Semiconductor memory device and driving method of the same

1. A semiconductor memory device comprising:

a semiconductor substrate including a semiconductor layer on a first insulation film;

a memory cell including a source formed in the semiconductor layer, a drain formed in the semiconductor layer, and a floating body region provided between the source and the drain, the memory cell storing data according to an amount of the charges accumulated in the floating body region;

a second insulation film provided on the floating body region of the memory cell;

a word line provided on the second insulation film;

a bit line connected to the drain;

a source line connected to the source; and

a plate electrode electrically insulated from the floating body region by the first insulation film, wherein

in at least a part of a period for writing data to the memory cell, a potential of the plate electrode is changed to reduce an absolute value of a threshold voltage of the memory cell before writing data,

data is written to the memory cell after the absolute value of the threshold voltage of the memory cell was reduced.

2. The semiconductor memory device according to claim 1 , wherein

in at least a part of a period for writing data to the memory cell, a potential difference between the plate electrode and the source line is reduced.

3. The semiconductor memory device according to claim 1 , wherein

in at least the part of the period for writing data to the memory cell, the absolute value of the potential of the plate electrode is reduced.

4. The semiconductor memory device according to claim 1 , wherein

the word line, the source line and the plate electrode are extended in parallel to each other in a memory cell array including the memory cells arranged in a matrix,

the bit line is orthogonal to the word line.

5. The semiconductor memory device according to claim 1 , wherein

the plate electrode is a plate-shape electrode provided for a plurality of the word lines.

6. The semiconductor memory device according to claim 1 , wherein

the plate electrode is a line-shape electrode provided for each word line.

7. The semiconductor memory device according to claim 1 , wherein

the memory cell is a FinFET.

8. A semiconductor memory device comprising:

a semiconductor substrate including a semiconductor layer on a first insulation film;

a memory cell including a source formed in the semiconductor layer, a drain formed in the semiconductor layer, and a floating body region provided between the source and the drain, the memory cell storing data according to an amount of the charges accumulated in the floating body region;

a second insulation film provided on the floating body region of the memory cell;

a word line provided on the second insulation film;

a bit line connected to the drain;

a source line connected to the source; and

a plate electrode electrically insulated from the floating body region by the first insulation film, wherein

in at least a part of a period for writing data to the memory cell, a potential of the plate electrode is changed to reduce an absolute value of a threshold voltage of the memory cell,

the memory cell is a FinFET,

the word line is connected to a first gate provided on one side of a Fin portion of the FinFET, and

the plate line is connected to a second gate provided on the other side of the Fin portion of the FinFET.

9. A semiconductor memory device comprising:

a semiconductor substrate including a semiconductor layer on a first insulation film;

a memory cell including a source formed in the semiconductor layer, a drain formed in the semiconductor layer, and a floating body region provided between the source and the drain, the memory cell storing data according to an amount of the charges accumulated in the floating body region;

a second insulation film provided on the floating body region of the memory cell;

a word line provided on the second insulation film;

a bit line connected to the drain;

a source line connected to the source; and

a plate electrode electrically insulated from the floating body region by the first insulation film, wherein

in at least a part of a period for writing data to the memory cell, a potential of the plate electrode is changed to reduce an absolute value of a threshold voltage of the memory cell,

the memory cell is a FinFET, and

the plate line is a second gate itself provided on the other side of the Fin portion of the FinFET.

10. A semiconductor memory device comprising:

a semiconductor substrate including a semiconductor layer on a first insulation film;

a memory cell including a source formed in the semiconductor layer, a drain formed in the semiconductor layer, and a floating body region provided between the source and the drain, the memory cell storing data according to an amount of charges accumulated in the floating body region;

a second insulation film provided on the floating body region of the memory cell;

a word line provided on the second insulation film;

a bit line connected to the drain; and

a source line connected to the source, wherein

the semiconductor substrate is electrically insulated from the floating body region by the first insulation film, and

in at least a part of a period for writing data to the memory cell, a potential of the semiconductor substrate is changed to reduce an absolute value of a threshold voltage of the memory cell before writing data,

data is written to the memory cell after the absolute value of the threshold voltage of the memory cell was reduced.

11. The semiconductor memory device according to claim 10 , wherein

in at least a part of a period for writing data to the memory cell, a potential difference between the semiconductor substrate and the source line is reduced.

12. The semiconductor memory device according to claim 10 , wherein

in at least the part of the period for writing data to the memory cell, the absolute value of the potential of the semiconductor substrate is reduced.

13. A driving method of a semiconductor memory device which comprises a semiconductor substrate including a semiconductor layer on a first insulation film; a memory cell including a source formed in the semiconductor layer, a drain formed in the semiconductor layer, and a floating body region provided between the source and the drain; a second insulation film provided on the floating body region of the memory cell; a word line provided on the second insulation film; a bit line connected to the drain; a source line connected to the source; and a plate electrode electrically insulated from the floating body region by the first insulation film,

the method comprising:

changing a potential of the plate electrode in a data write operation from a potential of the plate electrode in a data retention state to reduce an absolute value of a threshold voltage of the memory cell before writing data; and

writing data to the memory cell after the absolute value of the threshold voltage of the memory cell was reduced.

14. The driving method of a semiconductor memory device according to claim 13 , wherein

when data is written in the memory cell, a potential difference between the plate electrode and the source line is reduced.

15. The driving method of a semiconductor memory device according to claim 13 , wherein

when data is written in the memory cell, the absolute value of the potential of the plate electrode is reduced.

16. The driving method of a semiconductor memory device according to claim 13 , wherein

the memory cell is a FinFET.

17. A driving method of a semiconductor memory device which comprises a semiconductor substrate including a semiconductor layer on a first insulation film; a memory cell including a source formed in the semiconductor layer, a drain formed in the semiconductor layer, and a floating body region provided between the source and the drain; a second insulation film provided on the floating body region of the memory cell; a word line provided on the second insulation film; and a bit line connected to the drain; a source line connected to the source, wherein the semiconductor substrate is electrically insulated from the floating body region by the first insulation film,

the method comprising:

changing a potential of the semiconductor substrate in a data write operation from a potential of the semiconductor substrate in a data retention state to reduce an absolute value of a threshold voltage of the memory cell before writing data; and

writing data to the memory cell after the absolute value of the threshold voltage of the memory cell was reduced.

18. The driving method of a semiconductor memory device according to claim 17 , wherein

when data is written in the memory cell, a potential difference between the semiconductor substrate and the source line is reduced.

19. The driving method of a semiconductor memory device according to claim 17 , wherein

when data is written in the memory cell, the absolute value of the potential of the semiconductor substrate is reduced.