The discovery of enhanced magnetoresistance and oscillatory interlayer exchange coupling in transition metal multilayers just over a decade ago has enabled the development of new classes of magnetically engineered magnetic thin-film materials suitable for advanced magnetic sensors and magnetic random access memories. Magnetic sensors based on spin-valve giant magnetoresistive (GMR) sandwiches with artificial antiferromagnetic reference layers have resulted in enormous increases in the storage capacity of magnetic hard disk drives. The unique properties of magnetic tunnel junction (MTJ) devices has led to the development of an advanced high performance nonvolatile magnet random access memory with density approaching that of dynamic random-access memory (RAM) and read-write speeds comparable to static RAM. Both GMR and MTJ devices are examples of spintronic materials in which the flow of spin-polarized electrons is manipulated by controlling, via magnetic fields, the orientation of magnetic moments in inhomogeneous magnetic thin film systems. More complex devices, including three-terminal hot electron magnetic tunnel transistors, suggest that there are many other applications of spintronic materials.

Magnetically engineered spintronic sensors and memory

There are provided a magnetoresistance effect element, a magnetic head, a magnetic head assembly and a magnetic recording system, which have high sensitivity and high reliability. The magnetoresistance effect element has two ferromagnetic layers, a non-magnetic layer provided between the ferromagnetic layers, and a layer containing an oxide or nitride as a principal component, wherein the layer containing the oxide or nitride as the principal component contains a magnetic transition metal element which does not bond to oxygen and nitrogen and which is at least one of Co, Fe and Ni.

Magnetoresistance effect element

A storage element including a storage layer configured to hold information by use of a magnetization state of a magnetic material, with a pinned magnetization layer being provided on one side of the storage layer, with a tunnel insulation layer, and with the direction of magnetization of the storage layer being changed through injection of spin polarized electrons by passing a current in the lamination direction, so as to record information in the storage layer, wherein a spin barrier layer configured to restrain diffusion of the spin polarized electrons is provided on the side, opposite to the pinned magnetization layer, of the storage layer; and the spin barrier layer includes at least one material selected from the group composing of oxides, nitrides, and fluorides.

Storage element and memory

A magnetoresistive element has a ferromagnetic double tunnel junction having a stacked structure of a first antiferromagnetic layer/a first ferromagnetic layer/a first dielectric layer/a second ferromagnetic layer/a second dielectric layer/a third ferromagnetic layer/a second antiferromagnetic layer The second ferromagnetic layer that is a free layer consists of a Co-based alloy or a three-layered film of a Co-based alloy/a Ni—Fe alloy/a Co-based alloy A tunnel current is flowed between the first ferromagnetic layer and the third ferromagnetic layer

Magnetoresistive element and magnetic memory device

A method to switch a scalable magnetoresistive memory cell including the steps of providing a magnetoresistive memory device sandwiched between a word line and a digit line so that current waveforms can be applied to the word and digit lines at various times to cause a magnetic field flux to rotate the effective magnetic moment vector of the device by approximately 180°. The magnetoresistive memory device includes N ferromagnetic layers that are anti-ferromagnetically coupled. N can be adjusted to change the magnetic switching volume of the device.

Method of writing to scalable magnetoresistance random access memory element

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

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 as flux guide

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) 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 ferromagnetic layer and memory array using the cell

A magnetoresistive read sensor incorporates a multilayer sensing element formed of one or more magnetoresistive elements in a planar array, each magnetoresistive element having a multilayer structure of at least two ferromagnetic layers separated by a nonmagnetic layer. The ferromagnetic layers are coupled antiferromagnetically by magnetostatic coupling at opposing edges of the ferromagnetic layers. A bias layer separated from the magnetoresistive sensing element by a spacer layer provides a magnetic field to bias the magnetoresistive sensing element at a desired non-signal point for linear response. The magnetoresistive sensing element is formed by alternatively depositing layers of ferromagnetic material and layers of nonmagnetic material on a substrate and then patterning the resulting structure using photolithographic techniques to provide a planar array of magnetoresistive elements. A conductive layer is deposited over the array filling in the spaces separating the magnetoresistive elements to provide electrical conductivity between the elements in the plane of the structure.

Ching Hwa Tsang

Papers

Magnetic tunnel junction magnetoresistive sensor with in-stack biasing

Magnetic tunnel junction magnetoresistive read head with sensing layer as flux guide

Shielded magnetic tunnel junction magnetoresistive read head

Magnetic tunnel junction memory cell with in-stack biasing of the free ferromagnetic layer and memory array using the cell

Multilayer magnetoresistive sensor