Micro-LED-based display device

Abstract

An embodiment of a display device will be described. The display device includes a substrate (204) and sub-pixels (R1, R2) configured to emit display light having an emission spectrum including a first peak wavelength and a second peak wavelength. The sub-pixels include micro LEDs (218) disposed on the substrate and an NS-based CC layer (220) disposed on the micro LEDs. The NS-based CC layer includes QDs configured to emit first light having a first peak wavelength. The micro LEDs are configured to emit second light having a second peak wavelength. A first portion of the second light is absorbed by the QDs and down-converted to the first light, and a second portion of the second light passes through the NS-based CC layer (220).

Description

Technical Field

[0001] The present invention relates to a display device having sub-pixels with micro-sized light-emitting diodes (“micro LEDs”) and a color conversion (CC) layer.

Background Art

[0002] Light-emitting nanostructures (NSs) such as quantum dots (QDs) have the ability to emit light with a single spectral peak having a narrow linewidth, representing a type of phosphor that generates highly saturated colors. It is possible to adjust the emission wavelength according to the size of the NS. NSs are used in the manufacture of NS films that can be used as color conversion (CC) layers (also called color down-conversion layers) in display devices. The NS-based CC layer can down-convert light in the short-wavelength region of the visible light spectrum to light in the long-wavelength region of the visible light spectrum.

[0003] A display device can be based on micro LED technology and can include red, green, and blue light-emitting micro LEDs as light sources for its red, green, and blue sub-pixels. In these micro LED-based display devices, there is a trade-off between achieving a desired high color luminance (e.g., a luminance of about 50,000 nits or more) for the light emitted from the red, green, and / or blue sub-pixels and achieving a desired primary emission peak wavelength corresponding to a desired color point and / or color gamut in the RGB color space (e.g., the CIE1931 color space). For example, a GaN-based micro LED used for a red sub-pixel emits red light in a wavelength region of about 620 nm to about 630 nm, but has a low color luminance of about 5,000 nits or less and emits light at a low current density of about 2 A / cm 2 and emits light at a low current density of about 4 A / cm 2At the above high current density, it is not possible to emit the desired red light. Rather, the GaN-based micro-LED emits light in the wavelength range of about 580 nm to about 600 nm, which corresponds to orange light and the color point of orange on the CIE1931 color space, thus degrading the image quality of the display device.

[0004] One of the parameters used to define the light emitted from a display device is the chromaticity (x, y) coordinates of the CIE1931 chromaticity diagram shown in FIG. 1. The CIE1931 chromaticity diagram (also called the "CIE1931 color space") illustrates all colors perceived by the human eye. The horseshoe-shaped spectral locus 100 is a set of points representing the chromaticity (x, y) coordinates of spectral (monochromatic) colors, plotted according to wavelength. The chromaticity (x, y) coordinates of all colors existing in nature are located within the boundary of the spectral locus 100.

[0005] By connecting the chromaticity (x, y) coordinates of the three display color primaries of a display device, it is possible to delineate the gamut boundaries of various display device technologies or specifications within the CIE1931 chromaticity diagram. The gamut defines the limits of producible or defined colors for a display device technology or specification. FIG. 1 shows the gamut for the DCI specification as a triangle 102 with the respective display primaries of red, green, and blue (RGB) as vertices. The chromaticity (x, y) coordinates of the vertices of the triangle 102 are (0.680, 0.320), (0.265, 0.690), and (0.150, 0.060) for red, green, and blue, respectively. SUMMARY OF THE INVENTION

[0006] The present disclosure provides examples of micro-LED-based display devices that minimize or eliminate the existing trade-off between the brightness of a desired color and the achievement of a desired color point and / or gamut for light emitted from the red sub-pixels of a micro-LED-based display device. The present disclosure also provides an exemplary and inexpensive method for fabricating such improved devices.

[0007] In some embodiments, a micro-LED-based display device may include red, green, and blue sub-pixels. Each of the red, green, and blue sub-pixels may include a micro-LED. In some embodiments, the blue sub-pixel may include a micro-LED that emits blue light having a primary emission peak wavelength (PWL) in the wavelength range of about 435 nm to about 495 nm of the EM spectrum. In some embodiments, the green sub-pixel may include a micro-LED that emits green light having a primary emission PWL in the wavelength range of about 495 nm to about 570 nm of the EM spectrum. In some embodiments, the red sub-pixel may include, at a current density of about 4 A / cm 2 or higher, a micro-LED (e.g., a GaN-based micro-LED) that emits yellow, orange, or amber light having a primary emission PWL in the wavelength range of about 550 nm to about 610 nm with a high color luminance (e.g., about 25,000 nits or more, 50,000 nits or more). In some embodiments, the red sub-pixel may further include a nanostructure-based (NS-based) color conversion (CC) layer disposed on the micro-LED of the red sub-pixel. The NS-based CC layer may include light-emitting nanostructures having a primary emission PWL in the wavelength range of about 620 nm to about 750 nm that may correspond to red light.

[0008] In some embodiments, a first portion of the light from the red sub-pixel micro-LED may be absorbed by the light-emitting nanostructures of the NS-based CC layer and re-emitted as light having the primary emission PWL of the light-emitting nanostructures. In some embodiments, a second portion of the light from the red sub-pixel micro-LED may be able to pass through the NS-based CC layer. In some embodiments, the NS-based CC layer may be formed such that, through the NS-based CC layer, the micro-LED light at the primary emission PWL can be transmitted at about 70% to about 1% for an optical density of about 0.1 to about 3.0, respectively. As a result, the transmitted light from the red sub-pixel may have a dual PWL emission spectrum.

[0009] In some embodiments, the dual-PWL emission spectrum may include a first emission PWL corresponding to the primary emission PWL of the emissive nanostructure (e.g., from about 620 nm to about 750 nm) and a second emission PWL corresponding to the primary emission PWL of the transmitted micro-LED light (e.g., from about 550 nm to about 610 nm). In some embodiments, the dual-PWL emission spectrum may correspond to a single color point (also referred to as a “blend color point”) on the CIE1931 chromaticity diagram shown in FIG. 1. In some embodiments, the blend color point may have chromaticity (x,y) coordinates along a line between chromaticity (x,y) coordinates of about (0.5,0.5) and about (0.7,0.3) of the CIE1931 chromaticity diagram. In some embodiments, the dual-PWL emission spectrum may include a first emission PWL of about 640 nm and a second emission PWL of about 595 nm. This dual-PWL emission spectrum may correspond to a blend color point having chromaticity (x,y) coordinates of about (0.680,0.320), which is a red point on the CIE1931 color space in the perception by the human eye.

[0010] Thus, by using an NS-based CC layer having a red light-emitting emissive nanostructure on an orange-emitting micro-LED having an external quantum efficiency of more than about 2% in the red subpixel, it is possible to achieve red emission having a high red luminance (e.g., a luminance exceeding about 25,000 nits, or a luminance exceeding about 50,000 nits) from the red subpixel of a micro-LED-based display device.

[0011] According to some embodiments, a display device includes a substrate and a subpixel configured to emit display light having an emission spectrum with a first peak wavelength and a second peak wavelength. The subpixel includes a micro LED disposed on the substrate and an NS-based CC layer disposed on the micro LED. The NS-based CC layer includes QDs configured to emit first light having a first peak wavelength. The micro LED is configured to emit second light having a second peak wavelength. A first portion of the second light is absorbed by the QDs and down-converted into the first light, and a second portion of the second light passes through the NS-based CC layer.

[0012] According to some embodiments, the first peak wavelength is in a wavelength range of about 620 nm to about 750 nm.

[0013] According to some embodiments, the second peak wavelength is in a wavelength range of about 550 nm to about 610 nm.

[0014] According to some embodiments, the first peak wavelength and the second peak wavelength are in different adjacent wavelength regions of the electromagnetic (EM) spectrum.

[0015] According to some embodiments, the first peak wavelength is in the red wavelength region of the electromagnetic (EM) spectrum, and the second peak wavelength is in the orange or yellow wavelength region of the EM spectrum.

[0016] According to some embodiments, the intensity of the first peak wavelength is greater than the intensity of the second peak wavelength.

[0017] According to some embodiments, a range of the peak intensity ratio of the second peak wavelength to the first peak wavelength from about 0 to about 40 corresponds to a range of the light transmittance of the micro LED at the second peak wavelength from about 100% to about 1%.

[0018] According to some embodiments, the emission spectrum corresponds to a single color point having first chromaticity (x, y) coordinates on the RGB color space.

[0019] According to some embodiments, the range of the peak intensity ratio of the second peak wavelength to the first peak wavelength from about 0 to about 40 corresponds to the range of the first chromaticity (x, y) coordinates from about (0.6, 0.4) to about (0.7, 0.3), respectively.

[0020] According to some embodiments, the range of the optical density of the NS-based CC layer from about 0 to about 3.0 corresponds to the range of the first chromaticity (x, y) coordinates from about (0.6, 0.4) to about (0.7, 0.3), respectively.

