Ink containing light emitting element and method for manufacturing display device using the ink

Abstract

An ink and a method for manufacturing a display device using the ink are provided, wherein the ink includes a solvent and light-emitting elements dispersed in the solvent, each of the light-emitting elements including a semiconductor layer and an insulating film partially surrounding an outer surface of the semiconductor layer, wherein the solvent has a Hansen solubility parameter with a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11.

Description

Technical Field

[0001] Disclosed is an ink containing a light emitting element and a method of manufacturing a display device using the ink. Background Art

[0002] As multimedia technology develops, display devices are becoming more and more important. Therefore, various types of display devices such as organic light emitting display devices and liquid crystal display (LCD) devices are currently used.

[0003] The display device is used to display an image and includes a display panel such as an organic light emitting display panel or a liquid crystal display panel. Among them, the light emitting display panel may include a light emitting element. For example, a light emitting diode (LED) may include an organic light emitting diode (OLED) using an organic material as a fluorescent material and an inorganic light emitting diode using an inorganic material as a fluorescent material. Summary of the invention

[0004] A disclosed aspect provides an ink including a solvent capable of dispersing a light emitting element, so that the dispersibility of the light emitting element can be improved.

[0005] The disclosed aspects also provide a method of manufacturing a display device, which can improve dispersibility of a light emitting element after a printing process using ink.

[0006] It should be noted that the objects of the disclosure are not limited to the above-mentioned objects, and other objects of the disclosure will be apparent to those skilled in the art from the following description.

[0007] According to the disclosed embodiments, the solvent has a Hansen solubility parameter within a predetermined range and / or a specific functional group, so that the light-emitting element mixed in the solvent can be more dispersed.

[0008] According to the disclosed embodiments, it is possible to suppress light emitting elements in ink from sticking together when they are dropped onto sub-pixels, thereby suppressing poor alignment and achieving uniform brightness in the sub-pixels.

[0009] It should be noted that the effects of the disclosure are not limited to the effects described above, and other effects of the disclosure will be apparent to those skilled in the art from the following description.

[0010] According to the disclosed embodiments, the ink may include: a solvent; and a plurality of light emitting elements dispersed in the solvent, each of the plurality of light emitting elements including a plurality of semiconductor layers and an insulating film partially surrounding outer surfaces of the plurality of semiconductor layers. The solvent may have a Hansen solubility parameter with a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11.

[0011] In an embodiment, the solvent may include at least one ester group.

[0012] In an embodiment, the solvent may include a compound represented by the following Chemical Formula 1:

[0013] [Chemical formula 1]

[0014]

[0015] Each of R and R' may be hydrogen, a substituted or unsubstituted linear or branched alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkyl ether group having 1 to 10 carbon atoms, a substituted or unsubstituted alkyl ester group having 1 to 10 carbon atoms, or a substituted or unsubstituted phenyl group.

[0016] In an embodiment, the substituent of each of R and R' may be at least one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an ester group, an alkyl ester group having 1 to 10 carbon atoms, an ether group, an alkyl ether group having 1 to 10 carbon atoms, a carbonyl group, and a hydroxyl group.

[0017] In an embodiment, the solvent may include a compound represented by one of the following Chemical Formulas 2 to 9:

[0018] [Chemical formula 2]

[0019]

[0020] [Chemical formula 3]

[0021]

[0022] [Chemical formula 4]

[0023]

[0024] [Chemical formula 5]

[0025]

[0026] [Chemical formula 6]

[0027]

[0028] [Chemical formula 7]

[0029]

[0030] [Chemical formula 8]

[0031]

[0032] [Chemical formula 9]

[0033]

[0034] In an embodiment, the solvent may include 1 to 4 ester groups.

[0035] In an embodiment, the solvent may have a viscosity in a range of about 20 cP to about 200 cP at room temperature.

[0036] In an embodiment, the boiling point of the solvent may be equal to or less than about 400°C.

[0037] In an embodiment, the plurality of light emitting elements may be included in an amount of about 0.01 parts by weight to about 10 parts by weight based on 100 parts by weight of the ink.

[0038] In an embodiment, the plurality of semiconductor layers of each of the plurality of light emitting elements may include a first semiconductor layer, a second semiconductor layer, and a light emitting layer disposed between the first semiconductor layer and the second semiconductor layer. The insulating film may surround at least an outer surface of the light emitting layer.

[0039] According to the disclosed embodiments, a method of manufacturing a display device may include: preparing an ink including a solvent and a plurality of light emitting elements; preparing a target substrate on which a first electrode and a second electrode may be formed; applying the ink to the target substrate; and generating an electric field over the target substrate so that the plurality of light emitting elements are disposed on the first electrode and the second electrode. The solvent may have a Hansen solubility parameter with a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11.

[0040] In an embodiment, the solvent may include at least one ester group.

[0041] In an embodiment, the solvent may include a compound represented by the following Chemical Formula 1:

[0042] [Chemical formula 1]

[0043]

[0044] Each of R and R' may be hydrogen, a substituted or unsubstituted linear or branched alkyl group having 1 to 10 carbon atoms, a substituted or unsubstituted alkyl ether group having 1 to 10 carbon atoms, a substituted or unsubstituted alkyl ester group having 1 to 10 carbon atoms, or a substituted or unsubstituted phenyl group.

[0045] In an embodiment, the substituent of each of R and R' may be at least one selected from the group consisting of an alkyl group having 1 to 10 carbon atoms, an ester group, an alkyl ester group having 1 to 10 carbon atoms, an ether group, an alkyl ether group having 1 to 10 carbon atoms, a carbonyl group, and a hydroxyl group.

[0046] In an embodiment, the solvent may include a compound represented by one of the following Chemical Formulas 2 to 9:

[0047] [Chemical formula 2]

[0048]

[0049] [Chemical formula 3]

[0050]

[0051] [Chemical formula 4]

[0052]

[0053] [Chemical formula 5]

[0054]

[0055] [Chemical formula 6]

[0056]

[0057] [Chemical formula 7]

[0058]

[0059] [Chemical formula 8]

[0060]

[0061] [Chemical formula 9]

[0062]

[0063] In an embodiment, the solvent may include 1 to 4 ester groups.

[0064] In an embodiment, the solvent may have a viscosity in a range of about 20 cP to about 200 cP at room temperature.

[0065] In an embodiment, the boiling point of the solvent may be equal to or less than about 400°C.

[0066] In an embodiment, the method may further include: after generating an electric field over the target substrate so that the plurality of light emitting elements are disposed on the first electrode and the second electrode, performing a heat treatment to remove the solvent.

[0067] In an embodiment, the thermal treatment may be performed at a temperature in a range of about 100°C to about 400°C. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The above and other aspects and features of the disclosure will become more apparent by describing in detail embodiments of the disclosure with reference to the accompanying drawings, in which:

[0069] Figure 1 is a schematic plan view of a display device according to a disclosed embodiment;

[0070] Figure 2 is a schematic plan view showing a pixel of a display device according to a disclosed embodiment;

[0071] Figure 3 It is along Figure 2 Schematic cross-sectional views taken along line Q1-Q1', line Q2-Q2' and line Q3-Q3';

[0072] Figure 4 is a schematic perspective view showing a light emitting element according to a disclosed embodiment;

[0073] Figure 5 is a schematic perspective view showing a light emitting element according to another disclosed embodiment;

[0074] Figure 6 is a perspective view schematically showing an ink containing a light emitting element according to a disclosed embodiment;

[0075] Figure 7 is a diagram showing the degree of center alignment of a light emitting element according to a polarity parameter and a hydrogen bonding parameter of a solvent;

[0076] Figure 8 An image showing ink having light emitting elements mixed therein according to a disclosed embodiment;

[0077] Fig. 9 shows a graph showing changes in transparency and concentration of ink in which a light emitting element is mixed over time according to a disclosed embodiment;

[0078] Fig.10 An image of ink in which a light emitting element is mixed according to a comparative example is shown;

[0079] Fig.11 shows a graph showing changes over time in transparency and density of ink in which a light emitting element is mixed according to a comparative example;

[0080] Fig.12 is a diagram schematically illustrating an inkjet printing apparatus according to a disclosed embodiment;

[0081] Fig.13 is a flowchart for illustrating a method of manufacturing a display device according to a disclosed embodiment;

[0082] Figures 14 to 21 are schematic cross-sectional views showing some of the processing steps of manufacturing a display device according to a disclosed embodiment. DETAILED DESCRIPTION

[0083] The disclosure will now be described more fully below with reference to the accompanying drawings, in which some embodiments of the disclosure are shown. However, the disclosure may be implemented in different forms and should not be construed as being limited to the embodiments set forth herein. Instead, these embodiments are provided so that the disclosure will be thorough and complete and will convey the scope of the disclosure to those skilled in the art.

[0084] 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 one or more intervening layers may also be present. Throughout the specification, the same reference numerals refer to the same components.

[0085] It will be understood that although the terms "first", "second", etc. 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 example, without departing from the disclosed teachings, the first element discussed below may be referred to as the second element. Similarly, the second element may also be referred to as the first element.

[0086] Each of the features of the various disclosed embodiments can be combined or combined with each other in part or in whole, and various interlocks and drives are possible in technology. Each embodiment can be implemented independently of each other, or can be implemented together in association.

[0087] 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 the present disclosure belongs. It will also be understood that terms (such as those defined in commonly used dictionaries) should be interpreted as having a meaning consistent with their meaning in the relevant art and the context of the disclosure, and should not be interpreted in an idealized or overly formal sense, unless explicitly so defined herein.

[0088] Hereinafter, disclosed embodiments will be described with reference to the accompanying drawings.

[0089] Figure 1 is a schematic plan view of a display device according to a disclosed embodiment.

[0090] Reference Figure 1 , the display device 10 displays a dynamic image or a static image. The display device 10 may refer to any electronic device including a display screen. For example, the display device 10 may include a television, a laptop computer, a monitor, an electronic billboard, an Internet of Things device, a mobile phone, a smart phone, a tablet personal computer (PC), an electronic watch, a smart watch, a watch phone, a head-mounted display device, a mobile communication terminal, an electronic notebook, an electronic book, a portable multimedia player (PMP), a navigation device, a game console, a digital camera, and a video camera, etc.

[0091] The display device 10 includes 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, a field emission display panel, etc. In the following description, an inorganic light emitting diode display panel is used as an example of a display panel, but the disclosure is not limited thereto. Any other display panel may be used as long as the disclosed technical concept can be equally applied.

[0092] The shape of the display device 10 may be modified in various ways. For example, the display device 10 may have a shape such as a rectangle with longer sides, a rectangle with longer vertical sides, a square, a quadrilateral with rounded corners (vertices), other polygons, a circle, etc. The shape of the display area DPA of the display device 10 may be similar to the overall shape of the display device 10. Figure 1 The display device 10 and the display area DPA are shown in the shape of a rectangle having longer horizontal sides.

