CMos digital integrated circuits by Kang-Leblebici

[chaoseverlasting]

Im using CMos digital integrated circuits by Kang-Leblebici. On p85-86 a description of how a MOS layer works is given which I can't fully understand.

First, the MOS layer is likened to a capacitor. Then they discuss how the work functions and fermi levels of the metal, oxide layer and the semi conductor layer differ. When these layers are put together a bending in the fermi levels of the semi condutor takes place. Also, because of the difference in work functions, a potential drop occurs between the metal and semi conductor layer with the majority of the drop at the semi conductor and oxide junction.

I don't understand the part about the work functions causing a potential drop and the fermi layer bending. Why does the layer bend at all? Why doesn't the fermi layer of the metal layer also bend? Also, why is there maximum potential drop across the oxide/semiconductor junction?

Could someone please walk me through this? If any of the questions are not clear enough, please tell me and ill try to be clearer.

 

[chaoseverlasting]

Anybody?

 

[jsgruszynski]

It's not the best way to intuit how MOSFETs work. Good if you want to derive model equations.

Specific to the question: bending occurs because of continuity requirements - contacting two materials together with different work functions requires that they be equal at that point of contact. Thus they must bend.

Better is to consider the electrostatic induction effect of the gate through the oxide and into the semiconductor in terms of Gauss's law. This is how the basic models are derived ab initio for MOSFETs.