Gate array

A gate array or uncommitted logic array (ULA) is an approach to the design and manufacture of application-specific integrated circuits (ASICs), using a prefabricated chip with active devices like NAND-gates, that are later interconnected according to a custom order by adding metal layers in the factory.

Design

A gate array circuit is a prefabricated silicon chip circuit with no particular function, in which transistors, standard NAND or NOR logic gates, and other active devices are placed at regular predefined positions and manufactured on a wafer, usually called a master slice. Creation of a circuit with a specified function is accomplished by adding a final surface layer or layers of metal interconnects to the chips on the master slice late in the manufacturing process, joining these elements to allow the function of the chip to be customized as desired. This layer is analogous to the copper layer(s) of a printed circuit board (PCB).

Gate array master slices are usually prefabricated and stockpiled in large quantities regardless of customer orders. The design and fabrication according to the individual customer specifications may be finished in a shorter time compared with standard cell or full custom design. The gate array approach reduces the mask costs, since fewer custom masks need to be produced. In addition, manufacturing test tooling lead time and costs are reduced, since the same test fixtures may be used for all gate array products manufactured on the same die size. Gate arrays were the predecessor of the more advanced structured ASIC; unlike gate arrays, structured ASICs tend to include predefined or configurable memories and/or analog blocks.