High speed magneto-resistive random access memory

• US 5,173,873 A
• Filed: 06/28/1990
• Issued: 12/22/1992
• Est. Priority Date: 06/28/1990
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Katti, Romney R., Stadler, Henry L., Wu, Jiin-Chuan
• Primary Examiner(s): Popek, Joseph A.
• Application Number:
  US07/545,019
• Time in Patent Office: 908 Days
• Field of Search: 365/158, 365/173
• US Class Current: 365/173
• 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 11/1659 Cell access
• CPC Class Codes: G11C 11/1673 Reading or sensing circuits or methods
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods

Abstract

A high speed read MRAM memory element is configured from a sandwich of magnetizable, ferromagnetic films surrounding a magento-resistive film which may be ferromagnetic or not. One outer ferromagnetic film has a higher coercive force than the other and therefore remains magnetized in one sense while the other may be switched in sense by a switching magnetic field. The magneto-resistive film is therefore sensitive to the amplitude of the resultant field between the outer ferromagnetic films and may be constructed of a high resistivity, high magneto-resistive material capable of higher sensing currents. This permits higher read voltages and therefore faster read operations. Alternate embodiments with perpendicular anisotropy, and in-plane anisotropy are shown, including an embodiment which uses high permeability guides to direct the closing flux path through the magneto-resistive material. High density, high speed, radiation hard, memory matrices may be constructed from these memory elements.

Claims

1. A memory element, comprising:

a pair of magnetizable layers, each said magnetizable layer having a level of magnetization;

a magneto-resistive layer between the magnetizable layers for storing data as a level of resistivity; and

means for altering the resistivity of the magneto-resistive layer by altering the magnetization of at least one magnetizable layer.

2. The memory element claimed in claim 1 further comprising:

a pair of electrically insulating layers separating the magneto-resistive layer from the magnetizable layers.

3. The memory element claimed in claim 1 wherein the magneto-resistive layer is ferromagnetic.

4. The memory element claimed in claim 1 wherein the magneto-resistive layer is non-ferromagnetic.

5. The memory element claimed in claim 1 further comprising:

highly permeable means for guiding magnetic flux between the magnetizable layers.

6. The memory element claimed in claim 1 wherein one magnetizable layer has a higher coercive force than the other.

7. The memory element claimed in claim 6 further comprising:

means for applying a switching field having a force between the coercive forces of the magnetizable layers.

8. The memory element claimed in claim 7 wherein the magnetizable layers surround the magneto-resistive layer.

9. The memory element claimed in claim 1 wherein the magnetizable layers are planar and exhibit anisotropy which is not confined to the planes of said layers.

10. The memory element claimed in claim 1 wherein the magnetizable layers are planar and exhibit in-plane anisotropy.

11. The memory element claimed in claim 10 further comprising:

highly permeable means for guiding magnetic flux between the magnetizable layers.

12. A method of storing data, comprising:

positioning a pair of magnetizable layers on either side of a magneto-resistive layer; and

altering the resistivity of the magneto-resistive layer to store data as a level of resistivity by altering the magnetization of at least one magnetizable layer.

13. The method of storing data claimed in claim 12 further comprising:

electrically insulating the magneto-resistive layer from the magnetizable layers.

14. The method of storing data claimed in claim 12 wherein the magneto-resistive layer is ferromagnetic.

15. The method of storing data claimed in claim 12 wherein the magneto-resistive layer is non-ferromagnetic.

16. The method of storing data claimed in claim 12 further comprising:

guiding magnetic flux from the magnetizable layers through the magneto-resistive layer.

17. The method of storing data claimed in claim 12 wherein one magnetizable layer has a higher coercive force than the other.

18. The method of storing data claimed in claim 17 further comprising;

applying a switching field having a force between the coercive forces of the magnetizable layers.

19. The method of storing data claimed in claim 18 wherein the magnetizable layers surround the magneto-resistive layer.

20. The method of storing data claimed in claim 12 wherein the magnetizable layers exhibit perpendicular anisotropy.

21. The method of storing data claimed in claim 12 wherein the magnetizable layers exhibit in-plane anisotropy.

22. The method of storing data claimed in claim 21 further comprising:

guiding magnetic flux from the magnetizable layers through the magneto-resistive layer.