KR20190089101A - Method for surface treatment of substrate for flexible display - Google Patents

Abstract

A surface treatment method for a flexible display substrate for enhancing adhesion between the flexible display substrate and a buffer layer disposed on the flexible display substrate. The surface treatment method for a flexible display substrate according to an aspect of the present invention, comprises: a step (a) of forming a flexible display substrate on a mother substrate; a surface treatment step (b) of irradiating the surface of the flexible display substrate with an ion beam to impart hydrophilicity to the surface of the flexible display substrate; and a step (c) of depositing an inorganic material on the surface of the surface-treated flexible display substrate to form a buffer layer.

Description

[0001] METHOD FOR SURFACE TREATMENT OF SUBSTRATE FOR FLEXIBLE DISPLAY [0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for a substrate for a flexible display, and more particularly to a surface treatment method for a substrate for a flexible display for enhancing adhesion between a substrate for a flexible display and a buffer layer disposed on the substrate for a flexible display .

Flexible display refers to a next-generation display that can be deformed, such as folded or wheeled, unlike a flat display. In addition to being thin and light, strong against impact and easy to carry, it is applicable to various fields such as smart phones and wearable smart devices because it is relatively free from space and shape constraints and can be applied to various applications. The flexible display generally refers to a display formed on a flexible substrate.

The flexible display can display an image by driving a thin film transistor having a switching function. At this time, it is necessary to satisfy a high adhesion force with the buffer layer formed on the flexible substrate and sufficient mechanical characteristics. That is, in order for a flexible substrate to be used as a substrate for a display device, the characteristics required for manufacturing a display device must be satisfied.

On the other hand, in the case of a thin film transistor having a multilayer structure formed on a flexible substrate, cracking between the flexible substrate and the thin film transistor and delamination between layers may occur when the flexible substrate is bent.

If cracking and delamination occur, the physical properties of the flexible display may deteriorate, leading to defective display.

Therefore, there is a need for a method capable of stably forming a buffer layer on a flexible substrate.

As a background art related to the present invention, Korean Patent Laid-Open Publication No. 10-2010-0124014 (published on November 26, 2010) discloses a flexible display substrate processing method using ozone plasma.

It is an object of the present invention to provide a surface treatment method of a substrate for a flexible display for enhancing a deposition efficiency of a buffer layer.

According to another aspect of the present invention, there is provided a method of processing a surface of a substrate for a flexible display, comprising: (a) forming a substrate for a flexible display on a mother substrate; (b) a surface treatment step of irradiating the surface of the substrate for a flexible display with an ion beam to impart hydrophilicity to the surface of the substrate for a flexible display; And (c) depositing an inorganic material on the surface of the surface-treated substrate for a flexible display to form a buffer layer.

In the step (b), the substrate for a flexible display to which hydrophilicity is imparted may be surface-treated so that the surface contact angle is 53 DEG or less.

The substrate for a flexible display may include a polyimide-based substrate.

The ion beam may be performed for 75 seconds to 300 seconds.

The ion beam may be irradiated by applying a voltage of 0.5 to 1.5 kV.

The ion beam may include at least one of an argon ion beam of 10 to 50 sccm and an oxygen ion beam of 10 to 50 sccm.

The buffer layer is _{SiO 2, SiO 2-x,} SiN, SiN x, a-Si (amorphous silicon), Al 2 O 3, Al 2 O 3-x, a single-layer or multi-layer including at least one of AlN and AlN _x As shown in FIG.

The surface treatment method of the substrate for a flexible display according to the present invention can enhance the adhesion with the buffer layer formed on the substrate by controlling the condition of the ion beam and surface-treating the surface of the substrate from a hydrophobic state to a hydrophilic state.

