Metal Gate

A metal gate, in the context of a lateral Metal-Oxide-Semiconductor MOS stack, is just that--the gate material is made from a metal. For decades, the industry had moved away from metal as the gate material in the MOS stack due to fabrication complications. A material called Polysilicon (silicon, highly doped with donors or acceptors) was used instead because it can be deposited easily and is tolerant to subsequent manufacturing steps which involve extremely high temperatures (in excess of 900-1000 degrees Celsius), where metal was not. Furthermore, metal has a tendency to disperse into silicon during these Thermal Annealing steps.
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a type of MOS device that uses metal as the gate electrode.