Semiconductor memory device for storing multivalued data
Data storage circuits are connected to the bit lines in a one-to-one correspondence. A write circuit writes the data on a first page into a plurality of 5 first memory cells selected simultaneously by a word line. Thereafter, the write circuit writes the data on a second page into the plurality of first memory cell. Then, the write circuit writes the data on the first and second pages into second memory cells adjoining 10 the first memory cells in the bit line direction.
1. A semiconductor memory device comprising:
a memory cell array including:
a first block in which a plurality of first memory cells are provided in a matrix, the first memory cells connected to a plurality of first word lines and a plurality of bit lines, each of the first memory cells storing one of n values (n is a natural number equal to or larger than 3), and
a second block in which a plurality of second memory cells are provided in a matrix, the second memory cells connected to a plurality of second word lines and the bit lines, each of the second memory cells storing one of n values;
a plurality of data holding circuits connected to the bit lines, respectively, and holding data read from the first memory cells and from the second memory cells; and
a control circuit configured to control potentials of the first word lines, potentials of the second word lines, and potentials of the bit lines,
wherein
in a read operation to the first block, data in a first one of the first memory cells is read and stored to a first one of the data holding circuits, and data in a second one of the first memory cells is read and stored to a second one of the data holding circuits at the same time, and
output data from the first block of the memory device is determined from the data stored in the first one of the data holding circuits and the second one of the data holding circuits.
2. The semiconductor memory device according to claim 1 , wherein
the first one of the first memory cells and the second one of the first memory cell are connected to a same word line among the first word lines.
3. The semiconductor memory device according to claim 1 , wherein
the first memory cells and the second memory cells are nonvolatile memory cells.
4. The semiconductor memory device according to claim 1 , wherein
each of the first word lines and the second word lines extends in a first direction, and each of the bit lines extends in a second direction crossing the first direction.
5. The semiconductor memory device according to claim 1 , wherein
each of the first memory cells and the second memory cells includes a floating gate and a control gate, physically separated from each other.
6. The semiconductor memory device according to claim 1 , wherein
after a writing of the data is performed to the first memory cells and a verification for writing of data of (k−1) value (k≤n) is performed according to the data of the data holding circuits,
another verification for writing of data of k value is performed using a first level corresponding to a value less than the k value and a second level corresponding to the k value,
when a threshold voltage of the first memory cell does not reach the first level, the data of the a corresponding one of the data holding circuits is not changed,
when the threshold voltage of the first memory cell reaches the first level and does not reach the second level, the data of the a corresponding one of the data holding circuits is set as the data of the (k−1) value, and
when the threshold voltage of the first memory cell reaches the second level, the data of the a corresponding one of the data holding circuits is set as non-write data,
another writing of the data is performed to the first memory cells according to the data of the data hold circuits after the verification of the k value.
7. The semiconductor memory device according to claim 6 , wherein
before the writing of the data is performed to the first memory cells, an erase operation to the first block is performed.
8. The semiconductor memory device according to claim 1 , wherein
in a read operation to the second block, data in a first one of the second memory cells is read and stored to the first one of the data holding circuits, and data in a second one of the second memory cells is read and stored to the second one of the data holding circuits at the same time, and
output data from the second block of the memory device is determined from the data stored in the first one of the data holding circuits and the second one of the data holding circuits.
9. A method for controlling a semiconductor memory device,
the semiconductor memory device comprising:
a memory cell array including:
a first block in which a plurality of first memory cells are provided in a matrix, the first memory cells connected to a plurality of first word lines and a plurality of bit lines, each of the first memory cells storing one of n values (n is a natural number equal to or larger than 3), and
a second block in which a plurality of second memory cells are provided in a matrix, the second memory cells connected to a plurality of second word lines and the bit lines, each of the second memory cells storing one of n values;
a plurality of data holding circuits connected to the bit lines, respectively, and holding data read from the first memory cells and from the second memory cells; and
a control circuit configured to control potentials of the first word lines, potentials of the second word lines, and potentials of the bit lines,
the method comprising:
in a read operation to the first block, reading data in a first one of the first memory cells and causing a first one of the data holding circuits to store the read data, and reading data in a second one of the second memory cells and causing a second one of the data holding circuits to store the read data, at the same time, and
determining output data from the first block of the memory device based on the data stored in the first one of the data holding circuits and the date stored in the second one of the data holding circuits.