SyAF structure to fabricate Mbit MTJ MRAM
View Patent ↗A MTJ that minimizes error count (EC) while achieving high MR value, low magnetostriction, and a RA of about 1100 Ω-μm 2 for 1 Mbit MRAM devices is disclosed. The MTJ has a composite AP1 pinned layer made of a lower amorphous Co 60 Fe 20 B 20 layer and an upper crystalline Co 75 Fe 25 layer to promote a smoother and more uniform AlOx tunnel barrier. A “stronger oxidation” state is realized in the AlOx layer by depositing a thicker than normal Al layer or extending the ROX cycle time for Al oxidation and thereby reduces tunneling hot spots. The NiFe free layer has a low Fe content of about 8 to 21 atomic % and the Hf content in the NiFeHf capping layer is from 10 to 25 atomic %. A Ta hard mask is formed on the capping layer. EC (best) is reduced from >100 ppm to <10 ppm by using the preferred MTJ configuration.
1. A MTJ element for a magnetic memory device, comprising:
a pinned layer having an AP2/coupling layer/AP1 configuration wherein the AP2 layer is formed on an AFM layer and the AP1 layer is a composite having a lower amorphous CoFeB layer and an upper crystalline CoFe layer;
an AlOx tunnel barrier formed on the crystalline CoFe layer;
a free layer with low magnetostriction and low Hc formed on the AlOx tunnel barrier;
and a capping layer formed on the free layer wherein the capping layer is comprised of NiFeM where M is a metal having an oxidation potential greater than that of Ni and Fe.
2. The MTJ element of claim 1 wherein the amorphous CoFeB AP1 pinned layer has a composition represented by Co X Fe Y B Z where x+y+z=100, x is from about 40 to 60 atomic %, y is from about 20 to 40 atomic %, and z is from about 15 to 25 atomic %, and the upper crystalline CoFe layer has a composition represented by Co V Fe W where v+w=100 and w is about 20 to 50 atomic %.
3. The MTJ element of claim 1 wherein the free layer is comprised of Ni R Fe S where r+s=100 and s is from about 8 to 21 atomic %.
4. The MTJ element of claim 3 wherein M=Hf and the NiFeHf layer has a composition represented by (Ni R Fe S ) 100-T Hf T where T is about 10 to 25 atomic %.
5. The MTJ element of claim 4 wherein the capping layer is further comprised of a Ta layer formed on the NiFeHf layer.
6. The MTJ element of claim 5 wherein the capping layer is further comprised of a Ru layer formed on the Ta layer to give a NiFeHf/Ta/Ru capping layer configuration.
7. The MTJ element of claim 1 wherein a Ta hard mask about 400 to 600 Angstroms thick is formed on the capping layer.
8. The MTJ element of claim 1 wherein the magnetic memory device is a 1 Mbit MRAM and the MTJ is further comprised of a seed layer formed on a substrate and an AFM layer formed on the seed layer, said AFM layer contacts the AP2 layer in the pinned layer.