Metal oxide dispersions in acrylic medium

Abstract

Embodiments of the present disclosure generally relate to LED pixels and methods of fabricating LED pixels. A color conversion material of an LED pixel includes a quantum dot (QD) material, a surface tension modifier, an activator, and an acrylic medium. The acrylic medium including metal oxide particles and a dispersant material, the metal oxide particles have a critical dimension between about 100 nanometers to about 300 nanometers and the metal oxide particles are between about 0.2% and about 5% by weight of the color conversion material.

Description

METAL OXIDE DISPERSIONS IN ACRYLIC MEDIUMBACKGROUNDField

[0001] Embodiments of the present disclosure generally relate to LED pixels and methods of fabricating LED pixels.Description of the Related Art

[0002] A light emitting diode (LED) panel uses an array of LEDs, with individual LEDs providing the individually controllable pixel elements. Such an LED panel can be used for a computer, touch panel device, personal digital assistant (PDA), cell phone, television monitor, and the like. An LED panel that uses micron-scale LEDs based on lll-V semiconductor technology (also called micro-LEDs) would have a variety of advantages as compared to organic light emitting diodes (OLEDs), e.g., higher energy efficiency, brightness, and lifetime, as well as fewer material layers in the display stack which can simplify manufacturing. However, there are challenges to fabrication of micro-LED panels. Accordingly, what is needed in the art are LED pixels and methods of fabricating LED pixels.SUMMARY

[0003] In one embodiment, a color conversion material of an LED pixel includes is provided. The color conversion material includes a quantum dot (QD) material, a surface tension modifier, an activator, and an acrylic medium. The acrylic medium including metal oxide particles and a dispersant material, the metal oxide particles have a critical dimension between about 100 nanometers to about 300 nanometers and the metal oxide particles are between about 0.2% and about 5% by weight of the color conversion material.

[0004] In another embodiment, a device is provided. A device includes a backplane, micro-LEDs coupled to the backplane by electrodes, an encapsulation material disposed on the backplane, between the micro-LEDs. The encapsulation material disposed between an emitting surface of each of the micro-LEDs, such that the micro-LEDs are below a color conversion material. The device also includes an isolation substrate having subpixel isolation (SI) structures disposed therein, the SI structures defining wells of subpixels, the subpixels having the color conversionmaterial disposed in wells and on the isolation substrate. The color conversion material includes a quantum dot (QD) material, a surface tension modifier, an activator, and an acrylic medium. The acrylic medium includes metal oxide particles and a dispersant material, the metal oxide particles have a critical dimension between about 100 nanometers to about 300 nanometers and the metal oxide particles are between about 0.2% and about 5% by weight of the color conversion material.

[0005] In another embodiment, a method of making a color conversion material is provided. The method includes mixing a quantum dot (QD) material, a surface tension modifier, an activator an acrylic medium to form a first mixture and forming a color conversion material by adding a second mixture to the first mixture, the second mixture comprising metal oxide particles and a dispersant, the metal oxides have a critical dimension between about 100 nanometers to about 300 nanometers and the metal oxides are between about 0.2% and about 5% by weight of the color conversion material.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0007] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee. So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments of the present disclosure and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.

[0008] Figure 1A is cross-sectional view of a pixel having a first isolation arrangement according to some embodiments.

[0009] Figure 1 B is cross-sectional view of a pixel having a second isolation arrangement according to some embodiments.

[0010] Figure 2 is a flow diagram of a method of fabricating a color conversion material according to some embodiments.

[0011] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.DETAILED DESCRIPTION

[0012] Embodiments of the present disclosure generally relate to LED pixels and methods of fabricating LED pixels. Specifically, embodiments include a device includes a backplane, at least three micro-LEDs disposed on the backplane, subpixel isolation (SI) structures defining wells of at least three subpixels. The at least three of the subpixels have a color conversion material disposed in the wells.

[0013] Figure 1A is a schematic, cross-sectional view of a pixel 100 having a first isolation arrangement 100a. Figure 1 B is a schematic, cross-sectional view of a pixel 100 having a second isolation arrangement 100b.

[0014] The backplane 101 includes a backplane surface 101a. Micro-LEDs 109 are disposed over the backplane 101. The backplane 101 includes backplane electrodes 103 disposed on the backplane surface 101 a. Each micro-LED 109 has at least one micro-LED electrode 107 coupled to at least one backplane electrode 103 of the backplane 101. In some embodiments, pairs of micro-LED electrodes 107 to are coupled to pairs of backplane electrodes 103. The micro-LED electrodes 107 to are bonded to the backplane electrodes 103 with a first bond 170.

