Memory system including semiconductor memory and controller
A controller controls a memory including first and second strings. The first and second strings configure first and second string groups, respectively. In each string group, a set of memory cell transistors each from each string configures a unit. The controller is configured to: sequentially write, in the first string group, data in first units to which serially-coupled memory cell transistors respectively belong; sequentially write, in the second string group, data in first units to which serially-coupled memory cell transistors respectively belong; and sequentially write, in the first string group, data in second units to which serially-coupled memory cell transistors respectively belong.
1. A memory system connectable to a host device, the memory system comprising:
a nonvolatile semiconductor memory device; and
a controller configured to access the nonvolatile semiconductor memory device based on a command received from the host device, wherein
the nonvolatile semiconductor memory device includes:
first and second strings, each of the first and second strings including a plurality of memory cells and a select transistor, the plurality of memory cells being connected in series, the select transistor being electrically connected in series with the memory cells, the memory cells including a first memory cell, a second memory cell, a third memory cell, and a fourth memory cell;
a bit line electrically connected to the first and the second strings;
a first select gate line electrically connected to a gate of the select transistor of the first string;
a second select gate line electrically connected to a gate of the select transistor of the second string;
a first word line electrically connected to gates of the first memory cell of the first string and the first memory cell of the second string;
a second word line electrically connected to gates of the second memory cell of the first string and the second memory cell of the second string;
a third word line electrically connected to gates of the third memory cell of the first string and the third memory cell of the second string; and
a fourth word line electrically connected to gates of the fourth memory cell of the first string and the fourth memory cell of the second string,
the controller is configured to perform a first write process, to perform a second write process after the first write process, to perform a third write process after the second write process, and to perform a fourth write process after the third write process, the first write process includes writing data in the first memory cell of the first string and writing data in the second memory cell of the first string after the writing in the first memory cell of the first string,
the second write process includes writing data in the first memory cell of the second string and writing data in the second memory cell of the second string after the writing in the first memory cell of the second string,
the third write process includes writing data in the third memory cell of the first string and writing data in the fourth memory cell of the first string after the writing in the third memory cell of the first string, and
the fourth write process includes writing data in the third memory cell of the second string and writing data in the fourth memory cell of the second string after the writing in the third memory cell of the second string.
2. The memory system according to claim 1 , wherein:
a voltage for selection is applied to the first select gate line when the data are written in the first memory cell of the first string in the first write process,
the voltage for selection is applied to the second select gate line when the data are written in the first memory cell of the second string in the second write process,
the voltage for selection is applied to the first select gate line when the data are written in the second memory cell of the first string in the first write process,
the voltage for selection is applied to the second select gate line when the data are written in the second memory cell of the second string in the second write process,
the voltage for selection is applied to the first select gate line when the data are written in the third memory cell of the first string in the third write process,
the voltage for selection is applied to the second select gate line when the data are written in the third memory cell of the second string in the fourth write process,
the voltage for selection is applied to the first select gate line when the data are written in the fourth memory cell of the first string in the third write process, and
the voltage for selection is applied to the second select gate line when the data are written in the fourth memory cell of the second string in the fourth write process.
3. The memory system according to claim 1 , wherein:
the first memory cell of the first string is between the select transistor of the first string and the second memory cell of the first string,
the first memory cell of the first string is between the select transistor of the first string and the third memory cell of the first string,
the first memory cell of the second string is between the select transistor of the second string and the second memory cell of the second string, and
the first memory cell of the second string is between the select transistor of the second string and the third memory cell of the second string.
4. The memory system according to claim 1 , wherein:
the first to fourth word lines are located away from the bit line along a stack direction in the nonvolatile semiconductor memory device,
the first word line is closer to the bit line than the second word line,
the third word line is closer to the bit line than the fourth word line, and
the first word line is closer to the bit line than the third word line.
5. The memory system according to claim 1 , wherein:
the second word line is adjacent to the first word line,
the third word line is adjacent to the second word line, and
the fourth word line is adjacent to the third word line.
6. The memory system according to claim 1 , wherein:
the nonvolatile semiconductor memory device comprises a block as a unit of data erasing, and
the block comprises the first and second strings.
7. The memory system according to claim 1 , wherein:
each of the first to fourth memory cells is capable of storing data of two bits.
8. The memory system according to claim 1 , wherein:
each of the data written in the first memory cell of the first string, the data written in the second memory cell of the first string, the data written in the third memory cell of the first string, the data written in the fourth memory cell of the first string, the data written in the first memory cell of the second string, the data written in the second memory cell of the second string, the data written in the third memory cell of the second string and the data written in the fourth memory cell of the second string is based on data specified by a write command from the host device.