Patent Publication Number: US-2022216413-A1

Title: Oleds for micro transfer printing

Description:
FIELD OF THE INVENTION 
     The present invention relates to organic light-emitting diode (OLED) displays and to micro transfer printing. 
     BACKGROUND OF THE INVENTION 
     Flat-panel displays are widely used in conjunction with computing devices, in portable devices, and for entertainment devices such as televisions. Such displays typically employ a plurality of pixels distributed over a display substrate to display images, graphics, or text. In a color display, each pixel includes light emitters that emit light of different colors, such as red, green, and blue. For example, liquid crystal displays (LCDs) employ liquid crystals to block or transmit light from a backlight behind the liquid crystals and organic light-emitting diode (OLED) displays rely on passing current through a layer of organic material that glows in response to the current. Displays using inorganic light emitting diodes (LEDs) are also in widespread use for outdoor signage and have been demonstrated in a 55-inch television. 
     The various light-emitting technologies have different characteristics, advantages, and disadvantages. For example, liquid crystals are simple to control and have a highly developed and sophisticated technological infrastructure. Organic LEDs are area emitters, can be more efficient and flexible, and are demonstrated in a very thin form factor. Inorganic light-emitting diodes are very efficient and provide relatively saturated light in an environmentally robust structure. Lasers are also efficient, provide a virtually monochromatic light, but have a limited viewing angle. None of these technologies, however, meet all of a display viewer&#39;s needs under all circumstances. 
     Organic light-emitting diodes are widely used in portable electronic devices with displays and in some televisions. Organic LEDs are area emitters, can be efficient and flexible, can have a very thin form factor, and have an excellent viewing angle. However, the process used to manufacture OLED displays has some challenging steps. An OLED emitter typically includes several layers, for example a hole-injection layer, a light-emitting layer, and an electron-injection layer. The hole-injection layer is coated on a first electrode such as an anode and a second electrode such as a cathode is formed on an electron-injection layer. Alternatively, an electron-injection layer is formed on a cathode and the anode is formed on a hole-injection layer. 
     One type of OLED display is made with a common unpatterned light emitter for all pixels and patterned color filters that filter the light from each light-emitter in the display. Different color filters produce different colors and the common light emitter emits white light, for example a combination of blue and yellow light. This display type is similar to the color-filter approach found in LCDs and suffers from the loss of approximately two thirds of the emitted light in the color filters. 
     Another type of OLED display uses different organic material patterned over a display substrate. The different OLED materials are chosen to emit different colors of light and are patterned to form pixels, typically arranged in stripes. The strip pattern is formed by depositing organic material through a fine metal shadow mask. A different mask is used for each different set of materials, or at least for the different light-emitting layers. The alignment of the masks before deposition is difficult, and the repeated use of the masks can damage deposited materials. Moreover, the masks must be periodically cleaned, are easily damaged, difficult to make, and expensive. 
     There is a need, therefore, for devices, systems and methods for providing OLED light emitters that have improved efficiency, reduced costs, and fewer mechanical process steps. 
     SUMMARY OF THE INVENTION 
     The present invention provides structures, devices and methods for organic light-emitting diodes and color displays that require fewer or no shadow masks for evaporative deposition of organic materials. The organic light-emitting diode structures can be micro transfer printed and organic light-emitting diode structures that each emit different colors of light can be separately constructed on separate source substrates, released from the source substrate, and micro transfer printed to a destination display substrate. The organic light-emitting diode structures and methods mitigate the problems encountered with repeated use of fine metal shadow masks, such as alignment to a common display substrate and damage to organic materials deposited on the display substrate. 
     Moreover, in an embodiment, the use of fine metal shadow masks is unnecessary for patterning evaporated organic materials. Higher resolution OLED displays are thereby enabled. 
     In one aspect, the disclosed technology includes a structure including an organic light-emitting diode (OLED) having a first electrode, one or more layers of organic material disposed on at least a portion of the first electrode, and a second electrode disposed on at least a portion of the one or more layers of organic material; and at least a portion of a tether extending from a periphery of the organic light-emitting diode. 
     In certain embodiments, at least a portion of the first electrode is transparent. 
     In certain embodiments, at least a portion of the second electrode is transparent. 
     In certain embodiments, the layers of organic material comprise one or more of a hole-injection layer, a light-emitting layer, and an electron-injection layer. 
     In certain embodiments, the OLED has a light-emitting area that has a dimension parallel to the first electrode that is less than or equal to 40 microns, less than or equal to 20 microns, less than or equal to 10 microns, or less than or equal to 5 microns. 
     In certain embodiments, the OLED has a light-emitting area that is less than or equal to 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. 
     In certain embodiments, the first electrode comprises a transparent electrode in electrical contact with an opaque first electrode portion, and a transparent insulator, wherein the transparent insulator is at least partly in a common layer with the opaque first electrode portion. 
     In certain embodiments, the transparent electrode is disposed on a transparent insulator. 
     In certain embodiments, the first electrode comprises a first protrusion and the second electrode comprises a second protrusion separate from the first protrusion, the first and second protrusions extending in a direction from the second electrode to the first electrode. 
     In certain embodiments, the first electrode is a unitary electrical conductor. 
     In certain embodiments, the organic light-emitting diode is a top emitter. 
     In certain embodiments, the organic light-emitting diode is a bottom emitter. 
     In certain embodiments, the organic-light emitting diode a light-emissive area of less than 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. 
     In certain embodiments, the organic-light emitting diode has at least one of a width from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, a length from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, and a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm. 
     In certain embodiments, the structure includes a source substrate having a portion defining an anchor; and a sacrificial layer formed on the source substrate and adjacent to the anchor, wherein the OLED is disposed on the sacrificial layer and the tether is connected to the anchor. 
     In certain embodiments, an oxide layer or a pre-determined designated portion of the source substrate. 
     In certain embodiments, the sacrificial layer comprises a cavity between the organic light-emitting diode and the source substrate. 
     In certain embodiments, the structure includes a plurality of OLED structures formed on the source substrate, wherein the one or more layers of organic material in each of the OLED structures is the same. 
     In certain embodiments, at least one of the one or more layers of organic material emits red light, green light, or blue light. 
     In certain embodiments, the structure includes first and second OLED structures formed on the source substrate and wherein the first OLED structure comprises at least one layer of organic material that emits a first color of light and the second OLED structure comprises at least one layer of organic material that emits a second color of light different from the first color of light. 
     In certain embodiments, the structure includes a third OLED structure formed on the source substrate, wherein the third OLED structure comprises at least one layer of organic material that emits a third color of light different from the first color of light and different from the second color of light. 
     In certain embodiments, the first color of light is red, the second color of light is green, and the third color of light is blue. 
     In certain embodiments, the portion of a tether extending from the periphery of the organic light-emitting diode is a portion of a broken tether. 
     In certain embodiments, the structure includes a first conductive protrusion extending from the structure and electrically connected to the first electrode; and a second conductive protrusion extending from the structure and electrically connected to the second electrode. 
     In another aspect, the disclosed technology includes a display having printable organic light-emitting diode structures, including: a display substrate; one or more organic light-emitting diode structures described above and herein disposed on the display substrate; a first electrical conductor electrically connected to the first electrode; and a second electrical conductor electrically connected to the second electrode. 
     In certain embodiments, at least one of the first electrical conductor and the second electrical conductor is located on the display substrate. 
