  We propose schemes for efficiently destroying privacy data in a NAND flash
memory. Generally, even if privcy data is discarded from NAND flash memories,
there is a high probability that the data will remain in an invalid block. This
is a management problem that arises from the specificity of a program operation
and an erase operation of NAND flash memories. When updating pages or
performing a garbage collection, there is a problem that valid data remains in
at least one unmapped memory block. Is it possible to apply the obligation to
delete privacy data from existing NAND flash memory? This paper is the answer
to this question. We propose a partial overwriting scheme, a SLC programming
scheme, and a deletion duty pulse application scheme for invalid pages to
effectively solve privacy data destruction issues due to the remaining data.
Such privacy data destruction schemes basically utilize at least one state in
which data can be written to the programmed cells based on a multi-level cell
program operation. Our privacy data destruction schemes have advantages in
terms of block management as compared with conventional erase schemes, and are
very economical in terms of time and cost. The proposed privacy data
destruction schemes can be easily applied to many storage devices and data
centers using NAND flash memories.
