JP2018204059A - Flexible display aluminum alloy film and flexible display - Google Patents

Abstract

To provide a flexible display aluminum alloy film capable of suppressing electrical resistance increase and disconnection in a metal wiring even when repeatedly bent in a metal wiring aluminum alloy film used for a flexible display flexibility and freely bent.SOLUTION: The aluminum alloy film used for a flexible display comprises: at least one kind of X elements selected from a group consisting of Ta, Nb, Re, Zr, W, Mo, V, Hf, Ti, Cr and Pt; at least one kind of rare earth elements; at least one kind of Cu and Ge; at least one kind of Ni and Co; and the remainder consisting of Al and impurities.SELECTED DRAWING: Figure 1

Description

  The present invention is used for a display device such as a liquid crystal display using a flexible flexible substrate, and is useful as an electrode and a wiring material. An Al alloy film for a flexible display device and a flexible display device including the Al alloy film About.

  Al alloy films for display devices are mainly used as electrodes and wiring materials. As the electrodes and wiring materials, gates, source and drain electrodes and wiring materials for thin film transistors in a liquid crystal display (LCD), wiring materials, gates for thin film transistors in organic EL (Organic Light Emitting Diode: OLED), sources, and Drain electrode and wiring material, cathode and gate electrode and wiring material in field emission display (FED), anode electrode and wiring material in vacuum vacuum tube (VFD), plasma display panel (PDP) Address electrodes in And wiring materials, back electrodes in inorganic EL, and the like.

  Recently, a liquid crystal display having a large size exceeding 100 inches has been commercialized, and a low power consumption technology has been developed, which is widely used as a main display device. Some liquid crystal displays have different operating principles. Among them, active matrix liquid crystal displays that use thin film transistors (hereinafter referred to as “TFTs”) for switching pixels have high-precision image quality. And because it can handle high-speed video, it is the mainstay. Among these, TFTs using polycrystalline silicon or continuous grain boundary crystalline silicon as a semiconductor layer are used in liquid crystal displays that require further low power consumption and high-speed pixel switching.

  For example, an active matrix liquid crystal display includes a TFT substrate having a TFT that is a switching element, a pixel electrode made of a conductive oxide film, and a wiring including a scanning line and a signal line. Are electrically connected to the pixel electrode. Pure Al or an Al-based alloy film is used as a wiring material constituting the scanning lines and signal lines.

  By the way, in recent years, the demand for lightweight and thin display devices (displays) suitable for carrying is increasing, and among these display devices, in particular, a flexible material such as a film is used for a substrate, and it can be bent freely. There is a strong demand for flexible display devices that can be developed, and development is being promoted by companies, universities, research institutions, and the like.

  This flexible display device is lightweight and thin and highly portable. On the other hand, when the flexible display device is bent, a large bending stress is applied to the bent portion, which may cause various problems. In particular, the metal wiring (conductive layer) such as a pure Al film or an Al alloy film incorporated in the flexible display device can be subjected to bending stress repeatedly, thereby causing minute cracks in the metal wiring. Due to the occurrence of such minute cracks, the electrical resistance of the metal wiring may increase. Furthermore, when the density of cracks increases and many cracks are connected, there is a problem that a display failure of the flexible display device may occur due to disconnection of the metal wiring. Therefore, conventionally, methods for suppressing an increase in electrical resistance and disconnection in such metal wiring have been studied.

For example, Patent Document 1 discloses a storage elastic modulus G ′ at a frequency of 1 Hz in order to prevent a problem that a conductive layer is broken or peeled off from a substrate on a front substrate or a rear substrate when the display is bent. A flexible display electrode substrate having a stress relaxation layer (A) and a conductive layer (B) of 1 × 10 ⁴ Pa to 1 × 10 ⁸ Pa, the stress relaxation layer (A) and the conductive layer (B) By using a flexible display electrode substrate having an adhesion strength of 5 N / 25 mm or more, the surface resistivity increase rate of the conductive layer (B) when bent at a diameter of 3 mm can be suppressed to 20% or less. Technology has been proposed.

JP 2007-087771 A

  However, in the method of Patent Document 1 described above, the conductive layer serving as the metal wiring is protected by a predetermined stress relaxation layer to suppress breakage of the conductive layer, but the bending resistance of the conductive layer itself is improved. However, in order to further improve the bending resistance of the flexible display device, it has been desired to improve the bending resistance of the conductive layer itself.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to repetitively in an Al alloy film for metal wiring used for a flexible display device that is flexible and can be freely bent. An object of the present invention is to provide an Al alloy film for a flexible display device that can suppress an increase in electrical resistance and disconnection in metal wiring even when bent.

