Patent Publication Number: US-2023157059-A1

Title: Microcavity pixel array fabrication method

Description:
FIELD OF THE INVENTION 
     The present disclosure relates to microcavity pixel devices, and more particularly, organic light emitting diode (OLED) and vertical-cavity surface-emitting laser (VCSEL) microcavity design and fabrication processes for a high angular resolution, wide field of view, multiple view display. 
     BACKGROUND OF THE INVENTION 
     Light field displays provide multiple views, allowing a user to receive a separate view in each eye. While current displays in this category provide an interesting viewing experience, a captivating light field display requires a very high pixel density, very low angular separation between views, and a large viewing angle. It is desired that a user experiences smooth transitions between viewing zones, while maintaining an independent and perceivable view from the adjacent views. A fundamental requirement in achieving these viewing parameters is controlling the output characteristics of the emission source. Organic light-emitting diodes (OLEDs) bound in a microcavity allow control of the spectral bandwidth and output angle of the resulting light. 
     Organic light-emitting diodes consist of thin-film layers of organic material coated upon a substrate, generally made of glass, between two electrodes. OLEDs have a characteristic broad spectral width and Lambertian intensity distribution profile. The thin-film layers disposed between the anode and cathode commonly include one or more of an Organic Hole-Injection Layer (HIL), an Organic Hole-Transporting Layer (HTL), an Emissive Layer (EML), an Organic Electron-Transporting Layer (ETL), and an Organic Electron-Injection Layer. Light is generated in an OLED device when electrons and holes that are injected from the cathode and the anode (electrodes), respectively, flow through the ETL and the HTL and recombine in the EML. 
     One method for controlling the output characteristics of light is through the use of a microcavity. The microcavity is formed between two mirrors. The first mirror can be a metal cathode and the second mirror may be a layered stack of non-absorbing materials. The layered stack of non-absorbing materials is referred to as a distributed Bragg reflector (DBR). A DBR is an optical mirror composed of multiple pairs of two different dielectric layers with different refractive indices in an alternating order. The highest reflectivity is attained when the layer thicknesses are chosen such that the optical path length of each layer is one quarter of the resonance wavelength, commonly referred to as the Bragg Wavelength, λ Bragg . Two main design variables affecting the output characteristics of a microcavity are the reflectance of the top and bottom surfaces (i.e. opposing mirrors) and the optical path length. The optical path length between the mirrors is a multiple of the wavelength. The wavelength of the light output by such a resonant OLED structure is dependent, in part, upon this optical path length of the microcavity. The optical path length in the cavity can be manipulated in different ways, one of which is by changing the thickness of the layers that make up the microcavity. One challenge for the design of OLEDs which are suitable for light-field displays is how to determine the optimum optical path length of the microcavity to decrease the spectral bandwidth and output angle. 
     The traditional two electrode microcavity OLED design is such that the materials and thicknesses of all layers within the organic stack must be chosen based on electron-hole balancing requirements, leaving little room for color tuning of the microcavity. As a result, an additional filler layer is often added to adjust the microcavity and for a larger Q factor and a thicker filler layer is required. 
     U.S. Pat. No. 7,023,013 to Ricks et al. describes an array of light-emitting OLED microcavity pixels. The pixels disclosed use transparent conductive oxides (TCO) such as indium tin oxide (ITO) and indium-doped zinc oxide (IZO) as the filler layer. While the cavity adjustment is possible, the materials choice and thickness for the filler layer are the main constraints. In particular, the filler layer must be conductive because it is also in the pathway of the electrical current that drives the OLED. However, a thicker TCO layer is not preferable because of optical loss due to non-negligible light absorption with the TCO. 
     U.S. Pat. No. 10,340,480 to Peckham describes a microcavity OLED device that places the filler layer outside of the vertical path of electrical current driving the OLED light by utilizing transparent and/or semi-transparent electrodes adjacent to the filler layer. Compared to U.S. Pat. Nos. 7,023,013, 10,340,480 removes the filler material and thickness constraints as now insulating dielectric materials can be used. However in this design of the multi-color microcavity OLED pixel array different thicknesses are required for R,G,B color. With this design, an additional patterning step for the filler layer after OLED patterning is required onto the sensitive OLED materials. 
     This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a microcavity pixel device comprising an organic light emitting diode (OLED) for vertical-cavity surface-emitting laser (VCSEL) microcavity design and fabrication processes for a high angular resolution, wide field of view, multiple view display. It is another object of the present invention to provide a microcavity pixel design and structure allowing for tuning the optical cavity length of the microcavity of a microcavity pixel structure. This is achieved by including an intermediate electrode in the device which has an overhang region to form a connecting area to a bottom electrode, alleviating design restrictions in material type and dimensions throughout the optical microcavity tuning process. It is another object of the present invention to provide a method for the fabrication of a multi-colored microcavity pixel array facilitating the use of blanket deposition methods for select layers within a microcavity pixel structure. 
     In an aspect there is provided a microcavity OLED comprising: a bottom first electrode on a substrate; a filler layer on top of the first electrode; an intermediate electrode on top of the filler layer comprising an overhang region and a connecting area, the connecting area electrically connecting the intermediate electrode to the bottom first electrode; an organic light emitting diode stack on top of the intermediate electrode; and a top electrode on top of the organic light emitting diode stack. 
     In an embodiment, the filler layer is selected from an inorganic material and an organic material. 
     In another embodiment, the filler layer thickness is selected to emit a desired wavelength range of light from the MCOLED. 
     In another embodiment, the intermediate electrode consists of a semi-transparent thin film metal. 
     In another embodiment, the intermediate electrode consists of a transparent conductive oxide material. 
     In another embodiment, the top electrode consists of a metal reflective surface. 
     In another embodiment, the top electrode consists of a semi-transparent conductive material. 
     In another embodiment, the top electrode is transparent. 
     In another embodiment, the microcavity organic light emitting diode further comprises a reflective surface on the top electrode. 
     In another embodiment, the reflective surface is a distributed Bragg reflector (DBR). 
     In another aspect there is provided a method for fabrication of a multi-colored microcavity organic light emitting diode (MCOLED) array, the method comprising: patterning a bottom first series of electrodes on a substrate; depositing a first filler layer selected for a first color on top of a first group of electrodes in the series of electrodes; depositing a second filler layer selected for a second color on top of a second group of electrodes in the bottom first series of electrodes; depositing an intermediate series of electrodes on the first filler layer and the second filler layer, each electrode in the intermediate series of electrodes comprising an overhang region and a connecting area, the connecting area electrically connecting each electrode in the intermediate series of electrodes to an electrode in the bottom first series of electrodes; depositing an organic light emitting diode stack on the intermediate series of electrodes; and depositing a top series of electrodes on the organic light emitting diode stack. 
     In an embodiment, the first filler layer has a first thickness different than a thickness of the second filler layer. 
     In another embodiment, the first filler layer is comprised of a first material and the second filler layer is comprised of a second material different than the first material. 
     In another embodiment, the top series of electrodes comprises a reflective surface. 
     In another embodiment, the method further comprises depositing a reflective surface on the top series of electrodes. 
     In another embodiment, depositing the organic light emitting diode stack comprises depositing a first monochromatic OLED stack for the first color on the intermediate series of electrodes on top of the first filler layer and depositing a second monochromatic OLED stack for the second color on the intermediate series of electrodes on top of the second filler layer. 
     In another embodiment, depositing the organic light emitting diode stack comprises depositing a white OLED stack on the series of intermediate electrodes. 
     In another embodiment, the method further comprises depositing a third filler layer selected for a third color on top of a third group of electrodes in the bottom first series of electrodes. 
     In another embodiment, the method further comprises depositing a pixel definition layer to cover the overhang region and leaving a portion of each intermediate electrode uncovered by the pixel definition layer forming an active area of the intermediate electrode. 
     In another embodiment, the first filler layer and the second filler layer are comprised of an inorganic material or an organic material. 
     In another embodiment, the first filler layer and the second filler layer are comprised of one or more layers of different materials. 
     In another embodiment, the intermediate series of electrodes comprise a semi-transparent conductive material. 
     In another embodiment, the intermediate series of electrodes comprise a transparent conductive oxide material. 
     In another embodiment, the top series of electrodes comprise semi-transparent metal. 
     In another embodiment, the top series of electrodes consist of a transparent surface. 
     In another embodiment, the method further comprises depositing a reflective surface on the top series of electrodes. 
     In another embodiment, the reflective surface is a distributed Bragg reflector (DBR). 
     In another embodiment, the reflective surface is a shared distributed Bragg reflector covering the top series of electrodes comprising sublayers of alternating dielectric material. 
     In another embodiment, the first group of electrodes in the series of electrodes has a first distributed Bragg reflector and the second group of electrodes in the series of electrodes has a second distributed Bragg reflector, each distributed Bragg reflector comprising sublayers of alternating dielectric material deposited thereon. 
     In another aspect there is provided a multi-colored microcavity organic light emitting diode (MCOLED) array comprising: a bottom first series of electrodes on a substrate; a first filler layer selected for a first color on top of a first group of electrodes in the bottom first series of electrodes; a second filler layer selected for a second color on top of a second group of electrodes in the bottom first series of electrodes; an intermediate series of electrodes on the first filler layer and the second filler layer, each electrode in the intermediate series of electrodes comprising an overhang region and a connecting area, the connecting area electrically connecting each electrode in the intermediate series of electrodes to an electrode in the bottom first series of electrodes; an organic light emitting diode stack on the intermediate series of electrodes; and a top series of electrodes on the organic light emitting diode stack. 
