Leakage mechanism due to floating body and countermeasure on dynamic retention mode of SOI-DRAM

SOI-DRAM is expected to have long data retention time because the data leakage path is limited only through a cell transistor. High speed low power operation is realized due to reduced junction capacitances. Moreover, since the capacitance ratio Cb/Cs is reduced, the read out signal amplitude increases. For these reasons SOI is well suited to low power supply voltage DRAMs. However, because SOI uses body-floating transistors for memory cells, there is a possibility that majority carriers within the floating body can cause problems. To date, only the static data retention characteristics have been reported, with nothing written about the dynamic data retention characteristics for full DRAM operation. This paper details the results of an analysis of the floating body caused leakage mechanism and its effect on dynamic data retention. A proposal is made to obtain superior dynamic data retention time.