As its name implies, Physical Vapor Deposition (PVD) is a physical, rather than chemical process. In this technology, ions of a heavy, but inert, gas (typically argon) are electrically accelerated in a high vacuum toward a "target" of source material. These ions essentially chip off or "sputter" the target material, atom by atom. This sputtered material (pure metal or alloys, transparent conductive oxide (TCO)and metal oxide) deposits on the substrate, much like the way snow accumulates on a surface. The high-vacuum environment in the process chamber lets the atoms combine into grains of target material, which will then be patterned and etched to form the transistor structure and conducting circuits in a display.