Magnetic tunnel junction device with longitudinal biasing

• US 5,729,410 A
• Filed: 11/27/1996
• Issued: 03/17/1998
• Est. Priority Date: 11/27/1996
• Status: Expired due to Term

• Current Assignee: Western Digital Technologies Incorporated (Western Digital Corporation)
• Original Assignee: International Business Machines Corporation
• Inventors: Parkin, Stuart Stephen Papworth, Fontana, Robert Edward Jr.
• Primary Examiner(s): HEINZ, ALLEN J
• Application Number:
  US08/757,422
• Time in Patent Office: 475 Days
• Field of Search: 360/113, 257/421-427, 365/158, 365/171, 365/173
• US Class Current: 360/324.2
• CPC Class Codes: B82Y 10/00 Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
• CPC Class Codes: B82Y 25/00 Nanomagnetism, e.g. magnetoimpedance, anisotropic magnetoresistance, giant magnetoresistance or tunneling magnetoresistance
• CPC Class Codes: G01R 33/093 using multilayer structures, e.g. giant magnetoresistance sensors thin magnetic films H01F10/00
• CPC Class Codes: G01R 33/098 comprising tunnel junctions, e.g. tunnel magnetoresistance sensors
• CPC Class Codes: G11B 2005/3996 large or giant magnetoresistive effects [GMR], e.g. as generated in spin-valve [SV] devices
• CPC Class Codes: G11B 5/3903 using magnetic thin film layers or their effects, the films being part of integrated structures
• CPC Class Codes: G11B 5/3909 Arrangements using a magnetic tunnel junction
• CPC Class Codes: G11B 5/3932 Magnetic biasing films
• CPC Class Codes: G11C 11/161 details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell
• CPC Class Codes: G11C 11/1659 Cell access
• CPC Class Codes: G11C 11/1673 Reading or sensing circuits or methods
• CPC Class Codes: G11C 11/1675 Writing or programming circuits or methods
• CPC Class Codes: H10N 50/10 Magnetoresistive devices

Abstract

A magnetic tunnel junction device for use as a magnetic memory cell or a magnetic field sensor has one fixed ferromagnetic layer and one sensing ferromagnetic layer formed on opposite sides of the insulating tunnel barrier layer, and a hard biasing ferromagnetic layer that is electrically insulated from but yet magnetostatically coupled with the sensing ferromagnetic layer. The magnetic tunnel junction in the device 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 antfferromagnetic 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, and 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. The stack is generally rectangularly shaped with parallel side edges. A layer of hard biasing ferromagnetic material is located near to but spaced from the side edges of the sensing ferromagnetic layer to longitudinally bias the magnetic moment of the sensing ferromagnetic layer in a preferred direction. A layer of electrically insulating material isolates the hard biasing material from the electrical lead and the sensing ferromagnetic layer so that sense current is not shunted to the hard biasing material but is allowed to flow perpendicularly through the layers in the stack.

Claims

1. A magnetic tunnel junction device for connection to sense circuitry for detecting changes in electrical resistance within the device, the device comprising:

a substrate;

a first electrically conductive lead formed on the substrate;

a magnetic tunnel junction stack 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, and a sensing ferromagnetic layer in contact with the insulating tunnel barrier layer, the sensing ferromagnetic layer having a generally rectangular shape and two opposite side edges;

a second electrically conductive lead formed on and in contact with the magnetic tunnel junction stack;

a biasing ferromagnetic layer formed on the substrate on opposite sides of said stack and spaced from the side edges of the sensing ferromagnetic layer, the biasing ferromagnetic layer having a magnetic moment for biasing the magnetic moment of the sensing ferromagnetic layer in substantially the same direction as the moment of the biasing ferromagnetic layer in the absence of an applied magnetic field;

an electrically insulating layer separating the biasing ferromagnetic layer and the sensing ferromagnetic layer from contact with one another at said side edges of the sensing ferromagnetic layer;

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, and sense current is prevented by said insulating layer from shunting to said biasing ferromagnetic layer.

2. The magnetic tunnel junction device according to claim 1 wherein the magnetic moments of the fixed and sensing ferromagnetic layers are oriented generally parallel or antiparallel to one another in the absence of an applied magnetic field.

