KR101117934B1 - The fabrication method of light scattering layer - Google Patents

Abstract

Disclosed is a light scattering layer forming method capable of improving light emission efficiency by increasing extraction efficiency of light formed inside a light emitting device through diffuse reflection.

The method for forming a light scattering layer according to the present invention includes (a) spin coating a solution in which a nanoparticle having a refractive index equal to or higher than the refractive index of a transparent substrate is dispersed in a stamp having a pattern formed on the surface or a flat surface. step; (b) using the stamp to form a light scattering layer on a transparent substrate by Reverse Imprint Lithography; And (c) sintering the light scattering layer, wherein the nanoparticles dispersed in the step (a) have an average particle diameter of 5 to 100 nm, and have a content ratio of 5 to 50% by weight of the total weight of the solution. Characterized in that it is included.

Description

Light scattering layer formation method {THE FABRICATION METHOD OF LIGHT SCATTERING LAYER}

The present invention relates to a technology for improving light extraction efficiency of light emitting devices such as LED (Light Emitting Diode) devices, and more particularly, spin coating and reverse imprint of nano particle solutions in which high refractive materials are dispersed. By using reverse imprint lithography, a light scattering layer having a high refractive index and a high aspect ratio capable of inducing diffused reflection on a transparent substrate surface, such as a transparent indium tin oxide (ITO) electrode of an LED device, The present invention relates to a light scattering layer forming method capable of improving luminous efficiency by increasing extraction efficiency of light formed inside a light emitting device such as an LED device.

LED devices, which are mainly used as light sources and lighting fixtures such as LCD TVs, are a kind of pn junction diodes in which a p-type semiconductor layer and an n-type semiconductor layer are bonded together, and a band gap between a conduction band and a balance band. It is a light emitting device using the principle that electric energy of (band gap) is changed into energy of light.

That is, when a positive voltage is applied to the pn junction diode by a predetermined voltage or more, holes in the p-type semiconductor move toward the n-type semiconductor, and electrons in the n-type semiconductor move toward the p-type semiconductor, whereby electrons and holes are recombined to form a band. Light energy corresponding to the gap is emitted.

1 schematically illustrates a vertical cross section of a conventional gallium nitride (GaN) based LED device.

Referring to FIG. 1, in the case of a general gallium nitride (GaN) based LED device 100, a undoped GaN layer 120 is formed on a sapphire substrate 110, and an n-GaN layer 130 is an n-type semiconductor. A multi-quantum well layer 140 as a semiconductor light emitting active layer, a p-GaN layer 150 as a p-type semiconductor, and an ITO electrode layer 160 are sequentially stacked.

In such a conventional LED structure, the photon formed in the multi-layer well layer 140 is not easily emitted to the outside due to total reflection due to a high refractive index difference between the LED element and the outside, thereby lowering the luminous efficiency.

In order to solve this problem, researches to improve light extraction efficiency by increasing surface diffuse reflection by performing nano-surface texturing process on the surface of LED devices have been actively conducted. In order to exhibit the maximum luminous efficiency through such a technique, a technique for forming a nanostructure having a very regular period is required.

Various research groups increase the surface roughness by controlling the deposition conditions when depositing the p-GaN layer 150, or the ITO electrode layer 160, the p-GaN layer 150, and n by using a photolithography process. By etching the -GaN layer 130, nano-patterns are formed on the surface to reduce the amount of light reflected from the surface of the LED device to improve the efficiency of the device.

However, in the case of increasing the surface roughness by controlling the deposition conditions during the deposition of the p-GaN layer 150, it is impossible to form a regular nanostructure and to have a high aspect ratio.

In addition, in the technique of etching the ITO electrode layer 160, the p-GaN layer 150, and the n-GaN layer 130, plasma damage may occur during the etching process, and thus electrical characteristics, that is, PN junction properties may be sharply degraded. Can be. In this case, a leakage current that adversely affects the light emitting device may occur, and even if the light emitting efficiency of the device increases, the rate of improvement decreases.

Accordingly, in order to solve the above problem, a method of forming a light scattering pattern using a nanoimprint lithography process has been proposed, and the light emitting efficiency of an LED device is improved to some extent by using a nanoimprint lithography technique that does not require an etching process.

Recently, direct nano patterning technology of various functional materials using nano imprint lithography technology is being developed. Direct functional nano using polymer mold and nano particle solution to form functional nano pattern through simpler process Patterning techniques have been developed. The direct nano-patterning technology is a technique of forming a nano-pattern through an imprinting process after coating the nanoparticle solution on the substrate and aligning the polymer mold on top.

In order for the nanoparticles to move into the mold's pattern and form a pattern, the coated nanoparticle layer must contain a sufficient amount of organic solvent to maintain fluidity. Since it is removed, the pattern shrinkage phenomenon occurs naturally after the imprinting process.

