# US 8,772,886 B2 · Spin transfer torque magnetic random access memory (STTMRAM) having graded synthetic free layer

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 8,772,886 B2
- Document ID: US8772886B2
- Status: Granted
- Kind: B2
- Application number: 13/099,308
- Filed: 2011-05-02
- Published: 2012-01-26
- Granted: 2014-07-08
- Earliest claimed: 2010-07-26
- Assignees: Avalanche Technology, Inc.
- Applicants: Yiming Huai; Rajiv Yadav Ranjan; Ioan Tudosa; Roger Klas Malmhall; Yuchen Zhou
- Inventors: Yiming Huai; Rajiv Yadav Ranjan; Ioan Tudosa; Roger Klas Malmhall; Yuchen Zhou
- Web page: https://patentgrep.com/patent/US8772886B2

## CPC

- H10N 50/80: Constructional details
- B82Y 25/00: Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
- G11C 11/161: {details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell}
- H01F 10/3272: {by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets}
- 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}
- H10N 50/10: Magnetoresistive devices
- H10N 50/85: Materials of the active region
- H01F 10/3254: {the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]}
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- B82Y: SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
- G11C: STATIC STORES (semiconductor memory devices H10B)
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES

## Abstract

A spin transfer torque memory random access memory (STTMRAM) element is capable of switching states when electrical current is applied thereto for storing data and includes the following layers. An anti-ferromagnetic layer, a fixed layer formed on top of the anti-ferromagnetic layer, a barrier layer formed on top of the second magnetic layer of the fixed layer, and a free layer including a first magnetic layer formed on top of the barrier layer, a second magnetic layer formed on top of the first magnetic layer, a non-magnetic insulating layer formed on top of the second magnetic layer and a third magnetic layer formed on top of the non-magnetic insulating layer. A capping layer is formed on top of the non-magnetic insulating layer.

## Claims

### Claim 1

A spin transfer torque random access memory (STTMRAM) element capable of switching states when electrical current is applied thereto for storing data, the STTMRAM element comprising:
an anti-ferromagnetic layer;
a fixed layer formed on top of the anti-ferromagnetic layer, the fixed layer comprising:
a first fixed magnetic layer having a first fixed magnetic orientation substantially parallel to the layer plane thereof; and
a second fixed magnetic layer having a second fixed magnetic orientation substantially parallel to the layer plane thereof;
a barrier layer formed directly on top of the second fixed magnetic layer;
a free layer including:
a first free magnetic layer formed directly on top of the barrier layer and having associated therewith a first saturation magnetization (Ms), the first free magnetic layer having a first switchable magnetic orientation substantially parallel to the layer plane thereof;
a second free magnetic layer formed on top of the first free magnetic layer and having associated therewith a second Ms, the second free magnetic layer having a second switchable magnetic orientation substantially parallel to the layer plane thereof;
a non-magnetic insulating layer formed on top of the second free magnetic layer; and
a third free magnetic layer formed on top of the non-magnetic insulating layer, the third free magnetic layer having a third switchable magnetic orientation substantially parallel to the layer plane thereof;
wherein the first Ms of the first free magnetic layer is higher than the second Ms of the second free magnetic layer, the first and second switchable magnetic orientations have substantially the same direction that is substantially opposite to the third switchable magnetic orientation; and
a capping layer formed directly on top of the third free magnetic layer,
wherein the first fixed magnetic layer is made of a material comprising: silicon dioxide (SiO2), titanium dioxide (TiO2), tantalum oxide (Ta2O5), aluminum oxide (Al2O3), or any combination thereof.

### Claim 2 (depends on 1)

The STTMRAM element of claim 1, wherein the first fixed magnetic layer is formed on top of the anti-ferromagnetic layer, and the fixed layer further includes,
an anti-ferromagnetic coupling layer formed on top of the first fixed magnetic layer and configured to assist in making the magnetic orientation of the first fixed magnetic layer fixed, and wherein the second fixed magnetic layer is formed on top of the anti-ferromagnetic coupling layer of the fixed layer, the anti-ferromagnetic coupling layer further configured to make the magnetic orientation of the second fixed magnetic layer fixed,
wherein the first fixed magnetic layer and the second fixed magnetic layer have opposing magnetic orientations.

