ICs are made on a wafer. Circuits are built up with successive mask layers. The number of
masks used to define the interconnect and other layers is different between full-custom
ICs and programmable ASICs
All mask layers are customized in a full-custom ASIC.
It only makes sense to design a full-custom IC if there are no libraries available.
Full-custom offers the highest performance and lowest part cost (smallest die size) with the
disadvantages of increased design TIme, complexity, design expense, and highest risk.
Microprocessors were exclusively full-custom, but designers are increasingly turning to
semicustom ASIC techniques in this area too.
Other examples of full-custom ICs or ASICs are requirements for high-voltage (automobile),
analog/digital (communicaTIons), or sensors and actuators.
A cell-based ASIC (CBIC—“sea-bick”)
• Standard cells
• Possibly megacells, megafuncTIons, fullcustom
blocks, system-level macros (SLMs),
fixed blocks, cores, or FuncTIonal Standard
• All mask layers are customized—transistors and
• Custom blocks can be embedded
• Manufacturing lead time is about eight weeks.