KR20200138020A - Reflective anode electrode for organic el display - Google Patents

Abstract

The present invention relates to a reflective anode for an organic EL display capable of securing the high reflectivity. The reflective anode includes an Al alloy film and an oxide conductive film, and has a laminated structure in which a layer containing aluminum oxide as a main component is interposed at a contact interface between the Al alloy film and the oxide conductive film. The Al alloy film contains Si and rare earth elements. When the Si content is a (atom %) the total content of the rare earth elements is b (atom %), the relationships of 0.62 < {a/(a+b)}, 0.2 < a < 3, and 0.1 < b are satisfied. The layer having the aluminum oxide as a main component contains Si.

Description

Reflective anode electrode for organic EL display {REFLECTIVE ANODE ELECTRODE FOR ORGANIC EL DISPLAY}

The present invention relates to a reflective anode electrode used in an organic EL display (especially a top emission type). It also relates to a thin film transistor substrate and an organic EL display using the reflective anode electrode, and a sputtering target for forming an Al alloy film included in the reflective anode electrode.

An organic electroluminescent (hereinafter referred to as "organic EL") display is a flat panel display formed by arranging organic EL elements in a matrix on a substrate such as a glass plate.

Al is also good as a reflective film. For example, Patent Document 1 discloses an Al film or an Al-Nd film as a reflective film, and describes that the Al-Nd film is excellent in reflection efficiency and is preferable.

However, when the Al film or Al-Nd film is directly in contact with an oxide conductive film such as ITO or IZO as a reflective film, since the contact resistance (contact resistance) increases, sufficient current can be supplied for hole injection into the organic EL element. none.

Here, in Patent Document 2, an Al-Ni alloy film containing 0.1 to 2 atomic% of Ni is proposed as a reflective electrode (reflective film) directly connected to an oxide conductive film constituting a transparent electrode. According to this, high reflectivity and low contact resistance can be realized.

In addition, in Patent Document 3, by using an Al-based alloy film containing 0.1 to 6 atomic% of Ag, as in Patent Document 2, an Al-based alloy reflective film capable of realizing low contact resistance and high reflectance even when in direct contact with an oxide conductive film is provided. Is proposed.

Further, in Patent Document 4, an Al alloy film for display devices containing 0.05 to 0.5 atomic% of Ge and 0.05 to 0.45 atomic% of Gd and/or La in total is proposed.

Japanese Patent Publication No. 2005-259695 Japanese Patent Publication No. 2008-122941 Japanese Patent Publication No. 2011-108459 Japanese Patent Publication No. 2008-160058

In contrast to the above, in a top emission type organic EL display, when an Al alloy is used as the anode electrode, an insulating oxide film is inevitably formed on the surface of the Al alloy in an atmosphere in the presence of oxygen. Due to the insulating property of the oxide film, current becomes difficult to flow, and therefore, when a current of more than a predetermined value is attempted to flow, the required voltage value increases. Therefore, when the same light emission intensity is maintained, power consumption increases.

The present invention has been made in view of the above circumstances, and provides a reflective anode electrode for an organic EL display that can ensure low contact resistance and high reflectivity even when the Al alloy film, which is a reflective film, is directly contacted with an oxide conductive film, and has excellent heat resistance. The purpose.

Regarding the above object, the inventors have found that the Al alloy film used as the reflective film contains a predetermined amount of Si and at least one rare earth element, and Si is also contained in the layer containing the oxide interposed at the contact interface between the reflective film and the oxide conductive film. , Finding out that the above problems can be solved, and completing the present invention.

That is, the reflective anode electrode for an organic EL display according to the present invention includes an Al alloy film and an oxide conductive film, and has a laminated structure in which a layer containing aluminum oxide as a main component is interposed at the contact interface between the Al alloy film and the oxide conductive film. In the case where the Al alloy film contains Si and at least one rare earth element, the Si content is a (atomic%) and the total content of the rare earth elements is b (atomic%), 0.62<{ a/(a+b)}, 0.2<a<3, and 0.1<b are satisfied, and the layer containing aluminum oxide as a main component contains Si.

