Layout Design Rules

• Lambda Rules: scalable, unitless system used for prototyping and teaching
  • $\lambda$ is half the minimum transistor channel length
  • All other rules are multiples of $\lambda$
  • A layout can be easily ported to a new, more advanced process just by changing the value of $\lambda$

Cell Layout and Stick Diagrams

Standard Cell Layout

Stick Diagrams

• Line styles represent different layers

• Cross represents a contact between layers

• The final cell’s size is determined by the number of routing tracks (the space needed for a wire and its required spacing)

  • By counting the number of horizontal and vertical tracks in the stick diagram, you can accurately estimate the final cell dimensions

  

  Stick Diagram Feature	Circuit Diagram Action
  Poly over n-diffusion	Draw an nMOS transistor.
  Poly over p-diffusion	Draw a pMOS transistor.
  Shared Poly line	Connect the gates of those transistors.
  Diffusion line not broken by Poly	The transistors are in parallel.
  Diffusion line broken by Poly	The transistors are in series.
  Metal connected to p-diffusion at top	Connect pMOS source to VDD.
  Metal connected to n-diffusion at bottom	Connect nMOS source to GND.
  Metal connected to diffusion via 'X'	Connect that node to the drain of a transistor.
  Unconnected Metal line between drains	This is the Output node.
  Poly line entering cell	This is an Input signal.