  As a result of intensive studies, the present inventors have found that the Al alloy film used in the flexible display device can be provided with a specific alloy to solve the above problems, and have completed the present invention.

That is, the present invention relates to the following [1] to [8].
[1] An Al alloy film used in a flexible display device,
At least one X element selected from the group consisting of Ta, Nb, Re, Zr, W, Mo, V, Hf, Ti, Cr and Pt;
At least one kind of rare earth element,
At least one of Cu or Ge;
An Al alloy film for a flexible display, comprising at least one of Ni or Co, and comprising the balance Al and impurities.
[2] The Al alloy film for flexible display device according to [1], wherein the content of the X element is 0.1 to 1 atomic%.
[3] The Al alloy film for flexible display devices according to [1] or [2], wherein the content of the rare earth element is 0.1 to 1 atomic%.
[4] The Al alloy for flexible display devices according to any one of [1] to [3], wherein the content of at least one of Cu or Ge is 0.1 to 1 atomic%. film.
[5] The Al alloy for flexible display devices according to any one of [1] to [4], wherein the content of at least one of Ni or Co is 0.01 to 1 atomic%. film.
[6] The above [1] to [5], wherein the Al alloy film is formed directly on a resin substrate used in the flexible display device or via an insulating film. The Al alloy film for flexible displays as described in one.
[7] The Al alloy film is used as a wiring material for a gate electrode used in the flexible display device, and is directly connected to a gate insulating film used in the flexible display device. The Al alloy film for flexible display devices according to any one of [1] to [6] above.
[8] A flexible display device comprising the Al alloy film for flexible display device according to any one of [1] to [7].

  According to the present invention, in an Al alloy film for metal wiring used for a flexible display device that is flexible and can be bent freely, the electrical resistance in the metal wiring is increased even when it is repeatedly bent. It is possible to provide an Al alloy film for a flexible display device that can suppress breakage and breakage.

FIG. 1 is a graph showing the relationship of the rate of change of electrical resistance with respect to the number of bendings when a pure Al film or an Al alloy film according to the present invention is used in Examples.

  In the Al alloy film for metal wiring used in a flexible display device that is flexible and can be bent freely, the inventors of the present invention have an increase in electrical resistance in the metal wiring even with repeated bending. In order to provide an Al alloy film for a flexible display device that can suppress breakage and disconnection, intensive studies have been conducted.

  As a result, as an Al alloy film for flexible display devices, Ta (tantalum), Nb (niobium), Re (rhenium), Zr (zirconium), W (tungsten), Mo (molybdenum), V (vanadium), Hf (hafnium) ), Ti (titanium), Cr (chromium), and Pt (platinum), at least one element selected from the group consisting of rare earth elements, and at least one element selected from Cu (copper) or Ge (germanium) Al alloy film composed of at least one of Ni (nickel) and Co (cobalt) and the balance Al (aluminum) and impurities suppresses the increase in electrical resistance and disconnection in the metal wiring even against repeated bending As a result, the present invention has been completed.

  First, the Al alloy film for flexible display devices used in the present invention will be described in detail.

(Al alloy film for flexible display)
The Al alloy film for a flexible display device of the present invention includes at least one X element selected from the group consisting of Ta, Nb, Re, Zr, W, Mo, V, Hf, Ti, Cr, and Pt, and a rare earth element ( Rare Earth Metal (REM), an Al—X element-REM-Cu / Ge—Ni / Co alloy film containing at least one of Cu or Ge and at least one of Ni or Co.

  Here, the X element is composed of a refractory metal having a melting point of approximately 1600 ° C. or higher, and is an element that contributes to improving heat resistance at high temperatures. These elements may be added alone or in combination of two or more. Of the X elements, Ta and Ti are preferable, and Ta is more preferable.

  The content of X element (when contained alone, it is a single amount, and when two or more types are used in combination, it is the total amount) is preferably 0.1 atomic% or more, and 0.2 atoms. % Or more is more preferable. If the content of the X element is less than 0.1 atomic%, the mechanical strength due to the refinement of the crystal grain size cannot be sufficiently ensured, so that it is difficult to ensure sufficient flexibility. Further, the content of the X element is preferably 1 atomic% or less, and more preferably 0.7 atomic% or less. When the content of the X element exceeds 1 atomic%, there are problems that the electrical resistance of the Al alloy film itself becomes too high and that residues are easily generated during wiring processing.