[0021] According to some embodiments, the range of the light transmittance of the micro LED at the second peak wavelength from about 100% to about 1% corresponds to the range of the optical density of the NS-based CC layer from about 0 to about 3.0.

[0022] According to some embodiments, the emission spectrum corresponds to a single color point having a first chromaticity (x, y) coordinate along a coordinate line between a second chromaticity (x, y) coordinate of about (0.5, 0.5) and a third chromaticity (x, y) coordinate of about (0.7, 0.3) in the RGB color space.

[0023] According to some embodiments, the micro LED has a light transmittance through the NS-based CC layer of about 1% to about 70% at the second peak wavelength.

[0024] According to some embodiments, the NS-based CC layer includes a surface area of about 0.5 μm × about 0.5 μm to about 1000 μm × about 1000 μm.

[0025] According to some embodiments, the NS-based CC layer covers the entire upper surface region of the micro LED.

[0026] According to some embodiments, the upper surface area of the NS-based CC layer is larger than the upper surface area of the micro LED.

[0027] According to some embodiments, the NS-based CC layer includes a thickness of about 5 μm to about 40 μm.

[0028] According to some embodiments, the NS-based CC layer includes an optical density of from about 0.1 to about 3.0.

[0029] According to some embodiments, the display device further includes a second sub-pixel including a second micro-LED disposed on the substrate. The second micro-LED is configured to emit a second display light having an emission spectrum including a single peak wavelength within a wavelength range of from about 495 nm to about 570 nm of the electromagnetic (EM) spectrum.

[0030] According to some embodiments, the display device further includes a second sub-pixel including a second micro-LED disposed on the substrate. The second micro-LED is configured to emit a second display light having an emission spectrum including a single peak wavelength within a wavelength range of from about 435 nm to about 495 nm of the electromagnetic (EM) spectrum.

[0031] According to some embodiments, a display device includes a substrate and a first subpixel configured to emit first display light having a first emission spectrum including a first peak wavelength and a second peak wavelength. A second subpixel is configured to emit second display light having a second emission spectrum including a third peak wavelength and a fourth peak wavelength. The first subpixel includes a first micro-LED disposed on the substrate and a first nanostructure-based color conversion (NS-based CC) layer disposed on the first micro-LED. The first NS-based CC layer includes a first set of quantum dots (QDs) configured to emit first light having the first peak wavelength. The first micro-LED is configured to emit second light having the second peak wavelength. The second subpixel includes a second micro-LED disposed on the substrate and a second NS-based CC layer disposed on the second micro-LED. The second NS-based CC layer includes a second set of quantum dots (QDs) configured to emit third light having the third peak wavelength. The second micro-LED is configured to emit fourth light having the fourth peak wavelength.

[0032] According to some embodiments, the first emission spectrum corresponds to a first color point having first chromaticity (x,y) coordinates in the RGB color space, and the second emission spectrum corresponds to a second color point having second chromaticity (x,y) coordinates in the RGB color space. The second chromaticity (x,y) coordinates are different from the first chromaticity (x,y) coordinates.

[0033] According to some embodiments, the first and third peak wavelengths are in a wavelength range of about 620 nm to about 750 nm.

[0034] According to some embodiments, the second and fourth peak wavelengths are in a wavelength range of about 550 nm to about 610 nm.

[0035] According to some embodiments, the optical density of the first NS-based CC layer is different from the optical density of the second NS-based CC layer.

[0036] According to some embodiments, the thickness of the first NS-based CC layer is different from the thickness of the second NS-based CC layer.

[0037] According to some embodiments, the concentration of the first set of QDs is different from the concentration of the second set of QDs.

[0038] According to some embodiments, the first portion of the second light is absorbed by the first set of QDs, downconverted to the first light, and the second portion of the second light passes through the first NS-based CC layer.

[0039] According to some embodiments, the first portion of the fourth light is absorbed by the second set of QDs, downconverted to the third light, and the second portion of the fourth light passes through the second NS-based CC layer.

[0040] According to some embodiments, the first micro-LED has a first light transmittance of about 1% to about 70% at a second peak wavelength through the first NS-based CC layer, and the second micro-LED has a second light transmittance of about 1% to about 70% at a fourth peak wavelength through the second NS-based CC layer. The second light transmittance is different from the first light transmittance.

[0041] According to some embodiments, a method of fabricating a display device includes forming first and second micro-LEDs on a substrate, depositing a layer of quantum dots (QDs) on the first and second micro-LEDs, masking a first portion of the layer of QDs, performing a curing process on a second portion of the layer of QDs, and removing the first portion of the layer of QDs. The first micro-LED is formed to emit first display light having a first emission spectrum with a double peak wavelength, and the second micro-LED is formed to emit second display light having a second emission spectrum with a single peak wavelength.

[0042] According to some embodiments, depositing the QD layer includes spin coating, slot die coating, doctor blade coating, or draw bar coating a solution of QDs onto the first and second micro-LEDs.

[0043] According to some embodiments, masking a first portion of the QD layer includes selectively forming a photoresist layer on the first portion of the QD layer on the second micro-LED.

[0044] According to some embodiments, performing a curing process on a second portion of the QD layer includes curing the second portion of the QD layer on the first micro-LED with ultraviolet light.

[0045] According to some embodiments, removing a first portion of the QD layer includes washing the first portion of the QD layer in an alkaline solution.

[0046] According to some embodiments, a method of fabricating a display device includes forming first and second micro-LEDs on a substrate, forming a patterned template on the first and second micro-LEDs, depositing a layer of quantum dots (QDs) on the patterned template, masking a first portion of the QD layer, performing a curing process on a second portion of the QD layer, and removing the first portion of the QD layer. The first micro-LED is formed to emit first display light having a first emission spectrum with a double-peak wavelength, and the second micro-LED is formed to emit second display light having a second emission spectrum with a single-peak wavelength. The patterned template includes an opening over the first micro-LED.

[0047] According to some embodiments, forming the patterned template includes depositing a polymer layer on the first and second micro-LEDs and patterning the polymer layer to form an opening over the first micro-LED.

[0048] According to some embodiments, depositing a layer of QDs includes spin coating, slot die coating, doctor blade coating, or draw bar coating a solution of QDs onto a patterned template.

[0049] According to some embodiments, subjecting a second portion of the layer of QDs to a curing process includes curing the second portion of the layer of QDs disposed within the opening with ultraviolet light.

[0050] According to some embodiments, removing a first portion of the layer of QDs includes washing the first portion of the layer of QDs in toluene.

[0051] Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. It should be noted that the present invention is not limited to the specific embodiments described herein. Such embodiments are presented herein for illustrative purposes only. Additional embodiments will be apparent to those of ordinary skill in the relevant art based on the teachings contained herein.

[0052] The accompanying drawings, which are incorporated herein and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, explain the principles of the present disclosure and enable one of ordinary skill in the relevant art to make and use embodiments of the present disclosure.

Brief Description of the Drawings

[0053]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

DETAILED DESCRIPTION OF THE INVENTION

[0054] The features and advantages of the present invention will become more apparent from the detailed description set forth below when considered in conjunction with the drawings. In the drawings, like reference characters designate corresponding elements throughout. In the drawings, like reference numerals generally denote identical, functionally similar, and / or structurally similar elements. The discussion of elements with the same annotation applies to each other unless otherwise noted. Unless otherwise specified, throughout the present disclosure, the given drawings should not be construed as being drawn to scale.

[0055] In the case of descriptions of specific configurations and arrangements, it should be understood that this is done for illustrative purposes only. Those skilled in the relevant art will recognize that other configurations and arrangements can be used without departing from the spirit and scope of the present invention. Also, it will be apparent to those skilled in the relevant art that the present invention can be used for various other applications in addition to the applications specifically mentioned herein. It should be understood that the specific embodiments shown and described herein are examples and are not intended to limit the scope of this application in any way.

[0056] References herein to "one embodiment," "an embodiment," "exemplary embodiment," etc., indicate that the described embodiment may include a particular feature, structure, or characteristic, but it should be noted that not all embodiments necessarily include the particular feature, structure, or characteristic. Further, such expressions do not necessarily refer to the same embodiment. Further, if a particular feature, structure, or characteristic is described in connection with an embodiment, it will be within the knowledge of those skilled in the art to bring such feature, structure, or characteristic in connection with other embodiments, whether or not it is explicitly described.

[0057] In this specification, all numerical values indicating amounts, ratios of materials, physical properties of materials, and / or uses are to be understood as being modified by the term "about" unless otherwise explicitly indicated.

[0058] In some embodiments, the terms "about" and "substantially" may indicate a value of a given amount that varies within 5% of the value (e.g., ±1%, ±2%, ±3%, ±4%, ±5% of the value). These values are merely illustrative and not intended to be limiting. The terms "about" and "substantially" may indicate a percentage of the value as interpreted by those skilled in the relevant art in light of the teachings of this specification.

