MRAM device with improved stack structure and offset field for low-power toggle mode writing

• US 7,622,784 B2
• Filed: 01/10/2005
• Issued: 11/24/2009
• Est. Priority Date: 01/10/2005
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Trouilloud, Philip L.
• Primary Examiner(s): Phung; Anh
• Assistant Examiner(s): Lulis; Michael
• Application Number:
  US10/905,551
• Publication Number:
  US 20060152969A1
• Time in Patent Office: 1,779 Days
• Field of Search: 365/158, 257/421, 257/E21.665, 257/422, 257/427, 257/E27.006
• US Class Current: 257/421
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect

Abstract

A magnetic random access memory (MRAM) device includes a reference magnetic region having a resultant magnetic moment vector generally maintained in a desired orientation without the use of exchange coupling thereto. A storage magnetic region has an anisotropy easy axis and a resultant magnetic moment vector oriented in a position parallel or antiparallel to that of the reference magnetic region. A tunnel barrier is disposed between the reference magnetic region and the storage magnetic region, with the reference magnetic region, storage magnetic region and tunnel barrier defining a storage cell configured for a toggle mode write operation. The storage cell has an offset field applied thereto so as to generally maintain the resultant magnetic moment vector of the reference magnetic region in the desired orientation.

Claims

1. A magnetic random access memory (MRAM) device, comprising:

a reference magnetic region consisting of a single ferromagnetic layer having a resultant magnetic moment vector which is stabilized in a desired orientation only in the presence of an offset magnetic field;

a storage magnetic region having an anisotropy easy axis and a resultant magnetic moment vector oriented in a position parallel or antiparallel to that of said reference magnetic region;

a tunnel barrier disposed between said reference magnetic region and said storage magnetic region;

said reference magnetic region, said storage magnetic region and said tunnel barrier defining a storage cell configured for a write operation thereto by a toggle mode; and

said storage cell having said offset field applied thereto so as to stabilize said resultant magnetic moment vector of said reference magnetic region in said desired orientation, with said offset field allowing rotation, but not switching, of said resultant magnetic region by between about 30 degrees and about 45 degrees away with respect to a rest orientation during a write operation, wherein a magnitude of said offset magnetic field is smaller in magnitude than a write field applied during the write operation.

2. The MRAM device of claim 1, wherein said offset field further alters the magnitude of switching field used to perform said toggle mode write operation of said storage magnetic region.

3. The MRAM device of claim 1, further comprising a bias element configured to generate said offset field, said bias element disposed outside a vertical stack of said storage cell.

4. The MRAM device of claim 3, wherein said bias element is configured within an array of MRAM storage elements, said array of MRAM storage elements including said storage cell.

5. The MRAM device of claim 4, wherein said bias element is configured between said storage cell and an adjacent storage cell within said array.

6. The MRAM device of claim 5, wherein said bias element is oriented at about 45 degrees with respect to a wordline and a bitline axis of said array.

7. The MRAM device of claim 6, wherein said bias element is disposed proximate corresponding tunnel barriers of said storage cell and said adjacent storage cell.

8. The MRAM device of claim 1, wherein said reference magnetic region has a coercivity of less than about 100 Oersteds (Oe).

9. A magnetic random access memory (MRAM) device, comprising:

a reference magnetic region consisting of a single ferromagnetic layer having a resultant magnetic moment vector stabilized in a desired orientation by a bias element physically separated from said reference magnetic region by a spacer layer;

a storage magnetic region having an anisotropy easy axis and a resultant magnetic moment vector oriented in a position parallel or antiparallel to that of said reference magnetic region;

a tunnel barrier disposed between said reference magnetic region and said storage magnetic region;

said reference magnetic region, said storage magnetic region and said tunnel barrier defining a storage cell configured for a write operation thereto by a toggle mode;

said bias element and said spacer layer further configured within a vertical stack of said storage cell; and

said bias element configured to generate an offset magnetic field applied to said storage cell so as to stabilize said resultant magnetic moment vector of said reference magnetic region in said desired orientation, with said offset field allowing rotation, but not switching, of said resultant magnetic region by between about 30 degrees and about 45 degrees away with respect to a rest orientation during a write operation, wherein a magnitude of said offset magnetic field is smaller in magnitude than a write field applied during the write operation.

10. The MRAM device of claim 9, wherein said offset field further alters the magnitude of switching field used to perform said toggle mode write operation of said storage magnetic region.

11. The MRAM device of claim 9, wherein said spacer layer is configured as a diffusion barrier between said bias element and said tunnel barrier.

12. The MRAM device of claim 9, wherein said spacer layer has a thickness of at least about 50 angstroms.

13. The MRAM device of claim 9, wherein said bias element comprises a pinned ferromagnetic material and a pinning antiferromagnetic material.

14. The MRAM device of claim 9, wherein said reference magnetic region has a coercivity of less than about 100 Oersteds (Oe).