  In addition, rare earth elements (REM) include lanthanoid elements (a total of 15 elements from La (lanthanum) having atomic number 57 to Lu (lutetium) having atomic number 71 in the periodic table), Sc (scandium) and Y (yttrium). It means the element group which added and. In the present invention, the rare earth elements may be used alone or in combination of two or more. Among the rare earth elements, Nd (neodymium), La, and Gd (gadolinium) are preferable, and Nd and La are more preferable.

  The content of the rare earth element (in the case of containing alone, it is a single amount, and in the case of using two or more in combination) is preferably 0.1 atomic% or more, and 0.2 atoms % Or more is more preferable. If the rare earth element content is less than 0.1 atomic%, it is difficult to ensure sufficient flexibility because the mechanical strength due to the refinement of the crystal grain size cannot be sufficiently ensured. The rare earth element content is preferably 1 atomic% or less, and more preferably 0.8 atomic% or less. If the rare earth element content exceeds 1 atomic%, there are problems that the electrical resistance of the Al alloy film itself becomes too high and that residues are easily generated during wiring processing.

  The content of at least one of Cu or Ge (when contained alone is a single amount, and when two or more types are used in combination) is preferably 0.1 atomic% or more, More preferably, it is 0.2 atomic% or more. If the content of at least one kind of Cu or Ge is less than 0.1 atomic%, it is difficult to ensure sufficient flexibility because the mechanical strength due to the refinement of the crystal grain size cannot be sufficiently ensured. Further, the content of at least one of Cu or Ge is preferably 1 atomic% or less, and more preferably 0.6 atomic% or less. If the content of at least one of Cu or Ge exceeds 1 atomic%, there are problems that the electrical resistance of the Al alloy film itself becomes too high and that residues are easily generated during wiring processing. In addition, about Cu and Ge, Cu or Ge may be added independently and both may be added.

  The content of at least one of Ni or Co (a single amount when contained alone and a total amount when two or more types are used in combination) is preferably 0.01 atomic% or more, More preferably, it is 0.1 atomic% or more. If the content of at least one of Ni or Co is less than 0.01 atomic%, it is difficult to ensure sufficient flexibility because the mechanical strength due to the refinement of the crystal grain size cannot be sufficiently ensured. Further, the content of at least one of Ni or Co is preferably 1 atomic% or less, and more preferably 0.5 atomic% or less. If the content of at least one of Ni or Co exceeds 1 atomic%, there are problems that the electric resistance of the Al alloy film itself becomes too high and that residues are easily generated during wiring processing. As for Ni and Co, Ni or Co may be added alone, or both may be added.

  The Al alloy film contains each element described above, and the balance is Al and impurities.

  Here, examples of impurities include Fe (iron), Si (silicon), B (boron), and the like. Although the total amount of impurities is not particularly limited, inclusion up to approximately 0.5 atomic% is allowed. For each impurity element, Fe and Si are allowed to contain up to 0.12 atomic% and B up to 0.012 atomic%, respectively. In addition, if it is in the said range, not only the case where it contains as an unavoidable impurity but the case where it adds positively does not prevent the effect of this invention.

  The composition of the Al alloy film for flexible display device of the present invention has been described above.

  The thickness of the Al alloy of the present invention is preferably 50 nm or more, and more preferably 100 nm or more, particularly in order to ensure high temperature heat resistance and reduced wiring resistance. The upper limit is not particularly limited, but it is preferably 1 μm or less, more preferably 600 nm or less, considering the wiring taper shape and the like.

  The Al alloy film is preferably used for various wiring materials such as a source-drain electrode and a gate electrode used in a flexible display device, and more preferably used as a wiring material for a gate electrode that requires flexibility.

(Method for producing Al alloy film for flexible display)
The Al alloy film is desirably formed by a sputtering method using a sputtering target (hereinafter also referred to as “target”). This is because a thin film having excellent in-plane uniformity of components and film thickness can be easily formed as compared with a thin film formed by ion plating, electron beam vapor deposition or vacuum vapor deposition.

