The substrate on which the transistors are built must be properly biased. The way to do this is to add substrate contacts. The NMOS transistors are build on a p-type substrate, we will have to create a p-type substrate contact.
1. Draw a P-select square next to the NMOS transistor.
Since the contact will be made to p-substrate, the contact area will have to be p-type.
2. Draw a P-active square inside the P-select area.
This will define the active area of the substrate contact. make sure that you are not violating any design rules associated with active area spacing.
3. Draw the active contact square inside the p-type active area.
4. Make a metal connection to ground, covering the entire substrate contact.
Note that the susbtrate contact can also be created and placed as an
instance, instead of drawing every item seperately. this alternative approach
will be demonstrated in the next step,
for the n-well contact.
a production of
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