In a preferred embodiment of the present invention, the rare earth element contains at least one of Nd and La.

In a preferred embodiment of the present invention, the thickness of the oxide conductive film is 5 to 30 nm.

In a preferred embodiment of the present invention, the Al alloy film is formed by sputtering.

In a preferred embodiment of the present invention, the Al alloy film is electrically connected to the source/drain electrodes of the thin film transistor.

Further, the present invention also includes a thin film transistor substrate including any of the above reflective anode electrodes and an organic EL display including the thin film transistor substrate.

In addition, in the present invention, when it is a sputtering target for forming an Al alloy film contained in any of the above reflective anode electrodes, the Si content is a (atomic%) and the total content of the rare earth elements is b (atomic%), A sputtering target that satisfies the relationship of 0.62<{a/(a+b)}, 0.2<a<3, and 0.1<b is also included.

According to the reflective anode electrode for an organic EL display according to the present invention, even if an Al alloy film, which is a reflective film, is directly in contact with an oxide conductive film, and a layer containing aluminum oxide as a main component exists therebetween, low contact resistance and high reflectance can be secured. I can. In addition, since it is excellent also in heat resistance, it can be made without surface roughness (hillock).

By using this reflective anode electrode for a thin film transistor substrate and further an organic EL display, it is possible to efficiently pass current to the organic light-emitting layer, and to efficiently reflect light emitted from the organic light-emitting layer by the reflective film. An organic EL display excellent in luminance can be realized.

1 is a schematic cross-sectional view showing an example of an organic EL display including a reflective anode electrode according to an embodiment of the present invention.
2 is a diagram showing a Kelvin pattern used for measuring the contact resistance between an Al alloy film and an oxide conductive film.
3 is an EDX spectrum of a layer containing aluminum oxide as a main component during cross-sectional observation by TEM-EDX of the reflective anode electrode of Example 2. FIG.

Hereinafter, an embodiment for carrying out the present invention (this embodiment) will be described in detail. In addition, the present invention is not limited to the embodiments described below, and can be carried out with arbitrary changes within a range not departing from the gist of the present invention.

(Organic EL display)

First, an outline of an organic EL display using the reflective anode electrode of the present embodiment will be described using FIG. 1. In addition, the Al alloy film used in this embodiment is an Al-Si-REM alloy film (REM means one or more rare earth elements). Hereinafter, the Al-Si-REM alloy film is simply referred to as "Al alloy film". It is called.

A TFT 2 and a passivation film 3 are formed on the substrate 1, and a planarization layer 4 is formed thereon. A contact hole 5 is formed on the TFT 2, and the source/drain electrode (not shown) of the TFT 2 and the Al alloy film 6 are electrically connected via the contact hole 5.

An oxide conductive film 7 is formed directly on the Al alloy film 6 so as to contact the Al alloy film 6. However, in reality, a layer (not shown) containing aluminum oxide (Al ₂ O ₃ ) as a main component is formed at the contact interface between the Al alloy film 6 and the oxide conductive film 7 and is interposed therebetween. In addition, the main component in "a layer containing aluminum oxide as a main component" means a component most often contained in the layer, and specifically means a component contained in 70% by mass or more with respect to the total mass of the layer.

Since Al is very susceptible to oxidation, it is easy to combine with oxygen in the atmosphere to form a layer containing aluminum oxide on the surface of the Al alloy film. In addition, when the Al alloy film and the oxide conductive film are brought into contact with each other, Al takes away oxygen from the oxide conductive film, and a layer containing aluminum oxide as a main component is easily formed at the contact interface. Since this layer containing aluminum oxide as a main component is insulating, it causes an increase in contact resistance (contact resistance) between the Al alloy film and the oxide conductive film originally.

However, in this embodiment, by containing a specific amount of Si in the Al alloy film, Si is also included in the formed layer containing aluminum oxide as a main component. At this time, it is assumed that Si exists in the form of a bond of metal bonds in the layer containing aluminum oxide as a main component, and the presence of this Si is thought to be able to secure low contact resistance between the Al alloy film and the oxide conductive film. do.