The film formation conditions during sputtering are not particularly limited, but for example, the following conditions are preferably employed.
-Substrate temperature: room temperature to 50 ° C
・ Achieving vacuum: 1 × 10 ⁻⁵ Torr or less (1 × 10 ⁻³ Pa or less)
-Gas pressure during film formation: 0.1 to 1.0 Pa, oxygen partial pressure: 1 to 50%
DC sputtering power density (DC sputtering power per unit area of target): 1.0 to 20 W / cm ²

  Further, in order to form the Al alloy film by the sputtering method, if the Al alloy sputtering target having the same composition as the desired Al alloy film is used as the target, This is preferable because there is no fear and an Al alloy film having a desired component composition can be formed.

  Therefore, the present invention also includes a sputtering target having the same composition as the Al alloy film described above within the scope of the present invention. Specifically, it is a sputtering target for forming an Al alloy film used in a flexible display device, and includes a group consisting of Ta, Nb, Re, Zr, W, Mo, V, Hf, Ti, Cr, and Pt. A suitable sputtering target includes at least one selected X element, at least one rare earth element, at least one Cu or Ge, and at least one Ni or Co, and the balance Al and impurities. .

  Further, for the same reason as described for the Al alloy film, the content of the X element in the sputtering target (a single amount when contained alone, and a total amount when two or more types are used in combination). .) Is preferably at least 0.1 atomic%, more preferably at least 0.2 atomic%. Further, the content of the X element is preferably 1 atomic% or less, and more preferably 0.7 atomic% or less.

  In the sputtering target, the rare earth element content (individual amount when contained alone, and total amount when two or more types are used in combination) is preferably 0.1 atomic% or more. More preferably, it is 0.2 atomic% or more. The rare earth element content is preferably 1 atomic% or less, and more preferably 0.8 atomic% or less.

  The content of at least one of Cu or Ge in the sputtering target (a single amount when contained alone and a total amount when two or more types are used in combination) is 0.1 atomic% or more. It is preferable that it is 0.2 atomic% or more. Further, the content of at least one of Cu or Ge is preferably 1 atomic% or less, and more preferably 0.6 atomic% or less.

  The content of at least one of Ni or Co in the sputtering target (a single amount when contained alone and a total amount when two or more types are used in combination) is 0.01 atomic% or more. It is preferable that it is 0.1 atomic% or more. Further, the content of at least one of Ni or Co is preferably 1 atomic% or less, and more preferably 0.5 atomic% or less.

  The shape of the target includes those processed into an arbitrary shape (such as a square plate shape, a circular plate shape, or a donut plate shape) according to the shape or structure of the sputtering apparatus.

  As a method for producing the above target, a method of producing an ingot made of an Al-based alloy by a melt casting method, a powder sintering method, or a spray forming method, or a preform made of an Al-based alloy (the final dense body is prepared) Examples thereof include a method obtained by producing an intermediate before being obtained) and then densifying the preform by a densification means.

(Flexible display device)
In the flexible display device according to the present invention, the Al alloy film for a flexible display device described above is used as a metal wiring. According to the flexible display device using the Al alloy film according to the present invention as the metal wiring, an increase in electrical resistance or disconnection in the metal wiring can be suppressed even with repeated bending. Can be effectively prevented.

  The Al alloy film according to the present invention is directly formed on a flexible resin substrate (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), etc.) used for a flexible display device, for example, by sputtering. Alternatively, it is formed through an insulating film.

  The Al alloy film is used as a wiring material for a gate electrode used in a flexible display device, and is directly connected to a gate insulating film used in the flexible display device.

  In manufacturing a flexible display device provided with the Al alloy film of the present invention, a general process of the display device can be employed. For example, a manufacturing method described in JP-A-2007-157917 may be referred to. .

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples, and modifications are made within a range that can be adapted to the gist thereof. It is also possible to carry out and they are all included in the technical scope of the present invention.

<Example>
(Preparation of bending resistance test sample)
An alloy of Al-0.2 at% Ta-0.3 at% Nd-0.4 at% Ge-0.1 at% Ni-0.6 at% Zr on a 125 μm thick PET substrate as a sample for bending resistance test An Al alloy film having a composition (film thickness: 100 nm) was formed by DC magnetron sputtering (atmosphere gas = argon, pressure = 2 mTorr, substrate temperature = 25 ° C. (room temperature)).

  For the formation of the Al alloy film having the above-mentioned alloy composition, Al-0.2 at% Ta-0.3 at% Nd-0.4 at% Ge-0.1 at% Ni-0.6 at% produced by a vacuum melting method is used. An Al alloy target having an alloy composition of Zr was used as a sputtering target.