[0093] The display device 10 may include a display area DPA and a non-display area NDA. In the display area DPA, an image may be displayed. In the non-display area NDA, no image is 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 substantially occupy the center of the display device 10.

[0094] The display area DPA may include pixels PX. The pixels PX may be arranged in a matrix. In a plan view, the shape of each pixel PX may be, but is not limited to, a rectangle or a square. Each pixel PX may have a rhombus shape having sides inclined relative to a certain direction. The pixels PX may be arranged in a stripe pattern and Each of the pixels PX may include at least one light emitting element 30 (see Figure 2 ).

[0095] The non-display area NDA may be disposed around the display area DPA or adjacent to the display area DPA. The non-display area NDA may completely 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 a frame of the display device 10. A line or circuit driver included in the display device 10 may be disposed in each of the non-display areas NDA, or an external device may be installed.

[0096] Figure 2 is a schematic plan view showing a pixel of a display device according to a disclosed embodiment.

[0097] Reference Figure 2 , each of the pixels PX may include a sub-pixel PXn, where n is an integer ranging from one to three. For example, the pixel PX may include a first sub-pixel PX1, a second sub-pixel PX2, and a third sub-pixel PX3. The first sub-pixel PX1 may emit light of a first color, the second sub-pixel PX2 may emit light of a second color, and the third sub-pixel PX3 may 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, it will be understood that the disclosure is not limited thereto. All sub-pixels PXn may emit light of the same color. Although in Figure 2 In the example shown in FIG. 1 , the pixel PX includes three sub-pixels PXn, but the disclosure is not limited thereto. The pixel PX may include more than two sub-pixels PXn.

[0098] Each of the sub-pixels PXn of the display device 10 may include an emission area (or light emitting area) EMA and a non-emission area (not shown). In the emission area EMA, the light emitting element 30 may be arranged to emit light of a specific wavelength. In the non-emission area, the light emitting element 30 is not arranged, and the light emitted from the light emitting element 30 does not reach, and no light is emitted therefrom. The emission area EMA may include an area in which the light emitting element 30 is arranged, and may include an area adjacent to the light emitting element 30 where the light emitted from the light emitting element 30 is emitted.

[0099] However, it will be understood that the disclosure is not limited thereto. The emission area EMA may also include an area in which light emitted from the light emitting element 30 is reflected or refracted by other elements to exit. The light emitting element 30 may be disposed in each of the sub-pixels PXn, and the emission area EMA may include an area in which the light emitting element 30 is disposed and an adjacent area.

[0100] Each of the sub-pixels PXn may further include a cutting area CBA disposed in a non-emission area. The cutting area CBA may be disposed on one side of the emission area EMA in the second direction DR2. The cutting area CBA may be disposed between the emission areas EMA of the sub-pixels PXn adjacent along the second direction DR2. In the display area DPA of the display device 10, the emission area EMA and the cutting area CBA may be arranged. For example, the emission area EMA and the cutting area CBA may be arranged repeatedly in the first direction DR1, and may be arranged alternately in the second direction DR2. The interval between the cutting areas CBA in the first direction DR1 may be smaller than the interval between the emission areas EMA in the first direction DR1. The second bank BNL2 may be disposed between the cutting area CBA and the emission area EMA, and the distance between them may vary according to the width of the second bank BNL2. Although the light emitting element 30 is not disposed in the cutting area CBA and no light is emitted from the cutting area CBA, portions of the electrodes 21 and 22 disposed in each of the sub-pixels PXn may be disposed in the cutting area CBA. The electrodes 21 and 22 provided for each of the sub-pixels PXn may be provided separately from each other in the cutting area CBA.

[0101] Figure 3 It is along Figure 2 Schematic cross-sectional views taken along line Q1 - Q1 ′, line Q2 - Q2 ′, and line Q3 - Q3 ′. Figure 3 Shows the settings in Figure 2 FIG. 1 is a cross-section of the light emitting element 30 and other elements in the first sub-pixel PX1.

[0102] Combination Figure 2 Reference Figure 3 The display device 10 may include a first substrate 11, a semiconductor layer, a conductive layer, and an insulating layer disposed on the first substrate 11. The semiconductor layer, the conductive layer, and the insulating layer may form a circuit layer and an emission material layer of the display device 10.

[0103] Specifically, the first substrate 11 may be an insulating substrate. The first substrate 11 may be made of an insulating material such as glass, quartz, and polymer resin. The first substrate 11 may be a rigid substrate or a flexible substrate that can be bent, folded, or rolled.

[0104] The light shielding layer BML may be disposed on the first substrate 11. The light shielding layer BML may overlap with the active layer ACT of the first transistor T1 of the display device 10. The light shielding layer BML may include a material that blocks light, and thus may prevent light from entering the active layer ACT of the first transistor T1. For example, the light shielding layer BML may be formed of an opaque metal material that blocks light transmission. However, it will be understood that the disclosure is not limited thereto. In some embodiments, the light shielding layer BML may be omitted.

[0105] The buffer layer 12 may be completely disposed on the first substrate 11 including the light shielding layer BML. The buffer layer 12 may be formed on the first substrate 11 to protect the first transistor T1 of the pixel PX susceptible to moisture penetration from moisture penetrating through the first substrate 11, and the buffer layer 12 may also provide a flat surface. The buffer layer 12 may be formed of inorganic layers alternately stacked with each other. For example, the buffer layer 12 may be formed of a silicon oxide (SiO x ), silicon nitride (SiN x ) and silicon oxynitride (SiO x N y ) are made of a plurality of layers of inorganic layers alternately stacked with each other (or including silicon oxide (SiO x ), silicon nitride (SiN x ) and silicon oxynitride (SiO x N y ) are a plurality of layers in which inorganic layers of at least one of the above-mentioned types are alternately stacked with each other).

[0106] The semiconductor layer may be disposed on the buffer layer 12. The semiconductor layer may include an active layer ACT of the first transistor T1. These may be disposed to partially overlap with a gate electrode G1 of a first gate conductive layer to be described below.

[0107] Although only the first transistor T1 among the transistors included in the sub-pixel PXn of the display device 10 is depicted in the drawings, the disclosure is not limited thereto. The display device 10 may include a greater number of transistors. For example, in addition to the first transistor T1, the display device 10 may include more than one transistor (e.g., two or three transistors) in each of the sub-pixels PXn.

[0108] The semiconductor layer may include polycrystalline silicon, monocrystalline silicon, an oxide semiconductor, etc. In the case where the semiconductor layer includes an oxide semiconductor, each active layer ACT may include conductive regions ACT_a and ACT_b and a channel region ACT_c located 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), indium gallium zinc tin oxide (IGZTO), etc.

[0109] In other embodiments, the semiconductor layer may include polysilicon. Polysilicon may be formed by crystallizing amorphous silicon, and in this case, the conductive regions ACT_a and ACT_b of the active layer ACT may be doped regions doped with impurities.

[0110] The first gate insulating layer 13 may be disposed on the semiconductor layer and the buffer layer 12. The first gate insulating layer 13 may include a semiconductor layer and may be disposed on the buffer layer 12. The first gate insulating layer 13 may be used as a gate insulator of each of the thin film transistors. The first gate insulating layer 13 may be made of an inorganic material such as silicon oxide (SiO x ), silicon nitride (SiN x ) and silicon oxynitride (SiO x N y )) or can be formed by a stack of materials.

[0111] The first gate conductive layer may be disposed on the first gate insulating layer 13. The first gate conductive layer may include a gate electrode G1 of the first transistor T1 and a first capacitor electrode CSE1 of the storage capacitor. The gate electrode G1 may be disposed such that it overlaps with the channel region ACT_c of the active layer ACT in the thickness direction. The first capacitor electrode CSE1 may be disposed such that it overlaps with the second capacitor electrode CSE2 described below in the thickness direction. According to the disclosed embodiment, the first capacitor electrode CSE1 may be integrated with the gate electrode G1 or may be integral with the gate electrode G1. The first capacitor electrode CSE1 may be disposed such that it overlaps with the second capacitor electrode CSE2 in the thickness direction, and a storage capacitor may be formed therebetween.

[0112] The first gate conductive layer may be made of a single layer or multiple layers of one of molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd) and copper (Cu), or alloys thereof. However, it will be understood that the disclosure is not limited thereto.

[0113] The first interlayer dielectric layer 15 may be disposed on the first gate conductive layer. The first interlayer dielectric layer 15 may be used as an insulating layer between the first gate conductive layer and other layers disposed thereon. The first interlayer dielectric layer 15 may be disposed so that it covers the first gate conductive layer or overlaps with the first gate conductive layer to protect the first gate conductive layer. The first interlayer dielectric layer 15 may be made of an inorganic material such as silicon oxide (SiO x ), silicon nitride (SiN x ) and silicon oxynitride (SiO x N y )) is formed of an inorganic layer (or includes an inorganic material (such as silicon oxide (SiO x ), silicon nitride (SiN x ) and silicon oxynitride (SiO x N y )) of an inorganic layer), or can be formed by a stack of materials.

[0114] The first data conductive layer may be disposed on the first interlayer dielectric layer 15. The first data conductive layer may include a first source electrode S1 and a first drain electrode D1 of the first transistor T1, a data line DTL, and a second capacitor electrode CSE2.

[0115] The first source electrode S1 and the first drain electrode D1 of the first transistor T1 may respectively electrically contact the doping regions ACT_a and ACT_b of the active layer ACT through contact holes passing through the first interlayer dielectric layer 15 and the first gate insulating layer 13. The first source electrode S1 of the first transistor T1 may be electrically connected to the light shielding layer BML through another contact hole.

[0116] The data line DTL may apply a data signal to another transistor (not shown) included in the display device 10. Although not shown in the drawings, the data line DTL may be electrically connected to a source / drain electrode of another transistor to transmit a signal applied from the data line DTL.

[0117] The second capacitor electrode CSE2 may be disposed to overlap the first capacitor electrode CSE1 in the thickness direction. According to the disclosed embodiment, the second capacitor electrode CSE2 may be connected to and integrated with the first source electrode S1.

[0118] The first data conductive layer may be made of a single layer or multiple layers of one of molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), and copper (Cu), or alloys thereof. However, it will be understood that the disclosure is not limited thereto.

[0119] The second interlayer dielectric layer 17 may be disposed on the first data conductive layer. The second interlayer dielectric layer 17 may be used as an insulating layer between the first data conductive layer and other layers disposed thereon. The second interlayer dielectric layer 17 may cover the first data conductive layer or overlap the first data conductive layer to protect the first data conductive layer. The second interlayer dielectric layer 17 may be made of an inorganic material such as silicon oxide (SiO x ), silicon nitride (SiN x ) and silicon oxynitride (SiO x N y )) or can be formed by a stack of materials.

