Magnetic memory device that is protected against reading using an external magnetic field and method for operating such magnetic memory device

Patent metadata

Field	Value
Publication number	US-10115445-B2
Application number	US-201615741805-A
Country	US
Kind code	B2
Filing date	Jun 27, 2016
Priority date	Jul 7, 2015
Publication date	Oct 30, 2018
Grant date	Oct 30, 2018

Abstract

A magnetic memory device including a plurality of magnetic units, each unit including a first and second magnetic tunnel junctions—electrically connected in series by a current line and a strap. Each junction includes a first and second storage layer having a first and second storage magnetization and a first sense magnetic layer having a first and second senses magnetization. A field line is configured to provide an input signal generating a first and second magnetic field for varying the first and second sense magnetization. Each magnetic unit is provided with a data state such that the first and second storage magnetizations are aligned in opposed directions. The first and second magnetic field are adapted for varying respectively the first and second sense magnetization in a first and second direction opposed to the first direction.

First claim

What is claimed is:

1. A magnetic memory device configured to be used with a self-referenced read operation, the memory comprising a plurality of magnetic units, each unit including:
a first magnetic tunnel junction comprising a first storage layer having a first storage magnetization and a first sense magnetic layer having a first sense magnetization;
a second magnetic tunnel junction comprising a second storage layer having a second storage magnetization and a second sense magnetic layer having a second sense magnetization;
a current line and a strap electrically connecting the first and second magnetic tunnel junctions in series;
a field line comprising:
a first line portion for passing, during the read operation, a first current portion of a field current, the first current portion generating a first magnetic field adapted for varying the first sense magnetization and a first resistance of the first magnetic tunnel junction; and
a second line portion for passing a second current portion of the field current, the second current portion generating a second magnetic field adapted for varying the second sense magnetization direction and a second resistance of the second magnetic tunnel junction, the second current portion having a polarity opposed to the one of the first current portion;

each magnetic unit being provided with a data state such that the first storage magnetization is aligned in a direction opposed to the one of the second storage magnetization;
wherein the first magnetic field is adapted for varying the first sense magnetization in a first direction and the second magnetic field is adapted for varying the second sense magnetization in a second direction opposed to the first direction, such that, in each magnetic unit either, the first storage magnetization is parallel to the first sense magnetization and the second sense magnetization, or the first storage magnetization is antiparallel to the first sense magnetization and to the second sense magnetization;
the current line being configured for providing an output signal that varies in response to the sum of the resistances of the first and second magnetic tunnel junctions of each of said plurality of magnetic units, such that said data state can be determined only when the input signal is provided to the field line.

2. The magnetic memory device according to claim 1 ,
wherein the first line portion and the second line portion are addressable independently, such that the first current portion can be passed in the first line portion independently from passing the second current portion in the first line portion.

3. The magnetic memory device according to claim 1 ,
wherein the first line portion is electrically connected in series to the second line portion.

4. The magnetic memory device according to claim 2 ,
wherein the field line is U-shaped.

5. Method for operating a magnetic memory device comprising a plurality of magnetic units, each unit including:
a first magnetic tunnel junction comprising a first storage layer having a first storage magnetization and a first sense magnetic layer having a first sense magnetization;
a second magnetic tunnel junction comprising a second storage layer having a second storage magnetization and a second sense magnetic layer having a second sense magnetization;
a current line and a strap electrically connecting the first and second magnetic tunnel junctions in series;
a field line comprising a first line portion for passing a first current portion of a field current and a second line portion for passing a second current portion of the field current;
the current line being configured for providing an output signal that varies in response to the sum of the resistances of the first and second magnetic tunnel junctions of each of said plurality of magnetic units;
the method comprising:
providing a data state to be read in each magnetic unit such that the first storage magnetization direction is aligned in a direction opposed to the one of the second storage magnetization direction;
providing a field current to the field line comprising:
passing the first current portion having a first polarity in the first line portion, the first current portion generating a first magnetic field adapted for varying the first sense magnetization and a first resistance of the first magnetic tunnel junction;
passing the second current portion having a second polarity in the second line portion, the second current portion generating a second magnetic field adapted for varying the second sense magnetization direction and a second resistance of the second magnetic tunnel junction, the second current portion having a polarity opposed to the one of the first current portion, such as to align the first and second sense magnetizations in opposed directions;

measuring the sum of the resistances of the first and second magnetic tunnel junctions of said plurality of magnetic units; and
determining the stored data state from the measured sum of the resistances.

6. The method according to claim 5 ,
wherein said providing an input comprises:
passing the field current having a first polarity such as to align the first and second sense magnetizations in a first set of opposed directions; and
passing the field current having a second polarity such as to align the first and second sense magnetizations in a second set of opposed directions wherein the orientation of each of the first and second sense magnetization is opposed to the one in the first set of opposed directions.

7. The method according to claim 6 ,
wherein said measuring the sum of the resistances comprises measuring a first sum of the resistances when passing the field current having a first polarity and measuring a second sum of the resistances when passing the field current having a second polarity; and
wherein said determining the stored data state comprises determining a relative difference between the first sum of the resistance and the second sum of the resistance.

8. The method according to claim 7 ,
wherein the field current has an alternating polarity.

9. The method according to claim 5 ,
wherein the first and second magnetic tunnel junction further comprises a first and second antiferromagnetic layer pinning the first and second storage magnetization at a low temperature threshold and freeing it at a high temperature threshold; and
wherein said providing a data state comprises:
passing a heating current in the current line to heat the first and second magnetic tunnel junctions at the high temperature threshold such as to free the first and second storage magnetizations;
passing a write current in the field line such as to generate a first write magnetic field adapted for aligning the first storage magnetization in a first direction, and as to generate a second write magnetic field adapted for aligning the second storage magnetization in a second written direction opposed to the first written direction; and
cooling the first and second magnetic tunnel junctions to the low temperature threshold such as to pin the first and second storage magnetizations in the stored state.

Assignees

• Crocus Technology Sa

Inventors

• Stainer Quentin

Classifications

• G11C11/1675

  Writing or programming circuits or methods · CPC title

• H01F10/3254

  the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ] · CPC title

• H01F10/3268

  the exchange coupling being asymmetric, e.g. by use of additional pinning, by using antiferromagnetic or ferromagnetic coupling interface, i.e. so-called spin-valve [SV] structure, e.g. NiFe/Cu/NiFe/FeMn · CPC title

• G11C11/161

  details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell · CPC title

• G11C11/1673 Primary

  Reading or sensing circuits or methods · CPC title