     In certain embodiments, one or more of the OLED structures are grouped into pixels and the display comprises a pixel controller located on the display substrate electrically connected to the first and second electrodes of the pixels in the group to control the light output from the OLED structures. 
     In certain embodiments, the display includes one or more inorganic light-emitting diodes, wherein the one or more OLED structures comprises a first OLED structure that emits light of a first color and a second inorganic light-emitting diode that emits light of a second color different from the first color. 
     In certain embodiments, the one or more OLED structures comprises at least a first OLED structure that emits light of a first color and a second OLED structure that emits light of a second color different from the first color. 
     In certain embodiments, two or more of the OLED structures are grouped into pixels, each pixel including: a first OLED structure that emits light of the first color; a second OLED structure that emits light of the second color; and a pixel substrate, separate and distinct from the display substrate and the source substrate, on which the first and second OLED structures are disposed, wherein the pixel substrate is disposed on the display substrate. 
     In certain embodiments, the display includes a pixel controller located on the pixel substrate electrically connected to the first and second electrodes of each of the first and second OLED structures in the pixel to control the light output from the first and second OLED structures. 
     In certain embodiments, the organic light-emitting diode is a top emitter. 
     In certain embodiments, the organic light-emitting diode is a bottom emitter. 
     In certain embodiments, the organic-light emitting diode a light-emissive area of less than 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. 
     In certain embodiments, the organic-light emitting diode has at least one of a width from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, a length from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, and a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm. 
     In certain embodiments, the display substrate has a thickness from 5 to 10 microns, 10 to 50 microns, 50 to 100 microns, 100 to 200 microns, 200 to 500 microns, 500 microns to 0.5 mm, 0.5 to 1 mm, 1 mm to 5 mm, 5 mm to 10 mm, or 10 mm to 20 mm. 
     In certain embodiments, the display substrate comprises a polymer, plastic, resin, polyimide, PEN, PET, metal, metal foil, glass, a semiconductor, or sapphire. 
     In certain embodiments, the display substrate has a transparency greater than or equal to 50%, 80%, 90%, or 95% for visible light. 
     In certain embodiments, the organic light-emitting diode, when energized, emits light in a direction opposite the display substrate. 
     In certain embodiments, the organic light-emitting diode, when energized, emits light through the display substrate. 
     In another aspect, the disclosed technology includes a method of making an OLED structure, including: providing a source substrate; patterning a sacrificial layer on the source substrate; patterning a first electrode on the sacrificial layer; patterning one or more layers of organic material on at least a portion of the patterned first electrode; and patterning a second electrode on at least a portion of the one or more layers of organic material to form an OLED structure. 
     In certain embodiments, the method includes removing at least a portion of the sacrificial layer, thereby partially releasing the OLED structure from the source substrate. 
     In certain embodiments, the method includes micro transfer printing the OLED structure from the source substrate to a display substrate. 
     In certain embodiments, the one or more layers of organic material are one or more layers of organic material that emit blue light and the OLED structure is a blue OLED structure that emits blue light when a current is applied thereto. 
     In certain embodiments, the method includes forming a red OLED structure that emits red light when a current is applied thereto, including: providing a second source substrate; patterning a second sacrificial layer on or in the second source substrate; patterning a first electrode on the second sacrificial layer; patterning one or more layers of organic material that emit red light on at least a portion of the patterned first electrode on the second sacrificial layer; and patterning a second electrode on at least a portion of the one or more layers of organic material that emit red light; and forming a green OLED structure that emits green light when a current is applied thereto, including: providing a third source substrate; patterning a third sacrificial layer on or in the third source substrate; patterning a first electrode on the third sacrificial layer; patterning one or more layers of organic material that emit green light on at least a portion of the patterned first electrode on the third sacrificial layer; and patterning a second electrode on at least a portion of the one or more layers of organic material that emit green light. 
     In certain embodiments, the method includes micro transfer printing the red OLED structure from the red source substrate to a display substrate; micro transfer printing the green OLED structure from the green source substrate to the display substrate; and micro transfer printing the blue OLED structure from the blue source substrate to the display substrate. 
     In certain embodiments, the at least ten thousand, one-hundred thousand, one million, or ten million OLEDs are on each source substrate. 
     In certain embodiments, patterning the one or more layers of organic material on the patterned first electrode comprises depositing the layers of organic material through a fine metal shadow mask. 
     In certain embodiments, patterning the one or more layers of organic material on the patterned first electrode and patterning the second electrode on the one or more layers of organic material includes: blanket depositing the layers of organic material over an area of the source substrate; blanket depositing the second electrode over the layers of organic material; forming a patterned protective layer over the second electrode, the patterned protective layer defining the pattern of the one or more layers of organic material; patterning the second electrode by exposing the second electrode to an active material that removes second electrode material exposed to the line-of-flight of the active material; and patterning the one or more layers of organic material by exposing the one or more layers of organic material to an active material that removes the one or more layers of organic material exposed to the line-of-flight of the active material. 
     In certain embodiments, patterning the one or more layers of organic material on the patterned first electrode and patterning the second electrode on the one or more layers of organic material includes: removing the patterned protective layer. 
     In certain embodiments, patterning the one or more layers of organic material on the patterned first electrode and patterning the second electrode on the one or more layers of organic material includes: providing additional patterned second electrode material to form the patterned second electrode and protect the one or more layers of organic material. 
     In certain embodiments, the organic light-emitting diode is a top emitter. 
     In certain embodiments, the organic light-emitting diode is a bottom emitter. 
     In certain embodiments, the organic-light emitting diode a light-emissive area of less than 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. 
     In certain embodiments, the organic-light emitting diode has at least one of a width from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, a length from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, and a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm. 
     In another aspect, the disclosed technology includes a wafer of printable organic light-emitting diodes, including: a source substrate; a plurality of organic light-emitting diodes formed on the substrate, each organic light-emitting diode having a first electrode, one or more layers of organic material disposed on at least a portion of the first electrode, and a second electrode disposed on at least a portion of the one or more layers of organic material; one or more anchors on the source substrate; and a plurality of tethers, each organic light-emitting diode releasably secured to the source substrate by at least one anchor and at least one tether. 
     In certain embodiments, the wafer includes a sacrificial layer at least partially between the organic light-emitting diodes and the source substrate, wherein the plurality of organic light-emitting diodes are disposed on the sacrificial layer. 
     In certain embodiments, an oxide layer or a pre-determined designated portion of the source substrate. 
     In certain embodiments, the sacrificial layer comprises a cavity between the organic light-emitting diode and the source substrate. 
     In certain embodiments, there is an air gap between the organic light-emitting diodes and the source substrate. 
     In certain embodiments, the one or more layers of organic material in each of the organic light-emitting diodes is the same. 
     In certain embodiments, at least one of the one or more layers of organic material emits red light, green light, or blue light when a current is applied thereto. 
     In certain embodiments, at least ten thousand, one-hundred thousand, one million, or ten million OLEDs are on the source substrate. 
     In certain embodiments, the organic light-emitting diodes are top emitter. 
     In certain embodiments, the organic light-emitting diodes are bottom emitters. 
     In certain embodiments, the organic-light emitting diodes have a light-emissive area of less than 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. 
     In certain embodiments, the organic-light emitting diodes have at least one of a width from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, a length from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, and a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm. 
