in IGBT or MOSFET why gate terminal is insulated.

in IGBT or MOSFET why gate terminal is insulated. what is the advantage of insulated gate terminal over base terminal in Transistor..if gate is insulated how is works...
please help meee

There is an electric field between the insulated gate terminal and the source part in a Mos Field Effect Transistor (FET) called a Mosfet. "Mos" is Metal Oxide Semiconductor where it is an insulator.
You can learn about it in school, from books or in Google links.

it means you dont need continuous current to flow to keep it on.

i search a lot but i did not get it ..
please help meee

These are field effect devices. The current is allowed to pass (or not) depends on the electric field. To make an electric field you have to apply a potential to the gate. This is more like a small capacitor where the potential on the gate controls the electric field.

The base of a bipolar transistor needs DC current for the transistor to turn on. The gate of a Mosfet uses a voltage with no DC current (a field effect voltage on the insulated gate) for the Mosfet to turn on.

thank u sir for reply..
can elaborate
when u apply voltage to gate how filed create an current follow in collector to emitter or drain to source ...

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thank u r sir
but can explain
how electric field is crated when u apply voltage to gate terminal and current follow in collector to emitter or drain to source ...

Please refer any text book for details. Here in brief:

You apply a potential to the gate. The gate accepts some charge depending on its capacitance value. Some initial current must flow to charge this capacitor.

Imagine a traditional capacitor with two plates. The two plates have equal charges (but opposite in sign) and it creates an electric field within the dielectric.

In the case of the MOSFET, the substrate is the other electrode of the capacitor. A very high electric field will be setup because of the small gap between the electrodes. (E=v/d)

A significant amount of the electric field is taken over by the insulator but the effect will be felt in the depletion layer (it can also be an enhancement mode). That will modulate the current between the drain and source.

Basically the electric field modulates the number of carriers in this zone. Theoretically speaking, the electron band structure gets distorted by the presence of the strong electric field. As you know, only the top of the band structure is relevant and a small distorting can cause a large effect.