Thermally-assisted magnetic random access memory (MRAM)

• US 6,385,082 B1
• Filed: 11/08/2000
• Issued: 05/07/2002
• Est. Priority Date: 11/08/2000
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Abraham, David W., Trouilloud, Philip L.
• Primary Examiner(s): MAI, SON LUU
• Application Number:
  US09/708,253
• Time in Patent Office: 545 Days
• Field of Search: 365/145, 365/158, 365/171, 365/173, 257/295, 257/427, 257/421-426
• US Class Current: 365/171
• CPC Class Codes: G11C 11/15 using multiple magnetic layers G11C11/155 takes precedence
• CPC Class Codes: G11C 11/16 using elements in which the storage effect is based on magnetic spin effect
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods

Abstract

It is important to ensure good selectivity of a single magnetic tunnel junction storage cell within a memory array without affecting nearby storage cells. For this purpose, this memory array of storage cells preferably comprises a) an array of electrically conducting bit lines and electrically conducting word lines which form intersections therebetween, b) a storage cell disposed at each of said intersections, each storage cell comprising at least one reversible magnetic region or layer characterized by a magnetization state which can be reversed by applying thereto a selected external magnetic field, said reversible magnetic layer comprising a material whose magnetization state is more easily reversed upon a change in the temperature thereof, and c) a temperature change generator for changing the temperature of said reversible magnetic layer of only a selected one of said array of storage cells at any moment. To select a cell, it is preferable to select a cell by using a brief pulse of tunnelling current between the intersecting bit and word lines at that cell in order to provide sufficient Joule heating to facilitate a change in the magnetization state of its reversible magnetic layer, which preferably comprises a ferrimagnetic material.

Claims

1. A memory array of storage cells comprising:

a) an array of electrically conducting bit lines and electrically conducting word lines which form a plurality of intersections therebetween,

b) a storage cell disposed at each of said intersections, said storage cell comprising at least one changeable magnetic region characterized by a magnetization state which can be changed by applying thereto a selected external magnetic field, said changeable magnetic region comprising a material whose magnetization state is more easily changed upon a change in the temperature thereof, and

c) a heat generator for changing the temperature of said changeable magnetic region of only a selected one of said array of storage cells at any moment.

2. A memory array as set forth in claim 1 wherein said storage cell comprises a magnetic tunnel junction and said changeable magnetic region is a reversible magnetic region characterized by a magnetization state which can be reversed by applying thereto a selected external magnetic field, said reversible magnetic region comprising a material whose magnetization state is more easily reversed upon a change in the temperature thereof.

3. A memory array as set forth in claim 2, further comprising at least one fixed magnetic region characterized by a magnetization state which cannot be reversed by applying thereto said selected external magnetic field.

4. A memory array as set forth in claim 2, wherein said heat generator comprises a voltage source operable to heat said reversible magnetic region by passing electric tunnelling current therethrough.

5. A memory array as set forth in claim 4, wherein said tunnelling current is a writing current between a bit line and a word line for writing data into said storage cell.

6. A memory array as set forth in claim 5, wherein said writing current is passed through said reversible magnetic region for a time period which is chosen to be sufficiently short to prevent reversal of the magnetization state of other cells of said memory array by thermal leakage thereto.

7. A memory array as set forth in claim 1, wherein said changeable magnetic region comprises a ferrimagnetic material.

8. A memory array as set forth in claim 7, wherein said ferrimagnetic material is an alloy of Fe and a member selected from the group consisting of Gd, Tb, Dy.

9. A memory array as set forth in claim 7, wherein said ferrimagnetic material is selected from the group consisting of Gd₂₃Fe₇₇, Gd₂₄Fe₇₆, Tb₁₉Fe₈₁, Tb₂₁Fe₇₉, Dy₁₇Fe₈₃, and Dy₂₁Fe₇₉.

10. A memory array as set forth in claim 7, wherein said ferrimagnetic material is an alloy of Co and Sm.

11. A memory array as set forth in claim 7, wherein said changeable magnetic region is maintained at the compensation temperature of said material to maintain stored data in said memory array.