Novel DRAM cell transistor with asymmetric source and drain junction profiles improving data retention characteristics

A novel DRAM cell transistor with an asymmetric source and drain structure is proposed, for the first time, to realize reliable high density DRAM below 0.12 μm. The new cell structure could provide the optimized source and drain junction profiles independently. The junction profile at the storage node (SN) was designed to reduce electric field to minimize junction leakage current and thereby improving data retention time. On the other hand, the junction profile at the bit-line direct contact node (DC) was designed to suppress short channel effects of a cell transistor. It is considered to be highly scalable for device scaling and to solve fine printing and precise alignment requirements. The validity of the approach was directly confirmed by improvement in the refresh times of 512 Mb DRAM which was fabricated with 0.12 μm DRAM technology.