Semiconductor memory device which stores plural data in a cell
A memory cell array is configured to have a plurality of memory cells arranged in a matrix, each of the memory cells being connected to a word line and a bit line and being capable of storing n values (n is a natural number equal to or larger than 3). A control circuit controls the potentials of the word line and bit line according to input data and writes data into a memory cell. The control circuit writes data into the memory cell to a k-valued threshold voltage (k<=n) in a write operation, precharges the bit line once, and then changes the potential of the word line an i number of times to verify whether the memory cell has reached an i-valued (i<=k) threshold voltage.
1. A semiconductor memory device comprising:
a memory cell array including a plurality of memory cells arranged in a matrix, each of the memory cells being capable of storing data by n levels; and
a control circuit configured to control the memory cell array, wherein
the control circuit writes first data by m levels (m<n) to a first memory cell,
the control circuit subsequently writes second data by the m levels (m<n) to a second memory cell adjacent to the first memory cell, and
the control circuit subsequently writes, to the first memory cell, third data by the n levels formed of the first data by the m levels stored in the first memory cell and fourth data by (n−m) level.
2. The semiconductor memory device according to claim 1 , wherein
after the second data by the in levels is written to the second memory cell, the control circuit subsequently writes fifth data by the m levels to a third memory cell adjacent to the second memory cell, and
the control circuit subsequently writes, to the second memory cell, sixth data by the n levels for lied of the second data by the m-levels stored in the second memory cell and seventh data by (n−m) level.
3. The semiconductor memory device according to claim 1 , further comprising:
a first word line connected to the first memory cell; and
a second word line connected to the second memory cell,
wherein the first word line and the second word line are adjacent to each other.
4. The semiconductor memory device according to claim 2 , further comprising:
a first word line connected to the first memory cell;
a second word line connected to the second memory cell; and
a third word line connected to the third memory cell,
wherein the first word line and the second word line are adjacent to each other, and
the second word line and the third word line are adjacent to each other.
5. The semiconductor memory device according to claim 1 , where
the memory cells constitute a NAND flash memory.
6. The semiconductor memory device according to claim 2 , where
the third memory cell is adjacent to the second memory cell in a first row position different from a second row position of the first memory cell in the memory cell array.