3. The magnetic tunnel junction device according to claim 1 wherein the magnetic moments of the fixed and sensing ferromagnetic layers are oriented generally orthogonal to one another in the absence of an applied magnetic field.

4. The magnetic tunnel junction device according to claim 1 wherein the insulating layer also electrically insulates the biasing ferromagnetic layer from at least one of said leads.

5. The magnetic tunnel junction device according to claim 1 wherein the first electrical lead is the bottom lead, the magnetic tunnel junction stack is formed on the substrate such that the fixed ferromagnetic layer is in electrical connection with the first electrical lead, and the second electrical lead is the top lead and is in electrical contact with the sensing ferromagnetic layer.

6. The magnetic tunnel junction device according to claim 1 wherein the first electrical lead is the bottom lead, the magnetic tunnel junction stack is formed on the substrate such that the sensing ferromagnetic layer is in electrical connection with the first electrical lead, and the second electrical lead is the top lead and is in electrical contact with the fixed ferromagnetic layer.

7. The magnetic tunnel junction device according to claim 1 wherein all of the layers in said stack have generally the same rectangular shape with contiguous side edges.

8. The magnetic tunnel junction device according to claim 1 wherein the magnetic tunnel junction stack further comprises an antiferromagnetic layer in contact with the fixed ferromagnetic layer for fixing the magnetic moment of the fixed ferromagnetic layer in said preferred direction by interfacial exchange coupling.

9. A magnetic tunnel junction magnetoresistive read head for sensing data magnetically recorded on a medium, the head comprising:

a substrate;

a first electrode having a fixed ferromagnetic layer formed over the substrate, the magnetization direction of the fixed ferromagnetic layer being fixed along a preferred direction so as to be substantially prevented from rotation in the presence of an applied magnetic field from the medium;

a second electrode having a sensing ferromagnetic layer whose magnetization is oriented in a direction 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;

an insulating tunneling barrier layer located between the fixed and sensing ferromagnetic layers for permitting tunneling current in a direction generally perpendicular to the fixed and sensing ferromagnetic layers;

a biasing ferromagnetic layer for longitudinally biasing the magnetization direction of the sensing ferromagnetic layer in a direction generally perpendicular to the magnetization of the fixed ferromagnetic layer in the absence of an applied magnetic field;

an electrically insulating layer located between the biasing and sensing ferromagnetic layers for electrically isolating the biasing layer from the sensing layer; and

a pair of electrical leads, each lead being connected to a respective electrode and electrically isolated from the biasing layer by the insulating layer, whereby when a sense current is passed between the electrodes it passes generally perpendicularly through the insulating tunneling barrier layer without passing into the biasing layer.

10. The head according to claim 9 further comprising an antiferromagnetic layer in contact with the fixed ferromagnetic layer for fixing the magnetization direction of the fixed ferromagnetic layer by interfacial exchange coupling.

11. The head according to claim 10 wherein a first one of the electrical leads is formed on the substrate and wherein the antiferromagnetic layer is formed on the substrate and located between the substrate and the fixed ferromagnetic layer, the fixed ferromagnetic layer being formed on and in contact with the antiferromagnetic layer, whereby the magnetization direction of the fixed ferromagnetic layer is fixed by interfacial exchange coupling with the antiferromagnetic layer.

12. The head according to claim 9 wherein a first one of the electrical leads is formed on the substrate and wherein the second electrode is formed on the first one of the leads and is located between the substrate and the insulating tunneling barrier layer.

13. The head according to claim 9 wherein the sensing ferromagnetic layer has a generally rectangular perimeter with a sensing edge oriented toward the medium, a back edge generally parallel to the sensing edge and spaced from the medium and two generally perpendicular side edges, and wherein the biasing ferromagnetic layer is located adjacent to said two side edges but separated from said two side edges by the insulating layer, whereby the magnetization direction of the sensing ferromagnetic layer is longitudinally biased in a direction generally parallel to said sensing edge.

14. The head according to claim 9 wherein the fixed ferromagnetic layer, the tunnel barrier layer, and the sensing ferromagnetic layer are formed as a stack of layers with the fixed ferromagnetic layer and the tunnel barrier layer having edges generally coplanar with the rectangular edges of the sensing ferromagnetic layer, and wherein the insulating layer electrically insulates said stack from the biasing ferromagnetic layer and said electrical leads.