Hard/soft magnetic tunnel junction device with stable hard ferromagnetic layer

Claim 2

A magnetic tunnel junction device for connection to electrical circuitry that detects a change in electrical resistance of the device in the presence of an applied magnetic field, the device comprising: a hard ferromagnetic layer having a coercivity higher than applied magnetic fields in the range of interest of the device, whereby the hard ferromagnetic layer has a magnetic moment that is fixed in a preferred direction in the presence of an applied magnetic field in the range of interest; a soft ferromagnetic layer having a coercivity less than the coercivity of the hard ferromagnetic layer and whose magnetic moment is free to rotate in the presence of an applied magnetic field in the range of interest; an insulating tunneling barrier layer located between and in contact with the hard ferromagnetic layer and the soft ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the hard ferromagnetic layer and soft ferromagnetic layer; a biasing ferromagnetic layer having a magnetic moment generally transverse to the magnetic moment of the hard ferromagnetic layer, the biasing ferromagnetic layer having a coercivity different from the coercivity of the hard ferromagnetic layer; an insulating layer for electrically isolating the biasing ferromagnetic layer from the hard and soft ferromagnetic layers; and a substrate for supporting the hard ferromagnetic layer, tunneling barrier layer, soft ferromagnetic layer, transverse biasing ferromagnetic layer and insulating layer.

Claim 3

The magnetic tunnel junction device according to claim 1 wherein the transverse biasing ferromagnetic layer comprises a bilayer of a nonmagnetic film and a ferromagnetic film formed on the nonmagnetic film.

Claim 4

The magnetic tunnel junction device according to claim 2 wherein the nonmagnetic film is selected from the group consisting of Cr, a Cr-V alloy and a Cr-Mn alloy.

Claim 5

The magnetic tunnel junction device according to claim 2 wherein the ferromagnetic film formed on the nonmagnetic film is an alloy of Co-Pt-Cr.

Claim 6

The magnetic tunnel junction device according to claim 1 wherein the transverse biasing ferromagnetic layer and the hard ferromagnetic layer have different material compositions.

Claim 7

The magnetic tunnel junction device according to claim 1 wherein the transverse biasing ferromagnetic layer and the hard ferromagnetic layer have the same material compositions but different thicknesses.

Claim 8

The magnetic tunnel junction device according to claim 1 further comprising a nonmagnetic underlayer onto which the hard ferromagnetic layer is formed and a nonmagnetic underlayer onto which the transverse biasing ferromagnetic layer is formed.

Claim 9

The magnetic tunnel junction device according to claim 7 wherein the transverse biasing ferromagnetic layer and the hard ferromagnetic layer have the same material compositions and wherein the nonmagnetic underlayer onto which the hard ferromagnetic layer is formed has a thickness different from the thickness of the nonmagnetic underlayer onto which the transverse biasing ferromagnetic layer is formed.

Claim 10

The magnetic tunnel junction device according to claim 1 wherein the soft ferromagnetic layer has a surface area greater than the surface area of the hard ferromagnetic layer.

Claim 11

The magnetic tunnel junction device according to claim 1 wherein M represents magnetic moment per unit area and t represent thickness and wherein M*t of the transverse biasing ferromagnetic layer is greater than M*t of the soft ferromagnetic layer.

Claim 12

The magnetic tunnel junction device according to claim 1 wherein the hard ferromagnetic layer comprises a multilayer of a Co interface film in contact with the tunneling barrier layer and a Co-Pt alloy film in contact with the Co interface film.

Claim 13

The magnetic tunnel junction device according to claim 1 wherein the material of the soft ferromagnetic layer is selected from the group consisting of Co, alloys of Co, and alloys of Ni-Fe.

Claim 14

A hard/soft 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 read/write circuitry for altering and detecting the magnetic state of individual memory cells in the array, the memory cell comprising: a hard ferromagnetic layer having a coercivity higher than applied magnetic fields in the range of interest of the cell, whereby the hard ferromagnetic layer has a magnetic moment that is fixed in a preferred direction in the presence of an applied magnetic field in the range of interest; a soft ferromagnetic layer having a coercivity less than the coercivity of the hard ferromagnetic layer and whose magnetic moment is free to rotate between directions generally parallel and antiparallel to the magnetic moment of the hard ferromagnetic layer when exposed to said applied magnetic field; an insulating tunneling barrier layer located between and in contact with the hard ferromagnetic layer and the soft ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the hard ferromagnetic layer and soft ferromagnetic layer; a biasing ferromagnetic layer comprising first and second regions spaced on opposite sides of the soft ferromagnetic layer, the regions having magnetic moments generally transverse to the magnetic moment of the hard ferromagnetic layer, the biasing ferromagnetic layer having a coercivity different from the coercivity of the hard ferromagnetic layer; an insulating layer located between the transverse biasing regions and the hard and soft ferromagnetic layers for electrically isolating the transverse biasing regions from the hard and soft ferromagnetic layers; and a substrate for supporting the hard ferromagnetic layer, tunneling barrier layer, soft ferromagnetic layer, transverse biasing regions and insulating layer; whereby when the hard ferromagnetic layer and the soft ferromagnetic layer are connected to the read/write circuitry, the electrical resistance to current flow through the insulating tunnel barrier layer in a direction generally perpendicular to the hard ferromagnetic layer and the soft ferromagnetic layer is determined by said parallel or antiparallel magnetic moment of said soft ferromagnetic layer, the value of said electrical resistance thereby allowing the magnetic state of the memory cell to be determined.

