Birch, Stewart, Kolasch & Birch, LLP
Method of improving data retention ability of semiconductor memory device, and semiconductor memory device
This invention is a method of improving a data retention ability of a semiconductor memory device having a plurality of nonvolatile memory cells storing a plurality of memory states. The method includes the steps of: (a) selecting the nonvolatile memory cells in a first memory group each of which accumulates charges higher in level than a first threshold from the plurality of nonvolatile memory cells; (b) extracting the nonvolatile memory cells in a first sub-group each of which accumulates the charges lower in level than a second threshold from the nonvolatile memory cells in the first memory group; and (c) programming the nonvolatile memory cells in the first sub-group until each of the nonvolatile memory cells accumulates the charges higher in level than the second threshold.
Sharp Kabushiki Kaisha
G
G11C
inventional
Yoshinao Yoshifumi Masaru Akihide Hiroshi
Morikawa Yaoi Nawaki Shibata Iwata