Semiconductor memory device with variable resistance element

1. A semiconductor memory device comprising:

a variable resistance element configured to store a first data and a second data in accordance with a change in resistance value;

a current generator configured to generate a reference current for determining data of the variable resistance element, and having a middle admittance between an admittance of the variable resistance element storing the first data and an admittance of the variable resistance element storing the second data; and

a sense amplifier comprising a first input terminal connected to the variable resistance element and a second input terminal connected to the current generator, and configured to compare currents of the first input terminal and the second input terminal,

wherein the middle admittance Ymid satisfies the following equation

Y mid =( R max + R min)/(2 R max* R min)

where Rmin is a resistance value of the variable resistance element storing the first data, and Rmax is a resistance value of the variable resistance element storing the second data.

2. The device of claim 1 , wherein the current generator comprises resistance elements having the same structure as a structure of the variable resistance element.

3. The device of claim 1 , wherein the current generator comprises:

a first bit line, a second bit line, and a third bit line;

a first current path comprising a first resistance element connected between the first bit line and the second bit line, and a second resistance element connected between the second bit line and the third bit line; and

a second current path comprising a third resistance element connected between the first bit line and the second bit line, and a fourth resistance element connected between the second bit line and the third bit line,

the first resistance element and the second resistance element have the same resistance value as a resistance value of the variable resistance element storing the first data, and

the third resistance element and the fourth resistance element have the same resistance value as a resistance value of the variable resistance element storing the second data.

4. The device of claim 3 , wherein

the first bit line is connected to the second input terminal of the sense amplifier, and

the third bit line is grounded.

5. The device of claim 3 , wherein a variable resistance element as a memory element is connected between the first bit line and the second bit line.

6. The device of claim 3 , wherein

the first resistance element and the second resistance element are configured to supply a current in a direction to write the first data in a read operation, and

the third resistance element and the fourth resistance element are configured to supply a current in a direction to write the second data in the read operation.

7. The device of claim 3 , further comprising:

a first selection transistor connected to a first terminal of the first resistance element;

a second selection transistor connected to a first terminal of the second resistance element;

a third selection transistor connected to a first terminal of the third resistance element;

a fourth selection transistor connected to a first terminal of the fourth resistance element;

a first dummy word line connected to a gate of the first selection transistor;

a second dummy word line connected to a gate of the second selection transistor;

a third dummy word line connected to a gate of the third selection transistor; and

a fourth dummy word line connected to a gate of the fourth selection transistor.

8. The device of claim 7 , further comprising a row decoder configured to control the first dummy word line, the second dummy word line, the third dummy word line, and the fourth dummy word line.

9. The device of claim 3 , further comprising:

first and second selection transistors connected to a first terminal of the first resistance element;

third and fourth selection transistors connected to a first terminal of the second resistance element;

fifth and sixth selection transistors connected to a first terminal of the third resistance element;

seventh and eighth selection transistors connected to a first terminal of the fourth resistance element;

first and second dummy word lines connected to gates of the first and second selection transistors, respectively;

third and fourth dummy word lines connected to gates of the third and fourth selection transistors, respectively;

fifth and sixth dummy word lines connected to gates of the fifth and sixth selection transistors, respectively; and

seventh and eighth dummy word lines connected to gates of the seventh and eighth selection transistors, respectively.

10. The device of claim 9 , further comprising a row decoder configured to control the first to eighth dummy word lines.

11. The device of claim 1 , further comprising:

a selection transistor connected to a first terminal of the variable resistance element; and

a word line connected to a gate of the selection transistor.

12. The device of claim 1 , further comprising:

first and second selection transistors connected to a first terminal of the variable resistance element; and

first and second word lines connected to gates of the first and second selection transistors, respectively.

13. The device of claim 1 , wherein the variable resistance element comprises a fixed layer comprising a fixed magnetization direction, a recording layer comprising a variable magnetization direction, and a nonmagnetic layer between the fixed layer and the recording layer.