Multi-distributed Bragg reflector pixel array

Abstract

A microcavity pixel array device and method of manufacture having a shared multi-DBR system configured to cover a broad spectral bandwidth range. A wide emission band is achieved by depositing a first DBR on top of an OLED array and subsequently depositing a second DBR on top of the first DBR, where each DBR has a unique design. The multiple DBRs cover a wider spectral bandwidth range than a single DBR, and therefore almost total reflection is achieved for a series of OLEDs designed at different color wavelengths.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Patent Application No. 18 / 296,458, filed April 6, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to microcavity pixel devices, and more specifically, to the design and fabrication process of organic light-emitting diode (OLED) microcavities for high angular resolution, wide field of view, multi-view displays with multiple distributed Bragg reflectors (DBRs). Background Technology

[0004] Light field displays provide multiple views, allowing each of a user's eyes to receive a separate view. This enables viewers to experience a 3D view of a scene without the need for external hardware such as 3D glasses or headphones. While such light field displays currently offer an interesting viewing experience, truly captivating displays require very high pixel densities, very small angular separation between views, and large viewing angles. Users are also expected to experience smooth transitions between view areas while maintaining independent and perceptible views of adjacent views. A fundamental requirement for achieving these viewing parameters is controlling the output characteristics of the emission source. Organic light-emitting diodes (OLEDs) in microcavities allow for control over the spectral bandwidth and output angle of the resulting light.

[0005] Organic light-emitting diodes (OLEDs) consist of thin film layers of organic material coated on a substrate, typically made of glass, located between two electrodes. OLEDs are characterized by their broad spectral width and Lambertian intensity profile. The thin film layer between the anode and cathode typically includes one or more organic hole injection layers (HILs), organic hole transport layers (HTLs), emission layers (EMLs), organic electron transport layers (ETLs), and organic electron injection layers. Light is generated in an OLED device when electrons and holes injected from the cathode and anode (electrodes), respectively, flow through the ETL and HTL and recombine in the EML.

[0006] One method for controlling light output characteristics is the use of microcavities. Microcavity OLED devices offer enhanced performance and color purity due to their narrow-band emission. A microcavity can be formed between two mirrors. In one example of a microcavity OLED, the first mirror can be a metal cathode, and the second mirror can be a layered stack of non-absorbing materials. One type of layered stack of non-absorbing materials is a distributed Bragg reflector (DBR), a photonic structure typically used as a dielectric mirror consisting of multiple pairs of two different dielectric layers arranged in an alternating sequence with different refractive indices. The reflectivity of a DBR is highest when the layer thickness is chosen such that the optical path length of each layer is one-quarter of the microcavity resonant wavelength; this is often referred to as the Bragg wavelength λ_Bragg. Within the microcavity, light of a specific wavelength is reflected between the two mirrors, adding in phase until the resonant wavelength is reached. The resulting resonant wavelength will have increased intensity, while the intensity of other wavelengths within the microcavity will decrease, thus reducing the emission spectral bandwidth of the microcavity device.

[0007] Two key design variables affecting the output characteristics of a microcavity are the reflectivity of the top and bottom surfaces, which act as mirrors, and the optical path length, where the optical path length between the mirrors is a multiple of the wavelength. The wavelength of light output from this resonant OLED structure depends in part on this optical path length of the microcavity. The optical path length within the cavity can be manipulated in various ways, one of which is by varying the thickness of the layers constituting the microcavity. Adjusting the optical path length of a single microcavity adjusts the emitted color. For multi-color MCOLED arrays, adjusting the cavity layer thickness can also modulate the emitted color. A DBR shared by multiple microcavity devices can also be used to adjust the optical path length of each microcavity; however, a shared DBR structure deposited on microcavity devices with different emitted colors is limited to the stopband of a single DBR. The stopband typically ignores the lower and / or higher wavelengths emitted by pixels of different colors, thus emitting only a controlled beam to reduce the color spectrum of light. Furthermore, reflectivity decreases at the higher and lower wavelengths of the DBR stopband. For sub-pixels whose peak emission wavelength deviates from the DBR Bragg wavelength, such as those in the blue and red regions, this results in reduced optical resonance.

[0008] US Patent Application Publication No. US2022 / 0246673 by Suh et al. describes a display module having a substrate and a plurality of pixels disposed on the substrate, wherein each of the plurality of pixels has a first inorganic light-emitting element including a distributed Bragg reflector (DBR) layer, a second inorganic light-emitting element including a DBR layer, a third inorganic light-emitting element, a first color conversion layer disposed adjacent to the first inorganic light-emitting element, a second color conversion layer disposed adjacent to the second inorganic light-emitting element, and a first color filter disposed adjacent to the first color conversion layer. The second color filter is disposed near the first color conversion layer, and the size of the first color conversion layer is larger than the size of the first inorganic light-emitting element, and the size of the second color conversion layer is larger than the size of the second inorganic light-emitting element.

[0009] This background information is provided so that the applicant may consider known information that may be relevant to the present invention to be known. It does not necessarily imply an admission, nor should it be construed as any of the foregoing information constituting prior art to the present invention. Summary of the Invention

[0010] The object of this invention is to provide a device and method for increasing the emission spectral bandwidth of distributed Bragg reflectors (DBRs) in microcavity OLED displays. This can be achieved by using multiple stacked DBRs, which are stacked on top of each other in a multi-DBR structure, wherein each DBR in the structure has a different Bragg wavelength to extend the reflection spectral bandwidth of the entire multi-DBR structure. Multiple stacked DBR layers facilitate the fabrication of MCOLED arrays while providing a wide spectral emission bandwidth.

[0011] In one aspect, a microcavity organic light-emitting diode (MCOLED) array device is provided, comprising: a substrate; a plurality of sub-pixels deposited on the substrate, the sub-pixels having at least two different colors, each sub-pixel comprising: a bottom electrode; an organic stack deposited on the bottom electrode; and a top electrode deposited on the organic stack; and a shared multi-DBR system deposited on the plurality of sub-pixels, the multi-DBR system comprising: a first distributed Bragg reflector (DBR) having a first Bragg wavelength; and a second distributed Bragg reflector (DBR) located above the first DBR, the second DBR having a second Bragg wavelength different from the first Bragg wavelength.

[0012] In one implementation, the first DBR has a first stopband, the second DBR has a second stopband, and the first stopband and the second stopband overlap.

[0013] In another embodiment, the shared multi-DBR system has multiple DBR stopbands, which are the sum of the first stopband and the second stopband.

[0014] In another embodiment, the first DBR and the second DBR comprise silicon nitride (Si3N4), silicon dioxide (SiO2), zinc sulfide (ZnS), calcium fluoride (CaF2), and aluminum oxide (AlO2). x Magnesium fluoride (MgF2), lithium fluoride (LiF), tellurium oxide (TeO) x One or more layers of titanium dioxide (TiO2) and titanium dioxide (TiO2).

[0015] In another embodiment, the first DBR and the second DBR comprise alternating sublayers of high-refractive-index dielectric material and low-refractive-index dielectric material, and each sublayer provides an optical path length equal to one-quarter of the Bragg wavelength of the DBR.

[0016] In another embodiment, alternating sublayers of high-refractive-index dielectric material and low-refractive-index dielectric material have different refractive indices.

[0017] In another embodiment, the alternating high-refractive-index dielectric and low-refractive-index dielectric sublayers of the first DBR and the second DBR have different thicknesses.

[0018] In another embodiment, the alternating high-refractive-index dielectric and low-refractive-index dielectric sublayers used for each of the first DBR and the second DBR have one or more of different materials and different thicknesses.

