Semiconductor memory device and driving method thereof

• US 8,553,447 B2
• Filed: 09/20/2011
• Issued: 10/08/2013
• Est. Priority Date: 10/05/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Takemura, Yasuhiko
• Primary Examiner(s): LE, THONG QUOC
• Application Number:
  US13/236,982
• Publication Number:
  US 20120081948A1
• Time in Patent Office: 749 Days
• Field of Search: 365/145, 365/230.03, 365/149
• US Class Current: 365/149
• CPC Class Codes: G11C 11/404 with one charge-transfer gate, e.g. MOS transistor, per cell
• CPC Class Codes: G11C 11/4097 Bit-line organisation, e.g. bit-line layout, folded bit lines

Abstract

In a conventional DRAM, errors in reading data are likely to occur when the capacitance of a capacitor is reduced. A plurality of cells is connected to one main bit line Each cell includes a sub bit line and 2 to 32 memory cells. Further, each cell includes a selection transistor and a reading transistor, and a sub bit line is connected to a gate of the reading transistor. Since the parasitic capacitance of the sub bit line is sufficiently small, data of electric charge of a capacitor of each memory cell can be amplified without an error in the reading transistor and output to the main bit line.

Claims

1. A semiconductor memory device comprising:

one or more main bit lines;

one or more power supply lines;

four or more word lines; and

two or more cells,

wherein each of the cells includes a sub bit line, a selection transistor, a reading transistor, and two or more memory cells,

wherein a drain of the selection transistor and a drain of the reading transistor are connected to one of the main bit lines,

wherein a gate of the reading transistor is connected to the sub bit line,

wherein a source of the reading transistor is connected to one of the power supply lines,

wherein each of the memory cells includes a transistor and a capacitor,

wherein the capacitance of the capacitor is 1 fF or less, and

wherein a gate of the transistor of one of the memory cells is connected to one of the word lines.

2. The semiconductor memory device according to claim 1, wherein the selection transistor and the transistor of one of the memory cells are provided in different layers.

3. The semiconductor memory device according to claim 1, wherein a semiconductor used for the selection transistor and a semiconductor used for the transistor of one of the memory cells are of different kinds.

4. The semiconductor memory device according to claim 1, wherein the transistor of one of the memory cells and the transistor of another memory cell are provided in different layers.

5. The semiconductor memory device according to claim 1, wherein a conductivity type of the reading transistor is different from a conductivity type of the selection transistor.

6. The semiconductor memory device according to claim 1, wherein each of the cells includes 2 to 32 memory cells.

7. The semiconductor memory device according to claim 1, wherein a depth or a height of the capacitor is 1 μ

m or less.

8. The semiconductor memory device according to claim 1, wherein the resistance in an off-state of the transistor is 1×

10²⁴Ω

or higher.

9. A semiconductor memory device comprising:

a first main bit line and a second main bit line;

one or more power supply lines;

four or more word lines;

a first cell and a second cell,

wherein the first cell includes a first sub bit line, a first selection transistor, a first reading transistor, and two or more memory cells,

wherein the second cell includes a second sub bit line, a second selection transistor, a second reading transistor, and two or more memory cells,

wherein a drain of the first selection transistor and a drain of the first reading transistor are connected to the first main bit line,

wherein a source of the first selection transistor and a gate of the second reading transistor are connected to the first sub bit line,

wherein a source of the first reading transistor is connected to one of the power supply lines,

wherein each of the memory cells includes a transistor and a capacitor,

wherein the capacitance of the capacitor is 1 fF or less, and

wherein a gate of the transistor of one of the memory cells is connected to one of the word lines.

10. The semiconductor memory device according to claim 9, wherein the first selection transistor and the transistor of one of the memory cells are provided in different layers.

11. The semiconductor memory device according to claim 9, wherein a semiconductor used for the first selection transistor and a semiconductor used for the transistor of one of the memory cells are of different kinds.

12. The semiconductor memory device according to claim 9, wherein the transistor of one of the memory cells and the transistor of another memory cell are provided in different layers.

13. The semiconductor memory device according to claim 9, wherein a conductivity type of the first reading transistor is different from a conductivity type of the first selection transistor.

14. The semiconductor memory device according to claim 9, wherein the first cell includes 2 to 32 memory cells.

15. The semiconductor memory device according to claim 9, wherein a depth or a height of the capacitor is 1 μ

m or less.

16. The semiconductor memory device according to claim 9, wherein the resistance in an off-state of the transistor is 1×

10²⁴Ω

or higher.