Memory diagnosis and built-in self-repair

This chapter discusses memory diagnosis and built-in-self-repair. The purpose of memory diagnosis is twofold: (1) locating failures and subsequently repairing them, and (2) analyzing failures and defects and subsequently improving design and process. The chapter presents a hybrid built-in self-test (BIST) design-with diagnosis support-for embedded RAM. In association with the BIST design, the chapter also shows a diagnosis system (called MEGA) for automatic identification of the fault site and fault type. In addition to the fault locations necessary for repair, the syndromes of the detected faults can also be exported by the BIST circuit. By recording the fault locations and syndromes, the diagnosis system can identify the fault type of each faulty cell. Finally, this chapter presents a built-in self-repair (BISR) scheme for memories with 2D redundancy structures. The BISR design is composed of a BIST module and a built-in redundancy analysis (BIRA) module. It supports three test modes: (1) main memory testing, (2) spare memory testing, and (3) repair. The BIRA module also serves as the reconfiguration (address remapping) unit in normal mode.