Analysis of Retention Failure by Bulk Trap in DRAM

DRAM is a type of memory that stores each bit of data in a capacitor cell, leakage current is a very important electrical parameter to retain data. Therefore, larger cell capacitance and smaller leakage current have been regarded as key factors in continuous shrinkage of DRAM. Generally, gate induced drain leakage (GIDL) and junction leakage of cell transistor (CTR) are well-known, but our approach is focused on retention failure by bulk trap. In order to electrically observe the influence of bulk trap, we used the adjacent gate of CTR to control electron migration. Results show that there are many failure cells due to bulk trap, and dimension shrinkage accelerates this failure. Consequently, balancing among electrical bias point and transistor manufacturing process should be carefully considered with bulk traps.