Redundancy - The new device technology for circuits of the 80´s

This work provides an overview of the technologies associated with the widespread use of redundancy to improve die yields in VLSI memory circuits. Yield improvement benefits, the nature of repairable defects, methods to optimize the number and type of spare memory elements, and the reliability issues associated with redundancy are described. The paper focuses on the relative benefits of various technologies used which allow the replacement of a defective element with a redundant one. The two most popular techniques, those using on-chip transistors or off-chip lasers to disconnect fuses are discussed in detail. Comparisons are made between relative yield improvement, fuse programming physics, process variation effects on programming yield, and scalability with reduced process dimensions of these two techniques. Future applications for redundancy techniques are proposed.