Ferromagnetic tunnel junction element and method of driving ferromagnetic tunnel junction element

• US 9,680,088 B2
• Filed: 11/24/2014
• Issued: 06/13/2017
• Est. Priority Date: 03/06/2008
• Status: Active Grant

• Current Assignee: III Holdings 3, LLC (Intellectual Ventures LLC)
• Original Assignee: III Holdings 3, LLC (Intellectual Ventures LLC)
• Inventors: Ono, Takuya
• Primary Examiner(s): Wilczewski, Mary
• Assistant Examiner(s): CHIU, TSZ K
• Application Number:
  US14/551,095
• Publication Number:
  US 20150200356A1
• Time in Patent Office: 932 Days
• Field of Search: 257432
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• 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: H01F 10/3254 the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]
• CPC Class Codes: H01F 10/3268 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 Class Codes: H01F 10/3295 Spin-exchange coupled multilayers wherein the magnetic pinned or free layers are laminated without anti-parallel coupling within the pinned and free layers
• CPC Class Codes: H10B 61/00 Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
• CPC Class Codes: H10B 61/22 of the field-effect transistor [FET] type
• CPC Class Codes: H10N 50/10 Magnetoresistive devices
• CPC Class Codes: H10N 50/80 Constructional details
• CPC Class Codes: H10N 50/85 Magnetic active materials

Abstract

In a tunnel junction element having a ferromagnetic free layer, an insulating layer and a ferromagnetic fixed layer, in order to reduce the current necessary for spin-transfer magnetization reversal operation in the tunnel junction element, the ferromagnetic free layer comprises first and second ferromagnetic layers, a nonmagnetic metal layer is provided between these ferromagnetic layers, the nonmagnetic metal layer is such that magnetic coupling is preserved between the first and second ferromagnetic layers, also such that there is no influence on the crystal growth of the first and second ferromagnetic layers, the first ferromagnetic layer and the second ferromagnetic layer are placed such that the first ferromagnetic layer is in contact with the insulating layer, and the second ferromagnetic layer has a smaller magnetization than the first ferromagnetic layer.

Claims

1. A ferromagnetic tunnel junction element, comprising:

a ferromagnetic free layer;

an insulating layer; and

a ferromagnetic fixed layer that, together with the ferromagnetic free layer, sandwiches the insulating layer;

wherein the ferromagnetic free layer includes a first ferromagnetic layer in contact with the insulating layer, a nonmagnetic metal layer, and a second ferromagnetic layer that, together with the first ferromagnetic layer, sandwiches the nonmagnetic metal layer, and wherein the second ferromagnetic layer has a saturation magnetization smaller than a saturation magnetization of the first ferromagnetic layer; and

wherein a film thickness of the nonmagnetic metal layer is set to a film thickness at which the first ferromagnetic layer is ferromagnetically coupled to the second ferromagnetic layer to maintain a parallel state between the first ferromagnetic layer and the second ferromagnetic layer in which a magnetization direction of the first ferromagnetic layer is parallel with and in a same direction as a magnetization direction of the second ferromagnetic layer.

2. The ferromagnetic tunnel junction element of claim 1, wherein:

the first ferromagnetic layer comprises;

a single metal selected from a magnetic metal group consisting of iron, cobalt, and nickel;

or

an alloy comprising one metal selected from the magnetic metal group;

or

a compound comprising one metal selected from the magnetic metal group and a metalloid element; and

the insulating layer comprises magnesium oxide.

3. The ferromagnetic tunnel junction element of claim 1, wherein the insulating layer and the first ferromagnetic layer are epitaxially joined with each other, and wherein the nonmagnetic metal layer is selected from materials which prevent mutual influence of crystallinity of the first and second ferromagnetic layers.

4. The ferromagnetic tunnel junction element of claim 1, wherein the second ferromagnetic layer is of Permalloy.

5. A magnetic random access memory, comprising:

a plurality of storage elements, each storage element including a ferromagnetic tunnel junction element comprising a ferromagnetic free layer, an insulating layer, and a ferromagnetic fixed layer that, together with the ferromagnetic free layer, sandwiches the insulating layer;

wherein the ferromagnetic free layer includes a first ferromagnetic layer in contact with the insulating layer, a nonmagnetic metal layer, and a second ferromagnetic layer that, together with the first ferromagnetic layer, sandwiches the nonmagnetic metal layer, and wherein the second ferromagnetic layer has a saturation magnetization smaller than a saturation magnetization of the first ferromagnetic layer; and

wherein a film thickness of the nonmagnetic metal layer is set to a film thickness at which the first ferromagnetic layer is ferromagnetically coupled to the second ferromagnetic layer to maintain a parallel state between the first ferromagnetic layer and the second ferromagnetic layer in which a magnetization direction of the first ferromagnetic layer is parallel with and in a same direction as a magnetization direction of the second ferromagnetic layer.