[0019] In another embodiment, the sub-pixel color is red, green, or blue.

[0020] In another embodiment, the bottom electrode of each sub-pixel includes reflective metal or a reflective metal alloy.

[0021] In another embodiment, the bottom electrode comprises one or more layers of silver (Ag), aluminum (Al), gold (Au), Ag / Al, lithium (Li) / Al, or calcium (Ca) / Ag.

[0022] In another embodiment, the substrate is transparent.

[0023] In another embodiment, the bottom DBR structure is deposited above the bottom electrode and below the organic stack. In yet another embodiment, the bottom DBR structure is deposited below the organic stack.

[0024] In another embodiment, the top electrode comprises one or more of a metallic reflective surface and a semi-transparent conductive material.

[0025] In another embodiment, the top electrode is transparent.

[0026] In another embodiment, the shared multi-DBR system includes two or more distributed Bragg reflectors.

[0027] On the other hand, a microcavity organic light-emitting diode (MCOLED) array device is provided, comprising: a substrate; a sub-pixel array deposited on the substrate, each sub-pixel in the sub-pixel array comprising: a bottom electrode; an optical fill layer deposited above the bottom electrode for a specific color; a white organic stack deposited above the optical fill layer; and a top electrode deposited above the white organic stack; and a multi-DBR system deposited above the sub-pixel array, comprising: a first distributed Bragg reflector (DBR) having a first Bragg wavelength; and a second distributed Bragg reflector (DBR) located above the first DBR, the second DBR having a second Bragg wavelength different from the first Bragg wavelength.

[0028] In one implementation, the white organic stack is deposited on top of the subpixel array as a blanket deposition.

[0029] In another implementation, the thickness of the optical fill layer in each subpixel is selected to emit light of a specific color.

[0030] In another embodiment, the optical fill layer for each specific color of the subpixel has a different thickness and one or more different materials.

[0031] In another aspect, a method for fabricating a microcavity organic light-emitting diode (MCOLED) array is provided, comprising: depositing a first color sub-pixel on a substrate, including: depositing a first color bottom electrode; depositing a first color organic stack on the first color bottom electrode; and depositing a first top electrode on the first color organic stack; depositing a second color sub-pixel on a substrate, including: depositing a second bottom electrode on the substrate; depositing a second color organic stack on the second bottom electrode; and depositing a second top electrode on the second color organic stack; and depositing a multi-DBR system over the first color sub-pixel and the second color sub-pixel, the multi-DBR system comprising: a first distributed Bragg reflector (DBR) having a first Bragg wavelength; and a second distributed Bragg reflector, deposited over the first DBR, having a second Bragg wavelength different from the first Bragg wavelength.

[0032] In one implementation, the method further includes depositing a pixel definition layer over the first and second bottom electrodes.

[0033] In another embodiment, one of physical vapor deposition (PVD), sputtering, or chemical vapor deposition (CVD) techniques is used to deposit the bottom electrode.

[0034] In another aspect, a method for fabricating a microcavity organic light-emitting diode (MCOLED) array is provided, comprising: patterning a substrate to deposit a plurality of sub-pixels, including: depositing a bottom electrode; and depositing an optical fill layer over the bottom electrode of a specific color; depositing a white organic stack over the plurality of sub-pixels; depositing a top electrode over the white organic stack; and depositing a multi-DBR system over the top electrode, the multi-DBR system comprising: a first distributed Bragg reflector (DBR) having a first Bragg wavelength; and a second distributed Bragg reflector (DBR) located above the first DBR, the second DBR having a second Bragg wavelength different from the first Bragg wavelength.

[0035] In the implementation, white organic stacked blankets are deposited over multiple subpixels.

[0036] In another embodiment, the top electrode is blanket-deposited over a white organic stack.

[0037] The embodiments of the present invention described herein can be combined or substituted in any way. Attached Figure Description

[0038] To better understand the invention and its other aspects and further features, please refer to the following description, which will be used in conjunction with the accompanying drawings, wherein:

[0039] Figure 1 A cross-section of a multicolor MCOLED with multiple stacked DBR structures is shown.

[0040] Figure 2 This is a graph showing the relationship between reflectivity and wavelength for a multicolor MCOLED array with multiple shared DBR structures.

[0041] Figure 3 This is a graph showing the relationship between reflectance and wavelength for a multicolor MCOLED array with a single shared DBR.

[0042] Figure 4 A cross-section of a single blue MCOLED array with a multi-DBR structure is shown.

[0043] Figure 5 A multi-DBR system with a first DBR and a second DBR is shown, wherein the first DBR and the second DBR have a stopband overlap region.

[0044] Figure 6AA cross-sectional view of the first step of the proposed MCOLED manufacturing method is shown, which is used to deposit a bottom first electrode on a substrate.

[0045] Figure 6B A cross-sectional view of the second step of the proposed MCOLED manufacturing method is shown, which is used to deposit organic stacks on each bottom first electrode.

[0046] Figure 6C A cross-sectional view of the third step of the proposed MCOLED manufacturing method is shown, which is used to deposit a top electrode on each organic stack.

[0047] Figure 6D A cross-sectional view of the fourth step of the proposed MCOLED manufacturing process is shown, which uses a blanket deposition technique to deposit the first DBR over the top electrode.

[0048] Figure 7 A cross-sectional view is shown of the final step in forming a multi-DBR system by depositing a second DBR on top of the first DBR using a blanket deposition technique.

[0049] Figure 8 A cross-sectional view of an alternative implementation of the disclosed MCOLED array is shown, which has a white organic stacked structure.

[0050] Figure 9 A cross-sectional view of an alternative implementation of the disclosed MCOLED array is shown, the array having a bottom DBR. Detailed Implementation

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0052] In the specification and claims, unless the context clearly indicates otherwise, the singular forms “a,” “an,” and “the” all have a plural meaning.

[0053] The term “comprising” and any of its derivatives (e.g., including, containing) as used herein shall be construed as including the feature it refers to, and unless otherwise stated or implied, does not mean that any other feature is excluded. The term “comprising” as used herein shall also be understood to mean that the following list is not exhaustive and may include or exclude any other appropriate items, such as one or more other features, components and / or elements (as the case may be).

[0054] As used herein, the terms “having,” “comprising,” and “containing,” and their grammatical variations, are inclusive or open-ended and do not exclude other elements and / or method steps not listed. The following list is not exhaustive and may or may not include other suitable items, such as one or more additional features, components, and / or elements. In some embodiments, the compositions, apparatuses, articles, systems, uses, processes, or methods described herein that include certain elements and / or steps may consist primarily of those elements and / or steps; in other embodiments, they may consist of those elements and / or steps as well as other additional elements and / or steps, whether or not these embodiments are specifically mentioned.

[0055] As used herein, the term “about” refers to a variation of approximately + / - 10% of a given value. It should be understood that any given value provided herein, unless otherwise specified, always includes such variation. Unless otherwise stated herein, the ranges described herein are intended to convey the range and the individual values ​​falling within that range, whose numerical values ​​are the same as those used to represent ranges.

[0056] The use of any example or exemplary language (such as "for example", "exemplary embodiment", "illustrative embodiment" and "for example") is intended to illustrate or represent aspects, embodiments, variations, elements or features related to the present invention and is not intended to limit the scope of the invention.

