# US 8,786,036 B2 · Magnetic tunnel junction for MRAM applications

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- Number: US 8,786,036 B2
- Document ID: US8786036B2
- Status: Granted
- Kind: B2
- Application number: 12/930,877
- Filed: 2011-01-19
- Published: 2012-07-19
- Granted: 2014-07-22
- Earliest claimed: 2011-01-19
- Assignees: Headway Technologies, Inc.
- Applicants: Wei Cao; Cheng T. Horng; Witold Kula; Chyu Jiuh Torng
- Inventors: Wei Cao; Cheng T. Horng; Witold Kula; Chyu Jiuh Torng
- Web page: https://patentgrep.com/patent/US8786036B2

## CPC

- H10N 50/85: Materials of the active region
- G11C 11/161: {details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell}
- H10B 61/00: Magnetic memory devices, e.g. magnetoresistive RAM [MRAM] devices
- H10N 50/10: Magnetoresistive devices
- H10N 50/80: Constructional details
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- G11C: STATIC STORES (semiconductor memory devices H10B)
- H10B: ELECTRONIC MEMORY DEVICES

## Abstract

A MTJ in an MRAM array is disclosed with a composite free layer having a lower crystalline layer contacting a tunnel barrier and an upper amorphous NiFeX layer for improved bit switching performance. The crystalline layer is Fe, Ni, or FEB with a thickness of at least 6 Angstroms which affords a high magnetoresistive ratio. The X element in the NiFeX layer is Mg, Hf, Zr, Nb, or Ta with a content of 5 to 30 atomic % NiFeX thickness is preferably between 20 to 40 Angstroms to substantially reduce bit line switching current and number of shorted bits. In an alternative embodiments, the crystalline layer may be a Fe/NiFe bilayer. Optionally, the amorphous layer may have a NiFeM1/NiFeM2 configuration where M1 and M2 are Mg, Hf, Zr, Nb, or Ta, and M1 is unequal to M2. Annealing at 300° C. to 360° C. provides a high magnetoresistive ratio of about 150%.

## Claims

### Claim 1

A MTJ element in a magnetic device, comprising:
at least a pinned layer/tunnel barrier layer/free layer configuration wherein the tunnel barrier layer has a first interface with the pinned layer, and the free layer is a composite comprised of a crystalline magnetic layer that is Fe, Ni, or FeB which interfaces with the tunnel barrier layer, and an amorphous NiFeX layer where X is one of Hf, Zr, Nb, Ta, or Mg, said amorphous NiFeX layer contacts a side of the crystalline magnetic layer that is opposite the interface with the tunnel barrier layer.

### Claim 2 (depends on 1)

The MTJ element of claim 1 wherein the boron content in the FeB crystalline magnetic layer is from 0 to about 5 atomic %.

### Claim 3 (depends on 1)

The MTJ element of claim 1 wherein the amorphous NiFeX layer has a composition wherein X has a content between about 5 and 30 atomic %.

### Claim 4

A MTJ element in a magnetic device, comprising:
(a) a synthetic anti-ferromagnetic (SyAF) pinned layer formed on a substrate;
(b) a tunnel barrier layer on the SyAF pinned layer; and
(c) a composite free layer on the tunnel barrier layer, comprising:
(1) a crystalline magnetic layer consisting of Fe, Ni, or FeB which contacts a top surface of the tunnel barrier layer; and
(2) an amorphous NiFeX layer contacting a top surface of the crystalline magnetic layer wherein X is one of Hf, Zr, Nb, Ta, or Mg.

### Claim 5 (depends on 4)

The MTJ element of claim 4 wherein the amorphous NiFeX layer has a thickness between about 20 and 40 Angstroms.

### Claim 6 (depends on 4)

The MTJ element of claim 4 wherein the FeB crystalline magnetic layer has a boron content from 0 to about 5 atomic %.

### Claim 7 (depends on 5)

The MTJ element of claim 5 wherein the amorphous NiFeX layer has a composition wherein X has a content from about 5 to 30 atomic %.

### Claim 8 (depends on 6)

The MTJ element of claim 6 wherein the crystalline magnetic layer is Fe and said Fe layer has a thickness of at least 6 Angstroms.

### Claim 9 (depends on 1)

The MTJ element of claim 1 wherein the crystalline magnetic layer has a (001) crystal orientation to match a (001) crystal orientation in the tunnel barrier layer made of MgO.