Semiconductor memory device performing multi-bit programming using sequential write operations with reduced latch count
A semiconductor memory device includes bit lines, memory cells that are respectively connected to the bit lines, sense amplifier units that are respectively connected to the bit lines, and each of which includes m latch circuits, and a logic control circuit configured to input data to the m latch circuits and control a write operation on each of the memory cells using the data input to the m latch circuits. The logic control circuit executes an operation to write n bits to each of the memory cells, where n is 2 or more and greater than m, by executing a plurality of write operations, including a first write operation executed on the memory cells by inputting first m bits of data to the m latch circuits, and a second write operation executed on the memory cells by inputting second m bits of data to the m latch circuits.
1 . A semiconductor memory device comprising:
i bit lines;
i memory cells that are respectively and electrically connected to the i bit lines;
a word line commonly connected to gates of the i memory cells;
sense amplifier units that are respectively and electrically connected to the i bit lines, and each of which includes m latch circuits; and
a logic control circuit configured to input data to the m latch circuits and control a write operation including a program operation and a verify operation on each of the i memory cells using the data input to the m latch circuits, wherein
the logic control circuit executes an operation to write n bits to each of the i memory cells by executing the write operation x times, where n is 2 or more and greater than m and x is 2 or more, and
the x write operations include a first write operation executed by inputting first m bits of data to the m latch circuits, and a second write operation executed after the first write operation and by inputting second m bits of data different from the first m bits of data to the m latch circuits.
2 . The semiconductor memory device according to claim 1 , wherein the logic control circuit:
executes the program operation L times or less in each of the first write operation and the second write operation,
in the first write operation, executes the verify operation for a part of (2 m −1) verify levels corresponding to the first m bits of data, and
in the second write operation, executes the verify operation for a remaining part of the (2 m −1) verify levels corresponding to the second m bits of data.
3 . The semiconductor memory device according to claim 1 , wherein the logic control circuit
supplies a first voltage in the verify operation for at least one memory cell among the i memory cells during the first write operation, and
supplies a second voltage, which is higher than the first voltage, in the verify operation for the at least one memory cell among the i memory cells during the second write operation.
4 . The semiconductor memory device according to claim 1 , wherein the logic control circuit is configured to execute the first write operation in response to a first command.
5 . The semiconductor memory device according to claim 1 , wherein the logic control circuit is configured to execute the first write operation in response to a first command and one or more second commands, each of which designates a page address and page data to be stored in the memory cells.
6 . The semiconductor memory device according to claim 1 , wherein
in each of the first write operation and the second write operation, the program operation is executed L times or less, and
the logic control circuit, during the first write operation,
supplies a first program voltage to a memory cell, which is a target of the program operation, in an (L−1)-th program operation, and
supplies a second program voltage larger than the first program voltage to a memory cell, which is a target of the program operation, in an L-th program operation.
7 . The semiconductor memory device according to claim 1 , wherein
in each of the first write operation and the second write operation, the program operation is executed L times or less,
the logic control circuit, during the first write operation, supplies a first program voltage to a memory cell, which is a target of the program operation, in a first program operation, and
the logic control circuit, during the second write operation, supplies a second program voltage larger than the first program voltage to a memory cell, which is a target of the program operation, in a first program operation.
8 . The semiconductor memory device according to claim 1 , wherein
the logic control circuit is further configured to perform a read operation after consecutive execution of the first write operation and the second write operation.
9 . A method of writing n bits of data in each of a plurality of memory cells of a semiconductor memory device having a word line connected to gates of the memory cells, a plurality of bit lines respectively connected to the plurality of memory cells, and a plurality of sense amplifier units respectively connected to the bit lines, said method comprising the steps of:
(a) inputting m bits of data respectively to m data latches in each of the sense amplifier units, where n is 2 or more and greater than m, and executing multiple loops of first program operation and first verify operation for each of the memory cells, wherein the first verify operation is performed to verify whether or not the m bits of data inputted into the m data latches of the sense amplifier unit corresponding to the memory cell being programmed have been programmed in the memory cell; and
(b) inputting a second m bits of data respectively to the m data latches in each of the sense amplifier units, and executing multiple loops of second program operation and second verify operation, wherein the second verify operation is performed to verify whether or not the second m bits of data inputted into the m data latches of the sense amplifier unit corresponding to the memory cell being programmed have been programmed in the memory cell.
10 . The method according to claim 9 , wherein
step (a) is executed in response to a first command and one or more second commands received from the memory controller, and the second commands designate m page addresses and m pages of data to be stored in the memory cells, and
step (b) is executed in response to a third command and one or more fourth commands received from the memory controller, and the fourth commands designate m page addresses and m pages of data to be stored in the memory cells.
11 . The method according to claim 10 , wherein
in step (a), values of the m bits of data respectively input to the m data latches in each of the sense amplifier units are determined from values in the m pages of data designated by the second commands, and
in step (b), values of the m bits of data respectively input to the m data latches in each of the sense amplifier units are determined from values in the m pages of data designated by the fourth commands.