Unidirectional spin torque transfer magnetic memory cell structure
View Patent ↗Spin torque transfer magnetic random access memory devices configured to be programmed unidirectionally and methods of programming such devices. The devices include memory cells having two pinned layers and a free layer therebetween. By utilizing two pinned layers, the spin torque effect on the free layer from each of the two pinned layers, respectively, allows the memory cells to be programmed with unidirectional currents.
1. A method of operating a memory cell comprising:
modulating a spin torque effect of a bottom pinned layer of the memory cell; and
fixing a magnetization of a free layer of the memory cell to be antiparallel to a magnetization of the bottom pinned layer, comprising transmitting a non-spin-polarized programming current through the modulated bottom pinned layer of the memory cell in a direction perpendicular to the bottom pinned layer, wherein the non-spin-polarized programming current remains non-spin-polarized through the modulated bottom pinned layer of the memory cell.
2. The method of claim 1 , wherein modulating the spin torque effect of the bottom pinned layer of the memory cell comprises locally heating the bottom pinned layer of the memory cell.
3. The method of claim 2 , wherein locally heating the bottom pinned layer of the memory cell comprises transmitting a current through a heat generating layer formed below and in direct contact with the bottom pinned layer.
4. The method of claim 1 , wherein modulating the spin torque effect of the bottom pinned layer of the memory cell comprises applying voltage-induced stress to the bottom pinned layer.
5. The method of claim 4 , wherein applying the voltage-induced stress to the bottom pinned layer comprises utilizing piezoelectric materials within the memory cell.
6. The method of claim 1 , comprising:
after transmitting the programming current through the modulated bottom pinned layer of the memory cell, transmitting the programming current through the free layer of the memory cell, wherein a magnetization of the free layer is unchanged by the programming current.
7. The method of claim 6 , comprising:
after transmitting the programming current through the free layer, transmitting the programming current to a top pinned layer of the memory cell such that the programming current is spin polarized by the top pinned layer.
8. The method of claim 7 , wherein fixing the magnetization of the free layer of the memory cell comprises transmitting the spin polarized programming current through the free layer such that the magnetization of the free layer is fixed by the spin polarized programming current.