Silver alloy composition for forming conductive film and method for manufacturing the same

Abstract

The present invention relates to a Ag-Li alloy composition for display applications. The present invention proposes, as an embodiment, a silver alloy composition containing 0.5 to 3.0 wt% of lithium (Li) and the balance of silver (Ag) and inevitable impurities, and a method for manufacturing the same. The silver alloy composition of the present invention is suitable for application to electrodes and reflective films for displays, and can improve the service life of display elements such as OLEDs.

Description

Technical Field

[0001] The present invention relates to a silver alloy composition for forming a conductive film disposed on a reflective film or electrode of a display element. Background Technology

[0002] Recently, silver alloys have been used as reflective films and electrode materials for organic electroluminescent (EL) displays and touch panels. Generally, silver alloys are deposited in thin film form by sputtering, and through this process, they function as reflective films and electrodes for organic EL displays and touch panels.

[0003] Existing silver alloys are made by adding elements such as indium (In), copper (Cu), gold (Au), and aluminum (Al) to silver (Ag) to improve the shortcomings of pure silver, namely its heat resistance, moisture resistance, and corrosion resistance. Therefore, it is hoped that these alloys will possess the properties required for reflective films and electrode materials, such as low electrical resistance, high light reflectivity, and corrosion resistance.

[0004] However, while existing silver-based alloys exhibit excellent reflectivity, they have poor corrosion resistance and heat resistance, making them prone to hillocks and melt-out during OLED manufacturing, which may lead to dark spots and component defects.

[0005] [Existing Technical Documents]

[0006] [Patent Documents]

[0007] Korean Patent Publication No. 10-2012-0032050 (April 4, 2012) Summary of the Invention

[0008] Technical issues

[0009] To address the aforementioned problems, this invention proposes a silver alloy (Ag-Li) composition that alloys lithium (Li) in silver (Ag), thereby exhibiting excellent corrosion resistance and heat resistance, and can be used as a target material for forming reflective films and electrodes of display elements.

[0010] Furthermore, the present invention also proposes a method for manufacturing a silver alloy composition having excellent corrosion resistance and heat resistance and being able to form a conductive film that can be used as a reflective film and electrode for display elements.

[0011] Other detailed objectives of the present invention will be clearly grasped and understood by those skilled in the art through the specific details described below.

[0012] Technical solution

[0013] To address the aforementioned problems, the present invention, as an example, proposes a silver alloy composition containing 0.5 to 3.0% by weight of lithium (Li) and the balance being silver (Ag) and unavoidable impurities.

[0014] Such silver alloy compositions may also contain more than 0.1% by weight and less than 1.0% by weight of indium (In).

[0015] In addition, it may contain at least one element from the group consisting of copper (Cu), chromium (Cr), germanium (Ge), nickel (Ni), palladium (Pd) and platinum (Pt).

[0016] In addition, to solve the above problems, a method for manufacturing a silver alloy composition is proposed, comprising: a first step of adding a composition containing 0.5 to 3.0% by weight of lithium, with the balance being silver and unavoidable impurities, to a high-frequency induction furnace at 1,000 to 1,300°C, and melting and stirring simultaneously using argon (Ar) and charcoal to block the reaction with external oxygen; a second step of placing the molten composition from the first step into a mold to manufacture a casting; a third step of heating and forging the casting manufactured in the second step to form a forging; a fourth step of removing the oxide layer from the surface of the forging after the third step; a fifth step of performing a first heat treatment on the forging after the fourth step at a temperature of 600 to 800°C; a sixth step of rolling the material after the first heat treatment in the fifth step; a seventh step of performing a second heat treatment on the material after the sixth step at a temperature of 400 to 600°C; and an eighth step of processing the material after the seventh step into a certain shape.

[0017] In addition, in order to solve the above problems, the present invention provides, as an embodiment, a silver alloy target material manufactured by the above manufacturing method, containing 0.5 to 3.0% by weight of lithium and the balance being silver and unavoidable impurities, for use in the formation of reflective films and electrodes for displays.

