substrate
The body or base layer of an {integrated circuit},
onto which other layers are deposited to form the circuit.
The substrate is usually Silicon, though Sapphire is used for
certain applications, particularly military, where radiation
resistance is important. The substrate is originally part of
the {wafer} from which the {die} is cut. It is used as the
electrical {ground} for the circuit.
(1996-04-07)