     Organic light emitters have better power conversion efficiencies at low current density than some inorganic light emitters. It is an object of the present invention to provide organic emitters that supplement the emitter population of displays made from assemblies of micro scale inorganic LEDs. It is also an object of the present invention to provide photoluminescent down-converters for blue or violet micro-assembled inorganic LEDs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, aspects, features, and advantages of the present disclosure will become more apparent and better understood by referring to the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a cross section of an embodiment of the present invention; 
         FIGS. 2A-2I  are cross sections of successive structures useful in making the structure of  FIG. 1  in an embodiment of the present invention; 
         FIG. 3  is a cross section of an alternative embodiment of the present invention; 
         FIGS. 4A and 4B  are top views and bottom views respectively of the structure in  FIG. 3  in an embodiment of the present invention; 
         FIGS. 5A-5J  are cross sections of successive structures useful in making the structure of  FIG. 3  in an embodiment of the present invention; 
         FIG. 6  is a cross section of an alternative top-emitter or bottom-emitter embodiment of the present invention; and 
         FIGS. 7A-7O  are cross sections of successive structures useful in making the structures of  FIGS. 1, 3, and 5  in an alternative embodiment of the present invention that does not require shadow masks; 
         FIG. 8  is a perspective of a display in an embodiment of the present invention; 
         FIG. 9  is a perspective of a pixel having a separate substrate according to an embodiment of the present invention; 
         FIG. 10  is a perspective of a display in an embodiment of the present invention using the pixels of  FIG. 9 ; and 
         FIGS. 11 and 12  are flow diagrams illustrating methods in various embodiments of the present invention. 
     
    
    
     The features and advantages of the present disclosure will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The figures are not drawn to scale since the variation in size of various elements in the Figures is too great to permit depiction to scale. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to the cross section of  FIG. 1 , in an embodiment of the present invention an organic light-emitting diode (OLED) structure  10  includes an organic light-emitting diode  65  having a first electrode  55 , one or more layers of organic material  60  disposed on at least a portion of the first electrode  55 , and a second electrode  52  disposed on at least a portion of the one or more layers of organic material  60 . The OLED structure  10  includes at least a portion of a tether  12  extending from a periphery of the organic light-emitting diode  65 . In an embodiment, the OLED structure  10  is a micro transfer printable OLED  65 . 
     In the embodiment of  FIG. 1 , the first electrode  55  includes a first electrode portion  50  and a transparent electrode  40  that is in electrical contact with the first electrode portion  50 . The first electrode portion  50  can be opaque, for example made of an electrically conductive metal such as aluminum, silver, gold, tungsten, or titanium. The transparent electrode  40  can be any transparent conductor such as a transparent conductive metal oxide such as indium tin oxide or aluminum zinc oxide. The second electrode  52  can be a metal layer made of a conductive metal such as aluminum, silver, gold, tungsten, or titanium and can be made of the same material as the first electrode portion  50 , or a different material. 
     The OLED  65  can be constructed on a transparent insulator  30  and an insulator  32 . The insulator  32  can be transparent and comprise the same material as the transparent insulator  30  or the insulator  32  can be a different, opaque material. The transparent insulator  30  or insulator  32  can be, for example, silicon dioxide or silicon nitride. The transparent electrode  40  is formed at least partly on the transparent insulator  30  and the transparent insulator  30  is at least partly in a common layer with the opaque first electrode portion  50 . The transparent insulator  30  transmits light emitted from the one or more layers of organic material  60 . The insulator  32  electrically insulates the first electrode portion  50  from the second electrode  52  so that a voltage difference can be established between the first and second electrodes  55 ,  52  causing current to flow between the first and second electrodes  55 ,  52  through the one or more layers of organic material  60 , causing at least one of the one or more layers of organic material  60  to emit light. 
     The insulator  32  prevents electrical shorts between the first electrode portion  50  and the second electrode  52  and allows the first electrode  55  to extend beyond the second electrode  52  enabling an external electrical connection to the first electrode  55 , for example an external electrical connection on a display substrate (not shown in  FIG. 1 ). 
     The one or more layers of organic material  60  can be evaporatively deposited on the transparent electrode  40  and can include a hole-injection layer, a light-emitting layer, and an electron-injection layer. Bank insulators  34  formed on the edges or corners of the transparent electrode  40  prevents electrical shorts between the transparent electrode  40  and the second electrode  52  at the edges or corners of the transparent electrode  40 . 
     The OLED structure  10  includes a tether  12  physically connecting the OLED  65  extending from a periphery of the organic light-emitting diode  65 . In the embodiment of  FIG. 1 , the tether  12  is an extension of the transparent insulator  30  beyond the OLED  65  and is attached to a portion of a source substrate  20  forming an anchor  14 . A sacrificial layer  18  is formed beneath the OLED structure  10  so that the OLED structure  10  is only connected to the source substrate  20  by the tether  12  to the anchor  14 . Thus, the OLED structure  10  can be released from the source substrate  20  by contacting the OLED  65  with a stamp, pressing the stamp against the OLED  65  to fracture the tether  12 . The OLED  65  can then be micro transfer printed to a destination substrate such as a display substrate (not shown in  FIG. 1 ). 
     The sacrificial layer  18  can be a cavity that is etched out from under the OLED  65  to form the tether  12  and OLED structure  10 . Alternatively, according to embodiments of the present invention, the sacrificial layer  18  is a physical layer, such as an oxide layer on the source substrate  20  on which the OLED  65  is constructed. In another embodiment, the source substrate  20  is a semiconductor substrate, such as silicon (1 0 0) or silicon (1 1 1), and the sacrificial layer  18  is a pre-determined designated portion of the source substrate  20 . 
     The cross sections of  FIGS. 2A-2I  and the flow diagram of  FIG. 11  illustrate successive steps in making an embodiment of the present invention. As shown in  FIG. 2A , a source substrate  20  is provided in step  100 . The source substrate  20  can be any substrate on which the subsequent structures can be formed and can include a glass, plastic, or semiconductor substrate having opposing substantially planar surfaces on which lithographic processes can be performed. The embodiment described uses a semiconductor substrate, for example silicon (1 0 0) or silicon (1 1 1). 
     For clarity and brevity of exposition, in the following steps and also with respect to  FIGS. 5A-5J , repeated references are made to forming a patterned layer or structure. Patterned layers are typically made in the photolithographic arts by first depositing a blanket layer of a desired material, for example by evaporation or sputtering. A blanket layer is unpatterned and covers the exposed area of a substrate. A photoresist layer, either positive or negative and for example SUB, is then deposited in a blanket layer over the desired material and exposed to a pattern of electromagnetic radiation such as ultra-violet radiation to pattern-wise cure the photoresist. The uncured photoresist is then removed to expose a pattern of the desired material. The exposed desired material is then etched, for example with a wet etchant, a dry etch, a plasma, reactive ions, or other active materials to remove the exposed desired material. Optionally, the cured photoresist is then removed, for example using an etchant specific to the cured photoresist, leaving a pattern of the desired material. 
     Referring to  FIG. 2B , a first electrode portion  50  is deposited and patterned on or in the source substrate  20  in step  110 . For example, the first electrode portion  50  can be a metal such as aluminum, titanium, tungsten, gold, silver, or other electrically conductive materials including conductive inks, semiconductors, or doped semiconductors. 
