TW201815567A - Reflective electrode and aluminum alloy sputtering target - Google Patents

Abstract

An object of the present invention is to provide a reflective electrode having an organic electroluminescence (EL) display device, an organic electroluminescence lighting, and the like, which can sufficiently reduce its driving voltage and has a high reflectance. The present invention is a reflective electrode composed of a reflective film composed of an aluminum (Al) alloy and a transparent conductive film, characterized in that the main surface of the reflective film is in contact with the main surface of the transparent conductive film, and the aluminum alloy is The ratio contains 3 to 12 atomic% of zinc (Zn) and 0.01 to 0.5 atomic% of rare earth elements.

Description

Reflective electrode and aluminum alloy sputtering target

[0001] The present invention relates to a reflective electrode for an organic electroluminescence (EL) display device or an organic electroluminescence lighting element, and an aluminum (Al) alloy sputtering target for forming a reflective film on the reflective electrode.

[0002] Organic electroluminescence (EL) display devices or organic electroluminescence lighting are devices that utilize the electric field emission phenomenon of organic materials, and seek to reduce the power consumption by improving the light extraction efficiency of the elements. [0003] In a device such as a top emission organic electroluminescence display device that takes out light from the opposite direction to the substrate, an organic material is laminated on the reflective electrode. In order to reflect the light generated by the organic material on the substrate side and improve the extraction efficiency, a material with high light reflectivity is suitable for the reflective electrode. As a reflective film constituting the reflective electrode, it can be used in a high reflectance range in the visible light wavelength range. Silver (Ag) or aluminum (Al). In addition, since the reflective film may serve as an electrode or may be used as a part of wiring, it is also required to have a low electrical resistivity. [0004] Among silver-based metals, those having the highest reflectivity are precious metals, that is, the materials are expensive. Therefore, an aluminum-based metal having a higher reflectance than silver is suitable as a reflective film material. However, when aluminum is used as the reflective film, the reflective film is oxidized by oxygen in the transparent conductive film, and an aluminum oxide film is inevitably formed on the surface of the reflective film. Due to the existence of the aluminum oxide film, the driving voltage of the former element is higher than that of the element using silver as the reflective film in the top emission organic electroluminescence display device. [0005] Therefore, in Patent Document 1, it is proposed that a metal film made of tungsten or molybdenum be interposed between an aluminum reflective film and a transparent conductive film, and the metal film be used to prevent aluminum reflection due to oxygen in the transparent conductive film. Film oxidation. [Prior Art Document] [Patent Document] [0006] [Patent Document 1] Japanese Patent Laid-Open No. 2012-110904

[Problems to be Solved by the Invention] 000 [0007] However, in the method described in Patent Document 1, a tungsten film or a molybdenum film having a high resistivity is not sufficiently interposed between an aluminum (Al) reflective film and a transparent conductive film. Reduce the driving voltage of the entire device.目的 An object of the present invention is to provide a reflective electrode having an organic electroluminescence (EL) display device or an organic electroluminescence device, which can sufficiently reduce its driving voltage and has a high reflectance. [Means for Solving Problems] [0008] The inventors of this case conducted an intensive review in order to solve the above problems. As a result, it was found that by forming the reflective film as an aluminum alloy containing aluminum (Al) and zinc (Zn) and a rare earth element, the high reflectance and low electrical resistivity required as a reflective electrode and wiring can be maintained while being reduced. Driving voltage of an organic electroluminescence (EL) light emitting element. [0009] That is, the present invention relates to a reflective electrode composed of a reflective film composed of an aluminum alloy and a transparent conductive film, characterized in that the main surface of the reflective film is in contact with the main surface of the transparent conductive film, and The aforementioned aluminum alloy-based proportion contains 3 to 12 atomic percent of zinc (Zn) and 0.01 to 0.5 atomic percent of rare earth elements. [0010] According to the present invention, the aluminum alloy of the reflective film constituting the reflective electrode contains zinc in a specified ratio. This zinc is biased on the surface of the reflective film, and reduces the density of the aluminum oxide film formed on the surface of the reflective film, thereby deteriorating its insulation. Therefore, when the reflective electrode is used for an element such as an organic electroluminescence display device or an organic electroluminescence lighting, the driving voltage of the element can be reduced. [0011] In addition, the conventional aluminum reflective film has low surface smoothness, and thus reduces the reflectance of the reflective film. In addition, when zinc is contained in the above-mentioned manner, the driving voltage can be reduced, and on the other hand, the reflectance is reduced due to the decrease in surface smoothness. When a reflective electrode including an aluminum reflective film is used to form an element, there is a concern that the thickness of the organic layer is not uniform, which may cause a short circuit in an element including the reflective electrode including an aluminum reflective film. [0012] However, in the present invention, since the aluminum alloy constituting the reflective film contains a rare earth element in a specified ratio, even if zinc is contained, the surface smoothness of the reflective film can be improved. Accordingly, it is possible to suppress the above-described decrease in the reflectance of the reflective film. In addition, smoothing of the organic layer can further suppress short-circuiting of the element based on this. In one aspect of the present invention, the rare earth element contained in the aluminum alloy may be at least 1 selected from the group consisting of neodymium (Nd), lanthanum (La), cerium (Ce), and yttrium (Y). Kind of element. [0013] In one aspect of the present invention, the aluminum alloy contains at least one of nickel (Ni) and copper (Cu) in a total amount of 0.05 to 5.0 atomic%. Nickel and copper are heat treatments that increase the reflectivity of the reflective electrode, and can suppress or increase the size of crystal grains or compounds that form by-products. Therefore, it is possible to suppress the aluminum alloy, that is, the reflective film made of the aluminum alloy, and further reduce the resistivity of the reflective electrode after heat treatment, and to suppress the organic electroluminescence display device or organic electroluminescence lighting having the reflective electrode. The driving voltage of the components increases. [0014] The reflective film constituting the reflective electrode of the present invention can be formed by any method, for example, an aluminum alloy sputtering target of the same composition can be used and formed by a sputtering method. [0015] In addition, "~", which displays a numerical range, is used for the purpose of including the numerical value recorded before and after as a lower limit value and an upper limit value, and is not limited to a specific paragraph. In this specification, The use of "~" has the same meaning. [Effects of the Invention] [0016] As described above, according to the present invention, it is possible to provide a reflective electrode having high reflectance in an organic electroluminescence (EL) display device or an organic electroluminescence device, which can sufficiently reduce its driving voltage. .

