Patent ID: 9159440
Filing Date: 2015-10-13
Classification: G11C

Abstract:
1. A method for reading a nonvolatile memory system, comprising: a read step including reading a memory cell of the nonvolatile memory system by applying a first read voltage to the memory cell and performing a first error correction operation; a first soft decision read step including reading the memory cell of the nonvolatile memory system by applying a first set of read voltages to the memory cell and performing a second error correction operation when it is determined that the read step results in an error and cannot be corrected with the first error correction operation; and a second soft decision read step including reading the memory cell by applying a second set of read voltages and none of the voltages in the first set to the memory cell and performing a third error correction operation when it is determined that the first soft decision read step results in an error and cannot be corrected with the second error correction operation, wherein the second soft decision read step is performed by using a result of the first soft decision read step, wherein the first set of read voltages includes a second read voltage, and a third read voltage, the second read voltage is lower than the first read voltage and the third read voltage is higher than the first read voltage, and wherein the second set of read voltages includes a read voltage between the first read voltage and the second read voltage or between the first read voltage and the third read voltage.