Magnetic tunnel junction device with nonferromagnetic interface layer for improved magnetic field response

A 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 fixed ferromagnetic layer 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;
• a free ferromagnetic layer whose magnetic moment is free to rotate between directions generally parallel and antiparallel to the magnetic moment of the fixed ferromagnetic layer when exposed to an applied magnetic field caused by current from the read/write circuitry;
• an insulating tunnel barrier layer located between the fixed ferromagnetic layer and the free ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the fixed and free ferromagnetic layers;
• and
• a nonferromagnetic interface layer located between and in contact with the insulating tunnel barrier layer and one of said ferromagnetic layers for increasing the spacing and thereby decreasing the magnetic coupling between the fixed and free ferromagnetic layers;
• whereby when the ferromagnetic layers 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 ferromagnetic layers 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 layer 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;
• a free ferromagnetic layer whose magnetic moment is oriented generally perpendicular to the moment of the fixed ferromagnetic layer 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 the fixed ferromagnetic layer and the free ferromagnetic layer for permitting tunneling current in a direction generally perpendicular to the fixed and free ferromagnetic layers;
• and
• a nonferromagnetic interface layer located between and in contact with the insulating tunnel barrier layer and one of said ferromagnetic layers for increasing the spacing and thereby decreasing the magnetic coupling between the fixed and free ferromagnetic layers;
• whereby when the ferromagnetic layers 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 ferromagnetic layer and the electrical resistance to current flow through the insulating tunnel barrier layer in a direction generally perpendicular to the ferromagnetic layers will be altered, thereby allowing the external magnetic field to be detected.