Patent ID: 12243963

DETAILED DESCRIPTION OF THE EMBODIMENTS

The disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which some embodiments of the disclosure are shown. This disclosure may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will convey the scope of the disclosure to those skilled in the art.

In the specification and the claims, the phrase “at least one of” is intended to include the meaning of “at least one selected from the group of” for the purpose of its meaning and interpretation. For example, “at least one of A and B” may be understood to mean “A, B, or A and B.”

Unless otherwise defined or implied herein, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the disclosure, and should not be interpreted in an ideal or excessively formal sense unless clearly so defined herein.

It will also be understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other layer or substrate, or intervening layers may also be present. The same reference numbers indicate the same components throughout the specification.

It will be understood that, although the terms “first,” “second,” and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For instance, a first element discussed below could be termed a second element without departing from the teachings of the disclosure. Similarly, the second element could also be termed the first element.

Hereinafter, embodiments of the disclosure will be described with reference to the attached drawings.

FIG.1is a schematic plan view of a display device according to an embodiment.

Referring toFIG.1, a display device10may display a mobile image or a still image. The display device10may refer to any electronic device that provides a display screen. For example, the display device10may be used in televisions, laptop computers, monitors, billboards, internet of things devices, mobile phones, smartphones, tablet personal computers (PCs), electronic watches, smartwatches, watch phones, head mounted displays, mobile communication terminals, electronic notebooks, electronic books, portable multimedia players (PMPs), navigation system, game consoles, digital cameras, camcorders, and the like.

The display device10may include a display panel for providing a display screen. Examples of the display panel may include an inorganic light emitting diode display panel, an organic light emitting display panel, a quantum dot light emitting display panel, a plasma display panel, and a field emission display panel. Hereinafter, an inorganic light emitting diode display panel may be used as an example of the display panel, but the disclosure is not limited thereto. Any display panel may be used as the display panel as long as the same technical idea is applicable.

The shape of the display device10may be variously modified. For example, the display device10may have a shape such as a rectangle having longer horizontal sides, a rectangle having longer vertical sides, a square, a rectangle having rounded corners (vertexes), another polygon, or a circle. The shape of a display area DPA of the display device1may also be similar to the overall shape of the display device10.FIG.1illustrates a display device10and a display area DPA each having a rectangular shape having longer horizontal sides.

The display device10may include a display area DPA and a non-display area NDA. The display area DPA may be an area where an image may be displayed, and the non-display area NDA may be an area where an image is not displayed. The display area DPA may be referred to as an active area, and the non-display area NDA may be referred to as an inactive area. The display area DPA may generally occupy the center of the display device10.

The display area DPA may include pixels PX. The pixels PX may be arranged in a matrix direction. Each of the pixels PX may have a rectangular shape or a square shape in a plan view, but the shape thereof is not limited thereto. Each of the pixels PX may have a rhombic shape in which each side is inclined with respect to a direction. The respective pixels PX may be alternately arranged in a stripe or Pentile type. Each of the pixels PX may include at least one light emitting element30emitting light of a specific wavelength band to display a specific color.

The non-display area NDA may be disposed around the display area DPA. The non-display area NDA may entirely or partially surround the display area DPA. The display area DPA may have a rectangular shape, and the non-display area NDA may be disposed adjacent to four sides of the display area DPA. The non-display area NDA may form (or constitute) a bezel of the display device10. Wirings or circuit drivers included in the display device10may be disposed in the non-display area NDA, or external devices may be mounted in the non-display area NDA.

FIG.2is a schematic plan view illustrating a pixel of a display device according to an embodiment.

Referring toFIG.2, each of the pixels PX may include sub-pixels PXn (where n is an integer of 1 to 3). For example, a pixel PX may include a first sub-pixel PX1, a second sub-pixel PX2, and a third sub-pixel PX3. The first sub-pixel PX1may emit light of a first color, the second sub-pixel PX2may emit light of a second color, and the third sub-pixel PX3may emit light of a third color. For example, the first color may be blue, the second color may be green, and the third color may be red. However, the disclosure is not limited thereto, and each of the sub-pixels PXn may emit light of the same color. AlthoughFIG.2illustrates that the pixel PX may include three sub-pixels PXn, the disclosure is not limited thereto, and the pixel PX may include a larger number of sub-pixels PXn.

Each of the sub-pixels PXn of the display device10may include a light emitting area EMA and a non-light emitting area (not shown). The light emitting area EMA may be defined as an area in which the light emitting element30is disposed to emit light of a specific wavelength band, and the non-light emitting area may be defined as an area in which no light emitting element30is disposed and which rays of light emitted from the light emitting element30do not reach so that no light is emitted therefrom. The light emitting area EMA may include an area in which the light emitting element30is disposed, and an area adjacent to the light emitting element30to emit light emitted from the light emitting element30.

However, the disclosure is not limited thereto, and the light emitting area may also include an area in which light emitted from the light emitting element30is reflected or refracted by another member and then emitted. Light emitting elements30may be arranged in each of the sub-pixels PXn, and an area in which the light emitting elements30are arranged and an area adjacent thereto may form the light emitting area EMA.

Each of the sub-pixels PXn may include a cut area CBA disposed in the non-light emitting area. The cut area CBA may be disposed at a side of the light emitting area EMA in a second direction DR2. The cut area CBA may be disposed between the light emitting areas EMA of the neighboring sub-pixels PXn in the second direction DR2. Multiple light emitting areas EMA and multiple cut areas CBA may be arranged in the display area DPA of the display device10. For example, the light emitting areas EMA and the cut areas CBA may be repeatedly arranged in a first direction DR1, respectively, and may be alternately arranged in the second direction DR2. The distance between the cut areas CBA spaced apart from each other in the first direction DR1may be smaller than the distance between the light emitting areas EMA spaced apart from each other in the first direction DR1. A second bank BNL2may be disposed between the cut areas CBA and the light emitting areas EMA, and the distance therebetween may be changed depending on the width of the second bank BNL2. Since the light emitting element30is not disposed in the cut area CBA, light is not emitted therefrom, but some of electrodes21and22disposed in each of the sub-pixels PXn may be disposed in the cut areas CBA. The electrodes21and22disposed for each of the sub-pixels PXn may be disposed separately from each other in the cut area CBA.

FIG.3is a schematic cross-sectional view taken along lines Q1-Q1′, Q2-Q2′, and Q3-Q3′ ofFIG.2.FIG.3illustrates a cross section across ends of the light emitting element30disposed in the first sub-pixel PX1ofFIG.2.

Referring toFIG.3together withFIG.2, the display device10may include a first substrate11, and a semiconductor layer, conductive layers, and insulating layers, which are disposed on the first substrate11. The semiconductor layer, the conductive layers, and the insulating layers may form a circuit layer and a light emitting element layer of the display device10.

The first substrate11may be an insulating substrate. The first substrate11may be made of an insulating material such as glass, quartz, or polymer resin. The first substrate11may be a rigid substrate but may be a flexible substrate capable of bending, folding, rolling, or the like.

A light blocking layer BML may be disposed on the first substrate11. The light blocking layer BML is disposed to overlap an active layer ACT1of a first transistor T1. The active layer ACT1may include a first region ACT_a, a second region ACT_b, and a channel region ACT_c. The light blocking layer BML1may include a material blocking light, thereby preventing light from entering the active layer ACT1of the first transistor T1. For example, the light blocking layer BML may be formed of an opaque metal material that blocks light transmission. However, the disclosure is not limited thereto. For example, the light blocking layer BML may be omitted.

A buffer layer12may be entirely disposed on the first substrate11. For example, the buffer layer12may be disposed to cover or overlap the light blocking layer BML and the upper surface of the first substrate11. The buffer layer12may be formed on the first substrate11to protect the first transistors T1of the pixel PX from moisture penetrating through the first substrate11which is vulnerable to moisture permeation and may perform a surface planarization function.

The active layer ACT1may be disposed on the buffer layer12. The active layer ACT1may be disposed to partially overlap a gate electrode G1or a first conductive layer to be described below.

In the drawing, only the first transistor T1among the transistors included in the sub-pixel PXn of the display device10is illustrated in the drawings, but the disclosure is not limited thereto. The display device10may include a larger number of transistors. For example, the display device10may include two or three transistors, including one or more transistors in addition to the first transistor T1, for each sub-pixel PXn.

The active layer ACT1may include polycrystalline silicon, monocrystalline silicon, or an oxide semiconductor. In case that the active layer ACT1includes an oxide semiconductor, the active layer ACT1may include conducting regions and the channel region therebetween. The oxide semiconductor may be an oxide semiconductor containing indium (In). For example, the oxide semiconductor may be indium-tin oxide (ITO), indium-zinc oxide (IZO), indium-gallium oxide (IGO), indium-zinc-tin oxide (IZTO), indium-gallium-tin oxide (IGTO), indium-gallium-zinc oxide (IGZO), or indium-gallium-zinc-tin oxide (IGZTO).

In another embodiment, the active layer ACT1may include polycrystalline silicon. Polycrystalline silicon may be formed by crystallizing amorphous silicon, and in this case, the conducting regions of the active layer ACT1may be regions doped with impurities, respectively.

A first gate insulating layer13may be disposed on the active layer ACT1and the buffer layer12. For example, the first gate insulating layer13may be disposed to entirely cover or overlap the active layer ACT1and the buffer layer12. The first gate insulating layer13may function as a gate insulating film of each transistor.

The first conductive layer may be disposed on the first gate insulating layer13. The first conductive layer may include a gate electrode G1of the first transistor T1and a first capacitive electrode CSE1of the storage capacitor. The gate electrode G1may be disposed to overlap the channel region ACT_c of the active layer ACT1in a thickness direction. The first capacitive electrode CSE1may be disposed to overlap a second capacitive electrode CSE2, which will be described below, in the thickness direction. In an embodiment, the first capacitive electrode CSE1may be integral with the gate electrode G1. The first capacitor electrode CSE1may be disposed to overlap the second capacitor electrode CSE2in the thickness direction, and the storage capacitor may be formed therebetween.

A first interlayer insulating layer15may be disposed on the first conductive layer. The first interlayer insulating layer15may function as an insulating film between the first conductive layer and other layers disposed thereon. The first interlayer insulating layer15may be disposed to overlap the first conductive layer to perform a function of protecting the first conductive layer.

A second conductive layer may be disposed on the first interlayer insulating layer15. The second conductive layer may include a first source electrode S1and a first drain electrode D1of the first transistor T1, a data line DTL, and a second capacitive electrode CSE2.

The first source electrode S1and first drain electrode D1of the first transistor T1may contact the doped regions of the active layer ACT1through contact holes penetrating the first interlayer insulating layer15and the first gate insulating layer13, respectively. Further, the first source electrode S1of the first transistor T1may contact the light blocking layer BML through another contact hole.

