International Business Machines Corporation

Stuart Stephen Parkin

Robert Fontana

Virgil S Speriosu

Bruce Alvin Gurney

Ching Hwa Tsang

Dennis R Wilhoit

Bernard Dieny

William Joseph Gallagher

Frederick Hayes Dill

Daniele Mauri

Jonathan Zanhong Sun

John Casimir Slonczewski

Roger Hilsen Koch

Edward M Engler

Victor Y Lee

Ian L Sanders

Gang Xiao

Snorri Thorgeir Ingvarsson

Adel Issa Nazzal

Kevin P Roche

Roy E Scheuerlein

Tsann Lin

Luc Thomas

James Harvey Kaufman

Mason Lamar Williams

David Eugene Heim

Steven E Lambert

Ronald Franklin Marks

Omar U Need, Iii

Haralambos Lefakis

Serhat Metin

Robin Frederick Farrow

Robert B Beyers

Rai Moriya

Grace S Lim

Tsann Linn

Paul M Grant

In order to dampen magnetization changes in magnetic devices, such as magnetic tunnel junctions (MTJ) used in high speed Magnetic Random Access Memory (MRAM), a transition metal selected from thetransition metals andtransition metals is alloyed into the magnetic layer to be dampened. In a preferred form, a magnetic permalloy layer is alloyed with osmium (Os) in an atomic concentration of between 4% and 15% of the alloy.

Increased damping of magnetization in magnetic materials

In order to dampen magnetization changes in magnetic devices, such as tunnel junctions (MTJ) used in high speed Magnetic Random Access Memory (MRAM), a transition metal selected from the 4d transition metals and 5d transition metals is alloyed into the magnetic layer to be dampened. In a preferred form, a magnetic permalloy layer is alloyed with osmium (Os) in an atomic concentration of between 4% and 15% of the alloy.

An improved magnetic tunnel junction (MTJ) memory cell for use in a nonvolatile magnetic random access memory (MRAM) array has a free layer formed as two ferromagnetic films that are magnetostatically coupled antiparallel to one another by their respective dipole fields. The magnetostatic or dipolar coupling of the two ferromagnetic films occurs across a nonferromagnetic spacer layer that is selected to prevent exchange coupling between the two ferromagnetic films. The magnetic moments of the two ferromagnetic films are antiparallel to another so that the multilayer free layer structure has a reduced net magnetic moment. In the presence of an applied magnetic field, such as during writing to the cell, the moments of the two ferromagnetic films switch directions substantially simultaneously, so that the net magnetic moment of the multilayer free layer structure can have two possible orientations relative to the orientation of the fixed or pinned layer of the MTJ cell, thus resulting in the two stable magnetic states of the MTJ cell. The reduced net magnetic moment of the multilayer free layer structure reduces the magnetostatic coupling between the multilayer free layer and the pinned ferromagnetic layer in the MTJ cell, as well as the magnetostatic coupling between adjacent MTJ cells in the array. As a result, the cells, and thus the MRAM array, can be made smaller.

Magnetic memory array with magnetic tunnel junction memory cells having

A magnetic device uses laminated ferromagnetic layers containing antiferromagnetically coupled ferromagnetic films coupled together with improved antiferromagnetically coupling (AFC) films. The AFC films are formed of the binary and ternary alloys comprising combinations of Ru, Os and Re. The ferromagnetic film thicknesses, the AFC film thicknesses and the compositions of the films in the laminated layer can be varied to engineer the magnetic properties of the device. The magnetic devices whose properties are improved with the improved laminated layers include spin valve magnetoresistive read heads and magnetic tunnel junction (MTJ) devices for use as magnetic memory cells and magnetoresistive read heads.

Magnetic devices with laminated ferromagnetic structures formed with

A magnetic tunnel junction (MTJ) memory cell uses a biasing ferromagnetic layer in the MTJ stack of layers that is magnetostatically coupled with the free ferromagnetic layer in the MTJ stack to provide transverse and/or longitudinal bias fields to the free ferromagnetic layer. The MTJ is formed on an electrical lead on a substrate and is made up of a stack of layers. The layers in the MTJ 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 free 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, and whose moment, in the absence of any applied field, is generally either parallel or antiparallel to that of the fixed ferromagnetic layer, a biasing ferromagnetic layer that has its magnetic moment aligned generally in the plane of the MTJ, and a nonferromagnetic 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 layer magnetostatically couples with the edges of the free layer so as to provide a transverse bias field, which results in a coherent rotation of the moment of the free layer, and/or a longitudinal bias field, which assures that the two states of the memory cell are equally stable with respect to magnetic field excursions.

