Nonvolatile semiconductor memory

1. A nonvolatile semiconductor memory comprising:

a semiconductor substrate including a plurality of substrate contact lines;

a first substrate area in the semiconductor substrate, including a first substrate contact line;

a first cell unit in the first substrate area, the first cell unit including a first memory cell and a first transistor, and the first transistor having a control terminal connected to a first word line, using the first substrate area as a channel and supplying a read current or a write current to the first memory cell; and

a substrate potential setting circuit connected to the plurality of substrate contact lines, setting the first substrate area by the first substrate contact line to a first substrate potential when the read current is supplied to the first memory cell, and setting the first substrate area to a second substrate potential different from the first substrate potential when the write current is supplied to the first memory cell.

2. The memory of claim 1 , wherein

the first substrate area is P-type,

the first transistor is an N-channel FET,

the first substrate potential and the second substrate potential are positive potential, and

an absolute value of the second substrate potential is larger than an absolute value of the first substrate potential.

3. The memory of claim 2 , wherein

the substrate potential setting circuit sets the first substrate area to negative potential after reading or writing of the first memory cell is completed with the read current or the write current.

4. The memory of claim 1 , wherein

the first substrate area is N-type,

the first transistor is a P-channel FET,

the first substrate potential and the second substrate potential are negative potential, and

an absolute value of the second substrate potential is larger than an absolute value of the first substrate potential.

5. The memory of claim 4 , wherein

the substrate potential setting circuit sets the first substrate area to positive potential after reading or writing of the first memory cell is completed with the read current or the write current.

6. The memory of claim 1 , wherein

the substrate potential setting circuit sets the first substrate area to a third substrate potential different from the first substrate potential or the second substrate potential, after having set the first substrate area to the first substrate potential or the second substrate potential.

7. The memory of claim 6 , further comprising:

a second substrate area in the semiconductor substrate, the second substrate area being electrically isolated from the first substrate area; and

a second cell unit in the second substrate area, the second cell unit including a second memory cell and a second transistor, and the second transistor having a control terminal connected to a second word line, using the second substrate area as a channel and supplying a read current or a write current to the second memory cell, wherein

the substrate potential setting circuit sets the second substrate region to the third substrate potential when the read current or the write current is supplied to the first memory cell.

8. The memory of claim 1 , further comprising:

a switch element having a control terminal connected to the first word line to transfer the first substrate potential or the second substrate potential to the first substrate area.

9. The memory of claim 1 , wherein

the first memory cell and the second memory cell each have a first magnetic layer, a second magnetic layer, and a nonmagnetic layer disposed between the first magnetic layer and the second magnetic layer.

10. A nonvolatile semiconductor memory comprising:

a semiconductor substrate including a plurality of substrate contact lines;

a first substrate area in the semiconductor substrate, including a first substrate contact line;

a first cell unit in the first substrate area, the first cell unit including a first memory cell and a first transistor, and the first transistor having a control terminal connected to a first word line, using the first substrate area as a channel and supplying a read current or a write current to the first memory cell; and

a switch element connected to the first substrate contact line and having a control terminal connected to the first word line to transfer the potential of the first word line to the first substrate area when the read current or the write current is supplied to the first memory cell.

11. The memory of claim 10 , wherein

the first substrate area is P-type,

the first transistor is an N-channel FET, and

the potential of the first word line is a positive potential.

12. The memory of claim 10 , wherein

the first substrate area is N-type,

the first transistor is a P-channel FET, and

the potential of the first word line is a negative potential.

13. The memory of claim 10 , further comprising:

a second substrate area in the semiconductor substrate, the second substrate area being electrically isolated from the first substrate area; and

a second cell unit in the second substrate area, the second cell unit including a second memory cell and a second transistor, and the second transistor having a control terminal connected to a second word line, using the second substrate area as a channel and supplying a read current or a write current to the second memory cell, wherein

the second substrate area is set to a substrate potential different from the potential of the first word line when the read current or the write current is supplied to the first memory cell.