Magnetic tunnel junction device with ferromagnetic multilayer having fixed magnetic moment

A magnetic tunnel junction memory cell having two magnetic states and usable in a 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 fixed ferromagnetic multilayer whose magnetic moment is fixed in a preferred direction in the presence of an applied magnetic field caused by current from the read/write circuitry, the fixed multilayer comprising a first ferromagnetic layer having a coercivity substantially higher than said applied magnetic field and an interface ferromagnetic layer formed on and in contact with the first ferromagnetic layer, the interface layer having a magnetization substantially higher than the magnetization of the first ferromagnetic layer and being sufficiently thin relative to the thickness of the first ferromagnetic layer so that the multilayer does not have a coercivity substantially less than the coercivity of the first ferromagnetic layer, whereby the fixed multilayer's magnetic moment remains fixed in said preferred direction in the presence of said applied magnetic field;
• a free ferromagnetic layer whose magnetic moment is free to rotate between directions generally parallel and antiparallel to the magnetic moment of the fixed multilayer when exposed to said applied magnetic field;
• an insulating tunnel barrier layer located between and in contact with the interface ferromagnetic layer in said multilayer and the free ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the fixed multilayer and the free ferromagnetic layer;
• and
• a substrate, wherein the fixed multilayer, tunneling layer and free ferromagnetic layer are formed on the substrate;
• whereby when the fixed multilayer and the free 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 fixed multilayer and the free ferromagnetic layer is determined by said parallel or antiparallel magnetic moment of said free ferromagnetic layer, the value of said electrical resistance thereby allowing the magnetic state of the memory cell to be determined.

A magnetic tunnel junction memory cell having two magnetic states and usable in a 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 substrate;
• a fixed ferromagnetic multilayer whose magnetic moment is fixed in a preferred direction in the presence of an applied magnetic field caused by current from the read/write circuitry, the fixed multilayer comprising a ferromagnetic layer of an alloy comprising Co, Pt, and Cr formed on the substrate and having a coercivity substantially higher than said applied magnetic field and an interface ferromagnetic layer consisting essentially of Co formed on and in contact with the Co--Pt--Cr layer, the interface Co layer having a magnetization substantially higher than the magnetization of the Co--Pt--Cr layer and being sufficiently thin relative to the thickness of the Co--Pt--Cr layer so that the multilayer does not have a coercivity substantially less than the coercivity of the Co--Pt--Cr layer, whereby the fixed multilayer's magnetic moment remains fixed in said preferred direction in the presence of said applied magnetic field;
• a free ferromagnetic layer whose magnetic moment is free to rotate between directions generally parallel and antiparallel to the magnetic moment of the fixed multilayer when exposed to said applied magnetic field;
• an insulating tunnel barrier layer located between and in contact with the interface Co layer in said multilayer and the free ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the fixed multilayer and the free ferromagnetic layer;
• whereby when the fixed multilayer and the free 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 fixed multilayer and the free ferromagnetic layer is determined by said parallel or antiparallel magnetic moment of said free ferromagnetic layer, the value of said electrical resistance thereby allowing the magnetic state of the memory cell to be determined.

A magnetic tunnel junction magnetic field sensor for detecting external magnetic fields, the sensor comprising:

• a fixed ferromagnetic multilayer whose magnetic moment is fixed in a preferred direction in the presence of an applied magnetic field in the range of the external magnetic field to be sensed, the fixed multilayer comprising a first ferromagnetic layer having a coercivity substantially higher than said applied magnetic field and an interface ferromagnetic layer formed on and in contact with the first ferromagnetic layer, the interface layer having a magnetization substantially higher than the magnetization of the first ferromagnetic layer and being sufficiently thin relative to the thickness of the first ferromagnetic layer so that the multilayer does not have a coercivity substantially less than the coercivity of the first ferromagnetic layer, whereby the fixed multilayer's magnetic moment remains fixed in said preferred direction in the presence of said applied magnetic field;
• a free ferromagnetic layer whose magnetic moment is oriented generally perpendicular to the moment of the fixed multilayer in the absence of an applied magnetic field and is free to rotate away from said perpendicular orientation in the presence of an applied magnetic field in the range of the external magnetic field to be sensed;
• an insulating tunnel barrier layer located between and in contact with the interface layer and the free ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the fixed multilayer and the free ferromagnetic layer;
• and
• a substrate, wherein the fixed multilayer, tunneling barrier layer and free ferromagnetic layer are formed on the substrate;
• whereby when the fixed multilayer and the free ferromagnetic layer are exposed to the external magnetic field to be sensed, the moment of the free ferromagnetic layer will change its orientation relative to the moment of the fixed multilayer and the electrical resistance to current flow through the insulating tunnel barrier layer in a direction generally perpendicular to the fixed multilayer and the free ferromagnetic layer will be altered, thereby allowing the external magnetic field to be detected.