Magnetic tunnel junction (MTJ) to reduce spin transfer magnetization 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 made of a lower amorphous CoFeB layer and an upper crystalline CoFe layer;
a crystalline MgO tunnel barrier formed on the upper crystalline CoFe AP1 pinned layer;
an amorphous CoFeB free layer formed on the MgO tunnel barrier, both of said amorphous lower AP1 CoFeB layer and amorphous CoFeB free layer have an identical composition represented by Co x Fe y B z where 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 a composite capping layer formed on the CoFeB free layer wherein the composite capping layer is comprised of a lower layer that contacts the free layer and an upper layer, and said lower layer is made of a metal having an oxidation potential greater than that of Co, Fe, and Ta to provide a high oxygen gettering capability.
2. The MTJ element of claim 1 wherein the magnetic device is a Spin-RAM.
3. The MTJ element of claim 1 wherein the lower amorphous CoFeB AP1 pinned layer and amorphous CoFeB free layer have a Co 60 Fe 20 B 20 composition.
4. The MTJ element of claim 1 wherein the lower layer in the composite capping layer is comprised of Hf or Zr.
5. The MTJ element of claim 4 wherein the composite capping layer has a Hf/Ru configuration in which the lower Hf layer has a thickness from about 5 to 50 Angstroms and the upper Ru layer has a thickness from about 20 to 100 Angstroms.
6. The MTJ element of claim 1 wherein the AP2 portion of the pinned layer is comprised of CoFe and the coupling layer is Ru.
7. The MTJ element of claim 1 wherein the upper crystalline CoFe AP1 pinned layer has a Co 75 Fe 25 composition.