Trench capacitors allow memory densities of 64Mbit and higher. Design rules specify geometric constraints on the layout artwork. Provide a communication channel between the IC designer and the fabrication process engineer. To minimize the area of the circuit. To provide long term reliability of the circuit.
More aggressive rules increase performance.
Design rules represent a tolerance that ensures high probability of correct fabrication - rather than a hard boundary between correct and incorrect fabrication. Allow first order scaling by linearizing the resolution of the complete wafer implementation. To move a design from 4 micron to 2 micron, simply reduce the value of lambda. Worked well for 4 micron processes down to 1.2 micron processes. However, in general, processes rarely shrink uniformly.