  The read channel of a Flash memory cell degrades after repetitive program and
erase (P/E) operations. This degradation is often modeled as a function of the
number of P/E cycles. In contrast, this paper models the degradation as a
function of the cumulative effect of the charge written and erased from the
cell. Based on this modeling approach, this paper dynamically allocates voltage
using lower-voltage write thresholds at the beginning of the device lifetime
and increasing the thresholds as needed to maintain the mutual information of
the read channel in the face of degradation. The paper introduces the technique
in an idealized setting and then removes ideal assumptions about channel
knowledge and available voltage resolution to conclude with a practical scheme
with performance close to that of the idealized setting.