[0120] The second data conductive layer may be disposed on the second interlayer dielectric layer 17. The second data conductive layer may include a first voltage line VL1, a second voltage line VL2, and a first conductive pattern CDP. A high level voltage (or a first power supply voltage) may be applied to the first voltage line VL1 to be supplied to the first transistor T1, and a low level voltage (or a second power supply voltage) may be applied to the second voltage line VL2 to be supplied to the second electrode 22. An alignment signal for aligning the light emitting element 30 during a process of manufacturing the display device 10 may be applied to the second voltage line VL2.

[0121] The first conductive pattern CDP may be electrically connected to the second capacitor electrode CSE2 through a contact hole formed in the second interlayer dielectric layer 17. The second capacitor electrode CSE2 may be integral with the first source electrode S1 of 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 electrically contact a first electrode 21 described below. The first transistor T1 may transmit a first power supply voltage applied from a first voltage line VL1 to the first electrode 21 through the first conductive pattern CDP. Although in the example shown in the drawings, the second data conductive layer includes the second voltage line VL2 and the first voltage line VL1, the disclosure is not limited thereto. The second data conductive layer may include more than one first voltage line VL1 and second voltage line VL2.

[0122] The second data conductive layer may be made of a single layer or multiple layers of one of molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd), and copper (Cu), or alloys thereof. However, it will be understood that the disclosure is not limited thereto.

[0123] The first planarization layer 19 may be disposed on the second data conductive layer. The first planarization layer 19 may include an organic insulating material (eg, an organic material such as polyimide (PI)) to provide a flat surface.

[0124] A first bank BNL1 , electrodes 21 and 22 , a light emitting element 30 , contact electrodes CNE1 and CNE2 , and a second bank BNL2 may be disposed on the first planarization layer 19 . Insulating layers PAS1 , PAS2 , PAS3 , and PAS4 may be disposed on the first planarization layer 19 .

[0125] The first bank BNL1 may be directly disposed on the first planarization layer 19. The first bank BNL1 may have a shape extending in the second direction DR2 in each of the sub-pixels PXn, and may not extend to the adjacent sub-pixel PXn in the second direction DR2. The first bank BNL1 may be disposed in the emission area EMA. The first banks BNL1 are spaced apart from each other in the first direction DR1, and the light emitting element 30 may be disposed between the first banks BNL1. The first bank BNL1 may be disposed in each of the sub-pixels PXn to form a linear pattern in the display area DPA of the display device 10. Although two first banks BNL1 are shown in the drawings, the disclosure is not limited thereto. More than two first banks BNL1 may be provided according to the number of electrodes 21 and 22.

[0126] The first bank BNL1 may have a structure that at least partially protrudes from the upper surface of the first planarization layer 19. The protrusion of the first bank BNL1 may have an inclined side surface. Light emitted from the light emitting element 30 may be reflected by the electrodes 21 and 22 disposed on the first bank BNL1, so that the light may be emitted toward the upper side of the first planarization layer 19. The first bank BNL1 may provide a region in which the light emitting element 30 is disposed, and may also serve as a reflective partition wall that reflects light emitted from the light emitting element 30 upward. The side surface of the first bank BNL1 may be inclined in a linear shape, but the disclosure is not limited thereto. The first bank BNL1 may have a semicircular shape or a semi-elliptical shape with a curved outer surface. The first bank BNL1 may include, but is not limited to, an organic insulating material such as polyimide (PI).

[0127] The electrodes 21 and 22 may be disposed on the first bank BNL1 and the first planarization layer 19. The electrodes 21 and 22 may include a first electrode 21 and a second electrode 22. The electrodes 21 and 22 may extend in the second direction DR2 and may be spaced apart from each other in the first direction DR1.

[0128] The first electrode 21 and the second electrode 22 may extend in the second direction DR2 in each of the sub-pixels PXn, and they may be spaced apart from the other electrodes 21 and 22 in the cutting area CBA. For example, the cutting area CBA may be disposed between the emission areas EMA of the sub-pixels PXn adjacent along the second direction DR2, and the first electrode 21 and the second electrode 22 may be separated from the other first electrodes 21 and the second electrodes 22 disposed in the sub-pixels PXn adjacent along the second direction DR2 in the cutting area CBA. However, it will be understood that the disclosure is not limited thereto. For each of the sub-pixels PXn, some electrodes 21 and 22 may not be separated, but may extend in the second direction DR2 and be disposed to cross the adjacent sub-pixels PXn. As another example, only one of the first electrode 21 and the second electrode 22 may be separated.

[0129] The first electrode 21 may be electrically connected to the first transistor T1 through the first contact hole CT1, and the second electrode 22 may be electrically connected to the second voltage line VL2 through the second contact hole CT2. For example, an extension portion of the first electrode 21 in the first direction DR1 of the second bank BNL2 may electrically contact the first conductive pattern CDP through the first contact hole CT1 penetrating the first planarization layer 19. An extension portion of the second electrode 22 in the first direction DR1 of the second bank BNL2 may electrically contact the second voltage line VL2 through the second contact hole CT2 penetrating the first planarization layer 19. However, it will be understood that the disclosure is not limited thereto. According to another embodiment, the first contact hole CT1 and the second contact hole CT2 may be formed in the emission area EMA surrounded by the second bank BNL2 so that the first contact hole CT1 and the second contact hole CT2 do not overlap with the second bank BNL2.

[0130] Although one first electrode 21 and one second electrode 22 are provided for each of the sub-pixels PXn in the drawings, the disclosure is not limited thereto. More than one first electrode 21 and more than one second electrode 22 may be provided in each of the sub-pixels PXn. The first electrode 21 and the second electrode 22 provided in each of the sub-pixels PXn may not have a shape extending in a certain direction, and may have various structures. For example, the first electrode 21 and the second electrode 22 may have a partially bent or folded shape, and one electrode may be provided to surround the other electrode.

[0131] The first electrode 21 and the second electrode 22 may be directly disposed on the first bank BNL1, respectively. The first electrode 21 and the second electrode 22 may have a width greater than the width of the first bank BNL1. For example, the first electrode 21 and the second electrode 22 may be disposed to cover the outer surface of the first bank BNL1 or overlap the outer surface of the first bank BNL1. The first electrode 21 and the second electrode 22 may be disposed on the side surface of the first bank BNL1, respectively, and the distance between the first electrode 21 and the second electrode 22 may be less than the distance between the first bank BNL1. At least a portion of the first electrode 21 and the second electrode 22 may be directly disposed on the first planarization layer 19, so that at least a portion of the first electrode 21 and the second electrode 22 may be located on the same plane. However, it will be understood that the disclosure is not limited thereto. In some embodiments, the electrodes 21 and 22 may have a width less than the width of the first bank BNL1. It will be noted that the electrodes 21 and 22 may be disposed to overlap at least one side surface of the first bank BNL1 to reflect light emitted from the light emitting element 30.

[0132] Each of the electrodes 21 and 22 may include a conductive material having high reflectivity. For example, each of the electrodes 21 and 22 may include a metal such as silver (Ag), copper (Cu), and aluminum (Al) as a material having high reflectivity, and may be an alloy including aluminum (Al), nickel (Ni), lanthanum (La), etc. Each of the electrodes 21 and 22 may reflect light emitted from the light emitting element 30 and traveling toward the side surface of the first bank BNL1 toward the upper side of each of the sub-pixels PXn.

[0133] However, it will be understood that the disclosure is not limited thereto. Each of the electrodes 21 and 22 may also include a transparent conductive material. For example, each of the electrodes 21 and 22 may include materials such as indium tin oxide (ITO), indium zinc oxide (IZO), and indium tin zinc oxide (ITZO). In some embodiments, each of the electrodes 21 and 22 may have a structure in which one or more layers of a transparent conductive material and a metal layer with high reflectivity are stacked, or may be made of a single layer including them. For example, each of the electrodes 21 and 22 may have a stacked structure such as ITO / silver (Ag) / ITO / , ITO / Ag / IZO, or ITO / Ag / ITZO / IZO.

[0134] The electrodes 21 and 22 may be electrically connected to the light emitting element 30, and a predetermined voltage may be applied so that the light emitting element 30 may emit light. The electrodes 21 and 22 may be electrically connected to the light emitting element 30 through the contact electrodes CNE1 and CNE2, and may transmit an electrical signal applied thereto to the light emitting element 30 through the contact electrodes CNE1 and CNE2.

[0135] One of the first electrode 21 and the second electrode 22 may be electrically connected to an anode electrode of the light emitting element 30, and the other may be electrically connected to a cathode electrode of the light emitting element 30. However, it will be understood that the disclosure is not limited thereto.

[0136] The electrodes 21 and 22 may be used to form an electric field within the subpixel PXn to align the light emitting element 30. The light emitting element 30 may be disposed between the first electrode 21 and the second electrode 22 by the electric field formed on the first electrode 21 and the second electrode 22. The light emitting element 30 of the display device 10 may be ejected on the electrodes 21 and 22 via an inkjet printing process. In the case where ink droplets containing the light emitting element 30 are applied or ejected onto the electrodes 21 and 22, an alignment signal may be applied to the electrodes 21 and 22 to generate an electric field. The light emitting element 30 dispersed in the ink may be aligned on the electrodes 21 and 22 by receiving an electrophoretic force of the electric field generated on the electrodes 21 and 22.

[0137] The first insulating layer PAS1 may be disposed on the first planarization layer 19. The first insulating layer PAS1 may be disposed to overlap the first bank BNL1 and the first and second electrodes 21 and 22. The first insulating layer PAS1 may protect the first and second electrodes 21 and 22 and insulate them from each other. This may prevent the light emitting element 30 disposed on the first insulating layer PAS1 from being damaged by contact with other elements.

[0138] According to the disclosed embodiment, the first insulating layer PAS1 may include an opening OP partially exposing the first electrode 21 and the second electrode 22. The opening OP may partially expose portions of the electrodes 21 and 22 disposed on the upper surface of the first bank BNL1. Portions of the contact electrodes CNE1 and CNE2 may electrically contact the electrodes 21 and 22 exposed through the opening OP, respectively.

[0139] The first insulating layer PAS1 may have a level difference (or height difference) such that a portion of the upper surface is recessed between the first electrode 21 and the second electrode 22. For example, when the first insulating layer PAS1 is disposed to overlap the first electrode 21 and the second electrode 22, its upper surface may have a level difference along the shape of the electrodes 21 and 22 disposed thereunder. However, it will be understood that the disclosure is not limited thereto.

[0140] The second bank BNL2 may be disposed on the first insulating layer PAS1. The second bank BNL2 may be disposed in a grid pattern on the entire surface of the display area DPA including portions extending in the first direction DR1 and the second direction DR2 in a plan view. The second bank BNL2 may be disposed along a boundary of each of the sub-pixels PXn to distinguish adjacent sub-pixels PXn from each other.

[0141] The second bank BNL2 may be disposed to surround the emission area EMA and the cutting area CBA disposed in each of the subpixels PXn to distinguish them. The first electrode 21 and the second electrode 22 may extend in the second direction DR2, and may be disposed to cross a portion of the second bank BNL2 extending in the first direction DR1. A portion of the second bank BNL2 extending in the second direction DR2 may have a greater width between the emission areas EMA than between the cutting areas CBA. Therefore, the distance between the cutting areas CBA may be smaller than the distance between the emission areas EMA.

