Platinum and cobalt/copper-based multilayer thin film having low saturation magnetization and fabrication method thereof
A multilayer thin film for magnetic random access memory that includes thin platinum layers and thin cobalt-copper layers, and more particularly, to a multilayer thin film having magnetic layers including non-magnetic material copper that replaces a portion of the magnetic material cobalt.
1. A perpendicular magnetic anisotropy multilayer thin film for a magnetic random access memory, comprising:
a platinum layer and a cobalt-copper layer alternately deposited to form a multilayer thin film over a substrate,
wherein the cobalt-copper layer is thicker than the platinum layer;
wherein a content atomic ratio of cobalt:copper in the cobalt-copper layers is 50:50 to 90:10;
wherein the multilayer thin film including the platinum layer and the cobalt-copper layer is repeatedly stacked over the substrate 2-10 turns;
wherein the multilayer thin film has a total thickness of 0.3 nm-12.5 nm; and
wherein the multilayer thin film has a perpendicular magnetic anisotropy (PMA) energy density of 0.23˜5.66×10 6 erg/cm 3 at 300˜500 Celsius degrees, and a saturation magnetization value of 735 emu/cc or less.
2. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein a thickness f the platinum layer in the multilayer thin film ranges from 0.15 nm to 0.25 nm.
3. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein the thickness ratio of the cobalt-copper layer to the platinum layer is
1.1:1˜4.0:1.
4. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , further comprising:
a stack of a buffer layer and a seed layer, which are provided between the substrate and the multilayer thin film, and
a protective layer deposited over the multilayer thin film.
5. The perpendicular magnetic anisotropy multilayer thin film of claim 4 , wherein each of the buffer layer, the seed layer, and the protective layer independently includes gold (Au), palladium (Pd), copper (Cu), platinum (Pt), tantalum (Ta), ruthenium (Ru), or a combination thereof.
6. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein a critical current value required for a perpendicular magnetization switching is 1 MA/cm 2 or less.
7. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein the platinum layer has a thickness of 0.2 nm and the cobalt-copper layer has a thickness of 0.4, or 0.5 or 0.6 nm.
8. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein a content atomic ratio of cobalt:copper in the cobalt-copper layer is 85/15 to 70/30.
9. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein a thickness of the platinum layer in the multilayer thin film ranges from 0.15 nm to 0.25 nm and a ratio of a thickness of the cobalt-copper layer to the thickness of the platinum layer is 0.6:1 to 4.0:1.
10. The perpendicular magnetic anisotropy multilayer thin film of claim 1 , wherein the multilayer thin film has a total thickness of 0.96 nm-12.5 nm.
11. The perpendicular magnetic anisotropy multilayer thin of claim 1 , wherein the substrate is made of a material selected from the group consisting of silicon, glass, sapphire and magnesium oxide.
12. A magnetic random access memory device comprising the perpendicular magnetic anisotropy multilayer thin film of claim 1 .