Performance Comparison of Crucibles for OLED Evaporation: Tantalum, Graphite and Boron nitride

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According to the latest quarterly analysis of the natural gas market released by the International Energy Agency, global natural gas consumption will decline slightly this year and increase slowly in the following years because of soaring prices and the possibility of further reductions in Russian natural gas supplies. Global natural gas use this year is expected to be 0.5% lower than the 2021 level, and global natural gas demand is expected to increase by only 140 billion cubic meters over 2021 by 2025, the report said. The annual growth in 2021 will reach 175 billion cubic meters.

At the same time, the IEA's forecast for natural gas demand growth by 2024 was 60 per cent lower than its previous forecast, mainly due to "a weak economy and a smaller energy shift from coal or oil to natural gas", the report said.

It is worth noting that the South Korean Ministry of Industry, Trade and Resources announced on the same day that it plans to increase the proportion of nuclear power in South Korea's national energy structure to more than 30% by 2030. The proportion is 27.4% in 2021. The department also announced the resumption of the construction of two nuclear reactors. According to reports, after taking office, South Korean President Yoon Sik-Yue rejected the previous government's plan to phase out nuclear power and promised to increase investment in the nuclear power industry, so as to regain South Korea's status as a major exporter of safe nuclear reactors.

In addition, the supply and prices of many international bulk graphite powder are still very uncertain.

When it comes to display technology, in addition to the traditional LCD and LED liquid crystal display screen, OLED (organic light emitting diode) display technology has become a new mainstream.

OLED technology refers to the phenomenon of luminescence caused by carrier injection and recombination of organic semiconductor materials and light-emitting materials driven by electric field. As a solid-state self-illumination technology, OLED does not need to use the combination of LCD and LED backlight before, so it can make the TV thickness very thin, wider visual angle, lower power consumption, richer colors, and can be produced on different flexible substrate materials such as plastic, resin, etc., to achieve soft screen, so it is more and more popular by consumers.

In the manufacturing process of OLED, "evaporation" is both the essence and the difficulty. It means that in high vacuum, the material to be evaporated is heated by resistance or electron beam, and the OLED material is heated by crucible in the vacuum cavity to make the atoms evaporate and reach and attach to the surface of the substrate.

In OLED, in addition to luminous materials, even metal electrodes are steamed in this way, so the quality of the crucible directly affects the yield of the OLED process. If the unsuitable crucible is selected, the material in the crucible will not be evaporated completely, which cannot reach the boiling point required by the equipment, and cannot be attached to the surface of the substrate, resulting in the ineffective application of the evaporation material, the poor yield of the process and the burden of raw material cost.

Material of Crucibles For OLED Evaporation

The commonly used supports include W, Mo, Ta, high temperature resistant metal oxides, ceramic or graphite crucibles, etc., but it should also be noted that there may be reactions between the supporting materials and evaporation. At present, the OLED evaporation materials are mainly organic and metal, and the crucibles of the following three materials can be used.

Tantalum (Ta):

Tantalum is a kind of hard blue-gray rare transition metal. It has high ductility and high chemical stability. It does not react with other compounds and its melting point is as high as 2996 °C. it mainly exists in tantalite. Tantalum is of moderate hardness and malleable and can be drawn into thin wire foil. Its coefficient of thermal expansion is very small. Tantalum has excellent chemical properties and high corrosion resistance. It does not react to hydrochloric acid, concentrated nitric acid and "aqua regia" under both cold and hot conditions.

Tantalum can be used to make evaporating utensils, as well as electrodes, rectifiers and electrolytic capacitors of electronic tubes. it is often used as a secondary component of alloys and is medically used to make thin sheets or threads to repair damaged tissue. The corrosion resistance of tantalum mainly comes from the stable tantalum pentoxide (Ta2O5) protective film formed on its surface, which can resist oxidation very well, so it can be used as crucible material for vacuum evaporation parts. Tantalum is needed for many corrosion-resistant parts.

Graphite

Graphite is a kind of crystalline carbon. The colors are dark black, iron ink to dark gray. The melting point is 3652℃ and the boiling point is 4827℃. It is soft, smooth, conductive and inactive in chemical properties, and is not easy to react with acid and alkali, so it is often used to make crucibles, which is the most suitable crucible for melting of many kinds and small quantities of alloys. because of its good high temperature performance and long service life, it is used in large-scale alloy smelting casting process and ore melting analysis. At the same time, the graphite crucible has good anti-permeability of liquid and gas, can withstand high temperature and restrain the graphite powder prices are expected to rise in the future.

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