[0142] The second bank BNL2 may have a height greater than that of the first bank BNL1. The second bank BNL2 may prevent ink in which different light emitting elements 30 are dispersed from overflowing to adjacent sub-pixels PXn during an inkjet printing process of a process of manufacturing the display device 10, so that different sub-pixels PXn may be separated from each other and the ink is not mixed. Similar to the first bank BNL1, the second bank BNL2 may include, but is not limited to, polyimide (PI).

[0143] The light emitting element 30 may be disposed on the first insulating layer PAS1. The light emitting elements 30 may be spaced apart from each other in the second direction DR2 along which the electrodes 21 and 22 extend, and may be aligned substantially parallel to each other. The light emitting element 30 may have a shape extending in a certain direction. The direction along which the electrodes 21 and 22 extend may be substantially perpendicular to the direction along which the light emitting element 30 extends. However, it will be understood that the disclosure is not limited thereto. The light emitting element 30 may be positioned obliquely relative to the direction along which the electrodes 21 and 22 extend, rather than perpendicular to the direction along which the electrodes 21 and 22 extend.

[0144] The light emitting element 30 provided in each of the sub-pixels PXn may include a light emitting layer 36 including different materials (see Figure 4 ), and can emit light having different wavelength ranges to the outside. Therefore, the light of the first color, the second color, and the third color can be emitted from the first sub-pixel PX1, the second sub-pixel PX2, and the third sub-pixel PX3, respectively. However, it will be understood that the disclosure is not limited thereto. The sub-pixels PXn may include the same kind of light emitting elements 30, and may emit light of substantially the same color.

[0145] Both ends of the light emitting element 30 may be disposed on the electrodes 21 and 22 between the first bank BNL1. The length of the light emitting element 30 may be greater than the distance between the first electrode 21 and the second electrode 22, and both ends of the light emitting element 30 may be disposed on the first electrode 21 and the second electrode 22, respectively. For example, one end of each of the light emitting elements 30 may be located on the first electrode 21, and the other end thereof may be located on the second electrode 22.

[0146] The plurality of layers of the light emitting element 30 may be arranged in a direction perpendicular to the upper surface of the first substrate 11 or the first planarization layer 19. The light emitting element 30 may be arranged so that the light emitting element 30 extends in an extension direction parallel to the upper surface of the first planarization layer 19, and the semiconductor layers included in the light emitting element 30 may be sequentially arranged in a direction parallel to the upper surface of the first planarization layer 19. However, it will be understood that the disclosure is not limited thereto. In the case where the light emitting element 30 has a different structure, the semiconductor layers may be arranged in a direction perpendicular to the upper surface of the first planarization layer 19.

[0147] The end of each of the light emitting elements 30 may electrically contact the contact electrodes CNE1 and CNE2, respectively. Figure 4 ) is not formed at the end surface on the side surface along the extension direction, so the semiconductor layers 31 and 32 of the light emitting element 30 (see Figure 4 ) or electrode layer 37 (see Figure 4 ) may be exposed, and the exposed portions of the semiconductor layers 31 and 32 or the electrode layer 37 may electrically contact the contact electrodes CNE1 and CNE2. However, it will be understood that the disclosure is not limited thereto. At least a portion of the insulating film 38 may be removed so that the side surfaces of the semiconductor layers 31 and 32 of the light emitting element 30 may be partially exposed. The exposed side surfaces of the semiconductor layers 31 and 32 may electrically contact the contact electrodes CNE1 and CNE2.

[0148] The second insulating layer PAS2 may be partially disposed on the light emitting element 30. For example, the second insulating layer PAS2 may have a width smaller than the length of the light emitting element 30, and may be disposed on the light emitting element 30 so that both ends of the light emitting element 30 are exposed while being surrounded by the second insulating layer PAS2. During the process of manufacturing the display device 10, the second insulating layer PAS2 may be disposed to overlap the light emitting element 30, the electrodes 21 and 22, and the first insulating layer PAS1, and then the second insulating layer PAS2 may be removed so that both ends of the light emitting element 30 are exposed. The second insulating layer PAS2 may extend in the second direction DR2 on the first insulating layer PAS1 in a plan view, thereby forming a linear or island pattern in each of the sub-pixels PXn. The second insulating layer PAS2 may protect the light emitting element 30 and attach the light emitting element 30 during the process of manufacturing the display device 10.

[0149] Contact electrodes CNE1 and CNE2 and a third insulating layer PAS3 may be disposed on the second insulating layer PAS2.

[0150] The contact electrodes CNE1 and CNE2 may have a shape extending in a certain direction and may be disposed on the electrodes 21 and 22. The contact electrodes CNE1 and CNE2 may include a first contact electrode CNE1 disposed on the first electrode 21 and a second contact electrode CNE2 disposed on the second electrode 22. The contact electrodes CNE1 and CNE2 may be spaced apart from each other or disposed facing each other. For example, the first contact electrode CNE1 and the second contact electrode CNE2 may be disposed on the first electrode 21 and the second electrode 22, respectively, and may be spaced apart from each other in the first direction DR1. The contact electrodes CNE1 and CNE2 may form a stripe pattern in the emission area EMA of each of the subpixels PXn.

[0151] Each of the contact electrodes CNE1 and CNE2 may electrically contact the light emitting element 30. The first contact electrode CNE1 may electrically contact a first end of each of the light emitting elements 30, and the second contact electrode CNE2 may electrically contact a second end of each of the light emitting elements 30. The semiconductor layer is exposed at both end surfaces of the light emitting element 30 in the extension direction, and the contact electrodes CNE1 and CNE2 may electrically contact the semiconductor layer and may be electrically connected to the semiconductor layer. Sides of the contact electrodes CNE1 and CNE2 that electrically contact both ends of the light emitting element 30 may be disposed on the second insulating layer PAS2. The first contact electrode CNE1 may electrically contact the first electrode 21 through an opening OP that exposes a portion of the upper surface of the first electrode 21, and the second contact electrode CNE2 may electrically contact the second electrode 22 through an opening OP that exposes a portion of the upper surface of the second electrode 22.

[0152] The width of the contact electrodes CNE1 and CNE2 measured in a certain direction may be smaller than the width of the electrodes 21 and 22 measured in the direction. The contact electrodes CNE1 and CNE2 may electrically contact the first and second ends of the light emitting element 30 and may overlap a portion of the upper surface of each of the first and second electrodes 21 and 22. However, it will be understood that the disclosure is not limited thereto. The width of the contact electrodes CNE1 and CNE2 may be greater than the width of the electrodes 21 and 22 to overlap both sides of the electrodes 21 and 22.

[0153] The contact electrodes CNE1 and CNE2 may include a transparent conductive material. For example, the contact electrodes CNE1 and CNE2 may include ITO, IZO, ITZO, aluminum (Al), etc. Light emitted from the light emitting element 30 may pass through the contact electrodes CNE1 and CNE2 and travel toward the electrodes 21 and 22. However, it will be understood that the disclosure is not limited thereto.

[0154] Although two contact electrodes CNE1 and CNE2 are provided in the sub-pixel PXn in the drawing, the disclosure is not limited thereto. The number of the contact electrodes CNE1 and CNE2 may vary according to the number of the electrodes 21 and 22 provided for each of the sub-pixels PXn.

[0155] The third insulating layer PAS3 may be disposed to overlap with the first contact electrode CNE1. The third insulating layer PAS3 may be disposed to overlap with the side of the second insulating layer PAS2 on which the first contact electrode CNE1 is disposed. For example, the third insulating layer PAS3 may be disposed to overlap with the first contact electrode CNE1 and the first insulating layer PAS1 disposed on the first electrode 21. This arrangement may be formed by completely disposing an insulating material layer for forming the third insulating layer PAS3 in the emission region EMA, and removing a portion of the insulating material layer to form the third insulating layer PAS3. During the above process, the insulating material layer forming the third insulating layer PAS3 may be removed together with the insulating material layer forming the second insulating layer PAS2. One side of the third insulating layer PAS3 may be aligned with one side of the second insulating layer PAS2. One side of the second contact electrode CNE2 may be disposed on the third insulating layer PAS3, and may be insulated from the first contact electrode CNE1 with the third insulating layer PAS3 therebetween.

[0156] The fourth insulating layer PAS4 may be completely disposed in the display area DPA of the first substrate 11. The fourth insulating layer PAS4 may protect elements disposed on the first substrate 11 from the external environment. It will be noted that the fourth insulating layer PAS4 may be omitted.

[0157] Each of the first insulating layer PAS1, the second insulating layer PAS2, the third insulating layer PAS3, and the fourth insulating layer PAS4 described above may include an inorganic insulating material or an organic insulating material. For example, the first insulating layer PAS1, the second insulating layer PAS2, the third insulating layer PAS3, and the fourth insulating layer PAS4 may include an inorganic insulating material such as silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), aluminum oxide (Al 2 O 3 ) and aluminum nitride (AlN). As another example, they may include acrylic resin, epoxy resin, phenolic resin, polyamide resin, polyimide resin, unsaturated polyester resin, polyphenylene resin, polyphenylene sulfide resin, benzocyclobutene, cardo resin, siloxane resin, silsesquioxane resin, polymethyl methacrylate, polycarbonate, polymethyl methacrylate-polycarbonate synthetic resin, etc. as organic insulating materials. However, it will be understood that the disclosure is not limited thereto.

[0158] Figure 4 is a schematic perspective view showing a light emitting element according to a disclosed embodiment.

[0159] The light emitting element 30 may be a light emitting diode. Specifically, the light emitting element 30 may have a size in the range of micrometers to nanometers, and may be an inorganic light emitting diode made of an inorganic material. Since polarity is generated by forming an electric field in a specific direction between two electrodes, the inorganic light emitting diode may be aligned between two electrodes facing each other. The light emitting element 30 may be aligned between the two electrodes by an electric field formed above the two electrodes.

[0160] The light emitting element 30 according to the embodiment may have a shape extending in a certain direction. The light emitting element 30 may have a shape of a cylinder, a rod, a line, a tube, etc. It will be understood that the shape of the light emitting element 30 is not limited thereto. The light emitting element 30 may have various shapes including a polygonal column shape such as a cube, a cuboid, and a hexagonal column, or a shape extending in a certain direction and with a partially inclined outer surface. The semiconductor layers included in the light emitting element 30, which will be described later, may have a structure sequentially arranged or stacked along the direction.

[0161] The light emitting element 30 may include a semiconductor layer doped with conductive type (eg, p-type or n-type) impurities. The semiconductor layer may emit light of a certain wavelength band by transmitting an electrical signal applied from an external power source.

[0162] Reference Figure 4 The light emitting element 30 may include a first semiconductor layer 31 , a second semiconductor layer 32 , a light emitting layer 36 , an electrode layer 37 and an insulating film 38 .