     In an embodiment, the first filler layer and the second filter later are selected from an inorganic material and an organic material. 
     In another embodiment, the first filler layer has a first thickness different than a thickness of the second filler layer. 
     In another embodiment, the intermediate series of electrodes consist of a semi-transparent thin film metal. 
     In another embodiment, the intermediate series of electrodes consist of a transparent conductive oxide material. 
     In another embodiment, the top series of electrodes consist of a metal reflective surface. 
     In another embodiment, the top series of electrodes consist of a semi-transparent conductive material. 
     In another embodiment, the top series of electrodes are transparent. 
     In another embodiment, the MCOLED array further comprises a reflective surface on the top series of electrodes. 
     In another embodiment, the reflective surface is a distributed Bragg reflector (DBR). 
     In another aspect there is provided a method for fabrication of a multi-colored microcavity organic light emitting diode array, the method comprising: patterning a bottom first series of electrodes on a substrate; depositing a first filler layer selected for a first color on top of a first group of electrodes in the bottom first series of electrodes; depositing a second filler layer selected for a second color on top of a second group of electrodes in the bottom first series of electrodes; depositing an intermediate series of electrodes on the first filler layer and the second filler layers each electrode in the intermediate series of electrodes comprising an overhang region electrically connecting each intermediate electrode to a corresponding electrode in the bottom first series of electrodes; blanket depositing a white organic light emitting stack on the intermediate series of electrodes; and blanket depositing a top series of electrodes on the white organic light emitting stack. 
     In another embodiment, the top series of electrodes comprises a reflective surface. 
     In another embodiment, the method further comprises depositing a third filler layer selected for a third color on top of a third group of electrodes in the bottom first series of electrodes. 
     In another embodiment, the method further comprises depositing a pixel definition layer to cover the overhang region and the connecting area and leaving a portion of each intermediate electrode uncovered by the pixel definition layer forming an active area of the intermediate electrode. 
     In another embodiment, the first filler layer and the second filler layer are comprised of an inorganic material or an organic material. 
     In another embodiment, the first filler layer and the second filler layer are comprised of one or more layers of different materials. 
     In another embodiment, the intermediate series of electrodes comprise a semi-transparent thin film metal. 
     In another embodiment, the intermediate series of electrodes comprise a transparent conductive oxide material. 
     In another embodiment, the top series of electrodes comprise a semi-transparent metal. 
     In another embodiment, the top series of electrodes consist of a transparent surface. 
     In another embodiment, the method further comprises depositing a reflective surface on the top series of electrodes. 
     In another embodiment, the reflective surface is a distributed Bragg reflector (DBR). 
     In another embodiment, the reflective surface is a shared distributed Bragg reflector covering the top series of electrodes. 
     In another aspect there is provided a vertical surface emitting laser (VCSEL) comprising: a substrate; a bottom first electrode on the substrate; a Distributed Bragg Reflector (DBR) comprising multiple layers alternating between a high refractive index material and a low refractive index material; a filler layer on top of the DBR; an intermediate electrode on top of the filler layer comprising an overhang region and a connecting area, the connecting area electrically connecting the intermediate electrode to the bottom first electrode; a pixel definition layer on top of the intermediate electrode to cover the overhang region and leaving a portion of each intermediate electrode uncovered forming an active area of the intermediate electrode; a light emitting material stack on top of the active area of the second electrode; a third electrode on top of the light emitting material stack; and a distributed Bragg reflector deposited on top of the third electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of the invention will become more apparent in the following detailed description in which reference is made to the appended drawings. 
         FIG.  1 A : illustrates a microcavity organic light emitting diode (MCOLED) orientations as known in the art. 
         FIG.  1 B : illustrates a microcavity organic light emitting diode (MCOLED) orientations as known in the art. 
         FIG.  2   : illustrates an embodiment of a MCOLED as per the present disclosure including a top electrode which acts as a reflective surface to form the optical microcavity of the MCOLED. 
         FIG.  3   : illustrates an embodiment of a MCOLED as per the present disclosure including a multi layer filler layer. 
         FIG.  4   : illustrates an embodiment of a MCOLED as per the present disclosure including a reflective surface deposited on the top electrode to form the optical microcavity of the MCOLED. 
         FIG.  5   : illustrates an alternative embodiment of a MCOLED as per the present disclosure in which a distributed Bragg reflector (DBR) is deposited on top of the top electrode. 
         FIG.  6 A : illustrates the voltage connections of MCOLED structures known in the art. 
         FIG.  6 B : illustrates the voltage connections of MCOLED structures known in the art. 
         FIG.  7   : illustrates the voltage connections of MCOLED structure of the present disclosure. 
         FIG.  8   : illustrates adjusting the filler layer of a MCOLED thereby adjusting the microcavity for red, green, and blue MCOLED structures. 
         FIG.  9   : illustrates fillers layers of an R,G,B MCOLED array wherein the filler layers are of similar or same thickness. 
         FIG.  10   : illustrates a vertical-cavity surface-emitting laser (VCSEL) device as per the present disclosure. 
         FIG.  11 A : illustrates a side view of step  1  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 B : illustrates a top view of step  1  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 C : illustrates a side view of step  2  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 D : illustrates a top view of step  2  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 E : illustrates a side view of step  3  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 F : illustrates a top view of step  3  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 G : illustrates a side view of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  11 H : illustrates a top view of step  4  of the proposed MCOLED patterning process for depositing the bottom first and intermediate electrodes with color adjusted filler layer. 
         FIG.  12   : illustrates a side view of a multi-color MCOLED array with white OLED layer. 
         FIG.  13   : illustrates an embodiment for fabrication of a multi-color MCOLED array including a shared top electrode which acts as a reflective surface to form the optical microcavity of the MCOLED. 
         FIG.  14   : illustrates an embodiment for fabrication of a multi-color MCOLED array including a shared reflective surface on the top electrode to form the optical microcavity of the MCOLED. 
         FIG.  15   : illustrates an alternative embodiment for fabrication of a multi-color MCOLED array. 
         FIG.  16 A : illustrates a side view of a multi-color MCOLED with a common distributed Bragg reflector (DBR) structure. 
         FIG.  16 B : illustrates a side view of an alternative embodiment of a multi-color MCOLED with a common distributed Bragg reflector (DBR) structure. 
         FIG.  17 A : illustrates a side view of a multi-color MCOLED with individual distributed Bragg reflector (DBR) structures. 
         FIG.  17 B : illustrates a side view of an alternative embodiment of a multi-color MCOLED with individual distributed Bragg reflector (DBR) structures. 
         FIG.  18 A : illustrates a process schematic of a method for the design and optimization of a microcavity OLED. 
         FIG.  18 B : illustrates an improved process schematic of a method for the design and optimization of a microcavity OLED as per the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present disclosure relates generally to a microcavity organic light-emitting diode (OLED) design and structure and a method of tuning a multi-color microcavity organic light emitting diode (MCOLED) achieved by including an intermediate electrode to connect with a first electrode of a MCOLED structure to alleviate the re-evaluation of electron-hole balancing considerations when tuning the optical microcavity of the device. The addition of the intermediate electrode enables the designer to separate the optimization of the electrical properties of the organic material stack and the optical properties of the MCOLED structure. 
     Disclosed are methods for designing and making an OLED device for a red, green, or blue light emission comprising an intermediate electrode deposited on top of a filler layer, the intermediate electrode configured to connect with the first electrode of the OLED device, therefore alleviating electron-hole charge balancing requirement reconsideration when tuning the optical cavity. In addition to greater flexibility in material selection and thickness, the intermediate cathode connection with the first electrode allows for an optimized process for MCOLED array fabrication as no additional patterning step is required after OLED stack is patterned. 
     In an embodiment of the method, the MCOLED structure as described by the present disclosure may include a metal reflective surface as the third electrode and an opposing reflective surface comprising a distributed Bragg reflector (DBR). DBR design is an alternating stack of dielectric materials of specific thicknesses ensuring the optical path length is a quarter of the designed wavelength and suitable for use with an OLED of any colour. The highest reflectivity of a DBR is attained when the layer thicknesses are chosen such that the optical path length of each layer is one quarter of the resonance wavelength. With each layer having an optical path length of λ Bragg /4, all reflections will add in phase, and the transmissivity will decrease exponentially as a function of mirror thickness. At longer or shorter wavelengths than the stopband, the reflections begin to add out of phase, therefore the total reflections decreases [Ref. 01]. This gives a broad-band high-reflectivity region centered on the Bragg wavelength, called the stop band, with oscillating side-lobes on either side [Ref 04]. The DBR is generally composed of pairs of two different dielectric layer with different refractive indices, but may also be composed of multiple dielectric materials or other transparent materials with a contrast in n, as long as the optical path length of each layer is Δ Bragg /4. The multilayer mirror consists of alternating layers of substantially non-absorbing materials of appropriately chosen thickness. Typically, each layer is of thickness 
     
