Semiconductor memory device and method for driving the same

1. A semiconductor memory device comprising:

a first tunnel transistor and a second tunnel transistor whose gates and drains are cross-coupled;

a first node connected to the drain of the first tunnel transistor;

a second node connected to the drain of the second tunnel transistor;

a first access transistor connecting the first node to a first write bit line;

a second access transistor connecting the second node to a second write bit line; and

a third access transistor that supplies a voltage corresponding to a voltage of the first node to a first read bit line, wherein

the first access transistor is constructed of a tunnel transistor connected in such a manner as that current flows from the first node to the first write bit line upon turning-on in a forward biased state,

the second access transistor is constructed of a tunnel transistor connected in such a manner as that current flows from the second node to the second write bit line upon turning-on in a forward biased state, and

the semiconductor memory device further comprises a voltage supply circuit that supplies a voltage to the first and second write bit lines to apply reverse-bias voltages based on the voltage between sources and drains of the first and second access transistors in response to a refresh control signal upon a refresh operation.

2. The semiconductor memory device according to claim 1 , further comprising a fourth access transistor that supplies a voltage corresponding to a voltage of the second node to a second read bit line.

3. The semiconductor memory device according to claim 1 , wherein the third access transistor is constructed of a tunnel transistor connected in such a manner as that current flows from the first read bit line to the first node upon turning-on in a forward biased state.

4. The semiconductor memory device according to claim 2 , wherein the third access transistor is constructed of a tunnel transistor connected in such a manner as that current flows from the first read bit line to the first node upon turning-on in a forward biased state.

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

the first and second tunnel transistors and the third and fourth access transistors are N-type tunnel transistors, and

the first and second access transistors are P-type tunnel transistors.

6. The semiconductor memory device according to claim 1 , wherein the third access transistor includes a MOS transistor.

7. The semiconductor memory device according to claim 2 , wherein the third and fourth access transistors are NMOS transistors.

8. The semiconductor memory device according to claim 1 , wherein the third access transistor includes an NMOS transistor that has a gate connected to the first node, a source connected to a read word line and a drain connected to the first read bit line.

9. The semiconductor memory device according to claim 1 , wherein the voltage supply circuit supplies a power supply voltage on a high potential side to the first and second write bit lines in response to the refresh control signal.

10. The semiconductor memory device according to claim 1 , further comprising an intermediate voltage supply circuit that supplies a preset voltage between a power supply voltage on a high potential side and a ground potential to the first and second write bit lines upon a retention.

11. A method for driving a semiconductor memory device including

a first tunnel transistor and a second tunnel transistor whose gates and drains are cross-coupled,

a first node connected to the drain of the first tunnel transistor,

a second node connected to the drain of the second tunnel transistor,

a first access transistor whose main current path is connected between the first node and a first write bit line, the turning-on/off of which is controlled with a voltage applied to a write word line, and

a second access transistor whose main current path is connected between the second node and a second write bit line, the turning-on/off of which is controlled with a voltage applied to the write word line, in which

the first access transistor is constructed of a tunnel transistor connected in such a manner as that current flows from the first node to the first write bit line upon turning-on in a forward biased state, and

the second access transistor is constructed of a tunnel transistor connected in such a manner as that current flows from the second node to the second write bit line upon turning-on in a forward biased state,

the method for driving the semiconductor memory device, comprising, upon a refresh operation, applying a voltage that turns off the first and second access transistors to the write word line, and applying a voltage to the first and second write bit lines to form reverse-bias between sources and drains of the first and second access transistors.

12. The method for driving the semiconductor memory device according to claim 11 , wherein the first and second access transistors include P-type tunnel transistors, and wherein the applying the voltage to the first and second write bit lines includes, upon the refresh operation, applying a power supply voltage on a high potential side to the first and second write bit lines.

13. The method for driving the semiconductor memory device according to claim 11 , wherein the semiconductor memory device further including:

a third access transistor whose main current path is connected between the first node and a first read bit line, and whose gate is connected to a read word line; and

a fourth access transistor whose main current path is connected between the second node and a second read bit line, and whose gate is connected to the read word line,

wherein the method for driving the semiconductor memory device, further comprising applying a voltage to turn on the third and fourth access transistors to the read word line upon a read operation.

14. The method for driving the semiconductor memory device according to claim 11 , wherein the semiconductor memory device further including:

a third access transistor whose main current path is connected between a first read bit line and a read word line, and whose gate is connected to the first node; and

a fourth access transistor whose main current path is connected between a second read bit line and the read word line, and whose gate is connected to the second node,

wherein the method for driving the semiconductor memory device, upon a read operation, further comprising:

turning on/off the third access transistor according to a voltage of the first node; and

turning on/off the fourth access transistors according to a voltage of the second node.

15. The method for driving the semiconductor memory device according to claim 11 , wherein

the first and second tunnel transistors include N-type tunnel transistors, and the first and second access transistors include P-type tunnel transistors, and

the applying the voltage to the first and second write bit lines includes applying a power supply voltage on a high potential side to the first and second write bit lines upon the refresh operation.

16. The method for driving the semiconductor memory device according to claim 14 , wherein the third and fourth access transistors are constructed of MOS transistors, and

the method for driving the semiconductor memory device further comprises applying a voltage to the read word line to control the turning on/off of the third and fourth access transistors upon the read operation.

17. The method for driving the semiconductor memory device according to claim 13 , further comprising applying a voltage to the first and second read bit lines to forward-bias the third and fourth access transistors upon a write operation.

18. The method for driving the semiconductor memory device according to claim 13 , further comprising: upon a retention,

applying a voltage to the write word line to turn off the first and second access transistors;

applying a voltage to the read word line to turn off the third and fourth access transistors;

applying a voltage to the first write bit line to forward-bias the first access transistor;

applying a voltage to the second write bit line to forward-bias the second access transistor;

applying a voltage to the first read bit line to forward-bias the third access transistor; and

applying a voltage to the second read bit line to forward-bias the fourth access transistor.

19. The method for driving the semiconductor memory device according to claim 13 , further comprising applying a preset voltage between a power supply voltage on a high potential side and a ground potential to the first and second write bit lines upon a retention.