[0163] The first semiconductor layer 31 may be an n-type semiconductor. In the case where the light emitting element 30 emits light in the blue wavelength band, the first semiconductor layer 31 may include a semiconductor material having the following chemical formula: Al x Ga y In 1-x-y N(0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, it may be at least one of n-type doped AlGaInN, GaN, AlGaN, InGaN, AlN, and InN. The first semiconductor layer 31 may be doped with an n-type dopant, and the n-type dopant may be Si, Ge, Sn, Se, or the like. For example, the first semiconductor layer 31 may be n-GaN doped with n-type Si. The length of the first semiconductor layer 31 may be in the range of, but not limited to, about 1.5 μm to about 5 μm.

[0164] The second semiconductor layer 32 may be disposed on the light emitting layer 36 described below. The second semiconductor layer 32 may be a p-type semiconductor. In the case where the light emitting element 30 emits light in the blue or green wavelength band, the second semiconductor layer 32 may include a semiconductor material having the following chemical formula: Al x Ga y In 1-x-yN (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, it may be at least one of p-type doped AlGaInN, GaN, AlGaN, InGaN, AlN, and InN. The second semiconductor layer 32 may be doped with a p-type dopant, which may be Mg, Zn, Ca, Ba, or the like. For example, the second semiconductor layer 32 may be p-GaN doped with p-type Mg. The length of the second semiconductor layer 32 may be in the range of, but not limited to, about 0.05 μm to about 0.10 μm.

[0165] Although each of the first semiconductor layer 31 and the second semiconductor layer 32 is implemented as a single layer in the drawings, the disclosure is not limited thereto. Depending on the material of the light emitting layer 36, the first semiconductor layer 31 and the second semiconductor layer 32 may also include a greater number of layers, for example, a cap layer or a tensile strain barrier lowering (TSBR) layer.

[0166] The light emitting layer 36 may be disposed between the first semiconductor layer 31 and the second semiconductor layer 32. The light emitting layer 36 may include a material having a single quantum well structure or a multi-quantum well structure. In the case where the light emitting layer 36 includes a material having a multi-quantum well structure, the structure may include quantum layers and well layers stacked alternately with each other. When electron-hole pairs are combined in the light emitting layer 36 in response to an electrical signal applied through the first semiconductor layer 31 and the second semiconductor layer 32, the light emitting layer 36 may emit light. In the case where the light emitting layer 36 emits light in a blue band, the light emitting layer 36 may include materials such as AlGaN and AlGaInN. Specifically, in the case where the light emitting layer 36 has a multi-quantum well structure in which quantum layers and well layers are stacked alternately with each other, the quantum layers may include AlGaN or AlGaInN, and the well layers may include materials such as GaN and AlGaN. For example, the light emitting layer 36 includes AlGaInN as a quantum layer and AlGaN as a well layer, and as described above, the light emitting layer 36 may emit blue light having a central band of about 450nm to about 495nm.

[0167] However, it will be understood that the disclosure is not limited thereto. The light emitting layer 36 may have a structure in which a semiconductor material having a large band gap energy and a semiconductor material having a small band gap energy are alternately stacked with each other, and may include other III- to V-group semiconductor materials according to the wavelength range of the emitted light. Therefore, the light emitted from the light emitting layer 36 is not limited to light in the blue band. In some embodiments, the light emitting layer 36 may emit light in the red or green band. The length of the light emitting layer 36 may be, but is not limited to, in the range of about 0.05 μm to about 0.10 μm.

[0168] Light emitted from the light emitting layer 36 may be emitted not only through the outer surface of the light emitting element 30 in the longitudinal direction but also through both side surfaces. The direction in which light emitted from the light emitting layer 36 travels is not limited to a certain direction.

[0169] The electrode layer 37 may be an ohmic contact electrode. However, it will be understood that the disclosure is not limited thereto. The electrode layer 37 may be a Schottky contact electrode. The light emitting element 30 may include at least one electrode layer 37. Figure 4 In the example shown in , the light emitting element 30 includes one electrode layer 37, but the disclosure is not limited thereto. In some embodiments, the light emitting element 30 may include a greater number of electrode layers 37, or the electrode layer 37 may be omitted. Even if the number of electrode layers 37 is different or the electrode layer 37 includes other structures, the following description of the light emitting element 30 may also be applied in the same manner.

[0170] In the case where the light emitting element 30 is electrically connected to an electrode or a contact electrode in the display device 10 according to the disclosed embodiment, the electrode layer 37 can reduce the resistance between the light emitting element 30 and the electrode or the contact electrode. The electrode layer 37 may include a metal or a metal oxide having conductivity. For example, the electrode layer 37 may 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 layer 37 may include a semiconductor material doped with n-type or p-type impurities. The electrode layer 37 may include the same material or may include different materials. However, it will be understood that the disclosure is not limited thereto.

[0171] The insulating film 38 may be provided to surround the outer surfaces of the semiconductor layers 31 and 32 and the electrode layer 37 described above. For example, the insulating film 38 may be provided to surround at least the outer surface of the light emitting layer 36, and may extend in the direction in which the light emitting element 30 extends. The insulating film 38 may protect the elements described above. The insulating film 38 may be formed to surround the side surfaces of the element, and both ends of the light emitting element 30 in the longitudinal direction may be exposed.

[0172] Although in the example shown in the drawings, the insulating film 38 extends in the longitudinal direction of the light emitting element 30 to cover or overlap the side surface from the first semiconductor layer 31 to the electrode layer 37, the disclosure is not limited thereto. The insulating film 38 may cover only the outer surfaces of the semiconductor layers 31 and 32 and a portion of the light emitting layer 36, or may cover only a portion of the outer surface of the electrode layer 37 to partially expose the outer surface of the electrode layer 37. A portion of the upper surface of the insulating film 38 adjacent to at least one end of the electrode layer 37 in cross section may be rounded.

[0173] The thickness of the insulating film 38 may be, but is not limited to, in the range of about 10 nm to about 1.0 μm. Preferably, the thickness of the insulating film 38 may be about 40 nm.

[0174] The insulating film 38 may include a material having insulating properties, such as silicon oxide (SiO x ), silicon nitride (SiN x ), silicon oxynitride (SiO x N y ), aluminum nitride (AlN) and aluminum oxide (Al 2 O 3 ). Therefore, it is possible to prevent an electrical short circuit that may occur when the light emitting layer 36 is in electrical contact with an electrode that transmits an electrical signal to the light emitting element 30. Since the insulating film 38 surrounds the light emitting layer 36 to protect the outer surface of the light emitting element 30, it is possible to prevent a decrease in light emitting efficiency.

[0175] The outer surface of the insulating film 38 may be surface treated. The light emitting elements 30 may be dispersed in ink, and ink droplets may be ejected onto the electrodes. In this case, surface treatment may be applied to the insulating film 38 to make the insulating film 38 hydrophobic or hydrophilic to prevent the light emitting elements 30 dispersed in the ink from aggregating with each other. For example, the outer surface of the insulating film 38 may be surface treated with a material such as stearic acid and 2,3-naphthalene dicarboxylic acid.

[0176] The length h of the light emitting element 30 may be in a range from about 1 μm to about 10 μm or from about 2 μm to about 6 μm, and preferably approximately about 3 μm to about 5 μm. The diameter of the light emitting element 30 may be in a range from about 30 nm to about 700 nm, and the aspect ratio of the light emitting element 30 may be in a range from about 1.2 to about 100. However, it will be understood that the disclosure is not limited thereto. Depending on the composition difference of the light emitting layer 36, the light emitting element 30 included in the display device 10 may have different diameters. The diameter of the light emitting element 30 may be about 500 nm.

[0177] It will be noted that the shape and material of the light emitting element 30 are not limited to those of Figure 4 In some embodiments, light emitting element 30 may include a greater number of layers or may have a different shape.

[0178] Figure 5 is a schematic perspective view showing a light emitting element according to another disclosed embodiment.

[0179] Reference Figure 5According to the embodiment, the light emitting element 30' may further include a third semiconductor layer 33' disposed between the first semiconductor layer 31' and the light emitting layer 36', and a fourth semiconductor layer 34' and a fifth semiconductor layer 35' disposed between the light emitting layer 36' and the second semiconductor layer 32'. Figure 5 The light emitting element 30' and Figure 4 The light emitting element 30 of FIG. 1 is different at least in that semiconductor layers 33', 34' and 35' and electrode layers 37a' and 37b' are further provided, and the light emitting layer 36' includes different elements. In the following description, the description will focus on the differences, and redundant description will be omitted.

[0180] Figure 4 The light emitting layer 36 of the light emitting element 30 may include nitrogen (N) and may emit blue light or green light. Figure 5 In the light-emitting element 30', the light-emitting layer 36' and the other semiconductor layers can each be a semiconductor including at least phosphorus (P). The light-emitting element 30' according to the disclosed embodiment can emit red light with a central band of about 620nm to about 750nm. However, it will be understood that the central band of red light is not limited to the above values ​​and can cover all wavelength ranges that can be considered red in the art.

[0181] Specifically, the first semiconductor layer 31' may include a semiconductor layer having a chemical formula of In x Al y Ga 1-x-y The first semiconductor layer 31' may be a semiconductor material of P (0≤x≤1, 0≤y≤1, 0≤x+y≤1) as an n-type semiconductor layer. The first semiconductor layer 31' may be one or more of n-type InAlGaP, GaP, AlGaP, InGaP, AlP and InP. For example, the first semiconductor layer 31' may be n-InAlGaP doped with n-type Si.

[0182] Specifically, the second semiconductor layer 32' may include a semiconductor layer having a chemical formula In x Al y Ga 1-x-y The semiconductor material of P (0≤x≤1, 0≤y≤1, 0≤x+y≤1) is used as the p-type semiconductor layer. The second semiconductor layer 32' may be one or more of p-type InAlGaP, GaP, AlGaNP, InGaP, AlP and InP. For example, the second semiconductor layer 32' may be p-GaP doped with p-type Mg.

[0183] The light emitting layer 36' may be disposed between the first semiconductor layer 31' and the second semiconductor layer 32'. The light emitting layer 36' may include a material having a single quantum well structure or a multiple quantum well structure, and may emit light of a certain wavelength band. In the case where the light emitting layer 36' has a multiple quantum well structure in which quantum layers and well layers are alternately stacked with each other, the quantum layer may include AlGaP or InAlGaP, and the well layer may include GaP or AlInP. For example, the light emitting layer 36' may include InAlGaP as a quantum layer and AlInP as a well layer, and may emit red light having a central wavelength band of about 620nm to about 750nm.

[0184] Figure 5 The light emitting element 30' may include a coating disposed adjacent to the light emitting layer 36'. Figure 5 As shown in FIG. 1 , the third semiconductor layer 33 ′ and the fourth semiconductor layer 34 ′ disposed below and on the light emitting layer 36 ′ between the first semiconductor layer 31 ′ and the second semiconductor layer 32 ′ may be cladding layers.