The data line DTL may apply a data signal to another transistor (not shown) included in the display device10. Although not shown in the drawings, the data line DTL may be electrically connected to a source/drain electrode of another transistor to transfer a signal applied from the data line DTL.

The second capacitive electrode CSE2may be disposed to overlap the first capacitive electrode CSE1in the thickness direction. In an embodiment, the second capacitive electrode CSE2may be integral with and/or electrically connected to the first source electrode S1.

A second interlayer insulating layer17may be disposed on the second conductive layer. The second interlayer insulating layer17may function as an insulating film between the second conductive layer and other layers disposed thereon. The second interlayer insulating layer17may be disposed to overlap the second conductive layer to perform a function of protecting the second conductive layer.

A third conductive layer may be disposed on the second interlayer insulating layer17. The third conductive layer may include a first voltage line VL1, a second voltage line VL2, and a first conductive pattern CDP. A high-potential voltage (or first power voltage) supplied to the first transistor T1may be applied to first voltage line VL1, and a low-potential voltage (or second power voltage) supplied to the second electrode22may be applied to the second voltage line VL2. During the process of manufacturing the display device10, an alignment signal necessary to align the light emitting elements30may be applied to the second voltage line VL2.

The first conductive pattern CDP may be electrically connected to the second capacitive electrode CSE2through a contact hole formed in the second interlayer insulating layer17. The second capacitive electrode CSE2may be integral with the first source electrode S1of the first transistor T1, and the first conductive pattern CDP may be electrically connected to the first source electrode S1. The first conductive pattern CDP may contact a first electrode21, which will be described below, and the first transistor T1may transfer a first power voltage applied from the first voltage line VL1to the first electrode21through the first conductive pattern CDP. Although it is shown in the drawings that the third conductive layer includes one second voltage line VL2and one first voltage line VL1, the disclosure is not limited thereto. The third conductive layer may include a larger number of first voltage lines VL1and a larger number of second voltage lines VL2.

Each of the buffer layer12, the first gate insulating layer13, the first interlayer insulating layer15, the second interlayer insulating layer17, and a third interlayer insulating layer may be formed of inorganic layers alternately stacked. For example, each of the buffer layer12, the first gate insulating layer13, the first interlayer insulating layer15, and the second interlayer insulating layer17may be formed as double layers in which inorganic layers each including at least one of silicon oxide (SiOx), silicon nitride (SiNx), and silicon oxynitride (SiOxNy), or as multiple layers in which theses inorganic layers are alternately stacked. As another example, each of the above layers may also be formed of an inorganic layer.

A first planarization layer19may be disposed on the third conductive layer. The first planarization layer19may include an organic insulating material, for example, an organic material such as polyimide (PI), to perform a surface planarization function.

First banks BNL1, electrodes21and22, a light emitting element30, contact electrodes CNE1and CNE2, and a second bank BNL2may be arranged on the first planarization layer19. Further, insulating layers PAS1, PAS2, PAS3, and PAS4may be disposed on the first planarization layer19.

The first banks BNL1may be directly disposed on the first planarization layer19. A first bank BNL1may have a shape having a predetermined width and extending in the second direction DR2within each sub-pixel PXn but may not extend to another neighboring sub-pixel PXn in the second direction DR2and may be disposed in the light emitting area EMA. The first banks BNL1may be spaced apart from each other in the first direction DR1.

The first banks BNL1may be disposed in a sub-pixel PXn. Although it is shown in the drawings that two first banks BNL1are disposed for each sub-pixel PXn to form a linear pattern in the display area DPA, the disclosure is not limited thereto. A larger number of first banks BNL1may be arranged depending on the number of electrodes21and22. The number of the first banks BNL1may vary depending on the number of electrodes21and22and the arrangement of the light emitting elements30, or the first banks BNL1may have different shapes to form an island-shaped pattern.

The first bank BNL1may have a structure in which at least a part thereof protrudes from the upper surface of the first planarization layer19. The protruding portion of the first bank BNL1may have an inclined side surface, and the light emitted from the light emitting element30may be reflected from the electrodes21and22disposed on the first bank BNL1and emitted in an upward direction of the first planarization layer19. The first bank BNL1may provide an area in which the light emitting element30is disposed, and may function as a reflective barrier that reflects light emitted from the light emitting element30in an upward direction. The side surface of the first bank BNL1may be inclined in a linear shape but is not limited thereto. For example, the first bank BNL1may have a curved semi-circle or semi-ellipse shape. The first banks BNL1may include an organic insulating material such as polyimide (PI), but the material thereof is not limited thereto. The first banks BNL1may be omitted.

Electrodes21and22may have a shape extending in a direction and may be disposed for each sub-pixel PXn. The electrodes21and22may extend in the second direction DR2and may be disposed to be spaced apart from each other in the first direction DR1. For example, the first electrode21and the second electrode22spaced apart from the first electrode21in the first direction DR1may be disposed in a sub-pixel PXn. However, the disclosure is not limited thereto, and the positions of the electrodes21and22disposed in each sub-pixel PXn may vary depending on the number thereof or the number of light emitting elements30disposed in each sub-pixel PXn.

The first electrode21and the second electrode22may be disposed in the light emitting area EMA of each sub-pixel PXn, and parts thereof may be disposed to overlap the second bank BNL2in the thickness direction beyond the light emitting area EMA. The electrodes21and22may extend in the second direction DR2within the sub-pixel PXn and may be spaced apart from the electrodes21and22of another sub-pixel PXn in the second direction DR2in the cut area CBA.

Each of the first electrode21and the second electrode22may extend in the second direction DR2within the sub-pixel PXn and may be separated from other electrodes21and22in the cut area CBA. For example, the cut area CBA may be disposed between the light emitting areas EMA of the sub-pixels PXn neighboring in the second direction DR2, and the first electrode21and the second electrode22may be separated from other first and second electrodes21and22disposed in the sub-pixels PXn neighboring in the second direction DR2in the cut area CBA. However, the disclosure is not limited thereto. For example, some of the electrodes21and22may be disposed to extend beyond the sub-pixels PXn neighboring in the second direction DR2without being separated from each other for each sub-pixel PXn, or only one of the first electrode21and the second electrode22may be separated.

In the arrangement of the electrodes21and22, electrode lines extending in the second direction DR2may be formed and then be separated from each other in a subsequent process after the light emitting elements30are arranged. The electrode lines may be used to generate an electric field in the sub-pixel PXn in order to align the light emitting elements30during the process of manufacturing the display device10. For example, in case that the light emitting elements30are sprayed on the electrode lines through an inkjet printing process and an ink including the light emitting elements30is sprayed on the electrode lines, an alignment signal may be applied to the electrode lines to generate an electric field. The light emitting elements30dispersed in the ink may be arranged on the electrodes21and22by receiving a dielectrophoretic force by the generated electric field. After the light emitting elements30are arranged, some of the electrode lines may be separated from each other to form electrodes21and22separated in each sub-pixel PXn.

The electrodes21and22may be electrically connected to the third conductive layer such that signals for allowing the light emitting element30to emit light may be applied. The first electrode21may electrically contact the first conductive pattern CDP through a first contact hole CT1penetrating the third interlayer insulating layer under the first electrode21. The second electrode22may electrically contact the second voltage line VL2through a second contact hole CT2penetrating the third interlayer insulating layer under the second electrode22. The first electrode21may be electrically connected to the first transistor T1through the first conductive pattern CDP to apply a first power voltage, and the second electrode22may be electrically connected to the second voltage line VL2to apply a second power voltage.

The electrodes21and22may be electrically connected to the light emitting element30. Each of the electrodes21and22may be electrically connected to the ends of the light emitting element30through the contact electrodes CNE1and CNE2to be described below and may transmit an electric signal applied from the third conductive layer to the light emitting element30. Since the electrodes21and22are disposed separately in each sub-pixel PXn, the light emitting elements30of different sub-pixels PXn may emit light individually.

Although it is illustrated in the drawings that the first contact hole CT1and the second contact hole CT2are formed at a position overlapping the second bank BNL2, the disclosure is not limited thereto. For example, each of the contact holes CT1and CT2may be located in the light emitting area EMA surrounded by the second bank BNL2.

The electrodes21and22disposed in each sub-pixel PXn may be disposed on the first banks BNL1spaced apart from each other. Each of the electrodes21and22may be disposed on an inclined side surface of the first bank BNL1in the first direction DR1. In an embodiment, the width of the electrodes21and22measured in the first direction DR1may be smaller than the width of the first bank BNL1measured in the first direction DR1. Each of the electrodes21and22may be disposed to overlap at least one side of the first bank BNL1to reflect light emitted from the light emitting element30.

The distance between the electrodes21and22spaced apart from each other in the first direction DR1may be smaller than the distance between the first banks BNL1. Each of the electrodes21and22may have at least some regions directly disposed on the third interlayer insulating layer such that the electrodes21and22may be disposed on the same plane or layer.

Each of the electrodes21and22may include a conductive material having a high reflectance. For example, each of the electrodes21and22may include a metal such as silver (Ag), copper (Cu), or aluminum (Al) as the conductive material having a high reflectance or may include an alloy containing aluminum (Al), nickel (Ni), or lanthanum (La). Each of the electrodes21and22may reflect the light emitted from the light emitting element30and proceeding to the side surface of the first bank BNL1in the upward direction of each sub-pixel PXn.

However, the disclosure is not limited thereto, and each of the electrodes21and22may further include a transparent conductive material. For example, each of the electrodes21and22may include a material such as indium tin oxide (ITO), indium zinc oxide (IZO), or indium tin zinc oxide (ITZO). In some embodiments, each of the electrodes21and22may have a structure in which one or more transparent conductive material layers and one or more metal layers having high reflectivity are stacked or may be formed as a layer including them. For example, each of the electrodes21and22may have a stacked structure of ITO/Ag/ITO/, ITO/Ag/IZO, or ITO/Ag/ITZO/IZO.

The first insulating layer PAS1may be disposed on the electrodes21and22and the first bank BNL1. The first insulating layer PAS1may be disposed to overlap the first banks BNL1and the first and second electrodes21and22and may be disposed to expose a part of the upper surface of the first electrode21and a part of the upper surface of the second electrode22. An opening OP may be formed to expose a portion of the upper surfaces of the electrodes21and22that is disposed on the first bank BNL1, and the contact electrodes CNE1and CNE2may electrically contact the electrodes21and22through the opening OP.