The presence of Si in the layer containing aluminum oxide as a main component is, for example, a transmission electron microscope (TEM) (TEM-EDX) that combines XPS (X-ray photoelectron spectroscopy) and EDX (energy dispersive X-ray spectroscopy) analysis. ) Can be confirmed by observing the cross section of the reflective anode electrode.

Although it is difficult to actually measure the content of Si contained in the layer, in cross-sectional observation of the reflective anode electrode using TEM-EDX, it is preferable that Si is 0.8 atomic% or more.

Since the Al alloy film 6 and the oxide conductive film 7 act as reflective electrodes of the organic EL element and are electrically connected to the source and drain electrodes of the TFT 2, a layer mainly composed of aluminum oxide is formed. The contained Al alloy film 6 and the oxide conductive film 7 function as a reflective anode electrode.

An organic light emitting layer 8 is formed on the oxide conductive film 7 and a cathode electrode 9 is formed thereon.

In such an organic EL display, since light emitted from the organic light-emitting layer 8 is efficiently reflected by the reflective anode electrode of this embodiment, excellent light emission luminance can be realized. Further, the higher the reflectivity of the reflective anode electrode is, the better, and the reflectance for light having a wavelength of 450 nm is preferably 79% or more, more preferably 80% or more, and even more preferably 85% or more.

(Al alloy film)

Next, an Al alloy film used for the reflective anode electrode of the present invention will be described.

The Al alloy film contains Si and at least one rare earth element (REM), and their ratio is a case where the content of Si in the Al alloy film is a (atomic%) and the total content of REM is b (atomic%). E, 0.62<{a/(a+b)}, 0.2<a<3, and 0.1<b.

When a is more than 0.2 atomic%, the amount of Si required for securing low contact resistance can be set, and an increase in the driving voltage can be prevented. a is preferably more than 0.5 atomic%, more preferably more than 0.8 atomic%.

Moreover, by making a less than 3 atomic%, high reflectance can be maintained. a is preferably less than 2.5 atomic%, more preferably less than 1.5 atomic%.

When b is more than 0.1 atomic%, it is possible to suppress the occurrence of surface roughness (hillock) caused by heat history received in the process. The surface roughness becomes a cause of pixel short circuit. b is preferably 0.2 atomic% or more.

In addition, the upper limit of b is limited to the value of a from 0.62<{a/(a+b)}, but less than 1 atomic% is preferable, and less than 0.5 atomic% is more preferable.

Low contact resistance can be maintained by making the ratio represented by {a/(a+b)} more than 0.62. It is considered that this is because Si and rare earth elements contained in the Al alloy film form a compound, and it is possible to prevent concentration of Si from hardly occurring in a layer containing aluminum oxide as a main component. The ratio represented by {a/(a+b)} is preferably more than 0.7, and more preferably more than 0.8.

In addition, the ratio represented by {a/(a+b)} is preferably less than 0.9 from the viewpoint of securing reflectance.

Examples of the rare earth elements contained in the Al alloy film include La, Ce, Nd, Sm, Gd, and Tb. In addition, these elements may add plural kinds of elements at the same time. Among these, Nd and La are preferable, and it is more preferable to include at least one of Nd and La.

In addition to Al, Si, and REM, the Al alloy film may contain other elements within a range that does not impair the effects of the present invention.

As other elements, Ge, Cu, Ni, Ta, Ti, Zr, etc. are mentioned, for example. The total content of these other elements and impurities is preferably 1.0 atomic% or less, more preferably 0.7 atomic% or less with respect to the Al alloy film.

The film thickness of the Al alloy film is preferably 50 nm or more, and more preferably 100 nm or more from the viewpoint of securing the reflectance. In addition, the film thickness of the Al alloy film is preferably 300 nm or less, and more preferably 200 nm or less from the viewpoint of wiring workability and productivity.

The Al alloy film is preferably formed by a sputtering method or a vacuum evaporation method, and in the sputtering method, a sputtering target (hereinafter sometimes referred to as ``target'') is used to form the film with excellent in-plane uniformity of the composition or film thickness. It is more preferable in that a thin film can be easily formed.

