Stuck and Weakened Bits in SDRAM from a Heavy-Ion Microbeam

Stuck and weakened bits in the ISSI 512 Mb SDRAM was investigated in irradiation experiments with a heavy ion microbeam in the GSI facility. Delidded memories were tested in gold and calcium ion beams at 4.8 MeV/u, and stuck bits in the memory from the irradiation were investigated. To study weakened but not fully stuck bits after irradiation, parameters such as the refresh frequency of the memories was varied. The effect on the number of stuck bits from reading and writing the memory was studied, as well as the effect from waiting a time span between writing and reading the memory. These parameters were found to matter in the observed number of errors in the memory. Data on the findings from the microbeam irradiation from tests with different test modes are presented in this paper regarding suck bits and bit upsets. The test modes include dynamic March test and data retention tests with only refresh operations during irradiation.