[0185] The third semiconductor layer 33' may be disposed between the first semiconductor layer 31' and the light emitting layer 36'. The third semiconductor layer 33' may be an n-type semiconductor similar to the first semiconductor layer 31', and may include a semiconductor having a chemical formula In x Al y Ga 1-x-y P (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, the first semiconductor layer 31 ′ may be n-InAlGaP, and the third semiconductor layer 33 ′ may be n-AlInP. However, it will be understood that the disclosure is not limited thereto.

[0186] The fourth semiconductor layer 34' may be disposed between the light emitting layer 36' and the second semiconductor layer 32'. The fourth semiconductor layer 34' may be a p-type semiconductor like the second semiconductor layer 32', and may include a semiconductor having a chemical formula of In x Al y Ga 1-x-y The semiconductor material may be P (0≤x≤1, 0≤y≤1, 0≤x+y≤1). For example, the second semiconductor layer 32 ′ may be p-GaP, and the fourth semiconductor layer 34 ′ may be p-AlInP.

[0187] The fifth semiconductor layer 35' may be disposed between the fourth semiconductor layer 34' and the second semiconductor layer 32'. The fifth semiconductor layer 35' may be a p-type semiconductor similar to the second semiconductor layer 32' and the fourth semiconductor layer 34'. In some embodiments, the fifth semiconductor layer 35' may reduce the difference in lattice constant between the fourth semiconductor layer 34' and the second semiconductor layer 32'. The fifth semiconductor layer 35' may be a tensile strain barrier reduction (TSBR) layer. For example, the fifth semiconductor layer 35' may include, but is not limited to, p-GaInP, p-AlInP, p-InAlGaP, etc. The lengths of the third semiconductor layer 33', the fourth semiconductor layer 34', and the fifth semiconductor layer 35' may be, but are not limited to, a range of about 0.08 μm to about 0.25 μm.

[0188] The first electrode layer 37a' and the second electrode layer 37b' may be disposed on the first semiconductor layer 31' and the second semiconductor layer 32', respectively. The first electrode layer 37a' may be disposed on the lower surface of the first semiconductor layer 31', and the second electrode layer 37b' may be disposed on the upper surface of the second semiconductor layer 32'. However, it will be understood that the disclosure is not limited thereto. At least one of the first electrode layer 37a' and the second electrode layer 37b' may be omitted. For example, in the light emitting element 30', the first electrode layer 37a' may not be disposed on the lower surface of the first semiconductor layer 31', and only one second electrode layer 37b' may be disposed on the upper surface of the second semiconductor layer 32'.

[0189] The light emitting element 30 may be ejected onto the electrodes 21 and 22 by an inkjet printing process. The light emitting element 30 dispersed in a solvent may be ejected onto the electrodes 21 and 22, and an alignment signal is applied to the electrodes 21 and 22 so that the light emitting element 30 may be disposed between the electrodes 21 and 22. In the case where the alignment signal is applied to the electrodes 21 and 22, an electric field is formed over the electrodes 21 and 22, and the light emitting element 30 may receive a dielectrophoretic force by the electric field. In the case where the light emitting element 30 receives the dielectrophoretic force, the light emitting element 30 may be disposed between the first electrode 21 and the second electrode 22 as their positioning and position change.

[0190] In this case, the light emitting elements 30 dispersed in the ink may adhere together in the solvent due to the physical properties of the solvent. In that case, the light emitting elements 30 adhered together are aligned between the electrodes 21 and 22, so the light emitting elements 30 may be poorly aligned. If the light emitting elements 30 adhered together are arranged close to one side of the sub-pixel PXn, the brightness in the sub-pixel PXn becomes uneven.

[0191] According to the disclosed embodiment, the ink containing the light emitting element 30 may include a solvent having a Hansen solubility parameter and a hydrogen bonding parameter within a predetermined range and / or an ester group, thereby increasing the dispersibility of the light emitting element 30. Therefore, it is possible to suppress the light emitting element 30 from adhering together when the ink containing the light emitting element 30 is dropped onto the sub-pixel PXn, thereby suppressing poor alignment and achieving uniform brightness in the sub-pixel PXn.

[0192] Hereinafter, ink containing the light emitting element 30 will be described.

[0193] Figure 6 is a perspective view schematically showing ink containing a light emitting element according to a disclosed embodiment.

[0194] Reference Figure 6 The ink 200 according to the disclosed embodiment may include a solvent 220 and a light emitting element 30 dispersed in the solvent 220. The light emitting element 30 may be the above-mentioned Figure 4 and Figure 5 The light emitting element 30 or the light emitting element 30' is described. Figure 6 It is shown in Figure 4 The light emitting element 30 has been described above, and thus the solvent 220 will be described in detail below.

[0195] Since the light emitting element 30 is dispersed in the solvent 220, the solvent 220 can store the light emitting element 30 each including a semiconductor layer, and the solvent 220 can be an organic solvent that does not react with the light emitting element 30. The solvent 220 can have such a viscosity that the solvent 220 can be discharged in a liquid state through the nozzle of the inkjet printing device. The molecules of the solvent 220 can surround the surface of the light emitting element 30 and disperse the light emitting element 30. The ink 200 containing the light emitting element 30 can be prepared as a solution or a colloid.

[0196] According to the disclosed embodiment, the solvent 220 may satisfy a predetermined range of Hansen solubility parameters. The Hansen solubility parameters include dispersion parameters, polarity parameters, and hydrogen bonding parameters to express solubility characteristics. Among these parameters, the solvent 220 according to the embodiment may satisfy a predetermined range of polarity parameters and hydrogen bonding parameters.

[0197] Specifically, solvent 220 can have a polarity parameter (dP) ranging from about 4 to about 9. The polarity parameter represents the interaction of the polarity of the molecule. When the molecular structure is asymmetric, the polarity parameter can show a high value. In addition, solvent 220 can have a hydrogen bonding parameter (dH) ranging from about 6 to about 11. The hydrogen bonding parameter represents the intermolecular hydrogen bonding interaction. When there are more hydrogen bonding sites in the molecule, the hydrogen bonding parameter can show a higher value.

[0198] Figure 7 is a diagram showing the degree of center alignment of a light-emitting element according to the polarity parameter and hydrogen bonding parameter of a solvent.

[0199] Figure 7 The center alignment of the light emitting elements by adjusting the range of the polarity parameter and the hydrogen bonding parameter of the solvent 220 is schematically shown. As used herein, the center alignment refers to the percentage ratio of the light emitting elements correctly aligned in the sub-pixel to the total light emitting elements. The dots represent the center alignment of the light emitting elements. Specifically, the square represents the center alignment of the light emitting elements from about 70% to about 100%, the triangle represents the center alignment from about 50% to about 60%, the star represents the center alignment from about 30% to about 50%, and the circle represents the center alignment from about 0% to about 30%.

[0200] from Figure 7 It can be seen that most of the points representing the central alignment of the light emitting elements from about 70% to about 100% are concentrated within the range of the polarity parameter of the solvent 220 between about 4 and about 9 and the hydrogen bonding parameter between about 6 and about 11.

[0201] In view of the above, it can be seen that the optimal ranges of the polarity parameter and hydrogen bonding parameter of the solvent 220 that can exhibit excellent center alignment of the light emitting element 30 are about 4 to about 9 polarity parameters and about 6 to about 11 hydrogen bonding parameters.

[0202] Figure 8 An image of ink having light emitting elements mixed therein according to a disclosed embodiment is shown. Fig. 9 A graph showing changes in transparency and concentration of ink in which a light emitting element is mixed over time according to a disclosed embodiment is shown. Fig.10 An image of ink in which a light emitting element is mixed according to a comparative example is shown. Fig.11 A graph showing changes over time in transparency and density of ink in which a light emitting element is mixed according to a comparative example is shown.

[0203] first, Figure 8 The ink 200 is obtained by mixing the light emitting element 30 at a concentration of about 0.1 wt % in a solvent 220 having a polarity parameter of from about 4 to about 9 and a hydrogen bonding parameter of from about 6 to about 11. Figure 8 It can be seen that the light emitting element 30 is uniformly dispersed in the solvent 220 .

[0204] Reference Fig. 9, the horizontal axis of each of the graphs represents the height of the bottle, the far left is the bottom of the bottle, and the far right is the top of the bottle. The vertical axis of the graph (a) represents transparency, and the vertical axis of the graph (b) represents backscattering. The lines indicated by different colors represent different times over 24 hours from the start of measurement.

[0205] Reference Fig. 9 , as the bottle is filled with the ink 200 containing the light emitting element 30 according to the disclosed embodiment, the transparency and backscattering are measured over time. Referring to the graph (a), the transparency at the top of the bottle gradually increases over time, and the transparency is 0 throughout the rest of the bottle. Referring to the graph (b), the value of backscattering gradually decreases at the top of the bottle, and the value of backscattering is maintained throughout the rest of the bottle over time as is the transparency. It can be seen from the results that according to the disclosed embodiment, the light emitting element 30 is uniformly dispersed in the solvent 220 of the ink 200.

[0206] On the other hand, according to Fig.10 In a comparative example, an ink is obtained by mixing a light emitting element at a concentration of about 0.1 wt % in a solvent having a polarity parameter and a hydrogen bonding parameter outside the above range. Fig.10 It can be seen that the light emitting elements adhere together in the solvent.

[0207] Reference Fig.11 , since the bottle was filled with the ink containing the light emitting element according to the comparative example, the transparency and the backscattering were measured over time. Referring to the graph (a), in the whole bottle, the transparency was about 80% or more over time. Referring to the graph (b), in the whole bottle, the value of the backscattering also showed a value from about 20% to about 25% over time as did the transparency. It can be seen from the results that according to the comparative example, most of the light emitting elements adhered together in the solvent of the ink and sank to the bottom of the bottle in a short time.

[0208] In view of the above, since the solvent 220 has a polarity parameter from about 4 to about 9 and a hydrogen bonding parameter from about 6 to about 11, the solvent 220 according to the disclosed embodiment may improve the dispersibility of the light emitting element 30 .

[0209] According to another embodiment, the solvent 220 may contain a compound including an ester group. The light emitting element 30 may be as described above with reference to Figure 4 and Figure 5 Aluminum oxide (Al2O3) is described as the material of the insulating film 38. 2 O 3) is surrounded. That is, the insulating film 38 of the light emitting element 30 can be chemically combined with the solvent 220, and in particular, the ester group contained in the solvent 220 has a large interaction energy with aluminum oxide. Therefore, the light emitting element 30 can be uniformly dispersed in the solvent 220.

