Using Dynamic Allocation of Write Voltage to Extend Flash Memory Lifetime

TL;DR

This paper proposes a dynamic voltage allocation method for flash memory that extends its lifetime by adjusting write voltages based on cumulative charge effects, improving durability without requiring perfect channel knowledge.

Contribution

It introduces a novel model of flash memory degradation based on cumulative charge and develops a practical voltage allocation scheme that adapts over the device's lifetime.

Findings

The dynamic voltage scheme extends flash memory lifetime significantly.

Performance close to idealized models is achievable in practical settings.

The approach adapts to degradation without precise channel knowledge.

Abstract

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.