In an embodiment, a step or height difference may be formed in the first insulating layer PAS1such that a part of the upper surface of the first insulating layer PAS1is recessed between the first electrode21and the second electrode22. As the first insulating layer PAS1is disposed to cover or overlap the first electrode21and the second electrode22, the first insulating layer PAS1may have a height difference between the first electrode21and the second electrode22. However, the disclosure is not limited thereto. The first insulating layer PAS1may protect the first electrode21and the second electrode22and insulate them from each other. Further, the first insulating layer PAS1may prevent the light emitting element30disposed on the first insulating layer PAS1from being damaged by direct contact with other members.

A second bank BNL2may be disposed on the first insulating layer PAS1. The second bank BNL2may be disposed in a lattice pattern on the entire surface of the display area DPA while including portions extending in the first direction DR1and the second direction DR2on a plane (or a layer). The second bank BNL2may be disposed over the boundary between the respective sub-pixels PXn to distinguish neighboring sub-pixels PXn. Further, the second bank BNL2may be disposed to surround the light emitting area EMA and the cut area CBA disposed in each sub-pixel PXn to distinguish the light emitting area EMA and the cut area CBA. In the portion of the second bank BNL2extending in the second direction DR2, the portion disposed between the light emitting areas EMA may have a greater width than the portion disposed between the cut areas CBA. Accordingly, the distance between the cut areas CBA may be smaller than the distance between the light emitting areas EMA.

The second bank BNL2may be formed to have a height greater than that of the first bank BNL1. The second bank BNL2may prevent ink from overflowing to adjacent sub-pixels PXn in an inkjet printing process of the process of manufacturing the display device10, so that inks in which different light emitting elements30are dispersed for each pixel PXn may be separated from each other and not be mixed with each other. Similar to the first bank BNL1, the second bank BNL2may include polyimide (PI), but the material thereof is not limited thereto.

The light emitting element30may be disposed on the first insulating layer PAS1. The light emitting elements30may be arranged to be spaced apart from each other in the second direction DR2in which the electrodes21and22extend and may be aligned substantially parallel to each other. The light emitting element30may have a shape extending in a direction. The direction in which each of the electrodes21and22extends may be substantially perpendicular to the direction in which the light emitting element30extends. However, the disclosure is not limited thereto. For example, the light emitting element30may be disposed obliquely at a predetermined angle such that it does not extend perpendicular to the direction in which each of the electrodes21and22extends.

The light emitting element30may include semiconductor layers doped with different conductivity types of dopants. The light emitting element30may include semiconductor layers and may be aligned such that an end of the light emitting element30faces in a specific direction according to the direction of an electric field generated on the electrodes21and22. The light emitting element30may include a light emitting layer36(seeFIG.4) to emit light of a specific wavelength band. The light emitting elements30disposed in each sub-pixel PXn may emit light of different wavelength bands according to a material forming the light emitting layer36. However, the disclosure is not limited thereto. For example, the light emitting elements30disposed in each of the sub-pixels PXn may emit light of the same color.

The light emitting element30may be provided with layers in a direction perpendicular to the upper surface of the first substrate11. The light emitting element30of the display device10may be disposed such that an extending direction thereof is parallel to the upper surface of the first substrate11, and the semiconductor layers included in the light emitting element30may be sequentially arranged in a direction parallel to the upper surface of the first substrate11. However, the disclosure is not limited thereto. In some cases, in case that the light emitting element30has a different structure, the semiconductor layers may be arranged in a direction perpendicular to the upper surface of the first substrate11.

The light emitting element30may be disposed on each of the electrodes21and22between the first banks BNL1. For example, the light emitting element30may be disposed such that one end thereof is placed on the first electrode21and the other end thereof is placed on the second electrode22. The elongated length of the light emitting element30may be greater than the distance between the first electrode21and the second electrode22, and both ends of the light emitting element30may be disposed on the first electrode21and the second electrode22.

Both ends of the light emitting element30may electrically contact the contact electrodes CNE1and CNE2, respectively. Since the light emitting element30may not be provided with an insulating film38(seeFIG.4) on an end surface in a direction, and a part of the semiconductor layer may be exposed, the exposed semiconductor layer may contact the contact electrodes CNE1and CNE2. However, the disclosure is not limited thereto. In some cases, at least a part of the insulating film38may be removed, so that side surfaces of ends of the semiconductor layers may be partially exposed. The exposed side surfaces of the semiconductor layers may directly contact the contact electrodes CNE1and CNE2.

The second insulating layer PAS2may be partially disposed on the first insulating layer PAS1and the light emitting element30. For example, the second insulating layer PAS2may be disposed to partially surround the outer surface of the light emitting element30not to cover or overlap the end and the other end of the light emitting element30. The shape of the second insulating layer PAS2may be formed by a process of entirely placing the second insulating layer PAS2on the first insulating layer PAS1and then removing the second insulating layer PAS2to expose both ends of the light emitting element30during the process of manufacturing the display device10.

A portion of the second insulating layer PAS2disposed on the light emitting element30may be disposed to extend in the second direction DR2on the first insulating layer PAS1on the plane (or layer), thereby forming a linear or island-shaped pattern in each sub-pixel PXn. The second insulating layer PAS2may protect the light emitting element30and fix the light emitting element30in the process of manufacturing the display device10. The second insulating layer PAS2may be disposed to fill the space between the light emitting element30and the first insulating layer PAS1under the light emitting element30.

The contact electrodes CNE1and CNE2and the third insulating layer PAS3may be disposed on the second insulating layer PAS2. The first contact electrode CNE1and the second contact electrode CNE2of the contact electrodes CNE1and CNE2may be disposed on a part of the first electrode21and a part of the second electrode22, respectively. The first contact electrode CNE1may be disposed on the first electrode21, the second contact electrode CNE2may be disposed on the second electrode22, and each of the first contact electrode CNE1and the second contact electrode CNE2may have a shape extending in the second direction DR2. The first contact electrode CNE1and the second contact electrode CNE2may be spaced apart from each other in the first direction DR1and may form a linear pattern in the light emitting area EMA of each sub-pixel PXn.

Each of the contact electrodes CNE1and CNE2may electrically contact the light emitting element30and the electrodes21and22. In the light emitting element30, a semiconductor layer is exposed on both end surfaces in an extending direction, and the first contact electrode CNE1and the second contact electrode CNE2may electrically contact the light emitting element30on the end surface where the semiconductor layer is exposed. The end of the light emitting element30may be electrically connected to the first electrode21through the first contact electrode CNE1, and the other end thereof may be electrically connected to the second electrode22through the second contact electrode CNE2.

Although it is shown in the drawings that a first contact electrode CNE1and a second contact electrode CNE2are disposed in a sub-pixel PXn, the disclosure is not limited thereto. The numbers of first and second contact electrodes CNE1and CNE2may be changed depending on the numbers of electrodes21and22disposed in each sub-pixel PXn.

The contact electrodes CNE1and CNE2may include a conductive material. For example, the contact electrodes CNE1and CNE2may include ITO, IZO, ITZO, or aluminum (Al). The light emitted from the light emitting element30may pass through the contact electrodes CNE1and CNE2and proceed toward the electrodes21and22. However, the disclosure is not limited thereto.

The third insulating layer PAS3may be disposed between the first contact electrode CNE1and the second contact electrode CNE2. The third insulating layer PAS3may also be disposed on the first contact electrode CNE1and the second insulating layer PAS2, except for an area where the second contact electrode CNE2is disposed. The third insulating layer PAS3may insulate the first contact electrode CNE1and the second contact electrode CNE2from each other such that they do not directly contact each other. For example, in an embodiment, the first contact electrode CNE1and the second contact electrode CNE2may be disposed on different layers. The first contact electrode CNE1may be directly disposed on the second insulating layer PAS2, and the second contact electrode CNE2may be disposed directly on the third insulating layer PAS3.

Although the third insulating layer PAS3is disposed between the first contact electrode CNE1and the second contact electrode CNE2to insulate them from each other, as described above, the third insulating layer PAS3may be omitted. In this case, the first contact electrode CNE1and the second contact electrode CNE2may be disposed on the same layer.

A fourth insulating layer PAS4may be entirely disposed on the display area DPA of the first substrate11. The fourth insulating layer PAS4may function to protect members disposed on the first substrate11from external environments. However, the fourth insulating layer PAS4may be omitted.

Each of the above-described first insulating layer PAS1, second insulating layer PAS2, third insulating layer PAS3, and fourth insulating layer PAS4may include an inorganic insulating material or an organic insulating material. For example, each of the first insulating layer PAS1, the second insulating layer PAS2, the third insulating layer PAS3, and the fourth insulating layer PAS4may include an inorganic insulating layer such as silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiOxNy), aluminum oxide (Al2O3), or aluminum nitride (AlNx). As another example, each of the first insulating layer PAS1, the second insulating layer PAS2, the third insulating layer PAS3, and the fourth insulating layer PAS4may include an organic insulating layer such as acrylic resin, epoxy resin, phenol resin, polyamide resin, polyimide resin, unsaturated polyester resin, polyphenylene resin, polyphenylene sulfide resin, benzocyclobutene, cardo resin, siloxane resin, silsesquioxane resin, polymethyl methacrylate, polycarbonate, or polymethyl methacrylate-polycarbonate synthetic resin. However, the disclosure is not limited thereto.

FIG.4is a schematic perspective view of a light emitting element according to an embodiment.

The light emitting element30may be a light emitting diode. Specifically, the light emitting element30may be an inorganic light emitting diode having a size of a micrometer or a nanometer and made of an inorganic material. In case that an electric field is formed between two electrodes facing each other in a predetermined direction, the organic light emitting diode may be aligned between the two electrodes having polarities. The light emitting element30may be aligned between the two electrodes by the electric field formed on the two electrodes.

The light emitting element30may have a shape extending in a direction. The light emitting element30may have a shape of a cylinder, a rod, a wire, or a tube. However, the shape of the light emitting element30is not limited thereto, and the light emitting element30may have various shapes such as a cube, a cuboid, and a hexagonal column, or may have a shape extending in a direction and having a partially inclined outer surface. Semiconductors included in the light emitting element30to be described below may be sequentially arranged or stacked in a direction.

The light emitting element30may include semiconductor layers doped with impurities of any conductive type (for example, p-type or n-type). The semiconductor layers may receive an electrical signal applied from an external power source and emit light of a specific wavelength band.

Referring toFIG.4, the light emitting element30may include a first semiconductor layer31, a second semiconductor layer32, a light emitting layer36, an electrode layer37, and an insulating film38.

The first semiconductor layer31may be an n-type semiconductor layer. In case that the light emitting element30emits light of a blue wavelength band, the first semiconductor layer31may include a semiconductor material having a chemical formula of AlxGayIn1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, the semiconductor material may be at least one of AlGaInN, GaN, AlGaN, InGaN, AlN, and InN, each being doped with n-type impurities. The first semiconductor layer31may be doped with an n-type dopant. The n-type dopant may be Si, Ge, or Sn. For example, the first semiconductor layer31may be n-GaN doped with n-type Si. The length of the first semiconductor layer31may be in a range of about 1.5 μm to about 5 μm but is not limited thereto.