[0018] Technical effect

[0019] The silver alloy composition for forming a conductive film and its manufacturing method according to embodiments of the present invention have good reflectivity when used as a sputtering target, and have excellent corrosion resistance and heat resistance compared with existing pure silver and silver-based alloys. Therefore, they are suitable for use in electrodes and reflective films for displays.

[0020] Furthermore, compared to existing pure silver or silver-based alloys used in displays, it exhibits superior corrosion resistance and heat resistance when forming reflective films, thus minimizing component defects (dark spots, etc.) caused by silver ion migration. It also exhibits excellent heat resistance and transmittance when forming electrodes, thereby improving the lifespan of display components such as OLEDs.

[0021] Other effects of the present invention will be clearly understood and appreciated by those skilled in the art through the specific details described below or during the implementation of the present invention. Attached Figure Description

[0022] Figure 1 This is a flowchart illustrating a method for manufacturing a silver alloy composition according to an embodiment of the present invention. Detailed Implementation

[0023] This invention can be modified in many ways and can have many embodiments; therefore, specific embodiments will be described in detail.

[0024] However, this does not mean that the invention is limited to specific embodiments, but should be understood to include all modifications, equivalents, and even substitutions contained within the spirit and technical scope of the invention. The terminology used in this application is only for describing specific embodiments and is not intended to limit the invention.

[0025] Singular expressions include plural expressions unless otherwise expressly stated in the context. It should be understood that the terminology in this application is intended to specify the presence of features, numbers, constituent elements or their composition as described in the specification, and does not preclude the presence or additional possibilities of one or more other features, numbers, constituent elements or their composition.

[0026] Unless otherwise defined, all terms used herein, including technical or scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms as defined in commonly used dictionaries shall be interpreted as having the meaning consistent with their meaning in the context of the relevant art and shall not be interpreted as having an idealized or overly formal meaning, unless otherwise expressly defined in this application.

[0027] The following will describe in detail a silver alloy composition for forming a conductive film and a method for manufacturing the same, according to an embodiment of the present invention.

[0028] In the past, silver alloy targets used as reflective films had poor corrosion resistance and heat resistance, leading to silver ion migration (Ag Migration) during the metal deposition process. This resulted in hillocks, causing dark spots and component defects. Therefore, to solve this problem, there is an increasing need for a silver alloy with excellent corrosion and heat resistance, high reflectivity to improve component lifespan, and the ability to be used in both reflective films and electrodes.

[0029] In order to achieve the above objectives, the inventors of this invention conducted extensive research and finally discovered that silver alloy compositions containing specific amounts of specific alloying elements in addition to silver have excellent reflectivity, high corrosion resistance and heat resistance, and are therefore suitable as materials for reflective films and electrodes.

[0030] The silver alloy composition of the present invention for forming a conductive film is a silver alloy composition for forming a conductive film disposed on a reflective film or electrode of a display element, and can be used as a sputtering target.

[0031] Specifically, the silver alloy composition of the present invention may contain 97% by weight or more and 99.5% by weight or less silver as the main component, and 0.5% by weight or more and 3.0% by weight or less lithium (Li). When the Li content is less than 0.5% by weight, the corrosion resistance and heat resistance are poor, while when it exceeds 3.0% by weight, the reflectivity decreases.

[0032] Lithium is a light metal, and when alloyed with silver, its density is significantly reduced, while also exhibiting excellent electrical properties. Furthermore, by employing appropriate content, the microstructure and mechanical properties of silver alloys can be improved, thereby enhancing the durability of silver alloy sputtering targets by increasing wear resistance and impact resistance.

[0033] Furthermore, the aforementioned silver alloy composition may further contain 0.1% to 1.0% by weight of indium (In), and considering overall corrosion resistance, heat resistance, sheet resistance, and reflectivity, it is preferable to contain 0.1% to 0.5% by weight of indium (In). In this case, the silver content can be adjusted according to the amount of indium added.

