Nonvolatile memory device, with valley search for threshold voltage, memory controller, and reading method of storage device including the same

Abstract

A nonvolatile memory device includes a memory block including a memory area, an on-chip valley search (OVS) circuit performing an OVS sensing operation on the memory block, and a buffer memory storing at least one variation table including variation information of a threshold voltage of memory cells, obtained from the OVS sensing operation. A reading operation including an OVS sensing operation and a main sensing operation on the memory area is performed in response to a read command applied by a memory controller, the OVS sensing operation is performed at an OVS sensing level, and the main sensing operation is performed at a main sensing level reflecting the variation information. In the nonvolatile memory device, correction accuracy for deterioration of a word line threshold voltage may be improved, and a burden on a memory controller may be reduced.