6. The magnetic random access memory of claim 5, wherein the second ferromagnetic layer of each storage element is of Permalloy.

7. A ferromagnetic tunnel junction element, comprising:

a ferromagnetic free layer;

an insulating layer; and

a ferromagnetic fixed layer that, together with the ferromagnetic free layer, sandwiches the insulating layer;

wherein the ferromagnetic free layer includes a first ferromagnetic layer and a second ferromagnetic layer;

wherein the first ferromagnetic layer is in contact with the insulating layer and ferromagnetically coupled to the second ferromagnetic layer;

wherein the first ferromagnetic layer and the second ferromagnetic layer have a same direction of magnetization with respect to each other; and

wherein the second ferromagnetic layer has a saturation magnetization smaller than a saturation magnetization of the first ferromagnetic layer to obtain an effective saturation magnetization for the ferromagnetic free layer that is smaller than the saturation magnetization of the first ferromagnetic layer.

8. The ferromagnetic tunnel junction element of claim 7, wherein:

the first ferromagnetic layer comprises;

a single metal selected from a magnetic metal group consisting of iron, cobalt, and nickel;

or

an alloy comprising one metal selected from the magnetic metal group;

or

a compound comprising one metal selected from the magnetic metal group and a metalloid element; and

the insulating layer comprises magnesium oxide.

9. The ferromagnetic tunnel junction element of claim 7, wherein the insulating layer and the first ferromagnetic layer are epitaxially joined with each other, and wherein the nonmagnetic metal layer is selected from materials which prevent mutual influence of crystallinity of the first and second ferromagnetic layers.

10. The ferromagnetic tunnel junction element of claim 7, wherein the second ferromagnetic layer is of Permalloy.

11. A magnetic random access memory, comprising:

a plurality of bit lines;

a plurality of read word lines; and

a plurality of ferromagnetic tunnel junction elements;

wherein each ferromagnetic tunnel junction element is associated with a bit line of the plurality of bit lines and a read word line of the plurality of read word lines and includes a ferromagnetic fixed layer and a ferromagnetic free layer;

wherein the ferromagnetic fixed layer has a fixed magnetization direction;

wherein an associated bit line is configured to align a magnetization direction of the ferromagnetic free layer with the fixed magnetization direction to store a first bit value and reverse the magnetization direction with respect to the fixed magnetization direction to store a second bit value;

wherein the ferromagnetic free layer comprises a first ferromagnetic layer ferromagnetically coupled to a second ferromagnetic layer;

wherein magnetization of the first ferromagnetic layer and magnetization of the second ferromagnetic layer are directed in a common direction with each other; and

wherein the second ferromagnetic layer has a saturation magnetization smaller than a saturation magnetization of the first ferromagnetic layer to obtain an effective saturation magnetization for the ferromagnetic free layer that is smaller than the saturation magnetization of the first ferromagnetic layer.

12. The magnetic random access memory of claim 11, wherein:

the first ferromagnetic layer of each ferromagnetic tunnel junction element comprises;

a single metal selected from a magnetic metal group consisting of iron, cobalt, and nickel;

or

an alloy comprising one metal selected from the magnetic metal group;

or

a compound comprising one metal selected from the magnetic metal group and a metalloid element; and

the insulating layer of each ferromagnetic tunnel junction comprises magnesium oxide.

13. The magnetic random access memory of claim 12, wherein the insulating layer and the first ferromagnetic layer of each ferromagnetic tunnel junction element are epitaxially joined with each other, and wherein the nonmagnetic metal layer is selected from materials which prevent mutual influence of crystallinity of the first and second ferromagnetic layers of each ferromagnetic tunnel junction element.

14. The magnetic random access memory of claim 12, wherein the second ferromagnetic layer of each ferromagnetic tunnel junction element comprises Permalloy.