[0034] Indium is ductile and does not readily oxidize in air. In particular, it exhibits strong corrosion resistance by inhibiting the reaction with sulfur, a common reaction in silver alloys. Therefore, it has been used in silver alloys since ancient times due to its suitability for applications requiring corrosion resistance. Adding more indium can improve corrosion resistance while maintaining ductility.

[0035] Furthermore, as an additive element, it may include at least one element from the group consisting of copper (Cu), chromium (Cr), germanium (Ge), nickel (Ni), palladium (Pd) and platinum (Pt).

[0036] The added element is an element that is not easily soluble in silver (Ag) and is introduced as a dopant to prevent aggregation and grain growth, thereby preventing migration and suppressing the occurrence of hillocks.

[0037] Using this composition, silver alloy compositions with a grain size of 50 to 150 μm can be manufactured through melting, forging, rolling, and heat treatment processes.

[0038] The method for manufacturing a silver alloy composition according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0039] Figure 1 This is a flowchart illustrating a method for manufacturing a silver alloy composition according to an embodiment of the present invention.

[0040] The silver alloy composition according to embodiments of the present invention can be manufactured by processes of melting and casting, hot forging, milling, heat treatment, rolling, final heat treatment and final machining.

[0041] A preferred embodiment of the manufacturing method, by way of example, includes: (a) manufacturing a casting using alloying elements and by melting and casting (S10); (b) ensuring a uniform structure by hot forging (S20); (c) removing the oxide layer by milling (S30); (d) performing heat treatment to facilitate structural softening and machining (S40); (e) performing rolling (S50); (f) performing a final heat treatment to ensure fine grains (S60); and (g) ensuring dimensions by final machining (S70).

[0042] The following details each step.

[0043] (1) Castings are made by melting and casting alloying elements (S10).

[0044] First, 97% to 99.5% by weight of silver and 0.5% to 3% by weight of lithium (Li) are placed in a high-frequency induction furnace. Argon (Ar) and charcoal are used to block the reaction with external oxygen, while stirring for 30 minutes to 2 hours. At this point, as an additive element, indium (In) or at least one element from the group consisting of indium and copper (Cu), chromium (Cr), germanium (Ge), nickel (Ni), palladium (Pd), and platinum (Pt) can be added. This additive element can then replace a portion of the silver or lithium content.

[0045] Meanwhile, the crucible for the furnace is preferably a carbon crucible or other crucible with low oxygen content. When using a high-frequency induction furnace for stirring, care should be taken to prevent the segregation of alloying elements. The melting temperature varies slightly depending on the alloy composition, but is preferably in the range of 1,000 to 1,300°C.

[0046] Once the molten state stabilizes, the molten material is poured into a mold by tilting to create ingots. Regarding the type of mold, in addition to carbon molds with low oxygen content, iron molds or alumina molds can also be used. To confirm the alloy content of the casting, inductively coupled plasma (ICP) analysis can be performed. If the alloy composition exceeds the specified range, remelting is preferred. If the ICP analysis results show no problems, the next process is performed.

[0047] (2) A uniform microstructure (S20) is formed by hot forging.

[0048] The casting is placed in an atmospheric heat treatment furnace and heat-treated at 800-1000°C for 1 hour, then placed on a forging machine. To ensure a uniform microstructure of the silver alloy composition, forging is carried out in parallel along the width and length directions, while taking care to prevent cracking.

[0049] At this point, the reduction ratio is ideally between 50% and 80%. When the reduction ratio is below 50%, the molten structure does not fracture, while when the reduction ratio exceeds 80%, the likelihood of crack formation increases. This hot forging process refines the casting structure to ensure a uniform microstructure.