     A layer of transparent insulator  30  is patterned over the first electrode portion  50  in step  120 , leaving an exposed gap in the transparent insulator  30 , as shown in  FIG. 2C . A suitable transparent insulator  30  is silicon nitride or silicon dioxide. The transparent insulator  30  can be partially transparent, for example 50%, 70%, 80%, 90%, or 95% transparent to visible light. Two portions of transparent insulator  30  (a left and a right portion) are shown in  FIG. 2C . The right portion can be opaque and does not need to be transparent. As shown in  FIG. 1 , the right portion of the insulating layer is labeled as  32 , an insulator and can be formed and patterned separately from the transparent insulator  30  and can be a different material than the transparent insulator  30 . In an embodiment, however, both the transparent insulator  30  and insulator  32  of  FIG. 1  are transparent and are made in a common process with common materials so that the insulator  32  is also a transparent insulator  30 . 
     Referring next to  FIG. 2D , in step  130  a transparent electrode  40  is patterned over the transparent insulator  30  and in electrical contact with the first electrode portion  50 . The transparent electrode  40  is therefore in electrical contact with the first electrode portion  50  and the first electrode  55  includes both the first electrode portion  50  and the transparent electrode  40 . As shown in  FIG. 2E , bank insulators  34  are formed and patterned in step  140  on the edges of the transparent electrode  40 . The bank insulators  34  can be made of the same materials as the transparent insulator  30  or insulator  32 , or a different insulating material. The bank insulators  34  can, but need not, be transparent. 
     As shown in  FIG. 2F , one or more layers of organic material  60  are patterned over the transparent electrode  40  in step  150 . The one or more layers of organic material  60  can extend, but need not extend, over the bank insulators  34  and transparent insulators  30  (and insulator  32  as shown in  FIG. 1 ). In an embodiment, the one or more layers of organic material  60  are deposited by evaporation and patterned with a fine metal mask placed over the transparent conductor  40  and the bank insulators  34 . The fine metal mask has openings corresponding to the areas in which it is desired to deposit the organic layers, for example the exposed portion of the transparent electrode  40  between the bank insulators  34 . Elsewhere, any evaporated organic material is deposited on the fine metal mask. Alternatively, the one or more layers of organic material  60  are patterned using photolithographic processes described below. 
     Referring next to  FIG. 2G , the second electrode  52  is patterned over the one or more layers of organic material  60  in step  160 . The first and second electrodes  55 ,  52  and the one or more layers of organic material  60  form an organic light-emitting diode or OLED  65 . When a voltage is supplied across the first and second electrodes  55 ,  52  so that an electrical current flows between the first and second electrodes  55 ,  52  through the one or more layers of organic material  60 , light is emitted from one or more of the organic material layers. 
     As shown in  FIG. 2H , the transparent insulator  30  or insulator  32  ( FIG. 1 ) is further patterned to expose the first electrode portion  50  in step  170 . The sacrificial layer  18  is then removed in step  180  from beneath the first electrode portion  50  and transparent insulator (dielectric)  30 , for example by etching ( FIG. 2I ). In one embodiment of the present invention, the sacrificial layer  18  is simply a portion of the source substrate  20  that is etched, for example to form a cavity, as illustrated in  FIGS. 1 and 2I . In another embodiment a layer different from the source substrate  20  is patterned on the source substrate  20 , for example an oxide or nitride layer. The OLED structure  10  is formed on the sacrificial layer  18 , with the optional addition of an etch stop layer to protect the OLED structure  10  from the sacrificial layer  18  etch when it is removed in step  180  to form a cavity. After etching, the sacrificial layer  18  is a cavity. 
     The sacrificial layer  18  is patterned on the source substrate  20  so that the OLED  65  is completely undercut and so that a tether  12  extends from the periphery or edge of the OLED  65  to an anchor  14 . The anchor  14  can be a portion of the source substrate  20  that is not removed when the sacrificial layer  18  is removed to form the cavity. The tether  12  can be a portion of the transparent insulator  30  (as shown) or a portion of the first or second metal electrodes  55 ,  52 , or the bank insulator  34  (as shown in  FIG. 10  and discussed further below). Because of the tether  12 , anchor  14 , and underlying sacrificial layer  18 , the OLED structure  10  is suitable for micro transfer printing. During the micro transfer printing process, the tether  12  is fractured leaving only a portion of the tether  12  as a part of the OLED structure  10  of the present invention, and the OLED structure  10  can be transferred to a destination substrate such as a display substrate. 
     The OLED structure  10  of  FIG. 1  and as made by the process described in  FIGS. 2A-2I  includes first and second electrodes  55 ,  52 . After the OLED structure  10  is micro transfer printed to a destination substrate, conventional photolithographic methods can be used to electrically connect the first and second electrodes  55 ,  52  to a control, power, or ground circuit. 
     An alternative OLED structure  10  according to an embodiment of the present invention is illustrated in  FIG. 3  and a method of making the OLED structure  10  is illustrated in the successive cross section illustrations of  FIGS. 4A-4L . As shown in  FIG. 3 , the first electrode  55  includes a first protrusion  53  and the second electrode  52  includes a second protrusion  54  spatially and electrically separate from the first protrusion  53 . The first and second protrusions  53 ,  54  extend in a direction from the second electrode  52  to the first electrode  55 , i.e., toward the source substrate  20 . The remainder of the OLED  65  and OLED structure  10  are similar to those described above with respect to  FIG. 1 . 
       FIGS. 4A and 4B  illustrate top and bottom views of the OLED structure  10  of  FIG. 3  respectively, excluding the source substrate  20  and the transparent insulator  30  in the bottom view. As viewed from the top and as shown in  FIG. 4A , the OLED structure  10  includes a first electrode portion  50  extending to one side of the OLED structure  10 . The insulator  32  separates the first electrode portion  50  from the second electrode  52 . The insulator  32  (which can be the transparent insulator  30 ) extends to the other side of the OLED structure  10  and, where it extends past the protrusion  54 , forms the tether  12 . 
     As viewed from the bottom and as shown in  FIG. 4B , the OLED structure  10  includes a first electrode portion  50  extending to one side of the OLED structure  10 . The transparent insulator  30  separates the first electrode portion  50  from the bank insulator  34 . The one or more layers of organic material  60  can (but need not) extend past the bank insulator  34  and the second electrode  52  likewise can (but need not) extend past the one or more layers of organic material  60 . The insulator  32  (which can be the transparent insulator  30 ) extends to the other side of the OLED structure  10  and, where it extends past the protrusion  54  (which is a portion of the second electrode  52 ), forms the tether  12 . 
     The cross sections of  FIGS. 5A-5J  and the flow diagram of  FIG. 11  illustrate successive steps in making an embodiment of the present invention. As shown in  FIG. 5A , a source substrate  20  is provided in step  100  with spatially separated indentations formed in the source substrate  20 , for example by anisotropic etching, above a portion of the source substrate  20  pre-defined as the sacrificial layer  18 . The source substrate  20  can be any substrate on which the subsequent structures can be formed and can include a glass, plastic, or semiconductor substrate having opposing substantially planar surfaces on which lithographic processes can be performed. The embodiment described uses a semiconductor substrate, for example silicon (1 0 0) or silicon (1 1 1). 
