US 6,023,395 A · Magnetic tunnel junction magnetoresistive sensor with in-stack biasing

Abstract

A magnetic tunnel junction (MTJ) magnetoresistive (MR) read head has one fixed ferromagnetic layer and one sensing ferromagnetic layer on opposite sides of the tunnel barrier layer, and with a biasing ferromagnetic layer in the MTJ stack of layers that is magnetostatically coupled with the sensing ferromagnetic layer to provide either longitudinal bias or transverse bias or a combination of longitudinal and transverse bias fields to the sensing ferromagnetic layer. The magnetic tunnel junction in the MTJ MR head 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 antiferromagnetic 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, 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, a biasing ferromagnetic layer that has its magnetic moment aligned generally within the plane of the device and a nonmagnetic electrically conductive spacer layer separating the biasing ferromagnetic layer from the other layers in the stack. The self field or demagnetizing field from the biasing ferromagnetic layer magnetostatically couples with the edges of the sensing ferromagnetic layer to stabilize its magnetic moment, and, to linearize the output of the device. The electrically conductive spacer layer prevents direct ferromagnetic coupling between the biasing ferromagnetic layer and the other layers in the stack and allows sense current to flow perpendicularly through the layers in the MTJ stack.

Claims28

Dependent claims

A magnetic tunnel junction magnetoresistive sensor for sensing magnetic fields when connected to sense circuitry that detects changes in electrical resistance within the sensor, the sensor comprising:

a substrate;
a first electrically conductive lead formed on the substrate;
a magnetic tunnel junction stack of layers 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, a sensing ferromagnetic layer in contact with the insulating tunnel barrier layer, a biasing ferromagnetic layer for biasing the magnetic moment of the sensing ferromagnetic layer in a preferred direction in the absence of an applied magnetic field, and an electrically conductive nonferromagnetic spacer layer separating the biasing ferromagnetic layer from contact with the sensing ferromagnetic layer and the fixed ferromagnetic layer;
and
a second electrically conductive lead formed on and in contact with the magnetic tunnel junction stack;
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.

3 more elements

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

a substrate;
a bottom electrical lead formed on the substrate;
a fixed ferromagnetic layer formed over the bottom lead, the magnetization direction of the fixed ferromagnetic layer being fixed along a direction generally perpendicular to the sensing surface so as to be substantially prevented from rotation in the presence of an applied magnetic field from the medium;
an insulating tunneling barrier layer located on and in contact with the fixed ferromagnetic layer;
a sensing ferromagnetic layer located on and in contact with the tunneling barrier layer and whose magnetization is oriented in a direction generally parallel to the sensing surface and 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;
a biasing ferromagnetic layer having a magnetic moment that is oriented between approximately -90 degrees and approximately +90 degrees, where 0 degrees corresponds to a longitudinal direction generally parallel to the sensing surface, for stabilizing the magnetization direction of the sensing ferromagnetic layer;
an electrically conductive nonferromagnetic spacer layer located between the biasing ferromagnetic layer and the fixed ferromagnetic layer;
and
a top electrical lead for providing electrical connection with the sensing ferromagnetic layer, whereby the electrical resistance to current flow perpendicularly through the layers located between the bottom and top leads is determined by the relative magnetic moments of the fixed and sensing ferromagnetic layers.

6 more elements

Dependencies are inferred from the claim text.

Magnetic tunnel junction magnetoresistive sensor with in-stack biasing

Life of this patent

Magnetic tunnel junction magnetoresistive sensor with in-stack biasing

Life of this patent

Abstract

Claims28