Question

9.) Describe and diagram in detail how a MOS-FET works. Include a description of channel formation and pinch-off.

Answer 1

Other than the technical definition of what a MOSFET is, the best way to 'intuitively' see a MOSFET is to imagine it being a pipe which passes water through it.

Pipe is controlled by a valve which can open or close, thus controlling whether the water is going through the pipe or not. This is how MOSFETs are used as switches to control the flow of current and this is how the digital electronics is built. You can imagine using several of these pipes to implement NOR, NAND, XOR operations etc. which can then be combined to give additions, subtractions, multiplications etc. This is the basis of a basic computer.

Now, there is one more interesting property of the pipe. The valve when operated in a certain region, can not only control whether the water flows or not, but rather decide 'the shape' of the water as well. Hence, a small little valve can control a 'huge' amount of water. This is the basis of amplification and analog electronics.

Now to put it in terms of actual jargon, a small amount of voltage at the gate of the MOSFET can control a huger and much bigger amount of voltage through the channel. The shape at the gate of the voltage is 'reproduced' within the channel, but with amplification. So a 1mV sine wave at the gate can become 1V sine wave through the channel. This is almost like magic!