[0059] In some embodiments, the term "display device" refers to an array of elements that enables the visual representation of data on a display screen. Suitable display screens can include screens, films, sheets, or other structures of various planar, curved, or other shapes for visually displaying information to a user. The display devices described herein can include, for example, display systems incorporating liquid crystal displays (LCDs), televisions, computers, mobile phones, smartphones, personal digital assistants (PDAs), gaming devices, e-reader devices, digital cameras, tablets, wearable devices, car navigation systems, and the like.

[0060] In some embodiments, the term "nanostructure" refers to a structure having at least one region or characteristic dimension with a size of less than about 500 nm. In some embodiments, the nanostructure has dimensions of less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 20 nm, or less than about 10 nm. Typically, the region or characteristic dimension is along the smallest axis of the structure. Examples of such structures include nanowires, nanorods, nanotubes, branched nanostructures, nanotetrapods, tripods, bipods, nanocrystals, nanodots, quantum dots, nanoparticles, and the like. The nanostructure can be, for example, substantially crystalline, substantially single-crystalline, polycrystalline, amorphous, or combinations thereof. In some embodiments, each of the three dimensions of the nanostructure has a dimension of less than about 500 nm, less than about 200 nm, less than about 100 nm, less than about 50 nm, less than about 20 nm, or less than about 10 nm.

[0061] In some embodiments, the term “QD” or “nanocrystal” refers to nanostructures that are substantially single crystals. Nanocrystals have at least one region or characteristic dimension on the order of less than about 500 nm, less than about 1 nm. The terms “nanocrystal,” “QD,” “nanodot,” and “dot” are readily understood by those skilled in the art to represent similar structures and are used herein with substantially the same meaning. The present invention also encompasses the use of polycrystalline or amorphous nanocrystals.

[0062] In one embodiment, the term “diameter” of a nanostructure refers to the diameter of a cross-section perpendicular to a first axis of the nanostructure, where the first axis has the greatest difference in length with respect to a second and third axis (the second and third axes being the two axes having lengths that are most nearly equal to each other). The first axis is not necessarily the longest axis of the nanostructure. For example, in the case of a disk-shaped nanostructure, the cross-section is a substantially circular cross-section perpendicular to the minor axis of the disk. If the cross-section is not circular, the diameter is the average of the major and minor axes of the cross-section. In the case of an elongated nanostructure such as a nanowire or a high aspect ratio nanostructure, the diameter is measured across a cross-section perpendicular to the longest axis of the nanowire. In the case of a spherical nanostructure, the diameter is measured from one end to the other passing through the center of the sphere.

[0063] In certain embodiments, the terms "crystalline" or "substantially crystalline", when used with respect to a nanostructure, refer to the fact that the nanostructure typically exhibits long-range order over one or more dimensions of its structure. Since the order of a single crystal cannot extend beyond the boundaries of the crystal, those skilled in the art will understand that the term "long-range order" depends on the absolute size of a particular nanostructure. In this context, "long-range ordering" means substantial order over at least a majority of the dimensions of the nanostructure. In some cases, the nanostructure can have an oxide or other coating, or can include a core and at least one shell. In such cases, it will be understood that the oxide, shell, or other coating can exhibit such order, but does not necessarily have to (e.g., it can be amorphous, polycrystalline, or otherwise). In such cases, the phrases "crystalline", "substantially crystalline", "substantially single-crystalline", or "single-crystalline" refer to the central core of the nanostructure (excluding the coating layer or shell). As used herein, the terms "crystalline" or "substantially crystalline" are intended to encompass structures that exhibit substantial long-range order (e.g., order over at least about 80% of the length of at least one axis of the nanostructure or its core), including various defects, stacking defects, atomic substitutions, etc. Further, it will be understood that the interface between the core and the exterior of the nanostructure, or between the core and an adjacent shell, or between a shell and a second adjacent shell, can include an amorphous region and be amorphous. This does not prevent the nanostructure from being crystalline or substantially crystalline as defined herein.

[0064] In certain embodiments, the term "single crystal", when used with respect to a nanostructure, indicates that the nanostructure is substantially crystalline and substantially includes a single crystal. When used with respect to a nanostructure heterostructure that includes a core and one or more shells, "single crystal" indicates that the core is substantially crystalline and substantially includes a single crystal.

[0065] In certain embodiments, a "ligand" is, for example, a molecule that can interact (regardless of strength) with one or more faces of a nanostructure through covalent, ionic, van der Waals, or other molecular interactions with the surface of the nanostructure.

[0066] In certain embodiments, "quantum yield" (QY) is, for example, the ratio of photons emitted to photons absorbed by a nanostructure or a population of nanostructures. As is known in the art, the quantum yield is typically determined by a comparative method using a well-characterized standard sample having a known quantum yield value.

[0067] In some embodiments, the term "primary emission peak wavelength" refers to the wavelength at which the emission spectrum exhibits maximum intensity.

[0068] In some embodiments, the term "full width at half maximum" (FWHM) refers to a measure of spectral width. In an emission spectrum, the FWHM can refer to the width of the emission spectrum at half of the peak intensity value.

[0069] In some embodiments, the terms "luminance" and "brightness" are used herein to have substantially the same meaning and refer to a photometric measure of luminous intensity per unit area of a light source or an illuminated surface.

[0070] In some embodiments, the term "nanostructure (NS) film" refers to a film having emissive nanostructures.

[0071] In some embodiments, the term "red subpixel" refers to a pixel and / or region of a display device that emits light. This light can have a primary emission peak wavelength within the wavelength range of about 550 nm to about 750 nm of the electromagnetic (EM) spectrum. Additionally, or alternatively, this device can emit light having chromaticity (x, y) coordinates along a line between chromaticity (x, y) coordinates of about (0.5, 0.5) and about (0.7, 0.3) in the CIE1931 chromaticity diagram.

[0072] In some embodiments, the term "green subpixel" refers to a pixel and / or an area of a display device that emits light having a primary emission peak wavelength in the wavelength range of about 495 nm to about 570 nm of the EM spectrum.

[0073] In some embodiments, the term "blue subpixel" refers to a pixel and / or an area of a display device that emits light having a primary emission peak wavelength in the wavelength range of about 435 nm to about 495 nm of the EM spectrum.

[0074] The published patents, patent applications, websites, company names, and scientific literature referred to in this specification are hereby incorporated by reference in their entirety to the same extent as if each was specifically and individually indicated to be incorporated by reference. In the event of any conflict between the cited literature in this specification and the specific teachings of this specification, the latter shall prevail. Similarly, any conflict between the definition of a technical term as understood technically and the definition of a term specifically taught in this specification shall be resolved in favor of the latter.

[0075] The technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art to which this application pertains, unless otherwise defined. Various methodologies and materials known to those skilled in the art are referenced herein.

[0076] Examples of Embodiments of a Display Device FIG. 2A shows a top-down view of a micro-LED based display device 200 according to some embodiments. FIGS. 2B and 2D-2F show various cross-sectional views of the micro-LED based display device 200 along line A-A of FIG. 2A. FIG. 2C shows a cross-sectional view of the micro-LED based display device 200 along line B-B of FIG. 2A. FIGS. 2B-2F show cross-sectional views of the micro-LED based display device 200 having additional structures not shown in FIG. 2A for simplicity. Discussions of elements with the same annotations apply to each other unless otherwise specified.

[0077] Referring to FIG. 2A, in some embodiments, the micro-LED based display device 200 may include red sub-pixels R1-R8, green sub-pixels G1-G4, and blue sub-pixels B1-B4 disposed on a substrate 204. The number and arrangement of the red, green, and blue sub-pixels in the micro-LED based display device 200 shown in FIG. 2A are exemplary and not limiting. The micro-LED based display device 200 can have any number and any arrangement of red, green, and blue sub-pixels. Unless otherwise specified, (i) the discussion of red sub-pixel R1 applies to red sub-pixels R2-R8, (ii) the discussion of green sub-pixel G1 applies to green sub-pixels G2-G4, and (iii) the discussion of blue sub-pixel B1 applies to blue sub-pixels B2-B4.

[0078] In some embodiments, the micro-LED based display device 200 may further include a dielectric layer 206 disposed on the substrate 204 between the red sub-pixels R1-R8, green sub-pixels G1-G4, and blue sub-pixels B1-B4 as shown in FIGS. 2B-2F. The dielectric layer 206 can electrically and / or optically separate the red sub-pixels R1-R8, green sub-pixels G1-G4, and blue sub-pixels B1-B4 from each other. In some embodiments, the micro-LED based display device 200 may additionally or optionally include a light-shielding layer 208 (also referred to as the "black matrix layer 208") disposed on the dielectric layer 206 as shown in FIG. 2D. The light-shielding layer 208 can prevent or minimize light crosstalk between the red sub-pixels R1-R8, green sub-pixels G1-G4, and blue sub-pixels B1-B4. In some embodiments, as shown in FIG. 2E, the micro-LED based display device 200 may additionally or optionally include a sealing layer 210. In some embodiments, the sealing layer 210 may be disposed on the structures of FIGS. 2D and 2F. The sealing layer 210 may include an insulating oxide layer such as aluminum oxide to provide environmental encapsulation for the underlying layers and / or structures of the micro-LED based display device 200.

