2 research outputs found
Increasing Flash Memory Lifetime by Dynamic Voltage Allocation for Constant Mutual Information
The read channel in Flash memory systems degrades over time because the
Fowler-Nordheim tunneling used to apply charge to the floating gate eventually
compromises the integrity of the cell because of tunnel oxide degradation.
While degradation is commonly measured in the number of program/erase cycles
experienced by a cell, the degradation is proportional to the number of
electrons forced into the floating gate and later released by the erasing
process. By managing the amount of charge written to the floating gate to
maintain a constant read-channel mutual information, Flash lifetime can be
extended. This paper proposes an overall system approach based on information
theory to extend the lifetime of a flash memory device. Using the instantaneous
storage capacity of a noisy flash memory channel, our approach allocates the
read voltage of flash cell dynamically as it wears out gradually over time. A
practical estimation of the instantaneous capacity is also proposed based on
soft information via multiple reads of the memory cells.Comment: 5 pages. 5 figure
Histogram-Based Flash Channel Estimation
Current generation Flash devices experience significant read-channel
degradation from damage to the oxide layer during program and erase operations.
Information about the read-channel degradation drives advanced signal
processing methods in Flash to mitigate its effect. In this context, channel
estimation must be ongoing since channel degradation evolves over time and as a
function of the number of program/erase (P/E) cycles. This paper proposes a
framework for ongoing model-based channel estimation using limited channel
measurements (reads). This paper uses a channel model characterizing
degradation resulting from retention time and the amount of charge programmed
and erased. For channel histogram measurements, bin selection to achieve
approximately equal-probability bins yields a good approximation to the
original distribution using only ten bins (i.e. nine reads). With the channel
model and binning strategy in place, this paper explores candidate numerical
least squares algorithms and ultimately demonstrates the effectiveness of the
Levenberg-Marquardt algorithm which provides both speed and accuracy.Comment: 6 pages, 8 figures, Submitted to the IEEE International
Communications Conference (ICC) 201