Patent ID: 7002847
Filing Date: 2006-02-21
Classification: G11C

Abstract:
1. For an electrically programmable non-volatile multi-level memory device including a plurality of non-volatile multi-level memory cells, each of the multi-level memory cells having a non-volatile memory storage portion for determining an electrically alterable voltage threshold value, electrons being capable of being injected into the non-volatile memory storage portion, a method of operating the electrically alterable non-volatile multi-level memory device, comprising: determining a status of at least one non-volatile multi-level memory cell of the plurality of non-volatile multi-level memory cells to a plurality of states including at least a first level state of an erased state, a second level state, a third level state and a fourth level state of a plurality of programmed states, a level distance to the fourth level state from the first level state being larger than that to the third level state from the first level state and a level distance to the third level state from the first level state being larger than that to the second level state from the first level state; controlling an electrically alterable voltage threshold value of at least one non-volatile multi-level memory cell to a value which corresponds to one of the first level state of the erased state and the second level state of the programmed states in case that a higher bit of data to be stored in the least one non-volatile multi-level memory cell is unknown but a lower bit of the data to be stored in the least one non-volatile multi-level memory cell is known; and controlling the electrically alterable voltage threshold value of at least one non-volatile multi-level memory cell from the value which corresponds to the one of the first level state of the erased state and the second level state of the programmed states to another value which corresponds to one of the third level state and a fourth level state, both of programmed states, based on the lower bit of the data already stored in the at least one non-volatile multi-level memory cell in case that a higher bit of data to be stored in the least one non-volatile multi-level memory cell is known as a predetermined level for programming.