High-speed compare operation using magnetic tunnel junction elements including two different anti-ferromagnetic layers

• US 9,330,748 B2
• Filed: 05/09/2014
• Issued: 05/03/2016
• Est. Priority Date: 05/09/2014
• Status: Active Grant

• Current Assignee: Tower Semiconductor Limited
• Original Assignee: Tower Semiconductor Limited
• Inventors: Roizin, Yakov, Strum, Avi
• Primary Examiner(s): Hur, J. H.
• Application Number:
  US14/274,609
• Publication Number:
  US 20150325279A1
• Time in Patent Office: 725 Days
• US Class Current: 1/1
• 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
• CPC Class Codes: G11C 15/02 using magnetic elements

Abstract

A match-in-place-type compare operation utilizes a string of Magnetic Tunnel Junction (MTJ) elements including storage layers and sense layers having different anti-ferromagnetic structures respectively having higher and lower blocking temperatures. Confidential data is written into the storage layers of the MTJ elements by heating the elements above the higher blocking temperature, and then orienting the storage and sense layers in first storage magnetization directions using field lines. The elements are then cooled to an intermediate temperature between the higher and lower blocking temperatures, and the field lines are turned off, setting the sense layers to preliminary storage magnetization directions opposite to the first directions. During a pre-compare phase, an input logic pattern is written into the sense layers by heating to the intermediate temperature. During a compare operation, with the field lines turned off, resistance of the MTJ string is detected by passing a read current through the string.

Claims

1. A method for performing a high-speed compare operation to determine whether an input data bit value matches a previously stored confidential data bit value using at least one magnetic Tunnel Junction (MTJ) element including a non-volatile storage layer and a non-volatile sense layer separated by a tunnel junction layer, the method comprising:

during a write/program operation, writing said confidential data bit value into the MTJ element by fixing the non-volatile storage layer in an associated first storage magnetization direction determined by said confidential data bit value, and fixing the non-volatile sense layer in an associated preliminary storage magnetization direction that is opposite to the first magnetization direction, whereby said MTJ element exhibits a high resistance value at the end of said write/program operation;

during a pre-compare phase performed subsequent to the write/program operation, writing said input data bit value into the non-volatile sense layer by fixing the sense layer in an associated final storage magnetization direction determined by said input data bit value without changing said confidential data bit value non-volatilely stored in said non-volatile storage layer, whereby at the end of said pre-compare phase, said confidential data bit value is non-volatilely stored in said non-volatile storage layer and said input data bit value is non-volatilely stored in said non-volatile sense layer, wherein said MTJ element retains said high resistance value when said final storage magnetization direction is the same as said preliminary storage magnetization direction, and said MTJ element exhibits a low resistance value when said final storage magnetization direction is opposite to said preliminary storage magnetization direction; and

during a compare phase performed subsequent to the pre-compare phase, determining if the input data bit value matches the confidential data bit value by measuring a resistance of said MTJ element,

wherein said MTJ element further includes an associated field line that is magnetically coupled to said storage layer and said sense layer,

wherein writing said confidential data bit value comprises applying a first reference current on said field line,

wherein writing said input data bit value comprises applying a second reference current on said field line, and

wherein measuring said resistance of said MTJ element comprises applying a read current through the MTJ element while zero current is applied to said field line.

2. The method of claim 1,

wherein the non-volatile storage layer comprises a first antiferromagnetic structure contacting a first ferromagnetic structure, the first antiferromagnetic structure comprising a first material having a first blocking temperature,

wherein the sense layer comprises a second antiferromagnetic structure contacting a second ferromagnetic structure, the second antiferromagnetic structure comprising a second antiferromagnetic material having a second blocking temperature, and

wherein the writing a confidential data bit value into the MTJ element comprises:

heating the MTJ element to a temperature above the first blocking temperature,

generating a first external magnetic field such that both said first ferromagnetic structure and said second ferromagnetic structure are polarized in said first magnetization direction, and

fixing said first ferromagnetic structure in said first storage magnetization direction by cooling the MTJ element to an intermediate temperature below the first blocking temperature and above the second blocking temperature.

3. The method of claim 2, wherein heating the MTJ element comprises generating a first heating current that passes through said MTJ element.

4. The method of claim 2, wherein generating said first external magnetic field comprises applying a first reference current on a field line that is magnetically coupled to said storage layer and said sense layer.

5. The method of claim 2, wherein fixing said first ferromagnetic structure in said first storage magnetization further comprises maintaining said first external magnetic field while cooling the MTJ element to said intermediate temperature.

6. The method of claim 2,

wherein the storage layer and the sense layer of said MTJ element are magnetostatically coupled with an anti-parallel alignment of magnetization vectors, and

wherein writing said confidential data bit value into the MTJ element further comprises, after fixing said first ferromagnetic structure in said first storage magnetization direction, terminating said external magnetic field while the MTJ element is at said intermediate temperature, thereby causing the sense layer to assume said associated preliminary storage magnetization direction that is opposite to the first storage magnetization direction of the storage layer by said magnetostatic coupling.

7. The method of claim 6, further comprising, after causing the sense layer to assume said associated preliminary storage magnetization direction, fixing said preliminary storage magnetization direction by cooling said MTJ element below the second blocking temperature.

8. The method of claim 2, wherein writing said input data bit value into the sense layer comprises:

heating the MTJ element to said intermediate temperature,

generating a second external magnetic field such that said second ferromagnetic structure is polarized in said final storage magnetization direction, and

fixing said second ferromagnetic structure in said final storage magnetization direction by cooling the MTJ element below the second blocking temperature.

9. The method of claim 8, wherein heating the MTJ element comprises generating a second heating current that passes through said MTJ element.