[0015] An encapsulation material 160 is disposed on the backplane 101 , between the pairs of backplane electrodes 103, between the pairs of micro-LED electrodes 107, and between the micro-LEDs 109. The encapsulation material 160 defines an upper surface 160a between the micro-LEDs 109 such that the emitting surface 105of each of the micro-LEDs 109 is exposed to a color conversion material 115. The color conversion materials 115 include quantum dot materials, phosphor materials, or combinations thereof. The Encapsulation material 160 surrounds the micro-LEDs 109, the micro-LED electrodes 107, and the backplane electrodes 103. The encapsulation material 160 provides support for the backplane 101 and the connection between the micro-LEDs 109 and backplane 101. The Encapsulation material 160 includes organic encapsulation materials.

[0016] As shown in Figure 1A, the first isolation arrangement 100a of the pixel 100 includes subpixel isolation (SI) structures 113 disposed on the backplane surface 101a between the micro-LEDs 109. The SI structures 113 have an UV reflection greater than 90%. The optical density of the SI structures 113 provides for color isolation between each of the micro-LEDs 109. The SI structures 113 define wells 127 of the subpixels 112. The subpixels 112 have the color conversion material 115 disposed in the wells 127. The subpixels 112 include a red subpixel 112a with a red color conversion material 115a disposed in the well 127a of the red subpixel 112a, a green subpixel 112b with a green color conversion material 115b disposed in the well 127b of the green subpixel 112b, and a blue subpixel 112c with a blue color conversion material 115c disposed in the well 127c of the blue subpixel 112c. When a micro-LED 109 of the red subpixel 112a is turned on the red color conversion material will convert the light emitted from micro-LED 109 into red light. When a micro- LED 109 of the blue subpixel 112c is turned on the blue color conversion material 115c will convert the light emitted from micro-LED 109 into blue light.

[0017] As shown in Figure 1 B, the second isolation arrangement 100b of the pixel100 includes a transparent material 117. The transparent material 117 is disposed over the emitting surface 105 of the micro-LEDs 109. In an embodiment with a top substrate 123, the transparent material 117 is further disposed between the backplane101 and a surface of the top substrate 123. The transparent material 117 includes an adhesive material. The adhesive material includes, but is not limited to, an epoxy, an acrylic material, and combinations thereof. The acrylic material may be UV transparent material.

[0018] An isolation substrate 119 has SI structures 113 disposed on an isolation surface 119a. The isolation substrate 119 is disposed over the backplane 101. TheSI structures 113 define wells 127 of subpixels 112. The subpixels 112 have the color conversion material 115 disposed in the wells 127 and on the isolation surface 119a of the isolation substrate 119. The subpixels 112 have color filters 125 disposed on the top substrate surface 119b. The subpixels 112 include a red subpixel 112a with a red color conversion material 115a disposed in the well 127a of the red subpixel 112a, and a red color filter 125a disposed above the red color conversion material 115a. The subpixels 112 include a green subpixel 112b with a green color conversion material 115b disposed in the well 127b of the green subpixel 112b, and a green color filter 125b disposed above the green color conversion material 115b. The subpixels 112 include a blue subpixel 112c with a blue color conversion material 115c disposed in the well 127c of the blue subpixel 112c, and a blue color filter 125c disposed above the blue color conversion material 115c. When a micro-LED 109 of the red subpixel 112a is turned on the red color conversion material will convert the light emitted from micro-LED 109 into red light. When a micro-LED 109 of the blue subpixel 112c is turned on the blue color conversion material 115c will convert the light emitted from micro-LED 109 into blue light.

[0019] In some embodiments, the second isolation arrangement 100b includes a top substrate 123. The top substrate 123 includes isolation matrix structures 121 disposed between the top substrate 123 and the isolation substrate 119. The color filters 125 are disposed between the top substrate 123 and the isolation substrate 119. The color filters 125 include a photo resist with colorant. The isolation matrix structures 121 are aligned with the SI structures 113. The color filters 125 are aligned with the color conversion material 115.

[0020] The isolation matrix structures 121 and the color filters 125 are disposed between the isolation substrate 119 and the top substrate 123. The color filters 125 are defined by the isolation matrix structures 121 , the isolation substrate 119, and the top substrate 123. The top substrate 123, the isolation substrate 119, and the SI structures 113 are surrounded by and coupled to the transparent material 117. The isolation matrix structures 121 include, but are not limited to, black matrix materials.