[0210] According to the disclosed embodiment, the solvent 220 may include a compound represented by the following Chemical Formula 1:

[0211] [Chemical formula 1]

[0212]

[0213] Wherein, R and R' can be independently hydrogen, substituted or unsubstituted straight or branched alkyl with 1 to 10 carbon atoms, substituted or unsubstituted alkyl ether with 1 to 10 carbon atoms, substituted or unsubstituted alkyl ester with 1 to 10 carbon atoms, or substituted or unsubstituted phenyl. The substituent can be at least one selected from the group consisting of alkyl with 1 to 10 carbon atoms, ester group, alkyl ester group with 1 to 10 carbon atoms, ether group, alkyl ether group with 1 to 10 carbon atoms, carbonyl group and hydroxyl group. However, the disclosure is not limited thereto.

[0214] According to the disclosed embodiments, the solvent 220 may include a compound represented by one of the following Chemical Formulas 2 to 9:

[0215] [Chemical formula 2]

[0216]

[0217] [Chemical formula 3]

[0218]

[0219] [Chemical formula 4]

[0220]

[0221] [Chemical formula 5]

[0222]

[0223] [Chemical formula 6]

[0224]

[0225] [Chemical formula 7]

[0226]

[0227] [Chemical formula 8]

[0228]

[0229] [Chemical formula 9]

[0230]

[0231] The compounds represented by Chemical Formula 2 to Chemical Formula 9 may include at least one ester group. Each of the compounds may include 1 to 4 ester groups to improve dispersibility of the light emitting element 30 in the solvent 220.

[0232] According to the disclosed embodiment, triethyl citrate represented by chemical formula 2 and aluminum oxide (Al 2 O 3 ) has a large interaction energy of approximately -3.54. Since triethyl citrate has a large interaction energy that can break the bond between the solvent 220 and the light emitting element 30, the dispersibility of the light emitting element 30 increases, so that the light emitting element 30 is hardly adhered together. On the other hand, triethylene glycol monobutyl ether and aluminum oxide (Al 2 O 3 ) has a small interaction energy, ie, approximately -2.84, and thus many light emitting elements 30 adhere together in the solvent 220 of triethylene glycol monobutyl ether.

[0233] In view of the above, the solvent 220 containing an ester group according to the embodiment can improve the dispersibility of the light emitting elements 30 , thereby suppressing the light emitting elements 30 from being adhered together.

[0234] According to yet another embodiment, the solvent 220 may contain an ester group and may also satisfy Hansen solubility parameters of a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11.

[0235] According to an embodiment, the compounds represented by Chemical Formula 2 to Chemical Formula 9 described above may contain an ester group, and may satisfy a Hansen solubility parameter having a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11.

[0236] For example, triethyl citrate represented by Chemical Formula 2 has a polarity parameter of about 6 and a hydrogen bonding parameter of about 10.1. O-acetyl triethyl citrate represented by Chemical Formula 3 has a polarity parameter of about 4.7 and a hydrogen bonding parameter of about 7.2. Tributyl citrate represented by Chemical Formula 4 has a polarity parameter of about 4.3 and a hydrogen bonding parameter of about 7.3. Diisooctyl phthalate represented by Chemical Formula 5 has a polarity parameter of about 5.8 and a hydrogen bonding parameter of about 6.6. Butyl carbitol acetate represented by Chemical Formula 6 has a polarity parameter of about 4.8 and a hydrogen bonding parameter of about 6.5. Propylene glycol monomethyl ether acetate represented by Chemical Formula 7 has a polarity parameter of about 5.5 and a hydrogen bonding parameter of about 6.6. Triacetin represented by Chemical Formula 8 has a polarity parameter of about 5.8 and a hydrogen bonding parameter of about 8.7. Methyl salicylate represented by Chemical Formula 9 has a polarity parameter of about 8.7 and a hydrogen bonding parameter of about 10.2.

[0237] When the solvent 220 contains an ester group and satisfies Hansen solubility parameters of polarity parameters between about 4 and about 9 and hydrogen bonding parameters between about 6 and about 11, dispersibility of the light emitting element 30 in the solvent 220 can be further improved.

[0238] Incidentally, it is necessary to keep the light emitting element 30 dispersed before or during the printing process. According to the disclosed embodiment, the solvent 220 may have a viscosity of from about 20 cP to about 200 cP at room temperature. If the viscosity of the solvent 220 at room temperature is equal to or greater than about 20 cP, the light emitting element 30 may remain dispersed in the solvent 220. If the viscosity of the solvent 220 at room temperature is equal to or less than about 200 cP, the solvent 220 may be easily ejected onto the substrate via the printing process.

[0239] After the printing process of the light emitting element 30, the solvent 220 needs to be removed by evaporating the solvent 220. The solvent 220 may have a relatively high boiling point and may be adjusted so that the boiling point is not too high. According to the disclosed embodiment, the solvent 220 has a boiling point of about 400° C. or less so that the structure formed on the substrate is not damaged by high heat.

[0240] The content of the light emitting element 30 included in the ink 200 may vary according to the number of light emitting elements 30 per drop of ink 200 discharged through the nozzle during the printing process. According to the disclosed embodiment, the light emitting element 30 may be included in the solvent 220 at from about 0.01 parts by weight to about 10 parts by weight based on 100 parts by weight of the ink 200. However, it will be noted that this is merely illustrative, and the content of the light emitting element 30 may vary according to the number of light emitting elements 30 per drop of ink 200.

[0241] The ink 200 may further include a dispersant (not shown) that improves the dispersion of the light emitting element 30. The type of dispersant is not specifically limited herein. The content of the dispersant may be appropriately determined to further disperse the light emitting element 30. For example, based on 100 parts by weight of the light emitting element 30, from about 10 parts by weight to about 50 parts by weight of the dispersant may be included. However, it will be understood that the disclosure is not limited thereto.

[0242] The ink 200 according to the disclosed embodiment includes a solvent 220 satisfying a polarity parameter and a hydrogen bonding parameter within a predetermined range, and includes at least one ester group, thereby improving the dispersibility of the light emitting element 30. By doing so, it is possible to prevent the light emitting elements 30 from adhering together before and during the printing process. Therefore, it is possible to prevent poor alignment from occurring due to the light emitting elements 30 dispersed on the electrodes 21 and 22 adhering together.

[0243] During a process of manufacturing the display device 10 , a process of disposing the light emitting element 30 on the electrodes 21 and 22 may be performed, which may be performed via a printing process using the ink 200 .

[0244] Hereinafter, an inkjet printing apparatus for ejecting ink 200 containing light emitting elements 30 will be described.

[0245] Fig.12 is a diagram schematically illustrating an inkjet printing apparatus according to a disclosed embodiment.

[0246] Reference Fig.12 , the inkjet printing apparatus 1000 may include a discharge area DA, a circulation area CA, an injection area IA, and a preparation area PA.

[0247] In the discharge area DA, droplets of the ink 200 may be discharged. The print head unit 100 may be disposed in the discharge area DA, and may include a body 110 and nozzles of an inkjet head 120. The print head unit 100 may be disposed in the discharge area DA to discharge the ink 200 containing the light emitting element 30 through the nozzles of the inkjet head 120.

[0248] In the circulation area CA, the ink 200 to be supplied to the print head unit 100 circulates. By circulating the ink 200 containing the light emitting elements 30 in the circulation area CA, the variation in the number of light emitting elements 30 contained in the ink 200 can be reduced.

[0249] The circulation area CA may include an ink circulation unit 270. The ink circulation unit 270 may supply the ink 200 containing the light emitting element 30 to the print head unit 100, or may receive the ink 200 to circulate the ink 200.

[0250] The ink circulation unit 270 may be connected to the print head unit 100 through a first connection tube (also referred to as a "first injection line") IL1 and a second connection tube (also referred to as a "second injection line") IL2. Specifically, the ink circulation unit 270 may supply the ink 200 to the print head unit 100 through the first injection line IL1, and may receive the ink 200 from the print head unit 100 through the second injection line IL2.

[0251] The ink circulation unit 270 may include a first ink storage 260, a second ink storage 210, and a pressure pump 250. The first ink storage 260 may be connected to the print head unit 100 through a first injection line IL1. The first ink storage 260 may be connected to the second ink storage 210 through a fourth injection line IL4. The second ink storage 210 may be connected to the print head unit 100 through a second injection line IL2. The pressure pump 250 may be provided between the second ink storage 210 and the print head unit 100. They may form a single ink circulation system.

[0252] The first ink storage 260 may temporarily store or contain ink 200 before being supplied to the print head unit 100, and may deliver the ink 200 to the print head unit 100. The first ink storage 260 may deliver the ink 200 supplied from the second ink storage 210 through the fourth injection line IL4 to the print head unit 100 through the first injection line IL1.

[0253] The second ink storage 210 may store and / or contain the ink 200 before the ink 200 is supplied to the first ink storage 260, and may disperse the light emitting element 30 in the solvent 220. The second ink storage 210 may receive the ink 200 from the ink injection unit 300 through the third injection line IL3 and from the print head unit 100 through the second injection line IL2, and may disperse the light emitting element 30 in the ink 200 so that they do not precipitate. As a result, the ink 200 having a uniform dispersion degree may be supplied to the first ink storage 260. The second ink storage 210 may be used as a buffer storage in which a portion of the ink 200 circulating in the ink circulation system is stored.

[0254] The second ink storage 210 may include an agitator ST. The agitator ST may disperse the light emitting elements 30 in the ink 200. When the agitator ST rotates, the light emitting elements 30 in the ink 200 supplied to the second ink storage 210 may remain dispersed without sinking. Specifically, when the light emitting elements 30 sink to the bottom, the agitator ST of the second ink storage 210 may prevent different numbers of light emitting elements 30 in the ink 200 from being discharged through the inkjet head 120 at different processing times.

[0255] The pressure pump 250 may be provided between the print head unit 100 and the second ink storage 210. The remaining portion of the ink 200 after it is ejected from the print head unit 100 may be supplied to the second ink storage 210 by the pressure pump 250. The pressure pump 250 may transmit power to the fluid so that the ink 200 may circulate in the ink circulation system.

[0256] The injection area IA may receive the ink 200 from the ink bottle BO provided in the inkjet printing apparatus 1000 to supply it to the circulation area CA. The injection area IA may include an ink injection unit 300. The ink injection unit 300 converts the ink 200 having high viscosity stored in the ink bottle BO into the ink 200 having low viscosity and supplies it to the ink circulation unit 270. For example, in the case where the ink bottle BO is provided in the inkjet printing apparatus 1000, the ink injection unit 300 may convert the ink 200 into a solid or convert the liquid or colloid ink 200 having high viscosity into the liquid or colloid ink 200 having low viscosity and may supply it to the ink circulation unit 270. The ink injection unit 300 may convey the ink 200 supplied from the ink preparation unit 400 through the fifth injection line IL5 to the ink circulation unit 270 (e.g., the second ink storage 210) through the third injection line IL3.

[0257] In the preparation area PA, one or more ink bottles BO may be stored before or during a printing process. The preparation area PA may store the ink bottles BO under conditions such that sedimentation or settling of the light emitting element 30 does not occur to improve reliability of the printing process.

