Flash Read Disturb Management Using Adaptive Cell Bit-Density with In-Place Reprogramming
Tai-Chou Wua, Yu-Ping Mab and Li-Pin Changc
National Chiao-Tung University Hsinchu, Taiwan, R.O.C.
asm811001.cs04g@g2.nctu.edu.tw
bmyp497238@gmail.com
clpchang@cs.nctu.edu.tw
ABSTRACT
Read disturbance is a circuit‐level noise induced by flash read operations. Read refreshing employs data migration to prevent read disturbance from corrupting useful data. However, it costs frequent block erasure under read‐intensive workloads. Inspired by software‐controlled cell bit‐density, we propose to reserve selected threshold voltage levels as guard levels to extend the tolerance of read disturbance. Blocks with guard levels have a low cell bit‐density, but they can store frequently read data without frequent read refreshing. We further propose to convert a high‐density block into a low‐density one using in place reprogramming to reduce the need for data migration. Our approach reduced the number of blocks erased due to read refreshing by up to 85% and the average read response time by up to 22%.