     Referring to  FIG. 5B , in step  110  a first electrode portion  50  is deposited and patterned on or in one of the indentations in the source substrate  20  and a portion of the second electrode  52  is deposited and patterned on or in the other of the indentations in the source substrate  20 . For example, the first electrode portion  50  or second electrode portions  52  can be a metal such as aluminum, titanium, tungsten, gold, silver, or other electrically conductive materials including conductive inks, semiconductors, or doped semiconductors. 
     A layer of transparent insulator  30  is patterned over the first electrode portion  50  in step  120 , leaving an exposed gap in the transparent insulator  30 , as shown in  FIG. 2C . A suitable transparent insulator  30  is silicon nitride or silicon dioxide. The transparent insulator  30  can be partially transparent, for example 50%, 70%, 80%, 90%, or 95% transparent to visible light. A transparent insulator  30  is shown on the left in  FIG. 5C . The right portion can be opaque and does not need to be transparent. As shown in  FIG. 3 , the right portion of the insulating layer is labeled as  32 , an insulator and can be formed and patterned separately from the transparent insulator  30  and can be a different material than the transparent insulator  30 . In an embodiment, however, both the transparent insulator  30  and insulator  32  of  FIG. 1  are transparent and are made in a common process with common materials so that the insulator  32  is also a transparent insulator  30 . 
     Referring next to  FIG. 5D , in step  130  a transparent electrode  40  is patterned over the transparent insulator  30  and in electrical contact with the first electrode portion  50 . The transparent electrode  40  is therefore in electrical contact with the first electrode portion  50  and the first electrode  55  includes both the first electrode portion  50  and the transparent electrode  40 . As shown in  FIG. 5E , a via is opened in the transparent insulator  30  to expose a portion of the second electrode  52 . In an embodiment, this step is combined with the step illustrated in  FIG. 5F . As shown in  FIG. 5F , bank insulators  34  are formed and patterned in step  140  on the edges of the transparent electrode  40 . The bank insulators  34  can be made of the same materials as the transparent insulator  30  or insulator  32 , or a different insulating material. The bank insulators  34  can, but need not, be transparent. 
     As shown in  FIG. 5G , one or more layers of organic material  60  are patterned over the transparent electrode  40  in step  150 . The one or more layers of organic material  60  can, but need not, extend over the bank insulators  34  and transparent insulators  30  (and insulator  32  as shown in  FIG. 3 ). In an embodiment, the one or more layers of organic material  60  are deposited by evaporation and patterned with a fine metal mask placed over the transparent conductor  40  and the bank insulators  34 . The fine metal mask has openings corresponding to the areas in which it is desired to deposit the organic layers; for example, the exposed portion of the transparent electrode  40  between the bank insulators  34 . Elsewhere, any evaporated organic material is deposited on the fine metal mask. Alternatively, the one or more layers of organic material  60  are patterned using photolithographic processes described below. 
     Referring next to  FIG. 5H , the second electrode  52  is patterned over the one or more layers of organic material  60  in step  160  and is formed in electrical contact with the portion of the second electrode  52  through the via. The first and second electrodes  55 ,  52  and the one or more layers of organic material  60  form an organic light-emitting diode or OLED  65 . When a voltage is supplied across the first and second electrodes  55 ,  52  so that an electrical current flows between the first and second electrodes  55 ,  52  through the one or more layers of organic material  60 , light is emitted from one or more of the organic material layers. 
     As shown in  FIG. 5I , the transparent insulator  30  or insulator  32  ( FIG. 1 ) is further patterned to expose the first electrode portion  50  in step  170 . The sacrificial layer  18  is then removed in step  180  from beneath the first electrode portion  50  and transparent insulator (dielectric)  30 , for example by etching ( FIG. 5J ). In one embodiment of the present invention, the sacrificial layer  18  is simply a portion of the source substrate  20  that is etched, for example etched to form a cavity, as illustrated in  FIGS. 3 and 5J . In another embodiment a layer different from the source substrate  20  is patterned on the source substrate  20 , for example an oxide or nitride layer. The OLED structure  10  is formed on the sacrificial layer  18 , with the optional addition of an etch stop layer to protect the OLED structure  10  from the sacrificial layer  18  etch when it is removed in step  180  to form a cavity. After etching, the sacrificial layer  18  is a cavity. 
     The sacrificial layer  18  is patterned on the source substrate  20  so that the OLED  65  is completely undercut and so that a tether  12  extends from the periphery or edge of the OLED  65  to an anchor  14 . The anchor  14  can be a portion of the source substrate  20  that is not removed when the sacrificial layer  18  is removed to form the cavity. The tether  12  can be a portion of the transparent insulator  30  (as shown) or a portion of the first or second metal electrodes  55 ,  52 , or the bank insulator  34  (as shown in  FIG. 10  and discussed further below). Because of the tether  12 , anchor  14 , and underlying sacrificial layer  18 , the OLED structure  10  is suitable for micro transfer printing. During the micro transfer printing process, the tether  12  is fractured leaving only a portion of the tether  12  as a part of the OLED structure  10  of the present invention, and the OLED structure  10  can be transferred to a destination substrate such as a display substrate. 
     The OLED structure  10  of  FIG. 1  and as made by the process described in  FIGS. 2A-2I  includes first and second electrodes  55 ,  52 . In certain embodiments, one or more steps may be omitted. After the OLED structure  10  is micro transfer printed to a destination substrate, conventional photolithographic methods can be used to electrically connect the first and second electrodes  55 ,  52  to a control, power, or ground circuit. 
     Another embodiment of the present invention illustrate in the cross section of  FIG. 6  uses a unitary first electrode  55 . By unitary it is meant that the first electrode  55  consists of only one kind of material in a single structure in contrast to the first electrode  55  of the embodiments of  FIGS. 1 and 3 , in which the first electrode  55  has two parts, a first electrode portion  50  and a transparent electrode portion  40 . As shown in  FIG. 6 , the separate transparent electrode  40  is omitted and the tether  12  is formed by the bank insulator  34 . The structure shown in  FIG. 6  can also be used with the first and second protrusions  53 ,  54  shown in the embodiment of  FIG. 3 . 
     The evaporated organic materials can be patterned by using a fine metal shadow mask that prevents the deposition of organic particles on portions of a substrate covered by the shadow mask. In an embodiment of the present invention, the organic materials are patterned using photolithographic methods. Because the present invention contemplates the deposition of only a single set of organic materials on a source substrate  20  and multiple colors in a display are provided with different sets of organic materials on respective different source substrates  20  rather than on a common substrate, the photolithographic process do not damage pre-existing layers of organic materials. 
       FIG. 7A  illustrates a portion of an OLED structure  10  corresponding to the structures of  FIGS. 2F and 5G  except that the one or more layers of organic material  60  are unpatterned. Referring to  FIG. 7B , an unpatterned layer of electrically conductive material comprising the second electrode  52  is deposited on the unpatterned one or more layers of organic material  60 . 
     Next, as shown in  FIG. 7C , a protective layer  70  is patterned on the unpatterned second electrode  52  and then exposed to an active material, such as an etchant, a dry etchant, an ion etchant, or a plasma. The active material removes the exposed portions of the second electrode  52  as shown in  FIG. 7D . The process is then optionally repeated with the same or a different etchant ( FIG. 7E ) to form the patterned one or more layers of organic materials  60  illustrated in  FIG. 7F . 
