Spin transfer MRAM device with magnetic biasing

• US 7,508,042 B2
• Filed: 12/22/2006
• Issued: 03/24/2009
• Est. Priority Date: 12/22/2006
• Status: Active Grant

• Current Assignee: Taiwan Semiconductor Manufacturing Company Limited
• Original Assignee: MagIC Technologies Inc (TDK Corporation)
• Inventors: Guo, Yimin
• Primary Examiner(s): Jackson, Jr.; Jerome
• Assistant Examiner(s): Valentine; Jami M
• Application Number:
  US11/644,132
• Publication Number:
  US 20080151614A1
• Time in Patent Office: 823 Days
• Field of Search: 257421-427, 438/3, 438/57, 438/800
• US Class Current: 257/427
• 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

Abstract

The addition of segmented write word lines to a spin-transfer MRAM structure serves to magnetically bias the free layer so that the precessional motion of the magnetization vector that is set in play by the flow of spin polarized electrons into the free layer allows said magnetic vector to be switched rather than to oscillate between two easy axis directions.

Claims

1. A method to improve performance of a magnetic random access memory, comprising:

providing a driver layer having a magnetic easy axis that is normal to said driver layer'"'"'s surface, whereby said driver layer provides a spin polarized electric current;

providing an MTJ magnetic memory element, having an anisotropy field whose direction of magnetization in a free layer may be switched by passing said spin polarized current through said free layer, said spin polarized current having, in the absence of any external magnetic field, a first minimum value;

providing a magnetic biasing field generated by a current in a wire that passes over said MTJ;

through application of said magnetic biasing field, at a magnitude that about equals or exceeds said anisotropy field, enabling said MTJ free layer to be switched by passing through said free layer a spin polarized current having a second minimum value that is less than said first minimum value; and

thereby storing information through use of magnetization switching generated by spin transfer.

2. The method described in claim 1 wherein said first minimum value is at least two times said second minimum value.

3. The method described in claim 1 wherein said current that generates said magnetic biasing field is between about 1 and 20 mA whereby said magnetic biasing field is between about 10 and 200 Oe.

4. The method described in claim 1 wherein said wire passes within about 0.5 microns of said memory element.