FIG. 1 and FIG. 2 show the results of the surface contact angle change of the PI substrate according to the ion beam time.
FIG. 3 and FIG. 4 show the results of the surface contact angle change of the PI substrate according to the ion beam voltage of the present invention.
5 and 6 are graphs showing changes in surface contact angle of the PI substrate according to the gas flow rate of the ion beam according to the present invention.
FIGS. 7 and 8 are graphs showing changes in surface contact angle of the PI substrate according to the voltage at the conditions of Ar 25 sccm and O ₂ 25 sccm of the present invention.
9 shows the surface roughness of the PI substrate and the buffer layer (SiO ₂ ) after the ion beam irradiation according to the present invention.
10 shows the surface roughness of the PI substrate according to the ion beam condition of the present invention.
11 shows the results of measurement of the transmittance of the PI substrate of the present invention through UV-vis irradiation.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method of processing a surface of a substrate for a flexible display according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

A method for surface treatment of a substrate for a flexible display according to the present invention includes the steps of forming a substrate for a flexible display on a mother substrate, irradiating a surface of the substrate for the flexible display with an ion beam, And a step of depositing an inorganic material on the surface of the surface-treated substrate for a flexible display to form a buffer layer.

First, a substrate for a flexible display is formed on a mother substrate.

The parent substrate may be a solid plate-shaped glass substrate, but is not limited thereto. After the substrate for a flexible display is disposed on the mother substrate, the flexible display panel is manufactured through a plurality of subsequent processes, and the panel is separated from the mother substrate.

Metal foil, glass, and plastic substrates are used as substrates for flexible displays. Compared to two types of substrate materials, plastic substrates are lightweight, easy to process, and have few limitations in shape. There are many types of plastic substrates such as PC, PET, and PI. The most notable substrate material is PI (polyimide). The polyimide series is among the best materials in heat resistance, flexibility and strength. It is able to withstand no change in characteristics from minus 273 ℃ to 400 ℃, low amount of gas generation in vacuum environment, less strain and residue due to strong acid chemicals.

Therefore, it is preferable that the substrate for a flexible display includes a polyimide-based substrate.

The polyimide-based film is prepared by preparing a film by solution casting method of PAA (polyamic acid), which is a precursor obtained by preliminarily polymerizing an aromatic anhydride and an aromatic amine in a polar solvent, and then heating and imidizing the polyamide acid film to finally obtain a polyimide- Can be manufactured.

There are various methods such as spin coating, bar coating, and applicator, and the above method is applied to a supporting substrate such as a glass substrate. After coating, it is put into a dry oven at 50 ~ 70 ℃ for 10 ~ 60 minutes to stabilize. Subsequently, the substrate can be manufactured by curing using the curing conditions suitable for each reagent.

Next, the surface of the substrate for a flexible display is irradiated with an ion beam to perform a surface treatment for imparting hydrophilicity to the surface of the substrate for a flexible display.

The surface treatment has the effect of increasing the surface roughness of the substrate or replacing the functional groups on the surface, thereby changing the surface of the polymer from the hydrophobic state to the hydrophilic state, thereby enhancing the adhesion between the substrate and the buffer layer. Thus, since the deposition efficiency of the buffer layer is increased while maintaining the interface state having hydrophilicity, the buffer layer can be uniformly formed.

In the present invention, the hydrophilic property is referred to as hydrophilic when the arbitrary site is easily bonded to the water molecule, and the hydrophobic property is referred to as hydrophobic when the arbitrary site is not easily bonded to the water molecule.

The hydrophilicity determination can be confirmed by the contact angle, which is the angle formed when the liquid equilibrates thermodynamically on the solid surface. It is defined as the angle between the tangent to the surface of the liquid and the tangent to the surface of the solid. This is a measure of the wettability of a solid surface, which can be measured by a majority of water droplets adhered to it.

The surface treatment using the ion beam may be performed in a vacuum atmosphere. The vacuum atmosphere may be an initial pressure of 5 x 10 ^-6 Torr or less and an operating pressure of 1 mTorr or less, but is not limited thereto.

The ion beam can impart hydrophilicity to the surface of the substrate for the flexible display while irradiating the surface of the activated substrate with the ion beam.

The ion beam may be irradiated by applying a voltage of 0.5 to 1.5 kV, preferably by applying a voltage of 0.8 to 1.3 kV. If the voltage is lower than 0.5 kV, hydrophilicity of the substrate is not properly applied. On the other hand, when the dose exceeds 1.5 kV, the irradiation amount of the ion beam is increased, and the hydrophilicity of the substrate is not properly given.