[0050] After the required dimensions are obtained through forging, the composition of various locations in the casting can be analyzed using X-ray fluorescence spectrometry (XRF). If the analysis results are satisfactory, the next process is executed.

[0051] (3) Remove the oxide layer by milling (S30).

[0052] The casting is placed on a milling machine, and a milling cutter is used to perform longitudinal face milling. Milling removes the surface oxide layer and microcracks that occurred during forging. After obtaining dimensions suitable for later processing, the next process is performed.

[0053] If the oxide layer on the surface is not sufficiently removed, the resistivity of the target surface will increase, or cracks may appear in the oxide film during the rolling process. Therefore, this problem can be solved by the milling process.

[0054] (4) Perform intermediate heat treatment (S40) on the casting.

[0055] The purpose of intermediate heat treatment is to soften the microstructure of the casting. Intermediate heat treatment is suitable to be performed at 600°C to 800°C. This is because if the temperature exceeds 800°C, the properties of the silver alloy may deteriorate due to the coarsening of alloying elements; if the temperature is below 600°C, it is not suitable to ensure the softening of the silver alloy microstructure. Heat treatment of the casting ensures a hardness suitable for rolling processes. After heat treatment, the next process is performed.

[0056] (5) Rolling is performed on the heat-treated castings (S50).

[0057] Rolling is performed in both the length and width directions, with the reduction rate preferably in the range of 40% to 80%. If the reduction rate exceeds 80%, the likelihood of cracks occurring during rolling is higher, while if the reduction rate is below 40%, the casting structure generated during the casting process will not fracture, making it difficult to ensure a uniform microstructure after rolling and heat treatment.

[0058] Rolling is performed in the width direction until the target width is achieved, then the rolling process is switched to the length direction until the target length is achieved. After width and length rolling, each location is checked for cracks and corrected. Once rolling is complete, the next process is executed.

[0059] Alternatively, if the target shape is cylindrical, the heat-treated casting can be extruded and stretched to form a cylindrical shape instead of being rolled.

[0060] (6) Perform final heat treatment (S60).

[0061] The final heat treatment can be carried out at a temperature of 400°C to 600°C for 50 to 70 minutes. This results in a more homogeneous microstructure and finer grains, thereby improving the film's properties. After heat treatment, warpage is corrected using a press, leveler, etc. Correcting warpage is crucial to minimize losses during final processing.

[0062] After rolling, the grain size is determined by the final heat treatment. Recrystallization will not occur at temperatures below 400°C, so there will be significant deviations depending on the location. Temperatures above 600°C will cause grain growth, so when used as a sputtering target, it will become the cause of accelerated deposition rate or abnormal discharge.

[0063] This process ensures uniform grain size. The grain size of the microstructure is controlled below 150 μm, and preferably below 100 μm to ensure uniform film properties. After heat treatment, the next process is performed.

[0064] (7) Perform final processing (S70).

[0065] The heat-treated product is machined to size using CNC machine tools. Through roughing and finishing, the surface roughness is reduced to below 1.0 μm. When the surface roughness exceeds 1.0 μm, the possibility of arcing or spattering increases during sputtering using a target. After post-processing steps such as cleaning, a silver alloy composition can finally be manufactured.

[0066] The silver alloy composition manufactured in this way has good reflectivity when used as a conductive deposition layer formed by sputtering target, and has excellent corrosion resistance and heat resistance, so it is suitable for simultaneous application in display electrodes and reflective films.

[0067] Next, an embodiment of a silver alloy composition according to one embodiment of the present invention will be described in detail. The following embodiments and comparative examples illustrate only one implementation of the present invention, and the scope of the present invention is not limited to the following embodiments and comparative examples.