[0079] Referring to FIGS. 2A-2B and 2D-2F, in some embodiments, each of the green sub-pixels G1-G4 may include a micro-LED 212 capable of emitting green light having a primary emission PWL of about 495 nm to about 570 nm in the visible spectrum. Referring to FIGS. 2A and 2C, in some embodiments, each of the blue sub-pixels B1-B4 may include a micro-LED 214 capable of emitting blue light having a primary emission PWL of about 435 nm to about 495 nm in the visible spectrum. In some embodiments, the green sub-pixels G1-G4 and / or the blue sub-pixels B1-B4 may include a color filter 216 as shown in FIG. 2F. The color filter 216 adjusts the spectral emission width of the light emitted from the micro-LED 212 and / or 214, enabling the achievement of a desired color gamut on the CIE1931 color space. In some embodiments, instead of the color filter 216, the green sub-pixels G1-G4 and / or the blue sub-pixels B1-B4 may include an optically transparent substrate.

[0080] Referring to FIGS. 2A-2B and 2D-2F, in some embodiments, each of the red sub-pixels R1-R8 may include a micro-LED 218 disposed on a substrate 204 and an NS-based CC layer 220 disposed on the micro-LED 218. The micro-LED 218 has a primary emission PWL of about 550 nm to about 610 nm, an FWHM of about 20 nm to about 30 nm, and a high current density of about 4 A / cm 2 It may be an indium gallium nitride (InGaN) micro-LED configured to emit light having a high color luminance of about 25,000 nits to about 50,000 nits or about 50,000 nits or more at the above high current density. The light having a primary emission PWL of about 550 nm to about 610 nm may correspond to yellow, orange, or amber light in the visible spectrum.

[0081] In some embodiments, the NS-based CC layer 220 may include light-emitting nanostructures such as QDs (e.g., QD 1800 described with reference to FIG. 18) disposed in a matrix material (e.g., matrix material 1910 described with reference to FIG. 19). According to some embodiments, the light-emitting nanostructures can have a primary emission PWL of about 620 nm to about 750 nm and an FWHM of about 10 nm to about 40 nm, which can correspond to red light. In some embodiments, the light-emitting nanostructures can include indium phosphide (InP)-based or cadmium selenide (CdSe)-based QDs having a QY of about 65% to about 80%. In some embodiments, the red subpixels R1 to R8 may further include another optically transparent insulating layer or conductive layer (not shown) between the NS-based CC layer 220 and the micro-LED 218.

[0082] In some embodiments, the substrate 204 can include a circuit (not shown) for controlling the micro-LEDs 212, 214, and 218. Each of the micro-LEDs 212, 214, and 218 can have a lateral dimension of less than about 100 μm. The structure of the micro-LEDs 212, 214, and 218 can be based on a pn-junction diode having a direct bandgap semiconductor material such as a binary III-V (e.g., GaN) compound, a ternary III-V compound (e.g., InGaN), a quaternary III-V compound (e.g., AlInGaN), or combinations thereof.

[0083] In some embodiments, each NS-based CC layer 220 can have a thickness of about 5 μm to about 40 μm to appropriately output light having a desired PWL and a desired color point from each of the red subpixels R1 to R8, as described in detail below. Each NS-based CC layer 220 can have a surface area that covers the entire upper surface of each of the micro-LEDs 218 to minimize or prevent optical crosstalk between the micro-LEDs 212, 214, and 218. In some embodiments, each NS-based CC layer 220 can have a surface area of about 0.5 μm × about 0.5 μm to about 1000 μm × about 1000 μm (e.g., about 2 μm × about 2 μm to about 100 μm × about 100 μm).

[0084] In each of the red sub-pixels R1 to R8, the first portion of the light from the micro-LED 218 can be absorbed by the light-emitting nanostructures of the NS-based CC layer 220 and re-emitted as light having the primary emission PWL of the light-emitting nanostructures. The second portion of the light from the micro-LED 218 can be transmitted through the NS-based CC layer 220. As a result, the light transmitted from each of the red sub-pixels R1 to R8 can have a dual PWL emission spectrum. In some embodiments, the dual PWL emission spectrum can include a first emission PWL corresponding to the primary emission PWL of the light-emitting nanostructures (e.g., from about 620 nm to about 750 nm) and a second emission PWL corresponding to the primary emission PWL of the light transmitted from the micro-LED 218 (e.g., from about 550 nm to about 610 nm). The dual PWL emission spectrum can correspond to a single color point (also referred to as a "blend color point") on the CIE1931 chromaticity diagram shown in FIG. 1. In some embodiments, the blend color point can be a red point. Thus, by using the NS-based CC layer 220 on the micro-LED 218, light emission from the red sub-pixels R1 to R8 having a red point on the CIE1931 chromaticity diagram can be achieved without sacrificing color luminance of about 25,000 nits to about 50,000 nits or more than about 50,000 nits. As described above, due to the problem of micro-LEDs generating red light at such high color luminance, without using the NS-based CC layer 220, the red sub-pixels can emit orange light for such high color luminance.

[0085] In some embodiments, the blend color point may have chromaticity (x, y) coordinates along a coordinate line between chromaticity (x, y) coordinates of about (0.5, 0.5) and about (0.7, 0.3) in the CIE1931 chromaticity diagram. The coordinate line can be a part of the spectral locus 102 shown in FIG. 1. Based on the desired color points of the red sub-pixels R1 to R8, the blend color point of the light emitted from the red sub-pixels R1 to R8 is variable along this coordinate line due to the change in the optical density of the NS-based CC layer 220. Due to the change in the optical density of the NS-based CC layer 220, (i) the transmittance of the light from the micro-LED 218 through the NS-based CC layer 220, and (ii) the relative peak intensities of the first and second emission PWLs of the dual PWL emission spectrum become variable.

[0086] The optical density of the NS-based CC layer 220 is variable by adjusting the thickness of the NS-based CC layer 220, the concentration of the light-emitting nanostructures in the NS-based CC layer 220, and / or the concentration of the scattering particles in the NS-based CC layer 220 (described later with reference to FIG. 19). In some embodiments, the NS-based CC layer 220 can be formed with an optical density of about 0.1 to about 3.0, which allows light transmittance of about 70% to about 0.1% respectively through the NS-based CC layer 220 in the primary emission PWL from the micro-LED 218.

[0087] In some embodiments, due to the changes in the first and second emission PWLs of the dual PWL emission spectrum, the blend color points become variable along the coordinate lines. Due to the changes in the emission characteristics of the micro-LED 218 and the NS-based CC layer 220, the first and second emission PWLs become variable. In some embodiments, two or more of the red sub-pixels R1 to R8 have (i) NS-based CC layers 220 with different optical densities from each other, (ii) NS-based CC layers 220 with different concentrations of light-emitting nanostructures from each other, and / or (iii) operate at different current densities and emit light with different primary emission PWLs in the wavelength range of about 550 nm to about 610 nm. As a result, two or more of the red sub-pixels R1 to R8 can emit light having different dual PWL emission spectra and corresponding blend color points.

[0088] FIG. 3A shows an example of the dual PWL emission spectrum 322 of one or more of the red sub-pixels R1 to R8, and FIG. 3B shows the corresponding blend color point CP1 on a part of the CIE1931 chromaticity diagram. In this example, (i) the NS-based CC layer 220 can have an optical density of about 1.0 and a thickness of about 5 μm, (ii) the micro-LED 218 can have a primary emission PWL of about 595 nm and a light transmittance of about 10% at a PWL of about 595 nm, and (iii) the light-emitting nanostructure can have a primary emission PWL of about 640 and a FWHM of about 30 nm. The dual PWL emission spectrum 322 can include a first emission PWL 322A at about 640 nm and a second emission PWL 322B at about 595 nm. The peak intensity ratio between the first emission PWL 322A and the second emission PWL 322B can be about 3.36. The dual PWL emission spectrum 322 having a peak intensity ratio of about 3.36 can correspond to a blend color point CP1 having chromaticity (x, y) coordinates of about (0.663, 0.336), which is a red point in the CIE1931 color space perceived by the human eye. As shown in FIG. 3B, the color point CP1 corresponding to the dual PWL emission spectrum 322 is similar to the color point corresponding to a single PWL emission spectrum having a PWL in the wavelength range of about 615 to about 620 nm.

[0089] Figures 3A - 3B also show an example of the emission spectrum 324 of light emitted from the micro - LED 218 without passing through the NS - based CC layer 220 (i.e., 100% light transmittance at the primary emission PWL from the micro - LED 218), and the color point CP2 corresponding to the emission spectrum 324. The color point CP2 has chromaticity (x, y) coordinates of approximately (0.601, 0.398), which is an orange color point on the CIE1931 color space.

