Tunneling magnetoresistive (TMR) device with improved seed layer
A tunneling magnetoresistance (TMR) device has an improved seed layer for the lower or first ferromagnetic layer that eliminates the need for boron in the two ferromagnetic layers. The seed layer, for example a RuAl alloy, has a B2 crystalline structure with (001) texture when deposited on an amorphous pre-seed layer, meaning that the (001) plane is parallel to the surface of the TMR device substrate. The subsequently deposited first ferromagnetic layer, like a CoFe alloy, and the tunneling barrier layer, typically MgO, inherit the (001) texture of the seed layer.
1. A tunneling magnetoresistive (TMR) device comprising:
a substrate;
a seed layer having a crystalline structure and a (001) texture on the substrate, wherein the seed layer is selected from a RuAl alloy and a CrMo alloy;
a boron-free first ferromagnetic layer having a BCC crystalline structure and a (001) texture on the seed layer, the first ferromagnetic layer selected from a CoFe alloy, a Heusler alloy and a half-Heusler alloy;
a tunneling barrier layer having a rock salt crystalline structure or spinel structure and a (001) texture on the first ferromagnetic layer; and
a second ferromagnetic layer on the tunneling barrier layer.
2. The device of claim 1 wherein the tunneling barrier layer is selected from MgO, ZnO, MnO, CoO, TiO, VO, MgAl 2 O 4 and MgGa 2 O 4 .
3. The device of claim 1 further comprising an amorphous pre-seed layer between the substrate and the seed layer.
4. The device of claim 3 wherein the pre-seed layer is a layer or multilayer comprising a material selected from a NiFeTa alloy, a CoFeTa alloy, a CoFeB alloy, a CoFeBTa alloy and Ta.
5. The device of claim 1 wherein the first ferromagnetic layer comprises a nanolayer selected from Co and a CoFe alloy.
6. The device of claim 1 where the second ferromagnetic layer is a boron-free ferromagnetic layer.
7. The device of claim 1 wherein the first ferromagnetic layer comprises a CoFeNi-based alloy, Co 2 MnAl, Co 2 MnGe, Co 2 FeSi, Co 2 FeAl, or NiMnSb.
8. The device of claim 1 wherein the seed layer has a thickness of about 5 Å to about 50 Å.
9. The device of claim 1 wherein the first ferromagnetic layer has a thickness of about 20 Å to about 80 Å.
10. The device of claim 1 wherein the tunneling barrier layer has a thickness of about 4 Å to about 20 Å.
11. The device of claim 1 wherein, when the seed layer comprises the CrMo alloy, an atomic percent of Mo is about 30 to about 50.
12. The device of claim 1 wherein, when the seed layer comprises the RuAl alloy, an atomic percent of Ru is about 40 to about 65.
13. A tunneling magnetoresistive (TMR) device comprising:
a substrate;
an amorphous pre-seed layer on the substrate;
a seed layer selected from a RuAl alloy and a CrMo alloy and having a crystalline structure and a (001) texture on the pre-seed layer;
a boron-free alloy comprising Co and Fe first ferromagnetic layer having a BCC crystalline structure and a (001) texture on the seed layer;
a tunneling barrier layer consisting essentially of MgO on the first ferromagnetic layer; and
a second ferromagnetic layer on the tunneling barrier layer.
14. The device of claim 13 wherein the pre-seed layer is a layer or multilayer comprising a material selected from a NiFeTa alloy, a CoFeTa alloy, a CoFeB alloy, a CoFeBTa alloy and Ta.
15. The device of claim 13 wherein the seed layer consists essentially Ru x Al (100-x) where x is in atomic percent and is greater than or equal to 45 and less than or equal to 60.
16. The device of claim 13 wherein the first ferromagnetic layer comprises a nanolayer selected from Co and a CoFe alloy adjacent the tunneling barrier layer and the second ferromagnetic layer comprises a nanolayer selected from Co and a CoFe alloy adjacent the tunneling barrier layer.
17. The device of claim 13 where the second ferromagnetic layer is a boron-free ferromagnetic layer.
18. The device of claim 13 wherein the seed layer has a thickness of about 5 Å to about 50 Å.
19. The device of claim 13 wherein the first ferromagnetic layer has a thickness of about 20 Å to about 80 Å.
20. The device of claim 13 wherein the tunneling barrier layer has a thickness of about 4 Å to about 20 Å.
21. The device of claim 13 wherein, when the seed layer comprises the CrMo alloy, an atomic percent of Mo is about 30 to about 50.