MOSFET - Wikipedia, the free encyclopedia

MOSFET - Wikipedia, the free encyclopedia -  MOSFET...

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Unformatted text preview:  MOSFET From Wikipedia, the free encyclopedia Jump to: navigation , search The metal–oxide–semiconductor field-effect transistor ( MOSFET , MOS-FET , or MOS FET ) is a device used to amplify or switch electronic signals. It is by far the most common field-effect transistor in both digital and analog circuits. The MOSFET is composed of a channel of n-type or p-type semiconductor material (see article on semiconductor devices ), and is accordingly called an NMOSFET or a PMOSFET (also commonly nMOSFET, pMOSFET). Contents • 1 Etymol ogy • 2 Compo sition • 3 Circuit symbol s • 4 MOSF ET operati on • 4 . 1 M e t a l – o x i d e – s e m i c o n d u c t o r s t r u c [ edit ] Etymology The 'metal' in the name is now often a misnomer because the previously metal gate material is now a layer of polysilicon (polycrystalline silicon; why polysilicon is used will be explained below). Previously aluminium was used as the gate material until the 1980s when polysilicon became dominant, owing to its capability to form self-aligned gates . IGFET is a related, more general term meaning insulated-gate field-effect transistor , and is almost synonymous with MOSFET, though it can refer to FETs with a gate insulator that is not oxide. Some prefer to use "IGFET" when referring to devices with polysilicon gates, but most still call them MOSFETs. [ edit ] Composition Photomicrograph of two metal-gate MOSFETs in a test pattern. Probe pads for two gates and three source/drain nodes are labeled. Usually the semiconductor of choice is silicon , but some chip manufacturers, most notably IBM , have begun to use a mixture of silicon and germanium ( SiGe ) in MOSFET channels. Unfortunately, many semiconductors with better electrical properties than silicon, such as gallium arsenide , do not form good semiconductor-to-insulator interfaces and thus are not suitable for MOSFETs. However there continues to be research on how to create insulators with acceptable electrical characteristics on other semiconductor material. To overcome power consumption increase due to gate current leakage, high-κ dielectric is replacing silicon dioxide as the gate insulator, and metal gates are making a comeback by replacing polysilicon (see Intel announcement [1] ). The gate is separated from the channel by a thin insulating layer of what was traditionally silicon dioxide, but more advanced technologies used silicon oxynitride. Some companies have started to introduce a high-κ dielectric + metal gate combination in the 45 nanometer node. When a voltage is applied between the gate and source terminals, the electric field generated penetrates through the oxide and creates a so-called "inversion layer" or channel at the semiconductor-insulator interface. The inversion channel is of the same type – P-type or N-type – as the source and drain, so it provides a conduit through which current can pass. Varying the voltage between the gate and body modulates the conductivity of this layer and makes it possible to control the current flow between drain and source. [...
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This note was uploaded on 09/29/2010 for the course GENERAL AR ECE 250 taught by Professor Drcapps during the Spring '10 term at N.C. State.

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MOSFET - Wikipedia, the free encyclopedia -  MOSFET...

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