[0090] Figures 3A - 3B further show an example of the emission spectrum 326 of the light - emitting nanostructures in the NS - based CC layer 220 without the micro - LED 218, and the color point CP3 corresponding to the emission spectrum 326. The color point CP3 has chromaticity (x, y) coordinates of approximately (0.698, 0.302). Figure 3B also shows the color point CP4 corresponding to the red color according to the DCI specification, and the chromaticity (x, y) coordinates are approximately (0.680, 0.320).

[0091] Figure 4A shows another example of the double - PWL emission spectra 422 of one or more of the red sub - pixels R1 - R8, and Figure 4B shows the corresponding blend color point CP5 on a part of the CIE1931 chromaticity diagram. The configuration of the red sub - pixels R1 - R8 in this example is different from that shown in Figures 3A - 3B. In this example, (i) the NS - based CC layer 220 can have an optical density of about 0.3 and a thickness of about 5 μm, (ii) the micro - LED 218 can have a primary emission PWL of about 595 nm and a light transmittance of about 50% at the PWL of about 595 nm, and (iii) the light - emitting nanostructures can have a primary emission PWL of about 640 and an FWHM of about 30 nm.

[0092] Similar to the dual-PWL emission spectrum 322, the dual-PWL emission spectrum 422 may have a first emission PWL 422A at approximately 640 nm and a second emission PWL 422B at approximately 595 nm. However, because the optical density of the NS-based CC layer 220 is different in the examples of FIGS. 3A-3B and FIGS. 4A-4B, the peak intensity ratio of the first emission PWL 322A to the second emission PWL 322B is different from the peak intensity ratio of the first emission PWL 422A to the second emission PWL 422B. As a result, the blend color point CP5 in FIG. 4B is different from the blend color point CP1 in FIG. 3B. The peak intensity ratio of the first emission PWL 422A to the second emission PWL 422B can be approximately 0.37, and the blend color point CP5 has chromaticity (x, y) coordinates of approximately (0.615, 0.385).

[0093] FIGS. 4A-4B further show an exemplary emission spectrum 426 of the emission nanostructures in the NS-based CC layer 220 that do not have the color point CP5 corresponding to the micro-LED 218 and the emission spectrum 326. The emission spectra 326 and 426 can be different due to different configurations of the NS-based CC layer 220.

[0094] For various optical densities of the NS-based CC layer 220 shown in Table 1 below, various examples of blend color points CP7-CP12 on a part of the CIE1931 chromaticity diagram are shown in FIG. 5.

Table 1

[0095] In some embodiments, the micro-LED display device 200, although not shown for simplicity, may include other elements such as a display screen, a diffusion layer, and a buffer layer.

[0096] Example of a method for manufacturing a display device FIG. 6 is a flow diagram of an example of a method 600 for fabricating a micro-LED-based display device 200 according to some embodiments. For illustrative purposes, the operations shown in FIG. 6 are described with reference to an example of a fabrication process for fabricating a micro-LED-based display device 200 as shown in FIGS. 2A-2C. FIGS. 7-10 are cross-sectional views of a micro-LED-based display device 200 at various stages of manufacturing according to some embodiments. The operations may or may not be performed in a different order depending on the particular application. It should be noted that in method 600, a complete micro-LED-based display device 200 may not be manufactured. Thus, it is possible that additional processes may be provided before, during, and after method 600, and it is understood that some of the other processes may be described only briefly herein. Elements in FIGS. 7-10 that are annotated the same as elements in FIGS. 2A-2C have been described above.

[0097] In step 605, micro-LEDs of red, green, and blue sub-pixels are formed on a substrate. For example, as shown in FIG. 7, micro-LEDs 212 and 218 are formed on substrate 204. Micro-LED 214 is also formed, but is not visible in the cross-sectional view of FIG. 7. After the formation of micro-LEDs 212, 214, and 218, a dielectric layer 206 may be formed on substrate 204 as shown in FIG. 7.

[0098] Referring to FIG. 6, in step 610, an NS-based CC layer is deposited on the micro-LEDs. For example, as shown in FIG. 8, an NS-based CC layer 820 is deposited on the structure of FIG. 7. Similar to NS-based CC layer 220, NS-based CC layer 820 may include light-emitting nanostructures such as QDs in a UV-curable matrix material. In some embodiments, the NS-based CC layer 820 may be deposited by creating a solution of the light-emitting nanostructures and spin-coating the solution on the structure of FIG. 7. In some embodiments, the solution of the light-emitting nanostructures may include a tetraacrylate monomer.

[0099] Referring to FIG. 6, in step 615, a patterned masking layer is formed on the NS-based CC layer. For example, as shown in FIG. 9, a patterned masking layer 928 is formed on the structure of FIG. 8. In some embodiments, although it will be apparent to those skilled in the art, the patterned masking layer 928 may include a photoresist or any other suitable patterned masking material. The patterned masking layer 928 can be formed by a photolithography process.

[0100] Referring to FIG. 6, in step 620, a curing process is performed on the portion of the NS-based CC layer that is not covered by the patterned masking layer. For example, as shown in FIG. 9, a curing process is performed on the portion of the NS-based CC layer 820 that is not covered by the patterned masking layer 928. The curing process may include curing the exposed portion of the NS-based CC layer 820 with ultraviolet (UV) radiation at a temperature of about 100°C to about 180°C in air for about 60 minutes to about 120 minutes.

[0101] Referring to FIG. 6, in step 625, the portion of the NS-based CC layer that has not been exposed to the curing process is removed. For example, as shown in FIG. 10, during the curing process of step 620, the portion of the NS-based CC layer 820 under the patterned masking layer 928 is removed, and an NS-based CC layer 220 is formed on the micro-LED 218. These uncured portions of the NS-based CC layer 820 can be removed by washing the structure of FIG. 9 with an alkaline solution after the curing process.

[0102] FIG. 11 is a flowchart of another example of a method 1100 for fabricating a micro-LED-based display device 200 according to some embodiments. For illustrative purposes, the operations shown in FIG. 11 are described with reference to an example of a fabrication process for fabricating a micro-LED-based display device 200 as shown in FIGS. 2A-2C. FIGS. 12-17 are cross-sectional views of a micro-LED-based display device 200 at various stages of manufacturing according to some embodiments. The operations may or may not be performed in a different order depending on the particular application. It should be noted that in method 1100, a complete micro-LED-based display device 200 may not be manufactured. Thus, it is possible that additional steps may be provided before, during, and after method 1100, and it is understood that some of the other steps may be described only briefly herein. Elements in FIGS. 12-17 with the same annotations as elements in FIGS. 2A-2C and FIGS. 7-10 have been described above.

[0103] In step 1105, micro-LEDs of red, green, and blue sub-pixels are formed on a substrate. For example, as shown in FIG. 12, micro-LEDs 212 and 218 are formed on substrate 204. Micro-LED 214 is also formed but is not visible in the cross-sectional view of FIG. 12. After the formation of micro-LEDs 212, 214, and 218, a dielectric layer 206 may be formed on substrate 204 as shown in FIG. 12.

[0104] Referring to FIG. 11, in step 1110, a patterned template having an opening is formed over the micro-LEDs of the red sub-pixels. For example, as described with reference to FIGS. 13-14, a patterned template 1330 having an opening 1432 is formed over the structure of FIG. 12. The formation of the patterned template 1330 may include depositing a photoresist layer 1330 over the structure of FIG. 12 as shown in FIG. 13, and performing a photolithography process over the structure of FIG. 13 to form the opening 1432 as shown in FIG. 14.

[0105] Referring to FIG. 11, in step 1115, an NS-based CC layer is deposited on the patterned template. For example, as shown in FIG. 15, an NS-based CC layer 1520 is deposited on the structure of FIG. 14. Similar to the NS-based CC layer 220, the NS-based CC layer 1520 can include luminescent nanostructures such as QDs in a UV curable matrix material. In some embodiments, it is possible to deposit the NS-based CC layer 1520 by creating a solution of the luminescent nanostructures and spin-coating the solution onto the structure of FIG. 14. In some embodiments, the solution of the luminescent nanostructures can include a tetraacrylate monomer.

[0106] Referring to FIG. 11, in step 1120, a curing process is performed on a part of the NS-based CC layer within the opening. For example, as shown in FIG. 16, a curing process is performed on a part of the NS-based CC layer 1520 within the opening 1432. The curing process can sequentially include the operations of: (i) masking a part of the NS-based CC layer 1520 on the patterned template 1330 with a masking layer 1634, and (ii) curing the exposed portion of the NS-based CC layer 1520 within the opening 1432 with ultraviolet (UV) radiation at a temperature of about 100°C to about 180°C in air for about 60 minutes to about 120 minutes.

[0107] Referring to FIG. 11, in step 1125, the portions of the NS-based CC layer that have not been exposed to the curing process are removed. For example, as shown in FIG. 17, the portion of the NS-based CC layer 1520 that is under the masking layer 1634 during the curing process of step 1120 is removed, and an NS-based CC layer 220 is formed on the micro-LED 218. These uncured portions of the NS-based CC layer 1520 can be removed by washing the structure of FIG. 16 with toluene after the curing process.