In order to form an Al alloy film by sputtering, as the target, the aforementioned elements (Si and REM) are included, and an Al alloy sputtering target having the same composition as the desired Al alloy film may be used.

Therefore, it is a sputtering target for forming an Al alloy film included in the reflective anode electrode, and a sputtering target having the same composition as that of the Al alloy film is also included within the scope of the present invention.

Specifically, it is a sputtering target for forming an Al alloy film included in the reflective anode electrode, and when the Si content is a (atomic%) and the total content of the rare earth elements is b (atomic%), 0.62<{ a/(a+b)}, a sputtering target that satisfies the relationship of 0.2<a<3 and 0.1<b.

In addition, the preferred aspect of the composition of the target and the content represented by a and b is the same as the preferred aspect of the composition in the Al alloy film and the content represented by a and b, respectively.

As a manufacturing method of the target, a method obtained by manufacturing an ingot containing an Al-based alloy by melt casting method, powder sintering method, spray forming method, or the like, or a preform containing an Al-based alloy (intermediate before obtaining the final dense body). After manufacturing, the method obtained by densifying the preform by densification means is mentioned.

The substrate temperature in the sputtering method is preferably 25°C or higher from the viewpoint of suppressing the adsorption of moisture or gas on the substrate, and is preferably 200°C or lower, and more preferably 150°C or lower from the viewpoint of securing the surface smoothness of the Al alloy. .

(Oxide conductive film)

The oxide conductive film used in the present embodiment is not particularly limited, and commonly used ones such as indium tin oxide (ITO) and indium zinc oxide (IZO) are mentioned, but from the viewpoint of low resistance and stability of resistance, preferably It is indium tin oxide.

The thickness of the oxide conductive film is preferably 5 nm or more, and more preferably 10 nm or more, from the viewpoint of preventing pinholes from occurring in the oxide conductive film and causing dark spots. On the other hand, from the viewpoint of preventing a decrease in reflectance when used as a reflective anode electrode, the thickness of the oxide conductive film is preferably 30 nm or less, and more preferably 20 nm or less.

The oxide conductive film is preferably formed by a sputtering method from the viewpoint of being able to easily form a thin film having excellent in-plane uniformity of components and film thickness.

(Reflective anode electrode)

In addition to the excellent reflectance and low contact resistance, the reflective anode electrode obtained above has the work function of the oxide transparent conductive film located on the upper layer controlled to the same degree as when using a general-purpose Ag-based alloy, and has excellent heat resistance. , Used in organic EL displays.

The higher the reflectivity of the reflective anode electrode is, the better, and the reflectance for light having a wavelength of 450 nm is preferably 79% or more, more preferably 80% or more, and even more preferably 85% or more.

In addition, the low contact resistance is a method described in Examples to be described later, i.e., in measurement by a four-terminal method using a Kelvin pattern having a contact hole size of 80 × 80 μm, the contact resistance is preferably 10 kΩ·mm 2 or less, and 2 kΩ· More preferably less than or equal to mm 2.

A reflective anode electrode in which the Al alloy film is electrically connected to a source/drain electrode of a thin film transistor is also mentioned as a preferred embodiment of the present embodiment, further comprising a thin film transistor substrate including a reflective anode electrode or the thin film transistor substrate. The organic EL display to be described is also mentioned as a preferred aspect of the present embodiment.

<Example>

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples, and it is also possible to carry out changes within a range suitable for the purpose, and all of them It is included in the technical scope of the present invention.

(Preparation of reflective anode electrode)

An alkali-free glass plate (board thickness: 0.7 mm) was used as a substrate, and an Al alloy film (film thickness of 200 nm) as a reflective film was formed on the surface thereof by sputtering. The sputtering conditions were a substrate temperature of 25°C and a pressure of 0.26 Pa, and an Al alloy target was used at 5 to 20 W/cm 2 using a DC power supply. In addition, in the composition of the sputtering target and the formed Al alloy film, the content (atomic%) of Si, Nd and La is as shown in Table 1, and the remainder is Al and impurities. This composition was identified by ICP (inductively coupled plasma) emission spectroscopic analysis.

