Design of a 128-mb SOI DRAM using the floating body cell (FBC)

A 128-Mb SOI DRAM has been developed featuring the floating body cell (FBC). To keep the cell data state from being degraded by the word-line (WL) disturb due to the charge pumping and to reduce the refresh busy rate, a sense amplifier (S/A) is arranged for every bit-line (BL) and replenishes data "1" cells\´ bodies with holes which are lost by the disturb in every read and write cycle. The power is reduced by operating the S/As asymmetrically between the selected and the unselected thanks to that the number of holes to be replenished in the unselected S/As for charge pumping is two order of magnitude smaller than that required for writing the data "1". The multi-pair averaging of dummy cells generates a very accurate reference current for distinguishing the data "1" and "0" and a Monte Carlo simulation shows that it achieves a sensing scheme robust enough to realize all good parts of the DRAM with a reasonable amount of redundancy. The cell\´s feature of quasi-nondestructive read-out is also advantageous for making an SRAM interface of the DRAM or hiding refresh from uses without sacrificing the access time.