[0108] Examples of embodiments of the barrier layer-coated nanostructures Figure 18 shows a cross-sectional structure of a barrier-layer-coated light-emitting nanostructure (NS) 1800 according to some embodiments. In some embodiments, the population of NSs 1800 can be included in an NS-based CC layer 136. The barrier-layer-coated NS 1800 includes an NS 1801 and a barrier layer 1806. The NS 1801 includes a core 1802 and a shell 1804. The core 1802 includes a semiconductor material that emits light upon absorption of higher energy. Examples of semiconductor materials for the core 1802 include indium phosphide (InP), cadmium selenide (CdSe), zinc sulfide (ZnS), lead sulfide (PbS), indium arsenide (InAs), indium gallium phosphide (InGaP), cadmium zinc selenide (CdZnSe), zinc selenide (ZnSe), and cadmium telluride (CdTe). Any other II-VI, III-V, ternary, or quaternary semiconductor structure showing a direct bandgap can also be used. In some embodiments, the core 1802 can also include one or more dopants such as, by way of example, metals, alloys, etc. Examples of metal dopants include, but are not limited to, zinc (Zn), copper (Cu), aluminum (Al), platinum (Pt), chromium (Cr), tungsten (W), palladium (Pd), or combinations thereof. The presence of one or more dopants in the core 1802 enables improvement in the structural, optical stability, and QY of the NS 1801 as compared to an undoped NS.

[0109] According to some embodiments, the size of the core 1802 can be less than 20 nm in diameter. In another embodiment, the size of the core 1802 can be from about 1 nm to about 5 nm in diameter. The ability to adjust the size of the core 1802 and, by extension, the size of the NS 1801 in the nanometer range enables tuning of the light emission color across the optical spectrum. Generally, the larger the NS, the more it emits light towards the red end of the spectrum, and the smaller the NS, the more it emits light towards the blue end of the spectrum. This effect occurs because the energy level spacing is narrower in larger NSs than in smaller NSs. For this reason, the NS can absorb photons with lower energy, i.e., photons closer to the red end of the spectrum.

[0110] The shell 1804 surrounds the core 1802 and is disposed on the outer surface of the core 1802. The shell 1804 may include cadmium sulfide (CdS), zinc cadmium sulfide (ZnCdS), zinc selenium sulfide (ZnSeS), and zinc sulfide (ZnS). In some embodiments, the shell 1804 may have a thickness 1804t, for example, one or more monolayers. In other embodiments, the shell 1804 may have a thickness 1804t between about 1 nm and about 5 nm. The shell 1804 can be utilized to reduce lattice mismatch with the core 1802 and to improve the QY of the NS1801. The shell 1804 can also contribute to passivating and removing surface trap states such as dangling bonds on the core 1802, improving the QY of the NS1801. The presence of surface trap states results in non-radiative recombination centers and can contribute to a decrease in the emission efficiency of the NS1801.

[0111] In other embodiments, the NS1801 may include a second shell disposed on the shell 1804 or two or more shells surrounding the core 1802 without departing from the spirit and scope of the present invention. In some embodiments, the second shell can be on the order of two monolayers thick and, although not essential, is generally a semiconductor material. The second shell can provide protection for the core 1802. The material of the second shell can be zinc sulfide (ZnS), but other materials can also be used without departing from the scope or spirit of the present invention.

[0112] The barrier layer 1806 is configured to form a coating on the NS 1801. In some embodiments, the barrier layer 1806 is disposed on and in substantial contact with the outer surface 1804a of the shell 1804. In embodiments of the NS 1801 having one or more shells, the barrier layer 1806 may be disposed on and in substantial contact with the outermost shell of the NS 1801. In one exemplary embodiment, the barrier layer 1806 is configured to act as a spacer between the NS 1801 and one or more NSs in, for example, a solution, composition, and / or film having a plurality of NSs, where the plurality of NSs may be similar to the NS 1801 and / or the barrier layer-coated NS 1800. In such an NS solution, NS composition, and / or NS film, the barrier layer 1806 can contribute to preventing aggregation between the NS 1801 and adjacent NSs. Aggregation between the NS 1801 and adjacent NSs can result in an increase in the size of the NS 1801 and a decrease or quenching of the light emission characteristics of the aggregated NSs (not shown) including the NS 1801. In further embodiments, the barrier layer 1806 provides protection for the NS 1801 from, for example, moisture, air, and / or harsh environments (e.g., high temperatures and chemicals used during lithography of the NSs and / or during the manufacturing process of NS-based devices) that can adversely affect the structural and optical properties of the NS 1801.

[0113] The barrier layer 1806 includes one or more materials that are amorphous, optically transparent, and / or electrically inert. Suitable barrier layers include, but are not limited to, inorganic materials such as inorganic oxides and / or nitrides. Examples of materials for the barrier layer 1806 include oxides and / or nitrides of Al, Ba, Ca, Mg, Ni, Si, Ti, or Zr, according to various embodiments. The barrier layer 1806 may have a thickness 1806t in the range of about 8 nm to about 15 nm in various embodiments.

[0114] As shown in FIG. 18, according to some embodiments, the barrier layer coated NS1800 may additionally or optionally include a plurality of ligands or surfactants 1808. According to some embodiments, the ligand or surfactant 1808 may be adsorbed or bound to the outer surface of the barrier layer coated NS1800, such as the outer surface of the barrier layer 1806. The plurality of ligands or surfactants 1808 may include a hydrophilic or polar head 1808a and a hydrophobic or nonpolar tail 1808b. The hydrophilic or polar head 1808a may be bound to the barrier layer 1806. The presence of the ligand or surfactant 1808 serves to separate NS1800 and / or NS1801 from other NSs during their formation, for example in solutions, compositions, and / or films. When NSs are capable of aggregating during their formation, the quantum efficiency of NSs such as NS1800 and / or NS1801 may decrease. The ligand or surfactant 1808 may also be used to impart certain properties to the barrier layer coated NS1800, such as providing miscibility in nonpolar solvents or providing reactive sites (e.g., reverse micelle systems) for other compounds to bind to.

[0115] There are various ligands that can be used as ligand 1808. In some embodiments, the ligand is a fatty acid selected from lauric acid, caproic acid, myristic acid, palmitic acid, stearic acid, and oleic acid. In some embodiments, the ligand is an organic phosphine or organic phosphine oxide selected from trioctylphosphine oxide (TOPO), trioctylphosphine (TOP), diphenylphosphine (DPP), triphenylphosphine oxide, and tributylphosphine oxide. In some embodiments, the ligand is an amine selected from dodecylamine, oleylamine, hexadecylamine, and octadecylamine. In some embodiments, the ligand is trioctylphosphine (TOP). In some embodiments, the ligand is oleylamine. In some embodiments, the ligand is diphenylphosphine.

[0116] There are various surfactants that can be used as surfactant 1808. Nonionic surfactants can be used as surfactant 1808 in some embodiments. Some examples of nonionic surfactants include polyoxyethylene(5) nonylphenyl ether (trade name IGEPAL CO-520), polyoxyethylene(9) nonylphenyl ether (IGEPAL CO-630), octylphenoxypoly(ethyleneoxy)ethanol (IGEPAL CA-630), polyethylene glycol oleyl ether (Brij 93), polyethylene glycol hexadecyl ether (Brij 52), polyethylene glycol octadecyl ether (Brij S10), polyoxyethylene(10) isooctyl cyclohexyl ether (Triton X-100), and polyoxyethylene branched nonyl cyclohexyl ether (Triton N-101).

[0117] In certain embodiments, anionic surfactants can be used as surfactant 1808. Some examples of anionic surfactants include sodium dioctyl sulfosuccinate, sodium stearate, sodium lauryl sulfate, sodium monododecyl phosphate, sodium dodecylbenzenesulfonate, and sodium myristyl sulfate.

[0118] In some embodiments, NS1801 and / or 1800 can be synthesized to emit light in one or more various color ranges, such as in the red, orange, and / or yellow ranges. In some embodiments, NS1801 and / or 1800 can be synthesized to emit light in the green and / or yellow ranges. In some embodiments, NS1801 and / or 1800 can be synthesized to emit light in the blue, cyan, purple, and / or ultraviolet ranges. In some embodiments, NS1801 and / or 1800 can be synthesized to have a primary emission peak wavelength between about 605 nm and about 650 nm, between about 510 nm and about 550 nm, or between about 300 nm and about 480 nm.

[0119] NS1801 and / or 1800 can be synthesized to exhibit a high QY. In some embodiments, NS1801 and / or 1800 can be synthesized to exhibit a QY between 80% and 95% or between 85% and 90%.

[0120] Thus, according to various embodiments, NS1800 can be synthesized such that the presence of the barrier layer 1806 on NS1801 does not substantially change or quench the light emission characteristics of NS1801.

[0121] Examples of embodiments of the nanostructure film FIG. 19 shows a cross-sectional view of an NS film 1900 according to some embodiments. In some embodiments, the NS-based CC layer 220 can be similar to the NS film 1900.

