Methods of Restoring Data in Flash Memory Devices and Related Flash Memory Device Memory Systems

Abstract

Methods for setting a read voltage in a memory system which comprises a flash memory device and a memory controller for controlling the flash memory device, comprise sequentially varying a distribution read voltage to read page data from the flash memory device; constituting a distribution table having a data bit number and a distribution read voltage, the data bit number indicating an erase state among the page data respectively read from the flash memory device and the distribution read voltage corresponding to the read page data; detecting distribution read voltages corresponding to data bit numbers each indicating maximum points of possible cell states of a memory cell, based on the distribution table; and defining new read voltages based on the detected distribution read voltages.

1 . A method of setting a read voltage in a memory system which comprises a flash memory device that includes memory cells that store data by being set to one of a plurality of states, the method comprising:
 reading data from a plurality of memory cells of the flash memory device at each of a plurality of different distribution read voltages;   identifying, for each of the plurality of states, the one of the plurality of distribution read voltages for which a maximum number of the plurality of memory cells are in the one of the plurality of states; and   defining new read voltages based on the identifications as to the ones of the plurality of distribution read voltages for which a maximum number of the plurality of memory cells are in the one of the plurality of states.   
   
   
       2 . The method of  claim 1 , wherein the plurality of different distribution read voltages are generated by incrementing or decrementing a starting voltage by a predetermined increment. 
   
   
       3 . The method of  claim 1 , wherein the new read voltages are defined so as to have an intermediate value between adjacent ones of the identified distribution read voltage. 
   
   
       4 . The method of  claim 3 , further comprising carrying out a refresh operation on the flash memory device using the newly defined read voltages and verify read voltages of each of the plurality of states. 
   
   
       5 . The method of  claim 1 , further comprising providing a distribution read command to the flash memory device, wherein the read data is output to a memory controller associated with the flash memory device in response to the distribution read command, and wherein the new read voltages are provided to the flash memory device. 
   
   
       6 . The method of  claim 1 , further comprising performing a refresh operation using the new read voltages and verify read voltages of each of the plurality of states. 
   
   
       7 . The method of  claim 1 , wherein reading data from a plurality of memory cells of the flash memory device at each of a plurality of different distribution read voltages comprises reading data from all of the pages of the flash memory device at each of a plurality of different distribution read voltages. 
   
   
       8 . The method of  claim 1 , wherein reading data from a plurality of memory cells of the flash memory device at each of a plurality of different distribution read voltages comprises reading data from part of the pages of the flash memory device at each of a plurality of different distribution read voltages.