The second semiconductor layer32may be disposed on the light emitting layer36to be described below. The second semiconductor layer32may be a p-type semiconductor layer. In case that the light emitting element30emits light of a blue wavelength band or a green wavelength band, the second semiconductor layer32may include a semiconductor material having a chemical formula of AlxGayIn1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, the semiconductor material may be at least one of AlGaInN, GaN, AlGaN, InGaN, AlN, and InN, each being doped with p-type impurities. The second semiconductor layer32may be doped with a p-type dopant. The p-type dopant may be Mg, Zn, Ca, Se, or Ba. For example, the second conductive semiconductor320may be p-GaN doped with p-type Mg. The length of the second semiconductor layer32may be in a range of about 0.05 μm to about 0.10 μm but is not limited thereto.

Although it is shown inFIG.4that each of the first semiconductor layer31and the second semiconductor layer32is formed as a layer, the disclosure is not limited thereto. Each of the first semiconductor layer31and the second semiconductor layer32may further include a larger number of layers, for example, clad layers or tensile strain barrier reducing (TSBR) layers according to the material of the light emitting layer36.

The light emitting layer36may be disposed between the first semiconductor layer31and the second semiconductor layer32. The light emitting layer36may include a material of a single or multiple quantum well structure. In case that the light emitting layer36includes a material of a multiple quantum well structure, the light emitting layer36may have a structure in which quantum layers and well layers are alternately stacked. The light emitting layer36may emit light by the combination of electron-hole pairs according to an electrical signal applied through the first semiconductor layer31and the second semiconductor layer32. In case that the light emitting layer36emits light of a blue wavelength band, the light emitting layer36may include a material such as AlGaN or AlGaInN. In particular, in case that the light emitting layer36has a multiple quantum well structure in which quantum layers and well layers are alternately stacked, the quantum wells may include a material such as AlGaN or AlGaInN, and the well layers may include a material such as GaN or AlInN. For example, the light emitting layer36may include quantum wells each containing AlGaInN and well layers each containing AlInN, and thus the light emitting layer36may emit blue light having a central wavelength band of about 450 nm to about 495 nm as described above.

However, the disclosure is not limited thereto, and the light emitting layer36may have a structure in which semiconductor materials having a high bandgap energy and semiconductor materials having a low bandgap energy are alternately stacked and may include other group III to group V semiconductor materials depending on the wavelength band of light. The light emitted from the light emitting layer36is not limited to light of a blue wavelength band, and in some cases, the light emitting layer36may emit light of a red or green wavelength band. The length of the light emitting layer36may be in a range of about 0.05 μm to about 0.10 μm but is not limited thereto.

The light emitted from the light emitting layer36may be emitted to both side surfaces of the light emitting element30as well as the longitudinal outer surface of the light emitting element30. The direction of the light emitted from the light emitting layer36is not limited to a direction.

The electrode layer37may be an ohmic contact electrode. However, the disclosure is not limited thereto, and the electrode layer37may be a Schottky contact electrode. The light emitting element30may include at least one electrode layer37. Although it is shown inFIG.4that the light emitting element30includes an electrode layer37, the disclosure is not limited thereto. In some cases, the light emitting element30may include a larger number of electrode layers37, or the electrode layer37may be omitted. A description of the light emitting element30to be described below may be equally applied even if the number of electrode layers37is changed or the light emitting element30further includes other structures.

In case that the light emitting element30is electrically connected to an electrode or a contact electrode in the display device10according to an embodiment, the electrode layer37may reduce the resistance between the light emitting element30and the electrode or the contact electrode. The electrode layer37may include a conductive metal. For example, the electrode layer37may include at least one of aluminum (Al), titanium (Ti), indium (In), gold (Au), silver (Ag), indium tin oxide (ITO), indium zinc oxide (IZO), and indium tin-zinc oxide (ITZO). The electrode layer37may include a semiconductor material doped with n-type or p-type impurities. However, the disclosure is not limited thereto.

The insulating film38may be disposed to surround the outer surfaces of the above-described semiconductor layers and electrode layers. For example, the insulating film38may be disposed to surround at least the outer surface of the light emitting layer36and may extend in a direction in which the light emitting element30extends. The insulating film38may function to protect the members. For example, the insulating film38may be formed to surround the side surfaces of the members and may be formed such that both ends of the light emitting element30in a length direction are exposed.

Although it is shown inFIG.5that the insulating film38may extend in the length direction of the light emitting element30to cover or overlap the first semiconductor layer31to the side surface of the electrode layer37, the disclosure is not limited thereto. The insulating film38may overlap only the outer surface of a part of the semiconductor layer as well as the active layer330or overlap only a part of the outer surface of the electrode layer37to expose a part of the outer surface of the electrode layer37. The insulating film38may be formed to have a rounded cross-sectional upper surface in an area adjacent to at least one end of the light emitting element30.

The thickness of the insulating film38may be in a range of about 10 nm to about 1.0 μm but is not limited thereto. The thickness of the insulating film38may be about 40 nm.

The insulating film38may include a material having insulating properties, for example, silicon oxide (SiOx), silicon nitride (SiNx), silicon oxynitride (SiOxNy), aluminum nitride (AlNx), or aluminum oxide (AlOx). Thus, the light emitting layer36may prevent an electrical short that may occur in case that the light emitting layer36is directly contact an electrode through which an electrical signal is transmitted to the light emitting element30. Further, since the insulating film380protects the outer surface of the light emitting element30as well as the light emitting layer36, it is possible to prevent the deterioration in light emission efficiency.

Further, the outer surface of the insulating film38may be surface-treated. The light emitting elements30may be aligned by being sprayed onto the electrodes in a state in which they are dispersed in a predetermined ink. Here, the surface of the insulating film38may be hydrophobically or hydrophilically treated in order to maintain the light emitting elements30in a dispersed state without being aggregated with other adjacent light emitting elements30in the ink. For example, the outer surface of the insulating film38may be surface-treated with a material such as stearic acid or 2,3-naphthalene dicarboxylic acid.

The length h of the light emitting element30may be in a range of about 1 μm to about 10 μm, about 2 μm to about 6 μm, or about 3 μm to about 5 μm. The diameter of the light emitting element30may be in a range of about 30 nm to about 700 nm, and the aspect ratio of the light emitting element30may be in a range of about 1.2 to about 100. However, the disclosure is not limited thereto, and the light emitting elements30included in the display device10may have different diameters according to the composition difference of the light emitting layer36. For example, the diameter of the light emitting element30may be about 500 nm.

The shape and material of the light emitting element30is not limited to those ofFIG.4. In some embodiments, light emitting element30may include a larger number of layers or may have a different shape.

FIGS.5and6are schematic perspective views of light emitting elements according to other embodiments.

First, referring toFIG.5, a light emitting element30′ according to an embodiment may further include a third semiconductor layer33′ disposed between a first semiconductor layer31′ and a light emitting layer36′, a fourth semiconductor layer34′ and a fifth semiconductor layer35′ disposed between a light emitting layer36′ and a second semiconductor layer32′, and an insulating film38′. The light emitting element30′ ofFIG.5may be different from the light emitting element30ofFIG.4at least in that the semiconductor layers33′,34′,35′ and electrode layers37a′ and37b′ are further provided, and the light emitting layer36′ includes different elements. Hereinafter, repetitive descriptions thereof will be omitted, and differences therebetween will be mainly described.

In the light emitting element30ofFIG.4, the light emitting layer36may include nitrogen (N) to emit blue or green light. In contrast, in the light emitting element30′ ofFIG.5, the light emitting layer36′ and other semiconductor layers may be semiconductor layers each including at least phosphorus (P). The light emitting element30′ according to an embodiment may emit red light having a center wavelength band in a range of about 620 nm to about 750 nm. However, it should be understood that the central wavelength band of red light is not limited to the above-described range and may include all wavelength ranges that can be recognized as red in the art.

Specifically, the first semiconductor layer31′ may be an n-type semiconductor layer and may include a semiconductor material having a chemical formula of InxAlyGa1-x-yP (0≤x≤1, 0≤y≤1, 0≤x+y≤1). The first semiconductor layer31′ may include at least one of InAlGaP, GaP, AlGaP, InGaP, AlP, and InP, which are doped with n-type impurities. For example, the first semiconductor layer31′ may include n-AlGaInP doped with n-type Si.

The second semiconductor layer32′ may be a p-type semiconductor layer and may include a semiconductor material having a chemical formula of InxAlyGa1-x-yP (0≤x≤1, 0≤y≤1, 0≤x+y≤1). The second semiconductor layer32′ may include at least one of InAlGaP, GaP, AlGaNP, InGaP, AlP, and InP, which are doped with p-type impurities. For example, the second semiconductor layer32′ may include p-GaP doped with p-type Mg.

The light emitting layer36′ may be disposed between the first semiconductor layer31′ and the second semiconductor layer32′. The light emitting layer36′ may include a material having a single or multiple quantum well structure to emit light of a specific wavelength band. In case that the light emitting layer36′ has a multiple quantum well structure in which quantum layers and well layers are alternately stacked, the quantum layer may include a material such as AlGaP or AlInGaP, and the well layer may include a material such as GaP or AlInP. For example, the light emitting layer36′ may include the quantum layer including AlGaInP and the well layer including AlInP to emit red light having a central wavelength band of about 620 nm to about 750 nm.

The light emitting element30′ ofFIG.5may include a clad layer disposed adjacent to the light emitting layer36′. As shown inFIG.5, the third semiconductor layer33′ and the fourth semiconductor layer34′ disposed between the first semiconductor layer31′ and the second semiconductor layer32′ and disposed on and beneath the light emitting layer36′ may be clad layers.

The third semiconductor layer33′ may be disposed between the first semiconductor layer31′ and the light emitting layer36′. Similar to the first semiconductor layer31′, the third semiconductor layer33′ may be an n-type semiconductor layer and may include a semiconductor material having a chemical formula of InxAlyGa1-x-yP (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, the first semiconductor layer31′ may include n-AlGaInP, and the third semiconductor layer33′ may include n-AlInP.

The fourth semiconductor layer34′ may be disposed between the light emitting layer36′ and the second semiconductor layer32′. Similar to the second semiconductor layer32′, the fourth semiconductor layer34′ may be a p-type semiconductor layer and may include a semiconductor material having a chemical formula of InxAlyGa1-x-yP (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, the second semiconductor layer32′ may include p-GaP, and the fourth semiconductor layer34′ may include p-AlInP.

