Patent ID: 7561465
Filing Date: 2009-07-14
Classification: G11C

Abstract:
1. A method for recovering a nonvolatile memory array, comprising: analyzing whether a threshold voltage of an errant multi-bit memory cell has drifted outside of a number of initial allowable voltage windows, wherein each initial allowable voltage window corresponds to a different multi-bit value for non-errant cells of the array; if the threshold voltage of the errant cell has drifted outside of the number of initial allowable voltage windows, then adjusting at least one voltage boundary of at least one of the number of initial allowable voltage windows to form a subsequent allowable voltage window, where the voltage threshold of the errant cell falls within the subsequent allowable voltage window and voltage thresholds of at least some non-errant cells fall outside the subsequent allowable voltage window; and after forming the subsequent allowable voltage window, adjusting the threshold voltages of the at least some non-errant cells to bring them into the subsequent allowable voltage window.