Magnetic memory

1. A spin-transfer magnetic memory comprising:

a magnetoresistive element comprising a pinned layer, a free layer and a tunnel insulating layer between the pinned layer and the free layer;

a bit line connected to a first terminal of the magnetoresistive element;

a select transistor comprising a current path comprising a first end connected to a second terminal of the magnetoresistive element;

a source line connected to a second end of the current path of the select transistor; and

a pulse generator configured to generate a microwave pulse current configured to directly flow through the magnetoresistive element using the bit line and the source line, and to assist a magnetization switching of the free layer in a write operation.

2. The memory of claim 1 , wherein a frequency f of the pulse current satisfies the following equation,

ω=2 πf =γ(−4 πMeff ),

Meff = 4 πMs− 2 Ku/Ms

where Ms is saturation magnetization of the free layer, Ku is a magnetic anisotropy energy density of the free layer and γ is a gyromagnetic ratio.

3. The memory of claim 1 , wherein the pulse current is a direct current, configured to flow by a predetermined time at predetermined intervals.

4. The memory of claim 3 , wherein the pulse generator is configured to generate a first direction pulse current configured to flow through the magnetoresistive element while writing first data to the magnetoresistive element, and to generate a second direction pulse current configured to flow through the magnetoresistive element while writing second data to the magnetoresistive element.

5. The memory of claim 4 , wherein the pulse generator comprises:

a first P-type transistor comprising a current path comprising a first end connected to the bit line and a second end connected to a power supply terminal;

a first N-type transistor comprising a current path comprising a first end connected to the bit line and a second end connected to a power supply terminal;

a second P-type transistor comprising a current path comprising a first end connected to the source line and a second end connected to a power supply terminal; and

a second N-type transistor comprising a current path comprising a first end connected to the source line and a second end connected to a power supply terminal.

6. The memory of claim 5 , wherein

the first N-type transistor and the second P-type transistor are set to an off state, and either one of the first P-type transistor and the second N-type transistor is set to an on state while one of the second N-type transistor and the first P-type transistor is alternately switched between on and off states respectively, when the first data is written to the magnetoresistive element, and

the first P-type transistor and the second N-type transistor are set to an off state, and one of the first N-type transistor and the second P-type transistor is set to an on state while one of the second P-type transistor and the first N-type transistor and is alternately switched between on and off states respectively, when the second data is written to the magnetoresistive element.

7. The memory of claim 1 , wherein the pulse current is a current of the sum of a direct current and a pulse.

8. The memory of claim 7 , wherein the pulse generator is configured to generate a first direction pulse current configured to flow through the magnetoresistive element while writing first data to the magnetoresistive element, and to generate a second direction pulse current configured to flow through the magnetoresistive element while writing second data to the magnetoresistive element.

9. The memory of claim 8 , wherein the pulse generator comprises:

a first P-type transistor comprising a current path comprising a first end connected to the bit line and a second end connected to a power supply terminal;

a first N-type transistor comprising a current path comprising a first end connected to the bit line and a second end connected to a power supply terminal;

a second P-type transistor comprising a current path comprising a first end connected to the source line and a second end connected to a power supply terminal comprising a first potential;

a second N-type transistor comprising a current path comprising a first end connected to the source line and a second end connected to a power supply terminal comprising the first potential;

a third P-type transistor comprising a current path comprising a first end connected to the source line and a second end connected to a power supply terminal comprise a second potential; and

a third N-type transistor comprising a current path comprising a first end connected to the source line and a second end connected to a power supply terminal comprising the second potential.

10. The memory of claim 9 , wherein the pulse generator is configured to generate a pulse current switching between the first and second potentials.

11. The memory of claim 9 , wherein

the first N-type transistor, the second P-type transistor and the third P-type transistor are set to an off state, the first P-type transistor is set to an on state, and the second N-type transistor and the third N-type transistor are alternately switched between on and off states and set to complementary states when the first data is written to the magnetoresistive element, and

the first P-type transistor, the second N-type transistor and the third N-type transistor are set to an off state, the first N-type transistor is set to an on state, and the second P-type transistor and the third P-type transistor alternately switched between on and off states and are set to complementary states when the second data is written to the magnetoresistive element.

12. The memory of claim 1 , wherein the pulse generator is configured to generate a direct current larger than a pulse width of the pulse current configured to flow through the magnetoresistive element after the pulse current.

13. The memory of claim 1 , further comprising:

a first stitch interconnect extending in parallel with the bit line, and connected to the bit line via a first contact; and

a second stitch interconnect extending in parallel with the source line, and connected to the source line via a second contact.

14. The memory of claim 13 , wherein the source line is extending in the same direction as the bit line.

15. The memory of claim 13 , wherein the source line is extending in a direction crossing the bit line.

16. The memory of claim 1 , further comprising:

a plurality of bit lines;

a plurality of magnetoresistive elements connected to the bit lines; and

a multiplexer connected between the bit lines and the pulse generator.

17. The memory of claim 1 , wherein the select transistor comprises a self-aligned silicide (salicide) structure.

18. The memory of claim 1 , wherein the select transistor comprises an elevated source/drain structure.