# US 10,770,651 B2 · Perpendicular spin transfer torque memory (PSTTM) devices with enhanced perpendicular anisotropy and methods to form same

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- Number: US 10,770,651 B2
- Document ID: US10770651B2
- Status: Granted
- Kind: B2
- Application number: 16/463,326
- Filed: 2016-12-30
- Published: 2019-12-12
- Granted: 2020-09-08
- Earliest claimed: 2016-12-30
- Assignees: Intel Corporation
- Applicants: Intel Corporation
- Inventors: MD Tofizur Rahman; Christopher J. Wiegand; Kaan Oguz; Daniel G. Ouellette; Brian Maertz; Kevin P. O'Brien; Mark L. Doczy; Brian S. Doyle; Oleg Golonzka; Tahir Ghani
- Web page: https://patentgrep.com/patent/US10770651B2

## CPC

- H10B 61/10: {comprising components having two electrodes, e.g. diodes or MIM elements}
- H01F 10/3254: {the spacer being semiconducting or insulating, e.g. for spin tunnel junction [STJ]}
- H01F 10/3272: {by use of anti-parallel coupled [APC] ferromagnetic layers, e.g. artificial ferrimagnets [AFI], artificial [AAF] or synthetic [SAF] anti-ferromagnets}
- H10B 61/00: Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10B 61/22: {of the field-effect transistor [FET] type}
- H10N 50/01: Manufacture or treatment
- H10N 50/10: Magnetoresistive devices
- H10N 50/80: Constructional details
- H10N 50/85: Materials of the active region
- H10B: ELECTRONIC MEMORY DEVICES
- H01F: MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

A material layer stack for a pSTTM device includes a fixed magnetic layer, a tunnel barrier disposed above the fixed magnetic layer and a free layer disposed on the tunnel barrier. The free layer further includes a stack of bilayers where an uppermost bilayer is capped by a magnetic layer including iron and where each of the bilayers in the free layer includes a non-magnetic layer such as Tungsten, Molybdenum disposed on the magnetic layer. In an embodiment, the non-magnetic layers have a combined thickness that is less than 15% of a combined thickness of the magnetic layers in the stack of bilayers. A stack of bilayers including non-magnetic layers in the free layer can reduce the saturation magnetization of the material layer stack for the pSTTM device and subsequently increase the perpendicular magnetic anisotropy.

## Claims

### Claim 1

A material layer stack for a pSTTM device, the material layer stack comprising:
a fixed magnetic layer; a tunnel barrier disposed above the fixed magnetic layer; and
a free layer disposed on the tunnel barrier, wherein the free layer comprises a stack of bilayers, wherein an uppermost bilayer is capped by a magnetic layer, wherein each of the bilayers comprises a non-magnetic layer disposed on a magnetic layer, wherein the magnetic layer in a first of the bilayers has a thickness that is greater than a thickness of the magnetic layer in a second of the bilayers.

### Claim 2 (depends on 1)

The material layer stack of claim 1, wherein the number of bilayers is at least 2.

### Claim 3 (depends on 1)

The material layer stack of claim 1, wherein the number of bilayer stacks is between 2-12.

### Claim 4 (depends on 1)

The material layer stack of claim 1, wherein the non-magnetic layers in the stack of bilayers have a combined thickness that is less than 5% of the combined thickness of each of the magnetic layers in the stack of the bilayers.

### Claim 5 (depends on 1)

The material layer stack of claim 1, wherein the magnetic layer in the first of the bilayers is in contact with the tunnel barrier.

### Claim 6 (depends on 5)

The material layer stack of claim 5, wherein the magnetic layer in contact with the tunnel barrier has a thickness that is at least 0.45 nm.

### Claim 7 (depends on 1)

The material layer stack of claim 1, wherein the combined thickness of the magnetic layers in the free layer is at least 1.0 nm.

### Claim 8 (depends on 1)

The material layer stack of claim 1, wherein the non-magnetic layers in the stack of bilayers have a combined thickness that is less than 15% of a combined thickness of the magnetic layers in the stack of bilayers.

### Claim 9 (depends on 1)

The material layer stack of claim 1, wherein the combined thickness of the non-magnetic layers in the stack of bilayers is at least 0.05 nm.

### Claim 10 (depends on 1)

The material layer stack of claim 1, wherein the magnetic layer comprises cobalt, boron and iron.

### Claim 11 (depends on 1)

The material layer stack of claim 1, wherein the non-magnetic layer comprises a metal selected from the group consisting of but not limited to molybdenum, ruthenium, tungsten, tantalum, aluminum and hafnium.

