OLED is a popular display technology that uses organic semiconductors and luminescent materials to emit light when charge carriers are injected and recombined under an electric field. It offers several advantages, including thinner TV screens, wider viewing angles, lower power consumption, and more vibrant colors.
In OLED manufacturing, emitting materials and metal electrodes are deposited using vapor deposition. The materials are heated in a vacuum chamber until they vaporize and coat the substrate. Crucible quality directly impacts yield. Choosing the wrong crucible can lead to incomplete deposition and increased costs.
Material Selection for OLED Evaporation Crucible
Common materials used for OLED evaporation crucibles include tungsten, molybdenum, tantalum, metal oxides, ceramics, and graphite. It is crucial to consider the compatibility between the crucible material and the evaporated substances. Next, we will compare the following three commonly used materials of crucibles.
Tantalum (Ta)
Tantalum (Ta) is a rare transition metal known for its excellent properties. It is highly ductile, chemically stable, and has a high melting point of 2996°C. Tantalum is primarily found in tantalite ore and is commonly used in various applications due to its moderate hardness and exceptional ductility. One of its main advantages is its exceptional corrosion resistance. It does not react with hydrochloric acid, concentrated nitric acid, or aqua regia, even at high temperatures. This resistance is due to the formation of a stable oxide layer, tantalum pentoxide (Ta2O5), on its surface, which acts as a protective barrier against further oxidation and degradation. Therefore, it can be used as a crucible material for vacuum vapor deposition parts.
Graphite
Graphite is commonly used to make crucibles for melting alloys in small quantities. It has excellent high-temperature performance and a long lifespan. Graphite crucibles are widely used in large-scale alloy smelting, casting processes, and ore melting analysis. They have good resistance to liquid and gas penetration, high-temperature resistance, and can suppress dust generation.
Pyrolytic Boron Nitride(PBN)
Pyrolytic Boron Nitride (PBN) is an advanced ceramic material known for its hexagonal crystal structure. It is ivory white, non-toxic, and highly pure (up to 99.999%). PBN exhibits resistance to acids and alkalis, good thermal conductivity, excellent surface density, high-temperature resistance, and is non-porous and easy to process. It is produced through chemical vapor deposition using boron-containing gases (BCl3 or B2H6) under high-temperature, high-vacuum conditions. BCl3 is commonly preferred over B2H6 due to its lower toxicity. PBN growth is similar to the accumulation of hexagonal BN snowflakes on a heated graphite substrate.
PBN crucibles, known for their high purity, can withstand temperatures up to 1800°C under a vacuum and up to 2100°C under a nitrogen or argon atmosphere. They find applications in evaporation deposition, molecular beam epitaxy (MBE), and GaAs crystal growth. However, PBN crucibles are expensive and typically available in small sizes due to their slow deposition rate.
How to choose a crucible?
Crucible selection depends on specific production requirements and processes. Different materials have different boiling points, so customized crucibles are necessary for adequate deposition. Factors like density and thermal conductivity also need to be considered. Customized production is often required for optimal results in OLED deposition.
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