Abstract
The threshold voltage distribution after ideal programming in NAND flash memory cells is usually distorted by a combination of the random telegraph noise (RTN), cell-to-cell interference (CCI), and the retention process. To decide the original bits more accurately in this scenario, a precise channel model shall be utilized on the basis of the measured threshold voltages. This paper aims to characterize these various distortions occurring in multi-level cell (MLC) flash memories. A mathematical description of the overall distribution for the total flash channel distortion is presented. The final threshold voltage distribution for each symbol of MLC flash is also characterized, which is important for calculating the exact soft decisions of cell bits and the application of advanced flash error correction. The results of the theoretical analysis have been validated through Monte Carlo simulations of the flash channel.
Highlights
NAND flash memory is becoming essential as the storage media to a range of applications today, such as flash drive, solid state disks, mobile phone, etc. ⇤Corresponding author Email addresses: Preprint submitted to MeasurementGenerally speaking, the original information is firstly encoded with an error 5 correction code, and the resulted bit sequence is stored to flash memories by programming the cell threshold voltages to di↵erent levels
On the other hand, advanced soft decision-based error correction codes (ECC) such as low density parity check codes (LDPC) [1, 2, 3] are gradually replacing traditional ECC using hard decisions in the current flash memory design practice 15 in order to compensate for the high raw bit error probability
Decoding of these soft decision-based algorithms depends heavily on the accuracy of the reliability information obtained by multiple memory measurements, or a channel model with exactly characterized threshold voltage distribution
Summary
NAND flash memory is becoming essential as the storage media to a range of applications today, such as flash drive, solid state disks, mobile phone, etc. On the other hand, advanced soft decision-based error correction codes (ECC) such as low density parity check codes (LDPC) [1, 2, 3] are gradually replacing traditional ECC using hard decisions in the current flash memory design practice 15 in order to compensate for the high raw bit error probability Decoding of these soft decision-based algorithms depends heavily on the accuracy of the reliability information obtained by multiple memory measurements, or a channel model with exactly characterized threshold voltage distribution. The channel model based on this idea has been proposed recently by Moon et al and successfully used to instruct the error correction coding [9, 10] Such statistical way is not 40 capable to provide clear mathematical descriptions of the channel noises and final threshold voltage distribution.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