[0068] [Example 1]

[0069] To investigate the effects of this invention, silver with a purity of 99.9% or higher and lithium with a purity of 99.99% or higher, as additives, were prepared and placed in a graphite crucible, which was then placed in a high-frequency induction furnace. For the melting process, silver and lithium were simultaneously injected, and argon and charcoal were used to block contact with oxygen while melting. At this time, the lithium content was adjusted to 0.5% by weight. The molten alloy metal was thoroughly stirred by induction heating, and then silver alloy ingots were manufactured using cast iron molds. Subsequently, the ingots were heat-treated at 800-1000°C for 1 hour, then forged. After removing the oxide layer by milling, an intermediate heat treatment was performed at 600-800°C. The heat-treated silver alloy ingots were then repeatedly rolled in both the length and width directions to elongate them. This process resulted in a reduction rate of 40-80%. Furthermore, after the final heat treatment, a leveler is used to correct the warping, and the roughness is polished to below 1.0 μm while ensuring the required dimensions through final machining, thereby producing a silver alloy target with a diameter of 101.6 mm.

[0070] [Example 2]

[0071] Silver with a purity of 99.9% or higher and lithium (Li) with a purity of 99.99% or higher as an additive were prepared. The lithium was adjusted to a weight ratio of 1.0% by weight, and a silver alloy target with a diameter of 101.6 mm was manufactured by the same manufacturing method as in Example 1.

[0072] [Example 3]

[0073] Silver with a purity of 99.9% or higher and lithium (Li) with a purity of 99.99% or higher as an additive were prepared. The lithium was adjusted to a weight ratio of 1.5% by weight, and a silver alloy target with a diameter of 101.6 mm was manufactured by the same manufacturing method as in Example 1.

[0074] [Example 4]

[0075] Silver with a purity of 99.9% or higher and lithium (Li) with a purity of 99.99% or higher as an additive were prepared. The lithium was adjusted to a weight ratio of 2.0% by weight, and a silver alloy target with a diameter of 101.6 mm was manufactured by the same manufacturing method as in Example 1.

[0076] [Example 5]

[0077] Silver with a purity of 99.9% or higher and lithium (Li) with a purity of 99.99% or higher as an additive were prepared. The lithium was adjusted to a weight ratio of 2.5% by weight, and a silver alloy target with a diameter of 101.6 mm was manufactured by the same manufacturing method as in Example 1.

[0078] [Example 6]

[0079] Silver with a purity of 99.9% or higher and lithium (Li) with a purity of 99.99% or higher as an additive were prepared. The lithium was adjusted to a weight ratio of 3.0% by weight, and a silver alloy target with a diameter of 101.6 mm was manufactured by the same manufacturing method as in Example 1.

[0080] [Example 7]

[0081] Silver with a purity of 99.9% or higher and lithium (Li) and indium (In) with a purity of 99.99% or higher as additives are prepared. The lithium content is adjusted to 0.5% by weight and the indium content is adjusted to 0.5% by weight. A silver alloy target with a diameter of 101.6 mm is manufactured by the same manufacturing method as in Example 1.

[0082] [Example 8]

[0083] Silver with a purity of 99.9% or higher and lithium (Li) and indium (In) with a purity of 99.99% or higher as additives are prepared. The weight ratio of lithium is adjusted to 1.0% by weight and the weight ratio of indium is 0.5% by weight. A silver alloy target with a diameter of 101.6 mm is manufactured by the same manufacturing method as in Example 1.

[0084] [Comparative Example 1]

[0085] Silver with a purity of 99.9% or higher and indium (In) with a purity of 99.99% or higher were prepared as additives. The indium content was adjusted to 0.5% by weight, and a silver alloy target with a diameter of 101.6 mm was manufactured using the same manufacturing method as in Example 1. That is, lithium was excluded, and only indium, one of the existing components of silver alloys, was added.

[0086] [Comparative Example 2]

[0087] Prepare silver with a purity of 99.99% or higher, and manufacture a pure silver target with a diameter of 101.6 mm using the same manufacturing method as in Example 1.

