Lambda based design rules :
The Mead-conway approach is to characterize the process with a single scalable parameter called lambda, that is process-dependent and is defined as the maximum distance by which a geometrical feature on any one layer can stray from another feature, due to overetching, misalignment, distortion, over or under exposure etc. with a suitable safety factor included.
The purpose of defining lambda properly is to make the design itself independent of both process and fabrication and to allow the design to be rescaled at a future date when the fabrication tolerances are shrunk.
Scaling Theory :
The Scaling theory deals with the shrinking transistor and directs the behaviour of a device when its dimensions are reduced.
The most commonly used scaling models are the constant field scaling and constant voltage scaling. And another model for scaling the combination of constant field and constant voltage scaling. The scaling parameter s is the prefactor by which dimensions are reduced. It is s < 1.
(1) The scaling factors used are, 1/s and 1/ .
(2) 1/ is used for supply voltage VDD and gate oxide thickness .
(3) 1/s is used for linear dimensions of chip surface.
(4) For the constant field model and the constant voltage model, = s and = 1 are used.
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