Composition of MOSFET
In a test pattern the Photomicrograph of two metal-gate MOSFETs. Probe pads for two gates and three source or drain nodes are entitled.Generally the semiconductor of choice is silicon, but various chip manufacturers, most notably IBM and intel, currently started using a chemical compound of silicon and germanium (SiGe) in MOSFET channels. Unfortunately, several semiconductors with better electrical properties than silicon, like gallium arsenide, do not make good semiconductor-to-insulator interfaces, so are not suitable for MOSFETs. Research carries on creating insulators with acceptable electrical characteristics on another semiconductor material.
In order to conquer power consumption increase because of gate current leakage, high-κ dielectric replaces silicon dioxide for the gate insulator, whereas metal gates return by replacing polysilicon.The gate is separated from the channel through a thin insulating layer, usually of silicon dioxide and later of silicon oxynitride. A number of companies have started to introduce a high-κ dielectric + metal gate combination in the 45 nanometer node.
While a voltage is applied in between the gate and body terminals, the electric field generated penetrates by the oxide and creates an "inversion layer" or "channel" at the semiconductor-insulator interface. The inversion channel is of similar type, P-type or N-type, as the source and drain, so it gives a channel via which current can pass. Varying the voltage in between the gate and body modulates the conductivity of this layer and permits to control the current flow among the drain and source.