[0057] As used herein, “connected” and “connected” refer to any direct or indirect physical association between elements or features in this disclosure. Thus, these terms can be understood to mean elements or features that are partially or wholly contained within, attached to, coupled, set up, connected together, communicate, or are operationally related to each other, even if other elements or features are involved between elements or features described as connected.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0059] As used in this article, the term "DBR" refers to a distributed Bragg reflector. A distributed Bragg reflector (DBR) is a photonic device, typically used as an optical mirror, consisting of multiple pairs of alternating layers of two dielectric materials with different refractive indices, each layer having a thickness of λ / 4, where λ is the operating center wavelength.

[0060] As used in this article, the term "transparent" refers to materials that allow visible light to pass through.

[0061] As used herein, the term "transparent conductive oxide" or TCO refers to doped metal oxides commonly used in optoelectronic devices. TCO materials include, but are not limited to, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), and gallium-doped zinc oxide (ZnO).

[0062] As used in this article, the term "pixel" refers to the light source and emission mechanism used to create the display.

[0063] As used in this article, the term "vertical cavity surface-emitting laser (VCSEL)" refers to a semiconductor-based laser diode that emits light or a beam of light vertically from its top surface.

[0064] As used in this article, the term "electron-hole balance" refers to the charge balance within an organic light-emitting diode (OLED) device. Electrons and holes injected from various contact points recombine in the emitter region to form excitons, which then undergo radiative emission to produce light. The efficiency of the external device is determined by the proportion of light generated in the device stack and extracted into the air. In OLED devices, the efficiency of the internal device is highly dependent on the charge balance of the device.

[0065] As used herein, the term "subpixel" refers to a structure consisting of light-emitting devices housed within an optical microcavity. The optical microcavity is effectively associated with multiple reflective surfaces to substantially collimate, manipulate, or tune light. At least one reflective surface is a light-propagating reflective surface attached to the optical microcavity to propagate light out of the microcavity. This invention provides individually addressable red, green, and blue (RGB) pixels. The subpixel sizes described herein range from nanometers to several micrometers, significantly smaller than pixel sizes previously known in the art.

[0066] As used in this article, the acronym "FWHM" stands for "Full-Width Half-Maximum," which is a way of expressing the range of a function given by the difference between the two extreme values ​​of the independent variable, where the dependent variable is equal to half of its maximum value.

[0067] The term "OLED" used in this article refers to Organic Light-Emitting Diode, an electro-optical device that emits light under the influence of an external voltage. OLEDs can be divided into two main categories: one made of small organic molecules and the other made of organic polymers. An OLED is a light-emitting diode whose light-emitting electroluminescent layer consists of a thin film of organic compound that emits light under the influence of an electric current. Typically, an OLED is a solid-state semiconductor device containing at least one conductive organic layer located between and electrically connected to the anode and cathode. When a current is applied, the anode injects holes into the organic layer, and the cathode injects electrons into the organic layer. The injected holes and electrons migrate towards their respective oppositely charged electrodes. When electrons and holes are localized on the same molecule, excitons are formed; an exciton is a localized electron-hole pair with an excited energy state. When the exciton relaxes through a photoemission mechanism, light is emitted. Types of OLEDs include, but are not limited to:

[0068] a. Active Matrix OLED (AMOLED)

[0069] AMOLED has a complete cathode, organic molecule, and anode layer. The anode layer has parallel thin-film transistor (TFT) planes to form a matrix. This helps to switch each pixel on or off as needed, thus forming an image. Therefore, when a pixel is not needed or a black image is displayed on the screen, it is turned off, extending the device's battery life. This is the least power-consuming type of OLED and has a faster refresh rate, making it suitable for video. AMOLED's best applications are computer monitors, large-screen TVs, and electronic signs or billboards.

[0070] b. Top-emitting OLED

[0071] Top-emitting OLEDs use substrates that are either opaque or reflective. Top-emitting OLEDs are better suited for active-matrix applications because they can be more easily integrated with non-transparent transistor backplanes. Manufacturers use top-emitting OLED displays in smart cards.

[0072] c. Bottom-emitting OLED

[0073] An OLED is bottom-emitting if the emitted light passes through a transparent or translucent bottom electrode and substrate.

[0074] As used in this article, the term "microcavity" refers to a structure formed by reflective surfaces on both sides of a spacer layer or optical medium (such as an OLED).

[0075] As used herein, “microcavity OLED” (MCOLED) refers to OLED materials as described above, which are confined within a microcavity defined by two reflective surfaces. These reflective surfaces can be metallic materials, dielectric materials designed to reflect light within a specific wavelength range, or a combination of dielectric and metallic materials.

[0076] As used in this article, the term "electrode" refers to a conductor through which an electric current enters or leaves an object, substance, or area.

[0077] As used in this article, the term "cathode" refers to a negatively charged electrode through which electrons enter electrical equipment.

[0078] As used in this article, the term "anode" refers to a positively charged electrode through which electrons leave an electrical device.

[0079] As used in this article, the term “patterning” refers to a technique that uses a series of post-processing steps to chemically sculpt a transferred pattern into a target material, or to allow the deposition of new material within a transferred pattern on a target material.

[0080] As used in this article, the term “blanket deposition” refers to the deposition of material without the use of patterning techniques.

[0081] As used in this article, the term "mirror" refers to an object capable of reflecting light. For incident light within a certain wavelength range, the reflected light retains many or most of the detailed physical properties of the original light; this is called specular reflection. Two or more perfectly parallel and opposite mirrors can produce an infinite number of reflections; this is known as the infinity mirror effect.

[0082] As used herein, the term "optical path length," denoted by Λ, refers to the distance between two points (P1, P2), taking into account the refractive index (n) of the material through which light passes. In an example OLED device, the medium through which light passes may include one or more semi-transparent or transparent intermediate electrodes and other layers, as well as layers containing the white OLED stack. The optical path length is defined as a function of the following:

[0083]

[0084] As used in this article, the term "transmittance" refers to the percentage of light transmitted per unit of incident light.

[0085] As used in this article, the term “wavelength” is a measure of the distance between two identical crests (high points) or troughs (low points) in a wave, which is a repeating pattern of energy such as light or sound.

[0086] It is conceivable that those skilled in the art can implement any embodiment of the compositions, apparatus, articles, methods and uses disclosed herein as is, or make such variations or equivalent implementations without departing from the scope of the invention.

[0087] An organic light-emitting diode (OLED) structure typically includes a substrate, a first electrode, an OLED stack of organic material layers, and a second electrode. The organic material stack may include a hole injection layer (HIL), a hole transport layer (HTL), an electron injection layer (EIL), an electron transport layer (ETL), and an emitter layer (EML). The material and thickness design of the OLED stack layers in MCOLEDs are based on the required refractive index n and electron-hole balance requirements. Balanced charge injection is achieved by equal flow rates of electrons / holes to the emitter layer (EML). If the OLED device is unbalanced, electrons or holes will accumulate and charge the emitter layer, thus affecting the device output.

[0088] A microcavity organic light-emitting diode (MCOLED) is a device in which the OLED material is confined within a microcavity defined by two reflective surfaces arranged in a manner that allows light to be reflected within a specific range, or defined by a certain combination of dielectric and metallic materials. The organic materials constituting the OLED stack have a material thickness d. j The arrangement has an optical path length of L. j L j =n j xd j And where n j This refers to the refractive index of the OLED material. The sum of the optical path lengths between the reflective surfaces is designed to be equal to... Where λ i This is the peak design wavelength of the MCOLED. Therefore, the optical path length can be changed by altering the thickness of one or more materials between the reflective surfaces, or by adding one or more additional filler materials (optical filler layer 56). The optical filler layer 56 is selected to emit light from the MCOLED within the desired wavelength range. Using microcavities in the OLED structure reduces the spectral width of the OLED, decreases the angular output, and improves overall efficiency. Tuning the optical microcavity for a specific wavelength or color of light is a challenging task because it is achieved by generating resonance at a specific wavelength between the two reflective surfaces, which requires careful analysis and simulation to select and define material thickness, refractive index, and phase changes.