[0088] Subsequently, thin films were formed using the fabricated target via DC magnetron sputtering, and the films were evaluated. This was done under an initial vacuum atmosphere of 1.0 x 10⁻⁶. -4 Deposition was carried out under conditions of less than Pa, a gas flow rate of 10 sccm, and a working pressure of 0.15 Pa. Thin film properties were analyzed, including sheet resistivity, reflectivity, heat resistance, and corrosion resistance.

[0089] Evaluation of reflective film applications

[0090] Reflective films were formed using the targets of Examples 1-8 and Comparative Examples 1-2, and evaluated. After depositing a film thickness of 100 nm (1000 Å), sheet resistance, reflectivity at a wavelength of 450 nm, heat resistance, and corrosion resistance were evaluated. Heat resistance was evaluated by observing film damage over time after maintaining a temperature of 85°C and humidity of 85%. Corrosion resistance was evaluated in an atmosphere of H2S and NO2, with film damage observed after maintaining the conditions at 0.1 ppm for 24 hours. For heat resistance and corrosion resistance, pure silver was used as a baseline of 1, and the best performance was set as 5, with evaluations divided into levels from 1 to 5. These evaluation results are summarized in Table 1.

[0091] Table 1

[0092]

[0093] The evaluation results show that the reflective film formed using the target material of the example exhibits superior overall properties in terms of heat resistance and corrosion resistance compared to the reflective film formed using the target material of the comparative example.

[0094] Meanwhile, in compositions containing only lithium in silver, Examples 3 and 4 demonstrated improved heat resistance and corrosion resistance while maintaining high levels of sheet resistance (below 1 Ω / sq) and reflectivity (above 95%). Therefore, to achieve such results, a lithium content of 1.5% to 2.0% by weight is considered suitable.

[0095] Furthermore, the compositions of Examples 7 and 8, which added indium to the compositions of Examples 1 and 2, exhibited the best properties in terms of sheet resistance, reflectivity, heat resistance, and corrosion resistance. Therefore, to achieve such results, a lithium content of 0.5% to 1.0% by weight and an indium content of less than 0.5% by weight (specifically, 0.1% to 0.5% by weight) is expected to be suitable.

[0096] Although the foregoing detailed description of the invention has been described with reference to preferred embodiments of the invention, it should be understood by those skilled in the art or those with general knowledge in the art that various modifications and alterations can be made to the invention without departing from the spirit and technical scope of the invention as described in the technical solutions.

Claims

1. A silver alloy composition containing 0.5 to 3.0% by weight of lithium (Li) and the balance being silver (Ag) and unavoidable impurities.

2. The silver alloy composition according to claim 1, wherein: It also contains more than 0.1% by weight and less than 1.0% by weight of indium (In).

3. The silver alloy composition according to claim 2, wherein: It also contains at least one element from the group consisting of copper (Cu), chromium (Cr), germanium (Ge), nickel (Ni), palladium (Pd), and platinum (Pt).

4. A method for manufacturing a silver alloy composition, comprising: The first step involves adding a component containing 0.5 to 3.0% by weight of lithium and the balance being silver and unavoidable impurities in a high-frequency induction furnace at 1,000 to 1,300°C, and stirring under atmospheric atmosphere. The second step involves pouring the molten components from the first step into a mold to manufacture the casting. The third step involves heating and forging the casting produced in the second step to form the forging. The fourth step is to remove the oxide layer from the surface of the forging after the third step has been completed; The fifth step involves subjecting the forgings that have completed the fourth step to a first heat treatment at a temperature of 600 to 800°C. The sixth step involves rolling the material that has undergone the first heat treatment in the fifth step. The seventh step involves subjecting the material that has completed the sixth step to a second heat treatment at a temperature of 400 to 600°C. The eighth step involves processing the material from the seventh step into a specific shape.

5. A silver alloy target material, manufactured by the manufacturing method of claim 4, It has a composition containing 0.5 to 3.0% by weight of lithium and the balance being silver and unavoidable impurities. Used for forming reflective films and electrodes for displays.

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