JP2003249379A - Surface treatment method for transparent conductive film, transparent conductive film with surface modified by using the same, and charge injection luminescence element having surface modified transparent conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface treatment method for changing the charge injection efficiency of a transparent conductive film and, in turn, granting a desired luminescent pattern thereto, the transparent conductive film with a surface modified by using the same having selectively high-luminance luminescent regions and non-luminescent regions, and a charge injection luminescence element. <P>SOLUTION: The surface treatment method for the transparent conductive film comprises selectively changing the charge injection efficiency of the transparent conductive film by irradiating the transparent conductive film with ions in a plasma and then selectively irradiating it with electron beams having energy of a threshold value or larger for luminance disappearance, and, in turn, granting the desired luminescent pattern thereto. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface treatment method for selectively changing the charge injection efficiency of a transparent conductive film to give a desired light emission pattern, and a transparent conductive film surface-modified by such a method. And a charge injection type light emitting device selectively having a light emitting region and a non-light emitting region of high brightness.

[0002]

2. Description of the Related Art Since the light emission phenomenon of anthracene crystals was observed in the 1960s, various organic light emitting substances such as organic light emitting substances formed of a conjugated organic activator having a condensed benzene ring and a conjugated organic host substance have been observed. Matter has been studied. Organic
An organic light emitting device such as EL has a structure in which a light emitting layer containing these organic light emitting substances is sandwiched between a cathode and an anode, and excitons generated by recombination of electrons and holes injected into the light emitting layer are It utilizes the light emitted when it is deactivated. However, the organic ELs developed to date require a high driving voltage to obtain a sufficient light output, so that there is a problem that the deterioration rate of the material is fast and the light emission life is short. Therefore, development of an organic light emitting device having sufficient performance from the viewpoint of brightness and durability is desired.

Under the above circumstances, a transparent conductive film (ITO film or the like) which is widely used as an electrode of an organic EL or the like is required to have high performance, and the brightness of a light emitting element is increased.
It is strongly desired to increase not only the resistivity but also the charge injection efficiency. The characteristics of these ITO films are greatly affected by the crystallinity of ITO, and the crystallinity of ITO depends on the substrate temperature and the film formation rate during film formation. To form an ITO film on a substrate, a dry process such as vacuum deposition or sputtering is generally used, but the physical surface shape (surface roughness) and work function of the obtained ITO film should be significantly improved. However, the charge injection efficiency could not be significantly improved.

On the other hand, the organic EL has a feature that it is possible to emit light from blue to red by selecting the type of organic light-emitting substance. In order to obtain a full-color display utilizing this characteristic, it is possible to use three primary colors. It is necessary to arrange the light emitting regions for each pixel. When the light emitting region and the non-light emitting region are patterned in this way, the organic light emitting layer has insufficient resistance to the patterning process, and thus electrodes such as ITO films have been conventionally selectively etched. However, since the patterning of the ITO film by etching uses a method such as a photoresist, the process is complicated and there is a problem such as contamination by the substance used for the resist. Therefore, there is a strong demand for a simple and clean method for processing an ITO film, which gives fine patterning of a light emitting region and a non-light emitting region to an organic EL.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to selectively change the charge injection efficiency of a transparent conductive film,
By providing a surface treatment method for imparting a desired light emitting pattern, a transparent conductive film and a charge injection type light emitting element which are surface-modified by such a method and selectively have a high-luminance light emitting region and a non-light emitting region. is there.

[0006]

As a result of earnest research in view of the above-mentioned object, the inventors of the present invention irradiate the surface of the transparent conductive film with ions in plasma, and then irradiate an arbitrary region of the transparent conductive film with brightness. The present invention was discovered by discovering that the charge injection efficiency of the transparent conductive film is selectively changed by selectively irradiating with an electron beam having a loss energy equal to or more than the threshold energy.