[0258] The preparation area PA may include an ink preparation unit 400. The ink preparation unit 400 may provide an ink bottle BO in which previously produced ink 200 is stored to the inkjet printing apparatus 1000 or may store the ink bottle BO. The ink preparation unit 400 may supply the ink 200 stored in the ink bottle BO to the ink injection unit 300 through the fifth injection line IL5.

[0259] A method of manufacturing the display device 10 according to the disclosed embodiment will be described below, the method including a process of ejecting the ink 200 using the inkjet printing apparatus described above.

[0260] Fig.13 is a schematic flow chart for illustrating a method of manufacturing a display device according to a disclosed embodiment.

[0261] Reference Fig.13 The method of manufacturing the display device 10 according to the embodiment may include: preparing an ink 200 including a light emitting element 30 and a solvent 220 and a target substrate SUB on which electrodes 21 and 22 are formed (see Fig.15)(step S100); ejecting droplets of ink 200 onto a target substrate SUB (step S200); and generating an electric field over electrodes 21 and 22 so that light emitting element 30 is placed on electrodes 21 and 22 (step S300). According to the disclosed embodiment, solvent 220 has a Hansen solubility parameter with a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11, and includes at least one ester group, thereby improving the dispersibility of light emitting element 30. Hereinafter, a method for manufacturing display device 10 will be described in detail with reference to other drawings.

[0262] Figures 14 to 21 are schematic cross-sectional views showing some of the processing steps of manufacturing a display device according to a disclosed embodiment.

[0263] First, refer to Fig.14 and Fig.15 , an ink 200 including a light emitting element 30 and a solvent 220 and a target substrate SUB on which a first electrode 21, a second electrode 22, a first insulating layer PAS1, a first bank BNL1, and a second bank BNL2 are disposed are prepared. Although a pair of electrodes is disposed on the target substrate SUB in the drawings, a greater number of electrode pairs may be disposed on the target substrate SUB. In addition to the first substrate 11 of the display device 10 described above, the target substrate SUB may further include a circuit element disposed thereon. In the following description, the circuit element will be omitted for ease of explanation.

[0264] The ink 200 may include a solvent 220 and a light emitting element 30 dispersed therein. The solvent 220 may have a Hansen solubility parameter of a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11 and / or may include at least one ester group. The step of preparing the ink 200 may include a dispersion process of mixing the light emitting element 30 with the solvent 220.

[0265] The dispersion process is performed by mixing the light emitting element 30 in the solvent 220 and mixing it for 5 minutes or more. The light emitting element 30 may be included in the solvent 220 in an amount of from about 0.01 parts by weight to about 10 parts by weight based on 100 parts by weight of the total ink 200. The mixing process may be performed by an ultrasonic treatment process, a stirring process, a grinding process, or the like.

[0266] The ink 200 produced by the dispersion process can be stored at room temperature (25° C.). The solvent 220 may have a Hansen solubility parameter of a polarity parameter between about 4 and about 9 and a hydrogen bonding parameter between about 6 and about 11 and / or may include at least one ester group. Therefore, the dispersibility of the mixed light emitting elements 30 can be improved to prevent them from adhering together, so that they are hardly precipitated and can remain dispersed.

[0267] Then, refer to Fig.16 and Fig.17 , droplets of ink 200 are ejected onto the first insulating layer PAS1 on the target substrate SUB, which is overlapped with the first electrode 21 and the second electrode 22. According to the disclosed embodiment, droplets of ink 200 may be ejected onto the first insulating layer PAS1 by a printing process using the inkjet printing apparatus 1000 described above. Droplets of ink 200 may be ejected through nozzles of an inkjet head 120 included in the inkjet printing apparatus 1000. Droplets of ink 200 may be discharged onto the target substrate SUB through nozzles disposed in the inkjet head 120. Droplets of ink 200 ejected from the nozzles may be disposed on the first insulating layer PAS1, on which electrodes 21 and 22 disposed on the target substrate SUB are formed. The light emitting element 30 may have a shape extending in a certain direction, and may be dispersed in the ink 200 in randomly positioned directions.

[0268] When the light emitting elements 30 are emitted onto the first insulating layer PAS1, the ink 200 may be uniformly diffused in the second bank BNL2. Therefore, the light emitting elements 30 dispersed in the ink 200 may be uniformly distributed in the second bank BNL2.

[0269] Subsequently, an electric field is generated in the ink 200 so that the light emitting element 30 is disposed on the electrodes 21 and 22 (step S300 ), and the solvent 220 is removed (step S400 ).

[0270] Reference Fig.18 After ejecting droplets of ink 200 including light emitting elements 30 onto a target substrate SUB, an alignment signal is applied to electrodes 21 and 22 to generate an electric field EL over the target substrate SUB. The light emitting elements 30 dispersed in the solvent 220 may receive a dielectrophoretic force through the electric field EL and may be disposed on the electrodes 21 and 22 as their positioning and location are changed.

[0271] When the electric field EL is generated above the target substrate SUB, the light emitting element 30 may receive a dielectrophoretic force. When the electric field EL generated above the target substrate SUB is parallel to the upper surface of the target substrate SUB, the light emitting elements 30 may be aligned so that they are parallel to the target substrate SUB in the direction in which they extend, and may be disposed on the first electrode 21 and the second electrode 22. The light emitting elements 30 may be moved toward the electrodes 21 and 22 from the initially dispersed positions by the dielectrophoretic force. Both ends of each of the light emitting elements 30 may be disposed on the first electrode 21 and the second electrode 22, respectively, while their positioning may be changed by the electric field EL. Each of the light emitting elements 30 includes a semiconductor layer doped with a different conductivity type and may have a dipole moment therein. In the case where the light emitting element 30 is placed under the electric field EL, the light emitting element 30 having a dipole moment may receive a dielectrophoretic force so that both ends are disposed on the electrodes 21 and 22, respectively.

[0272] The "alignment degree" of the light emitting element 30 may mean a deviation in the positioning and position of the light emitting element 30 aligned on the target substrate SUB. For example, if there is a large deviation in the positioning and position of the light emitting element 30, the alignment degree of the light emitting element 30 is low. If there is a small deviation in the positioning and position of the light emitting element 30, the alignment degree of the light emitting element 30 is high or improved.

[0273] During the process of manufacturing the display device 10 , after the light emitting element 30 has been disposed between the electrodes 21 and 22 , a process of removing the solvent 220 by irradiating heat to the ink 200 may be performed.

[0274] Reference Fig.19 and Fig. 20 The process of removing the solvent 220 may be performed in a chamber VCD in which the internal pressure is adjustable. The chamber VCD may adjust the internal pressure therein, and may remove the solvent 220 by irradiating heat on the target substrate SUB while adjusting the pressure.

[0275] According to the method of manufacturing the display device 10, the solvent 220 can be completely removed by heat treatment in a low pressure environment. According to the disclosed embodiment, the process of removing the solvent 220 can be performed in about 10 -4 The heat treatment process in the chamber VCD may be performed at a pressure in a range of about 1 torr to about 1 torr and at a temperature in a range of about 100° C. to about 400° C. In the case where the heat treatment process is performed under the above pressure range, the boiling point of the solvent 220 is also reduced, so that the solvent 220 can be removed more easily. The heat treatment process in the chamber VCD may be performed for about 1 minute to about 30 minutes. However, it will be understood that the disclosure is not limited thereto.

[0276] Then, refer to Fig.21, insulating layers PAS2, PAS3, and PAS4 and contact electrodes CNE1 and CNE2 may be formed on the light emitting element 30 and the electrodes 21 and 22. By performing the above-described processes, the display device 10 including the light emitting element 30 may be manufactured.

[0277] The display device 10 according to the embodiment can be manufactured by using the ink 200 including the solvent 220. The solvent 220 may include an ester group and / or may have a polarity parameter and a hydrogen bonding parameter within a specific range of the Hansen solubility parameter, thereby increasing the dispersibility of the light-emitting element 30. Therefore, it is possible to suppress the light-emitting element 30 from adhering together when a drop of the ink 200 containing the light-emitting element 30 is dropped onto a sub-pixel, thereby preventing poor alignment and achieving uniform brightness in the sub-pixel. In this way, a uniform number of light-emitting elements 30 can be arranged with a high degree of alignment per unit area of ​​the display device 10, and the reliability of the display device 10 can be improved.

[0278] In summarizing the detailed description, it will be appreciated by those skilled in the art that many changes and modifications may be made to the embodiments without departing substantially from the principles of the disclosure. Therefore, the disclosed embodiments disclosed are used in a general and descriptive sense only and not for the purpose of limitation.

Claims

1. An ink, comprising: Solvents; as well as a plurality of light emitting elements dispersed in the solvent, each of the plurality of light emitting elements including a plurality of semiconductor layers and an insulating film partially surrounding outer surfaces of the plurality of semiconductor layers, wherein the solvent has a Hansen solubility parameter with a polarity parameter between 4 and 9 and a hydrogen bonding parameter between 6 and 11, Wherein, the solvent includes a compound represented by one of the following Chemical Formulas 1 to 5: [Chemical formula 1] [Chemical formula 2] [Chemical formula 3] [Chemical formula 4] [Chemical formula 5] 2. The ink according to claim 1, wherein The solvent has a viscosity in the range of 20 cP to 200 cP at room temperature.

3. The ink according to claim 1, wherein The boiling point of the solvent is equal to or lower than 400°C.

4. The ink according to claim 1, wherein The plurality of light emitting elements may be contained in an amount of 0.01 parts by weight to 10 parts by weight based on 100 parts by weight of the ink.

5. The ink according to claim 1, wherein The plurality of semiconductor layers of each of the plurality of light emitting elements comprises: a first semiconductor layer; a second semiconductor layer; and The light emitting layer is disposed between the first semiconductor layer and the second semiconductor layer, and the insulating film at least surrounds an outer surface of the light emitting layer.

6. A method for manufacturing a display device, the method comprising the following steps: preparing an ink including a solvent and a plurality of light emitting elements; preparing a target substrate having a first electrode and a second electrode formed thereon; applying the ink to the target substrate; as well as generating an electric field above the target substrate so that the plurality of light emitting elements are disposed on the first electrode and the second electrode, wherein the solvent has a Hansen solubility parameter with a polarity parameter between 4 and 9 and a hydrogen bonding parameter between 6 and 11, Wherein, the solvent includes a compound represented by one of the following Chemical Formulas 1 to 5: [Chemical formula 1] [Chemical formula 2] [Chemical formula 3] [Chemical formula 4] [Chemical formula 5] 7. The method according to claim 6, wherein: The solvent has a viscosity in the range of 20 cP to 200 cP at room temperature.

8. The method according to claim 6, wherein: The boiling point of the solvent is equal to or lower than 400°C.

9. The method according to claim 6, further comprising: After the electric field is generated over the target substrate so that the plurality of light emitting elements are disposed on the first electrode and the second electrode, heat treatment is performed to remove the solvent.

10. The method according to claim 9, wherein: The heat treatment is performed at a temperature ranging from 100°C to 400°C.

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