### Claim 12 (depends on 1)

The material layer stack of claim 1, wherein the material layer stack further comprises:
an oxide layer disposed on the free layer;
a protective layer disposed on the oxide layer; and
a conductive capping layer.

### Claim 13

A material layer stack for a pSTTM device, the material layer stack comprising:
a fixed magnetic layer;
a tunnel barrier disposed above the fixed magnetic layer;
a storage layer disposed on the tunnel barrier, wherein the storage layer comprises a first free layer disposed on the tunnel barrier, a coupling layer disposed on the first free layer, a second free layer disposed on the coupling layer, wherein one of the first free layer or the second free layer comprises a stack of bilayers, wherein an uppermost bilayer stack is capped by a magnetic layer, wherein each of the bilayers comprises a non-magnetic layer disposed on a magnetic layer, wherein the magnetic layer in a first of the bilayers has a thickness that is greater than a thickness of the magnetic layer in a second of the bilayers.

### Claim 14 (depends on 13)

The material layer stack of claim 13, wherein the first free layer comprises the stack of bilayers and the second free layer comprises a single magnetic layer.

### Claim 15 (depends on 14)

The material layer stack of claim 14, wherein the second free layer comprises a second stack of bilayers capped by a magnetic layer, wherein each of the second stack of bilayers comprises a non-magnetic layer disposed on a magnetic layer and wherein the magnetic layers in the second stack of stack of bilayer have a combined thickness that is less than that of the combined thickness of the magnetic layers in the stack of bilayers in the first magnetic layer.

### Claim 16 (depends on 13)

The material layer stack of claim 13, wherein the first free layer comprises a single magnetic layer and the second free layer comprises the stack of bilayers and wherein the combined thickness of the magnetic layers in the second free layer is less than the thickness of the first free layer that comprises a single magnetic layer.

### Claim 17 (depends on 13)

The material layer stack of claim 13, wherein the stack of bilayers formed in the first free layer has the magnetic layer of the first of the bilayers in contact with the tunnel barrier.

### Claim 18 (depends on 13)

The material layer stack of claim 13, wherein the combined total thickness of the magnetic layers in the first free layer is at least 1.0 nm and wherein the lowermost magnetic layer in the first free layer has a thickness that is at least 0.45 nm.

### Claim 19 (depends on 13)

The material layer stack of claim 13, wherein the combined total thickness of the non-magnetic layer in the first or in the second free layer is at least 0.045 nm.

### Claim 20 (depends on 13)

The material layer stack of claim 13, wherein the magnetic layer comprises cobalt, boron and iron and wherein the non-magnetic material is selected from the group consisting of molybdenum, ruthenium, tungsten, tantalum and aluminum.

### Claim 21 (depends on 13)

The material layer stack of claim 13, wherein the material layer stack further comprises:
a conductive oxide layer disposed on the storage layer;
a protective layer disposed on the conductive oxide layer;
a conductive capping layer;
a bottom electrode layer disposed below the fixed;
a top electrode layer disposed above the capping layer; and
a synthetic antiferromagnetic layer is disposed between the fixed layer and the bottom electrode layer.

### Claim 22 (depends on 13)

The material layer stack of claim 13, wherein the non-magnetic layers in the stack of bilayers have a combined thickness that is less than 15% of a combined thickness of the magnetic layers in the stack of the bilayers.

### Claim 23

A method of fabricating a material layer stack for a non-volatile memory device, the method comprising:
forming a bottom electrode layer;
forming a fixed magnetic layer; forming a tunnel barrier on fixed magnetic layer;
forming a storage layer, wherein forming a storage layer further comprises forming a first free layer on the tunnel barrier, forming a coupling layer on the first free layer, forming a second free layer on the coupling layer, forming a stack of bilayers in one of the first free layer or the second free layer, wherein each of the bilayer stacks further comprises forming a non-magnetic layer on a magnetic layer and capping an uppermost bilayer stack with the magnetic layer; forming a conductive oxide layer on the coupling layer;
forming a protective layer on the conductive oxide layer;
forming a conductive capping directly on the protective layer;
forming a top electrode layer on the conductive capping layer.

### Claim 24 (depends on 23)

The method of claim 23, wherein forming the stack of bilayers includes forming the stack of bilayers in the first free layer.

### Claim 25 (depends on 24)

The method of claim 24, wherein forming a second stack of bilayers, includes forming a second stack of bilayers in the second free layer capped by a magnetic layer, wherein each of the second stack of bilayers comprises a non-magnetic layer disposed on a magnetic layer and wherein the non-magnetic layers in the second stack of bilayers have a combined thickness that is less than 15% of a combined thickness of the magnetic layers in the second stack of bilayers.