       
         
           
             
               λ 
               
                 4 
                 ⁢ 
                 n 
               
             
             , 
           
         
       
     
     where λ is advantageously chosen to correspond approximately to the center wavelength of the EML emission spectrum, e.g., 500-550 nm. Such mirrors are well known. The reflectivity of the mirror depends in a known way on the number of layer pairs, layer thickness and the refractive index of the materials used. Exemplary material pairs in the visible wavelength region are Si 3 N 4 , SiO 2 , and TiO 2 . 
     In addition to MCOLED structures, an intermediate electrode can be implemented in a vertical-cavity surface-emitting laser (VCSEL) structure. A vertical orientation is more advantageous than the Edge Emitting Lasers (EEL) that emits light from the side or from the Light Emitting Diodes (LED) that produce light from the sides and top, as VCSELs discharge light perpendicular to the surface of a laser, which allows thousands of VCSELs to be processed all at one time in a wafer. Incorporating the intermediate electrode to connect with the first electrode in the VCSEL structure allows for increased material and thickness options for the remaining layers above the intermediate electrode by removing the requirement to re-evaluate electron-hole balancing requirements in the cavity region when tuning the optical cavity of the device. The advantages for this VCSEL structure mirror those achieved by the MCOLED regarding material and thickness selection in layers above the intermediate electrode. 
     Various features of the invention will become apparent from the following detailed description taken together with the illustrations in the Figures. The design parameters, design method, construction, and use of the microcavity OLED design process and structures disclosed herein are described with reference to various examples representing embodiments which are not intended to limit the scope of the invention as described and claimed herein. The skilled technician in the field to which the invention pertains will appreciate that there may be other variations, examples and embodiments of the invention not disclosed herein that may be practiced according to the teachings of the present disclosure without departing from the scope of the invention. 
     Definitions 
     Unless defined otherwise, 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. 
     The use of the word “a” or “an” when used herein in conjunction with the term “comprising” may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one” and “one or more than one.” 
     As used herein, the terms “comprising,” “having,” “including” and “containing,” and grammatical variations thereof, are inclusive or open-ended and do not exclude additional, unrecited elements and/or method steps. The term “consisting essentially of” when used herein in connection with a composition, device, article, system, use, or method, denotes that additional elements and/or method steps may be present, but that these additions do not materially affect the manner in which the recited composition, device, article, system, method, or use functions. The term “consisting of” when used herein in connection with a composition, device, article, system, use, or method, excludes the presence of additional elements and/or method steps. A composition, device, article, system, use, or method described herein as comprising certain elements and/or steps may also, in certain embodiments consist essentially of those elements and/or steps, and in other embodiments consist of those elements and/or steps, whether or not these embodiments are specifically referred to. 
     As used herein, the term “about” refers to an approximately +/−10% variation from a given value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to. 
     The recitation of ranges herein is intended to convey both the ranges and individual values falling within the ranges, to the same place value as the numerals used to denote the range, unless otherwise indicated herein. 
     The use of any examples or exemplary language, e.g. “such as”, “exemplary embodiment”, “illustrative embodiment” and “for example” is intended to illustrate or denote aspects, embodiments, variations, elements or features relating to the invention and not intended to limit the scope of the invention. 
     As used herein, the terms “connect” and “connected” refer to any direct or indirect physical association between elements or features of the present disclosure. Accordingly, these terms may be understood to denote elements or features that are partly or completely contained within one another, attached, coupled, disposed on, joined together, in communication with, operatively associated with, etc., even if there are other elements or features intervening between the elements or features described as being connected. 
     As used herein, the term “DBR” refers to a distributed Bragg reflector. A distributed Bragg reflector (DBR) is an optical mirror which is composed of multiple pairs of two different dielectric layers with different refractive indices in an alternative order [Ref. 06]. 
     As used herein, the term “transparent” refers to a material which allows visible light to pass through it. 
     As used herein, the term “transparent conductive oxide” or TCO refers to a doped metal oxide 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). 
     As used herein, the term “pixel” refers to a light source and light emission mechanism used to create a display. 
     As used herein, the term “vertical-cavity surface-emitting laser (VCSEL)” refers to a semiconductor-based laser diode that emits light or optical beam vertically from its top surface. 
     As used herein, the term “Q factor” refers to a dimensionless parameter and is used to indicate performance of a VCSEL. In optics, the Q factor of a resonant cavity refers to: 
         Q= 2π foE/P  
 
     where fois the resonant frequency, E is the energy stored in the cavity, P is the power dissipated. 
     As used herein, the term “electron-hole balancing” refers to the charge balance within an organic light emitting diode device. Electrons and holes injected from the respective contacts recombine in an emission zone to form excitons which undergo radiative emission to generate light. The external device efficiency is determined by the fraction of light, which is generated in the device stack and extracted to air. In an OLED device, the internal device efficiency is highly dependent on the charge balance of the device. 
     As used herein, the term “subpixel” refers to a structure comprised of a light emitting device housed within an optical microcavity. The optical microcavity is operatively associated with a plurality of reflective surfaces to substantially collimate, manipulate or tune the light. At least one of the reflective surfaces is a light propagating reflective surface connected to the optical microcavity to propagate the light out of the microcavity. The present disclosure provides individually addressable red, green, and blue (RGB) subpixels. The subpixel size as presently described is in a nanoscale to several microns range, which is significantly smaller than the pixel size previously known in the art. 
     As used herein, the acronym “FWHM” refers to ‘full width half maximum’, which is an expression of the extent of a function given by the difference between the two extreme values of the independent variable at which the dependent variable is equal to half of its maximum value. 
     As used herein, the term “OLED” refers to an Organic Light Emitting Diode, which is an opto-electronic device which emits light under the application of an external voltage. OLEDS can be divided into two main classes: those made with small organic molecules and those made with organic polymers. An OLED is a light-emitting diode in which the emissive electroluminescent layer comprises a film of organic compound that emits light in response to an electric current. Generally, an OLED is a solid-state semiconductor device [Ref 09] comprised at least one conducting organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layers. The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an exciton, which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. Types of OLEDs include, but are not limited to: [Ref. 09] 
     a. Active-Matrix OLEDs (AMOLED)
         AMOLEDs have full layers of cathode, organic molecules and anode. The anode layers have a thin film transistor (TFT) plane in parallel to it so as to form a matrix. This helps in switching each pixel to its on or off state as desired, thus forming an image. Hence, the pixels switch off whenever they are not required or there is a black image on the display, increasing the battery life of the device. This is the least power consuming type of OLED and has quicker refresh rates which makes them suitable for video. The best uses for AMOLEDs are computer monitors, large-screen TVs and electronic signs or billboards.       

     b. Top-Emitting OLEDs
         Top-emitting OLEDs have a substrate that is either opaque or reflective. Top-emitting OLEDs are better suited for active-matrix applications as they can be more easily integrated with a non-transparent transistor backplane. Manufacturers use top-emitting OLED displays in smart cards.       

     c. Bottom-Emitting OLEDs
         An OLED is bottom emitting if the emitted light passes through the transparent or semi-transparent bottom electrode and substrate.       

     As used herein, the term “microcavity” refers to a structure formed by reflecting faces on the two sides of a spacer layer or optical medium, such as, for example, an OLED. 
     As used herein, the term “microcavity OLED” (MCOLED) refers to the materials of an OLED, as previously described, bound in a microcavity defined by two reflective surfaces, in which the reflective surfaces can be metallic materials, dielectric materials arranged in such a way to reflect light within a specific range, or a combination of dielectric and metallic materials. 
     As used herein, the term “monochromatic microcavity organic light emitting diode (MCOLED)” refers to a MCOLED tuned to emit a single color. 
     As used herein, the term “electrode” refers to a conductor through which electricity enters or leaves an object, substance, or region. 
     As used herein, the term “cathode” refers to the negatively charged electrode by which electrons enter an electrical device. 
     As used herein, the term “anode” refers to the positively charged electrode by which the electrons leave an electrical device. 
     As used herein, the term “patterning” refers to a technique using a series of post treatments to chemically engrave a transferred pattern into or allow the deposition of new material in the transferred pattern upon a target material. 
     As used herein, the term “blanket deposition” refers to depositing material without using a patterning technique. 
     As used herein, the term “mirror” refers to an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection. Two or more mirrors aligned exactly parallel and facing each other can give an infinite regress of reflections, called an infinity mirror effect. 
     As used herein, the term “transmissivity” refers to the percentage of light transmitted per the incident light. 
     As used herein, the term “wavelength” is a measure of distance between two identical peaks (high points) or troughs (low points) in a wave, which is a repeating pattern of traveling energy such as light or sound. 
     As used herein, the term “simulation” refers to the production of a computer model of something, especially for the purpose of study or to develop and refine fabrication specifications. Various simulation methods can be used, including but not limited to the following. The finite-difference time-domain (FDTD) method is used to solve problems in electromagnetics and photonics, solving Maxwell&#39;s equations in complex geometries. FDTD is a versatile finite difference method in the time domain which treats nonlinear material properties in a natural way and allows a user to measure the system response over a wide range of frequencies. A comparable technique is Rigorous Coupled Wave Analysis (RCWA), which is a semi-analytical method, generally employed to solve field diffraction problems of a periodic structure. RCWA decomposes fields into a set of plane waves, representing the fields by a sum of spatial harmonics in Fourier-space. RCWA benefits from a decreased simulation complexity and time but suffers inaccuracy for more complex geometries. 
     It is contemplated that any embodiment of the compositions, devices, articles, methods and uses disclosed herein can be implemented by one skilled in the art, as is, or by making such variations or equivalents without departing from the scope and spirit of the invention. 
     Design Considerations for MCOLEDs 
     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 materials 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 emissive layer (EML). Material and thickness design considerations for the layers of the OLED stack of a MCOLED are based upon the desired indices of refraction n and electron-hole balancing requirements. A balanced charge injection results from the equal flow rate of electrons/holes to the emissive layer (EML). If an OLED device is unbalanced, the electrons or holes will accumulate and charge the emission layer, thereby compromising device output. 
     A microcavity organic light emitting diode (MCOLED) is a device in which the materials of an OLED are bound in a microcavity defined by two reflective surfaces arranged in such a way to reflect light within a specific range, or some combination of dielectric and metallic materials. The organic materials which make up the OLED stack are arranged with material thicknesses d j  which have an optical path length of L j , where L j =n j ×d j , and where n j  is the refractive index of the OLED material. The sum of the optical path length of the materials between the reflective surfaces is designed to equal 
     
