VLSI layout design query

[Yeahia Been Sayeed]

1.why do we use as much contacts during connecting different layers?explain elaborately please.
2.what will happen if we don't use any body connection tap?please explain broadly

 

[helioforero]

1. To answer the first Question easily you should think of the resistance between layers, each contact or VIA is a metal infusion that connects two layers, so if you only use one you would have a lot of resistance and therefore not a good connection, now if for any reason this connection were broken, by heat and cooling, or high currents or a problem in the manufacture you would have lost that connection, so in order to guaranty a good connection even over time an use we put a lot of connections and Vias.

2. If you don't use any connection tap the voltage in the body wouldn't be known, that means two things, first and most dangerous is that an extra current source of unknown value is added (Check the image) to both DC and AC analysis (Body effect) and this would interfere with any calculations you made beforehand. Plus you would have a floating node, this means more noise in this new current source and the voltage could go very high up, that means for example in a cascode the lower MOSFET (the one with lower voltage) could have a higher point of BIAS in all the conections.

I hope the explanations were broad enough!