In addition, in the pressing process using the polymer mold during the imprinting process, nanoparticles located between the convex portion of the polymer mold and the substrate cannot be easily moved by adhesion to the surface of the polymer mold, thereby inevitably forming a residual layer.

An object of the present invention is a light scattering layer having a high refractive index and a high aspect ratio on a transparent substrate surface by using spin coating and reverse imprint lithography of a nano particle solution in which a high refractive material is dispersed. ) To provide a light scattering layer forming method that can increase the extraction efficiency of light formed inside the light emitting device to the outside, and a light emitting efficiency improved LED including a light scattering layer formed by the method.

The method for forming a light scattering layer according to the present invention for achieving the above object is (a) a solution in which nanoparticles having a refractive index equal to or higher than the refractive index of a transparent substrate are dispersed in a stamp having a pattern formed on the surface or a flat surface. spin coating the solution); (b) using the stamp to form a light scattering layer on a transparent substrate by Reverse Imprint Lithography; And (c) sintering the light scattering layer; wherein the nanoparticles dispersed in the step (a) have an average particle diameter of 5 to 100 nm, and 5 to 50 wt% of the total weight of the solution. Characterized in that it is included in the content ratio of.

In this case, the reverse imprint lithography may include (b1) aligning the solution-coated stamp and the transparent substrate; (b2) through the heating and pressing process, the stamp and the transparent substrate are contacted to transfer the solution coated on the stamp to the transparent substrate, and the solvent included in the solution is removed to form a light scattering layer made of a high refractive material. Making; And (b3) separating the stamp and the transparent substrate.

On the other hand, the transparent substrate is made of an ITO material used as an electrode of the LED device, the solution may be dispersed at least one of the high refractive material of ITO, TiO ₂ and ZnO.

On the other hand, in order to minimize the thickness of the solution remaining in the reverse imprint lithography process, the RPM of the spin coating is preferably in the range of 1,000 ~ 8000 RPM.

On the other hand, the nano-pattern formed on the stamp may be formed with a high aspect ratio in the range of 0.5: 1 to 5: 1, the stamp may be a PDMS material, a stamp duplicated from the master stamp.

The light scattering layer may be formed on the transparent electrode layer of the LED device in which a growth substrate, an n-type semiconductor layer, a semiconductor light emitting active layer, a p-type semiconductor layer, and a transparent electrode layer are sequentially formed.

In the light scattering layer forming method according to the present invention, since the nanoparticle solution in which the high refractive material is dispersed in the polymer mold is first spin coated, an imprinting pattern without a residual layer may be formed. In addition, the light scattering layer manufactured through the reverse imprint lithography process may implement nano-patterns more effectively since shrinkage does not occur during the process.

In addition, the light scattering layer forming method according to the present invention, when the light scattering layer made of a high refractive material on the ITO transparent electrode of the LED device through a reverse imprint lithography process, the surface roughness increases even in the case of the light scattering layer without a pattern The light extraction efficiency can be improved. In the case where the regular nanopattern is formed, the effect of the regular nanostructure is added to the surface roughness improving effect by the high refractive material, and thus the light extraction efficiency can be improved more.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only the embodiments make the disclosure of the present invention complete, and those skilled in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

Hereinafter, a light scattering layer forming method according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

2 is a flowchart schematically showing a light scattering layer forming method according to the present invention. 3A to 3E are perspective views schematically illustrating a process of the light scattering layer forming method illustrated in FIG. 2. Hereinafter, the light scattering layer forming method illustrated in FIG. 2 will be described in detail with reference to FIGS. 3A to 3E.

Referring to FIG. 2, the light scattering layer forming method according to the present invention comprises a high refractive nano particle solution spin coating step (S210), a reverse imprint lithography step (S220), and a light scattering layer sintering step (S230). Include.

Spin Coating

In the high refractive nanoparticle solution spin coating step (S210), a spin coating solution having a high refractive index material having a refractive index higher than that of the transparent substrate is dispersed on a stamp having a pattern formed on the surface for about 30 seconds (FIG. 3B). At this time, the high refractive material may be a nano particle (nano particles) having an average particle diameter of 5 ~ 100nm. The pattern of the stamp may be formed in a periodic pattern having a pattern pitch of about 300 ~ 500nm.

The stamp 310 may be made of a polymer material such as polydimethylsiloxane (PDMS), and may be a stamp duplicated from a master stamp having an opposite pattern formed on a surface thereof (FIG. 3A). Stamps made of soft materials such as poly methy methacrylate (PMMA), poly vinyl chloride (PVC), poly carbonate (PC), poly vinyl acrylate (PVA), and polytetrafluoroethylene (PTFE) are more advantageous for processing and replication desirable.

