Method and system for using a pulsed field to assist spin transfer induced switching of magnetic memory elements

• US 7,502,249 B1
• Filed: 04/17/2007
• Issued: 03/10/2009
• Est. Priority Date: 07/17/2006
• Status: Active Grant

• Current Assignee: Renesas Electronics Corporation, Samsung Semiconductor Incorporated (Samsung Electronics Co. Ltd.)
• Original Assignee: Renesas Technology Corporation (Renesas Electronics Corporation), Grandis, Inc. (Samsung Electronics Co. Ltd.)
• Inventors: Ding, Yunfei
• Primary Examiner(s): Elms; Richard
• Assistant Examiner(s): Byrne; Harry W
• Application Number:
  US11/736,290
• Time in Patent Office: 693 Days
• Field of Search: 365/148, 365/158, 365/171, 365/173, 257/421, 438/3, 977/934, 977/935
• US Class Current: 365/158
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: G11C 11/1659 Cell access
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods
• CPC Class Codes: G11C 11/1693 Timing circuits or methods
• CPC Class Codes: G11C 11/5607 using magnetic storage elements
• CPC Class Codes: Y10S 977/934 Giant magnetoresistance, GMR
• CPC Class Codes: Y10S 977/935 Spin dependent tunnel, SDT, junction, e.g. tunneling magnetoresistance, TMR

Abstract

A method and system for providing and utilizing a magnetic memory are described. The magnetic memory includes a plurality of magnetic storage cells. Each magnetic storage cell includes magnetic element(s) programmable due to spin transfer when a write current is passed through the magnetic element(s) and selection device(s). The method and system include driving a first current in proximity to but not through the magnetic element(s) of a portion of the magnetic storage cells. The first current generates a magnetic field. The method and system also include driving a second current through the magnetic element(s) of the portion of the magnetic storage cells. The first and second currents are preferably both driven through bit line(s) coupled with the magnetic element(s). The first and second currents are turned on at a start time. The second current and the magnetic field are sufficient to program the magnetic element(s).

Claims

1. A method for programming a magnetic memory, the magnetic memory including a plurality of magnetic storage cells and a plurality of bit lines, each of the plurality of magnetic storage cells including at least one magnetic element programmable due to spin transfer when a write current is passed through the magnetic element and at least one selection device, at least one bit line of the plurality of bit lines coupled to the at least one magnetic element of the plurality of magnetic elements, wherein at least one magnetic layer of the at least one magnetic element has in-plane anisotropy, the method comprising:

driving a first current in proximity to but not through the at least one magnetic element of a portion of the plurality of magnetic storage cells, the first current being driven through a portion of the plurality of bit lines and generating a magnetic field;

driving a second current through the at least one magnetic element of the portion of the plurality of magnetic storage cells, the second current and the first current being turned on at a start time, the second current and the magnetic field being sufficient to program the at least one magnetic element;

wherein the at least one magnetic element makes an angle with the plurality of the bit lines in a film plane, the angle being based on the in-plane an isotropy.

2. The method of claim 1 wherein the in-plane anisotropy is a uniaxial anisotropy along an axis and having a strength K, wherein a data storage layer of the at least one magnetic element has a saturation magnetization of Ms, wherein the magnetic field has a strength H, and wherein a field angle between the magnetic field and the axis is between the field angle based upon the angle of 135°

and substantially ninety degrees plus one-half multiplied by the inverse sin of H multiplied by Ms divided by K.

3. The method of claim 1 wherein the first current corresponds to a first current pulse.

4. The method of claim 3 wherein the first current pulse has a rise time and the magnetic element has a magnetic relaxation time that is greater than the first current pulse rise time.