The fifth semiconductor layer35′ may be disposed between the fourth semiconductor layer34′ and the second semiconductor layer32′. Similar to the second semiconductor layer32′ and the fourth semiconductor layer34′, the fifth semiconductor layer35′ may be a p-type semiconductor layer. In some embodiments, the fifth semiconductor layer35′ may function to reduce a difference in lattice constant between the fourth semiconductor layer34′ and the second semiconductor layer32′. The fifth semiconductor layer35′ may be a tensile strain barrier reducing (TSBR) layer. For example, the fifth semiconductor layer35′ may include p-GaInP, p-AlInP, or p-AlGaInP, but the material thereof is not limited thereto. The length of each of the third semiconductor layer33′, the fourth semiconductor layer34′, and the fifth semiconductor layer35′ may be in a range of about 0.08 μm to about 0.25 μm but is not limited thereto.

The first electrode layer37a′ and the second electrode layer37b′ may be disposed on the first semiconductor layer31′ and the second semiconductor layer32′, respectively. The first electrode layer37a′ may be disposed on the lower surface of the first semiconductor layer31′, and the second electrode layer37b′ may be disposed on the upper surface of the second semiconductor layer32′. However, the disclosure is not limited thereto, and at least one of the first electrode layer37a′ and the second electrode layer37b′ may be omitted. For example, in the light emitting element30′, the first electrode layer37a′ may not be disposed on the lower surface of the first semiconductor layer31′, and only one second electrode layer37b′ may be disposed on the upper surface of the second semiconductor layer32′.

Subsequently, referring toFIG.6, a light emitting element30″ may30″ may have a shape extending in a direction, but may have a partially inclined side surface. For example, the light emitting element30″ according to an embodiment may have a partially conical shape.

The light emitting element30″ may be formed such that layers are not stacked in a direction and each layer surrounds the outer surface of another layer. The light emitting element30″ may include a semiconductor core having at least some regions extending in a direction and an insulating film38″ formed to surround the semiconductor core. The semiconductor core may include a first semiconductor layer31″, a light emitting layer36″, a second semiconductor layer32″, and an electrode layer37″.

The first semiconductor layer31″ may extend in a direction, and both end portions thereof may be formed to be inclined toward the centers thereof. The first semiconductor layer31″ may include a body portion having a rod shape or a cylindrical shape, and upper and lower end portions having inclined side surfaces and respectively formed on and under the body portion. The upper end portion of the body portion may have a slope steeper than the lower end portion.

The light emitting layer36″ may disposed to surround the outer surface of the body portion of the first semiconductor layer31″. The light emitting layer36″ may have an annular shape extending in a direction. The light emitting layer36″ may not be formed on the upper and lower end portions of the first semiconductor layer31″. However, the disclosure is not limited thereto. The light emitted from the light emitting layer36″ may be emitted to both side surfaces of the light emitting element30″ in a length direction as well as to both ends of the light emitting element30″ in the length direction. Compared to the light emitting element30ofFIG.4, the light emitting element30″ ofFIG.6may include the light emitting layer36″ having a large area and may thus emit a larger amount of light.

The second semiconductor layer32″ may be disposed to surround the outer surface of the light emitting layer36″ and the upper end portion of the first semiconductor layer31″. The second semiconductor layer32″ may include an annular body portion extending in a direction and an upper end portion having an inclined side surface. For example, the second semiconductor layer32″ may directly contact the parallel side surface of the light emitting layer36″ and the inclined upper end portion of the first semiconductor layer31″. However, the second semiconductor layer32″ is not formed on the lower end portion of the first semiconductor layer31″.

The electrode layer37″ may be disposed to surround the outer surface of the second semiconductor layer32″. The shape of the electrode layer37″ may be substantially identical to the shape of the second semiconductor layer32″. The electrode layer37″ may entirely contact the outer surface of the second semiconductor layer32″.

The insulating film38″ may be disposed to surround the outer surfaces of the electrode layer37″ and the first semiconductor layer31″. The insulating film38″ may directly contact the lower end portion of the first semiconductor layer31″ and the exposed lower portions of the light emitting layer36″ and the second semiconductor layer32″ as well as the electrode layer37″.

The light emitting elements30may be sprayed onto each of the electrodes21and22by an inkjet printing process. The light emitting elements30may be dispersed in a solvent to be prepared in an ink state and sprayed onto the electrodes21and22and may be disposed between the electrodes21and22by a process of applying an alignment signal to the electrodes21and22. In case that an alignment signal is applied to each of the electrodes21and22, an electric field may be formed thereon, and the light emitting element30may receive a dielectrophoretic force by the electric field. The light emitting element30having received the dielectrophoretic force may be disposed on the first electrode21and the second electrode22while the alignment direction and position of the light emitting element30are changed.

The light emitting element30may include semiconductor layers and may be generally made of (or include) a material having a specific gravity greater than that of a solvent. When the light emitting elements30are dispersed and stored in a solvent, the dispersion may be maintained for a predetermined period of time and then be gradually precipitated because of the difference in specific gravity. When the light emitting elements30are precipitated in the solvent, the number of light emitting elements30per ink droplet is not uniform. Therefore, when a device including the light emitting element30is manufactured using the ink, the number of light emitting elements30for each area is not constant, and thus the quality of products may be deteriorated.

According to an embodiment, the ink including the light emitting elements30may further include a thickener500(seeFIG.7), and thus viscosity of the ink may change according to the temperature of the solution. The ink including the light emitting elements30may have a high viscosity in a state in which the ink is stored in a container, or at room temperature, and thus the light emitting elements30may be stored in a dispersed state for a long time. Further, in case that the ink including the light emitting elements30is discharged through a nozzle in an inkjet printing process, the temperature of a nozzle of an inkjet printing apparatus may be adjusted to reduce the viscosity of the ink, and thus the ink may be readily discharged through the nozzle. Therefore, according to an embodiment, the ink including the light emitting elements30may be sprayed by including a uniform number of light emitting elements30in a unit area by a printing process while preventing precipitation of the light emitting element30. Hereinafter, the ink including the light emitting elements30will be described.

FIG.7is a schematic perspective view of a light emitting element ink according to an embodiment.

Referring toFIG.7, a light emitting element ink1000according to an embodiment may include a light emitting element solvent100, light emitting elements30dispersed in the light emitting element solvent100, and thickeners500. The light emitting element30may be one of the light emitting elements30,30′, and30″ described above with reference toFIGS.4to6, and the light emitting element30ofFIG.4is illustrated in the drawings. Since the description of the light emitting element30is the same as that described above, the light emitting element solvent100and the thickener500will be described in detail below.

The light emitting element solvent100may store the light emitting elements30having a high specific gravity, including semiconductor layers, in a dispersed state, and may be an organic solvent that does not react with the light emitting elements30. The light emitting element solvent100may have a viscosity sufficient to be discharged through a nozzle of an inkjet printing apparatus in a liquid state. The solvent molecules of the light emitting element solvent100may disperse the light emitting elements30while surrounding the surfaces of the light emitting elements30. The light emitting element ink1000may include the light emitting elements30to be prepared in a solution or colloid state. In an embodiment, examples of the light emitting element solvent100may include, but are not limited to, acetone, water, alcohol, toluene, propylene glycol (PG) or propylene glycol methyl acetate (PGMA), triethylene glycol monobutyl ether (TGBE), diethylene glycol monophenyl ether (DGPE), amide-based solvents, dicarbonyl-based solvents, diethylene glycol dibenzoate, tricarbonyl-based solvents, triethyl citrate, phthalate-based solvents, benzyl butyl phthalate, bis(2-ethylhexyl) phthalate, bis(2-ethylhexyl) isophthalate, bis(2-ethylhexyl) isophthalate, and ethylphthalyl ethyl glycolate. Examples of more various light emitting element solvents100will be described below.

In the specification, the term “light emitting element solvent100” refers to a solvent in which the light emitting elements30may be dispersed, or a medium thereof, and the term “solvent molecule101” refers to a molecule that is included in the light emitting element solvent100. For example, it may be understood that the term “light emitting element solvent100” is a liquid solvent including the solvent molecules101. However, these terms may not necessarily be used separately, and in some cases, the terms “light emitting element solvent100” and “solvent molecule101” are used interchangeably but may be substantially the same.

The thickeners500may be dispersed in the light emitting element solvent100together with the light emitting elements30. A predetermined amount of the thickeners500may be included in the light emitting element ink1000to change the viscosity of the solution according to the temperature of the light emitting element ink1000. According to an embodiment, the thickener500may be a polyol-based compound including a functional group capable of forming a hydrogen bond. The thickener500may form a hydrogen bond between the solvent molecules101or the thickeners500of the light emitting element solvent100to form a relatively strong attraction force between different molecules.

FIG.8is a schematic diagram illustrating an intermolecular bond between a thickener and a light emitting element solvent in the light emitting element ink ofFIG.7at room temperature.FIG.8is an enlarged view of area A ofFIG.7and illustrates the form of a molecule of the thickener500dispersed in the light emitting element solvent100in a state of the light emitting element ink1000is stored at room temperature or 25° C. In the specification, the term “room temperature” generally refers to about 25° C., but may refer to a temperature around the same, including 25° C. For example, the term “room temperature” may include a temperature in a range of about 20° C. to about 30° C.

Referring toFIG.8, the thickener500may include a hydroxyl group (—OH) as a polyol-based compound capable of forming a hydrogen bond. The thickener500may include a main chain portion CP to which at least one hydroxyl group (—OH) is bonded. The main chain portion CP may be a carbon chain such as an alkyl group, an alkenyl group, or an alkynyl group, but is not limited thereto, and may further include other functional groups such as an ether group (—O—). In a thickener500, the hydroxyl group (—OH) may form a hydrogen bond HB with a solvent molecule101of the light emitting element solvent100or an atom, for example, oxygen (O) or nitrogen (N), having a non-covalent electron pair of the hydroxyl group (—OH) of another thickener500. According to an embodiment, the thickener500may form a hydrogen bond with a molecule of another thickener500or the solvent molecule101and may form a network structure between the main chain portion CP and the solvent molecule101and between the main chain portions CP of other thickeners500at the room temperature of about 25° C. The light emitting element ink1000may have a high viscosity because of the network structure formed by the thickeners500, and the precipitation rate of the light emitting elements30may decrease in a state in which the light emitting element ink1000is stored.

For example, the light emitting element ink1000may have a viscosity in a range of about 30 cP to about 300 cP, measured at the room temperature (about 25° C.). In order to prevent the precipitation of the light emitting elements30, the light emitting element ink1000may have a viscosity of at least about 20 cP or greater in a state in which no shear stress is applied. In the light emitting element ink1000, the light emitting elements30may be kept in a dispersed state for a long time until a printing process using an inkjet printing apparatus. However, the disclosure is not limited thereto. The viscosity of the light emitting element ink1000may be adjusted within the range of 20 Cp or greater through the molecular structure and molecular weight of the thickener500.