[0021] Figure 2 is a flow diagram of a method 200 of forming a color conversion material 115 according to some embodiments. At operation 201 a first mixture isformed by mixing metal oxide particles, a surface tension modifier, an activator, a dispersant material, and an acrylic medium to form a first mixture.

[0022] The acrylic medium of the first mixture may include hexanediol diacrylate (HDDA), isobornyl acrylate, or other similar acrylic monomers. The acrylic medium of the first mixture may a monofunctional acrylate or difunctional acrylate monomer or a mixture of monofunctional and difunctional acrylate according to some embodiments. The dispersant material has an acid value of about 35 milligram KOH / g. The dispersant has an amine value between about 40 milligram KOH / g and about 60 milligram KOH / g, for example about 50 milligram KOH / g.

[0023] The dispersant has a dynamic viscosity of about 30,000 milliPa-second to about 175,000 milliPa-second at 25 °C for example, about 85,000 milliPa-second at 25 °C. The dispersant has a kinematic viscosity between about 27,000 millimeter squared per second at 25 °C to about 160,000 millimeter squared per second at 25 °C, for example about 80,000 millimeter squared per second at 25 °C. The dispersant has a density of about 1.098 gram per cubic centimeter at 25°C. In some embodiments, the dispersant is a polyester derivative.

[0024] The first mixture includes metal oxide particles with a concentration of about 10% to about 20% in the acrylic medium. The amount of dispersant added to the first mixture is between about 10% and 40% with respect to metal oxide particles, for example, about 30% with respect to metal oxide particles.

[0025] The activator is a curing activator. For example, the activator is an ultraviolet (UV) activator. The UV activator enables the color conversion material to cure with the application of UV radiation.

[0026] The first mixture may also include a solvent. For example, the first mixture may include between about 0% and about 30% of a solvent with respect to metal oxide particles. The solvent may be added to aid dispersion or to improve homogeneity after a spin-coating operation. The solvent may be an inert solvent. For example the solvent may be an inert solvent chosen from toluene, anisole, methyl ethyl ketone or any combination thereof. In other embodiments a solvent is not included.

[0027] At operation 203, a second mixture is added to the first mixture to form a color conversion material. In some embodiments, the second mixture includes a quantum dot (QD) material. In other embodiments, the second mixture includes QD material and metal oxide particles.

[0028] In some embodiments, the amount of dispersant in the color conversion material is between about 10% and about 40% by weight of the metal oxide particles. In some embodiments, the amount of dispersant in the color conversion material is about 1 % to about 4% by weight of color conversion material. In some embodiments, the amount of QD material in the color conversion material is about 5% to about 40% by weight of the color conversion material.

[0029] The metals of the metal oxide may be Titanium, Zirconium, Zinc, Aluminum, Silicon, and / or Cerium. The metal oxide particles may be titanium oxide particles, for example titanium dioxide particles. The metal oxide particles have a critical dimension defined at the largest straight line dimension of each particle. The critical dimension for the metal oxide particles is between about 100 nanometers and about 400 nanometers. For example the critical dimension is between 150 nanometers and about 250 nanometers.

[0030] The metal oxides may include a coating according to some embodiments, metal oxide coating may be a silane, a carboxylic acid, an amine, or any combination thereof.

[0031] The metal oxides are between about 0.2% and about 5% by weight of the color conversion material. For example, the metal oxides are less than about 3% by weight of the color conversion material.

[0032] The metal oxides may be dispersed by additional means. Additional means include the metal oxide particles dispersed by sonic energy, dispersed by sonication, and / or dispersed by dispersing tools. Dispersing tools may be agitators. The dispersed metal oxides are stable within the color conversion material for greater than 1 week. For example, the metal oxides stay dispersed in the color conversion material for between about 1 month and 6 months. For example, the metal oxides stay dispersed in the color conversion material for longer than 6 months. For example, themetal oxides stay dispersed in the color conversion material for longer than 12 months.

[0033] In some embodiments, the first mixture, the second mixture and / or the color conversion material may include the metal oxide particles dispersed from a paste. The paste may be a glycol paste, but other pastes are contemplated. For example, the color conversion material may include between about 0.9g and 1 .1 g of metal oxide particles disposed in glycol paste.

[0034] At operation 205, the color conversion material is applied to a pixel. The color conversion material may be the color conversion material 115 of the first isolation arrangement 100a in Figure 1A or the second isolation arrangement 100b of Figure 1 B, but other isolation arrangements are contemplated. The color conversion material may be applied to a pixel by a spin-coating technique, but other methods are contemplated.

