Test: The Body Effect - Electrical Engineering (EE) MCQ

The voltage difference between the source and the bulk, VBS changes the width of the depletion layer and therefore also the voltage across the oxide due to the change of the charge in the depletion region. This results in a difference in threshold voltage which equals the difference in charge in the depletion region divided by the oxide capacitance.

The change in threshold current is directly proportional to the square root of the drain current. For further assistance check the mathematical expression for the same.

 Vt = Vt0 + k[√(Vsb + 2φf) – √2φf]. In this expression k is the body effect parameter hence its units can be determined.

Vt = Vt0 + k[√(Vsb + 2φf) – √2φf]. use this expression to obtain the desired result.

The threshold voltage depends only on the temperature and it decreases by roughly 2 mV for every degree Celsius increase in the temperature.

As the voltage on the drain is increased, a value is reached at which the pn junction between the drain region and substrate suffers avalanche breakdown. This breakdown usually occurs at voltages of 20 V to 150 V and results in a somewhat rapid increase in current (known as a weak avalanche).

 Punch-through occurs in devices with relatively short channels when the drain voltage is increased to the point that the depletion region surrounding the drain region extends through the channel to the source. The drain current then increases rapidly. Normally, punch-through does not result in permanent damage to the device.

At velocity saturation the current depends linearly on the Vgs.

The breakdown of the oxide at the gate may occur when the voltage is around 30 V. This may also permanently damage the device.

All of the mentioned are some of the common issues that one may face while dealing with MOSFETs.