Magnetic tunnel junctions with controlled magnetic response

• US 5,650,958 A
• Filed: 03/18/1996
• Issued: 07/22/1997
• Est. Priority Date: 03/18/1996
• Status: Expired due to Term

• Current Assignee: GlobalFoundries, Inc.
• Original Assignee: International Business Machines Corporation
• Inventors: Sun, Jonathan Zanhong, Parkin, Stuart Stephen Papworth, Slonczewski, John Casimir, Gallagher, William Joseph
• Primary Examiner(s): Nelms, David C.
• Assistant Examiner(s): TRAN, MICHAEL THANH
• Application Number:
  US08/618,300
• Time in Patent Office: 491 Days
• Field of Search: 365/171, 365/173
• US Class Current: 365/173
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• CPC Class Codes: G11B 2005/3996 large or giant magnetoresistive effects [GMR], e.g. as generated in spin-valve [SV] devices
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

A magnetic tunnel junction (MTJ) device is usable as a magnetic field sensor or as a memory cell in a magnetic random access (MRAM) array. The MTJ device has a "pinned" ferromagnetic layer whose magnetization is oriented in the plane of the layer but is fixed so as to not be able to rotate in the presence of an applied magnetic field in the range of interest, a "free" ferromagnetic layer whose magnetization is able to be rotated in the plane of the layer relative to the fixed magnetization of the pinned ferromagnetic layer, and an insulating tunnel barrier layer located between and in contact with both ferromagnetic layers. The pinned ferromagnetic layer is pinned by interfacial exchange coupling with an adjacent antiferromagnetic layer. The amount of tunneling current that flows perpendicularly through the two ferromagnetic layers and the intermediate tunnel barrier layer depends on the relative magnetization directions of the two ferromagnetic layers. The ferromagnetic layers are formed in two separate spaced-apart planes that do not overlap in the region of the tunnel barrier layer, thereby eliminating any extraneous magnetic poles.

Claims

1. A magnetic tunnel junction device comprising:

a first electrode comprising a planar pinned ferromagnetic layer having first and second generally parallel surfaces and an antiferromagnetic layer formed on and in contact with the first surface of the pinned ferromagnetic layer, the antiferromagnetic layer pinning the magnetization of the pinned ferromagnetic layer in a preferred direction and substantially preventing its rotation in the presence of an applied magnetic field;

a second electrode having a planar free ferromagnetic layer whose magnetization is free to rotate in the presence of an applied magnetic field;

an insulating tunneling layer located between and in contact with the second surface of the pinned ferromagnetic layer of the first electrode and the free ferromagnetic layer of the second electrode for permitting tunneling current in a direction generally perpendicular to the planar pinned and free ferromagnetic layers, the pinned or free ferromagnetic layer having a lateral perimeter that does not extend beyond the lateral perimeter of the insulating tunneling layer, whereby the pinned and free ferromagnetic layers are maintained in substantially separate spaced-apart planes without overlapping the insulating tunneling layer; and

a substrate, the first and second electrodes and tunneling layer being formed on the substrate.

2. The magnetic tunnel junction device according to claim 1 wherein the magnetization directions of the pinned and free ferromagnetic layers are substantially parallel or antiparallel to one another in the absence of an applied magnetic field.

3. The magnetic tunnel junction device according to claim 1 wherein the lateral perimeters of the pinned and free ferromagnetic layers are generally rectangularly shaped, and wherein the magnetization directions of the pinned and free ferromagnetic layers are aligned generally along the lengths of the rectangles.

4. The magnetic tunnel junction device according to claim 1 wherein the free ferromagnetic layer'"'"'s magnetization direction is substantially perpendicular to the pinned ferromagnetic layer'"'"'s magnetization direction.

5. The magnetic tunnel junction device according to claim 1 wherein the antiferromagnetic layer of the first electrode is located between the substrate and the pinned ferromagnetic layer and the pinned ferromagnetic layer is located between the antiferromagnetic layer and the free ferromagnetic layer, and further comprising an insulator layer surrounding the lateral perimeter of the free ferromagnetic layer and a nonmagnetic conductor layer formed over the insulator layer and including a portion contacting the free ferromagnetic layer through the insulator layer.

6. The magnetic tunnel junction device according to claim 5 wherein the first electrode includes a ferromagnetic layer formed between the substrate and the antiferromagnetic layer and in contact with the antiferromagnetic layer for serving as a template for the subsequently deposited antiferromagnetic layer.

7. A magnetic tunnel junction memory cell having two magnetic states and usable in a nonvolatile magnetic memory array of memory cells, the array being connected to sense circuitry for detecting the magnetic state of individual memory cells in the array, the memory cell comprising:

a pinned ferromagnetic layer having first and second surfaces and a magnetization in the plane of said pinned ferromagnetic layer;

an antiferromagnetic layer in contact with the first surface of the pinned ferromagnetic layer for pinning the magnetization of the pinned layer in a preferred orientation to prevent its rotation when exposed to a magnetic field less than a predetermined field strength;

a free ferromagnetic layer having a magnetization free to rotate in the plane of said free ferromagnetic layer between directions parallel and antiparallel to the magnetization of the pinned ferromagnetic layer when exposed to a magnetic field less than said predetermined field strength;

an insulating tunnel barrier layer between the pinned and free ferromagnetic layers and in contact with the free ferromagnetic layer and the second surface of the pinned ferromagnetic layer; and

wherein the pinned ferromagnetic layer, the tunnel barrier layer, and the free ferromagnetic layer form a stack of layers;

whereby when the ferromagnetic layers are connected to the sense circuitry the electrical resistance to current flow through the tunnel barrier layer in a direction perpendicular to the ferromagnetic layers in the stack is determined by said parallel or antiparallel magnetization direction of said free ferromagnetic layer, the value of said electrical resistance thereby allowing the magnetic state of the memory cell to be determined.

8. The magnetic tunnel junction memory cell according to claim 7 wherein the stack of layers has a substantially rectangularly shaped base and wherein the magnetization of the pinned ferromagnetic layer is substantially parallel to the length of said rectangularly shaped base.

9. The magnetic tunnel junction memory cell according to claim 8 wherein all of the layers in said stack have substantially the same cross-sectional area, whereby the pinned and free ferromagnetic layers do not overlap the insulating tunnel barrier layer.