Magnetic tunnel junction memory cell with in-stack biasing of the free

A magnetoresistive sensor for use as the read sensor in magnetic recording disk drives uses a permalloy (approximate composition of Ni.sub.81,Fe.sub.19) sensor layer with a magnetoresistance coefficient significantly greater than prior art permalloy sensor layers for a range of permalloy film thicknesses. The permalloy film is deposited on a substrate, such as alumina, that is essentially non-reactive with permalloy at elevated temperatures while the substrate is heated. The permalloy films have a zero or slightly negative magnetostriction, low easy and hard axis coercivities, and a low anisotropy field. At very small film thicknesses the permalloy films formed with substrate heating exhibit an even greater percentage increase in magnetoresistance coefficient than at higher film thicknesses, thereby allowing the films to function in magnetic recording disk drive heads for use at very high linear recording densities. The precise composition of the Ni--Fe alloy forming the sensor layer can be varied slightly, depending on the film thickness, to provide a sensor layer with essentially zero or slightly negative magnetostriction.

Magnetoresistive magnetic recording head with permalloy sensor layer

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.

Magnetic tunnel junction magnetoresistive sensor with in-stack biasing

An improved magnetic tunnel junction (MTJ) device for use in a magnetic recording read head or in a magnetic memory storage cell is comprised of two ferromagnetic layers, a 'hard' or 'fixed' ferromagnetic layer and a sensing or 'free' ferromagnetic layer, which are separated by a thin insulating tunneling layer. Each of the ferromagnetic layers is a multilayer formed from two thinner ferromagnetic films coupled antiferromagnetically to one another across a thin antiferromagnetically coupling film. The antiferromagnetically coupling film is chosen, with regard to material composition and thickness, so that it causes the two ferromagnetic films which sandwich it to have their magnetic moments arranged antiparallel to one other in the absence of external magnetic fields. The magnetic moments of the fixed ferromagnetic multilayer and free ferromagnetic layer can be chosen to be arbitrarily small by making the two ferromagnetic films comprising each of them to have substantially the same magnetic moment. Thus the dipole fields from each of the fixed and free ferromagnetic multilayers can be minimized, thereby reducing the magnetic interaction between the fixed ferromagnetic multilayer and the free ferromagnetic multilayer.

Magnetic tunnel junction device with improved fixed and free

A magnetic tunnel junction (MTJ) of the type using soft (low magnetic coercivity) and hard (high magnetic coercivity) ferromagnetic layers separated by an insulating tunnel barrier (a hard/soft MTJ device) is stable without loss of magnetization after repeated cycling of its magnetic state. The MTJ device is based on the discovery that the mechanism of demagnetization in a hard/soft MTJ device is via coupling of the hard ferromagnetic layer to the soft ferromagnetic layer via the formation and motion of domain walls in the soft ferromagnetic layer. The MTJ device includes adjacent ferromagnetic structures that provide a transverse biasing magnetic field to the soft ferromagnetic layer. The transverse biasing field permits coherent rotation of the magnetic moment of the soft ferromagnetic layer without the formation of magnetic domains when suitable switching fields are applied. The elimination of the effect of domain walls in the soft ferromagnetic layer can also be achieved by an MTJ device with the soft ferromagnetic layer having a larger surface area than the hard ferromagnetic layer so that any domain walls are concentrated at the edges of the soft ferromagnetic layer and thus have minimal effect on the hard ferromagnetic layer.

Hard/soft magnetic tunnel junction device with stable hard ferromagnetic

A magnetic tunnel junction (MTJ) magnetoresistive read head for a magnetic recording system has the MTJ sensing or free ferromagnetic layer also functioning as a flux guide to direct magnetic flux from the magnetic recording medium to the tunnel junction. The MTJ fixed ferromagnetic layer and the MTJ tunnel barrier layer have their front edges substantially coplanar with the sensing surface of the head. Both the fixed and free ferromagnetic layers are in contact with opposite surfaces of the MTJ tunnel barrier layer but the free ferromagnetic layer extends beyond the back edge of either the tunnel barrier layer or the fixed ferromagnetic layer, whichever back edge is closer to the sensing surface. This assures that the magnetic flux is non-zero in the tunnel junction region. The magnetization direction of the fixed ferromagnetic layer is fixed in a direction generally perpendicular to the sensing surface and thus to the magnetic recording medium, preferably by interfacial exchange coupling with an antiferromagnetic layer. The magnetization direction of the free ferromagnetic layer is aligned in a direction generally parallel to the surface of the medium in the absence of an applied magnetic field and is free to rotate in the presence of applied magnetic fields from the medium. A layer of high coercivity hard magnetic material adjacent the sides of the free ferromagnetic layer longitudinally biases the magnetization of the free ferromagnetic layer in the preferred direction.

