Semiconductor devices - MOSFET
Semiconductor device tutorial
Semiconductor devices - MOSFETs
Semiconductor l oxide field effect transistors , also known as name of MOSFET, have greater significance and are a new addition to the FET family.
It has a lightly doped P-type substrate in which two heavily doped N-type areas are diffused. A unique feature of this device is its door construction. Here, the portal is completely isolated from the canal. When a voltage is applied to the grid, it will develop an electrostatic charge.
At this point, no current is allowed to flow through the grid area of the device. In addition, the door is an area of the device, which is covered with l. Usually, silicon dioxide is used as an insulating material between the gate and the channel. For this reason, it is also known as the Insulated Gate FET . There are two widely used MOSFETs:i) Depletion MOSFET ii) Enhancement MOSFET.
The following figures show the n-channel D-MOSFET and the symbol. The grid forms a capacitor with a grid like a plate, and the other plate is the channel with a layer of SiO 2 as dielectric. As the gate voltage varies, the electric field of the capacitor changes, which in turn changes the resistance of the n-channel.
In this case, we can apply positive or negative voltage to the door. When the MOSFET works with negative gate voltage it is called depletion mode and when it is used with positive gate voltage it is called MOSFET enhancement mode of operation.
The following figure shows an n-channel D-MOSFET in exhaustion operating mode.
It works as follows -
Most electrons are available on the gate as the grid is negative and it repels electrons from the channel n .
This action leaves positive ions in the part of the channel. In other words, some of the free electrons in the n channel are depleted. As a result, fewer electrons are available for current conduction through the n channel.
The higher the negative voltage at the gate, the lower the current from source to drain. So we can change the resistance of channel n and the current from source to drain. drain by varying the negative voltage on the gate.
The following figure shows the n channel D MOSFET in operating mode d 'improvement. Here the gate acts as a capacitor. However, in this case the gate is positive. It causes theelectrons in the n channel and the number of electrons increases in the n channel.
A positive gate voltage improves or increases the conductivity of the channel. The greater the positive voltage on the gate, the greater the conduction from source to drain.
So we can change the resistance of channel n and the current from source to drain by varying the positive voltage on the portal.
Transfer characteristics of D-MOSFET
The following figure shows the transfer characteristics of D-MOSFET.
When V GS becomes negative, I D falls below the value of I DSS , until it reaches zero and V GS = V GS (off) (exhaustion mode). When V GS is zero, I D = I DSS because the gate and the source terminals are short-circuited. I D increases above the value of I DSS , when V GS is positive and the MOSFET is in enhancement mode.