Gas: key materials for display manufacturing

- Jul 27, 2018-

About backplane/TFT

The thin-film transistor used in the display is a 2D gradation transistor, similar to the bulk CMOS before FinFET. The active matrix display has one transistor per pixel that drives an RGB color inside the transistor. As display resolution increases, transistors become smaller, but do not shrink to sub-micron dimensions of semiconductor devices. For example, a smart watch with a pixel density of 325 PPI has a transistor size of about 2 mm2, while a 4 K TV with an 80 PPI pixel density has a transistor size of about 8 mm2.

Backplane type

There are three main types of thin film transistor devices for display screens: amorphous silicon (a-Si), low temperature polysilicon (LTPS), and metal oxide (MO), also known as transparent amorphous oxide semiconductors (TAOS). AM-LCD panels use a-Si for low-resolution displays and televisions, while high-resolution displays use LTPS transistors. However, due to their high cost and limited scalability, they are commonly used in small and medium-sized displays. AMOLED panels use LTPS and MO transistors, where MO devices are commonly used in televisions and large displays (Figure 3).

How the gas is used

Due to technological changes, the gases required to produce AMOLED panels also change compared to AMLCD panels. As shown in Figure 4, a variety of gases are currently used in the production of displays.


These gases can be divided into two categories: electronic specialty gases (ESG) and electronic bulk gases (EBG). Electronic specialty gases include silane, nitrogen trifluoride, fluorine (on-site), sulfur hexafluoride, ammonia, and phosphine mixtures, accounting for 52% of the gases used in display manufacturing, while electronic bulk gases include nitrogen and hydrogen. Helium, oxygen, carbon dioxide and argon account for 48% of the gas used in display manufacturing.