MOSFET stands for metal oxide semiconductor fields effect transistor. A power MOSFET has three terminal drain source and gate,. It is unipolar device means its operations depends upon the flow of one carriers only. The power MOSFET is designed to handle large amounts of power. Compared to the other power semiconductor device s its main advantages are high commutation speed and good efficiency at low voltages. Power MOSFET is a voltage controlled device and it requires only small input current. It has extremely high input impedance and is widely used in switching devices. The power MOSFET is the most widely used low voltage switch and used in low power high frequency converters power suppliers DC to DC converters and low voltage motor controllers. MOSFET have a very thin silicon dioxide layer is kept very thin to ensure that the gate has good control over the gate current. This layer could be destroyed if a voltage higher than rated value is applied to the gate.
figure N - Channel V- MOSFET
Power MOSFET are usually constructed in v shape as shown in because of its v shapes sometimes it is called the v MOSFET or V EFT. V shaped cut penetrates from the device surface almost to the N substrate through N P and N layers as shown in the N layers are made heavily doped low resistive material and the N layers is made lightly doped high resistance region.
Figure symbol of power MOSFET N channel P channel
The silicon dioxide dielectric layer covers both the horizontal surface and v cut surface. The insulated gate is made by depositing a metal film on the silicon dioxide (Sio2) layer in the v cut. Source terminals are made by making a contact to the upper N+ and P layers through the layer. The drain terminal is made by N+ substrate of the device. The power MOSFET is an enhancement type MOSFET and in this type of MOSFET there is no channel exists between drain and source until the gate is positive with respect to the source. The symbol of power MOSFET is shown in this type of MOSFET there is an enhancement type and source until the gate is positive with respect to the source. The symbol of power MOSFET.