[0089] The reduced angular diffusion due to the microcavity can be approximated as:

[0090]

[0091] Similarly, the FWHM of the output spectrum was determined as:

[0092]

[0093] Where R Cathode It is the reflectivity of the cathode, and R DBR It is the reflectivity of DBR.

[0094] When selecting layer thickness d i The DBR structure achieves its maximum reflectivity when the optical path length of each layer is one-quarter of the resonant wavelength, or:

[0095]

[0096] Where λ Bragg This is the design wavelength of the DBR, which can be any value, but is chosen to ensure high reflectivity within the design wavelength range. Under these conditions, all reflections will be added in phase, and the transmittance will decrease exponentially as a function of the mirror thickness.

[0097] DBR in λ Bragg The reflectivity at that point can be approximated as:

[0098]

[0099] Where n1 is the low refractive index DBR at λ Bragg The refractive index at λ, n2 is the refractive index of the high refractive index DBR material at λ. Bragg The refractive index at a given wavelength is given by , and ∧ is the number of dielectric pairs. At longer or shorter wavelengths, reflections begin to superimpose out of phase, thus reducing the total reflection.

[0100] The result is in λ Bragg The broadband high reflectivity region centered on δλ is called the stopband. sb Determined as:

[0101]

[0102] Where n eff These are effective indices. These are the theoretical design variables considered for microcavity OLED structures with DBRs. The material of the DBR can be any opaque material within the design wavelength range. For example, in the visible light wavelength range, materials such as silicon nitride, titanium dioxide, silicon dioxide, and other dielectrics can be used.

[0103] The total optical path length of the microcavity is expressed as:

[0104] L i =L DBR +L organics +L cathode

[0105] Where LDBR L is the penetration depth in DBR. Organics It is the optical path length in OLED materials, and L Cathode It is the penetration depth in the metal cathode.

[0106] The optical path length in the material between the two reflective surfaces is the sum of the optical path lengths in each of the individual materials:

[0107]

[0108] Where n i and d i These are the layer index and thickness, respectively. The penetration depth into the DBR can be determined as:

[0109]

[0110] And the penetration depth into the metal cathode is:

[0111]

[0112] Where Φ m The phase shift at the metal reflector is given by the following formula:

[0113]

[0114] Where n Cavity It is the refractive index of the organic material in contact with the cathode, and n Cathode and k Cathode These are the real and imaginary parts of the refractive index of the metal cathode.

[0115] This paper introduces a microcavity OLED array and its fabrication method. The array employs a shared DBR structure for multiple pixels and subpixels, wherein the shared DBR structure comprises multiple shared DBR structures. Each individual DBR structure consists of multiple alternating layers of two different dielectric materials, each with a different refractive index. Increasing the logarithm in the DBR improves specular reflectivity, while increasing the refractive index contrast between the Bragg-aligned materials improves reflectivity and bandwidth. As understood herein, a multi-DBR structure comprises at least two distinct DBR structures, each having its own unique alternating layer structure, layer width, and / or layer materials, which differ from the DBRs in the multi-DBR structure, and wherein each distinct individual DBR structure in the multi-DBR structure has a different Bragg wavelength or λ. BraggFor example, in a multilayer DBR structure, the differences between each DBR layer may lie in, for example, the thickness of each alternating dielectric layer, the material of the dielectric layer, the microstructure of the dielectric layer, and / or the deposition method of the dielectric layer, where the properties of the dielectric layer can impart structural and functional operational characteristics to the DBR layer in which it resides. By using multiple stacked DBR structures on an OLED microcavity array, each DBR or Bragg structure having a different Bragg wavelength, a blanket fabrication technique can be used to deposit each layer in the fabrication of the microcavity OLED array, thus providing a simplified layering method with good optical performance. This device and method using multiple stacked DBRs increases the visible spectral coverage of the OLED array in the microcavity OLED display, providing a wide range of spectral emission bandwidths within a richer visible wavelength range in the visible spectrum emitted by the color subpixels in the OLED array.

[0116] Distributed Bragg reflectors (DBRs) are designed for tight spectral bandwidths, making them suitable for narrow color spectra. Known MCOLED devices using DBRs typically have unique DBR structures based on the pixel design and selection of the MCOLED. This is particularly advantageous for RGB displays, especially for devices where the DBR is deposited on top of an organic stack. Microscale multicolor microcavity OLED arrays face numerous fabrication challenges, necessitating techniques that facilitate precise and scalable material deposition, particularly blanket deposition, to provide more economical and repeatable manufacturing. Furthermore, using blanket deposition methods instead of photolithographic patterning to deposit the DBR prevents the underlying fragile organic layer from being exposed to undesirable developers used in photolithography.

[0117] Figure 1 The cross-section of the multicolor MCOLED array is shown, including blue sub-pixels 18, green sub-pixels 20, and red sub-pixels 22, which emit blue emission band λ. EMB 70. Green transmission band λ EMG 72 and the red emission band λ EMR74. Each of the three individual color sub-pixels (blue 18, green 20, and red 22) of the multicolor OLED array is deposited on substrate 10, wherein each sub-pixel is deposited on top of a separate bottom electrode 46a, 46b, 46c. It should be understood that each individual pixel 18, 20, 22 may include, but is not limited to, a bottom electrode (anode or cathode), such as bottom electrodes 46a, 46b, 46c, an organic semiconductor layer 48a, 48b, 48c specific to the sub-pixel color, and a top electrode 50a, 50b, 50c serving as a complementary anode or cathode to the second electrode and the bottom electrode. The organic semiconductor layer may, as needed, include one or more organic hole injection layers (HIL), organic hole transport layers (HTL), emission layers (EML), organic electron transport layers (ETL), and organic electron injection layers to generate photons emitted from the pixel. Optional pixel definition layers (PDL) 52a, 52b may be deposited between the sub-pixels.