The ion beam may include at least one of an argon ion beam of 10 to 50 sccm and an oxygen ion beam of 10 to 50 sccm. Preferably an argon ion beam of 10 to 25 sccm and an oxygen ion beam of 10 to 25 sccm. If it is outside this range, the ion beam irradiation is not properly performed and the surface treatment of the substrate may be insufficient.

The ion beam may be performed for 75 seconds to 300 seconds, preferably 100 seconds to 200 seconds. If it is outside this range, the ion beam may not be properly formed and the surface treatment of the substrate may be insufficient.

As described above, the ion beam can be used to impart hydrophilicity to the substrate for a flexible display, so that the surface contact angle of the substrate is less than 53 deg.

Subsequently, a buffer layer is formed on the surface of the substrate for a flexible display.

The buffer layer may be formed by sputtering, plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), wet coating, or the like.

The sputtering process is a process in which a gas ionized by a plasma in a vacuum atmosphere is collided with a target to deposit the target material on the substrate. The buffer layer is a thin film formed by sputtering and may be formed to a thickness of about 1 mu m or less, but is not limited thereto.

The buffer layer serves to prevent penetration of moisture and oxygen in the substrate for a flexible display. The buffer layer may be formed of an inorganic material containing at least one of SiO ₂ , SiO _{2 -x} , SiN, SiN _x , amorphous silicon, Al ₂ O ₃ , Al ₂ O _{3 -x} , AlN and AlN _x And may be formed as a single layer or multiple layers. For example, the buffer layer may be a structure in which a silicon nitride (SiN _x ) layer and a silicon oxide (SiO ₂ ) layer are repeatedly stacked.

A flexible display may be formed on the buffer layer by forming a structure in which a gate electrode, a gate insulating film, a channel layer, and a source / drain electrode are stacked.

The buffer layer is stably formed between the substrate for a flexible display and the stacked structure, thereby ensuring mechanical reliability and reliability of the substrate.

Hereinafter, a specific example of the surface treatment method of the substrate for a flexible display will be described.

In Figs. 1 to 11, Kaneka and Dongjin are the names of the companies that manufactured the PI substrate.

1, 2, and Table 1 show the change in surface contact angle of the PI substrate according to the ion beam time of the present invention. (Condition: Ar 50 sccm, voltage 1 kV)

 [Table 1]

The surface contact angle of the substrate is decreased when the surface of the PI substrate is subjected to surface treatment, compared to the case where the surface of the PI substrate is not treated (bare). Especially, when the ion beam time was 150s, the surface contact angle showed the minimum value, and the wettability of the substrate was large. In the case of 75s and 300s, the surface contact angle was slightly increased. When the buffer layer (SiO ₂ ) is coated on the surface of the substrate, the water spreads to such a degree that the surface contact angle can not be measured regardless of the ion beam time.

3, 4, and Table 2 show the change in surface contact angle of the PI substrate according to the voltage of the present invention. (Condition: Ar 50 sccm, ion beam time 150 s)

[Table 2]

The surface contact angle of the substrate is decreased when the surface of the PI substrate is subjected to surface treatment, compared to the case where the surface of the PI substrate is not treated (bare). Especially, when the voltage was 1kV, the surface contact angle showed the minimum value and the wettability of the substrate was large. When the voltage was 0.5kV and 1.5kV, the surface contact angle was slightly increased. When the buffer layer (SiO ₂ ) is coated on the surface, the water spreads to such a degree that the surface contact angle can not be measured regardless of the voltage magnitude.

5, 6 and Table 3 show the results of the surface contact angle change of the PI substrate according to the gas flow rate of the ion beam of the present invention. Here, the gas is a mixture of Ar gas and O ₂ gas, and the total flow rate of the gas is set to 50 sccm. (Condition: voltage 1kV, ion beam time 150s)

[Table 3]

When the surface treatment of the PI substrate surface is performed, the contact angle of the substrate surface decreases as the flow rate of the O ₂ gas increases in the range of 0 to 25 sccm. Particularly, when the flow rate of O ₂ gas was 25 sccm, the surface contact angle showed the minimum value and the wettability of the substrate was large. When the flow rate was 0 sccm, 10 sccm, and 40 sccm, the surface contact angle was slightly increased.