10. The method of claim 8, wherein generating said second external magnetic field comprises applying a second reference current on a field line that is magnetically coupled to said sense layer.

11. The method of claim 8, wherein fixing said second ferromagnetic structure in said final storage magnetization further comprises maintaining said second external magnetic field while cooling the MTJ element to said intermediate temperature.

12. The method of claim 11, wherein said detecting comprises:

terminating said second external magnetic field; and

applying a read current through the MTJ element such that said read current passes through said MTJ element when said final storage magnetization direction matches said first storage magnetization direction, and such that said read current is prevented from passing through said MTJ element when said final storage magnetization direction fails to match said first storage magnetization direction.

13. The method of claim 1,

wherein said at least one MTJ element further includes a field line that is magnetically coupled to said storage layer and said sense layer,

wherein writing said confidential data bit value comprises applying a first reference current on said field line,

wherein writing said input data bit value comprises applying a second reference current on said field line, and

wherein detecting said resistance of said MTJ element comprises applying a read current through the MTJ element while zero current is applied to said field line.

14. A method for performing a high-speed compare operation using a Magnetic Tunnel Junction (MTJ) string including a plurality of Magnetic Tunnel Junction (MTJ) elements connected in series, wherein each said MTJ element includes a storage layer and a sense layer separated by a tunnel junction layer, the method comprising:

during a write/program operation, writing a confidential data bit value into each of said MTJ elements by orienting the storage layer of each said MTJ element in an associated first storage magnetization direction, and orienting the sense layer of said each MTJ element in an associated preliminary storage magnetization direction that is opposite to the first magnetization direction, whereby each of said plurality of MTJ elements exhibits a high resistance value at the end of said write/program operation;

during a pre-compare phase performed subsequent to the write/program operation, writing an input data bit value into the sense layer of each of said MTJ elements by orienting the sense layer of each said MTJ element in an associated final storage magnetization direction without changing said confidential data bit value non-volatilely stored in said non-volatile storage layer of each said MTJ element, whereby at the end of said pre-compare phase, said confidential data bit values are non-volatilely stored in said non-volatile storage layers of said plurality of MTJ elements and said input data bit values are non-volatilely stored in said non-volatile sense layers of said plurality of MTJ elements, wherein said each MTJ element retains said high resistance value when said final storage magnetization direction is the same as said preliminary storage magnetization direction, and said each MTJ element exhibits a low resistance value when said final storage magnetization direction is opposite to said preliminary storage magnetization direction; and

during a compare phase performed subsequent to the pre-compare phase, detecting a resistance of said MTJ string by measuring a read current passed through said MTJ string,

wherein each of said plurality of MTJ elements further includes an associated field line that is magnetically coupled to said storage layer and said sense layer of said each MTJ elements,

wherein writing said confidential data bit values comprises applying first reference currents on said field lines,

wherein writing said input data bit values comprises applying second reference currents on said field lines, and

wherein detecting said resistance of said MTJ string comprises applying a read current through the plurality of MTJ elements while zero current is applied to said field lines.

15. The method of claim 14,

wherein the storage layer of each said MTJ element comprises a first antiferromagnetic structure contacting a first ferromagnetic structure, the first antiferromagnetic structure comprising a first material having a first blocking temperature,

wherein the sense layer of each said MTJ element comprises a second antiferromagnetic structure contacting a second ferromagnetic structure, the second antiferromagnetic structure comprising a second antiferromagnetic material having a second blocking temperature, and

wherein the writing a confidential data bit value into each said MTJ element comprises:

heating the MTJ string to a temperature above the first blocking temperature,

generating first external magnetic fields such that both said first ferromagnetic structure and said second ferromagnetic structure of each said MTJ element are polarized in first magnetization directions determined by an associated said first external magnetic field, and

fixing said first ferromagnetic structures of said plurality of MTJ elements in said first storage magnetization directions by cooling the MTJ string to an intermediate temperature below the first blocking temperature and above the second blocking temperature.

16. The method of claim 15,

wherein the storage layer and the sense layer of each said MTJ element are respectively magnetostatically coupled with an anti-parallel alignment of magnetization vectors, and

wherein writing said confidential data bit values into the plurality of MTJ elements further comprises, after fixing said first ferromagnetic structures in said first storage magnetization directions, terminating said external magnetic fields while the MTJ string is at said intermediate temperature, thereby causing the sense layer each said MTJ element to assume said associated preliminary storage magnetization direction that is opposite to the first storage magnetization direction of the storage layer of said each MTJ element.

17. The method of claim 16, further comprising, after causing the sense layers of said plurality of MTJ elements to assume said associated preliminary storage magnetization directions, fixing said preliminary storage magnetization directions by cooling said MTJ string below the second blocking temperature.

18. The method of claim 15, wherein writing said input data bit value into the sense layer of each said MTJ element comprises:

heating the MTJ string to said intermediate temperature,

generating second external magnetic fields such that said second ferromagnetic structure of each said MTJ element is polarized in said associated final magnetization directions determined by an associated said second external magnetic field, and

fixing said second ferromagnetic structures of said plurality of MTJ elements in said final storage magnetization directions by cooling the MTJ string below the second blocking temperature.

19. The method of claim 18, wherein said detecting comprises:

terminating said second external magnetic fields; and

applying a read current through said MTJ string, whereby said read current passes through said MTJ string when said final storage magnetization direction matches said first storage magnetization direction in all of said MTJ elements, said read current passing through said MTJ string when said final storage magnetization direction fails to match said first storage magnetization direction in at least one of said MTJ elements is lower than said read current passing through said MTJ string when said final storage magnetization direction matches said first storage magnetization direction in all of said MTJ elements.