Electrically programmable memory with improved retention of data and a method of writing data in said memory
First Claim
1. A method for writing a particular cell into a group of memory cells within a row of memory cells of an electrically programmable memory, each cell comprising only one floating gate transistor, comprising the steps of:
- reading a state of at least one of the memory cells within the row by using different read reference values to generate at least two readings for said at least one of the memory cells within the row;
verifying the compatibility of the said at least two readings of the said at least one of the memory cells;
when an absence of compatibility is found for the said at least one of the memory cells, rewriting at least the memory cells of the group of memory cells within the row in which the group of memory cells resides; and
writing the particular cell into the group of memory cells.
9 Assignments
0 Petitions
Accused Products
Abstract
The present invention concerns an electrically programmable memory and a method for writing within this memory. In order to avoid the degradation of information in a memory cell following a number of write cycles in the other cells of the same row, the present invention includes a sequence to be carried out before each write cycle of a word within a row. A systematic reading of all the words of a row by using three different read reference potentials is performed in order to find a cell that gives non-compatibility results between any two of the three read cycles. The words of the row are stored in a register. If a non-compatible result is found, which indicates a degradation of information in the row, a systematic re-write of all the words of the row is carried out.
103 Citations
49 Claims
-
1. A method for writing a particular cell into a group of memory cells within a row of memory cells of an electrically programmable memory, each cell comprising only one floating gate transistor, comprising the steps of:
-
reading a state of at least one of the memory cells within the row by using different read reference values to generate at least two readings for said at least one of the memory cells within the row; verifying the compatibility of the said at least two readings of the said at least one of the memory cells; when an absence of compatibility is found for the said at least one of the memory cells, rewriting at least the memory cells of the group of memory cells within the row in which the group of memory cells resides; and
writing the particular cell into the group of memory cells. - View Dependent Claims (2, 3, 4, 5, 6, 7)
-
-
8. An electrically programmable memory comprising:
-
a plurality of memory cells arranged in rows; means for performing three successive reads of a memory cell of a row by applying three different reference potentials to a terminal of the memory cell to generate three readings prior to a write of a word into the row; and means for rewriting a word into the row when the three readings give non-compatible results for at least one cell of the row. - View Dependent Claims (9, 11, 12, 13, 14)
-
-
10. An electrically programmable memory comprising:
-
a network of cells organized in rows of words; a read circuit, coupled to the network of cells, having an output that provides three different reference values to a first cell of the network of cells, to read three corresponding read values of the first cell; a register, coupled to the read circuit, that stores the three corresponding read values; a write sequencer, coupled to the network of cells, having an input that receives a write command to write an input word to a selected cell within a row of the memory, a first output that applies three different read values to at least one cell within the row to read three read results of the at least one cell, a second output that provides a rewrite to the defective cell within the row in response to a systematic rewrite command, and a third output that writes the input word to the write cell; and means, coupled to the write sequencer, for comparing the three read results to determine whether the defective cell is detected, and for providing the systematic rewrite command to the write sequencer when the defective cell is detected. - View Dependent Claims (15, 16, 17, 18, 19, 22)
-
-
20. A method for determining a degradation of a memory device, the method comprising the steps of:
-
applying a first voltage to a memory cell within the memory device to generate a first read value of the memory cell; applying a second voltage that is different from the first voltage to the memory cell within the memory device to generate a second read value of the memory cell; and comparing the first read value to the second read value. - View Dependent Claims (21, 23, 24, 25, 26, 27, 29, 30)
-
-
28. An apparatus for determining a degradation of a memory device, the apparatus comprising:
-
means for applying a first voltage to a memory cell within the memory device to generate a first read value of the memory cell; means for applying a second voltage that is different from the first voltage to the memory cell within the memory device to generate a second read value of the memory cell; and means for comparing the first read value to the second read value. - View Dependent Claims (31, 32, 33, 34, 35, 36)
-
-
37. A memory device comprising:
-
a plurality of memory cells, each of which is readable by application of a read voltage; and means for determining a likelihood that the memory device has a degraded state by applying each of a plurality of read voltages to a terminal of a first cell of the plurality of memory cells to generate a plurality of read results. - View Dependent Claims (38, 39, 40, 41, 42, 43)
-
-
44. A memory device comprising:
-
a plurality of memory cells, each of which is readable by application of a read voltage; a read circuit, having an output that provides each of a plurality of read voltages to a terminal of a first cell of the plurality of memory cells to generate a plurality of read results; and a comparator circuit, having an input that receives the plurality of read results from the read circuit and an output that provides an indication that a first cell of the plurality of memory cells has a degraded state. - View Dependent Claims (45, 46, 47, 48, 49)
-
Specification