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Basic Doubts in MOSFET..

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subbuindia

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Hi friends,

I have a few general doubts about MOSFETs.

1)Is it need to maintain same size and same doping for both source and drain.? If, why.?

2)What is the need of SiO2 for only gate and why not for source, drain.?

3)Why do we choose CMOS when MOSFET(NMOS) is present.?

Please, kindly reply these questions. I studied the concepts, but I didn't get any clarity..
 

Anand Cool B

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Hi friends,

I have a few general doubts about MOSFETs.

1)Is it need to maintain same size and same doping for both source and drain.? If, why.?

2)What is the need of SiO2 for only gate and why not for source, drain.?

3)Why do we choose CMOS when MOSFET(NMOS) is present.?

Please, kindly reply these questions. I studied the concepts, but I didn't get any clarity..



Good questions
I will explain these according to my understanding of the concepts
1)There is a counter doping which is followed for source and drain formation.The source and drain terminals are interchangeable so it will be good for the flow of current and the parasitics which get formed will be same if both are of the same size.For calculation of currents and transistor working regions by considering same areas parasitics will be easy.Go through miller capacitances you will get a clear idea about this.
2)As u might be knowing the gate with the substrate acts as a capacitor and silicon dioxide is nothing but the dielectric.So the gate with the dielectric helps in the formation of channel where as if Silicon dioxide was not present it would be like 2 metal plates shorted.For source and drain the metal is connected so no need of silicon dioxide there but to separate the transistors from neighbouring transistors LOCOS or STI processes are followed.
3)I dont know the gut level understanding as to why but with CMOS power dissipation will be less when compared to NMOS logic.

- - - Updated - - -

And the source area and the drain area is maintained as minimum as possible(as of DRC) because it can even reduce area.
 
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