Perpendicular spin transfer torque MRAM memory cell with cap layer to achieve lower current density and increased write margin

An apparatus, comprising:

• a fixed ferromagnetic layer having a fixed direction of magnetization;
• a free ferromagnetic layer having a direction of magnetization that can be switched;
• a tunnel barrier between the fixed ferromagnetic layer and the free ferromagnetic layer;
• a cap layer adjacent the free ferromagnetic layer;
• and
• a resistive heating layer adjacent the cap layer, the resistive heating layer has a resistivity of 1-10 Ωcm, the resistive heating layer includes germanium or is an amorphous BiGe alloy.

A method, comprising;

• writing to a non-volatile spin transfer torque MRAM memory cell that includes a magnetic tunnel junction and a cap layer adjacent the magnetic tunnel junction, the magnetic tunnel junction includes a free ferromagnetic layer having a direction of magnetization that can be switched, the writing comprises:
• conducting a current through the magnetic tunnel junction and the cap layer;
• the cap layer heating the magnetic tunnel junction while conducting the current in order to reduce current density in the magnetic tunnel junction, the cap layer contributes 20-50% of the resistance area product of the memory cell;
• and
• switching the direction of magnetization of the free layer from a first direction that is perpendicular to a plane of the free layer to a second direction that is perpendicular to the plane of the free layer in response to the current and the heating.