FIGS. 7 and 8 are graphs showing changes in surface contact angle of the PI substrate according to the voltage at the conditions of Ar 25 sccm and O ₂ 25 sccm of the present invention. (Conditions: Ion beam time 150s, using a 20 20 20 mm glass substrate, Kaneka PI reagent, spin coating rotational speed 1000 rpm, spin coating time 60 s)

Referring to FIGS. 7 and 8, as a result of changing the voltage under the condition where the contact angle is the lowest among the results measured previously, the contact angle is significantly lower than that of the bare without the surface treatment. In particular, the lowest value was found at a voltage of 1.5 kV, which was approximately 25 °, and the surface of the PI substrate was surface-treated with hydrophilic property.

9 and Table 4 show the surface roughness of the PI substrate and the buffer layer (SiO ₂ ) after the ion beam irradiation according to the present invention. (Condition: Ar 50 sccm)

[Table 4]

After the PI coating on the glass substrate, the roughness of the pristine film without surface treatment was very flat at 0.9 nm and 2.1 nm.

On the other hand, the surface roughness of the PI substrate and the buffer layer after irradiating the ion beam according to the present invention is 1.5 to 3.0 nm. This means that the surface of the PI substrate is surface-treated with a hydrophilic surface by irradiating the ion beam to increase the adhesion between the genital PI substrate and the buffer layer and to increase the deposition efficiency of the buffer layer.

10 shows the surface roughness of the PI substrate according to the ion beam condition of the present invention. Referring to FIG. 12, the surface roughness of the PI substrate was as high as 0.9 to 2.0 nm.

11 shows the results of measurement of the transmittance of the PI substrate of the present invention through UV-vis irradiation. 11, the rpm value refers to the rotational speed at the time of spin coating the PI reagent. For example, in (a) and (c), 300-1000-300 rpm is 300 rpm for 10 seconds to 1000 rpm for 60 seconds to 300 rpm for 10 seconds, and 1000 rpm for (b) and (d) is 1000 rpm for 60 seconds. The numeral shown in Fig. 11 means the light transmittance (%) in the wavelength range of 380 to 780 nm.

Referring to FIG. 11, in the case of surface treatment through an ion beam (ion beam 1 kV + SiO ₂ ) and formation of only a buffer layer (SiO ₂ ) on a PI substrate compared with the case without pristine treatment, Respectively. This means that the ion beam surface treatment or buffer layer formation increases the transmittance of the substrate.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, It is to be understood that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (7)

(a) forming a substrate for a flexible display on a mother substrate;
(b) a surface treatment step of irradiating the surface of the substrate for a flexible display with an ion beam to impart hydrophilicity to the surface of the substrate for a flexible display; And
(c) depositing an inorganic material on the surface of the surface-treated flexible display substrate to form a buffer layer.
The method according to claim 1,
Wherein the substrate for a flexible display to which hydrophilicity is imparted in the step (b) is surface-treated so that the surface contact angle is 53 DEG or less.
The method according to claim 1,
Wherein the substrate for a flexible display comprises a polyimide-based substrate.
The method according to claim 1,
Wherein the ion beam is performed for 75 seconds to 300 seconds.
The method according to claim 1,
Wherein the ion beam is irradiated with a voltage of 0.5 to 1.5 kV.
The method according to claim 1,
Wherein the ion beam includes at least one of an argon ion beam of 10 to 50 sccm and an oxygen ion beam of 10 to 50 sccm.
The method according to claim 1,
The buffer layer is _{SiO 2, SiO 2-x,} SiN, SiN x, a-Si (amorphous silicon), Al 2 O 3, Al 2 O 3-x, a single-layer or multi-layer including at least one of AlN and AlN _x Wherein the surface of the flexible substrate is made of a metal.

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