Tunnel junction head structure without current shunting
First Claim
1. A magnetic tunnel junction (MTJ) sensor, comprising:
- a substrate;
a first shield (S1) of ferromagnetic material formed on the substrate;
a magnetic tunnel junction (MTJ) stack formed on said first shield, the MTJ stack having a generally rectangular shape and two opposite side edges, said MTJ stack comprising;
an antiferromagnetic (AFM) layer;
a pinned layer of ferromagnetic material in contact with said AFM layer;
a free layer of ferromagnetic material; and
a tunnel junction layer of electrically insulating material disposed between said pinned layer and said free layer;
a second shield (S2) of ferromagnetic material formed on and in contact with said MTJ stack;
a first insulator layer formed on the first shield layer on opposite sides of said MTJ stack and in abutting contact to the side edges of said MTJ stack;
a hard bias layer of ferromagnetic material formed on the first insulator layer on opposite sides of said MTJ stack and in abutting contact to or overlapping said MTJ stack, said hard bias layer having a magnetic moment for biasing the magnetic moment of the free layer in substantially the same direction as the moment of the hard bias layer in the absence of an applied magnetic field; and
a second insulator layer formed on the hard bias layer and separating said hard bias layer from said second shield layer.
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Abstract
A magnetic tunnel junction (MTJ) device for use as a magnetic field sensor or as a memory cell in a magnetic random access (MRAM) array has one pinned ferromagnetic layer and one free ferromagnetic layer formed on opposite sides of an insulating tunnel barrier layer, and a hard biasing layer that is in proximate contact with and magnetostatically coupled to the free ferromagnetic layer. The magnetic tunnel junction in the sensor is formed on a first shield, which also serves as an electrical lead, and is made up of a stack of layers (MTJ stack). The layers in the MTJ stack are an antiferromagnetic layer, a pinned ferromagnetic layer, an insulating tunnel barrier layer, and a free ferromagnetic layer. The MTJ stack is generally rectangularly shaped with parallel side edges. A layer of hard biasing ferromagnetic material is in abutting contact to or overlapping the MTJ stack to longitudinally bias the magnetic moment of the free ferromagnetic layer in a preferred direction. A first layer of electrically insulating material isolates the hard biasing material from the first shield so that sensing current is not shunted to the hard biasing material but is allowed to flow perpendicularly through the layers in the MTJ stack. A second layer of electrically insulating material isolates the hard bias material from the second shield which also acts as an electrical lead for the MTJ stack.
159 Citations
20 Claims
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1. A magnetic tunnel junction (MTJ) sensor, comprising:
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a substrate; a first shield (S1) of ferromagnetic material formed on the substrate; a magnetic tunnel junction (MTJ) stack formed on said first shield, the MTJ stack having a generally rectangular shape and two opposite side edges, said MTJ stack comprising; an antiferromagnetic (AFM) layer; a pinned layer of ferromagnetic material in contact with said AFM layer; a free layer of ferromagnetic material; and a tunnel junction layer of electrically insulating material disposed between said pinned layer and said free layer; a second shield (S2) of ferromagnetic material formed on and in contact with said MTJ stack; a first insulator layer formed on the first shield layer on opposite sides of said MTJ stack and in abutting contact to the side edges of said MTJ stack; a hard bias layer of ferromagnetic material formed on the first insulator layer on opposite sides of said MTJ stack and in abutting contact to or overlapping said MTJ stack, said hard bias layer having a magnetic moment for biasing the magnetic moment of the free layer in substantially the same direction as the moment of the hard bias layer in the absence of an applied magnetic field; and a second insulator layer formed on the hard bias layer and separating said hard bias layer from said second shield layer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A disk drive system comprising:
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a magnetic recording disk; a magnetic tunnel junction (MTJ) sensor for sensing magnetically recorded data on said magnetic recording disk, said MTJ sensor comprising; a substrate; a first shield (S1) of ferromagnetic material formed on the substrate; a magnetic tunnel junction (MTJ) stack formed on said first shield, the MTJ stack having a generally rectangular shape and two opposite side edges, said MTJ stack comprising; an antiferromagnetic (AFM) layer; a pinned layer of ferromagnetic material in contact with said AFM layer; a free layer of ferromagnetic material; and a tunnel junction layer of electrically insulating material disposed between said pinned layer and said free layer; a second shield (S2) of ferromagnetic material formed on and in contact with said MTJ stack; a first insulator layer formed on the first shield layer on opposite sides of said MTJ stack and in abutting contact to the side edges of said MTJ stack; a hard bias layer of ferromagnetic material formed on the first insulator layer on opposite sides of said MTJ stack and in abutting contact to or overlapping said MTJ stack, said hard bias layer having a magnetic moment for biasing the magnetic moment of the free layer in substantially the same direction as the moment of the hard bias layer in the absence of an applied magnetic field; and a second insulator layer formed on the hard bias layer and separating said hard bias layer from said second shield layer; an actuator for moving said MTJ sensor across the magnetic recording disk so the MTJ sensor may access different regions of magnetically recorded data on the magnetic recording disk; and a recording channel coupled electrically to the MTJ sensor for detecting changes in resistance of the MTJ sensor caused by rotation of the magnetization axis of the free ferromagnetic layer relative to the fixed magnetization of the pinned layer in response to magnetic fields from the magnetically recorded data. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
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Specification