       
         
           
             
               
                 m 
                 ⁢ 
                 
                   λ 
                   i 
                 
               
               2 
             
             , 
           
         
       
     
     where λ i  is the peak design wavelength of the MCOLED. The optical path length can therefore be changed by changing the thickness of one or more of the materials between the reflective surfaces, or by adding one or more additional filler material. The use of a microcavity in an OLED structure decreases the spectral width of the OLED, decreases the angular output, and increases the overall efficiency. Tuning of the optical microcavity for specific wavelengths of light, or color, is a challenging task as tuning a microcavity is achieved by creating a resonance at a specific wavelength between two reflective surfaces, completed by selecting and defining material thickness, refractive index, and phase change through careful analysis and simulations. 
     A MCOLED as described in U.S. Pat. No. 7,023,013 is shown in  FIG.  1 A . This structure has a semi-transparent material as a bottom first electrode  30  on a substrate  34 . A filler layer  16  of transparent oxides such as indium tin oxide (ITO) and IZO are deposited on top of the bottom first electrode  30  as the filler layer. The OLED stack  42  is deposited on top of the filler layer  16  followed by the top electrode  18  which acts as a reflector to form an optical microcavity  28 . The OLED stack  42  in this structure consists of a HIL  20 , HTL  22 , emissive layers (EMLs)  24   a ,  24   b , ETL  26 , and EIL  36 . While adjustment of the optical microcavity  28  is possible, the materials choice and thickness for the filler layer  16  are the main constraints. In this art, the filler layer  16  must be conductive because it is in the pathway of the electrical current that drives the OLED. However, a thicker filler layer  16  layer is not preferable because of optical loss due to non-negligible light absorption with the filler layer  16  material. 
       FIG.  1 B  illustrates a MCOLED device as described in U.S. Pat. No. 10,340,480. This configuration with bottom first electrode  30  on a substrate  34  places the filler layer  16  outside of the vertical path of electrical current driving the OLED light by utilizing a transparent and/or semi-transparent top electrode  18  adjacent to the filler layer  16 . Compared to the device as described in U.S. Pat. No. 7,023,013, this configuration removes the filler layer  16  material and thickness constraints as now insulating dielectric materials can be used. With this design, an additional patterning step for the filler layer  16  after OLED patterning is then required to the fragile and sensitive materials of the OLED stack  42 . The OLED stack  42  includes an ETL  26 , EML  24 , HTL  22  and a HIL  20 . The transparent and/or semi-transparent top electrode  18  is deposited on top of the OLED stack  42  and a filler layer  16  is deposited on top of the top electrode  18  and a distributed Bragg reflector (DBR)  10  is positioned on top of the filler layer  16 . The DBR  10  consists of a series of alternating layers of high refractive index dielectric material  14  and low refractive index dielectric material  12 . The DBR  10  acts as the second reflective surface to form the optical microcavity  28 . 
       FIG.  2    illustrates an embodiment of a microcavity OLED device as disclosed herein. The MCOLED device has a bottom first electrode  30  deposited on a substrate  34 . A filler layer  16  is then deposited on the bottom first electrode  30 . A semi-transparent/transparent intermediate electrode  38  is then deposited on top of the filler layer  16 . The OLED stack  42  is then deposited on top of the intermediate electrode  38 . In this embodiment, the OLED stack  42  includes an EIL  36 , ETL  26 , EML  24 , HTL  22 , and a HIL  20 . A top electrode  18  is then deposited on the OLED stack  42  and the top electrode  18  is a reflective surface and therefore is used to form an optical microcavity  28 . The intermediate electrode  38  is deposited such that it covers the overhang of the filler layer  16  to form an overhang region  58  and connects to the bottom first electrode  30  to form a connecting area  40  thereby forming an electrical contact between the bottom first electrode  30  and the intermediate electrode  38 . The connection (the overhang region  58  and the connecting area  40 ) between the bottom first electrode  30  and the intermediate electrode  38  can be made with the same material, or any other conductive material, such as, for example, TCO. This connection formed by the connecting area  40  removes the requirement for reconsiderations of electron-hole charge balancing requirements for all material types and thicknesses of the layers of the OLED stack  42  when tuning the optical microcavity  28  by altering the optical path length of the microcavity. This is advantageous in that organic layer designs need not be altered to balance the charge of the OLED stack  42 , and the filler layer  16  thickness alone may be adjusted to alter the optical path length of the optical microcavity  28 . The bottom first electrode  30  may be an anode or a cathode, therefore the OLED device may be a conventional configuration or an inverted configuration. A conventional OLED configuration is one such that the bottom first electrode  30  before the OLED stack  42  is an anode and the top electrode  18  above the OLED stack  42  is a cathode. For inverted OLEDs, the bottom first electrode  30  before the OLED stack  42  is a cathode and the top electrode  18  above the OLED stack  42  is an anode. 
     The electron transport layer (ETL)  26  can be any substantially transparent material that can facilitate electron transport from the relevant electrode to the emissive layer  24 . Examples of such materials can include but are not limited to 2-(4-biphenyl)-5-phenyl-1,3,4-oxadiazole (PBD), butyl PBD, or either of these previously mentioned materials doped in an inert polymer such as poly(methyl methacrylate) (PMMA) or a poly(carbonate). Emissive layer (EML)  24  materials can include but are not limited to Alq (Tris(8-hydroxyquinolinato)aluminum), aromatic hydrocarbons, poly(phenylene vinylenes), oxadiazole and stilbene derivatives. The EML  24  material optionally can be a stable non-emissive host material doped with an emissive material which has an energy gap that is less than that of the primary component of the EML  24  material. The hole transport layer (HTL)  22  can be any substantially transparent material that can facilitate the transport of holes to the EML  24  layer, where electron-hole recombination takes place. Examples of suitable materials include but are not limited to diamines (e.g., N,N′-diphenyl-N,N′-bis (3-methylphenyl)-1,1′-biphenyl-4,4′-diamine) and poly(phenylene vinylenes). 
     The bottom first electrode  30  may be a transparent material such as indium tin oxide (ITO) or a conducting polymer such as doped polyaniline, or a thin layer (e.g., about 10 nm) of metal (e.g., Ag, Au or Al), and may be unpatterned or patterned (e.g., into rows or columns). The top electrode  18  can be a reflective metal, a semi-transparent, thin-film metal or a transparent conductive oxide such as, for example, Indium Tin Oxide (ITO), Fluorine Doped Tin Oxide (FTO) or Aluminum-doped Zinc Oxide (AZO) and Indium-doped Zinc Oxide (IZO), or Ga-doped Zinc Oxide (ZnO). The bottom first electrode  30  can be deposited, for example, with sputtering, evaporation, or spin coating techniques. Preferably, the bottom first electrode  30  is deposited by evaporation and/or sputtering. The patterning can be done, for example, using lithography or shadow mask. The intermediate  38  electrode can be deposited with sputtering, thermal evaporation, atomic layer deposition, or spin casting techniques, and is preferably deposited by sputtering. The patterning can be done using lithography or shadow mask, preferably shadow mask. The top electrode  18  can be deposited by, for example, sputtering, thermal evaporation, atomic layer deposition, or spin casting. Preferably, thermal evaporation can be used to reduce potential damage to the underlying organic layers. No patterning is required for top electrode  18  layer. 
     The filler layer  16  can be any substantially transparent material that is chemically stable under the manufacturing and operating conditions and that can be patterned by an appropriate technique. Examples of filler materials include organic materials such as transparent polymers (e.g., a polyimide) or inorganic materials such as transparent inorganic dielectrics (e.g., Si 3 N 4 . or SiO 2 ). In a top-emitting configuration of the OLED, the substrate  34  need not be transparent. It can be metal or a semiconductor, e.g., Silicon, however, is generally glass, or polyimide. This design is also suitable for active matrix OLED (AMOLED) displays as the bottom first electrode  30  can be connected to a TFT (thin film transistor) pixel circuit underneath. 
       FIG.  3    illustrates an embodiment of a microcavity OLED device as disclosed herein. The MCOLED device has a bottom first electrode  30  deposited on a substrate  34 . A multi layer filler layer  16   a ,  16   b  is then deposited on the bottom first electrode  30 . Each layer of the multi layer filler layer  16   a ,  16   b  may consist of the same material or of different materials. The filler layers  16   a ,  16   b  may be of the same or of different thicknesses. A semi-transparent/transparent intermediate electrode  38  is then deposited on top of the filler layer  16   a ,  16   b . The OLED stack  42  is then deposited on top of the intermediate electrode  38 . In this embodiment, the OLED stack  42  includes an EIL  36 , ETL  26 , EML  24 , HTL  22 , and a HIL  20 . A top electrode  18  is then deposited on the OLED stack  42  and the top electrode  18  is a reflective surface and therefore is used to form an optical microcavity  28 . The intermediate electrode  38  is deposited such that it covers the overhang of the filler layer  16   a ,  16   b  to form an overhang region  58  and connects to the bottom first electrode  30  to form a connecting area  40  thereby forming an electrical contact between the bottom first electrode  30  and the intermediate electrode  38 . The connection (the overhang region  58  and the connecting area  40 ) between the bottom first electrode  30  and the intermediate electrode  38  can be made with the same material, or any other conductive material, such as, for example, TCO. This connection formed by the connecting area  40  removes the requirement for reconsiderations of electron-hole charge balancing requirements for all material types and thicknesses of the layers of the OLED stack  42  when tuning the optical microcavity  28  by altering the optical path length of the microcavity. This is advantageous in that organic layer designs need not be altered to balance the charge of the OLED stack  42 , and the filler layer  16   a ,  16   b  individual or combined thickness may be adjusted to alter the optical path length of the optical microcavity  28 . The bottom first electrode  30  may be an anode or a cathode, therefore the OLED device may be a conventional configuration or an inverted configuration. A conventional OLED configuration is one such that the bottom first electrode  30  before the OLED stack  42  is an anode and the top electrode  18  above the OLED stack  42  is a cathode. For inverted OLEDs, the bottom first electrode  30  before the OLED stack  42  is a cathode and the top electrode  18  above the OLED stack  42  is an anode. 
       FIG.  4    illustrates an embodiment of a microcavity OLED device as disclosed herein. The MCOLED device has a bottom first electrode  30  deposited on a substrate  34 . A filler layer  16  is then deposited on the bottom first electrode  30 . A semi-transparent or transparent intermediate electrode  38  is then deposited on top of the filler layer  16 . The OLED stack  42  is then deposited on top of the intermediate electrode  38 . In this embodiment, the OLED stack  42  includes an EIL  36 , ETL  26 , EML  24 , HTL  22 , and a HIL  20 . A top electrode  18  is then deposited on the OLED stack  42  and an additional reflective surface  32  is deposited on top of the top electrode  18  to form an optical microcavity  28 . The intermediate electrode  38  is deposited such that it covers the overhang of the filler layer  16  to form an overhang region  58  and connects to the bottom first electrode  30  to form a connecting area  40  thereby forming an electrical contact between the bottom first electrode  30  and the intermediate electrode  38 . This connection formed by the connecting area  40  removes the requirement for reconsiderations of electron-hole charge balancing requirements for all material types and thicknesses of the layers of the OLED stack  42  when tuning the optical microcavity  28  by altering the optical path length of the microcavity. This is advantageous in that organic layer designs need not be altered to balance the charge of the OLED stack  42 , and the filler layer  16  thickness alone may be adjusted to alter the optical path length of the optical microcavity  28 . 
