Thermally assisted multi-level MRAM cell and method for writing a plurality of bits in the MRAM cell

Method for writing a plurality of data bits to a magnetic random access memory (MRAM) cell comprising a magnetic tunnel junction comprising a reference magnetic layer having a reference magnetization, a tunnel barrier layer, and a storage magnetic layer including a first storage layer having a first storage magnetization, a second storage layer having a second storage magnetization, a storage coupling layer magnetically coupling the first storage magnetization antiparallel with the second storage magnetization, and an antiferromagnetic storage layer, one of the first storage magnetization and the second storage magnetization being adjacent to the antiferromagnetic storage layer, the antiferromagnetic storage layer pinning, at a low temperature threshold, the one of the first storage magnetization and the second storage magnetization adjacent to the antiferromagnetic storage layer and freeing, at a high temperature threshold, said one of the first storage magnetization and the second storage magnetization adjacent to the antiferromagnetic storage layer, the method comprising:

• heating the magnetic tunnel junction to the high temperature threshold;
• applying a write magnetic field having a predetermined magnitude to orient the first and second storage magnetization;
• cooling the magnetic tunnel junction to the low temperature threshold to freeze the first and second storage magnetizations in their written orientation;
• storing a first memory state (‘11’) in the storage magnetic layer wherein the first storage magnetization is oriented in a first direction by applying a first or a third high temperature threshold and having the write magnetic field in a second direction;
• storing a second memory state (‘00’) in the storage magnetic layer wherein the first storage magnetization is oriented in said second direction by applying the first or the third high temperature threshold and having the write magnetic field in said first direction;
• storing a third memory state (‘01’) in the storage magnetic layer wherein the first storage magnetization makes an angle of α/2 with the second direction by applying a second high temperature threshold and having the write magnetic field in said first direction;
• and
• storing a fourth memory state (‘10’) in the storage magnetic layer wherein the first storage magnetization makes an angle of 180°−α/2 with the second direction by applying the second high temperature threshold and having the write magnetic field in said second direction, wherein:
• the write magnetic field is along the anisotropy axis of the storage layer in the first or second direction, said second direction being opposite to the first direction;
• at said first high temperature threshold the write magnetic field is between a coercive field and a spin-flop field of the storage magnetic layer, such that the first storage magnetization is oriented antiparallel to the second storage magnetization;
• at said second high temperature threshold the write magnetic field is above the spin-flop field of the storage magnetic layer, such that the first storage magnetization forms a predetermined angle α below 180° with respect to the second storage magnetization;
• and
• at said third high temperature threshold the write magnetic field is above a saturation field of the storage magnetic layer, such that the first storage magnetization is oriented parallel to the second storage magnetization.