Logic unit including magnetic tunnel junction elements having two different anti-ferromagnetic layers

Patent metadata

Field	Value
Publication number	US-9331123-B2
Application number	US-201414274601-A
Country	US
Kind code	B2
Filing date	May 9, 2014
Priority date	May 9, 2014
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

A logic unit for security engines or content addressable memory including Magnetic Tunnel Junction (MTJ) elements connected in series to form a NAND-type string, where each MTJ element includes a storage layer and a sense layer having different anti-ferromagnetic materials respectively having higher and lower blocking temperatures. During write/program, the string is heated above the higher blocking temperature, and magnetic fields are used to store bit values of a confidential logical pattern in the storage layers. The string is then cooled to an intermediate temperature between the higher and lower blocking temperatures and the field lines turned off to store bit-bar (opposite) values in the sense layers. During a pre-compare operation, the MTJ elements are heated to the intermediate temperature, and an input logical pattern is stored in the sense layers. During a compare operation, with the field lines off, a read current is passed through the string and measured.

First claim

The invention claimed is:

1. A logic unit comprising:
a plurality of Magnetic Tunnel Junction (MTJ) elements connected in series, each said MTJ element comprising:
a storage layer including a first antiferromagnetic structure contacting a first ferromagnetic structure, the first antiferromagnetic structure comprising a first material having a first blocking temperature;
a sense layer including a second antiferromagnetic structure contacting a second ferromagnetic structure, the second antiferromagnetic structure comprising a second antiferromagnetic material having a second blocking temperature; and
a tunnel dielectric layer disposed between the first ferromagnetic structure of the storage layer and the second ferromagnetic structure of the sense layer,
wherein the first blocking temperature of the first antiferromagnetic material is greater than the second blocking temperature of the second antiferromagnetic material;

a select transistor that is coupled in series with the plurality of MTJ elements between a voltage source and a ground terminal; and
a controller configured to control the select transistor such that:
during a first time period, said select transistor is activated to generate a first heating current that passes through said plurality of MTJ elements between said voltage source and said ground terminal, wherein said first heating current is generated such that said plurality of MTJ elements are heated to a first temperature above said first blocking temperature of the first antiferromagnetic material; and
during a second time period, said select transistor is activated to generate a second heating current that passes through said plurality of MTJ elements between said voltage source and said ground terminal, wherein said second heating current is generated such that said plurality of MTJ elements are heated to a second temperature between said first blocking temperature and said second blocking temperature of the second antiferromagnetic material.

2. The logic unit of claim 1 ,
wherein the first antiferromagnetic structure of each said MTJ element comprises a first antiferromagnetic material composed such that the first blocking temperature is in the range of 250-350° C., and
wherein the second antiferromagnetic structure of each said MTJ element comprises a second antiferromagnetic material composed such that the second blocking temperature is in the range of 150-250° C.

3. The logic unit of claim 2 ,
wherein the first antiferromagnetic material comprises at least one of PtMn and NiMn, and
wherein the second antiferromagnetic material comprises at least one of FeMn and IrMn.

4. The logic unit of claim 1 , wherein each said MTJ element has a width in the range of 50 to 500 nanometers, and a total thickness in the range of 5 to 200 nanometers.

5. The logic unit of claim 4 , wherein each said MTJ element has a width in the range of 120 to 250 nanometers.

6. The logic unit of claim 4 ,
wherein the first antiferromagnetic structure of each said MTJ element comprises a first film thickness in the range of 10 and 30 nm, and
wherein the second antiferromagnetic structure of each said MTJ element comprises second a film thickness in the range of 10 and 30 nm.

7. The logic unit of claim 6 , wherein the tunnel dielectric layer of each said MTJ element comprises one of magnesium oxide and aluminum oxide and has a third film thicknesses in the range of 5 to 20 Angstroms.

8. The logic unit of claim 1 , further comprising a plurality of field lines, each said field line being magnetically coupled to said storage layer and said sensing layer of a corresponding said MTJ element such that:
when said corresponding MTJ element is at a first temperature above the first blocking temperature and a first reference current is applied through said each field line, said each field line generates an associated first external magnetic field that orients both the first and second ferromagnetic structures in a common first storage magnetization direction, and
when said corresponding MTJ element is at an intermediate temperature between the first and second blocking temperature and a second reference current is applied through said each field line, said each field line generates an associated second external magnetic field that orients only the second ferromagnetic structure in a final storage magnetization direction.

9. The logic unit of claim 8 , wherein each said field line is magnetically coupled to said storage layer and said sensing layer of said corresponding MTJ element such that:
when said corresponding MTJ element cools from above the first blocking temperature to the intermediate temperature, the first ferromagnetic structure becomes fixed by the first AF layer such that the first ferromagnetic structure maintains said first storage magnetization direction when said first external magnetic field is subsequently terminated, and
when said corresponding MTJ element cools from said intermediate temperature below said second blocking temperature, the second ferromagnetic structure becomes fixed by the second AF layer such that the second ferromagnetic structure maintains said final storage magnetization direction when said second external magnetic field is subsequently terminated.

10. The logic unit of claim 1 , wherein the storage layer and the associated sense layer of each said MTJ element are magnetostatically coupled with an anti-parallel alignment of magnetization vectors such that, when said each MTJ element is at an intermediate temperature between the first and second blocking temperatures and the storage layer is fixed in a first storage magnetization direction, the associated sense layer is magnetically biased by said associated storage layer into a preliminary storage magnetization direction that is opposite to the first storage magnetization direction of the associated storage layer.

11. The logic unit of claim 1 , wherein said controller further comprises means for generating a read current through said plurality of MTJ elements during a compare operation.

12. The logic unit of claim 11 , further comprising a current sensor operably coupled to measure said read current during said compare operation.

13. The logic unit of claim 11 , further comprising a plurality of field lines, each said field line being magnetically coupled to said storage layer and said sensing layer of a corresponding said MTJ element,
wherein said controller further comprises a current sensor operably coupled to measure said read current during said compare operation.

14. A logic unit comprising:
a plurality of Magnetic Tunnel Junction (MTJ) elements connected in series, each said MTJ element comprising:
a storage layer including a first antiferromagnetic structure contacting a first ferromagnetic structure, the first antiferromagnetic structure comprising a first material having a first blocking temperature;
a sense layer including a second antiferromagnetic structure contacting a second ferromagnetic structure, the second antiferromagnetic structure comprising a second antiferromagnetic material having a second blocking temperature; and
a tunnel dielectric layer disposed between the first ferromagnetic structure of the storage layer and the second ferromagnetic structure of the sense layer, wherein the first blocking temperature of the first antiferromagnetic material is greater than the second blocking temperature of the second antiferromagnetic material;

a first select transistor coupled in series with said plurality of MTJ elements between a voltage source and a first ground terminal, and means for controlling the first select trans

Assignees

• Tower Semiconductor Ltd

Inventors

• Roizin Yakov
• Strum Avi

Classifications

• H01L27/228 Primary

  Electricity · mapped topic

• H01L43/02

  Electricity · mapped topic

• H03K19/00369

  Modifications for compensating variations of temperature, supply voltage or other physical parameters · CPC title

• G11C11/15

  using multiple magnetic layers (G11C11/155 takes precedence) · CPC title

• H03K19/18

  using galvano-magnetic devices, e.g. Hall-effect devices · CPC title