US 5,650,958 A · Magnetic tunnel junctions with controlled magnetic response

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.

Claims9

Dependent claims

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 more elements

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.

4 more elements

Dependencies are inferred from the claim text.

Magnetic tunnel junctions with controlled magnetic response

Life of this patent

Magnetic tunnel junctions with controlled magnetic response

Life of this patent

Abstract

Claims9