BACKGROUND

The present application relates to magnetoresistive random access memory (MRAM). More particularly, the present application relates to a bottom pinned magnetic tunnel junction (MTJ) stack having improved switching performance which can be used as a component/element of a spin-transfer torque (STT) MRAM device.

STT MRAM devices use a 2-terminal device which includes a MTJ stack that contains a magnetic pinned (reference) layer, a tunnel barrier layer and a magnetic free layer.FIG. 1illustrates a prior art bottom pinned MTJ stack that includes a magnetic pinned (or reference) layer10, a tunnel barrier layer12, and a magnetic free layer14; the arrow within the magnetic pinned layer10shows a possible orientation of that layer and the double headed arrow in the magnetic free layer14illustrates that the orientation in that layer can be switched. The magnetization of the magnetic pinned layer10is fixed in one direction (say pointing up as shown inFIG. 1) and a current passed through the junction makes the magnetic free layer14anti-parallel to the magnetic pinned layer10. A smaller current (of either polarity) is used to read the resistance of the device, which depends on the relative orientations of the magnetic pinned layer10and the magnetic free layer14.

STT MRAM has the advantages of lower power consumption and better scalability over conventional magnetoresistive random access memory which uses magnetic fields to flip the active elements. In STT MRAM, spin-transfer torque is used to flip (switch) the orientation of the magnetic free layer. Moreover, spin-transfer torque technology has the potential to make possible STT MRAM devices combining low current requirements and reduced cost; however, the amount of current needed to reorient (i.e., switch) the magnetization is at present too high for most commercial applications.

SUMMARY

A bottom pinned MTJ stack having improved switching performance is provided which can be used as a component/element of a STT MRAM device. The improved switching performance which, in turn, can reduce write errors and improve write voltage distributions, is obtained by inserting at least one heavy metal-containing layer into the magnetic free layer and/or by forming a heavy metal-containing layer on a MTJ capping layer that is located above the magnetic free layer. The term “heavy metal-containing layer” is used throughout the present application to denote a discrete layer that contains a metal or a combination of metals (i.e., a metal alloy) having an atomic number of equal to, or greater than, 42. The heavy metal-containing layer is in itself non-magnetic.

In one aspect of the present application, a bottom pinned MTJ stack having improved switching performance is provided. In one embodiment of the present application, the bottom pinned MTJ structure includes a tunnel barrier layer located on a magnetic pinned layer, and a magnetic free layer located on the tunnel barrier layer. In accordance with this embodiment, the magnetic free layer has at least one heavy metal-containing layer inserted (i.e., embedded) therein.

In some embodiments, the bottom pinned MTJ stack that contains the magnetic free layer having the at least one heavy metal-containing layer inserted therein further includes a MTJ capping layer and another heavy metal-containing layer located above the magnetic free layer.

In another embodiment of the present application, the bottom pinned MTJ structure includes a tunnel barrier layer located on a magnetic pinned layer, a magnetic free layer located on the tunnel barrier layer, a MTJ capping layer located on the magnetic free layer, and a heavy metal-containing layer located on the MTJ capping layer.

In another aspect of the present application, a STT MRAM device is provided that includes a bottom pinned MTJ stack located on a bottom electrode. In one embodiment of the present application, the bottom pinned MTJ structure that is present on the bottom electrode includes a tunnel barrier layer located on a magnetic pinned layer, and a magnetic free layer located on the tunnel barrier layer. In accordance with this embodiment, the magnetic free layer has at least one heavy metal-containing layer inserted therein.

In some embodiments, the bottom pinned MTJ stack that contains the magnetic free layer having the at least one heavy metal-containing layer inserted therein further includes a MTJ capping layer and another heavy metal-containing layer located above the magnetic free layer.

In another embodiment, the bottom pinned MTJ structure that is present on the bottom electrode includes a tunnel barrier layer located on a magnetic pinned layer, a magnetic free layer located on the tunnel barrier layer, a MTJ capping layer located on the magnetic free layer, and a heavy metal-containing layer located on the MTJ capping layer.