That is, in the surface treatment method of the transparent conductive film of the present invention, after the transparent conductive film is irradiated with ions in plasma, the transparent conductive film is selectively irradiated with an electron beam having a luminance disappearance threshold energy or more. By this, the charge injection efficiency of the transparent conductive film is selectively changed, thereby providing a desired light emission pattern. In the surface treatment method of the present invention, the plasma is preferably an inert gas plasma or an oxygen plasma, and electron beam excited plasma is preferably used as the plasma. The irradiation energy of the ions in the plasma is preferably 10 to 100 eV. The transparent conductive film used in the present invention is preferably an ITO film.

The transparent conductive film of the present invention is surface-modified by the surface treatment method of the present invention and is characterized by selectively having a light emitting region and a non-light emitting region. Further, the charge injection type light emitting device of the present invention uses a transparent conductive film surface-modified by the surface treatment method of the present invention as an electrode,
It is characterized by selectively having a light emitting region and a non-light emitting region.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION [1] Surface Treatment Method for Transparent Conductive Film The surface treatment method for a transparent conductive film of the present invention comprises (a) an ion irradiation step in plasma and (b) a selective electron beam. And an irradiation step. The steps (a) and (b) will be described in detail below. First, the outline of the surface treatment method of the present invention will be briefly described. In steps (a) and (b), the energy of ions and electrons in the plasma with which the transparent conductive film is irradiated is approximately equal to the voltage applied to the transparent conductive film.

FIG. 1 is a sectional view showing a surface treatment method for a transparent conductive film according to an embodiment of the present invention. In step (a), by irradiating the transparent conductive film 2 formed on the substrate 1 with ions I in the plasma, the unmodified transparent conductive film surface 2a has a high transparent charge conductivity. Membrane surface 2b
(Light emitting area). In the step (b), a mask 3 provided with holes having an arbitrary pattern is arranged on the transparent conductive film surface 2b via a spacer (not shown), and an electron beam E having a threshold energy of brightness disappearance or more is obtained. Irradiate. As a result, only the region irradiated with the electron beam E is changed to the transparent conductive film surface 2c (non-light emitting region) which has substantially no charge injection ability, and a desired light emitting pattern is imparted to the transparent conductive film. You can

According to the present invention, the steps (a) and (b) can be performed in the same plasma chamber by changing the type and energy of the electric charge (ion / electron beam) to be irradiated for each step. For example, the surface of the transparent conductive film can be easily modified. At this time, the transparent conductive film has a negative potential in the step (a) and a positive potential in the step (b).

Examples of plasma that can be used for the surface treatment include electron beam excited plasma, ion excited plasma, and light excited plasma. Among these plasmas, the electron beam excitation plasma has a low gas pressure (0.1 to several P
Even about a), high density plasma is generated, and the energy of ions and electrons in the plasma can be easily controlled by adjusting the external power source, which is preferable. The plasma density is preferably about 10 ⁹ to 10 ¹² cm ⁻³ so as not to damage the transparent conductive film such as the ITO film.

The transparent conductive film used in the surface treatment method of the present invention is, for example, an ITO film, a SnO ₂ film, a ZnO film, or a MgIn ₂ O ₄ film.
Membranes and the like can be mentioned. From the viewpoint of conductivity and transparency in the visible range, the transparent conductive film is preferably an ITO film.

(A) Ion irradiation step in plasma Not only is there unevenness of several nm to several tens of nm on the surface of the transparent conductive film from the time of film formation, but there are also floating substances in the air and organic solvents for cleaning. Residues are attached and hinder the improvement of work function. In the step (a), these deposits can be removed and the film surface can be planarized by physical / chemical sputtering, and the work function of the transparent conductive film can be increased without increasing the sheet resistance.

The plasma used in the present invention is preferably an inert gas or oxygen plasma. Since oxygen plasma is difficult to separate from electrons, when oxygen plasma is used, it is necessary to exchange the oxygen gas in the plasma chamber with an inert gas before the subsequent step (b).
Therefore, it is advantageous to use plasma of an inert gas in order to perform the surface treatment easily. As the inert gas, for example, helium, argon, neon or the like can be used, and preferably argon is used.

In order to effectively increase the charge injection efficiency of the transparent conductive film, the ion irradiation energy is 10 to 100 eV.
The plasma irradiation time is preferably 10 to 100 seconds.