       FIG.  5    illustrates an embodiment of a microcavity OLED device as disclosed herein. The MCOLED device has a bottom first electrode  30  deposited on a substrate  34 . A filler layer  16  is then deposited on the bottom first electrode  30 . A semi-transparent or transparent intermediate electrode  38  is then deposited on top of the filler layer  16 . The OLED stack  42  is then deposited on top of the intermediate electrode  38 . In this embodiment, the OLED stack  42  includes an EIL  36 , ETL  26 , EML  24 , HTL  22 , and a HIL  20 . A top electrode  18 , which in this embodiment is a transparent or semi-transparent electrode, is then deposited on the OLED stack  42  and a distributed Bragg reflector (DBR)  10  positioned on top of the top electrode  18 . The DBR  10  consists of a series of alternating layers of high refractive index dielectric material  14  and low refractive index dielectric material  12 . The DBR  10  acts as the second reflective surface for the optical microcavity  28 . The intermediate electrode  38  is deposited such that it covers the overhang of the filler layer  16  to form an overhang region  58  and connects to the bottom first electrode  30  to form a connecting area  40  thereby forming an electrical contact between the bottom first electrode  30  and the intermediate electrode  38 . This connection formed by the connecting area  40  removes the requirement for electron-hole charge balancing reconsiderations for all material types and thicknesses of the layers of the OLED stack  42  when adjusting the length of the optical microcavity  28  during the tuning process. This may now be achieved through altering the filler layer  16  thickness alone without the need for rebalancing of the electron-hole charges within the OLED stack  42 . The intermediate electrode  38  is a transparent conductive oxide such as, 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 semitransparent thin metal film such as Ag, Al, Ag, Ca, Li, Au and Ag:Mg alloy etc. It can also be single film or multi-layer film such as, for example, Ag/Al, Li/Al, and Ca/Ag. 
       FIG.  6 A  illustrates the electrical connection  44  between two electrodes in an OLED device, the two electrodes being the bottom first electrode  30  and the top electrode  18  as disclosed in U.S. Pat. No. 7,023,013. The filler layer  16  is positioned between the bottom first electrode  30  and top electrode  18 , and an additional reflective surface  32  is layered on top of the top electrode which with the bottom first electrode forms an optical microcavity  28 . Electron-hole charge balancing requirements must be considered in material and layer thickness alternation in the OLED stack  42  layers during the tuning process for this OLED device. The tuning process refers to changing the optical path length of a microcavity to the optimum dimension for desired output. 
       FIG.  6 B  illustrates the electrical connection  44  between two electrodes in an OLED device, the two electrodes being the bottom first electrode  30  and the top electrode  18  as disclosed in U.S. Pat. No. 10,340,480. The filler layer  16  is positioned between the OLED stack  42  and top electrode  18  and additional reflective surface  32  is layered on top of the top electrode which with the bottom first electrode which forms an optical microcavity  28 . In this device electron-hole charge balancing requirements must be considered in material and layer thickness alternation in the OLED stack  42  layers during the tuning process 
       FIG.  7    illustrates the electrical connection  44  between two electrodes in an OLED device as per the present disclosure. The electrical connection  44  as shown in this figure is formed between the bottom first electrode  30  and an intermediate electrode  38  by way of an overhang region  58  in the intermediate electrode which connects through connecting area  40 . The filler layer  16  is positioned between the bottom first electrode  30  and the intermediate electrode  38  and the OLED stack  42  is positioned above the intermediate electrode  38  therefore removing electron-hole charge balancing reconsideration within the OLED stack  42  during the tuning process. In this embodiment, the top electrode  18  acts as a reflective surface to form the optical microcavity  28 . An advantage of the intermediate electrode  38  having overhang region  58  is that in the optimization of the optical path length of the optical microcavity  28  of the device the thickness of the filler layer  16  may be adjusted to achieve the required optical path length without impacting the charge balance within the layers of the OLED stack  42 . 
       FIG.  8    illustrates an array of RGB (red, green, and blue) microcavity OLED structures on a single substrate  34 . This figure highlights the varying thickness of the filler layer required for tuning each individual color MCOLED. Each structure has a bottom first series of electrodes  30   a ,  30   b ,  30   c , and a filler layer for red color  46 , a filler layer for green color  48 , or a filler layer for blue color  50  is then deposited on the bottom first series of electrodes  30   a ,  30   b ,  30   c , respectively. The varying thicknesses required to achieve the optical path length required for each color, therefore each filler layer  46 ,  48 ,  50  must be deposited separately. The intermediate series of electrodes  38   a ,  38   b ,  38   c  are then deposited on the filler layers  46 ,  48 ,  50 , respectively. As shown, intermediate series of electrodes  38   a ,  38   b ,  38   c  have an overhang region  58   a ,  58   b ,  58   c  and connecting area  40   a ,  40   b ,  40   c  to electrically connect the intermediate series electrodes  38   a ,  38   b ,  38   c  to the bottom first series electrodes  30   a ,  30   b ,  30   c , respectively, and the color of the OLED structure is provided by the difference in thickness of the filler layer therebetween. The intermediate series of electrodes  38   a ,  38   b ,  38   c  are deposited on top of the entirety of the top surface of filler layers  46 ,  48 ,  50  and extend beyond the top surface of said filler layers  46 ,  48 ,  50 , thereby forming the overhang regions  58   a ,  58   b ,  58   c . The overhang regions  58   a ,  58   b ,  58   c  extend to connect with the bottom first series of electrodes  30   a ,  30   b ,  30   c  of each OLED. The connecting area  40   a ,  40   b ,  40   c  is formed by the intermediate series of electrodes  38   a ,  38   b ,  38   c  being deposited over top of the exposed bottom first series of  30   a ,  30   b ,  30   c  to form an electrical connection between the two layers. 
       FIG.  9    illustrates an array of RGB (red, green, and blue) microcavity OLED structures on a single substrate  34 . In this embodiment, the thickness of each filler layer required for tuning each individual color MCOLED may be similar or the same to one another if the material is varied to accommodate the structure of each individual color. Each structure has a bottom first series of electrodes  30   a ,  30   b ,  30   c . Then a filler layer for red color  46 , a filler layer for green color  48 , or a filler layer for blue color  50  is deposited on the bottom first series of electrodes  30   a ,  30   b ,  30   c , respectively. Depending on the properties of each selected filler layer  46 ,  48 ,  50  material, the thickness of filler layers  46 ,  48 ,  50  may be similar or equal. The intermediate series of electrodes  38   a ,  38   b ,  38   c  are then deposited on the filler layers  46 ,  48 ,  50 , respectively. As shown, intermediate series of electrodes  38   a ,  38   b ,  38   c  have an overhang region  58   a ,  58   b ,  58   c  and connecting area  40   a ,  40   b ,  40   c  to electrically connect the intermediate series of electrodes  38   a ,  38   b ,  38   c  to the bottom first series of electrodes  30   a ,  30   b ,  30   c , respectively. The intermediate series of electrodes  38   a ,  38   b ,  38   c  are deposited on top of the entirety of the top surface of filler layers  46 ,  48 ,  50  and extend beyond the top surface of said filler layers  46 ,  48 ,  50 , thereby forming the overhang regions  58   a ,  58   b ,  58   c . The overhang regions  58   a ,  58   b ,  58   c  extend to connect with the bottom first series of electrodes  30   a ,  30   b ,  30   c  of each OLED. The connecting area  40   a ,  40   b ,  40   c  is formed by the intermediate series of electrode(s)  38   a ,  38   b ,  38   c  being deposited over top of the exposed bottom first series of electrodes  30   a ,  30   b ,  30   c  to form an electrical connection between the two layers. 
     Vertical-Cavity Surface-Emitting Lasers (VCSELs) 
     As stated previously, a vertical-cavity surface-emitting laser (VCSEL) refers to a semiconductor-based laser diode that emits light or optical beam vertically from its top surface. This orientation is more advantageous than the Edge Emitting Lasers (EEL) that emits light from the side or from the Light Emitting Diodes (LED) that produce light from the sides and top, at least because as VCSELs discharge light perpendicular to the surface of a laser, thousands of VCSELs can be processed all at one time in a wafer. The performance of a VCSEL device can be quantified by a dimensionless parameter known as a Q factor. Similar to the MCOLED devices described previously, the addition of an intermediate cathode in a VCSEL device alleviates charge balancing reconsiderations in tuning the optical cavity of the device, the filler layer thickness is the variable that is to be changed to achieve the desired optical path length. 
       FIG.  10    illustrates a VCSEL device consisting of a bottom first electrode  30  deposited on a substrate  34 . A DBR  10  is deposited on top of the substrate which consists of a series of alternating layers of low refractive index dielectric material  12  and high refractive index dielectric material  14 . A filler layer  16  is deposited on the first DBR and an intermediate electrode  38  is deposited such that it covers the overhang of the filler layer  16  to form an overhang region  58  and connects to the bottom first electrode  30  to form a connecting area  40  thereby forming an electrical contact between the bottom first electrode  30  and the intermediate electrode  38 . This connection formed by the connecting area  40  removes the requirement for electron-hole charge balancing reconsiderations for all material types and thicknesses of the layers of the standard light emitting stack  78  deposited on top of the intermediate electrode  38  when adjusting the length of the optical microcavity  28  during the tuning process. A top electrode  18  is deposited on the light emitting stack  78  and a second DBR  10  is deposited on top of the substrate which is comprised of a series of alternating layers of low refractive index dielectric material  12  and high refractive index dielectric material  14  and acts as the second reflective surface to form the optical microcavity  28  of the VCSEL. Pixel definition layer (PDL)  52  is deposited such that it covers the overhang region  58  of the intermediate electrode  38  and the connecting area  40  but does not cover the active area of the filler layer  16 . 
     Microcavity OLED Fabrication Method and Considerations 
     Fabrication of microcavity OLED devices suitable for light field display technology is inherently complicated due the pixel size required to achieve the desired resolution for a high-quality display.  FIGS.  11 A-H  illustrate a step by step process of fabricating a MCOLED structure as per the present disclosure. 
       FIG.  11 A-B  illustrates a side and top view, respectively, of a bottom first electrode  30  deposited on a substrate  34 . 
       FIG.  11 C-D  illustrates a side and top view, respectively, of a filler layer  16  (for a single color) deposited on the bottom first electrode  30 , which is on a substrate  34 . 
       FIG.  11 E-F  illustrates a side and top view, respectively, an intermediate electrode  38  deposited such that it covers the overhang of the filler layer  16  to connect to the bottom first electrode  30  to form a connecting area  40  thereby forming a contact between the bottom first electrode  30  and the intermediate electrode  38 . As per an embodiment of the present disclosure, 
       FIG.  11 G-H  illustrate a side and top view, respectively, of the deposition of a pixel definition layer (PDL)  52  deposited on the bottom first electrode  30  and substrate  34 . The PDL  52  is deposited such that it covers the overhang portion of the intermediate electrode  38  and the connecting area  40  but does not cover the active area  54  of the filler layer  16  to allow for the subsequent deposition of an OLED stack. The pixel definition layer (PDL) may be composed of an inorganic material such as an insulting dielectric, for example Si 3 N 4  or SiO 2 , or an organic material such as, for example, a photosensitive polyimide. The PDL  52  can be deposited by, for example, physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. 
       FIG.  12    illustrates a side view of a multi-color MCOLED array with white OLED stack  56 . The method of fabricating this embodiment includes a bottom first series of electrodes  30   a ,  30   b ,  30   c  deposited on a single substrate  34 . The electrodes can be deposited by, for example, physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. Each structure in the MCOLED array has a filler layer deposited separately for each of red, green and blue, deposited as a filler layer for red color  46 , a filler layer for green color  48 , and a filler layer for blue color  50 . Each filler layer can be deposited by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering or chemical vapor deposition (CVD) methods such as atomic layer deposition or Plasma-enhanced chemical vapor deposition (PECVD), or by spin coating. An intermediate series of electrodes  38   a ,  38   b , and  38   c  can be deposited by way of by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering; or chemical vapor deposition(CVD) methods such as atomic layer deposition on the RGB filler layers  46 ,  48 , and  50  and forms a connection with each of the bottom first series of electrodes  30   a ,  30   b ,  30   c . The connection formed between the bottom first electrode and  30  and the intermediate electrode  38  now allows for blanket deposition of a common white OLED stack  56 . This is advantageous in that the white OLED stack  56  may be easily deposited over all devices in the array, regardless of color. The top electrode  18  is also able to be deposited using blanket deposition technique over the common white OLED stack  56 . 
     Theoretical Design Variables 
     When a light emitting material is placed between two reflective surfaces, the spontaneous-emission photon density of states is redistributed, resulting in an enhancement of emission intensity in the perpendicular direction as well as in narrowing of the emission spectra [Ref. 07]. This enhancement occurs when the total optical path length, Li, satisfies the relationship: [Ref 02] 
     