According to an embodiment, in the thickener500of the light emitting element solvent1000, the main chain portion CP to which at least one hydroxyl group (—OH) is bonded may be a substituted or unsubstituted alkyl group, alkene group, alkenyl group, or alkyl ether group, having 2 or more carbon atoms.

In some embodiments, the thickener500of the light emitting element ink1000may include a structure represented by Chemical Structural Formula 1 below.

In Chemical Structural Formula 1 above, R1may be a linear or branched alkyl group or alkyl ether having 1 to 3,000 carbon atoms, which is substituted with a hydroxyl group (—OH) or is unsubstituted, and I may be an integer of 1 to 10. The thickener500, which is a polyol-based compound, may form a hydrogen bond with the light emitting element solvent100, and the light emitting element ink1000may have a specific viscosity and boiling point.

In an embodiment, the thickener500of the light emitting element ink1000may be a compound represented by one of Formulas 1 to 8 below.

In Chemical Formulas 7 and 8 above, n may be an integer of 1 to 1,000.

Each of the compounds of Chemical Formulas 1 to 8 may include a main chain portion CP including a carbon chain or an alkyl ether group, and at least one hydroxyl group (—OH) bonded to the main chain portion CP. The hydroxyl group (—OH) of the thickener500may form a hydrogen bond with oxygen (O) or hydrogen (H) contained in another thickener500or the solvent molecule101of the light emitting element solvent100. In case that the light emitting element ink1000is stored at the room temperature, the thickener500may form a network structure through a hydrogen bond between molecules, and the light emitting element ink1000may have a high viscosity. Since the thickener500is a compound of one of Formulas 1 to 8, the thickener500itself may have a high boiling point at the room temperature. In an embodiment, the thickener500may have a boiling point in a range of about 200° C. to about 450° C. and may have a boiling point of about 350° C. However, the disclosure is not limited thereto. The light emitting element ink1000according to an embodiment may include the light emitting elements30and the thickener500having a relatively high specific gravity to prevent the precipitation of the light emitting elements30even at the room temperature.

As the structure of the thickener500, the above Chemical Formulas 1 to 8 have been discussed, but the disclosure is not limited thereto. In some embodiments, in case that the thickener500is a polyol-based compound including at least one hydroxyl group (—OH), the main chain portion CP of the thickener500may further be substituted with other substituents. For example, the main chain portion CP of the thickener500may further be substituted with functional groups including a halogen group, an ethoxy group, a thiol group, or a sulfanyl ethanol group.

Further, according to an embodiment, in order for the light emitting element solvent100of the light emitting element ink1000to have a high viscosity at the room temperature through a hydrogen bond with the thickener500, the light emitting element solvent100may also include a functional group capable of forming a hydrogen bond. For example, similarly to the thickener500, the solvent molecule101of the light emitting element solvent100may include at least one hydroxyl group (—OH) or may include an element such as oxygen (O), nitrogen (N), or fluorine (F) that may form a hydrogen bond with hydrogen (H) of the hydroxyl group (—OH) included in the thickener500. However, the light emitting element solvent100may have a structure to have a viscosity sufficient to disperse the light emitting elements30.

In an embodiment, the solvent molecule101of the light emitting element solvent100of the light emitting element ink1000may have a structure of Chemical Structural Formula 2 below as a structure including a benzene ring.

In Chemical Structural Formula 2 above, R2may include at least one of substituted or unsubstituted alcohol group, ether group, and ester group, each having 2 to 10 carbon atoms, and m may be an integer of 1 or 2. The solvent molecule101of the light emitting element solvent100may have a structure in which a benzene ring is substituted with at least one functional group of an alcohol group, an ether group, and an ester group as a functional group capable of forming a hydrogen bond with the hydroxyl group (—OH) of the thickener500. For example, the solvent molecule101of the light emitting element solvent100may be a compound represented by one of Chemical Formulas 9 to 25 below.

Among Chemical Formulas 9 to 25 above, in Chemical Formulas 9 to 12, each of the solvent molecules101of the light emitting element solvent100may include at least one hydroxyl group (—OH) to form a hydrogen bond with the thickener500. In contrast, in Chemical Formulas 13 to 25, each of the solvent molecules101of the light emitting element solvent100may include a carbonyl group or an ester group as a functional group capable of forming a hydrogen bond, and thus hydrogen (H) of the thickener500and oxygen (O) of the solvent molecule101may form a hydrogen bond with each other. As the solvent molecule101of the light emitting element solvent100includes a benzene ring, reactivity with the light emitting elements30may be low, and a degree of dispersion thereof may be further increased according to the surface treatment of the light emitting elements30. In case that the light emitting element solvent100of the light emitting element ink1000includes a compound represented by one of Chemical Formulas 9 to 25, a larger number of hydrogen bonds may be formed between the thickener500and the solvent molecule101, and thus the light emitting element ink1000may have a higher viscosity. Therefore, in case that the light emitting element ink1000is stored at the room temperature, the precipitation of the light emitting elements30may be more effectively prevented.

However, the disclosure is not limited thereto, and various solvents may be used as the light emitting element solvent100. For example, the light emitting element solvent100may be one of caffein, triethanol amine, glycerol, L-tyrosine, adrenalin, L-dopa, serotonin, dibenzlysebacate, ditridecyl phthalate, diethanol amine, benzyl butyl phthalate, nonyl phenol, paracetamol, triphenyl phosphate, 1,3-butanediol, 1,4-butanediol, 1-hexadecanol, oleyl alcohol, N-(2-hydroxyethyl)-2-pyrrolidone, tri-n-butyl citrate, di-(2-ethyl hexyl) sebacate, diethylene glycol, thymine, 1,9-nonanediol, benzoin, dipropylene glycol, sebacic acid, thiodiethylenglycol, 5,6-dihydroxyindole, di-(2-ethylhexyl)azelate, dihexyl phthalate, N-cyclohexyl-2-pyrrolidone, oleic acid, norephedrin, 1-naphthol, 2,4,6-trinitrophenol, N-benzyl pyrrolidone, hexane-1,6-diol, epsilon-caprolactam, tridecyl alcohol, acridine, and propylene glycol methyl ether acetate, in addition to the aforementioned examples. In case that the light emitting element solvent100includes the above-described compound, it may have a high boiling point, similarly to the thickener500. In an embodiment, the light emitting element solvent100may have a boiling point in a range of about 200° C. to about 350° C. However, the disclosure is not limited thereto.

In some embodiments, in the light emitting element ink1000, the thickener500may be glycerol having the structure of Chemical Formula 1, and the light emitting element solvent100may be a glycol ether-based compound. In case that the thickener500and the light emitting element solvent100of the light emitting element ink1000are a combination of the above-described compounds, the light emitting element ink1000may have a viscosity and a boiling point within the above-described ranges, and thus the light emitting element ink1000may have physical properties that readily discharge the light emitting elements30. However, the disclosure is not limited thereto, and the kinds of the thickener500and the light emitting element solvent100of the light emitting element ink1000may be variously changed within the range in which the light emitting element ink1000may have the viscosity and boiling point of the above-described ranges. Further, physical properties such as the viscosity and boiling point of the light emitting element ink1000may be variously changed according to a mixing ratio of the thickener500and the light emitting element solvent100.

In order for the light emitting element ink1000to be discharged through a nozzle, it should have a low viscosity. In the light emitting element ink1000, in case that the solvent molecule101and the thickener500receive energy at a predetermined temperature higher than the room temperature, molecular motion becomes active. For example, hydrogen bonds may be broken at a temperature at which an energy stronger than that of hydrogen bonds between the thickener500and the solvent molecule101or between the thickeners500may be transferred. In the light emitting element ink1000placed at a predetermined temperature or higher, the thickeners500may not form a network structure with the solvent molecules101of the light emitting element solvent100or other thickeners500, and thus the light emitting element ink1000may have a low viscosity.

FIG.9is a schematic diagram illustrating an intermolecular bond between a thickener and a light emitting element solvent of the light emitting element ink ofFIG.7at another temperature.FIG.9is an enlarged view of area A ofFIG.7and illustrates the form of a molecule of a thickener500′ dispersed in the light emitting element solvent100at a predetermined temperature of room temperature or higher.

Referring toFIG.9, in the printing process of the light emitting element ink1000, the light emitting element solvent100should have a viscosity of a predetermined value or less in order for the light emitting element ink1000to flow in an inkjet head of an inkjet printing apparatus or be discharged through a nozzle of an inkjet printing apparatus.

In the specification, the term “printing” of the light emitting elements30may mean that the light emitting elements30are discharged or ejected to a predetermined object by using an inkjet printing apparatus. For example, the term “printing” of the light emitting elements30may mean that the light emitting elements30are discharged directly through a nozzle of the inkjet printing apparatus or are discharged in a stated in which the light emitting elements30are dispersed in the light emitting element ink1000. However, the disclosure is not limited thereto, and the term “printing” of the light emitting elements30may mean that the light emitting elements30or the light emitting element ink1000in which the light emitting elements30are dispersed are ejected onto a target substrate SUB (seeFIG.11) to allow the light emitting elements30or the light emitting element ink1000to be mounted on the target substrate SUB.

In case that the light emitting element ink1000is discharged through the nozzle of the inkjet printing apparatus, the thickener500′ may not form a network structure when the temperature of the nozzle is adjusted such that the light emitting element ink1000is placed at the room temperature or higher. At the room temperature or higher, hydrogen bonds HB1and HB2between molecules of the thickener500′ of the light emitting element ink1000may be broken as molecular motion becomes active, and the thickeners500′ and the solvent molecules101of the light emitting element solvent100may be individually dispersed without forming a network structure.

According to an embodiment, the light emitting element ink1000may have a viscosity in a range of about 5 cP to about 15 cP, about 7 cP to about 13 cP, or a viscosity of about 10 cP, measured at a temperature in a range of about 40° C. to about 60° C. In case that the light emitting element ink1000has a viscosity within the above ranges, the light emitting element ink1000may be readily discharged through the nozzle, and the dispersion degree of the light emitting elements30may be maintained because a printing process is performed previously even if the light emitting elements30are gradually precipitated. For example, the number of light emitting elements30per unit droplet of the light emitting element ink1000discharged from the nozzle of the inkjet printing apparatus may be maintained uniformly. However, the viscosity of the light emitting element ink1000is not limited thereto, and the temperature inside the nozzle of an ink jet head and the viscosity of the light emitting element ink1000may be variously changed within a range in which the light emitting element ink1000may be discharged from the nozzle of the ink jet head.

