Magnetic devices having oxide antiferromagnetic layer next to free ferromagnetic layer
View Patent ↗Magnetic multilayer structures, such as magnetic or magnetoresistive tunnel junctions (MTJs) and spin valves, having a magnetic biasing layer formed next to and magnetically coupled to the free ferromagnetic layer to achieve a desired stability against fluctuations caused by, e.g., thermal fluctuations and astray fields. Stable MTJ cells with low aspect ratios can be fabricated using CMOS processing for, e.g., high-density MRAM memory devices and other devices, using the magnetic biasing layer. Such multilayer structures can be programmed using spin transfer induced switching by driving a write current perpendicular to the layers to switch the magnetization of the free ferromagnetic layer.
1. A device, comprising:
a substrate; and
a magnetic cell formed on the substrate and comprising:
a free ferromagnetic layer having a net magnetization direction that is changeable between a first direction and a second substantially opposite direction;
a magnetic biasing layer in contact with and magnetically coupled to the free ferromagnetic layer to increase coercivity of the free ferromagnetic layer and to allow the magnetization direction of the free ferromagnetic layer to be changeable between the first direction and the second substantially opposite direction, the magnetic biasing layer comprising (1) an oxide antiferromagnetic layer adjacent to or in contact with the free ferromagnetic layer to reduce a spin transfer torque switching current for switching the magnetization of the free ferromagnetic layer and to allow for tunneling of electrons through the oxide antiferromagnetic layer and (2) a metallic antiferromagnetic layer;
a fixed ferromagnetic layer having a fixed magnetization direction; and
a center layer formed between the free ferromagnetic layer and the fixed ferromagnetic layer.
2. The device as in claim 1 , wherein:
the center layer is a non-magnetic spacer, effectuating a spin valve with the fixed ferromagnetic layer, the free ferromagnetic layer and the magnetic biasing layer.
3. The device as in claim 1 , wherein:
the center layer is an insulator barrier layer to allow tunneling of electrons, effectuating a magnetic tunneling junction with the fixed ferromagnetic layer, the free ferromagnetic layer and the magnetic biasing layer.
4. The device as in claim 1 , wherein:
the oxide antiferromagnetic layer has a thickness from 0.5 nm to 15 nm.
5. The device as in claim 1 , wherein:
the free ferromagnetic layer comprises first and second ferromagnetic layers and a non-magnetic spacer between the first and second ferromagnetic layers.
6. The device as in claim 5 , wherein:
the non-magnetic spacer between the first and second ferromagnetic layers in the free ferromagnetic layer comprises Ru, Re, Cu, Ta or Cu, or an alloy that comprises Ru, Re, Cu, Ta or Cu.
7. The device as in claim 5 , wherein:
the non-magnetic spacer has a thickness between 4 and 10 angstroms.
8. The device as in claim 5 , wherein:
a ferromagnetic material for at least one of the first and second ferromagnetic layers in the multilayered free ferromagnetic stack comprises Co, an alloy comprising Co, Fe, an alloy comprising Fe, Ni, or an alloy comprising Ni.
9. The device as in claim 5 , wherein:
a ferromagnetic material for at least one of the first and second ferromagnetic layers in the multilayered free ferromagnetic stack comprises CoFe, CoFeB, CoFeNiB, CoFeTa, NiFe, CoPt, CoPd, FePt, Co 2 Mn(Al,Si) or Co 2 (Cr,Fe)(Al,Si).
10. The device as in claim 1 , wherein:
the oxide antiferromagnetic layer includes at least one of Ni(Fe)O, Fe(Co)O, Co(Fe)O, NiFe(Co)O and CrO.