[0122] The NS film 1900 can, according to some embodiments, include a plurality of barrier layer-coated core-shell NS1800s (FIG. 18) and a matrix material 1910. According to some embodiments, NS1800 can be embedded in or otherwise disposed within the matrix material 1910. As used herein, the term "embedded" is used to indicate that the NS is encapsulated or enclosed within the matrix material 1910 that constitutes most of the matrix. In some embodiments, NS1800 can be uniformly distributed throughout the matrix material 1910, but it should be noted that in other embodiments, NS1800 can be distributed according to a uniformity distribution function for a particular application. Those skilled in the art should note that even if NS1800 is shown to be of the same diameter, NS1800 can have a size distribution.

[0123] In some embodiments, NS1800 may include a homogeneous population of NSs having sizes that emit in the blue visible wavelength spectrum, the green visible wavelength spectrum, or the red visible wavelength spectrum. In other embodiments, NS1800 may include a first population of NSs having sizes that emit in the blue visible wavelength spectrum, a second population of NSs having sizes that emit in the green visible wavelength spectrum, and a third population of NSs that emit in the red visible wavelength spectrum.

[0124] The matrix material 1910 can be any suitable host matrix material capable of accommodating NS1800. Suitable matrix materials can be chemically and optically compatible with NS1800 and the surrounding packaging materials or layers used when applying the NS film 1900 to a device. Suitable matrix materials can include non-yellowing optical materials that are transparent to both primary and secondary light, thereby allowing both primary and secondary light to pass through the matrix material. In some embodiments, the matrix material 1910 can completely surround each of the NS1800. The matrix material 1910 can be flexible or can be flexible in applications where a flexible or moldable NS film 1900 is desired. Alternatively, the matrix material 1910 can include high-strength and non-flexible materials.

[0125] The matrix material 1910 may include polymers, organic and inorganic oxides. The polymers suitable for use in the matrix material 1910 can be any polymers known to those skilled in the art and usable for such purposes. The polymers can be substantially translucent or substantially transparent. Matrix materials include, but are not limited to, epoxies, acrylates, norbornenes, polyethylenes, poly(vinyl butyral):poly(vinyl acetate), polyureas, polyurethanes; silicones and silicone derivatives including aminosilicone (AMS), polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane, polydialkylsiloxane, silsesquioxane, fluorinated silicone, vinyl and hydride-substituted silicone, etc.; acrylic polymers and copolymers formed from monomers such as methyl methacrylate, butyl methacrylate, lauryl methacrylate, etc.; styrenic polymers such as polystyrene, aminopolystyrene (APS), poly(acrylonitrile ethylene styrene) (AES), etc.; polymers crosslinked with difunctional monomers such as divinylbenzene; crosslinking agents suitable for crosslinking ligand materials, epoxides that combine with ligand amines (e.g., APS or PEI ligand amines) to form epoxies, etc., may be included but are not limited to these.

[0126] In some embodiments, the matrix material 1910 includes scattering particles such as TiO2 microbeads, ZnS microbeads, or glass microbeads that can improve the light conversion efficiency of the NS film 1900.

[0127] In another embodiment, the matrix material 1910 has low oxygen permeability and moisture permeability, exhibits high light stability and chemical stability, shows a good refractive index, adheres to the outer surface of the NS1800, and can provide a hermetic seal that protects the NS1800. In another embodiment, the matrix material 1910 can be curable by UV or thermal curing methods to facilitate roll-to-roll processing.

[0128] According to some embodiments, the NS film 1900 can be formed by mixing NS1800 into a polymer (e.g., a photoresist), casting the NS-polymer mixture onto a substrate, mixing NS1800 with monomers and polymerizing them together, mixing NS1800 into a sol-gel to form an oxide, or by other methods known to those skilled in the art.

[0129] According to some embodiments, the formation of the NS film 1900 can include a film extrusion process. The film extrusion process may include forming a homogeneous mixture of a matrix material 1910 and a barrier layer-coated core-shell NS such as NS1800, and introducing the homogeneous mixture into a hopper attached to the top and supplied to an extruder. In some embodiments, the homogeneous mixture can be in the form of pellets. The film extrusion process may further include extruding the NS film 1900 from a slot die and passing the extruded NS film 1900 through a chill roll. In some embodiments, the extruded NS film 1900 can have a thickness in the range of less than about 75 μm, for example, about 70 μm to about 40 μm, about 65 μm to about 40 μm, about 60 μm to about 40 μm, or about 5 μm to about 40 μm. In some embodiments, the NS film 1900 has a thickness of less than about 10 μm. In some embodiments, the formation of the NS film 1900 can optionally include a secondary process following the film extrusion process. The secondary process may include processes such as coextrusion, thermoforming, vacuum forming, plasma treatment, forming, and / or embossing to impart a texture to the outermost surface of the NS film 1900. The textured outermost surface of the NS film 1900 can, for example, contribute to the improvement of the defined light diffusion characteristics and / or the defined angular light emission characteristics of the NS film 1900.

[0130] Examples of Embodiments of Light-Emitting Nanostructures This specification describes various compositions having luminescent nanostructures (NSs). Various properties of the luminescent nanostructures, including absorption properties, luminescence properties, and refractive index properties, can be adjusted according to various applications. The material properties of the NSs can be substantially homogeneous or, in certain embodiments, heterogeneous. The optical properties of the NSs can be determined by their particle size, chemical composition, or surface composition. Since the size of the luminescent NSs can be adjusted in the range of about 1 nm to about 15 nm, light emission can be covered in the entire optical spectrum, and a great diversity in color rendering can be achieved. Encapsulation of the particles can provide robustness against chemical substances and UV degradants.

[0131] The luminescent NSs used in the embodiments described in this specification can be manufactured using any method known to those skilled in the art. Suitable methods and examples of nanocrystals are disclosed in U.S. Patent No. 7,374,807, U.S. Patent Application No. 10 / 796,832 (filed March 10, 2004), U.S. Patent No. 6,949,206, and U.S. Patent Provisional Application No. 60 / 578,236 (filed June 8, 2004), the entire disclosures of each of which are incorporated herein by reference.

[0132] The luminescent NSs used in the embodiments disclosed herein can be fabricated from any suitable material, more preferably an inorganic conductive or semiconducting material, including inorganic materials. Suitable semiconductor materials can include any type of semiconductor such as II-VI, III-V, IV-VI, and IV group semiconductors, including those disclosed in U.S. Patent Application No. 10 / 796,832. Suitable semiconductor materials include Si, Ge, Sn, Se, Te, B, C (including diamond), P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SuS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF, CuCl, CuBr, CuI, Si3N4, Ge3N4, Al2O3, (Al, Ga, In)2(S, Se, Te)3, Al2CO, and any suitable combination of two or more such semiconductors, but are not limited thereto.

[0133] In certain embodiments, the luminescent NSs can have a dopant from the group consisting of p-type dopants or n-type dopants. The NSs can also have a II-VI or III-V group semiconductor. Examples of II-VI or III-V group semiconductor NSs can include any combination of an element from Group II of the periodic table, such as Zn, Cd, Hg, etc., and an element from Group VI of the periodic table, such as S, Se, Te, Po, etc.; and any combination of an element from Group III of the periodic table, such as B, Al, Ga, In, Tl, etc., and an element from Group V of the periodic table, such as N, P, As, Sb, Bi, etc.

[0134] The luminescent NSs described herein may also further include ligands conjugated, cooperating, associating, or adhering to their surfaces. Suitable ligands include any group known to those skilled in the art, including those disclosed in U.S. Patent No. 8,283,412, U.S. Patent Publication No. 2008 / 0237540, U.S. Patent Publication No. 2010 / 0110728, U.S. Patent No. 8,563,133, U.S. Patent No. 7,645,397, U.S. Patent No. 7,374,807, U.S. Patent No. 6,949,206, U.S. Patent No. 7,572,393, and U.S. Patent No. 7,267,875, the disclosures of each of which are incorporated herein by reference. By using such ligands, the ability of the luminescent NSs to be incorporated into various solvents and matrices including polymers can be enhanced. By enhancing the miscibility (i.e., the ability to mix without separating) of the luminescent NSs in various solvents and matrices, the NSs can be dispersed throughout the polymer composition so that they do not aggregate and thus do not scatter light. Such ligands are described herein as "miscibility-enhancing" ligands.

[0135] In certain embodiments, there are provided compositions having luminescent NSs dispersed or embedded in a matrix material. Suitable matrix materials can be any material known to those skilled in the art, including polymeric materials, organic and inorganic oxides. The compositions described herein can be a layer, encapsulant, coating, sheet, or film. In the embodiments described herein, when reference is made to a layer, polymer layer, matrix, sheet, or film, these terms are used in substantially the same sense, and the embodiments so described are not limited to any one type of composition, but are to be understood to encompass any matrix material or layer described herein or known in the art.

[0136] Down-converting NSs (such as those disclosed in U.S. Patent No. 7,374,807) utilize the luminescent properties of luminescent nanostructures that are adjusted to absorb light at a particular wavelength and then emit light at a second wavelength, thereby improving the performance and efficiency of an active light source (e.g., an LED).

