OLED Fabrication Techniques 1 - Vacuum Deposition
As a TV user, you may find an OLED TV is much more expensive than a regular LCD TV. Why? Because of OLED difficult fabrication techniques.
This article will introduce one of the OLED fabrication techniques, vacuum deposition for OLED, and the reason why it makes an OLED TV expensive.
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Vacuum Deposition: A technology that heats up materials to vaporize them in a vacuum environment and deposits them onto a glass substrate to form a thin film. Please notice that the so-called vacuum environment does not mean that there is no air at all, but that the pump is used to extract or capture as much air as possible in the cavity so that the air pressure in the cavity is very low.
Condition 1: Vaccum Environment
To support the vacuum deposition technique, the first condition is to create a vacuum environment. Given a shallow air pressure in the cavity, forming a thin film on the glass substrate is easier. Without the so-called vacuum environment, the thin film will be everywhere.
Condition 2: Heat To Vaporize Organic Material
Since the vacuum environment is set up, the second condition for vacuum fabrication is a heating environment. In this environment, organic material is steadily heated and vaporized to ensure it can be deposited onto the glass substrate. The general approach is to place the material on the crucible, then heat the crucible through current or other methods, and allow the material in the crucible to heat up and vaporize. Because there is no interference from other gases in the low-pressure vacuum environment, these vaporized molecules will have a relatively high mean free path and move upward more efficiently. After hitting the top glass substrate, these vaporized molecules will form a thin film due to the condensation effect.
Notes: Some material is hard to be vaporized. Maybe these material needs higher temperature to be vaporized. The organic material we use on OLED TV is just a perfect choice for now.
Condition 3: Necessary Mask
In the process of vacuum evaporation, we often use metal masks to define the locations where materials on the glass substrate need to be deposited. For example, if we aim to form RGB thin film on the glass substrate, we must repeat the process 3 times. When doing the Red thin film, we ensure the metal mask blocks the unnecessary location. Their luminescent layers are evaporated separately, so when we evaporate the luminescent material of red pixels, we need to rely on this metal mask to cover the green and blue components.
Depending on the needs, the metal masks are placed differently so only the wanted place will receive the material.
Vacuum Deposition: Challenge
Vacuum deposition is a smart technique for making an OLED TV. However, it has its own disadvantages: Low material utilization rate and mask-shadow effect.