  The content of each alloy element in the Al alloy film was determined by an ICP emission analysis (inductively coupled plasma emission analysis) method.

  An electrode pattern was formed by photolithography on the Al alloy film obtained as described above. The electrode pattern is a wiring having a length of 70 mm and a width of 0.5 mm, and electrode pads of 5 mm square are arranged at both ends for use as electrical contacts.

(Bending test)
A bending test was performed on the sample for bending resistance test produced above using the “unloaded U-shaped expansion / contraction test” of Yuasa System Equipment Co., Ltd. The bending test conditions were a curvature radius r = 2.5 mm, a bending speed of 90 rpm, and repeated bending up to 50,000 times.

(Measurement of DC electrical resistance)
In order to grasp the increase in the electrical resistance of the sample for bending resistance test due to the crack generated in the bending test, the direct current electric current between the electrode pads was repeated three times after 5000 times, 10000 times, and 50000 times. Resistance was monitored. The DC electric resistance was measured using “R8340” of Advanced Test Co., which is a high resistance measurement system. The calculation of the DC resistance value was determined using only the linear part of the acquired IV characteristic.

<Comparative example>
A bending resistance test sample was prepared in the same manner as in Example except that pure Al was used as a material for forming the bending resistance test sample, and the bending test and the measurement of DC electric resistance were performed.

(Change rate of electrical resistance with respect to the number of bendings)
FIG. 1 shows the relationship of the rate of change of electric resistance with respect to the number of bendings in the bending resistance test samples of Examples and Comparative Examples. The “electric resistance change rate” on the vertical axis in the graph of FIG. 1 is a value obtained by dividing the difference between the electrical resistance before and after the test by the initial electrical resistance value (before the start of the bending test). When the electrical resistance increases, it becomes a positive value.

  From the results shown in FIG. 1, in the initial stage where the number of bendings is about 20000, the pure Al film which is a comparative example has a lower rate of change in electrical resistance, but the Al alloy film which is an example is thereafter It can be seen that the rate of change in electrical resistance is lower. More specifically, when the number of flexing was 50000th, the change rate of the electric resistance was about 24% in the comparative example, but was suppressed to about 14% in the example.

  In addition, after 50,000 times of bending test, when the surface of each electrode pattern of an Example and a comparative example was observed visually, it was recognized that the crack generate | occur | produced around the bending part in any electrode. However, it was confirmed that the comparative example had a higher crack density at the bent portion and a longer average crack length than the example.

  In addition, considering from the above results, cracks in the metal wiring, part of the current conduction path was broken, resulting in a crack density of a certain level or more, the current that can not be ignored compared to the wiring width It is assumed that the electrical resistance has increased due to the increase in path length.

  From the above results, it is recognized that the Al alloy film defined in the present invention is effective as a metal wiring for a flexible display device capable of suppressing an increase in electrical resistance and disconnection in a metal wiring even against repeated bending. It is done.

Claims (8)

An Al alloy film used in a flexible display device,
At least one X element selected from the group consisting of Ta, Nb, Re, Zr, W, Mo, V, Hf, Ti, Cr and Pt;
At least one kind of rare earth element,
At least one of Cu or Ge;
An Al alloy film for a flexible display, comprising at least one of Ni or Co, and comprising the balance Al and impurities.   2. The Al alloy film for a flexible display according to claim 1, wherein the content of the X element is 0.1 to 1 atomic%.   3. The Al alloy film for flexible display according to claim 1, wherein the content of the rare earth element is 0.1 to 1 atomic%.   4. The Al alloy film for flexible display according to claim 1, wherein the content of at least one of Cu or Ge is 0.1 to 1 atomic%.   5. The Al alloy film for a flexible display according to claim 1, wherein the content of at least one of Ni or Co is 0.01 to 1 atomic%.   6. The flexible according to claim 1, wherein the Al alloy film is formed directly on a resin substrate used in the flexible display device or via an insulating film. Al alloy film for display devices.   2. The Al alloy film is used as a wiring material for a gate electrode used in the flexible display device, and is directly connected to a gate insulating film used in the flexible display device. The Al alloy film for flexible display devices according to any one of -6.   The flexible display apparatus provided with the Al alloy film for flexible display apparatuses of any one of Claims 1-7.

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