     The patterned protective layer  70  is optionally removed (not shown) or coated with a second layer  56  of the electrical conductor of the second electrode  52  ( FIG. 7G ) and patterned to further protect any exposed edges of the one or more layers of organic materials  60  ( FIG. 7H ). If not removed earlier, the patterned protective layer  70  is optionally removed ( FIG. 7I ) and an additional layer of second electrode  52  material is optionally provided ( FIG. 7J ). After patterning the organic materials layer  60  a barrier material  71  may be deposited and patterned to encapsulate the organic materials and at least a portion of the second electrode  52 , optionally having at least one opening to provide access to the second electrode  52 . A third conductive layer  72  that like the barrier material  71  has moisture or environmental protection characteristics may be deposited and patterned over some portion of the organic materials and the second electrode, thereby forming ( FIG. 7M ) a protecting encapsulation layer composed of a combination of barrier material  71  and the third conductive layer  72 . The insulator  32  is then patterned ( FIG. 7K ) and the sacrificial layer  18  etched ( FIG. 7L ) to form the OLED structure  10 , optionally having the protecting encapsulation layer ( FIG. 7N ). In some embodiments, the organic structure is photoluminescent and contains only organic layers and transparent dielectric or barrier layers with no exposed electrical terminals ( FIG. 7O ). 
     Therefore, a method of patterning the one or more layers of organic material  60  on the patterned first electrode  55  and patterning the second electrode  52  on the one or more layers of organic material  60  includes blanket depositing the layers of organic material  60  over an area of the source substrate  20 , blanket depositing the second electrode  52  over the layers of organic material  60 , and forming a patterned protective layer  70  over the second electrode  52 . The patterned protective layer defines the pattern of the one or more layers of organic material  60 . The second electrode  52  is patterned by exposing the second electrode  52  to an active material that removes second electrode material exposed to the line-of-flight of the active material. The one or more layers of organic material  60  are patterned by exposing the one or more layers of organic material  60  to an active material that removes the one or more layers of organic material  60  exposed to the line-of-flight of the active material. The patterned protective layer is optionally removed. Additional patterned second electrode material is optionally provided to form the patterned second electrode  52  and protect the one or more layers of organic material  60 . In an embodiment, the active material is a gas, a plasma, or not a liquid. 
     The process described in  FIGS. 7A-7L  does not require the use of fine metal shadow masks and is therefore not limited by the sizes of the mechanical structures inherent in the shadow masks. Instead, higher resolution photolithographic techniques are used and, in consequence, smaller OLED devices for higher resolution displays are possible. Therefore, according to an embodiment of the present invention, OLED  65  has a light-emitting area that has a dimension parallel to the extent of the first electrode  55  that is less than or equal to 40 microns, less than or equal to 20 microns, less than or equal to 10 microns, or less than or equal to 5 microns. Alternatively, or in addition, the OLED  65  has a light-emitting area that is less than or equal to 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. 
     According to different embodiments of the present invention, the OLED structure  10  can have a top-emitter configuration or a bottom-emitter configuration.  FIG. 1  and  FIGS. 2A-2I  illustrate a structure and method for a bottom-emitter embodiment in which light from the one or more layers of organic material  60  passes through the bottom, transparent electrode  40  and transparent insulator  30 . Referring to  FIG. 6 , a top-emitter embodiment uses a unitary opaque first electrode  55  that extends between the bank insulators  34  and under the one or more layers of organic material  60 . The bank insulators  34  are also helpful to insulate the transparent electrode  40  from the second electrode  52 . The second electrode  52  is transparent, for example made of a metal oxide such as indium tin oxide or aluminum zinc oxide. In other embodiments, for example alternative configurations of  FIGS. 1 and 3 , the transparent electrode  40  is replaced with an opaque and preferably reflective electrode and the second electrode  52  is transparent. In these embodiments of the present invention, light emitted from the one or more layers of organic material  60  in response to current flowing between the first and second electrodes  55 ,  52  passes through the top, transparent second electrode  52 . 
     As shown in  FIGS. 1, 3, and 6 , OLED structures  10  of the present invention can be constructed over a sacrificial layer  18  on a source substrate  20 . The source substrate  20  has a portion defining an anchor  14  and the sacrificial layer  18  is formed on the source substrate  20  and adjacent to the anchor  14 . The OLED  65  is disposed on the sacrificial layer  18  and the tether  12  is connected to the anchor  14 . This OLED structure  10  is adapted for micro transfer printing to a destination substrate such as a display substrate. 
     According to further embodiments of the present invention, a plurality of OLED structures  10  are formed on the source substrate  20 . In one embodiment, the one or more layers of organic material  60  in each of the OLED structures  10  is the same and at least one of the one or more layers of organic material  60  emits red light, green light, or blue light. 
     Alternatively, first and second OLED structures  10  are formed on the source substrate  20 . The first OLED structure  10  includes at least one layer of organic material that emits a first color of light and the second OLED structure  10  includes at least one layer of organic material that emits a second color of light different from the first color of light. Additionally, a third OLED structure  10  can be formed on the source substrate  20  that includes at least one layer of organic material that emits a third color of light different from the first color of light and different from the second color of light. The first color of light can be red, the second color of light can be green, and the third color of light can be blue. 
     Referring to the perspective of  FIG. 8 , a micro transfer printed OLED display  82  having printable organic light-emitting diode structures  10  includes a display substrate  80  having one or more organic light-emitting diode structures  10  disposed on the display substrate  80 . A first electrical conductor  98  is electrically connected to the first electrode  55  and a second electrical conductor  99  is electrically connected to the second electrode  52 . In various embodiments, the first electrical conductor  98  or the second electrical conductor  99  is located on the display substrate  80  or the first and second electrical conductors  98 ,  99  are both located on the display substrate  80 . The first and second electrical conductors  98 ,  99  can be connected to wires or form a bus  96  that is connected to a controller  92 . The controller  92  provides signals, power, or ground through the wires  96  and the first and second electrical conductors  98 ,  99  to control the organic light-emitting diode structures  10  to emit light. Although for clarity, the OLED structures  10  are shown interconnected serially by the first and second electrical conductors  98 ,  99 , in an alternative embodiment, the OLED structures  10  can be controlled using conventional column and row drivers. 
     The OLED structures  10  can be grouped into pixels  90 . The pixels  90  can have OLED structures  10  that all emit the same color of light or the pixels  90  can be full-color pixels  90  that each have different OLED structures  10 . For example, the pixels  90  can include at least a first OLED structure  10  that emits light of a first color and a second OLED structure  10  that emits light of a second color different from the first color. The pixels  90  can also include a third OLED structure  10  that emits light of third color different from the first and second colors. The colors can be red, green, and blue and the first OLED structure  10  can be a red OLED structure  10 R that emits red light, the second OLED structure  10  can be a green OLED structure  10 G that emits green light, and the third OLED structure  10  can be a blue OLED structure  10 B that emits blue light. 
     In an alternative embodiment of the present invention, not shown, a color display includes both organic light-emitting diodes and inorganic light-emitting diodes. Thus, the one or more OLED structures  10  can include a first OLED structure  10  that emits light of a first color and a second inorganic light-emitting diode that emits light of a second color different from the first color. Both the organic and inorganic light-emitting diodes can be micro transfer printed from a source substrate  20  to the display substrate  80  to form a heterogeneous display. For example, the red light emitter can be a red OLED and the green and blue light emitters can be inorganic light emitters. 