Magnetic tunnel junction magnetoresistive read head with sensing layer

A magnetic tunnel junction (MTJ) magnetoresistive read head for a magnetic recording system has the MTJ sensing or free ferromagnetic layer also functioning as a flux guide to direct magnetic flux from the magnetic recording medium to the tunnel junction. The MTJ fixed ferromagnetic layer has its front edge recessed from the sensing surface of the head. Both the fixed and free ferromagnetic layers are in contact with opposite surfaces of the MTJ tunnel barrier layer but the free ferromagnetic layer extends beyond the back edge of either the tunnel barrier layer or the fixed ferromagnetic layer, whichever back edge is closer to the sensing surface. This assures that the magnetic flux is non-zero in the tunnel junction region. The magnetization direction of the fixed ferromagnetic layer is fixed in a direction generally perpendicular to the sensing surface and thus to the magnetic recording medium, preferably by interfacial exchange coupling with an antiferromagnetic layer. The magnetization direction of the free ferromagnetic layer is aligned in a direction generally parallel to the surface of the medium in the absence of an applied magnetic field and is free to rotate in the presence of applied magnetic fields from the medium. A layer of high coercivity hard magnetic material adjacent the sides of the free ferromagnetic layer longitudinally biases the magnetization of the free ferromagnetic layer in the preferred direction.

A magnetic tunnel junction (MTJ) magnetoresistive read head for a magnetic recording system has the MTJ device located between two spaced-apart magnetic shields. The magnetic shields, which allow the head to detect individual magnetic transitions from the magnetic recording medium without interference from neighboring transitions, also function as electrical leads for connection of the head to sense circuitry. Electrically conductive spacer layers are located at the top and bottom of the MTJ device and connect the MTJ device to the shields. The thickness of the spacer layers is selected to optimize the spacing between the shields, which is a parameter that controls the linear resolution of the data that can be read from the magnetic recording medium. To reduce the likelihood of electrical shorting between the shields if the shield-to-shield spacing is too small, each of the shields can have a pedestal region with the MTJ device located between the two pedestals, so that the shield-to-shield spacing outside the pedestal regions is greater than in the pedestal regions.

Shielded magnetic tunnel junction magnetoresistive read head

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 formed as a sandwich of two antiferromagnetically coupled ferromagnetic layers separated by a metallic layer. The free and pinned ferromagnetic layers are located in separate spaced-apart planes so as to not overlap the tunnel barrier layer. An insulating layer surrounds the lateral perimeter of at least the free ferromagnetic layer and supports an electrical lead that makes contact with the free ferromagnetic layer.

Magnetic tunnel junction device with antiferromagnetically coupled

A magnetic tunnel junction device usable as a memory cell or an external magnetic field sensor uses a multilayer of ferromagnetic layers in place of a single hard high-coercivity ferromagnetic layer in one of the two magnetic tunnel junction electrodes. The magnetic tunnel junction element in the device is made up of a ferromagnetic multilayer structure that has high coercivity to maintain its magnetic moment fixed in the presence of an applied magnetic field in the range of interest, a single free ferromagnetic layer whose magnetic moment is free to rotate, and an insulating tunnel barrier layer located between and in contact with the ferromagnetic multilayer structure and the free ferromagnetic layer. The fixed ferromagnetic multilayer structure is made up of two layers, a first ferromagnetic layer with a coercivity substantially higher than the applied field and a thin ferromagnetic interface layer that exhibits high spin filtering and is located between and in contact with the first ferromagnetic layer and the insulating tunnel barrier layer. The material in the first ferromagnetic layer of the multilayer can have low magnetization and thus poor spin filtering because the spin filtering is provided by the interface layer. The interface ferromagnetic layer in the multilayer has relatively low coercivity but is kept thin so that the overall coercivity of the multilayer is not degraded.

Magnetic tunnel junction device with ferromagnetic multilayer having

A magnetic tunnel junction device, usable as a memory cell or an external magnetic field sensor, has a tunneling magnetoresistance response, as a function of applied magnetic field, that is substantially symmetric about zero field. The magnetic tunnel junction is made up of two ferromagnetic layers, one of which has its magnetic moment fixed and the other of which has its magnetic moment free to rotate, an insulating tunnel barrier layer between the ferromagnetic layers for permitting tunneling current perpendicularly through the layers, and a nonferromagnetic layer located at the interface between the tunnel barrier layer and one of the ferromagnetic layers. The nonferromagnetic layer increases the spacing between the tunnel barrier layer and the ferromagnetic layer at the interface and thus reduces the magnetic coupling between the fixed and free ferromagnetic layers, which has been determined to be the cause of unsymmetric tunneling magnetoresistance response about zero field. Even though the nonferromagnetic interface layer presents nonspin-polarized electronic states at the tunnel barrier layer interface, it unexpectedly does not cause a suppression of the tunneling magnetoresistance.

Growing community of inventors

San Jose, CA, United States of America

Stuart Stephen Parkin