[0017] Hereinafter, embodiments of the present invention will be described in detail. In the following description, "atomic%" and "at atomic%" are synonymous. [Reflection Film] (Amount of Zinc (Zn)) The aluminum alloy constituting the reflection film of the reflection electrode includes zinc in a range of 3 atomic% or more and 12 atomic% or less. At less than 3 atomic%, the effect of improving the electrical continuity with transparent conductive films such as indium tin oxide (ITO) is not sufficient. For organic electroluminescence display devices or organic electroluminescence devices with the reflective electrode, The driving voltage has no improvement. Above 12 atomic%, the reflectance will decrease, and the resistivity of the aluminum alloy will increase. As a result, the resistivity of the reflective film, that is, the reflective electrode, will increase, and the organic electroluminescence display device having the reflective electrode The driving voltage of elements such as organic electroluminescence lighting is increased. [0019] In addition, the reason why the amount of zinc exceeds 12 atomic% may increase the driving voltage of the device is not clear. It is considered that the concentration of zinc is too large, the thickness of the oxide film is increased, and the barrier is increased. . The amount of zinc is preferably 4 atomic% or more, and more preferably 11 atomic% or less. [0020] In addition, as described above, the aluminum alloy of the reflective film constituting the reflective electrode reduces the driving voltage of the element by including zinc in the above proportion because zinc is biased on the surface of the reflective film, so that the aluminum oxide film The reason is that the compactness is lowered, the insulation is deteriorated, and the electrical connection with the transparent conductive film is improved. [0021] (Rare Earth Element) The aluminum alloy constituting the reflective film of the reflective electrode contains a rare earth element in a range of 0.01 atomic% to 0.5 atomic% in total. With the addition of zinc, for example, when forming a film with a high film thickness of 100 nm or more, the surface cracking tends to be large. The addition of rare earth elements is used to suppress the increase of crystal grains in the film formation and to refine the structure of the thin film. While improving the smoothness of the film surface. In addition, it suppresses crystal growth due to heat treatment, and has the effect of maintaining high smoothness even after heat treatment. Therefore, since the above-mentioned range contains a rare earth element, the reflectance of the reflective film, that is, the reflective electrode can be kept sufficiently high, and when the reflective film is used to form an element or the like, short circuit of the element can be avoided. [0022] The total content of the rare earth elements is preferably 0.05 atomic% or more, and more preferably 0.3 atomic% or less. Among the rare-earth elements of the additive element, at least one element selected from the group consisting of neodymium (Nd), lanthanum (La), cerium (Ce), and yttrium (Y) is particularly preferable. [0023] In addition, the total content of the rare earth element is less than 0.01 atomic%, and the effect of miniaturization is small; if it exceeds 0.5 atomic%, the degree of decrease in reflectance increases. [0024] (Nickel and copper) The aluminum alloy constituting the reflective film of the reflective electrode preferably contains at least one of nickel (Ni) and copper (Cu) in a total of 0.05 atomic% or more and 5.0 atomic% or less. In order to increase the reflectivity of the reflective electrode, heat treatment is performed at, for example, about 250 ° C. However, by including at least one of nickel and copper in the above-mentioned content ratio of the reflective film, it is possible to suppress the formation of an oxide layer on the surface of the reflective film and ensure the conductivity, suppress the increase of crystal grains to make it finer, and disperse byproducts Of compounds. Therefore, it is possible to suppress the aluminum alloy, that is, the reflective film made of the aluminum alloy, and further reduce the resistivity of the reflective electrode after heat treatment, and to suppress the organic electroluminescence display device or organic electroluminescence lighting having the reflective electrode. The driving voltage of the components increases. [0025] When the total amount of nickel and copper added is set to be 0.05 atomic% or more, the above-mentioned effects can be fully exerted, so it is preferable. In addition, it is preferable that the reflectance can be maintained at a height of 5.0 atomic% or less. It is more preferably 0.1 atomic% or more, and still more preferably 3.0 atomic% or less. [Characteristics of Reflective Electrode] The electrical resistivity of the reflective electrode is preferably 10 μΩ · cm or less, more preferably 9 μΩ · cm or less, and even more preferably 8 μΩ · cm or less. Thereby, it is possible to suppress an