A 220-mm/sup 2/, four- and eight-bank, 256-Mb SDRAM with single-sided stitched WL architecture

Abstract

A 220-mm/sup 2/, 256-Mb SDRAM has been fabricated in fully planarized 0.22-/spl mu/m CMOS technology with buried strap trench cell. The single-sided stitched word-line (WL) architecture employs asymmetric block activation and shared row decoders to realize 86.7% cell/chip-length efficiency (57.3% cell/chip efficiency). A staggered WL driver arrangement makes it possible to build the drivers on a 0.484-/spl mu/m WL pitch in limited space. An intraunit address increment pipeline scheme having two logical 8-Mb arrays within one physical 16-Mb unit results in a burst frequency up to 200 MHz for single data rate, while allowing four- and eight-bank organizations. A data rate of 270 Mbits/s was confirmed with a 135-MHz frequency doubling test mode. Single-ended addresses and a single ended read-write-drive bus reduce the ICC/sub 4/ current to /spl sim/90 mA for 100-MHz seamless burst operation. A detailed shmoo analysis demonstrates address-access time of 13.5 ns and clock-access time of 5 ns. This design also uses a selectable row domain and divided column redundancy scheme that repairs up to /spl sim/1400 faults/chip with only 8% chip overhead.