(B) Selective electron beam irradiation step Since the mass of electrons is very small, sputtering does not occur even if an electron beam having a threshold energy of luminance disappearance or more is selectively irradiated in step (b). However, the charge injection efficiency of the transparent conductive film, which has been uniformly increased by the step (a), is selectively and extremely reduced by the heating effect of the high-density electron beam. It is considered that this is because in the region of the surface of the transparent conductive film where electrons collide, the change in crystal structure due to surface heating is promoted and the electrical resistance increases. If the density of the electron beam is higher than the density of the ions irradiated in the step (a) by two digits or more, the charge injection efficiency is significantly reduced. Here, the “threshold energy for disappearance of brightness” is the energy of an electron beam at a critical point at which the brightness of the transparent conductive film is substantially disappeared by electron beam irradiation.

The threshold energy of the electron beam for disappearing the brightness of the transparent conductive film depends on the material of the transparent conductive film, but is 40 eV in the case of ITO, for example. When the energy of the electron beam is smaller than the threshold value, the charge injection efficiency of the transparent conductive film is not sufficiently lowered, and even if the surface-modified transparent conductive film is used for a light emitting element, a sufficient contrast between the light emitting region and the non-light emitting region is obtained. Can't get The electron beam irradiation time is preferably 60 to 600 seconds. If the electron beam irradiation time is shorter than 60 seconds, the effect of electron beam irradiation is hard to appear, and even if the irradiation time is longer than 600 seconds, the charge injection efficiency is not further reduced.

In order to selectively irradiate the transparent conductive film with electrons, it is preferable to use a mask having holes of arbitrary shape. A mask provided with a hole having an arbitrary shape is fixed on the transparent conductive film while being electrically insulated from the transparent conductive film, and a voltage is applied so that the transparent conductive film has a positive potential. As a result, the ions in the plasma do not pass through the holes in the mask, but only the electron beam passes through the holes and irradiates the transparent conductive film.Therefore, charge injection is performed only in the region of the conductive film corresponding to the holes in the mask. Efficiency can be reduced.
It is desirable to use a material having high heat resistance for the mask, for example, it is desirable to use carbon, stainless steel, nickel or the like. Further, when a finer light emitting pattern which cannot be obtained by patterning using a mask is created, an electron beam generator capable of drawing a fine pattern may be used.

[2] Surface Modified Transparent Conductive Film and Charge Injection Type Light Emitting Element Using the Same The surface modified transparent conductive film of the present invention is a transparent surface modified by the surface treatment method of the present invention. The conductive film is selectively provided with a high-luminance light emitting region and a non-light emitting region. Generally, when the work function of the transparent conductive film and the value of the ionization potential of the charge transport layer formed on the conductive film are close to each other, the efficiency of positive charge injection from the transparent conductive film to the charge transport layer increases. The transparent conductive film whose work function is increased by the step (a) has a high efficiency of injecting positive charges into the charge transport layer, and is 5 to 5 times as compared with the case where an untreated transparent conductive film is used for the electrode.
The charge injection efficiency is ten times higher. On the other hand, the region irradiated with the electron beam in the step (b) has substantially no charge injection ability.

The charge injection type light emitting device of the present invention uses a transparent conductive film surface-modified by the surface treatment method of the present invention as an electrode and selectively has a light emitting region and a non-light emitting region. FIG. 2 is a vertical sectional view showing a charge injection type light emitting device according to an embodiment of the present invention. This light emitting device has a surface-modified transparent conductive film 2 on a substrate 1, and a hole transport layer 4, an electron transport light emitting layer 5 containing an organic light emitting substance, and a cathode 6 are sequentially formed. There is. The holes injected from the surface 2b of the transparent conductive film 2 having a high charge injection efficiency and the electrons injected from the cathode are recombined in the electron transport light emitting layer 5 to generate light. However, the transparent conductive film surface 2c in the region irradiated with the electron in the step (b) has the hole transport layer 4
Light emission does not occur because the efficiency of injecting a positive charge into is extremely low. In this way, the pattern of the light emitting region and the non-light emitting region is formed on the surface of the light emitting element.

