FET (Field Effect Transistor)
FET, a type of semi-conducting device which is comparatively more efficient than so called BJT’s .
FET can described to be a device which controls output current by changing voltage at one of the transistor terminals and it requires less input current than BJT.
They are of two types,
- Junction-Gate Field Effect Transistors.
- Metal-Oxide Field Effect Transistors.
MOSFET’s (Metal-Oxide Field Effect Transistors) are the one which are widely used.
MOSFET has 3 terminals all made of metal, those are source, gate and drain. Source and drain are connected to two separate region of n-type semiconductor which are separated by a p-type semiconductor region. Along one side of p-type there is a thin layer of silicon dioxide. The layer serves support to gate terminal and insulates it from p-region. Gate can be polysilicon (has capability to form self-aligned gates) or metallic gates (which have the ability to increase the speed of operation).
In MOSFET’s the current cannot flow between source and gate until a positive voltage is given to gate, this electric field which the gate produces extends through the oxide layer. This field then draws electrons from p-type region into a thin channel along the oxide layer. Thus the channel forms a conductive path in the p-type region between the source and the drain, allowing current to flow between the source and the drain.
A small change in the applied gate voltage results in large change in current between the source and drain. It is used as a switch because if no voltage is applied to the gate terminal then the current in source-drain circuit is completely blocked or if voltage is applied then the resistance offered to current flow in the source-drain circuit is eliminated depending on the voltage applied to gate.I hope u like this post....! if any queries, you can mail or post a comment.! if u would like to know anything about other electronic device..i would be happy to explain it to u..!! please do comment..!
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