Asymmetric dot shape for increasing select-unselect margin in MRAM devices

• US 6,798,691 B1
• Filed: 06/28/2002
• Issued: 09/28/2004
• Est. Priority Date: 03/07/2002
• Status: Expired due to Term

• Current Assignee: Monterey Research, LLC (Vector Capital Corporation)
• Original Assignee: Silicon Magnetic Systems Incorporated
• Inventors: Ounadjela, Kamel, Jenne, Frederick B.
• Primary Examiner(s): Lam, David
• Application Number:
  US10/184,232
• Time in Patent Office: 823 Days
• Field of Search: 365/158, 365/1, 365/171, 365/173, 365/39, 365/43, 365/55, 365/66
• US Class Current: 365/171
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• 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: H10N 50/10 Magnetoresistive devices

Abstract

A magnetic memory cell and method for improving the write selectivity of memory cells in an MRAM array is provided herein. In particular, the magnetic memory cell may have a magnetic layer with a shape that is substantially asymmetrical about at least one axis of the magnetic layer. Such asymmetry may advantageously reduce and/or eliminate the effects of variations in the fabrication process. In addition, an asymmetrical memory shape may induce a relatively consistent equilibrium vector state, allowing a single switching mechanism to set the magnetic direction of the cell. Furthermore, a method is provided for programming a memory cell, in which the amount of current needed during a writing procedure is advantageously reduced relative to the amount of current needed in conventional writing procedures. In this manner, the asymmetrical memory cell and method produces a storage medium having overall power requirements less than those associated with symmetrical memory cells.

Claims

1. A magnetic random access memory device configured to store a logic state of a bit with respect to magnetic directions of magnetic layers within a memory cell of the device, wherein the memory cell comprises a magnetic layer having a shape substantially asymmetrical along one dimension of the magnetic layer and substantially symmetrical along another dimension of the magnetic layer.

2. The magnetic random access memory device of claim 1, wherein the one dimension is an elongated dimension of the magnetic layer.

3. The magnetic random access memory device of claim 2, wherein the shape of the magnetic layer comprises a curved portion along at least one side of the magnetic layer aligned with the elongated dimension.

4. The magnetic random access memory device of claim 1, wherein the one dimension is a shortened dimension of the magnetic layer.

5. The magnetic random access memory device of claim 1, wherein at least one of the memory cells comprises a plurality of layers having shapes substantially similar to the shape of the magnetic layer.

6. A magnetic random access memory device configured to store a logic state of a bit with respect to magnetic directions of magnetic layers within a memory cell of the device, wherein the memory cell comprises a magnetic layer with a perimeter having a larger curvature along one side of the perimeter than an opposing side of the perimeter.

7. The magnetic random access memory device of claim 6, wherein the one side of the perimeter comprises a curved portion having a different radial length than other curved portions arranged along the one side of the perimeter.

8. The magnetic random access memory device of claim 6, wherein the opposing side is substantially straight.

9. The magnetic random access memory device of claim 6, wherein the opposing side is concave.

10. The magnetic random access memory device of claim 6, wherein the opposing side is convex.

11. The magnetic random access memory device of claim 6, wherein the one side of the perimeter and the opposing side of the perimeter are arranged along an elongated dimension of the magnetic layer.

12. The magnetic random access memory device of claim 6, wherein the magnetic layer comprises a shape that is substantially asymmetrical about an axis of the magnetic layer aligned with the one side of the perimeter and the opposing side of the perimeter.

13. A magnetic random access memory device configured to store a logic state of a bit with respect to magnetic directions of magnetic layers within a memory cell of the device, wherein the memory cell comprises a magnetic layer having a shape substantially asymmetrical about a reference axis aligned with a first dimension of the magnetic layer and positioned approximately midway along a second dimension of the magnetic layer perpendicular to the first dimension, and wherein a first area of the magnetic layer laterally bound by one side of the reference axis and the periphery of the magnetic layer is larger than a second area of the magnetic layer laterally bound by the opposing side of the reference axis and the periphery of the magnetic layer.

14. The magnetic random access memory device of claim 13, wherein the periphery of the magnetic layer has a larger curvature along one side of the periphery than an opposing side of the periphery.

15. The magnetic random access memory device of claim 14, wherein a portion of the opposing side is substantially straight.

16. The magnetic random access memory device of claim 14, wherein a portion of the opposing side is convex.

17. The magnetic random access memory device of claim 13, wherein the shape of the magnetic layer is additionally asymmetrical along the second dimension of the magnetic layer.

18. The magnetic random access memory device of claim 13, wherein the shape of the magnetic layer is asymmetrical along the second dimension of the magnetic layer.

19. The magnetic random access memory device of claim 13, wherein an aspect ratio of the first and second dimension is between approximately 1.0 and approximately 2.0.

20. The magnetic random access memory device of claim 13, wherein a memory cell comprising the magnetic layer comprises one or more layers having shapes substantially different than the shape of the magnetic layer.