The light emitting element ink1000may include a predetermined amount of light emitting elements30per unit weight, and the thickener500may be included in a predetermined content with respect to the weight of the light emitting elements30. According to an embodiment, the light emitting element ink1000may include about 5 to 50 parts by weight of the thickener500with respect to 100 parts by weight of the light emitting element ink1000. In case that the thickener500is included in an amount of less than about 5 parts by weight with respect to 100 parts by weight of the light emitting element ink1000, an effect of preventing the precipitation of the light emitting elements30in the storage state may be insufficient, and in case that the thickener500is included in an amount of about 50 parts by weight or more, the viscosity of the light emitting element ink1000may be too high, and thus the nozzle inlet may be blocked during the printing process. In case that the light emitting element ink1000includes the thickener500′ within the above ranges, the light emitting element ink1000may be smoothly discharged through the nozzle while preventing the precipitation of the light emitting elements30.

The content of the light emitting elements30included in the light emitting element ink1000may be changed depending on the number of the light emitting elements30per unit droplet of the light emitting element ink1000discharged through the nozzle during the printing process. In an embodiment, the light emitting elements30may be included in an amount of about 0.01 to about 1 part by weight with respect to 100 parts by weight of the light emitting element ink1000. However, this is an example, and the content of the light emitting elements30may vary depending on the number of light emitting elements30per unit droplet of the light emitting element ink1000.

The light emitting element ink1000may further include a dispersant (not shown) that improves the dispersion degree of the light emitting elements30. The kind of the dispersant is not particularly limited, and the dispersant may be added in an appropriate amount to further disperse the light emitting elements30. For example, the dispersant may be included in an amount of about 10 to about 100 parts by weight with respect to 100 parts by weight of the light emitting elements30. However, the content of the dispersant is not limited thereto.

According to an embodiment, the light emitting element ink1000may include the thickener500, and thus the viscosity of the light emitting element ink1000may vary during the process of manufacturing the display device10. The light emitting element ink1000may have a suitable viscosity for each storage step of the light emitting element ink1000and each printing step through a nozzle. In particular, in the storage step of the light emitting element ink1000, as the light emitting element ink1000has a high viscosity, the precipitation of the light emitting elements30may be prevented, and in the printing step through a nozzle, as the light emitting element ink1000has a low viscosity, the printing process of the light emitting elements30may be performed smoothly.

When a product including the light emitting elements30using the light emitting element ink1000is manufactured according to an embodiment, a uniform number of light emitting elements30may be disposed in each unit area, and the light emitting element solvent100and the thickener500, remaining as foreign matter, in a subsequent process may be completely removed. Accordingly, reliability of the product including the light emitting elements30may be improved. According to an embodiment, the display device10described above with reference toFIGS.1to3may be manufactured using the light emitting element ink1000.

In the process of manufacturing the display device10, a process of placing the light emitting elements30on the electrodes21and22may be performed, and this process may be formed by a printing process using the light emitting element ink1000.

Hereinafter, a process of manufacturing the display device10according to an embodiment will be described with reference to other drawings.

FIG.10is a flowchart illustrating a method of manufacturing a display device according to an embodiment.

Referring toFIG.10, a method of manufacturing a display device10according to an embodiment may include the steps of preparing a light emitting element ink1000and a target substrate SUB on which electrodes21and22are formed (S100); ejecting the light emitting element ink1000onto the target substrate SUB at a first temperature (S200); forming an electric field on the electrodes21and22to place the light emitting elements30on the electrodes21and22(S300); and removing a light emitting element solvent100and a thickener500of the light emitting element ink1000at a second temperature (S400).

The light-emitting device ink1000may have a high viscosity at room temperature and may be stored such that the light emitting elements30do not precipitate. The process of manufacturing the display device10may include a step of printing the light emitting element ink1000including the light emitting elements30on the target substrate SUB at a first temperature higher than room temperature; and a step of removing the light emitting element solvent100and the thickener500of the light emitting element ink1000at a second temperature different from the first temperature. In the light emitting element ink1000, the viscosity thereof may be changed depending on the temperature during the storage step and the printing step, and the light emitting element ink1000may be readily printed on the target substrate SUB while the precipitation of the light emitting elements is prevented. Hereinafter, the method of manufacturing the display device10will be described in detail with reference to other drawings.

FIGS.11to13are schematic cross-sectional views illustrating steps of a process of manufacturing a display device according to an embodiment.

First, referring toFIG.11, a light emitting element ink1000including light emitting elements30, a light emitting element solvent100, and a thickener500, and a target substrate SUB provided with a first electrode21and a second electrode22are prepared. Although it is shown in the drawing that a pair of electrodes is disposed on the target substrate SUB, a larger number of electrode pairs may be disposed on the target substrate SUB. The target substrate SUB may include circuit elements disposed on the first substrate11of the display device10in addition to the first substrate11. Hereinafter, for convenience of description, these circuit elements will be omitted.

The light emitting element ink1000may include a solvent100, light emitting elements30dispersed in the solvent, and a photodegradable thickener500. In some embodiments, the light emitting element ink1000may be stored at room temperature or at a temperature of about 25° C., and the thickener500may form hydrogen bonds between molecules to form a three-dimensional network structure in the solvent100. The light emitting element ink1000may have a high viscosity, for example, in a range of about 20 cp to about 300 cp even at room temperature and the light emitting elements30may be maintained in a dispersed state for a long time.

The step of preparing the light emitting element ink1000may be performed by a first dispersion process of mixing the light emitting elements30, the light emitting element solvent100, and a dispersant to prepare a solution, and by a second dispersion process of adding the thickener500to the solution prepared in the first dispersion process. For example, the first dispersion process may be performed by mixing the light emitting elements30and the dispersant with the light emitting element solvent100and then stirring the solution for 5 minutes or more. As described above, the light emitting element30may have a diameter of about 1 μm or less, or about 500 nm or less, and a length of about 1 μm to 10 μm or about 4 μm or greater. The light emitting elements30may be included in an amount of about 0.01 to about 1 part by weight with respect to 100 parts by weight of the light emitting element ink100, and the dispersant may be included in an amount of 10 to 100 parts by weight with respect to 100 parts by weight of the light emitting elements30. The mixing process may be performed by a sonication process, a stirring process, a milling process, or the like.

Subsequently, a second dispersion process in which a thickener500is further added to and mixed with the solution prepared in the first dispersion process is performed. The thickener500may be included in an amount of about 5 to about 50 parts by weight with respect to 100 parts by weight of the light emitting element ink1000. The mixing process may be performed by sequentially performing a sonication process and a stirring process each for 5 minutes or longer. In order for the thickener500to be mixed easily, the mixing process may be performed at a temperature higher than the room temperature (25° C.), for example, at about 40° C. or higher.

The light emitting element ink1000prepared by the first and second dispersion processes may be stored at room temperature (25° C.). The thickener500of the light emitting element ink1000may form an intermolecular hydrogen bond with the light emitting element solvent100and another thickener500, and the light emitting element ink1000may have a viscosity of at least about 20 cP or more. The light emitting elements30may be maintained in a dispersed state with little precipitation.

Subsequently, referring toFIGS.12and13, the light emitting element ink1000may be sprayed onto the first electrode21and the second electrode22on the target substrate SUB. In an embodiment, the light emitting element ink1000may be sprayed onto the electrodes21and22by a printing process using an inkjet printing apparatus. The light emitting element ink1000may be ejected through a nozzle of an inkjet head included in an inkjet printing apparatus. The light emitting element ink1000discharged from the nozzle may be attached onto the electrodes21and22disposed on the target substrate SUB. The light emitting element30may have a shape extending in a direction and may be dispersed in the light emitting element ink1000in a state in which the extending direction has a random alignment direction.

In some embodiments, before the light emitting element ink1000is ejected through a nozzle, a third dispersion process of redispersing the light emitting elements30and the thickener500may be performed. For example, the stored light emitting element ink1000may be subjected to a sonication process and a vortexing or stirring process each for 5 minutes or longer. Even if the light emitting element ink1000has a high viscosity and thus the light emitting elements30hardly precipitates, the third dispersion process of sufficiently dispersing the light emitting elements30may be performed before the printing process through the nozzle. Accordingly, the light emitting elements30of the light emitting element ink1000prepared in the inkjet printing apparatus may have a level of dispersion degree similar to that of the initial storage state.

According to an embodiment, in the printing process of the light emitting element ink1000, a discharge portion JP of the nozzle may be adjusted to a first temperature higher than the room temperature, and the light emitting element ink1000may have a relatively low viscosity at the first temperature and may be discharged onto the target substrate SUB through the discharge portion JP. In some embodiments, the first temperature may be in a range of about 40° C. to about 60° C., and at the first temperature, the light emitting element ink1000may have a viscosity in the range of about 5 cp to about 15 cp, or a viscosity of about 10 cp. During the printing process of the light-emitting element ink1000, in case that the temperature of the discharge portion JP of the nozzle is controlled to the first temperature of the room temperature or higher, the light emitting element ink1000may have a low viscosity and may be readily discharged from the nozzle to prevent nozzle clogging due to the viscosity of the solution.

FIG.14is a schematic graph illustrating a change in viscosity of the light emitting element ink according to the temperature.FIG.14illustrates a viscosity change (cP) of the light emitting element ink including the thickener500according to the temperature (° C.).

Referring toFIG.14, the light emitting element ink1000may have a high viscosity at the room temperature. At a temperature of about 25° C., the light emitting element ink1000may have a viscosity of 20 cP or more and 200 cP or less, for example, about 100 cP as the thickener500forms a three-dimensional network structure. In the storage state of the light emitting element ink1000, the light emitting elements30hardly precipitate and may maintain an initial dispersion state.

In contrast, the light emitting element ink1000may have a low viscosity at a temperature of room temperature or higher. In a temperature range of about 40° C. to about 60° C., the light emitting element ink1000may have a viscosity between about 5 cps and about 17 cps. A solution having a viscosity within the above range (“Jetable viscosity range” ofFIG.14) may be readily discharged through a nozzle, and the nozzle may not be clogged by the viscosity of the solution.

In case that the light emitting element ink1000has a low viscosity regardless of temperature or even at the room temperature, the light emitting elements30included in the light emitting element ink1000may not maintain an initial dispersion state over time and may be precipitated. When a printing process is performed by using the light emitting element ink1000in which the light emitting elements30are dispersed, the light emitting elements30may be precipitated, so that the number of light emitting elements30included per unit droplet of the solution may be less than the calculated value or may not be uniform per unit droplet. When a process of re-dispersing the precipitated light emitting elements30is performed, the process of manufacturing the display device10may become complicated, and in some case, it may not be easy to re-disperse the light emitting elements30at a desired dispersion degree. When a printing process is performed by using the light emitting element ink1000according to an embodiment, the light emitting elements30are dispersed and are hardly precipitated, the number of light emitting elements30included per unit droplet may be uniform per unit droplet. In the method of manufacturing the display device10, the display device10is manufactured by using the light emitting element ink1000, and the manufactured display device10may have a uniform number of light emitting elements30disposed per unit area, so that the product reliability may be improved. Simultaneously, during the printing process through a nozzle, the temperature is controlled such that the light emitting element ink1000may have a low viscosity, and thus the discharge portion JP of the nozzle may be prevented from being clogged during the printing process.

