Spin-transfer torque magnetic random access memory (STTMRAM) with laminated free layer
View Patent ↗A spin-torque transfer memory random access memory (STTMRAM) element includes a fixed layer having a magnetization that is substantially fixed in one direction and a barrier layer formed on top of the fixed layer and a free layer. The free layer has a number of alternating laminates, each laminate being made of a magnetic layer and an insulating layer. The magnetic layer is switchable and formed on top of the barrier layer. The free layer is capable of switching its magnetization to a parallel or an anti-parallel state relative to the magnetization of the fixed layer during a write operation when bidirectional electric current is applied across the STTMRAM element. Magnetic layers of the laminates are ferromagnetically coupled to switch together as a single domain during the write operation and the magnetization of the fixed and free layers and the magnetic layers of the laminates have either in-plane or perpendicular anisotropy.
1. A spin-torque transfer memory random access memory (STTMRAM) element comprising:
a fixed layer having a magnetization that is substantially fixed in one direction;
a barrier layer formed on top of the fixed layer;
a free layer having ‘n’ number of alternating laminates, ‘n’ being greater than one, a laminate made of a magnetic layer and an insulating layer, the magnetic layer being switchable and formed on top of the barrier layer, the free layer capable of switching its magnetization to a parallel or an anti-parallel state relative to the magnetization of the fixed layer during a write operation when bidirectional electric current is applied across the STTMRAM element, magnetic layers of the laminates being ferromagnetically coupled to switch together as a single domain during the write operation,
wherein the magnetization of the fixed layer and free layers and the magnetic layers of the laminates have either in-plane or perpendicular anisotropy.
2. The STTMRAM element, as recited in claim 1 , wherein the magnetic layer of each of the laminates is made of cobolt-iron-boron (CoFeB).
3. The STTMRAM element, as recited in claim 1 , wherein the insulating layer of each of the laminates is made of magnesium oxide (MgO).
4. The STTMRAM element, as recited in claim 1 , wherein the magnetic layer of each of the laminates is made of an alloy of cobolt iron boron (CoxFe(1−x)Bz) where x is greater than 10 atomic percent, and z is greater than 12 at %.
5. The STTMRAM element, as recited in claim 1 , wherein the magnetic layer of the laminate formed closest to the fixed layer is made of an alloy of cobolt iron boron (CoxFe(1−x)Bz) where x is greater than 10 atomic percent, and z is greater than 12 at % and the magnetic layer of each of the remaining laminates is made of one or more of CoFeY, Nickel Iron (NiFeY) or CoFeNiY where Y is chosen from one or more of boron (B), phosphorus (P), carbon (C), nitrogen (N), chromium (Cr), tantalum (Ta), titanium (Ti), niobium (Nb), Zirconium (Zr), tungsten (W), silicon (Si), copper (Cu), Rhodium (Rh), or hafnium (Hf).
6. The STTMRAM element, as recited in claim 1 , wherein the insulating layer of each of the laminates is made of one or more of the oxides or nitrides from the materials: aluminum oxide (Al 2 O 3 ), titanium oxide (TiO 2 ), tantalum oxide (Ta 2 O 5 ), hafnium oxide (HfO 2 ), zirconium oxide (ZrO 2 ), tungsten oxide (WO), niobium oxide (Nb 2 O 5 ), chromium oxide (Cr 2 O 3 ), silicon oxide (SiO 2 ), yitrium oxide (Y 2 O 3 ), vanadium oxide (VO 2 ), Ruthenium oxide (RuO), Strontium oxide (SrO), Zinc oxide (ZnO), Magnesium oxide (MgO), titanium nitride (TiN), tantalum nitride (TaN), aluminum nitride (AlN), silicon nitride (SiN).
7. The STTMRAM element, as recited in claim 1 , wherein the thickness of the magnetic layer of the laminate closest to the fixed layer is greater than 0.4 nano meters (nm) and the thickness of the magnetic layers of the remaining laminates is between 0.2 to 1.5 nano meter (nm).
8. The STTMRAM element, as recited in claim 1 , wherein the thickness of the insulating layer of each of the laminates is between 0.1 to 1.0 nano meters (nm).
9. The STTMRAM element, as recited in claim 1 , wherein ‘n’ is 2 through 10.
10. The STTMRAM element, as recited in claim 1 , wherein the barrier layer has a thickness that is greater than the thickness of each of the insulating layers.
11. The STTMRAM element, as recited in claim 1 , wherein the barrier layer has a thickness that is 0.5-2.0 nano meters (nm).
12. The STTMRAM element, as recited in claim 1 , wherein the barrier layer is made of one or more materials selected from a group consisting of: magnesium oxide (MgO), ruthenium oxide (RuO), Strontitum oxide (SrO), Zinc oxide (ZnO), Aluminum oxide (AlO), and titanium oxide (TiO2).
13. The STTMRAM element, as recited in claim 1 , wherein each of the insulating layers has a unique thickness and the thickness of each of the insulating layers increases from the insulating layer that is closest to the fixed layer.
14. The STTMRAM element, as recited in claim 1 , wherein the insulating layer of each of the laminates is made of one or more of the oxides or nitrides.