Highly manufacturable 1T1C 4 Mb FRAM with novel sensing scheme

A novel sensing scheme using a gate-oxide reference cell is developed for achieving high yield of 1T1C FRAM. The sensing scheme generates highly uniform and fatigue-free reference level, and thus provides a reliable sensing margin. A novel technology to evaluate charge distribution of all memory cells is used for identifying the root causes of bit failure which are most critical factor for yield loss. Using this technology, hydrogen damage and etching damage are found to be the major loss factors. By eliminating the etch-damage with wet treatment and by using robust hydrogen-barrier, a wide sensing window, /spl Delta/Qref=74 fC, was achieved for highly manufacturable FRAM.