Variable Hold Time in Dynamic RAMs: A New Silicon Defect Phenomenon.

We observed that the hold times of certain single memory cells in a Dynamic Random Access Memory (DRAM) spontaneously, abruptly and reversibly varied by up to an order of magnitude. Each memory cell showing this variable leakage had silicon dislocations in its charge storage area. Reported here is a history of our observation of variable hold time, a summary of its properties, and a description of the steps we have taken that insure our product against it as a possible failure mode. We also discuss possible physical mechanisms which may lead to the variable leakage.