[0035] At operation 207 the color conversion material is cured. The color conversion material is cured by exposure to UV radiation. Once cured, the optical density (OD) has shown to be larger the prior OD’s of previous color conversational materials. For example, the OD per micrometer of color conversional material is greater than 0.08, for example, greater than 0.13. For example, the OD per micrometer of color conversional material is between about 0.14 and about 0.16. For example, the OD per micrometer of color conversional material is about 15.7.

[0036] In addition, the color conversion material also has an enhanced photon conversion energy (PCE). The inventors have found that this new color conversion material in light wavelengths between the 588 and 780 nanometers has a PCE greater than 4%. For example, greater than 7%. For example, the PCE is between about 9% and 11 % between light in the 588 and 780 nanometer wavelengths. The improvements in OD and PCE enable the decrease in QD material, saving costs and enhancing pixel performance. With less QD in the matrix, performance reliability is increased as QDs are very sensitive to oxygen and moisture.

[0037] While the foregoing is directed to implementations of the present disclosure, other and further implementations of the disclosure may be devised without departingfrom the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

What is claimed is:1 . A color conversion material of an LED pixel comprising: a quantum dot (QD) material; a surface tension modifier; an activator; and an acrylic medium, the acrylic medium including metal oxide particles and a dispersant material, the metal oxide particles have a critical dimension between about 100 nanometers to about 300 nanometers and the metal oxide particles are between about 0.2% and about 5% by weight of the color conversion material.

2. The color conversion material of claim 1 , wherein the metal oxide particles are titanium oxide particles.

3. The color conversion material of claim 2, wherein the metal oxide particles are dispersed by sonication.

4. The color conversion material of claim 1 , further comprising a solvent.

5. The color conversion material of claim 4, wherein the solvent is an inert solvent and chosen from one of toluene, anisole, or methyl ethyl ketone.

6. The color conversion material of claim 1 , wherein the acrylic medium is an acrylic monomer.

7. The color conversion material of claim 6, wherein the acrylic monomer is isobornyl acrylate or hexanediol diacrylate.

8. The color conversion material of claim 1 , wherein the activator is an ultraviolet activator.

9. The color conversion material of claim 1 , wherein the dispersant has a dynamic viscosity between about 50,000 and about 150,000 milliPa-second.

10. The color conversion material of claim 1 , wherein the QD material is between about 5% and about 40% by weight of the color conversion material.11 . The color conversion material of claim 1 , wherein the color conversion material has an optical density per micrometer of color conversional material between about 0.14 and about 0.16.

12. The color conversion material of claim 1 , wherein the color conversion material has an photon conversion energy greater than 4% between light wavelengths between about 588 nanometers and about 780 nanometers.

13. A device, comprising: a backplane; micro-LEDs coupled to the backplane by electrodes; an encapsulation material disposed on the backplane, between the micro- LEDs, the encapsulation material disposed between an emitting surface of each of the micro-LEDs, such that the micro-LEDs are below a color conversion material the color conversion material comprising: a quantum dot (QD) material; a surface tension modifier; an activator; and an acrylic medium, the acrylic medium including metal oxide particles and a dispersant material, the metal oxide particles have a critical dimension between about 100 nanometers to about 300 nanometers and the metal oxide particles are between about 0.2% and about 5% by weight of the color conversion material; and an isolation substrate having subpixel isolation (SI) structures disposed therein, the SI structures defining wells of subpixels, the subpixels having the color conversion material disposed in wells and on the isolation substrate.

14. The device of claim 13, wherein the metal oxide particles are titanium dioxide particles.

15. The device of claim 13, wherein the QD material is about 5% to about 40% by weight of the color conversion material.

16. A method of making a color conversion material comprising: mixing metal oxide particles, a dispersant, a surface tension modifier, an activator an acrylic medium to form a first mixture, the metal oxides having a critical dimension between about 100 nanometers to about 300 nanometers; and forming a color conversion material by adding a second mixture to the first mixture, the second mixture comprising a quantum dot (QD) material, wherein the metal oxides are between about 0.2% and about 5% by weight of the color conversion material.

17. The method of claim 16, further comprising applying sonic energy to disperse the metal oxide particles.

18. The method of claim 16, wherein the metal oxide particles are titanium oxide particles.

19. The method of claim 16, wherein the QD material is between about 5% and about 40% by weight of the color conversion material.

20. The method of claim 16, wherein the color conversion material has an optical density per micrometer of color conversional material between about 0.14 and about 0.16.

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