Word-line architecture for highly reliable 64-Mb DRAM

A unique word-line voltage control method for the 64-Mb DRAM and beyond is proposed. It realizes a constant lifetime for a thin gate oxide. This method controls word-line voltage and compensates reliability degradation in the thin gate oxide for cell-transfer transistors. It keeps the time-dependent dielectric breakdown (TDDB) lifetime constant under any conditions of gate oxide thickness fluctuation, temperature variation, and supply voltage variation. This method was successfully implemented in a 64-Mb DRAM to realize high reliability. This chip achieved a 10⁵ times reliability improvement and a 0.3~1.8-V larger word-line voltage margin to write ONE data into the cell