Magnetic tunnel junction element, junction memory cell, and junction magnetic field sensor

摘要

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.