increase in driving voltage of an element such as an organic electroluminescence display device or an organic electroluminescence lighting. [0027] In the case of using as a reflective electrode, a thin film having a film thickness of 100 nm or more at a measured wavelength of 550 nm preferably has a reflectance of 85% or more, and more preferably 88% or more. Thereby, it is possible to improve the extraction efficiency of light generated by organic materials among elements such as organic electroluminescence display devices or organic electroluminescence lighting. In addition, when an organic electroluminescence element is used, the driving voltage is preferably an area current density of 50 mA / cm ² or less, and preferably 9 V or less. [0028] <Transparent conductive film> The transparent conductive film has its main surface in contact with the main surface of the reflective film. Generally, elements such as organic electroluminescence display devices or organic electroluminescence lighting are transparently laminated on the reflective film. Conductive film. [0029] For the transparent conductive film, materials that are commonly used, such as ITO (Sn doped with In ₂ O ₃ ), Ga doped with ZnO, Sb doped with SnO, and the like can be used. [0030] <Production of Reflective Electrode> The reflective film and the transparent conductive film constituting the reflective electrode may be formed by a physical vapor deposition method such as a sputtering method or an ion plating method, or a chemical vapor deposition method such as a CVD method. Since the film is formed by a method, a reflective electrode can be formed. Among these, a sputtering method that is easy to control and can also simply control the film thickness or composition is preferred. [0031] When a reflective electrode is formed by a sputtering method, for example, when forming a reflective film made of an aluminum alloy composed of the above-mentioned components, a sputtering target having the same composition as that of the aluminum alloy constituting the reflective film is prepared. This sputtering target is subjected to sputtering under predetermined conditions to obtain a desired reflective film. Specifically, zinc is contained in a range of 3 atomic% to 12 atomic%, and a rare earth element is included in a range of 0.01 atomic% to 0.5 atomic%. If necessary, it is 0.05 atomic% or more and 5.0 as the total content. The atomic% or lower range includes an aluminum alloy sputtering target including at least one of nickel and copper, and the sputtering target is subjected to sputtering under specified conditions to obtain a desired reflective film. In addition, if necessary, an aluminum alloy sputtering target including at least one element selected from the group consisting of neodymium, lanthanum, cerium, and yttrium of the rare-earth elements is prepared, and the sputtering target is prepared under specified conditions. Perform sputtering to obtain the desired reflective film. [0032] When a transparent conductive film is formed by a sputtering method, a sputtering target having the same composition as that of the transparent conductive film is also prepared, and the sputtering target is subjected to sputtering under specified conditions to obtain a desired transparent conductive film. . [0033] In the case where an oxide film such as a transparent conductive film is formed by sputtering, a reactive gas such as oxygen is preferably supplied to the film because oxygen deficiency in the film may occur. [0034] The above-mentioned aluminum alloy sputtering target and the like, in addition to the above-mentioned component composition, include elements inevitably mixed in the manufacturing process and the like, such as iron and silicon. The proportion of such inevitable impurities is generally 0.03% by weight or less, and preferably 0.01% by weight or less. [0035] The shape of the target may include a target processed into an arbitrary shape (for example, a square plate shape, a circular plate shape, a ring plate shape, or the like) corresponding to the shape or structure of the sputtering apparatus. [0036] Examples of the method for producing the target include a method of producing an ingot made of an aluminum-based alloy by a dissolution casting method, a powder sintering method, and a spray forming method, and A method in which a preform (an intermediate body before a final dense body is obtained) composed of an aluminum-based alloy is manufactured and then the preform is densified by a densification method. [Examples] [0037] (1) Production of organic electroluminescence (EL) elements On a glass substrate (EagleXG manufactured by Corning Corporation), the components shown in Tables 1 and 2 were composed of aluminum alloy. After forming a reflective film (anode electrode) with a thickness of 200 nm, a transparent conductive film of indium tin oxide (ITO) was formed at 10 nm. After that, patterning was performed to form a 2 mm wide wiring. Next, an infrared lamp heat treatment furnace was used to perform heat treatment in a nitrogen gas