       
         
           
             
               
                 
                   
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     where m is a positive integer and λ i  is the wavelength of peak emission from the cavity [Ref. 03]. 
     Emission Characteristics 
     The reduced angular spread due to the microcavity can be approximated as 
     
       
         
           
             
               
                 
                   
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     Similarly, the FWHM of the output spectrum is determined as: 
     
       
         
           
             
               
                 
                   
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     where R cathode  is the reflectance of the cathode, and R DBR  is the reflectance of the DBR. 
     Distributed Bragg Reflector 
     The highest reflectivity of the DBR structure is attained when the layer thicknesses, d i , are chosen such that the optical path length of each layer is one quarter of the resonance wavelength, or: 
     
       
         
           
             
               
                 
                   
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                   4 
                   ) 
                 
               
             
           
         
       
     
     where λ Bragg  is the design wavelength for the DBR, which can be any value but is chosen such that the reflectance is high in the wavelength range for the design [Ref 06]. Under these conditions, all reflections will add in phase, and the transmissivity will decrease exponentially as a function of mirror thickness. The reflectance of a DBR at λ Bragg  can be approximated as: 
     
       
         
           
             
               
                 
                   
                     R 
                     DBR 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           1 
                           - 
                           
                             
                               ( 
                               
                                 
                                   n 
                                   1 
                                 
                                 
                                   n 
                                   2 
                                 
                               
                               ) 
                             
                             
                               2 
                               ⁢ 
                               Λ 
                             
                           
                         
                         
                           1 
                           + 
                           
                             
                               ( 
                               
                                 
                                   n 
                                   1 
                                 
                                 
                                   n 
                                   2 
                                 
                               
                               ) 
                             
                             
                               2 
                               ⁢ 
                               Λ 
                             
                           
                         
                       
                       ) 
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     where n 1  is the refractive index of the low index DBR at λ Bragg , n 2  is the refractive index of the high index DBR material at λ Bragg , and Λ is the number of dielectric pairs [Ref 05]. At longer or shorter wavelengths, the reflections begin to add out of phase, therefore the total reflections decrease [Ref. 01]. The result is a broad-band high-reflectivity region centered on λ Bragg  referred to as the stop band, δλ Sb  determined as: 
     
       
         
           
             
               
                 
                   
                     δ 
                     ⁢ 
                     
                       λ 
                       sb 
                     
                   
                   = 
                   
                     2 
                     ⁢ 
                     
                       
                         
                           λ 
                           Bragg 
                         
                         ( 
                         
                           
                             n 
                             2 
                           
                           - 
                           
                             n 
                             1 
                           
                         
                         ) 
                       
                       
                         π 
                         ⁢ 
                         
                           n 
                           eff 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   6 
                   ) 
                 
               
             
           
         