     In a further embodiment of the present invention the display includes pixel controllers  94  (shown in  FIG. 9 ) associated with or a part of the pixels  90  that are electrically connected to the first and second electrodes  55 ,  52  of the OLED structures  10  in the pixel  90  group to control the OLED structures  10  to emit light. The pixel controllers  94  can be an integrated circuit that includes control circuits responsive to the controller  92  through the wires  96  and first and second electrical conductors  98 ,  99 . 
     In an embodiment of the present invention and as shown in  FIG. 9 , the pixel controllers  94  and the OLED structures  10  in a pixel  90  are disposed on a pixel substrate  84  that is separate and distinct from the display substrate  80  and forms a pixel component  16 . The pixel substrate  84  can be a semiconductor substrate on or in which the pixel controller circuits are formed (not shown), or the pixel substrate  84  can also be separate and distinct from the pixel controller  94  substrate (as shown). 
     As shown in  FIG. 10 , the pixel components  16  are then disposed on the display substrate  80 , for example by micro transfer printing to form a micro-transfer printed display  82  or by using pick-and-place technology. The pixel components  16  can be surface mount components. 
     The present invention provides an advantage over structures and methods of the prior art in that OLED structures  10  of the present invention emitting different colors of light can each be made on a different source substrate  20  so that each source substrate  20  can include OLED structures  10  that emit light of only a single color. This reduces alignment and tolerance issues and avoid repeatedly contacting the source substrate  20  with shadow masks. Referring to  FIG. 12 , a red source substrate  20 R is a source substrate  20  with an organic layer that emits red light, a green source substrate  20 G is a source substrate  20  with an organic layer that emits green light, and a blue source substrate  20 B is a source substrate  20  with an organic layer that emits blue light. Each of the red, green, and blue source substrates are different and separate source substrates  20  that can each supply a red, green, or blue OLED structure  10 R,  10 G, or  10 B, respectively. 
     As shown in  FIG. 12 , a red source substrate  20 R is provided in step  100 R, a green source substrate  20 G is provided in step  100 G, a blue source substrate  20 B is provided in step  100 B, and a destination substrate such as a displays substrate  80  is provided in step  105 . As shown in  FIG. 11 , the steps  110  through  140  form a first electrode structure in step  101  and the steps  160 - 180  form a second electrode structure in step  103 . After the different source and destination substrates  20 ,  80  are provided in  FIG. 12 , the first electrodes  55  are separately and independently formed on each of the red, green, and blue source substrates  20 R,  20 G, and  20 B in step  101 . One or more layers of organic material  60  that emit red light are then patterned on the red source substrate  20 R, one or more layers of organic material  60  that emit green light are then patterned on the green source substrate  20 G, and one or more layers of organic material  60  that emit blue light are then patterned on the blue source substrate  20 B in steps  150 R,  150 G,  150 B, respectively. The second electrodes  52  are separately and independently formed on each of the red, green, and blue layers of organic material on each of the red, green, and blue source substrates  20 R,  20 G, and  20 B in step  103 . The blue OLED structures  10 B are then micro transfer printed to the destination substrate  80 , the green OLED structures  10 G are micro transfer printed to the destination substrate  80 , and the red OLED structures  1 OR are micro transfer printed to the destination substrate  80  in steps  190 B,  190 G, and  190 R to form the display structure illustrated in  FIG. 8 . The steps  190 B,  190 G, and  190 R can be performed in any order. If pixel components  16  are desired, the red, green, and blue OLED structures  10 R,  10 G,  10 B from the red, green, and blue source substrates  20 R,  20 G, and  20 B, respectively, are each micro transfer printed onto the pixel substrate  84  and then the pixel substrates  84  are disposed on the destination substrate  80 . 
     The controller  92  and pixel controllers  94  can be made in one or more integrated circuits having separate, independent, and distinct substrates. For example, the pixel controllers  94  can be chiplets, small, unpackaged integrated circuits such as unpackaged dies interconnected with wires connected to contact pads on the chiplets. The chiplets can be disposed on an independent light-emitter substrate, such as a pixel substrate  84  or a display substrate  80 . If the chiplets are disposed on pixel substrates  84 , the pixel substrates  84  can be disposed on the display substrate  80 . In an embodiment, the chiplets are made on a semiconductor wafer and have a semiconductor substrate and the display substrate  80  is or includes glass, resin, polymer, plastic, or metal. The pixel substrates  84  can be made in semiconductor materials or in glass, resin, polymer, plastic, or metal. Semiconductor materials (for example silicon) and processes for making small integrated circuits are well known in the integrated circuit arts. Likewise, display substrates  80  (destination substrates) and means for interconnecting integrated circuit elements on the display substrate  80  are well known in the printed circuit board arts. The chiplets can be applied to the pixel substrates  84  or to the display substrate  80  using micro transfer printing. The pixel substrates  84  can be applied to the display substrate  80  using micro transfer printing. 
     In one method of the present invention the pixel substrates  84  are disposed on the display substrate  80  by micro transfer printing using compound micro assembly structures and methods, for example as described in U.S. patent application Ser. No. 14/822,868, filed Aug. 10, 2015, entitled  Compound Micro - Assembly Strategies and Devices,  which is hereby incorporated by reference in its entirety. However, since the pixel substrates  84  are larger than the chiplets, in another method of the present invention, the pixel substrates  84  are disposed on the display substrate  80  using pick-and-place methods found in the printed-circuit board industry, for example using vacuum grippers. The OLED structures  10  or pixel controllers  94  on the pixel substrates  84  can be interconnected using photolithographic methods and materials or on the display substrate  80  using printed circuit board methods and materials. 
     In useful embodiments the display substrate  80  includes material, for example glass or plastic, different from a material in an integrated-circuit or chiplet substrate, for example a semiconductor material such as silicon. The pixel controllers  94  can be formed separately on separate semiconductor substrates, assembled onto the pixel substrates  84 , and then the assembled unit is disposed on the surface of the display substrate  80 . This arrangement has the advantage that the OLED structure  10  can be separately tested on the pixel substrates  84  and the pixel substrate  84  accepted, repaired, or discarded before it is located on the display substrate  80 , thus improving yields and reducing costs. 
     The OLED structures  10  are electrically connected to one or more electrically conductive wires  98 ,  99  that electrically connect the OLED structures  10  and the pixel controllers  94  or controllers  92  to conduct power, a ground reference voltage, or signals for controlling the OLED structures  10 . In an embodiment, the wires  96  are connected to a controller  92  that is external to the display substrate  80 . In an alternative embodiment, not shown, the controller  92  is located on the display substrate  80  outside a display area including the OLED structures  10 . If individual pixel controllers  94  are used, they can be spatially distributed over the display substrate  80  in spatial correspondence to the pixels  90  or on pixel substrates  84  that are spatially distributed over the display substrate  80 . The controller  92  controls the OLED structures  10  or pixel controllers  92  by, for example, providing power, a ground reference signal, and control signals. 
