Built-in self-test and self-diagnosis scheme for embedded SRAM

Embedded memory test and diagnosis is becoming an important issue in system-on-chip (SOC) development. Direct access of the memory cores from the limited number of I/O pins is usually not feasible. Built-in self-diagnosis (BISD), which include built-in self-test (BIST), is rapidly becoming the most acceptable solution. We propose a BISD design and a fault diagnosis system for embedded SRAM. It supports manufacturing test as well as diagnosis for design verification and yield improvement. The proposed BISD circuit is on-line programmable for its March test algorithms. Test chips have been designed and implemented. Our experimental results show that the BISD hardware overhead is about 2.4% for a typical 128 Kb SRAM and only 0.65% for a 2 Mb SRAM.