[0118] Each sub-pixel 18, 20, 22 shares a single first DBR 26, wherein the alternating layer material has a low refractive index or low refractive index layer and a high refractive index or high refractive index layer. On top of the first DBR 26 is a second DBR 28, which also includes alternating high refractive index and low refractive index layers, but has a different layer thickness or a different layer structure and / or composition compared to the layers in the first DBR 26. In a specific example, each individual DBR may consist of, for example, eight pairs of alternating zinc sulfide (ZnS) layers as high refractive index layers and calcium fluoride (CaF2) layers as low refractive index layers, and the layer thicknesses of the first DBR 26 and the second DBR 28 are approximately 55.1 nm and 90.9 nm, respectively. Preferably, as... Figure 1 As shown, a thin low-refractive-index layer is first deposited above each sub-pixel 18, 20, and 22. A DBR26 with a thinner layer (i.e., a high-refractive-index layer) is then formed directly on top of sub-pixels 18, 20, and 22, creating a refractive index contrast or reflection between the OLED and the DBR. If a thicker low-refractive-index layer were deposited directly on the OLED, the refractive index difference between the OLED material and the low-refractive-index layer would be insufficient to create a refractive index contrast; therefore, the lower refractive-index layer would act as an extension of the cavity length defined by the OLED thickness. Depending on the DBR material, the low-refractive-index layer can be deposited directly on top of the microcavity device, but this is not preferred. Some examples of DBR materials include, but are not limited to, silicon nitride (Si3N4), silicon dioxide (SiO2), zinc sulfide (ZnS), calcium fluoride (CaF2), and aluminum oxide (AlO2). x Magnesium fluoride (MgF2), lithium fluoride (LiF), tellurium oxide (TeO) xThe first DBR 26 and the second DBR 28 have different structures, resulting in different Bragg wavelengths and providing reflective properties for the sub-pixels in the microcavity array across different wavelength ranges or reflection bands. The sum of the wavelength reflection ranges of the first DBR 26 and the second DBR 28, also known as the reflection band and reflection stopband, provides a wider overall reflection range or reflection stopband for the multi-DBR structure 44, enabling reflection and emission across a wider stopband than with a single DBR structure. An optional intermediate layer can be deposited between the OLED device and the multi-DBR system, particularly between the top electrode and the first DBR. The intermediate layer can be used, for example, to adjust the cavity length between the two mirrors to obtain a resonant wavelength / frequency. An optional capping layer can also be deposited on top of the multi-DBR system to adjust the phase shift as needed. The primary function of the optional capping layer is to enhance the light transmission (or light extraction) of the device. For example, without a capping layer, the light generated by the OLED device would propagate from the DBR into the air. Alternatively, by adding a capping layer, the light generated by the OLED device propagates from the DBR to the capping layer and then into the air. Inserting this additional medium creates a phase shift between the two interfaces and enhances the light intensity. Constructive interference can occur between the two interfaces, particularly between the DBR / capping layer interface and the capping layer / air interface.

[0119] Figure 2 This is a reflectance versus wavelength diagram for a multi-color MCOLED array with a shared multi-DBR structure, comprising red, green, and blue (RGB) pixels. The sub-pixel emission bands, i.e., the wavelength patterns and ranges emitted by each color sub-pixel, are shown as the blue emission band λ. EMB 70. Green transmission band λ EMG 72 and the red emission band λ EMR 74. The DBR operates as a mirror within the wavelength range of the device (referred to as the stopband). Reflectivity plots for a single DBR and multiple DBRs are shown, where the multiple DBR is composed of a single DBR and a second DBR. The plots for the two single DBRs constituting the multiple DBR structure, DBR1 and DBR2, are shown as λ. BraggDBR1 and λ BraggDBR2 Each has its unique Bragg wavelength. As mentioned earlier, the design of a single DBR takes into account the wavelength range or band of light that the sub-pixels in the array will reflect, as well as the optical path length of the cavity of the OLED or VSCEL in the array.

[0120] In a multi-DBR structure, the Bragg wavelength value λ of the first DBR (single DBR) is used. BraggDBR1 To calculate the stopband range δλ of the first DBR sbDBR1 The formula is as follows:

[0121]

[0122] in:

[0123] n 1DBR1 The low-refractive-index layer of the first DBR is at λ BraggDBR1 The refractive index at that point, and

[0124] n 2DBR1 The high refractive index layer of the first DBR material is at λ BraggDBR1 The refractive index at that point.

[0125] The Bragg wavelength value λ of the second DBR (located above the first DBR in this case). BraggDBR2 Used to calculate the stopband range of the second DBR. In, for example... Figure 1 In the configuration shown, where two DBRs are stacked together and positioned above a subpixel, a stacked multi-DBR structure is created above each individual pixel, thereby utilizing the lower limit δλ of the stopband range of the first DBR. sbDBR1 The upper limit of the stopband range δλ of the second DBR sbDBR2 Calculate the total multi-DBR stopband width δλ sb 16. In this case, the total stopband 16 is between approximately 430 nm and 775 nm, covering the long wavelength region of the visible spectrum. The stopband wavelength range δλ of the multi-DBR... sb The wavelength within 16 is emitted from the MCOLED, while the stopband δλ sb Wavelengths beyond 16 are in the non-reflective region, whether in the short-wavelength non-reflective region δλ NF 24a is still in the long-wavelength non-reflective region δλ NF 24b. By modifying the structures of the two DBRs in this example, the Bragg wavelengths of each structure can be further separated in the visible spectrum while preserving appropriate overlap to cover more of the visible spectrum and stopband 16 of the multi-DBR structure, thereby widening the spectral bandwidth of the MCOLED array. The total spectral stopband 16 width created by multiple distributed Bragg reflectors (DBRs) with multiple single DBR structures is wider than that achievable with a single DBR. Increasing the spectral stopband 16 to reflect a wider range of wavelengths of light increases the overall spectral bandwidth of the MCOLED display. Figure 1 An embodiment of a multi-DBR system is shown, wherein the Bragg wavelength of the first DBR is smaller than that of the second DBR. In an alternative embodiment of this disclosure, the Bragg wavelength of the first DBR in the multi-DBR system may be larger than that of the second DBR. Overall, multi-DBR systems must be designed to achieve the optical path length required for microcavity devices.

[0126] Figure 3This is a graph showing the reflectance versus wavelength for a multicolor MCOLED array with a single shared DBR. The multicolor microcavity OLED array has RGB subpixels, with each MCOLED in the array having a separate distributed Bragg reflector (DBR) on top. The total stopband δλ of the individual DBR is shown. sb The reflectivity range of 16 is approximately 425 nm to approximately 650 nm, with a total stopband of 175 nm. The blue sub-pixel emits in the λ band. EMB 70. Green sub-pixel emission band λ EMG 72 and red sub-pixel emission band λ EMR 74 is shown along the wavelength axis. It should be noted that the wavelength axis is also used to show the stopband δλ. sb The non-reflection frequencies λ on both sides of 16 NF 24a, 24b. Non-reflective region λ NF The wavelengths in 24a and 24b are outside the reflection stopband wavelength range of a single DBR and will not be reflected by the DBR, therefore they will not be emitted by the MCOLED array.

[0127] When the OLED device layer thickness (d) i When the optical path length of each layer is chosen to be one-quarter of the resonant wavelength, the highest reflectivity (90% reflectivity) of the DBR is reached, which is commonly referred to as the Bragg wavelength λ. Bragg For perpendicular incidence, the layer thickness should be d. i =λ Bragg / 4n i , where n i It is the refractive index of the layer material. Figure 3 In the example shown, the multicolor MCOLED array can have a first DBR consisting of 7 pairs of alternating layers of CaF2 (low refractive index, n1 = 1.4338) and ZnS (high refractive index material, n2 = 2.35521), where the material thicknesses of the low refractive index material and the high refractive index material are 90.9 nm and 55.1 nm, respectively. The Bragg wavelength λ of the RGB microcavity OLED shown is... Bragg The wavelength is 520nm, falling within the emission band λ of the green sub-pixel. EMG The emission wavelength range is 72 nm (approximately 495-580 nm). The result is a broadband high-reflectivity region, or stopband δλ. sb 16, the center is located at approximately 525 nm λ Bragg Above. Reflection stopband δλ sb 16 is the wavelength range for DBR reflection, defined by the minimum and maximum wavelengths that achieve maximum reflectivity within the DBR. Wavelength values ​​outside this range are transmitted through the DBR (i.e., not reflected), and are within the non-reflective region λ. NF 24a and 24b represent non-reflection frequencies. The non-reflection region λ NF24a and 24b are outside the reflection stopband wavelength range of a single DBR and will not be reflected by the DBR, therefore λ NF The emission of 24 is not controlled by the MCOLED. Shared DBR devices have the maximum achievable stopband δλ. sb 16 regions. Therefore, the stopband δλ sb 16 limits the emission wavelength range of MCOLEDs. For example, for a multicolor MCOLED with a single DBR as shown in the figure, δλ sb 16 is 175nm. Wavelengths below approximately 432.5nm and above approximately 607.5nm are considered non-reflective regions. NF The non-reflective frequencies in 24a and 24b, therefore, the unrestricted or uncontrolled undesired emissions that are ignored by MCOLEDs, are omitted. This MCOLED design emits light at the blue sub-pixel emission band λ. EMB 70 and green sub-pixel emission band λ EMG Effective wavelength coverage of blue and green subpixels was achieved in 72, but coverage was limited in the emission band λ of the red subpixel. EMR There is none in 74. Therefore, the red sub-pixel emits a wavelength λ. EMR Most of the higher non-reflective frequencies in 74 become stray emissions. The overall result of this single DBR design is that certain wavelengths in the pixel array's emission band, particularly in the red and blue regions, are poorly reflected by the DBR at the stopband edges and outside the DBR stopband. This results in incomplete reflection of wavelengths at the stopband edges. This leads to uncontrolled emission in the visible spectrum at and outside the DBR band edges, thus reducing the emission color intensity in these regions.