       
     
     where n eff  is the effective index [Ref. 04]. These are the theoretical design variables considered in the prior art for a microcavity OLED structure with a DBR, and similarly in the present disclosure. To enhance the output of the MCOLED and the MCOLED design, the present disclosure considers the optical path length of the microcavity. The materials of the DBR can be any material which are not opaque in the wavelength range of the design. For example, in the visible wavelength range, materials such as silicon nitride, titanium dioxide, silicon dioxide, and other dielectrics may be used. 
     Optical Path Length 
     The total optical path length of the microcavity is represented as: 
         L   i   =L   DBR   +L   Organics    L   Cathode   (7)
 
     where L DBR  is the penetration depth into the DBR, L Organics  is the optical path length in the OLED materials, and L Cathode  is the penetration depth into the metal cathode. The optical path length in the materials between the two reflective surfaces is found as the sum of the optical path lengths in each material: 
     
       
         
           
             
               
                 
                   
                     L 
                     Organics 
                   
                   = 
                   
                     
                       ∑ 
                       i 
                       N 
                     
                     
                       
                         n 
                         i 
                       
                       ⁢ 
                       
                         d 
                         i 
                       
                     
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     where n i  and d i  are the layer indices and thicknesses, respectively. The penetration depth into the DBR can be determined as [Ref 02, 08]: 
     
       
         
           
             
               
                 
                   
                     L 
                     DBR 
                   
                   = 
                   
                     
                       
                         λ 
                         Bragg 
                       
                       2 
                     
                     ⁢ 
                     
                       
                         n 
                         eff 
                       
                       
                         ( 
                         
                           
                             n 
                             2 
                           
                           - 
                           
                             n 
                             1 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   ( 
                   9 
                   ) 
                 
               
             
           
         
       
     
     and the penetration depth into the metal cathode is: 
     
       
         
           
             
               
                 
                   
                     L 
                     Cathode 
                   
                   = 
                   
                     
                       ❘ 
                       &#34;\[LeftBracketingBar]&#34; 
                     
                     
                       
                         
                           Φ 
                           m 
                         
                         
                           4 
                           ⁢ 
                           π 
                         
                       
                       ⁢ 
                       
                         λ 
                         i 
                       
                     
                     
                       ❘ 
                       &#34;\[RightBracketingBar]&#34; 
                     
                   
                 
               
               
                 
                   ( 
                   10 
                   ) 
                 
               
             
           
         
       
     
     where Φ m  is the phase shift at the metal reflector, given by: 
     
       
         
           
             
               
                 
                   
                     Φ 
                     m 
                   
                   = 
                   
                     
                       tan 
                       
                         - 
                         1 
                       
                     
                     ( 
                     
                       
                         2 
                         ⁢ 
                         
                           n 
                           Cavity 
                         
                         ⁢ 
                         
                           k 
                           Cathode 
                         
                       
                       
                         
                           n 
                           Cavity 
                           2 
                         
                         - 
                         
                           n 
                           Cathode 
                           2 
                         
                         - 
                         
                           k 
                           Cathode 
                           2 
                         
                       
                     