In addition, a release layer such as graphite coating or SAM (Self Assembled Monolayer) may be formed on the surface of the master stamp to facilitate separation of the replica stamp and the master stamp, and the stamp 310 used for light scattering layer formation. The same applies to the above, in which the light scattering layer made of a high refractive material can be easily separated in reverse imprint lithography.

The PMMA stamp used as the master stamp 301 and the PDMS stamp used for imprint can be easily formed as a soft polymer material, and have a pattern having a high aspect ratio of about 0.5: 1 to 5: 1. It can be formed easily.

The transparent substrate 330 to form a light scattering layer thereon may be made of indium tin oxide (ITO) material used as an electrode of a gallium nitride (GaN) -based LED device, wherein the solution 320 Oxide semiconductors such as ITO, TiO ₂ , and ZnO, which are equal to or higher than the refractive index of ITO, may be included alone or in combination of two or more thereof.

The reason for using the spin coating in this step is to ensure that the solution 320 in which the high refractive material is dispersed is sufficiently coated inside the pattern of the stamp 310. After the reverse imprint lithography step S220 described below, the thickness of the light scattering layer remaining on the stamp without being transferred to the transparent substrate 330 may affect the aspect ratio of the light scattering layer, which is a solution 320 in which the high refractive material is dispersed. It depends on the concentration and RPM of the spin coating. As a result of the experiment, there was almost no residual layer at 7,000 RPM, and considering the error range, the RPM of the spin coating is preferably in the range of 1,000 to 8000 RPM.

On the other hand, the high refractive material dispersed in the solution 320 may be included in the content ratio of 5 to 50% by weight of the total weight of the solution. When the content of the high refractive material is less than 5% by weight, it is difficult to control the coating thickness because the viscosity is too low, and the amount of the high refractive material is small in the light scattering layer formed by the removal of the solvent. On the other hand, when the content of the high refractive material exceeds 50% by weight, the spin coating is not well made, there is a problem that the solution remains in the stamp because the viscosity is too high.

Reverse Imprint Lithography

In the reverse imprint lithography step S220, the solution 320 forms a light scattering layer on the transparent substrate 330 by reverse imprint lithography using a spin-coated stamp 310 (FIG. 3C). 3d)

Reverse imprint lithography may specifically proceed as follows.

First, the stamp 310 coated with the solution 320 and the transparent substrate 330 are aligned (S221).

Next, it is heated to a temperature of about 50 ~ 200 ℃ and pressurized at a pressure of about 1 ~ 50 atmosphere (atm), the stamp 310 and the transparent substrate 330 by contacting for about 10 minutes to coat the stamp 310 The prepared solution 320 is transferred to the transparent substrate 330, and a solvent such as ethanol or water included in the solution 320 is removed. This step can be done in a vacuum.

As a result, a light scattering layer 321 made of a high refractive material from which the solvent is removed from the solution 320 is formed on the transparent substrate 330. (S222, FIG. 3C) In this process, the light scattering layer is formed on the surface of the transparent substrate 330. And strong adhesion.

Thereafter, the stamp 310 and the transparent substrate 330 are separated. (S223, FIG. 3D).

Sintering

In the light scattering layer sintering step (S230), the light scattering layer 321 formed of a high refractive material on the transparent substrate 330 through the reverse imprint lithography step (S220) is vacuumed for about 2 hours in a temperature range of about 200 to 800 ° C. Sintering at (Fig. 3e).

Through the sintering process, organic matter remaining in the light scattering layer 321 is removed, and the binding force and conductivity of the light scattering layer 321 are improved by causing necking between the high refractive materials constituting the light scattering layer 321. Let's do it.

4A and 4B illustrate SEM images of planes and cross sections of the light scattering layer formed by the light scattering layer forming method illustrated in FIG. 2. 4A and 4B, it can be seen that the light scattering layer formed by the above process has a certain nano pattern formed.

5A shows a light scattering layer formed using a conventional imprint lithography method, and FIG. 5B shows a light scattering layer formed using a reverse imprint lithography method according to the present invention.

  Referring to FIGS. 5A and 5B, in the conventional method, the shrinkage phenomenon occurs in the pattern of the light scattering layer formed after the imprint shown in FIG. 5A, rather than the pattern formed in the pre-imprint stamp shown in FIG. 5A. You can see what appeared. However, in the method according to the present invention, the pattern formed on the stamp before the reverse imprint shown in (a) of FIG. 5B and the pattern formed after the reverse imprint shown in (b) of FIG. 5B are almost the same, so that no shrinkage phenomenon occurs. Can be.

Figure 6 shows an embodiment of an LED device comprising a light scattering layer according to the present invention.