In the present invention, the material and structure of the light emitting device are not particularly limited and may be known ones. The light emitting element may have a structure in which an anode / hole transporting layer / electron transporting light emitting layer / cathode are laminated in this order as in the above-described embodiment.
A configuration in which a cathode, an anode / a hole transporting light emitting layer / an electron transporting layer / a cathode, and an anode / a hole transporting layer / a light emitting layer / an electron transporting layer / a cathode are laminated in this order can be adopted. The light emitting device of the present invention may have a hole injecting layer, an electron injecting layer, a protective layer for blocking moisture and air, and the like, and each layer may have a plurality of functions.

As the substrate, glass such as soda lime glass or non-alkali glass, plastic or the like can be used. When glass is used, the glass is preferably non-alkali glass. It is preferable that the plastic is excellent in heat resistance, dimensional stability, solvent resistance, electric insulation and processability, and has low air permeability and low hygroscopicity. Examples of such plastics include polyethylene terephthalate, polyethylene naphthalate, polystyrene and polycarbonate. The thickness of the substrate is not particularly limited as long as it is sufficient to maintain the mechanical strength, but is usually 0.2 mm or more. The film thickness of the anode formed of the surface-modified transparent conductive film formed on the substrate is preferably 10 nm to 5 μm.

As the light emitting substance, an organic substance excellent in quantum yield, film forming property and charge transporting property is suitable, and for example, a low molecular weight fluorescent dye, a high molecular weight fluorescent dye, a metal complex and the like are used. Specific examples of low molecular weight fluorescent dyes include ditoluyl vinyl biphenyl (DTVBi) and the like, and specific examples of high molecular weight fluorescent dyes include poly (p-phenylene vinylene) and π-conjugated polymers such as polyalkylthiophene. As specific examples of the metal complex, aluminum quinolinol complex (Alq ₃ ) such as tris (8-quinolinolato) aluminum complex, bis (benzoquinolinolato) beryllium complex (BeBq ₂ ), tri (dibenzoylmethyl) phenanthroline europium complex. (Eu (DBM) ₃ (Phe
n)) and the like.

A substance having a low ionization potential and a high hole mobility is suitable as the hole transporting substance, and an aromatic amine derivative such as tetraphenyldiamine (TPD) is often used. Further, a polymer compound having TPD incorporated in the main chain or side chain can also be used.

Examples of the electron-transporting substance include oxadiazole derivatives, triazole derivatives, triazine derivatives, nitro-substituted fluorenone derivatives, thiopyrandioxide derivatives, diphenylquinone derivatives, perylene tetracarboxyl derivatives, anthraquinodimethane derivatives and fluorenylidene methane. Derivatives, anthrone derivatives, perinone derivatives, oxine derivatives, quinoline complex derivatives and the like are widely used. In particular, since the triazole derivative has a large ionization potential, holes can be efficiently confined in the hole transport layer, and thus it is suitable as an electron transport layer in the case of providing a hole transport light emitting layer.

The cathode is preferably made of a metal or alloy having a small work function, a metal halide, a metal oxide, or the like, and may be selected in consideration of adhesion with an adjacent layer, ionization potential, stability and the like. Specifically, the cathode is preferably made of lithium, magnesium, silver, lead, tin, aluminum, manganese, chromium, indium, or the like or an alloy thereof. The film thickness of the cathode can be appropriately selected depending on the material, but is usually 10 nm to 5 μm.

Further, in order to obtain a light emitting device with higher definition and higher contrast, a black coloring composition obtained by dispersing a light absorbing material (carbon, titanium oxide, etc.) in a resin is applied to a non-light emitting area by an ink jet method or the like. You can also do it. It is effective to apply the black coloring composition to the transparent conductive film side of the glass substrate. As a result, the non-light emitting area becomes a so-called black matrix to prevent color bleeding between the light emitting areas.