[0128] Figure 4 A cross-section of a single blue MCOLED array with a multi-DBR structure is shown. In the MCOLED array, three individual color sub-pixels (blue, green, and red) are deposited on substrate 10. For simplicity, only the blue emission band λ is shown. EMBThe blue subpixels of 70 are used to illustrate the layers of each individual pixel. In an example of a given monochrome subpixel, a bottom electrode 46 is deposited on the substrate 10, followed by an organic layer suitable for a specific OLED subpixel color, in this case, the blue subpixel. The layer thickness and material are selected according to the desired subpixel color. It should be understood that each individual subpixel may include, but is not limited to, at least one first or bottom electrode layer 46, which may be an anode or cathode, and an organic stack 48 of blue subpixels, including one or more organic hole injection layers (HIL), organic hole transport layers (HTL), emitter layers (EML), organic electron transport layers (ETL), and organic electron injection layers (EIL), followed by a second or top electrode layer 50, which is a complementary anode or cathode to the bottom electrode layer 46. In this example embodiment, an electron transport layer 36, an emitter layer 38, a hole transport layer 40, and a hole injection layer 42 are shown. Figure 1 Consistently, in the multi-DBR system, the sub-pixel also has a first DBR 26 and a second DBR 28, which together form the multi-DBR structure 44. The first single DBR 26 shown has three pairs of alternating CaF2 (low refractive index layer 30a) and ZnS (high refractive index layer 32a) layers with thicknesses of 90.9 nm and 55.1 nm, respectively. However, it should be understood that this first DBR can have a series of pairs of low refractive index layers 30a and high refractive index layers 30b. Increasing the number of pairs in the DBR increases specular reflectivity, but the number of pairs (layers) must be balanced with the overall required device size, as increasing the number of DBR layers also increases the device size. The second DBR 28 also has multiple pairs of alternating CaF2 (low refractive index layer 30b) and ZnS (high refractive index layer 32b) layers with thicknesses of 110.1 nm and 66.7 nm, respectively. Some examples of alternative DBR materials include, but are not limited to, Si3N4, SiO2, AlOx, MgF2, LiF, TeOx, and TiO2. The wavelength δλ in the stopband wavelength range of the multi-DBR system 44... sbMBDR 16 are emitted from MCOLED.

[0129] Figure 5 A multi-DBR structure with two overlapping DBRs is shown, comprising a first DBR 26, a second DBR 28, and a stopband overlap region 34, wherein the stopband overlap region 34 has a band δλ. sbMDBR It can be represented as:

[0130] δλ sbMDBR =δλ sbDBR1 +δλ sbDBR2 -δλ OR

[0131] in:

[0132] δλ sbDBR1It is the stopband of the first DBR (DBR1).

[0133] δλ sbDBR1 It is the stopband of the second DBR (DBR2), and

[0134] δλ OR It is the band in the overlapping area of ​​DBR1 and DBR2.

[0135] Band δλ in overlapping region 34 OR The wavelength of light within the stopband range of both the first and second DBRs. The total stopband width (δλ) of the multiple DBRs. sbMDBR This allows for the capture of a wider range of desired wavelengths in the chromatography spectrum to achieve controlled emission. Therefore, the lower limit δλ of the stopband range of the first DBR is used. sbDBR1 The upper limit of the stopband range δλ of the second DBR sbDBR2 To calculate the total stopband width δλ of the multi-DBR sb It should be noted that the above equations are ideal equations and are independent of the period of the DBR (which is determined by the number of low / high n material alternation pairs).

[0136] The currently described multi-DBR system has an increased stopband wavelength range of approximately 432.5 to approximately 728.5 nm, with a total stopband of 16 δλ. sbMDBR 16 = 296 nm, to reflect and emit controlled beams of all wavelengths emitted by individual color subpixels blue 18, green 20, and red 22, thereby reducing the non-reflective wavelength λ. NF Compared to a single DBR system, the stopband wavelength range is increased by approximately 69%. The non-reflection frequency λ NF Located outside the reflection stopband wavelength range of the multi-DBR and not reflected by the multi-DBR structure. The wavelength range captured by the illustrated DBR system embodiment increases from 432.5nm-607.5nm for a single DBR to 432.5nm-728.5nm for the illustrated multi-DBR structure. It should be noted that the number of each DBR pair can be any integer value, but this is only for illustrative purposes.

[0137] manufacture

[0138] MCOLEDs used in high-resolution light field display applications are nanometer-sized, thus facing a significant manufacturing challenge: patterning. The term "patterning" refers to the chemical engraving of a transfer pattern into the target material using a series of post-processing techniques, or allowing the deposition of new material within the transfer pattern. It is advantageous to deposit as many material layers as possible within the array using deposition techniques that do not require patterning at all, such as blanket deposition, to avoid chemical etching and photolithography that could damage the pre-deposited layers. Apart from depositing a single DBR for each OLED, shared DBRs integrated into the array do not require patterning. Eliminating this patterning step in the fabrication of MCOLED arrays with strong cavity effects can reduce manufacturing time, complexity, and cost.

[0139] Figure 6A -E illustrates the step-by-step process for manufacturing an MCOLED array according to the present invention. Figure 6A A cross-sectional view is shown of the first step of an example MCOLED manufacturing process for depositing a bottom first electrode on a substrate. For each individual color sub-pixel, blue 18, green 20, and red 22, a bottom first series of bottom electrodes 46a, 46b, and 46c are deposited on a single substrate 10, respectively. The bottom electrodes 46a, 46b, and 46c can be deposited by, for example, physical vapor deposition (PVD) methods such as thermal evaporation, electron beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. The bottom electrodes 46a, 46b, and 46c can be made of reflective materials, such as reflective metals such as silver (Ag), aluminum (Al), gold (Au), combinations thereof, or alloys thereof, as a single-layer film or a multilayer film, such as Ag / Al, Li / Al, or Ca / Ag. In another embodiment of this disclosure, the bottom electrodes 46a, 46b, and 46c can be, for example, indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), gallium-doped zinc oxide (ZnO), or a semi-transparent thin metal film, such as Ag, Al, Ag, Ca, Li, Au, or Ag:Mg alloy. Furthermore, a bottom reflective layer or DBR can be deposited beneath the organic layer of the OLED to form the bottom reflective surface of the microcavity, replacing or supplementing the bottom electrodes 46a, 46b, and 46c. The bottom electrodes 46a, 46b, and 46c can also be single-layer or multi-layer films, such as Ag / Al, Li / Al, and Ca / Ag.