On the Al alloy film obtained above, as an oxide conductive film, an In-Sn-O (Sn: 10% by mass) thin film (ITO thin film) was laminated to a thickness of 10 nm by sputtering. The sputtering conditions were performed at a temperature of 2 to 4 W/cm 2 using a DC power supply with a substrate temperature of room temperature (about 25° C.) and a pressure of 0.26 Pa.

Thereafter, heat treatment (post annealing) was performed by holding at 250° C. for 1 hour in a nitrogen atmosphere to prepare a reflective anode electrode.

(Identification of a layer containing aluminum oxide as the main component)

With respect to the obtained reflective anode electrode, a layer containing aluminum oxide as a main component exists between the Al alloy film and the oxide conductive film by XPS (X-ray photoelectron spectroscopy), and Si is contained in the layer in a bonded state of metal bonds. I confirmed that there is.

In addition, transmission electron microscope (TEM-EDX) (TEM observation device: Field emission transmission electron microscope JEM-2010F manufactured by Nippon Denshi), acquisition camera: CCD UltraScan manufactured by Gatan, EDX analyzer: A cross-section of the reflective anode electrode was observed under conditions of an acceleration voltage of 200 kV and a beam diameter (EDX analysis) of about 1 nm using JED-2300T SDD (attached to JEM-2010F) manufactured by Nippon Denshi. For example, with respect to the reflective anode electrode of Example 2, cross-sectional observation was performed at 4 locations with a depth of 5 nm, 12 nm, 15 nm and 40 nm from the electrode surface (upper layer side), and from the obtained TEM image and EDX spectrum, respectively, oxidation It was confirmed that it corresponds to a conductive film, a layer containing aluminum oxide as a main component, an Al alloy film, and an Al alloy film.

Fig. 3 shows the EDX spectrum of the layer containing aluminum oxide as a main component in Example 2. From Fig. 3, it can be seen from the peaks of Al and O and their content (atomic%, at%) that this is a spectrum of a layer containing aluminum oxide as a main component. The Si peak was also observed in this layer, and its content was 2.5 atomic%.

(reflectivity)

With respect to the reflective anode electrode (after heat treatment), the spectral reflectance in the range of measurement wavelength: 1000 to 250 nm was measured using a visible/ultraviolet spectrophotometer "V-570" manufactured by Nippon Bunko Co., Ltd. Specifically, the value obtained by measuring the reflected light intensity of the sample with respect to the reflected light intensity of the reference mirror was taken as "reflectance". The reflectance at the measurement wavelength of 450 nm is shown in Table 1. If the reflectance is 79% or more, it is good and it is set as pass.

(Heat resistance)

Evaluation of the heat resistance of the reflective anode electrode (after heat treatment) was performed by observing the surface with an optical microscope and confirming the presence or absence of irregularities (surface roughness, hillock) at a magnification of 1000 times. Specifically, those with a number of hillocks having a diameter of 1 μm or more in a range of 140 × 100 μm that are less than five are judged as "no hillocks" and are set as good (○), and those with a diameter of 5 or more are determined as "hilllocks present" It was determined and it was set as defect (x).

Further, as the heat resistance of the reflective anode electrode, observation with a differential interference microscope was also performed on the surface of the electrode after the heat treatment, and the presence or absence of surface roughness (hillock) was confirmed. As a result, it was confirmed that all of the reflective anode electrodes judged as good (○) by surface observation of the optical microscope were smooth surfaces.

(Contact resistance)

For the contact resistance (contact resistance) between the Al alloy film and the oxide conductive film, the Kelvin pattern shown in Fig. 2 was used. In the Kelvin pattern, after forming the Al alloy film, a 10 nm thin film of In-Sn-O (Sn: 10% by mass) as an oxide conductive film is then laminated to form a wiring pattern, and then SiN as a passivation film on the surface thereof. A film (film thickness: 200 nm) was formed by a plasma CVD (chemical vapor deposition) apparatus.

