Magnetic random access memory with perpendicular interfacial anisotropy

1. A magnetic random access memory (MRAM) device comprising a plurality of memory elements, each of said memory element including a magnetic tunnel junction (MTJ) structure in between a non-magnetic seed layer and a non-magnetic cap layer, said MTJ structure comprising a magnetic free layer structure and a magnetic reference layer structure with an insulating tunnel junction layer interposed therebetween, wherein said magnetic free layer structure includes a first magnetic free layer formed adjacent to said insulating tunnel junction layer and a second magnetic free layer separated from said first magnetic free layer by a second non-magnetic perpendicular enhancement layer (PEL), said first and second magnetic free layers having respectively first and second variable magnetization directions that are substantially perpendicular to layer planes thereof and are oriented in a same direction, said magnetic reference layer structure includes a first magnetic reference layer formed adjacent to said insulating tunnel junction layer and a second magnetic reference layer separated from said first magnetic reference layer by a first non-magnetic perpendicular enhancement layer, said first and second magnetic reference layers having a first fixed magnetization direction substantially perpendicular to layer planes thereof, said second magnetic reference layer having a multilayer structure formed by interleaving two different types of materials with at least one of said two different types being magnetic.

2. The MRAM device according to claim 1 , wherein said MTJ structure further comprises:

an anti-ferromagnetic coupling layer formed adjacent to said second magnetic reference layer; and

a magnetic fixed layer formed immediately adjacent to said anti-ferromagnetic coupling layer, said magnetic fixed layer having a second fixed magnetization direction that is perpendicular to a layer plane thereof and is substantially opposite to said first fixed magnetization direction.

3. The MRAM device according to claim 2 , wherein said magnetic fixed layer has a multilayer structure formed by interleaving two different types of materials with at least one of said two different types being magnetic.

4. The MRAM device according to claim 3 , wherein one of said two different types of materials of said magnetic fixed layer is cobalt and the other one of said two different types of materials is palladium, platinum, or nickel.

5. The MRAM device according to claim 1 , wherein one of said two different types of materials of said second magnetic reference layer is cobalt and the other one of said two different types of materials is palladium, platinum, or nickel.

6. The MRAM device according to claim 1 , wherein said second magnetic reference layer comprises two magnetic layers with an intermediate metallic layer interposed therebetween.

7. The MRAM device according to claim 6 , wherein said two magnetic layers are made of cobalt, said intermediate metallic layer is made of palladium, platinum, or nickel.

8. The MRAM device according to claim 7 , wherein each of said two magnetic layers has a thickness in a range of about 0.2 nm to about 0.8 nm, said intermediate layer has a thickness in a range of about 0.2 nm to about 1.2 nm.

9. The MRAM device according to claim 1 , wherein each of said first and second non-magnetic perpendicular enhancement layers is made of tantalum or tantalum nitride and has a thickness in a range of about 0.2 nm to about 0.5 nm.

10. A magnetic random access memory (MRAM) device comprising a plurality of memory elements, each of said memory element including a magnetic tunnel junction (MTJ) structure in between a non-magnetic seed layer and a non-magnetic cap layer, said MTJ structure comprising a magnetic free layer structure and a magnetic reference layer structure with an insulating tunnel junction layer interposed therebetween, wherein said magnetic free layer structure has a variable magnetization direction substantially perpendicular to layer plane thereof, said magnetic reference layer structure includes a first magnetic reference layer formed adjacent to said insulating tunnel junction layer and a second magnetic reference layer separated from said first magnetic reference layer by a first non-magnetic perpendicular enhancement layer, said first and second magnetic reference layers have a first fixed magnetization direction substantially perpendicular to layer planes thereof, said second magnetic reference layer has a multilayer structure formed by interleaving two different types of materials with at least one of said two different types being magnetic, said first non-magnetic perpendicular enhancement layer comprises a tantalum layer formed adjacent to said first magnetic reference layer and a ruthenium layer formed adjacent to said second magnetic reference layer.

11. The MRAM device according to claim 10 , wherein said magnetic free layer structure includes a first magnetic free layer formed adjacent to said insulating tunnel junction layer and a second magnetic free layer separated from said first magnetic free layer by a second non-magnetic perpendicular enhancement layer.