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This term is a popular shortening of polycrystalline silicon. Polysilicon consists of many grains of crystalline silicon with abrupt discontinuities between grains. Because polysilicon does not have perfect crystalline structure, it is more electrically resistive than crystalline Si.

Highly-doped polysilicon is used as the MOSFET gate in modern integrated circuits. While polysilicon is an inferior gate material to metal--it is more resistive and suffers from the "depletion effect" which decreases the gate's control of the channel--it has the advantage that it can withstand subsequent high-temperature processing.

Polysilicon is easily deposited by chemical vapor deposition (CVD). The resistance of polysilicon in integrated circuits is usually greatly reduced by the formation of a metal silicide on top. These silicides can withstand high-temperature steps such as dopant annealing. Unfortunately, the depletion effect persists after silicidation.

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