                     ) 
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     where n Cavity  is the refractive index of the organic in contact with the cathode, and n Cathode  and k cathode  are the real and imaginary parts of the refractive index of the metal cathode [Ref. 02]. 
       FIG.  16 A  illustrates a side view of a multi-color MCOLED array with Red OLED stack  94 , Green OLED stack  96 , and Blue OLED stack  98  with a common shared distributed Bragg reflector  10 . The method of fabricating this embodiment includes bottom first series of electrodes  30   a ,  30   b ,  30   c  deposited on a single substrate  34 . The electrodes can be deposited by, for example, physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. Each structure in the MCOLED array has a filler layer deposited separately for each of red, green and blue, deposited as a filler layer for red color  46 , a filler layer for green color  48 , and a filler layer for blue color  50 . Each filler layer can be deposited by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering or chemical vapor deposition (CVD) methods such as atomic layer deposition or Plasma-enhanced chemical vapor deposition (PECVD), or by spin coating. An intermediate series of electrodes  38   a ,  38   b , and  38   c  can be deposited by way of by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering; or chemical vapor deposition(CVD) methods such as atomic layer deposition on the RGB filler layers  46 ,  48 , and  50  and forms a connection with each of the bottom first series of electrodes  30   a ,  30   b ,  30   c . In this embodiment, individual OLED stacks for each color, specifically Red OLED stack  94 , Green OLED stack  96 , and Blue OLED stack  98 , are deposited separately. In this embodiment, the top electrode  18  is deposited using blanket deposition technique over the individual R,G,B OLED stacks  94 ,  96 ,  98 . The top electrode  18  may also be individually deposited on top of each individual R,G,B OLED stacks  94 ,  96 ,  98 . A common distributed Bragg reflector (DBR)  10  is then deposited on top of the top electrode  18  to form the optical microcavities  28   a ,  28   b ,  28   c . The DBR  10  consists of a series of alternating layers of high refractive index dielectric material  14  and low refractive index dielectric material  12 . The DBR  10  acts as the second reflective surface for the optical microcavities  28   a ,  28   b ,  28   c.    
     As shown in  FIG.  16 B  illustrates a side view of a multi-color MCOLED array with white OLED stack  56 . The method of fabricating this embodiment includes a bottom first series of electrodes  30   a ,  30   b ,  30   c  deposited on a single substrate  34 . The electrodes can be deposited by, for example, physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. Each structure in the MCOLED array has a filler layer deposited separately for each of red, green and blue, deposited as a filler layer for red color  46 , a filler layer for green color  48 , and a filler layer for blue color  50 . Each filler layer can be deposited by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering or chemical vapor deposition (CVD) methods such as atomic layer deposition or Plasma-enhanced chemical vapor deposition (PECVD), or by spin coating. An intermediate series of electrodes  38   a ,  38   b , and  38   c  can be deposited by way of by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering; or chemical vapor deposition(CVD) methods such as atomic layer deposition on the RGB filler layers  46 ,  48 , and  50  and forms a connection with each of the bottom first series of electrodes  30   a ,  30   b ,  30   c . The connection formed between the bottom first electrode and  30  and the intermediate series of electrodes  38   a ,  38   b ,  38   c  now allow for blanket deposition of a common white OLED stack  56 . This is advantageous in that the white OLED stack  56  may be easily deposited over all devices in the array, regardless of color. The top electrode  18  is also able to be deposited using blanket deposition technique over the common white OLED stack  56 . A common distributed Bragg reflector (DBR)  10  is then deposited on top of the top electrode  18  to form the optical microcavity  28 . The DBR  10  consists of a series of alternating layers of high refractive index dielectric material  14  and low refractive index dielectric material  12 . The DBR  10  acts as the second reflective surface for the optical microcavity  28 . 
       FIG.  17 A  illustrates a side view of a multi-color MCOLED array with Red OLED stack  94 , Green OLED stack  96 , and Blue OLED stack  98  with individual distributed Bragg reflectors  10   a ,  10   b ,  10   c . The method of fabricating this embodiment includes a bottom first series of electrodes  30   a ,  30   b ,  30   c  deposited on a single substrate  34 . The electrodes can be deposited by, for example, physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. Each structure in the MCOLED array has a filler layer deposited separately for each of red, green and blue, deposited as a filler layer for red color  46 , a filler layer for green color  48 , and a filler layer for blue color  50 . Each filler layer can be deposited by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering or chemical vapor deposition (CVD) methods such as atomic layer deposition or Plasma-enhanced chemical vapor deposition (PECVD), or by spin coating. An intermediate series of electrodes  38   a ,  38   b , and  38   c  can be deposited by way of by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering; or chemical vapor deposition(CVD) methods such as atomic layer deposition on the RGB filler layers  46 ,  48 , and  50  and forms a connection with each of the series of bottom first electrodes  30 . In this embodiment, individual OLED stacks for each color  94 ,  96 ,  98  are deposited separately. As shown in  FIG.  13   , the OLED stack deposited on top of each individual intermediate electrode  38   a ,  38   b ,  38   c , may be a common white OLED stack. The connection formed between the bottom first electrode and  30  and the intermediate series of electrodes  38   a ,  38   b ,  38   c  allows for blanket deposition of a common white OLED stack. In In this embodiment, the top electrode  18  is deposited using blanket deposition technique over the individual R,G,B OLED stacks  94 ,  96 ,  98 . Individual distributed Bragg reflectors (DBR)  10   a ,  10   b ,  10   c  are then deposited on top of the top electrode  18  to form the optical microcavities  28   a ,  28   b ,  28   c . The DBRs  10   a ,  10   b ,  10   c  consist of a series of alternating layers of high refractive index dielectric material  14  and low refractive index dielectric material  12 . The DBRs  10   a ,  10   b ,  10   c  act as the second reflective surfaces for the optical microcavities  28   a ,  28   b ,  28   c.    
       FIG.  17 B  illustrates a side view of a multi-color MCOLED array with a common white OLED stack  56  with individual distributed Bragg reflectors  10   a ,  10   b ,  10   c . The method of fabricating this embodiment includes a bottom first series of electrodes  30   a ,  30   b ,  30   c  deposited on a single substrate  34 . The electrodes can be deposited by, for example, physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering, or by chemical vapor deposition (CVD) methods such as atomic layer deposition. Each structure in the MCOLED array has a filler layer deposited separately for each of red, green and blue, deposited as a filler layer for red color  46 , a filler layer for green color  48 , and a filler layer for blue color  50 . Each filler layer can be deposited by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering or chemical vapor deposition (CVD) methods such as atomic layer deposition or Plasma-enhanced chemical vapor deposition (PECVD), or by spin coating. An intermediate series of electrodes  38   a ,  38   b , and  38   c  can be deposited by way of by physical vapor deposition (PVD) such as thermal evaporation, electron-beam evaporation, sputtering; or chemical vapor deposition(CVD) methods such as atomic layer deposition on the RGB filler layers  46 ,  48 , and  50  and forms a connection with each of the bottom first series of electrodes  30   a ,  30   b ,  30   c . The connection formed between the bottom first series of electrodes and  30   a ,  30   b ,  30   c  and the intermediate series of electrodes  38   a ,  38   b ,  38   c  now allows for blanket deposition of a common white OLED stack  56 . This is advantageous in that the white OLED stack  56  may be easily deposited over all devices in the array, regardless of color. The connection formed between the bottom first series of electrodes  30   a ,  30   b ,  30   c  and the intermediate series of electrodes  38   a ,  38   b ,  38   c  allows for blanket deposition of a common white OLED stack  56 . A top electrode  18   a ,  18   b ,  18   c  is individually deposited on the white OLED stack  56  for each color, respectively. A common top electrode could also be deposited using blanket deposition as see in  FIG.  17 A . Individual distributed Bragg reflectors (DBR)  10   a ,  10   b ,  10   c  are then deposited on top of the top electrodes  18   a ,  18   b ,  18   c  to form the optical microcavities  28   a ,  28   b ,  28   c . The DBRs  10   a ,  10   b ,  10   c  consist of a series of alternating layers of high refractive index dielectric material  14  and low refractive index dielectric material  12 . The DBRs  10   a ,  10   b ,  10   c  act as the second reflective surfaces for the optical microcavities  28   a ,  28   b ,  28   c.    
     Design Methodology 
       FIGS.  18 A  and B illustrate processes for designing a microcavity pixel. In  FIG.  18 A , an initial design for the OLED  80  is selected which includes material selections and layer thicknesses. The electrical design of the pixel is then optimized  82 . This process consists of balancing the electron-hole charge within the material layers and electrode selection. The pixel design is next placed between two reflective materials, creating a microcavity OLED (MCOLED) which is then optimized  84  to achieve the desired optical path length of the microcavity of the OLED. In the method as illustrated by  FIG.  18 A , the optical path length is adjusted by adjusting different layers of the MCOLED structure. It should be noted that there are many ways to optimize the structure, including adding a filler layer above an electrode which can be changed to tune the optical path length, similarly varying the electrode thickness can be used, or tuning one or all of the OLED material thicknesses. Following optimization of the MCOLED design  84 , the electrical and optical compromise of the alterations to the structure resulting from the optimization are considered  86 . This can include re-design of the device layer materials and/or thicknesses to ensure that the resulting structure satisfies all electrical and optical requirements. Once this compromise has been achieved, the structure may be fabricated  88 . It should be noted that satisfying the electrical and optical requirements  86  limits material selection and layer thicknesses in optimizing the optical path length and subsequent performance of the device. 
     An optimized method for the design of a microcavity pixel device is illustrated in  FIG.  18 B . Similar to  FIG.  18 A , an initial design for the OLED  80  is selected which includes material selections and layer thicknesses. The electrical design of the pixel is then optimized  82 . This process consists of balancing the electron-hole charge within the material layers and electrode selection. The design of the microcavity OLED (MCOLED) is then optimized  84  to achieve the desired optical path length of the microcavity of the pixel. The MCOLED design as per the present disclosure includes an intermediate electrode which is deposited such that it covers the overhang of the filler layer of the device to connect to the bottom first electrode to form a connecting area thereby forming a contact between the first electrode and the intermediate electrode. The filler layer thickness of the device may be altered to achieve the desired optical path length of the microcavity. This presence of this connection removes the electrical and optical compromise in material type and thickness considerations resulting from the optimization of the MCOLED as seen in  FIG.  18 A . This advantage of this method is there is a much wider selection of materials and layer thicknesses suitable for optimizing the optical path length and performance of the device. 
     EXAMPLES 
     Example 1 
       FIG.  13    illustrates an example of a method for fabricating a multi-color microcavity OLED array as per the present disclosure. The method begins with deposition of a bottom first series of electrodes  30   a ,  30   b ,  30   c  on a single substrate  34 . A filler layer for red color  46  electrodes is deposited on the bottom first electrode  30   a . A filler layer for green color  48  electrodes is deposited on the bottom first electrode  30   b . A filler layer for blue color  50  electrodes is deposited the bottom first electrode  30   c . Although red, green, and blue are the selected and standard colors for OLED devices, it is understood that colors other than red, green, and blue may be used. A series of intermediate electrodes  38   a ,  38   b ,  38   c  is then deposited over the filler layers  46 ,  48 , and  50 , respectively, such that the intermediate series of electrodes  38   a ,  38   b ,  38   c  cover the overhang of the filler layer for red color  46  electrodes, the filler layer for green color  48  electrodes, and the filler layer for blue color  50  electrodes, respectively, to connect to the bottom first series of electrodes  30   a ,  30   b ,  30   c , thereby forming a contact between the bottom first series of electrodes  30   a ,  30   b ,  30   c  and the intermediate series of electrodes  38   a ,  38   b ,  38   c . In this example, an optional pixel definition layer (PDL)  52  is patterned such that such that the overhang area of the PDL  52  covers the connection area between the bottom first series of electrodes  30   a ,  30   b ,  30   c , and intermediate series of electrodes  38   a ,  38   b ,  38   c . A white OLED stack  56  is then deposited using blanket deposition over the series of intermediate electrodes  38 . A white OLED stack  56  containing a white emission layer  62  may be blanket deposited as it contains all three R,G,B prime colors, and with the optical microcavity  28 , only the desired color would exit the corresponding pixel as the optical microcavity  28  filters out other colors. The white OLED  56  stack comprises organic layers  90  beneath the emission layer  62 , which could include an EIL, ETL, EML, HTL, or a HIL, depending on the configuration of the OLED (inverted versus conventional). Additionally, the white OLED  56  stack comprises organic layers  92  on top of the emission layer  62 , which could include an EIL, ETL, EML, HTL, or a HIL, depending on the configuration of the OLED (inverted versus conventional). The top electrode is deposited by blanket deposition over the white OLED stack  56  common to all MCOLED structures. A top electrode  18  is deposited using blanket deposition over the white OLED stack  56 .  FIG.  14    illustrates an example of a method for fabricating a multi-color microcavity OLED array as per  FIG.  13    wherein an additional reflective surface  32  is deposited by blanket deposition over the common top electrode to form the optical microcavities  28  of each device. 
     Example 2 
       FIG.  15    illustrates an example method for fabricating a multi-color microcavity OLED array as per the present disclosure. The method begins with deposition of a bottom first series of electrodes  30   a ,  30   b ,  30   c  on a single substrate  34 . A filler layer for red color  46  electrodes is deposited on the bottom first electrode  30   a . A filler layer for green color  48  electrodes is deposited on the bottom first electrode  30   b . A filler layer for blue color  50  electrodes is deposited on the bottom first electrode  30   c . A series of intermediate series of electrodes  38   a ,  38   b ,  38   c  is deposited over the filler layers  46 ,  48 , and  50  such that the intermediate series of electrodes  38   a ,  38   b ,  38   c  cover the overhang of the filler layer for red color  46  electrodes, the filler layer for green color  48  electrodes, and the filler layer for blue color  50  electrodes, respectively, to connect to the bottom first series of electrodes  30   a ,  30   b ,  30   c , thereby forming a contact between the bottom first series of electrodes  30   a ,  30   b ,  30   c , and the intermediate series of electrodes  38   a ,  38   b ,  38   c . The layers of an OLED stack for a first color (Red)  72  before the red emissive layer (EML)  66  are deposited on the intermediate electrode  38   a  which is stacked on top of the filler layer for red color  46 . The layers of an OLED stack for a second color (Green)  74  before the green emissive layer (EML)  68  are deposited on the intermediate electrode  38   b  which is stacked on top of the filler layer optimized for the green color  48 . The layers of an OLED stack for a third color (Blue)  76  before the blue emissive layer (EML)  70  are deposited on the intermediate electrode  38   c  which is stacked on top of the filler layer optimized for the third color  50 . Layers of an OLED stack for each color  72 ,  74 ,  76  before the emissive layer  66 ,  68 ,  70  respectively, could include an EIL, ETL, EML, HTL, or a HIL, depending on the configuration of the OLED (inverted versus conventional). The emissive layers (EML) for each respective color (RGB) are then patterned individually over the respective layers before the EML for each color  72 ,  74 , and  76 . In this example, the organic layers  60  after the EMLs  72 ,  74 , and  76  may be blanket deposited over all EMLs  72 ,  74 , and  76  and could include an EIL, ETL, EML, HTL, or a HIL, depending on the configuration of the OLED (inverted versus conventional). A top electrode  18  is also deposited using blanket deposition and an additional reflective surface  32  to form the optical microcavity  28  of each structure. 
     The disclosures of all patents, patent applications, publications and database entries referenced in this specification are hereby specifically incorporated by reference in their entirety to the same extent as if each such individual patent, patent application, publication and database entry were specifically and individually indicated to be incorporated by reference. Although the invention has been described with reference to certain specific embodiments, various modifications thereof will be apparent to those skilled in the art without departing from the spirit and scope of the invention. All such modifications as would be apparent to one skilled in the art are intended to be included within the scope of the following claims. 
     REFERENCE LIST 
     
         
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