Subsequently, an electric field may be formed in the light emitting element ink1000to place the light emitting elements on the electrodes21and22, and the light emitting element solvent100and the thickener500may be removed (S400).

FIGS.15to17are schematic cross-sectional views illustrating other steps in a process of manufacturing a display device according to an embodiment.

First, referring toFIG.15, when the light emitting element ink1000including the light emitting elements30is ejected on the target substrate SUB, an alignment signal may be applied to the electrodes21and22to generate an electric field EL on the target substrate SUB. The light emitting elements30dispersed in the light emitting element solvent100may be subjected to a dielectrophoretic force by the electric field EL and may be arranged on the electrodes21and22while the alignment direction and position of the light emitting elements30are changed.

When the electric field EL is generated on the target substrate SUB, the light emitting elements30may be subjected to a dielectrophoretic force. In case that the electric field EL generated on the target substrate SUB is generated parallel to the upper surface of the target substrate SUB, the extending direction of the light emitting element is aligned to be parallel to the target substrate SUB, so that the light emitting elements30may be arranged on the first electrode21and the second electrode22. The light emitting elements30may move toward the electrodes21and22from the initially dispersed position by the dielectrophoretic force. Both ends of the light emitting element30may be disposed on the first electrode21and the second electrode22while the position and alignment direction thereof are changed by the electric field EL. The light emitting element30may include semiconductor layers doped with a dopant(s) of different conductivity types and may have a dipole moment therein. In case that the light emitting element30having a dipole moment is placed in the electric field EL, the light emitting element30may be subjected to the dielectrophoretic force such that both ends thereof are disposed on the electrodes21and22, respectively.

The term “degree of alignment” of the light emitting elements30may refer to a deviation in the alignment direction and mounted position of the light emitting elements30aligned on the target substrate SUB. For example, in case that the deviation in the alignment direction and mounted position of the light emitting elements30is great, it may be understood that the alignment degree of the light emitting elements30is low, and in case that the deviation in the alignment direction and mounted position of the light emitting elements30is small, it may be understood that the alignment degree of the light emitting elements30is high or is improved.

However, during the process of manufacturing the display device10, after the light emitting element30is disposed between the electrodes21and22, a process of removing the solvent100and the thickener500by applying heat or light to the light emitting element ink1000may be performed. The light emitting element ink1000may have a high viscosity because of an intermolecular hydrogen bond of the thickener500according to the temperature. Accordingly, the solvent100and the thickener500may not be removed easily and may remain as a foreign matter on the electrodes21and22or the light emitting elements30. Further, as the light emitting element ink1000has a high viscosity, the intensity of the dielectrophoretic force on the light emitting elements30by the electric field formed on the electrodes21and22may not be sufficient. Moreover, a high-temperature heat treatment may be required to remove the solvent100and the thickener500each having a high viscosity, and the initial alignment state of the light emitting elements30may be changed by an attraction force due to the flow of fluid or an attraction force between the thickener500and the light emitting elements30while the solvent100and the thickener500are removed.

In the method of manufacturing the display device10according to an embodiment, the solvent100and the thickener500may be removed at the second temperature and may be completely removed by a heat treatment process under a low-pressure for an easier removing process.

Referring toFIGS.16and17, the process of removing the light emitting element solvent100and the thickener500may be performed in a chamber VCD capable of adjusting internal pressure. In the chamber VCD, the internal pressure in the device may be adjusted, and the target substrate SUB may be heated in a state in which the internal pressure is adjusted, so as to remove the light emitting element solvent100and the thickener500. In the state in which the light emitting elements30are disposed on the electrodes21and22by the electric field EL, the thickener500may form an intermolecular hydrogen bond according to the temperature. The solvent100and the thickener500may be removed while the viscosity of the light emitting element ink1000is reduced by a heat treatment at the second temperature. However, an energy for removing a hydrogen bond between molecules of the light emitting element solvent100and the thickener500may be further required in addition to energy for volatilizing their respective molecules. In this case, the heat treatment process should be performed at a temperature above the boiling point of each molecule, and a high-temperature heat treatment process may damage the circuit layers of the display device10.

In the method of manufacturing the display device10, the light emitting element solvent100and the thickener500′ may be heat-treated under an environment of a low-pressure to completely remove them even at a temperature below the boiling point of the thickener500′. According to an embodiment, the process of removing the light emitting element solvent100and the thickener500′ may be performed at a pressure of about 10−4Torr to about 1 Torr and a temperature of about 25° C. to about 150° C. In cases where a heat treatment process is performed within the above pressure range, the boiling point of the thickener500′ and the light emitting element solvent100may be lowered, and a hydrogen bond therebetween may be more readily removed. For example, where the thickener500′ is a polyol-based compound, its boiling point may be between about 200° C. and about 450° C. However, the thickener500′ and the light emitting element solvent100may be readily removed even at a temperature range of about 150° C. or lower under a low-pressure environment as described above in the chamber VCD. The heat treatment process in the chamber VCD may be performed for about 1 minute to about 30 minutes. However, it is not limited thereto.

As the process of removing the light emitting element solvent100and the thickener500′ is performed by a heat treatment process under a low-pressure environment, the light emitting element solvent100and the thickener500′ that may remain as a foreign matter in a subsequent process may be completely removed. Further, in the process of removing the light emitting element solvent100and the thickener500′, a change in the initial alignment state of the light emitting elements30due to an attraction force by the flow of fluid or an attraction force between the thickener500′ and the light emitting elements30may be prevented. For example, in the display device10, the alignment degree of the light emitting elements30may be improved.

Subsequently, insulating layers and a contact electrode may be formed on the light emitting element30and the electrodes21and22to manufacture the display device10. By the above processes, the display device10including the light emitting elements30may be manufactured. The display device10may be manufactured using the light emitting element ink1000including the thickener500. In the display device10, a uniform number of light emitting elements30may be arranged for each unit area with a high alignment degree, and the product reliability may be improved.

After the light emitting element ink1000is discharged from the discharge portion JP of the nozzle, the viscosity may vary according to the temperature of the upper portion of the target substrate SUB. In case that the light emitting element ink1000applied on the target substrate SUB has a high viscosity, the process of aligning the light emitting elements30by the electric field EL may not be easy. According to an embodiment, during the manufacturing process of the display device10, the process of applying the light emitting elements30to the electrodes21and22may be performed at the first temperature similar to that of the discharge portion JP of the nozzle or at a temperature higher than the first temperature. For this purpose, in the process of generating the electric field EL on the electrodes21and22, a process or apparatus for controlling the temperature of the upper portion of the target substrate SUB may be further included.

FIG.18is a schematic cross-sectional view illustrating a step in a process of manufacturing a display device according to another embodiment.

Referring toFIG.18, in the process of manufacturing the display device10, in the step of forming an electric field EL on the electrodes21and22and applying the light emitting elements30onto the electrodes21and22, the electric field EL may be generated while the target substrate SUB is heat-treated (“Heat” inFIG.18). The heat treatment on the target substrate SUB may be a process for lowering the viscosity of the light emitting element ink1000by adjusting the light emitting element ink1000applied to the electrodes21and22to the first temperature or higher. As the light emitting element ink1000applied on the target substrate SUB has a low viscosity, the light emitting elements30whose position and orientation are changed by the electric field EL may more actively move because the resistance caused by the viscosity of fluid in the light emitting element ink1000is low. Accordingly, the light emitting elements30may be arranged on the electrodes21and22with a high degree of alignment. In the drawing, only a process by a separate heat treatment device is illustrated as a method of heat-treating the target substrate SUB, but the disclosure is not limited thereto. In some embodiments, the heat treatment on the target substrate SUB may be performed by placing the target substrate SUB on a stage including a heat source or a heat sink and then controlling the temperature of the upper surface of the stage.

During the process of manufacturing the display device10, in order to further improve the alignment degree of the light emitting elements30, a process of irradiating light may be further performed.

FIG.19is a schematic cross-sectional view illustrating a step in a process of manufacturing a display device according to another embodiment.

Referring toFIG.19, in the process of manufacturing the display device10, in the step of forming an electric field EL on the electrodes21and22, ultraviolet light UV may be applied to the light emitting elements30ejected on the target substrate SUB. The light emitting elements30may have a dipole moment, and when ultraviolet light UV is applied to the light emitting elements30, the light emitting elements30may react with the ultraviolet light UV to have a larger dipole moment. The light emitting elements30having a large dipole moment may be aligned such that an end thereof faces in a predetermined direction in response to the electric field EL formed on the electrodes21and22. At the same time, at least one end of the light emitting elements30may be disposed on the first electrode21or the second electrode22. For example, each of the light emitting elements30may have a first end disposed on the first electrode21and a second end disposed on the second electrode22.

In the step of placing the light emitting elements30on the electrodes21and22, when an electric field EL is formed while ultraviolet light UV is applied, the first ends of light emitting elements30may be aligned in a predetermined direction as the electrophoretic reactivity of the light emitting elements30increases. Accordingly, the light emitting elements30may be arranged on the electrodes21and22with a high alignment degree, and the product reliability of the display device10may be further improved.

The light emitting element ink according to an embodiment may include a thickener to have a different viscosity according to the temperature. In the storage state of the light emitting element ink at the room temperature, the viscosity of a solution may be high, so that precipitation of light emitting elements may be prevented. In the printing state of the light emitting element ink, the viscosity of the solution may be low, so that a nozzle may not be clogged, and thus the ink may be easily discharged.

In the method of manufacturing a display device according to an embodiment, the display device may be manufactured using the light emitting element ink, so that a printing process may be performed in a state in which light emitting elements are dispersed in the ink, a uniform number of light emitting elements in each unit area may be arranged with a high alignment degree. Further, by a heat treatment under a low-pressure environment, a light emitting element solvent and a thickener remaining as a foreign mater matter in a subsequent process may be completely removed. Therefore, a display device having increased product reliability may be manufactured.

In concluding the detailed description, those skilled in the art will appreciate that many variations and modifications can be made to the embodiments without substantially departing from the principles of disclosure. Therefore, the disclosed embodiments of the disclosure are used in a generic and descriptive sense only and not for purposes of limitation.