[0137] While methods known to those skilled in the art can be used to generate luminescent NSs, solution-phase colloidal methods can be used for the controlled growth of inorganic nanomaterial phosphors. See Alivisatos, A. P., “Semiconductor clusters, nanocrystals, and quantum dots,” Science 271:933 (1996); X. Peng, M. Schlamp, A. Kadavanich, A. P. Alivisatos, “Epitaxial growth of highly luminescent CdSe / CdS Core / Shell nanocrystals with photostability and electronic accessibility,” J. Am. Chem. Soc. 30:7019-7029 (1997); and C. B. Murray, D. J. Norris, M. G. Bawendi, “Synthesis and characterization of nearly monodisperse CdE (E=sulfur, selenium, tellurium) semiconductor nanocrystallites,” J Am. Chem. Soc. 115:8706 (1993). The entire disclosures of each are incorporated herein by reference.

[0138] According to some embodiments, by way of example, CdSe can be used as an NS material for visible light downconversion due to the relatively high level of maturity of the synthesis of this material. Substitution with non-cadmium-containing NSs is also possible due to the use of common surface chemistries.

[0139] In a semiconductor NS, photoinduced luminescence originates from the band-edge states of the NS. Band-edge luminescence from the luminescent NS competes with radiative and non-radiative decay channels that are attributed to surface electronic states. X. Peng, et al., J Am. Chem. Soc. 30:7019-7029 (1997). As a result, the presence of surface defects such as dangling bonds leads to non-radiative recombination centers and contributes to the reduction of luminescence efficiency. An efficient and permanent way to passivate and remove surface trap states is to epitaxially grow an inorganic shell material on the surface of the NS. X. Peng, et al., J. Am. Chem. Soc. 30:701 9-7029 (1997). The shell material can be selected such that the electronic energy levels are of type 1 with respect to the core material (e.g., with a larger bandgap to provide a potential step that localizes electrons and holes in the core). As a result, it is possible to reduce the probability of non-radiative recombination.

[0140] The core-shell structure can be obtained by adding an organometallic precursor containing the shell material to a reaction mixture containing the core NS. In this case, rather than nucleation followed by growth, the core serves as the nucleus and the shell grows from its surface. The reaction temperature is kept low to promote the addition of monomers of the shell material to the core surface while preventing the independent nucleation of nanocrystals of the shell material. A surfactant in the reaction mixture is present to induce a controlled growth of the shell material and to ensure solubility. When the lattice mismatch between the two materials is small, a uniform and epitaxially grown shell is obtained.

[0141] Examples of materials for preparing core-shell emissive NSs include, but are not limited to, Si, Ge, Sn, Se, Te, B, C (including diamond), P, Co, Au, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTc, BeS, BcSe, BcTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuP, CuCl, CuBr, CuI, Si3N4, Ge3N4, Al2O3, (Al, Ga, In)2(S, Se, Te)3, AlCO, and combinations thereof. Also, shell emissive NSs for use in the practice of the present invention include, but are not limited to, (denoted as core / shell) CdSe / ZnS, InP / ZnS, InP / ZnSe, PbSe / PbS, CdSe / CdS, CdTe / CdS, CdTe / ZnS, and others.

[0142] The emissive NSs for use in the embodiments described herein can have a size of less than about 100 nm and also less than about 2 nm, and the present invention absorbs visible light. As used herein, visible light is electromagnetic radiation having a wavelength between about 380 and about 780 nanometers that is visible to the human eye. Visible light can be divided into various colors of the spectrum such as red, orange, yellow, green, blue, indigo, violet. Blue light can include light having a wavelength of about 435 nm to about 495 nm, green light can include light having a wavelength of about 495 nm to about 570 nm, and red light can include light having a wavelength of about 620 nm to about 750 nm.

[0143] According to various embodiments, the emissive NSs can have a size and composition such that they absorb photons in the ultraviolet, near-infrared, and / or infrared spectra. The ultraviolet spectrum includes light having a wavelength of about 100 nm to about 400 nm, the near-infrared spectrum includes light having a wavelength of about 750 nm to about 100 μm, and the infrared spectrum can include light having a wavelength of about 750 nm to about 300 μm.

[0144] In various embodiments described herein, while it is possible to use the luminescent NSs of other suitable materials, in one embodiment, the NSs are ZnS, InAs, CdSe, or any combination thereof, and can form a population of nanocrystals for use in the embodiments described herein. As described above, in further embodiments, the luminescent NSs can be core / shell nanocrystals such as CdSe / ZnS, InP / ZnSe, CdSe / CdS, or InP / ZnS.

[0145] Suitable luminescent nanostructures and methods for preparing luminescent nanostructures including the addition of various solubility enhancing ligands are described in U.S. Patent Publication No. 2012 / 0113672, the disclosure of which is incorporated herein by reference in its entirety.

[0146] It should be understood that, although specific embodiments are illustrated and described herein, the claims are not limited to the specific forms or arrangements of the components described and shown. Although exemplary embodiments are disclosed herein and specific terms are used, they are used only in a general and descriptive sense and not for purposes of limitation. Modifications and variations of the embodiments are possible in light of the above teachings. Accordingly, it should be understood that the embodiments can be practiced in ways other than as specifically described.

Claims

1. circuit board and A subpixel configured to emit display light having an emission spectrum including a first peak wavelength and a second peak wavelength, Equipped with, The aforementioned subpixel is, A nanostructure-based color conversion (NS-based CC) layer comprising quantum dots (QDs) configured to emit first light having a first peak wavelength, A micro-LED disposed on a substrate configured to emit a second light having a second peak wavelength, Equipped with, The NS-based CC layer is arranged on the micro-LED. The first portion of the second light is absorbed by the QD and down-converted to the first light. The second portion of the second light is transmitted through the NS base CC layer. Display device.

2. The display apparatus according to claim 1, wherein the first peak wavelength is in the wavelength range of 620 nm to 750 nm.

3. The display apparatus according to claim 1 or 2, wherein the second peak wavelength is in the wavelength range of 550 nm to 610 nm.

4. The display apparatus according to claim 1 or 2, wherein the first and second peak wavelengths are in different and adjacent wavelength regions of the electromagnetic (EM) spectrum.

5. The display device according to claim 1 or 2, wherein the first peak wavelength is in the red wavelength region of the electromagnetic (EM) spectrum, and the second peak wavelength is in the orange or yellow wavelength region of the EM spectrum.

6. The display apparatus according to claim 1 or 2, wherein the intensity of the first peak wavelength is greater than the intensity of the second peak wavelength.

7. The display apparatus according to claim 1 or 2, wherein the range of the peak intensity ratio of the second peak wavelength to the first peak wavelength, from 0 to 40, corresponds to a range of 100% to 1% of the light transmittance of the microLED at the second peak wavelength.

8. The display apparatus according to claim 1 or 2, wherein the microLED has a light transmittance of 1% to 70% through the NS-based CC layer at the second peak wavelength.

9. The display apparatus according to claim 1 or 2, wherein the NS base CC layer includes a surface area of ​​0.5 μm × 0.5 μm to 1000 μm × 1000 μm.

10. The display apparatus according to claim 1 or 2, wherein the NS base CC layer covers the entire upper surface area of ​​the micro LED.

11. The display apparatus according to claim 1 or 2, wherein the upper surface area of ​​the NS base CC layer is larger than the upper surface area of ​​the micro LED.

12. The display apparatus according to claim 1 or 2, wherein the NS base CC layer includes a thickness of 5 μm to 40 μm.

13. The display apparatus according to claim 1 or 2, wherein the NS base CC layer includes an optical density of 0.1 to 3.

0.

14. The substrate further comprises a second subpixel including a second microLED disposed on the substrate, The display apparatus according to claim 1 or 2, wherein the second microLED is configured to emit a second display light having an emission spectrum that includes a single peak wavelength within the 435 nm to 495 nm wavelength range of the electromagnetic (EM) spectrum.

15. Forming first and second microLEDs on a substrate, Depositing layers of quantum dots (QDs) on the first and second micro-LEDs, Masking the first portion of the QD layer, The second portion of the QD layer is subjected to a hardening treatment, Removing the first portion of the QD layer, Includes, The first microLED is formed to emit first display light having a first emission spectrum including a double peak wavelength, The second microLED is formed to emit a second display light having a second emission spectrum including a single peak wavelength. A method for manufacturing a display device.

16. Forming first and second microLEDs on a substrate, Forming a patterned template on the first and second micro-LEDs, Depositing a layer of quantum dots (QDs) on the aforementioned patterned template, Masking the first portion of the QD layer, The second portion of the QD layer is subjected to a hardening treatment, Removing the first portion of the QD layer, Includes, The first microLED is formed to emit first display light having a first emission spectrum including a double peak wavelength, The second microLED is configured to emit a second display light having a second emission spectrum including a single peak wavelength, The patterned template includes an aperture on the first microLED, A method for manufacturing a display device.

Images