Referring to FIG. 6, the LED device 600 may include a semiconductor such as an n-type semiconductor layer 630 and a multi-quantum well layer on a growth substrate 610 such as a sapphire substrate, a SiC substrate, or the like. The light emitting active layer 640, the p-type semiconductor layer 650, and the transparent electrode layer 660 such as the ITO electrode are sequentially formed, and the light scattering layer 670 is formed on the transparent electrode layer 660.

As shown in FIG. 6, the LED device may be a gallium nitride (GaN) -based device, and the undoped semiconductor layer 620 may be formed on the growth substrate 610 before the n-type semiconductor layer 630 is formed. u-GaN) or a buffer layer (not shown) may be further formed.

2 to 6 described above with reference to an example in which a pattern is formed on the surface of the stamp. Of course, the light extraction efficiency is the highest when the pattern is formed on the surface of the stamp, but even if the surface of the stamp is a simple flat form without the pattern can be obtained some degree of light extraction efficiency.

Figure 7 shows the emission peak of the conventional blue LED device without a light scattering layer and the blue LED device with a light scattering layer according to the present invention.

In FIG. 7, 'A' shows an emission peak of a conventional blue LED device in which a light scattering layer is not formed, and 'B' and 'C' show emission peaks of a blue LED device in which a light scattering layer is formed by a method according to the present invention. In addition, "B" shows the case where a pattern is not formed, and "C" shows the emission peak in the case where a pattern is formed.

Referring to FIG. 7, in the case of the conventional blue LED device in which the light scattering layer denoted by 'A' is not formed, the main peak is exhibited at 451 nm, and its intensity is very low. However, in the case of 'B' and 'C' according to the present invention, the main peak appeared at 462 nm, and the intensity of the main peak was relatively higher than that of 'A'. In particular, in the case of 'C' formed to the pattern while the light scattering layer is formed, it can be seen that the intensity of the emission peak is very high. Under the same conditions, if the intensity of the main emission peak is large, it can be said that the luminous efficiency is also increased.

Therefore, in the case of the LED device including the light scattering layer formed by the light scattering layer forming method according to the present invention, it is possible to give a sufficient surface roughness, so that the total reflection on the LED surface is prevented instead of scattered reflection (scattered reflection) Is generated a lot, resulting in a very high luminous efficiency.

Although the above has been described with reference to one embodiment of the present invention, various changes and modifications can be made at the level of those skilled in the art. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

1 schematically illustrates a vertical cross section of a conventional GaN based LED device.

2 is a flowchart schematically showing a light scattering layer forming method according to the present invention.

3A to 3E are perspective views schematically illustrating a process of the light scattering layer forming method illustrated in FIG. 2.

4A and 4B illustrate SEM images of planes and cross sections of the light scattering layer formed by the light scattering layer forming method illustrated in FIG. 2.

5A shows a light scattering layer formed using a conventional imprint lithography method, and FIG. 5B shows a light scattering layer formed using a reverse imprint lithography method according to the present invention.

Figure 6 shows an embodiment of an LED device comprising a light scattering layer according to the present invention.

Figure 7 shows the emission peak of the conventional blue LED device without a light scattering layer and the blue LED device with a light scattering layer according to the present invention.

Claims (8)

(a) spin coating a nanoparticle dispersed solution having a refractive index of at least the refractive index of a transparent substrate made of indium tin oxide (ITO) step; (b) using the stamp to form a light scattering layer on a transparent substrate made of ITO material by Reverse Imprint Lithography; And (c) sintering the light scattering layer; The nanoparticles dispersed in the step (a) has an average particle diameter of 5 ~ 100nm, the light scattering layer forming method, characterized in that contained in the content ratio of 5 to 50% by weight of the total weight of the solution. The method of claim 1, The reverse imprint lithography (b1) aligning the stamp with the solution and the transparent substrate; (b2) through the heating and pressing process, the stamp and the transparent substrate are contacted to transfer the solution coated on the stamp to the transparent substrate, and the solvent included in the solution is removed to form a light scattering layer made of a high refractive material. Making; And (B3) separating the stamp and the transparent substrate; light scattering layer forming method comprising a. The method of claim 1, The solution is a method for forming a light scattering layer, characterized in that at least one material of ITO, TiO ₂ and ZnO is dispersed. The method of claim 1, RPM of the spin coating method of forming a light scattering layer, characterized in that in the range of 1,000 ~ 8000RPM. delete The method of claim 1, The pattern formed on the stamp has a aspect ratio (Aspect Ratio) in the range of 0.5: 1 to 5: 1. The method of claim 1, The stamp is a PDMS material, the light scattering layer forming method, characterized in that the stamp duplicated from the master stamp. delete

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