Defect and fault tolerant scan chains

Several fault tolerant scan chain designs are proposed, including the combinational one data flow and two data flow approaches, and the counter based approach. It is shown that these designs have no critical portion, where a single defect would make the chain inoperative. The yield of these chains is evaluated to show that a long intolerant chain is a predominant yield or harvest detractor, while a tolerant chain becomes an insignificant factor to system yield or harvest.