[0140] Figure 6BA second cross-sectional view of the proposed MCOLED method is shown, which involves depositing organic stacks 48a, 48b, 48c on each bottom first electrode 46a, 46b, 46c of each individual color subpixel (blue 18, green 20, and red 22) on a substrate 10. This embodiment illustrates an MCOLED array where each individual color subpixel (blue 18, green 20, and red 22) has a separate OLED stack for each color; specifically, each subpixel has a green OLED stack 48a, a blue OLED stack 48b, and a red OLED stack 48c deposited. The thickness of each OLED stack 48a, 48b, 48c determines the optical path length of that subpixel, and thus the color emitted by the subpixel. For example, the thickness of the red OLED stack 48c is greater than the thickness of the green OLED stack 48b, resulting in a longer optical path length because red light is required for red light emission (620-750 nm).

[0141] Figure 6C A cross-sectional view of the third step in the proposed MCOLED method for depositing top electrodes 50a, 50b, and 50c on each organic stack is shown. These electrodes can be deposited individually on each organic stack 48a, 48b, and 48c, and can be selectively patterned. It should be understood that each individual color sub-pixel 18, 20, and 22 on substrate 10 can also share a top electrode, which is deposited using a blanket deposition technique. Similar to the bottom electrodes 46a, 46b, and 46c, the top electrodes 50a, 50b, and 50c can be made of transparent conductive oxides, such as indium tin oxide (ITO), fluorine-doped tin oxide (FTO), aluminum-doped zinc oxide (AZO), indium-doped zinc oxide (IZO), gallium-doped zinc oxide (ZnO), or of a semi-transparent thin metal film, such as Ag, Al, Ag, Ca, Li, Au, and Ag:Mg alloys. They can also be single-layer or multi-layer films, such as Ag / Al, Li / Al, and Ca / Ag. The top electrode can be a cathode, and the bottom electrode can be an anode, or vice versa.

[0142] Figure 6DA cross-sectional view of the fourth step of the proposed MCOLED manufacturing process is shown, in which a first DBR 26 is deposited on the top electrodes 50a, 50b, and 50c using a blanket deposition technique. The DBR 26 acts as a mirror, forming optical microcavities between the DBR 26 above each bottom electrode 46a, 46b, and 46c and the top electrodes 50a, 50b, and 50c for each sub-pixel 18, 20, and 22, comprising an organic stack 48a, 48b, and 48c supported by a substrate 10. The first DBR 26 consists of alternating high-refractive-index dielectric layers 30a and low-refractive-index dielectric layers 32a. The number of high-refractive-index and low-refractive-index dielectric layers can be any integer; seven pairs are shown in this configuration, including fourteen layers.

[0143] Figure 7 A cross-sectional view of the fifth step of the proposed MCOLED manufacturing process is shown, in which a second DBR 28 is deposited on top of the first DBR 26 using a blanket deposition technique to form a multi-DBR system 44. For each sub-pixel 18, 20, 22, the multi-DBR system 44 is deposited over organic stacks 48a, 48b, 48c and top electrodes 50a, 50b, 50c. The second DBR 28 consists of alternating high-refractive-index dielectric layers 30b and low-refractive-index dielectric layers 32b. The number of high and low-refractive-index dielectric layers can be any integer; seven pairs are shown in this configuration, including fourteen layers. In this embodiment, the thickness of the first DBR 26 is ignored when calculating the optical length of the microcavity, and the top second DBR 28 serves as the first reflective surface of the optical microcavity for each OLED device in the OLED array. Optional pixel definition layers (PDLs) 52a, 52b are deposited on the substrate 10 between the bottom electrodes 46a, 46b, 46c and the sub-pixels. Pixel definition layers (PDLs) 52a and 52b can be composed of inorganic materials (such as insulating dielectrics, e.g., Si3N4, AlOx, TiO2, or SiO2) or organic materials (such as photosensitive polyimide). PDL 52 can be deposited using methods such as physical vapor deposition (PVD) (e.g., thermal evaporation, electron beam evaporation, sputtering) or chemical vapor deposition (CVD) (e.g., atomic layer deposition). Without depositing a PDL, identical subpixel array structures can be created between subpixels, with gaps between them. It has been found that using PDLs between subpixels can prevent inter-pixel electrical crosstalk by using insulating materials.

[0144] Figure 8A cross-section of an MCOLED array device according to an embodiment of the present invention is shown, which uses a white organic stack 54 instead of blue, green, and red organic stacks to form multiple sub-pixels. The white organic stack 54 is deposited on a series of optical filler layers 56a, 56b, and 56c via a blanket deposition technique, these filler layers being located on top of a series of bottom electrodes 46a, 46b, and 46c on a substrate 10. The optical path length of each sub-pixel in the MCOLED can be adjusted by adding one or more optical filler layers 56a, 56b, and 56c and adjusting the thickness of the optical filler layers to obtain the desired color, such as the blue emission band λ. EMB 70. Green transmission band λ EMG 72 and the red emission band λ EMR 74, thereby altering the thickness of one or more materials between the reflective surfaces above the OLED. Optional pixel definition layers (PDLs) 52a, 52b are deposited on the substrate 10 between the bottom electrodes 46a, 46b, 46c and the subpixels. A white organic stack 54 containing a white emitting layer can be deposited integrally because it is capable of emitting all three R, G, B primary colors. For each optical microcavity, only the desired color emerges from the corresponding pixel because the optical microcavity filters out other colors. The white organic stack 54 includes a series of organic layers beneath the emitting layer, which, depending on the MCOLED configuration, may include a hole injection layer (HIL), a hole transport layer (HTL), an electron injection layer (EIL), an electron transport layer (ETL), and an emitting layer (EML), and can be an inverted MCOLED or a conventional MCOLED configuration. In the illustrated embodiment, the top electrode 50 can be deposited on the white organic stack 54 using a blanket deposition technique, which is common to all MCOLED structures. In this embodiment, the reflective surface includes a first DBR26 and a second DBR28 deposited on a first DBR26. The first DBR 26 and the second DBR 28 together constitute the multi-DBR structure 44. Optical filler layers 56a, 56b, and 56c are designed with specific materials and widths to create the required optical path lengths for the blue sub-pixel 18, green sub-pixel 20, and red sub-pixel 22. Suitable filler layer materials include, but are not limited to, transparent oxides such as indium tin oxide (ITO) and indium-doped zinc oxide (IZO). It should be noted that optical filler layers 56a, 56b, and 56c can be formed from the same material or different materials.