In the method for manufacturing the light emitting device, known methods can be used except the surface treatment step of the transparent conductive film. A preferred production example is as follows. First, a transparent conductive film is formed on a glass substrate by an electron beam method, a sputtering method, a vapor deposition method, a chemical reaction method (sol-gel method, etc.), and a transparent surface is formed by the surface treatment method of the present invention. The surface of the conductive film is modified. On the obtained surface-modified transparent conductive film, a hole-transporting layer and an electron are formed by a known method such as a vacuum deposition method, a sputtering method, a dipping method, a spin coating method, a casting method, a bar coating method and a roll coating method. Transport layer,
An organic layer such as a light emitting layer and a cathode are formed. Finally, the cathode is formed by a method such as a vacuum vapor deposition method, a sputtering method, an ion plating method.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following examples, which should not be construed as limiting the invention thereto.

Example 1 A glass substrate on the surface of which an ITO film having a thickness of about 100 nm and an area of 2 × 2 cm ² was formed was placed in a chamber of an electron beam excitation plasma apparatus (manufactured by Nichimen Denko Ken Co., Ltd.). After holding and evacuating the chamber to 1.3 × 10 ^-4 Pa, argon gas was introduced until the pressure reached 4 × 10 ^-1 Pa. Then, the electron beam excitation plasma device was activated to generate argon plasma in the chamber, and a voltage of -60 V was applied to the ITO film at 15 V.
It was applied for 2 seconds (step (a)). As a result, 60
Argon ions with energy of eV were irradiated.

Next, on the ion-irradiated ITO film, a nickel plate having a thickness of 1 mm and having a hole having a shape of "C" was formed to a thickness of 0.5 m.
The ITO film was placed via a glass spacer of m and a positive voltage of 45 V was applied to the ITO film for 120 seconds (step (b)). In this step, since the potential of the substrate was positive, argon ions did not pass through the holes of the nickel plate and the ITO film was irradiated with only the electron beam.

On top of the surface-treated ITO film,
2,7-di [N, N-diphenyl-N, N-di (m-toluyl)] amino-9,
Hole transport layer consisting of 9-dimethylfluorene (film thickness: 30 n
m), an electron-transporting light-emitting layer (thickness: 50 nm) made of an aluminum quinolinol complex, and a cathode (thickness: 120 nm) made of aluminum were vapor-deposited to prepare an organic EL element as a charge injection type light-emitting element. . 8 in the obtained light emitting device
When a driving voltage of V was applied, a light emitting region with a brightness of 1200 cd / m ² and a “C” -shaped non-light emitting region were formed.

Reference Example 1 In order to investigate the influence of the energy of the electron beam applied to the ITO film on the brightness of the light emitting device, the glass substrate on which the ITO film was formed was held in argon plasma and the ITO film was exposed to 0%.
Voltages of V, 20 V, 30 V, 40 V and 50 V were applied for 120 seconds. At this time, the energy of the electron beam with which the ITO film is irradiated corresponds to 0 eV, 20 eV, 30 eV, 40 eV and 50 eV, respectively. An organic layer and a cathode were formed on each of the obtained electron beam-irradiated ITO films by the same method as in Example 1 to prepare a charge injection type light emitting device. A luminance was measured by applying a drive voltage of 8 V to each of the light emitting devices thus obtained. The results are shown in Fig. 3.

As is clear from FIG. 3, the luminance of the light emitting element is 30 V (applied energy: electron energy:
Up to 30 eV) as the voltage rises, but when the applied voltage exceeds 30 V, it drops sharply and the applied voltage becomes 40 V.
It barely emits light at (electron energy: 40 eV). Therefore, it was found that the threshold energy of the electron beam that causes the brightness of the ITO film to disappear is 40 eV.

Example 2 An ITO film irradiated with argon ions in plasma in the same manner as in Example 1 was subjected to 0 eV, 20 eV, 3 eV under the same conditions as in Reference Example 1.
The electron beams with energies of 0 eV, 40 eV and 50 eV were irradiated. A driving voltage of 8 V was applied to each charge injection type light emitting device in which an organic layer and a cathode were formed on each of the obtained electron beam irradiated ITO films by the same method as in Example 1, and the brightness was measured. As a result, the same tendency as shown in FIG. 3 was recognized, and the threshold energy of the electron beam that causes the brightness to disappear was 40 eV even for the ITO film surface-modified by plasma irradiation.