### Claim 3 (depends on 1)

The STTMRAM element of claim 1, wherein the first, second and third free magnetic layers are each made of a material selected from a group consisting of iron (Fe), nickel (Ni), cobalt (Co), platinum (Pt), copper (Cu), boron (B), tantalum (Ta), titanium (Ti), chromium (Cr), terbium (Tb), samarium (Sm), neodymium (Nd), gadolinium (Gd), titanium dioxide (TiO2), magnesium oxide (MgO), tantalum oxide (Ta2O5), aluminum oxide (Al2O3), and any combination thereof.

### Claim 4 (depends on 1)

The STTMRAM element of claim 1, wherein the first, second and third free magnetic layers are each made of alloys of cobolt-iron-boron (CoFeB).

### Claim 5 (depends on 1)

The STTMRAM element of claim 1, wherein the first and second free magnetic layers are made of different material.

### Claim 6 (depends on 1)

The STTMRAM element of claim 1, wherein the first and second free magnetic layers have different thicknesses.

### Claim 7 (depends on 1)

The STTMRAM element of claim 1, wherein the anti-ferromagnetic layer is configured to make the magnetic orientation of the fixed layer fixed.

### Claim 8 (depends on 1)

The STTMRAM element of claim 1, wherein the free layer further includes a fourth free magnetic layer formed on top of the non-magnetic insulating layer and below the capping layer.

### Claim 9 (depends on 8)

The STTMRAM element of claim 8, wherein the fourth free magnetic layer is made of a material selected from a group consisting of iron (Fe), nickel (Ni), cobalt (Co), platinum (Pt), copper (Cu), boron (B), tantalum (Ta), titanium (Ti), chromium (Cr), terbium (Tb), samarium (Sm), neodymium (Nd), gadolinium (Gd), titanium dioxide (TiO2), magnesium oxide (MgO), tantalum oxide (Ta2O5), aluminum oxide (Al2O3), and any combination thereof.

### Claim 10 (depends on 1)

The STTMRAM element of claim 1, further including an underlayer on top of which the anti-ferromagnetic layer is formed.

### Claim 11 (depends on 1)

The STTMRAM element of claim 1, wherein the first fixed magnetic layer is formed on top of the anti-ferromagnetic layer and the second fixed magnetic layer is formed on top of the first fixed magnetic layer.

### Claim 12 (depends on 1)

The STTMRAM element of claim 1, wherein the fixed layer further includes an anti-ferromagnetic coupling layer separating the first fixed magnetic layer from the second fixed magnetic layer.

### Claim 13 (depends on 1)

The STTMRAM element of claim 1, wherein the first fixed magnetic layer has a thickness within the range of 0.5 nano meters (nm) to 5 nm.

### Claim 14 (depends on 1)

The STTMRAM element of claim 1, wherein the first fixed magnetic layer and the second fixed magnetic layer are made of substantially the same material.

### Claim 15 (depends on 1)

The STTMRAM element of claim 1, wherein the first fixed magnetic layer and the second fixed magnetic layer have substantially the same thickness.

### Claim 16

A spin transfer torque magnetic random access memory (STTMRAM) element comprising:
an anti-ferromagnetic layer;
a magnetic fixed layer formed adjacent to the anti-ferromagnetic layer, the magnetic fixed layer comprising a first invariable magnetic subylayer and a second invariable magnetic subylayer with an anti-ferromagnetic coupling layer interposed therebetween;
a barrier layer formed adjacent to the magnetic fixed layer opposite to the anti-ferrogmagnetic layer;
a magnetic free layer comprising a first variable magnetic sublayer, a second variable magnetic sublayer, a non-magnetic insulating sublayer, and a third variable magnetic sublayer formed in sequential order with the first variable magnetic sublayer formed adjacent to the barrier layer opposite to the magnetic fixed layer; and
a capping layer formed adjacent to the third variable magnetic sublayer,
wherein each of the magnetic sublayers has a magnetic orientation parallel to respective layer plane thereof, the first, the second, and the third variable magnetic sublayers have respectively a first, a second, and a third saturation magnetizations, the first and third saturation magnetizations are higher than the second saturation magnetization.