[0145] Figure 9 A cross-sectional view of another embodiment of the disclosed MCOLED array is shown, featuring a shared bottom DBR76. The multicolor MCOLED array includes blue sub-pixels 18, green sub-pixels 20, and red sub-pixels 22, each emitting a blue band λ. EMB70. Green band λ EMG 72 and the red band λ EMR 74. Three independent color sub-pixels (blue 18, green 20, and red 22) in a multi-color OLED array are each deposited on top of independent bottom electrodes 46a, 46b, and 46c. A bottom shared DBR 76 is deposited on top of the bottom electrodes 46a, 46b, and 46c, with each color sub-pixel deposited on top of the bottom DBR 76. It should be understood that each individual pixel 18, 20, 22 may include organic semiconductor layers 48a, 48b, and 48c specific to the sub-pixel color, and top electrodes 50a, 50b, and 50c serving as complementary anodes or cathodes as second electrodes and bottom electrodes. Furthermore, the organic semiconductor layers may also be replaced by a combination of a general white OLED stack and optical fill layers to achieve the desired color for each sub-pixel as described herein. The organic semiconductor layers may, as needed, include one or more organic hole injection layers (HIL), organic hole transport layers (HTL), emission layers (EML), organic electron transport layers (ETL), and organic electron injection layers to generate photons emitted by the pixel. Each sub-pixel 18, 20, and 22 shares a first DBR 26, with alternating layers of low or high refractive index material. On top of the first DBR 26 is a second DBR 28, which also comprises alternating high and low refractive index layers, but with different layer thicknesses, or different layer structures and / or compositions, unlike the layers in the first DBR 26. The combination of the first DBR 26 and the second DBR 28 forms a multi-DBR 44, providing an extended stopband for the multi-color pixel array.

[0146] Optical resonance is achieved within a microcavity device when the wavelengths of light reflected between two mirrors are in phase. This condition is called constructive interference, where wavelengths in phase combine to produce a stronger beam. Wavelengths of light in different phases do not undergo constructive interference but cancel each other out (i.e., their intensity is significantly reduced to negligible levels). This light reflection occurs within the microcavity of the device. In this case, it is the microcavity of an OLED. By enhancing only the resonant frequency, the emission spectrum of light is narrowed / reduced. In other words, a DBR emits light with a narrower wavelength range compared to a device without a DBR structure.

[0147] As the microcavity effect is enhanced, the emission of microcavity devices can be narrowed, approaching that of lasers. For DBR designs, the resonant wavelength is the desired, strongest wavelength of the device output. To achieve this, the resonant wavelength is called the Bragg wavelength, and the thickness of each material layer in the alternating material pairs in each distributed Bragg reflector (DBR) is chosen such that the thickness is equal to the Bragg wavelength divided by four times the refractive index n of the material.

[0148] like Figure 3As shown, the spectrum emitted by the DBR device (stopband 16) includes a range of wavelengths. The stopband 16 decreases as the microcavity intensity increases (i.e., by increasing the number of alternating material layers). For RGB subpixels sharing a single DBR, there is a trade-off between achieving maximum intensity of stopband 16 and capturing the spectrum of blue, green, and red light. Adding an additional DBR structure on top of the first DBR structure increases the spectrum of the stopband 16 of the RGB subpixel without sacrificing the intensity of the output light. A single DBR device can only achieve a certain contrast between its high-refractive-index and low-refractive-index material layers. The introduction of a second DBR device deposited on top of the first DBR device creates an additional refractive index contrast boundary between the last layer of the first DBR and the first layer of the second DBR. In one embodiment, the low-refractive-index material layer and the high-refractive-index material of the first and second DBRs are the same material. In another embodiment, the low-refractive-index material layer and the high-refractive-index material of the first and second DBRs are different materials. Higher refractive index contrast results in higher reflectivity of the DBR device. Figure 7 As shown, the first DBR is designed for a lower Bragg wavelength, and the second DBR is designed for a higher Bragg wavelength. Both DBR devices have high reflectivity, thus creating two resonant conditions that increase the device's stopband without sacrificing output light intensity (color).

[0149] All publications, patents, and patent applications mentioned in this specification demonstrate the skill level of a person skilled in the art to which this invention pertains and are incorporated herein by reference. Any reference to prior art in this specification is not, and should not be construed as, an admission or in any way implying that such prior art constitutes part of common general knowledge.

[0150] As described above, the invention can obviously be varied in many ways. These variations should not be considered as departing from the scope of the invention, and all such modifications that are obvious to those skilled in the art should be included within the scope of the appended claims.

Claims

1. A microcavity organic light emitting diode (MCOLED) array device comprising: a substrate; a plurality of sub-pixels deposited over the substrate, the sub-pixels having at least two different colors, each sub-pixel comprising: a bottom electrode; an organic stack deposited over the bottom electrode; and a top electrode deposited over the organic stack; and a shared multi-DBR system deposited over the plurality of sub-pixels, the multi-DBR system comprising: a first distributed Bragg reflector (DBR) having a first Bragg wavelength; and a second distributed Bragg reflector (DBR) located over the first DBR, the second DBR having a second Bragg wavelength different from the first Bragg wavelength.

2. The device of claim 1, wherein, the first DBR has a first stopband, the second DBR has a second stopband, and the first stopband and the second stopband overlap.

3. The device of claim 2, wherein, the shared multi-DBR system has a multi-DBR stopband that is a sum of the first stopband and the second stopband.

4. The device of any of claims 1-3, wherein the first DBR and the second DBR comprise layers of one or more of silicon nitride (Si3N4), silicon dioxide (SiO2), zinc sulfide (ZnS), calcium fluoride (CaF2), aluminum oxide (AIO x ), magnesium fluoride (MgF2), lithium fluoride (LiF), tellurium oxide (TeO x ), and titanium dioxide (TiO2).

5. The device of any of claims 1-4, wherein the first DBR and the second DBR comprise sub-layers of alternating high and low refractive index dielectric materials, and each sub-layer provides an optical path length equal to one quarter of the Bragg wavelength of the DBR.

6. The device of claim 5, wherein, the sub-layers of alternating high and low refractive index dielectric materials have different refractive indices.

7. The device of claim 5, wherein, the sub-layers of alternating high and low refractive index dielectric materials of the first DBR and the second DBR have different thicknesses.

8. The device of claim 5, wherein, the sub-layers of alternating high and low refractive index dielectric materials for each of the first DBR and the second DBR have one or more of different materials and different thicknesses.

9. The array of devices of any of claims 1-8, wherein the sub-pixel colors are red, green, or blue.

10. The device of any of claims 1-9, wherein the bottom electrode of each sub-pixel comprises a reflective metal or a reflective metal alloy.

11. The device of any of claims 1-10, wherein the bottom electrode comprises one or more layers of silver (Ag), aluminum (Al), gold (Au), Ag / Al, lithium (Li) / Al, or calcium (Ca) / Ag.

12. The device of any of claims 1-11, wherein the substrate is transparent.

13. The device of any of claims 1-12, wherein a bottom DBR structure is deposited below the organic stack.

14. The device of any of claims 1-13, wherein the top electrode comprises one or more of a metallic reflective surface and a semi-transparent conductive material.

15. The device of any of claims 1-14, wherein the top electrode is transparent.

16. The device of any of claims 1-15, wherein the shared multi-DBR system comprises two or more distributed Bragg reflectors.

17. A microcavity organic light emitting diode (MCOLED) array device comprising: a substrate; a sub-pixel array deposited over the substrate, each sub-pixel in the sub-pixel array comprising: a bottom electrode; an optical fill layer deposited over the bottom electrode for a particular color; a white organic stack deposited over the optical fill layer; and a top electrode deposited over the white organic stack; and a multi-DBR system deposited over the sub-pixel array, comprising: a first distributed Bragg reflector (DBR) having a first Bragg wavelength; and a second distributed Bragg reflector (DBR) located over the first DBR, the second DBR having a second Bragg wavelength different from the first Bragg wavelength.

18. The device of claim 17, wherein, the white organic stack is deposited as a blanket deposition over the sub-pixel array.

19. The device of claim 17 or 18, wherein, a thickness of the optical fill layer in each sub-pixel is selected to emit light of a particular color.

20. The device of any of claims 17-19, wherein, the optical fill layer for each particular color of sub-pixel has one or more of a different thickness and a different material.

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