of claim 15 , wherein the CGL is thinned adjacent the dielectric barrier.

21. The apparatus of claim 15 , wherein the CGL is discontinuous near the dielectric barrier.

22. a color filter disposed over each anode, the color filter passing light having a color selected from the group consisting of red, blue, and green; The apparatus of claim 15 further comprising:

23. a microlens disposed above the color filter, wherein in operation, the microlens collimates light in a direction substantially perpendicular to a plane of the microlens, thereby reducing an aperture of the emitted light; 23. The apparatus of claim 22, further comprising:

24. 1. A method for reducing unwanted light generation in adjacent subpixels in an OLED microstructure, comprising: creating a dielectric barrier within the OLED microstructure, the dielectric barrier being created between and around the periphery of each separate anode, forming a relief pattern; 1. A first OLED stack; 2. A charge generation layer (CGL) of the OLED microstructure; 3. A second OLED stack; 4. a cathode having a lower surface and an upper surface, wherein the dielectric barrier extends over each respective anode into both the first OLED stack and the second OLED stack, the dielectric barrier being in a particular undulating shape, the particular undulating shape being characterized as follows: a. the dielectric barrier has a maximum height above each of the separate anodes that is less than a minimum height of the top surface of the cathode above each of the separate anodes; b. A method of reducing unwanted light generation in adjacent sub-pixels in an OLED microstructure, wherein a maximum height of the dielectric barrier is less than a minimum height of the lower surface of the cathode overlying each separate anode, thereby causing a CGL to have the particular undulating shape, such that during operation, when current flows through a desired sub-pixel, lateral current flow through the CGL to an adjacent sub-pixel is prevented, resulting in light generation by the desired sub-pixel and reducing unwanted light generation in sub-pixels adjacent to the desired sub-pixel.

25. The method of claim 24 , wherein the CGL is thinner adjacent the dielectric barrier.

26. The method of claim 24 , wherein the CGL is discontinuous near the dielectric barrier.

27. 25. The method of claim 24, further comprising adding a color filter over each separate anode, the color filter passing light having a color selected from the group consisting of red, blue, and green.

28. 25. The method of claim 24, further comprising forming a microlens over each separate anode, wherein, during operation, each microlens collimates light in a direction substantially perpendicular to a plane of the microlens, thereby reducing an aperture of the emitted light.

29. 30. The method of claim 28, wherein the forming includes heating and melting back a lens material to form the microlenses.

30. 30. The method of claim 28, wherein the forming comprises etching a lens material to form the microlenses.

31. 25. The method of claim 24, wherein the dielectric barrier is made of two different materials, a first material extending up from each separate anode to define a first region characterized by a first width, and a second material affixed to the first material and extending up from each separate anode to define a second region characterized by a second width, and the two different materials are processed to make the second width wider than the first width.

32. The cathode is a first layer, the first layer being a thin layer formed of a metal; 25. The method of claim 24, further comprising: a second layer, said second layer being a thicker layer formed of a transparent oxide.

33. 33. The method of claim 32, wherein the metal is selected from the group consisting of silver and silver / magnesium.

34. 33. The method of claim 32, wherein the transparent oxide is selected from the group consisting of indium tin oxide and indium zinc oxide.

35. 1. An organic light emitting diode (OLED) display device, comprising:

1. An OLED device, the OLED device being formed of a first OLED stack, a charge generation layer (CGL), a second OLED stack, and a color filter, the OLED device comprising: three sub-pixels, each sub-pixel having a separate anode, the separate anode having a periphery; a common cathode having a lower surface proximate to the separate anodes and an upper surface distal to the separate anodes; a dielectric barrier disposed between the separate anodes of the three sub-pixels and around the periphery of each separate anode, the dielectric barrier extending beyond the separate anodes of the three sub-pixels into both the first OLED stack and the second OLED stack, the dielectric barrier having a particular undulating shape, the particular undulating shape being characterized as follows:

1. The dielectric barrier has a maximum height above the separate anodes that is less than a minimum height of the top surface of the common cathode located above the separate anodes; 2. The maximum height of the dielectric barrier is less than the minimum height of the lower surface of the common cathode located above the separate anodes; a dielectric barrier, whereby the CGL assumes the particular contoured shape; a microlens having a planar surface, the microlens configured over each subpixel, and in operation, each microlens collimates light in a direction perpendicular to the plane, thereby minimizing stray light, and when current flows to a desired one of the three subpixels, lateral current flow through the CGL to an adjacent subpixel is prevented, resulting in light generation by the desired subpixel and reducing unwanted light generation in subpixels adjacent to the desired subpixel; The OLED device further comprises:

1. An organic light emitting diode (OLED) display device comprising:

36. 36. The apparatus of claim 35, further comprising a cover disposed over the microlens creating a gap between the microlens and a lower surface of the cover.

37. 37. The apparatus of claim 36, wherein the gap contains an inert gas.

38. 37. The apparatus of claim 36, wherein a vacuum is created in the gap.

39. 37. The apparatus of claim 36, wherein the gap is filled with a resin, the refractive index of the microlens material being greater than the refractive index of the resin.

40. 36. The apparatus of claim 35, wherein the CGL is thinned adjacent the dielectric barrier.

41. 41. The apparatus of claim 40, wherein the dielectric barrier has substantially vertical sides.

42. 36. The apparatus of claim 35, wherein the CGL is discontinuous near the dielectric barrier.

43. 43. The apparatus of claim 42, wherein the dielectric barrier is made of two different materials, a first material extending up from the separate anode and defining a first region characterized by a first width, and a second material affixed to the first material and extending up from the separate anode and defining a second region characterized by a second width, and the two different materials are processed to make the second width wider than the first width.

44. The first material is silicon dioxide (SiO ２ 44. The apparatus of claim 43, wherein the first material is made from silicon mononitride (SiN).

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