Example 3 A glass substrate on the surface of which an ITO film having a film thickness of about 100 nm and an area of 2 × 2 cm ² was formed was placed in the chamber of an electron beam excitation plasma device (manufactured by Nichimen Denko Kogyo Co., Ltd.). Hold the chamber and evacuate the chamber to 1.3 × 10 ^-4 Pa, then add oxygen gas to 2.7
It was introduced until the pressure became × 10 ^-1 Pa. Then, the electron beam excitation plasma device was operated to generate oxygen plasma in the chamber, and a voltage of −20 V was applied to the ITO film for 30 seconds (step (a)). Next, on the ion-irradiated ITO film,
A 1 mm thick nickel plate with holes having the shape of "C" was placed through a 0.5 mm thick glass spacer. The oxygen gas in the chamber was exchanged with argon gas to generate argon plasma, and a positive voltage of 50 V was applied to the ITO film for 180 seconds (step (b)).

On the surface-treated ITO film, an organic layer and a cathode were formed in the same manner as in Example 1 to prepare a charge injection type light emitting device. When a driving voltage of 8 V was applied to the light emitting device thus obtained, the brightness was 2 × 10 ⁴ cd /
A very high contrast emission pattern was formed with an emission area of m ² and a non-emission area of “C” shape.

[0039]

As described in detail above, the surface treatment method of the transparent conductive film of the present invention selectively changes the charge injection efficiency of the transparent conductive film by the two steps of ion irradiation in plasma and electron beam irradiation. As a result, a desired light emitting pattern is imparted to the transparent conductive film. The charge-injection type light emitting device using the obtained surface-modified transparent conductive film as an electrode has a light emitting region and a non-light emitting region on the surface and can form a highly precise light emitting pattern. Further, since the brightness of the light emitting region can be adjusted by changing the conditions of plasma irradiation, it is possible to fabricate the light emitting element in consideration of the optical contrast with the non-light emitting region. Further, if the non-light emitting area is made a black matrix, a display without color fringing can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a surface treatment method for a transparent conductive film according to an embodiment of the present invention, in which (a) shows an ion irradiation step in plasma and (b) shows selective electron beam irradiation. The process is shown.

FIG. 2 is a vertical cross-sectional view showing a charge injection type light emitting device according to an embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the voltage applied to the ITO film when plasma-irradiated ITO film is irradiated with an electron beam and the luminance of the light emitting device having the ITO film irradiated with the electron beam.

[Explanation of symbols]

1 ... Substrate 2 ... Transparent conductive film 3 ... Mask 4 ... Hole transport layer 5 ... Electron transport light emitting layer 6 ... Cathode

Claims (8)

[Claims] 1. The charge injection efficiency of the transparent conductive film is selected by irradiating the transparent conductive film with ions in plasma and then selectively irradiating with an electron beam having a threshold energy of brightness disappearance or more. Surface treatment method of a transparent conductive film, which is characterized by changing the shape of the transparent conductive film to give a desired light emission pattern. 2. The method for surface treatment of a transparent conductive film according to claim 1, wherein the plasma is plasma of an inert gas or oxygen. 3. The method for surface treatment of a transparent conductive film according to claim 1, wherein electron beam excitation plasma is used as the plasma. 4. The method for surface treatment of a transparent conductive film according to claim 1, wherein the irradiation energy of ions in the plasma is 10 to 100 eV. 5. The surface treatment method for a transparent conductive film according to claim 1, wherein the threshold energy of the electron beam for brightness disappearance is 40 eV. Processing method. 6. The surface treatment method for a transparent conductive film according to claim 1, wherein the transparent conductive film is IT.
A surface treatment method, which is an O film. 7. A transparent conductive film surface-modified by the method according to claim 1, wherein the transparent conductive film selectively has a light emitting region and a non-light emitting region. film. 8. A charge injection, characterized in that a transparent conductive film surface-modified by the method according to claim 1 is used as an electrode and selectively has a light emitting region and a non-light emitting region. Type light emitting device.