Magnetic tunnel junction device
The output voltage of an MRAM is increased by means of an Fe(001)/MgO(001)/Fe(001) MTJ device, which is formed by microfabrication of a sample prepared by the following steps. A single-crystalline MgO (001) substrate 11 is prepared. An epitaxial Fe(001) lower electrode (a first electrode) 17 with the thickness of 50 nm is grown on a MgO(001) seed layer 15 at room temperature, followed by annealing under ultrahigh vacuum (2×10 −8 Pa) and at 350° C. A MgO(001) barrier layer 21 with the thickness of 2 nm is epitaxially formed on the Fe(001) lower electrode (the first electrode) at room temperature, using a MgO electron-beam evaporation. A Fe(001) upper electrode (a second electrode) with the thickness of 10 nm is then formed on the MgO(001) barrier layer 21 at room temperature. This is successively followed by the deposition of a Co layer 21 with the thickness of 10 nm on the Fe(001) upper electrode (the second electrode) 23 . The Co layer 21 is provided so as to increase the coercive force of the upper electrode 23 in order to realize an antiparallel magnetization alignment.
1. A magnetoresistive device having a tunnel barrier junction structure, the magnetoresistive device comprising:
a first ferromagnetic material layer of BCC structure;
a second ferromagnetic material layer of a BCC structure; and
a tunnel barrier layer located between the first and second ferromagnetic material layers, and
wherein the tunnel barrier layer comprises:
a single-crystalline magnesium oxide layer in which (001) crystal plane is preferentially oriented or a poly-crystalline magnesium oxide layer in which (001) crystal plane is preferentially oriented, and
wherein the tunnel barrier layer has a tunnel barrier height ω in a range of 0.2 to 0.5 eV.
2. The magnetoresistive device according to claim 1 , wherein at least one of the first and second ferromagnetic material layers comprises CoFeB alloy.
3. The magnetoresistive device according to claim 1 , wherein said tunnel barrier height ψ is obtained by fitting J-V characteristics of the tunnel barrier junction structure to an equation (1)
J=[(2mψ) 1/2 /Δs](e/h) 2 ×exp[−(4 πΔs/h)×(2mψ) 1/2 ]×V (1)
where J is a tunnel current density flowing through the tunnel barrier layer, V is an applied bias voltage that is 100 mV or smaller, m is a mass of the free electron, e is the elementary electric charge, h is the Planck's constant, Δs is an effective thickness of the tunnel barrier layer that is approximately equivalent to (T MgO −0.5 nm), and t MgO is an actual thickness of the tunnel barrier layer determined using a cross-sectional transmission electron microscope image.
4. The magnetoresistive device according to claim 3 , wherein at least one of the first and second ferromagnetic material layers comprises CoFeB alloy.