Claim 15

A hard/soft 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 read/write circuitry for altering and detecting the magnetic state of individual memory cells in the array, the memory cell comprising: a hard ferromagnetic layer having a coercivity higher than applied magnetic fields in the range of interest of the cell, whereby the hard ferromagnetic layer has a magnetic moment that is fixed in a preferred direction in the presence of an applied magnetic field in the range of interest; a soft ferromagnetic layer having a coercivity less than the coercivity of the hard ferromagnetic layer and whose magnetic moment is free to rotate between directions generally parallel and antiparallel to the magnetic moment of the hard ferromagnetic layer when exposed to said applied magnetic field; an insulating tunneling barrier layer located between and in contact with the hard ferromagnetic layer and the soft ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the hard ferromagnetic layer and soft ferromagnetic layer; a biasing ferromagnetic layer comprising first and second regions spaced on opposite sides of the soft ferromagnetic layer, the regions having magnetic moments generally transverse to the magnetic moment of the hard ferromagnetic layer, the biasing ferromagnetic layer having a coercivity different from the coercivity of the hard ferromagnetic layer; an insulating layer located between the transverse biasing regions and the hard and soft ferromagnetic layers for electrically isolating the transverse biasing regions from the hard and soft ferromagnetic layers; and a substrate for supporting the hard ferromagnetic layer, tunneling barrier layer, soft ferromagnetic layer, transverse biasing regions and insulating layer; whereby when the hard ferromagnetic layer and the soft ferromagnetic layer are connected to the read/write circuitry, the electrical resistance to current flow through the insulating tunnel barrier layer in a direction generally perpendicular to the hard ferromagnetic layer and the soft ferromagnetic layer is determined by said parallel or antiparallel magnetic moment of said soft ferromagnetic layer, the value of said electrical resistance thereby allowing the magnetic state of the memory cell to be determined.

Claim 16

The magnetic tunnel junction memory cell according to claim 13 wherein the transverse biasing ferromagnetic layer comprises a bilayer of a nonmagnetic film and a ferromagnetic film formed on the nonmagnetic film.

Claim 17

The magnetic tunnel junction memory cell according to claim 14 wherein the nonmagnetic film is selected from the group consisting of Cr, a Cr-V alloy and a Cr-Mn alloy.

Claim 18

The magnetic tunnel junction memory cell according to claim 14 wherein the ferromagnetic film formed on the nonmagnetic film is an alloy of Co-Pt-Cr.

Claim 19

The magnetic tunnel junction memory cell according to claim 13 wherein the transverse biasing ferromagnetic layer and the hard ferromagnetic layer have different material compositions.

Claim 20

The magnetic tunnel junction memory cell according to claim 13 wherein the transverse biasing ferromagnetic layer and the hard ferromagnetic layer have the same material compositions but different thicknesses.

Claim 21

The magnetic tunnel junction memory cell according to claim 13 further comprising a nonmagnetic underlayer onto which the hard ferromagnetic layer is formed and a nonmagnetic underlayer onto which the transverse biasing ferromagnetic layer is formed.

Claim 22

The magnetic tunnel junction memory cell according to claim 19 wherein the transverse biasing ferromagnetic layer and the hard ferromagnetic layer have the same material compositions and wherein the nonmagnetic underlayer onto which the hard ferromagnetic layer is formed has a thickness different from the thickness of the nonmagnetic underlayer onto which the transverse biasing ferromagnetic layer is formed.

Claim 23

The magnetic tunnel junction memory cell according to claim 13 wherein the soft ferromagnetic layer has a surface area greater than the surface area of the hard ferromagnetic layer.

Claim 24

The magnetic tunnel junction memory cell according to claim 13 wherein M represents magnetic moment per unit area and t represent thickness and wherein M*t of the transverse biasing ferromagnetic layer is greater than or equal to M*t of the soft ferromagnetic layer.

Claim 25

The magnetic tunnel junction memory cell according to claim 13 wherein the hard ferromagnetic layer comprises a multilayer of a Co interface film in contact with the tunneling barrier layer and a Co-Pt alloy film in contact with the Co interface film.

Claim 26

The magnetic tunnel junction memory cell according to claim 13 wherein the material of the soft ferromagnetic layer is selected from the group consisting of Co, alloys of Co, and alloys of Ni-Fe.