Placement of repair circuits for in-field FPGA repair

With the growing density and shrinking feature size of modern semiconductors, it is increasingly difficult to manufacture defect free semiconductors that maintain acceptable levels of reliability for long periods of time. These systems are increasingly susceptible to wear-out by failing to meet their operational specifications for an extended period of time. The reconfigurability of FPGAs can be used to repair post-manufacturing faults by configuring the FPGA to avoid a damaged resource. This paper presents a method for repairing FPGA devices with wear-out faults by precomputing a set of repair circuits that, collectively, can repair a fault found in any logic block of the FPGA. This approach relies on logic placement to create "repair" circuits that avoid specific logic blocks. Three repair placement algorithms will be presented that generate a complete set of repair designs during the conventional placement process. The number of repairs needed to create a complete repair set depends heavily on the utilization of the FPGA resources. The three algorithms are tested against several benchmarks and with multiple area constraints for each benchmark. The best repair placement approach described in the paper generates a full set of repair circuits at a computation cost of 16X that of a conventional placer and with circuits of comparable quality.