5. A magnetic memory comprising:

a plurality of magnetic storage cells, each of the plurality of magnetic storage cells including at least one magnetic element programmable due to spin transfer when a write current is passed through the magnetic element and at least one selection device, the at least one magnetic element having an in-plane an isotropy;

a plurality of bit lines coupled to the at least one magnetic element of the plurality of magnetic storage cells, the plurality of bit lines for driving a first current and a second current, the first current being driven in proximity to but not through the at least one magnetic element of a portion of the plurality of magnetic storage cells, the first current generating a magnetic field, the second current being driven through the at least one magnetic element of the portion of the plurality of magnetic storage cells, the second current and the magnetic field being sufficient to program the at least one magnetic element;

wherein the at least one magnetic element makes an angle with the plurality of the bit lines in a film plane, the angle being based on the in-plane an isotropy.

6. The magnetic memory of claim 5 wherein the in-plane anisotropy is a uniaxial anisotropy along an axis and having a strength K wherein a data storage layer of the at least one magnetic element has a saturation magnetization of Ms, wherein the magnetic field has a strength H, and wherein a field angle between the magnetic field and the axis is between the field angle based upon the angle of 135°

and substantially ninety degrees plus one-half multiplied by the inverse sin of H multiplied by Ms divided by K.

7. The magnetic memory of claim 5 further comprising:

at least one isolation device connected to the plurality of bit lines, the first current passing through the at least one isolation device.

8. The magnetic memory of claim 5 further comprising:

at least one resistor connected to the plurality of bit lines and the at least one isolation device, the first current passing through the at least one resistor.

9. The magnetic memory of claim 5 further comprising:

at least one of a current source or a drain connected to the end of the at least one of the plurality of bit lines such that the first current does not pass through the at least one magnetic element.

10. The magnetic memory of claim 5 wherein the plurality of bit lines further includes at least one nonmagnetic conductive layer, the magnetic memory further comprising:

at least one magnetic layer adjacent to the at least one nonmagnetic conductive layer.

11. The magnetic memory of claim 10 wherein the at least one magnetic element includes a reference layer, a free layer, and a spacer layer residing between the reference layer and the free layer, the at least one magnetic layer having a first magnetic damping constant, the free layer having a second magnetic damping constant less than the first magnetic damping constant.

12. The magnetic memory of claim 5 wherein the in-plane anisotropy includes at least one of a shape anisotropy, a crystalline anisotropy, and an induced an isotropy.

13. The magnetic memory of claim 5 wherein the at least one magnetic layer of the magnetic element has an out of plane anisotropy.

14. The magnetic memory of claim 13 wherein the out of plane anisotropy includes at least one of a shape anisotropy, a crystalline anisotropy, an interface anisotropy, and an induced anisotropy.

15. The magnetic memory of claim 14 wherein the at least one magnetic element has a center and each of at least of a portion of the plurality of bit lines has a bit line center, the center of at least one magnetic element being offset from the bit line center by an angle, the angle being based on the perpendicular an isotropy.

16. The magnetic memory of claim 5 wherein the at least one magnetic storage cell further includes at least two magnetic element programmable due to spin transfer when a write current is passed through the magnetic elements and at least one selection device, the at least two magnetic elements having at least one of the in-plane anisotropy and an out-of-plane anisotropy.

17. The magnetic memory of claim 16 further comprising:

at least one of an isolation device and at least one optional resistive device connected to each of the plurality of bit lines, the first current passing through the bit line, the activated isolation device, and the optional resistive device.

18. The magnetic memory of claim 16 further comprising:

at least one of a current source and a drain connected to the at least one of the plurality of bit lines.

19. The magnetic memory of claim 16 wherein at least one of the plurality of bit lines further includes:

a nonmagnetic metal layer and at least one magnetic layer adjacent to the non-magnetic metal layer.

20. The magnetic memory of claim 5 further comprising:

a plurality of field lines, each of the plurality of field lines coupled to one of the at least two magnetic elements, the plurality of field lines for driving the first current, only a first field line of the plurality of field lines for driving the first and the second current, the second current being driven through all the magnetic elements of the portion of the plurality of magnetic storage cells, the second current generating a sufficient spin torque to program the at least one magnetic element coupled with the field line and insufficient spin torque to program another of the at least one magnetic element not coupled with the field line.