What is Polycrystalline Silicon?

Polycrystalline Silicon - also referred to as "polysilicon" or "Poly-Si" is a material consisting of multiple small silicon crystals and has long been used as the conducting gate material in MOSFET and CMOS processing technologies. For these technologies, Polycrystalline Silicon is deposited using LPCVD reactors at high temperatures and is usually heavily n or p-doped. The main advantage of Polycrystalline Silicon over other types of silicon is that the mobility can be orders of magnitude larger and the material also shows greater stability under electric field and light-induced stress. This allows far more complex, high-speed electrical circuits that can be created on the glass substrate along with the amorphous silicon devices, which are still needed for their low-leakage characteristics.

When Polycrystalline Silicon and Amorphous Silicon devices are used in the same process, this is called "hybrid processing."

A complete Polycrystalline Silicon active layer process is also used in some cases where a small pixel size is required, such as in projection displays.