atmosphere at 250 ° C. for 1 hour. After that, the surface was irradiated with a UV lamp. [0038] Next, on a transparent conductive film, a 60-nm-thick α-NPD (α-naphtyl phenil diamine) is formed by a vacuum evaporation method, and then a 50-nm-thick Alq3 (8 -hydroxy quinorine alminum) to form LiF of the electron injection layer with a thickness of 0.6 nm, and finally, aluminum with a thickness of 100 nm for the cathode electrode. Such a vapor deposition layer is formed using a mask having a width of 2 mm, and an organic electroluminescence device having a light emitting area of 2 mm × 2 mm is produced. [0039] Further, a reflective film, line 4 inch diameter aluminum alloy target, to 3 ~ 6W / cm ² electric power input formed by sputtering. Similarly, the transparent conductive film is formed by sputtering using an indium tin oxide target having a diameter of 4 inches at an input power of 3 to 6 W / cm ² . [0040] (2) The measurement and evaluation of the driving voltage of the organic electroluminescence element obtained by the above method, and the reflectance and resistivity of the reflective film (reflective electrode) are measured as follows. Reflectance: Absolute reflectance was measured with a V-570 spectrophotometer manufactured by JASCO Corporation. The value in the table is a value (representative value) with a wavelength of 450 nm. Resistivity: 4 probe method. Driving voltage: HP ( The semiconductor parameter analyzer (HP4156A) was manufactured, and the voltage sweep range was set to 0V-14V to measure the current and voltage of the components, and the voltage-current characteristics of each component were obtained. [0041] According to a measurement such as the above, it is acceptable to set a reflectance of 85% or more and an electrical resistivity of 9 μΩ · cm or less. In addition, the drive voltage was acceptable at an area current density of 50 mA / cm ² or lower at 9 V or less. The measurement results are shown in Tables 1 and 2. [0042] [0043] [0044] As can be seen from Table 1, Examples 1 to 7 in which the amount of zinc, the amount of rare earth elements, and the amount of nickel and copper in the aluminum alloy constituting the reflective film of the reflective electrode satisfy the requirements of the present invention, even after heat treatment, Display good reflectivity, electrical resistivity and driving voltage. [0045] On the other hand, it can be seen from Table 2 that in Comparative Examples 1 and 4 in which the reflective film is made of pure aluminum, since the reflective film, that is, the reflective electrode does not contain zinc element, the driving voltage of the element is Exceeding 14V or a higher value of 10.2V. [0046] In Comparative Examples 2, 3, 5, 6, and 7 that did not contain a rare earth element, the reflectance of the reflective film was reduced due to insufficient surface smoothness. [0047] Furthermore, in Comparative Example 8 which does not contain zinc and contains a large amount of nickel, the reflectance of the reflective film, that is, the reflective electrode is low. In Comparative Example 9 in which the amount of zinc exceeds the range of the present invention, the reflectance of the reflective film, that is, the reflective electrode is also low, and the driving voltage is high. [0048] The present invention has been described in detail based on the above specific examples, but the present invention is not limited to the above specific examples, and various modifications or changes can be made without departing from the scope of the present invention. This application is based on a Japanese patent application filed on August 26, 2016 (Japanese Patent Application No. 2016-166148), the contents of which are incorporated herein by reference.

Claims (5)

A reflective electrode is a reflective electrode composed of a reflective film made of an aluminum (Al) alloy and a transparent conductive film, characterized in that the main surface of the reflective film is in contact with the main surface of the transparent conductive film, and the aluminum The alloy system contains 3 to 12 atomic percent of zinc (Zn) and 0.01 to 0.5 atomic percent of rare earth elements. The reflective electrode according to item 1 of the scope of patent application, wherein the aforementioned rare earth element is at least one element selected from the group consisting of neodymium (Nd), lanthanum (La), cerium (Ce), and yttrium (Y). . For example, the reflective electrode described in item 1 of the patent application range, wherein the aforementioned aluminum alloy contains at least one of nickel (Ni) and copper (Cu) in a total amount of 0.05 to 5.0 atomic%. For example, the reflective electrode described in item 2 of the scope of patent application, in which the foregoing aluminum alloy contains at least one of nickel and copper in a total amount of 0.05 to 5.0 atomic%. An aluminum alloy sputtering target is characterized in that the aforementioned reflective film is formed as a reflective electrode as described in any one of items 1 to 4 of the scope of patent application.