     In an embodiment, the OLED structures  10  are transfer printed to the pixel substrates  84  or to the display substrate  80  in one or more transfers. For a discussion of micro-transfer printing techniques see, U.S. Pat. Nos. 8,722,458, 7,622,367 and 8,506,867, each of which is hereby incorporated by reference. The transferred OLED structures  10  are then interconnected, for example with conductive wires and optionally including connection pads and other electrical connection structures, to enable the controller  92  or pixel controllers  94  to electrically interact with the OLED structures  10  to emit light. In an alternative process, the transfer of the OLED structures  10  is performed before or after all of the first and second electrical conductors  98 ,  99  are in place. Thus, in embodiments the construction of the first and second electrical conductors  98 ,  99  can be performed before the OLED structures  10  are printed, or after the OLED structures  10  are printed, or both. In an embodiment, the controller  92  is externally located (for example on a separate printed circuit board substrate) and electrically connected to the conductive wires using connectors, ribbon cables, or the like. Alternatively, the controller  92  is affixed to the display substrate  80  outside the area on the display substrate  80  in which the OLED structures  10  are located and electrically connected to the first and second electrical conductors  98 ,  99  using wires and buses  96 , for example using surface mount and soldering technology. 
     According to various embodiments of the present invention, the micro-transfer-printed OLED display  82  can include a display substrate  80  on which the OLED structures  10  are disposed. The display substrate  80  usefully has two opposing smooth sides suitable for material deposition, photolithographic processing, or micro-transfer printing of OLED structures  10 . The display substrate  80  can have the size of a conventional display, for example a rectangle with a diagonal of a few centimeters to one or more meters. Such substrates are commercially available. The display substrate  80  can include polymer, plastic, resin, polyimide, PEN, PET, metal, metal foil, glass, a semiconductor, or sapphire and have a transparency greater than or equal to 50%, 80%, 90%, or 95% for visible light. In some embodiments of the present invention, the OLED structures  10  emit light through the display substrate  80 . In other embodiments, the OLED structures  10  emit light in a direction opposite the display substrate  80 . The display substrate  80  can have a thickness from 5 to 10 microns, 10 to 50 microns, 50 to 100 microns, 100 to 200 microns, 200 to 500 microns, 500 microns to 0.5 mm, 0.5 to 1 mm, 1 mm to 5 mm, 5 mm to 10 mm, or 10 mm to 20 mm. According to embodiments of the present invention, the display substrate  80  can include layers formed on an underlying structure or substrate, for example a rigid or flexible glass or plastic substrate. In an embodiment of the present invention, the OLED structures  10  have light-emissive areas of less than 1600 square microns, less than or equal to 800 square microns, less than or equal to 400 square microns, less than or equal to 200 square microns, less than or equal to 100 square microns, or less than or equal to 50 square microns. In other embodiments, the OLED structures  10  have physical dimensions that are less than 100 μm, for example having a width from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, having a length from 5 to 10 μm, 10 to 20 μm, or 20 to 50 μm, or having a height from 2 to 5 μm, 4 to 10 μm, 10 to 20 μm, or 20 to 50 μm. The OLED structures  10  can provide highly saturated display colors and a substantially Lambertian emission providing a wide viewing angle. 
     According to various embodiments, the micro-transfer-printed OLED display  82  of the present invention, includes a variety of designs having a variety of resolutions, OLED structure  10  sizes, and displays having a range of display areas. For example, display areas ranging from 1 cm by 1 cm to 10 m by 10 m in size are contemplated. The resolution of OLED structures  10  over a display area can also vary, for example from OLED structures  10  per inch to hundreds of light emitters per inch. Thus, the present invention has application in both low-resolution and very high-resolution displays and from very small to very large displays. 
     As shown in  FIGS. 1, 3, and 6 , the full-color pixels  90  form a regular array on the display substrate  80 . Alternatively, at least some of the full-color pixels  90  have an irregular arrangement on the display substrate  80 . 
     In an embodiment, the integrated circuits or chiplets are formed in substrates or on supports separate from the display substrate  80 . For example, the OLED structures  10  are separately formed in a semiconductor source wafer. The OLED structures  10  are then removed from the source wafer and transferred, for example using micro transfer printing, to the display substrate  80  or pixel substrate  84 . 
     By employing a multi-step transfer or assembly process, increased yields are achieved and thus reduced costs for the micro-transfer-printed OLED display  82  of the present invention. Additional details useful in understanding and performing aspects of the present invention are described in U.S. patent application Ser. No. 14/743,981, filed Jun. 18, 2015, entitled  Micro - Assembled Micro LED Displays and Lighting Elements,  which is hereby incorporated by reference in its entirety. 
     As is understood by those skilled in the art, the terms “over”, “under”, “above”, “below”, “beneath”, and “on” are relative terms and can be interchanged in reference to different orientations of the layers, elements, and substrates included in the present invention. For example, a first layer on a second layer, in some embodiments means a first layer directly on and in contact with a second layer. In other embodiments, a first layer on a second layer can include another layer there between. Additionally, “on” can mean “on” or “in.” As additional non-limiting examples, a sacrificial layer is considered “on” a substrate when a layer of sacrificial material is on top of the substrate, when a portion of the substrate itself is the sacrificial layer, or when the sacrificial layer comprises material on top of the substrate and a portion of the substrate itself. 
     Having described certain embodiments, it will now become apparent to one of skill in the art that other embodiments incorporating the concepts of the disclosure may be used. Therefore, the invention should not be limited to the described embodiments, but rather should be limited only by the spirit and scope of the following claims. 
     Throughout the description, where apparatus and systems are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are apparatus, and systems of the disclosed technology that consist essentially of, or consist of, the recited components, and that there are processes and methods according to the disclosed technology that consist essentially of, or consist of, the recited processing steps. 
     It should be understood that the order of steps or order for performing certain action is immaterial so long as the disclosed technology remains operable. Moreover, two or more steps or actions in some circumstances can be conducted simultaneously. The invention has been described in detail with particular reference to certain embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           10  organic light-emitting diode structure 
           10 R red organic light-emitting diode structure 
           10 G green organic light-emitting diode structure 
           10 B blue organic light-emitting diode structure 
           12  tether 
           14  anchor 
           16  pixel component 
           18  sacrificial layer 
           20  source substrate 
           20 R red source substrate 
           20 G green source substrate 
           20 B blue source substrate 
           30  transparent insulator 
           32  insulator 
           34  bank insulator 
           40  transparent electrode 
           50  first electrode portion 
           52  second electrode 
           53  first protrusion 
           54  second protrusion 
           55  first electrode 
           56  second layer of second electrode 
           60  organic material layer(s) 
           65  organic light-emitting diode 
           70  patterned protective layer 
           71  barrier material 
           72  third conductive layer 
           80  destination substrate/display substrate 
           82  micro-transfer-printed OLED display 
           84  pixel substrate 
           90  pixel 
           92  controller 
           94  pixel controller 
           96  wires/bus 
           98  first electrical conductor 
           99  second electrical conductor 
           100  provide source substrate step 
           100 R provide red source substrate step 
           100 G provide green source substrate step 
           100 B provide blue source substrate step 
           101  form first electrode structure step 
           103  form second electrode structure step 
           105  provide destination substrate step 
           110  pattern first electrode step 
           120  pattern transparent dielectric step 
           130  pattern transparent electrode step 
           140  pattern bank insulator step 
           150  pattern OLED layers step 
           150 R pattern red OLED layers step 
           150 G pattern green OLED layers step 
           150 B pattern blue OLED layers step 
           160  pattern second electrode step 
           170  pattern dielectric step 
           180  etch sacrificial layer step 
           190 R micro transfer print red OLED structure step 
           190 G micro transfer print green OLED structure step 
           190 B micro transfer print blue OLED structure step