Open/folded bit-line arrangement for ultra-high-density DRAM´s

An open/folded bit-line (BL) arrangement for scaled DRAM´s is proposed. This BL arrangement offers small die size and good array noise immunity. In this arrangement, one BL of an open BL pair is placed in between a folded BL pair, and the sense amplifiers (SA´s) for open BL´s and those for folded BL´s are placed alternately between the memory arrays. This arrangement features a small 6F² memory cell, where F is the device feature size, and a relaxed SA pitch of 6F. The die size of a 64-Mb DRAM can be reduced to 81.6% compared with the one using the conventional folded BL arrangement. The BL-BL coupling noise is reduced to one-half of that of the conventional folded BL arrangement, thanks to the shield effect. Two new circuit techniques, 1) a multiplexer for connecting BL´s to SA´s, and 2) a binary-to-ternary code converter for the multiplexer have been developed to realize the new BL arrangement