Magnetic tunnel junction (MTJ) to reduce spin transfer magnetizaton switching current
View Patent ↗A MTJ that minimizes spin-transfer magnetization switching current (Jc) in a Spin-RAM to <1×10 6 A/cm 2 is disclosed. The MTJ has a Co 60 Fe 20 B 20 /MgO/Co 60 Fe 20 B 20 configuration where the CoFeB AP1 pinned and free layers are amorphous and the crystalline MgO tunnel barrier is formed by a ROX or NOX process. The capping layer preferably is a Hf/Ru composite where the lower Hf layer serves as an excellent oxygen getter material to reduce the magnetic “dead layer” at the free layer/capping layer interface and thereby increase dR/R, and lower He and Jc. The annealing temperature is lowered to about 280° C. to give a smoother CoFeB/MgO interface and a smaller offset field than with a 350° C. annealing. In a second embodiment, the AP1 layer has a CoFeB/CoFe configuration wherein the lower CoFeB layer is amorphous and the upper CoFe layer is crystalline to further improve dR/R and lower RA to ≦10 ohm/μm 2 .
1. An MTJ element for reducing spin-transfer magnetization switching current in a magnetic 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 Co 60 Fe 20 B 20 layer having a thickness of about 12 to 18 Angstroms and an upper crystalline Co 75 Fe 25 layer with a thickness of about 5 to 7 Angstroms;
a crystalline MgO tunnel barrier formed on the crystalline CoFe layer in the composite AP1 pinned layer;
an amorphous CoFeB free layer formed on the MgO tunnel barrier;
and a capping layer formed on the CoFeB free layer wherein the capping layer is a layer of Hf or Zr to provide a high oxygen gettering capability and said layer contacts said amorphous CoFeB free layer.
2. The MTJ element of claim 1 wherein the magnetic device is a Spin-RAM.
3. The MTJ element of claim 1 wherein the AP2 portion of the pinned layer is comprised of CoFe and the coupling layer is Ru.
4. The MTJ element of claim 1 wherein the amorphous CoFeB free layer has a Co 60 Fe 20 B 20 composition.