US 5,729,410 A · Magnetic tunnel junction device with longitudinal biasing

Abstract

A magnetic tunnel junction device for use as a magnetic memory cell or a magnetic field sensor has one fixed ferromagnetic layer and one sensing ferromagnetic layer formed on opposite sides of the insulating tunnel barrier layer, and a hard biasing ferromagnetic layer that is electrically insulated from but yet magnetostatically coupled with the sensing ferromagnetic layer. The magnetic tunnel junction in the device is formed on an electrical lead on a substrate and is made up of a stack of layers. The layers in the stack are an antiferromagnetic layer, a fixed ferromagnetic layer exchange biased with the antfferromagnetic layer so that its magnetic moment cannot rotate in the presence of an applied magnetic field, an insulating tunnel barrier layer in contact with the fixed ferromagnetic layer, and a sensing ferromagnetic layer in contact with the tunnel barrier layer and whose magnetic moment is free to rotate in the presence of an applied magnetic field. The stack is generally rectangularly shaped with parallel side edges. A layer of hard biasing ferromagnetic material is located near to but spaced from the side edges of the sensing ferromagnetic layer to longitudinally bias the magnetic moment of the sensing ferromagnetic layer in a preferred direction. A layer of electrically insulating material isolates the hard biasing material from the electrical lead and the sensing ferromagnetic layer so that sense current is not shunted to the hard biasing material but is allowed to flow perpendicularly through the layers in the stack.

Claims14

Dependent claims

A magnetic tunnel junction device for connection to sense circuitry for detecting changes in electrical resistance within the device, the device comprising:

a substrate;
a first electrically conductive lead formed on the substrate;
a magnetic tunnel junction stack formed on the first lead and comprising a fixed ferromagnetic layer having its magnetic moment fixed in a preferred direction in the absence of an applied magnetic field, an insulating tunnel barrier layer in contact with the fixed ferromagnetic layer, and a sensing ferromagnetic layer in contact with the insulating tunnel barrier layer, the sensing ferromagnetic layer having a generally rectangular shape and two opposite side edges;
a second electrically conductive lead formed on and in contact with the magnetic tunnel junction stack;
a biasing ferromagnetic layer formed on the substrate on opposite sides of said stack and spaced from the side edges of the sensing ferromagnetic layer, the biasing ferromagnetic layer having a magnetic moment for biasing the magnetic moment of the sensing ferromagnetic layer in substantially the same direction as the moment of the biasing ferromagnetic layer in the absence of an applied magnetic field;
an electrically insulating layer separating the biasing ferromagnetic layer and the sensing ferromagnetic layer from contact with one another at said side edges of the sensing ferromagnetic layer;
whereby when the electrical leads are connected to the sense circuitry the electrical resistance to current flow perpendicularly through the layers in said stack is determined by the relative magnetic moments of the fixed and sensing ferromagnetic layers, and sense current is prevented by said insulating layer from shunting to said biasing ferromagnetic layer.

4 more elements

A magnetic tunnel junction magnetoresistive read head for sensing data magnetically recorded on a medium, the head comprising:

a substrate;
a first electrode having a fixed ferromagnetic layer formed over the substrate, the magnetization direction of the fixed ferromagnetic layer being fixed along a preferred direction so as to be substantially prevented from rotation in the presence of an applied magnetic field from the medium;
a second electrode having a sensing ferromagnetic layer whose magnetization is oriented in a direction generally perpendicular to the magnetization direction of the fixed ferromagnetic layer in the absence of an applied magnetic field and is free to rotate in the presence of an applied magnetic field from the medium;
an insulating tunneling barrier layer located between the fixed and sensing ferromagnetic layers for permitting tunneling current in a direction generally perpendicular to the fixed and sensing ferromagnetic layers;
a biasing ferromagnetic layer for longitudinally biasing the magnetization direction of the sensing ferromagnetic layer in a direction generally perpendicular to the magnetization of the fixed ferromagnetic layer in the absence of an applied magnetic field;
an electrically insulating layer located between the biasing and sensing ferromagnetic layers for electrically isolating the biasing layer from the sensing layer;
and
a pair of electrical leads, each lead being connected to a respective electrode and electrically isolated from the biasing layer by the insulating layer, whereby when a sense current is passed between the electrodes it passes generally perpendicularly through the insulating tunneling barrier layer without passing into the biasing layer.

5 more elements

Dependencies are inferred from the claim text.

Magnetic tunnel junction device with longitudinal biasing

Life of this patent

Magnetic tunnel junction device with longitudinal biasing

Life of this patent

Abstract

Claims14