Film formation conditions were substrate temperature: 280°C, gas ratio: SiH ₄ /NH ₃ /N ₂ =125/6/185, pressure: 137 Pa, and RF power: 100 W.

After patterning the formed SiN film, a Mo film (film thickness: 300 nm) was formed on the surface by sputtering, and the formed Mo film was patterned to obtain the Kelvin pattern in FIG. 2.

To measure the contact resistance, a Kelvin pattern shown in FIG. 2 (contact hole size: a square with one side of 80 μm) was prepared, and a four-terminal measurement (Al alloy \ITO laminated film current was passed, and Al alloy was performed at a separate terminal. A method of measuring the voltage drop between the \ITO laminated films) was performed. Specifically, FIG spilling a current I between two of I ₁ -I _2, V ₁ -V by monitoring the voltage between V _2, [R = the contact resistance portion _{R (V 1 -V 2) /} I 2 ]. The value obtained by multiplying the resistance R by the area of the contact portion and converted into area resistance (Ω·mm 2) was used as the contact resistance, and 10 kΩ·mm 2 or less (10000 Ω·mm 2 or less) was good and passed.

The composition and evaluation results of the Al alloy film of the obtained reflective anode electrode are combined in Table 1 and shown. In the general evaluation, when all of the above reflectance, heat resistance, and contact resistance are good, it is set as ◯, and a case where any one is defective is set as x. In addition, {a/(a+b)} in the Al alloy film is shown as {Si/(Si+REM)} in the table.

From the above, it was confirmed that by including Si in the Al alloy film, Si is also included in the layer containing as a main component aluminum oxide interposed between the Al alloy film and the oxide conductive film. By setting the content of Si and rare earth elements contained in the Al alloy film to 0.62<{Si/(Si+REM)}, 0.2<Si<3 and 0.1<REM, for the obtained reflective anode electrode, low contact resistance and high reflectance And it was confirmed that good heat resistance was realized.

Although the present invention has been described in detail and with reference to specific embodiments, it is clear to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.

This application is based on Japanese Patent Application No. 2019-101560 for which it applied on May 30, 2019, The content is taken in here as a reference.

1: substrate
2: TFT
3: passivation film
4: planarization layer
5: contact hole
6: Al alloy film
7: oxide conductive film
8: organic light emitting layer
9: cathode electrode

Claims (9)

It is a reflective anode electrode for organic EL displays,
It has a laminated structure comprising an Al alloy film and an oxide conductive film, wherein a layer containing aluminum oxide as a main component is interposed at a contact interface between the Al alloy film and the oxide conductive film,
When the Al alloy film contains Si and at least one rare earth element, the Si content is a (atomic%) and the total content of the rare earth elements is b (atomic%), 0.62<{a/ (a+b)}, satisfying the relationship of 0.2<a<3 and 0.1<b, and
The reflective anode electrode, wherein the layer containing the aluminum oxide as a main component contains Si. The method of claim 1,
The reflective anode electrode, wherein the rare earth element contains at least one of Nd and La. The method of claim 1,
The reflective anode electrode, wherein the oxide conductive film has a thickness of 5 to 30 nm. The method of claim 2,
The reflective anode electrode, wherein the oxide conductive film has a thickness of 5 to 30 nm. The method according to any one of claims 1 to 4,
The reflective anode electrode, wherein the Al alloy film is formed by a sputtering method. The method according to any one of claims 1 to 4,
A reflective anode electrode in which the Al alloy film is electrically connected to a source/drain electrode of a thin film transistor. A thin film transistor substrate comprising the reflective anode electrode according to any one of claims 1 to 4. An organic EL display comprising the thin film transistor substrate according to claim 7. It is a sputtering target for forming an Al alloy film contained in the reflective anode electrode in any one of Claims 1-4,
When the Si content is a (atomic%) and the total content of rare earth elements is b (atomic%), the relationship of 0.62<{a/(a+b)}, 0.2<a<3, and 0.1<b To meet the sputtering target.

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